Silk Sericin-Functionalized Bacterial Cellulose as a Potential Wound-Healing Biomaterial

Therapeutic potential of silkworm sericin in wound healing applications

Chronic wounds are characterised by an imbalance between pro and anti-inflammatory signals, which result in permanent inflammation and delayed re-epithelialization, consequently hindering wound healing. They are associated with bacterial infections, tissue hypoxia, local ischemia, reduced vascularization, and MMP-9 upregulation. The global prevalence of chronic wounds has been estimated at 40 million in the adult population, with an alarming annual growth rate of 6.6%, making it an increasingly significant clinical problem. Sericin is a natural hydrophilic protein obtained from the silkworm cocoon. Due to its biocompatibility, biodegradability, non-immunogenicity, and oxidation resistance, coupled with its excellent affinity for target biomolecules, it holds great potential in wound healing applications. The silk industry discards 50,000 tonnes of sericin annually, making it a readily available material. Sericin increases cell union sites and promotes cell proliferation in fibroblasts and keratinocytes, thanks to its cytoprotective and mitogenic effects. Additionally, it stimulates macrophages to release more therapeutic cytokines, thus improving vascularization. This review focuses on the biological properties of sericin that contribute towards enhanced wound healing process and its mechanism of interaction with important biological targets involved in wound healing. Emphasis is placed on diverse wound dressing products that are sericin based and the utilisation of nanotechnology to design sericin nanoparticles that aid in chronic wound management.

Protein Immobilization on Bacterial Cellulose for Biomedical Application

New carriers for protein immobilization are objects of interest in various fields of biomedicine. Immobilization is a technique used to stabilize and provide physical support for biological micro- and macromolecules and whole cells. Special efforts have been made to develop new materials for protein immobilization that are non-toxic to both the body and the environment, inexpensive, readily available, and easy to modify. Currently, biodegradable and non-toxic polymers, including cellulose, are widely used for protein immobilization. Bacterial cellulose (BC) is a natural polymer with excellent biocompatibility, purity, high porosity, high water uptake capacity, non-immunogenicity, and ease of production and modification. BC is composed of glucose units and does not contain lignin or hemicellulose, which is an advantage allowing the avoidance of the chemical purification step before use. Recently, BC-protein composites have been developed as wound dressings, tissue engineering scaffolds, three-dimensional (3D) cell culture systems, drug delivery systems, and enzyme immobilization matrices. Proteins or peptides are often added to polymeric scaffolds to improve their biocompatibility and biological, physical-chemical, and mechanical properties. To broaden BC applications, various ex situ and in situ modifications of native BC are used to improve its properties for a specific application. In vivo studies showed that several BC-protein composites exhibited excellent biocompatibility, demonstrated prolonged treatment time, and increased the survival of animals. Today, there are several patents and commercial BC-based composites for wounds and vascular grafts. Therefore, further research on BC-protein composites has great prospects. This review focuses on the major advances in protein immobilization on BC for biomedical applications.

Development and Application of an Advanced Biomedical Material-Silk Sericin

Sericin, a protein derived from silkworm cocoons, is considered a waste product derived from the silk industry for thousands of years due to a lack of understanding of its properties. However, in recent decades, a range of exciting properties of sericin are studied and uncovered, including cytocompatibility, low-immunogenicity, photo-luminescence, antioxidant properties, as well as cell-function regulating activities. These properties make sericin-based biomaterials promising candidates for biomedical applications. This review summarizes the properties and bioactivities of silk sericin and highlights the latest developments in sericin in tissue engineering and regenerative medicine. Furthermore, the extended application of sericin in developing flexible electronic devices and 3D bioprinting is also discussed. It is believed that sericin-based biomaterials have great potential of being developed into novel tissue engineering products and smart implantable devices for various medical applications toward improving clinical outcomes.

Functionalization of bacterial cellulose: Exploring diverse applications and biomedical innovations: A review

The demand for the functionalization of additive materials based on bacterial cellulose (BC) is currently high due to their potential applications across various sectors. The preparation of BC-based additive materials typically involves two approaches: in situ and ex situ. In situ modifications entail the incorporation of additive materials, such as soluble and dispersed substances, which are non-toxic and not essential for bacterial cell growth during the production process. However, these materials can impact the yield and self-assembly of BC. In contrast, ex situ modification occurs subsequent to the formation of BC, where the additive materials are not only adsorbed on the surface but also impregnated into the BC pellicle, while the BC slurry was homogenized with other additive materials and gelling agents to create composite films using the casting method. This review will primarily focus on the in situ and ex situ functionalization of BC then sheds light on the pivotal role of functionalized BC in advancing biomedical technologies, wound healing, tissue engineering, drug delivery, bone regeneration, and biosensors.

A comprehensive review of recent advances in silk sericin: Extraction approaches, structure, biochemical characterization, and biomedical applications

Silks are natural polymers that have been widely used for centuries. Silk consists of a filament core protein, termed fibroin, and a glue-like coating substance formed of sericin (SER) proteins. This protein is extracted from the silkworm cocoons (particularly Bombyx mori) and is mainly composed of amino acids like glycine, serine, aspartic acid, and threonine. Silk SER can be obtained using numerous methods, including enzymatic extraction, high-temperature, autoclaving, ethanol precipitation, cross-linking, and utilizing acidic, alkali, or neutral aqueous solutions. Given the versatility and outstanding properties of SER, it is widely fabricated to produce sponges, films, and hydrogels for further use in diverse biomedical applications. Hence, many authors reported that SER benefits cell proliferation, tissue engineering, and skin tissue restoration thanks to its moisturizing features, antioxidant and anti-inflammatory properties, and mitogenic effect on mammalian cells. Remarkably, SER is used in drug delivery depending on its chemical reactivity and pH-responsiveness. These unique features of SER enhance the bioactivity of drugs, facilitating the fabrication of biomedical materials at nano- and microscales, hydrogels, and conjugated molecules. This review thoroughly outlines the extraction techniques, biological properties, and respective biomedical applications of SER.

