Attachment and growth of fibroblast cells on silk fibroin

Insulin-like growth factor I releasing silk fibroin scaffolds induce chondrogenic differentiation of human mesenchymal stem cells

Growth factor releasing scaffolds are an emerging alternative to autologous or allogenous implants, providing a biologically active template for tissue (re)-generation. The goal of this study is to evaluate the feasibility of controlled insulin-like growth factor I (IGF-I) releasing silk fibroin (SF) scaffolds in the context of cartilage repair. The impact of manufacturing parameters (pH, methanol treatment and drug load) was correlated with IGF-I release kinetics using ELISA and potency tests. Methanol treatment induced water insolubility of SF scaffolds, allowed the control of bioactive IGF-I delivery and did not affect IGF-I potency. The cumulative drug release correlated linearly with the IGF-I load. To evaluate the chondrogenic potential of the scaffolds, hMSC were seeded on unloaded and IGF-I loaded scaffolds in TGF-beta supplemented medium. Chondrogenic differentiation of hMSC was observed on IGF-I loaded scaffolds, starting after 2 weeks and more strongly after 3 weeks, whereas no chondrogenic responses were observed on unloaded control scaffolds. IGF-I loaded porous SF scaffolds have the potential to provide chondrogenic stimuli to hMSC. Evidence for in vivo cartilage (re)generation must be demonstrated by future, pre-clinical proof of concept studies.

The biocompatibility of silk fibroin films containing sulfonated silk fibroin

Sulfonation reaction may be an effective method for preparation of heparin-like materials. However, no sulfonated polymer based on protein backbone was used for improving the blood compatibility of biomaterials. In this study, the biocompatibility of new kind of composite materials films obtained by blending silk fibroin (SF) with sulfonated silk fibroin (SSF) was evaluated. The anticoagulant activity was characterized with prothrombin time (PT), activated partial thromboplastin time (APTT), and thrombin time (TT), which all increased remarkably, the clot times exceeded the measurement limit of clot detection instrument. Its platelet adhesion was also investigated as another parameter of blood compatibility. The cell compatibility of composite films was evaluated through cell morphologies on the films and cell viability by methyl thiazolyl tetrazolium (MTT) assay. Tensile strength and elongation at break of the composite films reached to 44.6 MPa and 50.3%, respectively. All these results indicated that SF/SSF composite film was a potential material for blood-contact materials and tissue engineering matrix.

Silk as a Biomaterial

Silks are fibrous proteins with remarkable mechanical properties produced in fiber form by silkworms and spiders. Silk fibers in the form of sutures have been used for centuries. Recently regenerated silk solutions have been used to form a variety of biomaterials, such as gels, sponges and films, for medical applications. Silks can be chemically modified through amino acid side chains to alter surface properties or to immobilize cellular growth factors. Molecular engineering of silk sequences has been used to modify silks with specific features, such as cell recognition or mineralization. The degradability of silk biomaterials can be related to the mode of processing and the corresponding content of beta sheet crystallinity. Several primary cells and cell lines have been successfully grown on different silk biomaterials to demonstrate a range of biological outcomes. Silk biomaterials are biocompatible when studied in vitro and in vivo. Silk scaffolds have been successfully used in wound healing and in tissue engineering of bone, cartilage, tendon and ligament tissues.

Preparation and characterization of wet spun silk fibroin/poly(vinyl alcohol) blend filaments

Silk fibroin (SF)/poly(vinyl alcohol) (PVA) blend filaments were prepared by a wet spinning process. Regenerated SF and PVA were dissolved in formic acid and the dope solution exhibited good fiber formation in a methanol coagulation bath. Due to the miscibility of SF/PVA in formic acid, the filament had a smooth surface and dense structure with a circular cross-section. The crystalline structure and thermal properties were varied with different SF/PVA ratios. The mechanical properties of the filament were also controlled by blending PVA with SF. Especially, the knot strength of the SF filament, which is a very important suture property, could be significantly improved by blending with PVA.

