Mechanistic study of the Polymer -Induced Liquid -Precursor (PILP) process: Relevance to biomineralization

Biomineralization is a process in which cells construct a mineralization platform based on framework proteins and water-soluble proteins, and utilize some transportation vesicles, such as matrix vesicles to regulate the transportation of ions and precursor phases. The mineral morphologies formed by the Polymer-Induced Liquid-Precursor (PILP) process, which utilizes acidic polypeptides or polymers to mimic the acidic proteins in biominerals, have been shown to have a great similarity with many biominerals. This drives us to investigate the important factors and underlying mechanisms governing the generation, stabilization and transformation of polymer-induced liquid-precursor phases.;First, the PILP phase composition has been characterized during a reaction time series using a combination of measuring water loss with elemental analysis. This phase is found to be a highly hydrated phase with a large amount of acidic polymers entrapped within. By FT-Raman, it is found that these acidic polymers can chelate with calcium ions by breaking the initial calcium-water complexes, liberating free water near the calcium-polymer complexes. It is then shown that when calcium carbonate complexes are formed, most of the acidic polymer can be liberated from the formed precursor phase to re-induce more PILP phase. By FTIR, it is found that acidic polymers can stabilize the PILP amorphous phase. The extended stabilization lifetime of the PILP phase is due to the entrapped acidic polymers and the free water in the precursor phase. They disrupt the ordered packing of the calcium carbonate complexes.;Second, to investigate how different protein structures would affect the PILP phase quality, quantity, and stability, a series of synthetic peptides mimicking proteins involved in biomineralization were synthesized and applied to generate the PILP process using various techniques. Peptides with high charge density, phosphorylation density and molecular weight to a limit of 5000 Da in synthetic peptides have high capability to induce a stable amorphous precursor phase of high fluidity, including calcium carbonate and calcium phosphate.;Finally, the transformation stage of the PILP process was examined. The conditions and mechanisms for formation of different polymorphs of calcium carbonate were investigated by introducing various organic substrates into the PILP process. By exercising a tight control over the local supersaturation degree at the interface between the organic substrate and the crystallization solution via adding a certain amount of magnesium ions or by immobilizing a certain density of Pasp onto the substrate surface, monohydrated calcium carbonate (MCC), aragonite or vaterite thin films can be selectively synthesized. A dropwise technique was also used to sort out the polymorph influencing factors.