Nanosilicate-reinforced GelMA-PEGDA hydrogel promotes angiogenesis for bone regeneration

Bone tissue engineering has emerged as a pivotal field addressing the critical clinical needs of bone fractures. This study focused on developing multi-composite hydrogels by synergizing biocompatible GelMA macromolecules with synthetic PEGDA and reinforcing them with nanosilicates (SN). The incorporation of SN introduces crucial trace elements such as silicon, magnesium, and lithium, promoting both angiogenesis and osteogenesis. Characterizations revealed that PEGDA significantly reinforced the composite hydrogels' stability, while SN further enhanced the mechanical integrity of the GelMA-PEGDA-SN (GPS) hydrogels. Cell studies designated that GPS improved cell proliferation and migration, angiogenic VEGF/eNOS expression and osteogenic differentiation. In vivo experiments showed that GPS hydrogels effectively enhanced calvarial bone healing, with the GPS-2 formulation (2 % SN) displaying superior bone coverage and increased vascular formation. Assessments of osteogenic formation and the angiogenic marker CD31 validated the comprehensive bone regeneration potential of GPS hydrogels. These findings highlight the significant promise of GPS hydrogels in fostering bone healing with promoted angiogenesis.

Unveiling the versatility of gelatin methacryloyl hydrogels: a comprehensive journey into biomedical applications

Gelatin methacryloyl (GelMA) hydrogels have gained significant recognition as versatile biomaterials in the biomedical domain. GelMA hydrogels emulate vital characteristics of the innate extracellular matrix by integrating cell-adhering and matrix metalloproteinase-responsive peptide motifs. These features enable cellular proliferation and spreading within GelMA-based hydrogel scaffolds. Moreover, GelMA displays flexibility in processing, as it experiences crosslinking when exposed to light irradiation, supporting the development of hydrogels with adjustable mechanical characteristics. The drug delivery landscape has been reshaped by GelMA hydrogels, offering a favorable platform for the controlled and sustained release of therapeutic actives. The tunable physicochemical characteristics of GelMA enable precise modulation of the kinetics of drug release, ensuring optimal therapeutic effectiveness. In tissue engineering, GelMA hydrogels perform an essential role in the design of the scaffold, providing a biomimetic environment conducive to cell adhesion, proliferation, and differentiation. Incorporating GelMA in three-dimensional printing further improves its applicability in drug delivery and developing complicated tissue constructs with spatial precision. Wound healing applications showcase GelMA hydrogels as bioactive dressings, fostering a conducive microenvironment for tissue regeneration. The inherent biocompatibility and tunable mechanical characteristics of GelMA provide its efficiency in the closure of wounds and tissue repair. GelMA hydrogels stand at the forefront of biomedical innovation, offering a versatile platform for addressing diverse challenges in drug delivery, tissue engineering, and wound healing. This review provides a comprehensive overview, fostering an in-depth understanding of GelMA hydrogel's potential impact on progressing biomedical sciences.

Engineering Wet-Resistant and Osteogenic Nanocomposite Adhesive to Control Bleeding and Infection after Median Sternotomy

Median sternotomy surgery stands as one of the prevailing strategies in cardiac surgery. In this study, the cutting-edge bone adhesive is designed, inspired by the impressive adhesive properties found in mussels and sandcastle worms. This work has created an osteogenic nanocomposite coacervate adhesive by integrating a cellulose-polyphosphodopamide interpenetrating network, quaternized chitosan, and zinc, gallium-doped hydroxyapatite nanoparticles. This adhesive is characterized by robust catechol-metal coordination which effectively adheres to both hard and soft tissues with a maximum adhesive strength of 900 ± 38 kPa on the sheep sternum bone, surpassing that of commercial bone adhesives. The release of zinc and gallium cations from nanocomposite adhesives and quaternized chitosan matrix imparts remarkable antibacterial properties and promotes rapid blood coagulation, in vitro and ex vivo. It is also proved that this nanocomposite adhesive exhibits significant in vitro bioactivity, stable degradability, biocompatibility, and osteogenic ability. Furthermore, the capacity of nanocomposite coacervate to adhere to bone tissue and support osteogenesis contributes to the successful healing of a sternum bone defect in a rabbit model in vivo. In summary, these nanocomposite coacervate adhesives with promising characteristics are expected to provide solutions to clinical issues faced during median sternotomy surgery.

3D Bioprinting-Based Dopamine-Coupled Flexible Material for Nasal Cartilage Repair

INTRODUCTION

Since 3D printing can be used to design implants according to the specific conditions of patients, it has become an emerging technology in tissue engineering and regenerative medicine. How to improve the mechanical, elastic and adhesion properties of 3D-printed photocrosslinked hydrogels is the focus of cartilage tissue repair and reconstruction research.

MATERIALS AND METHODS

We established a strategy for toughening hydrogels by mixing GelMA-DOPA (GD), which is prepared by coupling dopamine (DA) with GelMA, with HAMA, bacterial cellulose (BC) to produce composite hydrogels (HB-GD). HB-GD hydrogel scaffolds were characterized in vitro by scanning electron microscopy (SEM), Young's modulus, swelling property and rheological property tests. And biocompatibility and chondrogenic ability were tested by live/dead staining, DNA quantitative analysis and immunofluorescence staining. Combined with 3D bioprinting technology, mouse chondrocytes (ADTC5) were added to form a biological chain to construct an in vitro model, and the feasibility of the model for nasal cartilage regeneration was verified by cytology evaluation.

RESULTS

With the increase of GD concentration, the toughness of the composite hydrogel increased (47.0 ± 2.7 kPa (HB-5GD)-158 ± 3.2 kPa (HB-20GD)), and it had excellent swelling properties, rheological properties and printing properties. The HB-GD composite hydrogel promoted the proliferation and differentiation of ATDC5. Cells in 3D printed scaffolds had higher survival rates (> 95%) and better protein expression than the encapsulated cultures.

CONCLUSION

The HB-10GD hydrogel can be made into a porous scaffold with precise shape, good internal pore structure, high mechanical strength and good swelling rate through extrusion 3D printing.

NO LEVEL ASSIGNED

This journal requires that authors assign a level of evidence to each submission to which Evidence-Based Medicine rankings are applicable. This excludes Review Articles, Book Reviews, and manuscripts that concern Basic Science, Animal Studies, Cadaver Studies, and Experimental Studies. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266.

Evolution of Hybrid Hydrogels: Next-Generation Biomaterials for Drug Delivery and Tissue Engineering

Hydrogels, being hydrophilic polymer networks capable of absorbing and retaining aqueous fluids, hold significant promise in biomedical applications owing to their high water content, permeability, and structural similarity to the extracellular matrix. Recent chemical advancements have bolstered their versatility, facilitating the integration of the molecules guiding cellular activities and enabling their controlled activation under time constraints. However, conventional synthetic hydrogels suffer from inherent weaknesses such as heterogeneity and network imperfections, which adversely affect their mechanical properties, diffusion rates, and biological activity. In response to these challenges, hybrid hydrogels have emerged, aiming to enhance their strength, drug release efficiency, and therapeutic effectiveness. These hybrid hydrogels, featuring improved formulations, are tailored for controlled drug release and tissue regeneration across both soft and hard tissues. The scientific community has increasingly recognized the versatile characteristics of hybrid hydrogels, particularly in the biomedical sector. This comprehensive review delves into recent advancements in hybrid hydrogel systems, covering the diverse types, modification strategies, and the integration of nano/microstructures. The discussion includes innovative fabrication techniques such as click reactions, 3D printing, and photopatterning alongside the elucidation of the release mechanisms of bioactive molecules. By addressing challenges, the review underscores diverse biomedical applications and envisages a promising future for hybrid hydrogels across various domains in the biomedical field.

