“Click” chemistry in polymeric scaffolds: Bioactive materials for tissue engineering

The European Polysaccharide Network of Excellence (EPNOE) research roadmap 2040: Advanced strategies for exploiting the vast potential of polysaccharides as renewable bioresources

Polysaccharides are among the most abundant bioresources on earth and consequently need to play a pivotal role when addressing existential scientific challenges like climate change and the shift from fossil-based to sustainable biobased materials. The Research Roadmap 2040 of the European Polysaccharide Network of Excellence (EPNOE) provides an expert's view on how future research and development strategies need to evolve to fully exploit the vast potential of polysaccharides as renewable bioresources. It is addressed to academic researchers, companies, as well as policymakers and covers five strategic areas that are of great importance in the context of polysaccharide related research: (I) Materials & Engineering, (II) Food & Nutrition, (III) Biomedical Applications, (IV) Chemistry, Biology & Physics, and (V) Skills & Education. Each section summarizes the state of research, identifies challenges that are currently faced, project achievements and developments that are expected in the upcoming 20 years, and finally provides outlines on how future research activities need to evolve.

Terminus-Selective Covalent Immobilization of Heparin on a Thermoresponsive Surface Using Click Chemistry for Efficient Binding of Basic Fibroblast Growth Factor

Cell therapy using endothelial cells (ECs) has great potential for the treatment of congenital disorders, such as hemophilia A. Cell sheet technology utilizing a thermoresponsive culture dish is a promising approach to efficiently transplant donor cells. In this study, a new method to prepare terminus-selective heparin-immobilized thermoresponsive culture surfaces is developed to facilitate the preparation of EC sheets. Alkynes are introduced to the reducing terminus of heparin via reductive amination. Cu-catalyzed azide-alkyne cycloaddition (CuAAC) facilitates efficient immobilization of the terminus of heparin on a thermoresponsive surface, resulting in a higher amount of immobilized heparin while preserving its function. Heparin-immobilized thermoresponsive surfaces prepared using CuAAC exhibit good adhesion to human endothelial colony-forming cells (ECFCs). In addition, upon further binding to basic fibroblast growth factor (bFGF) on heparin-immobilized surfaces, increased proliferation of ECFCs on the surface is observed. The confluent ECFC monolayer cultured on bFGF-bound heparin-immobilized thermoresponsive surfaces exhibits relatively high fibronectin accumulation and cell number and detaches at 22 °C while maintaining the sheet-like structure. Because heparin has an affinity for several types of bioactive molecules, the proposed method can be applied to facilitate efficient cultures and sheet formations of various cell types.

Exploring the Versatility of Aerogels: Broad Applications in Biomedical Engineering, Astronautics, Energy Storage, Biosensing, and Current Progress

Aerogels are unique and extremely porous substances with fascinating characteristics such as ultra-low density, extraordinary surface area, and excellent thermal insulation capabilities. Due to their exceptional features, aerogels have attracted significant interest from various fields, including energy, environment, aerospace, and biomedical engineering. This review paper presents an overview of the trailblazing research on aerogels, aiming at their preparation, characterization, and applications. Various methods of aerogel synthesis, such as sol-gel, supercritical drying, are discussed. Additionally, recent progress in the characterization of aerogel structures, including their morphology, porosity, and thermal properties, are extensively reviewed. Finally, aerogel's utilizations in numerous disciplines, for instance, energy storage, thermal insulation, catalysis, environmental remedy, and biomedical applications, are summarized. This review paper provides a comprehensive understanding of aerogels and their prospective uses in diverse fields, highlighting their unique properties for future research and development.

Stimuli-responsive polysaccharide-based smart hydrogels for diabetic wound healing: Design aspects, preparation methods and regulatory perspectives

Diabetes adversely affects wound-healing responses, leading to the development of chronic infected wounds. Such wound microenvironment is characterized by hyperglycaemia, hyperinflammation, hypoxia, variable pH, upregulation of matrix metalloproteinases, oxidative stress, and bacterial colonization. These pathological conditions pose challenges for the effective wound healing. Therefore, there is a paradigm shift in diabetic wound care management wherein abnormal pathological conditions of the wound microenvironment is used as a trigger for controlling the drug release or to improve properties of wound dressings. Hydrogels composed of natural polysaccharides showed tremendous potential as wound dressings as well as stimuli-responsive materials due to their unique properties such as biocompatibility, biodegradability, hydrophilicity, porosity, stimuli-responsiveness etc. Hence, polysaccharide-based hydrogels have emerged as advanced healthcare materials for diabetic wounds. In this review, we presented important aspects for the design of hydrogel-based wound dressings with an emphasis on biocompatibility, biodegradability, entrapment of therapeutic agents, moisturizing ability, swelling, and mechanical properties. Further, various crosslinking methods that enable desirable properties and stimuli responsiveness to the hydrogels have been mentioned. Subsequently, state-of-the-art developments in mono- and multi- stimuli-responsive hydrogels have been presented along with the case studies. Finally regulatory perspectives, challenges for the clinical translation and future prospects have been discussed.

Applications of Bioengineered Polymer in the Field of Nano-Based Drug Delivery

The most favored route of drug administration is oral administration; however, several factors, including poor solubility, low bioavailability, and degradation, in the severe gastrointestinal environment frequently compromise the effectiveness of drugs taken orally. Bioengineered polymers have been developed to overcome these difficulties and enhance the delivery of therapeutic agents. Polymeric nanoparticles, including carbon dots, fullerenes, and quantum dots, have emerged as crucial components in this context. They provide a novel way to deliver various therapeutic materials, including proteins, vaccine antigens, and medications, precisely to the locations where they are supposed to have an effect. The promise of this integrated strategy, which combines nanoparticles with bioengineered polymers, is to address the drawbacks of conventional oral medication delivery such as poor solubility, low bioavailability, and early degradation. In recent years, we have seen substantially increased interest in bioengineered polymers because of their distinctive qualities, such as biocompatibility, biodegradability, and flexible physicochemical characteristics. The different bioengineered polymers, such as chitosan, alginate, and poly(lactic-co-glycolic acid), can shield medications or antigens from degradation in unfavorable conditions and aid in the administration of drugs orally through mucosal delivery with lower cytotoxicity, thus used in targeted drug delivery. Future research in this area should focus on optimizing the physicochemical properties of these polymers to improve their performance as drug delivery carriers.

Pyrene Appendant Triazole-based Chemosensors for Sensing Applications

Over the last two decades, the design and development of fluorescent chemosensors for the targeted detection of Heavy Transition-metal (HTM) ions, anions, and biological analytes, have drawn much interest. Since the introduction of click chemistry in 2001, triazole moieties have become an increasingly prominent theme in chemosensors. Triazoles generated via click reactions are crucial for sensing various ions and biological analytes. Recently, the number of studies in the field of pyrene appendant triazole moieties has risen dramatically, with more sophisticated and reliable triazole-containing chemosensors for various analytes of interest described. This tutorial review provides a general overview of pyrene appendant-triazole-based chemosensors that can detect a variety of metal cations, anions, and neutral analytes by using modular click-derived triazoles.

