During the recent COVID-19 pandemic, the clinical exposure of medical students has been hindered while the impact on medical education is under investigation.The potential negative impact of medical students on transmission rates, along with the shortages of Personal Protective Equipment (PPE), their lack of proper training,and their limited ability to work independently, give rise to reasonable concerns regarding their involvement in pandemic management.Nevertheless, the heavy workload could soon provoke severe deficiencies in the frontline medical workforce. Hence, the possibility of covering gaps in humanresources by effectively deploying students should not be rejected in advance. Additionally, a pandemic poses a valuable learning opportunity for high-quality medical education.The aim of this commentary is to present a discussion with supporters and opponents of medical student engagement in the pandemic management and their involvement in placementsrequiring physical contact with patients. We also attempt to elucidate the necessary conditions for the students’ possible involvement in clinical settings. The novel Coronavirus SARS-COV-2, responsible for the COVID-19 disease, emerged from Wuhan, the capital city of the Hubei province in China,but rapidly spread geographically, affecting millions of people worldwide. This health crisis poses an unprecedented challenge for medical education.Since the pandemic outbreak, the disruption of medical training was inevitable due to the implementation of social distancing, the universal hindranceof clinical exposure for many medical students, and the halt of clinical attachments and electives to curtail transmission  . In this COVID-19 pandemic, medical educators across the globe have been forced to immediately generate distance learning environments by convertingin a few weeks the majority of face-to-face theoretical sessions to online sessions   - 6 .AlTo begin with, many medical schools have canceled activities with patient contact to assure student safety and to decrease the number of possible vectors.In general terms, students and residents are not always properly trained to follow hygiene protocols, especially in conditions of increased pressure  - 10 . CSecondly, students’ involvement with suspected or confirmed cases calls for additional Personal Protective Equipment (PPE) ,shortages of which have already been noted worldwide   - 14 .IFrom another viewpoint, students demand more attention and resources than the benefit they provide; they are short on experience and ability to work independently  . In canFurthermore, the uncertain clinical environment may affect medical staff’s mental well-being, leading to frustration, distress, anxiety,and other adverse psychological outcomes of unpredicted magnitude, especially when they provide care beyond their competency  , 15 .FOn the other hand, it is undeniable that the needs of the health workforce are augmented in such periods. The increasing number of cases,the recommendation for a 2-week self-isolation period for anyone who has tested positive for the virus, and the continuous amount of considerableclinical work unrelated to COVID-19 could soon limit the pool of available healthcare providers  .In thiTo further enhance this point of view, student commitment to contribute is remarkable, with medical student organizations, even at the initial stages of thishealth crisis, willing to offer their services. Their deep conviction is that they have already developed a set of clinical skills and a solid knowledge background,which render them more useful than any other group of volunteers that could be drafted to support the overworked healthcare professionals. An online survey,which included over two hundred students from central Europe, revealed that 70% of the students signed up for voluntary commitment, while almost half of theunwilling students were either already employed in hospitals or unable to sign up due to underlying health problems   . According to another perspective, the aging of the healthcare workforce further complicates the functional state of health systems. Considering the higher likelihoodof comorbidities, and the increased morbidity and mortality of COVID-19 in the higher age range, the suggestion to involve retired, thus even older, doctors seemsa quite dangerous practice   . StudenFrom a pedagogic point of view, student engagement in crisis management is a rare educational experience and a unique opportunity to realize the dynamic natureof medical knowledge   , 18 .MThe appropriate role of medical students in clinical programs during a pandemic is an issue of controversy amongst medical educators.In this direction, it would be rather efficient to form generally-accepted guidelines, which will clearly outline in which vacancies and under what scenariosstudents could be usefully deployed in clinical placements   , 20 .MAlthough medical students generally accept a social contract that includes possible hazardous duty, it is accepted that their involvementin health crises should be prioritizing safety with adequate access to PPE and knowledge of evidence-based up-to-date practices  , 20 .TIn addition, proper and continuous supervision of students is considered essential to ensure the safety of both themselves and patients  , 14 .TIt is widely perceived that the student role in response to these unprecedented circumstances is far from clear. However, medical training cannot behalted in every threat of a pandemic, and the medical education community is obliged to organize coordinated responses. Nevertheless, the idea of a singleholistic solution for all cases seems rather utopian. A more reasonable alternative would be the adoption of practices related to the prevailing conditions of each country. Naturally, this individualized decision for student involvement should depend on specific criteria. It is of paramount importance that the advantages of sucha decision should outweigh the risks so that the cost-benefit ratio will be truly beneficial not only for the overall crisis management, but alsofor medical students' education and professionalism. This condition gains even bigger value in the crucial point when medical demand outpaces medical capacity  . IndeedIn this article, we endeavored to describe in detail some of the lessons learned from medical educators during the current COVID-19 pandemic.To our knowledge, studies referring to the active role of medical students during pandemics and the necessary conditions for their participation in clinicaland outpatient settings are heterogenous. We combined some of these muddled data in an attempt to multilaterally address this topic. Nevertheless, we are aware of somelimitations of note. While we mainly focused on clinical settings and senior medical students, further research should look into the generalizability of thesepractices into non-clinical settings. In addition, a significant gap of sufficient research articles in the current relative bibliography was observed,the majority of which are based on descriptions of the experience gained by educators around the world. Thus, there is a need for longer-term studies to examinein detail the effects of the pandemic on medical education and the possible active contribution of students to its tackling, in order to draw safe conclusions.The outbreak of a large-scale contagious, infectious disease hampers inpatient education. Nevertheless, a pandemic poses a great learning opportunityfor students in tackling a health crisis. Concurrently, student contribution seems to be precious for an overburdened healthcare system.Therefore, the option to effectively deploy students, mainly in outpatient positions and primary care settings, but also in direct patient activities,should be promoted under specific conditions and cannot be rejected in advance. The formation of a clear framework for students’ roles in such circumstancesenhances the preparedness of the medical education community for related future challenges.


Peutz-Jeghers syndrome (PJS) is a rare autosomal dominant polyposis entity that often remains undiagnosed. The major problems associated with PJS are acute complications due to (i) polyp-related intestinal obstruction, (ii) intussusception, and (iii) the risk of cancer in the long-term. We report the case of a 32-year-old female who presented at the emergency room with signs of acute abdomen and died during the clinical workup. She had a one-month history of nausea, vomiting, and diarrhea and was pregnant at about 30 weeks. There was no contributing past history except for undergoing small bowel resection in infancy. The postmortem examination revealed multiple arborizing polyps throughout the gastrointestinal tract, chiefly in the small bowel. Intestinal obstruction was found at the proximal jejunum with necrosis, perforation, and peritonitis. Histologically, the polyps were composed of tree branch-like bundles of smooth muscle covered by normal-appearing glandular epithelium, confirming the diagnosis of hamartomatous polyps. No malignant or premalignant lesions were detected in the gastrointestinal tract or other organs. This case was an opportunity to analyze the natural history and the pathological features of the Peutz-Jeghers syndrome in an adult and to investigate the presence of neoplastic lesions associated with this condition. The presence of associated pre-neoplastic and neoplastic lesions in the gastrointestinal tract and other sites was also investigated.th week of gestation presented at the emergency room complaining of nausea, vomiting, and diarrhea for one month. The colicky abdominal pain had intensified over the last three days. On the abdominal examination, upper abdominal and periumbilical tenderness was found. She had signs of acute abdomen and died during the examination at the emergency room. An antecedent of laparotomy at the age of 4 years was noticed, but no history of familial polyposis was available.A 32-year-old pregnant female at about the 30The postmortem examination revealed multiple arborizing polyps throughout the gastrointestinal tract with a predilection for the small bowel . The duoIn the stomach, there were multiple small, sessile polyps covering the gastric mucosa A. FigureIn the colon, the polyps were fewer A, but soHistologically, all polyps were composed of tree branch-like bundles of smooth muscle covered by mature glandular epithelium A,B,C. ThPeutz Jeghers syndrome (PJS) is a rare polyposis syndrome that still has many controversies. Although recognized as a clinical entity many years ago, our understanding of the pathologic features of the lesions and their potential relationship with cancer development is still not clear. In the present case, the diagnosis of PJS was made at postmortem examination due to a polyp-related upper intestinal obstruction. It was an opportunity to analyze the pathologic features of PJS in an adult patient in the fourth decade, as well as to investigate the presence of premalignant or malignant lesions in the gastrointestinal tract and other organs.,In the present case, the majority of the polyps were located in the small bowel, as observed in adult patients with PJS.,Intussusception is the most frequent gastrointestinal complication in PJS patients and starts early in childhood.,The clinical diagnosis of PJS is based on: (1) detection of three or more histologically confirmed Peutz-Jeghers polyps, or (2) any number of Peutz-Jeghers polyps with a family history of the syndrome, or (3) characteristic, prominent mucocutaneous pigmentation in a patient with a family history of the syndrome, or (4) any number of Peutz-Jeghers polyps in a patient with prominent mucocutaneous pigmentation.,Mucocutaneous pigmentation is a hallmark feature for the diagnosis of PJS. Small, dark brown, oval, or circular macules occur most commonly on the lips, gums, oral mucosa, and hard palate.,Another interesting aspect of the present case is that the patient was pregnant at the third trimester of gestation when the complication of PJS occurred. This might suggest that the polyp number and size would have increased during gestation due to hormonal stimulation and enhanced polyp-related complications such as intussusception. The influence of estrogen and progesterone on tumor growth during pregnancy has been suggested, but few reports on tumor growth at pregnancy are available.,,The long-term cancer risk in PJS has been widely investigated. The majority of data on cancer risk in PJS comprises small single cohort studies.In conclusion, this autopsy case report shows the natural history and pathological features of the Peutz-Jeghers syndrome in an adult woman who had a hamartomatous polyp in childhood that was not followed and developed a fatal complication during pregnancy due to upper intestinal obstruction.


