HIERARCHICAL ASSEMBLY OF HYBRID NANOAPATITES: IMPLICATIONS FOR ORAL DRUG DELIVERY AND IMPLANT-BIOLOGICAL INTERFACES

摘要

This work describes the modulation of crystallization and hierarchical structuring of hydroxyapatite-chitosan hybrid nano-particulates mediated by chitosan. Trace amounts of chitosan introduced at the onset of crystallization aided in the formation of assembled chains of equiaxed nano-HA with a narrow size distribution. Equiaxed nano-HA particles are not indicative of equilibrium morphology, as these crystals take on distinct acicular growth morphology along their c-axis typically exhibiting high aspect-ratio crystals. The highlight of this study, however, is that upon solvent extraction these hybrid suspensions form graded iridescent films which exhibited clear indications of assembly at multiple length scales: (1) below 50 nm, the ordering of nHA particles on self-assembled fibrils of chitosan was observed and (2) between 500-2000 nm, a higher order structure resembling a nano-porous sponge consisting of an interpenetrating composite of HA and chitosan was observed. The extent of assembly was dependent on the concentration of chitosan added during synthesis. The cross-section of the films revealed both structural and compositional grading with mainly chitosan on one surface and HA at the other. The implication of such hybrid nanostructures with multiple levels of structure, especially for drug delivery devices and implant-biological interfaces, is discussed further.