Cell encapsulation in biodegradable hydrogels for tissue engineering applications

Calcium Phosphates: A Key to Next-Generation In Vitro Bone Modeling

The replication of bone physiology under laboratory conditions is a prime target behind the development of in vitro bone models. The model should be robust enough to elicit an unbiased response when stimulated experimentally, giving reproducible outcomes. In vitro bone tissue generation majorly requires the availability of cellular components, the presence of factors promoting cellular proliferation and differentiation, efficient nutrient supply, and a supporting matrix for the cells to anchor - gaining predefined topology. Calcium phosphates (CaP) are difficult to ignore while considering the above requirements of a bone model. Therefore, the current review focuses on the role of CaP in developing an in vitro bone model addressing the prerequisites of bone tissue generation. Special emphasis is given to the physico-chemical properties of CaP that promote osteogenesis, angiogenesis and provide sufficient mechanical strength for load-bearing applications. Finally, the future course of action is discussed to ensure efficient utilization of CaP in the in vitro bone model development field.

Transforming Cell-Drug Interaction through Granular Hydrogel-Mediated Delivery of Polyplex Nanoparticles for Enhanced Safety and Extended Efficacy in Gene Therapy

The utilization of hydrogels for DNA/cationic polymer polyplex nanoparticle (polyplex) delivery has significantly advanced gene therapy in tissue regeneration and cancer treatment. However, persistent challenges related to the efficacy and safety of encapsulated polyplexes, stemming from issues such as aggregation, degradation, or difficulties in controlled release during or postintegration with hydrogel scaffolds, necessitate further exploration. Here, we introduce an injectable gene therapy gel achieved by incorporating concentrated polyplexes onto densely packed hydrogel microparticles (HMPs). Polyplexes, when uniformly adhered to the gene therapy gel through reversible electrostatic interactions, can detach from the HMP surface in a controlled manner, contrasting with free polyplexes, and thereby reducing dose-dependent toxicity during transfection. Additionally, the integration of RGD cell adhesion peptides enhances the scaffolding characteristics of the gel, facilitating cell adhesion, migration, and further minimizing toxicity during gene drug administration. Notably, despite the overall transfection efficiency showing average performance, utilizing confocal microscopy to meticulously observe and analyze the cellular states infiltrating into various depths of the gene therapy gel resulted in the groundbreaking discovery of significantly enhanced local transfection efficiency, with primary cell transfection approaching 80%. This phenomenon could be potentially attributed to the granular hydrogel-mediated delivery of polyplex nanoparticles, which revolutionizes the spatial and temporal distribution and thus the "encounter" mode between polyplexes and cells. Moreover, the gene therapy gel's intrinsic injectability and self-healing properties offer ease of administration, making it a highly promising candidate as a novel gene transfection gel dressing with significant potential across various fields, including regenerative medicine and innovative living materials.

Exosome-loaded hydrogels for craniofacial bone tissue regeneration

It is common for maladies and trauma to cause significant bone deterioration in the craniofacial bone, which can cause patients to experience complications with their appearance and their ability to function. Regarding grafting procedures' complications and disadvantages, the newly emerging field of tissue regeneration has shown promise. Tissue -engineered technologies and their applications in the craniofacial region are increasingly gaining prominence with limited postoperative risk and cost. MSCs-derived exosomes are widely applied in bone tissue engineering to provide cell-free therapies since they not only do not cause immunological rejection in the same way that cells do, but they can also perform a cell-like role. Additionally, the hydrogel system is a family of multipurpose platforms made of cross-linked polymers with considerable water content, outstanding biocompatibility, and tunable physiochemical properties for the efficient delivery of commodities. Therefore, the promising exosome-loaded hydrogels can be designed for craniofacial bone regeneration. This review lists the packaging techniques for exosomes and hydrogel and discusses the development of a biocompatible hydrogel system and its potential for exosome continuous delivery for craniofacial bone healing.

Impact of Silk-Ionomer Encapsulation on Immune Cell Mechanical Properties and Viability

Encapsulation of single cells is a powerful technique used in various fields, such as regenerative medicine, drug delivery, tissue regeneration, cell-based therapies, and biotechnology. It offers a method to protect cells by providing cytocompatible coatings to strengthen cells against mechanical and environmental perturbations. Silk fibroin, derived from the silkworm Bombyx mori, is a promising protein biomaterial for cell encapsulation due to the cytocompatibility and capacity to maintain cell functionality. Here, THP-1 cells, a human leukemia monocytic cell line, were encapsulated with chemically modified silk polyelectrolytes through electrostatic layer-by-layer deposition. The effectiveness of the silk nanocoating was assessed using scanning electron microscopy (SEM) and confocal microscopy and on cell viability and proliferation by Alamar Blue assay and live/dead staining. An analysis of the mechanical properties of the encapsulated cells was conducted using atomic force microscopy nanoindentation to measure elasticity maps and cellular stiffness. After the cells were encapsulated in silk, an increase in their stiffness was observed. Based on this observation, we developed a mechanical predictive model to estimate the variations in stiffness in relation to the thickness of the coating. By tuning the cellular assembly and biomechanics, these encapsulations promote systems that protect cells during biomaterial deposition or processing in general.

Modern advances in spinal cord regeneration: hydrogel combined with neural stem cells

Severe spinal cord injuries (SCI) lead to loss of functional activity of the body below the injury site, affect a person's ability to self-care and have a direct impact on performance. Due to the structural features and functional role of the spinal cord in the body, the consequences of SCI cannot be completely overcome at the expense of endogenous regenerative potential and, developing over time, lead to severe complications years after injury. Thus, the primary task of this type of injury treatment is to create artificial conditions for the regenerative growth of damaged nerve fibers through the area of the SCI. Solving this problem is possible using tissue neuroengineering involving the technology of replacing the natural tissue environment with synthetic matrices (for example, hydrogels) in combination with stem cells, in particular, neural/progenitor stem cells (NSPCs). This approach can provide maximum stimulation and support for the regenerative growth of axons of damaged neurons and their myelination. In this review, we consider the currently available options for improving the condition after SCI (use of NSC transplantation or/and replacement of the damaged area of the SCI with a matrix, specifically a hydrogel). We emphasise the expediency and effectiveness of the hydrogel matrix + NSCs complex system used for the reconstruction of spinal cord tissue after injury. Since such a complex approach (a combination of tissue engineering and cell therapy), in our opinion, allows not only to creation of conditions for supporting endogenous regeneration or mechanical reconstruction of the spinal cord, but also to strengthen endogenous regeneration, prevent the spread of the inflammatory process, and promote the restoration of lost reflex, motor and sensory functions of the injured area of spinal cord.

3D Printing of Polysaccharide-Based Hydrogel Scaffolds for Tissue Engineering Applications: A Review

In tissue engineering, 3D printing represents a versatile technology employing inks to construct three-dimensional living structures, mimicking natural biological systems. This technology efficiently translates digital blueprints into highly reproducible 3D objects. Recent advances have expanded 3D printing applications, allowing for the fabrication of diverse anatomical components, including engineered functional tissues and organs. The development of printable inks, which incorporate macromolecules, enzymes, cells, and growth factors, is advancing with the aim of restoring damaged tissues and organs. Polysaccharides, recognized for their intrinsic resemblance to components of the extracellular matrix have garnered significant attention in the field of tissue engineering. This review explores diverse 3D printing techniques, outlining distinctive features that should characterize scaffolds used as ideal matrices in tissue engineering. A detailed investigation into the properties and roles of polysaccharides in tissue engineering is highlighted. The review also culminates in a profound exploration of 3D polysaccharide-based hydrogel applications, focusing on recent breakthroughs in regenerating different tissues such as skin, bone, cartilage, heart, nerve, vasculature, and skeletal muscle. It further addresses challenges and prospective directions in 3D printing hydrogels based on polysaccharides, paving the way for innovative research to fabricate functional tissues, enhancing patient care, and improving quality of life.