A Visible Light Cross-Linked Underwater Hydrogel Adhesive with Biodegradation and Hemostatic Ability

Hydrogel adhesives with integrated functionalities are still required to match their ever-expanding practical applications in the field of tissue repair and regeneration. A simple and effective safety strategy is reported, involving an in situ injectable polymer precursor and visible light-induced cross-linking. This strategy enables the preparation of a hydrogel adhesive in a physiological environment, offering wet adhesion to tissue surfaces, molecular flexibility, biodegradability, biocompatibility, efficient hemostatic performance, and the ability to facilitate liver injury repair. The proposed one-step preparation process of this polymer precursor involves the mixing of gelatin methacryloyl (GelMA), poly(thioctic acid) [P(TA)], poly(acrylic acid)/amorphous calcium phosphate (PAAc/ACP, PA) and FDA-approved photoinitiator solution, and a subsequent visible light irradiation after in situ injection into target tissues that resulted in a chemically-physically cross-linked hybrid hydrogel adhesive. Such a combined strategy shows promise for medical scenarios, such as uncontrollable post-traumatic bleeding.

Bioactive and biomimetic 3D scaffolds for bone tissue engineering using graphitic carbon nitride as a sustainable visible light photoinitiator

Graphitic carbon nitride (g-C3N4) is explored as a novel sustainable visible light photoinitiator for the preparation of biomimetic 3D hydrogel scaffolds comprising gelatin methacrylamide (GelMA) and dopamine methacrylamide for use in tissue engineering. The initiator efficiency was assessed by comparing the swelling behavior and the stability of photopolymerized hydrogels prepared with GelMA of different degrees of functionalization and different comonomer compositions. Bioactive composite hydrogels with a 50 wt% nanohydroxyapatite (nHAp) content, to closely mimic the actual bone composition, were successfully obtained by the introduction of nHAp in the prepolymer solutions followed by photopolymerization. The composite hydrogels demonstrated enhanced mechanical properties and excellent stability in PBS verifying the preparation of robust 3D scaffolds for use in cancellous or pre-calcified bone tissue engineering applications. The in vitro cell response of the composite scaffolds exhibited high cell viability and enhanced differentiation of pre-osteoblasts to mature osteoblasts, demonstrating their osteogenic potential. This work establishes, for the first time, the excellent properties of g-C3N4 as a sustainable, visible light initiator, fully satisfying the principles of green chemistry, for the preparation of robust and biologically relevant hydrogels, and proposes a new approach to overcome the main challenges of conventional photoinitiators in cell scaffold fabrication, such as photobleaching, high cost and non-scalable synthesis employing toxic organic precursors and solvents.

Multifunctional photothermally responsive hydrogel as an effective whole-process management platform to accelerate chronic diabetic wound healing

The management of chronic diabetic wounds is a complex issue that requires wound repair, regulation of inflammatory levels, and intervention to prevent bacterial infection. To address this issue, we developed a multifunctional photothermally responsive hydrogel (PAG-CuS) as an effective platform for managing the entire wound-healing process, including promoting wound healing, providing anti-inflammatory therapy, and performing photothermal sterilization. Constructed through copolymerization of acrylic acid (AA), methacrylic anhydride-modified gelatin (GelMA), and lipoic acid sodium (LAS) coated copper sulfide nanoparticles (CuS@LAS), PAG-CuS possessed a porous three-dimensional structure that promoted cell adhesion and had a substantial water-holding capacity. Additionally, the internal CuS@LAS not only conferred photothermal antibacterial properties to the hydrogel but also served as physical cross-linking agents, thus enhancing its mechanical strength. Under the NIR-induced photothermal effect, the porous hydrogel liberates CuS@LAS, and later CuS@LAS expels LAS via micelle deassembly to eliminate intracellular ROS. This results in the down-regulation of MMP-9 expression, promoting ECM production and facilitating wound healing. Meanwhile, the release of Cu2+ from PAG-CuS could enhance CD31 expression in endothelial cells, promoting microvessel formation, which is crucial for wound healing. In the diabetic wound model of GK rats, the PAG-CuS hydrogel reduced ROS levels, increased microvessel count, improved epithelialization, and enhanced wound healing. Therefore, this versatile photothermal hydrogel has the potential to be applied in sterilization, scavenging free radicals, and promoting angiogenesis, making it an effective and comprehensive solution to manage the challenges of diabetic wounds. STATEMENT OF SIGNIFICANCE: Assessment of functional recovery and timely adjustment of treatment strategy is critical in the management of chronic diabetic wounds. In this work, we prepared PAG-CuS composite hydrogels by integrating in situ reduction, chemical crosslinking, and nanoenhancement techniques. The near-infrared light-induced photothermal effect of PAG-CuS gel rapidly kills bacteria at the lesion site, and the generated heat simultaneously promotes the multilevel release of LAS from the gel, which could regulate the levels of ROS and MMP-9 to promote extracellular matrix formation. In addition, the Cu2+ released from the gel can promote the formation of blood vessels to improve blood oxygenation. Therefore, this project proposes a synergistic solution to realize the whole process of management to accelerate chronic diabetic wound healing.

3D Printed All-Natural Hydrogels: Flame-Retardant Materials Toward Attaining Green Sustainability

Biomass-based hydrogel is a promising flame-retardant material and has a high potential for applications in transportation, aerospace, building and electrical engineering, and electronics. However, rapid vat photopolymerization (VP) 3D printing of biomass-based hydrogels, especially that of all-natural ones, is still rare. Herein, a new class of VP 3D-printed hydrogels with strong covalent networks, fabricating using fully biomass materials and a commercial liquid crystal display (LCD) printer assembled with low-intensity visible light is presented. Encouragingly, the highly ordered layer-by-layer packing structures provided by VP 3D printing technology endow these hydrogels with remarkable flame retardancy, exceptional temperature resistance, advantageous combustion behaviors, and favorable mechanical strength, in particular, giving them a better limit oxygen index (83.5%) than various biomass-based hydrogels. The proposed approach enables the green design as well as the precise and efficient preparation for flame-retardant materials, paving the way for the future flame-retardant materials toward attaining green sustainability.

Photo-cross-linked Hydrogels for Cartilage and Osteochondral Repair

Photo-cross-linked hydrogels, which respond to light and induce structural or morphological transitions, form a microenvironment that mimics the extracellular matrix of native tissue. In the last decades, photo-cross-linked hydrogels have been widely used in cartilage and osteochondral tissue engineering due to their good biocompatibility, ease of fabrication, rapid in situ gel-forming ability, and tunable mechanical and degradable properties. In this review, we systemically summarize the different types and physicochemical properties of photo-cross-linked hydrogels (including the materials and photoinitiators) and explore the biological properties modulated through the incorporation of additives, including cells, biomolecules, genes, and nanomaterials, into photo-cross-linked hydrogels. Subsequently, we compile the applications of photo-cross-linked hydrogels with a specific focus on cartilage and osteochondral repair. Finally, current limitations and future perspectives of photo-cross-linked hydrogels are also discussed.

Injectable hydrogels: An emerging therapeutic strategy for cartilage regeneration

The impairment of articular cartilage due to traumatic incidents or osteoarthritis has posed significant challenges for healthcare practitioners, researchers, and individuals suffering from these conditions. Due to the absence of an approved treatment strategy for the complete restoration of cartilage defects to their native state, the tissue condition often deteriorates over time, leading to osteoarthritic (OA). However, recent advancements in the field of regenerative medicine have unveiled promising prospects through the utilization of injectable hydrogels. This versatile class of biomaterials, characterized by their ability to emulate the characteristics of native articular cartilage, offers the distinct advantage of minimally invasive administration directly to the site of damage. These hydrogels can also serve as ideal delivery vehicles for a diverse range of bioactive agents, including growth factors, anti-inflammatory drugs, steroids, and cells. The controlled release of such biologically active molecules from hydrogel scaffolds can accelerate cartilage healing, stimulate chondrogenesis, and modulate the inflammatory microenvironment to halt osteoarthritic progression. The present review aims to describe the methods used to design injectable hydrogels, expound upon their applications as delivery vehicles of biologically active molecules, and provide an update on recent advances in leveraging these delivery systems to foster articular cartilage regeneration.

