Surgical Materials: Current Challenges and Nano-enabled Solutions

Bioadhesive microneedle patches for tissue sealing

Sealing of soft tissues prevents leakage of gas and liquid, closes wounds, and promotes healing and is, therefore, of great significance in the clinical and medical fields. Although various formulations have been developed for reliable sealing of soft tissue, tradeoffs between adhesive properties, degradation profile, and tissue toxicity limit their clinical use. Hydrogel-based adhesives, for example, are highly biocompatible but adhere very weakly to the tissue and degrade quickly, while oxidized cellulose patches are poorly absorbed and may cause healing complications postoperatively. Here, we present a novel strategy for tissue sealing based on bioadhesive microneedle patches that can spontaneously adhere to tissue surface through electrostatic interactions and swell within it. A series of microneedle patches made of pullulan, chitosan, Carbopol, poly (lactic-co-glycolic acid), and a Carbopol/chitosan combination were fabricated and characterized for their use in tissue sealing. The effect of microneedle composition on the fabrication process, physical and mechanical properties, in vitro cytotoxicity, and in vivo biocompatibility were examined. The needle structure enables microneedles to strongly fix onto various tissues via physical interlocking, while their adhesive properties improve staying time and sealing capabilities. The microneedle patch comprising Carbopol needles and chitosan as a second pedestal layer presented the best results in terms of sealing and adhesion, a consequence of the needle's swelling and adhesion features combined with the supportive chitosan base layer. Finally, single Carbopol/chitosan patches stopped intense liver bleeding in a rat model significantly quicker and with less blood loss compared with commercial oxidized cellulose patches. These microneedles can be considered a promising cost-effective platform for adhering and sealing tissues as they can be applied quickly and painlessly, and require less trained medical staff and equipment.

Advances in Nanocarrier Systems for Overcoming Formulation Challenges of Curcumin: Current Insights

Curcumin, an organic phenolic molecule that is extracted from the rhizomes of Curcuma longa Linn, has undergone extensive evaluation for its diverse biological activities in both animals and humans. Despite its favorable characteristics, curcumin encounters various formulation challenges and stability issues that can be effectively addressed through the application of nanotechnology. Nano-based techniques specifically focused on enhancing solubility, bioavailability, and therapeutic efficacy while mitigating toxicity, have been explored for curcumin. This review systematically presents information on the improvement of curcumin's beneficial properties when incorporated, either individually or in conjunction with other drugs, into diverse nanosystems such as liposomes, nanoemulsions, polymeric micelles, dendrimers, polymeric nanoparticles, solid-lipid nanoparticles, and nanostructured lipid carriers. Additionally, the review examines ongoing clinical trials and recently granted patents, offering a thorough overview of the dynamic landscape in curcumin delivery. Researchers are currently exploring nanocarriers with crucial features such as surface modification, substantial loading capacity, biodegradability, compatibility, and autonomous targeting specificity and selectivity. Nevertheless, the utilization of nanocarriers for curcumin delivery is still in its initial phases, with regulatory approval pending and persistent safety concerns surrounding their use.

Synthetic Polypeptide Bioadhesive Based on Cation-π Interaction and Secondary Structure

Bioadhesives have garnered widespread attention in the biomedical field, for wound healing and tissue sealing. However, challenges exist due to the inferior performance of bioadhesives, including weak adhesion, poor biocompatibility, or lack of biodegradability. In this work, we demonstrate the fabrication of hydrogel adhesive based on polypeptides composed of lysine and glutamic acid. The cation-π interaction between the ammonium cations and phenyl groups endows the hydrogel with strong cohesion, and the hydrophobicity of the phenyl group significantly enhances the interaction between polypeptides and the substrate interface, leading to excellent adhesive performance. The equivalent molar ratio of ammonium cations and the phenyl group is beneficial for the enhancement of adhesiveness. Furthermore, we discover that the polypeptides with an α-helix exhibit better adhesiveness than the polypeptides with a β-sheet because the α-helical structure can increase the exposure of the side group on the polypeptide surface, which further strengthens the interaction between polypeptides and the substrate. Besides, this synthetic polypeptide adhesive can seal the tissue quickly and remain intact in water. This adhesive holds significant promise for application in wound healing and tissue sealing, and this study provides insight into the development of more peptide-based adhesives.

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.

Cellulose based composite sponges with oriented porous structure and superabsorptive capacity for quick hemostasis

Excessive bleeding is the leading cause of death in accidents and operations. Ca2+ crosslinked carboxyl nanocellulose (CN)/montmorillonite (MMT) composite (CaCNMMT) sponges were prepared by uniform mixing and directional freeze-drying methods which was inspired by the coordination mechanism of blood clot formation and coagulation cascade activation in natural hemostasis process. Carboxyl nanocellulose (CaCN) sponge has instantaneous water absorption capacity, and CaCNMMT sponges could further activate clotting factors. Therefore, CaCNMMT sponges achieved quick hemostasis by efficient concentrating blood, inducing hemocyte aggregation and stimulating coagulation cascade activation based on the synergistic effects of CN and MMT. Blood clotting index of CaCNMMT (15.90 ± 0.52 %) was significantly lower than CaCN (59.3 ± 1.43 %), and APTT time (22 ± 2 s) was almost equivalent to MMT (20 ± 2 s). CaCNMMT sponge showed good quick hemostatic effect on massive hemorrhage in both tail-breaking and liver injury model which provided a new strategy for the application of MMT in hemostatic and trauma treatment fields.

Multifunctional wet-adhesive chitosan/acrylic conduit for sutureless repair of peripheral nerve injuries

The incidence of peripheral nerve injury (PNI) is high worldwide, and a poor prognosis is common. Surgical closure and repair of the affected area are crucial to ensure the effective treatment of peripheral nerve injuries. Despite being the standard treatment approach, reliance on sutures to seal the severed nerve ends introduces several limitations and restrictions. This technique is intricate and time-consuming, and the application of threading and punctate sutures may lead to tissue damage and heightened tension concentrations, thus increasing the risk of fixation failure and local inflammation. This study aimed to develop easily implantable chitosan-based peripheral nerve repair conduits that combine acrylic acid and cleavable N-hydroxysuccinimide to reduce nerve damage during repair. In ex vivo tissue adhesion tests, the conduit achieved maximal interfacial toughness of 705 J m-2 ± 30 J m-2, allowing continuous bridging of the severed nerve ends. Adhesive repair significantly reduces local inflammation caused by conventional sutures, and the positive charge of chitosan disrupts the bacterial cell wall and reduces implant-related infections. This promises to open new avenues for sutureless nerve repair and reliable medical implants.

