Extensive studies demonstrate that macrophage response plays an important role in regulating angiogenesis via a paracrine way, which is crucial for skin wound repair. This study isolated and characterized nanosized exosomes from differently polarized macrophages (MΦ), including M0 (naïve), M1 (pro-inflammatory), and M2 (anti-inflammatory) macrophages, and further assessed their impacts on angiogenesis and skin regeneration. Our results indicated that compared to M0 and M1 counterparts, M2 macrophage-derived exosomes (M2-Exos) exhibited a pronounced ability to promote angiogenic ability of of human umbilical vein endothelial cells (HUVECs) by enhancing expression of angiogenic genes and proteins, increasing cell migration, and improving tubulogenesis. Bioinformatics analyses suggested that the distinct angiogenic potentials of three MΦ-Exos might be attributed to the differentially expressed angiogenesis-related miRNAs and their target genes such as Stat3, Smad 2, and Smad4. Moreover, these isolated MΦ-Exos were integrated with gelatine methacrylate (GelMA) hydrogels to achieve the sustained delivery at murine full-thickness cutaneous wound sites. In vivo results showed that Gel/M2-Exos significantly augmented angiogenesis, accelerated re-epithelialization, promoted collagen maturity, thereby promoting wound healing. In contrary, Gel/M1-Exos showed the opposite effects. Our findings provided compelling evidence that the polarization status of macrophages significantly affected angiogenesis and wound healing via the miRNA cargos of their derived exosomes. Moreover, this study opens a new avenue for developing nano-scale, cell-free exosome-based therapies in treating cutaneous wounds.

Proteases, such as trypsin, are essential for extracting collagen in various industrial applications. The potential applications of rare earth nanomaterials, specifically yttrium nanoparticles, have attracted significant interest across various fields due to their distinctive characteristics, including high dielectric constant and thermal stability. Biomineralization has emerged as a promising approach to synthesize protein-inorganic nanomaterials with hierarchical structures and desired functions. In the present investigation, a novel protease-templated biomineralization strategy was developed for synthesizing protease-(NH₄)₂Y₃F₁₁•H₂O hybrid nanomaterials using a one-pot method under very mild conditions. For modifying the morphologies of (NH₄)₂Y₃F₁₁•H₂O throughout biomineralization, protease has been demonstrated to be a highly promising biotemplate. Protease was utilized as a template for morphological control in the biomineralization procedure, which resulted in a gradual transformation of the initially formed (NH₄)₂Y₃F₁₁•H₂O octahedral structures into uniform nanospheres. The applicability of this approach was supported by successfully utilizing various proteases to synthesize protease-(NH₄)₂Y₃F₁₁•H₂O hybrid nanospheres. In addition to a strong and desirable luminescent signal, these hybrid nanospheres demonstrated extensive recycling because of their high enzymatic activity, stability and durability. The protease-mediated biomineralization approach offers an easy and robust approach to develop innovative protease-inorganic composites. Its moderate reaction conditions and simple operation render it a viable tool for developing stable and reusable enzyme reactors in various industrial applications.

Acellular dermal matrix (ADM) is one of the most promising scaffold materials due to its ability to retain natural extracellular matrix structure. Micronized acellular dermal matrix (mADM) was prepared with no intact cell nuclei and preserved growth factors by High Hydrostatic Pressure (HHP) approach. And mADM-collagen wound dressings were developed with different proportion of type I collagen and recombinant humanized type III collagen. The porous structure of the mADM-collagen wound dressings made them a good candidate for preventing excessive fluid accumulation, while the collagens with gel-like texture combined with mADM powder to form pasty texture wound dressing, which preserving the moisture at the wound site. Moreover, the paste texture of the mADM-collagen wound dressing was easy to reshape to conform any wound shapes and body contours. Furthermore, the resulted mADM-collagen wound dressings showed good biocompatibility by supporting fibroblasts adhesion and proliferation in vitro. Subsequently, a murine model of full-thickness skin wounds was employed to assess its effects on wound healing. Notably, mADM-75% Col-I exhibited superior effects throughout the wound healing process, specifically it promoted neovascularization, skin appendage growth and new skin regeneration. This formulation closely mimicked the collagen ratio found in healthy skin, facilitating the favorable wound repair. These results indicated the superior performance of this mADM-collagen wound dressing providing an optimal environment for wound healing.

