Structure and properties of regenerated Antheraea pernyi silk fibroin in aqueous solution

Gelation Dynamics, Formation Mechanism, Functionalization, and 3D Bioprinting of Silk Fibroin Hydrogel Materials for Biomedical Applications

Silk fibroin (SF), derived from silk cocoon fibers (Bombyx mori), is a natural protein polymer known for its biocompatibility, biodegradability, and sustainability. The protein can be processed into various material formats suitable for a range of applications. Among these, SF hydrogels are useful in the biomedical field, such as tissue engineering, due to the tailorable structures and properties achievable through tuning the gelation process. Therefore, the focus of this contribution is to comprehensively review and understand the formation, gelation mechanism, dynamic control, and functionalization of SF hydrogels. Unlike previous reviews, this work delves into understanding the strategies and mechanisms for tuning the gelation dynamics of SF from molecular assembly and crystallization points of view. Further, this review presents functionalization pathways and practical examples, such as for the 3D printing of SF hydrogels, to illustrate how these strategies, mechanisms, and pathways can be implemented in a specific application scenario. With these insights, researchers can gain a deeper understanding of how to manipulate or control the gelation process and the types of functionalization to achieve specific properties and features. This knowledge would further facilitate the development and application of SF hydrogel materials in various fields.

Facile Preparation of a Photo-Cross-Linked Silk Fibroin-Poly Ionic Liquid Hydrogel with Antifreezing and Ion Conductive Properties

The silk fibroin (SF)/ionic liquid (IL) based hydrogel is a kind of remarkable substrate for flexible devices because of its subzero-temperature elasticity, electrical conductivity, and water retention, although the procedure of the gelation is considered complex and time-consuming. In this work, we introduced an approximate method for the development of novel photo-cross-linked SF/IL hydrogel, that is, SF-IMA/PIL hydrogel via the modification of silk fibroin chain with 2-isocyanatoethyl methacrylate (SF-IMA) in a certain ionic liquid with an unsaturated double bond. The chemical cross-linking between methacrylated SF and IL was triggered by UV light, while the physical cross-linking of the hydrogel was attributed to the β-sheet formation of SF in SF-IMA/IL mixed solution. In addition to being a UV-induced three-dimensional (3D) printable one, the SF-IMA/PIL hydrogel performed significant ionic conductivity between room temperature and -50 °C and water retention within a wide range of relative humidity, which were the featured advantages as the ionic liquid involved. Moreover, the static and dynamic mechanical tests demonstrated that the hydrogel reserved its great elasticity at -50 °C and displayed its stiffness transition temperatures between -100 and -70 °C.

Advances in Preparation and Properties of Regenerated Silk Fibroin

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

Novel silk protein/hyaluronic acid hydrogel loaded with azithromycin as an immunomodulatory barrier to prevent postoperative adhesions

Peritoneal adhesions, a common postoperative complication of laparotomy, are still treated with physical barriers, but their efficacy and ease of use are controversial. In this paper, we developed a wound microenvironment-responsive hydrogel composed of Antheraea pernyi silk protein (ASF) from wild cocoons and tyramine-modified hyaluronic acid (HA-Ph) loaded with azithromycin (AZI), glucose oxidase (GOX), and horseradish peroxidase (HRP). In addition, GOX-catalyzed oxygen production enhanced the antibacterial ability of the hydrogel. Moreover, the drug-loaded hydrogel increased macrophage CD206 expression while decreasing IL-6 and TNF-α expression. More importantly, the retarding effect of this novel hydrogel system on AZI almost eliminated the appearance of postoperative adhesions in rats. It was also found that the novel hydrogel enhanced the modulation of the TLR-4/Myd88/NF-κB pathway and TGF-β/Smad2/3 pathway by azithromycin in the locally damaged peritoneum of rats, which accelerated the remodeling of damaged tissues and dramatically reduced the deposition of collagen. Therefore, spraying the novel drug-loaded hydrogel on postoperative abdominal wounds can effectively inhibit the formation of postoperative adhesions.