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

Antheraea pernyi silk fibroin fibers were dissolved by aqueous lithium thiocyanate to obtain regenerated A. pernyi silk fibroin solution. By means of circular dichroism, (13)C NMR and Raman spectroscopy, the molecular conformation of regenerated A. pernyi silk fibroin in aqueous solution was investigated. The relationship of environmental factors and sol-gel transformation behavior of regenerated A. pernyi silk fibroin was also studied. The molecular conformations of regenerated A. pernyi silk fibroin mainly were alpha-helix and random coil in solution. There also existed a little beta-sheet conformation. It was obviously different with Bombyx mori silk fibroin, whose molecular conformation in solution was only random coil but no alpha-helix existence. With the increase of temperature and solution concentration and with the decrease of solution pH value, the gelation velocity of regenerated A. pernyi silk fibroin solution increased. Especially, it showed that A. pernyi silk fibroin was more sensitive to temperature than B. mori silk fibroin during the sol-gel transformation. The velocity increased obviously when the temperature was above 30 degrees C. During the sol-gel transformation, the molecular conformation of regenerated A. pernyi silk fibroin changed from random coil to beta-sheet structure. The results of these studies provided important insight into the preparation of new biomaterials by silk fibroin protein.

Preparation and characterization of novel nanocomposite films formed from silk fibroin and nano-TiO2

This paper describes the synthesis and characterization of new regenerated silk fibroin (SF)/nano-TiO(2) composite films. The preparation method, based on the sol-gel technique using butyl titanate as oxide precursor, could avoid reagglomeration of the prepared nanoparticles. Samples were characterized mainly by X-ray diffraction (XRD), ultra-violet (UV) spectroscopy, atomic force microscopy (AFM), Fourier transform infrared (FT-IR) spectroscopy, and thermogravimetric analysis (TGA). The UV and AFM results indicated that TiO(2) nanoparticles could be well dispersed inside the SF film, and the size of TiO(2) was about 80nm. The XRD and FT-IR analysis implied that the formation of nano-TiO(2) particles may induce the conformational transition of silk fibroin to a typical Silk II structure partly with the increasing of crystallinity in the composite films. Compared to the pure SF films, the mechanical and thermal properties of composite films were improved, and the solubility in water was decreased due to the conformational transition of silk fibroin to Silk II structure.

Effect of Scaffold Design on Bone MorphologyIn Vitro

Silk fibroin is an important polymer for scaffold designs, forming biocompatible and mechanically robust biomaterials for bone, cartilage, and ligament tissue engineering. In the present work, 3D biomaterial matrices were fabricated from silk fibroin with controlled pore diameter and pore interconnectivity, and utilized to engineer bone starting from human mesenchymal stem cells (hMSC). Osteogenic differentiation of hMSC seeded on these scaffolds resulted in extensive mineralization, alkaline phosphatase activity, and the formation of interconnected trabecular- or cortical-like mineralized networks as a function of the scaffold design utilized; allowing mineralized features of the tissue engineered bone to be dictated by the scaffold features used initially in the cell culture process. This approach to scaffold predictors of tissue structure expands the window of applications for silk fibroin-based biomaterials into the realm of directing the formation of complex tissue architecture. As a result of slow degradation inherent to silk fibroin, scaffolds preserved their initial morphology and provided a stable template during the mineralization phase of stem cells progressing through osteogenic differentiation and new extracellular matrix formation. The slow degradation feature also facilitated transport throughout the 3D scaffolds to foster improved homogeneity of new tissue, avoiding regions with decreased cellular density. The ability to direct bone morphology via scaffold design suggests new options in the use of biodegradable scaffolds to control in vitro engineered bone tissue outcomes.

Stem cell-based tissue engineering with silk biomaterials

Silks are naturally occurring polymers that have been used clinically as sutures for centuries. When naturally extruded from insects or worms, silk is composed of a filament core protein, termed fibroin, and a glue-like coating consisting of sericin proteins. In recent years, silk fibroin has been increasingly studied for new biomedical applications due to the biocompatibility, slow degradability and remarkable mechanical properties of the material. In addition, the ability to now control molecular structure and morphology through versatile processability and surface modification options have expanded the utility for this protein in a range of biomaterial and tissue-engineering applications. Silk fibroin in various formats (films, fibers, nets, meshes, membranes, yarns, and sponges) has been shown to support stem cell adhesion, proliferation, and differentiation in vitro and promote tissue repair in vivo. In particular, stem cell-based tissue engineering using 3D silk fibroin scaffolds has expanded the use of silk-based biomaterials as promising scaffolds for engineering a range of skeletal tissues like bone, ligament, and cartilage, as well as connective tissues like skin. To date fibroin from Bombyx mori silkworm has been the dominant source for silk-based biomaterials studied. However, silk fibroins from spiders and those formed via genetic engineering or the modification of native silk fibroin sequence chemistries are beginning to provide new options to further expand the utility of silk fibroin-based materials for medical applications.

