Date(s) - 11/14/2012
Chair: Laurie GowerAbstract:Invertebrate organisms display a high degree of control over the deposition of their calcium carbonate biominerals. Work in our group has led to the hypothesis that charged polyelectrolytes, like acidic proteins, may be employed by organisms to direct crystal growth through an intermediate liquid phase in a process called the polymer-induced liquid-precursor (PILP) process. Recently, it has been proposed that calcium carbonate crystallization, even in the absence of any additives, follows a non-classical, multi-step crystallization process by first associating into prenucleation clusters. In contrast, others have found evidence of liquid-liquid phase separation occurring in calcium carbonate solutions (even without addition of polymer). The goal of this dissertation was to determine what species might be present under reaction conditions used for the PILP process, and whether or not these species might play a role in the PILP process. To achieve this goal, we have employed Ca2+ ion selective electrodes, pH electrodes, isothermal titration calorimetry, nanoparticle tracking analysis, 13C T2 relaxation measurements, and 13C PFG-STE diffusion NMR measurements. These studies provide evidence that, in the absences of additives, and at near neutral pH, a liquid precursor phase does indeed exist in the form of a bicarbonate-rich liquid condensed phase (LCP). The data further shows that addition of acidic polymer promotes/stabilizes the LCP in a distinct and pronounced fashion, providing a mechanistic understanding of the so called PILP process. As a demonstration of the utility of the biomimetic approach, we have used the PILP process to synthesize micron-sized core-shell particles for potential use in biomedical drug-delivery applications. Calcium carbonate coatings were deposited on the curved surfaces of micro-droplets of either emulsions or liposomes to make non-toxic, inexpensive, biodegradable microcapsules which can encapsulate chemicals-of-interest within the fluidic core. The microcapsules can be dried down to a powder, providing a convenient means of storage and transport of entrapped agents. The dissolution of the mineral shell is pH dependent, enabling a rapid triggered release of the active agent. These CaCO3 microcapsules could make ideal systems for drug/chemical delivery in their own right, or could provide a convenient system for which polymeric or other inorganic coatings could be further applied. In addition to drug delivery, other controlled release applications could be envisioned.