A Metal-Organic Framework-Incorporated Hydrogel for Delivery of Immunomodulatory Neobavaisoflavone to Promote Cartilage Regeneration in Osteoarthritis

The treatment of osteoarthritis (OA)-related cartilage defects is a great clinical challenge due to the complex pathogenesis of OA and poor self-repair ability of cartilage tissue. Combining local and long-term anti-inflammatory therapies to promote cartilage repair is an effective method to treat OA. In this study, a zinc-organic framework-incorporated extracellular matrix (ECM)-mimicking hydrogel platform was constructed for the inflammatory microenvironment-responsive delivery of neobavaisoflavone (NBIF) to promote cartilage regeneration in OA. The NBIF was encapsulated in situ in zeolitic imidazolate frameworks (ZIF-8 MOFs). The NBIF@ZIF-8 MOFs were decorated with polydopamine and incorporated into a methacrylate gelatin/hyaluronic acid hybrid network to form the NBIF@ZIF-8/PHG hydrogel. The hydrogel featured excellent cell/tissue affinity, providing a favorable microenvironment for recruiting cells and cytokines to the defect sites. The hydrogel enabled the on-demand NBIF released in response to a weakly acidic microenvironment at the injured joint site to resolve inflammatory responses during the early stages of OA. Consequently, the cooperativity of the loaded NBIF and hydrogel synergistically modulated the immune response and assisted in cartilage defect repair. In summary, the NBIF@ZIF-8/PHG hydrogel delivery platform represents an effective treatment strategy for OA-related cartilage defects and may attract attentions for applications in other inflammatory diseases.

Polysaccharides, proteins, and synthetic polymers based multimodal hydrogels for various biomedical applications: A review

Nature-derived or biologically encouraged hydrogels have attracted considerable interest in numerous biomedical applications owing to their multidimensional utility and effectiveness. The internal architecture of a hydrogel network, the chemistry of the raw materials involved, interaction across the interface of counter ions, and the ability to mimic the extracellular matrix (ECM) govern the clinical efficacy of the designed hydrogels. This review focuses on the mechanistic viewpoint of different biologically driven/inspired biomacromolecules that encourages the architectural development of hydrogel networks. In addition, the advantage of hydrogels by mimicking the ECM and the significance of the raw material selection as an indicator of bioinertness is deeply elaborated in the review. Furthermore, the article reviews and describes the application of polysaccharides, proteins, and synthetic polymer-based multimodal hydrogels inspired by or derived from nature in different biomedical areas. The review discusses the challenges and opportunities in biomaterials along with future prospects in terms of their applications in biodevices or functional components for human health issues. This review provides information on the strategy and inspiration from nature that can be used to develop a link between multimodal hydrogels as the main frame and its utility in biomedical applications as the primary target.

Poly-Catecholic Functionalization of Biomolecules for Rapid Gelation, Robust Injectable Bioadhesion, and Near-Infrared Responsiveness

Mussel-inspired catechol-functionalization of degradable natural biomaterials has garnered significant interest as an approach to achieve bioadhesion for sutureless wound closure. However, conjugation capacity in standard coupling reactions, such as carbodiimide chemistry, is limited by low yield and lack of abundant conjugation sites. Here, a simple oxidative polymerization step before conjugation of catechol-carrying molecules (i.e., 3,4-dihydroxy-l-phenylalanine, l-DOPA) as a potential approach to amplify catechol function in bioadhesion of natural gelatin biomaterials is proposed. Solutions of gelatin modified with poly(l-DOPA) moieties (GelDOPA) are characterized by faster physical gelation and increased viscosity, providing better wound control on double-curved tissue surfaces compared to those of l-DOPA-conjugated gelatin. Physical hydrogels treated topically with low concentrations of NaIO4 solutions are crosslinked on-demand via through-thickness diffusion. Poly(l-DOPA) conjugates enhance crosslinking density compared to l-DOPA conjugated gelatin, resulting in lower swelling and enhanced cohesion in physiological conditions. Together with cohesion, more robust bioadhesion at body temperature is achieved by poly(l-DOPA) conjugates, exceeding those of commercial sealants. Further, poly(l-DOPA) motifs introduced photothermal responsiveness via near-infrared (NIR) irradiation for controlled drug release and potential applications in photothermal therapy. The above functionalities, along with antibacterial activity, render the proposed approach an effective biomaterial design strategy for wound closure applications.

Cocktail-like gradient gelatin/hyaluronic acid bioimplant for enhancing tendon-bone healing in fatty-infiltrated rotator cuff injury models

The regeneration of enthesis tissue (native tendon-bone interface) at the post-surgically repaired rotator cuff remains a challenge for clinicians, especially with the emergence of degenerative affection such as fatty infiltration that exacerbate poor tendon-bone healing. In this study, we proposed a cocktail-like hydrogel with a four-layer structure (BMSCs+gNC@GH) for enhancing fatty infiltrated tendon-bone healing. As collagen and hyaluronic acid are the main biomacromolecules that constitute the extracellular matrix of enthesis tissue, this hydrogel was composed of UV-curable gelatin/hyaluronic acid (GelMA/HAMA) dual network gel (GH) with nanoclay (NC) and stem cells loaded. The results showed that NC exhibited a cocktail-like gradient distribution in GH, which effectively mimicked the structure of native enthesis and supported the long-term culture and encapsulation of BMSCs. What's more, the gradient variation of NC provided a biological signal for promoting gradient osteogenic differentiation of cells. Based on the in vivo results, BMSCs+gNC@GH effectively promoted fibrocartilage layer regeneration at the tendon-bone interface and inhibited fatty infiltration. Therefore, BMSCs+gNC@GH group exhibited better biomechanical properties. Thus, this cocktail-like implant may be a promising tissue-engineered scaffold for tendon-bone healing, and it provides a new idea for the development of scaffolds with the function of inhibiting degeneration.

A 3D multifunctional bi-layer scaffold to regulate stem cell behaviors and promote osteochondral regeneration

Osteochondral defect (OCD) regeneration remains a great challenge. Recently, multilayer scaffold simulating native osteochondral structures have aroused broad interest in osteochondral tissue engineering. Here, we developed a 3D multifunctional bi-layer scaffold composed of a kartogenin (KGN)-loaded GelMA hydrogel (GelMA/KGN) as an upper layer mimicking a cartilage-specific extracellular matrix and a hydroxyapatite (HA)-coated 3D printed polycaprolactone porous scaffold (PCL/HA) as a lower layer simulating subchondral bone. The bi-layer scaffolds were subsequently modified with tannic acid (TA) prime-coating and E7 peptide conjugation (PCL/HA-GelMA/KGN@TA/E7) to regulate endogenous stem cell behaviors and exert antioxidant activity for enhanced osteochondral regeneration. In vitro, the scaffolds could support cell attachment and proliferation, and enhance the chondrogenic and osteogenic differentiation capacity of bone marrow-derived mesenchymal stem cells (BMSCs) in a specific layer. Besides, the incorporation of TA/E7 significantly increased the biological activity of the bi-layer scaffolds including the pro-migratory effect, antioxidant activity, and the maintenance of cell viability against oxidative stress. In vivo, the developed bi-layer scaffolds enhanced the simultaneous regeneration of cartilage and subchondral bone when implanted into a rabbit OCD model through macroscopic, micro-CT, and histological evaluation. Taken together, these investigations demonstrated that the 3D multifunctional bi-layer scaffolds could provide a suitable microenvironment for endogenous stem cells, and promote in situ osteochondral regeneration, showing great potential for the clinical treatment of OCD.