Rocks are natural materials with a heterogeneous microstructure, and the heterogeneity of the microstructure plays a crucial role in the evolution of microcracks during the compression process. A numerical model of a rock with a heterogeneous structure under compression is developed by digital image processing techniques and the discrete element method. On the grain scale, the damage mechanism and microcrack characteristics of a heterogeneous Biotite granite under compression fracture are investigated. First, the process of constructing a digital image-based heterogeneous grain model is described. The microscopic characteristics of geometric heterogeneity, elastic heterogeneity, and contact heterogeneity are all considered in the numerical model. Then, the model is calibrated according to the macroscopic properties of biotite granite obtained in the laboratory, and the numerically simulated microcrack cracking processes and damage modes are obtained with a high degree of agreement compared to the experiments. Numerical simulations have shown the following: (1) Microcracking occurs first at the weak side of the grain boundaries, and the appearance of intragranular shear cracks indicates that the rock has reached its peak strength. (2) The stress concentration caused by the heterogeneity of the microstructure is an essential factor that causes rock cracks and induces rupture. Intragranular cracks occur successively in quartz, feldspar (plagioclase), and biotite, with far more intragranular cracks in quartz and feldspar (plagioclase) than in biotite. (3) Microcracking in quartz occurs as clusters, fork and fracture features, and in feldspar (plagioclase) it tends to cause penetration microcracking, which usually surrounds or terminates at the biotite. (4) As the confining pressure increases, the tensile break between the grains is suppressed and the number of shear cracks increases. At the macro level, the rock failure mode of the numerical model changes from split damage to shear destruction, which is consistent with the law shown in laboratory experiments. The deformation of rocks during compression is mainly caused by the closure, propagation, coalescence and eventual formation of macroscopic cracks in internal microfractures ,3,4,5,6.In the past few decades, numerous scholars have attempted to investigate the behavior of microcracking evolution during the compressional rupture of brittle rocks under heterogeneous conditions utilizing various advanced monitoring techniques. For example, the transient elastic waves generated by crack breakage are monitored through acoustic emission (AE), which indirectly records the crack development during the loading process of the rock ,24. ScanThe grain-scale modeling method belongs to the Discrete Element Method (DEM), and the common modeling types are circular particles and polygonal blocks, which essentially represent a collection of basic units that are cohesive and free to deform, displace and rotate ,31. ThesCircular particle modeling is called bonded particle model (BPM) in the DEM method and is mainly run in Particle Flow Code (PFC) . In the Another more popular DEM is the block element approach, which is usually represented by the Universal Discrete Element Code (UDEC) . SimilarIn this study, digital image processing was applied to the microstructure of the grain-based model to investigate the damage mechanism and microcrack evolution characteristics of Biotite granite. This method has advantages in studying the heterogeneity of rock microstructure and has been widely demonstrated ,43,44. FThe Voronoi mosaic framework has been verified to be naturally consistent with the granular mesoscopic or microscopic structure of the rock material ,44. UDECThe mechanical properties of the connection between Voronoi polygon blocks (representing both inter and intra grain bonds) obey the Coulomb friction law.In the normal direction, the contact force-displacement relation is assumed to be linear and governed by its normal stiffness In the shear direction, the response is controlled by contact shear stiffness After one contact breaks, forces are redistributed, and it might cause adjacent contacts to break. There is no need for a complex constitutive model to control cracking behavior during the process . Figure In the microscopic view, rocks are constitutionally heterogeneous materials, consisting of grain blocks of different mineral components crystallized and cemented together. Differences in composition, distribution, grain morphology and grain size of multiple minerals can significantly affect the strength and fracture mechanism of rocks. The rock sample in this study is a biotite granite from Changsha, Hunan, China. To investigate the evolution of cracks during the compression of the rock in a more realistic way, the effect of heterogeneity is considered in this paper. X-ray diffraction analysis of this rock sample showed that the main components of the sample consisted of plagioclase (36.2%), potassium feldspar (29.1%), quartz (27.8%), and biotite (5.7%), in addition to kaolinite (0.2%) and a small number of other materials (<1%) see . The graDigital image processing (DIP) is a computerized technique that electronically captures a scene and converts it into a two-dimensional pixel image, then extracts important information through mathematical algorithms. The use of DIP can effectively obtain the surface microstructure of rock samples ,43,44. If is the gray value; i, j represent the pixels corresponding to the rows and columns; and M, N is the total number of rows and columns of pixels, respectively. The numbers of the pixels along the i-axis and the j-axis are 400 and 200, respectively. The actual size of the image is 100 × 50 mm. Therefore, each pixel represents 0.25 mm.Firstly, the digital image of the granite specimen section is transformed into a grayscale image, where the image brightness is perceived at each pixel and assigned an integer value called gray level a,b. The Then, the K-means clustering algorithm was used to cluster the numerous integer values of gray levels, and the final four crystal components were clustered to match the actual ones, namely: plagioclase with the highest brightness (high gray level), potassium feldspar with the second-highest brightness (medium to high gray level), quartz with the second-lowest brightness (medium to low gray level), and biotite with the lowest brightness (low gray level). Subsequently, the image details were optimized and the coordinates of the pixel locations corresponding to the different components were extracted b. All thThe test samples and standards followed ISRM , the numThe grain block size in the numerical model also has a significant influence on the failure mode ,45,52. TIn UDEC-GBM, the rock material is considered a combination of glued structural units. Its mechanical behavior is controlled by the contact of microscopic parameters between grain blocks, which cannot be set directly from experiments. Therefore, the microscopic parameters need to be corrected to match the macroscopic physical properties before the numerical simulation, to ensure the validity and accuracy of the numerical model in the calculation. This is a very critical step before the numerical simulation.1.Calibration—Step 1: Macrophysical parameter settingMany studies have confirmed a certain connection between the selection of microscopic parameters and macroscopic physical quantities ,45,53. BThe microscopic grain block properties  of the four components plagioclase, K-feldspar, quartz and biotite are their own physical properties. Therefore, they can be set directly by the data obtained from the macroscopic experiments. The normal and shear stiffnesses of grain block contact are derived from equation :(7)kn at the beginning of the experiment. The stress–strain curve of the corrected model can be obtained in agreement with the experimental results (blue dashed line) shown in ci) is determined by the first appearance of the crack and the beginning of the stable extension of the crack; (2) crack damage stress threshold (σcd) is determined by the unstable development of cracks, mainly in the form of a sharp increase in the number of cracks starting or a reversal of the volume strain change. Both thresholds are identified by acoustic emission and strain monitoring. There is a gap between the numerical simulation method and acoustic emission detection in reality. However, acoustic emission characteristics can be approximated by detecting the stress state of joints and judging and recording the crack generation. This acoustic emission simulation method has been well used in previous studies [Eberhardt et al.  performe studies ,55,56. BFor most rocks, the crack initiation threshold is usually between 1/3 and 2/3 of the peak strength , and the-Stage I: crack consolidation;Stage II: linear elastic deformation;Stage III: crack initiation and stable crack growth;Stage IV: crack damage and unstable crack growth.Per-peak stage-Stage V: unstable crack growth with decreasing stress;Stage VI: unstable crack growth and failure of the rock specimen with decreasing stress.Post-peak stageGenerally, the crack development in the process of rock compression can be divided into five stages : -Per-peThe GBM-UDEC model did not consider the original cracks or pores in this study. Therefore, the crack closure stage is ignored, and the calculation starts from the elastic stage. Microcrack generation was investigated from Stage III to Stage VI, as shown in Since rock is a heterogeneous material, there is a great difference in the fracture pattern between grain blocks of different compositions during the compression process. The term ‘microcrack’ is classified as intragranular, transgranular, and intergranular cracks depending on the fracturing mechanism and the location where the cracks form . Intergrci, σcd, σpeak and σpcd, were selected for quantitative analysis according to the different fracture stages, see ci, boundary cracks appear first, the damage distribution of cracks is discrete and only tensile cracks on grain boundaries are produced. The angle of cracking is also mainly concentrated in the 90° direction, with small cracks and low distribution density, and no other cracks are produced.To show in more detail, the variation curves of the number of grain boundaries and transgranular cracks at different stages of damage with strain under tensile/shear damage are counted in cd, the grain boundary crack density gradually increases, the fracture of the grain boundary is not in the form of a single tensile, shear damage also occurs at the same time, forming mixed tensile-shear damage in the grain boundary. At the same time, a certain amount of transgranular damage also begins to appear, but only exhibits transgranular tensile damage. When the peak stress point is reached, the increase in the number of cracks in the form of tensile damage decreases, while the increase in the number of cracks in the form of shear damage increases, and shear cracks in the grain only start to appear after the peak strength is reached. When the peak stress point is reached, the increase in the number of cracks in the form of tensile damage decreases, while the increase in the number of cracks in the form of shear damage increases, and shear cracks in the grain only start to appear after the peak strength is reached. In combination with As the load increases, when the stress reaches σIn summary, on the microscopic scale, the fracture of microcracks in uniaxial compression tests occurs preferentially on the weak side of crystal boundaries, with the appearance of intracrystalline