Mechanically and functionally strengthened tissue adhesive of chitin whisker complexed chitosan/dextran derivatives based hydrogel

Triple-crosslinked double-network alginate/dextran/dendrimer hydrogel with tunable mechanical and adhesive properties: A potential candidate for sutureless keratoplasty

An ideal adhesive hydrogel must possess high adhesion to the native tissue, biocompatibility, eligible biodegradability, and good mechanical compliance with the substrate tissues. We constructed an interpenetrating double-network hydrogel containing polysaccharides (alginate and dextran) and nanosized spherical dendrimer by both physical and chemical crosslinking, thus endowing the hydrogel with a broad range of mechanical properties, adhesive properties, and biological functions. The double-network hydrogel has moderate pore sizes and swelling properties. The chelation of calcium ions significantly enhances the tensile and compressive properties. The incorporation of dendrimer improves both the mechanical and adhesive properties. This multicomponent interpenetrating network hydrogel has excellent biocompatibility, tunable mechanical and adhesive properties, and satisfied multi-functions to meet the complex requirements of wound healing and tissue engineering. The hydrogel exhibits promising corneal adhesion capabilities in vitro, potentially supplanting the need for sutures in corneal stromal surgery and mitigating the risks associated with donor corneal damage and graft rejection during corneal transplantation. This novel polysaccharide and dendrimer hydrogel also shows good results in sutureless keratoplasty, with high efficiency and reliability. Based on the clinical requirements for tissue bonding and wound closure, the hydrogel provides insight into solving the mechanical properties and adhesive strength of tissue adhesives.

Emerging Frontiers in In Situ Forming Hydrogels for Enhanced Hemostasis and Accelerated Wound Healing

With a surge in the number of accidents and chronic wounds worldwide, there is a growing need for advanced hemostatic and wound care solutions. In this regard, in situ forming hydrogels have emerged as a revolutionary biomaterial due to their inherent properties, which include biocompatibility, biodegradability, porosity, and extracellular matrix (ECM)-like mechanical strength, that render them ideal for biomedical applications. This review demonstrates the advancements of in situ forming hydrogels, tracing their evolution from injectable to more sophisticated forms, such as sprayable and 3-D printed hydrogels. These hydrogels are designed to modulate the pathophysiology of wounds, enhancing hemostasis and facilitating wound repair. The review presents different methodologies for in situ forming hydrogel synthesis, spanning a spectrum of physical and chemical cross-linking techniques. Furthermore, it showcases the adaptability of hydrogels to the dynamic requirements of wound healing processes. Through a detailed discussion, this article sheds light on the multifunctional capabilities of these hydrogels such as their antibacterial, anti-inflammatory, and antioxidant properties. This review aims to inform and inspire continued advancement in the field, ultimately contributing to the development of sophisticated wound care solutions that meet the complexity of clinical needs.

Progress in chitin/chitosan and their derivatives for biomedical applications: Where we stand

Chitin and its deacetylated form, chitosan, have demonstrated remarkable versatility in the realm of biomaterials. Their exceptional biocompatibility, antibacterial properties, pro- and anticoagulant characteristics, robust antioxidant capacity, and anti-inflammatory potential make them highly sought-after in various applications. This review delves into the mechanisms underlying chitin/chitosan's biological activity and provides a comprehensive overview of their derivatives in fields such as tissue engineering, hemostasis, wound healing, drug delivery, and hemoperfusion. However, despite the wealth of studies on chitin/chitosan, there exists a notable trend of homogeneity in research, which could hinder the comprehensive development of these biomaterials. This review, taking a clinician's perspective, identifies current research gaps and medical challenges yet to be addressed, aiming to pave the way for a more sustainable future in chitin/chitosan research and application.

Tissue adhesives based on chitosan for biomedical applications

Chitosan bio-adhesives bond strongly with various biological tissues, such as skin, mucosa, and internal organs. Their adhesive ability arises from amino acid and hydroxyl groups in chitosan, facilitating interactions with tissue surfaces through chemical (ionic, covalent, and hydrogen) and physical (chain entanglement) bonding. As non-toxic, biodegradable, and biocompatible materials, chitosan bio-adhesives are a safe option for medical therapies. They are particularly suitable for drug delivery, wound healing, and tissue regeneration. In this review, we address chitosan-based bio-adhesives and the mechanisms associated with them. We also discuss different chitosan composite-based bio-adhesives and their biomedical applications in wound healing, drug delivery, hemostasis, and tissue regeneration. Finally, challenges and future perspectives for the clinical use of chitosan-based bio-adhesives are discussed.

Present status and application prospects of green chitin nanowhiskers: A comprehensive review

Petrochemical resources are non-renewable, which has impeded the development of synthetic polymers. The poor degradability of synthetic polymers poses substantial environmental pressure. Additionally, the high cost of synthetic biopolymers with excellent degradation performance limits their widespread application. Thus, it is crucial to seek green, sustainable, low-cost polymers as alternatives to petrochemical-based synthetic polymers and synthetic biopolymers. Chitin is a natural and renewable biopolymer discovered in crustacean shells, insect exoskeletons, and fungal cell walls. Chitin chains consist of crystalline and amorphous regions. Note that various treatments can be employed to remove the amorphous region, enhancing the crystallinity of chitin. Chitin nanowhiskers are a high crystallinity nanoscale chitin product with a high aspect ratio, a large surface area, adjustable surface morphology, and biocompatibility. They discover widespread applications in biomedicine, environmental treatment, food packaging, and biomaterials. Various methods can be utilized for preparing chitin nanowhiskers, including chemical, ionic liquids, deacetylation, and mechanical methods. However, developing an environmentally friendly preparation process remains a big challenge for expanding their applications in different materials and large-scale production. This article comprehensively analyzes chitin nanowhiskers' preparation strategies and their drawbacks. It also highlights the extensive application in different materials and various fields, besides the potential for commercial application.

