Hyaluronic acid hydrogel for controlled self-renewal and differentiation of human embryonic stem cells

Nonwoven fiber meshes for oxygen sensing

Accurate oxygen sensing and cost-effective fabrication are crucial for the adoption of wearable devices inside and outside the clinical setting. Here we introduce a simple strategy to create nonwoven polymeric fibrous mats for a notable contribution towards addressing this need. Although morphological manipulation of polymers for cell culture proliferation is commonplace, especially in the field of regenerative medicine, non-woven structures have not been used for oxygen sensing. We used an airbrush spraying, i.e. solution blowing, to obtain nonwoven fiber meshes embedded with a phosphorescent dye. The fibers serve as a polymer host for the phosphorescent dye and are shown to be non-cytotoxic. Different composite fibrous meshes were prepared and favorable mechanical and oxygen-sensing properties were demonstrated. A Young's modulus of 9.8 MPa was achieved and the maximum oxygen sensitivity improved by a factor of ∼2.9 compared to simple drop cast film. The fibers were also coated with silicone rubbers to produce mechanically robust sensing films. This reduced the sensing performance but improved flexibility and mechanical properties. Lastly, we are able to capture oxygen concentration maps via colorimetry using a smartphone camera, which should offer unique advantages in wider usage. Overall, the introduced composite fiber meshes show a potential to significantly improve cell cultures and healthcare monitoring via absolute oxygen sensing.

Phototuning of Hyaluronic-Acid-Based Hydrogel Properties to Control Network Formation in Human Vascular Endothelial Cells

In vitro network formation by endothelial cells serves as a fundamental model for studies aimed at understanding angiogenesis. The morphogenesis of these cells to form a network is intricately regulated by the mechanical and biochemical properties of the extracellular matrix. Here the effects of modulating these properties in hydrogels derived from phenolated hyaluronic acid (HA-Ph) and phenolated gelatin (Gelatin-Ph) are presented. Visible-light irradiation in the presence of tris(2,2'-bipyridyl)ruthenium(II) chloride hexahydrate and sodium persulfate induces the crosslinking of these polymers, thereby forming a hydrogel and degrading HA-Ph. Human vascular endothelial cells form networks on the hydrogel prepared by visible-light irradiation for 45 min (42 W cm-2 at 450 nm) but not on the hydrogels prepared by irradiation for 15, 30, or 60 min. The irradiation time-dependent degradation of HA-Ph and the changes in the mechanical stiffness of the hydrogels, coupled with the expressions of RhoA and β-actin genes and CD44 receptors in the cells, reveal that the network formation is synergistically influenced by the hydrogel stiffness and HA-Ph degradation. These findings highlight the potential of tailoring HA-based hydrogel properties to modulate human vascular endothelial cell responses, which is critical for advancing their application in vascular tissue engineering.

Advancing Synthetic Hydrogels through Nature-Inspired Materials Chemistry

Synthetic extracellular matrix (ECM) mimics that can recapitulate the complex biochemical and mechanical nature of native tissues are needed for advanced models of development and disease. Biomedical research has heavily relied on the use of animal-derived biomaterials, which is now impeding their translational potential and convoluting the biological insights gleaned from in vitro tissue models. Natural hydrogels have long served as a convenient and effective cell culture tool, but advances in materials chemistry and fabrication techniques now present promising new avenues for creating xenogenic-free ECM substitutes appropriate for organotypic models and microphysiological systems. However, significant challenges remain in creating synthetic matrices that can approximate the structural sophistication, biochemical complexity, and dynamic functionality of native tissues. This review summarizes key properties of the native ECM, and discusses recent approaches used to systematically decouple and tune these properties in synthetic matrices. The importance of dynamic ECM mechanics, such as viscoelasticity and matrix plasticity, is also discussed, particularly within the context of organoid and engineered tissue matrices. Emerging design strategies to mimic these dynamic mechanical properties are reviewed, such as multi-network hydrogels, supramolecular chemistry, and hydrogels assembled from biological monomers.

Elastocapillary effects determine early matrix deformation by glioblastoma cell spheroids

During cancer pathogenesis, cell-generated mechanical stresses lead to dramatic alterations in the mechanical and organizational properties of the extracellular matrix (ECM). To date, contraction of the ECM is largely attributed to local mechanical stresses generated during cell invasion, but the impact of "elastocapillary" effects from surface tension on the tumor periphery has not been examined. Here, we embed glioblastoma cell spheroids within collagen gels, as a model of tumors within the ECM. We then modulate the surface tension of the spheroids, such that the spheroid contracts or expands. Surprisingly, in both cases, at the far-field, the ECM is contracted toward the spheroids prior to cellular migration from the spheroid into the ECM. Through computational simulation, we demonstrate that contraction of the ECM arises from a balance of spheroid surface tension, cell-ECM interactions, and time-dependent, poroelastic effects of the gel. This leads to the accumulation of ECM near the periphery of the spheroid and the contraction of the ECM without regard to the expansion or contraction of the spheroid. These results highlight the role of tissue-level surface stresses and fluid flow within the ECM in the regulation of cell-ECM interactions.

Bioactive injectable mucoadhesive thermosensitive natural polymeric hydrogels for oral bone and periodontal regeneration

Periodontitis is an inflammation-related condition, caused by an infectious microbiome and host defense that causes damage to periodontium. The natural processes of the mouth, like saliva production and eating, significantly diminish therapeutic medication residency in the region of periodontal disease. Furthermore, the complexity and diversity of pathological mechanisms make successful periodontitis treatment challenging. As a result, developing enhanced local drug delivery technologies and logical therapy procedures provides the foundation for effective periodontitis treatment. Being biocompatible, biodegradable, and easily administered to the periodontal tissues, hydrogels have sparked substantial an intense curiosity in the discipline of periodontal therapy. The primary objective of hydrogel research has changed in recent years to intelligent thermosensitive hydrogels, that involve local adjustable sol-gel transformations and regulate medication release in reaction to temperature, we present a thorough introduction to the creation and efficient construction of new intelligent thermosensitive hydrogels for periodontal regeneration. We also address cutting-edge smart hydrogel treatment options based on periodontitis pathophysiology. Furthermore, the problems and prospective study objectives are reviewed, with a focus on establishing effective hydrogel delivery methods and prospective clinical applications.

Hyaluronan in mesenchymal stromal cell lineage differentiation from human pluripotent stem cells: application in serum free culture

BACKGROUND

Hyaluronan (HA) is an extracellular glycosaminoglycan polysaccharide with widespread roles throughout development and in healthy and neoplastic tissues. In pluripotent stem cell culture it can support both stem cell renewal and differentiation. However, responses to HA in culture are influenced by interaction with a range of cognate factors and receptors including components of blood serum supplements, which alter results. These may contribute to variation in cell batch production yield and phenotype as well as heighten the risks of adventitious pathogen transmission in the course of cell processing for therapeutic applications. MAIN: Here we characterise differentiation of a human embryo/pluripotent stem cell derived Mesenchymal Stromal Cell (hESC/PSC-MSC)-like cell population by culture on a planar surface coated with HA in serum-free media qualified for cell production for therapy. Resulting cells met minimum criteria of the International Society for Cellular Therapy for identification as MSC by expression of. CD90, CD73, CD105, and lack of expression for CD34, CD45, CD14 and HLA-II. They were positive for other MSC associated markers (i.e.CD166, CD56, CD44, HLA 1-A) whilst negative for others (e.g. CD271, CD71, CD146). In vitro co-culture assessment of MSC associated functionality confirmed support of growth of hematopoietic progenitors and inhibition of mitogen activated proliferation of lymphocytes from umbilical cord and adult peripheral blood mononuclear cells, respectively. Co-culture with immortalized THP-1 monocyte derived macrophages (Mɸ) concurrently stimulated with lipopolysaccharide as a pro-inflammatory stimulus, resulted in a dose dependent increase in pro-inflammatory IL6 but negligible effect on TNFα. To further investigate these functionalities, a bulk cell RNA sequence comparison with adult human bone marrow derived MSC and hESC substantiated a distinctive genetic signature more proximate to the former.