shear cracks signaling that the rock has reached peak strength. Fracture of microcracks follows the following sequence of development: boundary-tensile (open) crack, boundary-shear (sliding) crack, transgranular-tensile crack, transgranular shear crack, macro-shear bond.In Stage III, initial cracking occurs mainly between the grain boundaries, mostly between quartz and other crystal particles , and mostly at the tips of crystals a. The maIn Stage IV, as the axial compressive stress increases and exceeds the crack damage stress, the extrusion between the grain boundaries becomes more severe, exceeding the bond strength value, and the fracture of the grain boundaries increases rapidly. The stress is transmitted from the weak part of the grain boundary to the internal skeleton b, and thIn Stages V and VI, after the peak strength is exceeded, the rock loses its main load-bearing capacity and cracks at the grain boundaries derive and join each other to form through macroscopic cracks. At this point, microscopic stress concentrations occur more often within the different components of the rock, with loads being carried mainly by grain blocks of the same composition c. AlthouIn order to compare the simulated failure mechanism of all microcracks A with thIt has been observed experimentally that there are usually one or two groups of joint planes in feldspar. These joint surfaces can easily expand into microcracks during loading ,60. It rCompared to quartz and feldspar, biotite has a relatively small modulus of elasticity, which significantly affects stress distribution and microcrack initiation and development . ExperimIn practice, compressional damage in rocks is more likely to occur under the combined effect of different confining pressure conditions. Therefore, this paper further investigates the development and evolution of microscopic grain boundary fracture and intracrystalline fracture under different confining pressure conditions , and the results of the numerical simulations are tabulated in As the stress increases, both forms of cracking occur, with initial micro-cracks appearing in small numbers in a discrete manner, steady growth, agglomerative growth, and eventually converging into macro-cracks. Boundary tensile cracks are the first to appear at the crack initiation and show a steady growth trend. A few boundary shear cracks and intragranular tensile cracks begin to appear when crack damage is reached, at which point the number of boundary tensile cracks is approximately twice the sum of the number of boundary and intragranular shear cracks. Intragranular shear cracking only starts to occur when approaching the peak stress, and at this time, the number of boundary cracks is much higher than the number of intracrystalline cracks. The boundary strength parameter mainly causes this cracking phenomenon  to be much lower than the intracrystalline strength parameter. The local stress concentration is mainly between the grain boundaries, thus causing microcracking. Tensile cracking has always been the dominant form of cracking in the evolution of cracking, with shear cracking occupying a secondary form. Grain boundary tensile cracks are approximately parallel to the axial  direction of loading , 0 MPa, 1.Confine pressure: 5 MPaThe initial cracking takes the form of grain boundary tensile cracking, which is consistent with crack generation in uniaxial compression mode, but the initial cracking requires higher stress conditions to occur and the rate of development of grain boundary tensile cracking is significantly reduced. When it reaches the crack damage stress threshold, the number of cracks produced at grain boundaries still dominates, with a small number of intracrystalline tensile cracks present. However, unlike the uniaxial compression case, grain boundary cracks are no longer dominated by tensile cracks, the number of grain boundary tensile cracks is equal to the number of grain boundary shear cracks and intra-grain shear cracks begin to appear. When the peak strength is exceeded, the interaction and combination of grain boundary microcracks and intracrystalline microcracks lead to the formation of macroscopic shear zones.2.Confine pressure: 10 MPaWhen the confining pressure is 10 MPa, the overall development of microcracking is dominated by grain boundary shear fracture. Initial cracks occur in the form of grain boundary tensile and shear cracks. Tensile cracks at grain boundaries develop more and more slowly, while shear cracks at grain boundaries develop rapidly. The main mechanism of crack initiation changes from shear to tensile. On the other hand, intracrystalline tensile and shear cracks increase rapidly as the peak strength is approached. Macroscopic cracking parallel to the loading direction gradually decreases and is dominated by inclined shear cracks.3.Confine pressure: 20 MPaThe test results are similar to those at 10 MPa confining pressure, producing micro-cracks mainly in the form of grain boundary shear cracks, with the number of cracks far exceeding other forms of cracking. Grain boundary tensile cracking is restrained and inhibited by the higher confining pressure. Initial cracking occurs only in the form of grain boundary shear cracking. When the crack damage stress threshold is reached, a small amount of intracrystalline cracking occurs, with grain boundaries still dominate by shear cracking. When the peak stress is reached, boundary cracks and intracrystalline tensile cracks begin to show an increase, especially in the post-peak stage when both boundary cracks show a larger increase.In summary, the patterns obtained from the numerical simulations are consistent with the experimental patterns. It further demonstrates that the UDEC-GBM model adopted in this study can effectively capture the key features of granite damage behavior.This paper investigates the damage mechanism and microcrack evolution signatures of granites with heterogeneous structures. The composition and contact heterogeneity of the rock microstructure is reconstructed in a numerical model using digital images. The intracrystalline fracture effect is constructed by forming multiple sub-polygonal blocks into crystalline particles of the same size as the actual one. The heterogeneity model was calibrated using triaxial and Brazilian splitting experiments, resulting in a numerical model that accurately reflects the macroscopic and microscopic dimensions.(1) The fracture of microcracks occurs preferentially on the weak side of grain boundaries, and the appearance of intracrystalline shear cracks marks that the rock has reached its peak strength. The fracture of microcracks follows the following sequence of development: boundary-tensile crack, boundary-shear crack, transgranular-tensile crack, transgranular-shear crack, macro-shear bond. (2) Initial cracking occurs mainly in the vicinity of quartz. Transgranular breaks generally occur after crack damage stress threshold and are most numerous in quartz, followed by feldspar and least in biotite, which is consistent with the experimentally observed pattern and suggests that heterogeneous stress concentration-induced breaks are also an essential factor in inducing quartz breaks. Feldspars play an interconnecting role in developing microcracks and are more likely to form through cracks. Biotite has a lower modulus of elasticity and a higher Poisson’s ratio, which allows for more significant elastic deformation and is less prone to stress concentration, so microcracks usually surround or terminate at the biotite in the fracture path, with fewer intracrystalline cracks.(3) An increase in confining pressure increases the number of boundary shear cracks, which gradually exceed the number of tensile cracks. The development of shear cracks at low confining pressures is slow until the peak strength and only increases dramatically at the post-peak. However, as the confining pressure increases, shear cracks grow sharply from the crack damage stress threshold and gradually suppress tensile cracks. The microcracks gradually transition from tensile to shear damage at the microscopic level. (4) At the macroscopic level, there is a shift from splitting cracks to shear zones, which is consistent with the regularity presented by the experiments. Under primary rock stress conditions, shear damage between the grains of the rock is the main factor causing macroscopic cracking. As the confining pressure increases, the peak strength increases and the total amount of cracks continues to increase, with more intracrystalline fracture after the peak stress and a higher risk of rock bursts. In this paper, the fractures between different crystal grains in microstructurally heterogeneous rocks are studied. It provides an explanation for the compression fracture mechanism in deep rock mass engineering. However, it is limited to two-dimensional exploration, and there is still a certain gap compared with the complexity of natural three-dimensional rock masses. Therefore, in future work, the study of three-dimensional fabric heterogeneity can be further considered.


Oral squamous cell carcinoma (OSCC) accounts for 90–95% of malignant tumors of the lip and oral cavity and is associated with high mortality in the advanced stages. Early diagnosis is a challenge for oral pathologists and dentists, due to the ambiguous appearance of early OSCC, which is often misdiagnosed, mistreated, and associated with diagnostic delay. The gold standards for OSCC diagnosis are biopsy and histopathological assessment, but these procedures are invasive and time-consuming. Adjunctive noninvasive techniques allow the definition of the malignant features of a suspicious lesion in real time and noninvasively, thus improving the diagnostic procedure. The present review aimed to focus on some of the main promising noninvasive imaging techniques, to highlight their perspective adoption in a three-step diagnosis, which is idealistically faster and better, as well as enables the patient’s compliance.Oral squamous cell carcinoma (OSCC) is the most prevalent form of cancer of lips and oral cavity, and its diagnostic delay, caused by misdiagnosis at the early stages, is responsible for high mortality ratios. Biopsy and histopathological assessment are the gold standards for OSCC diagnosis, but they are time-consuming, invasive, and do not always enable the patient’s compliance, mainly in cases of follow-up with the need for more biopsies. The use of adjunctive noninvasive imaging techniques improves the diagnostic approach, making it faster and better accepted by patients. The present review aims to focus on the most consolidated diagnostic techniques, such as vital staining and tissue autofluorescence, and to report the potential role of some of the most promising innovative techniques, such as narrow-band imaging, high-frequency ultrasounds, optical coherence tomography, and in vivo confocal microscopy. According to their contribution to OSCC diagnosis, an ideal three-step diagnostic procedure is proposed, to make the diagnostic path faster, better, and more accurate. Oral squamous cell carcinoma (OSCC) is a keratinocyte-derived malignancy affecting the oral mucosae of lips and oral cavity, accounting for 90–95% of malignant tumors of this anatomic region , while tAlcohol and/or tobacco consumption (whether smoked or not) , betel qOSCC often arises from precursor lesions and conditions with an increased risk of malignancy, recently grouped under the name of “oral potentially malignant diseases” (OPMDs) .Delays in the diagnosis of OSCC are responsible for high mortality and morbidity, mainly related to the lymph nodal and distant