The generation of germline transgenic silkworms for the production of biologically active recombinant fusion proteins of fibroin and human basic fibroblast growth factor

We generated germline transgenic silkworms bearing a fibroin light chain (FL) promoter-driven FL gene whose 3'-end was flanked with human basic fibroblast growth factor (bFGF) gene, FL/bFGF gene. The cocoons from transgenic worms were trypsinized to remove sericin layers, and treated with solution containing CaCl(2), ethanol, and water at a molar ratio of 1:2:8 (CaCl(2)/ethanol/water) to solubilize fibroin layers. Western blot analysis showed that the recombinant protein, r(FL/bFGF), was solubilized with CaCl(2)/ethanol/water, but not with trypsin, indicating that r(FL/bFGF) was in fibroin layers. Thus, it was concluded that the worms spun cocoons whose fibroin layers were composed of the inherent gene-derived natural fibroin (nF) and r(FL/bFGF). The mixture of nF and r(FL/bFGF) was dubbed r(FL/bFGF)nF. The solubilized r(FL/bFGF)nF was refolded using the glutathione redox system. Human umbilical vein endothelial cells (HUVECs) grew in the refolded r(FL/bFGF)nF-containing culture media, showing that bFGF in r(FL/bFGF) was biologically active. r(FL/bFGF)nF immobilized on a culture dish also supported the growth of HUVECs in bFGF-free media, suggesting the usefulness of r(FL/bFGF)nF as a new biomaterial for tissue engineering. The currently developed transgenic silkworms will be suitable for mass production of fibroins bearing a variety of biological activities.

Wound healing effect of silk fibroin/alginate-blended sponge in full thickness skin defect of rat

Silk fibroin (SF) and alginate (AA) have been proved to be invaluable natural materials in the field of biomedical engineering. This study was designed to compare the wound healing effect of SF, AA and SF/AA-blended sponge (SF/AA) with clinically used Nu Gauze(TM) (CONT) in a rat full thickness wound model. Two circular skin wounds on the back of rat were covered with either of CONT, SF, AA or SF/AA. On the postoperative days of 3, 7, 10 and 14, residual wound area was calculated, and skin wound tissues were biopsied to measure the area of regenerated epithelium and collagen deposition as well as the number of proliferating cell nuclear antigen (PCNA)-immunoreactive cells. Half healing time (HT(50)) of SF/AA was dramatically reduced as compared with that of SF, AA or CONT. Furthermore, SF/AA significantly increased the size of re-epithelialization and the number of PCNA positive cells, whereas the effect of SF/AA on collagen deposition was not significantly different as compared with that of SF or AA. These results demonstrate that the wound healing effect of SF/AA is the best among other treatments including SF and AA, and this synergic effect is mediated by re-epithelialization via rapid proliferation of epithelial cell.

Mixed Protein Blends Composed of Gelatin andBombyx moriSilk Fibroin: Effects of Solvent-Induced Crystallization and Composition

Novel protein blends have been prepared by mixing gelatin (G) with Bombyx mori silk fibroin (SF) and using aqueous methanol (MeOH) to post-induce SF crystallization. When co-cast from solution, amorphous blends of these polymers appear homogeneous, as discerned from visual observation, microscopy, and Fourier-transform infrared (FTIR) spectroscopy. Upon subsequent exposure to aqueous MeOH, SF undergoes a conformational change from random coil to beta sheet. This transformation occurs in pure SF, as well as in each of the G/SF blends, according to X-ray diffractometry and thermal calorimetry. The influence of MeOH-induced SF crystallization on structure and property development has been ascertained in terms of preparation history and blend composition. Thermal gravimetric analysis reveals that the presence of beta sheets in SF and G/SF blends improves thermal stability, while extensional rheometry confirms that SF crystallization enhances the tensile properties of the blends. By preserving a support scaffold above the G helix-to-coil transition temperature, the formation of crystalline SF networks in G/SF blends can be used to stabilize G-based hydrogels for biomaterial and pharmaceutical purposes. The present study not only examines the properties of G/SF blends before and after SF crystallization, but also establishes the foundation for future research into thermally responsive G/SF bioconjugates.