Stretching-Induced Conformational Transition of [3-13C]Ser- and [3-13C]Tyr-Antheraea yamamai Silk Fibroin before Spinning Investigated with 13C Solid-State NMR Spectroscopy

The conformational transition of [3-¹³C]Ser- and [3-¹³C]Tyr-Antheraea yamamai silk fibroin before spinning induced by stretching was investigated with ¹³C CP/MAS NMR spectroscopy. The α-helix content of the silk fibroin before stretching was found to be 31.6% based on the Ala and Ser peaks. With increasing stretching ratio, the α-helix and the random coil Ala Cβ peaks decreased gradually, while the β-sheet peak was observed at a stretching ratio of ×5 and increased rapidly upon further stretching. For Ser residue, the α-helix peak decreased monotonically with increasing stretching ratio, but the random coil peak increased slightly till the stretching ratio of ×5 and then decreased. A small β-sheet peak was observed before stretching and then increased rapidly starting from the stretching ratio of ×7. In contrast, a gradual decrease of random coil peak and an increase of β-sheet peak were observed for the Tyr residue. The results of this investigation may be helpful for further studies of fiber formation mechanism in A. yamamai and in the future design of artificial silk materials.

Nonmulberry silk fibroin-based biomaterials: Impact on cell behavior regulation and tissue regeneration

Silk fibroin (SF) is a promising biomaterial due to its good biocompatibility, easy availability, and high mechanical properties. Compared with mulberry silk fibroin (MSF), nonmulberry silk fibroin (NSF) isolated from typical nonmulberry silkworm silk exhibits unique arginine-glycine-aspartic acid (RGD) sequences with favorable cell adhesion enhancing effect. This inherent property probably makes the NSF more suitable for cell culture and tissue regeneration-related applications. Accordingly, various types of NSF-based biomaterials, such as particles, films, fiber mats, and 3D scaffolds, are constructed and their application potential in different biomedical fields is extensively investigated. Based on these promising NSF biomaterials, this review firstly makes a systematical comparison between the molecular structure and properties of MSF and typical NSF and highlights the unique properties of NSF. In addition, we summarize the effective fabrication strategies from degummed nonmulberry silk fibers to regenerated NSF-based biomaterials with controllable formats and their recent application progresses in cell behavior regulation and tissue regeneration. Finally, current challenges and future perspectives for the fabrication and application of NSF-based biomaterials are discussed. Related research and perspectives may provide valuable references for designing and modifying effective NSF-based and other natural biomaterials. STATEMENT OF SIGNIFICANCE: There exist many reviews about mulberry silk fibroin (MSF) biomaterials and their biomedical applications, while that about nonmulberry silk fibroin (NSF) biomaterials is scarce. Compared with MSF, NSF exhibits unique arginine-glycine-aspartic acid sequences with promising cell adhesion enhancing effect, which makes NSF more suitable for cell culture and tissue regeneration related applications. Focusing on these advanced NSF biomaterials, this review has systematically compared the structure and properties of MSF and NSF, and emphasized the unique properties of NSF. Following that, the effective construction strategies for NSF-based biomaterials are summarized, and their recent applications in cell behavior regulations and tissue regenerations are highlighted. Furthermore, current challenges and future perspectives for the fabrication and application of NSF-based biomaterials were discussed.

Recent Research Progress of Ionic Liquid Dissolving Silks for Biomedicine and Tissue Engineering Applications

Ionic liquids (ILs) show a bright application prospect in the field of biomedicine and energy materials due to their unique recyclable, modifiability, structure of cation and anion adjustability, as well as excellent physical and chemical properties. Dissolving silk fibroin (SF), from different species silkworm cocoons, with ILs is considered an effective new way to obtain biomaterials with highly enhanced/tailored properties, which can significantly overcome the shortcomings of traditional preparation methods, such as the cumbersome, time-consuming and the organic toxicity caused by manufacture. In this paper, the basic structure and properties of SF and the preparation methods of traditional regenerated SF solution are first introduced. Then, the dissolving mechanism and main influencing factors of ILs for SF are expounded, and the fabrication methods, material structure and properties of SF blending with natural biological protein, inorganic matter, synthetic polymer, carbon nanotube and graphene oxide in the ILs solution system are introduced. Additionally, our work summarizes the biomedicine and tissue engineering applications of silk-based materials dissolved through various ILs. Finally, according to the deficiency of ILs for dissolving SF at a high melting point and expensive cost, their further study and future development trend are prospected.

