Bombyx Mori Silk Fibroin Research Articles

A novel electrospinning approach to fabricate high strength aqueous silk fibroin nanofibers

The present paper describes a rapid method of producing concentrated aqueous regenerated Bombyx mori silk fibroin (RSF) solution by applying mild shearing under forced dehumidified air and generation of electrospun SF nanofibers from concentrated solution with high mechanical strength using free liquid surface electrospinning machine. The shear induced concentrating mechanism favoured the electrospinning process by enhancing the viscosity (>2.43Pas as onset for electrospinning) and decreasing the surface tension of the solution (40.1–37.7mN/m). Shearing reduced the β-turns and random coil molecular conformation and thereby, intensified the β-sheet content from 16.9% to 34% which is the minimum content needed to commence RSF nanofibers formation. Subsequently, electrospun nanofibrous mats were produced from different batches of concentrated SF solutions (15–21wt%). Among the concentrated RSF, 17wt% RSF solution was the most favourable concentration producing electrospun nanofibrous mat having lowest average fiber diameters of 183±55nm and good tensile strength. The mechanical strength of the nanofibrous sheet was further improved by cross-linking with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide (EDC+NHS) which might be due to enhancement of β-sheet content. These nanofibers exhibited 17.57±1.13MPa ultimate tensile strength, 12.48±1.46% tensile strain at break and 37.7% increase in root mean square surface roughness which is favourable feature for cell adhesion and neo-tissue formation.

Stability toward alkaline hydrolysis ofB.morisilk fibroin grafted with methacrylamide

Bombyx mori silk fibroin fibers were grafted with methacrylamide (MAA) and characterized by Raman and infrared (IR) vibrational spectroscopy before and after hydrolysis in NaOH 5% to elucidate the possible interactions between the two components and the stability of the fibers toward alkaline hydrolysis. Upon grafting, the fibers underwent conformational rearrangements toward a more unordered state and lost orientation at weight gains higher than 60%. Vibrational spectroscopy disclosed the occurrence of intermolecular interactions (mainly hydrogen bonds) between B. mori silk fibroin and polyMAA in the grafted fibers, and the formation of covalent bonds has been explored. These strong interactions made the grafted fibers as a whole more stable toward alkaline hydrolysis because they prevented the solubilization of the polymer upon hydrolysis and made slower the transformation of its CONH2 groups into COOH and COO− groups. Upon hydrolysis, silk fibroin underwent an enrichment in the β-sheet crystalline domains, because of the preferential removal of the unordered domains, which were more prone to the OH− attack. IR and Raman spectroscopy proved valid techniques to investigate the degradation mechanism and kinetics of grafted silk fibroin fibers and so for designing high-performing silk-based materials. The A731/A1004 Raman intensity ratio was proposed to spectroscopically evaluate the composition of the grafted samples; its value was found to linearly increase with weight gain (R2 = 0.998), envisaging the possibility of using Raman spectroscopy as a routine analytical technique for qualitative and quantitative characterization of grafted industrial samples. Copyright © 2016 John Wiley & Sons, Ltd.

