Attachment and growth of fibroblast cells on silk fibroin

Electrospun poly (ɛ-caprolactone)/silk fibroin core-sheath nanofibers and their potential applications in tissue engineering and drug release

One of the key tenets of tissue engineering is to develop scaffold materials with favorable biodegradability, surface properties, outstanding mechanical strength and controlled drug release property. In this study, we generated core-sheath nanofibers composed of poly (ɛ-caprolactone) (PCL) and silk fibroin (SF) blends via emulsion electrospinning. Nanofibrous scaffolds were characterized by combined techniques of scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), differential scanning calorimetry (DSC), contact angle and tensile measurements. An in vitro FITC release study was conducted to evaluate sustained release potential of the core-sheath structured nanofibers. We found that the conformation of SF contained in PCL/SF composite nanofibers was transformed from random coil to β-sheet when treated with methanol, leading to improved crystallinity and tensile strength of nanofibrous scaffolds. The hydrophobicity and diameter of nanofibers decreased when we increased the content of SF in PCL/SF composite nanofibers. Furthermore, we evaluated the potential of fabricated PCL/SF composite nanofibers as scaffold in vitro. The results confirmed that fabricated PCL/SF scaffolds improved cell attachment and proliferation. Our results demonstrated the feasibility to generate core-sheath nanofibers composed of PCL and SF using a single-nozzle technique. The produced nanofibrous scaffolds with sustained drug release have potential application in tissue engineering.

Preparation and Research of Tussah Silk Fibroin/Hydroxyapatite Composites

Tussah silk fibroin (TSF)/hydroxyapatite (HAP) composites were prepared using the co-precipitation method. The results indicate that pure HAP presents needle-like structure with a length of 120-160 nm and a width of 30-40 nm. TSF/HAP composite prepared by adding 8% TSF exhibits a spherical structure, while with the increase of TSF content, the morphology of the composites changed from spherical to short rod, and the length of composite increases from 78 to 146 nm, but the width keep stability. FTIR spectra show the absorption peaks of TSF/HAP composite attributed to the amide and PO43- shift with the addition of TSF, indicating the existence of interaction between HAP and TSF molecules. TSF/HAP composites show a weak crystalline structure, being similar to nano-HAP existed in human bone tissue, thus suggesting that TSF molecules affect the crystallinity of HAP. TG analysis shows that TSF/HAP composite prepared by adding 17.6% TSF contains 11% TSF.

Interactions between spider silk and cells--NIH/3T3 fibroblasts seeded on miniature weaving frames

Background

Several materials have been used for tissue engineering purposes, since the ideal matrix depends on the desired tissue. Silk biomaterials have come to focus due to their great mechanical properties. As untreated silkworm silk has been found to be quite immunogenic, an alternative could be spider silk. Not only does it own unique mechanical properties, its biocompatibility has been shown already in vivo. In our study, we used native spider dragline silk which is known as the strongest fibre in nature.

Methodology/Principal Findings

Steel frames were originally designed and manufactured and woven with spider silk, harvesting dragline silk directly out of the animal. After sterilization, scaffolds were seeded with fibroblasts to analyse cell proliferation and adhesion. Analysis of cell morphology and actin filament alignment clearly revealed adherence. Proliferation was measured by cell count as well as determination of relative fluorescence each after 1, 2, 3, and 5 days. Cell counts for native spider silk were also compared with those for trypsin-digested spider silk. Spider silk specimens displayed less proliferation than collagen- and fibronectin-coated cover slips, enzymatic treatment reduced adhesion and proliferation rates tendentially though not significantly. Nevertheless, proliferation could be proven with high significance (p<0.01).

Conclusion/Significance

Native spider silk does not require any modification to its application as a biomaterial that can rival any artificial material in terms of cell growth promoting properties. We could show adhesion mechanics on intracellular level. Additionally, proliferation kinetics were higher than in enzymatically digested controls, indicating that spider silk does not require modification. Recent findings concerning reduction of cell proliferation after exposure could not be met. As biotechnological production of the hierarchical composition of native spider silk fibres is still a challenge, our study has a pioneer role in researching cellular mechanics on native spider silk fibres.

