Collagen-fibril matrix properties modulate the kinetics of silica polycondensation to template and direct biomineralizat
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Necla Mine Eren and Osvaldo Campanella Department of Agricultural & Biological Engineering, Purdue University, West Lafayette, Indiana 47907, USA
Sherry L. Voytik-Harbin Weldon School of Biomedical Engineering, Purdue University, West Lafayette, IN 47907, USA; and Department of Basic Medical Sciences, Purdue University, West Lafayette, Indiana 47907, USA
Jenna L. Rickusa) Department of Agricultural & Biological Engineering, Purdue University, West Lafayette, Indiana 47907, USA; Physiological Sensing Facility at the Bindley Bioscience Center and Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907, USA; and Weldon School of Biomedical Engineering, Purdue University, West Lafayette, Indiana 47907, USA (Received 2 June 2015; accepted 4 January 2016)
Fibrillar collagen networks template and direct biocompatible silica mineralization to produce hybrid materials for biomedical applications. Silica mineralization kinetics is critical for precision-tuning material properties, including mechanical strength, microstructure, and interface thickness. We investigated the effect of varying collagen template fibril volume fraction (0.2–0.8) and elasticity (G9 200–1500 Pa) on silica mineralization rates. Measurement of the depletion of mono- and disilicic acids by silicomolybdic acid titration showed that silica condensation on collagen fibrils follows third-order kinetics. Resulting third-order rate constants increased linearly with storage modulus and quadratically with fibril volume fraction. A unique rheological approach used to probe the collagen template surface elasticity in real-time during silicification suggested a two-phase mechanism with high levels of surface-localized gelation in Phase 1 and high levels of bulk solution-localized gelation in Phase 2. These results provide a tool for controlling hybrid collagen-silica material properties by controlling local silica condensation rates.
I. INTRODUCTION
Sol–gel processing techniques have emerged as biocompatible methods to directly interface live cells and tissues with a siliceous mineral phase, conferring novel or enhanced material properties to biological composites. The mechanical strength, porosity, and optical clarity achievable in synthetic silica are advantageous partners for biological functions such as enzymatic activity, bioactivity, and physiologically designed microstructure. Mechanical strength and porosity are especially desirable properties for cell coating materials, with the potential to protect vulnerable cells and regulate transport across the cell surface by size.1–4 While traditional established methods for porous silica formation (e.g., block copolymer
Contributing Editor: Laurie Gower a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2016.5
templating) result in highly regular nano- and microstructural organization and narrow pore size distributions to facilitate precision size exclusion, their synthesis is not compatible with living cells.5,6 Adapting biocompatible sol–gel silica hyb
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