Rejoining of cut wounds by engineered gelatin–keratin glue

Alginate-Based Materials Loaded with Nanoparticles in Wound Healing

Alginate is a naturally derived polysaccharide widely applied in drug delivery, as well as regenerative medicine, tissue engineering and wound care. Due to its excellent biocompatibility, low toxicity, and the ability to absorb a high amount of exudate, it is widely used in modern wound dressings. Numerous studies indicate that alginate applied in wound care can be enhanced with the incorporation of nanoparticles, revealing additional properties beneficial in the healing process. Among the most extensively explored materials, composite dressings with alginate loaded with antimicrobial inorganic nanoparticles can be mentioned. However, other types of nanoparticles with antibiotics, growth factors, and other active ingredients are also investigated. This review article focuses on the most recent findings regarding novel alginate-based materials loaded with nanoparticles and their applicability as wound dressings, with special attention paid to the materials of potential use in the treatment of chronic wounds.

Marine Gelatin-Methacryloyl-Based Hydrogels as Cell Templates for Cartilage Tissue Engineering

Marine-origin gelatin has been increasingly used as a safe alternative to bovine and porcine ones due to their structural similarity, avoiding the health-related problems and sociocultural concerns associated with using mammalian-origin materials. Another benefit of marine-origin gelatin is that it can be produced from fish processing-products enabling high production at low cost. Recent studies have demonstrated the excellent capacity of gelatin-methacryloyl (GelMA)-based hydrogels in a wide range of biomedical applications due to their suitable biological properties and tunable physical characteristics, such as tissue engineering applications, including the engineering of cartilage. In this study, fish gelatin was obtained from Greenland halibut skins by an acidic extraction method and further functionalized by methacrylation using methacrylic anhydride, developing a photosensitive gelatin-methacryloyl (GelMA) with a degree of functionalization of 58%. The produced marine GelMA allowed the fabrication of photo-crosslinked hydrogels by incorporating a photoinitiator and UV light exposure. To improve the biological performance, GelMA was combined with two glycosaminoglycans (GAGs): hyaluronic acid (HA) and chondroitin sulfate (CS). GAGs methacrylation reaction was necessary, rendering methacrylated HA (HAMA) and methacrylated CS (CSMA). Three different concentrations of GelMA were combined with CSMA and HAMA at different ratios to produce biomechanically stable hydrogels with tunable physicochemical features. The 20% (w/v) GelMA-based hydrogels produced in this work were tested as a matrix for chondrocyte culture for cartilage tissue engineering with formulations containing both HAMA and CSMA showing improved cell viability. The obtained results suggest these hybrid hydrogels be used as promising biomaterials for cartilage tissue engineering applications.

Preparation Methods and Functional Characteristics of Regenerated Keratin-Based Biofilms

The recycling, development, and application of keratin-containing waste (e.g., hair, wool, feather, and so on) provide an important means to address related environmental pollution and energy shortage issues. The extraction of keratin and the development of keratin-based functional materials are key to solving keratin-containing waste pollution. Keratin-based biofilms are gaining substantial interest due to their excellent characteristics, such as good biocompatibility, high biodegradability, appropriate adsorption, and rich renewable sources, among others. At present, keratin-based biofilms are a good option for various applications, and the development of keratin-based biofilms from keratin-containing waste is considered crucial for sustainable development. In this paper, in order to achieve clean production while maintaining the functional characteristics of natural keratin as much as possible, four important keratin extraction methods—thermal hydrolysis, ultrasonic technology, eco-friendly solvent system, and microbial decomposition—are described, and the characteristics of these four extraction methods are analysed. Next, methods for the preparation of keratin-based biofilms are introduced, including solvent casting, electrospinning, template self-assembly, freeze-drying, and soft lithography methods. Then, the functional properties and application prospects of keratin-based biofilms are discussed. Finally, future research directions related to keratin-based biofilms are proposed. Overall, it can be concluded that the high-value conversion of keratin-containing waste into regenerated keratin-based biofilms has great importance for sustainable development and is highly suggested due to their great potential for use in biomedical materials, optoelectronic devices, and metal ion detection applications. It is hoped that this paper can provide some basic information for the development and application of keratin-based biofilms.

