Efficacy of surface coatings in prevention of microbial infection: an in vitro study

The increasing incidence of post-implant infection in the medical field has prompted further investigation into possible protective coatings to alleviate this problem. This study explores the use of a "scaffold" system to carry antimicrobial substances and prevent such infections. Hydroxyapatite (HAP), a calcium phosphate mineral phase, was used as a protective coating to bond with bone and act as a delivery system. Two polymers were also explored as delivery systems. PMMA (polymethyl-methacrylate) is a non-resorbable polymer, while PLGA (poly-lactide-glycolide) is resorbable and was expected to dissolve to release antimicrobials. The two antimicrobial agents were analyzed in the coatings were chlorhexidine and silver nitrate. Chlorhexidine has antimicrobial effects on a wide range of both gram-positive and gramnegative bacteria, and exhibits low resistance prevalence. Similarly, silver nitrate has been shown to inhibit growth of a wide range of microorganisms. The surfaces of the titanium alloy and stainless steel substrates were coated with combinations of HAP-based systems via the surface induced mineralization (SIM) method, and with the polymers through a dip-coating method. Fourier transform infrared spectroscopy (FTIR), X-ray diffraction spectroscopy (XRD), and scanning electron microscopy (SEM) were used to analyze the composition of the coatings and confirm their components. The efficacy of each type of coating in inhibiting microbial growth was tested in culture plates inoculated with Staphylococcus aureus, a common cause of the targeted infections. Metal rods coated with HAPlchlorhexidine and HAP/silver nitrate both showed inhibition of Staphylococcus aureus, whereas the uncoated rods, HAP-only coated rods, and all polymer coated rods exhibited no antimicrobial effects. A coating containing both HAP and chlorhexidine has the most potential for reduction of infection rates due to its in vitro display of the largest zones of inhibition, and would be the best choice for use in medicine.Honors College, Washington State UniversityDeatherage, Brooke Lynne Efficacy of surface coatings in prevention of microbial infection: an in vitro study ,Washington State University Honors College thesis, October 2001, 28 p