Generation of Nano-pores in Silk Fibroin Films Using Silk Nanoparticles for Full-Thickness Wound Healing.

Silk fibroin films are used in tissue engineering due to their biocompatibility, optical clarity, and slow biodegradability. However, the relatively smooth surface and low permeability of these systems may limit some applications; thus, here, a method was developed to generate nano-pores in methanol or ethanol-treated silk fibroin films. The first step was to induce the formation of nanoparticles (50-300 nm diam.) in silk fibroin solutions by autoclaving. After drying in air, the films formed were treated to induce silk ß-sheet structures, which condense the bulk silk phase and nanoparticles and phase separation and enlarge the space of bulk silk phase and nanoparticles. These films were then extracted with water to allow the condensed nanoparticles to escape, leaving homogeneous nano-pores (50-300 nm) in the silk fibroin matrix. The introduction of nano-pores resulted in enhanced permeability and minimized loss of the mechanical properties of the nano-porous silk fibroin films (NSFs) when compared to the un-autoclaving-treated silk fibroin films. NSFs promoted cell (human fibroblasts) proliferation and oxygen/nutrition perfusion and significantly enhanced the complete skin-thickness wound healing in a rat model, suggesting the potential use in tissue regeneration or as wound dressing biomaterials for clinical applications.

Silk fibroin-based woven endovascular prosthesis with heparin surface modification.

A novel seamless silk fibroin-based endovascular prosthesis (SFEPs) with bifurcated woven structure and anticoagulant function for the improvement of patency is described. The SFEPs were prepared from silk fibroin (SF) and polyester filaments using an installed weaving machine. The production processing parameters were optimized using orthogonal design methods. The inner surface of SFEPs was modified with polyethylenimine (PEI) and EDC/NHS-activated low-molecular-weight heparin (LMWH) to enhance anticoagulant function. The surface morphology and mechanical properties of the SFEPs were evaluated according to standard protocols. The thickness of modified SFEPs was lower than 0.085 ± 0.004 mm and water permeability was lower than 5.19 ± 0.30 mL/(cm2 × min). The results of mechanical properties showed that the diametral tensile strength and burst strength reached 61.6 ± 1.8 and 23.7 ± 2.2 MPa, respectively. Automatic coagulometer and energy-dispersive X-ray (EDX) confirmed LMWH immobilization on the surface of the SFEPs and the blood compatibility was improved with the heparin modification with PEI polymerization. In conclusion, the new prosthesis has potential applications in the blood vessel repairs where minimal thickness but superior mechanical strength and biocompatibility are important.

Antistricture Ureteral Stents with a Braided Composite Structure and Surface Modification with Antistenosis Drugs.

The present work describes the development of a drug-loaded ureteral stent with antistricture function based on a trilayer design in which the middle layer was braided from biodegradable poly(p-dioxanone) (PDO) monofilament. Antistenosis drugs rapamycin and paclitaxel were loaded into a silk fibroin (SF) solution and coated on the inner and outer layers of the braided PDO stent. The cumulative release of rapamycin and paclitaxel was sustained over 30 days, with a total release above 80%. The drug-loaded ureteral stents inhibited the proliferation of fibroblasts and smooth muscle cells in vitro. Subcutaneous implantation in rats showed that the drug-loaded ureteral stents were biocompatible with durable mechanical properties in vivo, revealing the inhibition of an excessive growth of fibroblasts and excessive deposition of collagen fibers. In conclusion, the dual-drug-loaded biodegradable ureteral stents show the possibility for treatment of ureteral strictures and avoid the occurrence of complications such as inflammation and restricture.

Silk fibroin catheter with stable bioinspired inner-surfaces for inhibition of bioadhesion.

