Preparation of dynamic covalently crosslinking keratin hydrogels based on thiol/disulfide bonds exchange strategy

Harnessing the potential of microbial keratinases for bioconversion of keratin waste

The increasing global consumption of poultry meat has led to the generation of a vast quantity of feather keratin waste daily, posing significant environmental challenges due to improper disposal methods. A growing focus is on utilizing keratinous polymeric waste, amounting to millions of tons annually. Keratins are biochemically rigid, fibrous, recalcitrant, physiologically insoluble, and resistant to most common proteolytic enzymes. Microbial biodegradation of feather keratin provides a viable solution for augmenting feather waste's nutritional value while mitigating environmental contamination. This approach offers an alternative to traditional physical and chemical treatments. This review focuses on the recent findings and work trends in the field of keratin degradation by microorganisms (bacteria, actinomycetes, and fungi) via keratinolytic and proteolytic enzymes, as well as the limitations and challenges encountered due to the low thermal stability of keratinase, and degradation in the complex environmental conditions. Therefore, recent biotechnological interventions such as designing novel keratinase with high keratinolytic activity, thermostability, and binding affinity have been elaborated here. Enhancing protein structural rigidity through critical engineering approaches, such as rational design, has shown promise in improving the thermal stability of proteins. Concurrently, metagenomic annotation offers insights into the genetic foundations of keratin breakdown, primarily predicting metabolic potential and identifying probable keratinases. This may extend the understanding of microbial keratinolytic mechanisms in a complex community, recognizing the significance of synergistic interactions, which could be further utilized in optimizing industrial keratin degradation processes.

Lacticaseibacillus rhamnosus encapsulated cross-linked Keratin-Chitosan hydrogel for removal of patulin from apple juice

In this study, we developed a hydrogel from cross-linked keratin and chitosan (KC) to remove patulin (PAT) from apple juice. We explored the potential of incorporating Lactobacillus rhamnoses into the KC hydrogel (KC-LR) and tested its effectiveness in removing PAT from simulated juice solutions and real apple juice. The KC hydrogel was developed through a dynamic disulfide cross-linking reaction. This cross-linked hydrogel network provided excellent stability for the probiotic cells, achieving 99.9 % immobilization efficiency. In simulated juice with 25 mg/L PAT, the KC and KC-LR hydrogels showed removal efficiencies of 85.2 % and 97.68 %, respectively, using 15 mg mL-1 of the prepared hydrogel at a temperature of 25 °C for 6 h. The KC and KC-LR hydrogels achieved 76.3 % and 83.6 % removal efficiencies in real apple juice systems, respectively. Notably, the encapsulated probiotics did not negatively impact the juice quality and demonstrated reusability for up to five cycles of the PAT removal process.

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.

Cation-π Interaction-Enhanced Self-Healing Injectable Hydrogels for Gastric Perforation Repair

Surgical operations are the preferred treatment for gastric perforation (GP) but incur postoperative complications such as gastrointestinal adhesions and bacterial infections, leading to inefficient wound healing and serious complications that may even threaten the life of the patient. Developing hydrogel dressings capable of adapting to the gastric environment (acid) and decreasing visceral adhesions and bacterial infections after GP treatment is crucial. In this article, we developed an injectable, self-healing hydrogel using cation-π interactions between protonated amines and aromatic rings under acidic conditions and explored it for GP repair. The hydrogels demonstrate exceptional self-healing capabilities under acidic conditions and can be effectively tailored for the gastric environment. In addition, the hydrogel demonstrated significant efficacy in preventing gastrointestinal adhesion, reducing inflammation, promoting angiogenesis, and effectively facilitating wound healing in a rat GP model. This novel hydrogel demonstrates adaptability to the gastric environment, rendering it highly promising for potential applications in gastric trauma healing.

