Mussel-Inspired Catechol-Functionalized Hydrogels and Their Medical Applications

Advances in Mussel Adhesion Proteins and Mussel-Inspired Material Electrospun Nanofibers for Their Application in Wound Repair

Mussel refers to a marine organism with strong adhesive properties, and it secretes mussel adhesion protein (MAP). The most vital feature of MAP is the abundance of the 3,4-dihydroxyphenylalanine (DOPA) group and lysine, which have antimicrobial, anti-inflammatory, antioxidant, and cell adhesion-promoting properties and can accelerate wound healing. Polydopamine (PDA) is currently the most widely used mussel-inspired material characterized by good adhesion, biocompatibility, and biodegradability. It can mediate various interactions to form functional coatings on cell-material surfaces. Nanofibers based on MAP and mussel-inspired materials have been exerting a vital role in wound repair, while there is no comprehensive review presenting them. This Review introduces the structure of MAPs and their adhesion mechanisms and mussel-inspired materials. Second, it introduces the functionalized modification of MAPs and their inspired materials in electrospun nanofibers and application in wound repair. Finally, the future development direction and coping strategies of MAP and mussel-inspired materials are discussed. Moreover, this Review can offer novel strategies for the application of nanofibers in wound repair and bring about new breakthroughs and innovations in tissue engineering and regenerative medicine.

Topical Application of Dexamethasone-Loaded Core-Multishell Nanocarriers Against Oral Mucosal Inflammation

Topical treatment of oral inflammatory diseases is challenging due to the intrinsic physicochemical barriers of the mucosa and the continuous flow of saliva, which dilute drugs and limit their bioavailability. Nanocarrier technology can be an innovative approach to circumvent these problems and thus improve the efficacy of topical drug delivery to the mucosa. Core-multishell (CMS) nanocarriers are putative delivery systems with high biocompatibility and the ability to adhere to and penetrate the oral mucosa. Ester-based CMS nanocarriers release the anti-inflammatory compound dexamethasone (Dx) more efficiently than a conventional cream. Mussel-inspired functionalization of a CMS nanocarrier with catechol further improves the adhesion of the nanocarrier and may enhance the efficacy of the loaded drugs. In the present study, the properties of the ester-based CMS 10-E-15-350 nanocarrier (CMS-NC) are further evaluated in comparison to the catechol-functionalized variant (CMS-C0.08). While the mucoadhesion of CMS-NC is inhibited by saliva, CMS-C0.08 exhibits better mucoadhesion in the presence of saliva. Due to the improved adhesion properties, CMS-C0.08 loaded with dexamethasone (Dx-CMS-C0.08) shows a better anti-inflammatory effect than Dx-CMS-NC when applied dynamically. These results highlight the superiority of CMS-C0.08 over CMS-NC as an innovative drug delivery system (DDS) for the treatment of oral mucosal diseases.

Environmentally stable and rapidly polymerized tin-tannin catalytic system hydroxyethyl cellulose hydrogel for wireless wearable sensing

In recent years, flexible sensors constructed mainly from hydrogels have played an indispensable role in several fields. However, the traditional hydrogel preparation process involves complex and time-consuming steps and the freezing or volatilization of water in the water gel in extreme environments greatly limits the further use of the sensor. Therefore, an ionic conductive hydrogel (SnHTD) was designed, which was composed of tannic acid (TA), metal ions Sn2+, hydroxyethyl cellulose (HEC), and acrylamide (AM) in a deep eutectic solvent (DES) and water binary solvent. It is worth noting that the gel time is shortened to less than 3 min by introducing the Sn-TA redox system. The addition of DES makes the hydrogel have a wide temperature tolerance range (-20 to 60 °C) and the ability to store for a long time (30 days). The introduction of HEC increased the tensile stress of hydrogel from 140.17 kPa to 219.89 kPa. Additionally, the hydrogel also has high conductivity, repeatable adhesion and UV shielding properties. In general, this research opens up a new way for room temperature polymerization of environmentally resistant hydrogel materials and effectively meets the growing demand for wireless wearable sensing.

Conducting polymer hydrogels based on supramolecular strategies for wearable sensors

Conductive polymer hydrogels (CPHs) are gaining considerable attention in developing wearable electronics due to their unique combination of high conductivity and softness. However, in the absence of interactions, the incompatibility between hydrophobic conductive polymers (CPs) and hydrophilic polymer networks gives rise to inadequate bonding between CPs and hydrogel matrices, thereby significantly impairing the mechanical and electrical properties of CPHs and constraining their utility in wearable electronic sensors. Therefore, to endow CPHs with good performance, it is necessary to ensure a stable and robust combination between the hydrogel network and CPs. Encouragingly, recent research has demonstrated that incorporating supramolecular interactions into CPHs enhances the polymer network interaction, improving overall CPH performance. However, a comprehensive review focusing on supramolecular CPH (SCPH) for wearable sensing applications is currently lacking. This review provides a summary of the typical supramolecular strategies employed in the development of high-performance CPHs and elucidates the properties of SCPHs that are closely associated with wearable sensors. Moreover, the review discusses the fabrication methods and classification of SCPH sensors, while also exploring the latest application scenarios for SCPH wearable sensors. Finally, it discusses the challenges of SCPH sensors and offers suggestions for future advancements.