Potentially functional polypeptides for modification of biomaterials

Event Abstract Back to Event Potentially functional polypeptides for modification of biomaterials Jiannan Wang1, Mingyang Wu1, Yunfei Liu1 and Fangfang Tu1 1 Soochow University, National Engineering Laboratory for Modern Silk, China Potentially functional polypeptides for modification of biomaterials Mingyang Wu, Yunfei Liu, Fangfang Tu, Jiannan Wang* National Engineering Laboratory for Modern Silk, College of Textile and Clothing Engineering, Soochow University, No. 199 Ren-ai Road, Suzhou Industrial Park, Suzhou, Jiangsu Province, 215123, China *Corresponding author: Jiannan Wang, wangjn@suda.edu.cn Silk fibroin is a native protein with regular amino acid sequence. Such as, Bombyx mori silk fibroin is composed of 12 repetitive and 11 non-repetitive regions, with the non-repetitive domain consisting of a hydrophilic polypeptide chain. The RGD tripeptides distribute in Antheraea yamamai and Antheraea pernyi silk fibroins up to 14 and 12 repeats, respectively. In order to determine the biomedical function of these typical peptides or potentially use them to modify materials, we cloned and extended a gene motif (f(1)) encoding the non-repetitive domain of Bombyx mori silk fibroin and a gene motif (-rgd-) encoding RGD-contained domain of Antheraea yamamai or Antheraea pernyi silk fibroins. These motif and their multimers were inserted into a glutathione S-transferase (GST)-tagged fusion-protein expression vector. Motif (f(1)) and multimers (f(4), f(8), (-rgd-)4, and (-rgd-)8) were expressed in Escherichia coli BL21 cells following isopropyl β-D-1-thiogalactopyranoside induction, purified by GST-affinity chromatography. All express products (GST-F(1), GST-F(4), GST-F(8), GST-(-RGD-)4, and GST-(-RGD-)8) were successfully expressed confirmed by SDS-PAGE, mass spectrometry (MS), amino acid composition and charge assay. The peptides F(1), F(4), F(8), (-RGD-)4, and (-RGD-)8 were all cleaved clearly from the GST-fusion tag following thrombin digestion. The molecular weight by MS, amino acid composition and isoelectric points of released peptides were all consistent with the predicted values. The peptides F(1), F(4), and F(8) were used to modify dacron membrane. Results showed F(1), F(4), and F(8) significantly improved water contact angle of dacron, and increased rapid adhesion and proliferation ability of cells. Cell adhesion and cell proliferation on (-RGD-)4 and (-RGD-)8 modified Bombyx mori silk fibroin films were better than that on unmodified film. The study indicated that the express products of F(1), F(4), and F(8) could improve the hydrophilicity of hydrophobe materials for better application in biomaterials. F(1), F(4), and F(8) exhibited a negative ζ-potential and the measured pI was about 3.3, 3.2 and 3.0, respectively, expecting to be used in vascular tissue engineering. The express products (-RGD-)4 and (-RGD-)8 could be used to modify cellular interface materials to improve cell adhesion and growth on materials surface. Acknowledgements This work was supported by National Natural Science Foundation of China (Nos. 51173125 and 51473108), Natural Science Foundation of Jiangsu Province of China (No. BK2012633), College Natural Science Research Project of Jiangsu Province of China (No. 12KJA43004). Refences [1] Y. X. Yang, H. Y. Huang, Z. F. Tian, et al. Textile Bioengineering and Informatics Symposium Proceedings, 2012, 70-75. [2] H. Y. Huang, Z. F. Tian, Y. X. Yang, et al. Journal of Donghua University (English Edition ), 2012, 29: 26-29. [3] H. R. Zhao, Y. X. Yang, H. G. Yi, et al. Bio-Medical Materials and Engineering, 2014, 24: 2057–2064. Conference: 10th World Biomaterials Congress, Montréal, Canada, 17 May - 22 May, 2016. Presentation Type: Poster Topic: Adhesive biomaterials Citation: Wang J, Wu M, Liu Y and Tu F (2016). Potentially functional polypeptides for modification of biomaterials. Front. Bioeng. Biotechnol. Conference Abstract: 10th World Biomaterials Congress. doi: 10.3389/conf.FBIOE.2016.01.02647 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 27 Mar 2016; Published Online: 30 Mar 2016. Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Jiannan Wang Mingyang Wu Yunfei Liu Fangfang Tu Google Jiannan Wang Mingyang Wu Yunfei Liu Fangfang Tu Google Scholar Jiannan Wang Mingyang Wu Yunfei Liu Fangfang Tu PubMed Jiannan Wang Mingyang Wu Yunfei Liu Fangfang Tu Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Rapid endothelialization and thin luminal layers in vascular grafts using silk fibroin.

The histological effects of silk fibroin (SF) in vascular grafts have not been clarified comprehensively in a large-animal model. This study aimed to observe the histological changes in vascular grafts by using Bombyx mori SF in a dog model. A splice graft consisting of SF and control grafts were implanted in the abdominal aorta of dogs, and the histological characteristics of the 2 types of grafts in each splice graft were compared. Five splice grafts consisted of one graft made of polyester (PE) fibers coated with SF and another coated with gelatin, 4 splice grafts consisted of one graft made of SF fibers coated with gelatin and another made of PE fibers coated with gelatin, and 2 splice grafts consisted of one graft made of SF fibers coated with SF and another made of PE fibers coated with SF. The graft made of PE fibers coated with SF showed more endothelial cells than the graft made of PE fibers coated with gelatin. The grafts using SF as a coating material or graft fibers showed a thinner luminal layer than the grafts made of PE fibers coated with gelatin. This study suggests that SF use for vascular grafts has advantages of rapid endothelialization and tendency to form thin luminal layers.

