Although the human eye is an easily accessible sensory organ, it remains a challenge for drug administration due to the presence of several anatomical and physiological barriers which limit the access of drugs to its internal structures. Molecular imprinting technology may be considered the avant-garde approach in advanced drug delivery applications and, in particular, in ocular therapy. In fact, molecularly imprinted polymers hold the promise to compensate for the current shortcomings of the available arsenal of drug delivery systems intended for ocular therapy. The present manuscript aims to review the recent advances, the current challenges and most importantly to raise awareness on the underexplored potential and future perspectives of molecularly imprinted polymer-based drug delivery systems intended for the treatment of eye diseases. Vision is responsible for most of the interactions of the human body with the outside world. A function of this importance is performed through complex, yet very fragile peripheral structures, the eyes. In the last decades, the rising life expectancy has favored a demographic transition towards a growing proportion of people over the age of 50, which are particularly at risk of developing non-communicable eye diseases capable of causing vision impairment or even blindness . AccordiThe architecture of the optical system and the eye itself is of the highest complexity. Although an easily accessible sensory organ, it remains a challenge for drug administration due to the presence of anatomical and physiological barriers which may limit the access of drugs to the internal eye structures . ConsideGiving new valences to already established polymeric materials coming from various fields of science and technology may represent a fast-track solution to further develop intelligent platforms acting as advanced drug reservoirs and delivery systems. The features of molecularly imprinted polymers (MIPs) demonstrated in separation science, align and compensate for the current shortcomings of the available arsenal of DDS intended for ocular therapy, such as limited loading capacity, suboptimal release time and profile, all converging towards an insufficient bioavailability of the active pharmaceutical ingredient (API).The present manuscript aims to review the recent advances, the current challenges and most importantly to raise awareness on the underexplored potential and future perspectives of molecularly imprinted polymer-based drug delivery systems intended for the treatment of eye diseases.The eye is one of the few areas of the body with immune privilege. The eye attempts to limit the local immune and inflammatory response to preserve transparency, and in the end, vision. Multiple mechanisms combine to provide this privilege: physical barriers , soluble factors that inhibit the activity of immune-competent cells (including TGF-β and neuropeptides), and anterior chamber immune deviation (ACAID), a unique response to antigens entering the eye, also a mechanism of tolerance to tissue-specific antigens in the healthy eye .The very surface of the eye, the cornea, must carry multiple functions and is the target of many of the DDS applied topically. It must remain transparent to function as a high-power lens (about 44 dioptries), but also must retain integrity as various aggressions constantly bombard it. Corneal surface is designed to be a highly effective barrier, restricting the access to the eye of high-volume molecules, including pathogens. The cornea, together with the lacrimal film, the conjunctiva, and the eyelids, form a functional system that maintain a double homeostasis of the ocular surface–tissular and optical.Cornea has a thickness of about 550 microns. It consists of three layers with different characteristics: epithelium, stroma, and endothelium, separated by Bowman and Descemet membranes. Epithelial cells have tight junctions (zonula ocludens), especially in the superficial layers, which provide water-tight seal and strong barrier effect. Corneal epithelium is the main obstacle for drug penetration into the eye . Stroma The corneal route is the main access for drugs deposited onto ocular surface, into the aqueous humor. Conjunctival surface is much greater, and the permeability is better than in cornea. Sclera lying beneath the conjunctiva  is also The corneal epithelium is lipophilic and limit the permeation of hydrophilic molecules. Intercellular pores measure 2.0 ± 0.2 nm in diameter that allow only drugs with a molecular weight of <500 Da/10 Å to penetrate . The strThe physiological barriers against the APIs and the need to increase the concentration of drugs in the inner structures of the eye have been permanent challenges for researchers in the attempt to optimize conventional pharmaceutical formulations but also to design new DDSs and to approach alternative routes of administration. An ideal ocular DDS ought to be fully biocompatible, to provide a controlled release for extended periods of time, to be compliant with non-invasive routes of administration and last but not least, to be in agreement with a patient-friendly posology. The majority of eye pathologies are addressed by topical administration, most often in the form of eye drops. A topical drug administration to the eye is convenient and well-accepted by patients, lacking the discomfort associated with injectable administrations, and is preferred in the diseases of the anterior segment of the eye like conjunctivitis, diseases of the iris or glaucoma . Eye droIncreasing the remanence of the API at conjunctival level ensures an increased absorption and improved tolerance of APIs; this goal can be achieved by using viscosity-modifying agents, the preparation of bioadhesive formulations, or the preparation of gel-forming solutions containing stimuli-responsive excipients ,16,17.The use of emulsions as vehicles for water-insoluble drugs has shown increased internalization of the API dissolved in the non-polar phase. The additional use of cationic polymers such as chitosan, able to increase remanence by an interaction with the negatively charged mucin, further improves the bioavailability parameters ,18. By gSeveral nanocarriers intended for both the anterior and posterior segment of the eye such as nanomicelles, dendrimers, nanoparticles, nanosuspensions and liposomes showed promising results as means to control drug release and to improve the permeability, the stability, the biocompatibility, and the bioavailability of APIs ,20. LipoContact lenses are hydrogel-based medical devices that are applied directly onto the cornea, initially designed to correct ametropia. Therapeutic contact lenses (CLs) obtained by the inclusion of APIs in the lens matrix are considered an excellent alternative for the treatment of ocular diseases, particularly for chronic ones. Direct contact with the cornea can ensure prolonged and/or controlled drug release, with numerous studies showing a more then 50% increase in bioavailability as compared to eye drops formulations . The criCL are composed of polymeric hydrogels or silicone hydrogels. Polyhydroxyethyl methacrylate (pHEMA), was the first monomer used to prepare CLs in the 1960s, and, along with N-vinylpyrrolidone (NVP), it remains the monomer of choice for the manufacture of CLs. Both materials are well tolerated as they confer the lens increased hydrophilicity, adequate mechanical properties, water swelling and oxygen permeability. To optimize these characteristics, other monomers or functionalized compounds can be incorporated into the lens matrix ,22. Intraocular injections are usually employed for an efficient drug delivery to the posterior eye segment in diseases like macular degeneration or diabetic retinopathy. Intravitreal injections were developed to bypass the natural barriers of the eye but at greater cost, inconvenience, and risk for the eye: infections, haemorrhages, rise of intraocular pressure, or unwanted perforations of the retina. Moreover, the distribution of the drugs in the vitreous body is variable, subjected to additional pathophysiological influences, and the administration could be painful, affecting patient acceptance . IntraviImplants are devices designed to ensure a prolonged effect of the drugs in the eye, while avoiding frequent intraocular injections, especially in the case of chronic vitreo-retinal diseases. Administration of biodegradable implants  are preferred due to their high tolerance . IntraviAnother treatment strategy proposes the use of microneedles technology, that can ensure the controlled release of high concentrations of APIs in the retina/choroid. The approach is promising for eye diseases that threaten vision such as macular degeneration, diabetic retinopathy and posterior uveitis .Alternative periocular routes like retrobulbar, peribulbar, sub-Tenon’s or subconjunctival injections are less invasive, being also capable to deliver drugs to the posterior segment of the eye by transscleral diffusion or through choroidal plexus, but usually in suboptimal concentrations