A Biomimetic Bilayer Hydrogel Actuator Based on Thermoresponsive Gelatin Methacryloyl-Poly(N-isopropylacrylamide) Hydrogel with Three-Dimensional Printability

Development of hydrogel-based actuators with programmable deformation is an important topic that arouses much attention in fundamental and applied research. Most of these actuators are nonbiodegradable or work under nonphysiological conditions. Herein, a temperature-responsive and biodegradable gelatin methacryloyl (GelMA)-poly(N-isopropylacrylamide) hydrogel (i.e., GN hydrogel) network was explored as the active layer of a bilayer actuator. Small-angle X-ray scattering (SAXS) revealed that the GN hydrogel formed a mesoglobular structure (∼230 Å) upon a thermally induced phase transition. Rheological data supported that the GN hydrogel possessed 3D printability and tunable mechanical properties. A bilayer hydrogel actuator composed of active GN and passive GelMA layers was optimized by varying the layer thickness and compositions to achieve large, reproducible, and anisotropic bending with a curvature of ∼5.5 cm^-1. Different patterns of the active layer were designed for actuation in programmable control. The 3D printed GN hydrogel constructs showed significant volume reduction (∼25-60% depending on construct design) at 37 °C with the resolution enhanced by the thermo-triggered actuation, while they were able to fully reswell at room temperature. A more intricate 3D printed butterfly actuator demonstrated the ability to mimic the wing movement through thermoresponsiveness. Furthermore, myoblasts laden in the GN hydrogel exhibited significant proliferation of ∼376% in 14 days. This study provides a new fabrication approach for developing biomimetic devices, artificial muscles, and soft robotics for biomedical applications.

Mussel-Based Biomimetic Strategies in Musculoskeletal Disorder Treatment: From Synthesis Principles to Diverse Applications

Musculoskeletal disorders are the second leading cause of disability worldwide, posing a huge global burden to the public sanitation system. Currently, tissue engineering-based approaches act as effective strategies, which are, however, challenging in limited application scenarios. Mussel-based biomimetic materials, exhibit numerous unique properties such as intense adhesion, biocompatibility, moisture resistance, and injectability, to name only a few, and have attracted extensive research interest. In particular, featuring state-of-the-art properties, mussel-inspired biomaterials have been widely explored in innumerable musculoskeletal disorder treatments including osteochondral defects, osteosarcoma, osteoarthritis, ligament rupture, and osteoporosis. Nevertheless, a comprehensive and timely discussion of their applications in musculoskeletal disorders is insufficient. In this review, we emphasize on (1) the main categories and characteristics of mussel foot proteins and their fundamental mechanisms for the spectacular adhesion in mussels; (2) the diverse synthetic methods and modification of various polymers; and (3) the emerging applications of mussel-biomimetic materials, the future perspectives, and challenges, especially in the area of musculoskeletal disorder. We envision that this review will provide a unique and insightful perspective to improve the development of a new generation of mussel biomimetic strategies.

Fabrication and characterization of electrospun GelMA/PCL/CS nanofiber composites for wound dressing applications

In the present study, the effect of different ratios of GelMA concentration has been exhibited for wound dressing implementation by the electrospinning method using a new polymer combination of Gelatin methacrylate (GelMA)/Polycaprolactone (PCL)/Chitosan (CS). The nanofiber composites were fabricated due to their biocompatible, biodegradable, improved mechanical strength, low degradation rate, and hydrophilic nature to develop cell-mimicking, cell adhesion, proliferation, and differentiation. Different concentrations of GelMA were added to the PCL/CS solution as 5, 10, and 20 wt%, respectively, in the formic acid/acetic acid (7:3) solution. A photoinitiator was added to the solution for photo-crosslinking of GelMA. The influence of different solution concentrations (5, 10, and 20 wt%) on the structure’s nanofiber production and fiber morphology was examined. SEM micrographs revealed that varied GelMA concentrations resulted in suitable and stable nanofiber composites. The average diameter of nanofiber composites grows as the GelMA concentration rises. FTIR, DSC, tensile test, degradation, and swelling test were evaluated. The results demonstrated that high mechanical strength, hydrophilic properties, and a slow degradation rate were observed with the presence and increment of GelMA concentration within the nanofiber composites. The antibacterial potential of GelMA/PCL/CS nanofiber composites was evaluated against P. aeruginosa and S. aureus using a disc diffusion assay. In vitro cell culture research was conducted by seeding NIH 3T3 fibroblast cells on nanofiber composites, proving these cells’ high cell proliferation rate, viability, and adhesion. 10 wt% GelMA-based nanofiber composites were found to have great potential for wound dressing applications.

Bio-macromolecular design roadmap towards tough bioadhesives

Emerging sutureless wound-closure techniques have led to paradigm shifts in wound management. State-of-the-art biomaterials offer biocompatible and biodegradable platforms enabling high cohesion (toughness) and adhesion for rapid bleeding control as well as robust attachment of implantable devices. Tough bioadhesion stems from the synergistic contributions of cohesive and adhesive interactions. This Review provides a biomacromolecular design roadmap for the development of tough adhesive surgical sealants. We discuss a library of materials and methods to introduce toughness and adhesion to biomaterials. Intrinsically tough and elastic polymers are leveraged primarily by introducing strong but dynamic inter- and intramolecular interactions either through polymer chain design or using crosslink regulating additives. In addition, many efforts have been made to promote underwater adhesion via covalent/noncovalent bonds, or through micro/macro-interlock mechanisms at the tissue interfaces. The materials settings and functional additives for this purpose and the related characterization methods are reviewed. Measurements and reporting needs for fair comparisons of different materials and their properties are discussed. Finally, future directions and further research opportunities for developing tough bioadhesive surgical sealants are highlighted.

Designing a Nitro-Induced Sutured Biomacromolecule to Engineer Electroconductive Adhesive Hydrogels

Nitro-functionality, with a large deficit of negative charge, embraces biological importance and has proven its therapeutic essence even in chemotherapy. Functionally, with its strong electron-withdrawing capability, nitro can manipulate the electron density of organic moieties and regulates cellular-biochemical reactions. However, the chemistry of nitro-functionality to introduce physiologically relevant macroscopic properties from the molecular skeleton is unknown. Therefore, herein, a neurotransmitter moiety, dopamine, was chemically modified with a nitro-group to explore its influence on synthesizing a multifunctional biomaterial for therapeutic applications. Chemically, while the nitro-group perturbed the aromatic electron density of nitrocatecholic domain, it facilitated the suturing of nitrocatechol moieties to regain its aromaticity through a radical transfer mechanism, forming a novel macromolecular structure. Incorporation of the sutured-nitrocatecholic strand (S-nCAT) in a gelatin-based hydrogel introduced an electroconductive microenvironment through the delocalization of π-electrons in S-nCAT, while maintaining its catechol-mediated adhesive property for tissue repairing/sealing. Meanwhile, the engineered hydrogel enriched with noncovalent interactions, demonstrated excellent mechano-physical properties to support tissue functions. Cytocompatibility of the bioadhesive was assessed with in vitro and in vivo studies, confirming its potential usage for biomedical applications. In conclusion, this novel chemical approach enabled designing a multifunctional biomaterial by manipulating the electronic properties of small bioactive molecules for various biomedical applications.

Design, synthesis, and characterization of a novel dual cross-linked gelatin-based bioadhesive for hard and soft tissues adhesion capability

Many surgical treatments require a suitable tissue adhesive that maintains its performance in wet conditions and can be applied simultaneously for hard and soft tissues. In the present study, a dual cross-linked tissue adhesive was synthesized by mixing the gelatin methacryloyl (Gel-MA) and gelatin-dopamine conjugate (Gel-Dopa). The setting reaction was based on a photopolymerization process in the presence of a combination of riboflavin and triethanolamine and a chemical cross-linking process attributed to the genipin as a natural cross-linker. Modified gelatin macromolecules were characterized and the best wavelength for free radical generation in the presence of riboflavin was obtained. Tissue adhesives were prepared with 30% hydrogels of Gel-MA and Gel-Dopa with different ratios in distilled water. The gelation occurred in a short time after light irradiation. The chemical, mechanical, physical, and cytotoxicity properties of the tissue adhesives were evaluated. The results showed that despite photopolymerization, chemical crosslinking with genipin played a more critical role in the setting process. Water uptake, degradation behavior, cytotoxicity, and adhesion properties of the adhesives were correlated with the ratio of the components. The SEM images showed a porous structure that could ensure the entry of cells and nutrients into the surgical area. While acceptable properties in most experiments were observed, all features were improved as the Gel-Dopa ratio increased. Also, the obtained hydrogels revealed excellent adhesive properties, particularly with bone even after wet incubation, and it was attributed to the amount of gelatin-dopamine conjugate. From the obtained results, it was concluded that a dual adhesive hydrogel based on gelatin macromolecules could be a good candidate as a tissue adhesive in wet condition.

