Biomimetic spatial control of Liesegang patterns of calcium phosphate in hydrogel employing sucrose and glycine

Abstract

The organic-inorganic interactions are nature’s way of controlling the formation of biominerals. Of the biominerals, calcium phosphate (CaP) phases have been implicated in the structure of hard tissues such as teeth and bones. Hydroxyapatite (HA) is known to be the most stable and abundant CaP in hard tissues. Formation of HA takes place in a stepwise manner through amorphous precursors via a process called the PILP (polymer-induced liquid precursor). The present work aims to elaborate on the mechanism of HA formation via PILP using Liesegang band formation. Periodically precipitating (the Liesegang patterns) systems with varying concentrations of the precursors of CaP formation were employed to understand its crystallization in the presence of additives such as sucrose and glycine. The precipitate was characterized using various techniques such as image analysis, IR, SEM, and PXRD. The spatiotemporal analysis showed that the spacing coefficient (p) trend was pglycine>pcontrol>psucrose. It was revealed that the HA was the dominant CaP present in all the samples but with varying degrees of crystallinity. The systems containing sucrose have more crystallinity than that of glycine. In all the systems, the crystallinity went on decreasing from older rings formed at the top to newer rings formed at the bottom of the tubes, which implies the formation of amorphous liquid-like phase(s) as the intermediates. Based on the observations, a mechanism was proposed for the pre-and postponement of the bands formed in the Liesegang rings.