Biocompatible hydroxyapatite nanoparticles as templates for the preparation of thin film polyelectrolyte multilayer nanocapsules

Thin films called polyelectrolyte multilayers could be formed by alternate adsorption of positively and negatively charged polyelectrolytes. In the case of adsorption on nanoparticles followed by the dissolution of the template, it is possible to prepare hollow polyelectrolyte capsules. Due to a large number of available polymeric compounds and easily tunable multilayer properties, these systems find their application in various fields such as biomedicine and catalysis. In this study we focused on the design, synthesis and characterization of capsules of nano meter dimensions made of nontoxic weak polyelectrolytes, poly(allylamine) and poly(acrylic acid) in a water medium using fully biocompatible hydroxyapatite nanoparticles as template. The formation of the poly electrolyte multilayer was monitored by measuring the electrophoretic mobility of particles. After the optimization of the core decomposition conditions, hollow polyelectrolyte capsules were prepared by dissolution of the template in the presence of HCl. Further characterization was performed using Fourier-transform infrared spectroscopy, energy dispersion X-ray spectroscopy, dynamic light scattering, scanning electron microscopy, and atomic force microscopy. With these techniques, the chemical composition, structure, size, morphology and stability of obtained nanocapsules were determined. It was found that the capsules are of a rather narrow size distribution ranging from 100 to 250 nm with a flexible capsule wall being only a few tens of nanometers thick which is very important in the case of future applications in the field of drug delivery. Moreover, the dispersions of nanocapsules were stable for at least 40 days. This extreme stability of nanocapsules could be probably attributed to their low mass, small dimensions, and high surface charge.