Infectious diseases, caused by the direct exposure of cellular or acellular pathogens, are found to be closely associated with multiple inflammation and immune responses, keeping one of the top threats to human health. As an indispensable trace element, Selenium (Se) plays important roles in antioxidant defence and redox state regulation along with a variety of specific metabolic pathways. In recent decades, with the development of novel nanotechnology, Selenium nanoparticles (Se NPs) emerged as a promising agent for biomedical uses due to their low toxicity, degradability and high bioavailability. Taking the advantages of the strong ability to trigger apoptosis or autophagy by regulating reactive oxygen species (ROS), Se NPs have been widely used for direct anticancer treatments and pathogen killing/clearance in host cells. With excellent stability and drug encapsulation capacity, Se NPs are now serving as a kind of powerful nano-carriers for anti-cancer, anti-inflammation and anti-infection treatments. Notably, Se NPs are also found to play critical roles in immunity regulations, such as macrophage and T effector cell activation, which thus provides new possibilities to achieve novel nano-immune synergetic strategy for anti-cancer and anti-infection therapies. In this review, we summarized the progress of preparation methods for Se NPs, followed by the advances of their biological functions and mechanisms for biomedical uses, especially in the field of anti-infection treatments. Moreover, we further provide some prospects of Se NPs in anti-infectious diseases, which would be helpful for facilitating their future research progress for anti-infection therapy. Mycobacterium tuberculosis and Staphylococcus aureus (S. aureus), are still major threat to public health with high infectivity and mortality worldwide. Current chemotherapeutic methods have contributed largely to the control of infectious diseases, however, the frequent use of antibiotics with low targeting effects always lead to low treatment efficiency and promoted drug resistance  have attracted extensive attention from researchers in biomedical fields due to their exclusive physical, chemical and biological properties . CompareMore interestingly, Se NPs are also capable of targeting macrophages and regulating macrophage polarization to initiate innate immunity for antimicrobial inhibition by regulating the production of cytokines . Se NPs Compared with traditional organic or inorganic selenium compounds, the chemical structure of Se NPs is more complicated. Numerous factors should be taken into consideration when the Se NPs are designed and synthesized for biomedical application, including size, shape, composition, surface property and dispersion. Thus, it is of vital importance to develop novel Se NPs with controllable size distribution, functional agents, morphological characteristics and surface properties.Physical, chemical and biological techniques are three most widely used approaches for the synthesis of Se NPs. With vitamin C, sodium sulfite, sodium thiosulfate and hydrazine as commonly reducing agents, Se NPs are always prepared by chemical reduction method, which is considered as the most convenience method for Se NPs preparation. In addition, Hydrothermal method, template method, laser ablation method, and biosynthesis method are also successfully applied for Se NPs preparation.via dissolution recrystallization. Se NPs with different diameters ranging from 10 to 1,000 nm can be obtained using this hydrothermal method.The hydrothermal synthesis was developed by Niu et al. With some advantages such as low cost, simple and efficient preparation for the synthesis of crystalline selenium nanostructures . TypicalUsing similar hydrothermal method, Shar et al. also prepared Se NPs using sodium selenite as a precursor and L-ascorbic acid as reducing and stabilizing agent, which showed very good hexagonal shape with a clean and smooth surface and revealed very narrow size distribution ranging from 100 to 200 nm . Shin etSe NPs can be formed from selenium element in the guidence of some chemical templates as stabilizers. PEG200 was introduced as a kind of template and surface decorator for Se NPs synthesis . FirstlyBased on chemical reductions, template method is most widely used in the preparation of Se NPs. Using different templates, Se NPs with different size, shapes, and surface properties can be obtained. Hu et al. introduced sulfate polysaccharidesv (SPS) as template to prepare Se NPs using a one-step method . PolysacAs the mostly widely used method, the reduction mechanism of sodium selenite by ascorbic acid is listed as below:chitosan , folate chitosan , hyalurochitosan ,polyethychitosan and ferulchitosan . In termUsing laser to irradiate the pure selenium pellet in the bottom of microcentrifuge tube, Guisbiers et al. have successfully prepared Se NPs to inhibit the bacteria growth . With quvia one step laser ablation route, which significantly improved the antibacterial activity of their pure blend  leaf  and unwanted chemical reagents, which may result in environmental pollution and unwanted toxicity of produced Se NPs . With grnt) leaf , Clausen extract , Theobro extract , gallic  extract , and so Azoarcus  on human hepatoma HepG2 cells . With reAnd except for the ability to kill cancer cells, apoptosis is also a common pathway for the destruction of intracellular bacteria, which is very important for the host immunity defense against bacterial infection . During As a catabolic process, autophagy is necessary and beneficial for cell homeostasis as it could prevent the toxic protein aggregation, remove damaged organelles and provide cell and organism with bioenergetic substrates for survival . HoweverAutophagy can suppress or promote tumors depending on the developmental stage and tumor type. Modulating autophagy for cancer treatment is an attractive therapeutic strategy currently under intense investigation . Apart fIt’s also important to note that autophagy can regulate immunological functions that influencing pathogen infection and pathogen survive in host cells. The host cells tend to kill the intracellular pathogens by autophagy pathways, but some bacteria have developed diverse strategies to avoid autophagy by interfering with autophagy signaling or the autophagy machinery . And in Taking the advantages of targeted drug delivery and controlled drug release, functional nanosystems provide novel therapeutic strategies for disease treatment. With low toxicity, high bioavailability and biocompatibility, Se NPs can be conjugated with different kind of agents for targeted drug delivery. Drugs can be loaded into Se NPs at high concentrations than their intrinsic solubility, which significantly enhanced their anticancer effects . Comparein vitro and in vivo tumor inhibition  modified Se NPs as doxorubicin (DOX) delivery system with active tumor-targeting property . And in hibition . Our prein vitro .Additionally, the drug delivery capacity of Se NPs can also be applied to enhance the killing efficiency of drugs against bacteria. Liu et al. introduced ciprofloxacin loaded engineered selenium lipid nanocarriers as effective drug delivery system for preventing lung infections of interstitial lung disease . Our recSe NPs have been proved to exhibit strong immunomodulatory activity by regulating different immune cells or modifying some important immune-associated signaling events . With thin vivo results indicated that Au@ Se NPs not only generated the anti-tumor immune responses with excellent cancer killing effect under the presence of tumor-associated antigens, but also effectively transformed the tumor associated macrophages (TAMs) from M2 to M1 phenotype. These effects could further promote T cell activation for tumor rejection, which also contributed to phagocytosis of the distant tumor. Hu et al. introduced the effects of Se NPs to up-regulate the expression of cytotoxicity related molecules including NKG2D, CD16, and IFN-γ in γδ T cells, meanwhile, downregulate PD-1 expression in γδ T cells, which significantly enhance the cancer killing effects and in vivo tumor growth inhibition  have been proved to enhance immunity and disease resistance in zebrafish against bacterium nfection . With thnfection . These wC. albicans biofilm, further confirming the fungicidal effects of Se NPs , one of the typical Gram-positive bacteria, is the major antibiotic-resistant pathogen inducing skin infections, pneumonia, enteritis and other deadly diseases . Biogenic Se NPs without any cytotoxicity exerted protective effects on intestinal barrier dysfunction caused by Enterotoxigenic E.coli K88, which played an essential role in promoting the growth of intestinal epithelial cells and maintaining intestinal microflora balance (coli might be closely associated with the ability of Se to reduce exopolysaccharide (EPS) synthesis, inhibit biofilm formation, and inactivate the mature E. coli biofilms  treatment combining the advantages of natural red blood cell membrane (RBCM) and bacteria-responsive gelatin nanoparticles , has become one of the top killers among infectious diseases. In recent decades, the occurrence of drug-resistant TB cases become an emerging issue, which requires the development of new alternative treatments beyond the current antibiotics or novel techniques to enhance the efficiency of current antibiotics. Estevez et al. found that Se NPs were able to inhibit the growth of Mtb by damaging their cell envelope integrity, which indicated a new opportunity for the use of Se NPs as antimycobacterial agents by themselves, or for the development of novel nanosystems that combine the action of these Se nanoparticles with other drugs (Tuberculosis (TB), caused er drugs .Up to now, the immune escape of Mtb from phagolysosomal destruction and limited drug delivery into infected cells remain biggest challenges for TB and drug-resistant TB treatments. To synchronously solve the above issues, we combined our decade-long nanotechnology and TB immunology expertise to innovate the macrophage-targeted Se NPs for synergistic antimicrobial and bactericidal destruction of Mtb in host cells . The manDuring the evolution together with human beings in thousands of years, Mtb has become one of the most outstanding and clever bacterial pathogens by its multiple ways to escape from immunological clearance. How to countercharge the immune escape of Mtb remains a substantial challenge for TB or drug-resistant TB treatment. Our works firstly reported that Se NPs, a kind of novel anti-bacteria agent, possessed the ability to regulate host cell immunity for intercepting Mtb immune escape . These rVirus, the most dangerous pathogens that causing millions of deaths every year, are now inducing more and more deaths due to the epidemic of COVID-19 virus. How to develop more effective treatments for virus infection becomes the most urgent demand for human health. Selenium has long been found to be directly involved in fighting against viruse infections, such as influenza virus , HepatitDifferent kinds of influenza virus are responsible for the seasonal flu epidemics each year, therefore severely threatening human health. Due to the low toxicity and excellent activity, the antiviral capabilities of Se NPs have