Cell-Tissue Interaction: The Biomimetic Approach to Design Tissue Engineered Biomaterials

The advancement achieved in Tissue Engineering is based on a careful and in-depth study of cell-tissue interactions. The choice of a specific biomaterial in Tissue Engineering is fundamental, as it represents an interface for adherent cells in the creation of a microenvironment suitable for cell growth and differentiation. The knowledge of the biochemical and biophysical properties of the extracellular matrix is a useful tool for the optimization of polymeric scaffolds. This review aims to analyse the chemical, physical, and biological parameters on which are possible to act in Tissue Engineering for the optimization of polymeric scaffolds and the most recent progress presented in this field, including the novelty in the modification of the scaffolds' bulk and surface from a chemical and physical point of view to improve cell-biomaterial interaction. Moreover, we underline how understanding the impact of scaffolds on cell fate is of paramount importance for the successful advancement of Tissue Engineering. Finally, we conclude by reporting the future perspectives in this field in continuous development.

The Influence of Textile Structure Characteristics on the Performance of Artificial Blood Vessels

Cardiovascular disease is a major threat to human health worldwide, and vascular transplantation surgery is a treatment method for this disease. Often, autologous blood vessels cannot meet the needs of surgery. However, allogeneic blood vessels have limited availability or may cause rejection reactions. Therefore, the development of biocompatible artificial blood vessels is needed to solve the problem of donor shortage. Tubular fabrics prepared by textile structures have flexible compliance, which cannot be matched by other structural blood vessels. Therefore, biomedical artificial blood vessels have been widely studied in recent decades up to the present. This article focuses on reviewing four textile methods used, at present, in the manufacture of artificial blood vessels: knitting, weaving, braiding, and electrospinning. The article mainly introduces the particular effects of different structural characteristics possessed by various textile methods on the production of artificial blood vessels, such as compliance, mechanical properties, and pore size. It was concluded that woven blood vessels possess superior mechanical properties and dimensional stability, while the knitted fabrication method facilitates excellent compliance, elasticity, and porosity of blood vessels. Additionally, the study prominently showcases the ease of rebound and compression of braided tubes, as well as the significant biological benefits of electrospinning. Moreover, moderate porosity and good mechanical strength can be achieved by changing the original structural parameters; increasing the floating warp, enlarging the braiding angle, and reducing the fiber fineness and diameter can achieve greater compliance. Furthermore, physical, chemical, or biological methods can be used to further improve the biocompatibility, antibacterial, anti-inflammatory, and endothelialization of blood vessels, thereby improving their functionality. The aim is to provide some guidance for the further development of artificial blood vessels.

Influence of Isocyanate Structure on Recyclable Shape Memory Poly(thiourethane)

In this study, poly(thiourethane) (PTU) with different structures is synthesized by click chemistry from trimethylolpropane tris(3-mercaptopropionate) (S3) and different diisocyanates (hexamethylene diisocyanate, HDI, isophorone diisocyanate, IPDI and toluene diisocyanate, TDI). Quantitative analysis of the FTIR spectra reveals that the reaction rates between TDI and S3 are the most rapid, resulting from the combined influence of conjugation and spatial site hindrance. Moreover, the homogeneous cross-linked network of the synthesized PTUs facilitates better manageability of the shape memory effect. All three PTUs exhibit excellent shape memory properties (R_r and R_f are over 90%), and an increase in chain rigidity is observed to negatively impact the shape recovery rate and fix rate. Moreover, all three PTUs exhibit satisfactory reprocessability performance, and an increase in chain rigidity is accompanied by a greater decrease in shape memory and a smaller decrease in mechanical performance for recycled PTUs. Contact angle (<90°) and in vitro degradation results (13%/month for HDI-based PTU, 7.5%/month for IPDI-based PTU, and 8.5%/month for TDI-based PTU) indicate that PTUs can be used as long-term or medium-term biodegradable materials. The synthesized PTUs have a high potential for applications in smart response scenarios requiring specific glass transition temperatures, such as artificial muscles, soft robots, and sensors.

An injectable all-small-molecule dynamic metallogel for suppressing sepsis

All-small-molecule dynamic hydrogels have shown great promise in cell culture, tissue engineering, and controlled drug release. The further development of more kinds of all-small-molecule dynamic hydrogels is severely hindered by the lack of enough commensurate building blocks from nature and on the market. Inspired by the widely developed metal-organic framework structures, herein we report a facile fabrication of metallogels by direct gelation of small molecular compounds including aminoglycosides (AGs), 2,2'-bipyridine-4,4'-dicarboxaldehyde (BIPY), and metal ions via coordination interactions and Schiff base reactions. These prepared metallogels exhibited good biodegradability and biosafety, excellent conductivity, tunable mechanical properties and potent antibacterial activities both in vitro and in vivo. This study provides a new strategy for expanding the scope of all-small-molecule dynamic metallogels for various biomedical applications.

Current Strategies for Engineered Vascular Grafts and Vascularized Tissue Engineering

Blood vessels not only transport oxygen and nutrients to each organ, but also play an important role in the regulation of tissue regeneration. Impaired or occluded vessels can result in ischemia, tissue necrosis, or even life-threatening events. Bioengineered vascular grafts have become a promising alternative treatment for damaged or occlusive vessels. Large-scale tubular grafts, which can match arteries, arterioles, and venules, as well as meso- and microscale vasculature to alleviate ischemia or prevascularized engineered tissues, have been developed. In this review, materials and techniques for engineering tubular scaffolds and vasculature at all levels are discussed. Examples of vascularized tissue engineering in bone, peripheral nerves, and the heart are also provided. Finally, the current challenges are discussed and the perspectives on future developments in biofunctional engineered vessels are delineated.

Click postsynthesis of microporous organic network@silica composites for reversed-phase/hydrophilic interaction mixed-mode chromatography

Recently, the good physical and chemical properties, well-defined pore architectures, and designable topologies have made microporous organic networks (MONs) excellent potential candidates in high-performance liquid chromatography (HPLC). However, their superior hydrophobic structures restrict their application in the reversed-phase mode. To solve this obstacle and to expand the application of MONs in HPLC, we realized the thiol-yne "click" postsynthesis of a novel hydrophilic MON-2COOH@SiO₂-MER (MER denotes mercaptosuccinic acid) microsphere for reversed-phase/hydrophilic interaction mixed-mode chromatography. SiO₂ was initially decorated with MON-2COOH using 2,5-dibromoterephthalic acid and tetrakis(4-ethynylphenyl)methane as monomers, and MER was then grafted via thiol-yne click reaction to yield MON-2COOH@SiO₂-MER microspheres (5 μm) with a pore size of ~1.3 nm. The -COOH groups in 2,5-dibromoterephthalic acid and the post-modified MER molecules considerably improved the hydrophilicity of pristine MON and enhanced the hydrophilic interactions between the stationary phase and analytes. The retention mechanisms of the MON-2COOH@SiO₂-MER packed column were fully discussed with diverse hydrophobic and hydrophilic probes. Benefiting from the numerous -COOH recognition sites and benzene rings within MON-2COOH@SiO₂-MER, the packed column exhibited good resolution for the separation of sulfonamides, deoxynucleosides, alkaloids, and endocrine-disrupting chemicals. A column efficiency of 27,556 plates per meter was obtained for the separation of gastrodin. The separation performance of the MON-2COOH@SiO₂-MER packed column was also demonstrated by comparing with those of MON-2COOH@SiO₂, commercial C18, ZIC-HILIC, and bare SiO₂ columns. This work highlights the good potential of the thiol-yne click postsynthesis strategy to construct MON-based stationary phases for mixed-mode chromatography.

