Effects of substratum surface chemistry and topography on extracellular matrix gene expression

The reactions at tissue-implant interfaces are key elements in the study of dental implantology. Most previous studies have been limited to assessment of the interface at the morphological and histological levels. The mechanisms underlying the tissue-implant interface reaction are largely unknown. In this thesis I hypothesized that the surface chemistry and microtopography of biomaterials could serve as signals to the attached cells and effectively regulate the interface reaction at the molecular level. I predicted that expression of genes coding for specific molecules involved in cell attachment and matrix assembly could be altered in vitro by substratum surface chemistry and topography. If the hypothesis and prediction were accurate, the results from this thesis would support the development of biomaterial-controlled interface reactions by modifying the signals of surface chemistry and topography. The hypothesis and prediction were tested in this thesis by examining the mRNA level, mRNA stability, gene product secretion and activity of two major extracellular proteins, fibronectin and 72 kDa gelatinase (MMP-2), in human gingival fibroblasts cultured on smooth or micromachined grooved titanium substrata to determine the effects of surface topography. Tissue culture plastic substrata were compared with smooth titanium substrata to determine the effects of surface chemistry. The study revealed that a grooved substratum surface significantly altered the shape and orientation of normal fibroblasts. Fibronectin mRNA levels, mRNA stability, amounts of secreted proteins and matrix-assembly activity were significantly increased in the cells on grooved titanium surfaces in comparison to the cells on smooth titanium surfaces. Compared to cells on smooth tissue culture plastic, the cells on smooth titanium surfaces showed altered levels of fibronectin mRNA, secretion and matrix-assembly activity, as well as reduced mRNA stability. The substratum surface topography and chemistry also altered the MMP-2 mRNA levels and stability. Cell proliferation and total secreted protein levels were essentially unchanged in the cells cultured on the different types of surfaces studied. These results indicated that the effects of surface topography and chemistry can sensitively and selectively regulate specific molecules at several levels. Thus, the techniques of molecular biology provide a sensitive and specific approach to the assessment of cell response to biomaterials.Dentistry, Faculty ofOral Biological and Medical Sciences (OBMS), Department ofGraduat