A pilot study on endoscopic delivery of injectable bioadhesive for esophageal repair in a porcine model

Endoscopic submucosal dissection (ESD) is the gold-standard surgical procedure for superficial esophageal cancer. A significant and challenging complication of this technique is post-ESD esophageal stricture. In this study, the feasibility of endoscopic catheter delivery of bioadhesive to esophageal lesions in a porcine model was tested. Injectable bioadhesive was composed of oxidized dextran (ODA) and chitosan hydrochloride (CS), its physicochemical properties, injectability, antibacterial activity, and cytocompatibility were investigated beforein vivotest. ODA-CS bioadhesive was delivered to the wound bed of the esophageal tissue using a custom-made catheter device after ESD in a porcine model. Our results show that the ODA-CS bioadhesive is of good injectability, tissue adhesive strength, antibacterial capacity, and blood compatibility.In vivodelivery was achieved by endoscopic spraying of ODA and CS in separate catheters fixed on the endoscopic probe. ODA and CS can be mixed well to allow in situ bioadhesive formation and firmly adhere to the esophageal wound surface. After two weeks, the bioadhesive maintained structural integrity and adhered to the surface of esophageal wounds. However, histological analysis reveals that the ODA-CS bioadhesive did not show improvement in attenuating inflammatory response after ESD. This pilot study demonstrates the feasibility of ODA-CS bioadhesive for shielding esophageal wounds after ESD, whereas efforts need to improve its anti-inflammatory activity to reduce fibrosis for stricture prevention.

Recent Advances in Whiskers: Properties and Clinical Applications in Dentistry

Whiskers are nanoscale, high-strength fibrous crystals with a wide range of potential applications in dentistry owing to their unique mechanical, thermal, electrical, and biological properties. They possess high strength, a high modulus of elasticity and good biocompatibility. Hence, adding these crystals to dental composites as reinforcement can considerably improve the mechanical properties and durability of restorations. Additionally, whiskers are involved in inducing the value-added differentiation of osteoblasts, odontogenic osteocytes, and pulp stem cells, and promoting the regeneration of alveolar bone, periodontal tissue, and pulp tissue. They can also enhance the mucosal barrier function, inhibit the proliferation of tumor cells, control inflammation, and aid in cancer prevention. This review comprehensively summarizes the classification, properties, growth mechanisms and preparation methods of whiskers and focuses on their application in dentistry. Due to their unique physicochemical properties, excellent biological properties, and nanoscale characteristics, whiskers show great potential for application in bone, periodontal, and pulp tissue regeneration. Additionally, they can be used to prevent and treat oral cancer and improve medical devices, thus making them a promising new material in dentistry.

Production and comparison of structural, thermal and physical characteristics of chitin nanoparticles obtained by different methods

This study examined the impact of acid hydrolysis, tempo oxidation, and mechanical grinding on the physical, thermal, and structural properties of α-chitin nanocrystals and nanofibers. The manufacturing methods could influence the diameter, functional groups, and crystal patterns of the resulting nanoparticles. Analysis of the DLS results revealed that the size of acidic nanocrystals were smaller and showed improved dispersibility. The XRD patterns indicated that the chemical and mechanical treatments did not alter the crystalline arrangement of the α-chitin. FT-IR spectra analysis revealed that the chemical and mechanical methods did not affect the functional groups of the nanoparticles. DSC results showed that the nanoparticles had good thermal stability up to 400 °C, and it was found that the nanofibers had better thermal resistance due to their longer length. In the FE-SEM images, the nanoparticles were observed as fiber mats with a length of more than 100 nm. It was also found that the diameter of the nanoparticles was less than 100 nm.

Progress of polysaccharide-based tissue adhesives

Recently, polymer-based tissue adhesives (TAs) have gained the attention of scientists and industries as alternatives to sutures for sealing and closing wounds or incisions because of their ease of use, low cost, minimal tissue damage, and short application time. However, poor mechanical properties and weak adhesion strength limit the application of TAs, although numerous studies have attempted to develop new TAs with enhanced performance. Therefore, next-generation TAs with improved multifunctional properties are required. In this review, we address the requirements of polymeric TAs, adhesive characteristics, adhesion strength assessment methods, adhesion mechanisms, applications, advantages and disadvantages, and commercial products of polysaccharide (PS)-based TAs, including chitosan (CS), alginate (AL), dextran (DE), and hyaluronic acid (HA). Additionally, future perspectives are discussed.

Adenosine Triphosphate/Chitin Whisker/Phenylboronic Acid-Modified Wool Fabrics with Enhanced Dyeability

Promoting the uptake of dyes is an important part of the sustainable processing of wool products. This study presents an effective modification approach to enhance the dyeability of wool fabric with adenosine triphosphate as an activator, 3-carboxyphenyl boronic acid as a ligand-binding agent, and chitin whisker as a couple agent. The structure and surface morphology of the as-prepared wool fabric was characterized in detail. Natural luteolin and acid red 1 were used to dye the modified wool fabric, and the effect of different dyeing parameters on dyeing properties was discussed. The results indicated that the modified wool gained better surface color depth (K/S) and uptake without additional agents than the untreated wool fabric. When the modified wool fabric was dyed at 45 °C with luteolin and at 60 °C with acid red 1, the dyeing processes of the two dyes on the modified wool fabrics followed the Langmuir isotherm and the pseudo-second-order kinetic model. Furthermore, the dyed modified wool fabrics possessed improved color fastness. Overall, this work offers a facile, effective, and sustainable way to improve the low-temperature dyeability of wool products.

