SilkBridge™: a novel biomimetic and biocompatible silk-based nerve conduit.

Silk fibroin (Bombyx mori) was used to manufacture a nerve conduit (SilkBridge™) characterized by a novel 3D architecture. The wall of the conduit consists of two electrospun layers (inner and outer) and one textile layer (middle), perfectly integrated at the structural and functional level. The manufacturing technology conferred high compression strength on the device, thus meeting clinical requirements for physiological and pathological compressive stresses. In vitro cell interaction studies were performed through direct contact assays with SilkBridge™ using the glial RT4-D6P2T cells, a schwannoma cell line, and a mouse motor neuron NSC-34 cell line. The results revealed that the material is capable of sustaining cell proliferation, that the glial RT4-D6P2T cells increased their density and organized themselves in a glial-like morphology, and that NSC-34 motor neurons exhibited a greater neuritic length with respect to the control substrate. In vivo pilot assays were performed on adult female Wistar rats. A 10 mm long gap in the median nerve was repaired with 12 mm SilkBridge™. At two weeks post-operation several cell types colonized the lumen. Cells and blood vessels were also visible between the different layers of the conduit wall. Moreover, the presence of regenerated myelinated fibers with a thin myelin sheath at the proximal level was observed. Taken together, all these results demonstrated that SilkBridge™ has an optimized balance of biomechanical and biological properties, being able to sustain a perfect cellular colonization of the conduit and the progressive growth of the regenerating nerve fibers.

Sol-gel 3-glycidoxypropyltriethoxysilane finishing on different fabrics: The role of precursor concentration and catalyst on the textile performances and cytotoxic activity.

In this paper, the influence of 3-glycidoxypropyltriethoxysilane (GPTES) based organic-inorganic coatings on the properties of treated textile fabrics was studied. All experimental results were deeply analyzed and thereafter correlated with the employed silica precursor concentration and with the presence of the BF3OEt2 (Boron trifluoride diethyl etherate), used as epoxy ring opening catalyst. SEM analysis, FT-IR spectroscopy, X-ray Photoelectron Spectroscopy (XPS), thermogravimetric analysis (TGA) and washing fastness tests of the sol-gel treated cotton fabric samples were firstly exploited in order to characterize the morphological and structural features of the achieved coatings. Finally, the influence of the resulting nanohybrid coatings was explored in terms of abrasion resistance, tensile strength and elongation properties of treated cotton, polyester and silk fabrics. The catalyst amounts seem to strongly improve the formation of coatings, but still they do not influence the wear resistance of treated textile fabrics to the same extent. Indeed, it was found that increasing catalyst/GPTES ratio leads to a more cross linked inorganic 3D-network. GPTES itself was not found to affect the bulk properties of the selected textile and the resulting coatings were not so rigid to hardly modify the mechanical properties of the treated samples. Finally, it is worth mentioning that in all case the obtained 3-glycidoxypropyltriethoxysilane-based chemical finishing have shown no cytotoxic effects on human skin cells.

Anionic fibroin-derived polypeptides accelerate MSC osteoblastic differentiation in a three-dimensional osteoid-like dense collagen niche.

Incorporation of anionic fibroin derived polypeptides into dense collagen gels provided a dynamic, three-dimensional, tissue-equivalent matrix together with biochemical cues that resembled the role of the bone morphogenic growth factors commonly used to promote osteogenic differentiation of mesenchymal stem cells.

Chemical and physical properties of sulfated silk fabrics.

Silk fabrics were treated with chlorosulphonic acid in pyridine for different times. The amount of sulfur bound to silk increased during the first 2 h of reaction and then reached a plateau. The amino acidic pattern of sulfated silk remained essentially unchanged for short reaction times (< or =2 h). Longer reaction times resulted in drastic changes in the concentration of Asp, Glu, and Tyr. Surface morphology and texture of silk fabrics changed upon sulfation. Warp and weft yarns became progressively thinner, and deposits of foreign material appeared on the fiber surface. Changes were more evident at longer reaction times (> or =2 h). Spectroscopic analyses performed by FT-IR and FT-Raman showed the appearance of new bands attributable to various vibrations of sulfated groups. The IR bands at 1049 and 1014 cm-1, due to organic sulfate salts, were particularly intense. Bands assigned to alkyl sulfates and sulfonamides appeared in the 1300-1180 cm-1 range. Organic covalent sulfates displayed a weak but distinct IR band at 1385 cm-1. Both IR and Raman spectra revealed that silk fibroin mainly bound sulfates through the hydroxyl groups of Ser and Tyr, while involvement of amines could not be proved. Changes observed in the amide I and II range indicated an increase of the degree of molecular disorder of sulfated silk. Accordingly, the I850/I830 intensity ratio between the two Tyr bands at 850-830 cm-1 increased from 1.41 to 1.52, indicating a more exposed state of Tyr residues in sulfated silk. TGA, DSC, and TG analyses showed that sulfated silk attained a higher thermal stability. A thermal transition attributable to sulfated silk fibroin fractions appeared at about 260 degrees C in the DSC thermograms.

Electron paramagnetic resonance and ultraviolet/visible study of compounds I and II in the horseradish peroxidase-H(2)O(2)-silk fiber reaction system.