Nanotechnology development in surgical applications: recent trends and developments

This paper gives a detailed analysis of nanotechnology's rising involvement in numerous surgical fields. We investigate the use of nanotechnology in orthopedic surgery, neurosurgery, plastic surgery, surgical oncology, heart surgery, vascular surgery, ophthalmic surgery, thoracic surgery, and minimally invasive surgery. The paper details how nanotechnology helps with arthroplasty, chondrogenesis, tissue regeneration, wound healing, and more. It also discusses the employment of nanomaterials in implant surfaces, bone grafting, and breast implants, among other things. The article also explores various nanotechnology uses, including stem cell-incorporated nano scaffolds, nano-surgery, hemostasis, nerve healing, nanorobots, and diagnostic applications. The ethical and safety implications of using nanotechnology in surgery are also addressed. The future possibilities of nanotechnology are investigated, pointing to a possible route for improved patient outcomes. The essay finishes with a comment on nanotechnology's transformational influence in surgical applications and its promise for future breakthroughs.

Enhancing Robustness of Adhesive Hydrogels through PEG-NHS Incorporation

Tissue wounds are a significant challenge for the healthcare system, affecting millions globally. Current methods like suturing and stapling have limitations as they inadequately cover the wound, fail to prevent fluid leakage, and increase the risk of infection. Effective solutions for diverse wound conditions are still lacking. Adhesive hydrogels, on the other hand, can be a potential alternative for wound care. They offer benefits such as firm sealing without leakage, easy and rapid application, and the provision of mechanical support and flexibility. However, the in vivo durability of hydrogels is often compromised by excessive swelling and unforeseen degradation, which limits their widespread use. In this study, we addressed the durability issues of the adhesive hydrogels by incorporating acrylamide polyethylene glycol N-hydroxysuccinimide (PEG-NHS) moieties (max. 2 wt %) into hydrogels based on hydroxy ethyl acrylamide (HEAam). The results showed that the addition of PEG-NHS significantly enhanced the adhesion performance, achieving up to 2-fold improvement on various soft tissues including skin, trachea, heart, lung, liver, and kidney. We further observed that the addition of PEG-NHS into the adhesive hydrogel network improved their intrinsic mechanical properties. The tensile modulus of these hydrogels increased up to 5-fold, while the swelling ratio decreased up to 2-fold in various media. These hydrogels also exhibited improved durability under the enzymatic and oxidative biodegradation induced conditions without causing any toxicity to the cells. To evaluate its potential for clinical applications, we used PEG-NHS based hydrogels to address tracheomalacia, a condition characterized by inadequate mechanical support of the airway due to weak/malacic cartilage rings. Ex vivo study confirmed that the addition of PEG-NHS to the hydrogel network prevented approximately 90% of airway collapse compared to the case without PEG-NHS. Overall, this study offers a promising approach to enhance the durability of adhesive hydrogels by the addition of PEG-NHS, thereby improving their overall performances for various biomedical applications.

Injectable Sealants Based on Silk Fibroin for Fast Hemostasis and Wound Repairing

Uncontrollable blood loss poses fatality risks and most recently developed sealants still share common limitations on controversial components, degradability, mechanical strength or gelation time. Herein, series of injectable sealants based on silk fibroin (SF) is developed. Random coil/β-sheet conformation transition in SF is achieved by forming dendritic intermediates under induction of the structurally compatible and chemically complementary assembly peptide (Ac-KAEA-KAEA-KAEA-KAEA-NH2 , KA16 ). A ratio of 1:5 (KA-SF-15) shown an accelerating gelation process (≈12 s) and enhanced mechanical strength at physiological conditions. The interweaved nanofibers effectively impeded the bleeding within 30 s and no obvious adverse effects are observed. The supramolecular interactions and in vivo degradation benefit the inflammatory host cells infiltration and cytokines diffusion. Without any exogenous factors, the increased expression of VEGF and PDGF led to a positive feedback regulation on fibroblasts and vascular endothelial cell growth/proliferation and promoted the wound healing. These findings indicated the few assembly-peptide can accelerate fibroin gelation transition at a limited physiological condition, and the injectable amino acid-based sealants show obvious advantages on biocompatibility, degradability, rapid gelation and matched strength, with strong potential to act as next generation of biomedical materials.

Degradable Bioadhesives Based on Star PEG-PLA Hydrogels for Soft Tissue Applications

Tissue adhesives are interesting materials for wound treatment as they present numerous advantages compared to traditional methods of wound closure such as suturing and stapling. Nowadays, fibrin and cyanoacrylate glues are the most widespread commercial biomedical adhesives, but these systems display some drawbacks. In this study, degradable bioadhesives based on PEG-PLA star-shaped hydrogels are designed. Acrylate, methacrylate, and catechol functional copolymers are synthesized and used to design various bioadhesive hydrogels. Various types of mechanisms responsible for adhesion are investigated (physical entanglement and interlocking, physical interactions, chemical bonds), and the adhesive properties of the different systems are first studied on a gelatin model and compared to fibrin and cyanoacrylate references. Hydrogels based on acrylate and methacrylate reached adhesion strength close to cyanoacrylate (332 kPa) with values of 343 and 293 kPa, respectively, whereas catechol systems displayed higher values (11 and 19 kPa) compared to fibrin glue (7 kPa). Bioadhesives were then tested on mouse skin and human cadaveric colonic tissue. The results on mouse skin confirmed the potential of acrylate and methacrylate gels with adhesion strength close to commercial glues (15-30 kPa), whereas none of the systems led to high levels of adhesion on the colon. These data confirm that we designed a family of degradable bioadhesives with adhesion strength in the range of commercial glues. The low level of cytotoxicity of these materials is also demonstrated and confirm the potential of these hydrogels to be used as surgical adhesives.

Robust but On-Demand Detachable Wet Tissue Adhesive Hydrogel Enhanced with Modified Tannic Acid

Adhesives with robust but readily detachable wet tissue adhesion are of great significance for wound closure. Polyelectrolyte complex adhesive (PECA) is an important wet tissue adhesive. However, its relatively weak cohesive and adhesive strength cannot satisfy clinical applications. Herein, modified tannic acid (mTA) with a catechol group, a long alkyl hydrophobic chain, and a phenyl group was prepared first, and then, it was mixed with acrylic acid (AA) and polyethylenimine (PEI), followed by UV photopolymerization to make a wet tissue adhesive hydrogel with tough cohesion and adhesion strength. The hydrogel has a strong wet tissue interfacial toughness of ∼1552 J/m2, good mechanical properties (∼7220 kPa cohesive strength, ∼873% strain, and ∼33,370 kJ/m3 toughness), and a bursting pressure of ∼1575 mmHg on wet porcine skin. The hydrogel can realize quick and effective adhesion to various wet biological tissues including porcine skin, liver, kidney, and heart and can be changed easily with triggering urea solution to avoid tissue damage or uncomfortable pain to the patient. This biosafe adhesive hydrogel is very promising for wound closure and may provide new ideas for the design of robust wet tissue adhesives.