Mussel‐Inspired Biomaterials: From Chemistry to Clinic

After several billions of years, nature still makes decisions on its own to identify, develop, and direct the most effective material for phenomena/challenges faced. Likewise, and inspired by the nature, we learned how to take steps in developing new technologies and materials innovations. Wet and strong adhesion by Mytilidae mussels (among which Mytilus edulis—blue mussel and Mytilus californianus—California mussel are the most well‐known species) has been an inspiration in developing advanced adhesives for the moist condition. The wet adhesion phenomenon is significant in designing tissue adhesives and surgical sealants. However, a deep understanding of engaged chemical moieties, microenvironmental conditions of secreted proteins, and other contributing mechanisms for outstanding wet adhesion mussels are essential for the optimal design of wet glues. In this review, all aspects of wet adhesion of Mytilidae mussels, as well as different strategies needed for designing and fabricating wet adhesives are discussed from a chemistry point of view. Developed muscle‐inspired chemistry is a versatile technique when designing not only wet adhesive, but also, in several more applications, especially in the bioengineering area. The applications of muscle‐inspired biomaterials in various medical applications are summarized for future developments in the field.

3D bioassembly of cell-instructive chondrogenic and osteogenic hydrogel microspheres containing allogeneic stem cells for hybrid biofabrication of osteochondral constructs

Recently developed modular bioassembly techniques hold tremendous potential in tissue engineering and regenerative medicine, due to their ability to recreate the complex microarchitecture of native tissue. Here, we developed a novel approach to fabricate hybrid tissue-engineered constructs adopting high-throughput microfluidic and 3D bioassembly strategies. Osteochondral tissue fabrication was adopted as an example in this study, because of the challenges in fabricating load bearing osteochondral tissue constructs with phenotypically distinct zonal architecture. By developing cell-instructive chondrogenic and osteogenic bioink microsphere modules in high-throughput, together with precise manipulation of the 3D bioassembly process, we successfully fabricated hybrid engineered osteochondral tissue in vitro with integrated but distinct cartilage and bone layers. Furthermore, by encapsulating allogeneic umbilical cord blood-derived mesenchymal stromal cells (UCB-MSCs), and demonstrating chondrogenic and osteogenic differentiation, the hybrid biofabrication of hydrogel microspheres in this 3D bioassembly model offers potential for an off-the-shelf, single-surgery strategy for osteochondral tissue repair.

Development of a multifunctional injectable temperature-sensitive gelatin-based adhesive double-network hydrogel

Gelatin-based bioadhesives are suitable for the treatment of wounds due to their inherent biocompatibility, lack of immunogenicity, and potential for modification. However, common limitations with such adhesives include their adhesive strength and versatility. In the present study, a multifunctional injectable temperature-sensitive gelatin-based adhesive double-network hydrogel (DNGel) was engineered using facile dual-syringe methodology. An integrative crosslinking strategy utilized the complexation of catechol-Fe³⁺ and NIPAAm-methacryloyl. As anticipated, the DNGel exhibited multifunctional therapeutic properties, namely temperature-sensitivity, mechanical flexibility, good adhesive strength, injectability, self-healing capability, antibacterial activity, and the capability to enable hemostasis and wound healing. The bioinspired dynamic double-network was stabilized by a number of molecular interactions between components in the DNGel, providing multifunctional therapeutic performance. In addition, comprehensive in vitro and in vivo testing confirmed that the adhesive hydrogel exhibited effective antihemorrhagic properties and accelerated wound healing by the promotion of revascularization, representing considerable potential as a next-generation multifunctional smart adhesive patch.

Mussel-inspired extracellular matrix-mimicking hydrogel scaffold with high cell affinity and immunomodulation ability for growth factor-free cartilage regeneration

Background

Injury to articular cartilage cause certain degree of disability due to poor self-repair ability of cartilage tissue. To promote cartilage regeneration, it is essential to develop a scaffold that properly mimics the native cartilage extracellular matrix (ECM) in the aspect of compositions and functions.

Methods

A mussel-inspired strategy was developed to construct an ECM-mimicking hydrogel scaffold by incorporating polydopamine-modified hyaluronic acid (PDA/HA) complex into a dual-crosslinked collagen (Col) matrix for growth factor-free cartilage regeneration. The adhesion, proliferation, and chondrogenic differentiation of cells on the scaffold were examined. A well-established full-thickness cartilage defect model of the knee in rabbits was used to evaluated the efficacy and functionality of the engineered Col/PDA/HA hydrogel scaffold.

Results

The PDA/HA complex incorporated-hydrogel scaffold with catechol moieties exhibited better cell affinity than bare negatively-charged HA incorporated hydrogel scaffold. In addition, the PDA/HA complex endowed the scaffold with immunomodulation ability, which suppressed the expression of inflammatory cytokines and effectively activated the polarization of macrophages toward M2 phenotypes. The in vivo results revealed that the mussel-inspired Col/PDA/HA hydrogel scaffold showed strong cartilage inducing ability to promote cartilage regeneration.

Conclusions

The PDA/HA complex-incorporated hydrogel scaffold overcame the cell repellency of negatively-charged polysaccharide-based scaffolds, which facilitated the adhesion and clustering of cells on the scaffold, and therefore enhanced cell-HA interactions for efficient chondrogenic differentiation. Moreover, the hydrogel scaffold modulated immune microenvironment, and created a regenerative microenvironment to enhance cartilage regeneration.

The translational potential of this article

This study gives insight into the mussel-inspired approach to construct the tissue-inducing hydrogel scaffold in a growth-factor-free manner, which show great advantage in the clinical treatment. The hydrogel scaffold composed of collagen and hyaluronic acid as the major component, providing cartilage ECM-mimicking environment, is promising for cartilage defect repair.

Multifunctional GelMA platforms with nanomaterials for advanced tissue therapeutics

Polymeric hydrogels are fascinating platforms as 3D scaffolds for tissue repair and delivery systems of therapeutic molecules and cells. Among others, methacrylated gelatin (GelMA) has become a representative hydrogel formulation, finding various biomedical applications. Recent efforts on GelMA-based hydrogels have been devoted to combining them with bioactive and functional nanomaterials, aiming to provide enhanced physicochemical and biological properties to GelMA. The benefits of this approach are multiple: i) reinforcing mechanical properties, ii) modulating viscoelastic property to allow 3D printability of bio-inks, iii) rendering electrical/magnetic property to produce electro-/magneto-active hydrogels for the repair of specific tissues (e.g., muscle, nerve), iv) providing stimuli-responsiveness to actively deliver therapeutic molecules, and v) endowing therapeutic capacity in tissue repair process (e.g., antioxidant effects). The nanomaterial-combined GelMA systems have shown significantly enhanced and extraordinary behaviors in various tissues (bone, skin, cardiac, and nerve) that are rarely observable with GelMA. Here we systematically review these recent efforts in nanomaterials-combined GelMA hydrogels that are considered as next-generation multifunctional platforms for tissue therapeutics. The approaches used in GelMA can also apply to other existing polymeric hydrogel systems.