CONCLUSION

Cultivation of human pluripotent stem cells on a planar substrate of HA in serum-free culture media systems is sufficient to yield a distinctive developmental mesenchymal stromal cell lineage with potential to modify the function of haematopoietic lineages in therapeutic applications.

Drug delivery systems for wound healing treatment of upper airway injury

INTRODUCTION

Endotracheal intubation is a common procedure to maintain an open airway with risks for traumatic injury. Pathological changes resulting from intubation can cause upper airway complications, including vocal fold scarring, laryngotracheal stenosis, and granulomas and present with symptoms such as dysphonia, dysphagia, and dyspnea. Current intubation-related laryngotracheal injury treatment approaches lack standardized guidelines, relying on individual clinician experience, and surgical and medical interventions have limitations and carry risks.

AREAS COVERED

The clinical and preclinical therapeutics for wound healing in the upper airway are described. This review discusses the current developments on local drug delivery systems in the upper airway utilizing particle-based delivery systems, including nanoparticles and microparticles, and bulk-based delivery systems, encompassing hydrogels and polymer-based approaches.

EXPERT OPINION

Complex laryngotracheal diseases pose challenges for effective treatment, struggling due to the intricate anatomy, limited access, and recurrence. Symptomatic management often requires invasive surgical procedures or medications that are unable to achieve lasting effects. Recent advances in nanotechnology and biocompatible materials provide potential solutions, enabling precise drug delivery, personalization, and extended treatment efficacy. Combining these technologies could lead to groundbreaking treatments for upper airways diseases, significantly improving patients' quality of life. Research and innovation in this field are crucial for further advancements.

Structural Homogeneity of Macromolecular Networks by End-to-End Click Chemistry between Discrete Tetrahedral Star Macromolecules

Cross-linking via the end-to-end click chemistry of multiarm star polymers creates polymer networks with minimal inhomogeneities. Although it has been suggested that the mechanical and swelling properties of such networks depend on the absence of defects, the structural details of homogeneous networks created by this method have not yet been studied at the molecular level. Here, we report the synthesis of discrete tetrahedral star macromolecules (dTSMs) composed of polylactide (PLA) arms with discrete molecular weight and sequence. Polymer networks prepared by 4 × 4 cross-linking by Cu-free strain-promoted cyclooctyne-azide click chemistry (SPAAC) reaction exhibited a high degree of swelling (>40 fold by weight) in solvents without sacrificing mechanical robustness (elastic modulus >4 kPa). The structural details of the networks were investigated by network disassembly spectrometry (NDS) using MALDI-TOF mass spectrometry. By implementing a cleavable repeating unit in the discrete PLA arms of dTSM in a sequence-specific manner, the networks could be disassembled into fragments having discrete molecular weights precisely representing their connectivity in the network. This NDS analysis confirmed that end-to-end click reactions of dTSM networks resulted in the formation of a homogeneous network above the critical concentration (∼10 w/v%) of building blocks in the solution.

Controllable and biocompatible 3D bioprinting technology for microorganisms: Fundamental, environmental applications and challenges

3D bioprinting is a new 3D manufacturing technology, that can be used to accurately distribute and load microorganisms to form microbial active materials with multiple complex functions. Based on the 3D printing of human cells in tissue engineering, 3D bioprinting technology has been developed. Although 3D bioprinting technology is still immature, it shows great potential in the environmental field. Due to the precise programming control and multi-printing pathway, 3D bioprinting technology provides a high-throughput method based on micron-level patterning for a wide range of environmental microbiological engineering applications, which makes it an on-demand, multi-functional manufacturing technology. To date, 3D bioprinting technology has been employed in microbial fuel cells, biofilm material preparation, microbial catalysts and 4D bioprinting with time dimension functions. Nevertheless, current 3D bioprinting technology faces technical challenges in improving the mechanical properties of materials, developing specific bioinks to adapt to different strains, and exploring 4D bioprinting for intelligent applications. Hence, this review systematically analyzes the basic technical principles of 3D bioprinting, bioinks materials and their applications in the environmental field, and proposes the challenges and future prospects of 3D bioprinting in the environmental field. Combined with the current development of microbial enhancement technology in the environmental field, 3D bioprinting will be developed into an enabling platform for multifunctional microorganisms and facilitate greater control of in situ directional reactions.

Zein-Induced Polyelectrolyte Complexes for Encapsulating Triterpenoid Phytochemicals

The hydrophobicity and aggregation of zein, a biopolymer, limit its application as an effective drug delivery carrier. Here, we developed a zein-induced polyelectrolyte (ZiP) complex and investigated its efficiency in delivering 1% hydrolyzed ginseng saponin, a compound K-rich fraction derived from the root of Panax ginseng. The ZiP complex was formulated by incorporating the self-assembled amphiphilic prolamin zein into the aqueous phase. The physical properties, encapsulation efficiency, and stability of the encapsulation system at room temperature (25 °C) and 45 °C were assessed. The effects of different ratios of zein, pullulan, and pectin on the formation of the ZiP complex, the encapsulation stability, and the cellular efficacy of ZiP complexes were also assessed. The ZiP complex was surface-modified with hydrophilic pullulan and pectin polysaccharides in a mass ratio of 1:2:0.2 through electrostatic interactions. The primary hydrophilic modification of the ZiP complex was formed by the adsorption of pullulan, which enhanced the encapsulation stability. The outermost hydrophilic layer comprised the gelling polysaccharide pectin, which further improved the stability of the macro-sized oil-encapsulated complex, reaching sizes over 50 μm. The size of the ZiP complex increased when the concentration of pectin or the total content of the ZiP complex increased to 2:4:0.2. Compound K was successfully encapsulated with a particle size of 294.8 nm and an encapsulation efficiency of 99.6%. The ZiP complex demonstrated stability at high temperatures and long-term stability of the encapsulated saponin over 24 weeks. These results revealed the potency of ZiP complexes that enhance the in vivo absorption of phytochemicals as effective drug delivery carriers that can overcome the limitations in industrial formulation development as a delivery system.