Bio-macromolecular design roadmap towards tough bioadhesives

Emerging sutureless wound-closure techniques have led to paradigm shifts in wound management. State-of-the-art biomaterials offer biocompatible and biodegradable platforms enabling high cohesion (toughness) and adhesion for rapid bleeding control as well as robust attachment of implantable devices. Tough bioadhesion stems from the synergistic contributions of cohesive and adhesive interactions. This Review provides a biomacromolecular design roadmap for the development of tough adhesive surgical sealants. We discuss a library of materials and methods to introduce toughness and adhesion to biomaterials. Intrinsically tough and elastic polymers are leveraged primarily by introducing strong but dynamic inter- and intramolecular interactions either through polymer chain design or using crosslink regulating additives. In addition, many efforts have been made to promote underwater adhesion via covalent/noncovalent bonds, or through micro/macro-interlock mechanisms at the tissue interfaces. The materials settings and functional additives for this purpose and the related characterization methods are reviewed. Measurements and reporting needs for fair comparisons of different materials and their properties are discussed. Finally, future directions and further research opportunities for developing tough bioadhesive surgical sealants are highlighted.

High-Strength Hydrogel Attachment through Nanofibrous Reinforcement

The repair of a cartilage lesion with a hydrogel requires a method for long-term fixation of the hydrogel in the defect site. Attachment of a hydrogel to a base that allows for integration with bone can enable long-term fixation of the hydrogel, but current methods of forming bonds to hydrogels have less than a tenth of the shear strength of the osteochondral junction. This communication describes a new method, nanofiber-enhanced sticking (NEST), for bonding a hydrogel to a base with an adhesive shear strength three times larger than the state-of-the-art. An example of NEST is described in which a nanofibrous bacterial cellulose sheet is bonded to a porous base with a hydroxyapatite-forming cement followed by infiltration of the nanofibrous sheet with hydrogel-forming polymeric materials. This approach creates a mineralized nanofiber bond that mimics the structure of the osteochondral junction, in which collagen nanofibers extend from cartilage into a mineralized region that anchors cartilage to bone.

Rapid Hemostasis Resulting from the Synergism of Self-Assembling Short Peptide and O-Carboxymethyl Chitosan

The development of novel hemostatic agents with distinct modes of action from traditional ones remains a formidable challenge. Self-assembling peptide hydrogels have emerged as a new hemostatic material, not only because of their inherent biocompatibility and biodegradability but also their designability. Especially, rational molecular design can make peptides and their hydrogelation responsive to biological cues. In this study, we demonstrated that transglutaminase-catalyzed reactions not only occurred among designed short peptide I₃QGK molecules but also between the peptide and a natural polysaccharide O-carboxymethyl chitosan. Because Factor XIII in the blood can rapidly convert into activated transglutaminase (Factor XIIIa) upon bleeding, these enzymatic reactions, together with the electrostatic attraction between the two hemostatic agents, induced a strong synergetic effect in promoting hydrogelation, blood coagulation, and platelet adhesion, eventually leading to rapid hemostasis. The study presents a promising strategy for developing alternative hemostatic materials and methods.

Functionalized Multiarmed Polycaprolactones as Biocompatible Tissue Adhesives

Existing tissue adhesives have a trade-off between adhesive strength and biocompatibility. Here, we report a series of biocompatible multiarmed polycaprolactones (PCL) as tissue adhesives that can be released from a hot glue gun and the length of each arm was kept at ∼2-3 kg mol^-1 in all the polymers. The adhesion properties were dependent on the number of functionalized (N-hydroxysuccinimide ester (NHS), aldehyde (CHO), and isocyanate (NCO)) arms of the multiarmed polymers. The more arms, the higher the adhesion strength. For example, the adhesion strength in binding cut rat skin increased from 2.3 N cm^-2 for 2PCL-NHS to 11.2 N cm^-2 for 8-PCL-NHS. CHO- and NCO-modified 8PCL also had suitable adhesive properties. All the multiarmed polymers had minimal cytotoxicity in vitro and good biocompatibility in vivo, suggesting their potential as promising alternative surgical adhesives.

