Improved mechanical properties and thermal-stability of collagen fiber based film by crosslinking with casein, keratin or SPI: Effect of crosslinking process and concentrations of proteins

Development of Innovative Biocomposites with Collagen, Keratin and Hydroxyapatite for Bone Tissue Engineering

This study follows the process for the development of an innovative biomimetic composite derived from bovine collagen with keratin, with hydroxyapatite being hybridized into its architecture, and it builds a comprehensive evaluation of the composite's characteristics. The novel biomimetic materials are tailored with special traits to be achieved for the repair of osteochondral defects (OCDs). The purpose of the present research is to create a reliable effective alternative to existing bone graft materials while leveraging the intrinsic properties of the components for enhanced osteoinduction and integration. The composites were characterized based on their morphological properties, including water absorption, through scanning electron microscopy (SEM), and their structural properties were characterized by Fourier-Transform Infrared Spectroscopy (FTIR). Biological performance was assessed in vitro using human bone marrow mesenchymal stem cells (BMSCs), focusing on cytotoxicity, cell viability, and the ability to support cell colonization with forthcoming results. This in vivo study illustrates the real potential that this class of novel composites exhibits in regard to bone and cartilage tissue engineering and encourages further exploration and development for future clinical applications.

The Effect of Nanoscale Modification of Nisin by Different Milk-Derived Proteins on Its Physicochemical Properties and Antibacterial Activity

Nisin is used as a natural food preservative because of its broad-spectrum antimicrobial activity against Gram-positive bacteria. However, free nisin is susceptible to various factors that reduce its antimicrobial activity. Milk protein, a protein derived from milk, has self-assembly properties and is a good carrier of bioactive substances. In this study, lactoferrin-nisin nanoparticles (L-N), bovine serum albumin-nisin nanoparticles (B-N), and casein-nisin nanoparticles (C-N) were successfully prepared by a self-assembly technique, and then their properties were investigated. The studies revealed that lactoferrin (LF) and nisin formed L-N mainly through hydrophobic interactions and hydrogen bonding, and L-N had the best performance. The small particle size (29.83 ± 2.42 nm), dense reticular structure, and good thermal stability, storage stability, and emulsification of L-N laid a certain foundation for its application in food. Further bacteriostatic studies showed that L-N enhanced the bacteriostatic activity of nisin, with prominent inhibitory properties against Listeria monocytogenes, Staphylococcus aureus, and Bacillus cereus, which mainly disrupted the cell membrane of the bacteria. The above results broaden our understanding of milk protein-nisin nanoparticles, while the excellent antibacterial activity of L-N makes it promising for application as a novel food preservative, which will help to improve the bioavailability of nisin in food systems.

Enhancing the properties of soy protein isolate and dialdehyde starch films for food packaging applications through tannic acid crosslinking

The utilization of naturally derived biodegradable polymers, including proteins, polysaccharides, and polyphenols, holds significant promise in addressing environmental concerns and reducing reliance on nonrenewable resources. This study aimed to develop films with enhanced UV resistance and antibacterial capabilities by covalently cross-linking soy protein isolate (SPI) with dialdehyde starch (DAS) through the incorporation of tannic acid (TA). The covalent crosslinking of TA with DAS and SPI was shown to establish a stable chemical cross-linking network. The tensile strength of the resulting SPI/DAS/15TA film exhibited a remarkable increase of 208.27 % compared to SPI alone and 52.99 % compared to SPI/DAS film. Notably, the UV absorption range of SPI/DAS/10TA films extended from 200 nm to 389 nm. This augmentation can be attributed to the oxidation of TA's phenolic hydroxyl groups to quinone under alkaline conditions, which then facilitated cross-linking with the SPI chain via Michael addition and Schiff base reactions. Furthermore, the film demonstrated robust antibacterial properties due to the incorporation of TA. Collectively, the observed properties highlight the significant potential of the SPI/DAS/10TA film for applications in food packaging, where its enhanced mechanical strength, UV resistance, and antibacterial characteristics can contribute to improved product preservation and safety.

A highly biocompatible CE-crosslinked collagen implant with exceptional anti-calcification and collagen regeneration capabilities for aging skin rejuvenation

Skin aging, a complex and inevitable biological process, results in wrinkles, dermal laxity, and skin cancer, profoundly influencing appearance and overall health. Collagen serves as the fundamental element of the dermal matrix; nevertheless, collagen is susceptible to enzymatic degradation within the body. Crosslinking is employed to enhance the physicochemical properties of collagen. However, conventional crosslinking agents may harbor potential issues such as cytotoxicity and calcification risks, constraining their application in the biomedical field. Therefore, we have for the first time developed a highly biocompatible CE-crosslinked collagen implant with exceptional anti-calcification and collagen regeneration capabilities for aging skin rejuvenation. A novel collagen crosslinking agent (CE) was synthesized through a reaction involving chitosan quaternary ammonium salt with 1,4-butanediol diglycidyl ether. Compared to collagen crosslinked with glutaraldehyde (GA), the CE-crosslinked collagen implant exhibited notable stability and durability. The implant demonstrated excellent injectability and viscosity, resisting displacement after implantation. Additionally, the CE-crosslinked collagen implant displayed superior biocompatibility, effectively promoting the proliferation and adhesion of HFF-1 cells compared with the GA-crosslinked collagen. The CE-crosslinked collagen represented a safer and more biologically active implant material. In vivo experiments further substantiated that the implant significantly facilitated collagen regeneration without inducing calcification. The innovative collagen implant has made substantial strides in enhancing aesthetics and reducing wrinkles, presenting the potential for revolutionary progress in the fields of skin rejuvenation and collagen regeneration.