Progress in injectable hydrogels for the treatment of incompressible bleeding: an update

Uncontrollable haemorrhage from deep, noncompressible wounds remains a persistent and intractable challenge, accounting for a very high proportion of deaths in both war and disaster situations. Recently, injectable hydrogels have been increasingly studied as potential haemostatic materials, highlighting their enormous potential for the management of noncompressible haemorrhages. In this review, we summarize haemostatic mechanisms, commonly used clinical haemostatic methods, and the research progress on injectable haemostatic hydrogels. We emphasize the current status of injectable hydrogels as haemostatic materials, including their physical and chemical properties, design strategy, haemostatic mechanisms, and application in various types of wounds. We discuss the advantages and disadvantages of injectable hydrogels as haemostatic materials, as well as the opportunities and challenges involved. Finally, we propose cutting-edge research avenues to address these challenges and opportunities, including the combination of injectable hydrogels with advanced materials and innovative strategies to increase their biocompatibility and tune their degradation profile. Surface modifications for promoting cell adhesion and proliferation, as well as the delivery of growth factors or other biologics for optimal wound healing, are also suggested. We believe that this paper will inform researchers about the current status of the use of injectable haemostatic hydrogels for noncompressible haemorrhage and spark new ideas for those striving to propel this field forward.

Polysaccharide-based hydrogels for medical devices, implants and tissue engineering: A review

Hydrogels are highly biocompatible biomaterials composed of crosslinked three-dimensional networks of hydrophilic polymers. Owing to their natural origin, polysaccharide-based hydrogels (PBHs) possess low toxicity, high biocompatibility and demonstrate in vivo biodegradability, making them great candidates for use in various biomedical devices, implants, and tissue engineering. In addition, many polysaccharides also show additional biological activities such as antimicrobial, anticoagulant, antioxidant, immunomodulatory, hemostatic, and anti-inflammatory, which can provide additional therapeutic benefits. The porous nature of PBHs allows for the immobilization of antibodies, aptamers, enzymes and other molecules on their surface, or within their matrix, potentiating their use in biosensor devices. Specific polysaccharides can be used to produce transparent hydrogels, which have been used widely to fabricate ocular implants. The ability of PBHs to encapsulate drugs and other actives has been utilized for making neural implants and coatings for cardiovascular devices (stents, pacemakers and venous catheters) and urinary catheters. Their high water-absorption capacity has been exploited to make superabsorbent diapers and sanitary napkins. The barrier property and mechanical strength of PBHs has been used to develop gels and films as anti-adhesive formulations for the prevention of post-operative adhesion. Finally, by virtue of their ability to mimic various body tissues, they have been explored as scaffolds and bio-inks for tissue engineering of a wide variety of organs. These applications have been described in detail, in this review.

Photopolymerizable, immunomodulatory hydrogels of gelatin methacryloyl and carboxymethyl chitosan as all-in-one strategic dressing for wound healing

Microenvironment regeneration in wound tissue is crucial for wound healing. However, achieving desirable wound microenvironment regeneration involves multiple stages, including hemostasis, inflammation, proliferation, and remodeling. Traditional wound dressings face challenges in fully manipulating all these stages to achieve quick and complete wound healing. Herein, we present a VEGF-loaded, versatile wound dressing hydrogel based on gelatin methacryloyl (GelMA) and carboxymethyl chitosan (CMCS), which could be easily fabricated using UV irradiation. The newly designed GelMA-CMCS@VEGF hydrogel not only exhibited strong tissue adhesion capacity due to the interactions between CMCS active groups and biological tissues, but also possessed desirable extensible properties for frequently moving skins and joints. Furthermore, the hydrogel demonstrates exceptional abilities in blood cell coagulation, hemostasis and cell recruitment, leading to the promotion of endothelial cells proliferation, adhesion, migration and angiogenesis. Additionally, in vivo studies demonstrated that the hydrogel drastically shortened hemostatic time, and achieved satisfactory therapeutic efficacy by suppressing inflammation, modulating M1/M2 polarization of macrophages, significantly promoting collagen deposition, stimulating angiogenesis, epithelialization and tissue remodeling. This work contributes to the design of versatile hydrogel dressings for rapid and complete wound healing therapy.

Bioadhesives with Antimicrobial Properties

Bioadhesives with antimicrobial properties enable easier and safer treatment of wounds as compared to the traditional methods such as suturing and stapling. Composed of natural or synthetic polymers, these bioadhesives seal wounds and facilitate healing while preventing infections through the activity of locally released antimicrobial drugs, nanocomponents, or inherently antimicrobial polers. Although many different materials and strategies are employed to develop antimicrobial bioadhesives, the design of these biomaterials necessitates a prudent approach as achieving all the required properties including optimal adhesive and cohesive properties, biocompatibility, and antimicrobial activity can be challenging. Designing antimicrobial bioadhesives with tunable physical, chemical, and biological properties will shed light on the path for future advancement of bioadhesives with antimicrobial properties. In this review, the requirements and commonly used strategies for developing bioadhesives with antimicrobial properties are discussed. In particular, different methods for their synthesis and their experimental and clinical applications on a variety of organs are reviewed. Advances in the design of bioadhesives with antimicrobial properties will pave the way for a better management of wounds to increase positive clinical outcomes.