Biofilm formation on indwelling medical devices such as catheters and ventilators due to the adhesion of bacteria poses significant challenges in healthcare. Surface modification with micro- and nano-structures offers a promising strategy to prevent bioadhesion and is safer than surface chemical modification approaches. Here, catheters were prepared using silk fibroin (SF) hydrogels and an infusion molding method, with the inner surface featuring a micropapillae structure inspired by lotus leaves (SF-CMP). After phenylethanol (PEA) fumigation treatment, the resulting catheters (SF-CMP PEA) displayed improved swelling resistance and mechanical properties compared to methanol-treated catheters (SF-CMP MeOH). PEA was more efficient than methanol in controlling the size, distribution, and content of silk crystalline ß-sheet blocks and thus the swelling and mechanical properties. Moreover, the micro-papillae structure on SF-CMP PEA remained stable over 35 days in solution, in contrast to SF-CMP MeOH, which lasted <7 days. SF-CMP PEA exhibited repellent effects against E. coli and S. aureusin vitro, and low cytotoxicity to the endothelial cells cultured on the unpatterned surface. Additionally, subcutaneous implantation studies showed reduced inflammation around the micropatterned samples compared to controls with a plain, unpatterned surface. The unique properties of SF-based materials, including tunable structures, biocompatibility, degradation, and drug-loading capability make them an attractive material for anti-bioadhesion in applications ranging from indwelling medical devices to tissue engineering scaffolds.

Mechanical biomimetic silk nano fiber-magnesium ion complex/hydroxyethylcellulose/glycerol hydrogel dressing with angiogenic capacity for accelerating scarless diabetic wound healing.

Quick scarless healing remains a key issue for diabetic wounds. Here, a stretchable elastomeric hydrogel dressing composed of hydroxyethylcellulose (HEC), silk nano fiber-magnesium ion complex (Mg2+-SNF) and glycerol (Gly) was developed to optimize mechanical niche, anti-inflammatory and angiogenic behavior simultaneously. The composite hydrogel dressing exhibited skin-like elasticity (175.1 ± 23.9 %) and modulus (156.7 ± 2.5 KPa) while Mg2+-SNF complex endowed the dressing with angiogenesis, both favoring quick scarless skin regeneration. In vitro cell studies revealed that the hydrogel dressing stimulated fibroblast proliferation, endothelial cell migration and vessel-like tube formation, and also induced anti-inflammatory behavior of macrophages. In vivo results revealed accelerated healing of diabetic wounds. The improved granulation ingrowth and collagen deposition suggested high quality repair. Both thinner epidermal layer and low collagen I/III ratio of the regenerated skin confirmed scarless tissue formation. This bioactive hydrogel dressing has promising potential to address the multifaceted challenges of diabetic wound management.

Recent advances in harnessing biological macromolecules for wound management: A review.

Wound dressings (WDs) are an essential component of wound management and serve as an artificial barrier to isolate the injured site from the external environment, thereby helping to prevent exogenous infections and supporting healing. However, maintaining a moist wound environment, providing protection from infection, good biocompatibility, and allowing for gas exchange, remain a challenge in device design. Functional wound dressings (FWDs) prepared from hybrid biological macromolecule-based materials can enhance efficacy of these systems for skin wound management. This review aims to provide an overview of the state-of-the-art FWDs within the field of wound management, with a specific focus on hybrid biomaterials, techniques, and applications developed over the past five years. In addition, we highlight the incorporation of biological macromolecules in WDs, the emergence of smart WDs, and discuss the existing challenges and future prospects for the development of advanced WDs.

Advances in pesticide biosensors: current status, challenges, and future perspectives.

Public concern over pesticide residues has been increasing dramatically owing to the high toxicity and bioaccumulation effects of pesticides and the serious risks that they pose to the environment and human health. It is therefore crucial to monitor pesticide residues by using various analytical methods and techniques, especially highly sensitive, highly selective, simple, rapid, cost-effective, and portable ones. Biosensor strategies have become research hotspots and ideal candidates for pesticide detection, having such features as high sensitivity, fast response, robustness, low cost and miniaturization, as well as in situ and real-time monitoring. This review covers advances in the design and fabrication of biosensors for pesticide detection since 2005. Special emphasis is placed on the state-of-art selection of receptors, the use of different transduction techniques and fast screening strategies, and the application of various biosensors developed in food and environmental safety. Both advantages and drawbacks of these techniques are then summarized. Finally, challenges, strategies, and perspectives in further developing pesticide biosensors are also discussed.

Silk Fibroin/Wool Keratin Composite Scaffold with Hierarchical Fibrous and Porous Structure.