Bioactive and chemically defined hydrogels with tunable stiffness guide cerebral organoid formation and modulate multi-omics plasticity in cerebral organoids

Organoids are an emerging technology with great potential in human disease modelling, drug development, diagnosis, tissue engineering, and regenerative medicine. Organoids as 3D-tissue culture systems have gained special attention in the past decades due to their ability to faithfully recapitulate the complexity of organ-specific tissues. Despite considerable successes in culturing physiologically relevant organoids, their real-life applications are currently limited by challenges such as scarcity of an appropriate biomimetic matrix. Peptide amphiphiles (PAs) due to their well-defined chemistry, tunable bioactivity, and extracellular matrix (ECM)-like nanofibrous architecture represent an attractive material scaffold for organoids development. Using cerebral organoids (COs) as exemplar, we demonstrate the possibility to create bio-instructive hydrogels with tunable stiffness ranging from 0.69 kPa to 2.24 kPa to culture and induce COs growth. We used orthogonal chemistry involving oxidative coupling and supramolecular interactions to create two-component hydrogels integrating the bio-instructive activity and ECM-like nanofibrous architecture of a laminin-mimetic PAs (IKVAV-PA) and tunable crosslinking density of hyaluronic acid functionalized with tyramine (HA-Try). Multi-omics technology including transcriptomics, proteomics, and metabolomics reveals the induction and growth of COs in soft HA-Tyr hydrogels containing PA-IKVAV such that the COs display morphology and biomolecular signatures similar to those grown in Matrigel scaffolds. Our materials hold great promise as a safe synthetic ECM for COs induction and growth. Our approach represents a well-defined alternative to animal-derived matrices for the culture of COs and might expand the applicability of organoids in basic and clinical research. STATEMENT OF SIGNIFICANCE: Synthetic bio-instructive materials which display tissue-specific functionality and nanoscale architecture of the native extracellular matrix are attractive matrices for organoids development. These synthetic matrices are chemically defined and animal-free compared to current gold standard matrices such as Matrigel. Here, we developed hydrogel matrices with tunable stiffness, which incorporate laminin-mimetic peptide amphiphiles to grow and expand cerebral organoids. Using multi-omics tools, the present study provides exciting data on the effects of neuro-inductive cues on the biomolecular profiles of brain organoids.

Alginate Beads as a Promising Tool for Successful Production of Viable and Pluripotent Human-Induced Pluripotent Stem Cells in a 3D Culture System

Purpose

Two-dimensional (2D)-based cell culture systems, limited by their inherent heterogeneity and scalability, are a bottleneck in the production of high-quality cells for downstream biomedical applications. Finding the optimal conditions for large-scale stem cell culture while maintaining good cellular status is challenging. The aim of this study was to assess the effects of three-dimensional (3D) culture on the viability, proliferation, self-renewal, and differentiation of human induced pluripotent stem cells (IPSCs).

Patients and Methods

Various culture conditions were evaluated to determine the optimal conditions to maintain the viability and proliferation of human IPSCs in a 3D environment: static versus dynamic culture, type of adhesion protein added to alginate (Matrigel™ versus gelatin), and the addition of Y-27632t on long-term 3D culture. The proliferation ability of the cells was evaluated via the MTS proliferation assay; the expression levels of the pluripotency markers Nanog and Oct3/4, PAX6 as an ectoderm marker, and laminin-5 and fibronectin as markers of extracellular matrix synthesis were assessed; and HIF1α and HIF2α levels were measured using quantitative reverse transcription polymerase chain reaction.

Results

Using a high-aspect-ratio vessel bioreactor with a gentle, low-sheer, and low-turbulence environment with sufficient oxygenation and effective mass transfer of nutrients and waste, we verified its ability to promote cell proliferation and self-renewal. The findings showed that human IPSCs have the ability to maintain pluripotency in a feeder-free system and by inhibiting ROCK signaling and using hypoxia to improve single-cell viability in 3D culture. Furthermore, these cells demonstrated increased self-renewal and proliferation when inoculated as single cells in 3D alginate beads by adding RI during the culture period.

Conclusion

Dynamic 3D culture is desirable for the large-scale expansion of undifferentiated human IPSCs.

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.

Cell-extracellular matrix mechanotransduction in 3D

Mechanical properties of extracellular matrices (ECMs) regulate essential cell behaviours, including differentiation, migration and proliferation, through mechanotransduction. Studies of cell-ECM mechanotransduction have largely focused on cells cultured in 2D, on top of elastic substrates with a range of stiffnesses. However, cells often interact with ECMs in vivo in a 3D context, and cell-ECM interactions and mechanisms of mechanotransduction in 3D can differ from those in 2D. The ECM exhibits various structural features as well as complex mechanical properties. In 3D, mechanical confinement by the surrounding ECM restricts changes in cell volume and cell shape but allows cells to generate force on the matrix by extending protrusions and regulating cell volume as well as through actomyosin-based contractility. Furthermore, cell-matrix interactions are dynamic owing to matrix remodelling. Accordingly, ECM stiffness, viscoelasticity and degradability often play a critical role in regulating cell behaviours in 3D. Mechanisms of 3D mechanotransduction include traditional integrin-mediated pathways that sense mechanical properties and more recently described mechanosensitive ion channel-mediated pathways that sense 3D confinement, with both converging on the nucleus for downstream control of transcription and phenotype. Mechanotransduction is involved in tissues from development to cancer and is being increasingly harnessed towards mechanotherapy. Here we discuss recent progress in our understanding of cell-ECM mechanotransduction in 3D.

Getting physical: Material mechanics is an intrinsic cell cue

Advances in biomaterial science have allowed for unprecedented insight into the ability of material cues to influence stem cell function. These material approaches better recapitulate the microenvironment, providing a more realistic ex vivo model of the cell niche. However, recent advances in our ability to measure and manipulate niche properties in vivo have led to novel mechanobiological studies in model organisms. Thus, in this review, we will discuss the importance of material cues within the cell niche, highlight the key mechanotransduction pathways involved, and conclude with recent evidence that material cues regulate tissue function in vivo.

Animal-derived products in science and current alternatives

More than fifty years after the 3Rs definition and despite the continuous implementation of regulatory measures, animals continue to be widely used in basic research. Their use comprises not only in vivo experiments with animal models, but also the production of a variety of supplements and products of animal origin for cell and tissue culture, cell-based assays, and therapeutics. The animal-derived products most used in basic research are fetal bovine serum (FBS), extracellular matrix proteins such as Matrigel™, and antibodies. However, their production raises several ethical issues regarding animal welfare. Additionally, their biological origin is associated with a high risk of contamination, resulting, frequently, in poor scientific data for clinical translation. These issues support the search for new animal-free products able to replace FBS, Matrigel™, and antibodies in basic research. In addition, in silico methodologies play an important role in the reduction of animal use in research by refining the data previously to in vitro and in vivo experiments. In this review, we depicted the current available animal-free alternatives in in vitro research.