Biological Efficacy Comparison of Natural Tussah Silk and Mulberry Silk Nanofiber Membranes for Guided Bone Regeneration

Biopolymer nanofiber membranes are attracting interest as promising biomaterial scaffolds with a remarkable range of structural and functional performances for guided bone regeneration (GBR). In this study, tussah silk nanofiber (TSn) and Bombyx mori silk nanofiber (BSn) membranes were prepared by physical shearing. The diameters of the TSn and BSn membranes were 146.09 ± 63.56 and 120.99 ± 91.32 nm, respectively. TSn showed a Young's modulus of 3.61 ± 0.64 GPa and a tensile strength of 74.27 ± 5.19 MPa, which were superior to those of BSn, with a Young's modulus of 0.16 ± 0.03 GPa and a tensile strength of 4.86 ± 0.61 MPa. The potential of TSn and BSn membranes to guide bone regeneration was explored. In vitro, the TSn membrane exhibited significantly higher cell proliferation for MC3T3-E1 cells than the BSn membrane. In a cranial bone defect in a rat model, the TSn and BSn membranes displayed superior bone regeneration compared to the control because the membrane prevented the ingrowth of soft tissue to the defective area. Compared to the BSn membrane, the TSn membrane improved damaged bone regeneration, presumably due to its superior mechanical properties, high osteoconductivity, and increased cell proliferation. The TSn membrane has a bionic structure, excellent mechanical properties, and greater biocompatibility, making it an ideal candidate for GBR.

Fabrication of Antheraea pernyi Silk Fibroin-Based Thermoresponsive Hydrogel Nanofibers for Colon Cancer Cell Culture

Antheraea pernyi silk fibroin (ASF)-based nanofibers have wide potential for biomaterial applications due to superior biocompatibility. It is not clear whether the ASF-based nanofibers scaffold can be used as an in vitro cancer cell culture platform. In the current study, we fabricated novel ASF-based thermoresponsive hydrogel nanofibers by aqueous electrospinning for colon cancer (LoVo) cells culture. ASF was reacted with allyl glycidyl ether (AGE) for the preparation of allyl silk fibroin (ASF-AGE), which provided the possibility of copolymerization with allyl monomer. The investigation of ASF-AGE structure by 1H NMR revealed that reactive allyl groups were successfully linked with ASF. ASF-based thermoresponsive hydrogel nanofibers (p (ASF-AGE-NIPAAm)) were successfully manufactured by aqueous electrospinning with the polymerization of ASF and N-isopropylacrylamide (NIPAAm). The p (ASF-AGE-NIPAAm) spinning solution showed good spinnability with the increase of polymerization time, and uniform nanofibers were formed at the polymerization time of 360 min. The obtained hydrogel nanofibers exhibited good thermoresponsive that the LCST was similar with PNIPAAm at about 32 °C, and good degradability in protease XIV PBS solution. In addition, the cytocompatibility of colon cancer (LoVo) cells cultured in hydrogel nanofibers was assessed. It was demonstrated that LoVo cells grown on hydrogel nanofibers showed improved cell adhesion, proliferation, and viability than those on hydrogel. The results suggest that the p (ASF-AGE-NIPAAm) hydrogel nanofibers have potential application in LoVo cells culture in vitro. This study demonstrates the feasibility of fabricating ASF-based nanofibers to culture LoVo cancer cells that can potentially be used as an in vitro cancer cell culture platform.

Silk Fibroin as a Green Material

Silk fibroin has been explored as a suitable biomaterial due to its biocompatibility, tunable degradability, low toxicity, and mechanical properties. To harness silk fibroin's innate properties, it is purified from native silkworm cocoons by removing proteins and debris that have the potential to cause inflammatory responses. Typically, within the purification and fabrication steps, chemical solvents, energy-intensive equipment, and large quantities of water are used to reverse engineer silk fibroin into an aqueous solution and then process into the final material format. Gentler, green methods for extraction and fabrication have been developed that reduce or remove the need for harmful chemical additives and energy-inefficient equipment while still producing mechanically robust biomaterials. This review will focus on the alternative green processing and fabrication methods that have proven useful in creating silk fibroin materials for a range of applications including consumer and medical materials.