metastases that frequently occur in late-stage OSCCs, which are related to shorter overall survival and poor quality of life of “survivors of advanced OSCC”, as a consequence of massive but necessary neck dissections and mutilating eradications of the primary tumor ,27.Despite easy access to the oral cavity, the varied clinical presentations of OSCCs are not always indicative of cancer and may mimic other oral lesions , which, In addition to prevention and elimination of risk factors, early diagnosis is the most powerful weapon to reduce OSCC mortality or the consequences deriving from its treatment in advanced stages. To date, the diagnostic procedure for diagnosing OSCC is time-consuming and invasive, since it must consider the multistep processes, always culminating in biopsy and histopathological assessment as gold standards . FurtherAll these reasons lead oral pathologists and oncologists to constantly research and apply novel noninvasive imaging techniques, able to add information during the clinical examination to shorten the time for biopsy and guide it by selectively identifying and targeting only highly suspicious lesions at their most representative sites .The present review aims to describe the methodology, basics principles, limitations, and future perspectives of a series of noninvasive imaging techniques, applied to oral cancer detection. In detail, on the basis of the direct experiences of the authors, the present review discusses the following: vital and virtual staining, tissue autofluorescence, narrow-band imaging, optical coherence tomography, high-frequency ultrasonography, and in vivo confocal microscopy.The vital dyes are consolidated auxiliary tools used in vivo, directly on the oral lesion, to evidence suspicious lesions and/or to better define their margins and extent. These dyes are nontoxic substances capable of penetrating living cells and binding to specific biological structures. In clinical practice, the most commonly used are toluidine blue (TB) and Lugol’s iodine (LI).On the basis of its acidophilic properties, the metachromatic dye TB selectively stains tissues rich in nucleic acids . Hence, Conversely, Lugol’s iodine (LI), also known as Lugol’s solution, marks the healthy tissues. LI is a solution generally consisting of 5 g of elemental iodine and 10 g of potassium iodide in 85 mL of distilled water with a total iodine content of 150 mg/mL . The priEpstein et al. compared the sensitivity and specificity of TB and LI alone and in association, revealing the sensitivity and specificity of 0.925 and 0.632 in TB and of 0.875 and 0.842 in LI, respectively. When associated, the two dyes showed a sensitivity of 0.850 and a specificity of 0.895, concluding that Lugol’s iodine has less sensitivity in identifying oral dysplasia and cancers but greater specificity, compared with TB .As a sort of “virtual staining”, tissue autofluorescence (AF) is based on the detection of the proper fluorescence emitted by tissues irradiated with a specific wavelength of light. In detail, “fluorescence is the property of some intrinsic molecules called fluorophores to absorb light at a particular wavelength and to re-emit it at a longer wavelength” .The light used in autofluorescence imaging, is blue light, at the wavelength of 400–460 nm, which, upon hitting the tissues, stimulates the emission of green fluorescence at the wavelength of 500–520 nm from endogenous fluorophores as keratin, collagen, elastin, and NADH; conversely, hemoglobin, porphyrins, and melanin tend to absorb the blue incident light, thus reducing tissue autofluorescence . The intThe light source to stimulate tissue autofluorescence is any blue light at the wavelength of 400–460 nm, but specific filters are necessary to detect the green fluorescent light emitted by the tissues .The examination must be performed in a dark room, and the emitted fluorescence can be recorded with digital cameras connected to the lamp. According to responsiveness to incident light, AF emitted by the tissue may be classified as “retained” (RF), gained (GF), and reduced or lost (LF), in addition to two further conditions, i.e., porphyrinic fluorescence (PF) and diascopic fluorescence (DF)  45]..45].RF is characteristic of the healthy oral mucosa, which emits an emerald green light, brighter at the masticatory mucosa than at the covering one a. HyperkLike TB, AF is also capable of highlighting occult early tumors and is a valid adjunct to presurgery identification of margins of excision of dysplastic epithelium/carcinoma escaping the naked eye. Furthermore, in a full-mouth AF, it also helps to screen subjects at risk and allows the follow-up of those with a history of OSCC or other SCC of the upper air/digestive ways.Lane et al. found that “using histology as the gold standard, the device (AF) achieved a sensitivity of 98% and specificity of 100% when discriminating normal lesions from high-risk oral premalignant lesions and invasive SCC ”; nevertNarrow-band imaging (NBI) is also known as virtual chromoendoscopy with magnification (VCM) and is extensively used in the diagnostic and follow-up management of pharyngeal and esophageal cancer, to distinguish tumor vascular patterns from other non-neoplastic affections .NBI consists of the association of common endoscopes with magnification and conventional white-light source potentiated with narrow-bandwidth filters able to sequentially emit green-blue light, changing the spectral characteristics of the incident light . BecauseType I, regular loops;Type II, dilatated and crossing loops;Type III, elongated and meandering loops;Type IV, disrupted loops and neoangiogenesis.The vessels analyzed by NBI are the so-called intraepithelial papillary capillary loops (IPCLs), which, close to the connective papillae of the oral mucosa, have an architecture characteristic related to the physiological or altered state of the overlying mucosa . In 2010The main works related to NBI in oral pathology  have defRegarding IPCL type III, its findings have been ubiquitously reported in leucoplakia with high-grade dysplasia, OSCC, and chronic inflammatory diseases and other benign lesions. Conditions that limit the use of NBI are as follows: markedly thick hyperkeratotic lesions, which obscure the vessel imaging, and lesions with hemorrhagic components, in which the blood impedes the visualization of the subepithelial capillaries. In these cases, NBI must be performed at the boundaries of the lesions, but the result can underestimate its malignancy .TD pattern: tortuous and dilated IPCLs;TE pattern: tortuous and elongated IPCLs;AD pattern: angiogenesis and IPCL destruction.Takano’s IPCL classification has been widely adopted in almost all studies on oral NBI, but Yang et al. proposed a simplified three-class classification, where IPCL patterns are equally statistically correlated with TNM, depth of tumor, and histological grade, as follows :TD patteThe NBI with magnification procedures usually follows the conventional white-light examination and it can orient the surgical margin of resection or the noninvasive follow-up of subjects with multiple lesions, as well as a history of OSCC and OPMDs, as the stepwise progression of different IPCL patterns correlates well with disease severity from normal oral mucosa to OSCC. In lesions showing more than one type of IPCL, the most advanced type detected is considered for classification. The use of NBI alone or in association with other diagnostic tools can potentiate the diagnostic process, as well as in cases of early cancers and high-grade dysplasia .Optical coherence tomography (OCT) represents a valid tool in generating images of the tissue layers, by measuring the intensity of the backscattered light ,61. OCT OCT stands as a useful and widely used device in various medical applications, and it has also been applied in oral science branches, proving to be an effective aid both on hard tissues and on mucous membranes; with a depth of penetration into tissues of 1–2 mm, OCT is considered suitable for oral mucosa , due to In 2008, Tsai et al.  developeWilder-Smith et al.  performeA recent in vitro study by Jerjes et al.  comparedOptical coherence tomography devices have proven the feasibility of assessing the oral mucosa, and the employment of this technique could contribute to the early diagnosis of oral squamous carcinoma. OCT images provide information on the epithelium, on the basal membrane and the lamina propria, enabling reliable measurement of epithelial thickness in vivo and ex vivo ,66,68. SBiopsy and histological examination are still considered the gold standard for evaluating lesions of the oral cavity, but OCT can represent an effective noninvasive in vivo examination, useful for the early diagnosis of preneoplastic and neoplastic lesions.Ultrasonography (US) is a diagnostic procedure that uses sound waves, emitted by piezoelectric crystals, and their echoes are capable of producing images of anatomical structures . UltrasoIntraoral ultrasound examination has the advantage of having direct contact with the region of interest, maintaining the characteristics of noninvasiveness, rapidity in execution, and repeatability, increasing the methods of possible applications . UltrasoR = 0.985). In a subsequent study [R = 0.988), compared to CT (R = 0.976) and MRI (R = 0.911). Other studies [The first intraoral application of ultrasound for OSCC imaging was initially described by Shintani et al. in 1997. This study aimed to evaluate and measure the extent of tumor thickness (TT), comparing it with the pathological sections and reporting a good agreement between the two techniques  and overestimate the aggressiveness of the exophytic neoplasia limited within the epithelial layers. For these reasons, in 2018, the American Joint Committee on Cancer Union for International Cancer Control (AJCC-UICC) introduced another feature to be considered in the process of OSCC tumor staging: the depth of invasion (DOI) of the tumor . DOI conSeveral studies have proposed the use of this instrument as an aid to surgical resection to mark the deep tumor margin . Other aIn conclusion, US imaging is an in vivo, noninvasive, and real-time diagnostic method that allows an accurate measurement of the tissues of the oral mucosa, and it can also be useful as a surgical aid. The value of this imaging technique appears to be superior, in terms of dimensional measurement, to techniques such as CT and MRI, in lesions with a thickness ≤5 mm. However, this instrument is operator-dependent and the learning curve is still very high.While the technologies reported above give additional but partial information about some neoplastic/dysplastic signs of a lesion, in vivo confocal microscopy (CM) goes further and allows performing a proper virtual biopsy of the tissues in their living context, offering real-time cytological and histological details, without anesthesia, surgery, or adverse reactions.In vivo confocal microscopes use a nonharmful incident laser light at specific wavelengths to stimulate the emission of fluorescent or refracted light from the living tissues, according to the presence of fluorophores or proportionally to the refractive indices of the various compounds of the tissue, respectively. In fluorescent confocal microscopy (FCM), an exogenous fluorescent substance is administered to the tissue and, due to its accumulation in different tissue components based on its chemical properties, it can highlight cellular and subcellular features by returning fluorescent light from the illuminated focal plane . In reflWhile FCM has been mainly reported in ex vivo studies  with fewUsed for the first time in