A self-assembled dynamic extracellular matrix-like hydrogel system with multi-scale structures for cell bioengineering applications

Extracellular matrix (ECM) provides various types of direct interactions with cells and a dynamic environment, which can be remodeled through different assembly/degradation mechanisms to adapt to different biological processes. Herein, through introducing polyphosphate-modified hyaluronic acid and bioactive glass (BG) nano-fibril into a self-assembled hydrogel system with peptide-polymer conjugate, we can realize many new ECM-like functions in a synthetic polymer network. The hydrogel network formation is mediated by coacervation, followed by a gradual transition of peptide structure from  α-helix to β-sheet. The ECM-like hydrogels can be degraded through a number of orthogonal mechanisms, including treatments with protease, hyaluronidase, alkaline phosphatase, and calcium ion. As 2D coating, the ECM-like hydrogels can be used to modify the planar surface to promote the adhesion of mesenchymal stromal cells, or to coat the cell surface in a layer-by-layer fashion to shield the interaction with the substrate. As ECM-like hydrogels for 3D cell culture, the system is compatible with injection and cell encapsulation. Upon incorporating fragmented electrospun bioactive glass nano-fibril into the hydrogels, the synergetic effects of soft hydrogel and stiff reinforcement nanofibers on recapitulating ECM functions result in reduced cell circularity in 3D. Finally, by injecting the ECM-like hydrogels into mice, gradual degradations over a time period of one month and high biocompatibility have been shown in vivo. The contribution of complex network dynamics and hierarchical structures to cell-biomatrix interaction can be investigated multi-dimensionally, as many mechanisms are orthogonal to each other and can be regulated individually. STATEMENT OF SIGNIFICANCE: A list of native ECM features has attracted the most interest and attention in the research of synthetic biomaterials. In this research, we have described a simple ECM-like hydrogel system in which the complex and elegant functions of native ECM can be recapitulated in a chemically defined synthetic system. The ECM-like hydrogel systems were developed to avoid undesired features of biological substances (e.g., ethical concerns, batch-to-batch variation, immunogenicity, and potential risk of contamination), as well as gaining new functions to facilitate bioengineering applications (e.g., 3D cell culture, injection, and high stability). To this end, we have developed an ECM-like hydrogel system and provide evidence that this purely synthetic biomaterial is a promising candidate for cell bioengineering applications.

Xeno-free culture and proliferation of hPSCs on 2D biomaterials

Human pluripotent stem cells (human embryonic stem cells (hESCs) and induced pluripotent stem cells (hiPSCs)) have unlimited proliferative potential, whereas adult stem cells such as bone marrow-derived stem cells and adipose-derived stem cells have problems with aging. When hPSCs are intended to be cultured on feeder-free or xeno-free conditions without utilizing mouse embryonic fibroblasts or human fibroblasts, they cannot be cultured on conventional tissue culture polystyrene dishes, as adult stem cells can be cultured but should be cultivated on material surfaces grafted or coated with (a) natural or recombinant extracellular matrix (ECM) proteins, (b) ECM protein-derived peptides and specific synthetic polymer surfaces in xeno-free and/or chemically defined conditions. This review describes current developing cell culture biomaterials for the proliferation of hPSCs while maintaining the pluripotency and differentiation potential of the cells into 3 germ layers. Biomaterials for the cultivation of hPSCs without utilizing a feeder layer are essential to decrease the risk of xenogenic molecules, which contributes to the potential clinical usage of hPSCs. ECM proteins such as human recombinant vitronectin, laminin-511 and laminin-521 have been utilized instead of Matrigel for the feeder-free cultivation of hPSCs. The following biomaterials are also discussed for hPSC cultivation: (a) decellularized ECM, (b) peptide-grafted biomaterials derived from ECM proteins, (c) recombinant E-cadherin-coated surface, (d) polysaccharide-immobilized surface, (e) synthetic polymer surfaces with and without bioactive sites, (f) thermoresponsive polymer surfaces with and without bioactive sites, and (g) synthetic microfibrous scaffolds.

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.

A review of challenges and prospects of 3D cell-based culture models used for studying drug induced liver injury during early phases of drug development

Drug-induced liver injury (DILI) is the leading cause of compound attrition during drug development. Over the years, a battery of in-vitro cell culture toxicity tests is being conducted to evaluate the toxicity of compounds prior to testing in laboratory animals. Two-dimensional (2D) in-vitro cell culture models are commonly used and have provided a great deal of knowledge; however, these models often fall short in mimicking natural structures of tissues in-vivo. Testing in humans is the most logical method, but unfortunately there are ethical limitations associated with human tests. To overcome these limitations better human-relevant, predictive models are required. The past decade has witnessed significant efforts towards the development of three-dimensional (3D) in-vitro cell culture models better mimicking in-vivo physiology. 3D cell culture has advantages in being representative of the interactions of cells in-vivo and when validated can act as an interphase between 2D cell culture models and in-vivo animal models. The current review seeks to provide an overview of the challenges that make biomarkers used for detection of DILI not to be sensitive enough during drug development and explore how 3D cell culture models can be used to address the gap with the current models.

Message in a Scaffold: Natural Biomaterials for Three-Dimensional (3D) Bioprinting of Human Brain Organoids

Brain organoids are invaluable tools for pathophysiological studies or drug screening, but there are still challenges to overcome in making them more reproducible and relevant. Recent advances in three-dimensional (3D) bioprinting of human neural organoids is an emerging approach that may overcome the limitations of self-organized organoids. It requires the development of optimal hydrogels, and a wealth of research has improved our knowledge about biomaterials both in terms of their intrinsic properties and their relevance on 3D culture of brain cells and tissue. Although biomaterials are rarely biologically neutral, few articles have reviewed their roles on neural cells. We here review the current knowledge on unmodified biomaterials amenable to support 3D bioprinting of neural organoids with a particular interest in their impact on cell homeostasis. Alginate is a particularly suitable bioink base for cell encapsulation. Gelatine is a valuable helper agent for 3D bioprinting due to its viscosity. Collagen, fibrin, hyaluronic acid and laminin provide biological support to adhesion, motility, differentiation or synaptogenesis and optimize the 3D culture of neural cells. Optimization of specialized hydrogels to direct differentiation of stem cells together with an increased resolution in phenotype analysis will further extend the spectrum of possible bioprinted brain disease models.

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.

Loss of multipotency in adipose-derived stem cells after culture in temperature-responsive injectable polymer hydrogels

Adipose-derived stem cells (AdSCs), a type of mesenchymal stem cell, are expected to be applicable to regenerative medicine and cellular delivery systems. The maintenance of cell multipotency and control of the differentiation direction are important for these applications. However, the differentiation direction of these cells is widely believed to depend on the physical properties of their scaffold. In this study, we explored whether the multipotency of AdSCs, that is, their ability to differentiate into multiple cells, is maintained when they are removed from injectable polymer (IP) hydrogels with various degrees of cross-linking and induced to differentiate into osteoblasts and adipocytes. We confirmed that AdSCs cultured in IP hydrogels maintained an undifferentiated state. However, their differentiation into osteoblasts and adipocytes cannot be ensured; specifically, the multipotency of AdSCs may decrease when they are cultured in IP hydrogels. When cultured in an IP hydrogel with extreme softness and poor cell adhesion properties, the AdSCs remained in an undifferentiated state, but their multipotency was reduced. These results provide important insights into stem cell delivery systems using IP hydrogels.

Microcarriers in application for cartilage tissue engineering: Recent progress and challenges

Successful regeneration of cartilage tissue at a clinical scale has been a tremendous challenge in the past decades. Microcarriers (MCs), usually used for cell and drug delivery, have been studied broadly across a wide range of medical fields, especially the cartilage tissue engineering (TE). Notably, microcarrier systems provide an attractive method for regulating cell phenotype and microtissue maturations, they also serve as powerful injectable carriers and are combined with new technologies for cartilage regeneration. In this review, we introduced the typical methods to fabricate various types of microcarriers and discussed the appropriate materials for microcarriers. Furthermore, we highlighted recent progress of applications and general design principle for microcarriers. Finally, we summarized the current challenges and promising prospects of microcarrier-based systems for medical applications. Overall, this review provides comprehensive and systematic guidelines for the rational design and applications of microcarriers in cartilage TE.

•

This review summarized fabrication techniques and cartilage repaired application of microcarriers.