Short Peptide Nanofiber Biomaterials Ameliorate Local Hemostatic Capacity of Surgical Materials and Intraoperative Hemostatic Applications in Clinics

Short designer self-assembling peptide (dSAP) biomaterials are a new addition to the hemostat group. It may provide a diverse and robust toolbox for surgeons to integrate wound microenvironment with much safer and stronger hemostatic capacity than conventional materials and hemostatic agents. Especially in noncompressible torso hemorrhage (NCTH), diffuse mucosal surface bleeding, and internal medical bleeding (IMB), with respect to the optimal hemostatic formulation, dSAP biomaterials are the ingenious nanofiber alternatives to make bioactive neural scaffold, nasal packing, large mucosal surface coverage in gastrointestinal surgery (esophagus, gastric lesion, duodenum, and lower digestive tract), epicardiac cell-delivery carrier, transparent matrix barrier, and so on. Herein, in multiple surgical specialties, dSAP-biomaterial-based nano-hemostats achieve safe, effective, and immediate hemostasis, facile wound healing, and potentially reduce the risks in delayed bleeding, rebleeding, post-operative bleeding, or related complications. The biosafety in vivo, bleeding indications, tissue-sealing quality, surgical feasibility, and local usability are addressed comprehensively and sequentially and pursued to develop useful surgical techniques with better hemostatic performance. Here, the state of the art and all-round advancements of nano-hemostatic approaches in surgery are provided. Relevant critical insights will inspire exciting investigations on peptide nanotechnology, next-generation biomaterials, and better promising prospects in clinics.

Transfer Learning Facilitates the Prediction of Polymer-Surface Adhesion Strength

Machine learning (ML) accelerates the exploration of material properties and their links to the structure of the underlying molecules. In previous work [Shi et al. ACS Applied Materials & Interfaces 2022, 14, 37161-37169.], ML models were applied to predict the adhesive free energy of polymer-surface interactions with high accuracy from the knowledge of the sequence data, demonstrating successes in inverse-design of polymer sequence for known surface compositions. While the method was shown to be successful in designing polymers for a known surface, extensive data sets were needed for each specific surface in order to train the surrogate models. Ideally, one should be able to infer information about similar surfaces without having to regenerate a full complement of adhesion data for each new case. In the current work, we demonstrate a transfer learning (TL) technique using a deep neural network to improve the accuracy of ML models trained on small data sets by pretraining on a larger database from a related system and fine-tuning the weights of all layers with a small amount of additional data. The shared knowledge from the pretrained model facilitates the prediction accuracy significantly on small data sets. We also explore the limits of database size on accuracy and the optimal tuning of network architecture and parameters for our learning tasks. While applied to a relatively simple coarse-grained (CG) polymer model, the general lessons of this study apply to detailed modeling studies and the broader problems of inverse materials design.

Skin-interfaced electronics: A promising and intelligent paradigm for personalized healthcare

Skin-interfaced electronics (skintronics) have received considerable attention due to their thinness, skin-like mechanical softness, excellent conformability, and multifunctional integration. Current advancements in skintronics have enabled health monitoring and digital medicine. Particularly, skintronics offer a personalized platform for early-stage disease diagnosis and treatment. In this comprehensive review, we discuss (1) the state-of-the-art skintronic devices, (2) material selections and platform considerations of future skintronics toward intelligent healthcare, (3) device fabrication and system integrations of skintronics, (4) an overview of the skintronic platform for personalized healthcare applications, including biosensing as well as wound healing, sleep monitoring, the assessment of SARS-CoV-2, and the augmented reality-/virtual reality-enhanced human-machine interfaces, and (5) current challenges and future opportunities of skintronics and their potentials in clinical translation and commercialization. The field of skintronics will not only minimize physical and physiological mismatches with the skin but also shift the paradigm in intelligent and personalized healthcare and offer unprecedented promise to revolutionize conventional medical practices.

Bioglues Based on an Elastin-Like Recombinamer: Effect of Tannic Acid as an Additive on Tissue Adhesion and Cytocompatibility

More than 260 million surgical procedures are performed worldwide each year. Although sutures and staples are widely used to reconnect tissues, they can cause further damage and increase the risk of infection. Bioadhesives have been proposed as an alternative to reconnect tissues. However, clinical adhesives that combine strong adhesion with cytocompatibility have yet to be developed. In this study, we explored the production of adhesives based on protein-engineered polymers bioinspired by the sequence of elastin (i.e., elastin-like recombinamers, ELRs). We hypothesized that the combination of polyphenols (i.e., tannic acid, TA) and ELRs would produce an adhesive coacervate (ELR+TA), as reported for other protein polymers such as silk fibroin (SF). Notably, the adhesion of ELR alone surpassed that of ELR+TA. Indeed, ELR alone achieved adhesive strengths of 88.8 ± 33.2 kPa and 17.0 ± 2.0 kPa on porcine bone and skin tissues, respectively. This surprising result led us to explore a multicomponent bioadhesive to encompass the complementary roles of elastin (mimicked here by ELR) and silk fibroin (SF), and subsequently mirror more closely the multicomponent nature of the extracellular matrix. Tensile testing showed that ELR+SF achieved an adhesive strength of 123.3 ± 60.2 kPa on porcine bone and excellent cytocompatibility. To express this in a more visual and intuitive way, a small surface of only 2.5 cm2 was able to lift at least 2 kg of weight. This opens the door for further studies focusing on the ability of protein-engineered polymers to adhere to biological tissues without further chemical modification for applications in tissue engineering.

Microneedle system for tissue engineering and regenerative medicine

Global increasing demand for high life quality and length facilitates the development of tissue engineering and regenerative medicine, which apply multidisciplinary theories and techniques to achieve the structural reconstruction and functional recovery of disordered or damaged tissues and organs. However, the clinical performances of adopted drugs, materials, and powerful cells in the laboratory are inescapably limited by the currently available technologies. To tackle the problems, versatile microneedles are developed as the new platform for local delivery of diverse cargos with minimal invasion. The efficient delivery, as well as painless and convenient procedure endow microneedles with good patient compliance in clinic. In this review, we first categorize different microneedle systems and delivery models, and then summarize their applications in tissue engineering and regenerative medicine mainly involving maintenance and rehabilitation of damaged tissues and organs. In the end, we discuss the advantages, challenges, and prospects of microneedles in depth for future clinical translations.