due to the presence of blood-ocular barriers which can limit drug access .Generally, a systemic administration of drugs is rarely used in ophthalmic diseases due to a low intraocular bioavailability of the active substance. Despite the easy access to the eye via the vascular choroid plexus, a systemically administered drug must pass through the anterior blood-aqueous barrier (BAB) or the posterior blood-retinal barrier (BRB) in order to gain access inside different segments of the eye. Particularly, tightly packed retinal pigment epithelial (RPE) cells in the outer blood-retinal barrier can significantly reduce the access of a systemically administered drug to the retina and vitreous body, usually less than 2% of the administered dose being available . AdditioBiocompatible polymeric matrices are convenient scaffold materials for the development of drug reservoirs intended for the prevention and treatment of various eye conditions. To increase the API’s bioavailability and the duration of its therapeutic effect, several approaches for drug loading in polymeric matrices may be used: soaking , chemical functionalization of the polymeric matrix aiming to induce guest-host interactions , polymerization in the presence of ionic compounds to promote electrostatic interactions with the API, carrier-mediated release , and molecular imprinting ,22.Hydrogels, mainly designed for topical application , represent networks of natural or synthetic monomers, crosslinked with multifunctional linkers, forming flexible structures upon free-radical polymerization initiated thermally or photochemically. These polymers are insoluble in water but must exhibit a swelling behavior in aqueous solutions while preserving the imprinted sites. Matrix swelling followed by the API‘s release at a certain rate represent fundamental properties of hydrogels and are influenced by the nature of the hydrophilic functional groups and by the degree of crosslinking. The crosslinking of the polymer can be achieved physically or chemically.Hydrogels can be specifically designed to obtain predictable characteristics (SMART hydrogels) by the appropriate choice of crosslinkers and by the changing of the crosslinking degree. Thus, it is possible to modulate the release rate of the API and the duration of the therapeutic effect by modeling the physical and mechanical characteristics of the hydrogel . Moreover, the addition of functional crosslinking agents enables the gel to react to external stimuli, with major implications on the designed formulation’s pharmacokinetics. Consequently, in situ gel formation at body temperature may occur, or the API‘s release may be triggered by changes in pH or photo-stimulation. Natural monomers used in the design of hydrogels include agar, alginic acid, collagen, chitosan, gelatin, fibrin, hyaluronic acid (HA), pectin, etc. The resulting polymers are biocompatible and biodegradable as they share a similar structure to ocular tissues (vitreous humor), and have been intensively studied for tissue engineering. Synthetic polymers, such as polyvinylpyrrolidone (PVP), poly(acrylic acid) (PAA), polyacrylamide (PAM), poly (PVA), poly(hydroxyethyl methacrylate) (PHEMA), poly(ethylene oxide) (PEO), and cellulose derivatives have lower biocompatibility; however, their manufacturing characteristics are more reproducible. Hydrogel forming polymers are currently used in practice for the design of a wide variety of pharmaceutical formulations in ocular drug delivery such as gel-forming solutions, intravitreal hydrogels, topical hydrogels, and contact lenses.Similar to hydrogel synthesis but exploiting a more tailored interaction between the API and the selected functional monomers, both chemically and sterically complementary binding sites (drug-specific cavities) towards the API molecule may be formed in a highly crosslinked polymeric network, through the process of molecular imprinting . The forMIPs can be rationally designed to obtain predictable characteristics by the appropriate choice of functional monomers and crosslinkers, and their molar ratio with respect to the API. Since their inception, MIPs were successfully developed and applied in analytical techniques, therefore the vast majority of MIP-based DDSs later developed were made from the same acrylic monomers and employing the non-covalent imprinting approach. The most adopted functional monomer is meth(acrylic) acid since its carboxyl group can form weak electrostatic attractions and/or functions as a hydrogen donor for H-bond acceptor drugs; most often it is coupled with EGDMA, as crosslinker. Furthermore, in ocular therapy, the traditional CLs were also based on acrylic monomers , thus the main adaptation of the polymerization mixture formulation was the decrease in the crosslinker concentration. Even though these polymers are already acknowledged as being biocompatible, the development of MIP-DDS for drug delivery applications is still in its infancy. In advanced ocular therapy, contact lenses acting as drug reservoirs are able to provide a sustained or controlled release over the wear duration. As formerly mentioned, there are two strategies for the incorporation of the API into the hydrogel: (i) post-synthesis, via the traditional approach of soaking the premade lens in a drug solution or (ii) during hydrogel polymerization. The first approach offers the advantage of simplicity and ease of fabrication, but it provides a drug release profile characterized by an initial burst release with potentially serious consequences for the patient, followed by subtherapeutic concentrations. In the latter case, drug incorporation occurs simultaneously with the lens synthesis process. Here a distinction needs to be made between the entrapment of drug during polymerization and the molecular imprinting approach. Not every polymer made in the presence of a drug molecule will result in a MIP, because the imprinting effect is not determined by the mere presence of a template in the polymerization mixture. The success of the imprinting depends upon the effectiveness in achieving imprinted cavities in a crosslinked polymer matrix, characterized by (i) shape complementarity to the template molecule  and (ii) specific spatial distribution of the functional groups able to promote multiple, mostly chemical interactions, with the template. This can only be achieved by optimizing the imprinting parameters for each API, since the template and its functionalities determines the choice of the functional monomer(s). As a matter of fact, a complex combination of factors including the nature, concentration and the ratio of the functional and crosslinking monomers, the functional monomer-template ratio, polymerization conditions  strongly affect the process of molecular imprinting . FollowiOn the other hand, in cross-linked polymer-based contact lenses in which the API is added during the polymerization process, its molecule is retained in the hydrogel’s polymeric network mainly by physical entrapment. Even though a so called “functional monomer” (i.e. substance capable of interacting with the drug) is used for CL production, they are not able to generate imprinted cavities due to the lack of sufficient and spatially-arranged functionalities that can provide multiple interaction points with the drug. Furthermore, if a subsequent drug washing step is performed, no “drug-specific” cavities will remain in the polymeric matrix, as the lack of effective crosslinking will cause their collapse. For all these reasons, the drug-entrapped contact lenses usually demonstrate low drug loading and a burst release of the API with poor control over the release behavior in comparison with the molecularly imprinted polymers.There is a long and sinuous road from the early days of these functional polymers towards the MIP-based drug delivery systems intended for ocular therapy, with several noteworthy milestones . In deveMIPs have been initially developed for and employed mainly in analytical applications, as stationary phases/selective sorbents in separations sciences  and moreHowever, in the case of MIP-based drug delivery systems, by the nature of their intended use as drug reservoirs with prolonged and, ideally, controlled release, the template removal step seems to be redundant, as long as any potentially unreacted component of the polymerization mixture holds no toxicity for the human tissues. If, however, a thorough wash needs to be carried out , a subsequent drug loading procedure is performed . ObviousIn ocular drug delivery, the template-functional monomer interactions are based mainly on weak, non-covalent associations responsible for faster binding and release properties during the analyte-polymer interactions, compared to the covalent imprinting approach. Most of the conventional MIPs intended for analytical applications are synthesized in organic aprotic solvents in order to stabilize the template-functional monomer complex during polymerization, but also to confer a macroporous polymeric structure enabling thus an easier diffusion of