Fabricating Oxidized Cellulose Sponge for Hemorrhage Control and Wound Healing

Uncontrolled hemorrhage and infection are the main reasons for many trauma-related deaths in both clinic and battlefield. However, most hemostatic materials have various defects and side effects, such as low hemostatic efficiency, poor biocompatibility, weak degradation ability, and lack of antimicrobial properties. Herein, an oxidized cellulose (OC) sponge with antibacterial properties and biosafety was fabricated for hemorrhage control and wound healing. The as-prepared OC sponges were prone to water triggered expansion and superabsorbent capacity, which could facilitate blood component concentration effectively. Importantly, they had significant biodegradability with little irritation to the skin. This hemostat could also reduce the plasma clotting time to 53.54% in vitro and demonstrated less blood loss than commercially available hemostatic agents (GS) in a mouse model of bleeding from liver defects. Furthermore, the biocompatibility antimicrobial properties and possible hemostatic mechanism of the OC sponge were also systematically evaluated. Importantly, the potential wound healing applications have also been demonstrated. Therefore, the materials have broad clinical application prospects.

A Nature-Inspired Versatile Bio-Adhesive

The application of most hydrogel bio-adhesives is greatly limited due to their high swelling, low underwater adhesion, and single function. Herein, a spatial multi-level physical-chemical and bio-inspired in-situ bonding strategy is proposed, to develop a multifunctional hydrogel bio-glue using polyglutamic acid (PGA), tyramine hydrochloride (TYR), and tannic acid (TA) as precursors and 4-(4,6-dimethoxytriazine-2-yl) -4-methylmorpholine hydrochloride(DMTMM) as condensation agent, which is used for tissue adhesion, hemostasis and repair. By introducing TYR and TA into the PGA chain, it is demonstrated that not only can the strong adhesion of bio-glue to the surface of various fresh tissues and wet materials be realized through the synergistic effect of spatial multi-level physical and chemical bonding, but also this glue can be endowed with the functions of anti-oxidation and hemostasis. The excellent performance of such bio-glue in the repair of the wound, liver, and cartilage is achieved, showing a great potential in clinical application for such bio-glue. This study will open up a brand-new avenue for the development of multifunctional hydrogel biological adhesive.

Nano-chitin reinforced agarose hydrogels: Effects of nano-chitin addition and acidic gas-phase coagulation

Hydrogels based on natural polymers such as agarose usually show low applicability due to their weak mechanical properties. In this work, we developed a dual cross-linked agarose hydrogel by adding different amounts of TEMPO-oxidized nano-chitin (0-0.2 %) to agarose hydrogel matrices and then physically cross-linked under acidic gas-phase coagulation. The prepared hydrogels were characterized by FTIR, XRD, TGA, and SEM. The effects of nano-chitin addition and acidic gas-phase coagulation on the properties of agarose hydrogels, such as gel strength, swelling degree, rheological properties, and methylene blue (MB) adsorption capacity, were also studied. Structural characterizations confirmed that nano-chitin was successfully introduced into agarose hydrogels. The gel strength, storage modulus, and MB adsorption capacity of agarose hydrogels gradually increased with the increasing nano-chitin addition, whereas the swelling degree decreased. After acidic gas-phase coagulation, agarose/nano-chitin nanocomposite hydrogels exhibited improved gel strength and storage modulus, while the swelling degree and MB adsorption capacity were slightly reduced. The combination of oxidized nano-chitin and acidic gas-phase coagulation is expected to be an effective way to improve the properties of natural polymer hydrogels.

An injectable hydrogel based on hyaluronic acid prepared by Schiff base for long-term controlled drug release

Drug-loaded injectable hydrogels have been studied widely in biomedical technology while the stable long-term controlled drug release and cytotoxicity are challenges. In this work, an injectable hydrogel with good swelling resistance was in situ synthetized using aminated hyaluronic acid (NHA) and aldehyde β-cyclodextrin (ACD) via Schiff-base reaction. The composition, morphology and mechanical property were characterized with FTIR, ¹³C NMR, SEM and rheology test, respectively. Voriconazole (VCZ) and Endophthalmitis was selected as a model drug and disease, respectively. The drug release, cytotoxicity and antifungal properties were detected in vitro. The results showed a long-term (> 60 days) drug release was realized, the NHA/ACD2/VCZ presented a zero-order release in the later stage. The cytotoxicity of NHA/ACD was detected by live/dead staining assay and Cell Counting Kit-8 (CCK-8). The survival rate of adult retina pigment epithelial cell line-19 (ARPE-19) was over 100 % after 3 d, it indicated a good cytocompatibility. The antifungal experiment presented samples had antifungal property. Biocompatibility in vivo proved NHA/ACD2 had no adverse effects on ocular tissues. Consequently, the injectable hydrogel based on hyaluronic acid prepared by Schiff base reaction provides a new option for long-term controlled drug release in the course of disease treatment from a material perspective.

