A mussel-inspired carboxymethyl cellulose hydrogel with enhanced adhesiveness through enzymatic crosslinking

Functionalized hydrogels as smart gene delivery systems to treat musculoskeletal disorders

Despite critical advances in regenerative medicine, the generation of definitive, reliable treatments for musculoskeletal diseases remains challenging. Gene therapy based on the delivery of therapeutic genetic sequences has strong value to offer effective, durable options to decisively manage such disorders. Furthermore, scaffold-mediated gene therapy provides powerful alternatives to overcome hurdles associated with classical gene therapy, allowing for the spatiotemporal delivery of candidate genes to sites of injury. Among the many scaffolds for musculoskeletal research, hydrogels raised increasing attention in addition to other potent systems (solid, hybrid scaffolds) due to their versatility and competence as drug and cell carriers in tissue engineering and wound dressing. Attractive functionalities of hydrogels for musculoskeletal therapy include their injectability, stimuli-responsiveness, self-healing, and nanocomposition that may further allow to upgrade of them as "intelligently" efficient and mechanically strong platforms, rather than as just inert vehicles. Such functionalized hydrogels may also be tuned to successfully transfer therapeutic genes in a minimally invasive manner in order to protect their cargos and allow for their long-term effects. In light of such features, this review focuses on functionalized hydrogels and demonstrates their competence for the treatment of musculoskeletal disorders using gene therapy procedures, from gene therapy principles to hydrogel functionalization methods and applications of hydrogel-mediated gene therapy for musculoskeletal disorders, while remaining challenges are being discussed in the perspective of translation in patients. STATEMENT OF SIGNIFICANCE: Despite advances in regenerative medicine, the generation of definitive, reliable treatments for musculoskeletal diseases remains challenging. Gene therapy has strong value in offering effective, durable options to decisively manage such disorders. Scaffold-mediated gene therapy provides powerful alternatives to overcome hurdles associated with classical gene therapy. Among many scaffolds for musculoskeletal research, hydrogels raised increasing attention. Functionalities including injectability, stimuli-responsiveness, and self-healing, tune them as "intelligently" efficient and mechanically strong platforms, rather than as just inert vehicles. This review introduces functionalized hydrogels for musculoskeletal disorder treatment using gene therapy procedures, from gene therapy principles to functionalized hydrogels and applications of hydrogel-mediated gene therapy for musculoskeletal disorders, while remaining challenges are discussed from the perspective of translation in patients.

Nanocellulose-based hydrogels as versatile materials with interesting functional properties for tissue engineering applications

Tissue engineering has emerged as a remarkable field aiming to restore or replace damaged tissues through the use of biomimetic constructs. Among the diverse materials investigated for this purpose, nanocellulose-based hydrogels have garnered attention due to their intriguing biocompatibility, tunable mechanical properties, and sustainability. Over the past few years, numerous research works have been published focusing on the successful use of nanocellulose-based hydrogels as artificial extracellular matrices for regenerating various types of tissues. The review emphasizes the importance of tissue engineering, highlighting hydrogels as biomimetic scaffolds, and specifically focuses on the role of nanocellulose in composites that mimic the structures, properties, and functions of the native extracellular matrix for regenerating damaged tissues. It also summarizes the types of nanocellulose, as well as their structural, mechanical, and biological properties, and their contributions to enhancing the properties and characteristics of functional hydrogels for tissue engineering of skin, bone, cartilage, heart, nerves and blood vessels. Additionally, recent advancements in the application of nanocellulose-based hydrogels for tissue engineering have been evaluated and documented. The review also addresses the challenges encountered in their fabrication while exploring the potential future prospects of these hydrogel matrices for biomedical applications.

Bioinspired wet adhesive carboxymethyl cellulose-based hydrogel with rapid shape adaptability and antioxidant activity for diabetic wound repair

Currently, adhesive hydrogels have shown promising effect in chronic diabetic wound repair. However, there are issues and challenges in treating diabetic wounds due to inadequate wet adhesion, unable to fill irregular and deep wounds, and oxidative stress. Herein, a mussel-inspired naturally hydrogel dressing with rapid shape adaptability, wet adhesion and antioxidant abilities for irregular, deep and frequently movement diabetic wounds repair was constructed by comprising catechol modified carboxymethyl cellulose (CMC-DA) and tannic acid. Benefiting from the reversible hydrogen bonding, the resulting hydrogels exhibited injectability, remarkable self-healing ability, rapid shape adaptability and strong tissue adhesion (45.9 kPa), thereby contributing to self-adaptive irregular-shaped wounds or moving joint parts. Especially, the adhesion strength of the hydrogel on wet tissue still remained at 14.9 kPa. Besides, the hydrogels could be easily detached from the skin by ice-cooling that avoided secondary damage caused by dressing change. Remarkably, the hydrogels possessed excellent antioxidant, satisfactory biocompatibility, efficient hemostasis and antibacterial properties. The in vivo evaluation further demonstrated that the hydrogel possessed considerable wound-healing promotion effect by regulating diabetic microenvironment, attributed to that the hydrogel could significantly reduce inflammatory response, alleviate oxidative stress and regulate neovascularization. Overall, this biosafe adhesive hydrogel had great potentials for diabetic wound management.

l-Carnosine loaded on carboxymethyl cellulose hydrogels for promoting wound healing

Wound management remains a challenge in clinical practice. Nowadays, patients have an increasing demand for wound repair with enhanced speed and quality; therefore, there is a great need to seek therapeutic strategies that can promote rapid and effective wound healing. In this study, we developed a carboxymethyl cellulose hydrogel loaded with l-carnosine (CRN@hydrogel) for potential application as a wound dressing. In vitro experiments confirmed that CRN@hydrogel can release over 80% of the drug within 48 h and demonstrated its favorable cytocompatibility and blood compatibility, thus establishing its applicability for safe utilization in clinical practice. Using a rat model, we found that this hydrogel could promote and accelerate wound healing more effectively. These results indicate that the novel hydrogel can serve as an efficient therapeutic strategy for wound treatment.

