In view of widening the biomedical utility of silk as a biomaterial, it is of interest to explore various chemical modification approaches able to complement the intrinsic outstanding properties of silk and to enhance its end-use performance. For example, effective antimicrobially active silk fibres can be prepared by treating silk with tannic acid or ethylenediaminotetraacetic dianhydride, followed by formation of metal complexes with silver, copper, and cobalt [1]. Covalent decoration of silk films with integrin recognition sequences (RGD) results in a stimulation of bone formation [2]. The biological properties and medical utility of sulphated polymers, including the carbohydrate heparin, are well established [3]. The purpose of this study is to explore whether sulphation can be used as a tool to produce functional silk substrates applicable in the medical field [4]. Silk fabrics were treated with chlorosulphonic acid in pyridine for different times. Susceptibility of the reactive sites of silk fibroin to form sulphate salts was investigated. Surface morphology, physical structure, and thermal behaviour of sulphated silk substrates were characterized by means of different analytical techniques (SEM, FT-IR, Raman, DSC, TMA, and TG). The amount of sulphur bound to silk increased during the first 2 h of reaction and then reached a plateau. The amino acidic pattern of sulphated silk remained essentially unchanged for short reaction times (≤ 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 sulphation. Warp and weft yarns became progressively thinner, and deposits of foreign material appeared on the fibre surface. Changes were more evident at longer reaction times (≥ 2 h). Spectroscopic analyses performed by FT--IR and FT-Raman showed the appearance of new bands attributable to various vibrations of sulphated groups. Both IR and Raman spectra revealed that silk fibroin mainly bound sulphates 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 sulphated silk. TGA, DSC, and TG analyses showed that sulphated silk attained a higher thermal stability. The accumulated results indicate that long treatment times should be avoided because the amount of bound sulphur does not increase too much while the risk of extensive fibre degradation becomes very high. In fact, an essential requirement for further application of sulphated silk fabrics is to maintain the intrinsic physical-chemical structure and texture of silk as much as possible. Biological investigations aimed at demonstrating the biomedical utility of sulphated silk are in progress. The recognized biomedical utility of sulphated polymers seems to suggest a possible exploitation of sulphation as a tool to produce functional silk substrates applicable in the medical field.

Chemical and physical properties of sulphated silk fabrics.

TADDEI, PAOLA
2007

Abstract

In view of widening the biomedical utility of silk as a biomaterial, it is of interest to explore various chemical modification approaches able to complement the intrinsic outstanding properties of silk and to enhance its end-use performance. For example, effective antimicrobially active silk fibres can be prepared by treating silk with tannic acid or ethylenediaminotetraacetic dianhydride, followed by formation of metal complexes with silver, copper, and cobalt [1]. Covalent decoration of silk films with integrin recognition sequences (RGD) results in a stimulation of bone formation [2]. The biological properties and medical utility of sulphated polymers, including the carbohydrate heparin, are well established [3]. The purpose of this study is to explore whether sulphation can be used as a tool to produce functional silk substrates applicable in the medical field [4]. Silk fabrics were treated with chlorosulphonic acid in pyridine for different times. Susceptibility of the reactive sites of silk fibroin to form sulphate salts was investigated. Surface morphology, physical structure, and thermal behaviour of sulphated silk substrates were characterized by means of different analytical techniques (SEM, FT-IR, Raman, DSC, TMA, and TG). The amount of sulphur bound to silk increased during the first 2 h of reaction and then reached a plateau. The amino acidic pattern of sulphated silk remained essentially unchanged for short reaction times (≤ 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 sulphation. Warp and weft yarns became progressively thinner, and deposits of foreign material appeared on the fibre surface. Changes were more evident at longer reaction times (≥ 2 h). Spectroscopic analyses performed by FT--IR and FT-Raman showed the appearance of new bands attributable to various vibrations of sulphated groups. Both IR and Raman spectra revealed that silk fibroin mainly bound sulphates 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 sulphated silk. TGA, DSC, and TG analyses showed that sulphated silk attained a higher thermal stability. The accumulated results indicate that long treatment times should be avoided because the amount of bound sulphur does not increase too much while the risk of extensive fibre degradation becomes very high. In fact, an essential requirement for further application of sulphated silk fabrics is to maintain the intrinsic physical-chemical structure and texture of silk as much as possible. Biological investigations aimed at demonstrating the biomedical utility of sulphated silk are in progress. The recognized biomedical utility of sulphated polymers seems to suggest a possible exploitation of sulphation as a tool to produce functional silk substrates applicable in the medical field.
COST 868, Biopolymers in Medical Applications
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G. Freddi; C. Arosio; P. Monti; P. Taddei
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11585/49441
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