Cover Picture: Macromol. Mater. Eng. 12/2015

Front Cover: The potential of silks is rapidly becoming a reality with the number of new silk-based systems growing at a fast pace. Early applications of Bombyx mori silk fibroin in the field of biomaterials have now been extended to other exciting areas, such as optics, photonics or electronics. Clearly, the future of silk is only dictated by researchers' creativity and imagination. Further details can be found in the article by R. F. P. Pereira, M. M. Silva, and V. de Zea Bermudez on page 1171.

Conformation of Crystalline and Noncrystalline Domains of [3-13C]Ala-, [3-13C]Ser-, and [3-13C]Tyr-Bombyx mori Silk Fibroin in a Hydrated State Studied with 13C DD/MAS NMR

Silk fibroin fiber is a well-known textile, but is also used as biomaterial that is of interest for use in a variety of applications, usually in a hydrated state. Thus, the determination of the hydrated silk fibroin structure is important for understanding the function and in designing novel biomaterials. In this work, 13C dipolar decoupling/magic angle spinning NMR was used to determine the local conformation of [3-13C]Ala-, [3-13C]Ser-, and [3-13C]Tyr -Bombyx mori silk fibroin in a hydrated state. Ser residues are present predominantly in the crystalline domains, Tyr predominantly in the noncrystalline domains and Ala residues in both domains. The fraction of β-sheet and two random coil distributions with fast and slow chain dynamics could be determined for all these residues by 13C conformation-dependent chemical shift. The fraction of β-sheet of these residues in the fiber and the crystalline fraction did not change significantly before and after hydration. The fraction of random coil conformations wi...

Optical properties of γ-irradiated Bombyx mori silk fibroin films

In the present work the Bombyx mori silk fibroin (SF) films were prepared by the solution casting method and effects of γ-irradiation on the optical properties and optical constants of the films have been studied by using Ultra Violet–Visible (UV–Vis) spectrophotometer. The recorded UV–Vis absorption and transmission spectra have been used to determine the optical band gap (Eg), refractive index (n), extinction coefficient (k), optical conductivity (σopt) and dielectric constants (ε*) of virgin and γ-irradiated films. Reduction in optical band gap and increase in refractive index with increasing radiation dosage were observed. It is also found that there is an increase in dielectric constants with increasing photon energy. The obtained results reveal that the refractive index of the SF films may be efficiently changed by γ-irradiation.

A novel bioceramic scaffold integrating silk fibroin in calcium polyphosphate for bone tissue-engineering

The advantages of bioceramics, such as biocompatibility and osteoconduction, have been widely used for bone repair and substitute as bone tissue-engineering materials. Bioceramic scaffolds however still need improvement to meet the requirements for complex bone repair. The aim of this study was to develop novel bioscaffolds for bone regeneration, based on the combination of silk fibroin (SF) and calcium polyphosphate (CPP) composite scaffolds. In this study, Bombyx mori silk fibroin (BMSF) and Antheraea pernyi silk fibroin (APSF) were prepared, and applied into CPP scaffolds with glutaraldehyde crosslinking to form the BMSF/CPP and APSF/CPP bioceramics. These scaffolds were then undergone the strength tests, morphology evaluation, and assessments for biodegradation and biocompatibility. Our results showed that the CPP-type bioceramics presented a higher compressive strength and enhanced degradation after the silk fibroin was doped into a CPP structure. Moreover, the BMSF/CPP and APSF/CPP-type scaffolds exhibited lower cellular toxicity than those of the CPP and HA types. Considering the improved mechanical characteristics and degradation as well as ready availability, SF/CPP may be considered a suitable bioceramic for bone tissue-engineering.