The present study describes a silk microfiber reinforced meniscus scaffold (SMRMS) with hierarchical fibrous and porous structure made from silk fibroin (SF) and wool keratin (WK) using electrospinning and freeze-drying technology. This study focuses on the morphology, secondary structure, mechanical properties, and water absorption properties of the scaffold. The cytotoxicity and biocompatibility of SMRMS are assessed in vivo and in vitro. The scaffold shows hierarchical fibrous and porous structure, hierarchical pore size distribution (ranges from 50 to 650 µm), robust mechanical properties (compression strength can reach at 2.8 MPa), and stable biodegradability. A positive growth condition revealed by in vitro cytotoxicity testing indicates that the scaffold is not hazardous to cells. In vivo assessments of biocompatibility reveal that only a mild inflammatory reaction is present in implanted rat tissue. Meniscal scaffold made of SF/WK composite shows a potential application prospect in the meniscal repair engineering field with its development.

Stabilization and Sustained Release of Fragrances Using Silk-PEG Microspheres.

Fragrances, which are commonly used in food, textiles, consumer products, and medical supplies, are volatile compounds that require stabilization and controlled release due to their sensitivity to environmental conditions such as light, oxygen, temperature, and humidity. Encapsulation in various material matrices is a desired technique for these purposes, and there is a growing interest in using sustainable natural materials to reduce environmental impact. In this study, fragrance encapsulation in microspheres made from silk fibroin (SF) was investigated. Fragrance-loaded silk fibroin microspheres (Fr-SFMSs) were prepared by adding fragrance/surfactant emulsions to silk solutions, followed by mixing them with polyethylene glycol under ambient conditions. The study investigated eight different fragrances, where citral, beta-ionone, and eugenol showed higher binding affinities to silk than the other five fragrances, resulting in better microsphere formation with uniform sizes and higher fragrance loading (10-30%). Citral-SFMSs showed characteristic crystalline ß-sheet structures of SF, high thermal stability (initial weight loss at 255 °C), long shelf life at 37 °C (>60 days), and sustained release (∼30% of citral remained after incubation at 60 °C for 24 h). When citral-SFMSs with different sizes were used to treat cotton fabrics, about 80% of the fragrance remained on the fabrics after one wash, and the duration of release from the treated fabrics was significantly longer than that of control samples treated with citral alone (no microspheres). This method of preparing Fr-SFMSs has potential applications in textile finishing, cosmetics, and the food industry.

Promotion of Wound Healing Using Nanoporous Silk Fibroin Sponges.

Wound dressings are important for wound repair. The morphology of the biomaterials used in these dressings, and in particular, the pore structure affects tissue regeneration by facilitating attachment and proliferation of cells due to the hierarchical multiscale, water absorbance, and nutrient transport. In the present study, silk fibroin (SF) sponges with walls containing nanopores (SFNS) were prepared from SF nanoparticles generated during the autoclaving of SF solutions, followed by leaching the SF nanoparticles from the freeze-dried sponges of SF. The nano/microporous structure, biofluid absorbance, and porosity of the SF sponges with and without nanopores were characterized. In vitro cell proliferation, in vivo biocompatibility, and wound healing were evaluated with the sponges. The results demonstrated that SFNS had significantly increased porosity and water permeability, as well as cell attachment and proliferation when compared with SF sponges without the nanopores (SFS). Wound dressings were assessed in a rat skin wound model, and SFNS was superior to SFS in accelerating wound healing, supported by vascularization, deposition of collagen, and increased epidermal thickness over 21 days. Hence, such a dressing material with a hierarchical multiscale pore structure could promote cell migration, vascularization, and tissue regeneration independently without adding any growth factor, which would offer a new strategy to design and engineer better-performed wound dressing.

Preparation and mechanical optimization of a two-layer silk/magnesium wires braided porous artificial nerve guidance conduit.

Peripheral nerve injures have long been a tricky problem in surgery and a feasible treatment is the transplantation of nerve guidance conduits (NGCs). This study presents a two-layer composite NGC with fair mechanical properties and good biocompatibility. The inner layer was made of degummed silk yarns/magnesium wires using braiding technology, and the outer layer was made from mixed solution of silk fibroin/chitosan (SF/CS) using freeze-drying treatment. Orthogonal experimental design was applied to rationally design the braided structural layer and obtain the optimal combination of technical process parameters. Meanwhile, the SF/CS porous outer layer was optimized from three concentrations of SF/CS solution. In vitro and in vivo study suggested that the textile-forming scaffold exhibited good biocompatibility and no toxicity. During 4 weeks' degradation, the skeleton of conduits retained its shape, and magnesium ions released from degraded magnesium wires contributed to sustainable release and uniform dispersion, proliferation and adhesion of Schwann cells, indicating potential approach in the development of NGCs.