Keratin-PNIPAM Hybrid Microgels: Preparation, Morphology and Swelling Properties

Combinations of synthetic polymers, such as poly(N-isopropylacrylamide) (PNIPAM), with natural biomolecules, such as keratin, show potential in the field of biomedicine, since these hybrids merge the thermoresponsive properties of PNIPAM with the bioactive characteristics of keratin. This synergy aims to produce hybrids that can respond to environmental stimuli while maintaining biocompatibility and functionality, making them suitable for various medical and biotechnological uses. In this study, we exploit keratin derived from wool waste in the textile industry, extracted via sulfitolysis, to synthesize hybrids with PNIPAM microgel. Utilizing two distinct methods-polymerization of NIPAM with keratin (HYB-P) and mixing preformed PNIPAM microgels with keratin (HYB-M)-resulted in hybrids with 20% and 25% keratin content, respectively. Dynamic light scattering (DLS) and transmission electron microscopic (TEM) analyses indicated the formation of colloidal systems with particle sizes of around 110 nm for HYB-P and 518 nm for HYB-M. The presence of keratin in both systems, 20% and 25%, respectively, was confirmed by spectroscopic (FTIR and NMR) and elemental analyses. Distinct structural differences were observed between HYB-P and HYB-M, suggesting a graft copolymer configuration for the former hybrid and a complexation for the latter one. Furthermore, these hybrids demonstrated temperature responsiveness akin to PNIPAM microgels and pH responsiveness, underscoring their potential for diverse biomedical applications.

Keratin Formed Bioadhesive Ophthalmic Gel for the Bacterial Conjunctivitis Treatment

Keratin has the potential to function as the gel matrix in an ophthalmic formulation for the encapsulation of the macrolide antibiotic azithromycin. The quality of this formulation was thoroughly evaluated through various analyses, such as in vitro release assessment, rheological examination, intraocular retention studies in rabbits, assessment of bacteriostatic efficacy, and safety evaluations. It is worth mentioning that the gel demonstrated shear thinning properties and exhibited characteristics of an elastic solid, thereby confirming its structural stability. The gel demonstrated a notable affinity for mucosal surfaces in comparison to traditional azithromycin aqueous solutions. In vitro release testing revealed that drug release transpired via diffusion mechanisms, following a first-order kinetic release pattern. Additionally, the formulated gel exhibited remarkable antibacterial efficacy against Staphylococcus aureus and Pseudomonas aeruginosa in bacteriostatic evaluations. Lastly, safety assessments confirmed that the gel eye drops induced minimal irritation and displayed no apparent cytotoxicity, indicating their good safety and biocompatibility for ocular application. Thus, these findings indicated that the prepared azithromycin gel eye drops complied with the requisite standards for ophthalmic preparations.

Gelatin/Polyacrylamide-Based Antimicrobial and Self-Healing Hydrogel Film for Wound Healing Application

In this study, a self-healing, adhesive, and superabsorbent film made of gelatin, poly(acrylamide), and boric acid (GelAA) was successfully synthesized using a free radical reaction mechanism. The optimized film showed a remarkable 2865 ± 42% water absorptivity and also exhibited excellent self-healing behavior. The GelAA films were further loaded with silver nanoclusters (AgNCs) and ursodeoxycholic acid (UDC) (loading efficiency = 10%) to develop UDC/Ag/GelAA films. The loading of AgNCs in UDC/Ag/GelAA films helped in exhibiting 99.99 ± 0.01% antibacterial activity against both Gram-positive and Gram-negative bacteria, making them very effective against bacterial infections. Additionally, UDC/Ag/GelAA films had 77.19 ± 0.52% porosity and showed 90% of UDC release in 30 h, which helps in improving the cell proliferation. Our research provides an easy but highly effective process for synthesizing a hydrogel film, which is an intriguing choice for wound healing applications without the use of antibiotics.

Leveraging Biomaterial Platforms to Study Aging-Related Neural and Muscular Degeneration

Aging is a complex multifactorial process that results in tissue function impairment across the whole organism. One of the common consequences of this process is the loss of muscle mass and the associated decline in muscle function, known as sarcopenia. Aging also presents with an increased risk of developing other pathological conditions such as neurodegeneration. Muscular and neuronal degeneration cause mobility issues and cognitive impairment, hence having a major impact on the quality of life of the older population. The development of novel therapies that can ameliorate the effects of aging is currently hindered by our limited knowledge of the underlying mechanisms and the use of models that fail to recapitulate the structure and composition of the cell microenvironment. The emergence of bioengineering techniques based on the use of biomimetic materials and biofabrication methods has opened the possibility of generating 3D models of muscular and nervous tissues that better mimic the native extracellular matrix. These platforms are particularly advantageous for drug testing and mechanistic studies. In this review, we discuss the developments made in the creation of 3D models of aging-related neuronal and muscular degeneration and we provide a perspective on the future directions for the field.