Cellulose/keratin–catechin nanocomposite hydrogel for wound hemostasis

Rapid wound hemostatic was achieved by a composite hydrogel based on human hair keratin–catechin nanoparticles and cellulose.

Biomimetic interconnected porous keratin-fibrin-gelatin 3D sponge for tissue engineering application

The medicated wound dressing material with highly interconnected pores, mimicking the function of the extracellular matrix was fabricated for the promotion of cell growth. In this study, keratin (K), fibrin (F) and gelatin (G) composite scaffold (KFG-SPG) was fabricated by freeze drying technique and the mupirocin (D) drug was successfully incorporated with KFG-SPG (KFG-SPG-D) intended for tissue engineering applications. The fabrication of scaffold was performed without the use of any strong chemical solvents, and the solid sponge scaffold was obtained with well interconnected pores. The porous morphology of the scaffold was confirmed by SEM analysis and exhibited competent mechanical properties. KFG-SPG and KFG-SPG-D possess high level of biocompatibility, cell proliferation and cell adhesion of NIH 3T3 fibroblast and human keratinocytes (HaCaT) cell lines thereby indicating the scaffolds potential as a suitable medicated dressing for wound healing.

K S, A G. Handling and managing bleeding wounds using tissue adhesive hydrogel: a comparative assessment on two different hydrogels

The present study explores the preparation and a comparative assessment on the physical, mechanical and biological properties of two different tissue adhesive hydrogels (TAHs) for the management of bleeding wounds.

pH and redox sensitive albumin hydrogel: A self-derived biomaterial

Serum albumin can be transformed to a stimuli (pH and redox) responsive hydrogel using the reduction process followed by oxidative refolding. The preparation of albumin hydrogel involves a range of concentrations (75, 150, 300, 450, 600 and 750 μM) and pH (2.0-10.0) values and the gelation begins at a concentration of 150 μM and 4.5-8.0 pH value. The hydrogel shows maximum swelling at alkali pH (pH > 9.0). The increase in albumin concentration increases hydrogel stability, rheological property, compressive strength, proteolytic resistance and rate of in vivo biodegradation. Based on the observed physical and biological properties of albumin hydrogel, 450 μM was determined to be an optimum concentration for further experiments. In addition, the hemo- and cytocompatibility analyses revealed the biocompatibility nature of albumin hydrogel. The experiments on in vitro drug (Tetracycline) delivery were carried out under non reducing and reducing conditions that resulted in the sustained and fast release of the drug, respectively. The methodology used in the preparation of albumin hydrogel may lead to the development of autogenic tissue constructs. In addition, the methodology can have various applications in tissue engineering and drug delivery.

In vitro and in vivo assessments of a 3-(3,4-dihydroxyphenyl)-2-propenoic acid bioconjugated gelatin-based injectable hydrogel for biomedical applications