the template molecule from and into the imprinted cavities. Nevertheless, the presence of residual organic solvents is undesirable in drug delivery applications and especially in the case of ocular DDSs. Moreover, the use of organic solvents in CLs fabrication is often conflicting and thus liquid monomers need to be exploited for template dissolution. As in the case of MIPs intended for analytical applications, the performances of the imprinted hydrogels developed for drug delivery purposes must be compared with the corresponding NIPs, which are prepared analogously as the imprinted ones, but without the addition of the template drug. In analytical applications (separation and sensing), one of the main features of the obtained functional polymers is selectivity, the supreme goal of an analyst being the specific binding of the target analyte. In drug delivery, however, other fundamental features are primarily sought after, such as: drug loading and releasing properties. Although, seemingly aiming for different objectives based on the field of their application, in fact these features are somewhat interconnected, as higher binding affinity of the template to the imprinted cavities generally implies improvements in drug loading capacity and may hold the premises for prolonged/controlled drug release. As being outlined in the previous section, MIP-based DDS may alleviate shortcomings related to the low bioavailability of various eye drops, non-imprinted polymeric hydrogels and ointments intended for non-invasive, topical, and especially long-term administration, stemming from their high physiological clearance, limited drug-loading, or excessively fast drug release rates, thus holding the promise of a fascinating area of research. Judging by the number of published research in the last two decades , the topMaybe the most promising direction in the current field of topical ophthalmic drug delivery is the molecular imprinting approach as it can offer real solutions to the problems exhibited by the conventional ocular drug delivery formulations  such as low bioavailability, exceedingly fast release profile, or insufficient loading capacity. Therefore, by creating imprinted binding sites in the polymer network in which numerous functional groups are concentrated and organized in such a manner to attain a strong interaction with the API, a better control over the release profile can be achieved. In fact, using MIPs as drug reservoirs, a sustained, zero-order drug release may be obtained for a long period of time, when compared to conventional drug delivery . The resFurthermore, the tailor-made imprinted pockets of the MIPs may help in protecting the active ingredient upon storage or therapeutic use from enzymatic, hydrolytic or photo-degradation, maintaining the drug for a longer period in its bioactive form, thus increasing its bioavailability. The molecular imprinting technique can be applied to any kind of template, ranging from ions to relatively small pharmaceutical compounds and even large (bio)molecules, like proteins. However, the increase in the size of the template, may hamper its efficient release from the cross-linked polymer, risking of being permanently stuck inside. From a pharmacological point of view, a very wide variety of APIs were used as templates in the process of imprinted-hydrogel synthesis, such as: β-blockers  are relying on a relatively high degree of cross-linking (50–90% cross-linker agent ) in ordeThe imprinted hydrogels, and especially the CLs, need to be flexible enough to ensure good biocompatibility and swelling behavior (water content). A high degree of crosslinking also affects the optical clarity and transparency of CLs . TherefoAchieving the right balance between high-fidelity imprinted sites and elasticity of the CLs it is not an easy and straightforward process and sometimes requires laborious optimization procedure for each targeted API. One of the most important considerations in developing imprinted CLs for drug delivery purposes is to preserve their biocompatibility and swelling behavior, as the latter is affecting the oxygen dissolution and diffusion into the surface of cornea . TherefoThe nature of the functional monomer is another essential factor affecting the imprinting efficiency. The ability of functional monomers to interact with drug templates during polymerization is different. Thus, the selection of co-monomers significantly influences the performance of the final MIP hydrogel, such as release rate, optical clarity, swelling and mechanical properties . SometimFirst studies investigated the influence of the functional monomer:template ratio using the empirical approach, in which the concentration of monomer was kept constant while the concentration of the template was varied . As expeBesides the key role of the functional monomer, functional (charged) additives may also bring unexpected advantages to the efficiency molecular imprinting. Long-chained negatively charged comfort agents, such as hyaluronic acid, commonly used as comfort agent to prevent protein deposition on silicone hydrogels , throughAlternative molecular imprinting strategies, such as metal-ion mediated imprinting, are able to increase the degree of order throughout the polymerization step by well-defined, spatially-directional coordinate bonds . This koThe empirical selection of the polymerization mixture’s components is time and resource-consuming and might not even offer the best performing imprinted hydrogels. The more efficient approach to achieve high affinity MIPs with appropriate morphological and physico-chemical properties is the computer-assisted molecular modeling, by helping in better understand, but also to rank the interactions taking place during the molecular imprinting process. Eroglu et al.  conducteThe implementation of computer-assisted techniques in the development of imprinted hydrogels can reduce the tedious and time-consuming laboratory work as well as the amounts of used chemicals, which is very important especially in the case of expensive template drugs.By far the main advantage of MI technology in the design of imprinted hydrogels is overcoming their low affinity for most drugs ,66. It wThe imprinting efficiency is determined by the stability of the functional monomer-template complex throughout the polymerization step. Therefore, as expected, the component with the highest impact on the drug-loading capacity, is the nature and the concentration of the functional monomer. Generally, the most favorable monomers for the imprinting process are those with the highest binding affinities to the template . FurtherDrug loading may depend also on the pH at which the drug-stripped hydrogel is exposed for the re-loading step. For example, HEMA-MAA imprinted hydrogel adsorbs the highest amount of timolol (template), at pH 5.5 and 7.5, at which the carboxylic groups of MAA are ionized and are capable of interacting with the positively charged timolol. At pH values where the non-ionic form of the hydrogel (pH < 5.5) and/or template (pH > 9.2) is predominant, a severe cutback of the drug rebinding occurs . The non-covalent interactions between the functional monomer-template are preferred from a drug release perspective due to the faster binding and release kinetics. The delayed kinetics of drug release and slower diffusion rate of the imprinted hydrogels in comparison with the non-imprinted ones, as prerequisites of drug reservoirs designed for long term treatment, are currently explained by the tumbling effect , i.e., tThe most notable differences between the release time, but also released amount of drug of the imprinted vs. non-imprinted CLs were observed when exposed to low concentrations of template during drug-rebinding . HoweverAs previously mentioned, by the right choice of functional monomer(s) and monomer:template ratio, depending on the therapeutic needs and on the required duration of wear in case of CLs , theAnother factor affecting the release behavior is the swelling property of the lens in aqueous media. Upon the rising of water content within the polymer network, the conformation of specific binding sites changes accordingly, which in turn impacts negatively on the hydrogel’s drug binding capacity. The addition of functional monomers  to HEMA significantly increases the water content of the hydrogel . HoweverAdditionally, to avoid potential pitfalls, care must also be taken during In vitro characterization and optimization of the imprinted drug-reservoirs, as the obtained drug-release kinetics may significantly differ for the same formulation in function of the selected experimental models. For example, using an infinite sink dynamic release of ketotifen fumarate from imprinted CLs showed a concentration dependent (Fickian) behavior, whereas testing the same CL under physiological volumetric flow rates and tear volumes using a PDMS microchip, a slower release rate, with an ideal, concentration independent (zero-order) release profile was recorded .A quick survey of the publications  shows thThe