Applications of hydrogels in tissue-engineered repairing of temporomandibular joint diseases

Epidemiological studies reveal that symptoms of temporomandibular joint disorders (TMDs) occur in 60-70% of adults. The inflammatory damage caused by TMDs can easily lead to defects in the articular disc, condylar cartilage, subchondral bone and muscle of the temporomandibular joint (TMJ) and cause pain. Despite the availability of various methods for treating TMDs, few existing treatment schemes can achieve permanent recovery. This necessity drives the search for new approaches. Hydrogels, polymers with high water content, have found widespread use in tissue engineering and regeneration due to their excellent biocompatibility and mechanical properties, which resemble those of human tissues. In the context of TMD therapy, numerous experiments have demonstrated that hydrogels show favorable effects in aspects such as articular disc repair, cartilage regeneration, muscle repair, pain relief, and drug delivery. This review aims to summarize the application of hydrogels in the therapy of TMDs based on recent research findings. It also highlights deficiencies in current hydrogel research related to TMD therapy and outlines the broad potential of hydrogel applications in treating TMJ diseases in the future.

Prospects and challenges for the application of tissue engineering technologies in the treatment of bone infections

Osteomyelitis is a devastating disease caused by microbial infection in deep bone tissue. Its high recurrence rate and impaired restoration of bone deficiencies are major challenges in treatment. Microbes have evolved numerous mechanisms to effectively evade host intrinsic and adaptive immune attacks to persistently localize in the host, such as drug-resistant bacteria, biofilms, persister cells, intracellular bacteria, and small colony variants (SCVs). Moreover, microbial-mediated dysregulation of the bone immune microenvironment impedes the bone regeneration process, leading to impaired bone defect repair. Despite advances in surgical strategies and drug applications for the treatment of bone infections within the last decade, challenges remain in clinical management. The development and application of tissue engineering materials have provided new strategies for the treatment of bone infections, but a comprehensive review of their research progress is lacking. This review discusses the critical pathogenic mechanisms of microbes in the skeletal system and their immunomodulatory effects on bone regeneration, and highlights the prospects and challenges for the application of tissue engineering technologies in the treatment of bone infections. It will inform the development and translation of antimicrobial and bone repair tissue engineering materials for the management of bone infections.

Advancements in fertility preservation strategies for pediatric male cancer patients: a review of cryopreservation and transplantation of immature testicular tissue

Recently, there has been increasing emphasis on the gonadotoxic effects of cancer therapy in prepubertal boys. As advances in oncology treatments continue to enhance survival rates for prepubertal boys, the need for preserving their functional testicular tissue for future reproduction becomes increasingly vital. Therefore, we explore cutting-edge strategies in fertility preservation, focusing on the cryopreservation and transplantation of immature testicular tissue as a promising avenue. The evolution of cryopreservation techniques, from controlled slow freezing to more recent advancements in vitrification, with an assessment of their strengths and limitations was exhibited. Detailed analysis of cryoprotectants, exposure times, and protocols underscores their impact on immature testicular tissue viability. In transplantation strategy, studies have revealed that the scrotal site may be the preferred location for immature testicular tissue grafting in both autotransplantation and xenotransplantation scenarios. Moreover, the use of biomaterial scaffolds during graft transplantation has shown promise in enhancing graft survival and stimulating spermatogenesis in immature testicular tissue over time. This comprehensive review provides a holistic approach to optimize the preservation strategy of human immature testicular tissue in the future.

Engineering Soft Spring Gauges for In Situ Biomaterial and Tissue Weighing

Hydrogels have gained great attention and broad applications in tissue engineering, regenerative medicine, and drug delivery due to their excellent biocompatibility and degradability. However, accurately and noninvasively characterizing the degradation process of hydrogels remains a challenge. To address this, we have developed a method using soft spring gauges (SSGs) for the in situ weighing of hydrogels. Our approach uses a simple hydrogel-based sacrificial template method to fabricate polydimethylsiloxane (PDMS) SSGs. The SSGs used in this study can characterize hydrogels with a minimum wet weight of approximately 30 mg. Through theoretical derivations, numerical simulations, and experimental characterization, we confirmed that the length change of the SSGs in a buffer solution correlates linearly with the applied hanging weights. This allows us to track and assess the solid mass change of hydrogels during degradation with high feasibility and accuracy. Additionally, we have demonstrated the potential application of SSGs for the in situ characterization of engineered tissue growth. This method represents an advanced approach for in situ hydrogel weighing, holding great promise for advancing the development of hydrogels and other biomaterials in biomedical applications.

Au nanozyme-based multifunctional hydrogel for inflammation visible monitoring and treatment

Chronic inflammation can delay wound healing, eventually leading to tissue necrosis and even cancer. Developing real-time intelligent inflammation monitoring and treatment to achieve effective wound management is important to promote wound healing. In this study, a smart multifunctional hydrogel (Hydrogel@Au NCs&DG) was proposed to monitor and treat the wound inflammation. It was prepared by mixing 3-carboxy-phenylboronic acid modified chitosan (CS-cPBA), β-glycerophosphate (β-GP), albumin-protected gold nanoclusters (BSA-Au NCs), and dipotassium glycyrrhizinate (DG) about 10 s. In this hydrogel, CS-cPBA and β-GP are crosslinked together by boric acid ester bond and hydrogen bond to form the main hydrogel network, endowing the hydrogel with self-healing and injectable properties to adapt irregular wounds. Importantly, the as-prepared hydrogel with good biocompatibility and excellent adhesion property could directly determine the H2O2 to monitor the wound microenvironment by visible fluorescence change of BSA-Au NCs and then guide the frequency of dressing change to eliminate inflammation. The results demonstrated that the as-prepared smart hydrogel could be expected to serve as an intelligent wound dressing to promote inflammation-infected wound healing.

Enhancing cartilage regeneration through spheroid culture and hyaluronic acid microparticles: A promising approach for tissue engineering

Cell therapy using chondrocytes has shown promise for cartilage regeneration, but maintaining functional characteristics during in vitro culture and ensuring survival after transplantation are challenges. Three-dimensional (3D) cell culture methods, such as spheroid culture, and hydrogels can improve cell survival and functionality. In this study, a new method of culturing spheroids using hyaluronic acid (HA) microparticles was developed. The spheroids mixed with HA microparticles effectively maintained the functional characteristics of chondrocytes during in vitro culture, resulting in improved cell survival and successful cartilage formation in vivo following transplantation. This new method has the potential to improve cell therapy production for cartilage regeneration.

Collagen Networks under Indentation and Compression Behave Like Cellular Solids

Simple synthetic and natural hydrogels can be formulated to have elastic moduli that match biological tissues, leading to their widespread application as model systems for tissue engineering, medical device development, and drug delivery vehicles. However, two different hydrogels having the same elastic modulus but differing in microstructure or nanostructure can exhibit drastically different mechanical responses, including their poroelasticity, lubricity, and load bearing capabilities. Here, we investigate the mechanical response of collagen-1 networks to local and bulk compressive loads. We compare these results to the behavior of polyacrylamide, a fundamentally different class of hydrogel network consisting of flexible polymer chains. We find that the high bending rigidity of collagen fibers, which suppresses entropic bending fluctuations and osmotic pressure, facilitates the bulk compression of collagen networks under infinitesimal applied stress. These results are fundamentally different from the behavior of flexible polymer networks in which the entropic thermal fluctuations of the polymer chains result in an osmotic pressure that must first be overcome before bulk compression can occur. Furthermore, we observe minimal transverse strain during the axial loading of collagen networks, a behavior reminiscent of open-celled cellular solids. Inspired by these results, we applied mechanical models of cellular solids to predict the elastic moduli of the collagen networks and found agreement with the moduli values measured through contact indentation. Collectively, these results suggest that unlike flexible polymer networks that are often considered incompressible, collagen hydrogels behave like rigid porous solids that volumetrically compress and expel water rather than spreading laterally under applied normal loads.