Enhancement of antioxidant ability of Bombyx mori silk fibroins by enzymatic coupling of catechin.

Enzymatic modification of Bombyx mori silk fibroin was carried out by using (+)-catechin, aiming at improving the antioxidant ability of the fibroin-based materials.The actions of tyrosinase on catechin were evaluated by using spectrophotometry, LC-MS, and Fourier transform infrared spectroscopy (FTIR). ε-Polylysine (ε-PLL) was used to investigate the possibility of the covalent reaction between catechin and the primary amine compound. The properties of the fibroin membranes before and after grafting of catechin were compared. The results revealed that catechin was oxidized into reactive o-quinones and subsequently formed catechin derivatives.Meanwhile, catechin could be efficiently grafted onto ε-PLL and led to a decrease in the amount of primary amine groups. 1H-NMR analysis verified the occurrence of the tyrosinase-catalyzed coupling of catechin onto the surface of silk fibroins. Improved antioxidant activity and better durability were obtained for the silk fibroin membrane based on catechin/tyrosinase treatment. Thermal behavior and biocompatibility for the catechin-grafted fibroin membranes did not noticeably change as compared to that of the untreated sample. The present work provided a novel method for preparation of the fibroin-based materials for biomedical applications.

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.

Incorporation of Human Recombinant Tropoelastin into Silk Fibroin Membranes with the View to Repairing Bruch's Membrane.

Bombyx mori silk fibroin membranes provide a potential delivery vehicle for both cells and extracellular matrix (ECM) components into diseased or injured tissues. We have previously demonstrated the feasibility of growing retinal pigment epithelial cells (RPE) on fibroin membranes with the view to repairing the retina of patients afflicted with age-related macular degeneration (AMD). The goal of the present study was to investigate the feasibility of incorporating the ECM component elastin, in the form of human recombinant tropoelastin, into these same membranes. Two basic strategies were explored: (1) membranes prepared from blended solutions of fibroin and tropoelastin; and (2) layered constructs prepared from sequentially cast solutions of fibroin, tropoelastin, and fibroin. Optimal conditions for RPE attachment were achieved using a tropoelastin-fibroin blend ratio of 10 to 90 parts by weight. Retention of tropoelastin within the blend and layered constructs was confirmed by immunolabelling and Fourier-transform infrared spectroscopy (FTIR). In the layered constructs, the bulk of tropoelastin was apparently absorbed into the initially cast fibroin layer. Blend membranes displayed higher elastic modulus, percentage elongation, and tensile strength (p < 0.01) when compared to the layered constructs. RPE cell response to fibroin membranes was not affected by the presence of tropoelastin. These findings support the potential use of fibroin membranes for the co-delivery of RPE cells and tropoelastin.

Facile preparation for robust and freestanding silk fibroin films in a 1‐butyl‐3‐methyl imidazolium acetate ionic liquid system

ABSTRACTSilk fibroin film (SFF) with excellent mechanical properties was prepared for the first time with Bombyx mori silk fibroin as the material and 1‐butyl‐3‐methyl imidazolium acetate ([Bmim]OAc) ionic liquid (IL) as the solvent. The aim was to understand whether the microstructure of SFF could be modified and whether the mechanical properties were improved when [Bmim]OAc IL was used as a solution. With this new system, the obtained SFF was easily peeled off of the substrate, and the silk fibroin proteins retained the α‐helix secondary structure (silk I). Further test results show that the tensile strength (126.8–129.7 MPa) and anti‐UV performance were stronger than the silk fibroin regenerated by traditional ways. Therefore, this study provided and identified a new method with [Bmim]OAc to obtain SFF with strong mechanical properties. This facile preparation and related SFF with excellent mechanical strength could have potential applications in biocompatible implants, synthetic coatings for artificial skin, and many other areas. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42822.

Optical properties of electron irradiated Bombyx mori silk fibroin films

Energetic electron irradiation effects on the optical properties of Bombyx mori silk fibroin (SF) films are studied using UV–visible spectrophotometer. The recorded UV–visible absorption and transmission graphs have been used to determine the optical band gap (E g ), refractive index (n), extinction coefficient (k), optical conductivity (σ opt ) and dielectric constants (e *) of the films. The studies have shown a reduction in optical band gap and increase in refractive index with increasing electron dosage. It is also observed that dielectric constants increase with increasing photon energy. The observed optical changes have been tried to be correlated with the structural changes, revealed through FT-IR spectroscopy. These results indicate that the refractive index of SF films can be changed efficiently by electron irradiation.