Silicate bioceramics have demonstrated great potential in hydrogel dressings for wound healing due to their special origins of promoting endothelial cell angiogenesis and inhibiting apoptosis of cardiomyocyte. However, there are still some deficiencies, such as insufficient biological activity, instability of silicate ion release, and lower wet adhesion on wounds with tissue exudate, limiting their further clinical applications. Herein, inspired by mussels, a multifunctional double-network hydrogel (FS/PAM-Gel-PDA) wound dressing composited gelatin with silicate ceramic powder with satisfactory wet adhesion, stable release of bioactive ions, hemostasis, and the ability of promoting vascular regeneration was engineered through specifically grafting dopamine to gelatin and introducing ferrous silicate ceramic powder into the hydrogel. The comprehensive experimental results substantiate that the FS/PAM-Gel-PDA has wet-adhesion strength of up to 21.78 kPa, and remains stably adherent to porcine myocardial tissues intuitively after bending, twisting, soaking in water, and stretching. The test results of ion release behavior in vitro show that the oxidation and agglomeration of ferrous silicate ceramic powder can be effectively inhibited by using dopamine to form an antioxidant layer on the surface of ceramic powder, and thus, the stable release of Fe²⁺ and SiO₄⁴⁻ effective ions can be realized. The animal experiment exhibits that FS/PAM-Gel-PDA can achieve rapid hemostasis in the lethal liver defect model. Meanwhile, the FS/PAM-Gel-PDA reveals the remarkable ability to promote wound healing in a full-thickness skin injury model, which can obviously accelerate skin re-epithelialization. To sum up, the FS/PAM-Gel-PDA has excellent wet adhesion and stable release of active ions to accelerate angiogenesis, which shows great potential in promoting wound healing.

Collagen, known for its excellent biocompatibility and biological properties, has limited in vivo maintenance duration after implantation, while hyaluronic acid faces challenges such as various complications and insufficient support for cell proliferation. In this study, an injectable hyaluronic acid/collagen (HCol) hydrogel was developed to achieve enhanced cell-material interactions and accelerated skin regeneration. Physical and chemical characterizations demonstrated that the HCol hydrogel was injectable and stable after the implantation. In vitro cell culture results illustrated that the hydrogel promoted the proliferation of human dermal fibroblasts, extracellular matrix expression and angiogenesis. The subcutaneous implantation in rats showed the superior biocompatibility of HCol hydrogel and enhanced secretion and deposition of extracellular matrix, compared with commercial hyaluronic acid dermal filler. MRI analysis showed that the hydrogel stably remained in vivo for at least three months. The histological examination and SHG signals further demonstrated that the hydrogel modulated fibroblast phenotype and stimulated vascular ingrowth and collagen synthesis, without inducing significant inflammation, swelling or erythema in vivo.

The objective of regenerative wound healing dressings is to accelerate skin tissue regeneration and restore normal physiological function at wound sites. Achieving this goal requires biomaterials capable of repairing distinct phases of wound healing in a way that balances material function, degradation, safety, and tissue growth. In this study, we introduced a novel dual-stage wound dressing system comprising methacrylic anhydride-modified recombinant humanized type III collagen (rhCol III-MA) and methacrylic anhydride-modified dopamine (DMA) (RMDM), which was synthesized through free radical polymerization and π-π stacking. Within this system, RMDM was formulated into two forms with identical compositions: hydrogel and sponge, tailored for application across various stages of wound repair. These materials displayed favorable hemocompatibility, biocompatibility, antioxidant properties, and angiogenic potential in vitro. Moreover, the in vivo experiments also demonstrated that sponges could rapidly stop the bleeding of wounds in mouse tail amputation and liver incision models. Notably, the sponge/gel (S/G) system accelerated wound healing compared to individual sponge and gel treatments in a rat full-thickness skin wound model, underscoring the synergistic benefits of combining sponge and gel materials for wound repair at different stages. Therefore, this research provides valuable insights into designing advanced biomaterials that can be tailored to specific stages of wound healing, which may have significant potential for biomedical applications.

Extrusion-based three-dimensional (3D) printing of gelatin (Gel) is crucial for fabricating bone tissue engineering scaffolds via additive manufacturing. However, the thermal instability of Gel remains a persistent challenge, as it tends to collapse at mild temperatures. Current approaches often involve simply mixing Gel particles with various materials, resulting in biomaterial inks that lack uniformity and have inconsistent degradation characteristics. In this study, acetic acid was used to dissolve Gel and polycaprolactone (PCL) separately, producing homogeneous Gel/PCL dispersions with optimal pre-treatment performance. These dispersions were then combined and hybridized with nano-hydroxyapatite (n-HA) to create a composite printing ink. By evaluating the printability of the ink, the optimal conditions were identified: a n-HA concentration of 50% (w/w), a printing temperature of 10–15 ℃, a printing pressure of 2.5 bar, and a printing speed of 7 mm/s. The resulting biomaterial inks, with a composition of 25% Gel, 25% PCL, and 50% n-HA, demonstrated excellent printability and stability, along with significantly enhanced mechanical properties. As a result, 3D scaffolds with high printability and shape fidelity can be printed at room temperature, followed by deep freezing at -80 ℃ and cross-linking with vanillin. The Gel-based composite scaffolds demonstrated excellent biocompatibility, cell adhesion, cell viability and nano-hydroxyapatite absorption in vitro. Additionally, in vivo experiments revealed that the bioactive scaffold biodegraded during implantation and significantly promoted bone regeneration at the defect site. This provides a promising strategy for treating bone defects in clinical setting. In conclusion, the Gel/PCL/n-HA biomaterial inks presented here offer an innovative solution for extrusion bioprinting in the field of bone tissue engineering.