Physiological cell bioprinting density in human bone-derived cell-laden scaffolds enhances matrix mineralization rate and stiffness under dynamic loading

Human organotypic bone models are an emerging technology that replicate bone physiology and mechanobiology for comprehensive in vitro experimentation over prolonged periods of time. Recently, we introduced a mineralized bone model based on 3D bioprinted cell-laden alginate-gelatin-graphene oxide hydrogels cultured under dynamic loading using commercially available human mesenchymal stem cells. In the present study, we created cell-laden scaffolds from primary human osteoblasts isolated from surgical waste material and investigated the effects of a previously reported optimal cell printing density (5 × 106 cells/mL bioink) vs. a higher physiological cell density (10 × 106 cells/mL bioink). We studied mineral formation, scaffold stiffness, and cell morphology over a 10-week period to determine culture conditions for primary human bone cells in this microenvironment. For analysis, the human bone-derived cell-laden scaffolds underwent multiscale assessment at specific timepoints. High cell viability was observed in both groups after bioprinting (>90%) and after 2 weeks of daily mechanical loading (>85%). Bioprinting at a higher cell density resulted in faster mineral formation rates, higher mineral densities and remarkably a 10-fold increase in stiffness compared to a modest 2-fold increase in the lower printing density group. In addition, physiological cell bioprinting densities positively impacted cell spreading and formation of dendritic interconnections. We conclude that our methodology of processing patient-specific human bone cells, subsequent biofabrication and dynamic culturing reliably affords mineralized cell-laden scaffolds. In the future, in vitro systems based on patient-derived cells could be applied to study the individual phenotype of bone disorders such as osteogenesis imperfecta and aid clinical decision making.

Hydrogel Microparticles for Bone Regeneration

Hydrogel microparticles (HMPs) stand out as promising entities in the realm of bone tissue regeneration, primarily due to their versatile capabilities in delivering cells and bioactive molecules/drugs. Their significance is underscored by distinct attributes such as injectability, biodegradability, high porosity, and mechanical tunability. These characteristics play a pivotal role in fostering vasculature formation, facilitating mineral deposition, and contributing to the overall regeneration of bone tissue. Fabricated through diverse techniques (batch emulsion, microfluidics, lithography, and electrohydrodynamic spraying), HMPs exhibit multifunctionality, serving as vehicles for drug and cell delivery, providing structural scaffolding, and functioning as bioinks for advanced 3D-printing applications. Distinguishing themselves from other scaffolds like bulk hydrogels, cryogels, foams, meshes, and fibers, HMPs provide a higher surface-area-to-volume ratio, promoting improved interactions with the surrounding tissues and facilitating the efficient delivery of cells and bioactive molecules. Notably, their minimally invasive injectability and modular properties, offering various designs and configurations, contribute to their attractiveness for biomedical applications. This comprehensive review aims to delve into the progressive advancements in HMPs, specifically for bone regeneration. The exploration encompasses synthesis and functionalization techniques, providing an understanding of their diverse applications, as documented in the existing literature. The overarching goal is to shed light on the advantages and potential of HMPs within the field of engineering bone tissue.

Manipulation of cross-linking in PEDOT:PSS hydrogels for biointerfacing

Conducting hydrogels can be used to fabricate bioelectronic devices that are soft for improved cell- and tissue-interfacing. Those based on conjugated polymers, such as poly(3,4-ethylene-dioxythiophene):polystyrene sulfonate (PEDOT:PSS), can be made simply with solution-based processing techniques, yet the influence of fabrication variables on final gel properties is not fully understood. In this study, we investigated if PEDOT:PSS cross-linking could be manipulated by changing the concentration of a gelling agent, ionic liquid, in the hydrogel precursor mixture. Rheology and gelation kinetics of precursor mixtures were investigated, and aqueous stability, swelling, conductivity, stiffness, and cytocompatibility of formed hydrogels were characterized. Increasing ionic liquid concentration was found to increase cross-linking as measured by decreased swelling, decreased non-network fraction, increased stiffness, and increased conductivity. Such manipulation of IL concentration thus afforded control of final gel properties and was utilized in further investigations of biointerfacing. When cross-linked sufficiently, PEDOT:PSS hydrogels were stable in sterile cell culture conditions for at least 28 days. Additionally, hydrogels supported a viable and proliferating population of human dermal fibroblasts for at least two weeks. Collectively, these characterizations of stability and cytocompatibility illustrate that these PEDOT:PSS hydrogels have significant promise for biointerfacing applications that require soft materials for direct interaction with cells.

Depth profiling via nanoindentation for characterisation of the elastic modulus and hydraulic properties of thin hydrogel layers

The accurate determination of the mechanical properties of hydrogels is of fundamental importance for a range of applications, including in assessing the effect of stiffness on cell behaviour. This is a particular issue when using thin hydrogel layers adherent to stiff substrate supports, as the apparent stiffness can be significantly influenced by the constraint of the underlying impermeable substrate, leading to inaccurate measurements of the elastic modulus and permeability of thin hydrogel layers. This study used depth profiling nanoindentation and a poroelastic model for spherical indentation to identify the elastic moduli and hydraulic conductivity of thin polyacrylamide (PAAm) hydrogel layers (∼27 μm-782 μm thick) on impermeable substrates. The apparent stiffness of thin PAAm layers increased with indentation depth and was significantly greater than those of thicker hydrogels, which showed no influence of indentation depth. The hydraulic conductivity decreased as the geometrical confinement of hydrogels increased, indicating that the fluid became more constrained within the confinement areas. The impact of geometrical confinement on the apparent modulus and hydraulic conductivity of thin PAAm hydrogel layers was then established, and their elastic moduli and intrinsic permeability were determined in relation to this effect. This study offers valuable insights into the mechanical characterisation of thin PAAm hydrogel layers used for the fundamental study of cell mechanobiology.

The Physics and Manipulation of Dean Vortices in Single- and Two-Phase Flow in Curved Microchannels: A Review

Microchannels with curved geometries have been employed for many applications in microfluidic devices in the past decades. The Dean vortices generated in such geometries have been manipulated using different methods to enhance the performance of devices in applications such as mixing, droplet sorting, and particle/cell separation. Understanding the effect of the manipulation method on the Dean vortices in different geometries can provide crucial information to be employed in designing high-efficiency microfluidic devices. In this review, the physics of Dean vortices and the affecting parameters are summarized. Various Dean number calculation methods are collected and represented to minimize the misinterpretation of published information due to the lack of a unified defining formula for the Dean dimensionless number. Consequently, all Dean number values reported in the references are recalculated to the most common method to facilitate comprehension of the phenomena. Based on the converted information gathered from previous numerical and experimental studies, it is concluded that the length of the channel and the channel pathline, e.g., spiral, serpentine, or helix, also affect the flow state. This review also provides a detailed summery on the effect of other geometric parameters, such as cross-section shape, aspect ratio, and radius of curvature, on the Dean vortices' number and arrangement. Finally, considering the importance of droplet microfluidics, the effect of curved geometry on the shape, trajectory, and internal flow organization of the droplets passing through a curved channel has been reviewed.

Allo Beta Cell transplantation: specific features, unanswered questions, and immunological challenge

Type 1 diabetes (T1D) presents a persistent medical challenge, demanding innovative strategies for sustained glycemic control and enhanced patient well-being. Beta cells are specialized cells in the pancreas that produce insulin, a hormone that regulates blood sugar levels. When beta cells are damaged or destroyed, insulin production decreases, which leads to T1D. Allo Beta Cell Transplantation has emerged as a promising therapeutic avenue, with the goal of reinstating glucose regulation and insulin production in T1D patients. However, the path to success in this approach is fraught with complex immunological hurdles that demand rigorous exploration and resolution for enduring therapeutic efficacy. This exploration focuses on the distinct immunological characteristics inherent to Allo Beta Cell Transplantation. An understanding of these unique challenges is pivotal for the development of effective therapeutic interventions. The critical role of glucose regulation and insulin in immune activation is emphasized, with an emphasis on the intricate interplay between beta cells and immune cells. The transplantation site, particularly the liver, is examined in depth, highlighting its relevance in the context of complex immunological issues. Scrutiny extends to recipient and donor matching, including the utilization of multiple islet donors, while also considering the potential risk of autoimmune recurrence. Moreover, unanswered questions and persistent gaps in knowledge within the field are identified. These include the absence of robust evidence supporting immunosuppression treatments, the need for reliable methods to assess rejection and treatment protocols, the lack of validated biomarkers for monitoring beta cell loss, and the imperative need for improved beta cell imaging techniques. In addition, attention is drawn to emerging directions and transformative strategies in the field. This encompasses alternative immunosuppressive regimens and calcineurin-free immunoprotocols, as well as a reevaluation of induction therapy and recipient preconditioning methods. Innovative approaches targeting autoimmune recurrence, such as CAR Tregs and TCR Tregs, are explored, along with the potential of stem stealth cells, tissue engineering, and encapsulation to overcome the risk of graft rejection. In summary, this review provides a comprehensive overview of the inherent immunological obstacles associated with Allo Beta Cell Transplantation. It offers valuable insights into emerging strategies and directions that hold great promise for advancing the field and ultimately improving outcomes for individuals living with diabetes.