Engineering proteins with catechol chemistry for biotechnological applications

Developing proteins with increased chemical space by expanding the amino acids alphabet has been an emerging technique to compete for the obstacle encountered by their need in various applications. 3,4-Dihydroxyphenylalanine (L-DOPA) catecholic unnatural amino acid is abundantly present in mussels foot proteins through post-translational modification of tyrosine to give a strong adhesion toward wet rocks. L-DOPA forms: bidentate coordination, H-bonding, metal-ligand complexes, long-ranged electrostatic, and van der Waals interactions via a pair of donor hydroxyl groups. Incorporating catechol in proteins through genetic code expansion paved the way for developing: protein-based bio-sensor, implant coating, bio-conjugation, adhesive bio-materials, biocatalyst, metal interaction and nano-biotechnological applications. The increased chemical spaces boost the protein properties by offering a new chemically active interaction ability to the protein. Here, we review the technique employed to develop a genetically expanded organism with catechol to provide novel properties and functionalities; and we highlight the importance of L-DOPA incorporated proteins in biomedical and industrial fields.

Mussel-Inspired Injectable Adhesive Hydrogels for Biomedical Applications

The impressive adhesive capacity of marine mussels has inspired various fascinating designs in biomedical fields. Mussel-inspired injectable adhesive hydrogels, as a type of promising mussel-inspired material, have attracted much attention due to their minimally invasive property and desirable functions provided by mussel-inspired components. In recent decades, various mussel-inspired injectable adhesive hydrogels have been designed and widely applied in numerous biomedical fields. The rational incorporation of mussel-inspired catechol groups endows the injectable hydrogels with the potential to exhibit many properties, including tissue adhesiveness and self-healing, antimicrobial, and antioxidant capabilities, broadening the applications of injectable hydrogels in biomedical fields. In this review, we first give a brief introduction to the adhesion mechanism of mussels and the characteristics of injectable hydrogels. Further, the typical design strategies of mussel-inspired injectable adhesive hydrogels are summarized. The methodologies for integrating catechol groups into polymers and the crosslinking methods of mussel-inspired hydrogels are discussed in this section. In addition, we systematically overview recent mussel-inspired injectable adhesive hydrogels for biomedical applications, with a focus on how the unique properties of these hydrogels benefit their applications in these fields. The challenges and perspectives of mussel-inspired injectable hydrogels are discussed in the last section. This review may provide new inspiration for the design of novel bioinspired injectable hydrogels and facilitate their application in various biomedical fields.

Metal-Drug Coordination Nanoparticles and Hydrogels for Enhanced Delivery

Drug delivery is a key component of nanomedicine, and conventional delivery relies on the adsorption or encapsulation of drug molecules to a nanomaterial. Many delivery vehicles contain metal ions, such as metal-organic frameworks, metal oxides, transition metal dichalcogenides, MXene, and noble metal nanoparticles. These materials have a high metal content and pose potential long-term toxicity concerns leading to difficulties for clinical approval. In this review, recent developments are summarized in the use of drug molecules as ligands for metal coordination forming various nanomaterials and soft materials. In these cases, the drug-to-metal ratio is much higher than conventional adsorption-based strategies. The drug molecules are divided into small-molecule drugs, nucleic acids, and proteins. The formed hybrid materials mainly include nanoparticles and hydrogels, upon which targeting ligands can be grafted to improve efficacy and further decrease toxicity. The application of these materials for addressing cancer, viral infection, bacterial infection inflammatory bowel disease, and bone diseases is reviewed. In the end, some future directions are discussed from fundamental research, materials science, and medicine.

Nanoparticles incorporated hydrogels for delivery of antimicrobial agents: developments and trends

The prevention and treatment of microbial infections is an imminent global public health concern due to the poor antimicrobial performance of the existing antimicrobial regime and rapidly emerging antibiotic resistance in pathogenic microbes. In order to overcome these problems and effectively control bacterial infections, various new treatment modalities have been identified. To attempt this, various micro- and macro-molecular antimicrobial agents that function by microbial membrane disruption have been developed with improved antimicrobial activity and lesser resistance. Antimicrobial nanoparticle-hydrogels systems comprising antimicrobial agents (antibiotics, biological extracts, and antimicrobial peptides) loaded nanoparticles or antimicrobial nanoparticles (metal or metal oxide) constitute an important class of biomaterials for the prevention and treatment of infections. Hydrogels that incorporate nanoparticles can offer an effective strategy for delivering antimicrobial agents (or nanoparticles) in a controlled, sustained, and targeted manner. In this review, we have described an overview of recent advancements in nanoparticle-hydrogel hybrid systems for antimicrobial agent delivery. Firstly, we have provided an overview of the nanoparticle hydrogel system and discussed various advantages of these systems in biomedical and pharmaceutical applications. Thereafter, different hybrid hydrogel systems encapsulating antibacterial metal/metal oxide nanoparticles, polymeric nanoparticles, antibiotics, biological extracts, and antimicrobial peptides for controlling infections have been reviewed in detail. Finally, the challenges and future prospects of nanoparticle-hydrogel systems have been discussed.

