Effect of Process Variables on the Microstructure of Hollow Hydroxyapatite Microspheres Prepared by a Glass Conversion Method


Green, David J. and Halloran, John and Johnson, David W. and Klein, Lisa


Solid microspheres (diameter=106-150 μm) of a Li2O-CaO-B2O3 glass were reacted in a K2HPO4 solution to form hollow hydroxyapatite (HA) microspheres. the effect of the temperature (25°-60°C), K2HPO4 concentration (0.01-0.25M), and pH (9-12) of the solution on the diameter (d) of the hollow core normalized to the diameter (D) of the HA microspheres, the surface area, and the pore size of the microsphere wall was studied. the statistically significant process variables that influenced these microstructural characteristics were evaluated using a factorial design approach. While the pH had little effect, the concentration of the solution had a marked effect on d/D, surface area, and pore size, whereas temperature markedly influenced d/D and pore size, but not the surface area. the largest hollow core size (d/D value ≈0.6) was obtained at the lowest temperature (25°C) or the lowest K2HPO4 concentration (0.02M), while microspheres with the highest surface area (140 m2/g), with pores of size 10−12 nm were obtained at the highest concentration (0.25M). the consequences of these results for potential application of these hollow HA microspheres as devices for local delivery of proteins, such as drugs or growth factors, are discussed.


Materials Science and Engineering

Keywords and Phrases

Microsphere; Hollow; Hydroxyapatite; Process Variable; Pore; Microsphere Preparation; Glass; Conversion Method; Pore Size; Surface Area; Microstructure; Hollow Core; Size

International Standard Serial Number (ISSN)

0002-7820; 1551-2916

Document Type

Article - Journal

Document Version


File Type





© 2010 Wiley-Blackwell, All rights reserved.

Publication Date

01 Jan 2010