Intelligent Vascularized 3D/4D/5D/6D-Printed Tissue Scaffolds

Blood vessels are essential for nutrient and oxygen delivery and waste removal. Scaffold-repairing materials with functional vascular networks are widely used in bone tissue engineering. Additive manufacturing is a manufacturing technology that creates three-dimensional solids by stacking substances layer by layer, mainly including but not limited to 3D printing, but also 4D printing, 5D printing and 6D printing. It can be effectively combined with vascularization to meet the needs of vascularized tissue scaffolds by precisely tuning the mechanical structure and biological properties of smart vascular scaffolds. Herein, the development of neovascularization to vascularization to bone tissue engineering is systematically discussed in terms of the importance of vascularization to the tissue. Additionally, the research progress and future prospects of vascularized 3D printed scaffold materials are highlighted and presented in four categories: functional vascularized 3D printed scaffolds, cell-based vascularized 3D printed scaffolds, vascularized 3D printed scaffolds loaded with specific carriers and bionic vascularized 3D printed scaffolds. Finally, a brief review of vascularized additive manufacturing-tissue scaffolds in related tissues such as the vascular tissue engineering, cardiovascular system, skeletal muscle, soft tissue and a discussion of the challenges and development efforts leading to significant advances in intelligent vascularized tissue regeneration is presented.

In situ forming macroporous biohybrid hydrogel for nucleus pulposus cell delivery

Degenerative intervertebral disc disease is a common source of chronic pain and reduced quality of life in people over the age of 40. While degeneration occurs throughout the disc, it most often initiates in the nucleus pulposus (NP). Minimally invasive delivery of NP cells within hydrogels that can restore and maintain the disc height while regenerating the damaged NP tissue is a promising treatment strategy for this condition. Towards this goal, a biohybrid ABA dimethacrylate triblock copolymer was synthesized, possessing a lower critical solution temperature below 37 °C and which contained as its central block an MMP-degradable peptide flanked by poly(trimethylene carbonate) blocks bearing pendant oligoethylene glycol groups. This triblock prepolymer was used to form macroporous NP cell-laden hydrogels via redox initiated (ammonium persulfate/sodium bisulfite) crosslinking, with or without the inclusion of thiolated chondroitin sulfate. The resulting macroporous hydrogels had water and mechanical properties similar to those of human NP tissue and were mechanically resilient. The hydrogels supported NP cell attachment and growth over 28 days in hypoxic culture. In hydrogels prepared with the triblock copolymer but without the chondroitin sulfate the NP cells were distributed homogeneously throughout in clusters and deposited collagen type II and sulfated glycosaminoglycans but not collagen type I. This hydrogel formulation warrants further investigation as a cell delivery vehicle to regenerate degenerated NP tissue. STATEMENT OF SIGNIFICANCE: The intervertebral disc between the vertebral bones of the spine consists of three regions: a gel-like central nucleus pulposus (NP) within the annulus fibrosis, and bony endplates. Degeneration of the intervertebral disc is a source of chronic pain in the elderly and most commonly initiates in the NP. Replacement of degenerated NP tissue with a NP cell-laden hydrogel is a promising treatment strategy. Herein we demonstrate that a crosslinkable polymer with a lower critical solution temperature below 37 °C can be used to form macroporous hydrogels for this purpose. The hydrogels are capable of supporting NP cells, which deposit collagen II and sulfated glycosaminoglycans, while also possessing mechanical properties matching those of human NP tissue.

Development of Biocompatible 3D-Printed Artificial Blood Vessels through Multidimensional Approaches

Within the human body, the intricate network of blood vessels plays a pivotal role in transporting nutrients and oxygen and maintaining homeostasis. Bioprinting is an innovative technology with the potential to revolutionize this field by constructing complex multicellular structures. This technique offers the advantage of depositing individual cells, growth factors, and biochemical signals, thereby facilitating the growth of functional blood vessels. Despite the challenges in fabricating vascularized constructs, bioprinting has emerged as an advance in organ engineering. The continuous evolution of bioprinting technology and biomaterial knowledge provides an avenue to overcome the hurdles associated with vascularized tissue fabrication. This article provides an overview of the biofabrication process used to create vascular and vascularized constructs. It delves into the various techniques used in vascular engineering, including extrusion-, droplet-, and laser-based bioprinting methods. Integrating these techniques offers the prospect of crafting artificial blood vessels with remarkable precision and functionality. Therefore, the potential impact of bioprinting in vascular engineering is significant. With technological advances, it holds promise in revolutionizing organ transplantation, tissue engineering, and regenerative medicine. By mimicking the natural complexity of blood vessels, bioprinting brings us one step closer to engineering organs with functional vasculature, ushering in a new era of medical advancement.

3D Printing of Noncytotoxic High-Resolution Microchannels in Bisphenol-A Ethoxylate Dimethacrylate Tissue-Mimicking Materials

The ability to create cell-laden fluidic models that mimic the geometries and physical properties of vascularized tissue would be extremely beneficial to the study of disease etiologies and future therapies, including in the case of cancer where there is increasing interest in studying alterations to the microvasculature. Engineered systems can present significant advantages over animal studies, alleviating challenges associated with variable complexity and control. Three-dimensional (3D)-printable tissue-mimicking hydrogels can offer an alternative, where control of the biophysical properties of the materials can be achieved. Hydrogel-based systems that can recreate complex 3D structures and channels with diameters <500 μm are challenging to produce. We present a noncytotoxic photo-responsive hydrogel that supports 3D printing of complex 3D structures with microchannels down to 150 μm in diameter. Fine tuning of the 3D-printing process has allowed the production of complex structures, where for demonstration purposes we present a helical channel with diameters between 250 and 370 μm around a central channel of 150 μm in diameter in materials with mechanical and acoustic properties that closely replicate those of tissue. The ability to control and accurately reproduce the complex features of the microvasculature has value across a wide range of biomedical applications, especially when the materials involved accurately mimic the physical properties of tissue. An approach that is additionally cell compatible provides a unique setup that can be exploited to study aspects of biomedical research with an unprecedented level of accuracy.

Materials Engineering to Help Pest Control: A Narrative Overview of Biopolymer-Based Entomopathogenic Fungi Formulations

Biopolymer-based formulations show great promise in enhancing the effectiveness of entomopathogenic fungi as bioinsecticides. Chitosan and starch, among other biopolymers, have been utilized to improve spore delivery, persistence, and adherence to target insects. These formulations offer advantages such as target specificity, eco-friendliness, and sustainability. However, challenges related to production costs, stability, and shelf life need to be addressed. Recently, biomimetic lure and kill approaches based on biopolymers offer cost-effective solutions by leveraging natural attractants. Further research is needed to optimize these formulations and overcome challenges. Biopolymer-based formulations have the potential to revolutionize pest control practices, providing environmentally friendly and sustainable solutions for agriculture.