ophthalmology , RCM maiAfter pilot studies to validate the method ,106,107,To date, the main in vivo RCM findings reported in OSCC are as follows: pleomorphisms of keratinocytes, necrotic keratinocytes, nuclear ploidies (indirectly defined by the presence of multiple and/or rod nucleoli within the cells), increased nuclear/cytoplasmic ratio, abnormalities in size and shape of subepithelial blood vessels, monstrous connective tissue papillae obscured by inflammatory infiltrates, keratinocytes visibly escaping to submucosal layers, and inflammatory cells infiltrating the epithelium. Furthermore, in vivo RCM can show the completely disarranged architecture of the various epithelial and subepithelial layers; the classical regular frosted-glass pattern of the spinous layer appears subverted, keratin pearls are visible in well-differentiated OSCCs, crowded keratinocytes cap the connective tissue papillae, and higher amounts than normal of the epithelial–connective tissue interdigitations are represented by an increase in the density of the connective tissue papillae .Due to the lack of stratum corneum and stratum lucidum present in the skin, oral mucosa can be easily imaged up to the submucosal layers, except for the thick hyperkeratinized lesions, whose strong superficial keratin content, highly refractive, obscures the light penetration to the lower layers.The improvement of ergonomics of the actual commercially available devices or the production of oral-dedicated ones will help the widespread use of RCM in clinical practice for experimental studies on follow-up of OPMDs and the responsiveness to therapies, without the need for recurrent biopsies, as well as guide surgeons to the margins free from cancer and shorten the time for OSCC treatment .OSCC is a malignancy associated with high mortality in its advanced stages. Despite easy access to the oral cavity, the multiform clinical presentations of early OSCCs are not always suggestive of cancer, may mimic other oral lesions, and, when misdiagnosed or mistreated, worsen and acquire invasiveness and metastasis. OPMDs may underline cancerization not identifiable with the routine conventional examination, thus requiring biopsy and histopathological assessment. Large evident OSCCs must be preliminarily mapped to orient surgeons toward the most representative tumoral area for choosing the more appropriate therapeutic approach.The diagnostic procedure of these conditions requires time, and, in lesions requiring prolonged follow-up over time, more biopsies are necessary. Adjunctive noninvasive imaging techniques performable at the chairside and that offer additional information in real time without hurting the patient could significantly improve the quality and the speed of the diagnostic procedure, enable the patient’s compliance, and allow discovering occult OSCCs and OPMDs cancerization. Each device has its qualities and limitations; some focus on two-dimensional macroscopic details, while others allow the measurement of the thicknesses and the depth of the lesions. RCM also allows the real-time preliminary consideration of the cytological and histological characteristics .Some of these techniques are conventionally used in clinical practice, such as vital (TB/LI) and virtual (AF) staining. Despite offering additional information on the nature and the extent of the lesions, their major limitations are the two-dimensional appraisal of the lesions and the operator-related interpretation. To overcome this second limitation, some authors have proposed digital image processing, using an artificial neural network ,51 or frA variant of AF is fluorescence induced by exogenous fluorophores, such as toluidine blue or 5-amino-laevulinic acid . In thesCandida colonization of the oral mucosa. Despite very preliminary, these trials open a new scenario for the detection of oral fungal infections and could offer a different, cost-effective, and real-time approach to the detection of oral mycosis [Recently, the off-label use of AF to examine the bacterial-induced porphyrin fluorescence on the tongue has allowed highlighting the negative association between porphyrin fluorescence and  mycosis .Despite the techniques above, HF US and OCT allow us to consider the three-dimensionality of the tumoral mass and accurately measure its thickness and the depth of infiltration.Furthermore, NBI adds relevant information about the vascular pattern, with IPCL type 4 being strongly associated with OSCC and high-grade dysplasia. RCM allows the optical biopsy of the tissue, allowing in vivo and real-time identification of the presence of OSCC microscopic indicators.However, despite its undoubted support in providing optical biopsy of living tissues with a resolution close to conventional histology, the widespread use as a chairside diagnostic method in oro-dental clinical practice of in vivo CM is still limited by some important restrictions. These are mainly the lack of medical devices ergonomically adaptable to each site of the oral cavity, and the need for experience and high-level training to correctly interpret the cytological and histological findings of CM. However, CM is extraordinarily useful in the clinical practice to also orient diagnosis of non-neoplastic diseases, as an alternative to conventional histology in some selected cases and for research purposes, to correlate molecular and classical histological findings within CM features ,135,136,In conclusion, despite the described techniques not always being able to replace conventional histology, if used properly and with the right know-how, they are a resource and to improve the quality of the diagnostic path in oral pathology and dentistry in the future, thus allowing the conduction of noninvasive follow-up of subjects at risk for OSCC or with history of SCC of the upper air/digestive ways, to discover signs of malignancies in OPMDs, and, in the case of advanced, large, multifocal OSCC, to presurgically map its superficial extent and its DOI, to orient surgeons to better approach the OSCC for a conclusive diagnosis and therapeutic excision in free margins.With this in mind, considering the potential of each method, we propose an idealistic three-step procedure  that simIn the proposed three-step diagnostic protocol, a series of noninvasive imaging techniques are introduced to improve the presurgical diagnostic accuracy of suspicious or frankly tumoral oral lesions. They are placed, chronologically and conceptually, before the conventional bioptic procedure.In the first phase (data collection), in addition to the diagnostic indicators obtained with conventional clinical examination and collection of anamnestic data, a series of adjunctive investigations allow obtaining additional information on the suspected lesion or carcinoma, in the context of the classical clinical–anamnestic protocol. The vital stains and the autofluorescence allow dichotomizing the diagnostic suspect as positive/negative. NBI and doppler ultrasound via HF US provide details on the vascular pattern and possible tumor neoangiogenesis. A preliminary detailed measurement of the tumor size  is obtained with HF US and OCT. Lastly, the optical biopsy allowed by in vivo RCM offers real-time cytoarchitectural information of the lesion at microscopic resolution.Having some or all these methods ideally available at the chairside, the performance of the examinations can be contextually planned during the first clinical evaluation or deferred for mere organizational reasons. In any case, the results can be integrated with conventional instrumental investigations and lab tests.The second step (data integration) comes before the biopsy (when required); after a possible re-evaluation in case of doubts or clinical changes, all the information collected allows the surgeon to define the need for surgery, plan the type of approach , and accurately define the three-dimensional extension of the incision/enucleation, to be able to conclude the diagnostic procedure with the conventional histopathological evaluation of the specimen (conclusive diagnosis).In conclusion, the proposed empowered diagnostic protocol allows the thorough presurgical definition of the suspicious lesion and its features, the mapping of extended or multifocal lesions to define the elective sites for biopsy, and the discrimination of lesions with different prognostic significance and surgical/therapeutic approach. This methodology also allows monitoring more conservatively those lesions requiring a “wait and see” approach, and it can be advantageous for following up the evolution of chronic lesions and diseases, thus reducing multiple biopsies, when unnecessary. Furthermore, it can be assumed that the patient will be more compliant and motivated to respect the periodic follow-up.Confronting OSCC and saving the patient is a battle against time; while some of these technologies are still under study and require practice and experience, we look forward to the near future where they will be applied clinically and routinely to increase patient survival and improve quality of life after cancer.


Propolis is a beekeeping product with a complex and highly variable chemical composition. Many beneficial health properties have been reported. In this review, we will be focusing on compiling the studies carried out with propolis on infectious diseases of greater medical relevance. Likewise, the promises and challenges that propolis has to consolidate itself as a complementary therapy for the treatment of these diseases are analyzed.Infectious diseases are a significant problem affecting the public health and economic stability of societies all over the world. Treatment is available for most of these diseases; however, many pathogens have developed resistance to drugs, necessitating the development of new therapies with chemical agents, which can have serious side effects and high toxicity. In addition, the severity and aggressiveness of emerging and re-emerging diseases, such as pandemics caused by viral agents, have led to the priority of investigating new therapies to complement the treatment of different infectious diseases. Alternative and complementary medicine is widely used throughout the world due to its low cost and easy access and has been shown to provide a wide repertoire of options for the treatment of various conditions. In this work, we address the relevance of the effects of propolis on the causal pathogens of the main infectious diseases with medical relevance; the existing compiled information shows that propolis has effects on Gram-positive and Gram-negative bacteria, fungi, protozoan parasites and helminths, and viruses; however, challenges remain, such as the assessment of their effects in clinical studies for adequate and safe use. Currently, most health systems around the world are based mainly on the prevention of diseases. The world is constantly exposed to a large number of pathogens that cause emerging and re-emerging disease. These pathogens differ widely in terms of severity and probability and have varying consequences for morbidity and mortality, jeopardizing not only health but also social and economic well-being. It is absolutely necessary to have a global health system that is able to prevent and respond effectively to the expanding and evolving infectious diseases, as well as solving an increasingly widespread antimicrobial resistance . The neeExisting natural products could be potential resources to find different compounds for the development of new drugs and relevant medicine , creatinOne of the main complications with diseases caused by bacteria is their resistance to the antibiotics commonly