•

The appropriate materials and design principle for microcarriers in cartilage tissue engineering are discussed.

•

Promising future perspectives and challenges in microcarriers fields are outlined.

Fabricating 3-dimensional human brown adipose microtissues for transplantation studies

Transplanting cell cultured brown adipocytes (BAs) represents a promising approach to prevent and treat obesity (OB) and its associated metabolic disorders, including type 2 diabetes mellitus (T2DM). However, transplanted BAs have a very low survival rate in vivo. The enzymatic dissociation during the harvest of fully differentiated BAs also loses significant cells. There is a critical need for novel methods that can avoid cell death during cell preparation, transplantation, and in vivo. Here, we reported that preparing BAs as injectable microtissues could overcome the problem. We found that 3D culture promoted BA differentiation and UCP-1 expression, and the optimal initial cell aggregate size was 100 μm. The microtissues could be produced at large scales via 3D suspension assisted with a PEG hydrogel and could be cryopreserved. Fabricated microtissues could survive in vivo for long term. They alleviated body weight and fat gain and improved glucose tolerance and insulin sensitivity in high-fat diet (HFD)-induced OB and T2DM mice. Transplanted microtissues impacted multiple organs, secreted protein factors, and influenced the secretion of endogenous adipokines. To our best knowledge, this is the first report on fabricating human BA microtissues and showing their safety and efficacy in T2DM mice. The proposal of transplanting fabricated BA microtissues, the microtissue fabrication method, and the demonstration of efficacy in T2DM mice are all new. Our results show that engineered 3D human BA microtissues have considerable advantages in product scalability, storage, purity, safety, dosage, survival, and efficacy.

Rheological Characterization and Theoretical Modeling Establish Molecular Design Rules for Tailored Dynamically Associating Polymers

Dynamically associating polymers have long been of interest due to their highly tunable viscoelastic behavior. Many applications leverage this tunability to create materials that have specific rheological properties, but designing such materials is an arduous, iterative process. Current models for dynamically associating polymers are phenomenological, assuming a structure for the relationship between association kinetics and network relaxation. We present the Brachiation model, a molecular-level theory of a polymer network with dynamic associations that is rooted in experimentally controllable design parameters, replacing the iterative experimental process with a predictive model for how experimental modifications to the polymer will impact rheological behavior. We synthesize hyaluronic acid chains modified with supramolecular host-guest motifs to serve as a prototypical dynamic network exhibiting tunable physical properties through control of polymer concentration and association rates. We use dynamic light scattering microrheology to measure the linear viscoelasticity of these polymers across six decades in frequency and fit our theory parameters to the measured data. The parameters are then altered by a magnitude corresponding to changes made to the experimental parameters and used to obtain new rheological predictions that match the experimental results well, demonstrating the ability for this theory to inform the design process of dynamically associating polymeric materials.

Dynamic gelatin-based hydrogels promote the proliferation and self-renewal of embryonic stem cells in long-term 3D culture

Long-term maintenance of embryonic stem cells (ESCs) in the undifferentiated state is still challenging. Compared with traditional 2D culture methods, 3D culture in biomaterials such as hydrogels is expected to better support the long-term self-renewal of ESCs by emulating the biophysical and biochemical properties of the extracellular matrix (ECM). Although prior studies showed that soft and degradable hydrogels favor the 3D growth of ESCs, few studies have examined the impact of the structural dynamics of the hydrogel matrix on ESC behaviors. Herein, we report a gelatin-based structurally dynamic hydrogel (GelCD hydrogel) that emulates the intrinsic structural dynamics of the ECM. Compared with covalently crosslinked gelatin hydrogels (GelMA hydrogels) with similar stiffness and biodegradability, GelCD hydrogels significantly promote the clonal expansion and viability of encapsulated mouse ESCs (mESCs) independent of MMP-mediated hydrogel degradation. Furthermore, GelCD hydrogels better maintain the pluripotency of encapsulated mESCs than do traditional 2D culture methods that use MEF feeder cells or medium supplementation with GSK3β and MEK 1/2 inhibitors (2i). When cultured in GelCD hydrogels for an extended period (over 2 months) with cell passaging every 7 days, mESCs preserve their normal morphology and maintain their pluripotency and full differentiation capability. Our findings highlight the critical role of the structural dynamics of the hydrogel matrix in accommodating the volume expansion that occurs during clonal ESC growth, and we believe that our dynamic hydrogels represent a valuable tool to support the long-term 3D culture of ESCs.

Heparinized Gelatin-Based Hydrogels for Differentiation of Induced Pluripotent Stem Cells

Chemically defined hydrogels are increasingly utilized to define the effects of extracellular matrix (ECM) components on cellular fate determination of human embryonic and induced pluripotent stem cell (hESC and hiPSCs). In particular, hydrogels cross-linked by orthogonal click chemistry, including thiol-norbornene photopolymerization and inverse electron demand Diels–Alder (iEDDA) reactions, are explored for 3D culture of hESC/hiPSCs owing to the specificity, efficiency, cytocompatibility, and modularity of the cross-linking reactions. In this work, we exploited the modularity of thiol-norbornene photopolymerization to create a biomimetic hydrogel platform for 3D culture and differentiation of hiPSCs. A cell-adhesive, protease-labile, and cross-linkable gelatin derivative, gelatin-norbornene (GelNB), was used as the backbone polymer for constructing hiPSC-laden biomimetic hydrogels. GelNB was further heparinized via the iEDDA click reaction using tetrazine-modified heparin (HepTz), creating GelNB-Hep. GelNB or GelNB-Hep was modularly cross-linked with either inert macromer poly(ethylene glycol)-tetra-thiol (PEG4SH) or another bioactive macromer-thiolated hyaluronic acid (THA). The formulations of these hydrogels were modularly tuned to afford biomimetic matrices with similar elastic moduli but varying bioactive components, enabling the understanding of each bioactive component on supporting hiPSC growth and ectodermal, mesodermal, and endodermal fate commitment under identical soluble differentiation cues.

Recent Advances in Cardiac Patches: Materials, Preparations, and Properties

Cardiac patches are biomaterials that can be used for transplantation and repair of damaged myocardium by combining seed cells with the ability to form cardiomyocytes and suitable scaffold materials. On the one hand, they provide temporary support to the infarcted area, and on the other hand, they repair the damaged myocardium by delivering cells or bioactive factors to integrate with the host, which have gradually become a hot research topic in recent years. This paper summarizes the structural properties of natural myocardium and reviews the recent research progress of cardiac patches, including the seed cells and scaffold materials used in patch preparation, as well as the main methods of scaffold preparation and the structure properties of various scaffolds. In addition, a comprehensive analysis of the problems faced in the clinical implementation of cardiac patches is presented. Finally, we look forward to the development of cardiac patches and point out that precisely tunable anisotropic tissue engineering scaffolds close to natural myocardial tissue will become an important direction for future research.

Design of chemically defined synthetic substrate surfaces for the in vitro maintenance of human pluripotent stem cells: A review

Human pluripotent stem cells (hPSCs) have the potential of long-term self-renewal and differentiation into nearly all cell types in vitro. Prior to the downstream applications, the design of chemically defined synthetic substrates for the large-scale proliferation of quality-controlled hPSCs is critical. Although great achievements have been made, Matrigel and recombinant proteins are still widely used in the fundamental research and clinical applications. Therefore, much effort is still needed to improve the performance of synthetic substrates in the culture of hPSCs, realizing their commercial applications. In this review, we summarized the design of reported synthetic substrates and especially their limitations in terms of cell culture. Moreover, much attention was paid to the development of promising peptide displaying surfaces. Besides, the biophysical regulation of synthetic substrate surfaces as well as the three-dimensional culture systems were described.

