Non-immunogenic, porous and antibacterial chitosan and Antheraea mylitta silk sericin hydrogels as potential dermal substitute

Expanding the boundaries of silk sericin biomaterials in biomedical applications

Silk sericin (SS) has a long history as a by-product of the textile industry. SS has emerged as a sustainable material for biomedical engineering due to its material properties including water solubility, diverse impact on biological activities including antibacterial and antioxidant properties, and ability to promote cell adhesion and proliferation. This review addresses the origin, structure, properties, extraction, and underlying functions of this protein. An overview of the growing research studies and market evolution is presented, along with highlights of the most common fabrication matrices (hydrogels, bioinks, porous and fibrous scaffolds) and tissue engineering applications. Finally, the future trends with this protein as a multifaceted toolbox for bioengineering are explored, along with the challenges with SS. Overall, the present review can serve as a foundation for the creation of innovative biomaterials utilizing SS as a fundamental building block that hold market potential.

Silk Sericin and Its Composite Materials with Antibacterial Properties to Enhance Wound Healing: A Review

Wound infections may disrupt the normal wound-healing process. Large amounts of antibiotics are frequently used to prevent pathogenic infections; however, this can lead to resistance development. Biomaterials possessing antimicrobial properties have promising applications for reducing antibiotic usage and promoting wound healing. Silk sericin (SS) has been increasingly explored for skin wound healing applications owing to its excellent biocompatibility and antioxidant, antimicrobial, and ultraviolet-resistant properties. In recent years, SS-based composite biomaterials with a broader antimicrobial spectrum have been extensively investigated and demonstrated favorable efficacy in promoting wound healing. This review summarizes various antimicrobial agents, including metal nanoparticles, natural extracts, and antibiotics, that have been incorporated into SS composites for wound healing and elucidates their mechanisms of action. It has been revealed that SS-based biomaterials can achieve sustained antimicrobial activity by slow-release-loaded antimicrobial agents. The antimicrobial-loaded SS composites may promote wound healing through anti-infection, anti-inflammation, hemostasis, angiogenesis, and collagen deposition. The manufacturing methods, benefits, and limitations of antimicrobial-loaded SS materials are briefly discussed. This review aims to enhance the understanding of new advances and directions in SS-based antimicrobial composites and guide future biomedical research.

Advances of regenerated and functionalized silk biomaterials and application in skin wound healing

The cocoon silk of silkworms (Bombyx mori) has multiple potential applications in biomedicine due to its good biocompatibility, mechanical properties, degradability, and plasticity. Numerous studies have confirmed that silk material dressings are more effective than traditional ones in the skin wound healing process. Silk material research has recently moved toward functionalized biomaterials and achieved remarkable results. Herein, we summarize the recent advances in functionalized silk materials and their efficacy in skin wound healing. In particular, transgenic technology has realized the specific expression of human growth factors in the silk glands of the silkworms, which lays the foundation for fabricating novel and low-cost functionalized materials. Without a green and safe preparation process, the best raw silk materials cannot be made into medically safe products. Therefore, we provide an overview of green and gentle approaches for silk degumming and silk sericin (SS) extraction. Moreover, we summarize and discuss the processing methods of silk fibroin (SF) and SS materials and their potential applications, such as burns, diabetic wounds, and other wounds. This review aims to enhance our understanding of new advances and directions in silk materials and guide future biomedical research.

Porous Poly(2-hydroxyethyl methacrylate) Hydrogel Scaffolds for Tissue Engineering: Influence of Crosslinking Systems and Silk Sericin Concentration on Scaffold Properties