Animal derived biopolymers for food packaging applications: A review

It is essential to use environment-friendly, non-toxic, biodegradable and sustainable materials for various applications. Biopolymers are derived from renewable sources like plants, microorganisms, and agricultural wastes. Unlike conventional polymers, biopolymer has a lower carbon footprint and contributes less to greenhouse gas emission. All biopolymers are biodegradable, meaning natural processes can break them down into harmless products such as water and biomass. This property is of utmost importance for various sustainable applications. This review discusses different classifications of biopolymers based on origin, including plant-based, animal-based and micro-organism-based biopolymers. The review also discusses the desirable properties that are required in materials for their use as packaging material. It also discusses the different processes used in modifying the biopolymer to improve its properties. Finally, this review shows the recent developments taking place in using specifically animal origin-based biopolymer and its use in packaging material. It was observed that animal-origin-based biopolymers, although they possess unique properties however, are less explored than plant-origin biopolymers. The animal-origin-based biopolymers covered in this review are chitosan, gelatin, collagen, keratin, casein, whey, hyaluronic acid and silk fibroin. This review will help in renewing research interest in animal-origin biopolymers. In summary, biopolymer offers a sustainable and environment-friendly alternative to conventional polymers. Their versatility, biocompatibility will help create a more sustainable future.

Advances in transglutaminase cross-linked protein-based food packaging films; a review

Pushed by the environmental pollution and health hazards of plastic packaging, the development of biodegradable food packaging films (FPFs) is a necessary and sustainable trend for social development. Most protein molecules have excellent film-forming properties as natural polymer matrices, and the assembled films have excellent barrier properties, but show defects such as low water resistance and poor mechanical properties. In order to improve the performance of protein-based films, transglutaminase (TG) is used as a safe and green cross-linking (CL) agent. This work covers recent developments on TG cross-linked protein-based FPFs, mainly comprising proteins of animal and plant origin, including gelatin, whey protein, zein, soy proteins, bitter vetch protein, etc. The chemical properties and reaction mechanism of TG are briefly introduced, focusing on the effects of TG CL on the physicochemical properties of different protein-based FPFs, including barrier properties, water resistance, mechanical properties and thermal stability. It is concluded that the addition of TG can significantly improve the physical and mechanical properties of protein-based films, mainly improving their water resistance, barrier, mechanical and thermal properties. It is worth noting that the effect of TG on the properties of protein-based films is not only related to the concentration of TG added, but also related to CL temperature and other factors. Moreover, TG can also be used in combination with other strategies to improve the properties of protein-based films.

Optimization of food-grade colloidal delivery systems for thermal processing applications: a review

Colloidal delivery systems are widely used in the food industry to enhance the dispersibility, stability, efficacy, or bioavailability. However, when exposed to the high temperature, delivery systems are often prone to degradation, which limits its application in thermal processing. In this paper, the effects of thermal processing on the performance of traditional protein-based or starch-based delivery systems are firstly described, including the molecular structure changes of proteins, starches or lipids, and the degradation of embedded substances. These effects are unfavorable to the application of the delivery system in thermal processing. Then, strategies of improving the heat resistance of food grade colloid delivery system and their use in frying, baking and cooking food are mainly introduced. The heat resistance of the delivery system can be improved by a variety of strategies, including the development of new heat-resistant materials, the addition of heat-resistant coatings to the surface of delivery systems, the cross-linking of proteins or starches using cross-linking agents, the design of particle structures, the use of physical means such as ultrasound, or the optimization of the ingredient formula. These strategies will help to expand the application of heat-resistant delivery systems so that they can be used in real thermal processing.

A facile strategy to fabricate high-barrier, water- and oil-repellent paper with carboxymethyl cellulose/collagen fiber/modified polyvinyl alcohol

Due to the increasingly serious environmental and human health hazards brought by traditional food packaging materials, paper-based packaging materials have become increasingly popular among consumers in recent years. Currently, the fabrication of fluorine-free degradable water- and oil-repellent paper using low-cost bio-based polymers by a simple method is a hot subject in the field of food packaging. In this work, we used carboxymethyl cellulose (CMC), collagen fiber (CF), and modified polyvinyl alcohol (MPVA) to create coatings that were impervious to water and oil. The homogeneous mixture of CMC and CF generated electrostatic adsorption to impart excellent oil repellency to the paper. PVA was chemically modified by sodium tetraborate decahydrate, and the MPVA coating imparted excellent water-repellent properties to the paper. Finally, the water- and oil-proof paper showed excellent water repellency (Cobb value: 1.12 g/m²), oil repellency (kit rating: 12/12), low air permeability (0.3 μm/Pa·s), and stronger mechanical properties (4.19 kN/m). This non-fluorinated degradable water- and oil-repellent paper with high barrier properties prepared by a convenient method is expected to be in widespread use in the food packaging field.