Sustainable Antibacterial and Anti-Inflammatory Silk Suture with Surface Modification of Combined-Therapy Drugs for Surgical Site Infection.

Silk sutures with antibacterial and anti-inflammatory functions were developed for sustained dual-drug delivery to prevent surgical site infections (SSIs). The silk sutures were prepared with core-shell structures braided from degummed silk filaments and then coated with a silk fibroin (SF) layer loaded with berberine (BB) and artemisinin (ART). Both the rapid release of drugs to prevent initial biofilm formation and the following sustained release to maintain effective concentrations for more than 42 days were demonstrated. In vitro assays using human fibroblasts (Hs 865.Sk) demonstrated cell proliferation on the materials, and hemolysis was 2.4 ± 0.8%, lower than that required by ISO 10993-4 standard. The sutures inhibited platelet adhesion and promoted collagen deposition and blood vessel formation. In vivo assessments using Sprague-Dawley (SD) rats indicated that the coating reduced the expression of pro-inflammatory cytokines interleukin-10 (IL-10) and tumor necrosis factor-α (TNF-α), shortening the inflammatory period and promoting angiogenesis. The results demonstrated that these new sutures exhibited stable structures, favorable biocompatibility, and sustainable antibacterial and anti-inflammatory functions with potential for surgical applications.

Multi-functional Calotropis gigantea fabric using self-assembly silk fibroin, chitosan and nano-silver microspheres with oxygen low-temperature plasma treatment.

The present paper describes a novel multi-functional Calotropis gigantea (CG) fabric with durable antibacterial property and comfortable wearability for various applications. First, antibacterial microspheres (AMs) were prepared by self-assembly of silk fibroin (SF), chitosan (CS) and nano-silver microspheres (NSMs). Oxygen low-temperature plasma (OLTP) treatment was used to improve the adhesion between AMs and CG yarn. The AMs modified CG fabric has soft hand feeling, high moisture regain (10.37 ± 1.87%), good breathability, strong wrinkle resistance, and durable antibacterial properties. The antibacterial rate of the modified CG fabric against Escherichia coli (E. Coil) and Staphylococcus aureus (S. Aureus) is as high as 99.9 ± 0.1%, and it still has an antibacterial activity after washing 20 times (90.24 ± 0.65% and 80.25 ± 1.14%, respectively). The in vivo biocompatibility test showed clear signs of angiogenesis at the implantation site in the rats. Thus, this study offers the foundation for the development of functional CG fiber-based biomedical textiles.

Intraarticularly injectable silk hydrogel microspheres with enhanced mechanical and structural stability to attenuate osteoarthritis.

A silk fibroin (silk) hydrogel was prepared by using diglycidyl ether (BDDE), a chemical crosslinker commonly used to generate Food and Drug Administration (FDA)-approved hyaluronic acid (HA) medical products. The silk/BDDE hydrogels exhibited high elasticity (compressive modulus of 166 ± 15.0 kPa), anti-fatigue properties, and stable structure and mechanical strength in aqueous solution. Chemical crosslinking was conducted in a high concentration (9.3 M) of lithium bromide (LiBr) solution, a salt that is commonly used to dissolve degummed silk fibers during silk solubilization. The unfolded and extended structure of silk molecules with these reaction conditions, as well as the unique ionic environment provided by LiBr facilitated a high degree of crosslinking in the hydrogel. Similar hydrogels were not obtained when the silk was dissolved in other silk fiber-dissolving reagents (e.g., Ajisawa's, formic acid (FA)/LiBr, FA/CaCl2 solutions), likely because partially folded silk structures and the ionic conditions with these reagents were less favorable for the crosslinking reaction. Based on these findings, silk/BDDE hydrogel spheres were prepared using an oil/water (o/w) emulsification method and biocompatibility and biodegradation were evaluated in vivo, along with other silk gel control systems (e.g., enzyme-catalyzed di-tyrosine and pulverized silk/BDDE gel particles with irregular shapes). Histological and immunohistochemical analyses demonstrated that the silk/BDDE hydrogel spheres were biocompatible and served as a bio-lubricant to treat osteoarthritis (OA). The intra-articular injection of the gel spheres reduced pain as measured with OA rats, reduced cartilage damage and resisted the digestive environment in the articular cavity for extended time frames (>4 weeks), suggesting utility for pain relief and sustained drug release for future OA treatments.