Current trend on preparation, characterization and biomedical applications of natural polysaccharide-based nanomaterial reinforcement hydrogels: A review

The tunable properties of hydrogels have led to their widespread use in various biomedical applications such as wound treatment, drug delivery, contact lenses, tissue engineering and 3D bioprinting. Among these applications, natural polysaccharide-based hydrogels, which are fabricated from materials like agarose, alginate, chitosan, hyaluronic acid, cellulose, pectin and chondroitin sulfate, stand out as preferred choices due to their biocompatibility and advantageous fabrication characteristics. Despite the inherent biocompatibility, polysaccharide-based hydrogels on their own tend to be weak in physiochemical and mechanical properties. Therefore, further reinforcement in the hydrogel is necessary to enhance its suitability for specific applications, ensuring optimal performance in diverse settings. Integrating nanomaterials into hydrogels has proven effective in improving the overall network and performance of the hydrogel. This approach also addresses the limitations associated with pure hydrogels. Next, an overview of recent trends in the fabrication and applications of hydrogels was presented. The characterization of hydrogels was further discussed, focusing specifically on the reinforcement achieved with various hydrogel materials used so far. Finally, a few challenges associated with hydrogels by using polysaccharide-based nanomaterial were also presented.

Effects of catechol grafting on chitosan-based coacervation and adhesion

In this study, we investigated detailedly the contribution of catechol in tuning the formation and adhesive properties of coacervates. We have constructed a series of catechol-grafted Chitosan (Chitosan-C), and investigated their coacervation with gum arabic (GA) and the corresponding adhesion. We demonstrate that, increasing catechol grafting ratio from 0 %-44 % impacted the coacervation moderately, while enhanced the adhesion of the coacervate up to 438 % when the catechol faction was 37 %. Further increasing the grafting ratio to 55 % led to precipitated coacervates associated with a declined adhesion. Our findings identify the optimal grafting threshold for coacervation and adhesion, providing insights into the underlying mechanism of coacervate binding. Moreover, the catechol enhancement on adhesion of coacervates tolerates different substrates and diverse polyelectrolyte pairs. The revealed principles shall be helpful for designing adhesive coacervates and boosting their applications in various industrial and biomedical areas.

A review of cellulose-based catechol-containing functional materials for advanced applications

With the increment in global energy consumption and severe environmental pollution, it is urgently needed to explore green and sustainable materials. Inspired by nature, catechol groups in mussel adhesion proteins have been successively understood and utilized as novel biomimetic materials. In parallel, cellulose presents a wide class of functional materials rating from macro-scale to nano-scale components. The cross-over among both research fields alters the introduction of impressive materials with potential engineering properties, where catechol-containing materials supply a general stage for the functionalization of cellulose or cellulose derivatives. In this review, the role of catechol groups in the modification of cellulose and cellulose derivatives is discussed. A broad variety of advanced applications of cellulose-based catechol-containing materials, including adhesives, hydrogels, aerogels, membranes, textiles, pulp and papermaking, composites, are presented. Furthermore, some critical remaining challenges and opportunities are studied to mount the way toward the rational purpose and applications of cellulose-based catechol-containing materials.

Fucoidan-coated cotton dressing functionalized with biomolecules capped silver nanoparticles (LB-Ag NPs-FN-OCG) for rapid healing therapy of infected wounds

The colonization of pathogenic microbes poses a significant clinical barrier that hinders the physiological wound-healing process. Addressing this challenge, we developed a novel wound dressing using a modified cotton gauze dressing coated with fucoidan and functionalized with silver nanoparticles (LB-Ag NPs-FN-OCG) for the rapid treatment of infected wounds. Firstly, phytochemical-capped LB-Ag NPs were synthesized and characterized using high performance liquid chromatography (HPLC), transmission electron microscopy (TEM), and zeta potential analysis. Secondly, different concentrations of LB-Ag NPs (0.1%-1%) were functionalized into FN-OCG to identify appropriate concentrations that were non-toxic with superior antibacterial activities. Screening assays, including antibacterial, hemolysis, chick chorioallantoic membrane (CAM) assay, and cytotoxicity assay, revealed that LB-Ag NPs (0.5%)-FN-OCG were non-toxic and demonstrated greater efficiency in inhibiting bacterial pathogens (Escherichia coli, Salmonella enterica, Staphylococcus aureus, and Listeria monocytogenes) and promoting fibroblast cell (NIH3T3) migration. In vivo assays revealed that LB-Ag NPs (0.5%)-FN-OCG treatment exhibited excellent wound healing activity (99.73 ± 0.01%) compared to other treatments by inhibiting bacterial colonization, maintaining the blood parameters, developing granulation tissue, new blood vessels, and collagen deposition. Overall, this study highlights that LB-Ag NPs (0.5%)-FN-OCG serve as a antibacterial wound dressing for infected wound healing applications.