The Hydrolysis of Pigment-Protein Phycoerythrin by Bromelain Enhances the Color Stability

Phycoerythrin (PE) is a natural protein-pigment complex with a strong pink color, but it is sensitive to thermal and light variations. In this study, PE was extracted from Porphyra haitanensis in a yield of 0.2% (w/w). The phycoerythrin hydrolysates (PEH) (3-10 kDa) were prepared by enzymatic hydrolysis of PE with bromelain (8000 U/g) at 47 °C for 30 min, with a degree of hydrolysis (DH) of 11.57 ± 0.39% and a color degradation rate of 7.98 ± 0.39%. The physicochemical properties of PEH were evaluated. The UV and fluorescence spectra indicated that bromelain changed the microenvironment around phycoerythrobilin (PEB). The infrared spectrum revealed that the bromelain hydrolysis increased the α-helix content of PEH. The scanning electron microscope showed that bromelain destroyed the dense and smooth structure of PE, resulting in irregular porous structures. The radical scavenging activities of DPPH and ABTS of PEH were increased relative to that of PE (p < 0.05). The thermal (50-80 °C)-, UV (0.5-3 h)-, visible light irradiation (2-8 h)-, and metal ion exposing stabilities of PEH were significantly improved (p < 0.05). This study provides a potential scheme for overcoming the sensitivity of PE to thermal and light variations and facilitates PEH as a natural colorant ingredient in food and pigment applications.

Protein Stability: Enhancement and Measurement

This chapter defines protein stability, emphasizes its importance, and surveys the field of protein stabilization, with summary reference to a selection of 2014-2021 publications. One can enhance stability, particularly by protein engineering strategies but also by chemical modification and by other means. General protocols are set out on how to measure a given protein's (i) kinetic thermal stability and (ii) oxidative stability and (iii) how to undertake chemical modification of a protein in solution.

Aligned nanofibrous collagen membranes from fish swim bladder as a tough and acid-resistant suture for pH-regulated stomach perforation and tendon rupture

Background

Wound closure in the complex body environment places higher requirements on suture’s mechanical and biological performance. In the scenario of frequent mechanical gastric motility and extremely low pH, single functional sutures have limitations in dealing with stomach bleeding trauma where the normal healing will get deteriorated in acid. It necessitates to advance suture, which can regulate wounds, resist acid and intelligently sense stomach pH.

Methods

Based on fish swim bladder, a double-stranded drug-loaded suture was fabricated. Its cytotoxicity, histocompatibility, mechanical properties, acid resistance and multiple functions were verified. Also, suture’s performance suturing gastric wounds and Achilles tendon was verified in an in vivo model.

Results

By investigating the swim bladder’s multi-scale structure, the aligned tough collagen fibrous membrane can resist high hydrostatic pressure. We report that the multi-functional sutures on the twisted and aligned collagen fibers have acid resistance and low tissue reaction. Working with an implantable “capsule robot”, the smart suture can inhibit gastric acid secretion, curb the prolonged stomach bleeding and monitor real-time pH changes in rabbits and pigs. The suture can promote stomach healing and is strong enough to stitch the fractured Achilles tendon.

Conclusions

As a drug-loaded absorbable suture, the suture shows excellent performance and good application prospect in clinical work.

Milk protein-based active edible packaging for food applications: An eco-friendly approach

Whey and casein proteins, in particular, have shown considerable promise in replacing fossil-based plastics in a variety of food applications, such as for O₂ susceptible foods, thereby, rendering milk proteins certainly one of the most quality-assured biopolymers in the packaging discipline. Properties like excellent gas barrier properties, proficiency to develop self-supporting films, adequate availability, and superb biodegradability have aroused great attention toward whey and other milk proteins in recent years. High thermal stability, non-toxicity, the ability to form strong inter cross-links, and micelle formation, all these attributes make it a suitable material for outstanding biodegradability. The unique structural and functional properties of milk proteins make them a suitable candidate for tailoring novel active package techniques for satisfying the needs of the food and nutraceutical industries. Milk proteins, especially whey proteins, serve as excellent carriers of various ingredients which are incorporated in films/coatings to strengthen barrier properties and enhance functional properties viz. antioxidant and antimicrobial. In this review, the latest techniques pertaining to the conceptualization of active package models/ systems using milk proteins have been discussed. Physical and other functional properties of milk protein-based active packaging systems are also reviewed. This review provides an overview of recent applications of milk protein-sourced active edible packages in the food packaging business.

A rethinking of collagen as tough biomaterials in meat packaging: assembly from native to synthetic

Due to the high moisture-associated typical rheology and the changeable and harsh processing conditions in the production process, packaging materials for meat products have higher requirements including a sufficient mechanical strength and proper ductility. Collagen, a highly conserved structural protein consisting of a triple helix of Gly-X-Y repeats, has been proved to be suitable packaging material for meat products. The treated animal digestive tract (i.e. the casing) is the perfect natural packaging material for wrapping meat into sausage. Its thin walls, strong toughness and impact resistance make it the oldest and best edible meat packaging. Collagen casing is another wisdom of meat packaging, which is made by collagen fibers from hide skin, presenting a rapid growth in casing market. To strengthen mechanical strength and barrier behaviors of collagen-based packaging materials, different physical, chemical, and biological cross-linking methods are springing up exuberantly, as well as a variety of reinforcement approaches including nanotechnology. In addition, the rapid development of biomimetic technology also provides a good research idea and means for the promotion of collagen's assembly and relevant mechanical properties. This review can offer some reference on fundamental theory and practical application of collagenous materials in meat products.