used against them. Antibiotics are chemical compounds that can act in two ways: inhibiting (bacteriostatic drugs) or killing  bacteria. These drugs are characterized by a specific interaction with a defined target in the bacterial cell, and they are arguably the most important medical intervention introduced by humans . CurrentStaphylococcus causes different infections in the human population like impetigo, scalded skin syndrome, toxic shock syndrome, pneumonia, endocarditis, and urinary tract infections, among others . No. NoS. epibiotics .Streptococcus is classified as Gram-positive and catalase-negative, appearing as cocci in pairs and chains on Gram stains. When grown on blood agar, they appear as small colorless colonies that cause beta or complete hemolysis . Se. SeS. pyn models , which wS. pneumoniae and S. pyogenes. The propolis from Ireland increased synergistic effect and the effectiveness of drugs that interact on cell-wall synthesis (vancomycin and oxacillin) . Pr. PrE. couercetin . As mentuercetin . In addiuercetin .Salmonella typhi, and Bulgarian propolis presented a bactericidal effect and a synergism with chloramphenicol, tetracycline, and neomycin (act on the ribosome) on this same pathogen .,36.KlebsP. aeruginosa. In all samples, gallic acid, caffeic acid, coumaric acid, artepillin C, and pinocembrin were identified . W. WG. lamIn this work, we addressed the properties of propolis in the defense against these parasitic diseases; in most cases, propolis showed interesting and promising antiprotozoal activities . HoweverHumans are exposed to a remarkable number of parasites, including protozoans (over 70 species), helminths (about 300 species), and arthropod parasites. There are two major phyla of helminths: the nematodes  and the Platyhelminthes (Trematoda and Cestoda) ,167. AccFasciola gigantica was reported. Alteration of the architecture was found as lifting base of the spines and large blisters in the apical cone, several of which seemed to have burst, generating injuries. The inhibitory activity on the viability and hatchability of immature F. gigantica eggs was also found, showing the highest inhibitory effect compared with other treatments. The chemical composition of these propolis was determined. Compounds such as diprenyl-dihydrocoumaric acids, coumarate esters, ferulate esters, hydroxy acetophenones, furanon derivative, furofuran lignans, benzofuran lignans, and valeric acids derivatives could be related to anthelmintic activity . T. TFascio problem ,178.Helminth parasites mainly continue to be a public health problem in countries with disadvantaged and low-resource communities. Currently available anthelmintic drugs include the benzimidazoles , pyrantel pamoate, and ivermectin . AlthougViruses need the host cells’ biosynthetic machinery to replicate ,183. VirTwo propolis from Czech Republic (aqueous and ethanolic extracts) were studied, and both showed great antiviral effect on herpes simplex virus type 2 (HSV-2). Both propolis decreased the infection and exhibited a concentration- and time-dependent antiviral effect. Additionally, the two propolis showed a high antiviral effect when viruses were pretreated prior to infection; thus, both propolis could be used to treat recurrent herpetic infection topically .+ lymphocytes and microglial cell in a concentration-dependent manner. In another study, propolis from the United States suppressed cell fusion HIV-1 in cultures of CD4+ lymphocytes, suggesting that the possible mechanism of propolis’ antiviral property in CD4+ lymphocytes is produced in part by inhibition viral entry into cells [In other research, the antiviral effect of different propolis from several geographic regions, such as the United States, Brazil, and China, was against human immunodeficiency virus type 1 (HIV-1). All propolis inhibited viral expression in CD4to cells .+ lymphocytes, and stimulation of immunological activity [The antiviral activity of four Brazilian propolis on influenza virus was examined, and all propolis presented anti-influenza virus effect in vitro. In this same study, the four propolis were studied in a murine influenza virus infection model , and only one propolis sample effectively prolonged the lifetime of infected mice. The authors concluded that the Brazilian propolis possessed antiviral effect and amelioration influenza symptoms in mice . In anotactivity . HoweverSome flavonoids and phenolic acids, also described in propolis, presented antiviral activity . One antSimilarly, the antiviral effect of aqueous and ethanolic extract of Czech Republic and some compounds identified in propolis against HSV-1 in cell culture was analyzed. Both samples presented high anti-HSV-1 effect in cells effect in prior to viral infection; of the compounds tested, galangin and chrysin were the most active components. However, the propolis with various compounds presented higher antiviral activities than the isolated constituents alone. The authors concluded that the antiherpetic activity of propolis is due to a combination of several components; therefore, the propolis from Czech Republic was found to be more effective on herpes infection than the individual compounds .In another study, the replication of HSV-1 and HSV-2 was inhibited with the propolis from the south of Turkey. Propolis started to suppress HSV-1 replication after 24 h of incubation and effect on HSV-2 started at 48 h after incubation. This activity of propolis on HSV-1 and HSV-2 was checked by a lower in the number of viral copies. They found that propolis showed activity similar to that of acyclovir, since both started to suppress HSV-1 replication following 24 h of incubation. They also found a synergistic effect of combined propolis and acyclovir on HSV-1 and HSV-2 replication compared with acyclovir alone. Some compounds in the propolis were identified. The propolis from the south of Turkey was found to present relevant antiherpetic activities in comparation with acyclovir; particularly, the synergism generated by the antiherpetic effect of propolis and acyclovir in combination has a stronger activity on HSV-1 and HSV-2 than acyclovir alone. The authors mentioned that the possible mechanism of synergism between acyclovir and propolis may be attributed to some of the components of propolis . As descAlthough little literature about the antiviral activity of propolis in clinical studies exists, in 2019, Jautová et al. reported that one lip cream with propolis extract from Central Europe produced a better effect than acyclovir to treat patients with herpes labialis in the vesicular phase, confirming the clinical efficacy of lip cream composed of European propolis in the early and late start of treatment during an episode of herpes labialis . SimilarThe current situation related to COVID, which has compromised all health systems, makes it necessary to search for therapies that prevent or mitigate the complications of this disease. Natural products such as propolis are an interesting option in the search of complete therapies. Some recent research mentions the potential benefits of using propolis against this disease. These studies are based on previously reported activities against other viruses and on in silico models that allow predictions of activities against this virus. These studies focus mainly on reported bioactive compounds in the different propolis; they include antiviral activities that could be applied against SARS-CoV-2 or immunomodulatory effects that would reduce the symptoms of the disease. One of the clearest examples is quercetin, one of the most abundant and consumed flavonoids in the diet. Quercetin has been shown to inhibit the replication cycle of the virus, since it reduces the functioning of the main protease (Mpro) and S protein of SARS-CoV-2. CAPE, one of the main components of many propolis, is able to inhibit the transmembrane protease serine 2 (TMPRSS2), angiotensin-converting enzyme-related carboxypeptidase (ACE-II), and Mpro; these molecules are crucial for access and replication viral of SARS-CoV-2 in cells. Another interesting compound is the rutin that reduced the function of S protein, ACE-II, and others non-structural proteins of SARS-CoV-2. These flavonoids are also able to regulate JAK/STAT-mediated signaling and the production of ROS, NO, pro- and anti-inflammatory cytokines, avoiding a cytokine storm. They even reduce the risk of comorbidities that complicate the betterment of patients with COVID-19 ,203,204.Considering all the research mentioned above, the search for new strategies for the control and complementary treatments of infections caused by viruses has become a global public health priority. However, more in vitro and clinical studies with propolis are needed to elucidate its mechanisms of action and identify the molecules responsible for the antiviral effects of this natural product.We collect the main studies of the effect of propolis on pathogens related to infectious diseases of medical relevance. The reports of the efficacy of the different propolis are encouraging: this bee product showed effectiveness on bacteria, fungi, protozoa, helminths, and viruses. Propolis presents a great spectrum of components that could be used to treat characteristic affections of distinct diseases. Not all propolis present the same activities; depending on the flora of the geographical area, each propolis has a different chemical composition with unique biological activities, making propolis a promising source of discovering molecules, which can be used in different clinical situations. Propolis offers potential for research into the treatment of infectious diseases that lack adequate therapies due to the resistance of pathogens to drugs, either isolating active components to be studied alone or combined with different current drugs. Despite the in vitro and in vivo evidence suggesting that propolis can be a reliable alternative to existing drugs, the effect of propolis must be investigated in the clinic to improve tour comprehension of the mechanisms of action of the different propolis, attain the synergism of their compounds, and generate a standardized and safe consumption protocol.Another relevant aspect is that clinical tests with propolis, bee products, or other natural products are scarce but necessary. From products used in traditional medicine, modern medicine has obtained compounds such as taxol, valproic acid, polycarpine, ephedrine, digoxin, and acetylsalicylic acid, just to name a few. The therapeutic uses and applications of natural products and their derivatives are promising in the search for new treatments, so clinical studies against diseases caused by microbes resistant to drugs or treated with toxic agents should be a priority in future clinical research.Finally, a new perspective to consider in future research is to investigate the presence and function of microRNAs (miRNAs) in propolis. Recent studies have proposed that the miRNAs present in honey from plants visited by bees during their collection could play a determining role in the development of larvae. The finding of these molecules could be surprising related to the beneficial effects on the health of consumers of this bee product. The identification of miRNAs in propolis would be crucial to understanding and explaining many of its biological and medicinal activities, and these activities are currently attributed mainly to compounds such as flavonoids and terpenes. miRNAs in bee products can be the subject of various investigations, and their clinical applications could generate new treatments based on nutritional supplements with various specific benefits for health ,206.