attracted increasing attention in recent years. Li et al. introduced oseltamivir decorated Se NPs for H1N1 virus treatment, which significantly interfered the binding of H1N1 influenza virus to host cells through inhibiting the activity of hemagglutinin and neuraminidase . Se NPs in vitro and in vivo. However, it’s worth to note that Amir et al. investigated the efficacy of hexanic extracts of Ficus carica and olive fruit and Se NPs on the immunogenicity of the inactivated avian influenza virus subtype H9N2 in broiler chickens, which indicated that the prepared Se NPs emulsions could elicit a little degree of immunity, but they could not inhibit the anamnestic response and infection , Enterovirus 71 (EV71) can induce different clinical symptoms and even death among infants and children under 6 years old. Unfortunately, at present, no effective treatment for EV71 is available, which requires the development of effective treatment strategies. Zhong et al. developed Se NPs as the carrier of oseltamivir to assess the anti-EV71 activity, which apparently enhanced the antiviral effect of oseltamivir to suppress EV71 proliferation and impede cell apoptosis by reducing the caspase-3 activity and ROS generation . Lin et Hepatitis virus (HV) infection is one of the most serious and prevalent health problems worldwide. The emergence of current anti-HV medications contributes to the slow down of HV induced epidemic, however, some drawbacks including adverse effects and drug resistance are requiring novel agents for more effective and safe treatments. Sodium selenite was found to suppress Hepatitis B virus (HBV) protein expression, transcription, and genome replication in hepatoma cell models in a dose- and time-dependent manner , which pThe prevalence of HBV infection has been significantly reduced by the approved HBV vaccine, which induces strong Th2 responses against that could protect HBV infection. However, there is a vital need to stimulate Th1 prophylactic immune response for more effective control of HBV infection. Mehdi et al. introduced a novel strategy by administration of Se NPs and the HBs antigen vaccine, which could affect lymphocyte proliferation and total antibody responses, and more importantly, could increase IFN-γ level and induce Th1 response . These iCOVID-19 is a widespread, highly contagious and extremely dangerous disease that has caused millions of deaths in the past year. The point-of-care tests for COVID-19 detection is of vital importance for its epidemic prevention and epidemiological investigation. Wang et al. presented a lateral flow immunoassay kit based on Se NPs-modified SARS-CoV-2 nucleoprotein, which detected anti-SARS-CoV-2 IgM and anti-SARS-CoV-2 IgG in human serum by the naked eye within 10 min . This woIt’s very interesting that the cure rates in some places are found to be significantly correlated with Selenium intake levels , which sCandida albicans is a major opportunistic fungus that very difficult to be controlled. Its biofilms coated by an exopolymeric substance or extracellular polymeric substance matrix can protect the pathogen from adverse environmental conditions, fungicides and hosts’ immunity (Candida albicans biofilms (Candida albicans biofilm at low Se NPs dosage. Aiming at the treatment of Candida and Aspergillus infections, Shakibaie et al. produced biogenic Se NPs to show the strong inhibitory effect on Candida albicans and Aspergillus fumigatus (Colletotrichum capsici and Alternaria solani, which highlighted the practical application of Se NPs to manage plant diseases in an ecofriendly manner (Fungi are ubiquitous and form their own kingdom to threat human health as infections would affect various parts of different species and bodies. Causing a spectrum of diverse diseases, immunity . Guisbiebiofilms . After aumigatus . Additioy manner . The broin vivo efficacy of Se NPs remains to be further explored.In addition to possessing antimicrobial effect towards bacteria, virus and fungi, Se NPs also present antiparasitic properties. Biogenic Se NPs were found to display powerful cytotoxicity in killing promastigote and amastigote forms of Leishmania. Major, which suggested that Se NPs could be emerged as a promising therapeutic agent for curing cutaneous leishmaniasis . Se NPs Schistosoma mansoni, indicating that Se NPs could possess therapeutic anti-schistosomal activity in the treatment of intestinal schistosomiasis (in vivo (in vivo findings along with the previously mentioned in vitro results collectively demonstrated that Se NPs could be served as nutritional supplements with powerful anti-parasite effects.Se NPs are found to be more effective than sodium selenite with regard to their anti-coccidial, anti-oxidant, anti-apoptotic and anti-inflammatory role against Eimeria parasite in the jejunum of mice . Furthersomiasis . Additio(in vivo . These iSelenium toxicity can occur with acute or chronic ingestion of excess selenium in humans, and similarly, the excess selenium contents would result in inevitable toxicity against bacteria, virus, fungi and parasite. The strong toxicity of selenium thus makes Se NPs a kind of anti-infection agents with direct killing or inhibition effects on different pathogens. However, it would be very tricky to control the dosages of Se NPs for anti-infection therapy if only the direct killing effects of Se NPs are applied, as the excessive selenium contents might also induce systemic toxicity of normal cells or tissues. Thus, other functions of Se NPs must be involved for more effective anti-infection treatment with low cytotoxicity.In infectious disease, there are many ways that the host metabolism and immune status can be affected, leading to a dysregulation of redox homeostasis and immunosuppression. Selenium has long been found to be closely associated with different pathogen infections by regulating the antioxidant defense system through selenoprotein functions. As part of antioxidant defense, selenoproteins, such as GPXs and TXNRDs, play an important role in controlling oxidative stress, which therefore results that reduced selenoprotein expression would induce weaken of the defense against infectious diseases . Dietaryin vitro works have confirmed the drug delivery capacity of Se NPs for infectious diseases treatment, however, more in vivo works are needed for their future applications.The effective drug delivery and controlled drug release ability of nanosystem are providing more effective tools to enhance the targeting effects of drugs against the specific disease sites. Our previous works have proved that drug delivery system could significantly enhance the intracellular pathogen clearance efficacy of antibiotic by targeting host cells . FurtherUp to now, most therapeutics against infectious diseases are focusing on the antibiotic treatments, however, the increasing emergence of drug-resistant mutants or multiple drug-resistant mutants requires novel treatments rather than more antibiotics that might worsen the drug-resistance conditions. Immune therapy is now serving as one of the most effective treatments in some important disease, such as tumor. It’s very attractive that Selenium status may affect the function of cells both in adaptive and innate immunity. We have recently demonstrated the ability of Se NPs to regulate host immunity against intracellular pathogens, which dramatically countercharge the immune escape of intracellular pathogens, such as lysosomal escape, host cell apoptosis/autophagy and macrophage polarization . This meSupranutritional selenium intake was shown to regulate adaptive immunity by favoring proliferation and differentiation of activated CD4-positive T cells toward Th1 cells, which play important roles in infectious disease defense . AlthougTaking the advantages of direct inhibition/killing effects on pathogens, targeted drug delivery against host cells or disease sites, chemosensitization effects on the current drugs, and the innate and adaptive immunity regulation effects, Se NPs are expected to be served as effective anti-infectious agents simultaneously manipulating the above activities. Considering the low toxicity, antioxidant and immunity regulation capabilities and other merits of Se NPs, it is desirable and reasonable to further explore the effects and mechanisms of Se NPs against different pathogens. With the development of nanotechniques, we hope that Se NPs can play more and more important roles in fighting against infectious pathogens, which would finally benefit the diagnosis, prevention and treatment of infectious diseases.As a kind of novel nanomaterials, Se NPs have drawn increasing attentions to address the dilemma of antibiotic resistance, thus showing attractive potentials for future clinical infectious diseases treatment. However, there are still some inevitable challenges that need to be addressed before their clinical transformations. During these challenges for Se NPs, the most urgent issue is the biocompability, which is the ability of a material being compatible with living tissue. Ideal biocompatible nanomaterials would not produce unexpected toxicity or immunological response when exposed to the body or bodily fluids. However, the toxicity of excess selenium is a dangerous assumption that Se NPs may introduce. The toxicity of Se NPs have been widely reported for anticancer or anti-infection treatment, however, the toxicity of Se NPs against normal cells or tissues remains to be further investigated. Thus, it would be important to understand the bridge between the Selenium and Se NPs, especially for their molecular events that are responsible for the therapeutic differences and toxicity effects that are critical for their biocompability. Otherwise, the degradation of Se NPs in body is still unclear, which might introduce unknown toxicity after long-term administration. Thus, more concerns about the degradation of Se NPs after long-term administration should be paid to verify the safety of Se NPs for clinical uses. Therefore, how to develop functional Se NPs with good biocompability and degradation property would be the most critical issues for the further clinical application of Se NPs against different infectious diseases.Another critical issue for the further studies of Se NPs would be focused on the exploration of their anti-infectious mechanisms, especially their effects and mechanism on immune regulations. The direct killing effects of Se NPs against different pathogens are the mostly investigated parts for their potential anti-infection applications. However, as widely known, one of the most important issues in infectious diseases would be the immune responses for infection controls. The immunity regulation functions of Selenium are thought to be closely associated with selenoproteins, which play critical roles in both metabolism and immune system. However, how selenium from Se NPs affect the immune responses by regulating selenoprotein activity remains to be further investigated. And in our opinion, Se NPs may also strongly influence the phagocyte functions to further regulate the immune responses. Thus, it would be important to explore the effects of Se NPs on phagocyte functions when they are used for infectious disease treatment, which may also activate anti-infection immunity for infections control.