Silkworm and spider silk electrospinning: a review

Issues of fossil fuel and plastic pollution are shifting public demand toward biopolymer-based textiles. For instance, silk, which has been traditionally used during at least 5 milleniums in China, is re-emerging in research and industry with the development of high-tech spinning methods. Various arthropods, e.g. insects and arachnids, produce silky proteinic fiber of unique properties such as resistance, elasticity, stickiness and toughness, that show huge potential for biomaterial applications. Compared to synthetic analogs, silk presents advantages of low density, degradability and versatility. Electrospinning allows the creation of nonwoven mats whose pore size and structure show unprecedented characteristics at the nanometric scale, versus classical weaving methods or modern techniques such as melt blowing. Electrospinning has recently allowed to produce silk scaffolds, with applications in regenerative medicine, drug delivery, depollution and filtration. Here we review silk production by the spinning apparatus of the silkworm Bombyx mori and the spiders Aranea diadematus and Nephila Clavipes. We present the biotechnological procedures to get silk proteins, and the preparation of a spinning dope for electrospinning. We discuss silk's mechanical properties in mats obtained from pure polymer dope and multi-composites. This review highlights the similarity between two very different yarn spinning techniques: biological and electrospinning processes.

Composition and in silico structural analysis of fibroin from liquid silk of non-mulberry silkworm Antheraea assamensis

Silk is spun from the liquid precursor known as liquid silk secreted from the posterior part and stored in the silk gland lumen with occurrence of many momentary events. The liquid silk in the silk gland is transformed to the spun silk fibre. In this study the elucidation of the protein components of liquid silk from the posterior part of the silk gland (PSG) of saturniid silkworm Antheraea assamensis along with its structural characterization has been reported. The 3D model of the N-terminal amorphous portion with some repeat crystalline motifs (19-255) of core protein fibroin has also been constructed. 1D and 2D electrophoresis revealed the homo-dimeric structure of the silk protein. Secondary structure analysis by Circular dichroism, FTIR spectroscopy showed α helical structural component as predominant conformation in the liquid silk. The crystalline structure investigated through X ray diffraction (XRD) analysis also revealed the presence of less ordered amorphous α helical conformation in the liquid silk. The 3D structural model proposed of the residues from 19 to 255 has revealed structural stability throughout the molecular dynamics simulation process. This study will provide the detailed structural information and in silico analysis of the core protein present in the liquid silk of PSG.

Kinetic Study on the Self-Assembly of Au(I)-Thiolate Lamellar Sheets: Preassembled Precursor vs Molecular Precursor

Molecular self-assembly has played an important role in nanofabrication. Due to the weak driving forces of noncovalent bonds, developing molecular nanoassemblies that have both robust preparation conditions and stable structure is a challenge. In our previous work, we have developed a reversible self-assembly system of Au(I)-thiolate coordination polymer (ATCP) to form colloidal lamellar sheets and demonstrated the high tailorability and stability of their structures, as well as their promising applications in gold nanocluster/nanoparticle fabrication and UV light shielding. Here, we first reported our progress in exploring a robust and green assembly protocol toward ATCP colloidal lamellar sheets in water by allowing the molecular precursors of HAuCl₄ and the thiol ligand to form ATCP preassembled intermediates. In this way, colloidal ATCP lamellar sheets can be prepared in a wide range of synthetic concentrations ([Au]₀ ≥ 2 × 10^-4 M) and at broad assembly temperatures (80-100 °C) with similar high yields (>80%). The assembly kinetics at different conditions are also studied in detail to help understand the robust assembly process. The robust and green synthetic protocols will pave a way for their real applications.