Bioactive and biomimetic 3D scaffolds for bone tissue engineering using graphitic carbon nitride as a sustainable visible light photoinitiator

Graphitic carbon nitride (g-C3N4) is explored as a novel sustainable visible light photoinitiator for the preparation of biomimetic 3D hydrogel scaffolds comprising gelatin methacrylamide (GelMA) and dopamine methacrylamide for use in tissue engineering. The initiator efficiency was assessed by comparing the swelling behavior and the stability of photopolymerized hydrogels prepared with GelMA of different degrees of functionalization and different comonomer compositions. Bioactive composite hydrogels with a 50 wt% nanohydroxyapatite (nHAp) content, to closely mimic the actual bone composition, were successfully obtained by the introduction of nHAp in the prepolymer solutions followed by photopolymerization. The composite hydrogels demonstrated enhanced mechanical properties and excellent stability in PBS verifying the preparation of robust 3D scaffolds for use in cancellous or pre-calcified bone tissue engineering applications. The in vitro cell response of the composite scaffolds exhibited high cell viability and enhanced differentiation of pre-osteoblasts to mature osteoblasts, demonstrating their osteogenic potential. This work establishes, for the first time, the excellent properties of g-C3N4 as a sustainable, visible light initiator, fully satisfying the principles of green chemistry, for the preparation of robust and biologically relevant hydrogels, and proposes a new approach to overcome the main challenges of conventional photoinitiators in cell scaffold fabrication, such as photobleaching, high cost and non-scalable synthesis employing toxic organic precursors and solvents.

Bioadhesive Technology Platforms

Bioadhesives have emerged as transformative and versatile tools in healthcare, offering the ability to attach tissues with ease and minimal damage. These materials present numerous opportunities for tissue repair and biomedical device integration, creating a broad landscape of applications that have captivated clinical and scientific interest alike. However, fully unlocking their potential requires multifaceted design strategies involving optimal adhesion, suitable biological interactions, and efficient signal communication. In this Review, we delve into these pivotal aspects of bioadhesive design, highlight the latest advances in their biomedical applications, and identify potential opportunities that lie ahead for bioadhesives as multifunctional technology platforms.

Efficient secretion of mussel adhesion proteins using a chaperone protein Spy as fusion tag in Bacillus subtilis

BACKGROUND

Mussel foot proteins (Mfps) are considered as remarkable materials due to their extraordinary adhesive capability. Recombinant expression is an ideal way to synthesis these proteins at large scale. However, secretory expression of Mfps into culture medium has not been achieved in a heterologous host.

METHODS AND RESULTS

Here, to realize the secretion of Mfp3 and Mfp5 in Bacillus subtilis, signal peptide screening was first performed. Minimal Mfp3-6×His was targeted into the growth medium with AmyE signal peptide. We found that a small chaperone protein Spy was secreted efficiently in B. subtilis, and the fusion proteins Spy-Mfp3-6×His and Spy-Mfp5-6×His could also be delivered into growth medium well. The yield of Spy-Mfp3-6×His and Spy-Mfp5-6×His reached 255 and 119 mg L-1 at shake flask conditions, respectively. Mfp3-6×His and Mfp5-6×His were finally purified via TEV protease cleavage and NTA affinity chromatography.

CONCLUSION

Mfp3-6×His and Mfp5-6×His could be efficiently secreted using a chaperone protein Spy as fusion tag in B. subtilis.

Facile Synthesis of Catechol-Containing Polyacrylamide Copolymers: Synergistic Effects of Amine, Amide and Catechol Residues in Mussel-Inspired Adhesives

The straightforward synthesis of polyamide-derived statistical copolymers with catechol, amine, amide and hydroxy residues via free radical polymerization is presented. In particular, catechol, amine and amide residues are present in natural mussel foot proteins, enabling strong underwater adhesion due to synergistic effects where cationic residues displace hydration and ion layers, followed by strong short-rang hydrogen bonding between the catechol or primary amides and SiO2 surfaces. The present study is aimed at investigating whether such synergistic effects also exist for statistical copolymer systems that lack the sequence-defined positioning of functional groups in mussel foot proteins. A series of copolymers is established and the adsorption in saline solutions on SiO2 is determined by quartz crystal microbalance measurements and ellipsometry. These studies confirm a synergy between cationic amine groups with catechol units and primary amide groups via an increased adsorptivity and increased polymer layer thicknesses. Therefore, the free radical polymerization of catechol, amine and amide monomers as shown here may lead to simplified mussel-inspired adhesives that can be prepared with the readily scalable methods required for large-scale applications.

