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Also known as
Water-loving coating, Lubricious coating, Hydrogel coating, Low-friction coating, Slippery coating, HC coating
Definition
A hydrophilic coating is a water-attracting surface layer; on penile prostheses, the hydrophilic covering in clinical use is based on polyvinylpyrrolidone, which reduces bacterial adhesion and adsorbs hydrophilic antibiotics before implantation.1 The coating makes the device components slippery and prevents bacterial attachment; it allows rapid absorption of antibiotics from an aqueous solution, and these water-soluble antibiotics then elute off the device into the implant spaces.2 Whereas an antibiotic-impregnated coating is applied during manufacturing, the hydrophilic coating absorbs antibiotics when the device is submerged in a solution before implantation,3 so the surgeon can tailor the antibiotic coating.1 Hydrophilic coatings are used on both inflatable and malleable penile prostheses.1 Among newer devices, Rigicon’s Infla10 inflatable penile prosthesis, released in 2019, is described in the literature as having a hydrophilic coating on all external surfaces.1
Clinical Context
According to the EAU Guidelines, the infection rate after primary implantation may be further reduced to 1-2% by implanting an antibiotic-impregnated or hydrophilic-coated prosthesis.4 In a voluntary manufacturer registry of 36,391 primary implants, 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. The antibiotics used for soaking were not recorded, so it is uncertain which selection gave the best results.2 A meta-analysis of 9,910 first-time implants reported infection rates of 1.11% with the hydrophilic coating alone, 0.55% after rifampin/gentamicin immersion and 4.42% after vancomycin/gentamicin immersion, compared with 2.32% for non-coated devices.5
The choice of dip therefore matters. Rifampin/gentamicin is the most studied combination, but the ideal antibiotic mixture has not been established and controlled comparisons are still needed.6 In laboratory studies, hydrophilic prosthesis surfaces dipped in vancomycin/gentamicin reduced bacterial adhesion more than surfaces dipped in 0.05% chlorhexidine gluconate, and irrigation with chlorhexidine or saline removed the dip solution adsorbed to the hydrophilic surface. These are in vitro findings that may not translate fully to clinical practice.7 Hydrophilic surfaces retrieved during revision surgery for mechanical failure kept their integrity and were again able to bind vancomycin and gentamicin ex vivo.8
A hydrophilic coating does not remove the need for other preventive measures, such as strict protocols that avoid prolonged wound exposure and minimise skin contact.4 Infecting organisms have shifted from Gram-positive bacteria toward Gram-negative bacteria and fungi,6 and coated implants have been associated with more atypical bacteria and fewer staphylococcal infections, which suggests that coatings may be shifting infection toward more virulent pathogens.3