One-Pot, Open-Air Synthesis of Flexible and Degradable Multifunctional Polymer Composites with Adhesion, Water Resistance, Self-Healing, Facile Drug Loading, and Sustained Release Properties

Developing proper wound management via wound dressings represents a global challenge. Ideal wound dressings shall encompass multiple integrated functionalities for variable, complex scenarios; however, this is challenging due to the complex molecular design and synthesis process. Here, polymer composites, cross-linked poly(styrene oxide-co-hexaphenylcyclotrisiloxane)/crosslinked poly(hexaphenylcyclotrisiloxane) (cP(SO-co-HPCTS)/cPHPCTS) with multiple functionalities are prepared by a one-step, open-air method using catalytic ring-opening polymerization. The introduction of a mobile polymer cP(SO-co-HPCTS) endows the composite with good flexibility and self-healing properties at human body temperature. The hydrophobic groups in the main chain provide hydrophobicity and good water resistance, while the hydroxyl groups contained in the end groups enable good adhesion properties. Drugs can be efficiently loaded by blending and then sustainably release from the polymer composite. The material can rapidly degrade in a tetrahydrofuran solution of tetrabutylammonium fluoride due to its SiOSi bonds. The facile, one-step, open-air synthesis procedure and multiple functional properties integrated into the composites provide good prospects for their extensive application and batch production as wound dressing materials.

Natural Small Biological Molecule Based Supramolecular Bioadhesives with Innate Photothermal Antibacterial Capability for Nonpressing Hemostasis and Effective Wound Healing

Bioadhesives with immediate wound closure, efficient hemostasis, and antibacterial properties that can well integrate with tissue are urgently needed in wound management. Natural small biological molecule based bioadhesives hold great promise for manipulating wound healing by taking advantage of integrated functionalities, synthetic simplification, and accuracy, cost efficiency and biosafety. Herein, a natural small biological molecule based bioadhesive, composed of natural small biological molecules (α-lipoic acid and tannic acid) and a small amount of ferric chloride, was prepared via an extremely simple and green route for wound management. In this system, covalent and noncovalent interactions between each component resulted in the self-healing supramolecular bioadhesive. It possessed appropriate wet-tissue adhesion, efficient nonpressing hemostasis and free radical scavenging abilities. More importantly, the interaction between tannic acid and Fe³⁺ endowed the bioadhesive with innate and steady photothermal activity, which showed excellent photothermal bactericidal activity to both E. coli and S. aureus. The bioadhesive promoted wound healing for linear and circular wounds in vivo, especially for infectious wounds under near-infrared (NIR) irradiation. This bioadhesive will have promising value as a safe and effective antimicrobial adhesive for infectious wound management.

Composition, host responses and clinical applications of bioadhesives

Bioadhesives are medical devices used to join or seal tissues that have been injured or incised. They have been classified into tissue adhesives, sealants, and hemostatic agents. Bioadhesives such as FloSeal®, CoSeal®, BioGlue®, Evicel®, Tisseel®, Progel™ PALS, and TissuGlu® have been commercialized and used in clinical setting. They can be formulated with natural or synthetic components or a combination of both including albumin, glutaraldehyde, chitosan, cyanoacrylate, fibrin and thrombin, gelatin, polyethylene glycol (PEG), along with urethanes. Each formulation has intrinsic properties and has been developed and validated for a specific application. This review article briefs the mechanisms by which bioadhesives forms adhesion to tissues and highlights the correlation between bioadhesives composition and their potential host responses. Furthermore, clinical applications of bioadhesives and their application-driven requirements are outlined.

Morphing-to-Adhesion Polysaccharide Hydrogel for Adaptive Biointerfaces

Reliable functions of medical implants highly depend on biocompatible, conformal, and stable biointerfaces for seamless biointegration with biological tissues. Though flexible biointerfaces based on synthetic hydrogels have shown promise in optimizing implant biointegration via surgical suturing, physical attachment, or manual preshaping, they still suffer from poor adaptability, such as tissue damage by surgical suturing, low bioactivity, and difficulties in conformal contact and stable fixation, especially for specific tissues of large surface curvatures. Here, we report a bilayer hydrogel-based adaptive biointerface (HAB) made of two polysaccharide derivates, N-hydroxysuccinimide (NHS) ester-activated alginate and chitosan, harnessing dual advantages of their different swelling and active groups. Leveraging on the differential swelling between the two hydrogel layers and covalent linkages with active groups at hydrogel interfaces, HABs can be programmed into sealed tubes with tunable diameters via water-induced compliable shape morphing and instant interfacial adhesion. We further demonstrate that the polysaccharide-based morphing-to-adhesion HAB possesses outstanding bioactivity in directing cellular focal adhesion and intercellular junction, versatile geometrical adaptability to diverse tubular tissues with a wide range of surface curvatures (2.8 × 10²-1.3 × 10³ m^-1), and excellent mechanical stability in high load-/shear-bearing physiological environments (blood flow volume: 85 mm·s^-1). HABs overcome the limitations of existing biointerfaces in terms of poor bioactivity and difficult biointegration with biological tissues of large surface curvatures, holding promise to open new avenues for adaptive biointerfaces and reliable medical implants.

Injectable Adhesive Hydrogels for Soft tissue Reconstruction: A Materials Chemistry Perspective

Injectable bioadhesives offer several advantages over conventional staples and sutures in surgery to seal and close incisions or wounds. Despite the growing research in recent years few injectable bioadhesives are available for clinical use. This review summarizes the key chemical features that enable the development and improvements in the use of polymeric injectable hydrogels as bioadhesives or sealants, their design requirements, the gelation mechanism, synthesis routes, and the role of adhesion mechanisms and strategies in different biomedical applications. It is envisaged that developing a deep understanding of the underlying materials chemistry principles will enable researchers to effectively translate bioadhesive technologies into clinically-relevant products.

Predicting Adhesive Free Energies of Polymer-Surface Interactions with Machine Learning

Polymer-surface interactions are crucial to many biological processes and industrial applications. Here we propose a machine learning method to connect a model polymer's sequence with its adhesion to decorated surfaces. We simulate the adhesive free energies of 20000 unique coarse-grained one-dimensional polymer sequences interacting with functionalized surfaces and build support vector regression models that demonstrate inexpensive and reliable prediction of the adhesive free energy as a function of sequence. Our work highlights the promising integration of coarse-grained simulation with data-driven machine learning methods for the design of functional polymers and represents an important step toward linking polymer compositions with polymer-surface interactions.