Development and characterization of crosslinked k-carrageenan/sericin blend with covalent agents or thermal crosslink for indomethacin extended release

Modified release of multiparticulate pharmaceutical forms is a key therapeutic strategy to reduce side effects and toxicity caused by high and repeated doses of immediate-release oral drugs. This research focused on the encapsulation of indomethacin (IND) in the crosslinked k-Car/Ser polymeric matrix by covalent and thermal methods to evaluate drug delivery modulation and properties of the crosslinked blend. Therefore, the entrapment efficiency (EE %), drug loading (DL %) and physicochemical properties of the particles were investigated. The particles presented a spherical shape and a rough surface with a mean diameter of 1.38-2.15 mm (CCA) and 1.56-1.86 mm (thermal crosslink). FTIR investigation indicated the presence of IDM in the particles and X-ray pattern showed the maintenance of crystallinity of IDM. The in vitro release in acidic medium (pH 1.2) and phosphate buffer saline solution (pH 6.8) was 1.23-6.81 % and 81-100 %, respectively. Considering the results, the formulations remained stable after 6 months. The Weibull equation was adequately fitted for all formulations and a diffusion mechanism, swelling and relaxation of chain were observed. IDM-loaded k-carrageenan/sericin/CMC increases cell viability (> 75 % for neutral red and > 81 % for MTT). Finally, all formulations present gastro-resistance, pH response and altered release and have the potential to be used as drug delivery careers.

Sericin mediated gold/silver bimetallic nanoparticles and exploration of its multi-therapeutic efficiency and photocatalytic degradation potential

The current investigation aimed at bimetallic gold-silver nanoparticles (Au/Ag NPs), here called BM-GS NPs, synthesis using sericin protein as the reducing agent in an easy, cost-effective, and sustainable way. The obtained BM-GS NPs were characterized by UV-Visible spectroscopy, Transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDS), atomic force microscopy (AFM), Dynamic light scattering (DLS) and Zeta potential, X-ray Powder Diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), and Thermogravimetric analysis followed by evaluation of its multitherapeutic and photocatalytic degradation potentials. The TEM analysis revealed its spherical nature and the EDS result displayed the presence of both Ag and Au elements, confirming the synthesis of BM-GS NPs. The XRD pattern verified the crystalline nature of the nanoparticles (NPs). The DLS analysis showed an average size of 86.08 d nm and the zeta potential showed a highly negative value (-26.3 mV) which specifies that the generated bimetallic NPs are stable. The BM-GS NPs exhibited positive wound healing potential (with 63.38% of wound closure rate at 25 μg/ml, as compared to 54.42% by the untreated control) with very negligible toxicity effect on the cell viability of the normal keratinocyte cells. It also demonstrated promising antioxidant properties with 65.00%, 69.23%, and 63.03% activity at 100 μg/ml concentration for ABTS (2, 2-azinobis) (3-ethylbenzothiazoline-6-sulfonic acid)), DPPH (1, 1 diphenyl-2-picrylhydrazyl) and SOD (superoxide dismutase enzyme) assays respectively, antidiabetic potential (with a significantly high α-glucosidase inhibition potential of 99.69% at 10μg/ml concentration and 62.11% of α-amylase enzyme inhibition at 100 μg/ml concentration) and moderate tyrosinase inhibitory potential (with 17.09% at 100 μg/ml concentration). Besides, it displayed reasonable antibacterial potential with the diameter of zone of inhibition ranging between 10.89 and 12.39 mm. Further, its antibacterial mode of action reveals that its effects could be due to being very smaller, the NPs could have penetrated inside the cellular membrane thereby causing rupture and damage to the interior materials leading to cellular lysis. The photocatalytic evaluation showed that synthesized BM-GS NPs have the efficiency of degrading methylene blue dye by 34.70% within 3 h of treatment. The above findings revealed the multi-therapeutic efficacy of the sericin globular protein-mediated BM-GS NPs and its potential future applications in the cosmetics and food sector and environmental contamination management industries.

Opportunities for bacterial nanocellulose in biomedical applications: Review on biosynthesis, modification and challenges

Bacterial nanocellulose (BNC) is a natural polysaccharide produced as extracellular material by bacterial strains and has favorable intrinsic properties for primary use in biomedical applications. In this review, an update on state-of-the art and challenges in BNC production, surface modification and biomedical application is given. Recent insights in biosynthesis allowed for better understanding of governing parameters improving production efficiency. In particular, introduction of different carbon/nitrogen sources from alternative feedstock and industrial upscaling of various production methods is challenging. It is important to have control on the morphology, porosity and forms of BNC depending on biosynthesis conditions, depending on selection of bacterial strains, reactor design, additives and culture conditions. The BNC is intrinsically characterized by high water absorption capacity, good thermal and mechanical stability, biocompatibility and biodegradability to certain extent. However, additional chemical and/or physical surface modifications are required to improve cell compatibility, protein interaction and antimicrobial properties. The novel trends in synthesis include the in-situ culturing of hybrid BNC nanocomposites in combination with organic material, inorganic material or extracellular components. In parallel with toxicity studies, the applications of BNC in wound care, tissue engineering, medical implants, drug delivery systems or carriers for bioactive compounds, and platforms for biosensors are highlighted.