Unmanned Aerial Vehicles have undergone rapid developments in recent decades. This has made them very popular for various military and civilian applications allowing us to reach places that were previously hard to reach in addition to saving time and lives. A highly desirable direction when developing unmanned aerial vehicles is towards achieving fully autonomous missions and performing their dedicated tasks with minimum human interaction. Thus, this paper provides a survey of some of the recent developments in the field of unmanned aerial vehicles related to safe autonomous navigation, which is a very critical component in the whole system. A great part of this paper focus on advanced methods capable of producing three-dimensional avoidance maneuvers and safe trajectories. Research challenges related to unmanned aerial vehicle development are also highlighted. Unmanned Aerial Vehicles (UAVs) have evolved greatly over recent decades with prevalent use in military and civilian applications such as search and rescue , wirelesMany researchers have contributed towards addressing the navigation problem for UAVs. This overview aims at surveying the developments made in the past ten years towards achieving fully autonomous operations. Some key approaches developed earlier than the considered time frame are also reported for the sake of completion. General definitions and research areas are also provided for new researchers interested in this field. Additionally, a list of useful open-source projects and tools is provided which may aid in quick development and deployment of new approaches related to UAVs as part of a complete autonomous stack.This survey is dedicated to the more complex problem of three-dimensional (3D) obstacle avoidance utilizing the full maneuvering capabilities of UAVs. Given the fact that many of the existing algorithms are developed considering general 3D kinematic models, they are applicable to vehicles moving in 3D, including different UAV types and autonomous underwater vehicles (AUVs). Similarly, some of the general approaches developed for AUVs are also reported here given that they are applicable to UAVs. Planar approaches usually consider flights at a fixed altitude to simplify the obstacle avoidance problem. These approaches may fail with the increased complexity of the environments where UAVs are needed; hence, utilizing 3D avoidance maneuvers is more desirable. However, some planar approaches are also reported here where they can potentially inspire extensions to more general 3D methods.This paper is organized as follows. A general overview of existing UAV types, classifications, autonomous navigation paradigms, and control structures is given in Micro: less than 250 g;Very Small: 0.25–2 kg;Small: 2–25 kg;Medium: 25–150 kg;Large: More than 150 kg.UAVs can be classified based on several factors such as size, mean takeoff weight, control configuration, autonomy level, etc. For example, classifications of UAVs based on size according to the Australian Civil Aviation Safety Authority (CASA) are:single-rotor ,16,17,18multi-rotor ,22,23,24fixed-wing ,26,27;hybrid ,29,30,31flapping wings ,36,37,38Large UAVs are mainly used in tactical missions and military applications; for more detailed classifications related to military use, see . Based oSingle-rotor aerial vehicles such as helicopters have not been utilized much as UAV platforms. Multi-rotors on the other hand have become the most popular choice in most civilian applications when it comes to maneuverability. Multi-rotors such as quadrotors, hexacopters and octocopters with fixed-pitch rotors share similar dynamical models for control. However, quadrotors are cheaper, faster, and highly maneuverable while hexacopters and octocopters can offer better flight stability, fault-tolerance, and more payload capacity. Multi-rotors with fixed-pitch rotors are underactuated systems where it is not possible to completely control all degrees of freedom. There have been recent advances in developing omnidirectional tilt-rotor UAVs which are fully actuated in 6DOF ,24,39,40Multi-rotors in general lie under the category of vertical-takeoff-and-landing (VTOL) vehicles with the ability to hover in place. On the contrary, fixed-wing UAVs are horizontal-takeoff-and-landing (HTOL) vehicles, and they cannot hover at a certain position due to nonholonomic constraints. Instead, they have to loiter around areas of interest. However, fixed-wing UAVs have advantages such as long endurance  and higher achievable speeds compared to multi-rotors. Hybrid UAVs combine both configurations of fixed wings and multiple rotors utilizing the advantages of both such as vertical takeoff and landing, hovering and long endurance flights. However, these vehicles are still under development, and more research is needed for reliable control, especially when switching between flight modes.Another type of UAV is one with flapping wings inspired by birds (Ornithopters) and insects (Entomopters). This type is still under development due to its complex dynamics and anticipated power problems . RecentlFully autonomous: UAV can carry out a delegated task/mission without human interaction where all decisions are made onboard based on sensors observations adapting to operational and environmental changes.Semi-autonomous: A human operator is needed for high-level mission planning and for interaction during the movement when some decisions are needed that the UAV is not capable of making. The vehicle can maintain autonomous operation in between these interactions. For example, an operator can provide a list of waypoints to guide the vehicle where it can manage to move safely towards these positions with obstacle avoidance capability.Teleoperated: The remote operator relies on feedback from onboard sensors to move the vehicle either by directly sending control commands or intermediate goals with no obstacle avoidance capabilities. This mode can be used in Beyond-Line-of-Sight (BLOS) applications.Remotely controlled: A remote pilot is needed to manually control the UAV without sensors feedback which can be used in Line-of-Sight (LOS) applications.Being completely able to carry out missions/tasks with minimum human interaction is an ultimate goal for unmanned aerial vehicles. Different levels of autonomy can be achieved towards that goal depending on the complexity of tasks and whether a fully autonomous solution exists or not for that specific application. These levels can be described based on the UAV mode of operation according to the National Institute of Standards and Technology (NIST) as follows :Fully auDeveloping a fully autonomous UAV is a very challenging and complex problem. A modular approach for both hardware and software architectural design is commonly adopted in the literature by most existing autonomous UAVs for a simpler and fault-tolerant solution.At the hardware level, a UAV in its simplest form consists of a frame, a propulsion system and a Flight Control System (FCS). The UAV’s size and propulsion system can be designed to support the needed payload and flight time as per the mission requirements. A propulsion system consists of a power source , motors drivers or electronic speed controllers (ESCs), motors (ex. brushless DC motors), propellers and/or control surfaces .The flight control system is simply an embedded system consisting of the autopilot, avionics and other hardware directly related to flight control . For exaFor more complex tasks/missions, an onboard computer with higher processing power, namely a mission computer, is required to achieve fully autonomous operations given that a UAV with proper size and power is used. In this structure, the mission computer usually implements high-level mission and motion planning by relying on information interpreted from high-bandwidth sensory data in addition to running required processes with expensive computational cost. It can also have its own communication link with a Ground Control Station (GCS) to stream high-bandwidth data such as images and depth point clouds.Different kinds of sensors can be used for advanced perception and planning, depending on the mission requirements, UAV available payload and power, and environmental conditions. Examples of commonly used sensors are cameras , range sensors  and other task-specific sensors . A summary of hardware and software components used with UAVs are shown in The software architecture of the autonomous stack implemented on the mission computer typically consists of several processes/modules running in parallel and a messaging middleware is used to interchange messages between processes on the mission computer or with other computers on the same network . Some of these modules are related to the mobility aspects that can ensure safe navigation which can be common among most UAV systems and other autonomous mobile robots. Other modules would implement logic that is application-specific such that the UAV can autonomously perform the delegated task. For example, in fire-fighting applications, a UAV is needed to autonomously locate and extinguish fires, which requires additional modules to be included within the autonomous stack including computer vision pipelines and an extinguisher control mechanism. In many remote sensing applications, the main task could be only collecting data either in the form of images or information from other onboard sensors to be analyzed and processed post-flight.Perception;Localization and Mapping;Motion Planning and Obstacle Avoidance;Control.Mobility-related modules are the core components needed to ensure collision-free navigation in all applications. By considering only the mobility-related components, a popular modular structure for autonomous navigation is adopted in the literature which consists of the following modules/subsystems :PerceptiThis modular approach of addressing the navigation problem offers a flexible expandable design with fault-tolerance. However, other possible designs can also be seen for less complex tasks or for vehicles with very limited resources by coupling control and planning, without the need for localization and mapping, in a reactive fashion, as will be shown in the next section.configurations while satisfying some kinematic and dynamic constraints. A configuration in this case refers to the position and orientation of a mobile robot where a configuration space is the set of all possible configurations. The dimension of the configuration space equals the number of controllable degrees of freedom. For example, planning motions for quadrotors can be carried out in a space of their 3D position coordinates and heading (yaw) angle while motions for omnidirectional (fully actuated) UAVs can be planned considering all translational and rotational states (6DOF).A crucial part of autonomous navigation is to ensure that the vehicle can move while avoiding collisions with its surroundings. This is a general problem in robotics which can be addressed by motion planning or reactive control. Generally, the motion planning problem can roughly be described as trying to find collision-free trajectories between initial and final In a decoupled approach, the UAV control system can execute motions planned by a high-level system, namely a motion planner, where these plans need to be feasible and safe . In other implementations, motion planning can be coupled with the control system design where reactive control laws are developed to directly generate obstacle avoidance maneuvers based on sensor measurements. Some refer to those in the literature in loose terms as obstacle/collision avoidance methods. The term collision avoidance is mostly used by the UAV research society in referring to avoiding collisions with other cooperative or noncooperative aerial vehicles  sharing the same flight space, while the term obstacle avoidance may be used more often in indoor, industrial and urban environments where the flight space is filled with other static/dynamic obstacles. That is, high-altitude flights commonly adopt the collision avoidance terminology and low-altitude flights may use the more general obstacle avoidance term. This terminology is also adopted more often in multi-UAV systems to differentiate between methods that only consider collision avoidance among