Implantable nerve guidance conduits: Material combinations, multi-functional strategies and advanced engineering innovations.

Nerve guidance conduits (NGCs) have attracted much attention due to their great necessity and applicability in clinical use for the peripheral nerve repair. Great efforts in recent years have been devoted to the development of high-performance NGCs using various materials and strategies. The present review provides a comprehensive overview of progress in the material innovation, structural design, advanced engineering technologies and multi functionalization of state-of-the-art nerve guidance conduits NGCs. Abundant advanced engineering technologies including extrusion-based system, laser-based system, and novel textile forming techniques in terms of weaving, knitting, braiding, and electrospinning techniques were also analyzed in detail. Findings arising from this review indicate that the structural mimetic NGCs combined with natural and synthetic materials using advanced manufacturing technologies can make full use of their complementary advantages, acquiring better biomechanical properties, chemical stability and biocompatibility. Finally, the existing challenges and future opportunities of NGCs were put forward aiming for further research and applications of NGCs.

1000 spider silkomes: Linking sequences to silk physical properties.

Spider silks are among the toughest known materials and thus provide models for renewable, biodegradable, and sustainable biopolymers. However, the entirety of their diversity still remains elusive, and silks that exceed the performance limits of industrial fibers are constantly being found. We obtained transcriptome assemblies from 1098 species of spiders to comprehensively catalog silk gene sequences and measured the mechanical, thermal, structural, and hydration properties of the dragline silks of 446 species. The combination of these silk protein genotype-phenotype data revealed essential contributions of multicomponent structures with major ampullate spidroin 1 to 3 paralogs in high-performance dragline silks and numerous amino acid motifs contributing to each of the measured properties. We hope that our global sampling, comprehensive testing, integrated analysis, and open data will provide a solid starting point for future biomaterial designs.

Low-Density Silk Nanofibrous Aerogels: Fabrication and Applications in Air Filtration and Oil/Water Purification.

A method was developed to fabricate light, water-insoluble silk fibroin nanofibrous aerogels (SNFAs) through solvent welding of lyophilized silk nanofibrous 3D networks at the junction points while converting silk structures from random-coils to ß-sheets (water insoluble). Aromatic alcohols, especially phenethyl alcohol (PEA), supported robust solvent welding and the structural conversion of silk. PEA vapor treatment was a better approach than solvent infusion to retain volume, density, and mechanical strength of the SNFAs. The mechanical properties of highly orientated SNFAs were superior to randomly distributed fibers. The SNFAs had a low density (3.5 mg/cm3), high hydrophobicity (140.9°), and a porous surface morphology on the individual nanofibers, resulting in high efficiency and selectivity for absorbing particulate matter and oils. Compared with commonly used inorganic aerogels, the SNFAs developed in this study are biocompatible, easily functionalized, environmentally friendly, and low-cost and therefore have potential for air and water purification, biosensors, drug delivery, and tissue engineering.

Sustained Photosynthesis and Oxygen Generation of Microalgae-Embedded Silk Fibroin Hydrogels.

