Highly Resilient Dual-Crosslinked Hydrogel Adhesives Based on a Dopamine-Modified Crosslinker

Formulation-Property Effects in Novel Injectable and Resilient Natural Polymer-Based Hydrogels for Soft Tissue Regeneration

The development of injectable hydrogels for soft tissue regeneration has gained significant attention due to their minimally invasive application and ability to conform precisely to the shape of irregular tissue cavities. This study presents a novel injectable porous scaffold based on natural polymers that undergoes in situ crosslinking, forming a highly resilient hydrogel with tailorable mechanical and physical properties to meet the specific demands of soft tissue repair. By adjusting the formulation, we achieved a range of stiffness values that closely mimic the mechanical characteristics of native tissues while maintaining very high resilience (>90%). The effects of gelatin, alginate, and crosslinker concentrations, as well as porosity, on the hydrogel's properties were elucidated. The main results indicated a compression modulus range of 2.7-89 kPa, which fits all soft tissues, and gelation times ranging from 5 to 30 s, which enable the scaffold to be successfully used in various operations. An increase in gelatin and crosslinker concentrations results in a higher modulus and lower gelation time, i.e., a stiffer hydrogel that is created in a shorter time. In vitro cell viability tests on human fibroblasts were performed and indicated high biocompatibility. Our findings demonstrate that these injectable hydrogel scaffolds offer a promising solution for enhancing soft tissue repair and regeneration, providing a customizable and resilient framework that is expected to support tissue integration and healing with minimal surgical intervention.

Clicked into Place: Biomimetic Copolymer Adhesive for Covalent Conjugation of Functionalities

Polydopamines (PDA) are a popular class of materials and promising candidates as adhesives for new fastening techniques. PDA layers can be formed on a wide range of substrates in various environments. Here, we present a novel method for functionalizing PDA-based copolymer films by using click chemistry. These copolymers adhere strongly to various surfaces and simultaneously have active groups that allow the attachment of functional groups. We discuss the coupling of two types of chitosan and a rhodamine B dye molecule to the alkyne groups of the copolymers by employing click reactions. Azidopropyl methacrylate (AzMA), methyl methacrylate (MMA), and dopamine methacrylamide (DOMA) are copolymerized and codeposited with (3-aminopropyl)triethoxysilane on silicon wafers, polyethylene (PE), and polytetrafluoroethylene (PTFE). AzMA provides the surfaces with azides for use in click reactions, MMA functions to control the polymer as a nonfunctional diluent, whereas DOMA provides adhesion, as well as cross-linking groups. After codeposition, the dyes are grafted to the copolymer to illustrate the ability of the films to link functional groups covalently. Fourier transform infrared spectroscopy confirms the successful click reaction in solution, and atomic force microscopy shows the surface morphologies following grafting. Fluorescence microscopy provides evidence of successful grafting. As an example of a possible application, layers exhibiting antifouling properties are prepared. Chitosan grafted to PE is tested for antifouling performance. These functionalized layers show nonspecific inhibition of protein adsorption. We find that chitosan can lower the adsorption of fluorescein-labeled bovine serum albumin (BSA) protein by more than 90% for the best performing fluorescein-labeled BSA protein and by more than 90% for the best-performing layer. These results demonstrate the viability of our PDA-based copolymers for surface functionalization through click chemistry grafting at challenging adhesion to surfaces.

Highly Resilient Noncovalently Associated Hydrogel Adhesives for Wound Sealing Patch

The development of hydrogel adhesives with high mechanical resilience and toughness remains a challenging task. Hydrogels must exhibit high mechanical resilience to withstand the inevitable movement of the human body while simultaneously demonstrating strong wet tissue adhesion and appropriate toughness to hold and seal damaged tissues; However, tissue adhesion, toughness, and mechanical resilience are typically negatively correlated. Therefore, this paper proposes a highly resilient double-network (DN) hydrogel wound-sealing patch that exhibits a well-balanced combination of tissue adhesion, toughness, and mechanical resilience. The DN structure is formed by introducing covalently and non-covalently crosslinkable dopamine-modified crosslinkers and physically interactable linear poly(vinyl imidazole) (PVI). The resulting hydrogel adhesive exhibits high toughness and mechanical resilience due to the presence of a DN involving reversible physical intermolecular interactions such as hydrogen bonds, hydrophobic associations, cation-π interactions, π-π interactions, and chain entanglements. Moreover, the hydrogel adhesive achieves strong wet tissue adhesion through the polar hydroxyl groups of dopamine and the amine group of PVI. These mechanical attributes allow the proposed adhesive to effectively seal damaged tissues and promote wound healing by maintaining a moist environment.

