Collagen-Silica Hybrid Materials with Tunable Kinetics and Microstructural Properties for Biomedical Applications
Silica-collagen hybrid materials have gained increasing importance to biomedical engineering applications, including cellular microencapsulation and regeneration of bone tissue. Informed design of their macro- and microstructural conformations, and thus functionality, is key to broadening their application. In this dissertation work, oligomeric collagen-fibril matrices with tunable microstructural properties were used to template and direct the formation of biocompatible mesoporous sol-gel silica to produce hybrid organic-inorganic materials. Silica mineralization kinetics is critical for precision-tuning hybrid material properties, including mechanical strength, porous microstructure, depth of silica penetration, and mass transport properties. This work investigates the effect of systematically varying collagen template volume fraction and elasticity, time of contact with silicifying solution, and silicifying solution concentration on the silicification kinetics, hybrid material microstructure, and functionality. The kinetics of collagen silicification was measured by the depletion of mono- and disilicic acids by silicomolybdic acid titration and rheology, unveiling a two-phase kinetics mechanism with high levels of surface-localized gelation in Phase 1 and high levels of bulk solution-localized gelation in Phase 2, with rates controlled by collagen fibril density. The material properties of hybrids were assessed using a combination of SEM imaging, EDX elemental analysis, and rheology. Control of material properties was achieved by modulation of silicification kinetics such that levels of silicification at the collagen surface correlated positively to collagen fibril density (and G’), time of exposure to silicifying solution, and concentration of silicifying solution. Depth of silica penetration correlated negatively to silicification concentration. Mechanical properties of the hybrid material were dominated by silica and tunable through modulation of the collagen fibril density and silicification time. Functionality of hybrid materials was demonstrated by diffusivity studies and formation of collagen-silica microspheres. Collectively, this research provides an in-depth understanding of silicification kinetics as it relates to material properties as well as a full suite of tools for understanding and designing collagen-silica hybrid materials for future biomedical use.
Rickus, Purdue University.
Chemistry|Biomedical engineering|Materials science
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