the vehicles within the system to those that also consider obstacle avoidance in obstacle-filled environments.deliberative , sensor-based  or hybrid ;Geometric methods ;Sampling-based methods ;Optimization-based methods .Existing navigation techniques for autonomous mobile robots in general can be classified into brid see . DeliberMany of these methods can find optimal paths if one exists at the expense of requiring full knowledge about the environment which is not suitable in unknown and dynamic environments. For more detailed information about such planning methods, the reader is referred to .sensor-based methods rely directly on current sensor measurements or a short history of the sensors’ observations  to plan safe paths in real time. The planning horizon can typically be very short for some period ahead of time or it could be carried out at each control update cycle in a receding horizon fashion. A special class of such methods is made up of reactive approaches where sensor measurements are coupled to control actions either directly [On the other hand, directly  or afterdirectly . Sensor-Hybrid approaches combine both deliberative and sensor-based methods to generate a more advanced navigation behavior benefiting from the advantages of both classes. It relies on low-latency local planning or reactive control to handle unknown and dynamic obstacles while using a high-level global planning method to guide the vehicle utilizing accumulated knowledge about the environment.map-based or mapless approaches [Navigation methods can alternatively be classified into proaches ,54. ThisMap-based strategies require a local  map representation of the environment which can be provided before navigation starts (deliberative approaches) or it can be built during navigation based on sensor measurements (some sensor-based approaches). Safe paths can then be found using local/global planning algorithms based on either metric or topological maps. Therefore, such methods are demanding in terms of computational resources, planning time and memory requirements, which is highly dependent on the environment size and its complexity. Nevertheless, local map-based methods are very commonly used with UAVs to generate local optimal solutions for technological advances where it is possible to have mini lightweight computers with high processing power onboard.mapless strategies (reactive methods) rely directly on sensor measurements to make motion decisions without the need for maintaining global maps and accurate localization (except when using GNSS). Hence, control actions can be directly coupled with either visual clues from image segmentation, optical flow or feature tracking in subsequent frames in vision-based methods [On the contrary,  methods  or interFrom a control perspective, different structures were adopted in the literature to deal with the high complexity of the navigation problem. As mentioned before, the most common structure is based on decoupling planning and control due to its simplicity in design. One can categorize the existing methods into seven different control structures, as shown in In decoupled approaches, some motion planning methods further simplify the problem by subdividing it into two stages. The first stage simply tries to find a collision-free geometric path satisfying kinematic constraints. Constraints can be considered directly in the planning algorithm, or the entire process can be further decomposed into finding a safe path first ignoring such constraints then applying path smoothing techniques to satisfy the kinematic constraints. Then, it is followed by a trajectory generation stage to obtain feasible trajectories satisfying dynamic constraints. Other approaches tackled this problem by directly planning trajectories using optimization-based methods which is a harder problem to solve.path planning and trajectory planning/generation. Path planning is the process of finding a geometric collision-free path between starting and end positions without a timing law. In trajectory planning, a timing law is associated with the planned collision-free geometric path represented as a trajectory which includes information about higher derivatives . Trajectories are mostly planned to satisfy dynamic constraints which can then be passed to a control system adopting a trajectory tracking control design. One of the common approaches for trajectory planning is by using a path planning algorithm to find an initial geometric path followed by formulating trajectory generation as an optimization problem to plan local optimal trajectories around the initial path subject to several constraints. Alternatively, some approaches adopt ideas from missile guidance, implementing path following control laws to track the geometric path given that it satisfies nonholonomic constraints whenever they exist without generating a trajectory.To differentiate between different motion planning paradigms, we highlight the differences between In the following subsections we will survey recent works adopting local motion planning or reactive paradigms in accordance with the considered control structures.A number of existing methods treat the problem through applying path planning algorithms locally to find feasible geometric paths assuming a general 2D/3D kinematic model. Examples of these methods include sampling-based ,56,57,58Adopting sampling-based methods helps address the high dimensionality problem of the 3D search space to generate collision-free paths in real time, which was considered in many works. In , a plannSome other works formulated the 3D path planning problem as an optimal control problem, such as ,62. The A more popular approach in addressing the local planning problem for UAVs is through planning feasible trajectories to further satisfy dynamical constraints and optimality of path smoothness with respect to higher derivatives enabling high-speed and aggressive movements. Generating smooth trajectories is important for high-speed applications to avoid sudden changes in actuators’ accelerations and mechanical vibration problems . TherefoGenerally, many of these approaches represent the trajectories as piecewise polynomials where the polynomial coefficients are used as decision variables in the optimization problem. Some works use Bernstein and B-splines polynomial bases and utilize their properties when formulating the problem ,78,87. FA trajectory generation method for quadrotors was suggested in  to find Similarly, a real-time trajectory generation method was proposed in  for quadloped in  to proviloped in , showingloped in  where a The works ,73 adoptAnother optimization-based method was suggested in  as an exIn contrast to optimization-based trajectory generation where dynamic constraints are considered in the optimization problem, motion primitives were considered as a simpler computationally efficient way to generate collision-free trajectories in 3D in some works such as ,92,93,94Generally, considering dynamic constraints and constraints due to collisions with obstacles in the planning problem makes it harder to solve in real time, causing potential convergence problems. This is known as kinodynamic planning, which is a motion planning problem in a higher dimensional space with differential and obstacle constraints . Some apThe motion planning problem for multi-rotors among dynamic obstacles was tackled in  at the cFormulating the 3D trajectory planning as a Quadratic Program (QP) was also considered in ,78,82. IRecently, there has also been some growing interest in the field of perception-aware trajectory planning considering perception constraints in the planning problem. The developed methods in this area take into account perception quality to minimize state estimation uncertainty , which cMost of the existing reactive methods are developed at a higher level considering different abstractions of UAV 2D/3D kinematic models with velocities/accelerations as control inputs. Collision avoidance can be ensured rigorously for some of these methods under certain technical assumptions  in contrA number of geometric-based reactive collision avoidance methods focused on noncooperative scenarios  for fixed-wing UAVs or vehicles with nonholonomic constraints adopting the idea of collision cones such as ,119,120.A different implementation of collision cones was carried out in  for AUVsAnother 3D reactive approach was developed in ,123,124 A different class of 3D reactive methods modified the Velocity Obstacle (VO) approach to allow navigation in dynamic environments such as ,126. In Artificial potential field was also considered in some approaches to handle navigation in dynamic environments as in ,128,129.The authors of  suggesteIn , a compuA number of reactive methods considers vision-based structure such as ,134,135.Some other methods relied on 3D distance measurements  obtained from LiDAR sensors or depth cameras such as ,100. TheConcepts from machine learning were also considered recently in some reactive methods to address obstacle avoidance problems for UAVs. However, these methods are more computationally expensive than other reactive methods, and there are still concerns related to how guaranteed a collision avoidance is as the performance relies on how good the training/learning stage is. Additionally, many of the existing approaches consider only generating motion decisions/policies in 2D without utilizing the full maneuverability of UAVs. Most of these methods are based on deep reinforcement learning ,142,143 A summary of the surveyed local motion planning methods is presented in kinematics and dynamics. Kinematic equations are mainly derived to represent the geometrical aspects of the motion in 3D spaces through defining translation and rotation relationships between different coordinate frames. Dynamics can be obtained through the application of Newton laws for a moving rigid body to derive linear and angular momentum equations. Application of Newton laws requires an inertial reference frame For control design and simulation purposes, it is necessary to have a valid mathematical model that can express the UAV motion. Generally, such a model consists of two main parts which are mes, see .A rotation matrix between the inertial and body-fixed coordinate frames can be used to define the attitude/orientation of the UAV. It is also common to use other representations such as Euler angles  is a popular choice in many implementations to provide estimates for the UAV attitude, linear and angular velocities by fusing data from different sensors. Position can also be estimated by fusing information from a positioning source such as GNSS, visual odometry, external positioning system, etc.A cascaded approach is very common in different control structures where the attitude dynamics  and (8)) are decoupled to avoid considering the full nonlinear system dynamics in the control design . A high-Multi-rotors are the most popular UAV type for many civilian applications due to their simplicity in mechanical design and control. Therefore, there have been many recent developments in nonlinear control of multi-rotors enabling high-speed navigation ,77, aggrQuadrotor dynamics are differentially flat, which was shown in  . Development of SLAM methods is a very active field of research in robotics as the performance of map-based navigation methods relies on SLAM accuracy. This overview is not intended to provide a detailed survey of SLAM methods; however, the reader is referred to the following surveys for more details on recent developments in this area ,178,179.Existing SLAM methods can be classified as either LiDAR-based or vision-based. LiDAR-based methods adopt scan matching algorithms, and they offer better accuracy ex. see ,183,184),184183,1There have been many developments in the field of UAVs in terms of perception, control, SLAM and path planning over recent years. Implementing a complete autonomous navigation stack would require a large team with different skill sets in these areas or collaborations among research groups. Moreover, a lot of time needs to be invested in implementation and dealing with technical issues to ensure the reliability of the overall system. Open-source projects contributed by many researchers have made it possible for others in the