Recent Advances in Environmentally Friendly and Green Degumming Processes of Silk for Textile and Non-Textile Applications

Self-Sanitization in a Silk Nanofibrous Network for Biodegradable PM0.3 Filters with In Situ Joule Heating

In the contemporary way of life, face masks are crucial in managing disease transmission and battling air pollution. However, two key challenges, self-sanitization and biodegradation of face masks, need immediate attention, prompting the development of innovative solutions for the future. In this study, we present a novel approach that combines controlled acid hydrolysis and mechanical chopping to synthesize a silk nanofibrous network (SNN) seamlessly integrated with a wearable stainless steel mesh, resulting in the fabrication of self-sanitizable face masks. The distinct architecture of face masks showcases remarkable filtration efficiencies of 91.4, 95.4, and 98.3% for PM0.3, PM0.5, and PM1.0, respectively, while maintaining a comfortable level of breathability (ΔP = 92 Pa). Additionally, the face mask shows that a remarkable thermal resistance of 472 °C cm2 W-1 generates heat spontaneously at low voltage, deactivating Escherichia coli bacteria on the SNN, enabling self-sanitization. The SNN exhibited complete disintegration within the environment in just 10 days, highlighting the remarkable biodegradability of the face mask. The unique advantage of self-sanitization and biodegradation in a face mask filter is simultaneously achieved for the first time, which will open avenues to accomplish environmentally benign next-generation face masks.

Sustainable Sources of Raw Materials for Additive Manufacturing of Bone-Substituting Biomaterials

The need for sustainable development has never been more urgent, as the world continues to struggle with environmental challenges, such as climate change, pollution, and dwindling natural resources. The use of renewable and recycled waste materials as a source of raw materials for biomaterials and tissue engineering is a promising avenue for sustainable development. Although tissue engineering has rapidly developed, the challenges associated with fulfilling the increasing demand for bone substitutes and implants remain unresolved, particularly as the global population ages. This review provides an overview of waste materials, such as eggshells, seashells, fish residues, and agricultural biomass, that can be transformed into biomaterials for bone tissue engineering. While the development of recycled metals is in its early stages, the use of probiotics and renewable polymers to improve the biofunctionalities of bone implants is highlighted. Despite the advances of additive manufacturing (AM), studies on AM waste-derived bone-substitutes are limited. It is foreseeable that AM technologies can provide a more sustainable alternative to manufacturing biomaterials and implants. The preliminary results of eggshell and seashell-derived calcium phosphate and rice husk ash-derived silica can likely pave the way for more advanced applications of AM waste-derived biomaterials for sustainably addressing several unmet clinical applications.

A novel method for silkworm cocoons self-degumming and its effect on silk fibers

INTRODUCTION

Conventional hot-alkaline cocoon degumming techniques greatly weaken the physicochemical and mechanical properties of silk fibroin fiber, thus affecting the quality of silk fabric. Moreover, it causes massive energy waste and serious environmental pollution.

OBJECTIVE

This study aims to establish a novel cocoon self-degumming method by genetic modification of silkworm varieties and silk fibers.

METHODS

The self-degummed cocoon material was generated by specifically overexpressing trypsinogen protein in the sericin layer of silk thread; the effect of cocoon self-degumming method was evaluated by the degumming rate of sericin protein, the cleanliness and equivalent diameter of silk fibroin fiber; the basic characteristics of silk fibroin fiber degummed by cocoon self-degumming method and conventional hot-alkaline degumming technique were determined by electron microscopy, Fourier infrared spectroscopy, X-ray diffraction and tensile tests; the composition and biological activity of degummed sericin protein was respectively analyzed by liquid chromatograph-mass spectrometry and cytological experiments.

RESULTS

The genetically engineered self-degumming cocoon containing trypsinogen protein was successfully created, and the content of trypsinogen protein in silk was 47.14 ± 0.90 mg/g. The sericin protein in the self-degumming cocoon was removed out in water or 1 mM Tris-HCl buffer (pH = 8.0). Compared to alkaline-degummed silk fibroin, self-degummed silk fibroin had better cleanliness, thicker equivalent diameter, more complete silk structure and better mechanical property. In addition, sericin protein degummed from self-degumming cocoons significantly promoted cell proliferation and caused no obvious cytotoxicity.

CONCLUSION

Compared to conventional hot-alkaline degumming technique, the cocoon self-degumming method by genetically overexpressing trypsinogen protein in sericin layer of silk thread can self-degummed in a mild degumming condition, and gain silk fiber with better quality and more biologically active sericin protein products. This strategy can not only reduce the environmental impact, but also generate greater economic value, which will accelerate its application in the silk and pharmaceutical industries.

