An Antibacterial and Antiadhesion In Situ Forming Hydrogel with Sol-Spray System for Noncompressible Hemostasis

A review of polysaccharide-based hydrogels: From structural modification to biomedical applications

Hydrogels prepared from natural polysaccharide possess excellent biocompatibility and adjustable physical properties similar to those of natural extracellular matrices, and have thus been extensively utilized in the biomedical field. However, natural polysaccharide hydrogels have limited applications owing to their performance deficiencies. For instance, poor mechanical properties restrict their application in tissue engineering, while instability hinders their adaptation to complex and dynamic physiological environments. The chemical modification of polysaccharides and their combination with other matrix materials, such as proteins, synthetic polymers, and inorganic materials, to form hybrid hydrogels have been utilized to enhance the properties of polysaccharide-based hydrogels for diverse applications. This paper reviews comprehensively and systematically the methods of natural polysaccharide modification and describes in detail the various types of polysaccharide-based hydrogels. Additionally, the applications of these hydrogels in drug delivery, wound dressings, tissue engineering and biosensing are summarized. Finally, the challenges and future directions for the application of polysaccharide-based hydrogels are envisioned to provide a reference for the design of novel multifunctional hydrogels.

Centrifugal Spinning-Derived Biomimetic Aerogel for Rapid Hemostasis with Minimal Blood Loss

For emergency treatment, especially in situations where rapid and effective hemostasis is required beyond the natural clotting mechanisms, advanced materials designed to reduce bleeding time and minimize blood loss have become an urgent need. Herein, a root hair-inspired aerogel is developed, which is characterized by a 99.99% interconnected pore structure and a three-dimensional network constructed by blocked aqueous isocyanates cross-linked grooved cellulose acetate and wrinkled thermoplastic polyurethane fibers via centrifugal spinning. The aerogel exhibits enhanced water absorption and minimal blood adsorption through rapid coagulation cascade activation. In vivo studies using rat tail, hepatic, and renal injury models demonstrate a substantial reduction in blood loss (∼94%) and hemostasis time (∼78%) compared to commercial hemostats. The developed aerogel offers a promising solution for urgent hemorrhage control.

C-phycocyanin and quaternized chitosan based antibiotic-free hydrogels with antioxidant and antibacterial activity for wound healing

Hydrogels with antioxidant and antibacterial activities have received increasing attention in wound healing due to excessive reactive oxygen species (ROS) and bacterial infection are common issues associated with wounds. Herein, we constructed a series of hydrogels with C-phycocyanin (C-PC), quaternized chitosan (QCS) and silk fibroin protein (SF) as matrixes, which with tetrakis hydroxymethyl phosphonium sulfate (THPS) as crosslinking agent to form dynamic covalent bonds with C-PC and SF. The hydrogel exhibited excellent stretchability and compressibility, which with adhesion strength reached 15 ± 3 kPa and rapid self-healing properties. The hydrogel possessed strong antioxidant activity with assessments of DPPH radical-scavenging capacity and total reducing power. In addition, the hydrogel possessed obvious coagulation function and good blood compatibility, which also showed strong antibacterial activity against E. coli and S. aureus. To improve the therapeutic effect, polydeoxyribonucleotide (PDRN) with the ability of promote wound healing was introduced into the hydrogel. The results showed that the hydrogel loading with PDRN possessed high biocompatibility and can promote cell migration. More importantly, the hydrogel loaded with PDRN can effectively promote wound healing by exerting anti-inflammatory and antioxidant effects, which may offer promising potential application value in the field of wound dressing and tissue repair.

Water triggered injectable polylactic acid hydrogel based on zwitterionic sulfobetaine modification for incompressible bleeding and tissue anti-adhesion

Massive blood loss is the main cause of prehospital trauma-related death, the development of rapid and effective hemostatic materials is imminent. Injectable hydrogels have the advantages of covering irregular bleeding sites and quickly closing the wound. However, its inherent viscosity can easily precipitate tissue adhesion in vivo and other complications. Based on the anti-protein properties of zwitterion and our previous work about in situ hemostatic/anti-adhesion hydrogel material, we have synthesized a series of injectable hydrogel composed of sulfobetaine-modified polylactic acid (PLA) and gelatin (Gel). These hydrogels could form a smooth film structure by simple water triggering, thereby conferring anti-adhesive properties. We visualized the changes in surface hydrophobicity using fluorescent probes and demonstrated tissue adhesion, rapid hydrophobic interface response, as well as rapid hemostasis for incompressible wounds through in vivo and in vitro experiments. Additionally, we explored the application of hydrogel materials in the scenario of postoperative bleeding, which can effectively prevent unnecessary adhesion through rapid film formation and the anti-protein property of sulfobetaine. We believe that this multifunctional hemostatic hydrogel has the potential to serve as a prehospital emergency treatment of incompressible bleeding and benefit to the postoperative recovery of patients.