Microalgae immobilized in hydrogels offer advantages over those cultured in suspension culture in terms of carbon fixation and oxygen emission. However, alginate as a commonly used hydrogel for microalgal immobilization encounters problems with mechanical strength and stability. To address this limitation, silk fibroin (silk) hydrogels prepared by ultrasonication were utilized to host microalgae when mixed with the presonicated protein solution prior to its gelation. The gelation time, stability, and light transmission of these silk gels were evaluated, and a silk concentration of 4% w/v and a gel thickness of 1 mm provided mechanical strength and stability during algal culture in comparison to alginate hydrogels. Furthermore, silk hydrogels with algal cell densities of 7.6 × 105 and 7.8 × 107 cells/mL had better stability than those with a lower cell density (3.2 × 103 cells/mL), likely due to cell confinement and impact on proliferation. The silk hydrogels with microalgae at a high density generated 6.13 mg/L of oxygen continuously for 7 days. An oxygen-generating device was fabricated by coating the surface of a dialysis tube with a thin layer of the microalgae-embedded silk hydrogel, where the microalgal cells were nourished with culture medium prefilled in the dialysis tube. When suspended in a sealed flask filled with CO2 gas, the system continuously produced oxygen (151 mL) for at least 60 days, with an oxygen production efficiency 6 times that of microalgal suspension culture controls. This microalgae embedding and cultivation technique could have potential utility in air purification, tissue repair, and other applications due to the efficient and sustained generation of oxygen.

A flexible and biocompatible bombyx mori silk fibroin/wool keratin composite scaffold with interconnective porous structure.

The paper describes the preparation of a porous bombyx mori silk fibroin (SF)/wool keratin (WK) composite scaffold with mimic structure and function for cartilage tissue engineering. A porous composite scaffold made from SF/WK in an appropriate concentration and mass ratio was prepared using a freeze-drying technique. Results showed that the composite scaffolds are water-insoluble; possess good mechanical properties, porosity above 80%, and pore size above 200 µm. Larger pore size and better connectivity of the composite scaffold than the pure SF scaffolds were contributed by the WK addition. The heat resistance and water-swelling of WK enhanced the thermal and mechanical properties of the composite scaffolds. In vitro cytotoxicity assessments showed cells with a good growth state, confirming no toxicity to the cells. The results of in vivo biocompatibility assessments exhibited that there is almost no inflammatory response in the implantation site tissue of the rats. The development of porous SF/WK composite scaffold has the potential in cartilage tissue engineering.

Porous nerve guidance conduits reinforced with braided composite structures of silk/magnesium filaments for peripheral nerve repair.

Peripheral nerve repair is a common but challenging surgical treatment. Many artificial nerve grafts have been developed, including nerve guidance conduits (NGCs) with biocompatibility, suitable mechanical properties and topography to guide axon growth. However, there remains a need to promote nerve regeneration and accelerate functional recovery using NGCs for nerve reconstruction. Here, silk fibroin (SF) and magnesium (S/Mg) filaments were braided into an inner layer of NGC and freeze-dried with a solution of SF and chitosan (CS). The mechanical stress of these S/Mg-SF/CS conduits reached 2.8 ± 0.2 N and possessed high compression strength. The conduits were evaluated with subcutaneous implantation. Sustainable mechanical function was demonstrated when used to repair 10 mm sciatic nerve gaps in rats. The hollow NGCs improved neurochemotaxis from the damaged nerves. The wet weight ratio of the gastrocnemius muscle, a target muscle for the sciatic nerve related to motor and sensory functions in the NGC group, reached 83.5% of that in the autologous group in 8 weeks; the nerve ports at both ends of the NGC grew well. When the distal end of the regenerated nerve was observed by Transmission Electron Microscopy (TEM), there was no significance difference in the diameter and thickness of the myelin sheath of the distal nerve between the autograft and S/Mg-SF/CS group, indicating that S/Mg-SF/CS NGC in this study promoted the growth of damaged nerves and provided appropriate physio mechanical guidance, thus suggesting potential utility for this approach in artificial nerve transplantation. STATEMENT OF SIGNIFICANCE: 1. Porous nerve guidance conduits (NGCs) is reinforced by a braided composite structure consisting of silk/magnesium filaments, which provides the NGC with appropriate physio-mechanical guidance as well as sufficient stability to support the biological micro-environment during early-stages of nerve regeneration and functional recovery. 2. Sufficient mechanical properties, biocompatibility with Schwan cells and good performance after sciatic nerve transplantation demonstrates that the S/Mg-SF/CS NGC in this study promotes the growth of damaged nerves and provides a suitable physio-mechanical guide for potential in artificial nerve transplantation. 3. A facile scalable manufacturing process is achieved by utilizing multidisciplinary engineering, such as textile technologies, biomaterial engineering and medical science.