The purpose of this study was to investigate the influence of the advanced structure of collagen on the chondrogenic differentiation of BMSCs encapsulated in collagen hydrogels, with an emphasis on MMPs which might affect the cell-material interactions. Collagen and gelatin-based hydrogels with comparable physicochemical properties but mainly distinctive in molecular structure were prepared and further utilized to load BMSCs to study the chondrogenesis. The detection results of MMPs in hydrogels with and without TIMP at both gene and protein levels suggested that MMPs were involved in cell recognition, adhesion, migration, proliferation and further remodeling of cell microenvironment. The chondrogenic gene detection, histological observation and extracellular matrix analysis indicated that the BMSCs were well differentiated into chondrocytes and maintained the phenotypes in collagen hydrogels (C group) which preserved the native structures, comparing with those results acquired from gelatin hydrogels (G group). Finally, the expression of several integrin subunits was investigated to analyze the connection of these cell membrane surface proteins and microenvironment remodeled by MMPs in collagen and gelatin hydrogels. The conclusion was drawn that the advanced structure of collagen affected the chondrogenesis of BMSCs via the cell-material interactions, among which MMPs were one of the major factors crucial to form appropriate microenvironment to modulate the BMSCs fate.

As one of the mainstream biodegradable materials, poly(butylene adipate-co-terephthalate) (PBAT) foams offer a sustainable alternative to traditional plastic foams, effectively reducing environmental pollution. However, the high cost and poor mechanical performance of PBAT foams impede their practical application. Herein, the glycidyl methacrylate-grafted biomass lignin (GML) was used to produce a PBAT/GML composite foam with good foaming performance and mechanical properties at high lignin-filling amounts by twin-screw melting free radical polymerization and supercritical CO₂ foaming process. The compatibility of GML in the PBAT matrix was improved due to the formation of ester bonds in modified lignin, endowing the PBAT/GML (PGML) composite foam with exceptional foaming performance. Additionally, the mechanical properties of PGML composite foam were remarkably enhanced due to the introduction of the abundant aromatic structures of GML and the construction of a stable covalent crosslinking network. The compressive strengths and compression modulus of the PGML foam were improved by 2.53 times and 2.47 times, while its bending strength and bending modulus were improved by 1.27 times and 3.92 times compared to the neat PBAT. This research affords a new strategy for developing low-cost biodegradable biomass PBAT/lignin composite foam materials with good foaming performance and mechanical properties.

Cellulose is widely distributed in higher plants and constitutes the most abundant natural biopolymer on Earth. Nanocellulose is a cellulose material with nanoscale dimensions, obtained through special processing and treatment. Up to now, nanocellulose has been widely investigated as a biosorbent to absorb various types of pollutants in wastewater due to its excellent properties, such as large specific surface area, antifouling behaviour, high aspect ratio, high heat resistance, excellent mechanical properties, biodegradability and biocompatibility. In addition, nanocellulose can be rationally structured by different recombination techniques such as membranes, sponges, aerogels, hydrogels and microspheres and provide specialised functionality for the adsorption of various types of pollutants from wastewater. This review introduces the basic properties, classification and modification methods of nanocellulose; discusses the preparation strategies of nanocellulose-based recombinant materials (including vacuum/pressurised filtration, sol–gel and electrospinning); reviews research progress in the adsorption of organic dyes and heavy metal Cr, as well as the separation of oil/water using nanocellulose-based recombinant materials; and explores the potential of nanocellulose in treating tannery wastewater. Finally, the problems faced by nanocellulose-based recombinant materials and future prospects are presented.

Male genitourinary dysfunction causes serious physical or mental distress, such as infertility and psychological harm, which leads to impaired quality of life. Current conventional treatments involving drug therapy, surgical repair, and tissue grafting have a limited effect on recovering the function and fertility of the genitourinary organs. To address these limitations, various biomaterials have been explored, with collagen-based materials increasingly gaining attention for reconstructing the male genitourinary system due to their superior biocompatibility, biodegradability, low antigenicity, biomimetic 3D matrix characteristics, hemostatic efficacy, and tissue regeneration capabilities. This review covers the recent biomedical applications of collagen-based materials including treatment of erectile dysfunction, premature ejaculation, penile girth enlargement, prostate cancer, Peyronie's disease, chronic kidney disease, etc. Although there are relatively few clinical trials, the promising results of the existing studies on animal models reveal a bright future for collagen-based materials in the treatment of male genitourinary diseases.

