Abstract

BACKGROUND CONTEXT The advancement of manufacturing techniques, such as 3D-printing, has facilitated the design of complex and previously unattainable implant surface topographies. Research has shown surface properties, especially surface roughness, of an implant directly influence cellular response at the cell-material interface. Alkaline phosphatase (ALP), an early cellular marker of osteoblast differentiation, has been studied extensively to understand osteogenic cellular responses to a substrate. The identification of implant surfaces that promote a osteogenic environment may help identify those that are optimal for healing. PURPOSE The objective of this study was to investigate the effect of a roughened 3D-printed surface on the cellular proliferation and ALP expression of human bone-marrow derived mesenchymal stem cells (BM-MSCs). STUDY DESIGN/SETTING In vitro cell culture study. PATIENT SAMPLE N/A OUTCOME MEASURES Cellular proliferation was measured using a colorimetric, viability assay (alamarBlue™) to estimate the cell count on each substrate at days 1, 3 and 7. ALP activity was measured from cell lysate using a standard ALP assay on day 7. ALP activity was normalized to the total protein in each lysate sample measured using a bicinchoninic acid (BCA) assay also performed on day 7. METHODS Roughness (Ra) was characterized for each substrate in the study using a profilometer. BM-MSCs were seeded at a density of 10,000 cells/cm2 onto smooth polyetheretherkeytone (PEEK), smooth titanium-alloy (TAV), and a roughened, 3DP titanium-alloy (r3DP) substrates (n=6 per group) and cultured for 7 days. Cells were given 4 hours to attach, after which cell medium was changed and the substrates were moved to a separate well plate to remove any unattached cells. Assays were performed to quantify specific ALP cellular signaling, indicative of osteoblast differentiation. RESULTS The r3DP substrates had 15-30 times greater Ra than PEEK and TAV (15.2µm, 1.0µm, and 0.4µm, respectively). Cell count on day 7 for r3DP was significantly greater than PEEK (p 0.05). ALP activity was significantly greater in the r3DP group (8.8±1.1nmol/µg) compared to both PEEK (5.7±1.4nmol/µg) and TAV (4.4±0.9 nmol/µg) (p 0.05). CONCLUSIONS Optimal cellular activity and osteogenic cell signaling are important for osteoblast differentiation, a process needed to foster a cellular environment favorable for healing. Cells on a roughened 3D-printed TAV substrate exhibited significantly higher proliferation compared to PEEK and significantly higher ALP activity than both TAV and PEEK. Therefore, the r3DP substrate facilitated a cellular environment more favorable for osteoblast differentiation than TAV and PEEK substrates. Future research in an animal model is necessary to evaluate the downstream effects of an implant with a roughened 3D-printed TAV surface on the healing process. FDA DEVICE/DRUG STATUS SABLE (Globus Medical) (Approved for this indication)

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