Fabrication of high-strength, flexible, porous collagen-based scaffolds to promote tissue regeneration

Collagen-based scaffolds lack mechanical strength, flexibility, and tunable pore structure, affecting tissue repair outcomes and restricting their wide clinical application. Here, two kinds of scaffolds were prepared by a combination of vacuum homogenization, natural air drying, water soaking, lyophilization, and crosslinking. Compared with the scaffolds made of collagen molecules (Col-M), the scaffolds made of collagen aggregates (Col-A) exhibited higher mechanical strength (ultimate tensile strength: 1.38 ​± ​0.26 ​MPa vs 15.46 ​± ​1.55 ​MPa), stronger flexibility, advanced cell adhesion, survival, and proliferation. Subcutaneous implantation in rats showed that Col-A scaffolds promoted cell infiltration, macrophage polarization, and vascularization. Furthermore, the Col-A scaffolds inhibited abdominal bulges due to their adequate mechanical support, and they also promoted vascularized muscle regeneration in a rat abdominal hernia defect model. Our study provides a novel strategy for generating high-strength, flexible, porous collagen-based scaffolds, which can be applied to tissue repair with mechanical strength requirements. It broadens their application range in the field of regenerative medicine.

Effects of enzymatic cross-linking combined with ultrasound on the oil adsorption capacity of chickpea protein

In order to improve the oil adsorption capacity of chickpea protein, enzymatic cross-linking combined ultrasound was used to modify chickpea protein. Electrophoretic results showed that enzymatic cross-linking made the protein bands thinner, but ultrasound had no significant effect. The oil adsorption capacity of chickpea protein increased from 1.88 to 2.43 g/g; the surface hydrophobicity increased from 3933 to 4575; the zeta potential and emulsification performance were improved.After enzymatic cross-linking, the content of the free sulfhydryl group and emulsifying stability were decreased, and the particle size and the content of disulfide bonds were increased.After ultrasonic treatment, these properties showed an opposite trend. Fourier Transform Infrared Spectroscopy showed that β-turn and random coil increased, the structure of protein became more loose and disordered. These results indicate that enzymatic cross-linking combined with ultrasound improves the functional properties of chickpea protein and extends its application.

Formation of lysozyme-caseinate heteroprotein complexes for encapsulation of lysozyme by spray-drying: Effect of mass ratio and temperature

The formation of heteroprotein complexes obtained by the interactions between sodium caseinate (CAS) and lysozyme (LYS) at pH 7 was investigated by using turbidimetric analysis, particle size distribution, and zeta potential at different CAS/LYS ratios. Moreover, isothermal titration calorimetry (ITC) was used to determine the type and magnitude of the energies involved in the CAS/LYS complexation process and evaluated the thermodynamic behavior of their complexation. Results revealed that the structure of CAS/LYS complexes drastically changed when CAS/LYS ratio increased to 1.0 and the structuring stages were characterized by exothermic signals and were controlled by favorable enthalpy changes due to electrostatic interactions between both proteins. In addition, the interaction between two proteins was temperature-dependent and mainly entropy-driven, which was verified by molecular dynamics (MD) simulations, and the hydrophobic interactions and hydrogen bonding were shown to play an important role in CAS/LYS interactions. Furthermore, CAS/LYS complexes showed minimum LYS enzymatic activity at CAS/LYS ratio 1.0. Though spray-drying of CAS/LYS complexes with ratio 1.0, the LYS activity in reconstituted solution was recovered >80 % of initial activity after calcium chloride addition. The present study provides useful information about CAS/LYS complexation and binding processes, which could facilitate their application in antimicrobial edible food packaging.

Performance and Structure Evaluation of Gln-Lys Isopeptide Bond Crosslinked USYK-SPI Bioplastic Film Derived from Discarded Yak Hair

To reduce the waste from yak hair and introduce resource recycling into the yak-related industry, an eco-friendly yak keratin-based bioplastic film was developed. We employed yak keratin (USYK) from yak hair, soy protein isolate (SPI) from soybean meal as a film-forming agent, transglutaminase (EC 2.3.2.13, TGase) as a catalytic crosslinker, and glycerol as a plasticizer for USYK-SPI bioplastic film production. The structures of the USYK-SPI bioplastic film were characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and X-Ray diffraction (XRD). The mechanical properties, the thermal behavior, light transmittance performance, and water vapor permeability (WVP) were measured. The results revealed that the added SPI possibly acted as a reinforcement. The formation of Gln-Lys isopeptide bonds and hydrophobic interactions led to a stable crosslinking structure of USYK-SPI bioplastic film. The thermal and the mechanical behaviors of the USYK-SPI bioplastic film were improved. The enhanced dispersion and formation of co-continuous protein matrices possibly produced denser networks that limited the diffusion of water vapor and volatile compounds in the USYK-SPI bioplastic films. Moreover, the introduction of SPI prompted the relocation of hydrophobic groups on USYK molecules, which gave the USYK-SPI bioplastic film stronger surface hydrophobicity. The SPI and USYK molecules possess aromatic amino residuals (tyrosine, phenylalanine, tryptophan), which can absorb ultraviolet radiation. Thus, the USYK-SPI bioplastic films were shown to have an excellent UV barrier. The synergy effect between USYK and SPI is not only able to improve rigidity and the application performance of keratin-based composite film but can also reduce the cost of the keratin-based composite film through the low-cost of the SPI alternative which partially replaces the high-cost of keratin. The data obtained from this research can provide basic information for further research and practical applications of USYK-SPI bioplastic films. There is an increasing demand for the novel USYK-SPI bioplastic film in exploit packaging material, biomedical materials, eco-friendly wearable electronics, and humidity sensors.