Collagen possesses high biocompatibility with all tissue and cell types in the body, enabling the creation of multifunctional composite materials for medical applications. In biomedical engineering, naturally-sourced collagen is often combined with diverse organic and inorganic bioactive components to eliminate defects and disorders in fields including orthopedics, dermatology, and more. At the same time, medical-related infection issues and the precise treatment needs of patients require collagen composite biomaterials to have antibacterial properties and customized structures. This paper reviews the antibacterial functionalization of collagen composite biomaterials in recent years, including the combination with inorganic or organic antibacterial agents, which is beneficial for preventing and controlling biological contamination in medical applications. Then, the existing problems and future development directions for the architecturalization of collagen composite materials with 3D printing were discussed, providing guidance for personalized customization of multifunctional materials to meet the specific needs of patients in the future.

The growing interest in valorizing industrial by-products has led researchers to focus on exploring different sources and optimizing collagen extraction conditions over the past decade. While bovine hide, cattle bones, pork, and pig skins remain the most abundant collagen sources, there is a growing trend in the industrial utilization of collagen from non-mammalian species. This review explores alternative marine collagen sources and summarizes emerging trends in collagen recovery from marine sources, with a particular focus on environmentally friendly methods. Additionally, this review covers the colloidal structure-forming properties of marine collagens, including foam, film, gel, and emulsion formation. It also highlights the potential and important applications of marine collagen in various food products. Based on the currently reported marine sources, collagens extracted from fish, jellyfish, and sea cucumbers were found to have the highest yield and mostly comprised type-I collagen, while crustaceans and mollusks yielded lower percentages of collagen. Traditional extraction techniques isolate collagen based on acetic acid and pepsin treatment, but they come with drawbacks such as being time-consuming, causing sample destruction, and using solvents. Conversely, marine collagen extracted using conventional methods assisted with ultrasonication resulted in higher yields and strengthened the triple-stranded helical structures. Recently, an increasing number of new applications have been found in the food industry for marine collagens, such as biodegradable film-forming materials, colloid stabilizers, foaming agents, and micro-encapsulating agents. Furthermore, collagen is a modern foodstuff and is extensively used in the beverage, dairy, and meat industries to increase the stability, consistency, and elasticity of products.

Osteoarthritis is a degenerative disease that affects articular cartilage, leading to changes on the macro and micro levels of this multi-component tissue. Understanding the processes underlying this pathology plays an important role in planning the following management tactics. Timely detection of the knee joint degradation at the level of tissue changes can prevent its progressive damage due to the early beginning of appropriate treatment. This study aimed to provide an overview of the current level of knowledge about the composition of cartilage and menisci using a wide range of different diagnostic methods. A systematic review of the literature published from 1978 to 2023 was conducted. Original studies of the knee joint cartilage (articular and meniscus) research, reporting content composition and mechanical properties, were included. Studies of the non-knee joint cartilage, tissue research other than cartilage and meniscus, or reporting treatment outcomes were excluded (n = 111). Thirty-one papers were included in this review, which reported on the composition of animal and human cartilage (articular and meniscus). The most frequently investigated parameters were quantitative proteoglycan determination and hydration level of the cartilage. Cartilage and meniscus degeneration, i.e., reduced collagen and proteoglycan content, reduced mechanical properties, and increased hydration level, was shown in every article about osteoarthritis. Among all diagnostic methods, laboratory methods (biochemical and histological analysis) are the most frequently used, compared to the instrumental ones (spectroscopy, MRI, and CT). At the same time, spectroscopy takes the lead and becomes the most common approach for determining cartilage composition (collagen and proteoglycans content).

Melamine resin (MR), traditionally synthesized using melamine and formaldehyde, is widely used in the leather industry. However, the emission of free formaldehyde poses a significant challenge for conventional MR. To address the issues of aldehyde in MR, extensive research has been conducted. This paper introduces a novel aldehyde-free MR (LTSL) retanning agent synthesized using cyanuric chloride, l-lysine, and sodium sulfanilate. The chemical structure of LTSL was analyzed via Fourier transform infrared spectroscopy, nuclear magnetic resonance, and X-ray photoelectron spectroscopy. The presence of amino, carboxyl, and sulfonic acid groups in LTSL enhanced its storability and imparted LTSL with an amphoteric character. The isoelectric point of LTSL was optimized to reach 4.37, and LTSL exhibited an appropriate size distribution with an average particle size of 254.17 nm and achieved high absorption rates of 87.77% and 95.84% for retanning and fatliquoring agents, respectively. Consequently, the thickness rate of LTSL reached up to 37%, with no detectable formaldehyde. Notably, LTSL also demonstrated excellent physical and mechanical properties, primarily attributed to the coordination and electrostatic interactions between the chrome-tanned collagen fiber and amino/carboxyl groups in LTSL. This research presents an innovative approach for developing an aldehyde-free MR retanning agent, significantly contributing to the sustainable development of leather manufacturing.

