Adhesion Index: A Novel Biocompatibility Assessment Standard for Medical Devices

Tens of millions of Americans receive medical devices and procedures annually at a cost of $170 billion. Unfortunately, over half of all hospital acquired infections result from a permanent or temporary implanted device procedure. Although deleterious bacteria adherent to medically implanted devices are major contributors to this problem, biocompatibility standards lack consideration for these adherence properties. A biocompatibility assessment that considers both the adhesion of invasive bacteria and host cells is needed to advance patient care. The quantitative determination of the effect of implant surface characteristics on bacterial adhesion, as well as our bodies natural cell adhesion, will lead to the development of more successful medical implants. The laser spallation technique has been used previously for measurements of biofilm and cell adhesion. Laser spallation has distinct advantages as it results in quantified adhesion strength through a non-contact high strain rate force. The non-contact force does not disturb or alter the living films pre-testing, which ensures accurate adhesion measurements. This mechanical test is implemented alongside one dimensional wave analysis and an interface adhesion strength is measured for the biomaterial-implant mimicking surface interfaces. In this study, use of laser spallation on a titanium surface mimicking a dental implant device is explored. Streptococcus mutans, an oral gram-positive facultative anaerobe, is chosen because it is a common oral microbe and earlier colonizer of dental biofilms. In as much as titanium dental implants require osseous-integration, MG 63, selected for its numerous osteoblastic traits that are typical of an immature osteoblast, is optimal for initial adhesion studies. Bacteria and cells are cultured on titanium substrates that have undergone large grit sandblasting to mimic the roughness of dental implant surfaces. We demonstrate a quantitative evaluation of adhesion strength of an oral biofilm on dental implant mimicking surfaces through the adaptation of the laser spallation technique. The adhesion values for both invasive bacteria and constructive cells are compared to determine the biocompatibility for dental implant surfaces, by obtaining a unitless ratio referred to as the Adhesion Index. The Adhesion Index can be used to determine the biocompatibility of other medical implant devices and optimize future implant designs.