community to focus on the development and improvement of a specific navigation component related to their research while easily integrating with other components made available by researchers, saving a lot of development time. The navigation problem for UAVs remains a very challenging one due to the wide range of tasks they are needed for. Navigating in unknown and highly dynamic environments is one of the most challenging problems, especially for micro-UAVs with limited payload capacity and onboard computation capabilities. Some of the existing 3D reactive navigation approaches were developed based on conservative assumptions about obstacles. Similarly, map-based local trajectory planning methods tend to simplify the problem by relaxing the collision avoidance constraints to make the optimization problem more tractable in real-time. Overall, more theoretically well-founded, and computationally efficient navigation solutions are needed to provide a high level of safety guarantees.Moreover, map-based navigation approaches are highly dependent on the performance of the localization system where a lot of ongoing research is focused on that area. Due to the limited payload capacity of small and micro-UAVs, vision sensors are the main source of information for localization and obstacle detection. However, this can be challenging in textureless environments. Furthermore, the small FOV provided by these sensors encourages more research in developing perception-aware navigation methods ex. see ,104,105),105104,1Developing fully autonomous UAVs targeting specific applications may involve additional layers of control; therefore, some of the applications where UAVs are used or can be potentially deployed are provided in the next section to bring to the reader’s attention the complexity and potential challenges in these areas. Moreover, using multiple UAVs in collaboration to carry out tasks can increase efficiency and reduce mission time. This makes the navigation and control problems of multi-vehicle UAVs an active field of research due to the higher complexity of these problems, which is highlighted in As UAVs continue to emerge in new applications, new challenges arise based on the complexity of required tasks. New developments in technologies related to UAVs can also open research directions to develop new advanced navigation algorithms that would not have been possible with existing older technologies. Over the past decade, UAVs have been utilized in many applications. However, many of these applications still do not adopt fully autonomous solutions due to the involved operational risks and immaturity of research related to some of these particular applications. Thus, this section explores different areas where UAVs are currently used or needed to attract more interest in using UAVs and to guide further developments for UAV technologies supporting these applications with increased autonomy levels.Precision Agriculture (PA) has attracted a lot of interest recently with a main goal of applying efficient solutions or resource management of soil and crops using different means of technology. UAVs offer great mobile solutions to increase productivity and to save resources in this area. Example applications related to PA include remote sensing [ sensing ,217,218, sensing ,220, pes sensing ,222, wee sensing ,224,225  sensing .Using UAVs for remote sensing applications in PA provides inspection data at higher temporal and spatial resolution than satellite imagery . UAVs caIn remote sensing applications, coverage path planning algorithms are normally applied generating optimal paths (ex. back-and-forth motion patterns) to survey areas of interest. For high-altitude flights, the coverage path planning problem can be simply solved using classical approaches assuming an obstacle-free flight space. In this case, simple path following control can be applied. This problem becomes more complex on the high level coverage planning when considering no-flight zones , multi-UAV cases and low-altitude flights. These cases also require proper local motion planning to handle dynamic obstacles, such as people and other noncooperative UAVs, and static obstacles such as trees, buildings, etc. Moreover, advanced control methods are needed to perform autonomous tasks such as harvesting, irrigating and weed control.Search and Rescue (SAR) operations have evolved over the years in considering robotic aid for improved results. This attracted attention to the field of Disaster Robotics. UAVs can add great value to SAR missions by carrying out different tasks including: localizing and tracking victims; survivors’ situation and environment assessments; delivering aid kits such as first aid and self-inflating emergency flotation devices; communicating messages from rescue teams to victims; providing wireless communication networks between SAR teams in remote inaccessible areas . ClearlyDeveloping fully autonomous SAR-enabled UAVs requires suitable navigation strategies depending on the environment (indoors or outdoors) and the required motion objectives. For example, some cases require UAVs to survey areas of concern where the application of coverage motion planning algorithms is needed similar to remote sensing applications. 3D exploration techniques can also be applied in indoors environments which is still an active research problem. Navigation in harsh indoor environments, such as tunnels and collapsed buildings, adds more challenges towards achieving fully autonomous operations. For example, there is a need for suitable control methods to handle flights in confined spaces, well developed SLAM methods to deal with poor conditions, and proper perception and obstacle avoidance capabilities. Solutions based on the use of cooperative UAVs in SAR missions are also attractive but require further development due to the higher complexity of these solutions.Examples of UAV-based solutions for SAR applications in different environments and scenarios such as: remote disaster areas and wilderness SAR ,231,232;Another area where UAVs can be very useful is livestock and wildlife monitoring. For example, UAVs can be used to count, classify, and track livestock animals ,243 to oThe low cost of UAVs makes them good tools to collect more information about hurricanes and tornadoes using dedicated sensors. Such collected data can help scientists to build better understanding of the trajectories of hurricanes and tornadoes. UAVs can also provide advanced warning and damage assessment for thunderstorms and tornadoes. There are few works in this area such as ,254,255.In the construction domain, deployment of UAVs in construction sites is good for aiding high-level management. Applications of UAVs in construction include : buildinNavigating in construction sites can be challenging due to being highly dynamic and crowded environments. Some tasks may also require UAVs to fly very close to buildings such as facade inspection and scanning buildings to build 3D models. This can be a potential application for reactive methods to maintain a certain distance from the building.UAVs have also started to attract interest in the oil and gas industry. For example, UAV-based magnetic surveys can be used to detect and identify abandoned wells . The useOther UAV applications include: solar panel inspection ,267; powThe use of multi-UAV systems has become more desirable in many applications for improved performance; thus, developing these systems is currently a very active field of research. Various challenges arise in this area to develop autonomous UAV swarms in tasks assignments, communication, trajectory planning and coordinated control. Different interactions between the vehicles are needed in order to collaboratively achieve a global objective assigned to the group.centralized, decentralized or distributed. Centralized approaches are implemented on a central computer where trajectories are computed for all agents/vehicles within the system. This requires measurements from all agents to be available to the central computer. Centralized algorithms can produce globally optimal solutions; however, the overall system is prone to failure if the central computer fails, or a communication problem occurs. On the other hand, decentralized and distributed algorithms offer more robustness and scalability with a more computationally efficient solution to systems with large number of vehicles. These approaches enable each vehicle to compute their own trajectories and control actions based on local interactions with neighboring UAVs either by relying directly on its sensors’ measurements  or by combining these with information communicated by neighbor vehicles (distributed). In other words, distributed methods distribute the computation and communication load among the vehicles [Algorithms developed for Multi-UAV systems can be either vehicles  to collaleader-follower, virtual and behavioral-based structures [leader-follower structures such as [virtual structure achieves motion formation through forcing each vehicle to follow a corresponding virtual target (or reference trajectory) such that the selection of these virtual references contributes towards the global objective; for example, see [Behavioral-based structure comprises of a set of rules followed by the vehicles contributing towards the collective behavior; flocking control, based on artificial potential fields, belongs to this category where a group of interacting agents move together to achieve some global objectives. One of the early models capturing the local interactions between agents under a flocking behavior is Reynolds’ model for the aggregate motion of flocks, which is based on three main rules: flock centering (cohesion), collision avoidance (separation) and velocity matching  [Formation control is one of the challenging areas for multi-UAV systems where each vehicle has a specific role with some constraints on its states  to achieructures . A physi such as ,294,295.ple, see ,300,301.ignment) ,303. Sevignment) ,310,311.ignment) ,312,313,ignment) ,311,314,ignment) ,308,315 ignment) .Many works have tackled the 3D motion coordination and collision avoidance problem for UAV swarms through a hierarchical approach with trajectory planning formulated as an optimization problem, similar to what was discussed earlier for single-UAV systems. Different centralized, decentralized and distributed approaches can be seen in the literature considering homogeneous and heterogeneous multi-UAV systems in addition to considering multi-vehicle systems working with aerial and ground vehicles; for example, see ,326,327.An example task that can be carried out by UAV swarms is carrying and transporting objects individually ,329,330 It is also very important to keep in mind communication challenges when designing control methods for large-scale networked multi-vehicle systems. Application of Networked Control Systems (NCSs) theory is thus suitable when analyzing the operation of networks of collaborating autonomous UAVs ,351,352.Rapid advances in UAV-related technologies allowed great development towards achieving fully autonomous operations in the areas of control, motion planning, perception and localization and mapping. This paper presented a survey about some recent advancements in these areas focusing more on allowing advanced autonomous 3D collision-free navigation for UAVs. The main differences between the adopted motion planning algorithms and control strategies were also highlighted, showing the advantages and disadvantages between different methods. This can provide guidance for researchers to determine suitable navigation methods based on their specific applications. Moreover, a list of some existing open-source projects was provided to aid researchers in quickly developing and deploying innovative technologies for UAVs. Developing fully autonomous UAVs remains very challenging due to the wide range of new applications and the various levels of the tasks’ complexity. Hence, active research challenges were also highlighted in this paper, including recent developments in motion control for multi-UAV systems. Additionally, several applications were mentioned to encourage the development of more mature fully autonomous solutions dedicated to emerging UAV applications.