Sericin/Human Placenta-Derived Extracellular Matrix Scaffolds for Cutaneous Wound Treatment-Preparation, Characterization, In Vitro and In Vivo Analyses

Human placenta is loaded with an enormous amount of endogenous growth factors, thereby making it a superior biomaterial for tissue regeneration. Sericin is a naturally occurring silk protein that is extensively used for biomedical applications. In the present work, sericin and human placenta-derived extracellular matrix were blended and fabricated in the form of scaffolds using the freeze-drying method for cutaneous wound treatment. The prepared sericin/placenta-derived extracellular matrix (SPEM) scaffolds were characterized to determine their morphology, functional groups, mechanical strength, and antibacterial activity. Scanning electron microscopic analysis of the scaffolds showed smooth surfaces with interconnected pores. In vitro MTT and scratch wound assays performed using HaCaT cells proved the non-toxic and wound-healing efficacy of SPEM scaffolds. In vivo CAM assay using fertilized chick embryos proved the angiogenic potency of the scaffolds. Animal experiments using Wistar albino rats proved that the open excision wounds treated with SPEM scaffolds significantly reduced wound size with collagen deposition. These results confirm that SPEM scaffolds can serve as a promising biomaterial for tissue regeneration.

PVA-Based Nanofibers Containing Chitosan Modified with Graphene Oxide and Carbon Quantum Dot-Doped TiO2 Enhance Wound Healing in a Rat Model

Electrospun nanofibrous constructs based on nanoparticles and biopolymers have recently been used in tissue engineering because of their similarity to the extracellular matrix in nature. In this study, electrospun chitosan-carbon quantum dot-titanium dioxide-graphene oxide (CS-CQD-TiO₂-GO) nanofibrous mats were synthesized for use as wound dressings by the electrospinning method. To increase the biodegradation rate and water resistance, the fabricated nanofibrous mats were cross-linked. SEM images showed a uniform and coherent structure of CS-CQD-TiO₂-GO nanocomposites and CS-CQD-TiO₂-GO electrospun nanofibers mats. FTIR analysis, XRD pattern, SEM mapping, and EDS spectrum demonstrate the accuracy of the synthesis as well as the elemental and chemical structure of the nanofibrous mat. The water contact angle indicated that the nanofibrous mat had a hydrophilic property, which is essential for controlling wound exudates. The tensile strength and elongation tests showed that the nanofibrous mat has suitable mechanical properties for wound dressing, including significant flexibility and strength. Interestingly, antimicrobial testing illustrated that the fabricated nanofibrous mat had antibacterial activity against Gram-negative and Gram-positive bacteria. Appropriate cell viability and cytocompatibility of treated mouse fibroblast NIH3T3 cells with the nanofibrous mat were determined using an MTT assay. The animal study results confirmed the proper potential of the nanofibrous mat in wound dressing applications.

Silk Sericin: A Promising Sustainable Biomaterial for Biomedical and Pharmaceutical Applications

Silk is a natural composite fiber composed mainly of hydrophobic fibroin and hydrophilic sericin, produced by the silkworm Bombyx mori. In the textile industry, the cocoons of B. mori are processed into silk fabric, where the sericin is substantially removed and usually discarded in wastewater. This wastewater pollutes the environment and water sources. However, sericin has been recognized as a potential biomaterial due to its biocompatibility, immunocompatibility, biodegradability, anti-inflammatory, antibacterial, antioxidant and photoprotective properties. Moreover, sericin can produce hydrogels, films, sponges, foams, dressings, particles, fibers, etc., for various biomedical and pharmaceutical applications (e.g., tissue engineering, wound healing, drug delivery, cosmetics). Given the severe environmental pollution caused by the disposal of sericin and its beneficial properties, there has been growing interest in upcycling this biomaterial, which could have a strong and positive economic, social and environmental impact.

Novel Amoxicillin-Loaded Sericin Biopolymeric Nanoparticles: Synthesis, Optimization, Antibacterial and Wound Healing Activities

Infected wounds are a major threat among diabetic patients. Technological advancements are currently increasing the number of new adjunctive therapies that may be potent agents for speeding recovery, lowering the amputation rate and limiting infection recurrences. A novel formula with promising antibacterial activity, namely sericin/propolis/Amoxicillin nanoparticles, was assessed as a potent treatment of infected wounds in normal and diabetic rats. Skin wound healing efficiency was assessed through wound healing scorings, bacterial load assessment and histological examinations. It was revealed that upon using sericin/propolis/Amoxicillin nanoparticles, complete wound healing was successfully achieved after 10 and 15 days postinjury for nondiabetic and diabetic rats, respectively. However, the bacterial load in the induced infected wounds was extremely low (0-10 CFU/mL) after 15 days post-treatment. The histological studies revealed that the dermis was more organized with new matrix deposition, and mature collagen fibers were observed among the treated animal groups. The present study is the first preclinical study which reported the importance of silk sericin in the form of nano-sericin/propolis loaded with Amoxicillin as an effective treatment against bacterial wound infections.

