Hydroxyapatite Nanoparticles and Nanobiocomposite Scaffold for
Protein Adsorption and Release

Abstract

Spherical, rod and fibrous hydroxyapatite (HA) nanoparticles synthesize through a common
co-precipitation technique and fabricate macroporous HA-gelatin nanobiocomposite scaffolds
for protein adsorption/release study. Three fundamental processing parameters such as
solution pH, temperature and Ca/P ratio synchronize the morphology and crystallinity of nano
HA from identical precursors Ca(CH3COO)2 and KH2PO4. Dispersion study illustrates the
HA nanoparticle suspension stability phenomenon in aqueous media. Rod shaped HA exhibits
relatively better bovine serum albumin (BSA) protein adsorption efficacy with compare to
other two morphologies. In aqueous media, one gram nanorod HA particle adsorb 28 mg BSA
within a time frame of 48 h and subsequently 75 wt.% release after 96 h in phosphate buffer
solution. Low temperature freeze casting of homogenous aqueous slurry of HA nanoparticles,
gelatin and biocompatible polyvinyl alcohol binder develops nano HA – gelatin
nanobiocomposite macroporous scaffolds. Freeze casted nanorod HA-gelatin macroporous
(70 vol.%) scaffold demonstrate highest yield compressive strength of ~2 MPa compare to
other scaffolds prepared from spherical and fibrous HA because of high surface area and the
effective anchoring. An optimum cryogenic treatment time at 77K promotes the mechanical
response of this low strength scaffold and designates as cryo-treated hydroxyapatite–gelatin
macroporous scaffold (CHAMPS). CHAMPS has a high degree of interconnected pores of
50-200 μm in size, compressive strength up to 5.6 MPa and larger strain failure up to 25%.
L929 mouse fibroblast cell interaction supports the cytotoxicity and cell adherence behaviour
with CHAMPS. Porous scaffold exhibits bioactivity in simulated body fluid (SBF) solution
through preferable deposition of carbonated apatite layer around the pores. Biodegradation of
scaffold in tris-HCl solution reveals a slow but systematic decrease in weight over incubation
up to 7 days. Importantly, the excellent adsorption (upto 50 wt.%) and release (upto 60 wt.%
of adsorbed protein) of BSA within 48 h has been uniquely attributed to the inherent porous
microstructure of the CHAMPS. Protein adsorption behaviour for both of the particles and
scaffolds follow the classical Langmuir isotherm. The extensive micro-computed tomography
(micro-CT) analysis establishes cancellous bone-like highly interconnected and complex
porous architecture of the protein loaded and original CHAMPS. Overall, the present study
provides an assessment of the interaction of protein with HA nanoparticles and their
cryotreated HA-gelatin scaffold in vitro to support as drug delivery media and tissue
engineering, respectively.