Structural characteristics and properties of silk fibroin/poly(lactic acid) blend films

This paper describes the preparation and characterization of blend films composed of regenerated silk fibroin (SF) and poly(lactic acid) (PLA). FT-IR and XRD of the SF/PLA blend films with different ratios indicated that the secondary structural transition of SF from Silk I to Silk II was induced upon blending with PLA. The effects of SF/PLA blend ratios on the mechanical and physical properties of the blend films were investigated. Compared to pure SF film, the mechanical and thermal properties of the blend films were improved, and surface hydrophilicity and swelling capacity decreased due to the secondary structural transition of SF to Silk II. Among the blend films with different ratios, the SF/PLA blend film with 7 wt% PLA content showed excellent mechanical properties. Meanwhile, the BSA adsorption amount on the blend film increased with the increase of PLA content. In vitro cell adhesion test showed that the blend film was a good matrix for the growth of L929 mouse fibroblast cells. Consequently, controlling the PLA content in the SF film can improve the mechanical and physical properties of the SF film and provide a promising opportunity to widen potential application of SF in the biomaterials field.

The effect of sericin with variable amino-acid content from different silk strains on the production of collagen and nitric oxide

Although silk sericin (SS) enhances the growth and attachment of fibroblast cells, its toxicity remains questionable. We investigated the effect of SS extracted by heat with variable amino-acid content on in vitro collagen promotion and nitric oxide synthesis. After 24 h of incubation, SS, especially from the Chul 1/1 strain which has the most methionine and cysteine content, enhanced fibroblast growth. The molecular mass of heat-extracted SS from these three strains showed a slightly different range, but within 20-200 kDa, which were all identified as sericin. SS from all strains promoted type-I collagen production in a concentration-dependent manner, while SS from Chul 1/1 strain could induce the highest amount of collagen synthesis when compared to SS from other strains. Nitric oxide was found in the culture medium after activation by SS from the Chul 1/1 strain but reached a level that was not toxic to the cells. We conclude that SS is not toxic to fibroblast cells. Moreover, methionine and cysteine content in SS are important factors to promote cell growth and collagen synthesis.

Electrospun silk biomaterial scaffolds for regenerative medicine

Electrospinning is a versatile technique that enables the development of nanofiber-based biomaterial scaffolds. Scaffolds can be generated that are useful for tissue engineering and regenerative medicine since they mimic the nanoscale properties of certain fibrous components of the native extracellular matrix in tissues. Silk is a natural protein with excellent biocompatibility, remarkable mechanical properties as well as tailorable degradability. Integrating these protein polymer advantages with electrospinning results in scaffolds with combined biochemical, topographical and mechanical cues with versatility for a range of biomaterial, cell and tissue studies and applications. This review covers research related to electrospinning of silk, including process parameters, post treatment of the spun fibers, functionalization of nanofibers, and the potential applications for these material systems in regenerative medicine. Research challenges and future trends are also discussed.

Biodegradation of silk biomaterials

Silk fibroin from the silkworm, Bombyx mori, has excellent properties such as biocompatibility, biodegradation, non-toxicity, adsorption properties, etc. As a kind of ideal biomaterial, silk fibroin has been widely used since it was first utilized for sutures a long time ago. The degradation behavior of silk biomaterials is obviously important for medical applications. This article will focus on silk-based biomaterials and review the degradation behaviors of silk materials.

Preparation and characterization of fibroin/hyaluronic acid composite scaffold

Hyaluronic acid (HA) was added into fibroin solution to prepare fibroin-based porous composite scaffolds. HA exhibited important effects on pore formation and hydrophilicity of fibroin-based scaffold. The aqueous-fibroin/HA scaffolds had highly homogeneous and interconnected pores with porosity of above 90% and controllable pore size ranging from 123 to 253 microm. The water take-up of fibroin/HA scaffolds increased significantly with the increase of HA content. Containing HA at a defined content range, such as 3-6%, fibroin-based scaffolds' affinity to primary neural cells was improved. In 6%HA/fibroin scaffolds, neurosphere-forming cell migrated from their original aggregate and adhered tightly to the surface of scaffolds.