In Situ Synthesized Porous Bacterial Cellulose/Poly(Vinyl Alcohol)-Based Silk Sericin and Azithromycin Release System for Treating Chronic Wound Biofilm

Chronic wounds are associated with infectious microbial complex communities called biofilms. The management of chronic wound infection is limited by the complexity of selecting an appropriate antimicrobial dressing with antibiofilm activity due to antimicrobial resistance in biofilms. Herein, the in situ developed bacterial cellulose/poly(vinyl alcohol) (BC-PVA) composite is ex situ modified with genipin-crosslinked silk sericin (SS) and azithromycin (AZM) (SSga). The composite is evaluated as a wound dressing material for preventing the development, dispersion, and/or eradication of microbial biofilm. FTIR spectroscopy confirms the intermolecular interactions between the components of BC-PVA@SSga scaffolds. The addition of PVA during BC production significantly increases the porosity from 53.5 ± 2.3 to 83.5 ± 2.9%, the pore size from 2.3 ± 1.9 to 16.8 ± 4.5 μm, the fiber diameter from 35.5 ± 10 to 120 ± 27.4 nm, and improves the thermal stability and flexibility. Studies using bacteria and fungi indicate high inhibition and disruption of biofilms upon AZM addition. In vitro biocompatibility analysis confirms the nontoxic nature of BC-PVA@SSga towards HaCaT and NIH3T3 cells, whereas the addition of SS enhanced cell proliferation. The developed BC-PVA@SSga accelerated wound healing in the infected mouse model, thus could be a promising wound dressing biomaterial. This article is protected by copyright. All rights reserved.

Bacterial cellulose: A promising biopolymer with interesting properties and applications

The ever-increasing demands for materials with desirable properties led to the development of materials that impose unfavorable influences on the environment and the ecosystem. Developing a low-cost, durable, and eco-friendly functional material with biological origins has become necessary to avoid these consequences. Bacterial cellulose generated by bacteria dispenses excellent structural and functional properties and satisfies these requirements. BC and BC-derived materials are essential in developing pure and environmentally safe functional materials. This review offers a detailed understanding of the biosynthesis of BC, properties, various functionalization methods, and applicability in biomedical, water treatment, food storage, energy conversion, and energy storage 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.

De novo strategy with engineering a multifunctional bacterial cellulose-based dressing for rapid healing of infected wounds

The treatment and healing of infected skin lesions is one of the major challenges in surgery. To solve this problem, collagen I (Col-I) and the antibacterial agent hydroxypropyltrimethyl ammonium chloride chitosan (HACC) were composited into the bacterial cellulose (BC) three-dimensional network structure by a novel membrane–liquid interface (MLI) culture, and a Col-I/HACC/BC (CHBC) multifunctional dressing was designed. The water absorption rate and water vapor transmission rate of the obtained CHBC dressing were 35.78 ± 2.45 g/g and 3084 ± 56 g m⁻²·day⁻¹, respectively. The water retention of the CHBC dressing was significantly improved compared with the BC caused by the introduced Col-I and HACC. In vitro results indicated that the combined advantages of HACC and Col-I confer on CHBC dressings not only have outstanding antibacterial properties against Staphylococcus aureus (S. aureus) compared with BC and CBC, but also exhibit better cytocompatibility than BC and HBC to promote the proliferation and spread of NIH3T3 cells and HUVECs. Most importantly, the results of in vivo animal tests demonstrated that the CHBC dressings fully promoted wound healing for 8 days and exhibited shorter healing times, especially in the case of wound infection. Excellent skin regeneration effects and higher expression levels of collagen during infection were also shown in the CHBC group. We believe that CHBC composites with favorable multifunctionality have potential applications as wound dressings to treat infected wounds.

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The antibacterial agent HACC and collagen I were introduced into BC structure by a novel membrane–liquid interface culture.

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CHBC dressing has favorable thermostability, water absorption, water retention rate and WVTRs.

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CHBC dressing has outstanding antibacterial properties against S. aureus.

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CHBC dressing promoted the proliferation and spread of NIH3T3 cells and HUVECs.

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CHBC dressing prevented wound infection caused by S. aureus and accelerated wound healing.

Investigation of the Repairing Effect and Mechanism of Oral Degraded Sericin on Liver Injury in Type II Diabetic Rats

In the sericulture and silk production industry, sericin is discharged in the degumming wastewater, resulting in a large amount of wasted natural protein and environmental pollution. This study investigated the effect of degraded sericin recovered by the Ca(OH)₂–ultrasound degumming method (a green process) on liver injury in T2D rats. After 4 weeks of dietary sericin supplementation, the liver masses and organ coefficients of the T2D rats improved compared with those of the model rats that were not fed sericin. Oral sericin activated the damaged PI3K/AKT/AMPK pathway to enhance glycogen synthesis, accelerate glycolysis, and inhibit gluconeogenesis. The protein expression levels of the inflammatory factors NF-κB, IL-6, and TNF-α in the T2D model group were up to two times higher than in the normal group. However, all three T2D groups that received oral sericin showed significant decreases in these factors to the level found in the normal group, indicating that inflammation in the body was significantly reduced. These results show that the sericin protein might improve glycogen synthesis, accelerate glycolysis, and inhibit gluconeogenesis by enhancing the anti-oxidation capability and reducing inflammatory reactions. Therefore, sericin recovered by Ca(OH)₂ degradation has potential use in the development of functional health foods that can lower blood sugar.

Recent Advances on Bacterial Cellulose-Based Wound Management: Promises and Challenges

Wound healing is a therapeutic challenge due to the complexity of the wound. Various wounds could cause severe physiological trauma and bring social and economic burdens to the patient. The conventional wound healing treatments using bandages and gauze are limited particularly due to their susceptibility to infection. Different types of wound dressing have developed in different physical forms such as sponges, hydrocolloids, films, membranes, and hydrogels. Each of these formulations possesses distinct characteristics making them appropriate for the treatment of a specific wound. In this review, the pathology and microbiology of wounds are introduced. Then, the most recent progress on bacterial cellulose- (BC-) based wound dressing discussed and highlighted their antibacterial and reepithelization properties in vitro and in vivo wound closure. Finally, the challenges and future perspectives on the development of BC-based wound dressing biomaterials are outlined.