Medical Adhesives and Their Role in Laparoscopic Surgery—A Review of Literature

Laparoscopic surgery is undergoing rapid development. Replacing the traditional method of joining cut tissues with sutures or staples could greatly simplify and speed up laparoscopic procedures. This alternative could undoubtedly be adhesives. For decades, scientists have been working on a material to bond tissues together to create the best possible conditions for tissue regeneration. The results of research on tissue adhesives achieved over the past years show comparable treatment effects to traditional methods. Tissue adhesives are a good alternative to surgical sutures in wound closure. This article is a review of the most important groups of tissue adhesives including their properties and possible applications. Recent reports on the development of biological adhesives are also discussed.

Antibacterial, wearable, transparent tannic acid-thioctic acid-phytic acid hydrogel for adhesive bandages

Making a hydrogel-based first-aid bandage with green resources, desirable biocompatibility, universal adhesive properties, low cost and simple production is a long-standing research aspiration. Considering this, three naturally existing organic acids, namely tannic acid, thioctic acid and phytic acid, were used to construct a novel adhesive gel (TATAPA hydrogel) for epidermal tissue bandage applications. This hydrogel could be synthesized under mild conditions with no need for a freeze-thawing shaping procedure, and was transparent, moldable and stretchable with good stability under continuous water immersion. In lap-shear tests, the TATAPA hydrogel could adhere to various hydrophilic and hydrophobic surfaces. Moreover, in the case of skin tissue adhesion, the hydrogel could be easily peeled off from the skin, meeting wearability requirements. Rheological tests showed that the hydrogel possessed thermal sensitive properties derived from multi-supramolecular interactions. The methicillin-resistant Staphylococcus aureus (MRSA)-infected burn wound test demonstrated that the hydrogel had desirable antibacterial activity and was beneficial for wound healing. A femoral artery bleeding assay was also used to reveal that the TATAPA hydrogel could be directly pasted onto the bleeding site for hemostasis. Overall, this hydrogel demonstrates potential as a surgical bioadhesive for a broad range of medical applications.

Multi-crosslinking hydrogels with robust bio-adhesion and pro-coagulant activity for first-aid hemostasis and infected wound healing

Bio-adhesive polysaccharide-based hydrogels have attracted much attention in first-aid hemostasis and wound healing for excellent biocompatibility, antibacterial property and pro-healing bioactivity. Yet, the inadequate mechanical properties and bio-adhesion limit their applications. Herein, based on dynamic covalent bonds, photo-triggered covalent bonds and hydrogen bonds, multifunctional bio-adhesive hydrogels comprising modified carboxymethyl chitosan, modified sodium alginate and tannic acid are developed. Multi-crosslinking strategy endows hydrogels with improved strength and flexibility simultaneously. Owing to cohesion enhancement strategy and self-healing ability, considerable bio-adhesion is presented by the hydrogel with a maximal adhesion strength of 162.6 kPa, 12.3-fold that of commercial fibrin glue. Based on bio-adhesion and pro-coagulant activity (e.g., the stimulative aggregation and adhesion of erythrocytes and platelets), the hydrogel reveals superior hemostatic performance in rabbit liver injury model with blood loss of 0.32 g, only 54.2% of that in fibrin glue. The healing efficiency of hydrogel for infected wounds is markedly better than commercial EGF Gel and Ag⁺ Gel due to the enhanced antibacterial and antioxidant properties. Through the multi-crosslinking strategy, the hydrogels show enhanced mechanical properties, fabulous bio-adhesion, superior hemostatic performance and promoting healing ability, thereby have an appealing application value for the first-aid hemostasis and infected wound healing.

•

The multifunctional hydrogel comprising polysaccharides and tannic acid was developed through multi-crosslinking strategy.

•

The multifunctional hydrogel showed 12.3-fold adhesion strength than commercial fibrin glue.

•

The multifunctional hydrogel revealed pro-coagulant activity and excellent hemostatic effect in vivo.

•

The multifunctional hydrogel effectively promoted the healing of infected wounds via multiple mechanisms.

Engineering a highly elastic bioadhesive for sealing soft and dynamic tissues

Injured tissues often require immediate closure to restore the normal functionality of the organ. In most cases, injuries are associated with trauma or various physical surgeries where different adhesive hydrogel materials are applied to close the wounds. However, these materials are typically toxic, have low elasticity, and lack strong adhesion especially to the wet tissues. In this study, a stretchable composite hydrogel consisting of gelatin methacrylol catechol (GelMAC) with ferric ions, and poly(ethylene glycol) diacrylate (PEGDA) was developed. The engineered material could adhere to the wet tissue surfaces through the chemical conjugation of catechol and methacrylate groups to the gelatin backbone. Moreover, the incorporation of PEGDA enhanced the elasticity of the bioadhesives. Our results showed that the physical properties and adhesion of the hydrogels could be tuned by changing the ratio of GelMAC/PEGDA. In addition, the in vitro toxicity tests confirmed the biocompatibility of the engineered bioadhesives. Finally, using an ex vivo lung incision model, we showed the potential application of the developed bioadhesives for sealing elastic tissues.

Gentamicin-thioctic acid multifunctional hydrogel for accelerating infected wound healing

Bacterial infections remain a major concern during wound healing and tissue bonding. The excessive proliferation of bacteria will seriously hinder the repair of wound and even lead to death. Generally,...

Highly Efficient Self-Healing Multifunctional Dressing with Antibacterial Activity for Sutureless Wound Closure and Infected Wound Monitoring

Wound healing represents a major clinical and public healthcare problem that is frequently challenged by infection risks, detrimental consequences on the surrounding tissues, and difficulties to monitor the healing process. Here we report on a novel self-healing, antibacterial, and multifunctional wound dressing for sutureless wound closure and real-time monitoring of the healing parameters. The self-healing elastomer contains cetyltrimethylammonium bromide (CTAB) and has high mechanical toughness (35 MJ m^-3 ), biocompatibility, and outstanding antibacterial activity (bactericidal rate is ≈90% in 12 h), enabling the wound dressing to effectively inhibit bacterial growth and accelerate infected wound healing. In vivo tests based on full-thickness skin incision model shows that the multifunctional wound dressing can help in contracting wound edges and facilitate wound closure and healing, as could be evidenced by notably dense and well-organized collagen deposition. The test provides an evidence that the integrated sensor array within the multifunctional wound dressing can monitor temperature, pH, and glucose level of the wound area in real-time, providing reliable and timely information of the condition of the wound. Ultimately, the reported multifunctional dressing would be of high value in managing the burden associated with wound healing via personalised monitoring and treatment approaches, digital and other people-centred solutions for health care.