The reconstruction of critical-size calvarial defects remains a fundamental challenge. Recombinant collagen has gained significant attention in bone tissue engineering owing to its remarkable bioactivity and non-immunogenicity. Herein, we have for the first time developed a bioactive poly(ethylene glycol)-chondroitin sulfate-triple helical recombinant collagen (PEG-ChS-THRC) hydrogel for enhanced bone regeneration in cranial defects. A simple and mild crosslinking reaction of two-arm polyethylene glycol active ester (NHS-PEG-NHS), adipic dihydrazide modified chondroitin sulfate (ChS-ADH) and triple helical recombinant collagen (THRC) leads to the formation of the PEG-ChS-THRC hydrogel. The hydrogel demonstrates interconnected porous structures, enhanced mechanical strength, diminished swelling ratios and adjustable biodegradability. It possesses exceptional biocompatibility and bioactivity, significantly facilitating cell proliferation, adhesion, migration, and osteogenic differentiation of BMSCs. Micro-computed tomography (micro-CT), magnetic resonance imaging (MRI) and histological characterization of rat models with critical-size cranial defects have consistently demonstrated that the PEG-ChS-THRC hydrogel significantly promotes bone tissues regeneration. The innovative bioactive scaffold provides a remarkably improved remedy for critical-size cranial defects, holding greatly promising applications in the fields of bone tissue regeneration.

Hydrophobicity enhancement of metal-free leather, which is crucial for improving its comprehensive performance, can be achieved by using amphiphilic copolymer retanning agents. However, the relationship between the sequential structure and the hydrophobic modification effect of amphiphilic copolymers remains unclear. Herein, an amphiphilic block copolymer was synthesized using stearyl methacrylate and 2-(dimethylamino)ethyl methacrylate via atom transfer radical polymerization, and the corresponding random copolymer with similar monomer compositions and molecular weights was prepared for comparison. The aggregation behavior of block and random copolymers was investigated. DLS and TEM results indicate that the block copolymer exhibits a larger aggregate size than the corresponding random copolymer. Molecular dynamics simulations suggest that the block copolymer aggregate exhibit a thicker hydrophilic shell and more concentrated distribution of cationic DMA block than the random copolymer aggregate. Subsequently, the block and random copolymers were used for the hydrophobic modification of metal-free tanned collagen fibers (CFs). The block copolymer shows superior binding capacity to CFs than the random one because of its larger size and more concentrated charge distribution. Hence, the block copolymer can form a dense and uniform hydrophobic film on the surface of collagen fibrils and endow CFs with higher hydrophobicity than the random one. This work provides theoretical guidance for modulating the hydrophobicity of CFs by tailoring the sequential structure of amphiphilic copolymers, which is expected to inspire the manufacturing of high-performance metal-free leather.

Footwear industries generate leather waste during the operation. Some of these wastes contain chromium, which may bring environmental concerns. This study aimed to reuse finished leather waste, the major part of these hazardous wastes, via producing a composite with thermoplastic polyurethane (TPU) for shoe soles. Finished leather waste containing black dyes and pigments was used to color the TPU. The finished leather waste was fragmented, milled, micronized and blended with TPU in a ratio of 10%, 15%, and 20% w/w to produce composite materials. The composite materials were evaluated by morphological and thermal characterizations, physical–mechanical analysis, and environmental tests (leaching and solubilization), which presented that the physical–mechanical and thermal properties were within the standard of shoe soles, and the composites can be classified as non-hazardous. The composites enabled a new way of coloring polymeric matrices and reusing leather waste.

Superwetting aerogel is a promising alternative for the remediation of emulsified oily wastewater for its high porosity combined with extreme wettability enabled high separation performances to emulsion wastewater. However, it remains challenging for superwetting aerogels to accomplish high-performance dual separation to surfactant-stabilized oil-in-water (O/W) and water-in-oil (W/O) emulsions with high stability. Herein, an environmentally benign superamphiphilic composite aerogel was prepared by a green synthesis route that relied on the utilization of natural amphiphilic biomass. Collagen fibers (CFs) were utilized to construct the three-dimensional (3D) supramolecular skeleton of aerogel to provide high storage capacity of water/oil and outstanding capillary effect to boost the mass transfer. The two-dimensional (2D) lamellar structure of gelatin (Gel) was further grown on the skeleton of CFs aerogel to play the role for simultaneously enhanced demulsifying capability and spreading of emulsions. The as-prepared superamphiphilic aerogel enabled the separation of highly stable surfactant-stabilized O/W and W/O emulsions with high separation efficiency and flux. Excellent recycling performances and anti-fouling performance were also confirmed. Our investigations therefore demonstrated that the structural engineering of superamphiphilic aerogel is a promising way to realize high-performance dual separation of surfactant-stabilized O/W and W/O emulsion wastewater.