Progress of polysaccharide-based tissue adhesives

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

Polyphenol-sodium alginate supramolecular injectable hydrogel with antibacterial and anti-inflammatory capabilities for infected wound healing

Injectable hydrogel has attracted appealing attention for skin wound treatment. Although multifunctional injectable hydrogels can be prepared by introducing bioactive ingredients with antibacterial and anti-inflammatory capabilities, their preparation remains complicated. Herein, a polyphenol-based supramolecular injectable hydrogel (PBSIH) based on polyphenol gallic acid and biological macromolecule sodium alginate is developed as a wound dressing to accelerate wound healing. We show that such PBSIH can be rapidly formed within 15 s by mixing the sodium alginate and gallic acid solutions based on the hydrogen bonding and hydrophobic interactions. The PBSIH shows excellent cytocompatibility, antibacterial, and antioxidant properties, which enhance infected wound healing by inhibiting bacterial infection and alleviating inflammation after treatment of 11 days. Moreover, we show that the preparative strategies of injectable supramolecular hydrogels can be extended to other polyphenols, including protocatechuic and tannic acids. This study provides a facile yet highly effective method to design injectable polyphenol- sodium alginate hydrogel for wound dressing based on naturally bioactive ingredients.

A highly stretchable, adhesive, and antibacterial hydrogel with chitosan and tobramycin as dynamic cross-linkers for treating the infected diabetic wound

Diabetic wounds pose a significant challenge due to their susceptibility to bacterial infection in a high-glucose environment, which impedes the wound healing process. To address this issue, there is a pressing need to develop suitable hydrogels that can promote the regeneration of diabetic wounds in clinical practice. In this study, we designed and fabricated a highly stretchable, adhesive, transparent, and antibacterial hydrogel through a one-pot radical polymerization of N-[Tris (hydroxymethyl) methyl] acrylamide (THMA) and acrylic acid (AA), and with chitosan and the antibiotic tobramycin as the dynamic physical crosslinkers. The copolymer contains a large number of carboxyl and hydroxyl groups, which can form an interpenetrating network structure with chitosan and tobramycin through multiple dynamic non-covalent bonds. This hydrogel exhibited over 1600 % elongation through an energy dissipation mechanism and strong adhesion to various surfaces without any chemical reaction. In vivo, studies conducted on a staphylococcus aureus-infected full-thickness diabetic skin wound model demonstrated that the hydrogel loaded with tobramycin as one of the crosslinkers had a long-lasting antibacterial activity and effectively accelerated wound healing. Therefore, the antibiotic-loaded adhesive hydrogel we proposed holds great promise as a treatment for bacteria-infected diabetic wounds.

Multifunctional chitosan-based gel sponge with efficient antibacterial, hemostasis and strong adhesion

Developing wound dressings with solid adhesive properties that enable efficient, painless hemostasis and prevent wound infection remain a huge challenge. Herein, the tris(hydroxymethyl) methyl glycine-modified chitosan derivative (CTMG) was prepared and freeze-dried after simply adjusting the concentration of CTMG to obtain the chitosan-based gel sponge with desired multi-hollow structure, special antibacterial and biocompatibility. The adhesion strength on porcine skin was impressive up to 113 KPa, much higher than fibrin glue. It can withstand the pressure that far exceeds blood pressure. CTMG exhibits bacteriostatic abilities as demonstrated in a bacteriostatic assay, and alongside biocompatibility, as shown in cytotoxicity and hemolytic assays. Moreover, CTMG gel sponge showed hemostatic properties in both in vivo and in vitro hemostasis experiments. During an experiment on liver hemorrhage in rats, CTMG gel sponge proved to be more effective in controlling bleeding than other hemostatic sponges available on the market, indicating its promising hemostatic properties. CTMG gel sponge possesses the potential to function as a wound dressing and hemostatic material, making it suitable for various clinical applications.