Tailored porous structures of poly(2-hydroxyethyl methacrylate) (PHEMA) and silk sericin (SS) were used to create porous hydrogel scaffolds using two distinct crosslinking systems. These structures were designed to closely mimic the porous nature of the native extracellular matrix. Conventional free radical polymerization of 2-hydroxyethyl methacrylate (HEMA) was performed in the presence of different concentrations of SS (1.25, 2.50, 5.00% w/v) with two crosslinking systems. A chemical crosslinking system with N'N-methylene bisacrylamide (MBAAm) and a physical crosslinking system with dimethylurea (DMU) were used: C-PHEMA/SS (crosslinked using MBAAm) and C-PHEMA/pC-SS (crosslinked using MBAAm and DMU). The focus of this study was on investigating the impact of these crosslinking methods on various properties of the scaffolds, including pore size, pore characteristics, polymerization time, morphology, molecular interaction, in vitro degradation, thermal properties, and in vitro cytotoxicity. The various crosslinked networks were found to appreciably influence the properties of the scaffolds, especially the pore sizes, in which smaller sizes and higher numbers of pores with high regularity were seen in C-PHEMA/1.25 pC-SS (17 ± 2 μm) than in C-PHEMA/1.25 SS (34 ± 3 μm). Semi-interpenetrating networks were created by crosslinking PHEMA-MBAAm-PHEMA while incorporating free protein molecules of SS within the networks. The additional crosslinking step involving DMU occurred through hydrogen bonding of the -C=O and -N-H groups with the SS, resulting in the simultaneous incorporation of DMU and SS within the PHEMA networks. As a consequence of this process, the scaffold C-PHEMA/pC-SS exhibited smaller pore sizes compared to scaffolds without DMU crosslinking. Moreover, the incorporation of higher loadings of SS led to even smaller pore sizes. Additionally, the gelation time of C-PHEMA/pC-SS was delayed due to the presence of DMU in the crosslinking system. Both porous hydrogel scaffolds, C-PHEMA/pC-SS and PHEMA, were found to be non-cytotoxic to the normal human skin dermal fibroblast cell line (NHDF cells). This promising result indicates that these hydrogel scaffolds have potential for use in tissue engineering applications.

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 evaluation of bioinspired pH-responsive sericin-chitosan-based hydrogel for controlled colonic delivery of PETase: Harnessing PETase-triggered degradation of microplastics

The gravity of threats posed by microplastic pollution to the environment cannot be overestimated. Being ubiquitous in the living environment, microplastics reach humans through the food chain causing various hazardous effects. Microplastics can be effectively degraded by PETase enzymes. The current study reports, for the first time, a hydrogel-encapsulated, bioinspired colonic delivery of PETase. A free radical polymerization-assisted hydrogel system was synthesized from sericin, chitosan, and acrylic acid using N,N'-methylenebisacrylamide as a crosslinker and ammonium persulfate as an initiator. The hydrogel was characterized with FTIR, PXRD, SEM, and thermal analysis to confirm the development of a stabilized hydrogel system. The hydrogel showed 61 % encapsulation efficiency, maximum swelling, and cumulative PETase release (96 %) at pH 7.4. The mechanism of PETase release exhibited the Higuchi pattern of release with an anomalous transport mechanism. SDS-PAGE analysis confirmed the preservation of the post-release structural integrity of PETase. The released PETase exhibited concentration- and time-dependent degradation of polyethylene terephthalate in vitro. The developed hydrogel system exhibited the intended features of a stimulus-sensitive carrier system that can be efficiently used for the colonic delivery of PETase.

Silk sericin as building blocks of bioactive materials for advanced therapeutics

Silk sericin is a class of protein biopolymers produced by silkworms. Increasing attention has been paid to silk sericin for biomedical applications in the last decade, not only because of its excellent biocompatibility and biodegradability but also due to the pharmacological activities stemming from its unique amino acid compositions. In this review, the biological properties of silk sericin, including curing specific diseases and promoting tissue regeneration, as well as underlying mechanisms are summarized. We consider the antioxidant activity of silk sericin as a fundamental property, which could account for partial biological activities, despite the exact mechanisms of silk sericin's effect remaining unknown. Based on the reactive groups on silk sericin, approaches of bottom-up fabrication of silk sericin-based biomaterials are highlighted, including non-covalent interactions and chemical reactions (reduction, crosslinking, bioconjugation, and polymerization). We then briefly present the cutting-edge advances of silk sericin-based biomaterials applied in tissue engineering and drug delivery. The challenges of silk sericin-based biomaterials are proposed. With more bioactivities and underlying mechanisms of silk sericin uncovered, it is going to boost the therapeutic potential of silk sericin-based biomaterials.