Sodium hyaluronate hydrogel for wound healing and human health monitoring based on deep eutectic solvent

Hydrogel dressings traditionally promote wound healing by maintaining moisture and preventing infection rather than by actively stimulating the skin to regulate cell behavior. Electrical stimulation (ES) is known to modulate skin cell behavior and to promote wound healing. This study describes the first multifunctional conductive hydrogel for wound healing and health monitoring based on a deep eutectic solvent (DES). Sodium hyaluronate and polydopamine constituted the hydrogel skeleton, and tea tree oil and Panax notoginseng extract were used as the active ingredients to induce adhesion, promote antioxidant and antibacterial activity, and support biocompatibility of the hydrogel. The inclusion of DES increases the temperature resistance of the hydrogel and improves its environmental adaptability. We used a small, portable coin battery-powered to provide electrical stimulation. Treatment with both the hydrogel and ES resulted in a stronger therapeutic effect than that provided by the commercial DuoDERM dressing. The hydrogel detected movement and strain when applied as a sensor. Overall, this study reports the development of a multifunctional conductive hydrogel dressing based on DES as a wound healing and health monitor.

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.

Polysaccharide hydrogel platforms as suitable carriers of liposomes and extracellular vesicles for dermal applications

Lipid-based nanocarriers have been extensively investigated for their application in drug delivery. Particularly, liposomes are now clinically established for treating various diseases such as fungal infections. In contrast, extracellular vesicles (EVs) - small cell-derived nanoparticles involved in cellular communication - have just recently sparked interest as drug carriers but their development is still at the preclinical level. To drive this development further, the methods and technologies exploited in the context of liposome research should be applied in the domain of EVs to facilitate and accelerate their clinical translation. One of the crucial steps for EV-based therapeutics is designing them as proper dosage forms for specific applications. This review offers a comprehensive overview of state-of-the-art polysaccharide-based hydrogel platforms designed for artificial and natural vesicles with application in drug delivery to the skin. We discuss their various physicochemical and biological properties and try to create a sound basis for the optimization of EV-embedded hydrogels as versatile therapeutic avenues.

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

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

Cellulose levulinate ester as a robust building block for the synthesis of fully biobased functional cellulose esters

Facile modification of cellulose or cellulosic derivatives is one of the important strategies to prepare materials with targeted properties, multifunctionality, thus extending their applications in various fields. Cellulose levulinate ester (CLE) has the structural advantage of acetyl propyl ketone moiety pendant, on which fully biobased cellulose levulinate ester derivatives (CLEDs) have been successfully designed and prepared via aldol condensation reaction of CLE with lignin-derived phenolic aldehydes catalyzed by DL-proline. The structure of CLEDs are featured by a phenolic α,β-unsaturated ketone structure, thus endowing them with good UV absorption properties, excellent antioxidant activity, fluorescence properties and satisfactory biocompatibility. The utility of this aldol reaction strategy, together with the facile tunable substitution degree of cellulose levulinate ester and the diversity of aldehydes, can provide potentially a large spectrum of structurally diverse functionalized cellulosic polymers and create new avenues to advanced polymeric architectures.

Hydrophobically modified hydrogel with enhanced tissue adhesion and antibacterial capacity for wound healing

The increasing emergence of drug-resistant bacteria and bacteria-infected wounds highlights the urgent need for new kinds of antibacterial wound dressing. Herein, we reported a novel bio-adhesive and antibacterial hydrogel consisting of hydrophobically modified gelatin, oxidized konjac glucomannan, and dopamine. This kind of functional hydrogel was endowed with developed stability in a liquid environment and strong tissue adhesion, even much higher than the commercial fibrin glue to wounds. The excellent bacteria-killing efficiency of hydrophobically modified hydrogel against S. aureus and E. coli was verified, as well as the low hemolysis ratio against erythrocytes in vitro. The hydrogel also exhibited good cytocompatibility in terms of supporting cell proliferation. Most importantly, these abovementioned properties could be customized by altering the substitution degree of hydrophobic groups during manufacturing, demonstrating its great potential in biomedical fields such as tissue adhesive and wound dressing.

Polysaccharide-Based Multifunctional Hydrogel Bio-Adhesives for Wound Healing: A Review

Wound healing is a long-term and complex biological process that involves multiple hemostasis, inflammation, proliferation, and remodeling stages. In order to realize comprehensive and systematic wound management, appropriate wound treatment bio-adhesives are urgently needed. Hydrogel bio-adhesives have excellent properties and show unique and remarkable advantages in the field of wound management. This review begins with a detailed description of the design criteria and functionalities of ideal hydrogel bio-adhesives for wound healing. Then, recent advances in polysaccharide-based multifunctional hydrogel bio-adhesives, which involve chitosan, hyaluronic acid, alginate, cellulose, dextran, konjac glucomannan, chondroitin sulfate, and other polysaccharides, are comprehensively discussed. Finally, the current challenges and future research directions of polysaccharide-based hydrogel bio-adhesives for wound healing are proposed to stimulate further exploration by researchers.

Highly gallol-substituted, rapidly self-crosslinkable, and robust chitosan hydrogel for 3D bioprinting

Although three-dimensional (3D) bioprinting is a promising technology for reconstructing artificial tissues and organs using bioink, there is a lack of a bioink that satisfies all requirements, including printability, gelation, mechanical properties, and cytocompatibility, Herein, a novel self-crosslinkable bioink derived from chitosan (CS) and gallic acid (GA) is presented. 3D printed scaffolds with excellent shape fidelity are realized by systematically analyzing the self-crosslinking mechanism of hydrogel formation from CS-GA conjugates and by optimizing various parameters of the printing process. The CS-GA hydrogel forms rapidly in a physiological pH without any chemical crosslinking agent. In addition, the CS-GA hydrogel exhibited various physical and chemical intermolecular interactions, fast gelation rates, and excellent mechanical properties (>337 kPa). Moreover, the CS-GA hydrogel singificantly improves the cell viability (>92 %) and proliferation of the bioink. Therefore, the self-crosslinkable CS-GA bioink has great potential to overcome the limitations of conventional bioinks.