Surface Activity Study of Water-Soluble Silk Fibroin Prepared using Cocoons and Ca(NO3)2 · 4H2O

The objective of this study was to analyze the relationship between structural changes and surface-activity of water-soluble silk fibroin prepared by treatment with calcium nitrate tetrahydrate (Ca(NO3)2 · 4 H2O). Ca(NO3)2 · 4 H2O, is a hygroscopic compound at room temperature and a suitable solvent upon melting at 100 °C, which was traditionally used as a solvent for dissolving cocoons or silk. The cocoons or silk were optimally dissolved by Ca(NO3)2 · 4 H2O when using a 40 % (w/w) Ca(NO3)2 solution, a 1 : 10 ratio of cocoons or silk to solvent and a dissolving time of 69 min. The results showed that the hydrophobic region of the silk fibroin was destroyed, resulting in the exposure of the hydrophobic groups. The emulsifying ability and the emulsion stability as well as the foaming ability and the foam stability, and the γCMC and CMC of soluble silk fibroin were 92.8 %, 97.3 %, 213.3 %, 88.1 %, 65.83 mN/m and 0.42 mg/mL, respectively. The molecular conformation of silk fibroin chains was the β-sheet, as shown by the intense amide I–III bands at 3 163 cm−1, 1 627 cm−1, 1 518 cm−1, and 1 231 cm−1. The random coil/α-helix structure induced from Ca(NO3)2 convert to β-sheet conformation. Owing to the calcium nitrate's dissolution, silk fibroin can be dissolved in water by changing its structure, and shows excellent surface activity.

Physico-chemical characterization of Antheraea mylitta silk mats for wound healing applications

In the field of plastic reconstructive surgery, development of new innovative matrices for skin repair is in demand. The ideal biomaterial should promote attachment, proliferation and growth of cells. Additionally, it should degrade in an appropriate time period without releasing harmful substances, not exerting a pathological immune response. The materials used should display optimized mechanical properties to sustain cell growth and limit scaffold contraction. Wound healing is a biological process directed towards restoration of tissue that has suffered an injury. An important phase of wound healing is the generation of a basal epithelium wholly replacing the epidermis of the wound. Wild silk from Antheraea mylitta meets these demands to a large extent. To evaluate the effects of the treatment, Antheraea mylitta and Bombyx mori samples were characterized by SEM-EDX, FT-IR, XRD and TGA-DSC techniques. Preliminary cell growth behavior was carried out by culturing epidermal cells and proliferation was quantified via viability assay. Moreover, Antheraea mylitta possesses excellent cell-adhesive capability, effectively promoting cell attachment and proliferation. Antheraea mylitta serves as a delivery vehicle for cells. With all these unique features, it is expected that Antheraea mylitta mat will have wide utility in the areas of tissue engineering and regenerative medicine.

Mimicking Form and Function of Native Small Diameter Vascular Conduits Using Mulberry and Non-mulberry Patterned Silk Films

Autologous graft replacement as a strategy to treat diseased peripheral small diameter (≤6 mm) blood vessel is often challenged by prior vein harvesting. To address this issue, we fabricated native-tissue mimicking multilayered small diameter vascular graft (SDVG) using mulberry (Bombyx mori) and Indian endemic non-mulberry (Antheraea assama and Philosamia ricini) silk. Patterned silk films were fabricated on microgrooved PDMS mold, casted by soft lithography. The biodegradable patterned film templates with aligned cell sheets were rolled onto an inert mandrel to mimic vascular conduit. The hemocompatible and mechanically strong non-mulberry films with RGD motif supported ∼1.2 folds greater proliferation of vascular cells with aligned anchorage. Elicitation of minimal immune response on subcutaneous implantation of the films in mice was complemented by ∼45% lower TNF α secretion by in vitro macrophage culture post 7 days. Pattern-induced alignment favored the functional contractile phenotype of smooth muscle cells (SMCs), expressing the signature markers-calponin, α-smooth muscle actin (α-SMA), and smooth muscle myosin heavy chain (SM-MHC). Endothelial cells (ECs) exhibited a typical punctuated pattern of von Willebrand factor (vWF). Deposition of collagen and elastin by the SMCs substantiated the aptness of the graft with desired biomechanical attributes. Furthermore, the burst strength of the fabricated conduit was in the range of ∼915-1260 mmHg, a prerequisite to withstand physiological pressure. This novel fabrication approach may eliminate the need of maturation in a pulsatile bioreactor for obtaining functional cellular phenotype. This work is thereby an attestation to the immense prospects of exploring non-mulberry silk for bioengineering a multilayered vascular conduit similar to a native vessel in "form and function", befitting for in vivo transplantation.