Flat Silk Cocoon-Based Dressing: Daylight-Driven Rechargeable Antibacterial Membranes Accelerate Infected Wound Healing

One of the leading causes of death globally, especially in underdeveloped countries, is bacterial infection. Recently, the prevalence of infections from antibiotic-resistant bacteria has been increasing, which makes the need for innovative antibacterial wound dressings urgent. It is reported that g-C₃ N₄ -based flat silk cocoons (FSCs) with rechargeable antibacterial activity can efficiently generate reactive oxygen species (ROS) under daylight irradiation. The photoactive FSCs store the ROS and then release them in the dark. The engineered FSCs exhibit integrated properties of good biocompatibility, strong mechanical characteristics, robust photoactivity with photostorability, and excellent bactericidal efficiency (99.9% contact killing). In a rat model of infected wounds, the photoactive FSCs induce faster healing and reduce bacterial infections. The successful application of these FSC materials as wound dressings may provide a versatile platform for exploring the use of green photoactive antibacterial materials for accelerated wound healing and prevention of infections.

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.

Nonmulberry silk proteins: multipurpose ingredient in bio-functional assembly

The emerging field of tissue engineering and regenerative medicines utilising artificial polymers is facing many problems. Despite having mechanical stability, non-toxicity and biodegradability, most of them lack cytocompatibility and biocompatibility. Natural polymers (such as collagen, hyaluronic acid, fibrin, fibroin, and others), including blends, are introduced to the field to solve some of the relevant issues. Another natural biopolymer: silkworm silk gained special attention primarily due to its specific biophysical, biochemical, and material properties, worldwide availability, and cost-effectiveness. Silk proteins, namely fibroin and sericin extracted from domesticated mulberry silkwormBombyx mori, are studied extensively in the last few decades for tissue engineering. Wild nonmulberry silkworm species, originated from India and other parts of the world, also produce silk proteins with variations in their nature and properties. Among the nonmulberry silkworm species,Antheraea mylitta(Indian Tropical Tasar),A. assamensis/A. assama(Indian Muga), andSamia ricini/Philosamia ricini(Indian Eri), along withA. pernyi(Chinese temperate Oak Tasar/Tussah) andA. yamamai(Japanese Oak Tasar) exhibit inherent tripeptide motifs of arginyl glycyl aspartic acid in their fibroin amino acid sequences, which support their candidacy as the potential biomaterials. Similarly, sericin isolated from such wild species delivers unique properties and is used as anti-apoptotic and growth-inducing factors in regenerative medicines. Other characteristics such as biodegradability, biocompatibility, and non-inflammatory nature make it suitable for tissue engineering and regenerative medicine based applications. A diverse range of matrices, including but not limited to nano-micro scale structures, nanofibres, thin films, hydrogels, and porous scaffolds, are prepared from the silk proteins (fibroins and sericins) for biomedical and tissue engineering research. This review aims to represent the progress made in medical and non-medical applications in the last couple of years and depict the present status of the investigations on Indian nonmulberry silk-based matrices as a particular reference due to its remarkable potentiality of regeneration of different types of tissues. It also discusses the future perspective in tissue engineering and regenerative medicines in the context of developing cutting-edge techniques such as 3D printing/bioprinting, microfluidics, organ-on-a-chip, and other electronics, optical and thermal property-based applications.

Current knowledge of immunomodulation strategies for chronic skin wound repair

In orchestrating the wound healing process, the immune system plays a critical role. Hence, controlling the immune system to repair skin defects is an attractive approach. The highly complex immune system includes the coordinated actions of several immune cells, which can produce various inflammatory and antiinflammatory cytokines and affect the healing of skin wounds. This process can be optimized using biomaterials, bioactive molecules, and cell delivery. The present review discusses various immunomodulation strategies for supporting the healing of chronic wounds. In this regard, following the evolution of the immune system and its role in the wound healing mechanism, the interaction between the extracellular mechanism and immune cells for acceleration wound healing will be firstly investigated. Consequently, the immune-based chronic wounds will be briefly examined and the mechanism of progression, and conventional methods of their treatment are evaluated. In the following, various biomaterials-based immunomodulation strategies are introduced to stimulate and control the immune system to treat and regenerate skin defects. Other effective methods of controlling the immune system in wound healing which is the release of bioactive agents (such as antiinflammatory, antigens, and immunomodulators) and stem cell therapy at the site of injury are reviewed.