In Vitro and In Vivo Biological Assessments of 3D-Bioprinted Scaffolds for Dental Applications

Three-dimensional (3D) bioprinting is a unique combination of technological advances in 3D printing and tissue engineering. It has emerged as a promising approach to address the dilemma in current dental treatments faced by clinicians in order to repair or replace injured and diseased tissues. The exploration of 3D bioprinting technology provides high reproducibility and precise control of the bioink containing the desired cells and biomaterial over the architectural and dimensional features of the scaffolds in fabricating functional tissue constructs that are specific to the patient treatment need. In recent years, the dental applications of different 3D bioprinting techniques, types of novel bioinks, and the types of cells used have been extensively explored. Most of the findings noted significant challenges compared to the non-biological 3D printing approach in constructing the bioscaffolds that mimic native tissues. Hence, this review focuses solely on the implementation of 3D bioprinting techniques and strategies based on cell-laden bioinks. It discusses the in vitro applications of 3D-bioprinted scaffolds on cell viabilities, cell functionalities, differentiation ability, and expression of the markers as well as the in vivo evaluations of the implanted bioscaffolds on the animal models for bone, periodontal, dentin, and pulp tissue regeneration. Finally, it outlines some perspectives for future developments in dental applications.

Advances in the study of acetaminophen-induced liver injury

Acetaminophen (APAP) overdose is a significant cause of drug-induced liver injury and acute liver failure. The diagnosis, screening, and management of APAP-induced liver injury (AILI) is challenging because of the complex mechanisms involved. Starting from the current studies on the mechanisms of AILI, this review focuses on novel findings in the field of diagnosis, screening, and management of AILI. It highlights the current issues that need to be addressed. This review is supposed to summarize the recent research progress and make recommendations for future research.

High Nutritional Quality of Human-Induced Pluripotent Stem Cell-Generated Proteins through an Advanced Scalable Peptide Hydrogel 3D Suspension System

Cell-cultured protein technology has become increasingly attractive due to its sustainability and climate benefits. The aim of this study is to determine the nutritional quality of the human-induced pluripotent stem cell (hiPSC)-cultured proteins in an advanced 3D peptide hydrogel system for the highly efficient production of cell-cultured proteins. Our previous study demonstrated a PGmatrix peptide hydrogel for the 3D embedded culture of long-term hiPSC maintenance and expansion (PGmatrix-hiPSC (PG-3D)), which showed significantly superior pluripotency when compared with traditional 2D cell culture on Matrigel and/or Vitronectin and other existing 3D scaffolding systems such as Polyethylene glycol (PEG)-based hydrogels. In this study, we designed a PGmatrix 3D suspension (PG-3DSUSP) system from the PG-3D embedded system that allows scaling up a hiPSC 3D culture volume by 20 times (e.g., from 0.5 mL to 10 mL). The results indicated that the PG-3DSUSP was a competitive system compared to the well-established PG-3D embedded method in terms of cell growth performance and cell pluripotency. hiPSCs cultured in PG-3DSUSP consistently presented a 15-20-fold increase in growth and a 95-99% increase in viability across multiple passages with spheroids with a size range of 30-50 μm. The expression of pluripotency-related genes, including NANOG, OCT4, hTERT, REX1, and UTF1, in PG-3DSUSP-cultured hiPSCs was similar to or higher than that observed in a PG-3D system, suggesting continuous pluripotent maintenance. The nutritional value of the hiPSC-generated proteins from the PG-3DSUSP system was further evaluated for amino acid composition and in vitro protein digestibility. The amino acid composition of the hiPSC-generated proteins demonstrated a significantly higher essential amino acid content (39.0%) than human skeletal muscle protein (31.8%). In vitro protein digestibility of hiPSC-generated proteins was significantly higher (78.0 ± 0.7%) than that of the commercial beef protein isolate (75.7 ± 0.6%). Taken together, this is the first study to report an advanced PG-3DSUSP culture system to produce highly efficient hiPSC-generated proteins that possess more essential amino acids and better digestibility. The hiPSC-generated proteins with superior nutrition quality may be of particular significance as novel alternative proteins in food engineering and industries for future food, beverage, and supplement applications.

Human epidermal keratinocytes and human dermal fibroblasts interactions seeded on gelatin hydrogel for future application in skin in vitro 3-dimensional model

Introduction: Plenty of biomaterials have been studied for their application in skin tissue engineering. Currently, gelatin-hydrogel is used to support three-dimensional (3D) skin in vitro models. However, mimicking the human body conditions and properties remains a challenge and gelatin-hydrogels have low mechanical properties and undergo rapid degradation rendering them not suitable for 3D in vitro cell culture. Nevertheless, changing the concentration of hydrogels could overcome this issue. Thus, we aim to investigate the potential of gelatin hydrogel with different concentrations crosslinked with genipin to promote human epidermal keratinocytes and human dermal fibroblasts culture to develop a 3D-in vitro skin model replacing animal models. Methods: Briefly, the composite gelatin hydrogels were fabricated using different concentrations as follows 3%, 5%, 8%, and 10% crosslinked with 0.1% genipin or non-crosslinked. Both physical and chemical properties were evaluated. Results and discussion: The crosslinked scaffolds showed better properties, including porosity and hydrophilicity, and genipin was found to enhance the physical properties. Furthermore, no alteration was prominent in both formulations of CL_GEL 5% and CL_GEL8% after genipin modification. The biocompatibility assays showed that all groups promoted cell attachment, cell viability, and cell migration except for the CL_GEL10% group. The CL_GEL5% and CL_GEL8% groups were selected to develop a bi-layer 3D-in vitro skin model. The immunohistochemistry (IHC) and hematoxylin and eosin staining (H&E) were performed on day 7, 14, and 21 to evaluate the reepithelization of the skin constructs. However, despite satisfactory biocompatibility properties, neither of the selected formulations, CL_GEL 5% and CL_GEL 8%, proved adequate for creating a bi-layer 3D in-vitro skin model. While this study provides valuable insights into the potential of gelatin hydrogels, further research is needed to address the challenges associated with their use in developing 3D skin models for testing and biomedical applications.

Three-Dimensional Bioprinting of Naturally Derived Hydrogels for the Production of Biomimetic Living Tissues: Benefits and Challenges

Three-dimensional bioprinting is the process of manipulating cell-laden bioinks to fabricate living structures. Three-dimensional bioprinting techniques have brought considerable innovation in biomedicine, especially in the field of tissue engineering, allowing the production of 3D organ and tissue models for in vivo transplantation purposes or for in-depth and precise in vitro analyses. Naturally derived hydrogels, especially those obtained from the decellularization of biological tissues, are promising bioinks for 3D printing purposes, as they present the best biocompatibility characteristics. Despite this, many natural hydrogels do not possess the necessary mechanical properties to allow a simple and immediate application in the 3D printing process. In this review, we focus on the bioactive and mechanical characteristics that natural hydrogels may possess to allow efficient production of organs and tissues for biomedical applications, emphasizing the reinforcement techniques to improve their biomechanical properties.

Antibacterial and Cytocompatible pH-Responsive Peptide Hydrogel

A short peptide, FHHF-11, was designed to change stiffness as a function of pH due to changing degree of protonation of histidines. As pH changes in the physiologically relevant range, G' was measured at 0 Pa (pH 6) and 50,000 Pa (pH 8). This peptide-based hydrogel is antimicrobial and cytocompatible with skin cells (fibroblasts). It was demonstrated that the incorporation of unnatural AzAla tryptophan analog residue improves the antimicrobial properties of the hydrogel. The material developed can have a practical application and be a paradigm shift in the approach to wound treatment, and it will improve healing outcomes for millions of patients each year.

Synthesis, Characterization, Properties, and Biomedical Application of Chitosan-Based Hydrogels

The prospective applications of chitosan-based hydrogels (CBHs), a category of biocompatible and biodegradable materials, in biomedical disciplines such as tissue engineering, wound healing, drug delivery, and biosensing have garnered great interest. The synthesis and characterization processes used to create CBHs play a significant role in determining their characteristics and effectiveness. The qualities of CBHs might be greatly influenced by tailoring the manufacturing method to get certain traits, including porosity, swelling, mechanical strength, and bioactivity. Additionally, characterization methods aid in gaining access to the microstructures and properties of CBHs. Herein, this review provides a comprehensive assessment of the state-of-the-art with a focus on the affiliation between particular properties and domains in biomedicine. Moreover, this review highlights the beneficial properties and wide application of stimuli-responsive CBHs. The main obstacles and prospects for the future of CBH development for biomedical applications are also covered in this review.