Charge-conversional click polyprodrug nanomedicine for targeted and synergistic cancer therapy

Polyprodrug nanomedicines hold great potential for combating tumors. However, the functionalization of polyprodrug nanomedicines to improve therapeutic efficacy is restricted by conventional polymerization methods. Herein, we fabricated a charge-conversional click polyprodrug nanomedicine system by metal-free azide-alkyne cycloaddition click polymerization (AACCP) for targeted and synergistic cancer therapy. Specifically, Pt(IV) prodrug-backboned diazide monomer, DMC prodrug-pendent diazide monomer, dialkyne-terminated PEG monomer and azide-modified folate were click polymerized to obtain the target polyprodrug (P1). P1 could self-assemble into nano-micelles (1-NM), where PEG was the hydrophilic shell with folate on the surface, Pt(IV) and DMC prodrugs as the hydrophobic core. Taking advantage of PEGylation and folate-mediated tumor cell targeting, 1-NM achieved prolonged blood circulation time and high tumor accumulation efficiency. Tumor acidic microenvironment-responsive cleavage and cascade activation of pendant DMC prodrug induced surface charge conversion of 1-NM from negative to positive, which promoted tumor penetration and cellular internalization of the remaining 1-NM. After internalization into tumor cells, the reduction-responsive activation of Pt(IV) prodrug to Pt(II) further showed synergetic effect with DMC for enhanced apoptosis. This first designed charge-conversional click polyprodrug nanomedicine exhibited targeted and synergistic efficacy to suppress tumor proliferation in living mice bearing human ovarian tumor model.

Research Progress in Enzymatically Cross-Linked Hydrogels as Injectable Systems for Bioprinting and Tissue Engineering

Hydrogels have been developed for different biomedical applications such as in vitro culture platforms, drug delivery, bioprinting and tissue engineering. Enzymatic cross-linking has many advantages for its ability to form gels in situ while being injected into tissue, which facilitates minimally invasive surgery and adaptation to the shape of the defect. It is a highly biocompatible form of cross-linking, which permits the harmless encapsulation of cytokines and cells in contrast to chemically or photochemically induced cross-linking processes. The enzymatic cross-linking of synthetic and biogenic polymers also opens up their application as bioinks for engineering tissue and tumor models. This review first provides a general overview of the different cross-linking mechanisms, followed by a detailed survey of the enzymatic cross-linking mechanism applied to both natural and synthetic hydrogels. A detailed analysis of their specifications for bioprinting and tissue engineering applications is also included.

Dual-responsive bioconjugates bearing a bifunctional adaptor for robust cytosolic peptide delivery

Peptide drugs have been successfully used for the treatment of various diseases. However, it is still challenging to develop therapeutic peptides working on intracellular targets due to their poor membrane permeability. Here, we proposed a type of dual-responsive bioconjugates bearing a heterobifunctional adaptor containing both aldehyde and catechol moieties for efficient cytosolic peptide delivery. Hydrazine-terminated cargo peptides were tagged to a boronated dendrimer with the help of the adaptor via dynamic acylhydrazone and catechol‑boronate linkages. The bioconjugates efficiently delivered peptides with distinct physicochemical properties into various cells, and could release the cargo peptides triggered by intracellular reactive oxygen species and endolysosomal acidity, restoring the biofunctions of delivered peptides. In addition, the designed complexes efficiently delivered a pro-apoptotic peptide into osteosarcoma cancer cells and successfully inhibited the tumor growth both in vitro and in vivo. This study provides a universal and efficient platform for cytosolic therapeutic peptide delivery to intracellular targets for treating various diseases.

Mutual leveraging of proximity effects and click chemistry in chemical biology

Nature has the remarkable ability to realize reactions under physiological conditions that normally would require high temperature and other forcing conditions. In doing so, often proximity effects such as simultaneous binding of two reactants in the same pocket and/or strategic positioning of catalytic functional groups are used as ways to achieve otherwise kinetically challenging reactions. Though true biomimicry is challenging, there have been many beautiful examples of how to leverage proximity effects in realizing reactions that otherwise would not readily happen under near-physiological conditions. Along this line, click chemistry is often used to endow proximity effects, and proximity effects are also used to further leverage the facile and bioorthogonal nature of click chemistry. This review brings otherwise seemingly unrelated topics in chemical biology and drug discovery under one unifying theme of mutual leveraging of proximity effects and click chemistry and aims to critically analyze the biomimicry use of such leveraging effects as powerful approaches in chemical biology and drug discovery. We hope that this review demonstrates the power of employing mutual leveraging proximity effects and click chemistry and inspires the development of new strategies that will address unmet needs in chemistry and biology.

PEGylated and functionalized polylactide-based nanocapsules: An overview

Polymeric nanocapsules (NC) are versatile mixed vesicular nanocarriers, generally containing a lipid core with a polymeric wall. They have been first developed over four decades ago with outstanding applicability in the cosmetic and pharmaceutical fields. Biodegradable polyesters are frequently used in nanocapsule preparation and among them, polylactic acid (PLA) derivatives and copolymers, such as PLGA and amphiphilic block copolymers, are widely used and considered safe for different administration routes. PLA functionalization strategies have been developed to obtain more versatile polymers and to allow the conjugation with bioactive ligands for cell-targeted NC. This review intends to provide steps in the evolution of NC since its first report and the recent literature on PLA-based NC applications. PLA-based polymer synthesis and surface modifications are included, as well as the use of NC as a novel tool for combined treatment, diagnostics, and imaging in one delivery system. Furthermore, the use of NC to carry therapeutic and/or imaging agents for different diseases, mainly cancer, inflammation, and infections is presented and reviewed. Constraints that impair translation to the clinic are discussed to provide safe and reproducible PLA-based nanocapsules on the market. We reviewed the entire period in the literature where the term "nanocapsules" appears for the first time until the present day, selecting original scientific publications and the most relevant patent literature related to PLA-based NC. We presented to readers a historical overview of these Sui generis nanostructures.