New process to form a silk fibroin porous 3-D structure

A new process to form fibroin spongy porous 3-D structure is reported herein. The process involves freezing and thawing fibroin aqueous solution in the presence of a small amount of an organic solvent. The process requires no freeze-drying, chemical cross-linking, or the aid of other polymeric materials. The solvent concentration, fibroin concentration, freezing temperature, and freezing duration affect the sponge formation, its porous structure, and its mechanical properties. Measurements by XRD and FTIR indicate that silk I and silk II crystalline structures exist in the fibroin sponge and that the secondary structure of fibroin is transformed to a beta-sheet from a random coil during this process. The tensile strength decreased slightly, but the fibroin sponge showed no deformation after autoclaving. Therefore, the fibroin sponge was sterilized using an autoclave. For 3 weeks, MC3T3 cells proliferated in the sterilized fibroin sponge. The fibroin sponge formed by this new process is applicable as a tissue-engineering scaffold because it is formed from biocompatible pure silk fibroin and offers both porous structure and mechanical properties that are suitable for cell growth and handling.

In Vitro Study of the Proteolytic Degradation ofAntheraea pernyiSilk Fibroin

In this study, Antheraea pernyi silk fibroin (Ap-SF) films were incubated with Protease Type XXI from Streptomyces griseus, at 37 degrees C, to investigate the degradation behavior in an in vitro model system. The enzyme-resistant fractions of Ap-SF films and the soluble peptides formed by proteolytic degradation were collected at specified times, from 1 to 17 days, and analyzed by high performance liquid chromatography, differential scanning calorimetry, FT-Raman, and FT-IR spectroscopy. Proteolysis resulted in extensive weight loss and progressive fragmentation of films, especially at long degradation times. A range of soluble peptides was formed by proteolysis. By high performance-size exclusion chromatography it was found that their average molecular weight changed with the time of incubation. The chemical analysis of the enzyme-resistant fraction of Ap-SF films at different times of degradation indicated that the proteolytic attack preferentially occurred in the less ordered Gly rich sequences and that the contribution of the Ala rich crystalline regions to the composition of biodegraded films became progressively larger. Accordingly, DSC and spectroscopic results showed an enhancement of the crystalline character of the biodegraded films. From the behavior of the most important thermal transitions, it was deduced that the alpha-helix domains probably represent the most enzyme-resistant fraction. The in vitro approach used in the present study seems to be a valid tool for studying the rate and mechanism of degradation of Ap-SF films and of other biopolymers of potential biomedical utility.

Effect of beta-sheet crystals on the thermal and rheological behavior of protein-based hydrogels derived from gelatin and silk fibroin

Novel protein-based hydrogels have been prepared by blending gelatin (G) with amorphous Bombyx mori silk fibroin (SF) and subsequently promoting the formation of beta-sheet crystals in SF upon exposure to methanol or methanol/water solutions. Differential scanning calorimetry of the resultant hydrogels confirms the presence and thermoreversibility of the G helix-coil transition between ambient and body temperature at high G concentrations. At low G concentrations, this transition is shifted to higher temperatures and becomes progressively less pronounced. Complementary dynamic rheological measurements reveal solid-liquid cross-over at the G helix-coil transition temperature typically between 30 and 36 degrees C in blends prior to the formation of beta-sheet crystals. Introducing the beta-sheet conformation in SF stabilizes the hydrogel network and extends the solid-like behavior of the hydrogels to elevated temperatures beyond body temperature with as little as 10 wt.-% SF. The temperature-dependent elastic modulus across the G helix-coil transition is reversible, indicating that the conformational change in G can be used in stabilized G/SF hydrogels to induce thermally triggered encapsulant release.