Biomimetic multifunctional hybrid sponge via enzymatic cross-linking to accelerate infected burn wound healing

Preparing sponge dressings with stable wet adhesion remains difficult in wound repair, especially in burn wounds with bleeding and large amounts of exudate. In this work, a multifunctional hybrid sponge dressing (DHGT+PHMB+TiO₂NPs) with good wet adhesion was developed by combining biomimetic and enzymatic cross-linking reactions. The sponge dressing matrix (DHGT) was prepared by tyrosinase-catalyzed cross-linking of dopamine-modified hyaluronic acid (DOPA-HA) and gelatin. The multifunctional hybrid sponge dressing was obtained by loading polyhexamethylene biguanide (PHMB) and titanium dioxide nanoparticles (TiO₂NPs) onto the DHGT matrix. The newly developed sponge dressing exhibited high mechanical properties, good wet adhesion, antibacterial activity, reactive oxygen species (ROS) scavenging, biocompatibility, and excellent hemostasis ability. In vivo studies showed that the multifunctional hybrid sponge dressing could significantly accelerate the healing of infected full-thickness burn wounds by inhibiting bacterial growth, accelerating skin tissue reepithelialization, collagen deposition, and angiogenesis, as well as regulating the expression of inflammatory factors and cytokines.

Bioinspired multifunctional injectable hydrogel for hemostasis and infected wound management

Routine wound management faces significant challenges including rebleeding and bacterial infection that affect millions of people each year. However, conventional wound dressings (e.g., gauze, bandage) are limited to simply cover the injured surfaces and rarely show special functionality to promote the wound recovery. Currently, injectable hydrogels have been widely designed as multifunctional wound dressings to manage the hemostatic and wound healing process. Nevertheless, the integration of multiple functions through simple composition and easy construction is still difficult and hardly achieved. Herein, we reported a bioinspired multifunctional injectable hydrogel (CQCS@gel) consisted of only two components, catechol-functionalized quaternized chitosan (CQCS) and dibenzaldehyde-terminated poly(ethylene glycol) (DB-PEG₂₀₀₀). The building blocks endowed CQCS@gel with tissue-adhesive, antibacterial, antioxidant, self-healing and pH-responsive properties. Based on the in vivo hemostatic study, quick hemostasis for acute tissue injuries such as liver and carotid wounds was realized owing to the rapid gelation rate and strong tissue-adhesiveness of CQCS@gel. Moreover, CQCS@gel remarkably boosted the chronic recovery process of MRSA-infected cutaneous wounds by promoting collagen deposition, hair follicles regeneration and angiogenesis. Overall, this multifunctional injectable hydrogel shows potentials as a universal wound dressing in clinical applications, enabling both hemostasis and infected wound management. STATEMENT OF SIGNIFICANCE: This is the first report showing the multifunctional injectable hydrogel (CQCS@gel) consisted of catechol-functionalized quaternized chitosan and dibenzaldehyde-terminated poly(ethylene glycol). The incorporation of quaternary ammonium groups imparted the CQCS@gel with outstanding contact-active bacterial killing efficiency and the catechol moieties enhanced its tissue adhesive and antioxidant properties. Moreover, the reversible imine crosslinks endowed the CQCS@gel with self-healing and pH-responsive drug release capabilities. These multiple functions were integrated into a single injectable hydrogel system with easy availability and low cost. In vitro and in vivo results showed that the newly designed hydrogel was biocompatible, realized successful sealing hemostasis under multiple bleeding scenarios and enabled accelerated healing of infected skin wounds.

Polysaccharides-Based Injectable Hydrogels: Preparation, Characteristics, and Biomedical Applications

Polysaccharides-based injectable hydrogels are a unique group of biodegradable and biocompatible materials that have shown great potential in the different biomedical fields. The biomolecules or cells can be simply blended with the hydrogel precursors with a high loading capacity by homogenous mixing. The different physical and chemical crosslinking approaches for preparing polysaccharide-based injectable hydrogels are reviewed. Additionally, the review highlights the recent work using polysaccharides-based injectable hydrogels as stimuli-responsive delivery vehicles for the controlled release of different therapeutic agents and viscoelastic matrix for cell encapsulation. Moreover, the application of polysaccharides-based injectable hydrogel in regenerative medicine as tissue scaffold and wound healing dressing is covered.

Synthesis and characterization of protocatechuic acid grafted carboxymethyl chitosan with oxidized sodium alginate hydrogel through the Schiff's base reaction

Excessive accumulation of free radicals is closely related to the occurrence and development of various neurodegenerative diseases. In this study, a novel protocatechuic acid grafted carboxymethyl chitosan with oxidized sodium alginate (PCA-g-CMCS/OSA) hydrogel was developed to maintain the oxidation-antioxidation balance activities. By optimizing the pH-soluble range (pH > 6.4) of CMCS, PCA was grafted onto CMCS skeleton via EDC/NHS, and then conjugated with aldehyde group of OSA to form Schiff's base hydrogel at physiological temperature. The gelation time can be adjusted rapidly within 1-3 min by controlling the content of OSA. The shaped hydrogel exhibited porous network structure with high porosity (>90 %), swelling ratio (2000-3000 %) and rheological property, which is beneficial to cell growth and proliferation. The conjugates preserved excellent DPPH and ABTS radicals scavenging abilities and adequate biodegradability within 5 weeks. Moreover, with the release of PCA monomer due to degradation of the PCA-g-CMCS/OSA, the hydrogel also exhibited excellent biocompatibility and protective effect on H2O2-induced oxidative damage in PC12 cells. These results suggested that the PCA-g-CMCS/OSA hydrogel would appear to be a more attractive candidate for potential biomedical applications such as antioxidant drug release and tissue engineering implant material.