Bacterial cellulose-based composites for biomedical and cosmetic applications: Research progress and existing products

Bacterial cellulose (BC) is a promising unique material for various biomedical and cosmetic applications due to its morphology, mechanical strength, high purity, high water uptake, non-toxicity, chemical controllability, and biocompatibility. Today, extensive investigation is into the manufacturing of BC-based composites with other components such as nanoparticles, synthetic polymers, natural polymers, carbon materials, and biomolecules, which will allow the development of a wide range of biomedical and cosmetic products. Moreover, the addition of different reinforcement substances into BC and the organized arrangement of BC nano-fibers have proven a promising improvement in their properties for biomedical applications. This review paper highlights the progress in synthesizing BC-based composites and their applications in biomedical fields, such as wound healing, drug delivery, tissue engineering, and cancer treatment. It emphasizes high-performance BC-based materials and cosmetic applications. Furthermore, it presents challenges yet to be defeated and future possibilities for BC-based composites for biomedical and cosmetic applications.

Bacterial Cellulose: Functional Modification and Wound Healing Applications

Significance: Wound dressings are frequently used for wound covering and healing. Ideal wound dressings should provide a moist environment for wounds and actively promote wound healing and skin recovery. The materials used as ideal wound dressings should possess specific properties, thus accelerating skin tissue regeneration process. Recent Advances: Bacterial cellulose (BC) is a natural polymer synthesized by some bacteria. As a kind of natural biopolymer, BC shows good biological activity, biodegradability, and biological adaptability. It has many unique physical, chemical, and biological properties, such as ultrafine nanofiber network, high crystallinity, high water absorption and retention capacity, and high tensile strength and elastic modulus. These excellent properties of BC have laid the foundation for its application as dressing in wound healing. Critical Issues: To optimize the biocompatibility and antimicrobial activity of BC, different methods including microbial fermentation, physical modification, chemical modification, and compound modification have been adopted to modify BC to ensure a better application in wound healing. BC-based wound dressings have been applied in infected wounds, acute traumatic injuries, burns, and diabetic wounds, showing remarkable therapeutic effects on promoting wound healing. Furthermore, there have been some commercial BC-based dressings and they have been utilized in clinical practice. Future Directions: Because of its excellent physicochemical characteristics and biological properties, BC shows high clinical value to be used as a wound dressing for skin tissue regeneration.

Immune Response to Silk Sericin-Fibroin Composites: Potential Immunogenic Elements and Alternatives for Immunomodulation

The unique properties of silk proteins (SPs), particularly silk sericin (SS) and silk fibroin (SF), have attracted attention in the design of scaffolds for tissue engineering over the past decades. Since SF has good mechanical properties, while SS displays bioactivity, scaffolds combining both proteins should exhibit complementary properties enhancing the potential of these materials. Unfortunately, SS-SF composites can generate chronic immune responses and their immunogenic element is not completely clear. The potential of SS-SF composites in tissue engineering, elements which may contribute to their immunogenicity, and alternatives for their preparation and design, to modulate the immune response and take advantage of their useful properties, are discussed in this review. It is known that SS can enhance β-sheet formation in SF, which may act as hydrophobic regions with a strong affinity for adsorption proteins inducing the chronic recruitment of inflammatory cells. Therefore, tailoring the exposure of hydrophobic regions at the scaffold surface should represent a viable strategy to modulate the immune response. This can be achieved by coating SS-SF composites with SS or other hydrophilic polymers, to take advantage of their antibiofouling properties. Research is still needed to realize the full potential of these composites for tissue engineering.

Degraded Sericin Significantly Regulates Blood Glucose Levels and Improves Impaired Liver Function in T2D Rats by Reducing Oxidative Stress

Sericin could be degraded well into low-molecular-weight sericin (SS) through a novel and environmentally friendly recycling process using an ultrasonically degumming method in Ca(OH)₂ aqueous solution. The oral administration of the SS has an evidently hypoglycemic effect on STZ-induced T2D rats. At oral doses of 2.5 and 5% SS for four weeks, the fasting blood glucose decreased by over 60% compared with that in the untreated model group. Oral glucose tolerance and insulin tolerance were ameliorated by the peptide treatment. The serum insulin level was reduced by approximately 35%, the insulin resistance index was reduced by more than 66%. The 8-hydroxy-2 deoxyguanosine level showed a large reduction of 20%, and the total antioxidant activities significantly increased. Hematoxylin-eosin staining and fluorescent immunostaining sections showed that liver and pancreas damage was partly recovered in T2D rats. In summary, oral SS demonstrated evidently hypoglycemic effects mainly related to reducing oxidative stress in the damaged liver and pancreas of T2D rats. Therefore, these results have suggested that the degraded sericin has a potential use in SS-based healthy functional food or hypoglycemic drugs as a waste recovered from sericulture resources.

Applications of Bacterial Cellulose as a Natural Polymer in Tissue Engineering

Choosing the material with the best regeneration potential and properties closest to that of the extracellular matrix is one of the main challenges in tissue engineering and regenerative medicine. Natural polymers, such as collagen, elastin, and cellulose, are widely used for this purpose in tissue engineering. Cellulose derived from bacteria has excellent mechanical properties, high hydrophilicity, crystallinity, and a high degree of polymerization and, therefore, can be used as scaffold/membrane for tissue engineering. In the current study, we reviewed the latest trends in the application of bacterial cellulose (BC) polymers as a scaffold in different types of tissue, including bone, vascular, skin, and cartilage. Also, we mentioned the biological and mechanical advantages and disadvantages of BC polymers. Given the data presented in this study, BC polymer could be suggested as a favorable natural polymer in the design of tissue scaffolds. Implementing novel composites that combine this polymer with other materials through modern or rapid prototyping methods can open up a great prospect in the future of tissue engineering and regenerative medicine.