Colorimetric pH-responsive and hemostatic hydrogel-based bioadhesives containing functionalized silver nanoparticles

Here we develop and characterize a dual-cross-linked pH-responsive hydrogel based on the carboxyethyl chitosan-oxidized sodium alginate (CAO) containing silver nanoparticles (Ag NPs) functionalized with tannic acid/red cabbage (ATR). This hybrid hydrogel is formed via covalent and non-covalent cross-linking. The adhesive strength measured in contact with cow skin and compression strength is measured more than 3 times higher than that of CAO. Importantly, the incorporation of 1 ​wt% ATR into CAO significantly enhances the compression strength of CAO from 35.1 ​± ​2.1 ​kPa to 97.5 ​± ​2.9 ​kPa. Moreover, the cyclic compression tests confirm significantly higher elastic behavior of CAO after the addition of ATR-functionalized NPs to CAO. The CAO/ATR hydrogel is pH-sensitive and indicated remarkable color changes in different buffer solutions. The CAO/ATR also shows improved hemostatic properties and reduced clotting time compared to the clotting time of blood in contact with CAO hydrogel. In addition, while CAO/ATR is effective in inhibiting the growth of both Gram-positive and Gram-negative bacteria, CAO is only effective in inhibiting the growth of Gram-positive bacteria. Finally, the CAO/ATR hydrogel is cytocompatible with L929 fibroblasts. In summary, the resulting CAO/ATR hydrogel shows promising results in designing and constructing smart wound bioadhesives with high cytocompatibility, antibacterial properties, blood coagulation ability, and fast self-healing properties.

Review: Application of chitosan and its derivatives in medical materials

Chitin is a natural polymeric polysaccharide extracted from marine crustaceans, and chitosan is obtained by removing part of the acetyl group (usually more than 60 %) in chitin's structure. Chitosan has attracted wide attention from researchers worldwide due to its good biodegradability, biocompatibility, hypoallergenic and biological activities (antibacterial, immune and antitumor activities). However, research has shown that chitosan does not melt or dissolve in water, alkaline solutions and general organic solvents, which greatly limits its application range. Therefore, researchers have carried out extensive and in-depth chemical modification of chitosan and prepared a variety of chitosan derivatives, which have expanded the application field of chitosan. Among them, the most extensive research has been conducted in the pharmaceutical field. This paper summarizes the application of chitosan and chitosan derivatives in medical materials over the past five years.

A triple-network carboxymethyl chitosan-based hydrogel for hemostasis of incompressible bleeding on wet wound surfaces

Hydrogel is a kind of hemostatic agent with good application prospect. However, the water molecules on the wound made the hydrogel less adhesive to wet wound tissue. Herein, the carboxymethyl chitosan (CMCS)/oxidized dextran (OD)/γ-polyglutamic acid (γ-PGA) hydrogel was prepared using a double-barreled syringe for hemostasis of diffuse and incompressible wound bleeding. The hydrogel formation was based on the intramolecular lactam bonds, intermolecular amide bonds, and Schiff base bonds. In the hydrogel, the super hydrophilic γ-PGA could drain the surface moisture of the wound and create a local dry environment for enhanced surface adhesion. In vivo study showed that the CMCS/ODex/γ-PGA hydrogel possesses a good biosafety and biodegradability. Interestingly, the CMCS/ODex/γ-PGA hydrogel exhibited excellent hemostatic abilities in dynamic humid environment and resisted a high blood pressure of 238 mmHg, which exceeds the threshold systolic blood pressure of healthy adults (i.e., 120 mmHg). Together with the antibacterial and reactive nitrogen species scavenging activities, this study is expected to provide a new method to design the wet-surface adhesives for the efficient hemostatic application.

Chitin, Chitosan, and Nanochitin: Extraction, Synthesis, and Applications

Crustacean shells are a sustainable source of chitin. Extracting chitin from crustacean shells is ongoing research, much of which is devoted to devising a sustainable process that yields high-quality chitin with minimal waste. Chemical and biological methods have been used extensively for this purpose; more recently, methods based on ionic liquids and deep eutectic solvents have been explored. Extracted chitin can be converted into chitosan or nanochitin. Once chitin is obtained and modified into the desired form, it can be used in a wide array of applications, including as a filler material, in adsorbents, and as a component in biomaterials, among others. Describing the extraction of chitin, synthesis of chitosan and nanochitin, and applications of these materials is the aim of this review. The first section of this review summarizes and compares common chitin extraction methods, highlighting the benefits and shortcomings of each, followed by descriptions of methods to convert chitin into chitosan and nanochitin. The second section of this review discusses some of the wide range of applications of chitin and its derivatives.

Recent advances in polysaccharide-based in situ forming hydrogels

Polysaccharides comprise an important class of natural polymers; they are abundant, diverse, polyfunctional, typically benign, and are biodegradable. Using polysaccharides to design in situ forming hydrogels is an attractive and important field of study since many polysaccharide-based hydrogels exhibit desirable characteristics including self-healing, responsiveness to environmental stimuli, and injectability. These characteristics are particularly useful for biomedical applications. This review will discuss recent discoveries in polysaccharide-based in situ forming hydrogels, including network architecture designs, curing mechanisms, physical and chemical properties, and potential applications.