Exploration of the tight structural-mechanical relationship in mulberry and non-mulberry silkworm silks

The Bombyx mori silkworm is well known as it has been bred by our ancestors with mulberry tree leaves for thousands of years. However, Bombyx mori is not the only silkworm that can produce silk, many other kinds of silkworms can also make silks for commercial use. In this research, we compare the mechanical properties of five different commercial silk fibres including domesticated mulberry Bombyx mori, non-mulberry semi-domesticated eri Samia ricini, and wild tropical tasar Antheraea mylitta and muga Antheraea assamensis. The results demonstrate that the non-mulberry silk fibres have a relatively high extensibility as compared to the mulberry silk fibres. In the meantime, the non-mulberry silk fibres show comparatively unique toughness to the mulberry silk fibres. Synchrotron radiation FTIR microspectroscopy, synchrotron radiation wide angle X-ray diffraction, and Raman dichroism spectroscopy are used to analyze the structural differences among the five species of silk fibres comprehensively. The results clearly show that the mechanical properties of both mulberry and non-mulberry silk fibres are closely related to their structures, such as β-sheet content, crystallinity, and the molecular orientation along the fibre axis. This study aims to understand the differences in the structural and mechanical properties of different mulberry and non-mulberry silk fibres, which are of importance to the related research on understanding and utilizing the non-mulberry silk as a biomaterial. We believe these investigations not only provide insight into the biology of silk fibroins from the non-mulberry silkworms but also offer guidelines for further biomimetic investigations into the design and manufacture of artificial silk protein fibres with novel morphologies and associated material properties for future use in different fields like bioelectronics, biomaterials and biomedical devices.

Spermine-modified Antheraea pernyi silk fibroin as a gene delivery carrier

The development of a novel cationized polymer used as a gene delivery carrier that can conveniently and effectively transfect cells resulting in a stably expressed target gene remains a challenge. Antheraea pernyi silk fibroin (ASF) is a cytocompatible and biodegradable natural polymer, and it possesses Arg-Gly-Asp sequences but a negative charge. In order to render ASF amenable to packaging plasmid DNA (pDNA), spermine was used to modify ASF to synthesize cationized ASF (CASF), which was used as a gene delivery carrier. CASF was characterized using trinitrobenzene sulfonic acid assay, the zeta potential determination, and a Fourier transform infrared analysis, and the results of these characterizations indicated that the -NH2 in spermine effectively reacts with the -COOH in the side chains of ASF. Spermine grafted to the side chains of ASF resulted in the conversion of the negative charge of ASF to a positive charge. CASF packaged pDNA and formed CASF/pDNA complexes, which exhibited spherical morphology with average particle sizes of 215-281 nm and zeta potential of approximately +3.0 mV to +3.2 mV. The results of the MTT assay, confocal laser scanning microscopy, and flow cytometry analysis in a human endothelial cell line revealed that CASF/pDNA complexes exhibited lower cytotoxicity and higher transfection efficiency compared to the pDNA complexes of polyethyleneimine. These results indicate that our synthesized CASF, a cationized polymer, is a potential gene delivery carrier with the advantages of biodegradability and low cytotoxicity.

Biosynthesis and characterization of a non-repetitive polypeptide derived from silk fibroin heavy chain

