Cytobiocompatibility of collagen and ePTFE membranes on osteoblast-like cells in vitro.

In guided bone regeneration (GBR), a semipermeable membrane is placed over an osseous defect to create a secluded environment in which bone formation can proceed without ingrowth of connective tissue cells from the overlaying soft tissue. Although the cell-occlusive property of GBR membranes appear to be essential to new bone formation, the role of transmembrane tissue fluid diffusion is not known. The objective of this study was to evaluate the degree to which diffusion across commonly used GBR membranes can support functional properties of osteoblast-like cells in vitro. Cells from an established osteoblast-like line (SAOS-2) were cultured on membranes of cross-linked collagen, noncross linked collagen, and ePTFE. The membranes rested on metal grids which allowed the membranes to lightly contact the surface of the culture medium. As a control, cells were directly plated and cultured in control wells. At days 7 and 21, cells were harvested by scraping the membranes or culture wells and analyzed for expression of alkaline phosphatase (ALP), core binding factor 1 (cbfa-1), bone sialoprotein-2 (BSP-2), and osteocalcin (OC). Expression was determined by quantitative real-time PCR. Glucose-6-phosphate dehydrogenase (G6PD) served as a reference gene. The membranes were examined by transmission light microscopy. RT-PCR revealed up-regulation of ALP of up to 60-fold and of cbfa-1 and BSP of up to threefold relative to G6PDH. Expression of OC was less then onefold. The expression profile for each of the four genes tested demonstrated small variations among cells grown on different membranes. Microscopic observations revealed remnants of undisrupted osteoblast-like cells attached to both collagen membranes. Cell morphology and spatial arrangement indicated that vitality was maintained. Diffusion through the three membranes evaluated in this study was sufficient to support osteoblast-like cell differentiation.