Fabrication of films with tailored properties by regulating the swelling of collagen fiber through pH adjustment

Self-Assembly Behavior of Collagen and Its Composite Materials: Preparation, Characterizations, and Biomedical Engineering and Allied Applications

Collagen is the oldest and most abundant extracellular matrix protein and has many applications in biomedical, food, cosmetic, and other industries. Previous reviews have already introduced collagen's sources, structures, and biosynthesis. The biological and mechanical properties of collagen-based composite materials, their modification and application forms, and their interactions with host tissues are pinpointed. It is worth noting that self-assembly behavior is the main characteristic of collagen molecules. However, there is currently relatively little review on collagen-based composite materials based on self-assembly. Herein, we briefly reviewed the biosynthesis, extraction, structure, and properties of collagen, systematically presented an overview of the various factors and corresponding characterization techniques that affect the collagen self-assembly process, and summarize and discuss the preparation methods and application progress of collagen-based composite materials in different fields. By combining the self-assembly behavior of collagen with preparation methods of collagen-based composite materials, collagen-based composite materials with various functional reactions can be selectively prepared, and these experiences and outcomes can provide inspiration and practical techniques for the future development directions and challenges of collagen-based composite biomaterials in related applications fields.

Interacting collagen and tannic acid Particles: Uncovering pH-dependent rheological and thermodynamic behaviors

HYPOTHESIS

Biomaterials such as collagen and tannic acid (TA) particles are of interest in the development of advanced hybrid biobased systems due to their beneficial therapeutic functionalities and distinctive structural properties. The presence of numerous functional groups makes both TA and collagen pH responsive, enabling them to interact via non-covalent interactions and offer tunable macroscopic properties.

EXPERIMENT

The effect of pH on the interactions between collagen and TA particles is explored by adding TA particles at physiological pH to collagen at both acidic and neutral pH. Rheology, isothermal titration calorimetry (ITC), turbidimetric analysis and quartz crystal microbalance with dissipation monitoring (QCM-D) are used to study the effects.

FINDINGS

Rheology results show significant increase in elastic modulus with an increase in collagen concentration. However, TA particles at physiological pH provide stronger mechanical reinforcement to collagen at pH 4 than collagen at pH 7 due to the formation of a higher extent of electrostatic interaction and hydrogen bonding. ITC results confirm this hypothesis, with larger changes in enthalpy, |ΔH|, observed when collagen is at acidic pH and |ΔH| > |TΔS| indicating enthalpy-driven collagen-TA interactions. Turbidimetric analysis and QCM-D help to identify structural differences of the collagen-TA complexes and their formation at both pH conditions.

Changes in Structures and Properties of Collagen Fibers during Collagen Casing Film Manufacturing

Collagen casing is an edible film, which is widely used in the industrial production of sausages. However, the detailed changes in the collagen fibers, from the raw material to the final collagen film, have rarely been reported. In this research, the changes in the collagen fibers during the manufacturing process, including the fiber arrangement, the triple-helix structure and the thermal stability, were investigated using scanning electron microscopy (SEM), thermogravimetric analysis (TGA), X-ray diffraction (XRD), differential scanning calorimetry (DSC) and Fourier-transform infrared (FTIR) spectroscopy. The relationship between the structure stability and the arrangement of the collagen fibers was also discussed. According to the SEM, XRD, TGA, DSC and FTIR results, the collagen fibers were depolymerized during the acid swelling and became uniformly aligned after the homogenization process. Degassing had no obvious effect on the triple-helix structure. Alkaline neutralization with ammonia destroyed the triple-helix structure, which could be partly reversed through the washing and soaking processes. During the final drying step, the depolymerized triple helix of the collagen fibers recombined to form new structures that showed decreased thermal stability. This study expands our knowledge about the behavior of collagen fibers during the industrial process of producing collagen biobased casings.

Collagen processing with mesoscale aggregates as templates and building blocks

Collagen presents a well-organized hierarchical multilevel structure. Microfibers, fibers, and fiber bundles are the aggregates of natural collagen; which achieve an ideal balance of mechanical strength and toughness at the mesoscopic scale for biological tissue. These mesostructured aggregates of collagen isolated from biological tissues retain these inherent organizational features to enable their use as building blocks for constructing new collagen materials with ideal mechanical performance, thermal and dimensional stability. This strategy is distinct from the more common bottom-up or molecular-level design and assembly approach to generating collagen materials. The present review introduces the hierarchical structure of biological collagen with a focus on mesostructural features. Isolation strategies for these collagen aggregates (CAs) are summarized. Recent progress in the use of these mesostructural components for the construction of new collagen materials with emerging applications is reviewed, including in catalysis, environmental applications, biomedicine, food packaging, electrical energy storage, and flexible sensors. Finally, challenges and prospects are assessed for controllable production of CAs as well as material designs.

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.

Protein-Based Systems for Topical Antibacterial Therapy

Recently, proteins are gaining attention as potential materials for antibacterial therapy. Proteins possess beneficial properties such as biocompatibility, biodegradability, low immunogenic response, ability to control drug release, and can act as protein-mimics in wound healing. Different plant- and animal-derived proteins can be developed into formulations (films, hydrogels, scaffolds, mats) for topical antibacterial therapy. The application areas for topical antibacterial therapy can be wide including bacterial infections in the skin (e.g., acne, wounds), eyelids, mouth, lips, etc. One of the major challenges of the healthcare system is chronic wound infections. Conventional treatment strategies for topical antibacterial therapy of infected wounds are inadequate, and the development of newer and optimized formulations is warranted. Therefore, this review focuses on recent advances in protein-based systems for topical antibacterial therapy in infected wounds. The opportunities and challenges of such protein-based systems along with their future prospects are discussed.

Application of amphoteric polymers in the process of leather post-tanning

Abstract

With the characteristics of controllable charge and environmental friendliness, amphoteric polymers can be used in post-tanning process to solve the problems that arise during leather making and are caused by the low absorption rate of single-charge chemicals, incompatibility with new tanning methods, and complex operation process. In this review, the structure, performance, and preparation of amphoteric polymers are reported. Then, the charge change of collagen during different tanning and pH treatments is introduced. Finally, the application and development of amphoteric polymers during the post-tanning process of leather making are discussed. This review has certain guiding significance to the preparation and application of amphoteric polymers for tanning system.

Graphical abstract

Strategies for Fabricating Protein Films for Biomaterials Applications

Proteins are naturally occurring functional building blocks that are useful for the fabrication of materials. Naturally-occurring proteins are biodegradable and most are biocompatible and non-toxic, making them attractive for the fabrication of biomaterials. Moreover, the fabrication of protein-based materials can be conducted in a green and sustainable manner due to their high aqueous solubility. Consequently, the applicability of protein-based materials is limited by their aqueous and mechanical instability. This review summarizes strategies for the stabilization of protein films, highlighting their salient features and potential limitations. Applications of protein films ranging from food packaging materials, tissue engineering scaffolds, antimicrobial coatings etc. are also discussed. Finally, the need for robust and efficient fabrication strategies for translation to commercial applications as well as potential applications of protein films in the field of sensing, diagnostics and controlled release systems are discussed.