Marrow stromal osteoblast function on a poly(propylene fumarate)/β-tricalcium phosphate biodegradable orthopaedic composite

The objective of this study was to assess the osteoconductivity of a poly(propylene fumarate)/β-tricalcium phosphate (PPF/β-TCP) composite in vitro. We examined whether primary rat marrow stromal cells would attach, proliferate, and express differentiated osteoblastic function when seeded on PPF/β-TCP substrates. Attachment studies showed that a confluent monolayer of cells had adhered to the substrates within an 8 h time frame for marrow stromal cells seeded at confluent numbers. Proliferation and differentiated function of the cells were then investigated for a period of 4 weeks for an initial seeding density of 42 000 cells/cm2. Rapid proliferation during the first 24 h as determined by 3H-thymidine incorporation was mirrored by an initial rapid increase in total cell number by DNA assay. A lower proliferation rate and a gradual increase in cell number persisted for the remainder of the study, resulting in a final cell number of 128 000 cells/cm2. Differentiated cell function was assessed by measuring alkaline phosphatase (ALP) activity and osteocalcin (OC) production throughout the time course. Both markers of osteoblastic differentiation increased significantly over a 4-week period. By day 28, cells grown on PPF/β-TCP reached a maximal ALP activity of 11 (±1)×10−7 μmol/min/cell, while the OC production reached 40 (±1)×10−6 ng/cell. These data show that a PPF/β-TCP composite exhibits in vitro osteoconductivity similar to or better than that of control tissue culture polystyrene.