Mussel-Inspired Adhesive and Self-Healing Hydrogel as an Injectable Wound Dressing

This study develops a multi-functional hydrogel with a dual injection system based on the adhesive and self-healing properties of the byssus excretion found in mussels. Through precisely controlling the composite cross-linking hydrophobic association (HA) structure composed of A and B solutions, a high-strength, temperature-sensitive injectable hydrogel can be obtained, and it has good self-healing properties. The main composition of A solution contains the surfactant SDS, which can form amphiphilic micelles, the strength increasing component stearyl methacrylate (C18), and NIPAAm, which provides thermo-sensitivity. Solution B contains dopamine acrylate (DAA), which has self-healing properties, and ferric chloride (FeCl₃), which is a connecting agent. The rheological behavior shows that when the temperature is increased from 25 °C to 32 °C, the gel can be completed in seven minutes to form a composite hydrogel of NIPAAm-DAA-HA. When NMR identification was conducted on composite DAA, it was found that when comparing DAA and dopamine hydrochloride there were new peaks with specific characteristics, which confirm that this study successfully prepared DAA; swelling tests found that swelling could surpass a rate of 100%, and a higher ratio of crosslinking agent decreased the amount of moisture absorbed; the results of the compression test showed that the addition of hydrophobic micelles C18 effectively enhanced the mechanical properties of hydrogel, allowing it to withstand increased external stress; the adhesiveness results show that an increase in the catechol-Fe³⁺ concentration of the NIPAAm-DAA-HA hydrogel results in an increased adhesiveness of 0.0081 kg/cm² on pig skin; the self-healing tests show that after taking damage, NIPAAm-DAA-HA hydrogel can be reactivated with catechol-Fe³⁺ and self-heal at a rate of up to 70% after 24 h; antibacterial tests show that hydrogel has good bacterial resistance to against E. coli, staphylococcus epidermidis, and bacillus cereus; through in vitro transdermal absorption, it can be seen that the release ability of drugs within the hydrogel can reach up to 8.87 μg/cm². The NIPAAm-DAA-HA hydrogel prepared by this study performed excellently in both adhesion and self-healing tests. The thermo-sensitive and antibacterial properties can be applied to the treatment of deep wounds and address some of the flaws of traditional wound dressings.

Novel Trends in Hydrogel Development for Biomedical Applications: A Review

Nowadays, there are still numerous challenges for well-known biomedical applications, such as tissue engineering (TE), wound healing and controlled drug delivery, which must be faced and solved. Hydrogels have been proposed as excellent candidates for these applications, as they have promising properties for the mentioned applications, including biocompatibility, biodegradability, great absorption capacity and tunable mechanical properties. However, depending on the material or the manufacturing method, the resulting hydrogel may not be up to the specific task for which it is designed, thus there are different approaches proposed to enhance hydrogel performance for the requirements of the application in question. The main purpose of this review article was to summarize the most recent trends of hydrogel technology, going through the most used polymeric materials and the most popular hydrogel synthesis methods in recent years, including different strategies of enhancing hydrogels’ properties, such as cross-linking and the manufacture of composite hydrogels. In addition, the secondary objective of this review was to briefly discuss other novel applications of hydrogels that have been proposed in the past few years which have drawn a lot of attention.

Dual-Action Icariin-Containing Thermosensitive Hydrogel for Wound Macrophage Polarization and Hair-Follicle Neogenesis

Bone morphogenetic protein (BMP) pathway is essential for M2 macrophage polarization and hair-follicle neogenesis. Icariin, a flavonoid derived from Epimedium, is a mediator of the BMP pathway. Here, we develop a hydrogel formulation functionalized with icariin for regulation of macrophage polarization to accelerate wound healing and hair-follicle neogenesis. Compared to skin defects without icariin treatment, those treated with icariin+PEG hydrogel healed faster and had new hair follicles. Results in vivo showed that icariin+PEG hydrogel induced a higher level of M2 phenotypic transformation of macrophages. Moreover, icariin+PEG hydrogel significantly accelerated wound-repair process by reducing the invasion of inflammation, excessive deposition of collagen, immoderate activation of myofibroblasts, and increasing the regeneration of hair follicles. Furthermore, studies in vitro demonstrated that the icariin+PEG hydrogel induced macrophages to polarize to the M2 phenotype and dermal papilla cell to hair follicles. Finally, molecular analysis demonstrated that the icariin+PEG hydrogel increased the expression of BMP4 and Smad1/5 phosphorylation in skin wounds. These results demonstrate the therapeutic potential of icariin-containing thermosensitive hydrogels for inducing M2 macrophage polarization to accelerate wound healing and promote hair-follicle neogenesis by regulating the BMP pathway.