Porous biodegradable scaffolds provide a physical substrate for cells allowing them to attach, proliferate and guide the formation of new tissues. A variety of techniques have been developed to fabricate tissue engineering (TE) scaffolds, among them the most relevant is the thermally-induced phase separation (TIPS). This technique has been widely used in recent years to fabricate three-dimensional (3D) TE scaffolds. Low production cost, simple experimental procedure and easy processability together with the capability to produce highly porous scaffolds with controllable architecture justify the popularity of TIPS. This paper provides a general overview of the TIPS methodology applied for the preparation of 3D porous TE scaffolds. The recent advances in the fabrication of porous scaffolds through this technique, in terms of technology and material selection, have been reviewed. In addition, how properties can be effectively modified to serve as ideal substrates for specific target cells has been specifically addressed. Additionally, examples are offered with respect to changes of TIPS procedure parameters, the combination of TIPS with other techniques and innovations in polymer or filler selection. Tissue engineering (TE) is a very tested field of biotechnology that has been developed for over two decades ,2. TE ai3D biodegradable polymer scaffolds with a porous structure usually act as temporary template for seeding, adhesion, growth and proliferation of living cells to guide regeneration and formation of new tissues, while the biodegradable polymer matrix is subjected to biodegradation ,6. MoreoAnother important application of biodegradable polymeric scaffold is their use as support materials for different drug loadings. Scaffolds can be designed to allow drug release in a sustained and controlled manner over a desired period of time ,10.co-glycolide) (PLGA) , na, na64], ctively)  and the ctively) . In thisctively) . Specifictively) ,84,85. Fctively) .When a polymer-solvent system experiences a solid-liquid phase separation, the final structure and pore architecture of the resulting foam widely depends on the used solvent and its crystallization temperature, the phase separation temperature, the polymer concentration and the temperature gradient which has applied to the system . TypicalBy controlling the cooling process, matrices produced by solid-liquid phase separation may have isotropic or anisotropic architectures. Matrices with a randomly-oriented (isotropic) pore structure are formed by transferring quickly the homogeneous solution to a cooling device that allows solvent crystallization and solid-liquid phase separation. Indeed, when the crystallization direction is controlled and a uniaxial temperature gradient is applied to the system  an oriented-pore structure (anisotropic) is achieved.1/2), is added to the system, the interactions between the polymer and solvent are lowered. As a result, a liquid–liquid demixing occurred at the temperatures higher than the solvent crystallization temperature.Liquid–liquid phase separation in a polymer solution may occur during the cooling process, when the polymer-solvent affinity is very weak. Schugens et al.  and Nam mixG is the Gibbs free energy of mixing per lattice site, dϕ  and pϕ  are the volume fraction of solvent and polymer, dx and px are the number of lattice sites being respectively occupied by the molecules of solvent and polymer, and χ is the Flory–Huggins interaction parameter which is affected by the strength of interactions between polymer and solvent.The Flory–Huggins equation for the polymer-solvent system is shown in Equation (1) :(1)ΔGmixχ). Weak interactions between polymer and solvent lead to a large and positive value of χ, resulting in a positive ∆mixG that led to a liquid–liquid demixing. By contrast, when the strength of interactions between polymer and solvent is high , occurrence of liquid–liquid phase separation is more difficult . In this situation, the homogenous one-phase region in the phase diagram , the phase separation can take place with different behaviours ,87. The The second scenario which is called spinodal decomposition (SD), can take place when the spinodal curve is crossed for a given polymer concentration under cooling. The region below the spinodal curve is called unstable, where there is no activation barrier against phase separation. Any fluctuations in composition cause free energy to decrease and a wave of fluctuations throughout the solution is triggered. In this region, the system separates into two phases through a well-known SD mechanism, resulting in formation of a bicontinuous and interconnected structure of polymer-rich and polymer-lean phases ,87,91. A2 drying technology is an effective alternative for the reduction of the duration and environmental cost of the whole process that is being successfully developed by scientists ..20].With the rapid progress in the field of tissue engineering, a great variety of scaffolding materials have been developed, being effectively used as biomedical materials in the treatment of tissue defects and the alleviation of the suffering of patients ,181. VarChen et al. synthesized PLLGC terpolyester by melt copolymerization process and then utilized it for preparation of porous scaffolds by TIPS technique. By varying some TIPS processing parameters like polymer concentration (from 2.5 to 15 wt%) and freezing temperature (from 4 to −60 °C) structural and mechanical properties could be controlled. Results showed larger pores and higher porosity, but a lower compressive strength when the polymer concentration was decreased, or the freezing temperature was increased. Furthermore, regular and interconnected pore structures with uniform pore size was achieved, although at high polymer concentration some pores were linear with uneven distribution and inconsistent pore sizes. The decrease in the freezing temperature caused a structural change from an irregular pore distribution to an orientated micro-tubular structure. Changes could be justified considering the crystallization of the employed 1,4-dioxane solvent throughout the phase separation process and the influence of the temperature gradient, which is more significant at lower freezing temperatures .Materials currently employed in tissue engineering are mainly derived from natural polymers and synthetic materials. Natural-based polymers such as alginate (Alg), GEL, gelatin methacryloyl (GelMA), hyaluronic acid (HAc), CS, Col, fibrin, and decellularized ECM, play an important role in the field of biofabrication. Natural polymers generally enjoy considerable advantages in terms of biocompatibility, biodegradability and supporting bioactivity . AdditioCol as a kind of ECM proteins plays an important role in supporting cell attachment, migration and proliferation, due to its excellent biocompatibility, biodegradability and low immunogenicity . Due to Si et al.  fabricatThe prepared scaffolds logically showed good cytocompatibility to L929 fibroblasts, lack of toxicity and great capability to promote the attachment, migration and proliferation of Schwann cells. A modulated degradation behaviour without any inflammatory reaction was found when the Col/CS scaffolds were subcutaneously implanted in rabbits, indicating the potential application of these TIPS-obtained and natural-based scaffolds in tissue engineering .Although biomaterials from both synthetic or natural resources are potential candidates for tissue engineering applications, the synthetic ones can be better modified in terms of geometric structure, biocompatibility, porosity and mechanical properties . HoweverTIPS appears an advantageous technique since it is highly flexible to blend the polymer-solvent system with other polymers, solvents or inorganic fillers for specific purposes. Salehi et al. employed solid-liquid phase separation to produce porous scaffolds from PLLA and CS. Such blending was aimed to mimic cellular microenvironment and anatomical structure of nerve tissue. The scaffold behaviour and properties were compared with those made from pure PLLA or CS. CS/acetic acid:water (50:50) solution was specifically added to a PLLA/chloroform one, and then solid-liquid phase separation was induced by quenching the mixture to −80 °C . After freeze-drying the resulting scaffolds were soaked in glutaraldehyde to cross-link the CS. The blend scaffolds were highly porous with interconnected porosities and showed proper mechanical properties. In addition, they were more porous and hydrophilic, and had higher degradation rate and lower amounts of free radicals compared to neat PLLA. Furthermore, the blended scaffold could better support human nerve cells than pure PLLA and CS scaffolds, indicating than an effective strategy to prepare promising scaffolds for nerve tissue engineering applications was developed [Bone is a hard tissue that acts a supporting framework or skeleton of the body and protects organs . Bone tiCollagen type 1 (Col1) and HA are the major constituents of human natural bone tissue and consequently have widely been studied as promising materials for scaffold preparation. Thus, Wang et al. reported the usefulness of porous Col1/nHA scaffolds for restoration of critical-size bone defects . BioactiReves et al. recommended pore sizes of 100–800 µm for microparticle-based scaffolds , being tOsteochondral tissue is comprised of an articular cartilage region and a subchondral bone region, while a calcified cartilage connects these two microenvironments . MultiphD,L-lactide) P(DLLA), PCL or their copolymers [Binary hybrid materials made of biodegradable and bioresorbable polymers such as PGA, PLLA , poly  due to agglomeration effects and the corresponding reduction of the interfacial contact with the polymer matrix [Díaz et al.  producedr matrix .Particle dispersion in the polymeric matrix is a parameter with crucial importance and that must be controlled to obtain homogeneous nanocomposite materials. Achievement of a good dispersion is still one of the main problems when preparing composites through mechanical stirring or ultrasound mixing methods. “In situ synthesis” of nanoparticles within the polymer matrix is an efficient alternative to the conventional mechanical methods of particle dispersion, enabling to overcome the strong agglomeration trend of nanoparticles which leads to form micrometric aggregates. In this method, fillers are directly synthesized in the hosting polymeric matrix, hence, particle aggregation is prevented and dispersion is improved . InteresIn a recent study, Esposti et al.  producedAlthough both scaffold groups inhibited pre-osteoblast cell adhesion and proliferation, and could promote osteogenesis, the scaffolds loaded with in situ-synthesized HA produced the highest amount of alkaline phosphatase and the typical morphology of the terminal differentiation stages of osteoblasts. These findings justify extending this new TIPS-based fabrication process to other polymeric matrices or inorganic nanoparticles, as a simple and scalable tool for the preparation of high surface area polymer-based composites with tailored properties .Pure PLA still has some deficiencies to be used as a biomaterial in bone tissue engineering. Bone tissue engineering puts a great demand on mechanical properties. However, among all PLA deficiencies for its right application in bone tissue engineering, it should be emphasized its moderate strength makes it an unsuitable choice for bone fixation at the site of loadbearing , and alsPolyester-based scaffolds reinforced with multiwalled carbon nanotubes (MWCNTs) have recently been produced by TIPS ,243,244.Díaz et al.  incorporThey reported that the addition of small quantities of carbon nanotubes (0.1–0.5 wt%) to PLGA scaffold could modify in vitro degradation, magnetic properties and cytotoxicity of the scaffolds . The effGandolfi et al.  tried toPCL scaffolds containing different ratios of micro-fluorcanasite (μFC) glass-ceramic particulates, as potential bioactive reinforcements, have recently been prepared by TIPS. Chloroform was selected as polymer solvent, ultrasonication was applied to disperse glass-ceramic particulates in the polymer solution, and liquid nitrogen to freeze the samples and induce phase separation. All the produced matrices revealed porous cellular microarchitectures. The interconnected microporous structure was enhanced with high amounts  of μFC glass-ceramic particulates, a feature that attributed to a possible nucleating effect of particulates. A tunable biodegradation was also found since the increase of glass-ceramic content resulted