Fabrication of flexible accelerated-wound-healing chitosan/dopamine-based bilayer hydrogels for strain sensors

Flexible conductive hydrogels have great potential for healthcare and human motion sensing. However, it is difficult to simultaneously achieve conductive hydrogel epidermal sensors with reliable adhesion capabilities and excellent sensing properties, as well as accelerated wound healing performance in wearable hydrogels. Here, an epidermal sensor with excellent adhesion (0.6 kPa) and tensile strain (218.0 %) properties was assembled from an easy-to-prepare bilayer antimicrobial hydrogel, which effectively accelerates wound healing, as well as for human motion sensing. The upper hydrogel layer was composed of PVA, which could effectively enhance the mechanical properties of the bilayer hydrogel. The lower hydrogel layer consisted of polyacrylamide (PAm) and chitosan-dopamine (CC-DA). PAm with good adhesion properties adhered effectively to the skin surface. CC-DA not only had adhesion properties, but also has good antibacterial effects. It inhibited the growth of bacteria, which assisted in wound healing and infection prevention. Therefore, the design of the bilayer hydrogel combined the mechanical enhancement of PVA with the adhesion properties and antimicrobial effect of PAm and CC-DA to provide better wound repair. In addition, the double-layer hydrogel with good electrical conductivity (1.65 S·m-1) could sensitively monitor the tiny electrophysiological signals emitted by the human body during exercise rehabilitation training.

A light-responsive wound dressing hydrogel: Gelatin based self-healing interpenetrated network with metal-ligand interaction by ferric citrate

Interpenetrated network (IPN) hydrogels with desired mechanical properties were prepared based on gelatin. A copolymer of dimethyl aminoethyl methacrylate (DMAEMA) with 2-Acrylamido-2-methylpropane sulfonic acid (AMPS) in gelatin was chemically cross-linked with methylene bis acrylamide (MBA) to form a semi-IPN hydrogel. Also, IPN hydrogel is fabricated from the AMPS-co-DMAEMA and gelatin in the presence of ferric ions with both chemical and physical cross-linkers. According to the compression test, the metal-ligand interaction has a remarkable impact on the mechanical strength of hydrogel. Ferric ions caused a decrease in the pores size confirmed by the SEM images of hydrogels, resulting in preserving its mechanical stability during the swelling test due to a more robust structure of hydrogel. Ferric to ferrous ions reduction is observed under visible light irradiation, which results in a light-sensitive hydrogel with a higher rate of biodegradation compared to semi-IPN hydrogels. MTT assay results implied that the synthesized hydrogels are non-toxic for the L-929 cell line. Also, for more detailed investigations, histological studies are conducted as in vivo tests. With regards to the improvements of mechanical properties harnessed in IPN hydrogels by ferric ions along with the extraordinary self-healing capability, IPNs would be considered an appropriate option for tissue engineering.

Progress of tissue adhesives based on proteins and synthetic polymers

In recent years, polymer-based tissue adhesives (TAs) have been developed as an alternative to sutures to close and seal incisions or wounds owing to their ease of use, rapid application time, low cost, and minimal tissue damage. Although significant research is being conducted to develop new TAs with improved performances using different strategies, the applications of TAs are limited by several factors, such as weak adhesion strength and poor mechanical properties. Therefore, the next-generation advanced TAs with biomimetic and multifunctional properties should be developed. Herein, we review the requirements, adhesive performances, characteristics, adhesive mechanisms, applications, commercial products, and advantages and disadvantages of proteins- and synthetic polymer-based TAs. Furthermore, future perspectives in the field of TA-based research have been discussed.

