Complex Formation of Silk Fibroin with Poly(acrylic acid)

Abstract

ABSTRACT:Silk fibroin (SF) and poly(acrylic acid) (PAA) can interact when their aqueous solutions were mixed. Viscometric study showed that SF/PAA complex formation depended on the ratios of SF and PAA in dilute solution. SF/ PAA complexes varied from soluble state to gel and to precipitate when both concentrations of mixed solution were increased gradually. FT-IR results showed that PAA and SF were liable to form interpolymer hydrogen bonds, and SF conformation changed in the complexes. FT-IR spectra also suggested the formation and crystal perfection of PAA/SF complex crystal relied on the ratios of SF and PAA, which were confirmed by the observation of X-ray diffraction.KEY WORDS Complex/ Silk Fibroin I Poly(acrylic acid) I Hydrogen Bond I Silk fibroin (SF) fibers from Bombyx mori silkworm have primarily been used in textile industry for thousands of years. In the past two decades, materials concerning with SF had also been utilized in the areas of biomedical and biochemical applications. 1 -3 Blends of SF with other natural or synthetic polymers, such as poly(vinyl alcohol) (PVA), The complexation of PAA with poly(amino acids), such as poly (L-lysine) (PLL) 24 · 25 and poly(L-proline) (PLP), 26 was also invested, and interpolymer interaction between PAA and poly(amino acids) caused the conformation change ofpoly(amino acids).Recently, we have been interested in various acrylic polymers and SF blends. In our previous articles, it was found that SF was immiscible with polyacrylonitrile, but was partly miscible with poly(acrylonitrile-co-methyl acrylate) (PANMA). 27 · 28 Because of the formation of hydrogen bonds between SF and P ANMA, conformation change of SF in their blends was observed. In systems of SF/poly(potassium acrylic acid) (PAA-K) blend as well as SF/polyalanine (PALA) blend, 29 the specific interaction and conformation change of SF in these blends were observed as well. In order to provide further evidence on the specific interactions and conformation change of SF in blends, we explored the blend of SF/PAA system in present work. SF/PAA complex forming by hydrogen bond could be detected with viscometric, FT-IR and Xray diffraction. The crystallinity and perfection of complex crystal were both dependent on SF/PAA ratios. EXPERIMENTAL MaterialsPreparation of SF solution : Degummed SF from Bombyx mori silk fibers was dissolved in 9.3 mol L -l LiBr aqueous solution under constant stirring for several hours at room temperature. 6 After dialysis against deionized water for three days, the solution was filtered. This solution was further diluted with deionized water to prepare the required concentration.Preparation of PAA solution: PAA was synthesized according to the reference, 30 and molecular weight, as determined by intrinsic viscosity from the equation, 31 [TJ] =8.5 X 10-4 M 112 , is 35000. Then PAA aqueous solutions ofrequired concentration were prepared.Preparation of dilute SF/PAA mixture solution: mixed solutions were prepared by dropwise adding required amount ofO.1 wt% PAA into 0.1 wt% SF s...

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