Carboxymethyl chitosan/dialdehyde quaternized pullulan self-healing hydrogel loaded with tranexamic acid for rapid hemostasis

In this study, we designed novel self-healing hydrogels (CMC/DAQP-HGs) using carboxymethyl chitosan (CMC) and dialdehyde quaternized pullulan (DAQP), aimed at loading tranexamic acid (TA) for rapid hemostasis. Meanwhile, CMC/dialdehyde pullulan (DAP) hydrogels (CMC/DAP-HGs) were prepared for comparison with CMC/DAQP-HGs. Experimental results showed that (1) DAQP, DAP, CMC/DAQP-HGs, and CMC/DAP-HGs were successfully prepared; (2) both types of hydrogels demonstrated excellent swelling (swelling ratio of 12.66-22.18 g/g), water retention (> 24 h), self-healing, and injectable properties, biocompatibility (hemolysis ratio < 2 %, relative cell viability of L929 and HSF > 80 %), and degradability; (3) CMC/DAQP-HGs had superior adhesive, antibacterial, and hemostatic properties compared to CMC/DAP-HGs, with CMC/DAQP-HG1 showing the best performance, including a tissue adhesion strength of 6.54 kPa, ~100 % of inhibition against E. coli and S. aureus, and hemostasis time in the three animal models <312 s; (4) the novel hydrogels effectively encapsulated tranexamic acid (TA) and controlled TA release; and (5) the addition of TA significantly enhanced the hydrogels' hemostatic efficacy, with the hemostasis time values in the TA-loaded CMC/DAQP-HG1 (TA/CMC/DAQP-HG1) group being reduced by >56 % compared to those in the gelatin sponge group, indicating that TA/CMC/DAQP-HG1 had the potential to be an ideal hemostatic dressing.

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.

Highly biocompatible, antioxidant and antibacterial gelatin methacrylate/alginate - Tannin hydrogels for wound healing

Gelatin (Gel) hydrogels are widely utilized in various aspects of tissue engineering, such as wound repair, due to their abundance and biocompatibility. However, their low strength and limited functionality have constrained their development and scope of application. Tannic acid (TA), a naturally occurring polyphenol found in plants and fruits, has recently garnered interest as a crosslinking, anti-inflammatory, and antioxidant agent. In this study, we fabricated novel multifunctional gelatin methacrylate/alginate-tannin (GelMA/Alg-TA) hydrogels using chemical and physical crosslinking strategies with gelatin methacrylate (GelMA), alginate (Alg), and TA as the base materials. The GelMA/Alg-TA hydrogels maintained a stable three-dimensional porous structure with appropriate water content and exhibited excellent biocompatibility. Additionally, these hydrogels demonstrated significant antioxidant and antibacterial properties and substantially promoted wound healing in a mouse model of full-thickness skin defects by modulating inflammatory responses and enhancing granulation formation. Therefore, our study offers valuable insights into the design principles of novel multifunctional GelMA/Alg-TA hydrogels, highlighting their exceptional biocompatibility, antioxidant, and antibacterial properties. GelMA/Alg-TA hydrogels are promising candidates for wound healing applications.

A multifunctional gingival retraction cord with antibacterial and hemostasis properties based on Chitosan/Propolis/Tranexamic acid for dental treatment

A novel gingival retraction cord named P/TA@CSy was prepared using chitosan yarns (CSy) loaded with tranexamic acid (TA) and Propolis (P). P/TA@CSy has good toughness with a breaking strength of 41.3 Pa, benefiting from the twisting structure and Propolis coating. A short coagulation time of 456 s was achieved for P/TA@CSy because of the potent blood absorption ability from the effective attachment of tranexamic acid. Moreover, excellent antibacterial ability was obtained with the antibacterial rates against E. coli of 94.73 %, S. aureus of 99.99 % and S. mutans of 99.99 %, contributing to Propolis's antibacterial ability. In addition, suppression of the expression of pro-inflammatory cytokines (IL-6 and TNF-α) was found, which could prevent wound infection. P/TA@CSy displayed excellent cytocompatibility with the cell activity of 100 % after 24 h. Therefore, P/TA@CSy could rapidly respond to gingival hemostasis and infection prevention, showing excellent potential in dental treatment.