3D printable, stretchable, anti-freezing and rapid self-healing organogel-based sensors for human motion detection

Self-healing hydrogels have promising applications in sensors and wearable devices. However, self-healing hydrogels prepared with water as the dispersion medium inevitably freeze at sub-zero temperature, resulting in a loss of the self-healing and sensing ability. The black phosphorene / ethylene glycol / polyvinyl alcohol / sodium tetraborate / sodium alginate (BP/EG-SPB) organogels were prepared by 3D printing technology and solvent displacement method. The organogel exhibits high stretchability (1900 % strain), excellent self-healing property (25 s) and outstanding anti-freezing property (lower than -120 °C freezing point). Furthermore, the organogel can rapidly self-healed (150 s) at a low temperature (-80 °C) without any external stimulation. Additionally, this organogel-based flexible sensor possesses excellent sensitivity (gauge factor: 28.66 at 1900 % strain) and fast response capability, allowing for effective detection of human motion. This work provides a novel method for preparing multifunctional organogel-based sensors for use in harsh climates.

Injectable smart stimuli-responsive hydrogels: pioneering advancements in biomedical applications

Hydrogels have established their significance as prominent biomaterials within the realm of biomedical research. However, injectable hydrogels have garnered greater attention compared with their conventional counterparts due to their excellent minimally invasive nature and adaptive behavior post-injection. With the rapid advancement of emerging chemistry and deepened understanding of biological processes, contemporary injectable hydrogels have been endowed with an "intelligent" capacity to respond to various endogenous/exogenous stimuli (such as temperature, pH, light and magnetic field). This innovation has spearheaded revolutionary transformations across fields such as tissue engineering repair, controlled drug delivery, disease-responsive therapies, and beyond. In this review, we comprehensively expound upon the raw materials (including natural and synthetic materials) and injectable principles of these advanced hydrogels, concurrently providing a detailed discussion of the prevalent strategies for conferring stimulus responsiveness. Finally, we elucidate the latest applications of these injectable "smart" stimuli-responsive hydrogels in the biomedical domain, offering insights into their prospects.

Photothermal Modulation of Dynamic Covalent Poly(ethylene glycol)/PEDOT Composite Hydrogels for On-Demand Drug Delivery

Hydrogels are cross-linked three-dimensional polymer networks that have tissue-like properties. Dynamic covalent bonds (DCB) can be utilized as hydrogel cross-links to impart injectability, self-healing ability, and stimuli responsiveness to these materials. In our research, we utilized dynamic thiol-Michael bonds as cross-links in poly(ethylene glycol) (PEG)-based hydrogels. Because the equilibrium of the reversible, exothermic thiol-Michael reaction can be modulated by temperature, we investigated the possibility of using thermal and photothermal stimuli to modulate the gel-to-sol transition of these materials with the aim of developing an on-demand pulsatile cargo release system. For this purpose, we incorporated poly(3,4-ethylenedioxythiophene) (PEDOT) nanoparticles within the hydrogel to facilitate photothermal modulation using near-infrared light. PEDOT nanoparticles of 50 nm in diameter and with strong near-infrared absorption were prepared by oxidative emulsion polymerization. We then used Michael addition of thiol-ene pairs from 4-arm PEG-thiol (PEG-SH) and 4-arm PEG-benzylcyanoacetamide (PEG-BCA) to form dynamically cross-linked hydrogels. PEDOT nanoparticles were entrapped in situ to form Gel/PEDOT composites. Rheology and inverted tube test studies showed that the gel-to-sol transition occurred at 45-50 °C for 5 wt % gels and that this transition could be tailored by varying the wt % of the polymer precursors. The hydrogels were found to be capable of self-healing and being injected with a clinically relevant injection force. Bovine serum albumin-fluorescein isothiocyanate (BSA-FITC), a fluorescently labeled protein, was then loaded into the Gel/PEDOT as a therapeutic mimic. Increased release of BSA-FITC upon direct thermal stimulation and photothermal stimulation with an 808 nm laser was observed. Pulsatile release of BSA-FITC over seven cycles was demonstrated. MTS and live-dead assays demonstrated that Gel/PEDOT was cytocompatible in MDA-MB-231 breast cancer and 3T3 fibroblast cell lines. Further studies demonstrated that the encapsulation and laser-triggered release of the chemotherapeutic agent doxorubicin (DOX) could also be achieved. Altogether, this work advances our understanding of the temperature-dependent behavior of a dynamic covalent hydrogel, Gel/PEDOT, and leverages that understanding for application as a photothermally responsive biomaterial for controlled release.