critical features of such imprinted polymer backbones used for CL manufacture are biocompatibility and non-immunogenicity. Due to their topical route of administration, biodegradability it is not a decisive feature as after payload release, they are removed from the surface of the eye. Process control during optimization and manufacturing of CLs should involve the following In vitro tests: optical transparency, water content, wettability, tribology, refractive index, and oxygen and ion permeability. Furthermore, In vivo studies should validate the aforementioned characteristics and should demonstrate (pre)clinical efficiency.The imprinted hydrogel-based CLs rely mainly on the same acrylic functional  and crosslinking monomers  as the ones employed in analytical applications. Therefore, the transfer of this technology in CLs development does not require multiple adjustments, besides lowering the degree of crosslinking.The other material of choice in mass-fabricating vision corrective CLs is silicone, however only a few studies attempted to employ it in developing silicone-based molecularly imprinted hydrogels ,40,49,58Commercially available, silicone hydrogel-based contact lens materials , might not always offer high enough imprinting efficiencies. In this respect, the admix of additional functional monomers (i.e. AA) and crosslinkers (PEG200DMA and EGDMA) lead to considerable enhancement of HPMC loading capacity and release rates . ObviousIn the design of therapeutical CLs combined drug loading strategies may also be applied, where the simultaneous and sustained delivery of two or more APIs may be achieved by MI and layer-by-layer (LbL) coating. As such, the inner core of the CL may be imprinted by a drug of interest , whereas by LbL deposition of various polyelectrolytes , besides the fine-tuning of the drug-release through drug-polyelectrolye interactions, additionally biocompatibility, non-antigenicity, anti-fouling and antibacterial properties may be conferred to the CLs surface ,70.To conclude, probably the most promising way of formulating drug-imprinted hydrogels as drug reservoirs is through therapeutic CLs, as it combines the features of a robust drug loading platform, with multiple means of controlling drug release profiles of one or several APIs, while ensuring a patient friendly, non-invasive means of treatment for extended periods of time.Even though the ocular bioavailability of drugs applied on the corneal surface through classical ophthalmic preparations (ocular drops and ointments) is very poor (~5%), the use and commercialization of more advanced ocular DDS are very limited, and they seem to have come to a standstill. Therapeutical contact lenses can be a viable alternative as they can enhance ocular bioavailability of drugs, while reducing the side effects and increasing patient compliance. However, the mere soaking and entrapment of APIs into the polymeric matrix of contact lenses do not provide targeted delivery and sufficient control over the release. Despite its early developing stage in the field of drug delivery, molecular imprinting represents the most promising technology to be employed in the development of efficient ocular drug delivery devices. Imprinted contact lenses proved that they have the ability to improve the drug delivery profile, to prolong the release and residence time of the drug and even to favor the drug loading capacity. According to the reviewed studies, good imprinting efficiency can be achieved without sacrificing the critical properties a standard, vision corrective contact lens should possess, such as optical transparency, good mechanical properties, ion and gas permeability, wettability, or refractive index. Nevertheless, occasionally the lack of careful planning of the experimental goals in line with the particularities of ocular therapy, misleading data interpretation may throw off course the development/optimization process .In spite of the promising results of numerous In vitro studies published in recent years, consistent In vivo data is still missing. Apart from the known limitations brough on by the MI process , several other possible reasons may be invoked for the scarcity of In vivo reports. In no particular order of importance, one may be the lack of interdisciplinary approach, as the most active research groups dealing with molecular imprinting are still in the field of materials science, with limited access to animal research facilities. Another important reason might be the lack of appropriate animal models  that relevantly translate the observed pharmacokinetic/pharmacodynamic results to human applications. The use of animal models sharing a higher degree of similarity with the human eye  imply significantly higher costs or more expensive research infrastructure, but most importantly runs into serious ethical issues concerning their inclusion in such studies.Future studies should focus on expanding the body of knowledge related to the performance of such molecularly imprinted DDSs in order to ensure the fields maturity towards clinical validation which will pave the way for marketing authorization and ultimately improve the patient’s quality of life.


The novel coronavirus disease (COVID-19) has as of mid of October 2021, affected over 220 countries  The potential dose-response relation underlying the accumulation of experienced stress types and neuropsychological risk factors during COVID-19 pandemic; (2) The interplay between effects of CM and COVID-19 stressors, examining independent contributions of co-occurring chronic and acute stress, that may contribute to the onset and maintenance of neuropsychological problems in children; and (3) Moderators of these associations including COVID-19 stressor  and CM type  The child neuroplasticity allowing the brain to be malleable, i.e., cerebral mechanisms of neuronal renewal and changes  paper-and pencil  and computerized tasks  can improve interpersonal communication . The modules should be organized to provide an order that children gradually acquire abilities that require building up from the most basic  to the most demanding or complex processes .To complement the NR program, we propose making (online) information and (psycho)education sessions available to caregivers, educators, and clinicians (joining an online consultation platform) to rapport building and provide them with information to recognize, report and respond to CM  neuropsychological issues, (possible) exhaustion and safety concerns might be considered. Carers of children with CM experiences always deserve particular attention, but especially so in this extraordinary period of lockdowns when caregiving in general (or cohabitation) can be extremely challenging. Within the household, parents are facing new demands with meeting basic and educational childcare needs and working remotely within in the home environment . Reports might include consistent responses to specific (COVID-19 stress related) behavior(s), suggestions to adapt, simplify or develop daily activity schedule, safety assessment and crisis plan, and development of beginner communication systems. Importantly, intervention efforts are needed to strengthen positive parenting behaviors . We recommend using emotion regulation and coping strategies  report should be written addressed to the caregivers , formulated in lay language, with sufficiently detailed recommendations, Here, we proposed a novel NR program that might be helpful to reduce neuropsychological problems in children, taking into account the special needs of children affected by CM and COVID-19 stressors. Childhood is a sensitive period of neurological, cognitive, social, and emotional development, during which a neuropsychological intervention can make an important difference and shift the balance between risk and protective factors  children, for whom both behavioral and domain-specific cognitive demands of formal schooling are quite novel challenges. An extra training and education for health professionals and educators on CM and its consequences on the neuropsychological functioning could contribute to the development of most adequate preventive and intervention measures and strengthen the collaboration between hospital services and schools.Although the proposed NR program has a high theoretical foundation and a high potential to sustainably improve the neuropsychological functioning in children affected by CM in the context of the COVID-19 pandemic, many challenges regarding its implementation and empirical studies are needed to examine its feasibility, efficacy, and cost-effectiveness.NEF-O: conceptualization, investigation, writing original draft, and writing—review and editing. ST: conceptualization, writing—review and editing, and supervision. Both authors approved the final version of the submitted manuscript.NEF-O was supported by the German Academic Exchange Agency DAAD: Deutscher Akademischer Austauschdienst (91629413).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.All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.