Collagen Fibril-Assembled Skin-Simulated Membrane for Continuous Molecular Separation

A skin-simulated thin-film-composite membrane was fabricated using a vacuum-assisted interfacial polymerization method. A negatively charged surface-selective layer on a polyacrylonitrile (PAN) substrate was cross-linked using trimesoyl chloride to form polyamide and polyester with a three-layer structure that was similar to skin. The loading of collagen fibrils assembled on the membrane surface was varied, and a selective layer was obtained, of which the thickness, morphology, and hydrophilicity can be manipulated. The optimal membrane decorated with 0.5 mg of collagen fibril had a selective layer thickness of around 130 nm with pure water permeability up to 84.7 LMH bar^-1. Furthermore, the membrane exhibited impressive rejections toward dyes (Congo red with a molecular weight of 696.68 Da: 99.6%, reactive blue 19 with a molecular weight of 626.54 Da: 99.8%, and Coomassie blueG-250 with a molecular weight of 854.02 Da: 98.6%) while high permeations of Na₂SO₄ and NaCl were achieved. This facile strategy provides a useful guideline for constructing bionic membranes through biomaterials.

A Collagen Basketweave from the Giant Squid Mantle as a Robust Scaffold for Tissue Engineering

The growing applications of tissue engineering technologies warrant the search and development of biocompatible materials with an appropriate strength and elastic moduli. Here, we have extensively studied a collagenous membrane (GSCM) separated from the mantle of the Giant squid Dosidicus Gigas in order to test its potential applicability in regenerative medicine. To establish the composition and structure of the studied material, we analyzed the GSCM by a variety of techniques, including amino acid analysis, SDS-PAGE, and FTIR. It has been shown that collagen is a main component of the GSCM. The morphology study by different microscopic techniques from nano- to microscale revealed a peculiar packing of collagen fibers forming laminae oriented at 60-90 degrees in respect to each other, which, in turn, formed layers with the thickness of several microns (a basketweave motif). The macro- and micromechanical studies showed high values of the Young's modulus and tensile strength. No significant cytotoxicity of the studied material was found by the cytotoxicity assay. Thus, the GSCM consists of a reinforced collagen network, has high mechanical characteristics, and is non-toxic, which makes it a good candidate for the creation of a scaffold material for tissue engineering.

Self-Assembly of Phycoerythrin with Oligochitosan by Electrostatic Interaction for Stabilization of Phycoerythrin

Phycoerythrin (PE) is a natural water-soluble pigment protein with characteristic phycobilins and is sensitive to thermal and light environmental changes. In this study, PE was extracted from Porphyra haitanensis and PE-oligochitosan complexes (POC) were fabricated by a self-assembly approach. The effects of cationic oligochitosan on the binding interaction, structure, size distribution, and color stability of PE were evaluated. The stoichiometric number n was calculated to be 21.67 ± 2.65 (oligochitosan/PE) and the binding constant K was (6.47 ± 0.48) × 10⁵ M^-1. Cationic oligochitosan could electrostatically interact with PE and affect the PE structure by increasing the α-helix content. In addition, high concentrations of oligochitosan led to the formation of dense phycoerythrin protein granules. Moreover, at a reaction ratio of 20.0:1 (oligochitosan/PE), being approximately the predicted stoichiometric number n, the thermal stability (40-80 °C), natural light stability, and ultraviolet light irradiation (254 nm) stability of the POC were improved. This study provides an approach to reduce the susceptibility of PE upon environmental changes by forming a stable self-assembly complex, which will promote the application of PE as a natural pigment protein in food and chemical applications.

Developing exquisite collagen fibrillar assemblies in the presence of keratin nanoparticles for improved cellular affinity

Recently, the collagen-keratin (CK) composites have received much attention for the purpose of biomedical applications due to the intrinsic biocompatibility and biodegradability of these two proteins. However, few studies have reported the CK composites developed by the self-assembly approach and the influence of the keratin on the collagen self-assembly in vitro was still unknown. In this study, the keratin nanoparticles (KNPs) were successfully prepared by the reduction method, and we focused on investigating the effect of the varying concentrations of KNPs on the mechanism of the fibrillogenesis process of collagen. The intermolecular interaction between the two proteins revealed by the ultraviolet spectroscopy, Fourier transform-infrared (FT-IR) spectroscopy and circular dichromatic (CD) spectroscopy showed that KNPs would interact with the collagen, and keratin significantly influenced the hydrogen bonding interaction existed in collagen molecules. The SEM images exhibited the formation of exquisite fibrillar networks after incorporating the KNPs into collagen, and it was conspicuous that the KNPs could uniformly distribute on the surface of collagen fibrils via electrostatic interaction, for both of the two proteins possessed many charged moieties. In addition, the AFM images confirmed the presence of the characteristic D-periodicity of collagen fibrils, indicating that the introduction of KNPs did not disrupt the self-assembly nature of the native collagen. The cell adhesion, proliferation and migration experiments on the CK fibrils were also performed in this study. The results demonstrated that the CK composites showed a better cellular affinity compared with the collagen, thus it might be a promising candidate for the biomedical applications.

Effects of Gamma Radiation-Induced Crosslinking of Collagen Type I Coated Dental Titanium Implants on Osseointegration and Bone Regeneration

This study aimed to compare two methods of crosslinking collagen type I on implanted titanium surfaces, that is, using glutaraldehyde (GA) or gamma-rays (GRs), in a beagle dog model. For in vivo experiments, implants were allocated to three groups and applied to mandibular bone defects in beagle dogs; Group SLA; non-treated Sandblasted, large grit, acid-etched (SLA) implants, Group GA; SLA implants coated with GA crosslinked collagen type I, Group GR; SLA surface implants coated with collagen type I and crosslinked using 25 kGy of ⁶⁰Co gamma radiation. New bone μCT volumes were obtained, and histologic and histometric analyses were performed in regions of interest. The GR group had significantly better new bone areas (NBAs) and bone to implant contact (BIC) results than the SLA group (p < 0.05), but the GA and GR groups were similar in this respect. New bone volumes and inter-thread bone densities (ITBD) were non-significantly different in the three groups (p > 0.05). Within the limits of this study, gamma-ray collagen crosslinking on titanium implants can be considered a substitute for glutaraldehyde crosslinking.