Anionic exopolysaccharide from Cryptococcus laurentii 70766 as an alternative for alginate for biomedical hydrogels

Alginates are widely used polysaccharides for biomaterials engineering, which functional properties depend on guluronic and mannuronic acid as the building blocks. In this study, enzymatically crosslinked hydrogels based on sodium alginate (Na-Alg) and the exopolysaccharide (EPS) derived from Cryptococcus laurentii 70766 with glucuronic acid residues were synthesized and characterized as a new potential source of polysaccharide for biomaterials engineering. The EPS was extracted (1.05 ± 0.57 g/L) through ethanol precipitation. Then the EPS and Na-Alg were functionalized with tyramine hydrochloride to produce enzymatically crosslinked hydrogels in the presence of horseradish peroxidase (HRP) and H₂O₂. Major characteristics of the hydrogels such as gelling time, swelling ratio, rheology, cell viability, and biodegradability were studied. The swelling ratio and degradation profile of both hydrogels showed negative values, indicating an increased crosslinking degree and a lower water uptake percentage. The EPS hydrogel showed similar gelation kinetics compared to the Alg hydrogel. The EPS and its hydrogel were found cytocompatible. The results indicate the potential of EPS from C. laurentii 70766 for biomedical engineering due to its biocompatibility and degradability. Further studies are needed to confirm this EPS as an alternative for Alg in tissue engineering applications, particularly in the development of wound dressing products.

Cohesion mechanisms for bioadhesives

Due to the nature of non-invasive wound closure, the ability to close different forms of leaks, and the potential to immobilize various devices, bioadhesives are altering clinical practices. As one of the vital factors, bioadhesives' strength is determined by adhesion and cohesion mechanisms. As well as being essential for adhesion strength, the cohesion mechanism also influences their bulk functions and the way the adhesives can be applied. Although there are many published reports on various adhesion mechanisms, cohesion mechanisms have rarely been addressed. In this review, we have summarized the most used cohesion mechanisms. Furthermore, the relationship of cohesion strategies and adhesion strategies has been discussed, including employing the same functional groups harnessed for adhesion, using combinational approaches, and exploiting different strategies for cohesion mechanism. By providing a comprehensive insight into cohesion strategies, the paper has been integrated to offer a roadmap to facilitate the commercialization of bioadhesives.

Rapid fabrication of bionic pyrogallol-based self-adhesive hydrogel with mechanically tunable, self-healing, antibacterial, wound healing, and hemostatic properties

Hydrogels are functional materials that are similar to human skin and have received much attention in recent years for biomedical applications. However, the preparation of nontoxic, highly adhesive, and antimicrobial hydrogels in an efficient way remains a great challenge. Inspired by adhesive mussel foot proteins (mfps) which consist of abundant catecholic amino acids and lysine (Lys) residues, gallic acid-modified ε-poly-L-lysine (EPL/GA) was synthesized, and an active functional monomer (AA-EPL/GA) was then created through a reaction with acrylic acid (AA). The polymerization of AA-EPL/GA occurred rapidly (30-160 s) under blue light (λ = 405 nm) irradiation to produce a biomimetic PAA-EPL/GA hydrogel under mild conditions. The biomimetic pyrogallol-Lys distribution endowed the PAA-EPL/GA hydrogels with superior adhesion in humid environments (with an adhesive strength of 50.02 kPa toward wet porcine skin) and tunable mechanical and self-healing properties. Additionally, the PAA-EPL/GA hydrogels exhibited outstanding antibacterial ability due to the inherent characteristics of GA and EPL. In a mouse model, PAA-EPL/GA adhered firmly around the wound tissues. Photographs of the wound and the histological results demonstrated the ability of the hydrogel to promote wound healing, control wound infection, and suppress scar formation. Moreover, the hydrogel had a good hemostatic effect on liver bleeding. Our results highlighted the promising application potential of GA-based hydrogels, which were easily, harmlessly, and efficiently fabricated by blue light irradiation.

Hard, Soft, and Hard-and-Soft Drug Delivery Carriers Based on CaCO3 and Alginate Biomaterials: Synthesis, Properties, Pharmaceutical Applications

Because free therapeutic drug molecules often have adverse effects on normal tissues, deliver scanty drug concentrations and exhibit a potentially low efficacy at pathological sites, various drug carriers have been developed for preclinical and clinical trials. Their physicochemical and toxicological properties are the subject of extensive research. Inorganic calcium carbonate particles are promising candidates as drug delivery carriers owning to their hardness, porous internal structure, high surface area, distinctive pH-sensitivity, low degradability, etc, while soft organic alginate hydrogels are also widely used because of their special advantages such as a high hydration, bio-adhesiveness, and non-antigenicity. Here, we review these two distinct substances as well as hybrid structures encompassing both types of carriers. Methods of their synthesis, fundamental properties and mechanisms of formation, and their respective applications are described. Furthermore, we summarize and compare similarities versus differences taking into account unique advantages and disadvantages of these drug delivery carriers. Moreover, rational combination of both carrier types due to their performance complementarity (yin-&yang properties: in general, yin is referred to for definiteness as hard, and yang is broadly taken as soft) is proposed to be used in the so-called hybrid carriers endowing them with even more advanced properties envisioned to be attractive for designing new drug delivery systems.

Injectable multifunctional CMC/HA-DA hydrogel for repairing skin injury

Injectable Hydrogels with adhesive, antioxidant and hemostatic properties are highly desired for promoting skin injury repair. In this study, we prepared a multi-functional carboxymethyl chitosan/hyaluronic acid-dopamine (CMC/HA-DA) hydrogel, which can be crosslinked by horseradish peroxidase and hydrogen peroxide. The antioxidation, gelation time, degradability, rheology and antihemorrhagic properties of hydrogels can be finely tuned by varying composition ratio. The cytocompatibility test and hemolysis test confirmed that the designed hydrogel holds good biocompatibility. More importantly, the repair effect of the hydrogel on full-thickness skin injury model in mice was studied. The results of wound healing, collagen deposition, immunohistochemistry and immunofluorescence showed that CMC/HA-DA hydrogel could significantly promote angiogenesis and cell proliferation at the injured site. Notably, the inflammatory response can also be regulated to promote the repair of full-thickness skin defect in mice. Results indicate that this injectable CMC/HA-DA hydrogel holds high application prospect for promising wound healing.