A Dual-Crosslinked Hydrogel Based on Gelatin Methacryloyl and Sulfhydrylated Chitosan for Promoting Wound Healing

The skin is the largest organ of the human body. Skin injuries, especially full-thickness injuries, are a major treatment challenge in clinical practice. Therefore, wound dressing materials with therapeutic effects have great practical significance in healthcare. This study used photocrosslinkable gelatin methacryloyl (GelMA) and sulfhydrylated chitosan (CS-SH) to design a double-crosslinked hydrogel for wound dressing. When crosslinked together, the resulting hydrogels showed a highly porous inner structure, and enhanced mechanical properties and moisture retention capacity. The compression modulus of the GelMA/CS-SH hydrogel (GCH) reached up to about 40 kPa and was much higher than that of pure GelMA hydrogel, and the compression modulus was increased with the amount of CS-SH. In vitro study showed no cytotoxicity of obtained hydrogels. Interestingly, a higher concentration of CS-SH slightly promoted the proliferation of cells. Moreover, the double-crosslinked hydrogel exhibited antibacterial properties because of the presence of chitosan. In vivo study based on rats showed that full-thickness skin defects healed on the 15th day. Histological results indicate that the hydrogel accelerated the repair of hair follicles and encouraged the orderly growth of collagen fibers in the wound. Furthermore, better blood vessel formation and a higher expression of VEGFR were observed in the hydrogel group when compared with the untreated control group. Based on our findings, GCH could be a promising candidate for full-thickness wound dressing.

A combination of surface-initiated atom transfer radical polymerization and photo-initiated "thiol-ene" click chemistry: Fabrication of functionalized macroporous adsorption resins for enrichment of glycopeptides

A hydrophilic adsorbent (Cys@poly(AMA)@MAR) was successfully prepared for the enrichment of N-glycopeptides via surface-initiated atom transfer radical polymerization (SI-ATRP) and photo-initiated "thiol-ene" reaction using monodisperse macroporous adsorbent resin (MAR) as adsorption matrix. Due to the presence of electron-deficient acrylic groups and electron-rich vinyl groups in allyl methacrylate (AMA), both of them can participate in free radical reaction. Therefore, the polymerization time of SI-ATRP was optimized. The resulting poly(AMA)@MAR was modified with l-cysteine (L-Cys) via photo-initiated "thiol-ene" reaction, and the amount of vinyl retained was determined by measuring the adsorption of Cu²⁺. The Cys@poly(AMA)@MAR pendant brushes with high density of amine and carboxyl groups could capture N-glycopeptides from IgG digest and human serum digest by hydrophilic interaction. The 22 N-glycopeptides were identified from IgG digest and the limit of detection reached 10 fmol. The 319 N-glycosylation sites and 583 N-glycopeptides were identified from 2 μL human serum digest and mapped to 147 glycoproteins. It demonstrates great potential and commercialization prospects for the enrichment of N-glycopeptides.

Hyaluronic acid based next generation bioink for 3D bioprinting of human stem cell derived corneal stromal model with innervation

Corneal transplantation remains gold standard for the treatment of severe cornea diseases, however, scarcity of donor cornea is a serious bottleneck. 3D bioprinting holds tremendous potential for cornea tissue engineering (TE). One of the key technological challenges is to design bioink compositions with ideal printability and cytocompatibility. Photo-crosslinking and ionic crosslinking are often used for the stabilization of 3D bioprinted structures, which can possess limitations on biological functionality of the printed cells. Here, we developed a hyaluronic acid-based dopamine containing bioink using hydrazone crosslinking chemistry for the 3D bioprinting of corneal equivalents. First, the shear thinning property, viscosity, and mechanical stability of the bioink were optimized before extrusion-based 3D bioprinting for the shape fidelity and self-healing property characterizations. Subsequently, human adipose stem cells (hASCs) and hASC-derived corneal stromal keratocytes were used for bioprinting corneal stroma structures and their cell viability, proliferation, microstructure and expression of key proteins (lumican, vimentin, connexin 43,α-smooth muscle actin) were evaluated. Moreover, 3D bioprinted stromal structures were implanted intoex vivoporcine cornea to explore tissue integration. Finally, human pluripotent stem cell derived neurons (hPSC-neurons), were 3D bioprinted to the periphery of the corneal structures to analyze innervation. The bioink showed excellent shear thinning property, viscosity, printability, shape fidelity and self-healing properties with high cytocompatibility. Cells in the printed structures displayed good tissue formation and 3D bioprinted cornea structures demonstrated excellentex vivointegration to host tissue as well asin vitroinnervation. The developed bioink and the printed cornea stromal equivalents hold great potential for cornea TE applications.

Multifunctional Scaffolds Based on Emulsion and Coaxial Electrospinning Incorporation of Hydroxyapatite for Bone Tissue Regeneration

Tissue engineering is nowadays a powerful tool to restore damaged tissues and recover their normal functionality. Advantages over other current methods are well established, although a continuous evolution is still necessary to improve the final performance and the range of applications. Trends are nowadays focused on the development of multifunctional scaffolds with hierarchical structures and the capability to render a sustained delivery of bioactive molecules under an appropriate stimulus. Nanocomposites incorporating hydroxyapatite nanoparticles (HAp NPs) have a predominant role in bone tissue regeneration due to their high capacity to enhance osteoinduction, osteoconduction, and osteointegration, as well as their encapsulation efficiency and protection capability of bioactive agents. Selection of appropriated polymeric matrices is fundamental and consequently great efforts have been invested to increase the range of properties of available materials through copolymerization, blending, or combining structures constituted by different materials. Scaffolds can be obtained from different processes that differ in characteristics, such as texture or porosity. Probably, electrospinning has the greater relevance, since the obtained nanofiber membranes have a great similarity with the extracellular matrix and, in addition, they can easily incorporate functional and bioactive compounds. Coaxial and emulsion electrospinning processes appear ideal to generate complex systems able to incorporate highly different agents. The present review is mainly focused on the recent works performed with Hap-loaded scaffolds having at least one structural layer composed of core/shell nanofibers.

Photocurable Thiol-yne Alginate Hydrogels for Regenerative Medicine Purposes

Every year millions of people worldwide undergo surgical interventions, with the occurrence of mild or severe post-treatment consequences meaning that rehabilitation plays a key role in modern medicine. Considering the cases of burns and plastic surgery, the pressing need for new materials that can be used for wound patches or body fillers and are able to sustain tissue regeneration and promote cell adhesion and proliferation is clear. The challenges facing next-generation implant materials also include the need for improved structural properties for cellular organization and morphogenic guidance together with optimal mechanical, rheological, and topographical behavior. Herein, we propose for the first time a sodium alginate hydrogel obtained by a thiol-yne reaction, easily synthesized using carbodiimide chemistry in a two-step reaction. The hydrogels were formed in all cases within a few minutes of light irradiation, showing good self-standing properties under solicitation. The mechanical, rheological, topographical, and swelling properties of the gels were also tested and reported. Lastly, no cytotoxicity was detected among the hydrogels. Soluble extracts in culture media allowed cell proliferation, and no differences between samples were detected in terms of metabolic activity and DNA content. These results suggest the potential use of these cytocompatible hydrogels in tissue engineering and regenerative medicine.