Multiscale Invasion Assay for Probing Macrophage Response to Gram-Negative Bacteria

The immune system is a complex network of various cellular components that must differentiate between pathogenic bacteria and the commensal bacteria of the human microbiome, where misrecognition is linked to inflammatory disorders. Fragments of bacterial cell wall peptidoglycan bind to pattern recognition receptors within macrophages, leading to immune activation. To study this complex process, a methodology to remodel and label the bacterial cell wall of two different species of bacteria was established using copper (I) catalyzed azide-alkyne cycloaddition (CuAAC) and strain-promoted azide-alkyne cycloaddition (SPAAC). Additionally, an approach for three-dimensional (3D) culture of human macrophages and their invasion with relevant bacteria in a well-defined hydrogel-based synthetic matrix inspired by the microenvironment of the gut was established. Workflows were developed for human monocyte encapsulation and differentiation into macrophages in 3D culture with high viability. Bacteria invaded into macrophages permitted in situ peptidoglycan labeling. Macrophages exhibited biologically-relevant cytokine release in response to bacteria. This molecularly engineered, multi-dimensional bacteria-macrophage co-culture system will prove useful in future studies to observe immunostimulatory, bacterial fragment production and localization in the cell at the carbohydrate level for insights into how the immune system properly senses bacteria.

Engineered Customizable Microvessels for Progressive Vascularization in Large Regenerative Implants

Inspired by the rapid angiogenesis of natural microvessels in vivo, engineered customizable microvessels (ECMVs) are developed which can naturally angiogenic sprout and induce vascular network formation via combing a celluar coaxial microfluidic extrusion technique with microsurgery post-process. ECMVs can be used for customization of primarily pre-vascularized soft tissue regenerative implants with personalized shape and vascular density with the aid of sacrificial printing technology. After collaborating with surrounding cells, ECMVs angiogenic sprouted and formed daughter vascular networks. Through techniques such as injection and suturing, ECMVs can also be introduced into large bone repair implants for pre-vascularization and osteogenesis promotion. Furthermore, the microvessel networks with personalized shapes are customized by connecting the coaxial microfluidic system to a 3D printer. It is further demonstrated that the vascularization promotion and anastomose with host vessels of the ECMVs in vivo. Thus, ECMVs provide a simple engineering strategy for rapid vascularization of clinically large regenerative soft/hard tissue implants.

Engineering the multiscale complexity of vascular networks

The survival of vertebrate organisms depends on highly regulated delivery of oxygen and nutrients through vascular networks that pervade nearly all tissues in the body. Dysregulation of these vascular networks is implicated in many common human diseases such as hypertension, coronary artery disease, diabetes and cancer. Therefore, engineers have sought to create vascular networks within engineered tissues for applications such as regenerative therapies, human disease modelling and pharmacological testing. Yet engineering vascular networks has historically remained difficult, owing to both incomplete understanding of vascular structure and technical limitations for vascular fabrication. This Review highlights the materials advances that have enabled transformative progress in vascular engineering by ushering in new tools for both visualizing and building vasculature. New methods such as bioprinting, organoids and microfluidic systems are discussed, which have enabled the fabrication of 3D vascular topologies at a cellular scale with lumen perfusion. These approaches to vascular engineering are categorized into technology-driven and nature-driven approaches. Finally, the remaining knowledge gaps, emerging frontiers and opportunities for this field are highlighted, including the steps required to replicate the multiscale complexity of vascular networks found in nature.

Light manipulation for fabrication of hydrogels and their biological applications

The development of biocompatible materials with desired functions is essential for tissue engineering and biomedical applications. Hydrogels prepared from these materials represent an important class of soft matter for mimicking extracellular environments. In particular, dynamic hydrogels with responsiveness to environments are quite appealing because they can match the dynamics of biological processes. Among the external stimuli that can trigger responsive hydrogels, light is considered as a clean stimulus with high spatiotemporal resolution, complete bioorthogonality, and fine tunability regarding its wavelength and intensity. Therefore, photoresponsiveness has been broadly encoded in hydrogels for biological applications. Moreover, light can be used to initiate gelation during the fabrication of biocompatible hydrogels. Here, we present a critical review of light manipulation tools for the fabrication of hydrogels and for the regulation of physicochemical properties and functions of photoresponsive hydrogels. The materials, photo-initiated chemical reactions, and new prospects for light-induced gelation are introduced in the former part, while mechanisms to render hydrogels photoresponsive and their biological applications are discussed in the latter part. Subsequently, the challenges and potential research directions in this area are discussed, followed by a brief conclusion. STATEMENT OF SIGNIFICANCE: Hydrogels play a vital role in the field of biomaterials owing to their water retention ability and biocompatibility. However, static hydrogels cannot meet the dynamic requirements of the biomedical field. As a stimulus with high spatiotemporal resolution, light is an ideal tool for both the fabrication and operation of hydrogels. In this review, light-induced hydrogelation and photoresponsive hydrogels are discussed in detail, and new prospects and emerging biological applications are described. To inspire more research studies in this promising area, the challenges and possible solutions are also presented.

The Topical Hemostatic Materials for Coagulopathy

Medical sciences have witnessed significant progresses in hemostatic materials which have saved lives by supporting natural hemostatic ability. However, for the treatment of coagulopathy, where natural hemostatic ability is dysfunctional,...

Advancements in 3D Cell Culture Systems for Personalizing Anti-Cancer Therapies

Over 90% of potential anti-cancer drug candidates results in translational failures in clinical trials. The main reason for this failure can be attributed to the non-accurate pre-clinical models that are being currently used for drug development and in personalised therapies. To ensure that the assessment of drug efficacy and their mechanism of action have clinical translatability, the complexity of the tumor microenvironment needs to be properly modelled. 3D culture models are emerging as a powerful research tool that recapitulates in vivo characteristics. Technological advancements in this field show promising application in improving drug discovery, pre-clinical validation, and precision medicine. In this review, we discuss the significance of the tumor microenvironment and its impact on therapy success, the current developments of 3D culture, and the opportunities that advancements that in vitro technologies can provide to improve cancer therapeutics.

Polysaccharide-Based Hydrogels for Microencapsulation of Stem Cells in Regenerative Medicine

Stem cell-based therapy appears as a promising strategy to induce regeneration of damaged and diseased tissues. However, low survival, poor engraftment and a lack of site-specificity are major drawbacks. Polysaccharide hydrogels can address these issues and offer several advantages as cell delivery vehicles. They have become very popular due to their unique properties such as high-water content, biocompatibility, biodegradability and flexibility. Polysaccharide polymers can be physically or chemically crosslinked to construct biomimetic hydrogels. Their resemblance to living tissues mimics the native three-dimensional extracellular matrix and supports stem cell survival, proliferation and differentiation. Given the intricate nature of communication between hydrogels and stem cells, understanding their interaction is crucial. Cells are incorporated with polysaccharide hydrogels using various microencapsulation techniques, allowing generation of more relevant models and further enhancement of stem cell therapies. This paper provides a comprehensive review of human stem cells and polysaccharide hydrogels most used in regenerative medicine. The recent and advanced stem cell microencapsulation techniques, which include extrusion, emulsion, lithography, microfluidics, superhydrophobic surfaces and bioprinting, are described. This review also discusses current progress in clinical translation of stem-cell encapsulated polysaccharide hydrogels for cell delivery and disease modeling (drug testing and discovery) with focuses on musculoskeletal, nervous, cardiac and cancerous tissues.