Novel dopamine-modified cellulose acetate ultrafiltration membranes with improved separation and antifouling performances

Cellulose acetate (CA) is widely used in the preparation of ultrafiltration membranes due to its many excellent characteristics, especially chemical activity and biodegradability. To improve the inherent hydrophobic and antifouling properties of CA membrane, in this work, CA was successfully modified with dopamine (CA-2,3-DA) through selective oxidation and Schiff base reactions, which was confirmed by FTIR and ¹H NMR measurements. Then, CA-2,3-DA membrane with high water permeability and excellent antifouling property was prepared by the phase inversion method. Compared with the original CA membrane, the CA-2,3-DA membrane maintained a higher rejection ratio for BSA (92.5%) with a greatly increased pure water flux (167.3 L m^-2 h^-1), which could overcome the trade-off between permeability and selectivity of the traditional CA membrane to a certain extent. According to static protein adsorption and three-cycle dynamic ultrafiltration experiments, the CA-2,3-DA membrane showed good antifouling performance and superior long-term performance stability, as supported by the experimental results, including flux recovery ratio, flux decline ratio, and filtration resistance. It is expected that this approach can greatly expand the high-value utilization of modified natural organic polysaccharides in separation engineering.

Recent advances in the hybridization of cellulose and carbon nanomaterials: Interactions, structural design, functional tailoring, and applications

Due to the good biocompatibility and flexibility of cellulose and the excellent optical, electronic, as well as mechanical properties of carbon nanomaterials (CNMs), cellulose/CNM hybrid materials have been widely synthesized and used in energy storage, sensors, adsorption, biomedicine, and many other fields. In this review, we present recent advances (2016-current) in the design, structural design, functional tailoring and various applications of cellulose/CNM hybrid materials. For this aim, first the interactions between cellulose and CNMs for promoting the formation of cellulose/CNM materials are analyzed, and then the hybridization between cellulose with various CNMs for tailoring the structures and functions of hybrid materials is introduced. Further, abundant applications of cellulose/CNM hybrid materials in various fields are presented and discussed. This comprehensive review will be helpful for readers to understand the functional design and facile synthesis of cellulose-based nanocomposites, and to promote the high-performance utilization and sustainability of biomass materials in the future.

Emerging Biopolymer-Based Bioadhesives

Bioadhesives have been widely used in healthcare and biomedical applications due to their ease-of-operation for wound closure and repair compared to conventional suturing and stapling. However, several challenges remain for developing ideal bioadhesives, such as unsatisfied mechanical properties, non-tunable biodegradability, and limited biological functions. Considering these concerns, naturally derived biopolymers have been considered good candidates for making bioadhesives owing to their ready availability, facile modification, tunable mechanical properties, and desired biocompatibility and biodegradability. Over the past several years, remarkable progress has been made on biopolymer-based adhesives, covering topics from novel materials designs and advanced processing to clinical translation. The developed bioadhesives have been applied for diverse applications, including tissue adhesion, hemostasis, antimicrobial, wound repair/tissue regeneration, and skin-interfaced bioelectronics. Here in this comprehensive review, recent progress on biopolymer-based bioadhesives is summarized with focuses on clinical translations and multifunctional bioadhesives. Furthermore, challenges and opportunities such as weak adhesion strength at the hydrated state, mechanical mismatch with tissues, and unfavorable immune responses are discussed with an aim to facilitate the future development of high-performance biopolymer-based bioadhesives.

Relationship between Structure and Rheology of Hydrogels for Various Applications

Hydrogels have gained a lot of attention with their widespread use in different industrial applications. The versatility in the synthesis and the nature of the precursor reactants allow for a varying range of hydrogels with different mechanical and rheological properties. Understanding of the rheological behavior and the relationship between the chemical structure and the resulting properties is crucial, and is the focus of this review. Specifically, we include detailed discussion on the correlation between the rheological characteristics of hydrogels and their possible applications. Different rheological tests such as time, temperature and frequency sweep, among others, are described and the results of those tests are reported. The most prevalent applications of hydrogels are also discussed.

Preparation of sodium hyaluronate/dopamine/AgNPs hydrogel based on the natural eutetic solvent as an antibaterial wound dressing

Baesd on previous researches, the natural deep eutectic solvent (DES) has enormous potential to be used in the fabrication of hydrogel wound dressing due to its outstanding properties including cytocompatibility, degradability and solubility. In order to further improve the antibaterial capacity of hydrogel, in the present study sodium hyaluronate (SH) and the natural DES were utilized to develop a novel hydrogel wound dressing by dopamine (DA) coated SH with in situ reduction of silver nanoparticles (DES-DASH@Ag). Furthermore, during the preparation process, we discovered for the first time that the DES can be used to fill the freeze-dried DASH to prepare a hydrogel (DES-DASH), which was promising to utilized in the fabrication of other hydrogels. Besides, the chemical and physical properties as well as wound healing capacity of the DES-DASH@Ag hydrogel were characterized. As a result, the DES-DASH@Ag hydrogel presented good cytocompatibility tested using NIH-3 T3 fibroblast cells, and prominent antibacterial effect against two types of bacteria infecting exposed wound. Furthermore, the hydrogel facilitated regeneration of mouse skin tissue in the wound area. The overall performance of DES-DASH@Ag hydrogel suggested that it could be a promising wound dressing in modern medicine.