M, Zarrintaj P, Formela K, Saeb MR, Bencherif SA. Clickable Polysaccharides for Biomedical Applications: A Comprehensive Review

Recent advances in materials science and engineering highlight the importance of designing sophisticated biomaterials with well-defined architectures and tunable properties for emerging biomedical applications. Click chemistry, a powerful method allowing specific and controllable bioorthogonal reactions, has revolutionized our ability to make complex molecular structures with a high level of specificity, selectivity, and yield under mild conditions. These features combined with minimal byproduct formation have enabled the design of a wide range of macromolecular architectures from quick and versatile click reactions. Furthermore, copper-free click chemistry has resulted in a change of paradigm, allowing researchers to perform highly selective chemical reactions in biological environments to further understand the structure and function of cells. In living systems, introducing clickable groups into biomolecules such as polysaccharides (PSA) has been explored as a general approach to conduct medicinal chemistry and potentially help solve healthcare needs. De novo biosynthetic pathways for chemical synthesis have also been exploited and optimized to perform PSA-based bioconjugation inside living cells without interfering with their native processes or functions. This strategy obviates the need for laborious and costly chemical reactions which normally require extensive and time-consuming purification steps. Using these approaches, various PSA-based macromolecules have been manufactured as building blocks for the design of novel biomaterials. Clickable PSA provides a powerful and versatile toolbox for biomaterials scientists and will increasingly play a crucial role in the biomedical field. Specifically, bioclick reactions with PSA have been leveraged for the design of advanced drug delivery systems and minimally invasive injectable hydrogels. In this review article, we have outlined the key aspects and breadth of PSA-derived bioclick reactions as a powerful and versatile toolbox to design advanced polymeric biomaterials for biomedical applications such as molecular imaging, drug delivery, and tissue engineering. Additionally, we have also discussed the past achievements, present developments, and recent trends of clickable PSA-based biomaterials such as 3D printing, as well as their challenges, clinical translatability, and future perspectives.

Biomaterials for Tissue Engineering Applications and Current Updates in the Field: A Comprehensive Review

Tissue engineering has emerged as an interesting field nowadays; it focuses on accelerating the auto-healing mechanism of tissues rather than organ transplantation. It involves implanting an In Vitro cultured initiative tissue or a scaffold loaded with tissue regenerating ingredients at the damaged area. Both techniques are based on the use of biodegradable, biocompatible polymers as scaffolding materials which are either derived from natural (e.g. alginates, celluloses, and zein) or synthetic sources (e.g. PLGA, PCL, and PLA). This review discusses in detail the recent applications of different biomaterials in tissue engineering highlighting the targeted tissues besides the in vitro and in vivo key findings. As well, smart biomaterials (e.g. chitosan) are fascinating candidates in the field as they are capable of elucidating a chemical or physical transformation as response to external stimuli (e.g. temperature, pH, magnetic or electric fields). Recent trends in tissue engineering are summarized in this review highlighting the use of stem cells, 3D printing techniques, and the most recent 4D printing approach which relies on the use of smart biomaterials to produce a dynamic scaffold resembling the natural tissue. Furthermore, the application of advanced tissue engineering techniques provides hope for the researchers to recognize COVID-19/host interaction, also, it presents a promising solution to rejuvenate the destroyed lung tissues.

Hydrolytically Degradable PEG-Based Inverse Electron Demand Diels-Alder Click Hydrogels

Hydrogels cross-linked by inverse electron demand Diels–Alder (iEDDA) click chemistry are increasingly used in biomedical applications. With a few exceptions in naturally derived and chemically modified macromers, iEDDA click hydrogels exhibit long-term hydrolytic stability, and no synthetic iEDDA click hydrogels can undergo accelerated and tunable hydrolytic degradation. We have previously reported a novel method for synthesizing norbornene (NB)-functionalized multiarm poly(ethylene glycol) (PEG), where carbic anhydride (CA) was used to replace 5-norbornene-2-carboxylic acid. The new PEGNB_CA-based thiol-norbornene hydrogels exhibited unexpected fast yet highly tunable hydrolytic degradation. In this contribution, we leveraged the new PEGNB_CA macromer for forming iEDDA click hydrogels with [methyl]tetrazine ([m]Tz)-modified macromers, leading to the first group of synthetic iEDDA click hydrogels with highly tunable hydrolytic degradation kinetics. We further exploited Tz and mTz dual conjugation to achieve tunable hydrolytic degradation with an in vitro degradation time ranging from 2 weeks to 3 months. Finally, we demonstrated the excellent in vitro cytocompatibility and in vivo biocompatibility of the new injectable PEGNB_CA-based iEDDA click cross-linked hydrogels.

Tailoring Cu2+-loaded electrospun membranes with antibacterial ability for guided bone regeneration

Copper (Cu)-loaded electrospun membranes were tailored for guided bone regeneration (GBR), targeting the stimulation of innate cells active in bone growth and the prevention of bacterial infections. Functional GBR membranes were produced via an electrospinning set-up using a silk-based solution associated with polyethylene oxide (Silk/PEO - control). Experimental groups were loaded with copper oxide using varying weight percentages (0.05 % to 1 % of CuO). The morphological, structural, chemical, and mechanical properties of membranes were evaluated. Direct and indirect in vitro cytocompatibility experiments were performed with primary human bone mesenchymal stem cells and primary human umbilical vein endothelial cells. The antibacterial potential of membranes was tested with Staphylococcus aureus and Fusobacterium nucleatum biofilm. CuO was successfully incorporated into membranes as clusters without compromising their mechanical properties for clinical applicability. Increased Cu concentrations generated membranes with thinner nanofibers, greater pore areas, and stronger antimicrobial effect (p < 0.01). Cu²⁺ ion was released from the nanofiber membranes during 1 week, showing higher release in acidic conditions. CuO 0.1 % and CuO 0.05 % membranes were able to support and stimulate cell adhesion and proliferation (p < 0.05), and favor angiogenic responses of vascular cells. In addition, detailed quantitative and qualitative analysis determined that amount of the attached biofilm was reduced on the tailored functional Cu²⁺-loaded GBR membrane. Importantly, these qualities represent a valuable strategy to improve the bone regeneration process and diminish the risk of bacterial infections.

Clickable Biomaterials for Modulating Neuroinflammation

Crosstalk between the nervous and immune systems in the context of trauma or disease can lead to a state of neuroinflammation or excessive recruitment and activation of peripheral and central immune cells. Neuroinflammation is an underlying and contributing factor to myriad neuropathologies including neurodegenerative diseases like Alzheimer’s disease and Parkinson’s disease; autoimmune diseases like multiple sclerosis; peripheral and central nervous system infections; and ischemic and traumatic neural injuries. Therapeutic modulation of immune cell function is an emerging strategy to quell neuroinflammation and promote tissue homeostasis and/or repair. One such branch of ‘immunomodulation’ leverages the versatility of biomaterials to regulate immune cell phenotypes through direct cell-material interactions or targeted release of therapeutic payloads. In this regard, a growing trend in biomaterial science is the functionalization of materials using chemistries that do not interfere with biological processes, so-called ‘click’ or bioorthogonal reactions. Bioorthogonal chemistries such as Michael-type additions, thiol-ene reactions, and Diels-Alder reactions are highly specific and can be used in the presence of live cells for material crosslinking, decoration, protein or cell targeting, and spatiotemporal modification. Hence, click-based biomaterials can be highly bioactive and instruct a variety of cellular functions, even within the context of neuroinflammation. This manuscript will review recent advances in the application of click-based biomaterials for treating neuroinflammation and promoting neural tissue repair.