Two-in-One Composite Fibers With Side-by-Side Arrangement of Silk Fibroin and Poly(l-lactide) by Electrospinning

1D fibers of Bombyx mori silk fibroin (SF) and poly(l-lactide) (SF-s-PLLA) with side-by-side parallel arrangement of the two components in a single fiber made by electrospinning are presented. The side-by-side arrangement in both randomly oriented and aligned two-in-one fibers was confirmed by scanning electron and confocal laser scanning microscope studies. The molecular orientation and secondary structure of SF and PLLA were dependent on the fiber alignment and annealing conditions. The two sides retained their individual secondary structure before and after annealing without affecting each other in a significant way. The two-in-one fibers after post treatment with methanol and heat at 80 °C showed tensile strength 16.5 ± 1.4 MPa, modulus 205 ± 20.6 MPa, and an elongation at break of 53 ± 8%.

Stretching-Induced Conformational Transition of the Crystalline and Noncrystalline Domains of 13C-Labeled Bombyx mori Silk Fibroin Monitored by Solid State NMR

It is important to understand the conformational changes of both the crystalline and the noncrystalline domains of Bombyx mori silk fibroin as they are stretched from soluble Silk I to the mature Silk II fiber, to be able to design man-made strong and tough silk fibers. Here, the Ser, Tyr, and Ala Cβ of silk fibroin were labeled by 13C to obtain domain-specific structural information, because Ser residues are present predominantly in the crystalline domains, Tyr predominantly in the noncrystalline domains and Ala residues in both domains. The conformational change was monitored by 13C CP/MAS NMR using the conformation-dependent 13C NMR chemical shift. With increasing stretching ratio, initially there is a change from Silk I* (a repeated type II β-turn structure) to β-sheet in the longer AGSGAG sequences, followed by shorter AGSGAG sequences, while the noncrystalline domains change gradually from random coil to β-sheet during the whole conformational change.

Silk Semi‐Interpenetrating Network Hydrogels for Biomedical Applications

SummaryThe Bombyx mori silk fibroin (SF) has recently received much attention as promising hydrogel matrices due to its biocompatibility, hydrophilicity and good permeability. Beside these, porous SF is too brittle in its dry state that does not provide sufficient strength for practical use. To overcome this drawback, semi‐interpenetrating networks of SF were synthesized by a redox‐initiated reaction using poly(ethylene glycol) diacrylate (PEGa) as a precursor to form a primary network. Various hydrogel properties, including swelling ability, gelation kinetics, morphology and drug release, were evaluated through both physical and spectroscopic techniques. For all hydrogels, the gelation time, sol‐gel fraction and equilibrium water content (EWC) were found to decrease with the increasing of PEGa content. Moreover, a sustained delivery of a model compound, Rhodamine B, was also observed. This could be explained in terms of tighter interconnected network and the retardation effects mediated by SF. The proposed method had thus, demonstrated its potential use to improve performance of silk‐based materials for drug delivery applications.

Nonmulberry Silk Fibroin Scaffold Shows Superior Osteoconductivity Than Mulberry Silk Fibroin in Calvarial Bone Regeneration.

Recent years have witnessed the advancement of silk biomaterials in bone tissue engineering, although clinical application of the same is still in its infancy. In this study, the potential of pure nonmulberry Antheraea mylitta (Am) fibroin scaffold, without preloading with bone precursor cells, to repair calvarial bone defect in a rat model is explored and compared with its mulberry counterpart Bombyx mori (Bm) silk fibroin. After 3 months of implantation, Am scaffold culminates in a completely ossified regeneration with a progressive increase in mineralization at the implanted site. On the other hand, the Bm scaffold fails to repair the damaged bone, presumably due to its low osteoconductivity and early degradation. The deposition of bone matrix on scaffolds is evaluated by scanning electron and atomic force microscopy. These results are corroborated by in vitro studies of enzymatic degradation, colony formation, and secondary conformational features of the scaffold materials. The greater biocompatibility and mineralization in pure nonmulberry fibroin scaffolds warrants the use of these scaffolds as an "ideal bone graft" biomaterial for effective repair of critical size defects.