Tissue-adhesive, stretchable and compressible physical double-crosslinked microgel-integrated hydrogels for dynamic wound care

Integrated wound care through sequentially promoting hemostasis, sealing, and healing holds great promise in clinical practice. However, it remains challenging for regular bioadhesives to achieve integrated care of dynamic wounds due to the difficulties in adapting to dynamic mechanical and wet wound environments. Herein, we reported a type of dehydrated, physical double crosslinked microgels (DPDMs) which were capable of in situ forming highly stretchable, compressible and tissue-adhesive hydrogels for integrated care of dynamic wounds. The DPDMs were designed by the rational integration of the reversible crosslinks and double crosslinks into micronized gels. The reversible physical crosslinks enabled the DPDMs to integrate together, and the double crosslinked characteristics further strengthen the formed macroscopical networks (DPDM-Gels). We demonstrated that the DPDM-Gels simultaneously possess outstanding tensile (∼940 kJ/m3) and compressive (∼270 kJ/m3) toughness, commercial bioadhesives-comparable tissue-adhesive strength, together with stable performance under hundreds of deformations. In vivo results further revealed that the DPDM-Gels could effectively stop bleeding in various bleeding models, even in an actual dynamic environment, and enable the integrated care of dynamic skin wounds. On the basis of the remarkable mechanical and appropriate adhesive properties, together with impressive integrated care capacities, the DPDM-Gels may provide a new approach for the smart care of dynamic wounds. STATEMENT OF SIGNIFICANCE: Integrated care of dynamic wounds holds great significance in clinical practice. However, the dynamic and wet wound environments pose great challenges for existing hydrogels to achieve it. This work developed robust adhesive hydrogels for integrated care of dynamic wounds by designing dehydrated, physical double crosslinked microgels (DPDMs). The reversible and double crosslinks enabled DPDMs to integrate into macroscopic hydrogels with high mechanical properties, appropriate adhesive strength and stable performance under hundreds of external deformations. Upon application at the injury site, DPDM-Gels efficiently stopped bleeding, even in an actual dynamic environment and showed effectiveness in integrated care of dynamic wounds. With the fascinating properties, DPDMs may become an effective tool for smart wound care.

A ROS-responsive and scavenging hydrogel for postoperative abdominal adhesion prevention

Postoperative abdominal adhesion (PAA) widely occurs after abdominal surgery, which often produces severe complications. However, there were still no satisfactory anti-adhesive products including barriers and anti-adhesive agents. Herein, we developed a ROS-responsive and scavenging hydrogel barrier, termed AHBC/PSC, wherein the monomer AHBC was synthesized by phenylboronic acid (PBA)-modified hyaluronic acid (HA-PBA) further grafted with adipic dihydrazide (ADH) and PBA-based chlorogenic acid (CGA) via ROS-sensitive borate ester bond, and the other monomer PSC was constructed by polyvinyl alcohol (PVA) grafted with sulfated betaine (SB) and p-hydroxybenzaldehyde (CHO). Further, the double crosslinked AHBC/PSC hydrogel was successfully fabricated between AHBC and PSC via forming dynamic covalent acylhydrazone bonds and borate ester bonds. Results showed that AHBC/PSC hydrogel had in situ gelation behavior, satisfactory mechanical properties (storage modulus of about 1 kPa and loss factor Tan δ of about 0.5), suitable wet tissue adhesion strength of about 2.3 kPa on rat abdominal wall, and good biocompatibility, achieving an ideal physical barrier. Particularly, CGA could be responsively released from the hydrogel by breakage of borate ester bonds between CGA and PBA based on high reactive oxygen species (ROS) levels of damaged tissue and exhibited great ROS scavenging capability to regulate inflammation and promote the polarization of macrophages from pro-inflammatory M1 phenotype to anti-inflammatory M2 phenotype. Moreover, the grafted SB as a zwitterionic group could reduce protein adsorption and fibroblast adhesion. Finally, the in vivo experiments revealed that AHBC/PSC hydrogel with good safety and in vivo retention behavior of about 2 weeks, effectively prevented PAA by regulating the inflammatory microenvironment and alleviating the fibrosis process. In brief, the versatile AHBC/PSC hydrogel would provide a more convenient and efficient approach for PAA prevention. STATEMENT OF SIGNIFICANCE: Postoperative abdominal adhesion (PAA) widely occurs after surgery and is often accompanied by severe complications. Excessive inflammation and oxidative stress are very crucial for PAA formation. This study provides a ROS-responsive and scavenging hydrogel with suitable mechanical properties, good biocompatibility and biodegradability, and resistance to protein and fibroblast. The antioxidant and anti-inflammatory active ingredient could be responsively released from the hydrogel via triggering by the high ROS levels in the postoperative microenvironment thereby regulating the inflammatory balance. Finally, the hydrogel would effectively regulate the development process of PAA thereby achieving non-adhesion wound healing.