Scaffold Pore Curvature Influences ΜSC Fate through Differential Cellular Organization and YAP/TAZ Activity

Tissue engineering aims to repair, restore, and/or replace tissues in the human body as an alternative to grafts and prostheses. Biomaterial scaffolds can be utilized to provide a three-dimensional microenvironment to facilitate tissue regeneration. Previously, we reported that scaffold pore size influences vascularization and extracellular matrix composition both in vivo and in vitro, to ultimately influence tissue phenotype for regenerating cranial suture and bone tissues, which have markedly different tissue properties despite similar multipotent stem cell populations. To rationally design biomaterials for specific cell and tissue fate specification, it is critical to understand the molecular processes governed by cell-biomaterial interactions, which guide cell fate specification. Building on our previous work, in this report we investigated the hypothesis that scaffold pore curvature, the direct consequence of pore size, modulates the differentiation trajectory of mesenchymal stem cells (MSCs) through alterations in the cytoskeleton. First, we demonstrated that sufficiently small pores facilitate cell clustering in subcutaneous explants cultured in vivo, which we previously reported to demonstrate stem tissue phenotype both in vivo and in vitro. Based on this observation, we cultured cell-scaffold constructs in vitro to assess early time point interactions between cells and the matrix as a function of pore size. We demonstrate that principle curvature directly influences nuclear aspect and cell aggregation in vitro. Scaffold pores with a sufficiently low degree of principle curvature enables cell differentiation; pharmacologic inhibition of actin cytoskeleton polymerization in these scaffolds decreased differentiation, indicating a critical role of the cytoskeleton in transducing cues from the scaffold pore microenvironment to the cell nucleus. We fabricated a macropore model, which allows for three-dimensional confocal imaging and demonstrates that a higher principle curvature facilitates cell aggregation and the formation of a potentially protective niche within scaffold macropores which prevents MSC differentiation and retains their stemness. Sufficiently high principle curvature upregulates yes-associated protein (YAP) phosphorylation while decreased principle curvature downregulates YAP phosphorylation and increases YAP nuclear translocation with subsequent transcriptional activation towards an osteogenic differentiation fate. Finally, we demonstrate that the inhibition of the YAP/TAZ pathway causes a defect in differentiation, while YAP/TAZ activation causes premature differentiation in a curvature-dependent way when modulated by verteporfin (VP) and 1-oleyl-lysophosphatidic acid (LPA), respectively, confirming the critical role of biomaterials-mediated YAP/TAZ signaling in cell differentiation and fate specification. Our data support that the principle curvature of scaffold macropores is a critical design criterion which guides the differentiation trajectory of mesenchymal stem cells’ scaffolds. Biomaterial-mediated regulation of YAP/TAZ may significantly contribute to influencing the regenerative outcomes of biomaterials-based tissue engineering strategies through their specific pore design.

Crosslinkers for polysaccharides and proteins: Synthesis conditions, mechanisms, and crosslinking efficiency, a review

Polysaccharides and proteins are important macromolecules for developing hydrogels devoted to biomedical applications. Chemical hydrogels offer chemical, mechanical, and dimensional stability than physical hydrogels due to the chemical bonds among the chains mediated by crosslinkers. There are many crosslinkers to synthesize polysaccharides and proteins based on hydrogels. In this review, we revisited the crosslinking reaction mechanisms between synthetic or natural crosslinkers and polysaccharides or proteins. The selected synthetic crosslinkers were glutaraldehyde, carbodiimide, boric acid, sodium trimetaphosphate, N,N'-methylene bisacrylamide, and polycarboxylic acid, whereas the selected natural crosslinkers included transglutaminase, tyrosinase, horseradish peroxidase, laccase, sortase A, genipin, vanillin, tannic acid, and phytic acid. No less important are the reactions involving click chemistry and the macromolecular crosslinkers for polysaccharides and proteins. Literature examples of polysaccharides or proteins crosslinked by the different strategies were presented along with the corresponding highlights. The general mechanism involved in chemical crosslinking mediated by gamma and UV radiation was discussed, with particular attention to materials commonly used in digital light processing. The evaluation of crosslinking efficiency by gravimetric measurements, rheology, and spectroscopic techniques was presented. Finally, we presented the challenges and opportunities to create safe chemical hydrogels for biomedical applications.

Scaffolds the backbone of tissue engineering: Advancements in use of polyhydroxyalkanoates (PHA)

Our body is built to heal from inside out naturally but wide-ranging medical conditions necessitate the need for artificial assistance, and therefore, something that can assist the body to heal wounds and damaged tissues quickly and efficiently is of utmost importance. Tissue engineering technology helps to regenerate new tissue to replace the diseased or injured one. The technology uses biodegradable porous three-dimensional scaffolds for mimicking the structure and functions of the natural extracellular matrix. The material and design of scaffolds are critical areas of biomaterial research. Biomaterial-based three-dimensional structures have been the most promising material to serve as scaffolds for seeding cells, both in vivo and in vitro. One such material is polyhydroxyalkanoates (PHAs) which are thermoplastic biopolyesters that are highly suitable for this purpose due to their enhanced biocompatibility, biodegradability, thermo-processability, diverse mechanical properties, non-toxicity and natural origin. Moreover, they have tremendous possibilities of customization through biological physical and chemical modification as well as blending with other materials. They are being used for several tissue engineering applications such as bone graft substitute, cardiovascular patches, stents, for nerve repair and in implantology as valves and sutures. The present review overviews usage of a multitude of PHA-based biomaterials for a wide range of tissue engineering applications, based on their properties suitable for the specific applications.

Fabrication of Polymer/Graphene Biocomposites for Tissue Engineering

Graphene-based materials (GBM) are considered one of the 21st century’s most promising materials, as they are incredibly light, strong, thin and have remarkable electrical and thermal properties. As a result, over the past decade, their combination with a diverse range of synthetic polymers has been explored in tissue engineering (TE) and regenerative medicine (RM). In addition, a wide range of methods for fabricating polymer/GBM scaffolds have been reported. This review provides an overview of the most recent advances in polymer/GBM composite development and fabrication, focusing on methods such as electrospinning and additive manufacturing (AM). As a future outlook, this work stresses the need for more in vivo studies to validate polymer/GBM composite scaffolds for TE applications, and gives insight on their fabrication by state-of-the-art processing technologies.