How to Design Catechol-Containing Hydrogels for Cell Encapsulation Despite Catechol Toxicity

Catechol (cat) is a highly adhesive diphenol that can be chemically grafted to polymers such as chitosan (CH) to make them adhesive as well. However, catechol-containing materials experimentally show a large variability of toxicity, especially in vitro. While it is unclear how this toxicity emerges, most concerns are directed toward the oxidation of catechol into quinone that releases reactive oxygen species (ROS) which can, in turn, cause cell apoptosis through oxidative stress. To better understand the mechanisms at play, we examined the leaching profiles, hydrogen peroxide (H₂O₂) production, and in vitro cytotoxicity of several cat-chitosan (cat-CH) hydrogels that were prepared with different oxidation levels and cross-linking methods. To create cat-CH with different propensities toward oxidation, we grafted either hydrocaffeic acid (HCA, more prone to oxidation) or dihydrobenzoic acid (DHBA, less prone to oxidation) to the backbone of CH. Hydrogels were cross-linked either covalently, using sodium periodate (NaIO₄) to trigger oxidative cross-linking, or physically, using sodium bicarbonate (SHC). While using NaIO₄ as a cross-linker increased the oxidation levels of the hydrogels, it also significantly reduced in vitro cytotoxicity, H₂O₂ production, and catechol and quinone leaching in the media. For all gels tested, cytotoxicity could be directly related to the release of quinones rather than H₂O₂ production or catechol release, showing that oxidative stress may not be the main reason for catechol cytotoxicity, as other pathways of quinone toxicity come into play. Results also suggest that the indirect cytotoxicity of cat-CH hydrogels fabricated through carbodiimide chemistry can be reduced if (i) catechol groups are chemically bound to the polymer backbone to prevent leaching or (ii) the chosen cat-bearing molecule has a high resistance to oxidation. Coupled with the use of other cross-linking chemistries or more efficient purification methods, these strategies can be adopted to synthesize various types of cytocompatible cat-containing scaffolds.

Room Temperature Ca2+-Initiated Free Radical Polymerization for the Preparation of Conductive, Adhesive, Anti-freezing and UV-Blocking Hydrogels for Monitoring Human Movement

In recent years, conductive hydrogels have received increasing attention as wearable electronics due to the electrochemical properties of conductive polymers combined with the softness of hydrogels. However, conventional hydrogels are complicated to prepare, require high temperature or UV radiation to trigger monomer polymerization, and are frozen at low temperatures, which seriously hinder the application of flexible wearable devices. In this paper, a conductive sensor integrating mechanical properties, adhesion, UV shielding, anti-dehydration, and anti-freeze was prepared based on Ca²⁺-initiated radical polymerization at room temperature using the synergy of sodium lignosulfonate, acrylamide (AM), and calcium chloride (CaCl₂). Metal ions can activate ammonium persulfate to generate free radicals that allow rapid gelation of AM monomers at room temperature without external stimuli. Due to ionic cross-linking and non-covalent interaction, the hydrogels have good tensile properties (1153% elongation and 168 kPa tensile strength), high toughness (758 KJ·m^-3), excellent adhesive properties (48.5 kPa), high ionic conductivity (7.2 mS·cm^-1), and UV resistance (94.4%). CaCl₂ can inhibit ice nucleation, so that the hydrogels have anti-dehydration and frost resistance properties and even at -80 °C can maintain flexibility, high conductivity, and adhesion. Assembled into a flexible sensor, it can sense various large and small movements such as compression, bending, and talking, which is a flexible sensing material with wide application prospects.

Bio-inspired conductive adhesive based on calcium-free alginate hydrogels for bioelectronic interfaces

Electrode impedance is one of the greatest challenges facing neural interfacing medical devices and the use of electrical stimulation-based therapies in the fields of neurology and regenerative medicine. Maximizing contact between electronics and tissue would allow for more accurate recordings of neural activity and to stimulate with less power in implantable devices as electric signals could be more precisely transferred by a stable interfacial area. Neural environments, inherently wet and ion-rich, present a unique challenge for traditional conductive adhesives. As such, we look to marine mussels that use a 3,4-dihydroxyphenyl-L-analine (DOPA)-containing proteinaceous excretion to adhere to a variety of substrates for inspiration. By functionalizing alginate, which is an abundantly available natural polymer, with the catechol residues DOPA contains, we developed a hydrogel-based matrix to which carbon-based nanofiller was added to render it conductive. The synthesized product had adhesive energy within the range of previously reported mussel-based polymers, good electrical properties and was not cytotoxic to brain derived neural precursor cells.