in a delayed biodegradation of PCL matrices . Owing to favourable microporous architecture and tunable degradation, PCL/μFC biocomposite scaffolds appear as potential matrices for bone tissue engineering .2 has been identified as an effective biological material because the presence of surface OH groups induces formation of HA from simulated body fluid (SBF) [2 nanoparticles [2 nanoparticles with oleic acid (OA) and prepared PLLA nanocomposite scaffolds by means of the TIPS technique. Microporous structures were obtained after homogenizing the nanocomposite PLLA/TiO2/dioxane suspensions by ultrasonication and applying the typical TIPS process. In terms of morphology, a highly porous and anisotropic architecture with characteristic interconnected and elongated pores  was produced. The pore architecture was not influenced by the incorporation of nanoparticles, but nice and evenly distributed nanoparticles were observed as small white dots. The effect of incorporating functionalized nanoparticles on biodegradability, bioactivity and cytocompatibility was also evaluated. Interestingly, scaffolds were bioactive in supersaturated fluids, but became less degradable in simulated body fluid (SBF) than pure PLLA scaffolds. Adding 5 wt% (with respect to the polymer content) of OA-functionalized TiO2 nanoparticles enhanced cell viability and proliferation, but the increase to 10 wt% led to worse cell proliferation and higher cytotoxicity [Developing innovative ceramic fillers in bioengineering, TiOid (SBF) . Howeverarticles . Functioarticles . Buzarovtoxicity .Highly porous interconnective network with isotropic or randomly-oriented pore structure can be obtained under different thermodynamic and kinetic conditions of phase separation  as detailed in the ECM is the ideal 3D template for cell adhesion, proliferation and differentiation and is the reservoir for many growth factors ,254. MosSeveral techniques have recently been investigated so far to prepare 3D nanofibrous scaffolds, including electrospinning ,257,258,graft-poly(L-lactide) (PHAA-g-PLLA) through TIPS [d,l-lactide)-b-poly(γ-benzyl-l-glutamate) (PDLLA-b-PBLG), which underwent nanofibrous self-assembly by α-helix formation of the PBLG segment during controlled TIPS process  (PEI). The ammonolytic agent,  was dropwise added into PLLA/dioxane solutions to perform a typical TIPS process. The aminolysis reaction led to covalent bonds between amino groups of PEI and the ester groups of PLLA. Experimental conditions  affected the formation tendency, morphology of nanofibres and scaffold properties. Optimized conditions rendered a homogenous nanofibrous structure with high hydrophilicity, appropriate mechanical properties, high capacity to favour osteoblast proliferation and a great bone-bioactivity  .Physiological and mechanical properties of many tissues, such as tendon, nerve, blood vessel, bone, ligament, spinal cord and cartilage, are closely associated with their oriented structure . Accordiw/v% concentrations were dissolved in DMSO while a thermal-resistance wrap was employed to control crystallization in a uniaxial direction during the TIPS process . Mechanical properties of the anisotropic scaffolds were also optimized by altering polyurethane types and concentrations to match properties of the native human myocardium. The prepared biohybrid scaffolds were subsequently combined with decellularized and digested porcine myocardium-derived extracellular ECM to improve biocompatibility without affecting mechanical properties. The biohybrid scaffolds had morphologies similar to the acellular porcine myocardial matrix with good tissue compatibility and a minimal immune system response when they were subcutaneously implanted in rats [To simulate the anisotropic architecture of native heart muscle, Xu et al. , by empl process . After s process . The ave in rats .Scaffolds with an oriented porous architecture can significantly promote cell infiltration and bioactive interflow between neo-host tissues ,72. DiffRecently, Dai et al.  have fabThis construct enabled deep migration of bone marrow stem cells and could induce regular cell and ECMs alignment. It was also reported a simultaneous formation of cartilage and subchondral bone layers integrated with each other, while the smooth neo-tissues were well-integrated with the surrounding host tissues. Regeneration results were demonstrated to be much better than those found using PLGA scaffolds with random pores after the same implantation period, indicating the oriented-pore PLGA scaffold is a promising material for osteochondral regeneration . Using nECM-mimetic scaffolds based on silk fibroin (SF) and Col with different pore structures, including random pores, radially-aligned and axially-aligned pores were recently prepared by Feng et al.  using teAlthough a satisfactory regeneration of osteochondral tissue with hyaline cartilage formation was observed in both aligned scaffold groups, the regeneration was faster in the radially-aligned scaffold group. Formation of hybrid cartilage  was reported for the randomly oriented porous structure. Finally, the aligned SF/Col scaffolds, especially the radially-aligned ones, provided a promising alternative for regeneration of osteochondral defects, with a considerable potential to be translated into medical devices .When, due to thermodynamic conditions, a semicrystalline polymer-solvent system involves driving forces for liquid-liquid phase separation and crystallization of the polymer, the major factor determining which mechanism occurs is the strength of polymer-solvent interactions. In case of strong interactions , the solution undergoes solid-liquid phase separation via crystallization of polymer during cooling. When the interactions are weak (great differences between interaction parameter), the polymer concentration determines the mechanism. Lloyd et al. reported that at high polymer concentration  tallowamine system) solid-liquid phase separation occurs  and controls the morphology of the foam. At lower polymer concentrations  liquid-liquid phase separation occurs and subsequently polymer crystalizes and stabilizes the phase separated structure. In the latter case, liquid-liquid phase separation controls the morphology .Although a concentrated polymer solution has been used to fabricate various foams and monoliths for applications like membrane formation, generally low-concentrated solutions are used for preparing TE scaffolds (to achieve high porosity). Accordingly, individual utilization of solid-liquid phase separation  as the main mechanism for fabrication of TE scaffolds does not occur very often. Nevertheless, crystallization of the polymer is occasionally observed when solid-liquid  and liquid-liquid phase separations have been employed for fabrication of TE scaffolds. In such conditions crystallization of the polymer stabilizes the phase-separated structure and sometimes its corresponding morphological trace is observed throughout the microstructure of phase-separated regions .Kinetic is another factor that may limit crystallization of the polymer during the TIPS process, even if it is thermodynamically favoured. The kinetic of phase separation process determines whether or not, and also to what extent the thermodynamically favoured mechanism occurs . Since TOnder et al. , by prov2 drying. Crystallinity, porosity, pore size and structure could be controlled by altering two TIPS processing parameter  and solvent system quality   after inducing phase separation/gelation by quenching. Resultant gels were stabilized by exchanging the solvent system with ethanol and porous scaffolds were obtained after quenching and supercritical COo 82/18) . The difPLA monoliths are suitable to be used in several fields, such as tissue engineering, drug delivery and filtration technology. These monoliths have been produced using TIPS methods based on binary solvent systems of THF-water  and 1,4-Porous biodegradable scaffolds play a critical role in tissue engineering. Scaffolds, by mimicking the native ECM, provide physical bio-templates for cells, allowing them to attach, proliferate and guide the formation of new tissues. TIPS is one of the scaffold fabrication methodologies with a great potential for production of highly porous scaffolds with a wide range of pore size/architecture and a proper structural interconnectivity. These characteristics, together with a simple, low-cost and tunable fabrication process, which allows the scientist to incorporate various fillers and/or bioactive agents, have made it a popular method for fabricating polymeric and composite scaffolds. The process enables the generation of a variety of structures with different properties being desirable for regeneration of tissues using specific target cells. Although TIPS is a conventional method for preparing tissue engineering scaffolds, researchers have successfully innovated new approaches in terms of biomaterial selection and variations on the processing parameters, being enhanced its capability and versatility. Herein we reviewed the latest innovations and the recent advancements in scaffolds fabricated by the TIPS technique from the viewpoint of methodology, materials selection and structural features. Owing to the outstanding potentials and promising achievements of this method in producing tissue engineering scaffolds, conducting more investigations and up-to-date surveys in this field seems inevitable.


Decades of study on cell cycle regulation have provided great insight into human cellular life span barriers, as well as their dysregulation during tumorigenesis. Telomeres, the extremities of linear chromosomes, perform an essential role in implementing these proliferative boundaries and preventing the propagation of potentially cancerous cells. The tumor-suppressive function of telomeres relies on their ability to initiate DNA damage signaling pathways and downstream cellular events, ranging from cell cycle perturbation to inflammation and cell death. While the tumor-suppressor role of telomeres is undoubtable, recent advances have pointed to telomeres as a major source of many of the genomic aberrations found in both early- and late-stage cancers, including the most recently discovered mutational phenomenon of chromothripsis. Telomere shortening appears as a double-edged sword that can function in opposing directions in carcinogenesis. This review focuses on the current knowledge of the dual role of telomeres in cancer and suggests a new perspective to reconcile the paradox of telomeres and their implications in cancer etiology. The emergence of eukaryotic cells was accompanied by a transition from a circular genome to multiple linear chromosomes, enabling the propagation of multicellular organisms. Nascent linear chromosomes, however, have created many additional challenges. For instance, their DNA ends are recognized as DNA breaks and need constant shielding from DNA damage surveillance mechanisms. This task has been accomplished by the refinement of chromosome architectures and the evolution of telomeres, conserved guanine-rich terminal structures bound by specialized proteins, acting to evade and suppress most DNA damage signaling and repair pathways.In humans, telomeres comprise 4–12 kb of double-stranded TTAGGG repeats, ending in 50–400 nucleotides of single-stranded G-rich overhang . Both siElectron microscopy has revealed telomeres in the form of a closed T-loop (telomere loop) configuration, stemming from the invasion of the 3′ TTAGGG overhang into the duplex region of the same telomere  Figure . Since iShelterin prevents chromosome termini from activating a network of signaling cascades known as the DNA damage response (DDR) . This fuOver 40 years ago, the Soviet scientist Alexei Olovnikov and American scientist James Watson recognized a fundamental problem linked to the replication of linear DNA molecules . Both scIn contrast to cancer cell lines, human somatic cells derived from healthy tissues lack TMMs (telomere maintenance mechanisms) and their telomeres shorten at a rate of 50–150 bp with each round of DNA replication . Accordia) an intermediate state that is partly protective, as telomeres enable DDR signaling but can sufficiently bind shelterin to suppress fusions, and (b) an uncapped state, where telomeres are both DDR positive and fusogenic, potentially resulting from a level of shelterin binding that is insufficient to suppress DNA repair machineries ] and crisis [mortality stage 2 (M2)]  Figure . SenesceSenescence and crisis are two independent cellular programs, induced by qualitatively distinct telomere states, defined