Synthesis, characterization and immunogenicity of silk fibroin-l-asparaginase bioconjugates

L-asparaginase (ASNase) is one basic drug in the treatment of acute lymphoblastic leukemia (ALL). Because its half-life time is too short and it is easy to arouse allergic reaction, use in practical clinic is considerably limited. Silk fibroin (SF) with different molecular mass from 40 to 120 kDa is a natural biocompatible protein and could be used as a novel bioconjugate for enzyme modification to overcome its usual shortcomings mentioned above. When the enzyme was bioconjugated covalently with the water-soluble fibroin by glutaraldehyde, the enzyme kinetic properties and immune characteristics in vivo of the resulting silk fibroin-L-asparaginase (SF-ASNase) bioconjugates were investigated in detail. The results show that the modified ASNase was characterized by its higher residual activity (nearly 80%), increased heat and storage stability and resistance to trypsin digestion, and its longer half-life (63 h) than that of intact ASNase (33 h). The abilities of intact and modified ASNases to arouse allergic reaction are 2(4) and 2(1) antibody titers, respectively. Bioconjugation of silk fibroin significantly helps to reduce the immunogenicity and antigenicity of the enzyme. The apparent Michaelis constants of the modified ASNase (K(m(app))=0.844 x 10(-3)mol L(-1)) was approximately six times lower than that of enzyme alone, which suggests that the affinity of the enzyme to substrate l-asparagine elevated when bioconjugated covalently with silk fibroin. SF-ASNase bioconjugates could overcome the common shortcomings of the native form. Therefore, the modified ASNase coupled with silk fibroin has the potential values of being studied and developed as a new bioconjugate drug.

Nano-scaled hydroxyapatite/polymer composite III. Coating of sintered hydroxyapatite particles on poly(4-methacryloyloxyethyl trimellitate anhydride)-grafted silk fibroin fibers

A novel composite coupling between nano-scaled hydroxyapatite (HAp) particles and poly[4-methacryloyloxyethyl trimellitate anhydride (4-META)]-grafted silk fibroin (SF) through ionic interaction was synthesized. The weight gain of poly(4-META) by graft-polymerization increased with increasing the reaction time, eventually reaching a plateau value of about 20 wt%. The HAp nano-particles were adsorbed equally and dispersively on the treated SF fiber surface. The HAp content in the composite was 4.554 wt% +/- 0.098 (n = 4), confirmed by thermogravimetry (TG). This synthetic system requires no heat to connect HAp to SF and is useful when applying to non-heat-resistant polymers. The L-929 cell-adhesion test shows that the HAp/SF composite improves bioactivity compared to the original SF.

Soluble fibroin enhances insulin sensitivity and glucose metabolism in 3T3-L1 adipocytes

Type 2 diabetes is characterized by hyperglycemia and hyperinsulinemia, features of insulin resistance. In vivo treatment of ob/ob mice with hydrolyzed fibroin reverses these pathological attributes. To explore the mechanism underlying this effect, we used the murine, 3T3-L1 adipocyte cell line, which has been used extensively to model adipocyte function. Chronic exposure of 3T3-L1 adipocytes to insulin leads to a 50% loss of insulin-stimulated glucose uptake. Chronic exposure to different preparations of fibroin partially blocked the response to insulin but also increased the sensitivity of control cells to the acute action of insulin. The latter effect was most robust at physiologic concentrations of insulin. Fibroin did not prevent the insulin-induced downregulation of the insulin receptor or the tyrosine kinase activity associated with the receptor. Further, fibroin had no effect on the activity of the insulin-sensitive downstream kinase, Akt. Interestingly, fibroin accelerated glucose metabolism and glycogen turnover independent of insulin action. In addition, fibroin upregulated glucose transporter (GLUT)1, which increased its expression at the cell surface and enhanced GLUT4 translocation. Together, these phenomena may underlie the improvement in diabetic hyperglycemia noted in vivo in response to fibroin.