L-DOPA coating improved phosphate glass fibre strength and fibre/matrix interface

The levodopa (L-DOPA) has been reported as a promising adhesive for various materials. In this study, we utilized L-DOPA as an interfacial agent for phosphate glass fibre/polycaprolactone (PGF/PCL) composites, with the aim to enhance the interfacial properties between the fibres and polymer matrix. The PGFs were dip-coated in varying concentrations of L-DOPA solution ranging between 5 and 40 g L-1. The fibre strength and interfacial shear strength (IFSS) of the composites were measured via a single fibre tensile test and single fibre fragmentation test, respectively. It was found that the L-DOPA agent (at conc. 10 g L-1) significantly improved the IFSS of the composites up to 27%. Also, the L-DOPA coating (at conc. 40 g L-1) significantly increased the glass fibre strength up to 18%. As a result, an optimum coating level could be tailored depending on application and whether fibre strength or IFSS was of greater importance. In addition, SEM and TGA analyses were used to detect and quantify the coating agents. FTIR and XPS further confirmed presence of the coating and indicated the zwitterionic crystals of L-DOPA and the formation of a melanin-like polymer layer. The spectroscopy data also evidenced that both catechol and amine groups contributed to the interaction between the L-DOPA and the PGF surface.

Design, synthesis, and characterization of a novel dual cross-linked gelatin-based bioadhesive for hard and soft tissues adhesion capability

Many surgical treatments require a suitable tissue adhesive that maintains its performance in wet conditions and can be applied simultaneously for hard and soft tissues. In the present study, a dual cross-linked tissue adhesive was synthesized by mixing the gelatin methacryloyl (Gel-MA) and gelatin-dopamine conjugate (Gel-Dopa). The setting reaction was based on a photopolymerization process in the presence of a combination of riboflavin and triethanolamine and a chemical cross-linking process attributed to the genipin as a natural cross-linker. Modified gelatin macromolecules were characterized and the best wavelength for free radical generation in the presence of riboflavin was obtained. Tissue adhesives were prepared with 30% hydrogels of Gel-MA and Gel-Dopa with different ratios in distilled water. The gelation occurred in a short time after light irradiation. The chemical, mechanical, physical, and cytotoxicity properties of the tissue adhesives were evaluated. The results showed that despite photopolymerization, chemical crosslinking with genipin played a more critical role in the setting process. Water uptake, degradation behavior, cytotoxicity, and adhesion properties of the adhesives were correlated with the ratio of the components. The SEM images showed a porous structure that could ensure the entry of cells and nutrients into the surgical area. While acceptable properties in most experiments were observed, all features were improved as the Gel-Dopa ratio increased. Also, the obtained hydrogels revealed excellent adhesive properties, particularly with bone even after wet incubation, and it was attributed to the amount of gelatin-dopamine conjugate. From the obtained results, it was concluded that a dual adhesive hydrogel based on gelatin macromolecules could be a good candidate as a tissue adhesive in wet condition.

Bioinspired gelatin based sticky hydrogel for diverse surfaces in burn wound care

Proper burn wound management considers patient’s compliance and provides an environment to accelerate wound closure. Sticky hydrogels are conducive to wound management. They can act as a preventive infection patch with controlled drug delivery and diverse surface adherence. A hypothesis-driven investigation explores a bioinspired polydopamine property in a gelatin-based hydrogel (GbH) where polyvinyl alcohol and starch function as hydrogel backbone. The GbH displayed promising physical properties with O–H group rich surface. The GbH was sticky onto dry surfaces (glass, plastic and aluminium) and wet surfaces (pork and chicken). The GbH demonstrated mathematical kinetics for a transdermal formulation, and the in vitro and in vivo toxicity of the GbH on test models confirmed the models’ healthy growth and biocompatibility. The quercetin-loaded GbH showed 45–50% wound contraction on day 4 for second-degree burn wounds in rat models that were equivalent to the silver sulfadiazine treatment group. The estimates for tensile strength, biochemicals, connective tissue markers and NF-κB were restored on day 21 in the GbH treated healed wounds to imitate the normal level of the skin. The bioinspired GbH promotes efficient wound healing of second-degree burn wounds in rat models, indicating its pre-clinical applicability.

In silico prediction and in vitro validation of the effect of pH on adhesive behaviour of the fused CsgA-MFP3 protein

Recombinant production of mussel foot proteins among marine-inspired proteinaceous adhesive materials has been attracted high attention for medical applications, due to their exceptional versatility potential of hierarchically arranged nanostructures. Various biochemical and proteinous factors such as amyloid CsgA curli protein have been used as a synergistic factor to enhance the constancy of obtained bio-adhesion but their mechanistic interactions have not yet been deeply investigated widely in different pH conditions. To this end, the present study has first sought to assess molecular simulation and prediction by using RosettaFold to predict the 3-dimensional structure of the fused CsgA subunit and the MFP3 protein followed by in vitro verification. It was developed an ensemble of quantitative structure-activity relationship models relying on simulations according to the surface area and molecular weight values of the fused proteins in acidic to basic situations using PlayMolecule (protein preparation app for MD simulations) online databases followed by molecular dynamic simulation at different pHs. It was found that acidic conditions positively affect adhesive strength throughout the chimeric structure based on comparative structure-based analyses along with those obtained in prevailing literature. Atomic force microscopy analysis was confirmed obtained in silico data which showed enhanced adhesive properties of fused protein after self-assembly in low pH conditions. In conclusion, the augmented model for reactivity predictions not only unravels the performance and explain ability of the adhesive proteins but in turn paves the way for the decision-making process for chimeric subunits modifications needed for future industrial production.