Imparting functional properties on a biomaterial for high end applications is always a challenging task. In the present study, an attempt was made to construct an injectable hydrogel through bioconjugation of dihydroxy phenolic acids to a gelatin backbone. Bioconjugating caffeic acid with gelatin followed by oxidation with mild oxidation agents provided a hydrogel with all the requisite properties (biocompatibility, controlled biodegradability, and antioxidant, antimicrobial and wound healing ability). Bioconjugation was performed using EDC/NHS and the resultant gel named as caffeic acid bioconjugated gel (CBG gel). The physicochemical, rheological, swelling, in vitro (biocompatibility, biodegradability, antimicrobial properties, antioxidant properties and drug release properties) and in vivo (biocompatibility, biodegradability and wound healing properties) studies on the CBG gel were carried out using standard protocols. The bioconjugation was confirmed by ¹H NMR and UV-Vis analysis. Rheological analysis of the CBG gel revealed that the storage modulus was greater than the loss modulus at all the frequencies and suggested the elastic nature of the gel. About 50% weight gain within 12 hours during swelling studies and 50% weight loss within 12 hours during evaporation suggested the suitability of the CBG gel as a drug carrier. The drug release studies implied that there was an initial burst and later the release was sustained. The CBG gel promotes cell migration and demonstrates radical scavenging behavior. When subcutaneously injected into the animal, as in situ CBG gel, the gel was highly biocompatible and did not cause any necrosis. The crosstalk with adjacent tissue cells was smooth and the gel completely degraded within 24 days. The wound healing efficacy on full-thickness wounds suggested that the CBG gel accelerated healing and imparted high strength on the healed skin at an appreciable level. With all these additional functional properties, the CBG gel could be useful for biomedical applications.

Organ repair, hemostasis, and in vivo bonding of medical devices by aqueous solutions of nanoparticles

Sutures are traumatic to soft connective tissues, such as liver or lungs. Polymer tissue adhesives require complex in vivo control of polymerization or cross-linking reactions and currently suffer from being toxic, weak, or inefficient within the wet conditions of the body. Herein, we demonstrate using Stöber silica or iron oxide nanoparticles that nanobridging, that is, adhesion by aqueous nanoparticle solutions, can be used in vivo in rats to achieve rapid and strong closure and healing of deep wounds in skin and liver. Nanoparticles were also used to fix polymer membranes to tissues even in the presence of blood flow, such as occurring after liver resection, yielding permanent hemostasis within a minute. Furthermore, medical devices and tissue engineering constructs were fixed to organs such as a beating heart. The simplicity, rapidity, and robustness of nanobridging bode well for clinical applications, surgery, and regenerative medicine.

Preparation and characterization of in-situ crosslinked pectin-gelatin hydrogels

Crosslinked hydrogels were developed by in-situ reaction of periodate oxidized pectin (OP) and gelatin. The reaction takes place through the formation of Schiff bases between aldehyde groups of OP and amino groups of gelatin. The effect of various process parameters such as reaction time, reaction temperature, pH of the reaction and composition on the efficacy of the crosslinking was investigated. Field emission scanning electron micrsocopy (FESEM) revealed that homogenous, single phase systems are obtained after the crosslinking of OP and gelatin. The swelling characteristics of the hydrogels were monitored. The equilibrium swelling varies in the range of 195-324% with a variation in the gelatin content (10-40%). Glycerol, when used as a plasticizer, improved the flexibility and the handling characteristics of the crosslinked hydrogels. Plasticized films retained good tensile strengths in the range of 19-48 MPa. By proper selection of the reaction conditions, the efficiency of crosslinking can be controlled to obtain the optimum results.

Novel on-demand bioadhesion to soft tissue in wet environments

Current methods of tissue fixation rely on mechanical-related technologies developed from the clothing and carpentry industries. Herein, a novel bioadhesive method that allows tuneable adhesion and is also applicable to biodegradable polyester substrates is described. Diazirine is the key functional group that allows strong soft tissue crosslinking and on-demand adhesion based on a free radical mechanism. Plasma post-irradiation grafting makes it possible to graft diazirine onto PLGA substrates. When the diazirine-PLGA films, placed on wetted ex vivo swine aortas, are activated with low intensity UV light, lap shear strength of up to 450 ± 50 mN cm(-2) is observed, which is one order of magnitude higher than hydrogel bioadhesives placed on similar soft tissues. The diazirine-modified PLGA thin films could be added on top of previously developed technologies for minimally invasive surgeries. The present work is focused on the chemistry, grafting, and lap shear strength of the alkyl diazirine-modified PLGA bioadhesive films.