In our recent studies with osteoblasts in the simulated microgravity environment of rotating-wall vessels (RWVs), we have observed the formation of cell aggregates and glass surface layers. In those studies, surface modified bioactive glass particles were employed as microcarriers. The growth and coverage of cells on the glass microcarriers were observed to be limited. We have also studied this problem from a numerical modeling viewpoint. Our numerical analysis of the particle dynamics in RWVs has revealed that the limited coverage noted in the experiments may be attributable to both the high shear stress imparted to the particle surface and the collisions experienced by the microcarrier with the outer wall of the vessel. The high shear stress and wall collisions arise primarily as a result of the high density of the microcarrier material. Here, we report the development of novel hollow bioceramic microspheres with an apparent density in the range 0.8 ∼ 1.0 g/cm3. These microcarriers alleviate the aforementioned problems. The hollow ceramic microspheres have an inner shell with composition of 58–72% SiO2, 28–42% Al2O3 (in % by weight) and a porous calcium phosphate surface. This surface was deposited using a fine particle sedimentation method. The hollow microspheres were sintered at 800°C for 1h. FTIR analysis indicated that crystalline calcium hydroxyapatite (HA) was present in the porous surface. Particle trajectory analyses in both an inertial frame and a rotating frame have shown that these microspheres remain suspended in the RWV environment during the entire cell culture period without experiencing collisions with the outer wall of the vessel. Furthermore, the shear stress imparted on the microsphere surface is low (∼ 0.6 dyn/cm2. Our cell culture studies in the HARV employing the hollow microcarriers have shown that osteoblastic cells form 3-D aggregates. Extensive extracellular matrix and mineralization were also observed in these aggregates.

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