Biomimetic intrafibrillar silicification of collagen fibrils

Abstract

Event Abstract Back to Event Biomimetic intrafibrillar silicification of collagen fibrils Changmin Hu1* and Mei Wei2* 1 University of Connecticut, Institute of Materials Science, United States 2 University of Connecticut, Materials Science & Engineering, Institute of Materials Science, United States Introduction: Silicon is the most abundant element on earth, and the study of the effect of silicon on biological system has attracted extensive attention. Si-containing biomaterials have been found to be osteoinductive as well as to be able to stimulate neovascularization, induce apatite deposition, and increase extracellular matrix (ECM) synthesis.[1] Since type I collagen is the most abundant component of ECM, it has been used extensively as the ideal component to produce silicified hybrid materials. The biomimetic silicification of collagen fibrils is templated by the self-assembly of triple helix collagen molecules, inspired by biomimetic silicification of collagen fibrils from diatom frustules. In this abstract, we report two approaches to fabricate biomimetic intrafibrillar silicification of collagen fibrils. In the first approach, a two-step process was used, where collagen fibrils were self-assembled and then silicification occurred. In the second approach, a single-step approach was employed, where the self-assembly and silicification of collagen fibrils occurred simultaneously. A combination of poly(allylamine) hydrochloride (PAH) and sodium tripolyphosphate (TPP) was used to act as a stabilizing agent and a templating analog, respectively. Methods: Type I collagen stock solution (4.5 mg/mL), 1.5% PAH stabilized silica precursors (PAH-SA), and collagen self-assembling (CSA) solution were prepared as reported previously.[2][3][4] In two-step approach, collagen molecules self-assembled in the CSA solution at 37 °C for 1 day, and then PAH-SA precursors were added (Col/SA weight ratio is 3:4) to the collagen fibrils and incubate at 37 °C for 1 day (T-Col-PAH-SA). In single-step approach, collagen stock solution was diluted using CSA, and then PAH-SA solution (Col/SA=3:4) was added dropwise to the collagen solution, then the mixture was incubated at 37 °C for 1 day to form S-Col-PAH-SA. In two-step approach, collagen molecules self-assembled in CSA solution at 37 °C for 1 day, TPP (1 wt%) was added, and then followed with PAH-SA precursors at a ratio of Col/SA=3:4 to silicify collagen fibrils at 37 °C for 1 day (T-Col-PAH-SA-TPP). In the later approach, collagen stock solution was diluted using CSA, and TPP was added at a concentration of 1 wt%. Then PAH-SA solution (Col/SA=3:4) was added dropwise to the collagen solution, and finally the mixture was incubated at 37 °C for 1 day (S-Col-PAH-SA-TPP). Results: Intrafibrillar silicified collagen fibrils were produced using either a two-step or a single-step approach (Fig. 1B1, 1B2). PAH was used to stabilize silica precursors to form fluidic nanoprecursors (Fig. 2), and TPP was used to template silica deposition within collagen fibrils (Fig. 1A1, 1B1). Fig. 1A1 and 1A2 show that the single-step process for S-Col-PAH-SA produces twisted collagen fibrils, indicating that the self-assembly of collagen fibrils and the silicification process occurred simultaneously. Both two-step and single-step processes for preparation of Col-PAH-SA-TPP produce silicified collagen fibrils with clear D-bandings (Fig. 1B1, 1B2), indicating the formation of intrafibrillar silicification. Fig. 1 TEM images of T-Col-PAH-SA (A1), S-Col-PAH-SA (A2), T-Col-PAH-SA-TPP (B1), and S-Col-PAH-SA-TPP (B2) fibrils. In B1 and B2, D-banding of the fibrils is clearly seen. Fig. 2 (A) Low and (B) high magnification images of the fluidic silica precursors infiltrated into the collagen fibrils during the collagen self-assembly process. White arrow in B: Vague D-banding. Conclusions: Biomimetic intrafibrillar silicification of collagen fibrils has been successfully achieved using either a single-step or a two-step approach at the presence of PAH for stabilizing silica to form fluidic nanoprecursors and TPP as a templating analog. The authors would like to thank the support from NSF grants (CBET-1133883 and CBET-1347130) and GEMS Fellowship.