The risk prediction of future cardiovascular events is mainly based on conventional risk factor assessment by validated algorithms, such as the Framingham Risk Score, the Pooled Cohort Equations and the European SCORE Risk Charts. The identification of subclinical atherosclerosis has emerged as a promising tool to refine the individual cardiovascular risk identified by these models, to prognostic stratify asymptomatic individuals and to implement preventive strategies. Several imaging modalities have been proposed for the identification of subclinical organ damage, the main ones being coronary artery calcification scanning by cardiac computed tomography and the two-dimensional ultrasound evaluation of carotid arteries. In this context, echocardiography offers an assessment of cardiac calcifications at different sites, such as the mitral apparatus , aortic valve and ascending aorta, findings that are associated with the clinical manifestation of atherosclerotic disease and are predictive of future cardiovascular events. The aim of this paper is to summarize the available evidence on clinical implications of cardiac calcification, review studies that propose semiquantitative ultrasound assessments of cardiac calcifications and evaluate the potential of ultrasound calcium scores for risk stratification and prevention of clinical events. Cardiovascular (CV) diseases, primarily ischemic heart disease (IHD) and stroke, are still the leading cause of global mortality and a major contributor to disability. Indeed, prevalent cases of total CV diseases nearly doubled from 271 million in 1990 to 523 million in 2019, and the number of CV deaths steadily increased from 12.1 million in 1990, reaching 18.6 million in 2019 [The European Society of Cardiology (ESC) SCORE charts , the AmeAlthough algorithms are aimed to customize risk, they have at least three well-acknowledged limitations. First, they are primarily influenced by age; therefore, an asymptomatic young person with multiple TRFs is likely to be identified as low risk, while, conversely, an elderly person is likely to be identified as high risk regardless of actual risk ,6. SeconReclassification means changing the risk class of a subject after complementing risk algorithms with other data; for example, an imaging technique . ObviousDetecting atherosclerosis (the consequences of which we aim to avoid) is better than simply identifying TRF exposure;Reclassification of low-risk subjects into higher-risk strata may guide appropriate therapy;Disease visualization might improve adherence to risk-modifying interventions by increasing awareness.It is increasingly clear that the use of preventive models based on the detection of subclinical atherosclerosis and organ damage is useful ,13. IndeSeveral imaging modalities have been evaluated and proposed for the identification of preclinical atherosclerosis and phenotypic evidence of disease . There aThis imaging modality allows the physician to detect both the presence of increased carotid intima-media thickness (CIMT) and carotid plaques . ConflicCoronary calcium detection by computed tomography (CT) is the most commonly used technique for the detection of subclinical disease, prognostic stratification of asymptomatic individuals and implementation of preventive strategies . It is pHowever, both of these techniques have limitations to consider. Regarding the 2D ultrasound imaging of the carotid arteries, despite providing a simple noninvasive (and relatively inexpensive) modality for detecting subclinical atherosclerosis, results show more subjects moving from intermediate-risk to lower-risk categories than to higher-risk categories. This implies the possibility of not undertaking preventive interventions in subjects who could benefit from them . The majGiven these considerations, we would argue for the use of routine echocardiography as a practical technique in the detection of subclinical atherosclerosis. In this review, we discuss the utility of ultrasound assessment of cardiac calcifications as a tool to identify the presence of coronary atherosclerosis and improve risk stratification of asymptomatic subjects.Cardiac calcifications are frequently encountered on routine echocardiographic examination or CT scanning. They are generally asymptomatic, and their prevalence varies according to the site evaluated, age and presence of cardiovascular risk factors /calcification (AVC) is defined as the presence of sclerotic and calcific lesions that reside within the aortic valve leaflets, not involving the aortic annulus , with or without obstruction to the outflow . DetectiMAC is a chronic, degenerative process of the fibrous support structure of the mitral valve, which most often affects the posterior annulus . MAC is The question of whether MAC and AVC are expressions of atherosclerotic disease or simply reflect a primary degenerative process progressing with advancing age was partially clarified in the late 1980s and 1990s. Several authors ,45 reporThe clinical utility of AVC and MAC detected by noninvasive imaging is supported by a rich literature that highlights the prognostic impact of these two entities. In fact, a landmark paper published in 1999 that analyzed data from the Cardiovascular Health Study showed that the presence of AVS/AVC was associated with near double the risk of all-cause mortality and cardiovascular death, as well as an increased number of atherosclerotic events, including myocardial infarction (MI), stroke and heart failure over a follow-up period of five years (the increased risk remained after adjustment for confounders) . These fSimilar findings are available regarding MAC. Fox et al. , in the More than a meta-analysis ,62 publiThus, the recognition of even small calcium deposits on valves and other cardiac structures is clinically relevant, both as a marker of systemic atherosclerosis and as a predictor of cardiovascular events. At this point, it is important to note that there is no proven method to reduce the burden of cardiac calcification . The proCurrently, there are no standardized echocardiographic methods, similar to the Agatston coronary calcium score obtained on CT, to quantitatively assess the extent of cardiac calcification. However, conventional ultrasound imaging, which is widely available, low cost and radiation-free, can provide a semiquantitative assessment of this disease process . Early sA semiquantitative echocardiographic algorithm  using siGaibazzi et al.  demonstrA new echocardiographic calcification score “echoCCS” ,81 Tabl proved iThe need for a true quantitative assessment of cardiac calcification by echocardiography led to the development of a new technique that uses a multipulse scheme termed “eSCAR” . It has It should be emphasized that the only validated imaging technique capable of quantifying noncoronary cardiac calcium is gated CT. The extent of cardiac calcification on CT can be expressed by applying the same Agatston  score usTherefore, after having already addressed and clarified both the intrinsic limitations of cardiac CT  and the clinical utility of the detection of cardiac calcifications, it remains to be established whether the above-mentioned ultrasound scores correlate adequately with the “real” cardiac calcium quantified by the CT. Therefore, while cardiac CT remains the reference method to quantify coronary and noncoronary cardiac calcium, the use of echocardiography for this purpose, if validated against CT, would portend the inherent advantages of low cost, portability and radiation safety. The first study that tried to answer this question was that of Pressman et al. . The autSome intrinsic limitations of classical ultrasound need to be highlighted. Primarily, ultrasound is an operator-dependent imaging technique presenting unique challenges, such as low imaging quality caused by noise and artifacts. To interpret correctly the information acquired by the scan, clinical experience is required. Despite these inherent limitations to quantification by echocardiography, multiple studies have found the various echocardiographic calcium scores to have good reproducibility, with acceptable intra- and interobserver variability ,77,81. MIn conclusion, the scientific evidence suggests that the detection of cardiac calcifications by ultrasound represents a promising tool for identifying subclinical atherosclerosis and improving risk stratification in asymptomatic subjects. Echocardiography provides an easy, inexpensive and “bedside” tool for the reclassification of subjects into higher- or lower-CV-risk group categories, leading to the more appropriate application of preventive treatments and more appropriate use of diagnostic tests for identifying significant coronary or extracoronary artery stenosis. An appropriately designed and powered prospective study would appear to be the next step in the investigation of this promising method of detecting subclinical atherosclerosis.