Antimicrobial Peptide Dendrimers and Quorum-Sensing Inhibitors in Formulating Next-Generation Anti-Infection Cell Therapy Dressings for Burns

Multidrug resistance infections are the main cause of failure in the pro-regenerative cell-mediated therapy of burn wounds. The collagen-based matrices for delivery of cells could be potential substrates to support bacterial growth and subsequent lysis of the collagen leading to a cell therapy loss. In this article, we report the development of a new generation of cell therapy formulations with the capacity to resist infections through the bactericidal effect of antimicrobial peptide dendrimers and the anti-virulence effect of anti-quorum sensing MvfR (PqsR) system compounds, which are incorporated into their formulation. Anti-quorum sensing compounds limit the pathogenicity and antibiotic tolerance of pathogenic bacteria involved in the burn wound infections, by inhibiting their virulence pathways. For the first time, we report a biological cell therapy dressing incorporating live progenitor cells, antimicrobial peptide dendrimers, and anti-MvfR compounds, which exhibit bactericidal and anti-virulence properties without compromising the viability of the progenitor cells.

Conductive chitosan/polyaniline hydrogel with cell-imprinted topography as a potential substrate for neural priming of adipose derived stem cells

Biophysical characteristics of engineered scaffolds such as topography and electroconductivity have shown potentially beneficial effects on stem cell morphology, proliferation, and differentiation toward neural cells. In this study, we fabricated a conductive hydrogel made from chitosan (CS) and polyaniline (PANI) with induced PC12 cell surface topography using a cell imprinting technique to provide both topographical properties and conductivity in a platform. The engineered hydrogel's potential for neural priming of rat adipose-derived stem cells (rADSCs) was determined in vitro. The biomechanical analysis revealed that the electrical conductivity, stiffness, and hydrophobicity of flat (F) and cell-imprinted (CI) substrates increased with increased PANI content in the CS/PANI scaffold. The conductive substrates exhibited a lower degradation rate compared to non-conductive substrates. According to data obtained from F-actin staining and AFM micrographs, both CI(CS) and CI(CS-PANI) substrates induced the morphology of rADSCs from their irregular shape (on flat substrates) into the elongated and bipolar shape of the neuronal-like PC12 cells. Immunostaining analysis revealed that both CI(CS) and CI (CS-PANI) significantly upregulated the expression of GFAP and MAP2, two neural precursor-specific genes, in rADSCs compared with flat substrates. Although the results reveal that both cell-imprinted topography and electrical conductivity affect the neural lineage differentiation, some data demonstrate that the topography effects of the cell-imprinted surface have a more critical role than electrical conductivity on neural priming of ADSCs. The current study provides new insight into the engineering of scaffolds for nerve tissue engineering.

Synthesis, Characterization and Safety Evaluation of Sericin-Based Hydrogels for Controlled Delivery of Acyclovir

Conventional formulations of antiviral drug acyclovir have various limitations such as low bioavailability. The current study was aimed at developing polymeric matrices for the controlled delivery of acyclovir using sericin as polymer and acrylic acid (AA) as a monomer. The free radical polymerization technique was used for hydrogel formulation. Briefly, sericin was chemically cross-linked with acrylic acid. N′-N′-methylene bis-acrylamide (MBA) and ammonium persulfate (APS) were used as cross-linker and initiator, respectively. FTIR spectra showed that acyclovir was successfully loaded into sericin hydrogel. SEM micrographs revealed that the outer surface was solid-like and smooth. According to DSC thermograms, the developed polymeric network was thermally stable. Amorphous nature of acyclovir was observed in XRD. The pH of medium and reactants’ concentration affected swelling dynamics and acyclovir release pattern. In addition, drug release occurred through a diffusion-controlled process. Sericin hydrogel suspension was well tolerable up to 3800 mg/kg of rabbits’ body weight. Haematology and serum chemistry results were well within the range signifying normal liver and kidney functions. Similarly, histopathology slides of the rabbit’s vital organs were also in normal condition without causing any histopathological change. It was concluded from the findings that sericin-co-AA polymeric matrices are ideal for the pH-dependent delivery of acyclovir.