Nafcillin-Loaded Photocrosslinkable Nanocomposite Hydrogels for Biomedical Applications

Skin infections are frequently treated via intravenous or oral administration of antibiotics, which can lead to serious adverse effects and may sometimes contribute to the proliferation of resistant bacterial strains. Skin represents a convenient pathway for delivering therapeutic compounds, ensured by the high number of blood vessels and amount of lymphatic fluids in the cutaneous tissues, which are systematically connected to the rest of the body. This study provides a novel, straightforward method to obtain nafcillin-loaded photocrosslinkable nanocomposite hydrogels and demonstrates their performance as drug carriers and antimicrobial efficacy against Gram-positive bacteria. The novel formulations obtained, based on polyvinylpyrrolidone, tri(ethylene glycol) divinyl ether crosslinker, hydrophilic bentonite nanoclay, and/or two types of photoactive (TiO₂ and ZnO) nanofillers, were characterized using various analytical methods (transmission electron microscopy (TEM), scanning electron microscopy-energy-dispersive X-ray analysis (SEM-EDX), mechanical tests (tension, compression, and shear), ultraviolet-visible spectroscopy (UV-Vis), swelling investigations, and via specific microbiological assays ("agar disc diffusion method" and "time-kill test"). The results reveal that the nanocomposite hydrogel possessed high mechanical resistance, good swelling abilities, and good antimicrobial activity, demonstrating a decrease in the bacteria growth between 3log₁₀ and 2log₁₀ after one hour of direct contact with S. aureus.

A Review of Research Progress on the Performance of Intelligent Polymer Gel

Intelligent polymer gel, as a popular polymer material, has been attracting much attention for its application. An intelligent polymer gel will make corresponding changes to adapt to the environment after receiving stimuli; therefore, an intelligent polymer gel can play its role in many fields. With the research on intelligent polymer gels, there is great potential for applications in the fields of drug engineering, molecular devices, and biomedicine in particular. The strength and responsiveness of the gels can be improved under different configurations in different technologies to meet the needs in these fields. There is no discussion on the application of intelligent polymer gels in these fields; therefore, this paper reviews the research progress of intelligent polymer gel, describes the important research of some intelligent polymer gel, summarizes the research progress and current situation of intelligent polymer gel in the environment of external stimulation, and discusses the performance and future development direction of intelligent polymer gel.

Multi compartmental 3D breast cancer disease model–recapitulating tumor complexity in in-vitro

Breast cancer is the most common ailment among women. In 2020, it had the highest incidence of any type of cancer. Many Phase II and III anti-cancer drugs fail due to efficacy, durability, and side effects. Thus, accelerated drug screening models must be accurate. In-vivo models have been used for a long time, but delays, inconsistent results, and a greater sense of responsibility among scientists toward wildlife have led to the search for in-vitro alternatives. Stromal components support breast cancer growth and survival. Multi-compartment Transwell models may be handy instruments. Co-culturing breast cancer cells with endothelium and fibroblasts improves modelling. The extracellular matrix (ECM) supports native 3D hydrogels in natural and polymeric forms. 3D Transwell cultured tumor spheroids mimicked in-vivo pathological conditions. Tumor invasion, migration, Trans-endothelial migration, angiogenesis, and spread are studied using comprehensive models. Transwell models can create a cancer niche and conduct high-throughput drug screening, promising future applications. Our comprehensive shows how 3D in-vitro multi compartmental models may be useful in producing breast cancer stroma in Transwell culture.

Classification, processing, and applications of bioink and 3D bioprinting: A detailed review

With the advancement in 3D bioprinting technology, cell culture methods can design 3D environments which are both, complex and physiologically relevant. The main component in 3D bioprinting, bioink, can be split into various categories depending on the criterion of categorization. Although the choice of bioink and bioprinting process will vary greatly depending on the application, general features such as material properties, biological interaction, gelation, and viscosity are always important to consider. The foundation of 3D bioprinting is the exact layer-by-layer implantation of biological elements, biochemicals, and living cells with the spatial control of the implantation of functional elements onto the biofabricated 3D structure. Three basic strategies underlie the 3D bioprinting process: autonomous self-assembly, micro tissue building blocks, and biomimicry or biomimetics. Tissue engineering can benefit from 3D bioprinting in many ways, but there are still numerous obstacles to overcome before functional tissues can be produced and used in clinical settings. A better comprehension of the physiological characteristics of bioink materials and a higher level of ability to reproduce the intricate biologically mimicked and physiologically relevant 3D structures would be a significant improvement for 3D bioprinting to overcome the limitations.

A Nanoparticle Ink Allowing the High Precision Visualization of Tissue Engineered Scaffolds by MRI

Hydrogels are widely used as cell scaffolds in several biomedical applications. Once implanted in vivo, cell scaffolds must often be visualized, and monitored overtime. However, cell scaffolds appear poorly contrasted in most biomedical imaging modalities such as magnetic resonance imaging (MRI). MRI is the imaging technique of choice for high-resolution visualization of low-density, water-rich tissues. Attempts to enhance hydrogel contrast in MRI are performed with "negative" contrast agents that produce several image artifacts impeding the delineation of the implant's contours. In this study, a magnetic ink based on ultra-small iron oxide nanoparticles (USPIONs; <5 nm diameter cores) is developed and integrated into biocompatible alginate hydrogel used in cell scaffolding applications. Relaxometric properties of the magnetic hydrogel are measured, as well as biocompatibility and MR-visibility (T₁ -weighted mode; in vitro and in vivo). A 2-week MR follow-up study is performed in the mouse model, demonstrating no image artifacts, and the retention of "positive" contrast overtime, which allows very precise delineation of tissue grafts with MRI. Finally, a 3D-contouring procedure developed to facilitate graft delineation and geometrical conformity assessment is applied on an inverted template alginate pore network. This proof-of-concept establishes the possibility to reveal precisely engineered hydrogel structures using this USPIONs ink high-visibility approach.

Alginate sulfate/ECM composite hydrogel containing electrospun nanofiber with encapsulated human adipose-derived stem cells for cartilage tissue engineering

Stem cell therapy is a promising strategy for cartilage tissue engineering, and cell transplantation using polymeric scaffolds has recently gained attention. Herein, we encapsulated human adipose-derived stem cells (hASCs) within the alginate sulfate hydrogel and then added them to polycaprolactone/gelatin electrospun nanofibers and extracellular matrix (ECM) powders to mimic the cartilage structure and characteristic. The composite hydrogel scaffolds were developed to evaluate the relevant factors and conditions in mechanical properties, cell proliferation, and differentiation to enhance cartilage regeneration. For this purpose, different concentrations (1-5 % w/v) of ECM powder were initially loaded within an alginate sulfate solution to optimize the best composition for encapsulated hASCs viability. Adding 4 % w/v of ECM resulted in optimal mechanical and rheological properties and better cell viability. In the next step, electrospun nanofibrous layers were added to the alginate sulfate/ECM composite to prepare different layered hydrogel-nanofiber (2, 3, and 5-layer) structures with the ability to mimic the cartilage structure and function. The 3-layer structure was selected as the optimum layered composite scaffold, considering cell viability, mechanical properties, swelling, and biodegradation behavior; moreover, the chondrogenesis potential was assessed, and the results showed promising features for cartilage tissue engineering application.

