Quantitative analysis of three-dimensional fluid flow in rotating bioreactors for tissue engineering.

Tissue engineering has emerged as a viable alternative to the problem of organ and tissue shortage. Our laboratory has developed matrices for bone tissue engineering based on sintered spherical particles and, using bioreactor technology, has demonstrated the ability to produce highly mineralized matrices in vitro. In this study, porous microcapsule scaffolds were developed for bone tissue engineering in the high aspect ratio vessel rotating bioreactor. The motion of individual microcapsules as well as scaffolds in the bioreactor were studied by numerical simulation and in situ imaging analysis. Results show that spherical microcapsules with density less than the surrounding fluid exhibited two motions: (1) a periodic circular orbit with tangential speed equal to the free fall speed of the particle, and (2) an inward radial migration of the circular orbit toward the center of the bioreactor vessel. Lighter-than-water scaffolds were fabricated by sintering poly(lactic-co-glycolic acid) hollow microcarriers with diameter from 500 to 860 microm into a fixed three-dimensional geometry with approximately 30% pore volume and 180 to 190 microm median pore size. Scaffolds were fabricated with aggregate densities ranging from 0.65 g/mL and 0.99 g/mL by appropriate combinations of hollow and solid microcarriers within the scaffold. Scaffold velocity in the bioreactor for the above range of densities was accurately predicted by numerical simulation and ranged from 100 mm/s to 3 mm/s. Maximum shear stress estimation due to media flow over the exterior of the scaffold ranged from 0.3 N/m(2) to 0.006 N/m(2). Internal perfusion velocity through scaffolds also was calculated and ranged from 13 mm/s to 0.2 mm/s. Estimates of maximum interior shear stress ranged from 0.03 to 0.0007 N/m(2). These analytical methods provide an excellent vehicle for the study of bone tissue synthesis in three-dimensional culture with fluid flow.