Abstract:
Development of controlled release biomolecules by
surface modification of hydroxyapatite nanoparticles has recently
gained popularity in the areas of bionanotechnology and
nanomedicine. However, optimization of these biomolecules for
applications such as drug delivery, nutrient delivery requires a
systematic understanding of binding mechanisms and interfacial
kinetics at the molecular level between the nanomatrix and the
active compound. In this research, urea is used as a model molecule
to investigate its interactions with two morphologically different
thin films of hydroxyapatite nanoparticles. These thin films were
fabricated on quartz crystal piezoelectric sensors to selectively
expose Ca2+ and PO4
3− sites of hydroxyapatite. Respective urea
adsorption and desorption on both of these sites were monitored in
situ and in real time in the phosphate buffer solution that mimics body fluids. The measured kinetic parameters, which corroborate
structural predisposition for controlled release, show desorption rates that are one-tenth of the adsorption rates on both surfaces.
Furthermore, the rate of desorption from the PO4
3− site is one-half the rate of desorption from the Ca2+ site. The Hill kinetic model
was found to satisfactorily fit data, which explains cooperative binding between the hydroxyapatite nanoparticle thin film and urea.
Fourier transform infrared spectra and X-ray photoemission spectra of the urea adsorbed on the above surfaces confirm the
cooperative binding. It also elucidates the different binding mechanisms between urea and hydroxyapatite that contribute to the
changes in the interfacial kinetics. These findings provide valuable information for structurally optimizing hydroxyapatite
nanoparticle surfaces to control interfacial kinetics for applications in bionanotechnology and nanomedicine