The solvent effect modulates the formation of homogeneous polyphenol composite hydrogels with improved transparency and mechanical strength for antibacterial delayed sternal closure films

The usage of delayed sternal closure films after thoracotomy surgery helps doctors deal with emergency conveniently. There is a growing demand to develop suturable, antibacterial and transparent films for delayed sternal closure. Although polyphenol incorporated hydrogels provide good suture ability, they lose transparency because of the heterogeneous distribution of polyphenols during the post-immersion process. Here, a solvent exchange method is proposed to fabricate homogeneous polyphenol composite hydrogels in a bottom-up manner, which utilizes the distinct solvent effect of DMSO and H₂O to modulate the association and disassociation between polyphenols and the polymer backbones on demand. DMSO first provides a protective environment to turn off the intermolecular interactions and allows tannic acid (TA) to be dispersed into the polymer network PEG-lysozyme (PEG-LZM) homogeneously. The following water rehydration turns on the intermolecular interactions between titanic acid and PEG-lysozymes, and results in a homogeneous titanic acid toughened composite hydrogel (PEG-LZM-TA (DH)), which has an improved transparency and mechanical properties than those of the materials prepared by the post-immersion method. In addition, the TA integration provides antibacterial function to the hydrogels. We establish a rabbit delayed sternal closure model to demonstrate that PEG-LZM-TA (DH) films can be sutured to temporarily close the thoracic cavity of rabbits, provide a transparent window to inspect the wound at any time, and control the bacterial contamination efficiently. We further explore the solvent exchange method to other polyphenols and polymeric hydrogel composites. The results suggest that the solvent exchange method provides generic opportunities to fabricate homogeneous polyphenol strengthened hydrogel systems with high performance.

A photoelectric effect integrated scaffold for wireless regulation of nerve cellular behaviors

Electrical signal is regarded as a key factor to promote nerve cell neurogenesis. However, the usually used exogenous electrical stimulus mode needs additional equipment sources and complicated wirings, which is...

Facile engineering of ECM-mimetic injectable dual crosslinking hydrogels with excellent mechanical resilience, tissue adhesion, and biocompatibility

Injectable hydrogels have aroused ever-increasing interest for their cell/biomaterial delivery ability through minimally invasive procedures. Nevertheless, it is still a challenge to simply fabricate natural biopolymer-based injectable hydrogels possessing satisfactory mechanical properties, bioadhesion, and cell delivery ability. Herein, we describe a facile dual crosslinking (DC) strategy for preparing extracellular matrix (ECM) mimetic hydrogels with desirable comprehensive performance. The chondroitin sulfate (CS)- and gelatin (Gel)-based single crosslinked (SC) hydrogels were first developed via reversible borate ester bonds, and further strengthened through the Michael-addition crosslinking reaction or visible-light initiated photopolymerization with thiol-containing polyethylene glycol (PEG) crosslinkers. The dynamic SC hydrogels showed good injectability, pH-sensitive gel-sol transformation, and self-adhesion ability to various biological tissues such as skin, liver, and intervertebral disc. The mechanically tough DC hydrogels displayed tunable stiffness, and resilience to compression load (up to 90% strain) owing to the effective energy dissipation mechanism. The formed DC hydrogels after subcutaneous injection well integrated with surrounding tissues and exhibited fast self-recovery properties. Moreover, the photoencapsulation of human mesenchymal stem cells (hMSCs) within the developed DC hydrogels was achieved and has been proved to be biocompatible, highlighting the great potential of the photopolymerized DC hydrogels in cell delivery and three-dimensional (3D) cell culture. This biomimetic, mechanically resilient, adhesive, and cytocompatible injectable DC hydrogel could serve as a promising candidate for tissue engineering.

Photoinduced Gelatin-Methacrylate Scaffolds to Examine the Impact of Extracellular Environment on Trabecular Meshwork Cells

Glaucoma is the leading cause of irreversible blindness in the world, currently impacting 80 million people. Patients suffering from primary open-angle glaucoma experience aqueous humor accumulation within the eye causing an increase in intraocular pressure (IOP). The main cause of this rise in IOP is due to poor outflow of aqueous humor through the trabecular meshwork (TM), a tissue composed of collagen and glycosaminoglycans (GAGs) embedded with TM cells. The behavior of TM cells is impacted by their microenvironment, and studies conducted on two-dimensional plastic substrates do not necessarily reflect how TM cells would behave in their native setting. Here, we cultured human TM (hTM) cells on 3D biocompatible hydrogels composed of gelatin methacrylate (GelMA) incorporated with the glycosaminoglycans (GAGs) chondroitin sulfate (CS) and hyaluronic acid (HA). Mechanical properties were quantified by storage moduli and viscosity data. Cellular response was measured by quantifying cellular proliferation and expression of an important extracellular matrix protein, fibronectin. We have shown substrate mechanical properties to impact hTM cell proliferation over 2 weeks. It was found that the incorporation of GAGs impacted cell proliferation and fibronectin expression in hTM cells. This work will help elucidate hTM cell response with changes in their microenvironment.

3D Bioprinting of Biomimetic Bilayered Scaffold Consisting of Decellularized Extracellular Matrix and Silk Fibroin for Osteochondral Repair

Recently, three-dimensional (3D) bioprinting technology is becoming an appealing approach for osteochondral repair. However, it is challenging to develop a bilayered scaffold with anisotropic structural properties to mimic a native osteochondral tissue. Herein, we developed a bioink consisting of decellularized extracellular matrix and silk fibroin to print the bilayered scaffold. The bilayered scaffold mimics the natural osteochondral tissue by controlling the composition, mechanical properties, and growth factor release in each layer of the scaffold. The in vitro results show that each layer of scaffolds had a suitable mechanical strength and degradation rate. Furthermore, the scaffolds encapsulating transforming growth factor-beta (TGF-β) and bone morphogenetic protein-2 (BMP-2) can act as a controlled release system and promote directed differentiation of bone marrow-derived mesenchymal stem cells. Furthermore, the in vivo experiments suggested that the scaffolds loaded with growth factors promoted osteochondral regeneration in the rabbit knee joint model. Consequently, the biomimetic bilayered scaffold loaded with TGF-β and BMP-2 would be a promising strategy for osteochondral repair.

Key considerations on the development of biodegradable biomaterials for clinical translation of medical devices: With cartilage repair products as an example

With the interdisciplinary convergence of biology, medicine and materials science, both research and clinical translation of biomaterials are progressing at a rapid pace. However, there is still a huge gap between applied basic research on biomaterials and their translational products - medical devices, where two significantly different perspectives and mindsets often work independently and non-synergistically, which in turn significantly increases financial costs and research effort. Although this gap is well-known and often criticized in the biopharmaceutical industry, it is gradually widening. In this article, we critically examine the developmental pipeline of biodegradable biomaterials and biomaterial-based medical device products. Then based on clinical needs, market analysis, and relevant regulations, some ideas are proposed to integrate the two different mindsets to guide applied basic research and translation of biomaterial-based products, from the material and technical perspectives. Cartilage repair substitutes are discussed here as an example. Hopefully, this will lay a strong foundation for biomaterial research and clinical translation, while reducing the amount of extra research effort and funding required due to the dissonance between innovative basic research and commercialization pipeline.

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To elucidate the chain of medical devices development and basic research process.

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To propose rationales of biomaterial research with mindset of clinical translation.

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To elaborate with established medical devices for cartilage repairs as examples.

Tough and Resilient Hydrogels Enabled by a Multifunctional Initiating and Cross-Linking Agent

Many high-strength hydrogels have been developed in recent years; however, few of them are both tough and resilient, and their intrinsic paradoxical nature makes designing a gel with both high toughness and high resilience a great challenge. To address this problem, we introduced both N,N,N,N-pentamethyldiethylenetriamine (PA) and N,N-methylenebisacrylamide (MBA) into polyacrylamide hydrogel networks to construct an entangled network that contains chemically cross-linked chains and branched chains simultaneously. The entanglements of branched chains can act as a physical cross-linking point to uniformly disperse stress on molecular chains, and chemical cross-linking ensures the stability of the hydrogel network. The increase in the number and length of branched chains is able to achieve an enhancement in strength while the slip of the entangled polymer chains can effectively achieve energy dissipation and can improve the toughness of the gel. Moreover, the resultant hydrogels exhibit an excellent resilience (>98%). Therefore, high toughness and resilience are achieved simultaneously. In addition, we also investigated the initiation mechanism of PA. This strategy creates a new way for the preparation of next-generation high toughness and high resilience hydrogel-based materials, which have promising applications in wearable, flexible strain/pressure sensors.