by contrasting features and, most importantly, associated with different biological outcomes . The curSenescence has long been seen as a powerful tumor-suppressive mechanism that prevents cells with extensive DNA damage or a very active stress signaling response from becoming immortal. Many triggers can induce senescence, such as oncogene activation, DSBs, oxidative stress, nutrient depletion, epigenetic changes, and, of course, telomere dysfunction. Here, we focus on replicative senescence, which is triggered by replication-associated telomere shortening.Replicative senescence is induced by intermediate-state telomeres capable of initiating DDR signaling pathways with no concomitant fusions. It was initially reported that senescence coincides with the disappearance of the G-rich 3′-ended telomeric overhang and that it is the global loss of this overhang that initiates senescence . ParalleWaf1/Cip1 and p16Ink4a/Rb pathways  . The SASSenescence is not accompanied by gross chromosomal abnormalities . CytogenCrisis is a fascinating mechanism that serves to clear cells from the population that have bypassed or escaped replicative senescence. Since such cells have lost p53- and Rb-dependent tumor suppressors, crisis had to evolve p53-/Rb-independent pathways to trigger cell death. Here, we focus on recent developments that address mechanisms of cell death in replicative crisis.Following the inactivation of cell cycle checkpoints, senescence-bypassed cells reach a second proliferative barrier known as crisis, during which critically short telomeres can no longer bind shelterin proteins and become vulnerable to fusions with other telomeres or nontelomeric DSBs. The pattern of accumulation of fused chromosomes suggests that crisis involves both qualitative changes from the senescence state (intermediate state in senescence versus uncapped state in crisis) and quantitative changes (few linear telomeres in senescence versus many in crisis). Fusion of telomeres in crisis is often associated with deletions and microhomology at the fusion site, which are characteristic of alt-EJ rather than c-NHEJ, which is independent of resection . HoweverIn contrast to senescence, cells undergoing replicative crisis are not permanently arrested in interphase. Instead they suffer from delayed mitotic progressions that can last up to several hours . This soATG3, 5, and 7) resisted cell death, continued to proliferate, and bypassed the crisis plateau  . Cells t plateau . Crisis  plateau . CollectThe role for autophagy in suppressing tumor initiation is further supported by mouse genetic studies showing a considerable increase of tumor frequency when autophagy is impaired . It is wThe ability of critically short telomeres to induce autophagy-dependent cell death during crisis relies on the release of nuclear DNA into the cytosol and activation of the cGAS-STING DNA-sensing pathway . Crisis a) nuclear herniation of large amounts of chromatin from the nucleus, and/or (b) entry of harmful cytoplasmic components (endo- or exonucleases) into the nuclear space and formation of acentric fragments. Further studies are needed to uncover the underlying mechanisms.There are still many unanswered questions about how critically short telomeres drive the formation of cytosolic DNA species. MN are frequent in cells experiencing telomere fusions, yet the underlying mechanisms are not defined. Previous observations have indicated that dicentric chromosomes, products of telomere fusions, contribute to the nuclear envelope breakdown via a process called NERDI (nuclear envelope rupture during interphase) . Such evUpon loss of the cGAS-STING pathway, cells evade autophagy-dependent cell death and continue to divide past the crisis barrier . Such ceTelomere fusions are a major source of genomic alterations found among different tumors. These include amplifications, loss of heterozygosity, and translocations through BFB cycles . The repA recent study has provided a mechanistic explanation for how short telomeres during crisis could lead to chromothripsis . The autReplicative crisis has a profound antitumor effect. It functions by eliminating the majority of the cells that have lost tumor-suppressor pathways and bypassed senescence. While the tumor-suppressive aspect is undoubtable, several lines of evidence have pointed to telomere crisis as the origin of cellular transformation and malignancy. For instance, telomeres in cancer are usually shorter than those in corresponding normal tissues . Further5–107 cells are reported to escape from crisis and evolve progressively to a neoplastic state, potentially bypassing through the M3 plateau. Postcrisis or post-M3 cells exhibit many properties similar to those of the cells composing malignant tumors, including sustained proliferative signaling, replicative immortality, and genomic catastrophe -based assay has been developed to detect telomere fusion events, a hallmark feature of crisis cells. Using this approach, researchers have observed evidence for crisis in CLL, colorectal adenomas, and other tumors .TERC as a template to catalytically add telomeric repeats to the 3′ end of telomeres during S phase , which can be found in up to 90% of glioblastomas , death domain-associated protein (DAXX), and the histone variant H3.3 are frequently associated with ALT . Indeed,tivation . It willATRX triggers decompaction and alterations of telomeric chromatin (ATRX due to the transient loss of macroH2A1.2 upon replication stress (Taken together, the current ALT model suggests that ALT induction is driven by altered telomeric chromatin , which, hromatin , as wellhromatin  and telohromatin . This isn stress .A considerable fraction of cancers show no apparent TMM . There aThe transition from normal to cancerous cells involves multiple genetic and epigenetic events, including the activation proto-oncogenes and the inactivation of tumor suppressors. These changes must occur successively through a multistep mode. Additionally, cells have to acquire alterations that enable them to overcome proliferation barriers and activate a TMM. The molecular events regulating the escape from crisis are ill defined. In the current model, spontaneous TMM activation enables some cells to exit crisis and generate immortal cell lines. This model, however, is too simplistic and does not take into account recent data on autophagy-dependent cell death during crisis . Therefo


Sickle cell anemia (SCA) is a genetic blood disorder that puts children at a risk of serious medical complications, early morbidity and mortality, and high health care utilization. Until recently, hydroxyurea was the only disease-modifying treatment for this life-threatening disease and has remained the only option for children younger than 5 years. Evidence-based guidelines recommend using a shared decision-making (SDM) approach for offering hydroxyurea to children with SCA  aged as early as 9 months. However, the uptake remains suboptimal, likely because caregivers lack information about hydroxyurea and have concerns about its safety and potential long-term side effects. Moreover, clinicians do not routinely receive training or tools, especially those that provide medical evidence and consider caregivers’ preferences and values, to facilitate a shared discussion with caregivers.The aim of this study is to understand how best to help parents of young children with sickle cell disease and their clinicians have a shared discussion about hydroxyurea .We designed our study to compare the effectiveness of two methods for disseminating hydroxyurea guidelines to facilitate SDM: a clinician pocket guide  and a clinician hydroxyurea SDM toolkit (H-SDM toolkit). Our primary outcomes are caregiver reports of decisional uncertainty and knowledge of hydroxyurea. The study also assesses the number of children (aged 0-5 years) who were offered and prescribed hydroxyurea and the resultant health outcomes.The Ethics Committee of the Cincinnati Children’s Hospital Medical Center approved this study in November 2017. As of February 2021, we have enrolled 120 caregiver participants.The long-term objective of this study is to improve the quality of care for children with SCA. Using multicomponent dissemination methods developed in partnership with key stakeholders and designed to address barriers to high-quality care, caregivers of patients with SCA can make informed and shared decisions about their health.ClinicalTrials.gov NCT03442114; https://clinicaltrials.gov/ct2/show/NCT03442114DERR1-10.2196/27650 Sickle cell anemia (SCA) is a genetic blood disorder that affects approximately 100,000 individuals in the United States . SCA is only targeted clinician motivation. Pocket guides do not provide training to build clinician self-efficacy in prescribing medications, feedback to reinforce behavior change, or decision support tools to help clinicians engage and support caregivers in SDM.NHLBI guidelines encourage using shared decision making (SDM) when providers offer hydroxyurea, which involves a collaborative process wherein clinicians, patients, and families work together to reach a mutual agreement about the course of treatment ,10. HoweWe developed the hydroxyurea SDM toolkit (H-SDM toolkit), which is a caregiver-centered, technology-enhanced decision support tool. We designed the H-SDM toolkit to strengthen SDM, reduce caregiver uncertainty, allay potential fears, increase the offering of hydroxyurea, and ultimately improve hydroxyurea uptake ,11. In tReach: does the intervention reach the intended population?; (2) Efficacy or effectiveness: does the intervention impact the essential outcomes?; (3) Adoption: is the intervention supported by staff, settings, or institutions?; (4) Implementation: is the intervention delivered consistently?; and (5) Maintenance: what is in place to ensure that the intervention continues over time? ) concerning the continuation, modification, or termination of the study. Given the study is low risk, there are 2 conference calls scheduled each year.Although no adverse events are anticipated, we will ensure that each site has procedures to refer any parents who become upset to appropriate resources for follow-up. The principal investigator (PI), a clinical psychologist with experience in managing parental distress, will provide study staff and clinician training. The PI and site PI will be notified if any individual needs psychological follow-up due to study participation. The IRB at CCHMC will be notified as soon as the immediate needs of the participant are addressed. For any severe adverse events , the study staff will inform the PI within 1 working day. All serious adverse events will be reported to the IRB within 48 hours of the event.The ENGAGE HU trial was funded in August 2017, and the Ethics Committee of CCHMC approved the study  in November 2017. Patient recruitment started in July 2018 and will end in November 2021. The study will be completed in February 2022. As of February 2021, we have enrolled 120 caregiver participants. We expect to disseminate the findings of the trial through peer-reviewed journals in the summer of 2022.The ENGAGE HU trial compares the existing ASH clinician pocket guide with the H-SDM toolkit, which is a caregiver-centered, technology-enhanced decision support toolkit to help clinicians implement SDM for hydroxyurea . We desiSeveral aspects of this trial will enable the rapid adoption of findings into practice. First, we developed the H-SDM toolkit with substantial clinician and caregiver input; thus, it contains components these stakeholders felt were feasible, acceptable, and essential for improving clinical care. Second, we designed the H-SDM toolkit with core and optional components so that it can be tailored to the needs of individual families and be broadly applicable across many clinical settings. Third, virtual reality simulation provides guided practice in facilitating an SDM process. It is also a low-cost clinician training intervention that will be made accessible on national SCA-focused websites shared across SCA networks. Virtual reality training can occur in person or using web-based video conferencing tools  , which iThere are some limitations to this study that should be acknowledged. A critical consideration for the ENGAGE HU trial is that SCA primarily affects individuals of African and Hispanic or Latino descent. Although the ENGAGE HU trial design includes best-practice strategies for recruiting people of color in research, we may experience recruitment difficulties because potential participants are mistrustful or have child care and transportation issues . Further