Synthesis and Characterization of Catechol-Containing Polyacrylamides with Adhesive Properties

In this study, a row of four analogous dopamine acryl- and methacrylamide derivatives, namely N-(3,4-dihydroxyphenyethyl) acrylamide, N-(3,4-dihydroxyphenyethyl) meth acrylamide, N-phenethyl methacrylamide, N-(4-hydroxyphenethyl) methacrylamide were synthesized and characterized by ¹H-NMR and ¹³C-NMR, followed by further solvent-based radical polymerization with N-hydroxyethyl acrylamide. All copolymers were characterized by ¹H-NMR, dynamic differential calorimetry, and gel permeation chromatography. The dependency of the used comonomer ratios to the molecular mass of the corresponding copolymers has been described. The synthesis of the various polymers serves as a feasibility study and provides important data for a future biometric application in the medical field. We synthesized N-(3,4-dihydroxyphenyethyl) acrylamide copolymer up to 80 mol% by free radical polymerization without using any protecting groups. All polymers show identical perfect adhesive properties by a simple scratch test. Further, the monomers were used as a photo reactive glue formulation to test its adherence to a medical titanium surface sample by tensile shear test.

Quercetin-Crosslinked Chitosan Films for Controlled Release of Antimicrobial Drugs

Natural polymer-based films, due to their favorable biological and mechanical properties, have demonstrated great potential as coatings for biomedical applications. Among them, chitosan films have been widely studied both as coating materials and as controlled drug release systems. Crosslinkers are often used to tune chitosan’s crosslinking degree and thus to control the drug release kinetics. For this purpose, quercetin, a plant-derived natural polyphenol, has gained attention as a crosslinker, mainly for its intrinsic anti-inflammatory, antioxidant, and antibacterial features. In this study, chitosan films crosslinked with three different concentrations of quercetin (10, 20, and 30% w/w) have been used as controlled release systems for the delivery of the antibacterial drug trimethoprim (TMP, 10% w/w). Physicochemical and antimicrobial properties were investigated. Surface wettability and composition of the films were assessed by contact angle measurements, X-ray photoelectron spectroscopy (XPS), and Fourier-transform infrared spectroscopy (FTIR), respectively. The release kinetic of TMP in phosphate-buffered saline (PBS) and 2-(N-morpholino) ethanesulfonic acid (MES) was studied over time. Finally, antibacterial properties were assessed on E. coli and S. aureus through Kirby–Bauer disc diffusion and micro-dilution broth assays. Results show that quercetin, at the tested concentrations, clearly increases the crosslinking degree in a dose-dependent manner, thus influencing the release kinetic of the loaded TMP while maintaining its bactericidal effects. In conclusion, this work demonstrates that quercetin-crosslinked chitosan films represent a promising strategy for the design of antibiotic-releasing coatings for biomedical applications.

Engineering a naturally derived hemostatic sealant for sealing internal organs

Controlling bleeding from a raptured tissue, especially during the surgeries, is essentially important. Particularly for soft and dynamic internal organs where use of sutures, staples, or wires is limited, treatments with hemostatic adhesives have proven to be beneficial. However, major drawbacks with clinically used hemostats include lack of adhesion to wet tissue and poor mechanics. In view of these, herein, we engineered a double-crosslinked sealant which showed excellent hemostasis (comparable to existing commercial hemostat) without compromising its wet tissue adhesion. Mechanistically, the engineered hydrogel controlled the bleeding through its wound-sealing capability and inherent chemical activity. This mussel-inspired hemostatic adhesive hydrogel, named gelatin methacryloyl-catechol (GelMAC), contained covalently functionalized catechol and methacrylate moieties and showed excellent biocompatibility both in vitro and in vivo. Hemostatic property of GelMAC hydrogel was initially demonstrated with an in vitro blood clotting assay, which showed significantly reduced clotting time compared to the clinically used hemostat, Surgicel®. This was further assessed with an in vivo liver bleeding test in rats where GelMAC hydrogel closed the incision rapidly and initiated blood coagulation even faster than Surgicel®. The engineered GelMAC hydrogel-based seaalant with excellent hemostatic property and tissue adhesion can be utilized for controlling bleeding and sealing of soft internal organs.

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.

From Supramolecular Hydrogels to Multifunctional Carriers for Biologically Active Substances

Supramolecular hydrogels are 3D, elastic, water-swelled materials that are held together by reversible, non-covalent interactions, such as hydrogen bonds, hydrophobic, ionic, host-guest interactions, and metal-ligand coordination. These interactions determine the hydrogels' unique properties: mechanical strength; stretchability; injectability; ability to self-heal; shear-thinning; and sensitivity to stimuli, e.g., pH, temperature, the presence of ions, and other chemical substances. For this reason, supramolecular hydrogels have attracted considerable attention as carriers for active substance delivery systems. In this paper, we focused on the various types of non-covalent interactions. The hydrogen bonds, hydrophobic, ionic, coordination, and host-guest interactions between hydrogel components have been described. We also provided an overview of the recent studies on supramolecular hydrogel applications, such as cancer therapy, anti-inflammatory gels, antimicrobial activity, controlled gene drug delivery, and tissue engineering.