The enzymatic oxidation of silk with H(2)O(2) in the presence of horseradish peroxidase (HRP) has been investigated. Two intermediate complexes have been observed during this reaction. Both can be attributed to Fe(4+) ions axially bonded to an oxygen atom and to a porphyrin radical (P). In the most unstable of them, indicated as compound II, the chemical bond between [Fe(IV)=O](2+) and P was weaker than in the other, indicated as compound I. The former compound disappeared within 1 h of the reaction, at difference with the latter, traces of which were observed even after 3 weeks with dried samples. However, the chemical bond between [Fe(IV)=O](2+) and P in compound I weakened during the sample ageing. All these phenomena have been enlightened by electron paramagnetic resonance (EPR) and spectrophotometric ultraviolet/visible (UV/Vis) measurements.

In vitro evaluation of the inflammatory potential of the silk fibroin.

Silk fibroin membranes recently have been suggested as matrices for biomedical applications, such as guided tissue regeneration and burn wound dressings. The aim of this study was to evaluate the inflammatory potential of fibroin films and to compare the fibroin films with two model materials with completely different physico-chemical properties: poly(styrene) and poly(2-hydroxyethyl methacrylate). Fibroin bound lower levels of fibrinogen than did the two synthetic polymers while the same amounts of adsorbed human plasma complement fragment C3 and IgG were detected. Studies of the binding strength of C3 to fibroin, evaluated by a novel experimental procedure, indicated the occurrence of strong hydrophobic interactions at the interface. The activation of the mononuclear cells by fibroin, measured as interleukin 1beta production, was lower than the reference materials. Adhesion experiments showed the ability of the macrophages to adhere to fibroin by filopodia without a complete spreading of the cells. The results achieved in this study demonstrate that the interactions of fibroin with the humoral components of the inflammatory system were comparable with those of the two model surfaces while the degree of activation and adhesion of the immunocompetent cells appeared more limited.

Swelling and dissolution of silk fibroin (Bombyx mori) in N-methyl morpholine N-oxide.

Bombyx mori silk fibers were dissolved in N-methyl morpholine N-oxide (MMNO), an organic cyclic amine oxide used for the solvent spinning of regenerated cellulosic fibers. The commercial MMNO monohydrate used in this study as a solvent for silk is a hygroscopic compound crystalline at room temperature, which becomes an active solvent after melting at 76 degrees C. The degree of hydration of MMNO was checked by DSC measurements. The solvation power of MMNO towards silk fibroin drastically decreased at a water content > or = 20-21% w/w. Dissolution of silk required both thermal and mechanical energy. The optimum temperature was 100 degrees C. At lower temperatures dissolution proceeded very slowly. At higher temperatures, rapid depolymerization of silk fibroin occurred. The value of the Flory-Huggins interaction parameter chi for the MMNO-H2O-silk fibroin system was -8.5, suggesting that dissolution is a thermodynamically favored process. The extent of degradation of silk fibroin was assessed by measuring the intrinsic viscosity and determining the amino acid composition of silk after regeneration with an aqueous methanol solution, which was effective in removing the solvent and coagulating silk. Regenerated silk fibroin membranes were characterized by infrared spectroscopy, differential scanning calorimetry and scanning electron microscopy. The prevailing molecular conformation of silk fibroin chains was the beta-sheet structure, as shown by the intense amide I-III bands at 1704, 1627, 1515, 1260, and 1230 cm(-1). The value of the I1260/I1230 intensity ratio (crystallinity index) was 0.68, comparable to that of the fibers. The DSC thermogram was characteristic of a silk fibroin material with unoriented beta-sheet crystalline structure, with an intense decomposition endotherm at 294 degrees C. The SEM examination of fractured surfaces showed the presence of a dense microstructure with a very fine texture formed by densely packed roundish particles of about 100-200 nm diameter.

Anastomotic disjunction in long-term patent vascular synthetic grafts in Dacron.

This study follows the recently published paper on the in vivo behaviour of patent Dacron vascular prostheses and focuses in particular on anastomotic disjunction. The question of the evolution of anastomoses was tackled by examining its three basic components: prosthetic tissue, suture thread and arterial wall. The authors' observations were based on material taken from reoperations performed between 7 and 18 years after the first graft. These data enable the authors to affirm that the prosthesis undergoes a general physical and chemical deterioration which varies in intensity according to the type of weaving. On the contrary, in the anastomotic zone this phenomenon is not intense enough to jeopardize the anchorage of the suture thread since the original weft does not show any loss of compactness. In spite of surface morphological deterioration of various intensity, the suture threads maintain satisfactory mechanical properties and structural integrity. The artery wall in the anastomotic zone shows a massive degeneration in terms of its true anatomic structure responsible for the rupture of the suture rima. On the basis of these results the authors conclude that this phenomenon represents the "Achilles' heel" of anastomotic junction.

[Biodegradation of dacron vascular prostheses. Physico-chemical, histological, morphometric and ultrastructural study]. / Biodegradazione delle protesi vascolari in Dacron. Studio chimico-fisico, istologico, morfometrico ed ultrastrutturale.

The paper deals with study of long-term stability as far as concerns Dacron vascular prostheses in woven and knitted double velour. Among our vascular prostheses case-reports, we evaluated three of them explanted after 11, 12, 20 years; all of the prostheses were patent. Chemical-physical, histopathological and ultrastructural analysis have been carried on in order to evaluate in vivo ageing of the examined prostheses. The results all indicate strong alterations of the original properties related to double velour of knitted prostheses and weak alterations of woven one.