Lightning Podiums: Spinal Gumbo - 803A

Presented by: B.D. Boyan

Author(s):

B.D. Boyan(1), Z. Schwartz(1)

(1) Virginia Commonwealth University, Biomedical Engineering, Richmond, VA, United States

Abstract

During incremental bone formation typical of bone healing, multipotent connective tissue progenitor cells migrate from existing bone to sites of injury. When the existing bone ends are not apposed, as is seen during interbody fusion, bone graft and bone graft substitutes are used to provide an osteoconductive surface to enable mesenchymal stem cell (MSC) and osteoprogenitor cell migration. In this study we used an in vitro cell culture model to assess whether polyethylene terephthalate (PET) mesh would have an impact on MSC and osteoprogenitor cells migration from the vertebral plates onto the bone graft and ultimately on the biological response of these cells to the bone graft. Human MSCs isolated from bone marrow as well as normal human osteoblasts (NHOsts) were cultured on Sprague Dawley rat bone particles that were prepared by a method used clinically. Inserts containing PET mesh were laid over the bone graft particles and then cells were added. MSCs and NHOsts were permitted to attach to the mesh and to the underlying graft particles. At 24h post-confluence in control cultures that contained inserts but not bone graft or mesh, all cultures were assessed for cell phenotype. Compared to cells cultured on tissue culture polystyrene (TCPS), NHOst cell number (DNA) and alkaline phosphatase activity were highest on the bone particles whereas osteocalcin production was lowest, indicating early osteoblastic differentiation. Cells cultured on bone particles with mesh inserts present had lower DNA, alkaline phosphatase, and osteoprotegerin (OPG) than when no mesh was present, but osteocalcin was higher, suggesting that these cells were at a later stage of osteoblast differentiation. Moreover, the presence of the mesh stimulated VEGF production and BMP2 production whether the cells were on TCPS or on the bone allograft particles. MSC DNA was highest on bone particles, whether inserts were present or not. Alkaline phosphatase activity was highest in cells cultured on TCPS in osteogenic medium (OM), but cells on bone particles also had elevated enzyme activity, and this was not affected by the mesh. Osteocalcin was highest in MSCs cultured on TCPS in OM. With the exception of cells on TCPS in growth medium (GM), regardless of substrate, the osteocalcin was increased when the mesh was present. No OPG or VEGF were detected in cells cultured on the bone particles either in the presence or absence of mesh. However, mesh increased OPG in cultures grown on TCPS in both media. BMP2 was elevated by mesh under all conditions except on bone particles in OM. Substrate, media and mesh all had no effect on BMP4 production. Our results indicate that growth on bone particles stimulates early differentiation of NHOsts compared to TCPS, but delays terminal differentiation, potentially due to reduced production of BMP2 and BMP4. MSCs responded to the bone particles with an increase in number but only minimal evidence of differentiation unless the mesh was present. Taken together these results indicate that the presence of mesh does not have a negative impact on the ability of cells to attach to bone particles, nor does it impede their ability to proliferate or differentiate along an osteoblastic pathway.