Chitosan grafted/cross-linked with biodegradable polymers: A review

Public perception of polymers has been drastically changed with the improved plastic management at the end of their life. However, it is widely recognised the need of developing biodegradable polymers, as an alternative to traditional petrochemical polymers. Chitosan (CH), a biodegradable biopolymer with excellent physiological and structural properties, together with its immunostimulatory and antibacterial activity, is a good candidate to replace other polymers, mainly in biomedical applications. However, CH has also several drawbacks, which can be solved by chemical modifications to improve some of its characteristics such as solubility, biological activity, and mechanical properties. Many chemical modifications have been studied in the last decade to improve the properties of CH. This review focussed on a critical analysis of the state of the art of chemical modifications by cross-linking and graft polymerization, between CH or CH derivatives and other biodegradable polymers (polysaccharides or proteins, obtained from microorganisms, synthetized from biomonomers, or from petrochemical products). Both techniques offer the option of including a wide variety of functional groups into the CH chain. Thus, enhanced and new properties can be obtained in accordance with the requirements for different applications, such as the release of drugs, the improvement of antimicrobial properties of fabrics, the removal of dyes, or as scaffolds to develop bone tissues.

Sericin-chitosan-glycosaminoglycans hydrogels incorporated with growth factors for in vitro and in vivo skin repair

Globally, skin repair costs billion dollars per annum. Diversified matrices are fabricated to address this important area of healthcare. Most common limitations associated with them are the inflated production cost and insufficient functional repair. Our work explores the fabrication and potential utilization of Antheraea mylitta silk protein sericin (possessing inherent anti-bacterial and antioxidant properties) based hydrogels for skin tissue. The integrity of the hydrogels is achieved by combining sericin, chitosan (provide anti-bacterial and structural support), and glycosaminoglycans (component of biologically formed extracellular matrix). The hydrogels are functionalized by incorporation of vascular endothelial growth factor and transforming growth factor-β. They exhibit enhanced cellular functions in terms of their growth, production of matrix metalloproteinase, and collagen along with the recovery of impairment and the reconstruction of the lost dermal tissue. The in vivo biocompatibility analyses reveal that sericin-containing hydrogels promote the repair of skin tissue, angiogenesis, and illicit minimal immune response. These unique hydrogels mimicking the naturally occurring skin tissue and imparting additional beneficial features provide an appropriate physical environment and biological cues for the promotion of skin tissue repair.

Sericin based nanoformulations: a comprehensive review on molecular mechanisms of interaction with organisms to biological applications

BACKGROUND

The advances in products based on nanotechnology have directed extensive research on low-cost, biologically compatible, and easily degradable materials.

MAIN BODY

Sericin (SER) is a protein mainly composed of glycine, serine, aspartic acid, and threonine amino acids removed from the silkworm cocoon (particularly Bombyx mori and other species). SER is a biocompatible material with economic viability, which can be easily functionalized due to its potential crosslink reactions. Also, SER has inherent biological properties, which makes possible its use as a component of pharmaceutical formulations with several biomedical applications, such as anti-tumor, antimicrobials, antioxidants and as scaffolds for tissue repair as well as participating in molecular mechanisms attributed to the regulation of transcription factors, reduction of inflammatory signaling molecules, stimulation of apoptosis, migration, and proliferation of mesenchymal cells.

CONCLUSION

In this review, the recent innovations on SER-based nano-medicines (nanoparticles, micelles, films, hydrogels, and their hybrid systems) and their contributions for non-conventional therapies are discussed considering different molecular mechanisms for promoting their therapeutic applications.

Sericin based nanoformulations: a comprehensive review on molecular mechanisms of interaction with organisms to biological applications

BACKGROUND

The advances in products based on nanotechnology have directed extensive research on low-cost, biologically compatible, and easily degradable materials.

MAIN BODY

Sericin (SER) is a protein mainly composed of glycine, serine, aspartic acid, and threonine amino acids removed from the silkworm cocoon (particularly Bombyx mori and other species). SER is a biocompatible material with economic viability, which can be easily functionalized due to its potential crosslink reactions. Also, SER has inherent biological properties, which makes possible its use as a component of pharmaceutical formulations with several biomedical applications, such as anti-tumor, antimicrobials, antioxidants and as scaffolds for tissue repair as well as participating in molecular mechanisms attributed to the regulation of transcription factors, reduction of inflammatory signaling molecules, stimulation of apoptosis, migration, and proliferation of mesenchymal cells.

CONCLUSION

In this review, the recent innovations on SER-based nano-medicines (nanoparticles, micelles, films, hydrogels, and their hybrid systems) and their contributions for non-conventional therapies are discussed considering different molecular mechanisms for promoting their therapeutic applications.

