Fabrication, characterization and evaluation of bioceramic hollow microspheres used as microcarriers for 3-D bone tissue formation in rotating bioreactors

Novel bioactive ceramic hollow microspheres with an apparent density in the range 0.8-1.0 g cm(-3) have been developed as microcarriers for 3-D bone t issue formation in rotating-wall vessels (RWV). Hollow ceramic microspheres with a composition of 58-72% SiO2, 28-42% Al2O3 (wt%) and an apparent dens ity 0.8-1.0 g cm(-3) were pretreated in 1.0N NaOH for 2 h before being coat ed with synthesized calcium hydroxyapatite (HA) particulate sol. The HA-coa ted hollow microspheres were sintered for 1 h at 600, 800 and 1000 degrees C. SEM analysis revealed that the grain size and pore size of the calcium p hosphate coating increased with the sintering temperature. FTIR analysis sh owed that crystalline calcium hydroxyapatite was present in the coatings si ntered at 600 and 800 degrees C, When sintered at 1000 degrees C, the coati ng consisted of cz-tricalcium phosphate. All the coatings adhered well, ind ependent of sintering temperature. The trajectory analysis revealed that th e hollow microsphere remained suspended in a rotating-wall vessel (RWV), an d experienced a low shear stress (similar to 0.6 dyn cm(-2)). Cell culture studies using rat bone marrow stromal cells and osteosarcoma cells (ROS 17/ 2.8) showed that the cells attached to and formed 3-D aggregates with the h ollow microspheres in a RWV. Extracellular matrix was observed in the aggre gates. These data suggest that these hollow bioactive ceramic microspheres can be used as microcarriers for 3-D bone tissue formation in vitro, as wel l as for the study of the effects of microgravity on bone cell functions. ( C) 1999 Elsevier Science Ltd. All rights reserved.