Dynamic reversible adhesives based on crosslinking network via Schiff base and Michael addition

It is of practical interest to obtain polymers with complex material properties in a simplified synthetic manner for a broader range of practical applications. In this work, we constructed a dynamic reversible adhesive based on branched polyamine (PA) and p-formylphenyl acrylate (FPA) by simultaneously performing Michael addition reaction and Schiff base reaction. Branched polyamines provide a large number of amino groups as reaction sites that can react with both carbon-carbon double bonds and aldehyde groups. This enables the branched polymeric adhesive system to have a large number of Schiff base bonds within it, an important property of Schiff base bonds is that they are dynamically reversible. This allows us to prepare adhesives with hyperbranched crosslinking networks and recycling properties, and we have verified that FPA-PA adhesives do not exhibit significant fatigue after multiple recycling through the gluing-destruction-gluing process. The resulting FPA-PA adhesives produce tough bonding on multi-substrates such as steel, aluminum, glass, PVC, PTFE, birch and moso bamboo, which exhibited by lap shear strength of 2.4 MPa, 1.7 MPa, 1.4 MPa, 1.3 MPa, 0.4 MPa, 1.6 MPa, and 1.8 MPa, respectively. The feasibility of the synthesis idea of simultaneous Michael addition reaction and Schiff base reaction was demonstrated, as well as the excellent performance and great application potential of FPA-PA adhesives to be recyclable on multi-substrates.

Adhesion advances: from nanomaterials to biomimetic adhesion and applications

The field of adhesion has revealed a significant impact on numerous applications such as wound healing, drug delivery, electrically conductive adhesive, dental adhesive, and wood industry. Nanotechnology has continued to be the primary means to achieve adhesion. Among them, biological systems based on the unique structure of the nano-levels have developed excellent adhesion capabilities after billions of years of evolution and natural selection. Therefore, the research on bionic adhesion inspired by biological systems has gradually emerged. This review firstly focuses on the mechanism of adhesion, and secondly reports the effects of different nanomaterials on adhesion properties. Then based on the structure of mussels, geckos, tree frogs, octopuses, and other organisms, the research progress of biomimetic nanotechnology to achieve adhesion is summarized. Finally, the applications, challenges, and future directions of nanotechnology in new adhesive materials are provided.

Ternary Complex Coacervate of PEG/TA/Gelatin as Reinforced Bioadhesive for Skin Wound Repair

Bioadhesives have attracted more attention in surgery due to their easy operability and abilities of promoting wound closure and tissue healing. However, it is still a great challenge to develop a robust and biocompatible bioadhesive through a facile preparation method. Herein, a ternary complex coacervate comprised of tannic acid (TA), polyethylene glycol (PEG), and gelatin (TPG) is proposed as a novel bioadhesive, which is fabricated by simple physical blending method. The adhesion capacity of TPG was reinforced through programming the cross-linking network of TPG matrix and tailoring the interfacial interactions between matrix and tissue. Curing parameters (pH, temperature, and period) and gelatin content in TPG have crucial impacts on the final comprehensive adhesion performance. The adhesion strength of the optimized formulation, fabricated with 10% (m/m) gelatin (TPG10), was over 3 folds of TPG0 (without gelatin inclusion) after 24 h curing at pH 6 and 37 °C. The mechanism of the reinforced comprehensive adhesion was also investigated, suggesting TA provided tough interfacial adhesion, covalent cross-link of TA-gelatin improved mechanical properties, and the hydrogen bonds mediated dynamic cross-link between TA and PEG enabled the bulk matrix to dissipate energy upon deformation. Furthermore, the additional antibacterial activity, biocompatibility, and suitable degradability endowed TPG10 with desirable wound closure and tissue repairing efficacy on rat skin wound model. Such low-cost, readily prepared, and function-efficient bioadhesive could provide a versatile platform for tissue repair and regeneration.

Dextran and peptide-based pH-sensitive hydrogel boosts healing process in multidrug-resistant bacteria-infected wounds

Traumatic multidrug-resistant (MDR) bacterial infections are deadly threat to the public. To combat MDR bacteria, we developed a dual functional pH-sensitive hydrogel based on peptide DP7 (VQWRIRVAVIRK) and oxidized dextran (DP7-ODEX hydrogel). As an antimicrobial peptide, DP7 can synergize with many antibiotics; thus, we loaded ceftazidime into DP7-ODEX hydrogel, which showed an obvious advantage in MDR P. aeruginosa inhibition. Additionally, due to the interaction between aldehyde groups in oxidized dextran and amine groups from wound tissue, the hydrogel could extend on the irregular surface of skin defects and promote epithelial cells adhesion. DP7 could also be used as a wound-healing peptide and accelerate the healing process. We confirmed that the DP7-ODEX hydrogel exerted formidable therapeutic effects in normal or diabetic wound infection model. According to histomorphology analysis we found that DP7 hydrogel also have a scarless wound healing ability. In summary, we developed a hydrogel fabricated by the dual functional peptide DP7 that can kill multidrug-resistant bacteria colonizing the wound bed and boost scarless wound healing.

Chitin Nanocrystals: Environmentally Friendly Materials for the Development of Bioactive Films

Biobased nanomaterials have gained growing interest in recent years for the sustainable development of composite films and coatings, providing new opportunities and high-performance products. In particular, chitin and cellulose nanocrystals offer an attractive combination of properties, including a rod shape, dispersibility, outstanding surface properties, and mechanical and barrier properties, which make these nanomaterials excellent candidates for sustainable reinforcing materials. Until now, most of the research has been focused on cellulose nanomaterials; however, in the last few years, chitin nanocrystals (ChNCs) have gained more interest, especially for biomedical applications. Due to their biological properties, such as high biocompatibility, biodegradability, and antibacterial and antioxidant properties, as well as their superior adhesive properties and promotion of cell proliferation, chitin nanocrystals have emerged as valuable components of composite biomaterials and bioactive materials. This review attempts to provide an overview of the use of chitin nanocrystals for the development of bioactive composite films in biomedical and packaging systems.