Crosslink bio-adhesives for bronchoscopic lung volume reduction: current status and future direction

Several bronchoscopic lung volume reduction (BLVR) treatments have been developed to reduce hyperinflation in emphysema patients. Lung bio-adhesives are among the most promising new BLVR treatment options, as they potentially provide a permanent solution for emphysematous patients after only a single application. To date, bio-adhesives have mainly been used as haemostats and tissue sealants, while their application in permanently contracting and sealing hyperinflated lung tissue has recently been identified as a novel and enticing opportunity. However, a major drawback of the current adhesive technology is the induction of severe inflammatory responses and adverse events upon administration. In our review, we distinguish between and discuss various natural, semi-synthetic and synthetic tissue haemostats and sealants that have been used for pulmonary applications such as sealing air/fluid leaks. Furthermore, we present an overview of the different materials including AeriSeal and autologous blood that have been used to achieve lung volume reduction and discuss their respective advantages and drawbacks. In conclusion, we describe the key biological (therapeutic benefit and biocompatibility) and biomechanical (degradability, adhesive strength, stiffness, viscoelasticity, tunability and self-healing capacity) characteristics that are essential for an ideal lung bio-adhesive material with the potential to overcome the concerns related to current adhesives.

Nanoparticle-assembled bioadhesive coacervate coating with prolonged gastrointestinal retention for inflammatory bowel disease therapy

A key challenge for the effective treatment of gastrointestinal diseases including inflammatory bowel disease is to develop an orally administered drug delivery system capable of prolonged retention in the gastrointestinal tract. Herein we report a bioadhesive liquid coacervate based on hydrogen bonding-driven nanoparticle assembly. Free from electrostatic interactions, our fluid nanoparticle-assembled coacervate demonstrates significant pH- and salt-independent structural stability and forms a physically adhesive coating on a large surface area of intestinal tract with an extended residence time of more than 2 days to mediate the sustained release of preloaded water-soluble small molecule drugs in vivo. The orally administered drug-laden nanoparticle-assembled coacervate significantly mitigates the symptoms of inflammatory bowel disease, restores the diversity of gut microbiota, reduces systemic drug exposure, and improves the therapeutic efficacy in a rat acute colitis model compared with the oral administration of the same amount of drug in solution form. We suggest that the nanoparticle-assembled coacervate provides a promising drug delivery platform for management and treatment of numerous gastrointestinal diseases where controlled drug release with extended residence time is desired.

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.

A chitosan hydrogel sealant with self-contractile characteristic: From rapid and long-term hemorrhage control to wound closure and repair

Emergent and long-term hemorrhage control is requisite and beneficial for reducing global mortality and postoperative complications (e.g., second bleeding and adverse tissue adhesion). Despite recent advance in injectable hydrogels for hemostasis, achieving rapid gelation, strong tissue-adhesive property and stable mechanical strength under fluid physiological environment is still challenging. Herein, we developed a novel chitosan hydrogel (CCS@gel) via dynamic Schiff base reaction and mussel-inspired catechol chemistry. The hydrogel possessed high gelation rate (<10 s), strong wet adhesiveness, excellent self-healing performance and biocompatibility. More importantly, the CCS@gel exhibited saline-induced contractile performance and mechanical enhancement, promoting its mechanical property in moist internal conditions. In vivo studies demonstrated its superior hemostatic efficacy for diverse anticoagulated visceral and carotid bleeding scenarios, compared to commercialized fibrin glue. The hydrogel-treated rats survived for 8 weeks with minimal inflammation and postoperative adhesion. These results revealed that the promising CCS@gel would be a facile, efficient and safe sealant for clinical hemorrhage control.

Biocompatible therapeutic albumin/genipin bioglue for postoperative wound adhesion and residual tumor ablation

Surgical adhesives have partly replaced traditional sutures to seal and reattach tissues due to their superiorities in preventing liquids leakage and avoiding secondary damage in the surrounding wound area. Most of the existing adhesives are committed to promoting wound healing and functional recovery. A therapeutic adhesive that assists in clearing the residual tumors in the surgical area is undoubtedly meaningful to obtain a better clinical outcome. Herein, enlightened by commercial BioGlue (albumin/glutaraldehyde sealant), a biocompatible therapeutic albumin/genipin bioglue is designed for postoperative wound adhesion and tumor ablation. The albumin/genipin bioglue is formed by simple mixing of bovine serum albumin (BSA) and genipin (GP) under a 35 °C water bath for 24 h without further purification. The obtained dark-blue fluorescent adhesive exhibits a significant temperature increase accompanied by heating-induced curing once irradiated with an 808-nm laser. This unique characteristic allows BSA-GP a therapeutic adhesive for postoperative wound adhesion and photothermal elimination of residual tumors under laser irradiation. Moreover, its easy injectability and impressive photothermal efficacy also make it feasible for in situ tumor photothermal ablation. The ultrasimple synthetic strategy by mimicking BioGlue endows BSA-GP adhesive with large-scale production capacity and clinical transformation potential, which is a successful paradigm for reforming existing clinical products.

Emerging bioadhesives: from traditional bioactive and bioinert to a new biomimetic protein-based approach

Bioadhesives have reached significant milestones over the past two decades. Research has shown not only to produce adhesives capable of adhering to dry tissue but recently wet tissue as well. However, most bioadhesives developed have exhibited high adhesion strength yet lack other properties required for versatility in application, such as elasticity, biocompatibility and biodegradability. Adapting from limitations met from early bioadhesives and meeting the current demand allows novel bioadhesives to reach new milestones for the future. In this review, we overview the progression and variations of bioadhesives, current trends, characterisation techniques and conclude with future perspectives for bioadhesives for tissue engineering applications.

Translational Applications of Hydrogels

Advances in hydrogel technology have unlocked unique and valuable capabilities that are being applied to a diverse set of translational applications. Hydrogels perform functions relevant to a range of biomedical purposes-they can deliver drugs or cells, regenerate hard and soft tissues, adhere to wet tissues, prevent bleeding, provide contrast during imaging, protect tissues or organs during radiotherapy, and improve the biocompatibility of medical implants. These capabilities make hydrogels useful for many distinct and pressing diseases and medical conditions and even for less conventional areas such as environmental engineering. In this review, we cover the major capabilities of hydrogels, with a focus on the novel benefits of injectable hydrogels, and how they relate to translational applications in medicine and the environment. We pay close attention to how the development of contemporary hydrogels requires extensive interdisciplinary collaboration to accomplish highly specific and complex biological tasks that range from cancer immunotherapy to tissue engineering to vaccination. We complement our discussion of preclinical and clinical development of hydrogels with mechanical design considerations needed for scaling injectable hydrogel technologies for clinical application. We anticipate that readers will gain a more complete picture of the expansive possibilities for hydrogels to make practical and impactful differences across numerous fields and biomedical applications.