Wool keratin/zeolitic imidazolate framework-8 composite shape memory sponge with synergistic hemostatic performance for rapid hemorrhage control

Uncontrollable hemorrhage and subsequent wound infection pose severe threats to life, especially in the case of deep, non-compressible, massive bleeding. Here, a wool keratin/zeolitic imidazolate framework-8 (WK/ZIF-8) composite shape memory sponge is prepared by incorporating ZIF-8 nanoparticles into wool keratin. The combination of keratin and ZIF-8 particles not only reduces the effect of ZIF-8 particles on cell viability but also bolsters the mechanical properties of the keratin sponge and endows it with antibacterial efficacy. Due to the synergistic effect of the excellent hemostatic performance of keratin and Zn2+ release from ZIF-8 nanoparticles, the porous structure suitable for blood cell adhesion and the shape recovery ability of sponges, the WK/ZIF-8 composite sponge exhibits superior hemostatic performance to commercial medical sponges in SD rat and rabbit hemorrhage models. In addition, in vitro and in vivo antibacterial experiments demonstrate the anti-infection activity of the composite sponge. Overall, the WK/ZIF-8 composite sponge provides a promising approach to rapidly control bleeding and promote wound healing.

Seamlessly Adhesive Bionic Periosteum Patches Via Filling Microcracks for Defective Bone Healing

Current artificial designs of the periosteum focus on osteogenic or angiogenic properties, while ignoring the filling and integration with bone microcracks, which trigger a prolonged excessive inflammatory reaction and lead to failure of bone regeneration. In this study, seamless adhesive biomimetic periosteum patches (HABP/Sr-PLA) were prepared to fill microcracks in defective bone via interfacial self-assembly induced by Sr ions mediated metal-ligand interactions among pamidronate disodium-modified hyaluronic acid (HAPD), black phosphorus (BP), and hydrophilic polylactic acid (PLA). In vitro, HABP/Sr-PLA exhibited excellent self-healing properties, seamlessly filled bone microcracks, and significantly enhanced osteogenesis and angiogenesis. Furthermore, in a rat cranial defect model, HABP/Sr-PLA was demonstrated to significantly promote the formation of blood vessels and new bone under mild 808 nm photothermal stimulation (42.8 °C), and the highest protein expression of CD31 and OPN was five times higher than that of the control group and other groups. Therefore, the proposed seamless microcrack-filled bionic periosteum patch is a promising clinical strategy for promoting bone repair.

Underlying mechanisms of egg white thinning in hot spring eggs during storage: Weak gel properties and quantitative proteome analysis

As a weakly gelling protein, hot spring egg white underwent thinning during storage. This study explored the mechanism of thinning in hot spring egg white from the perspective of "gel structure and protein composition" using quantitative proteomics, SEM, SDS-PAGE, and other techniques. Quantitative proteomics analysis showed that there were 81 (44 up-regulated and 21 down-regulated) key proteins related to thinning of hot spring egg white. The changes in the relative abundance of proteins such as ovalbumin-related Y, mucin-6, lysozyme, ovomucoid, and ovotransferrin might be important reasons for thinning in hot spring egg white. SEM results indicated that the gel network gradually became regular and uniform, with large pores appearing on the cross-section and being pierced. Along with the decrease in intermolecular electrostatic repulsion, protein molecules gradually aggregated. The particle size gradually increased from 139.1 nm to 422.5 nm. Meanwhile, the surface hydrophobicity, and disulfide bond content gradually increased. These changes might be the reasons for thinning in hot spring egg white during storage. It can provide a new perspective for studying the thinning mechanism of weakly gelling egg whites.

Effects of environmental pH on protein properties and flavor factors of hairtail (Trichiurus haumela) in thermal processing

The flavor and texture of hairtail (Trichiurus haumela) products easily change depending on the processing conditions including the programed temperature, environmental pH, and so on. In the present study, we aimed to explore the differences in the overall texture and flavor of hairtail under heat treatment with varied environmental pH. The results indicated that the secondary structure of the myofibrillar protein in thermal processed hairtail meat presented a transformation from α-helix to β-sheet structure with the decrease of solution pH. Moreover, heat treatment in an acidic solution environment effectively improved the sensory and flavor properties of hairtail. In addition, pH-mediated changes on protein characteristics of cooked hairtail meat showed significant correlation with the texture properties, while weakly correlated with the flavor.

Cysteine Redox Chemistry in Peptide Self-Assembly to Modulate Hydrogelation

Cysteine redox chemistry is widely used in nature to direct protein assembly, and in recent years it has inspired chemists to design self-assembling peptides too. In this concise review, we describe the progress in the field focusing on the recent advancements that make use of Cys thiol-disulfide redox chemistry to modulate hydrogelation of various peptide classes.