Cross-linking of carbonic anhydrase and formate dehydrogenase based on amino acid specific recognition: Conversion of carbon dioxide to formic acid

Inspired by the cascades performed in vivo, the assembly of multiple enzymes in vitro has strongly moved into the focus of researchers in the field of biocatalysis. In this study, a new, mild and accurate enzyme cross-linking method is revealed. Microbial transglutaminase (MTG) acts as a "cross-linking medium" by identifying the amide group of the glutamine and the primary amine group of lysine in the artificial peptide tags specifically to form an iso-peptide bond. Here, carbonic anhydrase (CA) and formate dehydrogenase (FDH) with different peptide tags that can be recognized by MTG were linked together to obtain different proportions of cross-linked enzymes for efficient conversion of greenhouse gas carbon dioxide to formic acid. After cross-linking, we obtained "one-to-one" and "one-to-more" cross-linked enzyme aggregates. There is a minor residual loss of the two enzymes, the remaining enzyme activity of CA is more than 93%, and the remaining enzyme activity of FDH is more than 84%. In particular, the overall catalytic efficiency of the cross-linked enzyme is increased by 5.8 times compared with free enzymes and the thermal stability of FDH at different temperatures is improved. The applied strategy demonstrates the potential application of MTG in multi-enzyme assembly and synthetic biology.

An understanding of the changes in water holding capacity of rehydrated shiitake mushroom (Lentinula edodes) from cell wall, cell membrane and protein

Water holding capacity (WHC) is an important factor for the evaluation of rehydrated shiitake mushroom as WHC largely affects sensory attributes. Here, WHC of the rehydrated shiitake mushroom as affected by different hot-air drying temperature was investigated from aspects of cell membrane integrity, status of cell wall fibrous material and protein denaturation. Among the three factors, protein denaturation played the most important role to affect the WHC of rehydrated mushroom as protein denaturation was closely related to the maintenance of porous structure after rehydration. Effect of status of the cell wall fibrous material to the WHC changes was relatively weak and was largely correlated to the WHC changes at high temperature (>80 °C). Cell membrane was unlikely to contribute to WHC changes of the rehydrated shiitake mushroom due to the loss of integrity.

Mild Enzyme-Induced Gelation Method for Nanoparticle Stabilization: Effect of Transglutaminase and Laccase Cross-Linking

Low-environment-sensitive nanoparticles were prepared by enzymatic cross-linking of electrostatic complexes of dextran-grafted whey protein isolate (WPI-Dextran) and chondroitin sulfate (ChS). The effect of transglutaminase (TG) and laccase cross-linking on nanoparticle stability was investigated. Covalent TG cross-linking and grafted dextran cooperatively contributed to the stability of nanoparticles against dissociation and aggregation under various harsh environmental conditions (sharply varying pH, high ionic strength, high temperature, and their combined effects). However, fragmentation induced by laccase treatment did not promote nanoparticle stability. Structural characterization showed that the compact structure promoted by TG-induced covalent isopeptide bonds repressed dissociation against varying environmental conditions and thermal-induced aggregation. Furthermore, the increasing α-helix and decreasing random coil contents benefited the formation of disulfide bonds, further contributing to the enhanced stability of nanoparticles cross-linked by TG, whereas weak hydrophobic interactions and hydrogen bonding as evidenced by the increase in β-sheet and microenvironmental changes were not able to maintain the stability of nanoparticles treated with laccase. Encapsulated cinnamaldehyde presented sustained release from TG-cross-linked nanoparticles, and the bioaccessibility was considerably enhanced to 50.7%. This research developed a novel mild strategy to enhance nanoparticle stability in harsh environments and digestive conditions, which could be an effective delivery vehicle for hydrophobic nutrients and drug applications in food and pharmaceutical industries.

Preparation of PEG-modified wool keratin/sodium alginate porous scaffolds with elasticity recovery and good biocompatibility

To improve mechanical properties of keratin (KR) porous scaffolds, we prepared a PEGylated keratin through thiol-ene click reaction. Several porous scaffolds were prepared by blending PEGylated keratin with sodium alginate (SA). The surface morphology, mechanical properties, and porosity of scaffolds were detailed studied at different KR/SA proportions. The results showed the content of SA had an effect on pore formation and mechanical properties. When the mass ratio of KR to SA was 2:1, the stress of yield point of the keratin porous scaffold reached 1.24 MPa, and also showed good deformation recovery ability. The PEGylated keratin porous scaffold had a high porosity and great cytocompatibility. Its' porosity is up to 81.7% and the cell viability is about 117.78%. This allows it to absorb the simulated plasma quickly (9.20 ± 0.37 g/g). In addition, the structural stability and acid-base stability of the keratin porous scaffold were also improved after PEGylation. Overall, the PEGylated keratin porous scaffold will be promising in tissue materials due to its great physical, chemical, and biological properties.