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.

Mussel-Inspired Catechol Functionalisation as a Strategy to Enhance Biomaterial Adhesion: A Systematic Review

Biomaterials have long been explored in regenerative medicine strategies for the repair or replacement of damaged organs and tissues, due to their biocompatibility, versatile physicochemical properties and tuneable mechanical cues capable of matching those of native tissues. However, poor adhesion under wet conditions (such as those found in tissues) has thus far limited their wider application. Indeed, despite its favourable physicochemical properties, facile gelation and biocompatibility, gellan gum (GG)-based hydrogels lack the tissue adhesiveness required for effective clinical use. Aiming at assessing whether substitution of GG by dopamine (DA) could be a suitable approach to overcome this problem, database searches were conducted on PubMed^® and Embase^® up to 2 March 2021, for studies using biomaterials covalently modified with a catechol-containing substituent conferring improved adhesion properties. In this regard, a total of 47 reports (out of 700 manuscripts, ~6.7%) were found to comply with the search/selection criteria, the majority of which (34/47, ~72%) were describing the modification of natural polymers, such as chitosan (11/47, ~23%) and hyaluronic acid (6/47, ~13%); conjugation of dopamine (as catechol “donor”) via carbodiimide coupling chemistry was also predominant. Importantly, modification with DA did not impact the biocompatibility and mechanical properties of the biomaterials and resulting hydrogels. Overall, there is ample evidence in the literature that the bioinspired substitution of polymers of natural and synthetic origin by DA or other catechol moieties greatly improves adhesion to biological tissues (and other inorganic surfaces).

Hydrogel Preparation Methods and Biomaterials for Wound Dressing

Wounds have become one of the causes of death worldwide. The metabolic disorder of the wound microenvironment can lead to a series of serious symptoms, especially chronic wounds that bring great pain to patients, and there is currently no effective and widely used wound dressing. Therefore, it is important to develop new multifunctional wound dressings. Hydrogel is an ideal dressing candidate because of its 3D structure, good permeability, excellent biocompatibility, and ability to provide a moist environment for wound repair, which overcomes the shortcomings of traditional dressings. This article first briefly introduces the skin wound healing process, then the preparation methods of hydrogel dressings and the characteristics of hydrogel wound dressings made of natural biomaterials and synthetic materials are introduced. Finally, the development prospects and challenges of hydrogel wound dressings are discussed.

Development of the mussel-inspired pH-responsive hydrogel based on Bletilla striata polysaccharide with enhanced adhesiveness and antioxidant properties

Recently, smart hydrogels have attracted much attention for their abilities to respond to subtle changes in external and internal stimuli. Also, natural polysaccharide-based biomaterials are more appealing for their biocompatibility and biodegradability. However, limitations owing to their complex compositions and mechanisms, cumbersome synthetic routes, and single function call for a simple and effective strategy to develop novel multifunctional smart hydrogels. Herein, this developed work was achieved based on Bletilla striata polysaccharide (BSP), a kind of natural glucomannan with diverse bioactivities and biocompatibility, we fabricated a low-cost multifunctional hydrogel by oxidizing the catechol groups of carboxymethylated BSP(CBSP)-dopamine(DA) conjugate with adhesion, antioxidant, and pH-responsive properties. In this hydrogel system, CBSP as the backbone material, was negatively charged and conferred the hydrogel with pH sensitivity. The presence of catechol groups greatly enhanced the tissue adhesion and antioxidant capacities of the hydrogel. Meanwhile, the highly porous structure of hydrogel allowed berberine to be encapsulated and released to exhibit excellent and long-lasting antibacterial activity. In summary, the adhesion, antioxidant, pH-sensitive, and antibacterial multifunctional hydrogel showed massive potential in the biomedical field.

Recent advancements in enzyme-mediated crosslinkable hydrogels: In vivo-mimicking strategies

Enzymes play a central role in fundamental biological processes and have been traditionally used to trigger various processes. In recent years, enzymes have been used to tune biomaterial responses and modify the chemical structures at desired sites. These chemical modifications have allowed the fabrication of various hydrogels for tissue engineering and therapeutic applications. This review provides a comprehensive overview of recent advancements in the use of enzymes for hydrogel fabrication. Strategies to enhance the enzyme function and improve biocompatibility are described. In addition, we describe future opportunities and challenges for the production of enzyme-mediated crosslinkable hydrogels.

Water-based carbodiimide mediated synthesis of polysaccharide-amino acid conjugates: Deprotection, charge and structural analysis

We report here a one-step aqueous method for the synthesis of isolated and purified polysaccharide-amino acid conjugates. Two different types of amino acid esters: glycine methyl ester and L-tryptophan methyl ester, as model compounds for peptides, were conjugated to the polysaccharide carboxymethylcellulose (CMC) in water using carbodiimide at ambient conditions. Detailed and systematic pH-dependent charge titration and spectroscopy (infrared, nuclear magnetic resonance: ¹H, ¹³C- DEPT 135, ¹H- ¹³C HMBC/HSQC correlation), UV-vis, elemental and ninhydrin analysis provided solid and direct evidence for the successful conjugation of the amino acid esters to the CMC backbone via an amide bond. As the concentration of amino acid esters increased, a conjugation efficiency of 20-80% was achieved. Activated charcoal aided base-catalyzed deprotection of the methyl esters improved the solubility of the conjugates in water. The approach proposed in this work should have the potential to tailor the backbone of polysaccharides containing di- or tri-peptides.