Bioinspired mineralization in hydrogels for sustainable materials processing

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2018.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (pages 91-106).Biominerals have been widely studied due to their unique mechanical properties, afforded by their inorganic-organic composite structure and well-controlled growth in macromolecular environments. More recently, growing concerns over climate change and environmental sustainability and the emerging relevance of green chemistry make biomineralization an even more attractive process to study. In this thesis, we focus on the earlier stages of mineral nucleation and growth, where the organic, hydrogel-like matrix dominates the bulk of the material and the mineral is distributed throughout the matrix as nano- and/or microparticles. The phase, morphology, and size of the particles can be controlled using the choice of the hydrogel, functional moieties on the gel polymer backbone or ends, and soluble additives. Depending on the choice of organic matrix and inorganic mineral, the matrix can be dissolved to leave highly uniform particles with tailored properties for a variety of industrial applications, or the matrix can be left intact, creating a hydrogel-mineral composite with improved mechanical properties through organic-inorganic interfacial interactions or additional functionality, such as magnetic properties. In particular, we studied a gelatin-calcium carbonate mineralization system and demonstrated the use of rheology as a mechanoscopic characterization technique for monitoring mineral growth in hydrogels. We also investigated mineralization in metal-coordinate hydrogels, specifically magnetite in Fe-catechol crosslinked gels. We showed that magnetite mineralization occurs at the network crosslinks, leading to mechanical reinforcement of the hydrogel while introducing magnetic properties to the material. Finally, we used tannic acid to modify the growth of calcium carbonate particles, which we employed as green additives for reducing the friction and wear of lubricants.by Abigail U. Regitsky.Ph. D