12. Effect of Host Surface Factors on Biocompatible Adhesion Index

Biofilm formation is a significant problem in America, accounting for 17 million infections, and causing 550,000 deaths annually. An understanding of factors that contribute to strong biofilm surface adhesion at implant interfaces can guide the development of surfaces that prevent deleterious biofilms and promote osseointegration. The aim of this research is to develop a metric that quantifies the adhesion strength differential between a bacterial biofilm and an osteoblast-like cell monolayer to a medical implant-simulant surface. This metric will be used to quantify the biocompatible effect of implant surfaces on bacterial and cell adhesion. The laser spallation technique employs a high-amplitude short-duration stress wave to initiate spallation of biological films. Attenuation of laser energy results in failure statistics across increasing fluence values, which are calibrated via interferometry to obtain interface stress values. Several metrology challenges were overcome including how membrane tension may influence laser spallation testing and how to determine stress wave characteristics when surface roughness precludes in situ displacement measurements via interferometry. Experiments relating loading region within biofilm to centroid of biofilm revealed that location played no role in failure rate. A reflective panel was implemented to measure stress wave characteristics on smooth and rough titanium, which showed no difference in peak compressive wave amplitude. After overcoming these metrology challenges, the adhesion strength of Streptococcus mutans biofilms and MG 63 monolayers on smooth and rough titanium substrates is measured. An Adhesion Index is developed by obtaining the ratio of cell adhesion to biofilm adhesion. This nondimensionalized parameter represents the effect of surface modifications on increases or decreases in biocompatibility. An increase in Adhesion Index value is calculated for roughened titanium compared to smooth titanium. The increase in Adhesion Index values indicates that the increase in surface roughness has a more positive biological response from MG 63 than does S. mutans. In this work further experiments quantifying impact of various surface coating including blood plasma, and adhesion proteins found within the extracellular matrix to expand the Adhesion Index.