Mussel Adhesive Mimetic Silk Sericin Prepared by Enzymatic Oxidation for the Construction of Antibacterial Coatings

With the rapid development and advancement in orthodontic and orthopedic technologies, the demand for biomedical-grade titanium (Ti) alloys is growing. The Ti-based implants are susceptible to bacterial infections, leading to poor healing and osteointegration, resulting in implant failure or repeated surgical intervention. Silk sericin (SS) is hydrophilic, biocompatible, and biodegradable and could induce a low immunological response in vivo. As a result, it would be intriguing to investigate the use of hydrophilic SS in surface modification. In this work, the tyrosine moiety in SS was oxidized by tyrosinase (or polyphenol oxidase) to the 3,4-dihydroxyphenylalanine (DOPA) form, generating the catechol moiety-containing SS (SSC). Inspired by the adhesion of mussel foot proteins, the SSC coatings could be directly deposited onto multiple surfaces in SS and tyrosinase mixed stock solutions to create active surfaces with catechol groups. Further, the SSC-coated Ti surfaces were hybridized with silver nanoparticles (Ag NPs) via in situ silver ion (Ag⁺) reduction. The antibacterial properties of the Ag NPs/SS-coated Ti surfaces are demonstrated, and they can prevent bacterial cell adhesion as well as early-stage biofilm formation. In addition, the developed Ag NPs/SSC-coated Ti surfaces exhibited a negligible level of cytotoxicity in L929 mouse fibroblast cells.

Homogeneous and efficient production of a bacterial nanocellulose-lactoferrin-collagen composite under an electric field as a matrix to promote wound healing

BNC was functionalized with collagen (COL) and lactoferrin (LF) to form three different composites: BNC/COL, BNC/LF and BNC/LF/COL using a novel electrophoresis-based technology. The technology is less time-consuming than traditional immersion-adsorption methods and offers the additional advantages of greater protein loading, better homogeneity and a lower requirement for processing solution. Significantly, it has general applicability and great potential for fabricating other similar composites. The water-holding capability and water vapor transmission rate (WVTR) of BNC composites were significantly improved, particularly in the case of BNC/LF/COL, with a WVTR of 2600 g m-2 d-1, indicating that the composite maintains a moderately moist environment over the wound bed, which would enhance epithelial cell migration during the healing process. Compared with BNC and BNC/COL, the LF-impregnated composites mediated a reduction in bacterial viability of at least 77%. Impregnation with COL significantly improved the cytocompatibility of BNC composites to promote the adhesion and proliferation of fibroblast cells. Furthermore, a greater therapeutic effect of BNC/LF/COL was observed in a rat model of wound healing, with a new epithelium formed within 9 days and without any significant adverse reactions. These results suggest that BNC/LF/COL obtained using the electrophoresis method represents a promising wound dressing for use in practical applications.

A review of functionalised bacterial cellulose for targeted biomedical fields

Bacterial cellulose (BC), which can be produced by microorganisms, is an ideal biomaterial especially for tissue engineering and drug delivery systems thanks to its properties of high purity, biocompatibility, high mechanical strength, high crystallinity, 3 D nanofiber structure, porosity and high-water holding capacity. Therefore, wide ranges of researches have been done on the BC production process and its structural and physical modifications to make it more suitable for certain targeted biomedical applications thoroughly. BC's properties such as mechanical strength, pore diameter and porosity can be tuned in situ or ex situ processes by using various polymer and compounds. Besides, different organic or inorganic compounds that support cell attachment, proliferation and differentiation or provide functions such as antimicrobial effectiveness can be gained to its structure for targeted application. These processes not only increase the usage options of BC but also provide success for mimicking the natural tissue microenvironment, especially in tissue engineering applications. In this review article, the studies on optimisation of BC production in the last decade and the BC modification and functionalisation studies conducted for the three main perspectives as tissue engineering, drug delivery and wound dressing with diverse approaches are summarized.

Homogeneous and efficient production of a bacterial nanocellulose-lactoferrin-collagen composite under an electric field as a matrix to promote wound healing

A novel BNC/LF/COL membrane fabricated using an electrophoresis-based technology showed superior advantages in water-holding capability and antibacterial activity, with higher cytocompatibility as well as greater therapeutic effect in wound healing.

Rational Design of Ag/ZnO Hybrid Nanoparticles on Sericin/Agarose Composite Film for Enhanced Antimicrobial Applications

Silver-based hybrid nanomaterials are receiving increasing attention as potential alternatives for traditional antimicrobial agents. Here, we proposed a simple and eco-friendly strategy to efficiently assemble zinc oxide nanoparticles (ZnO) and silver nanoparticles (AgNPs) on sericin-agarose composite film to impart superior antimicrobial activity. Based on a layer-by-layer self-assembly strategy, AgNPs and ZnO were immobilized on sericin-agarose films using the adhesion property of polydopamine. Scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray powder diffraction spectroscopy were used to show the morphology of AgNPs and ZnO on the surface of the composite film and analyze the composition and structure of AgNPs and ZnO, respectively. Water contact angle, swelling ratio, and mechanical property were determined to characterize the hydrophilicity, water absorption ability, and mechanical properties of the composite films. In addition, the antibacterial activity of the composite film was evaluated against Gram-positive and Gram-negative bacteria. The results showed that the composite film not only has desirable hydrophilicity, high water absorption ability, and favorable mechanical properties but also exhibits excellent antimicrobial activity against both Gram-positive and Gram-negative bacteria. It has shown great potential as a novel antimicrobial biomaterial for wound dressing, artificial skin, and tissue engineering.