Litter to Leaf: The Unexplored Potential of Silk Byproducts

Silk has remained the most preferred protein fiber since its discovery in 3000 BC. However, the cost, availability, and resources required to rear the silkworms and process silk are imposing considerable constraints on the future of silk. It is often unrealized that apart from the fibers, production and processing of silk are a source for a diverse range of sustainable, biodegradable, and biocompatible polymers. Hence, delineating itself from being the primary source of protein fibers for millenniums, the silk industry worldwide is transitioning into a biobased industry and as a source for pharmaceuticals, biomaterials, cosmetics, food, and energy. Toward this, byproducts (BPs) and co-products (CPs) that are inevitably generated are now being considered to be of immense economic value and could be up to 10 times more valuable than the silk fibers. Here, we elucidate the properties and potential applications of silk BPs and CPs to present the true potential of silkworms and to promote the establishment of silkworm-based bioeconomy and biorefineries.

Natural-based Hydrogels: A Journey from Simple to Smart Networks for Medical Examination

Natural hydrogels, due to their unique biological properties, have been used extensively for various medical and clinical examinations that are performed to investigate the signs of disease. Recently, complex-crosslinking strategies improved the mechanical properties and advanced approaches have resulted in the introduction of naturally derived hydrogels that exhibit high biocompatibility, with shape memory and self-healing characteristics. Moreover, the creation of self-assembled natural hydrogels under physiological conditions has provided the opportunity to engineer fine-tuning properties. To highlight recent studies of natural-based hydrogels and their applications for medical investigation, a critical review was undertaken using published papers from the Science Direct database. This review presents different natural-based hydrogels (natural, natural-synthetic hybrid and complex-crosslinked hydrogels), their historical evolution, and recent studies of medical examination applications. The application of natural-based hydrogels in the design and fabrication of biosensors, catheters and medical electrodes, detection of cancer, targeted delivery of imaging compounds (bioimaging) and fabrication of fluorescent bioprobes is summarised here. Without doubt, in future, more useful and practical concepts will be derived to identify natural-based hydrogels for a wide range of clinical examination applications.

Natural Polymer-Based Antimicrobial Hydrogels without Synthetic Antibiotics as Wound Dressings

Wound healing is usually accompanied by bacterial infection. The excessive use of synthetic antibiotics leads to drug resistance, posing a significant threat to human health. Hydrogel-based wound dressings aimed at mitigating bacterial infections have emerged as an effective wound treatment. The review presented herein particularly focuses on the hydrogels originating from natural polymers. To further enhance the performance of wound dressings, various strategies and approaches have been developed to endow the hydrogels with excellent broad-spectrum antibacterial activity. Those that are summarized in the current review are the hydrogels with intrinsic or stimuli-triggered bactericidal properties and others that serve as vehicles for loading antibacterial agents without synthetic antibiotics. Specific attention is paid to antimicrobial mechanisms and the antibacterial performance of hydrogels. Practical antibacterial applications to accelerate the wound healing employing these antibiotic-free hydrogels are also introduced along with the discussion on the current challenges and perspectives leading to new technologies.

Recent Advancement of Molecular Structure and Biomaterial Function of Chitosan from Marine Organisms for Pharmaceutical and Nutraceutical Application

Chitosan is an innate cationic biological polysaccharide polymer, naturally obtained from chitin deacetylation, that possesses broad-spectrum properties such as antibacterial, biodegradability, biocompatibility, non-toxic, non-immunogenicity, and so on. Chitosan can be easily modified owing to its molecular chain that contains abundant active amino and hydroxyl groups, through various modifications. Not only does it possess excellent properties but it also greatly accelerates its solubility and endows it with additional special properties. It can be developed into bioactive materials with innovative properties, functions, and multiple uses, especially in the biomedical fields. In this paper, the unique properties and the relationship between the molecular structure of chitosan and its derivatives are emphasized, an overview of various excellent biomedical properties of chitosan and its current progress in the pharmaceutical and nutraceutical field have prospected, to provide the theoretical basis for better development and utilization of new biomedical materials of chitosan and its derivatives.

