Fabrication of dense and porous biphasic calcium phosphates: Effect of dispersion on sinterability and microstructural development

Abstract

AbstractThe particle size distribution of a commercial Mg‐doped hydroxyapatite powder was tailored through two different milling procedures, carried out under wet or dry conditions. Wet milling gave rise to finer particles, with a narrower size distribution. Tailoring the particles size was the key to produce homogeneous gelcast green bodies, as well as fully dense and fine microstructures. In fact, wet‐milled samples achieved full densification and compressive strength of about 300 MPa, five times higher than the values achieved by the dry milled samples. During the calcination treatments, HA progressively decomposed into β‐ and α‐TCP phases, promoted by the progressive Mg2+ substitution inside the HA and β‐TCP lattices. As a result, a biphasic (HA/β‐TCP) calcium phosphate ceramic was successfully obtained. Gelcast macroporous materials were prepared by direct foaming, starting from both milled powders. Highly porous samples (73%‐77% porosity) with a high degree of interconnectivity within pores were successfully produced. However, dry milled‐foamed materials were characterized by a significant residual porosity within the struts, whereas in wet‐milled foams struts and pore windows were highly compact, the key to provide sufficient mechanical strength to such highly porous open‐cell foams, thus suggesting a possible use as implantable scaffolds.