Silk fibroin heavy chain is the major protein component of Bombyx mori silk fibroin and is composed of 12 repetitive and 11 non-repetitive regions, with the non-repetitive domain consisting of a hydrophilic polypeptide chain. In order to determine the biomedical function of the non-repetitive domain or potentially use it to modify hydrophobic biomaterials, high-purity isolation is necessary. Previously, we cloned and extended a gene motif (f(1)) encoding the non-repetitive domain. Here, this motif and its multimers are inserted into a glutathione S-transferase (GST)-tagged fusion-protein expression vector. Motif f(1) and multimers f(4) and f(8) were expressed in Escherichia coli BL21 cells following isopropyl β-D-1-thiogalactopyranoside induction, purified by GST-affinity chromatography, and single bands of purified fusion proteins GST-F(1), GST-F(4), and GST-F(8), were visualized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Target polypeptides F(1), F(4), and F(8), were cleaved clearly from the GST-fusion tag following thrombin digestion. Mass spectrometry results indicate that the molecular weights associated with fusion proteins GST-F(1), GST-F(4), and GST-F(8) are 31.5, 43.8, and 59.0kDa, respectively, and with the cleaved polypeptides F(1), F(4), and F(8) are 4.8, 16.8, and 32.8kDa, respectively. The F(1), F(4), and F(8) polypeptide chains are negatively charged with isoelectric points (pI) of 3.3, 3.2, and 3.0, respectively. The molecular weight and pI values of the polypeptide chains are consistent with the predicted values and the amino acid compositions similar to predicted sequences. FTIR and CD results show the molecular conformation of F(1) was mainly random coil, and more stable α-helix structure formed in longer molecular chain.

Molecular architecture of silk fibroin of Indian golden silkmoth, Antheraea assama

The golden silk spun by Indian golden silkmoth Antheraea assama, is regarded for its shimmering golden luster, tenacity and value as biomaterial. This report describes the gene coding for golden silk H-fibroin (AaFhc), its expression, full-length sequence and structurally important motifs discerning the underlying genetic and biochemical factors responsible for its much sought-after properties. The coding region, with biased isocodons, encodes highly repetitious crystalline core, flanked by a pair of 5′ and 3′ non-repetitious ends. AaFhc mRNA expression is strictly territorial, confined to the posterior silk gland, encoding a protein of size 230 kDa, which makes homodimers making the elementary structural units of the fibrous core of the golden silk. Characteristic polyalanine repeats that make tight β-sheet crystals alternate with non-polyalanine repeats that make less orderly antiparallel β-sheets, β-turns and partial α-helices. Phylogenetic analysis of the conserved N-terminal amorphous motif and the comparative analysis of the crystalline region with other saturniid H-fibroins reveal that AaFhc has longer, numerous and relatively uniform repeat motifs with lower serine content that assume tighter β-crystals and denser packing, which are speculated to be responsible for its acclaimed properties of higher tensile strength and higher refractive index responsible for golden luster.

Characterization of Silk Fibroin/Chitosan 3D Porous Scaffold and In Vitro Cytology

Bone tissue engineering is a powerful tool to treat bone defects caused by trauma, infection, tumors and other factors. Both silk fibroin (SF) and chitosan (CS) are non-toxic and have good biocompatibility, but are poor biological scaffolds when used alone. In this study, the microscopic structure and related properties of SF/CS composite scaffolds with different component ratios were examined. The scaffold material most suitable for osteoblast growth was determined, and these results offer an experimental basis for the future reconstruction of bone defects. First, via freeze-drying and chemical crosslinking methods, SF/CS composites with different component ratios were prepared and their structure was characterized. Changes in the internal structure of the SF and CS mixture were observed, confirming that the mutual modification between the two components was complete and stable. The internal structure of the composite material was porous and three-dimensional with a porosity above 90%. We next studied the pore size, swelling ratio, water absorption ratio, degradation and in vitro cell proliferation. For the 40% SF-60% CS group, the pore size of the scaffold was suitable for the growth of osteoblasts, and the rate of degradation was steady. This favors the early adhesion, growth and proliferation of MG-63 cells. In addition to good biocompatibility and satisfactory cell affinity, this material promotes the secretion of extracellular matrix materials by osteoblasts. Thus, 40% SF-60% CS is a good material for bone tissue engineering.