Preparation and Application of Hemostatic Hydrogels

Hemorrhage remains a critical challenge in various medical settings, necessitating the development of advanced hemostatic materials. Hemostatic hydrogels have emerged as promising solutions to address uncontrolled bleeding due to their unique properties, including biocompatibility, tunable physical characteristics, and exceptional hemostatic capabilities. In this review, a comprehensive overview of the preparation and biomedical applications of hemostatic hydrogels is provided. Particularly, hemostatic hydrogels with various materials and forms are introduced. Additionally, the applications of hemostatic hydrogels in trauma management, surgical procedures, wound care, etc. are summarized. Finally, the limitations and future prospects of hemostatic hydrogels are discussed and evaluated. This review aims to highlight the biomedical applications of hydrogels in hemorrhage management and offer insights into the development of clinically relevant hemostatic materials.

Carbonized Cellulose Aerogel Derived from Waste Pomelo Peel for Rapid Hemostasis of Trauma-Induced Bleeding

Uncontrollable massive bleeding caused by trauma will cause the patient to lose a large amount of blood and drop body temperature quickly, resulting in hemorrhagic shock. This study aims to develop a hemostatic product for hemorrhage management. In this study, waste pomelo peel as raw material is chosen. It underwent processes of carbonization, purification, and freeze-drying. The obtained carbonized pomelo peel (CPP) is hydrophilic and exhibits a porous structure (nearly 80% porosity). The water/blood absorption ratio is significantly faster than the commercial Gelfoam and has a similar water/blood absorption capacity. In addition, the CPP showed a water-triggered shape-recoverable ability. Moreover, the CPP shows ideal cytocompatibility and blood compatibility in vitro and favorable tissue compatibility after long terms of subcutaneous implantation. Furthermore, CPP can absorb red blood cells and fibrin. It also can absorb platelets and activate platelets, and it is capable of achieving rapid hemostasis on the rat tail amputation and hepatectomized hemorrhage model. In addition, the CPP not only can quickly stop bleeding in the rat liver-perforation and rabbit heart uncontrolled hemorrhage models, but also promotes rat liver and rabbit heart tissue regeneration in situ. These results suggest the CPP has shown great potential for managing uncontrolled hemorrhage.

What else should hemostatic materials do beyond hemostasis: A review

Massive blood loss due to injury is the leading cause of prehospital deaths in disasters and emergencies. Hemostatic materials are used to realize rapid hemostasis and protect patients from death. Researchers have designed and developed a variety of hemostatic materials. However, in addition to their hemostatic effect, hemostatic materials must be endowed with additional functions to meet the practical application requirements in different scenarios. Here, strategies for modifications of hemostatic materials for use in different application scenarios are listed: effective positioning at the site of deep and narrow wounds to stop bleeding, resistance to high blood pressure and wound movement to maintain wound formation, rapid and easy removal from the wound without affecting further treatment after hemostasis is completed, and continued function when retained in the wound as a dressing (such as antibacterial, antiadhesion, tissue repair, etc.). The problems encountered in the practical use of hemostatic materials and the strategies and progress of researchers will be further discussed in this review. We hope to provide valuable references for the design of more comprehensive and practical hemostatic materials.