Sulfation of silk fibroin by chlorosulfonic acid and the anticoagulant activity

Silk fibroin (Bombyx mori) was sulfated using chlorosulfonic acid in pyridine. FT-IR spectra showed introduction of sulfate group by this reaction; NMR spectra indicated that sulfation occurred mainly at tyrosine and serine residues. Molecular size decreased and dispersed with sulfation. The molecular weight was estimated in around 20,000 by GPC using protein standards. Amino acid composition suggested that sulfated fibroin came from H-chain of fibroin; the crystal region of fibroin molecule remained in sulfated fibroin. The amount of sulfate groups increased with overall reaction time. The maximum amount was estimated in 1.0 mmol/g by acidimetric titration. Sulfation efficiency was calculated as 66.7%. Blood coagulation was prevented by 0.5 mg of sulfated fibroin in 1 ml of blood, while original fibroin did not show any effect. Anticoagulant activity of sulfated fibroin strongly depends on the amount of sulfate groups introduced. These results indicate that sulfate group introduction results in addition of anticoagulant function to silk fibroin. Sulfated fibroin is a new type of anticoagulant material having a protein backbone.

Production and characterization of a silk-like hybrid protein, based on the polyalanine region of Samia cynthia ricini silk fibroin and a cell adhesive region derived from fibronectin

There are a variety of silkworms and silk fibroins produced by them. Silks have many inherent suitable properties for biomaterials. In this paper, a novel silk-like hybrid protein, [DGG(A)(12)GGAASTGRGDSPAAS](5), which consists of polyalanine region of silk fibroin from a wild silkworm, Samia cynthia ricini, and cell adhesive region including Arg-Gly-Asp (RGD) sequence, derived from fibronectin, was designed and produced. The genes encoding the hybrid protein were constructed and expressed in Escherichia coli. The main conformation of the polyalanine region, that is, either alpha-helix or beta-sheet, could be easily controlled by treatment with different acidic solvents, trifluoroacetic acid or formic acid, respectively. This structural change was monitored with 13C CP/MAS NMR. Higher cell adhesive and growth activities of the hybrid protein compared with those of collagen were obtained.

Enhanced production of carcinoembryonic antigen by CW-2 cells cultured on polymeric membranes immobilized with extracellular matrix proteins

Cell growth and the production of carcinoembryonic antigen (CEA) were investigated in human colorectal adenocarcinoma tumor (CW-2) cells cultured on extracellular matrix (ECM) protein membranes, heat-treated poly(vinyl alcohol-co-ethylamine) (PVA-EA) membranes, and PVA-EA membranes containing immobilized ECM proteins. The highest concentration of CEA was found in the cell culture media of CW-2 cells on collagen (COL)-immobilized PVA-EA membranes. This is explained by the flexible mobility of COL on the COL-immobilized PVA-EA membranes causing a specific cell response for the production of CEA. An inverse relationship was observed between either the cell density or the CEA concentration in the cell culture media and the amount of fibronectin (FN) adsorbed on the COL-immobilized membranes. The CEA concentration in the cell culture media was directly related to the cell density, which, in turn, is inversely related to the amount of FN secreted by CW-2 cells. These findings indicate that cells tend to attach to the surface by secreting ECM proteins such as FN when they are grown on substrates that provide weak cell attachment.

Compliant film of regenerated Antheraea pernyi silk fibroin by chemical crosslinking

A compliant film was prepared by chemical crosslinking of fibroin from silk fiber of wild silkworm, Antheraea pernyi. The silk fiber was dissolved in concentrated aqueous lithium thiocyanate and desalinated by dialysis. The film was cast from the regenerated aqueous solution, and crosslinked by polyethylene glycol diglycidyl ether (PEG-DE). This film showed high water resistively while maintaining random coil and alpha-helix structure, unlike films prepared by organic solvent treatment that causes beta-sheet formation. The films containing about 20wt.% crosslinker were remarkably compliant and tenacious. These features, combined with the living-cell affinity of the wild silkworm fibroin, are expected to be useful in biomedical applications.

Production of interferon-beta by fibroblast cells on membranes prepared with RGD-containing peptides