Silk biomaterials in wound healing and skin regeneration therapeutics: From bench to bedside

Silk biomaterials are known for biomedical and tissue engineering applications including drug delivery and implantable devices owing to their biocompatible and a wide range of ideal physico-chemical properties. Herein, we present a critical overview of the progress of silk-based matrices in skin regeneration therapeutics with an emphasis on recent innovations and scientific findings. Beginning with a brief description of numerous varieties of silks, the review summarizes our current understanding of the biological properties of silk that help in the wound healing process. Various silk varieties such as silkworm silk fibroin, silk sericin, native spider silk and recombinant silk materials have been explored for cutaneous wound healing applications from the past few decades. With an aim to harness the regenerative properties of silk, numerous strategies have been applied to develop functional bioactive wound dressings and viable bio-artificial skin grafts in recent times. The review examines multiple inherent properties of silk that aid in the critical events of the healing process such as cell migration, cell proliferation, angiogenesis, and re-epithelialization. A detailed insight into the progress of silk-based cellular skin grafts is also provided that discusses various co-culture strategies and development of bilayer and tri-layer human skin equivalent under in vitro conditions. In addition, functionalized silk matrices loaded with bioactive molecules and antibacterial compounds are discussed, which have shown great potential in treating hard-to-heal wounds. Finally, clinical studies performed using silk-based translational products are reviewed that validate their regenerative properties and future applications in this area. STATEMENT OF SIGNIFICANCE: The review article discusses the recent advances in silk-based technologies for wound healing applications, covering various types of silk biomaterials and their properties suitable for wound repair and regeneration. The article demonstrates the progress of silk-based matrices with an update on the patented technologies and clinical advancements over the years. The rationale behind this review is to highlight numerous properties of silk biomaterials that aid in all the critical events of the wound healing process towards skin regeneration. Functionalization strategies to fabricate silk dressings containing bioactive molecules and antimicrobial compounds for drug delivery to the wound bed are discussed. In addition, a separate section describes the approaches taken to generate living human skin equivalent that have recently contributed in the field of skin tissue engineering.

Development of the PVA/CS nanofibers containing silk protein sericin as a wound dressing: In vitro and in vivo assessment

Skin and soft tissue infections are major concerns with respect to wound repair. Recently, anti-bacterial wound dressings have been emerging as promising candidates to reduce infection, thus accelerating the wound healing process. This paper presents our work to develop and characterize poly(vinyl alcohol) (PVA)/chitosan (CS)/silk sericin (SS)/tetracycline (TCN) porous nanofibers, with diameters varying from 305 to 425 nm, both in vitro and in vivo for potential applications as wound dressings. The fabricated nanofibers possess a considerable capacity to take up water through swelling (~325-650%). Sericin addition leads to increased hydrophilicity and elongation at break while decreasing fiber diameter and mechanical strength. Moreover, fibroblasts (L929) cultured on the nanofibers with low sericin content (PVA/CS/1-2SS) displayed greater proliferation compared to those on nanofibers without sericin (PVA/CS). Nanofibers loaded with high sericin and tetracycline content significantly inhibited the growth of Escherichia coli and Staphylococcus aureus. In vivo examination revealed that PVA/CS/2SS-TCN nanofibers enhance wound healing, re-epithelialization, and collagen deposition compared to traditional gauze and nanofibers without sericin. The results of this study demonstrate that the PVA/CS/2SS-TCN nanofiber creates a promising alternative to traditional wound dressing materials.

The wound healing and antibacterial potential of triple-component nanocomposite (chitosan-silver-sericin) films loaded with moxifloxacin

AIM

The current study reports the development and evaluation of chitosan-sericin-silver nanocomposite (CSSN) films without and with moxifloxacin (Mox).

METHODOLOGY

The film preparation method involved the in-situ synthesis of silver nanoparticles within the chitosan-sericin colloidal composite followed by preparation into a film by solvent casting technique. In-situ formation and the particle size analysis of the silver nanoparticles was performed via UV-Visible and zeta-size spectrometer. The prepared films were tested for swelling ratio, contents uniformity, in-vitro Mox release, and permeation analysis. The morphological (SEM), elemental (EDX), spectral (FT-IR), structural (XRD), and thermal (TGA and DSC) properties of the composites were also inspected. The antibacterial activity of the CSSN films was performed against seven pathogenic bacterial strains including five ATCC and two clinical strains. The potential wound healing activity of the composite films was evaluated on burn wound model induced in Sprague Dawley male rats.