Chemically Modified Biopolymers for the Formation of Biomedical Hydrogels

Biopolymers are natural polymers sourced from plants and animals, which include a variety of polysaccharides and polypeptides. The inclusion of biopolymers into biomedical hydrogels is of great interest because of their inherent biochemical and biophysical properties, such as cellular adhesion, degradation, and viscoelasticity. The objective of this Review is to provide a detailed overview of the design and development of biopolymer hydrogels for biomedical applications, with an emphasis on biopolymer chemical modifications and cross-linking methods. First, the fundamentals of biopolymers and chemical conjugation methods to introduce cross-linking groups are described. Cross-linking methods to form biopolymer networks are then discussed in detail, including (i) covalent cross-linking (e.g., free radical chain polymerization, click cross-linking, cross-linking due to oxidation of phenolic groups), (ii) dynamic covalent cross-linking (e.g., Schiff base formation, disulfide formation, reversible Diels-Alder reactions), and (iii) physical cross-linking (e.g., guest-host interactions, hydrogen bonding, metal-ligand coordination, grafted biopolymers). Finally, recent advances in the use of chemically modified biopolymer hydrogels for the biofabrication of tissue scaffolds, therapeutic delivery, tissue adhesives and sealants, as well as the formation of interpenetrating network biopolymer hydrogels, are highlighted.

Pastable, Adhesive, Injectable, Nanofibrous, and Tunable (PAINT) Biphasic Hybrid Matrices as Versatile Therapeutic Carriers

A critical challenge in many pharmaceutical fields is developing versatile adjuvant devices that can reduce the off-target delivery of therapeutic materials to target lesions. Herein, a biphasic hybrid fibrous system that can manipulate the spatial and temporal delivery of various therapeutic agents to target lesions by integrating multiple distinct systems and technologies such as fluffy coaxial electrospun polycaprolactone (PCL)/polystyrene (PS) fibers, cyclohexane-mediated leaching to remove PS layers selectively, amine display on PCL fibers, conjugation of naturally occurring adhesive gallol molecules onto hyaluronic acid (HA-g), and electrostatically complexing the aminated PCL fibers with the gallol-conjugated HA. In the context of "paintable" systems on target lesions, the resulting system is called a PAINT matrix (abbreviated according to the initial letter of its features: pastable, adhesive, injectable, nanofibrous, and tunable). Its viscoelastic property, which was attributed by coalescing aminated PCL fibers with viscous HA-g, enabled it to be noninvasively injected and fit into any cavity in the body with various morphologies, manually pasted on tissue surfaces, and adhered onto moisture-rich surfaces to ensure the secure delivery of therapeutics toward the target lesions. The PAINT matrix efficiently supplied immunomodulatory human neural stem cells (hNSCs) at rat hemisectioned spinal cord injury (SCI) sites and promoted both locomotive and sensory recovery in SCI models, presumably by protecting hNSCs against host immunosurveillance. The PAINT matrix will be broadly utilized for efficiently delivering therapeutics to difficult-to-reach target lesions by direct infusion or conventional biomaterial-mediated approaches due to their locations, wet surfaces, or complicated ambient environments.

Natural Polymeric Scaffolds for Tissue Engineering Applications

Natural polymeric scaffolds can be used for tissue engineering applications such as cell delivery and cell-free supporting of native tissues. This is because of their desirable properties such as; high biocompatibility, tunable mechanical strength and conductivity, large surface area, porous- and extracellular matrix (ECM)-mimicked structures. Specifically, their less toxicity and biocompatibility makes them suitable for several tissue engineering applications. For these reasons, several biopolymeric scaffolds are currently being explored for numerous tissue engineering applications. To date, research on the nature, chemistry, and properties of nanocomposite biopolymers are been reported, while the need for a comprehensive research note on more tissue engineering application of these biopolymers remains. As a result, this present study comprehensively reviews the development of common natural biopolymers as scaffolds for tissue engineering applications such as cartilage tissue engineering, cornea repairs, osteochondral defect repairs, and nerve regeneration. More so, the implications of research findings for further studies are presented, while the impact of research advances on future research and other specific recommendations are added as well.

Hydrogels: A potential platform for induced pluripotent stem cell culture and differentiation

Induced pluripotent stem cells (iPSCs) can be used to generate desired types of cells that belong to the three germ layers (i.e., ectoderm, endoderm and mesoderm). These cells possess great potential in regenerative medicine. Before iPSCs are used in various biomedical applications, the existing xenogeneic culture methods must be improved to meet the technical standards of safety, cost effectiveness, and ease of handling. In addition to commonly used 2D substrates, a culture system that mimics the native cellular environment in tissues will be a good choice when culturing iPS cells and differentiating them into different lineages. Hydrogels are potential candidates that recapitulate the native complex three-dimensional microenvironment. They possess mechanical properties similar to those of many soft tissues. Moreover, hydrogels support iPSC adhesion, proliferation and differentiation to various cell types. They are xeno-free and cost-effective. In addition to other substrates, such as mouse embryonic fibroblast (MEF), Matrigel, and vitronectin, the use of hydrogel-based substrates for iPSC culture and differentiation may help generate large numbers of clinical-grade cells that can be used in potential clinical applications. This review mainly focuses on the use of hydrogels for the culture and differentiation of iPSCs into various cell types and their potential applications in regenerative medicine.

Structurally Dynamic Hydrogels for Biomedical Applications: Pursuing a Fine Balance between Macroscopic Stability and Microscopic Dynamics

Owing to their unique chemical and physical properties, hydrogels are attracting increasing attention in both basic and translational biomedical studies. Although the classical hydrogels with static networks have been widely reported for decades, a growing number of recent studies have shown that structurally dynamic hydrogels can better mimic the dynamics and functions of natural extracellular matrix (ECM) in soft tissues. These synthetic materials with defined compositions can recapitulate key chemical and biophysical properties of living tissues, providing an important means to understanding the mechanisms by which cells sense and remodel their surrounding microenvironments. This review begins with the overall expectation and design principles of dynamic hydrogels. We then highlight recent progress in the fabrication strategies of dynamic hydrogels including both degradation-dependent and degradation-independent approaches, followed by their unique properties and use in biomedical applications such as regenerative medicine, drug delivery, and 3D culture. Finally, challenges and emerging trends in the development and application of dynamic hydrogels are discussed.