Robust and precise characterization of the interactions between nanoengineered materials and biosystems is vital for the development of safe, efficient diagnostic and therapeutic nanomedicines. This comment discusses the key aspects of nanoparticle characteristics affecting the interpretation of nano-bio interface data. For example, the nanotechnology regulatory science research plan guidance documents of the US Food and Drug Administration (FDA) state, “We intend our regulatory approach to be adaptive and flexible and to take into consideration the specific characteristics and the effects of nanomaterials in the particular biological context of each product and its intended use” (https://www.fda.gov/science-research/nanotechnology-programs-fda/fdas-approach-regulation-nanotechnology-products). Without using the correct characterization techniques that match the intended use, the outcomes may be misleading and lead to incorrect assumptions about the safety, blood residency, and therapeutic efficacy of nanoparticles.Incomplete characterization of an object may cause significant misinterpretation of outcomes Fig. . Collect2.For example, conventional characterization techniques  would identify patchy charged and uniform charged mesoporous silica nanoparticles as identical but can have significantly different in vivo outcomes. Patchy charged nanoparticles are reported to be immediately captured by white blood cells, while uniformly charged nanoparticles remain in circulation3 in addition, the ζ potential measurement of these positively charged nanoparticles in phosphate buffered saline demonstrated negative surface charge3. If these nanoparticles were used without recharacterization in the laboratory for protein corona preparation and analysis, the proteomics outcomes of such study would have been full of errors! To avoid errors and misinterpretation of the nanomedicine characteristics, accurate recharacterization of the purchased, gifted, and/or common materials in a compatible media for the intended use of nanoparticles is essential.Failure to robustly characterize the purchased, gifted, synthesized (using well-defined protocols), and/or common materials can cause significant errors in the results of the intended use of nanoparticles. This is mainly because the provided physical and chemical properties of the (nano)materials  may change significantly due to the (i) environmental and methodological factors  and/or (ii) the essential buffering conditions for the intended use of nanoparticles . For example, a commercial amine-modified polystyrene nanoparticle with the size of 100 nm (according to the manufacturer) demonstrated poor dispersity, and therefore much larger sizes, by dynamic light scattering  when recharacterized in laboratory;4. Rigorous authentication and reporting full information of the biological parameters are, therefore, another essential factor that can significantly reduce the heterogeneity surrounding nanomedicine reproducibility1.Aside from the need for accurate recharacterization of the purchased, gifted, and/or common nanoparticles, accurate and validated information on the biological systems  is essential to achieve robust nanobio interfaces. This is mainly because the characteristics of biological systems can significantly affect the safety and diagnostic/therapeutic efficacy of nanomedicine. For example the biological interactions and the fate of the nanoparticles can be influenced by if the source is animal or human, if testing is done in serum, plasma or whole blood, if biological tissues and fluids are from healthy or diseased donors and even by if the samples are fresh or stored5. For example, formation of protein corona on the surface of silica nanoparticles weakens their adhesion to cell membrane and, thus, reduce nanoparticles’ uptake by the cells, as compared to the pristine nanoparticles6. Therefore, reports on a particular nanomedicine should include accurate data on both pristine and corona-coated nanoparticles, and the comprehensiveness of the presented data should depend on their intended use. In addition, because the nature of the protein corona evolves over time, continued characterization based on intended use may be essential. For example, for cancer therapeutic nanoparticles, evolution of the protein corona in the tumor microenvironment is of crucial interest in better understanding the interactions between nanoparticles and the immune system  and cancer cells.Obtaining robust data on nanoparticles’ size, charge, and other physical and chemical properties  before and after interactions with biological systems is simultaneously of particular interest and a substantial challenge. This is mainly because the biomolecular/protein corona formed on the surface of nanoparticles changes their physical and chemical properties and, therefore, determines their interactions with biological systems For biomedical application, it is essential to conduct and report deep and combined analysis of the physical and chemical properties of nanoparticles, the biological parameters tested, and the nanobio interfaces . Without such comprehensive datasets, the safety and therapeutic efficacy nanoparticles cannot be accurately predicted and, therefore, are incompatible with regulatory guidelines.https://www.intertek.com/analysis-differential-centrifugal-sedimentation/), is more challenging than the pristine nanoparticles mainly because DCS requires that nanoparticles have a particular density. Although the density of some particles is well defined in their pristine state, the density of corona-coated nanoparticles cannot be defined accurately due to the significant debate/challenges regarding the density of proteins11 within the corona layer. As another example, common microscopy images often fail to define (protein) coating boundaries, yielding underestimated sizes; while light scattering can produce overestimates1. Therefore, reporting both datasets on pristine and corona-coated nanoparticles  will improve our understanding of the characteristics of the nan-bio interface , providing better clarity regarding the biological responses to nanoparticles1. While even subtle changes  may not have a significant effect on the characteristics of pristine nanoparticles, it can result in a completely different protein corona composition12 and substantially alter the safety and therapeutic/diagnostic efficacy of nanoparticles.It is substantially more difficult to perform robust characterization analysis of corona-coated nanoparticles than pristine nanoparticles, and the degree of difficulty depends on the characterization technique and factors affecting the results Table . For exa13 for more accurate analysis of the thickness of the protein corona.To overcome issues associated with any single technique, researchers should use at least one other complementary characterization technique to overcome the weaknesses of a single technique. For example, DCS analysis could be paired with a complementary characteristics approach such as cryo-transmission electron microscopy14 that may not be identified by non-AFM experts . An AFM experts, on the other hand, can easily recognize the source of the artifact provide testing guidelines 14 to produce artifact-free images.Another critical aspect is to collaborate/consult with experts in each characterization technique; results that seem dramatic to non-experts may be only artifacts to expert eyes! For example, characterization images of nanoparticles using atomic force microscopy (AFM) technique may contain significant series of artifacts , scanner , vibration, feedback and parameter settings, and image processing software)15. To avoid possible confusion caused by interlaboratory variations, one strategy is to recheck the characterization outcomes with standard labs including National Cancer Institute’s Nanotechnology Characterization Lab .Another important aspect of characterization is the role of interlaboratory variations. It has been shown