The interior environment of articular cartilage in osteoarthritis (OA) presents substantial hurdles, leading to the malfunction of chondrocytes and the breakdown of collagen II-enriched hyaline cartilage matrix. Despite this, most clinical treatments primarily provide temporary relief from OA discomfort without arresting OA progression. This study aimed to alleviate OA by developing intra-articular injectable dECM-enhanced hyaluronic (HE) microgels. The HE hydrogel was engineered and shaped into uniformly sized microgels using microfluidics and photopolymerization techniques. These microgels provided a spatiotemporal cascade effect, facilitating the rapid release of growth factors and a slower release of ECM macromolecules and proteins. This process assisted in the recovery of OA chondrocytes’ function, promoting cell proliferation, matrix synthesis, and cartilage-specific gene expression in vitro. It also effectively aided repair of the collagen II-enriched hyaline cartilage and significantly reduced the severity of OA, as demonstrated by radiological observation, gross appearance, histological/immunohistochemical staining, and analysis in an OA rat model in vivo. Collectively, the HE injectable microgels with spatiotemporal release of cartilage-specific molecules have shown promise as a potential candidate for a cell-free OA therapy approach.

The study investigates the potential of anaerobic co-digestion (AcoD) as a sustainable solution for managing putrescible organic waste generated by leather processing. Three experiments were conducted to assess the impact of various tannery wastes, pretreatment methods, and waste combinations on methane production. Experiment 1 demonstrated that co-digesting tannery wastewater primary sludge (TWPS) and fleshings significantly increased methane yield compared to digesting TWPS alone, though the addition of chromium- and vegetable-tanned leather wastes decreased yield. Experiment 2 explored TWPS pretreatment methods and found that ultrasonic pretreatment increased soluble chemical oxygen demand (SCOD) but did not significantly improve methane yield, suggesting that pretreatment may not be necessary. Experiment 3 revealed that increasing the proportion of fleshings to TWPS resulted in higher methane yield, ranging from 226.52 mL/gVS with 6% fleshings to 395.71 mL/gVS and 538.34 mL/gVS with 12% and 20% of fleshings, respectively. Additionally, this increase in fleshings also led to a reduction in digester volume. These findings highlight the importance of AcoD in addressing both environmental and economic challenges in the leather industry.

Reduced graphene oxide (rGO) films suffer from low capacitance for inner unreduced oxygen functional groups, restacking of sheets and high contact resistance. Herein, carbon spheres derived from renewable xylan were added to graphene oxide with large sheet area to fabricate film by gelation and filtration, followed by in situ reduction for high-performance flexible supercapacitor. rGO film with transverse size about 13 μm showed a good specific capacitance of 967 mF/cm² at a scanning rate of 5 mV/s and increased to 1786 mF/cm² by in situ reducing its inner part, which generally remained oxidized due to outer hindering from hydrophobic graphene. Then, by hydrothermal carbonization of xylan and activation with KOH, activated carbon sphere (aXCS) was prepared, which had a diameter of 150–200 nm and a specific capacitance of 270 F/g. The aXCS acted as spacer and connector to avoid restacking of graphene sheets and decrease interlayer contact resistance, resulting 94% increase in capacitance performance from rGO film to aXCS/rGO film. Therefore, combined in situ reduction and enhancement through compositing aXCS, the final film (aXCS/rGO-AA) showed a boosted specific capacitance of 755 mF/cm² at 1 mA/cm² in double electrode system, power density of 22.5–2250 mW/cm², and energy density of 11.88–25.2 mWh/cm². Meanwhile, aXCS/rGO-AA had outstanding cycling stability that its specific capacitance maintained 108.7% after 10,000 cycles of charge–discharge, showing promising potential in wearable and portable electronics.

The global scenario on PVC plasticizer is experiencing a drastic change from petroleum-based, toxic di-(2-ethylhexyl) phthalate (DEHP) toward renewable, non-toxic bio-alternatives. However, replacing diisodecyl phthalate (DIDP), a DEHP analogue specifically intended for plasticizing PVC automotive upholstery, with bio-alternative remains a challenge as few bio-plasticizer volatilizes from PVC as slowly as DIDP, a crucial aspect compulsorily required by automotive industry. Here, we demonstrate that covalently attaching two short esters at the α-position of all components of a traditional epoxidized fatty acid methyl ester via a two-step, hydrogen-to-ester nucleophilic substitution in a one-pot procedure yields an epoxidized fatty acid tri-ester bio-plasticizer with remarkably suppressed volatilization from PVC, and hence an extremely low fogging value comparable to DIDP. With this strategy in hand, DIDP, long deemed irreplaceable despite its toxicity and non-renewable nature, may ultimately be phased out.

