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Also known as
Surface treatment for medical devices, Bioactive surface modification, Implant surface functionalization, Biomaterial coating, Medical device surface treatment, Biocompatible surface modification, Anti-infective coating
Definition
A biocompatible coating is a surface layer applied to an implanted medical device to modify how it interacts with surrounding tissue and bacteria. On inflatable penile prostheses, two types of infection-retardant coating are in clinical use: an antibiotic-impregnated coating of minocycline and rifampin applied during manufacture, and a hydrophilic coating that absorbs antibiotics when the device is immersed in an antibiotic solution before implantation.1 One hydrophilic coating in clinical use is based on polyvinylpyrrolidone, which is described as reducing bacterial adhesion and adsorbing antibiotics before implantation;2 such a coating also makes the device slippery and allows water-soluble antibiotics to elute from the device into the implant spaces.3 Other coatings serve mechanical purposes: a parylene microcoating has been applied to inflatable cylinders to increase durability and reduce friction between components.2 Among newer devices, Rigicon’s Infla10 inflatable penile prosthesis is described in the literature as having a hydrophilic coating on all external surfaces.2
Clinical Context
Infection and mechanical failure are the two main complications of penile prosthesis implantation.4 According to the EAU Guidelines, careful surgical technique with appropriate antibiotic prophylaxis reduces infection rates to 2-3% after primary implantation in low-risk patients at high-volume centers, and the rate may be further reduced to 1-2% by implanting an antibiotic-impregnated or hydrophilic-coated prosthesis.4 Coated prostheses, together with strict surgical protocols that avoid prolonged wound exposure and minimize skin contact (no-touch technique), are among the methods that appear to decrease infection rates.4
A meta-analysis of 14 studies including 9,910 first-time implants found infection rates of 2.32% with non-coated and 0.89% with coated inflatable prostheses, and concluded that coatings that allow antibiotics to elute from the device decrease the incidence of device infection by approximately 50%.5 Voluntary manufacturer registries, which record revision due to infection rather than all infections, point in the same direction. In one, initial revision due to infection was reported in 1.1% of 35,737 men with minocycline/rifampin-impregnated implants and 2.5% of 3,268 men with non-impregnated implants at up to 7.7 years.6 In another, 1.4% of hydrophilic-coated implants (followed for up to 8 years) and 4.6% of non-coated implants (followed for up to 11 years) were removed or replaced because of infection, although the antibiotics used for soaking were not recorded.3
After implantation, antibacterial coatings continue to elute from the device for around two weeks.2 Coatings do not replace other preventive measures: in revision surgery with antibiotic-coated implants, infection occurred in 10% of cases without an antiseptic washout and in 3% with washout.7 Coatings may also change the microbiology of infection. Coated devices have been associated with more atypical bacteria and fewer staphylococcal infections, which suggests that they may be shifting the pattern of infecting organisms toward more virulent pathogens.1
For the mechanical parylene coating, coated cylinders from one manufacturer were reported to increase 3-year revision-free survival from 78.6% to 87.4% compared with non-coated versions.2 Evidence for antibiotic coating of the artificial urinary sphincter (AUS) is less favorable. In a single-surgeon comparison of 213 consecutive antibiotic-coated and 213 uncoated sphincters, infection rates were identical (3.3% in each group), and the coating did not affect the infection rate in the revision subgroup.8