Does low hydroxyl group surface density explain less bacterial adhesion on porous alumina?

BACKGROUND: Bacterial adhesion depends on surface materials. Recently it was suggested that ceramic-on-ceramic bearings could be less prone to infection than other bearings. We examined the possibility that porous alumina ceramic could be less susceptible to bacterial adhesion. HYPOTHESIS: As hydroxyl groups (OH) on material surface are a major factor governing the surface properties (for example: adsorption, first non-specific step of bacterial adhesion), we hypothesized that alumina had lower OH group density than other material. Thus, we asked (i) if bacterial adhesion was lower on alumina than on titanium alloy, stainless steel and polyethylene and (ii) if OH group density was also lower on alumina. MATERIAL AND METHODS: We performed (i) in vitro bacterial cultures on porous alumina, titanium, stainless steel and polyethylene using Staphylococcus aureus and Pseudomonas aeruginosa, known to adhere to surfaces. Bacterial cultures were done 3 times in duplicate for each material and each strain. Colony Forming Units (CFU) per cm2 were measured; (ii) Neutral red reagent helped obtaining OH density estimates using spacer arms. UV-visible spectrophotometry method with Neutral red test, reproduced twice for each surface, provided µg/cm2 measurements of OH density. RESULTS: There was significantly less P. aeruginosa adherent on porous alumina (2.25×104 CFU/cm2) than on titanium (4.27×105 CFU/cm2, p=0.01), on stainless steel (2.44×105 CFU/cm2, p=0.02) and on polyethylene (7.29×105 CFU/cm2, p<0.001). S. aureus was significantly less adherent on porous alumina (3.22×105 CFU/cm2) than on polyethylene (5.23×106 CFU/cm2, p=0.01), but there was no difference with titanium (1.64×106 CFU/cm2, p=0.08) and stainless steel (1.79×106 CFU/cm2, p=0.1). There was significantly lower Neutral red grafted on porous alumina (0.09µg/cm2) than on titanium (8.88µg/cm2, p<0.0001), on stainless steel (39.8µg/cm2, p=0.002) and on polyethylene (4.5µg/cm2, p<0.01). However, no correlation was found between bacterial adherence and OH group density. DISCUSSION: Bacterial adherence on porous alumina was lower than on other bearings. Although there were less surface OH groups on porous alumina, we failed establishing a statistical correlation between bacterial adherence and OH group density. LEVEL OF EVIDENCE: IV, in vitro study.

Alumina Biocompatibility.

Alumina (Al2O3) ceramic is widely used for medical devices and its biocompatibility is well known and is reported in articles and textbooks. However, finding proof of this assertion gathered over more than 40 years can be challenging. We performed a literature review about alumina biocompatibility to compile data from the literature. We searched for articles on the biocompatibility of alumina in relation to the ISO 10993-1 International Standard, which defines the biocompatibility of biomaterials. For every biological effect listed in the norm, such as cytotoxicity, sensitization, implantation, and genotoxicity, in vitro and in vivo tests in animals and humans did not reveal any abnormal biological response. Proof for the the well-known biocompatibility of alumina is summarized in this review.