Cell and Tissue Response to Polyethylene Terephthalate Mesh Containing Bone Allograft in Vitro and in Vivo

Abstract

Background: Extended polyethylene terephthalate mesh (PET, Dacron) can provide containment of compressed particulate allograft and autograft. This study assessed if PET mesh would interfere with osteoprogenitor cell migration from vertebral plates through particulate graft, and its effect on osteoblast differentiation or the quality of bone forming within fusing vertebra during vertebral interbody fusion.

Methods: The impact of PET mesh on the biological response of normal human osteoblasts (NHOst cells) and bone marrow stromal cells (MSCs) to particulate bone graft was examined in vitro. Cells were cultured on rat bone particles +/- mesh; proliferation and osteoblast differentiation were assessed. The interface between the vertebral endplate, PET mesh, and newly formed bone within consolidated allograft contained by mesh was examined in a sheep model via microradiographs, histology, and mechanical testing.

Results: Growth on bone particles stimulated proliferation and early differentiation of NHOst cells and MSCs, but delayed terminal differentiation. This was not negatively impacted by mesh. New bone formation in vivo was not prevented by use of a PET mesh graft containment device. Fusion was improved in sites containing allograft/demineralized bone matrix (DBM) versus autograft and was further enhanced when stabilized using pedicle screws. Only sites treated with allograft/DBM+screws exhibited greater percent bone ingrowth versus discectomy or autograft. These results were mirrored biomechanically.

Conclusions: PET mesh does not negatively impact cell attachment to particulate bone graft, proliferation, or initial osteoblast differentiation. The results demonstrated that bone growth occurs from vertebral endplates into graft material within the PET mesh. This was enhanced by stabilization with pedicle screws leading to greater bone ingrowth and biomechanical stability across the fusion site.

Clinical relevance: The use of extended PET mesh allows containment of bone graft material during vertebral interbody fusion without inhibiting migration of osteoprogenitor cells from vertebral end plates in order to achieve fusion.

Level of evidence: 5.

Keywords: Dacron mesh; MSCs; allograft; bone marrow stromal cells.

Figure 1

CellCrown inserts (Sigma-Aldrich) with sterile polyethylene terephthalate (PET) meshes used in all in vitro experiments.

Figure 2

In vitro normal human osteoblasts (NHOst) response of cells cultured on tissue culture plastic (TCPS) or particulate bone graft (mineralized bone matrix [MBM]) in the presence or absence of polyethylene terephthalate mesh (PET). Response was examined by measuring markers that indicate the initiation of differentiation including (A) DNA; (B) alkaline phosphate specific activity; factors that indicate late stage osteoblast differentiation including (C) osteocalcin and (D) osteoprotegerin (OPG); and production of factors associated with osteogenesis, including bone morphogenetic proteins (BMPs) 2 (E) and 4 (F) and (G) vascular endothelial growth factor-A (VEGF). P < .05 # versus no mesh, @ versus no MBM.

Figure 3

In vitro bone marrow stromal cell (MSC) response of cells cultured on tissue culture plastic (TCPS) or mineralized bone matrix (MBM), with MSC growth media (GM) or osteogenic media (OM), in the presence or absence of polyethylene terephthalate mesh (PET). Response was examined by measuring markers that indicate the initiation of differentiation including (A) DNA; (B) alkaline phosphate specific activity; factors that indicate late stage osteoblast differentiation including (C) osteocalcin and (D) osteoprotegerin (OPG); and production of factors associated with osteogenesis, including bone morphogenetic proteins (BMPs) 2 (E) and 4 (F) and (G) vascular endothelial growth factor-A (VEGF). P < .05 # versus no mesh, @ versus no MBM. % versus GM.

Figure 4

Representative parasagittal images of histologic (left) and microradiograph (right) samples from each interbody treatment including discectomy, autograft, allograft/demineralized bone matrix (DBM), and allograft/DBM plus pedicle screws. One hundred micrograms undecalcified samples were stained using the Villanueva Osteochrome Bone Stain, and embedded in polymethylmethacrylate. Microradiographs of the histologic sections were obtained using a Faxitron x-ray.

Figure 5

Quantification of bone ingrowth in the microradiographs. *P < .05, versus all other groups.

Figure 6

Mechanical testing: (A) axial rotation range of motion; (B) flexion-extension range of motion; and (C) lateral bending range of motion. Sites treated with allograft/demineralized bone matrix (DBM) plus pedicle screws were tested with the screws in place (Allo/DBM Screws) and after removal of the screws with dissection of the facet joints (Allo/DBM Screws Removed). *P < .05, versus allograft/DBM alone.