Injectable and adhesive hydrogels for dealing with wounds

INTRODUCTION

The development of wound dressing materials that combine healing properties, ability to self-repair the material damages, skin-friendly adhesive nature, and competent mechanical properties have surpassing functional importance in healthcare. Due to their specificity, hydrogels have been recognized as a new gateway in biological materials to treat dysfunctional tissues. The design and creation of injectable hydrogel-based scaffolds have extensively progressed in recent years to improve their therapeutic efficacy and to pave the way for their easy minimally invasive administration. Hence, injectable hydrogel biomaterials have been prepared to eventually translate into minimally invasive therapy and pose a lasting effect on regenerative medicine.

AREAS COVERED

This review highlights the recent development of adhesive and injectable hydrogels that have applications in wound healing and wound dressing. Such hydrogel materials are not only expected to improve therapeutic outcomes but also to facilitate the easy surgical process in both wound healing and dressing.

EXPERT OPINION

Wound healing seems to be an appealing approach for treating countless life-threatening disorders. With the average increase of life expectancy in human societies, an increase in demand for injectable skin replacements and drug delivery carriers for chronic wound healing is expected.

An in situ catechol functionalized ε-polylysine/polyacrylamide hydrogel formed by hydrogen bonding recombination with high mechanical property for hemostasis

In situ hydrogel has attracted widely attention in hemostasis due to its ability to match irregular defects, but its application is limited by insufficient mechanical strength and long gelation time. Although some specifical in situ chemically cross-linked hydrogels could be fast formed and exhibit high mechanical strength, they unable to absorb blood. Hence their applications were further limited in emergency hemostasis usage. In this study, a robust hydrogel formed by hydration of powders was developed using multiple hydrogen bonds crosslinking. Here, catechol groups modified ε-polylysine (PL-CAT) and polyacrylamide (PAAM) were used to construct the PL-CAT/PAAM hydrogel. This hydrogel could be formed within 7 s to adhere and seal bleeding sites. The catechol groups endowed the hydrogel outstanding adhesive strength, which was 3.5 times of fibrin glue. Besides, the mechanical performance of in-situ PL-CAT/PAAM hydrogel was explored and the results showed that the hydrogel exhibited high compressive strength (0.47 MPa at 85% strain). Most importantly, the blood loss of wound treated with PL-CAT/PAAM hydrogel powders was 1/7 of untreated group, indicating the hydrogel's excellent hemostatic effect. And the cytotoxicity studies indicated that the PL-CAT/PAAM hydrogel had low toxicity. To summarize, this hydrogel could be a potential hemostatic material in emergency situations.

Homogeneous deacetylation and degradation of chitin in NaOH/urea dissolution system

Since being discovered, alkali/urea has been widely used in the dissolution of natural polysaccharides and the preparation of functional materials such as hydrogels, fibers, films and nanoparticles. This work will focus on verifying the structural stability, homogeneous degradation and deacetylation of chitin in alkali-soluble systems. The chitin was dissolved in NaOH/urea solution and stored at different temperature. At the specific time, the structure, viscosity, acetylation degree (DA) and biocompatibility of chitin and prepared chitosan were determined. The results indicated that dissolution process did not affect the structure and bioactivity of chitin. However, with the increase of storage time and temperature, chitin undergone significant homogeneous deacetylation (DA from 99.5% to 33.2%) and degradation (viscosity from 9284 cP to 1538 cP), accompanying by changes in crystalline structure and thermal stability. Moreover, the processed chitins were no-toxic for the biomedicine applications. This work will provide new ideas for the application of alkali-soluble systems.

Strong, Multifaceted Guanidinium-Based Adhesion of Bioorganic Nanoparticles to Wet Biological Tissue

Gluing dynamic, wet biological tissue is important in injury treatment yet difficult to achieve. Polymeric adhesives are inconvenient to handle due to rapid cross-linking and can raise biocompatibility concerns. Inorganic nanoparticles adhere weakly to wet surfaces. Herein, an aqueous suspension of guanidinium-functionalized chitin nanoparticles as a biomedical adhesive with biocompatible, hemostatic, and antibacterial properties is developed. It glues porcine skin up to 3000-fold more strongly (30 kPa) than inorganic nanoparticles at the same concentration and adheres at neutral pH, which is unachievable with mussel-inspired adhesives alone. The glue exhibits an instant adhesion (2 min) to fully wet surfaces, and the glued assembly endures one-week underwater immersion. The suspension is lowly viscous and stable, hence sprayable and convenient to store. A nanomechanic study reveals that guanidinium moieties are chaotropic, creating strong, multifaceted noncovalent bonds with proteins: salt bridges comprising ionic attraction and bidentate hydrogen bonding with acidic moieties, cation-π interactions with aromatic moieties, and hydrophobic interactions. The adhesion mechanism provides a blueprint for advanced tissue adhesives.

Ultrafast in-situ forming halloysite nanotube-doped chitosan/oxidized dextran hydrogels for hemostasis and wound repair

A series of halloysite nanotube (HNT)-doped chitosan (CS)/oxidized dextran (ODEX) adhesive hydrogels were developed through a Schiff base reaction. The resultant CS/ODEX/HNT hydrogels could not only form in situ on wounds within only 1 s when injected, but could also adapt to wounds of different shapes and depths after injection. We established four rat and rabbit hemorrhage models and demonstrated that the hydrogels are better than the clinically used gelatin sponge for reducing hemostatic time and blood loss, particularly in arterial and deep noncompressible bleeding wounds. Moreover, the natural antibacterial features of CS and ODEX provided the hydrogels with strong bacteria-killing effects. Consequently, they significantly promoted methicillin-resistant Staphylococcus aureus -infected-wound repair compared to commercial gelatin sponge and silver-alginate antibacterial wound dressing. Hence, our multifunctional hydrogels with facile preparation process and utilization procedure could potentially be used as first-aid biomaterials for rapid hemostasis and infected-wound repair in emergency injury events.