Application of silk fibroin coatings for biomaterial surface modification: a silk road for biomedicine

Silk fibroin (SF) as a natural biopolymer has become a popular material for biomedical applications due to its minimal immunogenicity, tunable biodegradability, and high biocompatibility. Nowadays, various techniques have been developed for the applications of SF in bioengineering. Most of the literature reviews focus on the SF-based biomaterials and their different forms of applications such as films, hydrogels, and scaffolds. SF is also valuable as a coating on other substrate materials for biomedicine; however, there are few reviews related to SF-coated biomaterials. Thus, in this review, we focused on the surface modification of biomaterials using SF coatings, demonstrated their various preparation methods on substrate materials, and introduced the latest procedures. The diverse applications of SF coatings for biomedicine are discussed, including bone, ligament, skin, mucosa, and nerve regeneration, and dental implant surface modification. SF coating is conducive to inducing cell adhesion and migration, promoting hydroxyapatite (HA) deposition and matrix mineralization, and inhibiting the Notch signaling pathway, making it a promising strategy for bone regeneration. In addition, SF-coated composite scaffolds can be considered prospective candidates for ligament regeneration after injury. SF coating has been proven to enhance the mechanical properties of the substrate material, and render integral stability to the dressing material during the regeneration of skin and mucosa. Moreover, SF coating is a potential strategy to accelerate nerve regeneration due to its dielectric properties, mechanical flexibility, and angiogenesis promotion effect. In addition, SF coating is an effective and popular means for dental implant surface modification to promote osteogenesis around implants made of different materials. Thus, this review can be of great benefit for further improvements in SF-coated biomaterials, and will undoubtedly contribute to clinical transformation in the future.

Could an Anterior Cruciate Ligament Be Tissue-Engineered from Silk?

Silk has a long history as an exclusive textile, but also as a suture thread in medicine; nowadays, diverse cell carriers are manufactured from silk. Its advantages are manifold, including high biocompatibility, biomechanical strength and processability (approved for nearly all manufacturing techniques). Silk's limitations, such as scarcity and batch to batch variations, are overcome by gene technology, which allows for the upscaled production of recombinant "designed" silk proteins. For processing thin fibroin filaments, the sericin component is generally removed (degumming). In contrast to many synthetic biomaterials, fibroin allows for superior cell adherence and growth. In addition, silk grafts demonstrate superior mechanical performance and long-term stability, making them attractive for anterior cruciate ligament (ACL) tissue engineering. Looking at these promising properties, this review focusses on the responses of cell types to silk variants, as well as their biomechanical properties, which are relevant for ACL tissue engineering. Meanwhile, sericin has also attracted increasing interest and has been proposed as a bioactive biomaterial with antimicrobial properties. But so far, fibroin was exclusively used for experimental ACL tissue engineering approaches, and fibroin from spider silk also seems not to have been applied. To improve the bone integration of ACL grafts, silk scaffolds with osteogenic functionalization, silk-based tunnel fillers and interference screws have been developed. Nevertheless, signaling pathways stimulated by silk components remain barely elucidated, but need to be considered during the development of optimized silk cell carriers for ACL tissue engineering.

Bromelain: a review of its mechanisms, pharmacological effects and potential applications

The utilization of plant-derived supplements for disease prevention and treatment has long been recognized because of their remarkable potential. Ananas comosus, commonly known as pineapple, produces a group of enzymes called bromelain, which contains sulfhydryl moieties. Recent studies have shown that bromelain exhibits a wide range of activities, including anti-inflammatory, anti-diabetic, anti-cancer, and anti-rheumatic properties. These properties make bromelain a promising drug candidate for the treatment of various diseases. The anti-inflammatory activity of bromelain has been shown to be useful in treating inflammatory conditions such as osteoarthritis, rheumatoid arthritis, and asthma, whereas the anti-cancer activity of bromelain is via induction of apoptosis, inhibition of angiogenesis, and enhancement of the body's immune response. The anti-diabetic property of bromelain is owing to the improvement in glucose metabolism and reduction in insulin resistance. The therapeutic potential of bromelain has been investigated in numerous preclinical and clinical studies and a number of patents have been granted to date. Various formulations and delivery systems are being developed in order to improve the efficacy and safety of this molecule, including the microencapsulated form to treat oral inflammatory conditions and liposomal formulations to treat cancer. The development of novel drug delivery systems and formulations has further ameliorated the therapeutic potential of bromelain by improving its bioavailability and stability, while reducing the side effects. This review intends to discuss various properties and therapeutic applications of bromelain, along with its possible mechanism of action in treating various diseases. Recent patents and clinical trials concerning bromelain have also been covered.