Bioinspired adhesive hydrogel based on serotonin-modified gelatin and oxidized hyaluronic acid for rapid hemostasis and wound healing

A hybrid hydrogel system (GSOHA) consisting of serotonin-grafted gelatin and oxidized hyaluronic acid (OHA) was developed in this study to efficiently control bleeding and prevent bacterial infections during surgery and trauma. The study results showed that the incorporation of serotonin successfully produced hydrogels with rapid hemostatic, antibacterial, and antioxidant properties. The GSOHA hydrogel exhibited considerably stronger tissue adhesion (15.55 ± 0.36 kPa) to porcine skin than the commercial fibrin glue (1.09 ± 0.04 kPa). In addition, the hydrogel could rapidly absorb blood cells and stimulate cell conjugation with serotonin addition. In vitro experiments using endothelial cells and erythrocytes demonstrated the excellent biocompatibility and hemocompatibility of the hydrogel. Most importantly, the GSOHA hydrogel accelerated the wound healing process in a full-thickness skin defect mice model, and the histological staining results demonstrated that GSOHA significantly promoted collagen deposition and vascularization. In conclusion, this study demonstrated the significant potential of the GSOHA hydrogel as an adhesive dressing for rapid hemostasis and wound healing.

Antimicrobial research of carbohydrate polymer- and protein-based hydrogels as reservoirs for the generation of reactive oxygen species: A review

Reactive oxygen species (ROS) play an important role in biological milieu. Recently, the rapid growth in our understanding of ROS and their promise in antibacterial applications has generated tremendous interest in the combination of ROS generators with bulk hydrogels. Hydrogels represent promising supporters for ROS generators and can locally confine the nanoscale distribution of ROS generators whilst also promoting cellular integration via biomaterial-cell interactions. This review highlights recent efforts and progress in developing hydrogels derived from biological macromolecules with embedded ROS generators with a focus on antimicrobial applications. Initially, an overview of passive and active antibacterial hydrogels is provided to show the significance of proper hydrogel selection and design. These are followed by an in-depth discussion of the various approaches for ROS generation in hydrogels. The structural engineering and fabrication of ROS-laden hydrogels are given with a focus on their biomedical applications in therapeutics and diagnosis. Additionally, we discuss how a compromise needs to be sought between ROS generation and removal for maximizing the efficacy of therapeutic treatment. Finally, the current challenges and potential routes toward commercialization in this rapidly evolving field are discussed, focusing on the potential translation of laboratory research outcomes to real-world clinical outcomes.

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.

State of the art, trends, hotspots, and prospects of injection materials for controlling bleeding

Traumatic haemorrhage is a prevalent clinical condition, and effective and timely haemostasis is crucial for the preservation of patients' lives. In recent years, injectable hemostatic materials have gained significant attention due to their excellent hemostatic efficacy, biocompatibility, and biodegradability, making them widely applied in the treatment of incompressible traumatic haemorrhage. Systematic analysis of injectable hemostatic materials is crucial for research in this area. This article provides a comprehensive review of the development and research trends of injectable hemostatic materials over the past 20 years using visualization techniques. Analysis of collaboration and co-citation networks revealed localized research collaboration networks, highlighting the need for enhanced international collaboration in the field of injectable hemostatic materials. Current research focuses primarily on hemostatic materials, hemostatic processes, and hemostatic mechanisms. Injectable hemostatic materials with excellent performance offer promising strategies for wound healing. This review provides a comprehensive and systematic summary of injectable hemostatic materials, offering valuable guidance for the development and clinical application of novel injectable hemostatic materials. Additionally, visualized methodology and mapping analysis are effective data mining methods that provide approaches and strategies for clear knowledge network analysis. These methods facilitate better understanding and interpretation of research dynamics in the field of injectable hemostatic materials, thereby guiding and inspiring future research.

A multifunctional hydrogel dressing with high tensile and adhesive strength for infected skin wound healing in joint regions

Most hydrogel dressings are designed for skin wounds in flat areas, and few are focused on the joint skin regions which undergo frequent movement. The mismatch of mechanical properties and poor fit between a hydrogel dressing and a wound in joint skin results in hydrogel shedding, bacterial infection and delayed healing. Therefore, it is of great significance to design and prepare a multifunctional hydrogel with high tensile and tissue-adhesive strength as well as other therapeutic effects for the treatment of joint skin wounds. In this work, a multifunctional hydrogel was reasonably prepared by simply mixing polyvinyl alcohol (PVA), borax, tannic acid (TA) and iron(III) chloride in certain proportions, which was further used to treat the skin wounds at the joint of the hind limb. Acting as the physical crosslinkers, borax and TA dynamically bond with PVA and provide the resulting hydrogel with strong tensile, fast shape-adaptive and self-healing properties. The photothermal bacteriostatic activity of the hydrogel is attributed to the formation of a metallic polyphenol network (MPN) between ferric ions and TA. In addition, the hydrogel exhibits high levels of adhesion, hemostatic performance, antioxidant abilities, and biocompatibility, and shows great potential to promote joint skin wound healing.