Photo-crosslinked adhesive hydrogel loaded with extracellular vesicles promoting hemostasis and liver regeneration

Hepatectomy is an effective surgical method for the treatment of liver diseases, but intraoperative bleeding and postoperative liver function recovery are still key issues. This study aims to develop a composite hydrogel dressing with excellent hemostatic properties, biocompatibility, and ability to promote liver cell regeneration. The modified gelatin matrix (GelMA, 10%) was mixed with equal volumes of sodium alginate-dopamine (Alg-DA) at concentrations of 0.5%, 1%, and 2%. Then a cross-linking agent (0.1%) was added to prepare different composite hydrogels under UV light, named GelMA/Alg-DA-0.5, GelMA/Alg-DA-1 and GelMA/Alg-DA-2, respectively. All the prepared hydrogel has a porous structure with a porosity greater than 65%, and could be stabilized in a gel state after being cross-linked by ultraviolet light. Physicochemical characterization showed that the elastic modulus, water absorption, adhesion, and compressibility of the composite hydrogels were improved with increasing Alg-DA content. Furthermore, the prepared hydrogel exhibits in vitro degradability, excellent biocompatibility, and good hemostatic function. Among all tested groups, the group of GelMA/Alg-DA-1 hydrogel performed the best. To further enhance its application potential in the field of liver regeneration, adipose-derived mesenchymal stem cell exosomes (AD-MSC-Exo) were loaded into GelMA/Alg-DA-1 hydrogel. Under the same conditions, GelMA/Alg-DA-1/Exo promoted cell proliferation and migration more effectively than hydrogels without extracellular vesicles. In conclusion, the prepared GelMA/Alg-DA-1 composite hydrogel loaded with AD-MSC-Exo has great application potential in liver wound hemostasis and liver regeneration.

Recent progress of antibacterial hydrogels in wound dressings

Hydrogels are essential biomaterials due to their favorable biocompatibility, mechanical properties similar to human soft tissue extracellular matrix, and tissue repair properties. In skin wound repair, hydrogels with antibacterial functions are especially suitable for dressing applications, so novel antibacterial hydrogel wound dressings have attracted widespread attention, including the design of components, optimization of preparation methods, strategies to reduce bacterial resistance, etc. In this review, we discuss the fabrication of antibacterial hydrogel wound dressings and the challenges associated with the crosslinking methods and chemistry of the materials. We have investigated the advantages and limitations (antibacterial effects and antibacterial mechanisms) of different antibacterial components in the hydrogels to achieve good antibacterial properties, and the response of hydrogels to stimuli such as light, sound, and electricity to reduce bacterial resistance. Conclusively, we provide a systematic summary of antibacterial hydrogel wound dressings findings (crosslinking methods, antibacterial components, antibacterial methods) and an outlook on long-lasting antibacterial effects, a broader antibacterial spectrum, diversified hydrogel forms, and the future development prospects of the field.

Self-healing hybrid hydrogels with sustained bioactive components release for guided bone regeneration

Guided bone regeneration (GBR) is widely used in treating oral bone defects to exclude the influence of non-osteogenic tissue on the bone healing process. The traditional method of GBR with a titanium mesh to treat large-area bone defects is limited by the deficiency of increased trauma and costs to patients. Herein, a bi-layered scaffold for GBR composed of a fiber barrier layer and a self-healing hydrogel repair layer is successfully fabricated. The barrier layer is a fibrous membrane material with specific porosity constructed by electrospinning, while the functional layer is a self-healing hydrogel material formed by multiple dynamic covalent bonds. The system can provide an osteogenic microenvironment by preventing the infiltration of connective tissue to bone defects, maintain the stability of the osteogenic space through the self-healing property, and regulate the release of bioactive substances in the dynamic physical condition, which is beneficial to osteoblast proliferation, differentiation, and bone regeneration. This study focused on exploring the effects of different crosslinkers and bonding methods on the comprehensive properties of hydrogels. and proved that the hybrid scaffold system has good biocompatibility, cell barrier function and can enhance bone regeneration activity. Thereby it could be a promising clinical strategy for bone regeneration.