Mussel-inspired hydrogels as tough, self-adhesive and conductive bioelectronics: a review

To overcome the wearable sensor's defects and achieve the goal of robust mechanical properties, long-term adhesion, sensitive electrical conductivity, the multifunctional hydrogels were inspired by various mussels on the base of catechol and its analogues. In this review, we review the strategies for improving the mechanical strength, adhesion, conductivity and antibacterial properties of mussel-inspired hydrogels as bioelectronics. Double network structures, nanocomposites, supramolecular block polymers and other strategies were utilized for achieving tough hydrogels to prevent tensile fractures under high deformation. Many mussel-inspired chemistries were incorporated for constructing skin-attachable hydrogel strain sensors and some strategies for controlling the oxidation of catechol were employed to achieve long-term adhesion. In addition, electrolytes, conductive fillers, conductive polymers and their relevant hydrophilic modifications were introduced for fabricating the conductive hydrogel bioelectronics to enhance the conductivity properties. Finally, the challenges and outlooks in this promising field are featured from the perspective of materials chemistry.

Recent developments in mussel-inspired materials for biomedical applications

Over the decades, researchers have strived to synthesize and modify nature-inspired biomaterials, with the primary aim to address the challenges of designing functional biomaterials for regenerative medicine and tissue engineering. Among these challenges, biocompatibility and cellular interactions have been extensively investigated. Some of the most desirable characteristics for biomaterials in these applications are the loading of bioactive molecules, strong adhesion to moist areas, improvement of cellular adhesion, and self-healing properties. Mussel-inspired biomaterials have received growing interest mainly due to the changes in mechanical and biological functions of the scaffold due to catechol modification. Here, we summarize the chemical and biological principles and the latest advancements in production, as well as the use of mussel-inspired biomaterials. Our main focus is the polydopamine coating, the conjugation of catechol with other polymers, and the biomedical applications that polydopamine moieties are used for, such as matrices for drug delivery, tissue regeneration, and hemostatic control. We also present a critical conclusion and an inspired view on the prospects for the development and application of mussel-inspired materials.

Design, preparation, and characterization of CS/PVA/SA hydrogels modified with mesoporous Ag2O/SiO2 and curcumin nanoparticles for green, biocompatible, and antibacterial biopolymer film

One of the most significant factors affecting the rapid and effective healing of wounds is the application of appropriate wound dressings. In the present study, novel antibacterial wound dressings are fabricated that consist of Chitosan (CS)/Polyvinyl alcohol (PVA)/Sodium Alginate (SA), which are all biocompatible, functionalized with mesoporous Ag₂O/SiO₂ and curcumin nanoparticles as reinforcements. In this research nanocomposites are fabricated (0 wt%, 5 wt%, 10 wt%, 15 wt%, and 20 wt% of Ag₂O/SiO₂). After the composition of nanocomposites using the cross-linked technique, Fourier Transform Infrared (FT-IR) spectroscopy is performed to confirm the functional groups that are added to the polymer at each step. X-ray diffraction (XRD) is done to show the crystallinity of Ag₂O/SiO₂. Field emission scanning electron microscopy (FE-SEM) studies are performed to demonstrate the morphology of the structure, Energy-dispersive X-ray spectroscopy (EDS) is done to examine the elements in the wound dressing and atomic force microscopy (AFM) study is performed to show surface roughness and pores. Then the nanocomposites with different weight percentages are cultured in three bacteria called Acinetobacter baumannii, Staphylococcus epidermidis, and Proteus mirabilis, all three of which cause skin infections. Finally, by performing the tensile test, the results related to the tensile strength of the wound dressings are examined. The results show that with the increase of Ag₂O/SiO₂, the mechanical properties, as well as the healing properties of the wound dressing, have increased significantly. Fabricating these nanocomposites helps a lot in treating skin infections.

CS/PVA/SA hydrogels modified with mesoporous Ag₂O/SiO₂ and curcumin nanoparticles for antibacterial biopolymer film.

Phenol-Hyaluronic Acid Conjugates: Correlation of Oxidative Crosslinking Pathway and Adhesiveness

Hyaluronic acid (HA) is a natural polysaccharide with great biocompatibility for a variety of biomedical applications, such as tissue scaffolds, dermal fillers, and drug-delivery carriers. Despite the medical impact of HA, its poor adhesiveness and short-term in vivo stability limit its therapeutic efficacy. To overcome these shortcomings, a versatile modification strategy for the HA backbone has been developed. This strategy involves tethering phenol moieties on HA to provide both robust adhesiveness and intermolecular cohesion and can be used for oxidative crosslinking of the polymeric chain. However, a lack of knowledge still exists regarding the interchangeable phenolic adhesion and cohesion depending on the type of oxidizing agent used. Here, we reveal the correlation between phenolic adhesion and cohesion upon gelation of two different HA–phenol conjugates, HA–tyramine and HA–catechol, depending on the oxidant. For covalent/non-covalent crosslinking of HA, oxidizing agents, horseradish peroxidase/hydrogen peroxide, chemical oxidants (e.g., base, sodium periodate), and metal ions, were utilized. As a result, HA–catechol showed stronger adhesion properties, whereas HA–tyramine showed higher cohesion properties. In addition, covalent bonds allowed better adhesion compared to that of non-covalent bonds. Our findings are promising for designing adhesive and mechanically robust biomaterials based on phenol chemistry.

Stretchable and Bioadhesive Gelatin Methacryloyl-Based Hydrogels Enabled by in Situ Dopamine Polymerization

Hydrogel patches with high toughness, stretchability, and adhesive properties are critical to healthcare applications including wound dressings and wearable devices. Gelatin methacryloyl (GelMA) provides a highly biocompatible and accessible hydrogel platform. However, low tissue adhesion and poor mechanical properties of cross-linked GelMA patches (i.e., brittleness and low stretchability) have been major obstacles to their application for sealing and repair of wounds. Here, we show that adding dopamine (DA) moieties in larger quantities than those of conjugated counterparts to the GelMA prepolymer solution followed by alkaline DA oxidation could result in robust mechanical and adhesive properties in GelMA-based hydrogels. In this way, cross-linked patches with ∼140% stretchability and ∼19 000 J/m³ toughness, which correspond to ∼5.7 and ∼3.3× improvement, respectively, compared to that of GelMA controls, were obtained. The DA oxidization in the prepolymer solution was found to play an important role in activating adhesive properties of cross-linked GelMA patches (∼4.0 and ∼6.9× increase in adhesion force under tensile and shear modes, respectively) due to the presence of reactive oxidized quinone species. We further conducted a parametric study on the factors such as UV light parameters, the photoinitiator type (i.e., lithium phenyl-2,4,6-trimethylbenzoylphosphinate, LAP, versus 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone, Irgacure 2959), and alkaline DA oxidation to tune the cross-linking density and thereby hydrogel compliance for better adhesive properties. The superior adhesion performance of the resulting hydrogel along with in vitro cytocompatibility demonstrated its potential for use in skin-attachable substrates.

The effects of GelMA hydrogel on nerve repair and regeneration in mice with spinal cord injury

Background

To determine the effects of gelatin methacryloyl (GelMA) hydrogel on nerve repair and regeneration in mice with spinal cord injury (SCI).