Dual-Drug Delivery via Zein In Situ Forming Implants Augmented with Titanium-Doped Bioactive Glass for Bone Regeneration: Preparation, In Vitro Characterization, and In Vivo Evaluation

In situ forming implants (IFIs) are non-surgical approach using biodegradable polymers to treat bone fractures. The study aimed at preparing dual-drug-loaded IFIs to deliver pitavastatin (osteogenic drug) and tedizolid (antibiotic) using zein as the implant matrix via solvent-induced phase inversion method. At first, several investigations were done on pitavastatin-loaded zein IFIs, where three concentrations of zein were used (10, 20, and 30% w/v). IFIs were evaluated for their solidification time, rheological properties, injectability, and in vitro release. IFIs containing bioactive glass nanoparticles were prepared by the addition of non-doped bioactive glass nanoparticles (BGT₀; 1, 3, 5, and 10% w/v) or titanium-doped bioactive glass nanoparticles (BGT₅; 1% w/v) to the selected concentration of zein (30% w/v) and then evaluated. The optimized dual-medicated implant (D-ZIFI 1) containing pitavastatin, tedizolid, sodium hyaluronate (3% w/v), and BGT₅ (1% w/v) was prepared and compared to IFI lacking both sodium hyaluronate and BGT₅ (D-ZIFI 2). D-ZIFI 1 and 2 sustained the release profiles of both drugs for 28 days. SEM images proved the interconnected porous structure of D-ZIFI 1 due to sodium hyaluronate. In vivo studies on surgically induced bone defects in Sprague–Dawley rats signified the proper accelerated bone healing ability of D-ZIFI 1 over D-ZIFI 2. Results presented D-ZIFI 1 as a promising, effective, non-surgical approach for bone healing.

Click Chemistry Hydrogels for Extrusion Bioprinting: Progress, Challenges, and Opportunities

The emergence of 3D bioprinting has allowed a variety of hydrogel-based "bioinks" to be printed in the presence of cells to create precisely defined cell-loaded 3D scaffolds in a single step for advancing tissue engineering and/or regenerative medicine. While existing bioinks based primarily on ionic cross-linking, photo-cross-linking, or thermogelation have significantly advanced the field, they offer technical limitations in terms of the mechanics, degradation rates, and the cell viabilities achievable with the printed scaffolds, particularly in terms of aiming to match the wide range of mechanics and cellular microenvironments. Click chemistry offers an appealing solution to this challenge given that proper selection of the chemistry can enable precise tuning of both the gelation rate and the degradation rate, both key to successful tissue regeneration; simultaneously, the often bio-orthogonal nature of click chemistry is beneficial to maintain high cell viabilities within the scaffolds. However, to date, relatively few examples of 3D-printed click chemistry hydrogels have been reported, mostly due to the technical challenges of controlling mixing during the printing process to generate high-fidelity prints without clogging the printer. This review aims to showcase existing cross-linking modalities, characterize the advantages and disadvantages of different click chemistries reported, highlight current examples of click chemistry hydrogel bioinks, and discuss the design of mixing strategies to enable effective 3D extrusion bioprinting of click hydrogels.

Click chemistry in the synthesis of catalytically relevant organoselenium compounds: development and applications of catalysts for organic synthesis

Use of click chemistry in synthesizing organoselenium compounds and the applications of metal complexes of such compounds as catalysts for various chemical transformations have been critically analyzed.

Self-Assembly of Poly(Janus particle)s into Unimolecular and Oligomeric Spherical Micelles

Using shape-persistent Janus particles to construct poly(Janus particle)s and studying their self-assembly behaviors are of great interest, but remain largely unexplored. In this work, we reported a type of amphiphiles constructed by the ring-opening metathesis polymerization of nonspherical molecular Janus particles (APOSS-BPOSS), called poly(Janus particle)s (poly(APOSS-BPOSS)_n, n = 12, 17, 22, and 35, and M_n = 35-100 kg/mol). Unlike traditional bottlebrush polymers consisting of flexible side chains, these poly(Janus particles) consist of rigid hydrophilic and hydrophobic polyhedral oligomeric silsesquioxane (POSS) cages as side chains. Interestingly, instead of maintaining an expected extended chain conformation, they could also collapse and then self-assemble to form unconventional unimolecular or oligomeric spherical micelles in solutions with a feature size smaller than 7 nm. More importantly, unlike traditional amphiphilic polymer brushes that could form unimolecular micelles at a relatively high degree of polymerization by self-assembly, these poly(Janus particles)s could accomplish self-assembly at a quite low degree of polymerization because of their unique chemical structure and molecular topology. The formation of unimolecular and oligomeric micelles was also further confirmed by dissipative particle dynamics simulations. This study of introducing the POSS-based poly(Janus particle)s as a class of shape amphiphiles will provide a model system for generating unimolecular and oligomeric micellar nanostructures through solution self-assembly.

Targeted delivery by pH-responsive mPEG-S-PBLG micelles significantly enhances the anti-tumor efficacy of doxorubicin with reduced cardiotoxicity

Stimuli-responsive nanotherapeutics hold great promise in precision oncology. In this study, a facile strategy was used to develop a new class of pH-responsive micelles, which contain methoxy polyethylene glycol (mPEG) and poly(carbobenzoxy-l-glutamic acid, BLG) as amphiphilic copolymer, and β-thiopropionate as acid-labile linkage. The mPEG-S-PBLG copolymer was synthesized through one-step ring-opening polymerization (ROP) and thiol-ene click reaction, and was able to efficiently encapsulate doxorubicin (DOX) to form micelles. The physicochemical characteristics, cellular uptake, tumor targeting, and anti-tumor efficacy of DOX-loaded micelles were investigated. DOX-loaded micelles were stable under physiological conditions and disintegrated under acidic conditions. DOX-loaded micelles can be internalized into cancer cells and release drugs in response to low pH in endosomes/lysosomes, resulting in cell death. Furthermore, the micellar formulation significantly prolonged the blood circulation, reduced the cardiac distribution, and selectively delivered more drugs to tumor tissue. Finally, compared with free DOX, DOX-loaded micelles significantly improved the anti-tumor efficacy and reduced systemic and cardiac toxicity in two different tumor xenograft models. These results suggest that mPEG-S-PBLG micelles have translational potential in the precise delivery of anti-cancer drugs.

Advanced Hydrogels for Cartilage Tissue Engineering: Recent Progress and Future Directions

Cartilage is a tension- and load-bearing tissue and has a limited capacity for intrinsic self-healing. While microfracture and arthroplasty are the conventional methods for cartilage repair, these methods are unable to completely heal the damaged tissue. The need to overcome the restrictions of these therapies for cartilage regeneration has expanded the field of cartilage tissue engineering (CTE), in which novel engineering and biological approaches are introduced to accelerate the development of new biomimetic cartilage to replace the injured tissue. Until now, a wide range of hydrogels and cell sources have been employed for CTE to either recapitulate microenvironmental cues during a new tissue growth or to compel the recovery of cartilaginous structures via manipulating biochemical and biomechanical properties of the original tissue. Towards modifying current cartilage treatments, advanced hydrogels have been designed and synthesized in recent years to improve network crosslinking and self-recovery of implanted scaffolds after damage in vivo. This review focused on the recent advances in CTE, especially self-healing hydrogels. The article firstly presents the cartilage tissue, its defects, and treatments. Subsequently, introduces CTE and summarizes the polymeric hydrogels and their advances. Furthermore, characterizations, the advantages, and disadvantages of advanced hydrogels such as multi-materials, IPNs, nanomaterials, and supramolecular are discussed. Afterward, the self-healing hydrogels in CTE, mechanisms, and the physical and chemical methods for the synthesis of such hydrogels for improving the reformation of CTE are introduced. The article then briefly describes the fabrication methods in CTE. Finally, this review presents a conclusion of prevalent challenges and future outlooks for self-healing hydrogels in CTE applications.