Effect of mechanical deformation on the structure of regenerated Bombyx mori silk fibroin films as revealed using Raman and infrared spectroscopy.

To better understand the effect of mechanical stress during the spinning of silk, the protein orientation and conformation of Bombyx mori regenerated silk fibroin (RSF) films have been studied as a function of deformation in a static mode or in real time by tensile-Raman experiments and polarization modulation infrared linear dichroism (PM-IRLD), respectively. The data show that either for step-by-step or continuous stretching, elongation induces the progressive formation of β-sheets that align along the drawing axis, in particular above a draw ratio of ~2. The formation of β-sheets begins before their alignment during a continuous drawing. Unordered chains were, however, never found to be oriented, which explains the very low level of orientation of the amorphous phase of the natural fiber. Stress-perturbed unordered chains readily convert into β-sheets, the strain-induced transformation following a two-state process. The final level of orientation and β-sheet content are lower than those found in the native fiber, indicating that various parameters have to be optimized in order to implement a spinning process as efficient as the natural one. Finally, during the stress relaxation period in a step-by-step drawing, there is essentially no change of the content and orientation of the β-sheets, suggesting that only unordered structures tend to reorganize.

Small diameter electrospun silk fibroin vascular grafts: Mechanical properties, in vitro biodegradability, and in vivo biocompatibility.

To overcome the drawbacks of autologous grafts currently used in clinical practice, vascular tissue engineering represents an alternative approach for the replacement of small diameter blood vessels. In the present work, the production and characterization of small diameter tubular matrices (inner diameter (ID)=4.5 and 1.5 mm), obtained by electrospinning (ES) of Bombyx mori silk fibroin (SF), have been considered. ES-SF tubular scaffolds with ID=1.5 mm are original, and can be used as vascular grafts in pediatrics or in hand microsurgery. Axial and circumferential tensile tests on ES-SF tubes showed appropriate properties for the specific application. The burst pressure and the compliance of ES-SF tubes were estimated using the Laplace's law. Specifically, the estimated burst pressure was higher than the physiological pressures and the estimated compliance was similar or higher than that of native rat aorta and Goretex® prosthesis. Enzymatic in vitro degradation tests demonstrated a decrease of order and crystallinity of the SF outer surface as a consequence of the enzyme activity. The in vitro cytocompatibility of the ES-SF tubes was confirmed by the adhesion and growth of primary porcine smooth muscle cells. The in vivo subcutaneous implant into the rat dorsal tissue indicated that ES-SF matrices caused a mild host reaction. Thus, the results of this investigation, in which comprehensive morphological and mechanical aspects, in vitro degradation and in vitro and in vivo biocompatibility were considered, indicate the potential suitability of these ES-SF tubular matrices as scaffolds for the regeneration of small diameter blood vessels.

Silk scaffolds with tunable mechanical capability for cell differentiation

Bombyx mori silk fibroin is a promising biomaterial for tissue regeneration and is usually considered an “inert” material with respect to actively regulating cell differentiation due to few specific cell signaling peptide domains in the primary sequence and the generally stiffer mechanical properties due to crystalline content formed in processing. In the present study, silk fibroin porous 3D scaffolds with nanostructures and tunable stiffness were generated via a silk fibroin nanofiber-assisted lyophilization process. The silk fibroin nanofibers with high β-sheet content were added into the silk fibroin solutions to modulate the self-assembly, and to directly induce water-insoluble scaffold formation after lyophilization. Unlike previously reported silk fibroin scaffold formation processes, these new scaffolds had lower overall β-sheet content and softer mechanical properties for improved cell compatibility. The scaffold stiffness could be further tuned to match soft tissue mechanical properties, which resulted in different differentiation outcomes with rat bone marrow-derived mesenchymal stem cells toward myogenic and endothelial cells, respectively. Therefore, these silk fibroin scaffolds regulate cell differentiation outcomes due to their mechanical features.