(331a) Cell Detachment from Porous Poly(L-Lactic Acid) Scaffolds Cultured Under Flow Perfusion for Bone Tissue Engineering

Cell adherence is crucial to long term culturing of cells seeded on porous scaffolds using flow perfusion. Development of tissues from osteoblasts cultured in flow perfusion systems is important for the growth of tissue engineered bone grafts. Mechanotransduction of preosteoblastic cells from fluid shear forces has been found to promote cell differentiation and the production and calcification of extracellular matrix (ECM). High fluid shear also causes the disengagement of cells from scaffold surfaces immediately subsequent to seeding. These same high fluid shear forces also instigate detachment of cells from developed ECM that is secreted from cells at later culturing points. Measuring cell detachment numbers and creating detachment profiles for porous 3-dimensional (3D) cellular constructs will shed light on how cells cultured under flow perfusion can have their disengagement from scaffolds reduced while exposing them to ample stimulatory shear forces.

Characterization of different fluid shear rates on the detachment of preosteoblastic mesenchymal stem cells (MSC) seeded and cultured on porous 3D poly(L-lactic acid)(PLLA) scaffolds using a perfusion bioreactor is preformed in this study. Using oscillatory flow perfusion to homogeneously distribute cells, MSC's were seeded on scaffolds. These scaffolds were then cultured under unidirectional flow of 0.15mL/min for time periods up to 12 days using osteoblastic media. After each time period, cells were detached from scaffolds using increasing fluid flows. Serial collection of detached cells was used to generate a detachment profile. Critical flow rates were established for each culture time period analogous to a different cell microenvironment where significant cell disengagement occurred.

PLLA scaffolds made by the solvent casting with substrate leaching technique have random internal architectures. These random architectures create complex shear force environments that cannot be accurately characterized by simple bulk mathematical calculations. To characterize the internal shear environment, mathematical modeling using Lattice Boltzmann method was employed. Mathematical modeling was also coupled with the detachment of cells from flat nonporous PLLA surfaces under equivalent shear forces to those exerted in the 3D microenvironments of the scaffolds under flow perfusion.