Microcarriers currently used in cell and tissue cultures in microgravity environment simulated by rotating-wall bioreactors are primarily biocompatible polymers. For bone cell cultures and tissue formation, bioactive glasses and ceramics have unique advantages, such as bone bonding ability and stimulation of bone cell functions.1 However, they are difficult to be processed into spherical microcarriers and have not been used in simulated microgravity environment until recently.2 In this study, we developed composite microspheres by incorporating bioactive glasses and ceramics into a polymer microsphere to combine the osteoconductivity of bioactive glasses and ceramics with the ease of polymer processing. In addition, the wide range of mechanical and biological properties of polymer offers the possibility of making composite microspheres with various desired properties, such as biodegradation.
Another important factor in the microsphere design is the density of the microcarrier. Previous numerical analysis of the particle dynamics in a rotating-wall bioreactor has revealed that the shear stress imparted to a microcarrier increases with the density difference between the microcarrier and the culture medium.34 Solid ceramic particles would experience a high shear stress due to their high density and, as a results, affect cell attachment and cause cell damage.4 To alleviate the problem, microcarriers with a density close to that of the culture medium are desired. By combining biodegradable polymer with bioactive glasses and ceramics, the density of the composite microsphere could be adjusted and significantly reduced in comparison to solid ceramic microspheres.
In this study, we report development and characterization of novel bioactive and degradable composite microspheres for 3-D bone tissue engineering in simulated microgravity environment.