Natural polymers are of great interest in the biomedical field due to their intrinsic properties such as biodegradability, biocompatibility, and non-toxicity. Layer-by-layer (LbL) assembly of natural polymers is a versatile, simple, efficient, reproducible, and flexible bottom-up technique for the development of nanostructured materials in a controlled manner. The multiple morphological and structural advantages of LbL compared to traditional coating methods , make LbL one of the most useful techniques for building up advanced multilayer polymer structures for application in several fields, e.g., biomedicine, energy, and optics. This review article collects the main advances concerning multilayer assembly of natural polymers employing the most used LbL techniques  leading to multilayer polymer structures and the influence of several variables  in this LbL assembly process. Finally, the employment of these multilayer biopolymer films as platforms for tissue engineering, drug delivery, and thermal therapies will be discussed. Over the last decades, polymers obtained from biomass, known as natural polymers, have been widely employed for a variety of biomedical applications due to their intrinsic properties such as biocompatibility and non-toxicity. They are naturally produced in large quantities because they are present in or created by living organisms such as plants, microorganisms, algae, and animals . PolysacNatural polymers are biodegradable under physiological conditions through enzymatic degradation or hydrolytic processes leading to body-friendly degradation products. However, rapid degradation can be undesirable for their employment in some biomedical applications  . In ordeIn 1999, Elbert et al.  developeThis review article provides an overview of the state-of-the-art concerning layer-by-layer assembly of natural polymers, from fundamentals regarding the influence of different experimental parameters on the final morphology and properties of the resulting natural multilayers to the biomedical applications. Firstly, the main LbL deposition techniques employed for the buildup of natural polymers leading to multilayer structures and coatings will be addressed, highlighting the influence of different parameters, such as molecular weight or the nature of the polyelectrolytes, on the self-assembly process and architecture of the resulting films. Then, different strategies for the design of natural multilayer films for biomedical applications will be described including procedures for cross-linking or tunability of the architecture of the multilayers to modulate cell adhesion. Finally, the employment of multilayers derived from natural polymers as bioactive functional coatings and platforms for tissue engineering or drug delivery and thermal therapies will be discussed.Multilayer assembly through the LbL technique involves different types of intermolecular interactions, e.g., electrostatic, charge-transfer, host–guest, hydrophobic interactions, coordination chemistry interactions, and hydrogen and covalent bonding being the electrostatic interactions that are the most studied . The eleTwo main buildup mechanisms, linear and exponential, have been reported during the electrostatic LbL assembly. Linear growth is the simplest one in which the thickness and mass of the film increase linearly with the number of deposited bilayers, and each polyelectrolyte layer interpenetrates only with the adjacent ones . In cont10, whereas a lower thickness was achieved during spray LbL (~90 nm) but exhibiting and exponential growth . O. O51]. Oa on adsorption, at the same pH environment ..Staphylo100 multilayer films mimicking the features of the native ECM could be also used for skin wound healing. The results point to a progress of the wound healing process after 21 days, showing a thin epidermal layer and epidermal papillaes in the case of HA–DN films. Additionally, the mastocyte population was also reduced for HA–DN films leading to a highest decrease in inflammation . F. F47]. Ftructure c 126]. . n multiAnother important natural polycation employed is PLL, which has been combined with HA leading to multilayer PLL/HA films. These films were loaded with antitumor drugs and showed a decrease in human colonic adenocarcinoma HT29 cell viability over three days . In anot3O4) nanoparticles can be used as heating agents for magnetic hyperthermia therapies. The incorporation of Fe3O4 NPs within CHI/ALG multilayer structure gave rise to thermomagnetic films (TMFs) .A summary of all works referenced in this review article is collected in This article presented a comprehensive overview of layer-by-layer assembly of natural polymers for biomedical applications being polysaccharides and polyamino acids, the most employed for the LbL assembly of multilayer polymer films. In particular, chitosan (CHI) and poly (L-lysine) (PLL) are commonly employed as polycations, whereas alginate (ALG) and hyaluronic acid (HA) are the most studied polyanions as seen in In relation to the different methods of preparation found in the literature for the preparation of multilayer films from natural polymers, it is possible to conclude that even if dipping LbL was the first LbL technique employed and the technique most commonly employed, many works employ spray LbL since its discovery by Ciba Vision. Hence, spray LbL constitutes an advantageous and powerful technique not only for scientific research but also for industrial purposes. Apart from these two LbL techniques, spin coating and, very recently, brush coating have also been employed for building up multilayer polymer films. The influence of several experimental variables  was also discussed, highlighting their influence on the growth mechanism  as it was exhibited by each specific polycation/polyanion system which, in turn, controls the final properties of the multilayers.From our point of view, the employment of natural polymers as building blocks of advanced materials for biomedical applications will continue to increase scientific and technological interest, not only because of their intrinsic characteristics as to their biodegradability and biocompatibility but also because of their versatility to be functionalized to get semi-synthetic polymers. LbL assembly of natural polyelectrolytes constitutes a straightforward methodology to produce polymer multilayer films (self-standing and as coatings of organic and inorganic substrates) under mild reaction conditions as reported in this manuscript. Current trends in the fabrication of LbL materials from natural polymers that exploit the assembly of these polyelectrolytes onto soft colloidal nanostructures  can be developed as templates for the design of biomaterials for the encapsulation and controlled release of active molecules. In this regard, three-dimensional LbL assembly of natural-based polymers modified and/or functionalized with biological moieties will extend the range of biomedical applications reported herein. The addition of inorganic nanoparticles within LbL multilayer films to yield nanocomposite polymer films constitutes a current strategy for functionalization of multilayer polymer films which has also been addressed in this review. In our opinion, research efforts on the development of nanocomposite multilayers need to be made in order to promote effective interaction between the nanoparticles and the polymer matrix  in order to control the nanoparticle’s degree of dispersion and, hence, the final properties exhibited by the multilayers.


The substantial clinical burden and disability after stroke injury urges the need to explore therapeutic solutions. Recent compelling evidence supports that neurogenesis persists in the adult mammalian brain and is amenable to regulation in both physiological and pathological situations. Its ability to generate new neurons implies a potential to contribute to recovery after brain injury. However, post-stroke neurogenic response may have different functional consequences. On the one hand, the capacity of newborn neurons to replenish the damaged tissue may be limited. In addition, aberrant forms of neurogenesis have been identified in several insult settings. All these data suggest that adult neurogenesis is at a crossroads between the physiological and the pathological regulation of the neurological function in the injured central nervous system (CNS). Given the complexity of the CNS together with its interaction with the periphery, we ultimately lack in-depth understanding of the key cell types, cell–cell interactions, and molecular pathways involved in the neurogenic response after brain damage and their positive or otherwise deleterious impact. Here we will review the evidence on the stroke-induced neurogenic response and on its potential repercussions on functional outcome. First, we will briefly describe subventricular zone (SVZ) neurogenesis after stroke beside the main evidence supporting its positive role on functional restoration after stroke. Then, we will focus on hippocampal subgranular zone (SGZ) neurogenesis due to the relevance of hippocampus in cognitive functions; we will outline compelling evidence that supports that, after stroke, SGZ neurogenesis may adopt a maladaptive plasticity response further contributing to the development of post-stroke cognitive impairment and dementia. Finally, we will discuss the therapeutic potential of specific steps in the neurogenic cascade that might ameliorate brain malfunctioning and the development of post-stroke cognitive impairment in the chronic phase. Stroke is a major cause of death and disability worldwide . ClinicaThe brain has an intrinsic capability to self-repair after stroke  and, in In contrast with the frequent spontaneous motor recovery during the chronic phase, cognitive function tends to worsen long-term after stroke . As suchIn physiological situations, newborn neurons generated in the SVZ migrate through the rostral migration stream (RMS) toward the olfactory bulb (OB) where they finally differentiate into interneurons to contribute to olfactory functions . An amouThe enhancement of SVZ neurogenesis after global ischemia was first described in 1998 . After tIn a longitudinal analysis performed on a mouse model of cortical ischemia by permanent MCAO induced by ligature, we found that cortical stroke has a triphasic effect on the total number of cells in proliferation at the SVZ, first with an early acute reduction of proliferation on post-stroke day 1, a second slow increase with a maximum on post-stroke day 14 and, finally, a reduction of proliferating cells at 28 days after ischemia onset. Our results also showed that this process was bilateral in all the conditions and at all the time points studied, supporting an important effect of ventricular cerebrospinal fluid (CSF) composition at this level . This biSVZ has been identified as the main source of neuroblasts generated after stroke. Neuroblasts migrate ectopically from the pre-defined RMS to the injured area , a proceInterestingly, in our longitudinal study, we also analyzed the physiological, eutopic RMS route (from the SVZ to the OB) . Our resA great deal of evidence supports that post-stroke neurogenesis in the SVZ could be involved in the functional improvement that stroke patients undergo during the first months after the establishment of the lesion . SVZ newAccording to the literature, the SGZ in the hippocampus is the other neurogenic region of the adult brain where neurons are continuously generated throughout life. New granule cells are born in the SGZ of the DG, from where they migrate into the granule cell layer (GCL) and become functionally integrated into neuronal networks. The generation and integration of these newborn neurons seems to be strictly regulated, which is of paramount importance considering that hippocampal neurogenesis is a fundamental process for the formation and retrieval of spatial memories and, specifically, for hippocampal pattern separation .After brain ischemia, the proliferation and differentiation of neuronal progenitors in the DG is also strongly stimulated, leading to a significant increase in neurogenesis . In expeTherefore, stroke increases the production of new neurons in the SGZ, but how the hippocampal neurogenic response influences disease outcome, positively or negatively, is still controversial. In global cerebral ischemia models, in which a massive death is observed in the hippocampus, new hippocampal CA1 neurons are detected after the injury . AlthougNeurogenesis can be controlled at different steps including NSC maintenance, proliferation, fate specification and differentiation, migration, fully maturation and, finally, newborn neuron integration into the local circuitry . All theFor hippocampal neurogenesis, the number and the type of NSCs/NPCs are key regulators in steady-state conditions. NSCs are located in the SGZ of the DG, at the interface of the hilus and the granular cell layer. Through different intermediate progenitors, they finally generate immature neuroblasts that eventually convert into young neurons . PrototyIn the context of cerebral ischemia, several studies have characterized the contribution of the different types of NSCs/NPCs to the increased post-stroke proliferation . Six houare similar mechanisms guiding a heterogeneous SGZ NSCs activation upon ischemic injury? Further studies using single cell transcriptomics are required to deepen our knowledge on the heterogeneous nature of SVZ and SGZ neural precursor population after stroke. These studies will provide insights on the intrinsic regulatory mechanisms controlling NSCs activation upon stroke in both niches and about the type of stimuli that mediates NSCs priming and activation.An important point is whether this NSC heterogeneity also exists after stroke, and even more, if all NSCs are equally activated or, if on the contrary, just a subpopulation of them is sensitive to the ischemic stimulus. Although this has not been explored yet in the post-stroke hippocampus, some recent data may suggest that NSC heterogeneity exists in the hippocampus after some pathological situations like epileptic disorders, or in the SVZ after ischemic injury. In the first scenario, by performing intrahippocampal injections of low and high doses of kainic acid (KA) to model epileptiform activity (EA) or mesial temporal lobe epilepsy (MTLE), Apart from the features of neurogenesis which are intrinsic to the cells that populate the niche, the microenvironment plays a fundamental role in guiding the neurogenic process. Quiescent NSCs in both SGZ and SVZ display an enriched expression of genes related to cell-cell adhesion and cell-microenvironment interaction, suggesting that intrinsic and extrinsic signals are actively involved in maintaining stem cell quiescence . Support(1)Mediators of post ischemic excitotoxicity or cortical spreading depression, such as K+ and glutamate elevations, could be involved, as both have been implicated in an enhanced proliferation of immature cells while at the same time directing toxicity in mature cell types (ll types . Granulell types .