Gelatin-based adhesive hydrogel with self-healing, hemostasis, and electrical conductivity

As a kind of natural protein derived material, gelatin has been widely used in the preparation of medical hydrogels due to its good biocompatibility, non-immunogenicity and the ability of promoting cell adhesion. Functionalization of gelatin-based hydrogels is a hot topic in research and its clinic application. Herein, a novel gelatin-based adhesive hydrogel was prepared via mussel-inspired chemistry. Gelatin was firstly functionalized by dopamine to form dopamine grafted gelatin (GelDA). After the mixture with 1,4-phenylenebisboronic acid and graphene oxide (GO), the GelDA/GO hydrogels were obtained by H₂O₂/HRP (horseradish peroxidase) catalytic system. Based on the self-healing and tissue adhesion of the hydrogels, the hemostatic property has been exhibited in the rat hepatic hemorrhage model. Additionally, the incorporation of GO endowed conductivity and enhanced the mechanical property of GelDA/GO hydrogels. The electromyography (EMG) signals of finger movement were successfully monitored by using hydrogel as the adhesive electrodes of EMG monitor. L929 cell experiments showed that the hydrogels had good cytocompatibility. The results indicated the potential application of GelDA/GO hydrogels in tissue adhesives, wound dressings, and wearable devices.

Stimuli responsive dynamic transformations in supramolecular gels

Supramolecular gels are formed by the self-assembly of small molecules under the influence of various non-covalent interactions. As the interactions are individually weak and reversible, it is possible to perturb the gels easily, which in turn enables fine tuning of their properties. Synthetic supramolecular gels are kinetically trapped and usually do not show time variable changes in material properties after formation. However, such materials potentially become switchable when exposed to external stimuli like temperature, pH, light, enzyme, redox, and chemical analytes resulting in reconfiguration of gel matrix into a different type of network. Such transformations allow gel-to-gel transitions while the changes in the molecular aggregation result in alteration of physical and chemical properties of the gel with time. Here, we discuss various methods that have been used to achieve gel-to-gel transitions by modifying a pre-formed gel material through external perturbation. We also describe methods that allow time-dependent autonomous switching of gels into different networks enabling synthesis of next generation functional materials. Dynamic modification of gels allows construction of an array of supramolecular gels with various properties from a single material which eventually extend the limit of applications of the gels. In some cases, gel-to-gel transitions lead to materials that cannot be accessed directly. Finally, we point out the necessity and possibility of further exploration of the field.

Biomaterials for Bioprinting Microvasculature

Microvasculature functions at the tissue and cell level, regulating local mass exchange of oxygen and nutrient-rich blood. While there has been considerable success in the biofabrication of large- and small-vessel replacements, functional microvasculature has been particularly challenging to engineer due to its size and complexity. Recently, three-dimensional bioprinting has expanded the possibilities of fabricating sophisticated microvascular systems by enabling precise spatiotemporal placement of cells and biomaterials based on computer-aided design. However, there are still significant challenges facing the development of printable biomaterials that promote robust formation and controlled 3D organization of microvascular networks. This review provides a thorough examination and critical evaluation of contemporary biomaterials and their specific roles in bioprinting microvasculature. We first provide an overview of bioprinting methods and techniques that enable the fabrication of microvessels. We then offer an in-depth critical analysis on the use of hydrogel bioinks for printing microvascularized constructs within the framework of current bioprinting modalities. We end with a review of recent applications of bioprinted microvasculature for disease modeling, drug testing, and tissue engineering, and conclude with an outlook on the challenges facing the evolution of biomaterials design for bioprinting microvasculature with physiological complexity.

Physical and Chemical Factors Influencing the Printability of Hydrogel-based Extrusion Bioinks

Bioprinting researchers agree that "printability" is a key characteristic for bioink development, but neither the meaning of the term nor the best way to experimentally measure it has been established. Furthermore, little is known with respect to the underlying mechanisms which determine a bioink's printability. A thorough understanding of these mechanisms is key to the intentional design of new bioinks. For the purposes of this review, the domain of printability is defined as the bioink requirements which are unique to bioprinting and occur during the printing process. Within this domain, the different aspects of printability and the factors which influence them are reviewed. The extrudability, filament classification, shape fidelity, and printing accuracy of bioinks are examined in detail with respect to their rheological properties, chemical structure, and printing parameters. These relationships are discussed and areas where further research is needed, are identified. This review serves to aid the bioink development process, which will continue to play a major role in the successes and failures of bioprinting, tissue engineering, and regenerative medicine going forward.