that the characteristics outcomes of identical nanoparticles obtained by different laboratories were significantly different4. For example, Caruso and co-workers16 proposed the checklist referred to as Minimum Information Reporting in Bio-Nano Experimental Literature (MIRIBEL) to improve the reproducibility and robustness of nanomedicine reports. Various responses from experts in the field1, despite supporting the initial goal of the MIRIBEL checklist, demonstrated the need for a list more closely tailored to the intended use of nanoparticles. Such tailored checklists can be developed only by integrated functioning of all stakeholders , with timely and effective creation of optimal protocols to maximize reproducibility and transparency in nanomedicine. Until stakeholders agree on tailored checklists for specific nanoparticles and their particular applications, the best strategy is to follow the following proposed guidelines for transparency, openness, and reproducibility, which addresses eight standards: citations, data transparency, analytic methods (code) transparency, research materials transparency, design and analysis transparency, preregistration of studies, preregistration of analysis plans, and replication17.Standardization of characterization techniques  is being considered in the field of nanomedicine, in order to ensure the accuracy, reliability, and reproducibility of the outcomes presented and also to enable meta-analysis evaluation of the literature and comparison of experimental data18. Therefore, the scientific community needs to ensure that such a tailored standardization process would not hinder research breakthroughs from scientists/faculty members who may not yet have ready access to all such resources18.It is noteworthy, however, that providing robust and comprehensive characterization data  may be challenging for early-career scientists, as it requires critical resources more likely to be available to senior scientists/faculties, e.g., the amount of funding, collaborative network, their interdisciplinary capacity, and long-term experience in using various characteristics techniqueshttps://www.fda.gov/science-research/nanotechnology-programs-fda/fdas-approach-regulation-nanotechnology-products)“Industry remains responsible for ensuring that its products meet all applicable legal requirements, including safety standards. … industry must work with current information in product development, and continue to monitor products once marketed.”  must have the highest possible standard based on their intended use, more strict attention and emphasis should be placed on translational industry reports. This is mainly because of the direct influence of these reports on healthcare systems and the needs of regulatory organizations to access all relevant data to better assess the safety and efficacy of translational products. As stated by FDA’s nanotechnology regulatory guidelines:16. This is, at least in part, due to the fact that published articles contain “polished narratives which convey the impression that everything went smoothly according to the proposed research plan”19, which increases the risk of having considerable wrong or false conclusions. This issue in translational industry reports is more concerning than the current literature, mainly because of the possibility of financial conflicts of interest and serious consequences to the healthcare system and patients’ health. It is noteworthy that reproducibility problems in clinical trials are not limited to nanomedicine; for example, the rate of reproducibility among 67 preclinical studies in general biology was reported to be only 20–25%20. As another example, reproducibility checks of cancer biology projects revealed that, among the five most highly cited research studies in the field, only two could be successfully reproduced22. Clear and transparent discussion about reports helps regulatory decision-makers consider all aspects of the reports in making decisions that may affect healthcare. Such discussions require integrated functioning among all stakeholders including the scientific community  to identify insufficiently comprehensive and/or misleading science through the peer-review and post-publication processes.There are considerable transparency and reproducibility issues regarding the current literature in nanomedicine23. To begin to address these issues in a timely and effective manner, I call upon stakeholders  to work together to improve transparency, openness, and reproducibility across the field of nanomedicine.In summary, the central message of this comment paper is to shed more light on the reproducibility, robustness, and comprehensiveness/integrity of nanomedicine characterization reports, which may cause serious misinterpretation in prediction of nanoparticles’ safety and diagnostic/therapeutic efficacy. Achieving reproducibility and transparency during the characteristics of nanomedicine products may improve the current low rate of success in clinical translation of nanomedicine products


Our bodily experience arises primarily from the integration of sensory, interoceptive, and motor signals and is mapped directly into the sensorimotor cortices . This viThe present collection of articles emphasizes the relevance of bodily and action systems for higher-order cognitive processes and self-awareness . It assiThe bodily instantiation of cognitive operations is referred to as “embodiment” and is equated with actions such as symbolic processing, emotion, language, and attention . Neverthagency. Regarding the role of body feeling in clinical practice, and especially in neurorehabilitation, one study highlighted the high relevance of bodily processes considering the clinical contributions of different pathologies . The authors introduced convergent studies on neural damage to the fronto-parietal-insular network that disrupts body sensation, which can lead to a sense of disembodiment or a sense of disownership [Palmiero et al.  emphasizwnership . This peBodily awareness can be quite easily manipulated in healthy participants by the rubber hand illusion , and sucSensorimotor representations are also essential for building and maintaining corporeal awareness. Indeed, not only does the mere motor imagination (MI) of an action enhance the motor representation of the imagined action , but theMuscle-specific modulation of spinal reflexes in lower limb muscles during action observation, with and without motor imagination of walking, suggests that the muscle-specific facilitation of spinal reflexes is related to the strength of connectivity between the sensorimotor area and the muscle during the actual movement. Although research originally focused on the relationship between performed and observed actions, more recent studies highlight the importance of multimodal experiences modulated by auditory , somaticThis primary adaptive mode of perceptuo-motor control also requires an additional representational transformation to a body-centered, one-person perspective. The representational transformation is thought to embody imitation, which allows one to reproduce the actions of another person from a different perspective to achieve a goal. In an interesting study  on motorSoA may also be enhanced by detecting errors in one’s own actions with changes in the environment. In a study presented in this Special Issue , particiTaken together, the papers in this Special Issue have covered and expanded the surprising range of cognitive processes that can be explained by linkages to body systems, such as creativity, memory, and sensorimotor representations, which are essential for rebuilding and maintaining self-awareness of body consciousness.These papers will stimulate interest in further basic and clinical research on the role of embodied cognition mechanisms and multisensory stimulation to support appropriate clinical treatment development regarding altered body representation, expanding our knowledge of this research topic.