(2)Injury-induced circulating factors might directly affect neural progenitors that are in physical contact with the vasculature inflammatory response elicited by the injured brain, whereby astrocytes and microglia activation could lead to the secretion of a variety of growth factors and immune modulators able to affect progenitor proliferation and survival. In addition, several studies associate pro-inflammatory cytokines released after stroke with proliferation, migration, differentiation, and survival of neural precursors  and the loxP-STOP-loxP-IRES-DTA gene cassette is knocked into the NSE  gene  gene , 2008. A 2) gene , support 2) gene , and strniche-dependent fashion. Thus, instead of a complete modulation of the post-stroke neurogenic response, strategies should be directed to enhance or inhibit specific steps of the post-stroke neurogenesis.The post-stroke neurogenic burst in both SVZ and SGZ niches may have different functional consequences in stroke outcome. While increasing SVZ neurogenesis could promote functional recovery, augmentation of hippocampal neurogenesis could further exacerbate the development of post-stroke cognitive impairment. Therefore, in order to consider neurogenesis as a potential therapeutic post-stroke target, it would be necessary to design specific strategies in a One potential specific maneuver after stroke might be the enhancement of the survival and integration of SVZ-derived neuroblasts in the injured brain. In this context, given the very low degree of survival of neuroblasts that migrate to the damaged tissue and their low differentiation into mature neurons, the major emphasis from a therapeutic standpoint should probably be put on approaches that improve these processes. Thus, different strategies have focused on trying to regenerate damaged tissue by either increasing endogenous neurogenesis  or by stOn its hand, at the level of the SGZ, strategies should focus toward the prevention of the cases of maladaptive neurogenesis leading to aberrant morphologies of newborn granule neurons and their detrimental consequences.Although we are still a long way from having a whole picture of the post-stroke neurogenesis process, current investigations will likely allow us to dissect the multi-step neurogenic response in both niches, gaining insight on how all these processes are initiated and maintained, and paving the way to develop new therapeutic avenues for stroke patients.MC, AG-C, and MM conceptualized the study. IL and MM were responsible for the funding acquisition. MC, AG-C, and MM contributed to the writing . MC, AG-C, CT-L, VM, EF, SV-R, JG-S, IL, and MM contributed to the writing (review and editing). All authors read and approved the final manuscript.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.


Appetite loss/anorexia of aging is a highly prevalent and burdensome geriatric syndrome that strongly impairs the quality of life of older adults. Loss of appetite is associated with several clinical conditions, including comorbidities and other geriatric syndromes, such as frailty. Despite its importance, appetite loss has been under-evaluated and, consequently, under-diagnosed and under-treated in routine clinical care. The International Conference on Frailty and Sarcopenia Research (ICFSR) Task Force met virtually on September 27th 2021 to debate issues related to appetite loss/anorexia of aging. In particular, topics related to the implementation and management of appetite loss in at-risk older adult populations, energy balance during aging, and the design of future clinical trials on this topic were discussed. Future actions in this field should focus on the systematic assessment of appetite in the care pathway of older people, such as the Integrated Care for Older People (ICOPE) program recommended by the World Health Organization. Moreover, clinical care should move from the assessment to the treatment of appetite loss/anorexia. Researchers continue to pursue their efforts to find out effective pharmacologic and non-pharmacologic interventions with a favorable risk/benefit ratio. Appetite is thought to be a major determinant of nutritional status during aging. Its loss, ie, anorexia of aging, is a common clinical condition in older adulthood  Task Force met virtually to discuss issues related to appetite loss and aging. In particular, the implementation and management of appetite loss in at-risk older adult populations, energy balance during aging, and the design of future clinical trials on the anorexia of aging were discussed.As a core element of nutritional status in older adulthood, loss of appetite plays a significant role in the frailty syndrome. Frailty is considered as a medical syndrome of multidimensional etiology and characterized by decreased physiological reserves  to combat internal and external stressors. Consequently, frailty increases the individual’s vulnerability to adverse health events , 20, incAs it is the case for frailty, appetite control is also influenced by several determinants at different levels , encompaRaising awareness around the multidimensional causes of loss of appetite and its interaction with frailty is crucial for the care of older adults in the current context of social restrictions and containments imposed by the COVID-19 pandemic. Indeed, these social isolation measures can have deleterious effects on both anorexia of aging and frailty, alongside other conditions such as sarcopenia . They caThe World Health Organization (WHO) has recently recognized the importance of nutrition, and appetite loss as a central element of nutritional health, for the care of older individuals by introducing nutritional status as a core measure in the Integrated Care for Older People (ICOPE) program , 26. TheThe ICOPE program has started to be implemented in different clinical settings and countries around the world. In the Toulouse area , primary care providers , in partBeyond the data displayed on Table The ICOPE program is designed to screen, assess and treat deficits in intrinsic capacity in order to keep functional ability for as long as possible, thus preventing or delaying the onset of disabilities and care dependence. ICOPE and its guiding line model of intrinsic capacity have been released only recently. Evolutions in founding concepts, particularly regarding the construct of vitality , are being proposed, which cNutritional health represents a dynamic process throughout the life span. According to recent data using the gold standard assessment of energy expenditure double-labelled water (DLW), the human organism requires more energy in the development phases during childhood, followed by a decline up to around 30 years-old, when a plateau is observed until 60 years-old, and then a further progressive decline is observed in late ages . AlthougThere are several gaps in the field of energy expenditure during aging: first, very few reliable data on energy expenditure through the life course is currently available; this lack of data is still more pronounced for people over 80 years-old. As a consequence, there is an absence of normative data on energy expenditure in older adulthood. Second, studies on DLW have mostly relied on cross-sectional data. Longitudinal data is therefore needed in order to better control for interindividual variability, which is much important during aging. Investigations on energy expenditure during aging are crucial to inform the development of evidence-based nutritional recommendations for older people, with potential implications for research  and clinical practice.Anorexia of aging , as all age-related conditions including frailty, shares biological and physiological alterations partly driven by the aging process, with particular importance to oral/sensory health , gastrointestinal function  and body composition changes ; this latter constituting one of the core components of the aging phenotype , 36. As Anorexia can be seen as an early sign of an evolving malnutrition condition, being a symptom that, in most cases, would precede weight loss. HoweverTherefore, the lack of energy driven by anorexia results in poor physical performance and adverse health events in the elderly; these associations are in part independent of other clinical conditions. The assessment and management of anorexia of aging, and more globally of malnutrition, must be taken into account in routine clinical practice among geriatric patients. There are simple scales assessing anorexia that can be appropriate for clinical use, such as the Functional Assessment of Anorexia/Cachexia Therapy (FAACT) and the Simplified Nutritional Assessment Questionnaire (SNAQ). To date, drugs to combat anorexia of aging  are still of limited utility in clinical practice mostly due to an unfavorable risk/benefit balance. Therefore, other nutritional interventions , without useful drugs that clearly present a favorable risk/benefit ratio. Given the prevalence and burden of anorexia of aging , efforts to develop effective pharmacological interventions to combat this condition, which may ultimately prevent and decrease the severity of malnutrition, should be stimulated and pursued. In this context, it is of utmost importance that trialists define the essential methodological aspects for a study aiming at testing the effects of a molecular agent on appetite loss/anorexia. This represents a major challenge given the multifactorial etiology of anorexia and the multidimensional nature of its contributors. Indeed, due to this multitude of etiological factors and determinants, several types of appetite loss may exist under the umbrella term of anorexia of aging. For instance, providing an appetite-stimulating medication to a person with depression-dependent anorexia is arguable since the origin of the syndrome is not addressed. On the other hand, subdividing anorexia into various subtypes will complexify the study design and may render the development of future investigations unreasonable and almost impossible to be achieved due to issues such as statistical study power (sample size will be larger if the study must account for the effects of a drug on each anorexia subtype) and consequent economic burden. One potential intermediate solution is to have two main anorexia subtypes: 1) anorexia with associated cachexia and 2) anorexia without cachexia. Future trials might target one of these two subtypes or ideally be powered to address both. Besides the difficulty of defining the best target population (inclusion/exclusion criteria), other challenges that must be solved involve defining: the most appropriate assessment tool for appetite, the pre-planned primary/secondary outcome measures, and study length. Although there are short and simple questionnaires to measure appetite in older adults with good sensitivity and specificity to detect weight loss, such as the 8-item Council on Nutrition appetite questionnaire (CNAQ) or its 4-item derivative SNAQ, no goldLoss of appetite/anorexia of aging is a prevalent and burdensome geriatric syndrome. Yet, it is under-evaluated and, as a consequence, under-diagnosed and under-treated in routine clinical practice. Future actions in this field should focus on the systematic assessment of appetite loss in the care pathway of older people, as it is the case for the ICOPE program launched by WHO. Moreover, clinical care should move from assessment to the treatment of this syndrome, whereas researchers pursue their efforts to find effective pharmacologic and non-pharmacologic interventions with a favorable risk/benefit ratio.