Self-healing hydrogels for bone defect repair

Severe bone defects can be caused by various factors, such as tumor resection, severe trauma, and infection. However, bone regeneration capacity is limited up to a critical-size defect, and further intervention is required. Currently, the most common clinical method to repair bone defects is bone grafting, where autografts are the "gold standard." However, the disadvantages of autografts, including inflammation, secondary trauma and chronic disease, limit their application. Bone tissue engineering (BTE) is an attractive strategy for repairing bone defects and has been widely researched. In particular, hydrogels with a three-dimensional network can be used as scaffolds for BTE owing to their hydrophilicity, biocompatibility, and large porosity. Self-healing hydrogels respond rapidly, autonomously, and repeatedly to induced damage and can maintain their original properties (i.e., mechanical properties, fluidity, and biocompatibility) following self-healing. This review focuses on self-healing hydrogels and their applications in bone defect repair. Moreover, we discussed the recent progress in this research field. Despite the significant existing research achievements, there are still challenges that need to be addressed to promote clinical research of self-healing hydrogels in bone defect repair and increase the market penetration.

Influence and effect mechanism of disulfide bonds linkages between protein-coated lipid droplets and the protein matrix on the physicochemical properties, microstructure, and protein structure of ovalbumin emulsion gels

In this study, disulfide bonds between the interfacial protein film formed on the lipid particles and the protein in ovalbumin emulsion gels were blocked with 0, 1, 3, 5 and 10 mM of the N-ethylmaleimide (NEM) to explore the influence and effect mechanism of disulfide bonds between the interfacial proteins on the physicochemical properties, microstructure, and protein structure of sunflower oil-ovalbumin emulsion gels. Ovalbumin emulsion gels with NEM-treated ovalbumin emulsion (N-OE) had lower hardness, free sulfhydryl content, water holding capacity (WHC), and surface hydrophobicity, but higher spin-spin relaxation time (T₂) than ovalbumin emulsion gels with NEM-treated ovalbumin substrate solution (N-OSS). In addition, N-OE and N-OSS had lower hardness, free sulfhydryl content, WHC and surface hydrophobicity, as well as a more coarse and disordered microstructure than non-NEM treated ovalbumin emulsion gel (control group). The free sulfhydryl content, hardness, WHC, and surface hydrophobicity of the ovalbumin emulsion gels all decreased as the NEM concentration rose (p < 0.05), whereas the amide A band changed to higher wave numbers. These results collectively indicated that the reduction of disulfide between the interfacial layer and the proteins inhibited the hydrophobic effect, the formation of hydrogen bonds, and prevented the formation of larger aggregates. Thus the disulfide bonds between the interfacial proteins contribute to the hardness enhancement and water stabilization of the ovalbumin gel.

Design of Injectable Bioartificial Hydrogels by Green Chemistry for Mini-Invasive Applications in the Biomedical or Aesthetic Medicine Fields

Bioartificial hydrogels are hydrophilic systems extensively studied for regenerative medicine due to the synergic combination of features of synthetic and natural polymers. Injectability is another crucial property for hydrogel mini-invasive administration. This work aimed at engineering injectable bioartificial in situ cross-linkable hydrogels by implementing green and eco-friendly approaches. Specifically, the versatile poly(ether urethane) (PEU) chemistry was exploited for the development of an amphiphilic PEU, while hyaluronic acid was selected as natural component. Both polymers were functionalized to expose thiol and catechol groups through green water-based carbodiimide-mediated grafting reactions. Functionalization was optimized to maximize grafting yield while preserving group functionality. Then, polymer miscibility was studied at the macro-, micro-, and nano-scale, suggesting the formation of hydrogen bonds among polymeric chains. All hydrogels could be injected through G21 and G18 needles in a wide temperature range (4-25 °C) and underwent sol-to-gel transition at 37 °C. The addition of an oxidizing agent to polymer solutions did not improve the gelation kinetics, while it negatively affected hydrogel stability in an aqueous environment, suggesting the occurrence of oxidation-triggered polymer degradation. In the future, the bioartificial hydrogels developed herein could find application in the biomedical and aesthetic medicine fields as injectable formulations for therapeutic agent delivery.

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.