Design and characterization of plasticized bacterial cellulose/waterborne polyurethane composite with antibacterial function for nasal stenting

A nasal stent capable of preventing adhesions and inflammation is of great value in treating nasal diseases. In order to solve the problems of tissue adhesion and inflammation response, we prepared plasticized bacterial cellulose (BCG) and waterborne polyurethane (WPU) composite with antibacterial function used as a novel nasal stent. The gelation behavior of BCG could contribute to protecting the paranasal sinus mucosa; meanwhile, the WPU with improved mechanical property was aimed at supporting the narrow nasal cavity. The thickness, size and the supporting force of the nasal stent could be adjusted according to the specific conditions of the nasal. Thermogravimetric analysis, contact angle and water absorption test were applied to investigate the thermal, hydrophilic and water absorption properties of the composite materials. The composite materials loaded with poly(hexamethylene biguanide) hydrochloride maintained well antibacterial activity over 12 days. Animal experiments further revealed that the mucosal epithelium mucosae damage of BCG-WPU composite was minor compared with that of WPU. This new type of drug-loaded nasal stent can effectively address the postoperative adhesions and infections while ensuring the health of nasal mucosal, and thus has an immense clinical application prospects in treating nasal diseases.

Fabrication of Bacterial Cellulose-Curcumin Nanocomposite as a Novel Dressing for Partial Thickness Skin Burn

The current study aimed to fabricate curcumin-loaded bacterial cellulose (BC-Cur) nanocomposite as a potential wound dressing for partial thickness burns by utilizing the therapeutic features of curcumin and unique structural, physico-chemical, and biological features of bacterial cellulose (BC). Characterization analyses confirmed the successful impregnation of curcumin into the BC matrix. Biocompatibility studies showed the better attachment and proliferation of fibroblast cells on the BC-Cur nanocomposite. The antibacterial potential of curcumin was tested against Escherichia coli (E. coli), Pseudomonas aeruginosa (P. aeruginosa), Salmonella typhimurium (S. typhimurium), and Staphylococcus aureus (S. aureus). Wound healing analysis of partial-thickness burns in Balb^c mice showed an accelerated wound closure up to 64.25% after 15 days in the BC-Cur nanocomposite treated group. Histological studies showed healthy granulation tissues, fine re-epithelialization, vascularization, and resurfacing of wound bed in the BC-Cur nanocomposite group. These results indicate that combining BC with curcumin significantly improved the healing pattern. Thus, it can be concluded that the fabricated biomaterial could provide a base for the development of promising alternatives for the conventional dressing system in treating burns.

N-halamine modified multiporous bacterial cellulose with enhanced antibacterial and hemostatic properties

Bacterial cellulose (BC) is a natural polymer with remarkable superiority for fabricating biomaterials. In this study, a multiporous bacterial cellulose (MBC) film was modified with N-isopropylacrylamide (NIPAM), and the modified MBC film was imbued with antibacterial properties after chlorination. The dried chlorinated samples showed superb antibacterial efficacy and could inactivate 6.19 log of inoculated S. aureus and 6.29 log of E. coli within 1 min of contact. After releasing active chlorine for 12 h, 3.67 log of S. aureus and 3.97 log of E. coli were inactivated within 30 min of contact. The prepared films displayed high porous and layered structures with a resultant excellent water retention which can be applied as material for wound dressings. In addition, the chlorinated films showed hemostatic ability on wound bleeding and good biocompatibility. The prepared N-halamine functionalized MBC films might have great potential applications as wound dressings.

Current progress on the production, modification, and applications of bacterial cellulose

Adoption of biomass for the development of biobased products has become a routine agenda in evolutionary metabolic engineering. Cellulose produced by bacteria is a "rising star" for this sustainable development. Unlike plant cellulose, bacterial cellulose (BC) shows several unique properties like a high degree of crystallinity, high purity, high water retention, high mechanical strength, and enhanced biocompatibility. Favored with those extraordinary properties, BC could serve as ideal biomass for the development of various industrial products. However, a low yield and the requirement for large growth media have been a persistent challenge in mass production of BC. A significant number of techniques has been developed in achieving efficient BC production. This includes the modification of bioreactors, fermentation parameters, and growth media. In this article, we summarize progress in metabolic engineering in order to solve BC growth limitation. This article emphasizes current engineered BC production by using various bioreactors, as well as highlighting the structure of BC fermented by different types of engineered-bioreactors. The comprehensive overview of the future applications of BC, aims to provide readers with insight into new economic opportunities of BC and their modifiable properties for various industrial applications. Modifications in chemical composition, structure, and genetic regulation, which preceded the advancement of BC applications, were also emphasized.

Bacterial cellulose: Biosynthesis, production, and applications

Bacterial cellulose (BC) is a natural polymer produced by the acetic acid producing bacterium and has gathered much interest over the last decade for its biomedical and biotechnological applications. Unlike the plant derived cellulose nanofibres, which require pretreatment to deconstruct the recalcitrant lignocellulosic network, BC are 100% pure, and are extruded by cells as nanofibrils. Moreover, these nanofibrils can be converted to macrofibers that possess excellent material properties, surpassing even the strength of steel, and can be used as substitutes for fossil fuel derived synthetic fibers. The focus of the review is to present the fundamental long-term research on the influence of environmental factors on the organism's BC production capabilities, the production methods that are available for scaling up/scaled-up processes, and its use as a bulk commodity or for biomedical applications.