Upregulated proteins associated with fibroin synthesis in posterior silk glands of Antheraea pernyi fifth instar larvae

Antheraea pernyi is a typical wild silkworm with larval silk glands specific for the synthesis and secretion of silk proteins. We examined changes in the protein profile in the posterior section of the silk glands on days 1 and 4 of the last larval instar. Two-dimensional gel electrophoresis over the pH range of 4-7 followed by silver staining revealed about 350 protein spots. Twenty-three proteins upregulated on day 4 were analyzed using matrix-assisted laser desorption/ionization time-of-flight/time-of-flight (MALDI-TOF/TOF). Search for homologous sequences in NCBI databases identified seven proteins probably involved in the regulation of transcription, translation, and general cell metabolism. Among these, glutathione S-transferase theta (GSTT) and ribosomal protein L8 (RPL8) were selected for investigations at the mRNA level. Real-time quantitative PCR showed that the expression of GSTT peaked on day 4, whereas that of RPL8 peaked on day 3, confirming the upregulation of these proteins during the last larval instar. These results show that expressions of GSTT and RPL8 may play a role in fibroin synthesis in A. pernyi.

A high contrast method of unstained biological samples under a thin carbon film by scanning electron microscopy

The contrast of biological samples in scanning electron microscopy (SEM) is very weak. To examine a biological specimen by SEM, many steps and/or special equipment are required to prepare the sample. Here, we describe a method using an unstained biological sample under a 40 nm carbon film to give a high contrast image, where the image is detected by the secondary electron (SE) signal at a low accelerating voltage of 1.5 kV. Under these conditions, it is hard to detect a direct signal from a biological specimen. The high contrast image is created by the SEs from the lower surface of the thin carbon film. Therefore, the damage to the sample from the electron beam is very low. Our method can be utilized to observe various biological samples of bacteria, viruses, and protein complexes.

Skeletal tissue engineering using silk biomaterials

Silks have been proposed as potential scaffold materials for tissue engineering, mainly because of their physical properties. They are stable at physiological temperatures, flexible and resist tensile and compressive forces. Bombyx mori (silkworm) cocoon silk has been used as a suture material for over a century, and has proved to be biocompatible once the immunogenic sericin coating is removed. Spider silks have a similar structure to silkworm silk but do not have a sericin coating. This paper provides a general overview on the use of silk protein in biomaterials, with a focus on skeletal tissue engineering.

Silk fibroin protein from mulberry and non-mulberry silkworms: cytotoxicity, biocompatibility and kinetics of L929 murine fibroblast adhesion

Silks fibers and films fabricated from fibroin protein of domesticated mulberry silkworm cocoon have been traditionally utilized as sutures in surgery and recently as biomaterial films respectively. Here, we explore the possibility of application of silk fibroin protein from non-mulberry silkworm cocoon as a potential biomaterial aid. In terms of direct inflammatory potential, fibroin proteins from Antheraea mylitta and Bombyx mori are immunologically inert and invoke minimal immune response. Stimulation of murine peritoneal macrophages and RAW 264.7 murine macrophages by these fibroin proteins both in solution and in the form of films assayed in terms of nitric oxide and TNFalpha production showed comparable stimulation as in collagen. Kinetics of adhesion of L929 murine fibroblasts, for biocompatibility evaluation, monitored every 4 h from seeding and studied over a period of 24 h, reveal A. mylitta fibroin film to be a better substrate in terms of rapid and easier cellularization. Cell viability studies by MTT assay and flow cytometric analyses indicate the ability of fibroin matrices to support cell growth and proliferation comparable to collagen for long-term culture. This matrix may have potential to serve in those injuries where rapid cellularization is essential.

Mulberry non-engineered silk gland protein vis-à-vis silk cocoon protein engineered by silkworms as biomaterial matrices

Silk fibroin from silk gland of Bombyx mori 5th instar larvae was utilized to fabricate films, which may find possible applications as two-dimensional matrices for tissue engineering. Bombyx mori cocoon fibroin is well characterized as potential biomaterial by virtue of its good mechanical strength, water stability, thermal properties, surface roughness and biocompatibility. The present study aims to characterize the biophysical, thermal, mechanical, rheological, swelling properties along with spectroscopic analysis, surface morphology and biocompatibility of the silk gland fibroin films compared with cocoon fibroin. Fibroin solutions showed increased turbidity and shear thinning at higher concentration. The films after methanol treatment swelled moderately and were less hydrophilic compared to the untreated. The spectroscopic analysis of the films illustrated the presence of various amide peaks and conformational transition from random coil to beta sheet on methanol treatment. X-ray diffraction studies also confirmed the secondary structure. Thermogravimetric analysis showed distinct weight loss of the films. The films were mechanically stronger and AFM studies showed surfaces were rougher on methanol treatment. The matrices were biocompatible and supported L929 mouse fibroblast cell growth and proliferation. The results substantiate the silk gland fibroin films as potential biomaterial matrices.

