Adhesion index integrates cell and bacterial responses to titanium across protein conditioning and surface roughness

Biofilm formation is a primary cause of implant-associated infections in dental and orthopedic devices. Early interactions between bacteria and host cells at the implant surface critically influence subsequent infection or successful integration. Therefore, biocompatibility screening should evaluate both biofilm formation and cell adhesion. Adhesion Index, defined as the ratio of cell adhesion to biofilm adhesion, provides a non-dimensional number to optimize towards that end. In this work, the laser spallation technique is implemented to compare the effects of implant surface characteristics (rough and smooth titanium) and protein coatings (blood plasma and fibronectin) on bacterial biofilm (Streptococcus mutans, Staphylococcus aureus) and cell monolayer (MG-63) adhesion, to obtain quantitative adhesion measurements of each biological film. Over 18 different adhesion measurements are presented across surface roughness, biofilm type, cell type, and protein coating. Failure statistics are analyzed using two-parameter Weibull cumulative distribution functions to determine interfacial adhesion strengths and confidence intervals. Results show that MG-63 osteoblast-like cell adhesion strength increases with surface roughness from 143 MPa (95% CI: 114-176) on smooth to 292 MPa (95% CI: 267-306) on rough titanium. Fibronectin coating enhances cell adhesion on smooth titanium but reduces adhesion on rough surfaces relative to uncoated controls. Plasma coating yields similarly high cell adhesion strengths on both smooth and rough titanium, 268.7 MPa (95% CI: 248.8-289.3) and 269.4 MPa (95% CI: 249.7-289.6), respectively. In contrast, S. mutans and S. aureus exhibit minimal response to surface roughness. Plasma and fibronectin coatings reduce S. mutans adhesion on both smooth and rough surfaces, while S. aureus remains largely unaffected. Adhesion Index results indicate plasma-coated smooth titanium is optimal for dental applications, whereas rough titanium and plasma coating on both rough and smooth titanium are most favorable for orthopedic implants. These findings provide quantitative guidance for tailoring implant surface design to specific clinical applications.