Bacterial nanocellulose: Present status, biomedical applications and future perspectives

Bacterial nanocellulose (BNC) has emerged as a natural biopolymer of significant importance in diverse technological areas due to its incredible physicochemical and biological characteristics. However, the high capital investments, production cost and lack of well-organized scale-up processes resulting in low BNC production are the major impediments need to be resolved. This review enfolds the three different and important portions of BNC. Firstly, advancement in production technologies of BNC like cell-free extract technology, static intermittent fed batch technology and novel cost-effective substrates that might surmount the barriers associated with BNC production at industrial level. Secondly, as BNC and its composites (with other polymers/nanoparticles) represents the utmost material of preference in current regenerative and diagnostic medicine, therefore recently reported biomedical applications of BNC and functionalized BNC in drug delivery, tissue engineering, antimicrobial wound healing and biosensing are widely been focused here. The third and the most important aspect of this review is an in-depth discussion of various pitfalls associated with BNC production. Recent trends in BNC research to overcome the existing snags that might pave a way for industrial scale production of BNC thereby facilitating its feasible application in various fields are highlighted.

Hydrophobic IR780 loaded sericin nanomicelles for phototherapy with enhanced antitumor efficiency

The near-infrared dye, IR780 iodide, has been utilized in photodynamic therapy (PDT) and photothermal therapy (PTT). However, the hydrophobicity and photosensitivity of IR780 limit its further applications in biomedical fields. Herein, the hydrophilic sericin was modified with hydrophobic cholesterol to form an amphiphilic macromolecular conjugate (Ser-Chol). The tumor-targeting agent, folic acid (FA), was further linked to the conjugate (FA-Ser-Chol). The IR780 could be encapsulated into such amphiphilic macromolecule to form stable micelles (FA-Ser-Chol/IR780) by self-assembly, and the solubility and photo-stability of IR780 were greatly improved. The FA-Ser-Chol/IR780 micelles could be efficiently absorbed by FA-positive gastric cancer cells (BGC-823) through FA receptors, while the uptake micelles showed remarkable PDT and PTT cytotoxicity towards BGC-823 cells under laser irradiation of 808 nm. Therefore, FA-Ser-Chol micelles may serve as a promising IR780 carrier for PDT and PTT therapy.

Facile preparation of a Ca(ii) carboxymethyl cellulose complex with enhanced calcium bioavailability for treatment of osteoporosis

At present, though calcium (Ca) reagents with high calcium contents are widely synthesized, their wide application is limited due to their low absorption rates and poor bioavailability. Here we use a carboxymethyl cellulose (CMC) derivative with high water solubility and biocompatibility as a ligand to bind Ca2+. The resulting CaCMC complex exhibits remarkable solubility and absorbability under both basic and acidic conditions as well as in stomach mimicking and the gastrointestinal tract. Importantly, this Ca reagent shows high in vivo calcium bioavailability. Data from osteoporosis mouse models show that the CaCMC complex is superior to calcium carbonate in the treatment of osteoporosis. Therefore, the resulting CaCMC complex is used as a new, highly effective and desirable Ca supplement for daily life and clinical applications.

High-toughness natural polymer nonwoven preforms inspired by silkworm cocoon structure

As the interest in environmentally friendly materials and concerns regarding depletion of petroleum resources has increased, the research on natural polymers is being actively pursued. Among the various materials based on natural polymeric resources, the interest in using natural fibers in bio-composites has grown due to their lightweight, non-toxicity, low cost, and abundance. However, the lack of interfacial adhesion between filaments and poor water resistance make the use of natural fiber-based polymer composites less attractive. To overcome these drawbacks, formaldehyde-based synthetic binders have been used. However, this requires an additional synthesis of the binder, and potential toxicity problems exist. In this work, robust and rigid natural polymer nonwoven preforms were prepared by mixing jute fibers with silk sericin (SS). SS was employed as a natural facile binder and the strong binding between jute fibers and SS resulted in remarkable enhancements in tensile strength, elongation, and toughness, which increased up to 539.1, 385.7, and 1943.8%, respectively, compared with the pristine jute nonwoven. In addition, the dense and rigid structure obtained through SS coating ensured the structural stability of the nonwoven preforms in moisture environments. Silkworm cocoon-structured natural polymer nonwoven preforms with excellent mechanical strength and higher physical stability may have more potential utilization in the composite material fields.

Silk sericin-enhanced microstructured bacterial cellulose as tissue engineering scaffold towards prospective gut repair

As a first step towards the production of functional cell sheets applicable for the regeneration of gut muscle layer, microstructured bacterial cellulose (mBC) was assessed for its ability to support the growth of enteric nervous system (ENS) and gut smooth muscle cells (SMCs). To improve the cellular response, mBC was modified with silk sericin (SS) which has renowned abilities in supporting tissue regeneration. While SS did not impair the line structures imparted to BC by PDMS templates, similarly to the patterns, it affected its physical properties, ultimately leading to variations in the behavior of cells cultured onto these substrates. Enabled by the stripes on mBC, both SMCs and ENS cells were aligned in vitro, presenting the in vivo-like morphology essential for peristalsis and gut function. Interestingly, cell growth and differentiation remarkably enhanced upon SS addition to the samples, indicating the promise of the mBC-SS constructs as biomaterial not only for gut engineering, but also for tissues where cellular alignment is required for function, namely the heart, blood vessels, and similars.