Three-Dimensional Evaluation of the Cytotoxicity and Antibacterial Properties of Alpha Lipoic Acid-Capped Silver Nanoparticle Constructs for Oral Applications

There is a need to develop bifunctional scaffolds that provide antibacterial protection while encouraging host cell attachment/proliferation. This study evaluates HyStem^®-C, and photo-cross-linked GelMA hydrogels for encapsulation and stabilisation of silver nanoparticles (AgNPs). We studied the behaviour of AgNPs and matrix interactions within both hydrogel systems. The cell viability of encapsulated human gingival fibroblasts (HGFs) was determined by Prestoblue^® assay and live/dead staining. The release of AgNPs was monitored by inductively coupled plasma-mass spectroscopy. The antibacterial properties of the GelMA-AgNP constructs were determined using disc diffusion. Even distribution of AgNPs in GelMA induced a significant decrease in cell viability (p < 0.0001), whereas AgNP aggregates did not induce cytotoxicity in HyStem^®-C. AgNPs doses ≥ 0.5 µg/mL in GelMA were significantly toxic to the HGFs (p < 0.0001). The release of AgNPs from GelMA after 48 h was 20% w/w for 0.1 µg/mL and 51% for 100 µg/mL of AgNPs. At ≥5 µg/mL, a significant intra-construct bactericidal effect was observed. The disc diffusion assay shows that GelMA-incorporated AgNPs were found to be effective against both Escherichia coli and Staphylococcus aureus at 50 and 100 µg/mL, respectively. Visible photo-cross-linked GelMA stably incorporated AgNPs to provide an antimicrobial regenerative construct for oral applications.

Bioactive composite hydrogels as 3D mesenchymal stem cell encapsulation environment for bone tissue engineering: in vitro and in vivo studies

Although decellularized bone matrix (DBM) has often been used in scaffold form for osteogenic applications, its use as a stem cell encapsulation matrix adaptable to surgical shaping procedures has been neglected. This study aimed to investigate the feasibility of utilizing solubilized DBM and nanohydroxyapatite (nHAp)-incorporated DBM hydrogels as encapsulation matrix for bone marrow-derived MSCs (BM-MSCs). First, DBM and DBM/nHAp hydrogels were assessed by physical, chemical, turbidimetric, thermal, and mechanical methods; then, in vitro cytocompatibility and in vitro hemocompatibility were investigated. An in vivo study was performed to evaluate the osteogenic properties of hydrogels alone or with BM-MSCs encapsulated in them. The findings revealed that hydrogels retained high levels of collagen and glycosaminoglycans after successful decellularization. They were found to be cytocompatible and hemocompatible in vitro, and were able to gel with sufficient mechanical stability at physiological temperature. BM-MSCs survived in culture for at least 2 weeks as metabolically active when encapsulated in both DBM and DBM/nHAp. Preliminary in vivo study showed that DBM-nHAp has higher osteogenicity than DBM. Moreover, BM-MSC encapsulated DMB/nHAp showed predominant bone-like tissue formation at 30 days in the rat ectopic site compared to its cell-free form.

Hydrogel-based microenvironment engineering of haematopoietic stem cells

Haematopoietic Stem cells (HSCs) have the potential for self-renewal and multilineage differentiation, and their behaviours are finely tuned by the microenvironment. HSC transplantation (HSCT) is widely used in the treatment of haematologic malignancies while limited by the quantity of available HSCs. With the development of tissue engineering, hydrogels have been deployed to mimic the HSC microenvironment in vitro. Engineered hydrogels influence HSC behaviour by regulating mechanical strength, extracellular matrix microstructure, cellular ligands and cytokines, cell-cell interaction, and oxygen concentration, which ultimately facilitate the acquisition of sufficient HSCs. Here, we review recent advances in the application of hydrogel-based microenvironment engineering of HSCs, and provide future perspectives on challenges in basic research and clinical practice.

Advances in polymer-based cell encapsulation and its applications in tissue repair

Cell microencapsulation is a more widely accepted area of biological encapsulation. In most cases, it involves fixing cells in polymer scaffolds or semi-permeable hydrogel capsules, providing the environment for protecting cells, allowing the exchange of nutrients and oxygen, and protecting cells against the attack of the host immune system by preventing the entry of antibodies and cytotoxic immune cells. Hydrogel encapsulation provides a three-dimensional (3D) environment similar to that experienced in vivo, so it can maintain normal cellular functions to produce tissues similar to those in vivo. Embedded cells can be genetically modified to release specific therapeutic products directly at the target site, thereby eliminating the side effects of systemic treatments. Cellular microcarriers need to meet many extremely high standards regarding their biocompatibility, cytocompatibility, immunoseparation capacity, transport, mechanical, and chemical properties. In this article, we discuss the biopolymer gels used in tissue engineering applications and the brief introduction of cell encapsulation for therapeutic protein production. Also, we review polymer biomaterials and methods for preparing cell microcarriers for biomedical applications. At the same time, in order to improve the application performance of cell microcarriers in vivo, we also summarize the main limitations and improvement strategies of cell encapsulation. Finally, the main applications of polymer cell microcarriers in regenerative medicine are summarized.

Chitosan, chondroitin sulfate, and hyaluronic acid based in-situ forming scaffold for efficient cell grafting

Current cell grafting techniques are majorly dependent on seeding cells on a pre-formed scaffold. However, cells grow in a 2-dimensional (2D) space in such constructs, not mimicking the tissue's 3-dimensional (3D) architecture. The present study evaluated a unique poly-electrolyte complexation (PEC) based strategy for the 3D engraftment of cells in a porous polymeric scaffold. The scaffold was synthesized using a positively charged polysaccharide chitosan (CH) and negatively charged glycosaminoglycans chondroitin sulfate (CS) and hyaluronic acid (HA). Two different scaffolds were synthesized, one using CH and CS [CH-CS] and another using CH and CS + HA [CH-(CS-HA)]. The physicochemical characterization of both the PECs confirmed electrostatic interactions, leading to a porous and viscoelastic PEC formation. Fibroblast cells were grafted and seeded in both scaffolds to evaluate the effect of different scaffold compositions and the difference between seeded and grafted cells. Imaging studies confirmed that grafting of the fibroblast cells supports cellular proliferation. The qPCR studies demonstrated increased expression of functional markers TGF-β, α-SMA, collagen-I, and fibronectin in the CH-(CS-HA) grafted cells. In summary, it was demonstrated that an in-situ forming PEC of CH, CS, and HA had good physicochemical properties for cell grafting and supported grafted cells with improved function.

Translational Nanomedicines Across Human Reproductive Organs Modeling on Microfluidic Chips: State-of-the-Art and Future Prospects

Forecasting the consequence of nanoparticles (NPs) and therapeutically significant molecules before materializing for human clinical trials is a mainstay for drug delivery and screening processes. One of the noteworthy obstacles that has prevented the clinical translation of NP-based drug delivery systems and novel drugs is the lack of effective preclinical platforms. As a revolutionary technology, the organ-on-a-chip (OOC), a coalition of microfluidics and tissue engineering, has surfaced as an alternative to orthodox screening platforms. OOC technology recapitulates the structural and physiological features of human organs along with intercommunications between tissues on a chip. The current review discusses the concept of microfluidics and confers cutting-edge fabrication processes for chip designing. We also outlined the advantages of microfluidics in analyzing NPs in terms of characterization, transport, and degradation in biological systems. The review further elaborates the scope and research on translational nanomedicines in human reproductive organs (testis, placenta, uterus, and menstrual cycle) by taking the advantages offered by microfluidics and shedding light on their potential future implications. Finally, we accentuate the existing challenges for clinical translation and scale-up dynamics for microfluidics chips and emphasize its future perspectives.

Tuning the Mechanical Properties of Multiarm RAFT-Based Block Copolyelectrolyte Hydrogels via Ionic Cross-Linking for 3D Cell Cultures

Hydrogels that serve as native extracellular matrix (ECM) mimics are typically naturally derived hydrogels that are physically cross-linked via ionic interactions. This means rapid gelation of synthetic polymers, which give control over the chemical and physical cues in hydrogel formation. Herein, we combine the best of both systems by developing a synthetic hydrogel with ionic cross-linking of block copolyelectrolytes to rapidly create hydrogels. Reversible addition-fragmentation chain-transfer (RAFT) polymerization was used to synthesize oppositely charged polyelectrolyte molecules and, in turn, modulate the mechanical property of stiffness. The mechanical stiffness of a range of 900-3500 Pa was tuned by varying the number of charged ionic groups, the length of the polymer arms, and the polymer concentration. We demonstrate the synthetic polyelectrolyte hydrogel as an ECM mimic for three-dimensional (3D) in vitro cell models using MCF-7 breast cancer cells.