Tough adhesion enhancing strategies for injectable hydrogel adhesives in biomedical applications

Injectable hydrogel adhesives have gained widespread attention due to their ease of use, fast application time, and suitability for minimally invasive procedures. Several biomedical applications depend on tough adhesion between hydrogel adhesives and tissues, including wound closure and healing, hemostasis, tissue regeneration, drug delivery, and wearable electronic devices. Compared with bulk hydrogel adhesives formed ex situ, injectable hydrogel adhesives are more difficult to achieve strong adhesion strength due to a further balance of cohesion and adhesion while maintaining their flowability. In this review, the critical principles in designing tough adhesion of injectable hydrogel adhesives are summarized, including simultaneously enhancing their intrinsic interfacial toughness (Γ0inter) and mechanical dissipation (ΓDinter). Thereafter, various design strategies to enhance the Γ0inter and ΓDinter are discussed and evaluated respectively, involving multiple noncovalent/covalent interactions, topological connections, and polymer network structures. Furthermore, targeted biomedical applications of injectable hydrogel adhesives for specific tissue needs are systematically highlighted. In the end, this review outlines the challenges and trends in producing next-generation multifunctional injectable hydrogels for both practical and translational applications.

Prevention strategies of postoperative adhesion in soft tissues by applying biomaterials: Based on the mechanisms of occurrence and development of adhesions

Postoperative adhesion (POA) widely occurs in soft tissues and usually leads to chronic pain, dysfunction of adjacent organs and some acute complications, seriously reducing patients' quality of life and even being life-threatening. Except for adhesiolysis, there are few effective methods to release existing adhesion. However, it requires a second operation and inpatient care and usually triggers recurrent adhesion in a great incidence. Hence, preventing POA formation has been regarded as the most effective clinical strategy. Biomaterials have attracted great attention in preventing POA because they can act as both barriers and drug carriers. Nevertheless, even though much reported research has been demonstrated their efficacy on POA inhibition to a certain extent, thoroughly preventing POA formation is still challenging. Meanwhile, most biomaterials for POA prevention were designed based on limited experiences, not a solid theoretical basis, showing blindness. Hence, we aimed to provide guidance for designing anti-adhesion materials applied in different soft tissues based on the mechanisms of POA occurrence and development. We first classified the postoperative adhesions into four categories according to the different components of diverse adhesion tissues, and named them as "membranous adhesion", "vascular adhesion", "adhesive adhesion" and "scarred adhesion", respectively. Then, the process of the occurrence and development of POA were analyzed, and the main influencing factors in different stages were clarified. Further, we proposed seven strategies for POA prevention by using biomaterials according to these influencing factors. Meanwhile, the relevant practices were summarized according to the corresponding strategies and the future perspectives were analyzed.

Production of novel elastic bacterial nanocellulose/polyvinyl alcohol conduits via mercerization and phase separation for small-caliber vascular grafts application

Size and properties of tubular bacterial nanocellulose (BNC) can be regulated by controllable mercerization with thinner tube walls, better mechanical properties, and improved biocompatibility. Although mercerized BNC (MBNC) conduits have considerable potential as small-caliber vascular grafts (<6 mm), poor suture retention and lack of compliance that cannot match natural blood vessels increase the difficulty of surgery and limit potential clinical application. Polyvinyl alcohol (PVA) is a kind of hydrophilic polymer with good biocompatibility and elasticity, which can precipitate in alkaline solutions. In this study, novel elastic mercerized BNC/PVA conduits (MBP) are manufactured combining mercerization of BNC tubes with precipitation and phase separation of PVA with thinner tube wall, improved suture retention, better elasticity, good hemocompatibility and great cytocompatibility. The MBP obtained with 12.5 % PVA is selected for transplantation in a rat abdominal aorta model. For 32 weeks, normal blood flow is observed using Doppler sonographic inspection, which demonstrates long-term patency. Immunofluorescence staining results also indicate the formation of endothelium and smooth muscle layers. The results indicate the introduction of PVA, and its phase separation into mercerization of tubular BNC can endow MBP conduits with better compliance and suture retention, making it a promising candidate for blood vessel replacement.