Methods

A total of 30 ICR mice (6–8 weeks old) were randomly assigned into the control group, the model group, and the experimental group via the random digits table method. There were 10 mice in each group. All mice underwent a T8 laminectomy. For mice in the experimental group and the model group, after the T8 laminectomy, SCI models were constructed by clamping the mice spinal cord tissue for 1 minute using an aneurysm clip (25 g). Additionally, the SCI area of each mouse in the experimental group was locally injected with 0.05–0.7 mL GelMA hydrogel [10% (w/v)] and photocrosslinking was initiated under a blue light source with a wavelength of 405 nm. The exercise performance of each mouse was tested via the bedside mobility scale (BMS) on post-operative days 1, 3, 7, and 14. After 14 days, mice were sacrificed and the dorsal root ganglion (DRG) sensory neurons were isolated and cultured for 3 days in vitro. The axon lengths of the neurons were then evaluated. Immunohistochemical staining was performed to assess the development of syringomyelia in the area. Western blots (WB) and immunofluorescence staining were performed to quantify the expression of glial fibrillary acidic protein (GFAP), growth associated protein (GAP)43, and nestin in the DRG neurons from each group of mice.

Results

Compared with mice in the control group, mice in the SCI model group showed a notable decrease in exercise ability, while the exercise ability of mice in the experimental group recovered markedly after treatment with GelMA hydrogel. Administration of GelMA hydrogel lengthened the axon of DRG neurons in mice and reduced the area of syringomyelia. Furthermore, GelMA hydrogel inhibited scar formation and promoted the recovery of neurological function by upregulating GAP43 and nestin expression and downregulating GFAP expression.

Conclusions

In mice with SCI, local injection of GelMA hydrogel strongly inhibited scar formation, reduced the area of syringomyelia, and promoted nerve regeneration and recovery of limb movement function.

Polyacrylamide/Chitosan-Based Conductive Double Network Hydrogels with Outstanding Electrical and Mechanical Performance at Low Temperatures

Hydrogel-based electronics have received growing attention because of their great flexibility and stretchability. However, the fabrication of conductive hydrogels with high stretchability, excellent toughness, outstanding sensitivity, and low-temperature stability still remains a great challenge. In this study, a type of conductive hydrogels consisting of a double network (DN) structure is synthesized. The dynamically cross-linked chitosan (CS) and the flexible polyacrylamide network doped with polyaniline constitute the DN through the hydrogen bonds between the hydroxyl, amide, and aniline groups. This type of hydrogels displays excellent mechanical performance, striking conductivity, and remarkable freezing tolerance. The flexible electronic sensors based on the double-network hydrogels demonstrate superior strain sensitivity and linear response on various deformations. Additionally, the good antifreezing property of the hydrogels allows the sensors to exhibit excellent performance at -20 °C.

Snake extract-laden hemostatic bioadhesive gel cross-linked by visible light

Bioadhesives reduce operation time and surgical complications. However, in the presence of blood, adhesion strength is often compromised. Inspired by the blood clotting activity of snake venom, we report a visible light-induced blood-resistant hemostatic adhesive (HAD) containing gelatin methacryloyl and reptilase, which is a hemocoagulase (HC) extracted from Bothrops atrox HAD leads to the activation and aggregation of platelets and efficiently transforms fibrinogen into fibrin to achieve rapid hemostasis and seal the tissue. Blood clotting time with HAD was about 45 s compared with 5 to 6 min without HAD. HAD instantaneously achieved hemostasis on liver incision (~45 s) and cut rat tail (~34 s) and reduced blood loss by 79 and 78%, respectively. HAD is also efficient in sealing severely injured liver and abdominal aorta. HAD has great potential to bridge injured tissues by combing hemostasis with adhesives.

3D Electrospun Nanofiber-Based Scaffolds: From Preparations and Properties to Tissue Regeneration Applications

Electrospun nanofibers have been frequently used for tissue engineering due to their morphological similarities with the extracellular matrix (ECM) and tunable chemical and physical properties for regulating cell behaviors and functions. However, most of the existing electrospun nanofibers have a closely packed two-dimensional (2D) membrane with the intrinsic shortcomings of limited cellular infiltration, restricted nutrition diffusion, and unsatisfied thickness. Three-dimensional (3D) electrospun nanofiber-based scaffolds can provide stem cells with 3D microenvironments and biomimetic fibrous structures. Thus, they have been demonstrated to be good candidates for in vivo repair of different tissues. This review summarizes the recent developments in 3D electrospun nanofiber-based scaffolds (ENF-S) for tissue engineering. Three types of 3D ENF-S fabricated using different approaches classified into electrospun nanofiber 3D scaffolds, electrospun nanofiber/hydrogel composite 3D scaffolds, and electrospun nanofiber/porous matrix composite 3D scaffolds are discussed. New functions for these 3D ENF-S and properties, such as facilitated cell infiltration, 3D fibrous architecture, enhanced mechanical properties, and tunable degradability, meeting the requirements of tissue engineering scaffolds were discovered. The applications of 3D ENF-S in cartilage, bone, tendon, ligament, skeletal muscle, nerve, and cardiac tissue regeneration are then presented with a discussion of current challenges and future directions. Finally, we give summaries and future perspectives of 3D ENF-S in tissue engineering and clinical transformation.

A Collagen-Mimetic Organic-Inorganic Hydrogel for Cartilage Engineering

Promising strategies for cartilage regeneration rely on the encapsulation of mesenchymal stromal cells (MSCs) in a hydrogel followed by an injection into the injured joint. Preclinical and clinical data using MSCs embedded in a collagen gel have demonstrated improvements in patients with focal lesions and osteoarthritis. However, an improvement is often observed in the short or medium term due to the loss of the chondrocyte capacity to produce the correct extracellular matrix and to respond to mechanical stimulation. Developing novel biomimetic materials with better chondroconductive and mechanical properties is still a challenge for cartilage engineering. Herein, we have designed a biomimetic chemical hydrogel based on silylated collagen-mimetic synthetic peptides having the ability to encapsulate MSCs using a biorthogonal sol-gel cross-linking reaction. By tuning the hydrogel composition using both mono- and bi-functional peptides, we succeeded in improving its mechanical properties, yielding a more elastic scaffold and achieving the survival of embedded MSCs for 21 days as well as the up-regulation of chondrocyte markers. This biomimetic long-standing hybrid hydrogel is of interest as a synthetic and modular scaffold for cartilage tissue engineering.

Bioinspired pressure-sensitive adhesive: evaluation of the effect of dopamine methacrylamide comonomer as a general property modifier using molecular dynamics simulation

The use of catechol-containing comonomers as a general property enhancer to achieve unique properties has received particular attention for designing bioinspired polymeric materials. In this study, molecular dynamics simulation was used to investigate the role of dopamine methacrylamide (DMA) and N-phenethyl methacrylamide (PMA) comonomers in chain conformation and their effects on the mechanical properties and adhesion of poly(n-butyl acrylate-co-acrylic acid) copolymer. Addition of 4% by weight of DMA comonomer in the terpolymer structure reduces the gyration radius of the poly(n-butyl acrylate-co-acrylic acid) copolymer. This reduction is due to the formation of intramolecular hydrogen bond interactions. A further increase in the DMA up to 12.2% by weight increases the radius of gyration by 5%. The effect of PMA on the gyration radius of the poly(n-butyl acrylate-co-acrylic acid) copolymer is more extensive, compared to DMA. While DMA enhances both van der Waals and electrostatic components of the cohesive energy density through increasing π–π interactions and hydrogen bond formations, PMA only improves the van der Waals component. Assessment of mechanical properties revealed that the addition of DMA comonomer resulted in a transition from brittle to tough behavior in poly(n-butyl acrylate-co-acrylic acid) pressure-sensitive adhesive. Ductility index improvement by DMA is higher than that by PMA. DMA comonomers accumulate on the silica surface resulting in the terpolymer chains approaching the dry silica surface from the hydroxyl groups of the catechol. Accumulation of DMA only enhances the cohesive energy and does not improve the adhesive energy.

The use of catechol-containing comonomers as a general property enhancer to achieve unique properties has received particular attention for designing bioinspired polymeric materials.