Advances in Preparation and Properties of Regenerated Silk Fibroin

Over the years, silk fibroin (SF) has gained significant attention in various fields, such as biomedicine, tissue engineering, food processing, photochemistry, and biosensing, owing to its remarkable biocompatibility, machinability, and chemical modifiability. The process of obtaining regenerated silk fibroin (RSF) involves degumming, dissolving, dialysis, and centrifugation. RSF can be further fabricated into films, sponges, microspheres, gels, nanofibers, and other forms. It is now understood that the dissolution method selected greatly impacts the molecular weight distribution and structure of RSF, consequently influencing its subsequent processing and application. This study comprehensively explores and summarizes different dissolution methods of SF while examining their effects on the structure and performance of RSF. The findings presented herein aim to provide valuable insights and references for researchers and practitioners interested in utilizing RSF in diverse fields.

Comparative Study of the Preparation of High-Molecular-Weight Fibroin by Degumming Silk with Several Neutral Proteases

Removing sericin from the periphery of silk without damage to silk fibroin (SF) to obtain high-molecular-weight SF is a major challenge in the field of SF-based biomaterials. In this study, four neutral proteases, subtilisin, trypsin, bromelain and papain, were used to degum silk, and the degumming efficiency of the proteases and their influence on the molecular weight (MW) of regenerated silk fibroin were studied. The results indicated that all four neutral proteases could remove sericin from silk almost completely, and they caused less damage to SF fibers than Na2CO3 degumming did. The degumming efficiency of trypsin and papain was strong, but they caused relatively high damage to SF, whereas bromelain caused the least damage. The results of sodium dodecyl sulfate-polyacrylamide gel electrophoresis, gel permeation chromatography and shear viscosity showed that the MWs of regenerated SF derived from neutral protease degumming were significantly higher than that of SF derived from Na2CO3 degumming. The MW of regenerated SF derived from bromelain degumming was the highest, while the MWs of regenerated SF derived from papain and trypsin degumming were relatively low. This study provides an efficient and environmentally friendly biological degumming method for obtaining high-molecular-weight silk fibroin.

Characterization of high-yield Bacillus subtilis cysteine protease for diverse industrial applications

Bacterial proteases have extensive applications in various fields of industrial microbiology. In this study, protease-producing organisms were screened on skimmed milk agar media using serial dilution. Through microbial biomass production, biochemical tests, protease-specific activity, and 16 s RNA gene sequencing, the isolates were identified as Bacillus subtilis and submitted to NCBI. The strain accession numbers were designated as A1 (MT903972), A2 (MT903996), A4 (MT904091), and A5 (MT904796). The strain A4 Bacillus subtilis showed highest protease-specific activity as 76,153.84 U/mg. A4 Bacillus subtilis was unaffected by Ca2+, Cu2+, Fe2+, Hg2+, Mg2+, Na, Fe2+, and Zn2+ but was inhibited by 80% by Mn2+ (5 mM). The protease activity was inhibited by up to 30% by iodoacetamide (5 mM). These findings confirm the enzyme to be a cysteine protease which was further confirmed by MALDI-TOF. The identified protease showed 71% sequence similarity with Bacillus subtilis cysteine protease. The crude cysteine protease significantly aided in fabric stain removal when added to a generic detergent. It also aided in the recovery of silver from used X-ray films and de-hairing of goat skin hides and showed decent application in meat tenderization. Thus, the isolated cysteine protease has high potential for industrial applications.

Silk sericin-based materials for biomedical applications

Silk sericin, a natural protein extracted from silkworm cocoons, has been extensively studied and utilized in the biomedical field because of its superior biological activities and controllable chemical-physical properties. Sericin is biocompatible and naturally cell adhesive, enabling cell attachment, proliferation, and differentiation in sericin-based materials. Moreover, its abundant functional groups from variable amino acids composition allow sericin to be chemically modified and cross-linked to form versatile constructs serving as alternative matrixes for biomedical applications. Recently, sericin has been constructed into various types of biomaterials for tissue engineering and regenerative medicine, including various bulk constructions (films, hydrogels, scaffolds, conduits, and devices) and micro-nano formulations. In this review, we systemically summarize the properties of silk sericin, introduce its different forms, and demonstrate their newly-developed as well as potential biomedical applications.