Polymeric Hydrogel Systems as Emerging Biomaterial Platforms to Enable Hemostasis and Wound Healing

Broad interest in developing new hemostatic technologies arises from unmet needs in mitigating uncontrolled hemorrhage in emergency, surgical, and battlefield settings. Although a variety of hemostats, sealants, and adhesives are available, development of ideal hemostatic compositions that offer a range of remarkable properties including capability to effectively and immediately manage bleeding, excellent mechanical properties, biocompatibility, biodegradability, antibacterial effect, and strong tissue adhesion properties, under wet and dynamic conditions, still remains a challenge. Benefiting from tunable mechanical properties, high porosity, biocompatibility, injectability and ease of handling, polymeric hydrogels with outstanding hemostatic properties have been receiving increasing attention over the past several years. In this review, after shedding light on hemostasis and wound healing processes, the most recent progresses in hydrogel systems engineered from natural and synthetic polymers for hemostatic applications are discussed based on a comprehensive literature review. Most studies described used in vivo models with accessible and compressible wounds to assess the hemostatic performance of hydrogels. The challenges that need to be tackled to accelerate the translation of these novel hemostatic hydrogel systems to clinical practice are emphasized and future directions for research in the field are presented.

Marine-Derived Polymeric Materials and Biomimetics: An Overview

The review covers recent literature on the ocean as both a source of biotechnological tools and as a source of bio-inspired materials. The emphasis is on marine biomacromolecules namely hyaluronic acid, chitin and chitosan, peptides, collagen, enzymes, polysaccharides from algae, and secondary metabolites like mycosporines. Their specific biological, physicochemical and structural properties together with relevant applications in biocomposite materials have been included. Additionally, it refers to the marine organisms as source of inspiration for the design and development of sustainable and functional (bio)materials. Marine biological functions that mimic reef fish mucus, marine adhesives and structural colouration are explained.

Mussel-inspired bioadhesives in healthcare: design parameters, current trends, and future perspectives

Mussels are well-known for their extraordinary capacity to adhere onto different surfaces in various hydrophillic conditions. Their unique adhesion ability under water or in wet conditions has generated considerable interest towards developing mussel inspired polymeric systems that can mimic the chemical mechanisms used by mussels for their adhesive properties. Catechols like 3,4-dihydroxy phenylalanine (DOPA) and their biochemical interactions have been largely implicated in mussels' strong adhesion to various substrates and have been the centerpoint of research and development efforts towards creating superior tissue adhesives for surgical and tissue engineering applications. In this article, we review bioadhesion and adhesives from an engineering standpoint, specifically the requirements of a good tissue glue, the relevance that DOPA and other catechols have in tissue adhesion, current trends in mussel-inspired bioadhesives, strategies to develop mussel-inspired tissue glues, and perspectives for future development of these materials.

An overview of advanced biocompatible and biomimetic materials for creation of replacement structures in the musculoskeletal systems: focusing on cartilage tissue engineering

Tissue engineering, as an interdisciplinary approach, is seeking to create tissues with optimal performance for clinical applications. Various factors, including cells, biomaterials, cell or tissue culture conditions and signaling molecules such as growth factors, play a vital role in the engineering of tissues. In vivo microenvironment of cells imposes complex and specific stimuli on the cells, and has a direct effect on cellular behavior, including proliferation, differentiation and extracellular matrix (ECM) assembly. Therefore, to create appropriate tissues, the conditions of the natural environment around the cells should be well imitated. Therefore, researchers are trying to develop biomimetic scaffolds that can produce appropriate cellular responses. To achieve this, we need to know enough about biomimetic materials. Scaffolds made of biomaterials in musculoskeletal tissue engineering should also be multifunctional in order to be able to function better in mechanical properties, cell signaling and cell adhesion. Multiple combinations of different biomaterials are used to improve above-mentioned properties of various biomaterials and to better imitate the natural features of musculoskeletal tissue in the culture medium. These improvements ultimately lead to the creation of replacement structures in the musculoskeletal system, which are closer to natural tissues in terms of appearance and function. The present review article is focused on biocompatible and biomimetic materials, which are used in musculoskeletal tissue engineering, in particular, cartilage tissue engineering.

In situ-forming, mechanically resilient hydrogels for cell delivery

Injectable, in situ-forming hydrogels can improve cell delivery in tissue engineering applications by facilitating minimally invasive delivery to irregular defect sites and improving cell retention and survival. Tissues targeted for cell delivery often undergo diverse mechanical loading including high stress, high strain, and repetitive loading conditions. This review focuses on the development of hydrogel systems that meet the requirements of mechanical resiliency, cytocompatibility, and injectability for such applications. First, we describe the most important design considerations for maintaining the viability and function of encapsulated cells, for reproducing the target tissue morphology, and for achieving degradation profiles that facilitate tissue replacement. Models describing the relationships between hydrogel structure and mechanical properties are described, focusing on design principles necessary for producing mechanically resilient hydrogels. The advantages and limitations of current strategies for preparing cytocompatible, injectable, and mechanically resilient hydrogels are reviewed, including double networks, nanocomposites, and high molecular weight amphiphilic copolymer networks. Finally, challenges and opportunities are outlined to guide future research in this developing field.