Hemostatic materials in wound care

Blood plays an essential role in the human body. Hemorrhage is a critical cause of both military and civilian casualties. The human body has its own hemostatic mechanism that involves complex processes and has limited capacity. However, in emergency situations such as battlefields and hospitals, when the hemostatic mechanism of the human body itself cannot stop bleeding effectively, hemostatic materials are needed for saving lives. In this review, the hemostatic mechanisms and performance of the most commonly used hemostatic materials, (including fibrin, collagen, zeolite, gelatin, alginate, chitosan, cellulose and cyanoacrylate) and the commercial wound dressings based on these materials, will be discussed. These materials may have limitations, such as poor tissue adhesion, risk of infection and exothermic reactions, that may lessen their hemostatic efficacy and cause secondary injuries. High-performance hemostatic materials, therefore, have been designed and developed to improve hemostatic efficiency in clinical use. In this review, hemostatic materials with advanced performances, such as antibacterial capacity, superhydrophobicity/superhydrophilicity, superelasticity, high porosity and/or biomimicry, will be introduced. Future prospects of hemostatic materials will also be discussed in this review.

Engineering elastic sealants based on gelatin and elastin-like polypeptides for endovascular anastomosis

Cerebrovascular ischemia from intracranial atherosclerosis remains difficult to treat. Although current revascularization procedures, including intraluminal stents and extracranial to intracranial bypass, have shown some benefit, they suffer from perioperative and postoperative morbidity. To address these limitations, here we developed a novel approach that involves gluing of arteries and subsequent transmural anastomosis from the healthy donor into the ischemic recipient. This approach required an elastic vascular sealant with distinct mechanical properties and adhesion to facilitate anastomosis. We engineered two hydrogel-based glues: an elastic composite hydrogel based on methacryloyl elastin-like polypeptide (mELP) combined with gelatin methacryloyl (GelMA) and a stiff glue based on pure GelMA. Two formulations with distinct mechanical characteristics were necessary to achieve stable anastomosis. The elastic GelMA/mELP composite glue attained desirable mechanical properties (elastic modulus: 288 ± 19 kPa, extensibility: 34.5 ± 13.4%) and adhesion (shear strength: 26.7 ± 5.4 kPa) to the blood vessel, while the pure GelMA glue exhibited superior adhesion (shear strength: 49.4 ± 7.0 kPa) at the cost of increased stiffness (elastic modulus: 581 ± 51 kPa) and reduced extensibility (13.6 ± 2.5%). The in vitro biocompatibility tests confirmed that the glues were not cytotoxic and were biodegradable. In addition, an ex vivo porcine anastomosis model showed high arterial burst pressure resistance of 34.0 ± 7.5 kPa, which is well over normal (16 kPa), elevated (17.3 kPa), and hypertensive crisis (24 kPa) systolic blood pressures in humans. Finally, an in vivo swine model was used to assess the feasibility of using the newly developed two-glue system for an endovascular anastomosis. X-ray imaging confirmed that the anastomosis was made successfully without postoperative bleeding complications and the procedure was well tolerated. In the future, more studies are required to evaluate the performance of the developed sealants under various temperature and humidity ranges.

Non-oxidized cellulose nanofibers as a topical hemostat: In vitro thromboelastometry studies of structure vs function

Hemorrhage remains a significant cause of morbidity and mortality following trauma and during complex surgeries. A variety of nanomaterials, including oxidized cellulose nanofibers (OCNFs), have been studied to overcome the disadvantages of current commercial topical hemostats. However, the relationship between nano-structural characteristics and hemostatic efficacy of non-oxidized cellulose nanofibers (CNFs) has not been elucidated. Herein, we present the first report of the correlation between structure and hemostatic performance of CNFs. In vitro thromboelastometry studies on CNFs, synthesized by ball-milling, showed that there is an optimum balance point between the aspect ratio (AR) and specific surface area (SSA) of nanofibers in terms of their maximum contribution to platelet function and plasma coagulation. The optimized CNFs with high SSA (17 m²/g) and a high AR (166) shortened normal whole blood clotting time by 68 %, outperforming cellulose-based hemostats. Additionally, CNFs reduced clotting time in platelet-deficient blood (by 80 %) and heparinized blood (by 54 %).

Reversible electroadhesion of hydrogels to animal tissues for suture-less repair of cuts or tears

Electroadhesion, i.e., adhesion induced by an electric field, occurs between non-sticky cationic and anionic hydrogels. Here, we demonstrate electroadhesion between cationic gels and animal (bovine) tissues. When gel and tissue are placed under an electric field (DC, 10 V) for 20 s, the pair strongly adhere, and the adhesion persists indefinitely thereafter. Applying the DC field with reversed polarity eliminates the adhesion. Electroadhesion works with the aorta, cornea, lung, and cartilage. We demonstrate the use of electroadhesion to seal cuts or tears in tissues or model anionic gels. Electroadhered gel-patches provide a robust seal over openings in bovine aorta, and a gel sleeve is able to rejoin pieces of a severed gel tube. These studies raise the possibility of using electroadhesion in surgery while obviating the need for sutures. Advantages include the ability to achieve adhesion on-command, and moreover the ability to reverse this adhesion in case of error.

The authors demonstrate strong adhesion of cationic hydrogels to bovine tissues under a DC electric field. Such electroadhesion can be reversed by switching the polarity of the field. This approach could enable simpler surgeries, where sutures are not needed.

Hydrogel-mesh composite for wound closure

During operations, surgical mesh is commonly fixed on tissues through fasteners such as sutures and staples. Attributes of surgical mesh include biocompatibility, flexibility, strength, and permeability, but sutures and staples may cause stress concentration and tissue damage. Here, we show that the functions of surgical mesh can be significantly broadened by developing a family of materials called hydrogel-mesh composites (HMCs). The HMCs retain all the attributes of surgical mesh and add one more: adhesion to tissues. We fabricate an HMC by soaking a surgical mesh with a precursor, and upon cure, the precursor forms a polymer network of a hydrogel, in macrotopological entanglement with the fibers of the surgical mesh. In a surgery, the HMC is pressed onto a tissue, and the polymers in the hydrogel form covalent bonds with the tissue. To demonstrate the concept, we use a poly(N-isopropylacrylamide) (PNIPAAm)/chitosan hydrogel and a polyethylene terephthalate (PET) surgical mesh. In the presence a bioconjugation agent, the chitosan and the tissue form covalent bonds, and the adhesion energy reaches above 100 J⋅m^-2 At body temperature, PNIPAAm becomes hydrophobic, so that the hydrogel does not swell and the adhesion is stable. Compared with sutured surgical mesh, the HMC distributes force over a large area. In vitro experiments are conducted to study the application of HMCs to wound closure, especially on tissues under high mechanical stress. The performance of HMCs on dynamic living tissues is further investigated in the surgery of a sheep.