Vegetable tannins are environmentally friendly tanning agents. However, they generally impart a dark colour to the tanned leather and highly contribute to the organic load in wastewaters. In this study, we employed a purification protocol separately on chestnut tannin (CT) and sulfited quebracho tannin (QT) to obtain the purified fractions (PCT and PQT). These samples were characterised by GPC, ¹H NMR, ¹³C NMR, FT-IR, and HPLC–DAD techniques and applied for tanning tests. Through the purification process, non-tannin components and smaller molecules such as gallic acid, glucopyranose, and catechin were effectively removed from CT and QT, which consequently led to the reduced moisture content, pH value, and lighter colour of purified fractions. The crust leathers processed with PCT and PQT showed desirable light shades. Moreover, the organic loads in PCT and PQT tanning wastewater were reduced by 13.5% and 19.1%, respectively, when compared to those in traditional CT and QT tanning wastewater. Additionally, the physical and mechanical characteristics of crust leathers processed with PCT and PQT were comparable to those processed with CT and QT. Thus, purification of vegetable tannins may serve as a feasible strategy for producing light-colored vegetable-tanned leather while minimizing organic pollutant discharge during the vegetable tanning process.

Fish scales, considered as low-value by-products, contain peptides and hydroxyapatite that can be applied to produce peptide chelated calcium directly. This study developed a sustainable and one-pot fabrication method for the peptide-chelated calcium from fish scale hydrolysates (FSP-Ca). During pepsin hydrolysis, the releases of peptides (FSP), calcium, and phosphate from fish scales occurred simultaneously, and the chelation was also effectively performed. After a 6-h hydrolysis, the yield of FSP was 46.18%, and the dissolution rate of calcium was 49.53%. Under the optimal conditions (pH 7, chelation time of 25 min, and chelation temperature of 48 °C), a high chelation rate of 86.16% was obtained, with a calcium content of 81.8 mg/g. The results of UV absorption, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM) confirmed the successful chelation between FSP and calcium derived from fish scales. The –NH₂, –COO^–, N–H, C=O, C–H, and –OH groups in FSP participated in the formation of FSP-Ca.

Leather dyeing is a critical step in leather manufacturing, as it is responsible for providing leather products with an eye-catching visual aspect and adequate quality properties to meet customers' expectations. This step is becoming more and more challenging as the leather industry advances hand in hand with new environmentally friendly policies and regulations to achieve a safer and healthier planet by replacing the highly polluting Cr-based leather tanning technology with greener alternatives. As a result, achieving high-performance dyeing of organic chrome-free leather is one of the bottlenecks for the sustainable development of the leather industry. Herein, we propose a novel strategy to fabricate an isocyanate-based oligomeric dye (IBD) with high coloring capabilities (component content higher than 62.8%) based on toluene 2,4-diisocyanate and reactive red dye 180. This material has been tested for the dyeing of biomass-derived aldehyde (BDA)-tanned leather with excellent outcomes. The experimental results showed that the crust leather dyed with our novel IBD dyeing agent had higher color fastness and better fullness than the leather dyed with conventional anionic (CAD) or reactive red 180 (RRD-180) dyes. These excellent and promising results open new avenues in manufacturing high-performance organic Cr-free leather products and help to ensure the sustainable transition of the leather industry from Cr-based leather tanning to more sustainable alternatives, maintaining the final quality of the leather products.

It is urgent to develop low-reflection electromagnetic interference shielding material to shield electromagnetic waves (EMW) and reduce their secondary radiation pollution. Herein, an electromagnetic interference shielding nanofiber film is composed of ZnO and carbon nanofiber (CNF) via electrospinning and carbonization approachs, and subsequently coating perfuorooctyltriethoxysilane as a protective layer. On the one hand, ZnO coated by porous carbon, which is derived from ZIF-8, endows the nanofiber film low reflection property through optimizing impedance matching between free space and the nanofiber film. On the other hand, the nanofiber film possesses high electromagnetic interference shielding efficiency, which is beneficial by excellent electrical conductivity of CNF derived from waste leather scraps. Furthermore, the nanofiber film involves abundant interface, which contributes to high interfacial polarization loss. Thus, the nanofiber film with a thickness of 250 μm has electrical conductivity of 53 S/m and shielding efficiency of 50 dB. The reflection coefficient of the nanofiber film is inferior to 0.4 indicates that most of EMW are absorbed inside the materials and the nanofiber film is effective in reducing secondary radiation contamination of electromagnetic waves. Fortunately, the nanofiber film exhibits outstanding solar harvesting performance (106 ℃ at 1 sun density) and good self-cleaning performance, which ensure that the nanofiber film can work in harsh environments. This work supplies a credible reference for fabricating low-reflection electromagnetic shielding nanofiber film to reduce secondary radiation pollution and facilitates the upcycling of waste leather scraps.

An environmentally friendly method using real or artificial bovine milk permeate to both depilate and preserve sheepskins has been reported which completely and cleanly removed the wool from the hair follicle and had no detrimental effects on the skin. A proteomic analysis, assessing the relative abundance of proteins in matched permeate-depilated and chemically depilated (sulfide) sheepskins, showed variations in the levels of specific collagen types in the skin's basement membrane and other proteins associated with the follicles. These findings were corroborated by biochemical analyses of matched permeate depilated and raw skin samples, and provide clues to the mechanism of non-invasive and complete depilation. They also support the observation that permeate-depilated skins were smoother than their sulfide-depilated counterparts and resulted in leather with a superior surface.

