Chitosan-mediated crystallization and assembly of hydroxyapatite nanoparticles into hybrid nanostructured films

Abstract

The synthesis and subsequent assembly of nearly spherical nano-hydroxyapatite (nHA) particles in the presence of trace amounts of the polysaccharide chitosan was carried out employing a wet chemical approach. Chitosan addition during synthesis not only modulated HA crystallization but also aided in the assembly of nHA particles onto itself. Solvent extraction from these suspensions formed iridescent films, of which the bottom few layers were rich in self-assembled nHA particle arrays. The cross-section of these hybrid films revealed compositional and hence structural grading of the two phases and exhibited a unique morphology in which assembled nHA particles gradually gave way to chitosan-rich top layers. Transmission electron microscope and selected area electron diffraction studies suggested that the basal plane of HA had interacted with chitosan, and scanning electron microscope studies of the hybrid films revealed multi-length scale hierarchical architecture composed of HA and chitosan. Phase identification was carried out by X-ray diffraction (XRD) and Rietveld analysis of digitized XRD data showed that the basic apatite structure was preserved, but chitosan inclusion induced subtle changes to the HA unit cell. The refinement of crystallite shape using the Popa method clearly indicated a distinct change in the growth direction of HA crystallites from [001] to [100] with increasing chitosan concentration. The paper also discusses the likelihood of chitosan phosphorylation during synthesis, which we believe to be a pathway, by which chitosan molecules chemically interact with calcium phosphate precursor compounds and orchestrate the crystallization of nHA particles. Additionally, the paper suggests several interesting biomedical applications for graded nHA-chitosan nanostructured films.

Biopolymer Thin Films Synthesized by Advanced Pulsed Laser Techniques

“…The morphology is quite similar for L and OL thin films obtained by MAPLE exhibiting a spatial orientation due to a collective influence of evaporation-induced assembly with the specific linkages of the linear structures of polysaccharides. These assembling morphologies were also found for nano-hydroxyapatite (nHA) -chitosan composites [140]. It is considered that the nanostructured assembling, which induces a larger specific surface area, boosts the surface properties of the biopolymer.…”

Fabrication method, structure, mechanical, and biological properties of decellularized extracellular matrix for replacement of wide bone tissue defects

“…The region between 2500 and 2000 cm À 1 corresponds to atmospheric absorption. The absorbance peak at 2100 cm À 1 , which can be ascribed to the stretching vibrations of P-OH bonds, was only observed in the intact bone spectrum (Cheng et al, 1998;Bertoni et al, 1998;Kumar et al, 2008). The FTIR spectra in the range of 1200-2000 cm À 1 can be assigned to the absorption from organic matrix of the bone.…”

Preparation of fibrous hydroxyapatite particles by homogeneous precipitation and microwave-assisted hydrothermal heating

“…Such intense reflection of 300 indicates the preferred orientation of a-plane, which reflects the anisotropic crystal growth 33 . The low ratio of peak intensity of the planes 002 and 300, i.e., R 002/300 = I 002 /I 300 , suggests the suppression of the growth along the c-plane 33 . On the other hand, the preferential crystal growth of HAp particles seems to occur along a-plane.…”