In vivo degradation of three-dimensional silk fibroin scaffolds

Three-dimensional porous scaffolds prepared from regenerated silk fibroin using either an all-aqueous process or a process involving an organic solvent, hexafluoroisopropanol (HFIP), have shown promise in cell culture and tissue engineering applications. However, their biocompatibility and in vivo degradation have not been fully established. The present study was conducted to systematically investigate how processing method (aqueous vs. organic solvent) and processing variables (silk fibroin concentration and pore size) affect the short-term (up to 2 months) and long-term (up to 1 year) in vivo behavior of the protein scaffolds in both nude and Lewis rats. The samples were analyzed by histology for scaffold morphological changes and tissue ingrowth, and by real-time RT-PCR and immunohistochemistry for immune responses. Throughout the period of implantation, all scaffolds were well tolerated by the host animals and immune responses to the implants were mild. Most scaffolds prepared from the all-aqueous process degraded to completion between 2 and 6 months, while those prepared from organic solvent (hexafluoroisopropanol (HFIP)) process persisted beyond 1 year. Due to widespread cellular invasion throughout the scaffold, the degradation of aqueous-derived scaffolds appears to be more homogeneous than that of HFIP-derived scaffolds. In general and especially for the HFIP-derived scaffolds, a higher original silk fibroin concentration (e.g. 17%) and smaller pore size (e.g. 100-200microm) resulted in lower levels of tissue ingrowth and slower degradation. These results demonstrate that the in vivo behavior of the three-dimensional silk fibroin scaffolds is related to the morphological and structural features that resulted from different scaffold preparation processes. The insights gained in this study can serve as a guide for processing scenarios to match desired morphological and structural features and degradation time with tissue-specific applications.

Silklike materials constructed from sequences of Bombyx mori silk fibroin, fibronectin, and elastin

Two silklike proteins, [TGRGDSPAGG(GAGAGS)3AS]5 (FS5) and [TGRGDSPA-(GVPGV)2GG(GAGAGS)3AS]8 (FES8) were designed to demonstrate the superior performance as biomaterials of silklike proteins. The former protein consists of the crystalline domain sequence, (GAGAGS)n from Bombyx mori silk fibroin and cell-adhesive sequence TGRGDSPA coming from fibronectin-containing RGD triplet. The additional sequence (GVPGV)n from elastin was included in the latter protein. The considerably higher cell-adhesion activities of these proteins for NHDF and VERO cells were observed by comparing with those of silklike materials without RGD sequences and also the crystalline fraction of B. mori silk fibroin. This tendency was independent of the treatments, 4.5M LiClO4 or formic acid (FA), on silklike proteins. Their activities are also higher than those of commercial Fibronectin F for NHDF cell. Their structural characterization was studied using 13C solid-state NMR. Although the overlapped peaks in usual 13C CP/MAS NMR spectra make the detailed structural analysis difficult, the methyl resonance regions observed using dipolar dephasing NMR were very useful for the analysis. The presence of both random coil and beta-sheet structures was observed in these proteins clearly. The content of beta-sheet structure in both proteins increases after FA treatment when compared with the lyophilized samples. The production of electrospun nanofibers from their hexafluoroacetone solution was also tried. The silklike protein FES8 could prepare nonwoven silk fibers although FS5 could not.

Preparation, characterization, and properties of nano-TiO2/silk fibroin hybrid films by sol–gel processing

By sol-gel processing, the regenerated nano-TiO(2)/SF (silk fibroin) hybrid films were synthesized using different ratios of TiO(2) to SF. The experimental results revealed that the nano-TiO(2) particles were well dispersed in the regenerated SF. The diameter of the nano-TiO(2) particles processed by sol-gel method was about 80 nm. Through Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray energy dispersive spectrometer (EDS), Thermogravimetric analysis (TGA), and Derivative thermogravimetry (DTG), the structures and properties of these hybrid films were characterized. The XRD measurement indicated that the crystal structures of the hybrid films were transited from typical Silk I to typical Silk II. However, it was found that excessive increase in the content of nano-TiO(2) led to the breakage of the crystal structures of the hybrid films. The FTIR and EDS analysis showed that new bonds were formed between the nano-TiO(2) particles and the SF. Through TGA and DTG, it was demonstrated that the heat transition temperature of the hybrid films was also enhanced.