The production of interferon-beta by NB1-RGB fibroblast cells cultured on protein and peptide membranes prepared from silk fibroin, motif peptides of silk fibroin [(AG)(n)] containing arginine-glycine-aspartic acid (RGD) peptide, and Pronectin was investigated. The cell density on various protein and peptide membranes was approximately the same, although the production of interferon-beta depended significantly on the membranes where the cells were cultured. The highest production of interferon-beta was observed when the cells were cultured on (AG)(6)RGD(AG)(7) membranes prepared with hexafluoroacetone (HFA) as the casting solvent. On RGD-containing peptide membranes more centrally located in the peptides, the cells produced more interferon-beta when the peptide membranes were prepared with HFA as the casting solvent. However, there was no enhanced production of interferon-beta by cells on (AG)(6)RGD(AG)(7) membranes prepared with 9 mol/L LiBr or 4.5 mol/L LiClO(4) solution as the casting solvent. Therefore, both the chemical composition and the secondary and higher order structure of the peptide membranes are important for enhanced production of interferon-beta. The blocking of integrin beta(1) on the cells by anti-integrin beta(1) antibody prevented the enhanced production of interferon-beta on (AG)(6)RGD(AG)(7) membranes prepared with HFA. We suggest that the cells must bind to the RGD sequence having the appropriate conformation through their integrin beta(1) for enhanced production of interferon-beta.

Enzymatic degradation behavior of porous silk fibroin sheets

We investigated the degradation behavior of porous silk fibroin sheets by in vitro enzymatic experiments with alpha-chymotrypsin, collagenase IA, and protease XIV. With 1.0 U/ml protease XIV, 70% of a silk fibroin sheet was degraded within 15 days at 37 degrees C. When the fibroin sheet was exposed to collagenase IA, the amount of Silk II crystalline structure in the sheets decreased slightly, and a small amount of Silk I crystalline structure was formed. When protease XIV was used, almost all Silk II disappeared, but the crystallinity increased overall because the amount of Silk I increased. During digestion with protease XIV, the pore size of the fibroin sheets increased with increasing degradation time, until the sheets finally collapsed and became totally shapeless. The average molecular weight of the products after degradation with the three enzymes followed the order protease XIV < collagenase IA < alpha-chymotrypsin. More than 50% of the products resulting from degradation with protease XIV were free amino acids.

Structure and properties of silk fibroin-poly(vinyl alcohol) gel

A series of porous silk fibroin-poly(vinyl alcohol) blend gels were prepared from corresponding aqueous mixtures by freeze- or air-drying, and their structure and mechanical properties were examined. The air-dried gels had higher crystallinity and much greater strengths than the freeze-dried gels, and therefore are suitable for mechanical uses. The freeze-dried gels had characteristic porous structure potentially useful as cell culture substrate. Its structure could be systematically varied by changing freezing temperature and freeze-thaw pretreatments before drying.

Functionalized silk-based biomaterials for bone formation

Silks are being reassessed as biomaterial scaffolds due to their unique mechanical properties, opportunities for genetic tailoring of structure and thus function, and recent studies clarifying biocompatibility. We report on the covalent decoration of silk films with integrin recognition sequences (RGD) as well as parathyroid hormone (PTH, 1-34 amino acids) and a modified PTH 1-34 (mPTH) involved in the induction of bone formation. Osteoblast-like cell (Saos-2) responses to the decorated silk films indicate that the proteins serve as suitable bone-inducing matrices. Osteoblast-like cell adhesion was significantly increased on RGD and PTH compared to plastic, mPTH, and the control peptide RAD. At 2 weeks of culture, message levels of alkaline phosphatase were similar on all substrates, but by 4 weeks, alkaline phosphatase mRNA was greatest on RGD. At 2 weeks of culture, alpha 1(I) procollagen mRNA was elevated on silk, RGD, RAD, and PTH, and hardly detectable on mPTH and plastic. However, by 4 weeks RGD demonstrated the highest level compared to the other substrates. Osteocalcin message levels detected by RT-PCR were greatest on RGD at both time points. Calcification was also significantly elevated on RGD compared to the other substrates with an increase in number and size of the mineralized nodules in culture. Thus, RGD covalently decorated silk appears to stimulate osteoblast-based mineralization in vitro.

Cytotoxicity and L-amino acid oxidase activity of crude insect drugs

The cytotoxicity of crude insect drugs was measured using HeLa cells originating from human cervix and uterine cancer, using the dye uptake assay in order to find potential anticancer agents. Three kinds of extracts (buffer, methanol and ethylacetate) were prepared from 26 insects and used as raw materials for the activity assay. Among these, the buffer extracts from Tabanus, Mylabris and Huechys showed a potent anticancer activity, and those from Catharsius, Red ant, Scorpion, Tabanus and Vespae Nidus showed a strong L-amino acid oxidase (AAO) activity as well as cytotoxicity. In contrast, buffer extracts from Gryllotalpa orientalis and Apriona germari larvae showed greater/more rapid Hela cell growth than that of other insects.