The incidence rates of depression are increasing year by year. As one of the main clinical manifestations of depression, sleep disorder is often the first complication. This complication may increase the severity of depression and lead to poor prognosis in patients. In the past decades, there have been many methods used to evaluate sleep disorders, such as polysomnography and electroencephalogram, actigraphy, and videography. A large number of rodents and non-human primate models have reproduced the symptoms of depression, which also show sleep disorders. The purpose of this review is to examine and discuss the relationship between sleep disorders and depression. To this end, we evaluated the prevalence, clinical features, phenotypic analysis, and pathophysiological brain mechanisms of depression-related sleep disturbances. We also emphasized the current situation, significance, and insights from animal models of depression, which would provide a better understanding for the pathophysiological mechanisms between sleep disturbance and depression. Sleep is an essential physiological requirement for human and most animals. A mechanistic link is evident between sleep and depression at the molecular and neurophysiological level. The periodic regulation of awake and sleep requires the participation of many neurotransmitters, including excitatory neurotransmitters (such as acetylcholine) and inhibitory neurotransmitters . Abnormalities of these neurotransmitter systems not only lead to sleep-wake rhythm disorders, but also can contribute to developing depression. Depression and sleep disturbances are common co-morbid conditions , 2. MoreSleep is vital for human beings and most animals, and control mechanisms are embodied in all levels of biological organizations, from genes and intracellular mechanisms to cell population networks, and then to all central nervous systems, including systems that control movement, arousal, autonomic function, behavior, and cognition. Mammalian sleep is characterized by the periodic alternation of rapid eye movement sleep (REMs) and non-rapid eye movement sleep (NREMs). NREMs includes two stages: slow-wave sleep (SWS) and light sleep. In humans, SWS and REMs, which are the specific modes of potential electric field oscillations and neuromodulator activities, dominate the first half of the night and the latter half of the night, respectively .The mutual transformation between sleep and wakefulness is caused by the excitation or inhibition of many neurotransmitters in the brain, which are released by sleep-promoting neurons in the anterior hypothalamus or sleep-inhibiting neurons in the lateral and posterior hypothalamus activity. These neurons release excitatory or inhibitory neurotransmitters to promote the brainstem to control the mutual transformation of wakefulness and sleep , 4.The ascend arousal system mainly comes from a group of explicit cells with definite neurotransmitters. The arousal system actually consists of two channels . The ascThe pathogenesis of sleep disorder is closely related to sleep-wake homeostasis, but the specific mechanism remains still unclear. During NREMs and REMs, different kinds of neurotransmitters are released in the brain. The interaction between aminergic neurons and cholinergic neurons at the meso-pontine junction leads each other to bring about the Ultradian rhythms alternation of REMs and NREMs. During NREMs, aminergic inhibition is decreased and cholinergic excitation is increased. At the onset of REMs, aminergic inhibition is turned off, cholinergic excitability reaches a peak, and other outputs are inhibited . When awIn short, the growth and decline of these neurotransmitters promote the mutual transformation between sleep and wake. If these related neurotransmitters are released abnormally, it will cause sleep problems, such as difficulties in falling asleep and maintaining sleep state, changes of REMs latency, abnormal REMs behavior, and disturbed alternating pattern of REMs/NREMs.Depression is the main cause of the burden of mental health-related diseases in the world, and about 300 million people around the world are affected by depression . One aspEpidemiological investigations confirm that there is a closer relationship between insomnia and the onset of depression. It is reported that most patients often have insomnia and depressive episodes at the same time . ApproxiSince the 1960s, polysomnography (PSG) sleep studies have repeatedly shown that depression is also associated with disrupted sleep architecture. These abnormalities include increase in RA (REMs activity) and RD (REMs density), as well as a decrease in REMs latency and SWS . During The increase of serotonin content may be the main reason affecting REMs . AntidepGlutamatergic and GABAergic neurons also play a role in the generation of REMs . KetaminThe REMs density of patients with depression continues to increase, which is regarded as an endophenotype. The reduction of the initial latency and the delta sleep ratio  of the rapid eye movement can be explained by cholinergic-aminergic imbalance . The monThe initiation and maintenance of NREMs also seem to be dependent on the role of monoamine neurotransmitters . SedativIn addition, other types of antidepressants can also improve sleep. For example, antidepressants with anti-histaminergic action, such as mirtazapine and ipsapirone, act on their own receptors to support homeostatic maintenance of monoamine levels, block specifically monoamine receptors to enhance serotoninergic neurotransmission. Some patients' sleep can become better even after the first treatment of mirtazapine . HoweverIt is necessary to obtain the best animal model for studying disease in biomedical research. Validity of animal models depends on the extent to which how they can mimic human diseases. Researchers have made exogenous and endogenous animal models to simulate the symptoms of depressed patients and elucidate the mechanisms of antidepressant action, involving acute and chronic stress model, secondary depression model, and genetic model . TranslaRodents are more usual choice of preclinical models to develop new pharmacological and non-pharmacological strategies. In the study of sleep deprivation, rodents  and humans have many similarities in sleep electroencephalogram (EEG) and sleep structure . ExternaAs for the effect of stress on rodents' total sleep time, the primary stressors are immobilization and mild electrical shock. Immobilization increased the time spent in SWS and REMs, while electrical shock resulted in a decrease in total sleep time and total REMs time . SimilarContinuous light exposure (LL) increases depressive-like behavior in mice, and light exposure at night (LAN) can lead to depressive-like behavior in diurnal rodents, such as grass rats and hamsters –111. ThiFor social species such as rats and mice, repeated fighting and/or defeat may be a more natural source of stress. Often, the consequences of chronic social defeat stress (CSDS) can persist until the termination of the stressors, which makes it a particularly attractive method to model stress-related psychiatric illnesses . PreviouNHPs bridge the gap between rodents and humans . Like huEEG is a common method in sleep research, which can provide objective functional indexes for sleep . AlthougResearchers have used NHPs to make great efforts in the research of depression. It has been demonstrated for the first time that long-term intracerebroventricular administration of IFN-α (5 days/week for 6 weeks) can induce the monkeys showing considerable depressive-like symptoms with changes in the concentration of monoamine metabolites . The relIn addition, researchers have employed NHPs animal model to make many beneficial explorations on the association between light deprivation and depression. The results showed that monkeys could develop the main symptoms of seasonal affective disorder under short lighting conditions . AnalogoThere is increasing evidence that sleep plays a causal role in emotional processing and regulation . DepressIn any way whatever, the research on animal models of sleep disorders provides a good clue and basis for clinical diagnosis and treatment of depression. NHPs are considered as a further valuable and translational animal model, which is necessary for sleep and related diseases , 138. ItDQ, LX, XL, and ML designed the structure. ML, JC, BX, YW, CF, and DQ wrote the first draft of the manuscript. DQ, LX, and XL supervised and revised the final version of the manuscript. All authors contributed substantially to the scientific process, writing of the manuscript, and have approved the final version of the manuscript being submitted.This work was supported by the National Natural Science Foundation of China , the Applied Basic Research Programs of Science and Technology Commission Foundation of Yunnan Province (2019FA007), the Joint Project of Applied Basic Research of Yunnan University of Chinese Medicine & Yunnan Provincial Science and Technology Department [2019FF002(-001)], Yunnan Provincial Department of Education Science Research Fund Project (2020Y0203), the Key Realm R&D Program of Guangdong Province (2019B030335001), the China Postdoctoral Science Foundation (2018M631105), and the Yunnan Provincial Academician and Expert Workstation (202005AF150017 and 2019IC051).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.All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. 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