Ion-induced fabrication of silk fibroin nanoparticles from Chinese oak tasar Antheraea pernyi

Silk protein fibroin in nanoparticles form is a promising material for drug delivery due to its pleiotropic properties, including biocompatibility, biodegradability, ease in fabrication into smaller diameters, high bioavailability, and therapeutic retention at target sites. In the present study, silk nanoparticles are fabricated from regenerated fibroin solution of the Chinese temperate oak tasar Antheraea pernyi by novel ion-induced self-assembly in a very short time under mild conditions. The resultant fibroin nanoparticles range in size from 100 to 500 nm. The molecular conformation of regenerated fibroin changes from α-helical to a β-sheet structure as a rapid function of the ionic strength and the hydrophobic and electrostatic interactions. The mild conditions are potentially advantageous for the encapsulation of sensitive drugs and therapeutic molecules such as doxorubicin hydrochloride, an amphiphilic anticancer therapeutic. In vitro release of doxorubicin from nanoparticles is pH sensitive, with approx. 65% doxorubicin remaining in the fibroin nanoparticles after 11 days. The activity of fibroin nanoparticles on hepatomas indicates the efficacy of the fibroin nanoparticles to maintain the bioactivity of the loaded doxorubicin and impart a dose-dependent cell growth inhibition. The results suggest that Chinese temperate oak tasar silk fibroin nanoparticles can be used as a sustained drug delivery vehicle.

Isolation and processing of silk proteins for biomedical applications

Silk proteins of silkworms are chiefly composed of core fibroin protein and glycoprotein sericin that glues fibroin. Unique mechanical properties, cyto-compatibility and controllable biodegradability facilitate the use of fibroin in biomedical applications. Sericin serves as additive in cosmetic and food industries, as mitotic factor in cell culture media, anti-cancerous drug, anticoagulant and as biocompatible coating. For all these uses; aqueous solutions of silk proteins are preferred. Therefore, an accurate understanding of extraction procedure of silk proteins from their sources is critical. A number of protocols exist, amongst which it is required to settle a precise and easy one with desired yield and least down-stream processing. Here, we report extraction of proteins employing methods mentioned in literature using cocoons of mulberry and nonmulberry silks. This study reveals sodium carbonate salt-boiling system is the most efficient sericin extraction procedure for all silk variants. Lithium bromide is observed as the effective fibroin dissolution system for mulberry silk cocoons; whereas heterogeneous species-dependent result is obtained in case of nonmulberry species. We further show the effect of common post processing on nanoscale morphology of mulberry silk fibroin films. This knowledge eases the adoption and fabrication of silk biomaterials in devices and therapeutic delivery systems.

Silk fibroin biomaterials for tissue regenerations

Regeneration of tissues using cells, scaffolds and appropriate growth factors is a key approach in the treatments of tissue or organ failure. Silk protein fibroin can be effectively used as a scaffolding material in these treatments. Silk fibers are obtained from diverse sources such as spiders, silkworms, scorpions, mites and flies. Among them, silk of silkworms is a good source for the development of biomedical device. It possesses good biocompatibility, suitable mechanical properties and is produced in bulk in the textile sector. The unique combination of elasticity and strength along with mammalian cell compatibility makes silk fibroin an attractive material for tissue engineering. The present article discusses the processing of silk fibroin into different forms of biomaterials followed by their uses in regeneration of different tissues. Applications of silk for engineering of bone, vascular, neural, skin, cartilage, ligaments, tendons, cardiac, ocular, and bladder tissues are discussed. The advantages and limitations of silk systems as scaffolding materials in the context of biocompatibility, biodegradability and tissue specific requirements are also critically reviewed.

Acylation Modification ofAntheraea pernyiSilk Fibroin Using Succinic Anhydride and Its Effects on Enzymatic Degradation Behavior

The degradation rate of tissue engineering scaffolds should match the regeneration rate of new tissues. Controlling the degradation behavior of silk fibroin is an important subject for silk-based tissue engineering scaffolds. In this study,Antheraea pernyisilk fibroin was successfully modified with succinic anhydride and then characterized by zeta potential, ninhydrin method, and FTIR.In vitro, three-dimensional scaffolds prepared with modified silk fibroin were incubated in collagenase IA solution for 18 days to evaluate the impact of acylation on the degradation behavior. The results demonstrated that the degradation rate of modified silk fibroin scaffolds was more rapid than unmodified ones. The content of theβ-sheet structure in silk fibroin obviously decreased after acylation, resulting in a high degradation rate. Above all, the degradation behavior of silk fibroin scaffolds could be regulated by acylation to match the requirements of various tissues regeneration.