Chitin and chitosan on the nanoscale

In a matter of decades, nanomaterials from biomass, exemplified by nanocellulose, have rapidly transitioned from once being a subject of curiosity to an area of fervent research and development, now reaching the stages of commercialization and industrial relevance. Nanoscale chitin and chitosan, on the other hand, have only recently begun to raise interest. Attractive features such as excellent biocompatibility, antibacterial activity, immunogenicity, as well as the tuneable handles of their acetylamide (chitin) or primary amino (chitosan) functionalities indeed display promise in areas such as biomedical devices, catalysis, therapeutics, and more. Herein, we review recent progress in the fabrication and development of these bio-nanomaterials, describe in detail their properties, and discuss the initial successes in their applications. Comparisons are made to the dominant nanocelluose to highlight some of the inherent advantages that nanochitin and nanochitosan may possess in similar application.

Effect of chitin nanowhiskers on mechanical and swelling properties of Gum Arabic hydrogels nanocomposites

Hydrogels based on biopolymers like Gum Arabic (GA) usually show low applicability due to weak mechanical properties. To overcome this issue, (nano)fillers are utilized as reinforcing agents. Here, GA hydrogels were reinforced by chitin nanowhiskers (CtNWs, aspect ratio of 14) isolated from the biopolymer chitin through acid hydrolysis. Firstly, GA was chemically modified with glycidyl methacrylate (GMA), which allowed its crosslinking by free radical reactions. Next, hydrogel samples containing different concentrations of CtNWs (0-10 wt%) were prepared and fully characterized. Mechanical characterization revealed that 10 wt% of CtNWs promoted an increase of 44% in the Young's modulus and 96% the rupture force values compared to the pristine hydrogel. Overall, all nanocomposites were stiffer and more resistant to elastic deformation. Due to this feature, the swelling capacity of the nanocomposites decreased. GA hydrogel without CtNWs exhibited a swelling degree of 975%, whereas nanocomposites containing CtNWs exhibited swelling degrees under 725%.

Fabrication and characterization of biodegradable KH560 crosslinked chitin hydrogels with high toughness and good biocompatibility

Chitin hydrogels have multiple advantages of nontoxicity, biocompatibility, biodegradability, and three-dimensional hydrophilic polymer network structure similar to the macromolecular biological tissue. However, the mechanical strength of chitin hydrogels is relatively weak. Construction of chitin hydrogels with high mechanical strength and good biocompatibility is essential for the successful applications in biomedical field. Herein, we developed double crosslinked chitin hydrogels by dissolving chitin in KOH/urea aqueous solution with freezing-thawing process, then using KH560 as cross-linking agent and coagulating in ethanol solution at low temperature. The obtained chitin/ KH560 (CK) hydrogels displayed good transparency and toughness with compressed nanofibrous network and porous structure woven with chitin nanofibers. Moreover, the optimal CK hydrogels exhibited excellent mechanical properties (σ_b = 1.92 ± 0.21 Mpa; ε_b = 71 ± 5 %), high swelling ratio, excellent blood compatibility, biocompatibility and biodegradability, which fulfill the requirements of biomedical materials and showing potential applications in biomedicine.

Chitin and Chitosan Derivatives as Biomaterial Resources for Biological and Biomedical Applications

Chitin is a long-chain polymer of N-acetyl-glucosamine, which is regularly found in the exoskeleton of arthropods including insects, shellfish and the cell wall of fungi. It has been known that chitin can be used for biological and biomedical applications, especially as a biomaterial for tissue repairing, encapsulating drug for drug delivery. However, chitin has been postulated as an inducer of proinflammatory cytokines and certain diseases including asthma. Likewise, chitosan, a long-chain polymer of N-acetyl-glucosamine and d-glucosamine derived from chitin deacetylation, and chitosan oligosaccharide, a short chain polymer, have been known for their potential therapeutic effects, including anti-inflammatory, antioxidant, antidiarrheal, and anti-Alzheimer effects. This review summarizes potential utilization and limitation of chitin, chitosan and chitosan oligosaccharide in a variety of diseases. Furthermore, future direction of research and development of chitin, chitosan, and chitosan oligosaccharide for biomedical applications is discussed.

Leveraging the water electrolysis reaction in bipolar electrophoresis to form robust and defectless chitosan films

Electrophoresis of chitosan and its composites are widely used to form a coating on selective substrates, but the parasitic water electrolysis causes structural defects that weaken the resulting film. In this work, we demonstrate a bipolar electrophoresis technique that leverages the water electrolysis to produce a chitosan film with less porosity and surface cavities. The process involves a negative bias to deposit the protonated chitosan molecules from the solution, followed by a positive bias to remove the entrapped hydrogen bubbles via the re-protonation of chitosan deposit. Since water electrolysis occurs for both positive and negative bias, the bipolar profile is designed to engender pH changeup near the electrode for "surface conditioning" of chitosan film. The bipolar electrophoresis route demonstrates better coulomb efficiency than that of conventional potentiostatic electrophoresis, resulting in a free-standing chitosan film with sufficient mechanical strength and large area.