Implantation of regenerative complexes in traumatic brain injury canine models enhances the reconstruction of neural networks and motor function recovery

Rationale: The combination of medical and tissue engineering in neural regeneration studies is a promising field. Collagen, silk fibroin and seed cells are suitable options and have been widely used in the repair of spinal cord injury. In this study, we aimed to determine whether the implantation of a complex fabricated with collagen/silk fibroin (SF) and the human umbilical cord mesenchymal stem cells (hUCMSCs) can promote cerebral cortex repair and motor functional recovery in a canine model of traumatic brain injury (TBI). Methods: A porous scaffold was fabricated with cross-linked collagen and SF. Its physical properties and degeneration rate were measured. The scaffolds were co-cultured with hUCMSCs after which an implantable complex was formed. After complex implantation to a canine model of TBI, the motor evoked potential (MEP) and magnetic resonance imaging (MRI) were used to evaluate the integrity of the cerebral cortex. The neurologic score, motion capture, surface electromyography (sEMG), and vertical ground reaction force (vGRF) were measured in the analysis of motor functions. In vitro analysis of inflammation levels was performed by Elisa while immunohistochemistry was used in track the fate of hUCMSCs. In situ hybridization, transmission electron microscope, and immunofluorescence were used to assess neural and vascular regeneration. Results: Favorable physical properties, suitable degradation rate, and biocompatibility were observed in the collagen/SF scaffolds. The group with complex implantation exhibited the best cerebral cortex integrity and motor functions. The implantation also led to the regeneration of more blood vessels and nerve fibers, less glial fibers, and inflammatory factors. Conclusion: Implantation of this complex enhanced therapy in traumatic brain injury (TBI) through structural repair and functional recovery. These effects exhibit the translational prospects for the clinical application of this complex.

Blended Natural Support Materials-Collagen Based Hydrogels Used in Biomedicine

Due to their unique properties-the are biocompatible, easily accessible, and inexpensive with programmable properties-biopolymers are used in pharmaceutical and biomedical research, as well as in cosmetics and food. Collagen is one of the most-used biomaterials in biomedicine, being the most abundant protein in animals with a triple helices structure, biocompatible, biomimetic, biodegradable, and hemostatic. Its disadvantages are its poor mechanical and thermal properties and enzymatic degradation. In order to solve this problem and to use its benefits, collagen can be used blended with other biomaterials such as alginate, chitosan, and cellulose. The purpose of this review article is to offer a brief paper with updated information on blended collagen-based formulations and their potential application in biomedicine.

Incorporation of gelatin improves toughness of collagen films with a homo-hierarchical structure

In this study, gelatin (type A and type B) with/without transglutaminase (TGase) were added to collagen fiber films to form hierarchical structure and its effects on the film were investigated. The analysis of mechanical properties indicate that gelatin significantly increased the toughness of the collagen film, where the 10 wt% type A gelatin -contained films had highest tensile strength, elongation at break and work of fracture. However, TGase crosslinking compromised the benefits of type A gelatin greatly, while type B gelatin showed a slight improvement, due to the difference in crosslinking activity between them. In the meantime, the hydrogen bonds were formed between the collagen and gelatin according to the results of the Fourier transformation infrared. In general, it is expected that the hierarchical structure formed in the collagen/gelatin films can be used as an effective strategy to enhance the collagen matrix films' mechanical properties.

Dry vs. wet: Properties and performance of collagen films. Part I. Mechanical behaviour and strain-rate effect

Collagen forms one-third of the body proteome and has emerged as an important biomaterial for tissue engineering and wound healing. Collagen films are used in tissue regeneration, wound treatment, dural substitute etc. as well as in flexible electronics. Thus, the mechanical behaviour of collagen should be studied under different environmental conditions and strain rates relevant for potential applications. This study's aim is to assess the mechanical behaviour of collagen films under different environmental conditions (hydration, submersion and physiological temperature (37 °C)) and strain rates. The combination of all three environment factors (hydration, submersion and physiological temperature (37 °C)) resulted in a drop of tensile strength of the collagen film by some 90% compared to that of dry samples, while the strain at failure increased to about 145%. For the first time, collagen films were subjected to different strain rates ranging from quasi-static (0.0001 s^-1) to intermediate (0.001 s^-1, 0.01 s^-1) to dynamic (0.1 s^-1, 1 s^-1) conditions, with the strain-rate-sensitivity exponent (m) reported. It was found that collagen exhibited a strain-rate-sensitive hardening behaviour with increasing strain rate. The exponent m ranged from 0.02-0.2, with a tendency to approach zero at intermediate strain rate (0.01 s^-1), indicating that collagen may be strain-rate insensitive in this regime. From the identification of hyperelastic parameter of collagen film, it was found that the Ogden Model provides realistic results for future simulations.

Fabrication of Delivery Gels with Micellar Casein Concentrates (MCC) Using Microfiltration Embedding Lactobacillus Rhamnosus GG (LGG): Effect of Temperature on Structure, Rheological Behavior, and Texture

To obtain natural protein gels as delivery systems loading with probiotics and protect the probiotics from heat treatment, we fabricated casein-based gels using micellar casein concentrates (MCC) via microfiltration and then embedded with Lactobacillus Rhamnosus GG (LGG). Rheological analysis indicated that MCC with a protein concentration of 12% would form gels greatly. The results of SDS-polyacrylamide gel electrophoresis showed that the contents of macromolecule in the gels increased as the heat treatment time is prolonged. After heat treatment, a fibrillated structure and a more stable structure were obtained in MCC-LGG gels by scanning electron microscopy and Fourier transform infrared spectroscopy, respectively. The different changes of rheological behavior and texture of the gels were evaluated using a rheometer and texture analyzer, respectively. Similarly, centrifugation could reduce the property modified by heat inducing and contribute to LGG embedding completely. Importantly, LGG with a survival rate of 7.12% was in the gels after heat treatment at 75 °C for 10 min. Results showed that MCC could offer a protecting circumstance for living LGG cells from heat treatment. Therefore, MCC-LGG gels would be a potential healthy food for improving intestinal microflora in the dairy industry.