Self-assembled peptide fibers from valylvaline bola-amphiphiles by a parallel beta-sheet network

A series of dipeptide-based bola-amphiphiles, bis(N-alpha-amide-L-valyl-L-valine) 1, n-alkane dicarboxylate (n=4-12), have been synthesized. The bola-amphiphiles with n=4 and 6 self-assembled to form crystalline solids in water, whereas those with n=7-12 produced peptide fibers. FT-IR spectroscopy and X-ray diffraction patterns revealed that the peptide fibers have parallel-type beta-sheet networks between the valylvaline units. FT-IR deconvolution study of carboxyl regions indicated that these crystalline solids and peptide fibers are stabilized by interlayer bifurcated and intralayer lateral hydrogen-bond networks between the end carboxylic acid groups, respectively.

An image analysis method for the study of cell adhesion to biomaterials

This fluorescence image analysis method for the quantitative determination of cell adhesion on biomaterials allows bone cells labelled with propidium iodide to be counted automatically, directly on their support. The reliability of the estimation by fluorescence image analysis was validated by comparison with visual counting and with results obtained by an electronic particle counter. In this way it was possible to demonstrate that the adhesive properties of bone cells are dependent on the type of substrate--enstatite (MgO, SiO2, CaO-P2O5-Al2O3), Thermanox (modified polyethyleneterephthalate), or glass. In contrast, the spread of the cell cytoplasm, labelled with fluorescein isothiocyanate and measured by image analysis, does not vary significantly according to the substrate. The characterisation by SKIZ tessellation of the spatial cell arrangement shows that the bone cells have a random organisation on Thermanox and glass, whereas they form aggregates on enstatite.

Cultivation of fibroblast cells on keratin-coated substrata

By means of a cell culture method, the attachment and growth of mouse L929 fibroblast cells were studied on matrices of the (-SDS)- and (+SDS)-keratins, which were extracted from wool in the absence and presence of sodium dodecyl sulfate, respectively. The (+SDS)-keratin showed some toxic effect on the cell growth, but upon washing with a pH 7/phosphate buffer, the protein behaved similarly to a substratum of the (-SDS)-keratin. The comparative culture assay on the keratins, collagen (type I), and glass revealed that the keratins were more adhesive to the cells and more supportive for cell proliferation than the collagen and glass. The results were explained by an enhanced initial adsorption of mediator proteins from fetal bovine serum onto the keratin substrata.

Effect of the chemical modification of the arginyl residue in Bombyx mori silk fibroin on the attachment and growth of fibroblast cells

We prepared matrices of Bombyx mori silk fibroin (SF) with different degrees of modification of arginyl residues by reaction between 1,2-cyclohexanedione (CHD) and SF. Two kinds of SF, namely native SF (NSF), obtained from the silk gland of silkworm larvae, and regenerated SF (RSF), prepared from cocoons of the same silkworm, were used in this study because their amino acid compositions were slightly different from each other. The attachment and growth of mouse fibroblast (L-929) cells on the matrices of the NSF and RSF, in which half or almost all of the arginyl residues were modified (NSF50, RSF50, NSF100, and RSF100), were studied using a cell culture method. Both NSF50 and NSF100 exhibited higher cell attachment than did the unmodified NSF. While the cell growth on NSF50 was not significantly different from that on NSF and NSF100, the growth on NSF100 was higher than that on NSF. The cells attached to NSF50 and NSF100 were extensively spread out and their filopodia were visible by SEM. The cell attachment and growth on RSF were comparable to those on NSF100. Although RSF50 exhibited almost the same cell attachment as did the unmodified RSF, RSF100 exhibited a lower cell attachment than did the unmodified RSF and RSF50. There were no significant differences in the cell growth among RSF series. The cells attached to RSF50 and RSF100 aggregated to form masses, and their filopodia could not be found. The relationship of cell attachment to the basicity of the substrate is considered because the modification of the positively charged arginyl residue changed the basicity of the substrate and the cell attachment on the substrate.