3D Human Tumor Tissues Cultured in Dynamic Conditions as Alternative In Vitro Disease Models

The slow knowledge progression about cancer disease and the high drug clinical failure are mainly due to the inadequacy of the simplistic pre-clinical in vitro and in vivo animal tumor models. To overpass these limits, in recent years many 3D matrix-based cell cultures have been proposed as challenging alternatives, since they allow to better recapitulate the in vitro cells-cells and cells-matrix reciprocal interactions in a more physiological context. Among many natural polymers, alginate has been adopted as an extracellular matrix surrogate to mimic the 3D spatial organization. After their expansion, cancer cells are suspended in an alginate solution and dropped within a crosslinking solution enabling gelification. The result is the generation of a 3D hydrogel embedding a single cell suspension: Cells are equally distributed throughout the gel, and they are free to proliferate generating clonal spheroids. Moreover, according to the hydrogel matrix stiffness that can be easily tuned, tumor cells can spread within the 3D structure and migrate outside, where they may become circulating tumor cells and infiltrate secondary tumor sites when these 3D tumor tissues are cultured in a fluid dynamic environment (i.e., organ on chip).

Soft hydrogel-shell confinement systems as bacteria-based bioactuators and biosensors

Genetically engineered (GE) bacteria were utilized for developing functional systems upon confinement within a restricted space. Use of natural soft hydrogel such as alginate, gelatin, and agarose, have been investigated as promising approaches to design functional architectures. Nevertheless, a challenge is to develop functional microenvironments that support biofilm-like confinement in a relevant three-dimensional (3D) format for long-term studies. We demonstrate a natural soft hydrogel bioactuator based on alginate core-shell structures (0.25-2 mm core and 50-300 μm shell thickness) that enables 3D microbial colonization upon confinement with high cell density. Specially, our study evaluates the efficiency of bacteria-functional system by recapitulating various GE bacteria which can produce common reporter proteins, to demonstrate their actuator functions as well as dynamic pair-wise interactions. The structural design of the hydrogel can endure continued growth of various bacteria colonies within the confined space for over 10 days. The total amount of cellular biomass upon hydrogel-shell confinement was increased 5-fold compared to conventional techniques without hydrogel-shell. Furthermore, the enzymatic activity increased 3.8-fold and bioluminescence signal by 8-fold compared to the responses from conventional hydrogel systems. The conceptualized platform and our workflow represent a reliable strategy with core-shell structures to develop artificial hydrogel habitats as bacteria-based functional systems for bioactuation.

Key aspects for conception and construction of co-culture models of tumor-stroma interactions

The tumor microenvironment is crucial in the initiation and progression of cancers. The interplay between cancer cells and the surrounding stroma shapes the tumor biology and dictates the response to cancer therapies. Consequently, a better understanding of the interactions between cancer cells and different components of the tumor microenvironment will drive progress in developing novel, effective, treatment strategies. Co-cultures can be used to study various aspects of these interactions in detail. This includes studies of paracrine relationships between cancer cells and stromal cells such as fibroblasts, endothelial cells, and immune cells, as well as the influence of physical and mechanical interactions with the extracellular matrix of the tumor microenvironment. The development of novel co-culture models to study the tumor microenvironment has progressed rapidly over recent years. Many of these models have already been shown to be powerful tools for further understanding of the pathophysiological role of the stroma and provide mechanistic insights into tumor-stromal interactions. Here we give a structured overview of different co-culture models that have been established to study tumor-stromal interactions and what we have learnt from these models. We also introduce a set of guidelines for generating and reporting co-culture experiments to facilitate experimental robustness and reproducibility.

Development of chondrocyte-laden alginate hydrogels with modulated microstructure and properties for cartilage regeneration

Alginate hydrogel is an attractive biomaterial for cell microencapsulation. The microarchitecture of hydrogels can regulate cellular functions. This study aims to investigate the applicability of sodium citrate buffer (SCB) as a culture medium supplement for modulating the microstructure of alginate microbeads to provide a favorable microenvironment for chondrogenic induction. The chondrocyte-laden microbeads, with and without TGF-β3 incorporation, were produced through an encapsulator. The obtained small-sized microbeads (~300 μm) were exposed to a treatment medium containing SCB, composed of varied concentrations of sodium citrate (1.10-1.57 mM), sodium chloride (3.00-4.29 mM), and ethylenediaminetetraacetic acid (0.60-0.86 mM) to partially degrade their crosslinked structure for 3 days, followed by culture in a normal medium until day 21. Scanning electron microscope micrographs demonstrated a loose hydrogel network with an enhanced pore size in the SCB-treated microbeads. Increasing the concentration of SCB in the treatment medium reduced the calcium content of the microbeads via a Na⁺ /Ca²⁺ exchange process and improved the water absorption of the microbeads, resulting in a higher swelling ratio. All the tested SCB concentrations were non-cytotoxic. Increases in aggrecan and type II collagen gene expression and their corresponding extracellular matrix accumulation, glycosaminoglycans, and type II collagen were vividly detected in the TGF-β3-containing microbeads with increasing SCB concentrations in the treatment medium. Our findings highlighted that the combination of SCB treatment and TGF-β3 incorporation in the chondrocyte-laden microbeads is a promising strategy for enhancing cartilage regeneration, which may contribute to a versatile application in cell delivery and tissue engineering.

pH and Thrombin Concentration Are Decisive in Synthesizing Stiff, Stable, and Open-Porous Fibrin-Collagen Hydrogel Blends without Chemical Cross-Linker

Fibrin-collagen hydrogel blends exhibit high potential for tissue engineering applications. However, it is still unclear whether the underlying cross-linking mechanisms are of chemical or physical nature. It is here hypothesized that chemical cross-linkers play a negligible role and that instead pH and thrombin concentration are decisive for synthetizing blends with high stiffness and hydrolytic stability. Different fibrin-collagen formulations (pure and with additional transglutaminase) are used and the blends' compaction rate, hydrolytic stability, compressive strength, and hydrogel microstructure are investigated. The effect of thrombin concentration on gel compaction is examined and the importance of pH control during synthesis observed. It is revealed that transglutaminase impairs gel stability and it is deduced that fibrin-collagen blends mainly cross-link by mechanical interactions due to physical fibril entanglement as opposed to covalent bonds from chemical cross-linking. High thrombin concentrations and basic pH during synthesis reduce gel compaction and enhance stiffness and long-term stability. Scanning electron microscopy reveals a highly interpenetrating fibrous network with unique, interconnected open-porous microstructures. Endothelial cells proliferate on the blends and form a confluent monolayer. This study reveals the underlying cross-linking mechanisms and presents enhanced fibrin-collagen blends with high stiffness, hydrolytic stability, and large, interconnected pores; findings that offer high potential for advanced tissue engineering applications.

Current Advances in 3D Dynamic Cell Culture Systems

The traditional two-dimensional (2D) cell culture methods have a long history of mimicking in vivo cell growth. However, these methods cannot fully represent physiological conditions, which lack two major indexes of the in vivo environment; one is a three-dimensional 3D cell environment, and the other is mechanical stimulation; therefore, they are incapable of replicating the essential cellular communications between cell to cell, cell to the extracellular matrix, and cellular responses to dynamic mechanical stimulation in a physiological condition of body movement and blood flow. To solve these problems and challenges, 3D cell carriers have been gradually developed to provide a 3D matrix-like structure for cell attachment, proliferation, differentiation, and communication in static and dynamic culture conditions. 3D cell carriers in dynamic culture systems could primarily provide different mechanical stimulations which further mimic the real in vivo microenvironment. In this review, the current advances in 3D dynamic cell culture approaches have been introduced, with their advantages and disadvantages being discussed in comparison to traditional 2D cell culture in static conditions.