Microbial Transglutaminase as a Tool to Improve the Features of Hydrocolloid-Based Bioplastics

Several proteins from animal and plant origin act as microbial transglutaminase substrate, a crosslinking enzyme capable of introducing isopeptide bonds into proteins between the aminoacids glutamines and lysines. This feature has been widely exploited to modify the biological properties of many proteins, such as emulsifying, gelling, viscosity, and foaming. Besides, microbial transglutaminase has been used to prepare bioplastics that, because made of renewable molecules, are able to replace the high polluting plastics of petrochemical origin. In fact, most of the time, it has been shown that the microbial enzyme strengthens the matrix of protein-based bioplastics, thus, influencing the technological characteristics of the derived materials. In this review, an overview of the ability of many proteins to behave as good substrates of the enzyme and their ability to give rise to bioplastics with improved properties is presented. Different applications of this enzyme confirm its important role as an additive to recover high value-added protein containing by-products with a double aim (i) to produce environmentally friendly materials and (ii) to find alternative uses of wastes as renewable, cheap, and non-polluting sources. Both principles are in line with the bio-economy paradigm.

Physical Properties of Composite Films from Tilapia Skin Collagen with Pachyrhizus Starch and Rambutan Peel Phenolics

Different composite films composed of tilapia skin collagen (TSC) with Pachyrhizus starch (PS) or rambutan peel phenolics (RPP) were prepared, and the physical properties of these films were determined. The effects of PS and RPP on TSC films were investigated, and our results indicated that PS and RPP could improve the physical properties of TSC films. Opacity and film thickness showed an enhanced trend with increasing PS and RPP contents in TSC films, whereas solubility in water, elongation-at-break (EAB), and water vapor permeability (WVP) showed declining trends. TSC film with 10% PS and 0.5% RPP had the highest tensile strength, and the tensile strength dropped drastically when the content of PS and RPP increased. The light transmittances of the films could decrease with the incorporation of PS and RPP. Differential scanning calorimetry (DSC) demonstrated that the addition of PS and RPP improved the thermal stability of TSC films. In addition, X-ray diffraction indicated that the crystallinity of the films decreased and the amorphous structure of the films tended to become more complex with the addition of PS and RPP. As shown by fourier transform infrared spectroscopy (FTIR) analysis, PS and RPP can strongly interact with TSC, resulting in a modification of its structure. Scanning electron microscope (SEM) analysis showed that there was a good compatibility between TSC, PS, and RPP. The results indicated that TSC film incorporated with 10% PS and 0.5% RPP was an effective method for improve the physical properties of the film. TSC–PS–RPP composite films can be used not only in biomedical applications, but also as active food packaging materials.

Improved structure-stability and packaging characters of crosslinked collagen fiber-based film with casein, keratin and SPI

BACKGROUND

To improve the structure-stability and packing characters of collagen fiber, we manufactured crosslinked collagen fiber (CColF)-based edible films using transglutaminase (TGase). Then we made a comparison on structure-stability and packing characteristics among the CColF-based films loaded with casein (CN), keratin (KRT) and soy protein isolate (SPI), respectively.

RESULTS

Observed from scanning electron microscopy (SEM), the CColF loaded with CN, KRT and SPI showed some unique morphology of the additional proteins. The CColF-protein films performed better packing characteristics including barrier properties, mechanical properties and thermal-stability properties, compared with CColF films. Importantly, with 500 g kg^-1 CN (of CColF) addition, CColF-based films possessed a greater thermal stability than the other films judged from differential scanning calorimetry (DSC). Meanwhile, the CColF loaded with 100 g kg^-1 CN provided a higher value of tensile strength (TS) and the CColF loaded with 100 g kg^-1 KRT showed a higher value in elongation-at-break (EAB) than the other films.

CONCLUSION

In conclusion, the collagen fiber-based edible films with better structure-stability and packing characteristics for food packaging was obtained which could be an advantage to promote the development of the application of collagen in packing products. © 2019 Society of Chemical Industry.

Preparation and characterization of homogeneous and enhanced casein protein-based composite films via incorporating cellulose microgel

Gelatin-coupled cellulose (GCC) microgel with whisker-like structure is prepared and used to incorporate into casein (CA) matrix to construct reinforced CA-based composite films by solution casting. The GCC microgel has excellent dispersibility and stability in water, which contributes to the hydrophobicity and significantly reduces the moisture absorption of the composite films, as well as a decrease in the water vapor permeability with an increase of GCC content at different relative humidity is also observed. Compared with pure casein material, the resultant CA-based composite films show more homogeneous and dense cross-sectional structure, and the cleavage temperature of the hydrogen bonds increases by 16 °C. In particular, their tensile strength and Young’s modulus increase by 6 and 3.5 times, respectively. These indicators are superior to that of the nanoparticle enhanced CA-based composite film. Moreover, the light transmittance of the CA-based films at 550 nm is about 88% when GCC content is higher than 9%. The above results could be attributed to the strong hydrogen bonds formed between GCC components and CA matrix, as further confirmed by fourier transform infrared spectra and X-ray diffraction analysis.