The Normal and Shear Strength of the Cell-Implant Interface: Accelerated Negative Buoyancy as a Method of Cell Adhesion Assessment

Abstract

The strength of adhesion at the cell-substrate interface is an important parameter in the design of many prosthetic implant material surfaces, due to the desire to create and maintain a strong implant-tissue bond. This study focuses on the mechanical strength of the interface and the ease of cell removal from ceramic coatings using normal and shear forces, but also looks at cell proliferation rates on the same series of surfaces. This systematic study of cell proliferation and adhesion has been carried out on a series of oxide coated Ti6Al4V based substrates with a range of surface morphologies and chemistries. Oxide coatings were formed using Plasma Electrolytic Oxidation (the PEO process). Cells were seeded at a low concentration onto substrates and proliferation monitored for up to three weeks. The same cell concentrations were seeded on samples for adhesion testing. These were cultured for a few days to ensure well established adhesion of viable cells. The normal and shear strength of osteoblasts (bone cells) and chondrocytes (cartilage cells) adhered to these substrates was measured using accelerated negative buoyancy within an ultracentrifuge. The variation in proliferation rates on, and adhesive strengths to, the range of coatings, is discussed and related to morphological and chemical differences in the coatings. A comparison is made between the normal and shear strengths of the cell-coating bonds and the differences between the behaviour of the two cell types discussed.