A Strong Dual-Component Bioadhesive Based on Solventless Thiol-isocyanate Click Chemistry

Isocyanate is an efficient tissue anchor for engineering of strong bioadhesives. However, isocyanate-containing adhesives were seldom manufactured due to their requirement of water-free administration and time-consuming moisture-induced solidification. To address this issue, here, a solventless dual-component bioadhesive based on thiol-isocyanate cross-linking chemistry is reported. This dual-component bioadhesive consists of a hyperbranched polymer with thiol groups (HBPTE) and an isocyanate-modified polyethylene glycol (PEGNCO). HBPTE and PEGNCO are low-viscosity fluids at room temperature and hence could be used directly as adhesive components, in the absence of a catalyst and a solvent. The thiol-isocyanate click chemistry of components provides the HBPTE-PEGNCO mixture with a gelation time of 1.8-3 min, which makes it acceptable for practical applications. The abundance of isocyanate groups in the adhesive molecule provides strong bonding strength through formation of chemical linkages with reactive groups on the tissue. Moreover, in vitro and in vivo evaluations showed excellent biocompatibility of the HBPTE-PEGNCO adhesive. This dual-component bioadhesive based on solventless thiol-isocyanate click chemistry displayed a fast gelation time and excellent bonding performance, providing a pioneering idea for engineering isocyanate-containing bioadhesives.

Lignin Nanoparticles and Their Nanocomposites

Lignin nanomaterials have emerged as a promising alternative to fossil-based chemicals and products for some potential added-value applications, which benefits from their structural diversity and biodegradability. This review elucidates a perspective in recent research on nanolignins and their nanocomposites. It summarizes the different nanolignin preparation methods, emphasizing anti-solvent precipitation, self-assembly and interfacial crosslinking. Also described are the preparation of various nanocomposites by the chemical modification of nanolignin and compounds with inorganic materials or polymers. Additionally, advances in numerous potential high-value applications, such as use in food packaging, biomedical, chemical engineering and biorefineries, are described.

Hemostatic Self-Healing Hydrogel with Excellent Biocompatibility Composed of Polyphosphate-Conjugated Functional PNIPAM-Bearing Acylhydrazide

Biocompatible self-healing hydrogels present an effective application as drug-releasing vehicles for tissue engineering and wound repairing. At the same time, the effective hemostatic property of the hydrogels also improves the application property as wound dressing materials. In this research, the PNIPAM-bearing acylhydrazide P(NIPAM-co-AH) was synthesized and then hemostatic polyphosphate (PolyP) was imported to prepare polyphosphate-conjugated P(NIPAM-co-AH) (PNAP). Through the acylhydrazone connection of PNAP and aldehyde functional PEO (PEO DA), the self-healing hydrogel with a hemostatic property was fabricated with good flexibility and sealing effect. The resultant hydrogels kept excellent biocompatibility and showed controlled drug release behavior. More importantly, the hydrogel accelerated the coagulation rate in vitro and presented a strong hemostatic effect as the binder in the hemorrhage model in vivo, which endow the hemostatic hydrogel with a very useful drug delivery carrier for wound healing applications or first aid treatment of the wounded in critical situations.

Tissue Adhesives: From Research to Clinical Translation

Sutures, staples, clips and skin closure strips are used as the gold standard to close wounds after an injury. In spite of being the present standard of care, the utilization of these conventional methods is precarious amid complicated and sensitive surgeries such as vascular anastomosis, ocular surgeries, nerve repair, or due to the high-risk components included. Tissue adhesives function as an interface to connect the surfaces of wound edges and prevent them from separation. They are fluid or semi-fluid mixtures that can be easily used to seal any wound of any morphology - uniform or irregular. As such, they provide alternatives to new and novel platforms for wound closure methods. In this review, we offer a background on the improvement of distinctive tissue adhesives focusing on the chemistry of some of these products that have been a commercial success from the clinical application perspective. This review is aimed to provide a guide toward innovation of tissue bioadhesive materials and their associated biomedical applications.

Polymeric Tissue Adhesives

Polymeric tissue adhesives provide versatile materials for wound management and are widely used in a variety of medical settings ranging from minor to life-threatening tissue injuries. Compared to the traditional methods of wound closure (i.e., suturing and stapling), they are relatively easy to use, enable rapid application, and introduce minimal tissue damage. Furthermore, they can act as hemostats to control bleeding and provide a tissue-healing environment at the wound site. Despite their numerous current applications, tissue adhesives still face several limitations and unresolved challenges (e.g., weak adhesion strength and poor mechanical properties) that limit their use, leaving ample room for future improvements. Successful development of next-generation adhesives will likely require a holistic understanding of the chemical and physical properties of the tissue-adhesive interface, fundamental mechanisms of tissue adhesion, and requirements for specific clinical applications. In this review, we discuss a set of rational guidelines for design of adhesives, recent progress in the field along with examples of commercially available adhesives and those under development, tissue-specific considerations, and finally potential functions for future adhesives. Advances in tissue adhesives will open new avenues for wound care and potentially provide potent therapeutics for various medical applications.

Hemostatic strategies for uncontrolled bleeding: A comprehensive update

Uncontrolled bleeding remains the leading cause of morbidity and mortality across the entire macrocosm. It refers to excessive loss of blood that occurs inside of body, due to unsuccessful platelet plug formation at the injury site. It is not only limited to the battlefield, but remains the second leading cause of death amongst the civilians, as a result of traumatic injury. Startlingly, there are no effective treatments currently available, to cater the issue of internal bleeding, even though early intervention is of utmost significance in minimizing the mortality rates associated with it. The fatal issue of uncontrolled bleeding is ineffectively being dealt with the use of pressure dressings, tourniquet, and surgical procedures. This is not a practical approach in combat arenas or in emergency situations, where the traumatic injury inflicted is deep inside the body, and cannot be addressed externally, by the application of topical dressings. This review focuses on the traditional hemostatic agents that are used to augment the process of hemostasis, such as mineral zeolites, chitosan based products, biologically active agents, anti-fibrinolytics, absorbable agents, and albumin and glutaraldehyde, as well as the micro- and nano-based hemostatic agents such as synthocytes, thromboerythrocytes, thrombosomes, and the synthetic platelets.