An UV-photo and ionic dual responsive interpenetrating network hydrogel with shape memory and self-healing properties

Shape memory hydrogels have attracted extensive attention in fields such as artificial tissues, biomimetic devices and diagnostics, and intelligent biosensors. However, the practical applications were hindered by the absence of self-healing capability and multi-stimuli-responsiveness. To address these issues, we developed a shape memory hydrogel with self-healing and dual stimuli-response performance. The hydrogel system was constructed via an interpenetrating network consisting of in situ radical polymerization and host-guest interaction. The hydrogel exhibited rapid self-healing property, which can be stretched after self-healing for 1 min at 25 °C. Besides, the hydrogel displayed varied swelling performance in different light or solvent conditions. Moreover, the hydrogel showed a dual stimuli-responsive shape memory effect to ultraviolet (UV) light and ionic strength in 1 min. Such a shape memory hydrogel with self-healing ability and multi-stimuli-responsive properties will offer an option toward intelligent soft materials for biomedical and bionic research.

Sustainable Applications of Animal Waste Proteins

Currently, the growth of the global population leads to an increase in demand for agricultural products. Expanding the obtaining and consumption of food products results in a scale up in the amount of by-products formed, the development of processing methods for which is becoming an urgent task of modern science. Collagen and keratin make up a significant part of the animal origin protein waste, and the potential for their biotechnological application is almost inexhaustible. The specific fibrillar structure allows collagen and keratin to be in demand in bioengineering in various forms and formats, as a basis for obtaining hydrogels, nanoparticles and scaffolds for regenerative medicine and targeted drug delivery, films for the development of biodegradable packaging materials, etc. This review describes the variety of sustainable sources of collagen and keratin and the beneficial application multiformity of these proteins.

Recent advances in dynamic covalent bond-based shape memory polymers

Dynamic covalent bond-based shape memory polymers (DCB-SMPs) are one of most important SMPs which have a wide potential application prospect. Different from common strong covalent bonds, DCBs own relatively weak bonding energy, similarly to the supramolecular interactions of noncovalent bonds, and can dynamically combine and dissociate these bonds. DCB-SMP solids, which can be designed to respond for different stimuli, can provide excellent self-healing, good reprocessability, and high mechanical performance, because DCBs can obtain dynamic cross-linking without sacrificing ultrahigh fixing rates. Furthermore, besides DCB-SMP solids, DCB-SMP hydrogels with responsiveness to various stimuli also have been developed recently, which have special biocompatible soft/wet states. Particularly, DCB-SMPs can be combined with emerging 3D-printing techniques to design various original shapes and subsequently complex shape recovery. This review has summarized recent research studies about SMPs based on various DCBs including DCB-SMP solids, DCB-SMP hydrogels, and the introduction of new 3D-printing techniques using them. Last but not least, the advantages/disadvantages of different DCB-SMPs have been analyzed via polymeric structures and the future development trends in this field have been predicted.

Composite Dynamic Hydrogels Constructed on Boronic Ester Cross-Links with NIR-Enhanced Diffusivity

Dynamic hydrogels with thermosensitive cross-links are highly promising platforms for "on-demand" drug delivery systems. However, there is a problem with triggering a response in their whole volume, which reduces their efficiency. To achieve better thermoresponsiveness, a graphene oxide-filled composite hydrogel based on boronic ester cross-links, composed of hyperbranched polyglycidol, HbPGL, and poly(acrylamide-ran-2-acrylamidephenylboronic acid), poly(AM-ran-2-AAPBA), has been constructed. The homogeneous embedment of graphene oxide (GO) in the network assured near-infrared (NIR)-photothermal response in its bulk due to the rapid light-to-heat conversion. The rate and amplitude of materials response increase with graphene oxide concentration. The temperature of the hydrogel containing graphene oxide at a concentration of 13.2 mg/mL increased from 36.6 to 41 °C in 29 s upon NIR irradiation. The network diffusivity and the extent of its change with temperature can be regulated by the length of the applied boronic acid-based cross-linking agent. The hydrogel constructed on the shorter copolymer (M_n = 23 000 g/mol) displayed a significant increase in diffusivity with temperature. A diffusion ordered NMR study revealed that the diffusion coefficient determined for niacin, a model drug encapsulated in the hydrogel, increased from 6.09 × 10^-10 at 25 °C to 1.28 × 10^-9 m²/s at 41 °C. In the case of the hydrogel constructed on the longer acrylamide copolymer (M_n = 43 000 g/mol), in which physical entanglements stabilize the network, the change of encapsulated niacin diffusion coefficient was significantly smaller, i.e., from 3.83 × 10^-10 at 25 °C to 6.63 × 10^-10 m²/s at 41 °C. The possibility of on-demand NIR-regulated diffusivity of the reported boronic ester-based hydrogels makes them promising candidates for controlled drug delivery platforms.