Leather, a by-product of the meat industry, has unique strength, elasticity, water vapor permeability, resistance to abrasion, durability, and longevity. In the background of ISO 15115:2019, the authenticity of leather has become a subject matter of concern. There is a need to distinguish leather (animal origin) from other leather-like materials derived from fossil fuel (PU, faux leather, etc.) and agro-product-driven vegan materials, which are also sold in the market as leather. For this purpose, this work relies on the signature FTIR bands of collagen (the skin-making protein) as a starting point to distinguish between animal origin and rest. A detailed investigation of all types of materials used in lifestyle products has been carried out to assess the boundary lines of this hypothesis. It is reasonably concluded that the signature Amide I, II, and III bands of collagen occurring at 1600, 1500, and 1200 cm⁻¹ could serve as the first line to distinguish against all materials other than nylon and in the case of nylon, and the Amide A band at 3200 cm⁻¹, forms the basis for differentiation from nylon. In essence, the FTIR spectra can be used as a robust, easy and unambiguous technique to distinguish leather from leather-like materials currently available on the market.

The limitations of native collagen, such as thermal stability and solubility in physiological environments, can be improved by applying bioconjugation and synthetic chemistry techniques. However, the exquisite control of the modification site of collagen remains a challenge. In this work, pH-responsive poly(acrylic acid) (PAA) with different chain lengths was attached to the N-terminal α-amino groups of succinylated collagen using a site-specific modification strategy. Additionally, the structure, thermal stability, and pH sensitivity of succinylated collagen were explored. The modification rate of amino groups in the succinylated collagen-PAA bioconjugate (SPSC-PAA) was evaluated by the 2,4,6-trinitrobenzene sulfonic acid assay. The impact of N-terminal modification of PAA and its chain length on the thermal stability of collagen was explored by CD and DSC. These techniques revealed that the thermal stability of SPSC-Col is pH-responsive and closely related to the chain length of grafted PAA. The pH sensitivity of SPSC-PAA was further explored by rheology and turbidity. Subsquently, the critical pH and isoelectric point of SPSC-PAAs were also examined by turbidity and isoelectric point titration, respectively. This work provides a new insight into the N-terminal modification of collagen on its properties.

Biodegradability is a crucial indicator to evaluate the sustainability of leather. Herein, a rapid method for biodegradation test in an aqueous medium by measuring biochemical oxygen demand was used to determine the biodegradability of leather from different tanning methods, tanning conditions and process stages. In addition, the difference in biodegradability between leather and leather-like synthetic materials were investigated. Chrome-free tanned leather showed higher degree of biodegradation and faster biodegradation rate than chrome tanned leather. Among them, leathers tanned with biomass-based tanning agents were much easier to biodegrade because the crosslinking network of tanned leather constructed with biomass was more susceptible to microbial attack. The enhancement of tanning effects through changing tanning methods and conditions (such as tanning agent dosage, pH and temperature) resulted in the decline of leather biodegradability. Future development of novel chrome-free tanning technologies should balance between these two aspects. The biodegradability of leather from tanning to post-tanning to finishing showed a stepwise decrease because various chemicals were applied and bound to leather during processing. Even so, finished leather still possessed significantly higher biodegradability compared to leather-like PU and microfiber synthetic materials, demonstrating superior environmental sustainability of natural leather. The results are expected to provide support for the evaluation of the ecological properties of leather and green upgrade of the leather industry.

The regeneration of articular cartilage posed a formidable challenge due to the restricted treatment efficacy of existing therapies. Scaffold-based tissue engineering emerges as a promising avenue for cartilage reconstitution. However, most scaffolds exhibit inadequate mechanical characteristics, poor biocompatibility, or absent cell adhesion sites. In this study, cartilage-like protein-polysaccharide hybrid hydrogel based on DOPA-modified hyaluronic acid, bovine type I collagen (Col I), and recombinant humanized type II collagen (rhCol II), denoted as HDCR. HDCR hydrogels possessed the advantage of injectability and in situ crosslinking through pH adjustment. Moreover, HDCR hydrogels exhibited a manipulable degradation rate and favorable biocompatibility. Notably, HDCR hydrogels significantly induced chondrogenic differentiation of rabbit bone marrow mesenchymal stem cells in vitro, as demonstrated by the upregulation of crucial chondrogenic genes (type II collagen, aggrecan) and the abundant accumulation of glycosaminoglycan. This approach presented a strategy to manufacture injectable, biodegradable scaffolds based on cartilage-like protein-polysaccharide polymers, offering a minimally invasive solution for cartilage repair.