Influence of ZnO doping in calcium phosphate ceramics

Tricalcium phosphate (TCP) and hydroxyapatite (HAp) samples with varying concentrations of zinc oxide (ZnO) ranging from 0.5 to 3.5 wt.% were fabricated by uniaxial pressing followed by sintering at 1250 and 1300 °C to understand the role of ZnO in densification, microhardness and cell-materials interaction. Variation in the amount of ZnO present in TCP and HAp showed differences in sintering behavior. At a sintering temperature of 1250 °C both TCP and HAp experienced an increase in densification with increasing ZnO content. Up to 2.5 wt.% of ZnO addition increased microhardness for TCP, and then decreased it. Samples sintered at 1250 °C proved to be harder than those sintered at 1300 °C. Analysis of microstructure using SEM revealed that grain size changed due to ZnO doping in TCP, but had limited influence on HAp. Preliminary in vitro cell–materials interaction study showed that osteoblast cells were adhered well after 5 days on surfaces containing up to 1.5 wt.% ZnO. Higher ZnO doping had deleterious effects on cell attachments and growth. For 3.5 wt.% ZnO doped samples, cell death was observed.