A facile, versatile hydrogel bioink for 3D bioprinting benefits long-term subaqueous fidelity, cell viability and proliferation

Both of the long-term fidelity and cell viability of three-dimensional (3D)-bioprinted constructs are essential to precise soft tissue repair. However, the shrinking/swelling behavior of hydrogels brings about inadequate long-term fidelity of constructs, and bioinks containing excessive polymer are detrimental to cell viability. Here, we obtained a facile hydrogel by introducing 1% aldehyde hyaluronic acid (AHA) and 0.375% N-carboxymethyl chitosan (CMC), two polysaccharides with strong water absorption and water retention capacity, into classic gelatin (GEL, 5%)-alginate (ALG, 1%) ink. This GEL-ALG/CMC/AHA bioink possesses weak temperature dependence due to the Schiff base linkage of CMC/AHA and electrostatic interaction of CMC/ALG. We fabricated integrated constructs through traditional printing at room temperature and in vivo simulation printing at 37°C. The printed cell-laden constructs can maintain subaqueous fidelity for 30 days after being reinforced by 3% calcium chloride for only 20 s. Flow cytometry results showed that the cell viability was 91.38 ± 1.55% on day 29, and the cells in the proliferation plateau at this time still maintained their dynamic renewal with a DNA replication rate of 6.06 ± 1.24%. This work provides a convenient and practical bioink option for 3D bioprinting in precise soft tissue repair.

Spatially controlled glycocalyx engineering for growth factor patterning in embryoid bodies

Growth factor (GF) patterning in stem cell spheroids, such as embryoid bodies (EBs), has been sought to guide their differentiation and organization into functional 3D tissue models and organoids. Current approaches relying on exposure of EBs to gradients of GFs suffer from poor molecular transport in the spheroid microenvironment and from high cost of production and low stability of recombinant GFs. We have developed an alternative method for establishing GF gradients in EBs utilizing stem cell surface engineering with membrane-targeting heparan sulfate-glycomimetic co-receptors for GFs. We have capitalized on the ability of amphiphilic lipid-functionalized glycopolymers with affinity for FGF2 to assemble into nanoscale vesicles with tunable dimensions and extracellular matrix penetrance. Upon size-dependent diffusion into EBs, the vesicles fused with the plasma membranes of stem cells, giving rise to concentric gradients of cells with enhanced FGF2-binding. The extracellular matrix-assisted cell surface remodeling process described is the first example of spatially-targeted glycocalyx engineering in multicellular systems to control GF localization. The glycopolymer structure, vesicle dimensions, and remodeling conditions determine the level of FGF2 adhesion and gradient slope. The increased chemical and thermal stability of the synthetic glycomimetics and the tunability of their GF-binding profile, which is defined by their glycosylation and may be extended to other recombinant or endogenous morphogens beyond FGF2, further increase the versatility of this method.

Conformal single cell hydrogel coating with electrically induced tip streaming of an AC cone

Encapsulation of single cells in a thin hydrogel provides a more precise control of stem cell niches and better molecular transport. Despite the recent advances in microfluidic technologies to allow encapsulation of single cells, existing methods rely on special crosslinking agents that are pre-coated on the cell surface and subject to the variation of the cell membrane, which limits their widespread adoption. This work reports a high-throughput single-cell encapsulation method based on the "tip streaming" mode of alternating current (AC) electrospray, with encapsulation efficiencies over 80% after tuned centrifugation. Dripping with multiple cells is curtailed due to gating by the sharp conic meniscus of the tip streaming mode that only allows one cell to be ejected at a time. Moreover, the method can be universally applied to both natural and synthetic hydrogels, as well as various cell types, including human multipotent mesenchymal stromal cells (hMSCs). Encapsulated hMSCs maintain good cell viability over an extended culture period and exhibit robust differentiation potential into osteoblasts and adipocytes. Collectively, electrically induced tip streaming enables high-throughput encapsulation of single cells with high efficiency and universality, which is applicable for various applications in cell therapy, pharmacokinetic studies, and regenerative medicine.

Soft Materials by Design: Unconventional Polymer Networks Give Extreme Properties

Hydrogels are polymer networks infiltrated with water. Many biological hydrogels in animal bodies such as muscles, heart valves, cartilages, and tendons possess extreme mechanical properties including being extremely tough, strong, resilient, adhesive, and fatigue-resistant. These mechanical properties are also critical for hydrogels' diverse applications ranging from drug delivery, tissue engineering, medical implants, wound dressings, and contact lenses to sensors, actuators, electronic devices, optical devices, batteries, water harvesters, and soft robots. Whereas numerous hydrogels have been developed over the last few decades, a set of general principles that can rationally guide the design of hydrogels using different materials and fabrication methods for various applications remain a central need in the field of soft materials. This review is aimed at synergistically reporting: (i) general design principles for hydrogels to achieve extreme mechanical and physical properties, (ii) implementation strategies for the design principles using unconventional polymer networks, and (iii) future directions for the orthogonal design of hydrogels to achieve multiple combined mechanical, physical, chemical, and biological properties. Because these design principles and implementation strategies are based on generic polymer networks, they are also applicable to other soft materials including elastomers and organogels. Overall, the review will not only provide comprehensive and systematic guidelines on the rational design of soft materials, but also provoke interdisciplinary discussions on a fundamental question: why does nature select soft materials with unconventional polymer networks to constitute the major parts of animal bodies?

Evaluation of the Effect of Hyaluronic Acid-Based Biomaterial Enriched With Tenascin-C on the Behavior of the Neural Stem Cells

One of the most important natural extracellular constituents is hyaluronic acid (HA) with the potential to develop a highly organized microenvironment. In the present study, we enriched HA hydrogel with tenascin-C (TN-C) and examined the viability and survival of mouse neural stem cells (NSCs) using different biological assays. Following NSCs isolation and expansion, their phenotype was identified using flow cytometry analysis. Cell survival was measured using MTT assay and DAPI staining after exposure to various concentrations of 50, 100, 200, and 400 nM TN-C. Using acridine orange/ethidium bromide staining, we measured the number of live and necrotic cells after exposure to the combination of HA and TN-C. MTT assay revealed the highest NSCs viability rate in the group exposed to 100 nM TN-C compared to other groups, and a combination of 1% HA + 100 nM TN-C increased the viability of NSCs compared to the HA group after 24 hours. Electron scanning microscopy revealed the higher attachment of these cells to the HA + 100 nM TN-C substrate relative to the HA substrate. Epifluorescence imaging and DAPI staining of loaded cells on HA + 100 nM TN-C substrate significantly increased the number of NSCs per field over 72 hours compared to the HA group (P < 0.05). Live and dead assay revealed that the number of live NSCs significantly increased in the HA + 100 TN-C group compared to HA and control groups. The enrichment of HA substrate with TN-C promoted viability and survival of NSCs and could be applied in neural tissue engineering approaches and regenerative medicine.

The Use of Biologics for Hip Preservation

PURPOSE OF REVIEW

A wide array of nonoperative modalities to treat hip pain are aimed at restoring and maintaining the structural and physiologic characteristics of the joint. The purpose of this review is to describe the current understanding of biologics in hip pathology by providing an evidence-based overview of treatment modalities available for orthopedic surgeons.

RECENT FINDINGS

The use of biologics as a primary treatment or adjunct to traditional management has shown encouraging results for the treatment of hip pain. Studies have demonstrated safety with minimal complications when using platelet rich plasma, hyaluronic acid, or stem cells to treat hip pain caused by osteoarthritis, femoroacetabular impingement syndrome, tendinopathy, or osteonecrosis of the femoral head. Several studies have been able to demonstrate meaningful clinical results that can improve treatment standards for hip pain; however, more work must be performed to better delineate the appropriate protocols, indications, and limitations of each modality. Recent advances have inspired renewed interest in biologics for patients with hip pain. We present a concise review of platelet rich plasma, hyaluronic acid, stem cells, and matrix metalloprotease inhibitors and their applicability to hip preservation surgery.