RESULTS

The prepared films displayed good swelling profile with a sustained in-vitro Mox release and permeation profile; attaining maximum of 78.57% (CSSM3) release and 55.05% (CSSM1) permeation (CSSM1) in 24 h. The prepared films, particularly the Mox-loaded CSSN films displayed a promising antibacterial activity against all the tested strains with the activity being highest against MRSA (clinical isolates). The prepared films indicated a remarkable wound healing applications with successful fibrosis, collagen reorganization, neovascularization, and mild epidermal regeneration after 7 days of treatment with no silver ions detection in animal's blood.

CONCLUSION

The obtained findings strongly suggest the use of the prepared novel composite dressing for wound care applications.

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.

Prospects of nonmulberry silk protein sericin-based nanofibrous matrices for wound healing - In vitro and in vivo investigations

Recently, the progress in biomaterials for biomedical applications brings the focus of the research community toward nanomaterials. The nanofibrous matrices offer certain advantages (structural similarity to extracellular matrix, high surface area-to-volume ratio, increased elasticity, biostability, and strength) compared to other prevalent type of materials. This affirms their superiority and flexibility to be used in regenerative medicine. We have fabricated nonmulberry (Antheraea mylitta) silk protein sericin-based nanofibrous matrices (fiber thickness; 80-400 nm) with improved mechanical strength and desired stability (>4 weeks) as required for tissue reconstruction. These matrices support the adhesion, proliferation, and cellular interconnection of human keratinocytes. These are minimally hemolytic, nonimmunogenic, and capable of wound healing in vivo. Antibiotic (cephalexin hydrate [CH])-loaded nanofibrous matrices accelerate the full-thickness wound repair with minimal inflammation and without any signs of infection. The histological analysis authenticates skin restoration with re-epithelialization, generation of associated skin appendages, and synthesis of dense collagen fibrils. In addition, analysis of inflammatory genes and immunohistochemical assays have proved their biocompatibility and wound healing potential. Angiogenesis is also prevalent in the animal tissue treated with nanofibrous matrices. The results of in vitro and in vivo experimentations indicate a clear prospect of the fabricated sericin-based nanofibrous matrices to be used for skin regeneration.

STATEMENT OF SIGNIFICANCE

Nonmulberry silk protein sericin-based nanofibrous matrix is a useful biomaterial for wound healing, collagen production, and skin tissue repair. It has been used in different formulations including hydrogels and nanofibrous membranes with chitosan (CS) and polyvinyl alcohol (PVA). No experiments have been carried out to evaluate sericin-based nanofibrous membranes for skin tissue engineering application. The present study shows that the nanofibrous matrices fabricated by electrospinning nonmulberry silk protein sericin with CS and PVA mimic the architectural environment of the extracellular matrix fibrils. These matrices are minimally hemolytic, are nonimmunogenic, and support better growth of human keratinocytes in vitro and wound healing in vivo with re-epithelialization of the skin tissue and angiogenesis. This work indicates that these nonmulberry sericin-based nanofibrous matrices with CS may be used as an ideal physical environment and biological cues for the promotion of skin tissue reconstruction and repair.

The regulatory effects of L. plantarum peptidoglycan microspheres on innate and humoral immunity in mouse

OBJECTIVE

To study the effects of Lactobacillus Plantarum cell wall peptidoglycan (LPG) microspheres on mouse intestinal flora changes, peptidoglycan recognitions protein (PGRP) and cytokines expression levels.

METHOD

Plate counting was used for enumeration of the intestinal flora. Real-time PCR was used for quantification PGRP in different tissues. Cytokines content were determined by ELISA kits.

RESULT

The mouse administered orally with LPG microspheres showed significantly higher number of Lactobacillus and Bifidobacterium in caecum contents (p < 0.01). The amount of PGRP expression in different organs was highest in LPG microspheres-treated group. IL-4, 12, IFN-γ, TNF-α contents in serum from LPG microspheres-treated mouse were significantly higher than those in normal saline-treated group (p < 0.01).

CONCLUSIONS

This study shows that the LPG microspheres can regulate intestinal flora imbalance and improve systemic immunity, improve both Th1 and Th2 immune response, which provide some basis for the use of LPG as potential adjuvants.