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The effects of surface topography on the behaviour of cells attached to percutaneous implants

University of British Columbia

Epithelial downgrowth on implants can result in deep pockets or sinus tracts which in turn can lead to marsupialization and eventual failure of the implant. One solution to this problem would be to have a surface of an implant that has the ability to impede the apical migration of epithelium. The present studies were aimed to determine whether surface topography could be used to impede epithelial downgrowth on percutaneous implants based on those principles that have been found to control the direction and rate of cell migration in vitro. Studies in culture have indicated that cells can be guided by the grooved surfaces, a phenomenon called contact guidance. In the first series of experiments, the effects of a V-shaped, 10-μim-deep grooved epoxy or titanium-coated epoxy substrata were studied on epithelial (E) cell behaviour. In vitro, grooved surfaces encouraged E cell adhesion and oriented clusters of E cells along their long axis. Seven or 10 days after percutaneous implantation of grooved and control smooth surfaces in rats, grooved surfaces significantly inhibited epithelial downgrowth on the epoxy or titanium-coated epoxy implants. In the second series of experiments, the effects of groove parameters such as depth, spacing and orientation were tested in vivo. Grooves were produced with a 39, 30 and 7 μm pitch and depths of 19, 10 or 3 μm. After 7 days percutaneous implantation of titanium-coated implants epithelial downgrowth was accelerated on the vertically oriented, 3 or 10 μm-deep, grooved surfaces and inhibited on the horizontally oriented grooved surfaces; an observation that could represent the most direct evidence of contact guidance occurring in vivo. In the shallower horizontal grooves [≤10 μm-deep] epithelial downgrowth was probably inhibited by contact guidance because there was no evidence of fibroblasts (F) inserting into the implant surface. However, in the 19 μm-deep grooved surfaces, E cells bridged over the grooves and their migration appeared to be inhibited by the F that inserted into the implant surface. In the third series of experiments, the ultrastructural observations indicated that E cells closely attached to the smooth, and interdigitated with, the 3 μm and 10 μm grooved surfaces of titanium-coated implants. This attachment appeared to be through basal lamina and hemidesmosome-like structures. The ultrastructural observations on the orientation of E cells and F attached to the implant verified those noted at the light microscopic level. The attachment of F to the titanium surface was mediated by two zones; a thin [≈20 nm], amorphous, electron dense zone immediately contacting the titanium surface, and a fine fibrillar zone extending from the amorphous zone to the cell membrane. The objectives of the fourth experiment were [1] to examine cell behaviour on implants in which connective tissue contacted surfaces of various topographies and epithelium encountered only a smooth surface; [2] to compare one-stage and two-stage surgical techniques. Implants delivered micromachined surfaces to the connective tissue and a smooth control surface to the epithelium and implants were removed l,2,and 3 weeks following percutaneous implantation. A complex connective tissue organization that changed with time was noted on the micromachined surfaces whereas a capsule formed on the smooth surfaces. In some cases foci of mineralization were observed on the micromachined surfaces placed using a two-stage surgical technique. Apical migration of the epithelium was significantly (p<.05) inhibited on all surfaces placed by the two-stage technique and by those micromachined surfaces that produced connective tissue ingrowth. In the fifth study, the ultrastructural observations of the mineralized tissue formed on the micromachined surfaces, identified osteocyte-like cells and in some areas revealed close juxtapositioning of collagen and minerals to titanium without an intervening amorphous layer. The findings collectively indicate that contact guidance occurs on artificial surfaces in vivo, and micromachined surfaces could be incorporated advantageously to the design of implant surfaces to optimize their performance.

Text

2011-01-31

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http://hdl.handle.net/2429/30984

Biology

University of British Columbia

Graduate