Biotechnological Applications of Polymeric Nanofiber Platforms Loaded with Diverse Bioactive Materials

This review article highlights the critical research and formative works relating to nanofiber composites loaded with bioactive materials for diverse applications, and discusses the recent research on the use of electrospun nanofiber incorporating bioactive compounds such as essential oils, herbal bioactive components, plant extracts, and metallic nanoparticles. Inevitably, with the common advantages of bioactive components and polymer nanofibers, electrospun nanofibers containing bioactive components have attracted intense interests for their applications in biomedicine and cancer treatment. Many studies have only concentrated on the production and performance of electrospun nanofiber loaded with bioactive components; in this regard, the features of different types of electrospun nanofiber incorporating a wide variety of bioactive compounds and their developing trends are summarized and assessed in the present article, as is the feasible use of nanofiber technology to produce products on an industrial scale in different applications.

Supramolecular Click Product Interactions Induce Dynamic Stiffening of Extracellular Matrix-Mimetic Hydrogels

Progressive stiffening of the extracellular matrix (ECM) is observed in tissue development as well as in pathologies such as cancer, cardiovascular disease, and fibrotic disease. However, methods to recapitulate this phenomenon in vitro face critical limitations. Here, we present a poly(ethylene glycol)-based peptide-functionalized ECM-mimetic hydrogel platform capable of facile, user-controlled dynamic stiffening. This platform leverages supramolecular interactions between inverse-electron demand Diels-Alder tetrazine-norbornene click products (TNCP) to create pendant moieties that undergo non-covalent crosslinking, stiffening a pre-existing network formed via thiol-ene click chemistry over the course of 6 h. Pendant TNCP moieties have a concentration-dependent effect on gel stiffness while still being cytocompatible and permissive of cell-mediated gel degradation. The robustness of this approach as well as its simplicity and ease of translation give it broad potential utility.

Design Challenges in Polymeric Scaffolds for Tissue Engineering

Numerous surgical procedures are daily performed worldwide to replace and repair damaged tissue. Tissue engineering is the field devoted to the regeneration of damaged tissue through the incorporation of cells in biocompatible and biodegradable porous constructs, known as scaffolds. The scaffolds act as host biomaterials of the incubating cells, guiding their attachment, growth, differentiation, proliferation, phenotype, and migration for the development of new tissue. Furthermore, cellular behavior and fate are bound to the biodegradation of the scaffold during tissue generation. This article provides a critical appraisal of how key biomaterial scaffold parameters, such as structure architecture, biochemistry, mechanical behavior, and biodegradability, impart the needed morphological, structural, and biochemical cues for eliciting cell behavior in various tissue engineering applications. Particular emphasis is given on specific scaffold attributes pertaining to skin and brain tissue generation, where further progress is needed (skin) or the research is at a relatively primitive stage (brain), and the enumeration of some of the most important challenges regarding scaffold constructs for tissue engineering.

Modular synthesis of amphiphilic chitosan derivatives based on copper-free click reaction for drug delivery

Amphiphilic chitosan derivatives have attracted wide attention as drug carriers due to their physicochemical properties. However, obtaining a desired amphiphilic chitosan derivative by tuning the various functional groups was complex and time-consuming. Therefore, a facile and common synthesis strategy would be promising. In this study, a modular strategy based on strain-promoted azide-alkyne cycloaddition (SPAAC) click reaction was designed and applied in synthesizing deoxycholic acid- or octanoic acid-modified N-azido propionyl-N,O-sulfate chitosan through tuning the hydrophobic groups. Additionally, chitosan derivatives with the same substitute groups were prepared via amide coupling as controls. We demonstrated that these derivates via the two strategies showed no obvious difference in physicochemical properties, drug loading ability and biosafety, indicating the feasibility of modular strategy. Notably, the modular strategy exhibited advantages including high reactivity, flexibility and reproducibility. We believe that this modular strategy could provide varied chitosan derivatives in an easy and high-efficiency way for improving multifunctional drug carriers.

A chondroitin sulfate based injectable hydrogel for delivery of stem cells in cartilage regeneration

Chondroitin sulfate (CS), as a popular material for cartilage tissue engineering scaffolds, has been extensively studied and reported for its safety and excellent biocompatibility. However, the rapid degradation of pure CS scaffolds has brought a challenge to regenerate neo-tissue similar to natural articular cartilage effectively. Meanwhile, the poly(ethene glycol) (PEG) -based biopolymer is frequently applied as a structural constituent material because of its remarkable mechanical properties, long-lasting in vivo stability, and hypo-immunity. Here, we report that the combination of CS and hyperbranched multifunctional PEG copolymer (HB-PEG) could synergistically promote cartilage repair. The thiol functionalised CS (CS-SH)/HB-PEG hydrogel scaffolds were fabricated via thiol-ene reaction, which exhibits rapid gelation, excellent mechanical properties and prolonged degradation properties. We found that rat adipose-derived mesenchymal stem cells presented great cell viability and improved chondrogenesis in CS-SH/HB-PEG hydrogels. Moreover, the injectable hydrogel scaffolds reduced stem cell inflammatory response, consistent with the well-documented anti-inflammatory activities of CS.

Advances in versatile anti-swelling polymer hydrogels

Swelling is ubiquitous for traditional as-prepared hydrogels, but is unfavorable in many situations, especially biomedical applications, such as tissue engineering, internal wound closure, soft actuating and bioelectronics, and so forth. As the swelling of a hydrogel usually leads to a volume expansion, which not only deteriorates the mechanical property of the hydrogel but can bring about undesirable oppression on the surrounding tissues when applied in vivo. In contrast, anti-swelling hydrogels hardly alter their volume when applied in aqueous environment, therefore reserving the original mechanical performance and size-stability and facilitating their potential application. In the past decade, with the development of advanced hydrogels, quite a number of anti-swelling hydrogels with versatile functions have been developed by researchers to meet the practical applications well, through integrating anti-swelling property with certain performance or functionality, such as high strength, self-healing, injectability, adhesiveness, antiseptics, etc. However, there has not been a general summary with regard to these hydrogels. To promote the construction of anti-swelling hydrogels with desirable functionalities in the future, this review generalizes and analyzes the tactics employed so far in the design and manufacture of anti-swelling hydrogels, starting from the viewpoint of classical swelling theories. The review will provide a relatively comprehensive understanding of anti-swelling hydrogels and clues to researchers interested in this kind of materials to develop more advanced ones suitable for practical application.