Design of infection-resistant antibiotic-releasing polymers - II. Controlled release of antibiotics through a plasma-deposited thin film barrier

In the first paper in this series, we described the methods to synthesize a n antibacterial polyurethane (PU) incorporating ciprofloxacin as the releas able antibiotic and poly(ethylene glycol) as the pore-forming agent. Here, we report that a thin, RF-plasma-deposited, n-butyl methacrylate (BMA) over layer on this drug-loaded PU can act as a rate-limiting barrier to achieve a constant, sustained release of ciprofloxacin. Deposition power and deposi tion time during the coating process were optimized to give an appropriate crosslinked coating barrier that yielded desirable release rates, above the minimum required killing rate, N-kill. Electron spectroscopy for chemical analysis (ESCA), also known as X-ray photoelectron spectroscopy (XPS), was used to characterize the coating, and its crosslinking degree was indirectl y related to the CIO ratio. Increasing either deposition power (10-60 W) or duration (5-25 min) resulted in increased C/O ratios and decreased ciprofl oxacin release rates. The correlation between increased C/O ratios and redu ced release rates is believed to be due to the increased crosslinking, incr eased hydrophobicity and increased thickness of the coating. The optimal pl asma conditions to attain an appropriate crosslinked plasma-deposited film (PDF) required argon etching, pre-treatment of the matrices with an 80W-BMA plasma for 1 min, followed by immediate BMA plasma deposition at 40 W and 150 mT for 20 min. By using these plasma deposition protocols, we eliminate d the initial burst effect, significantly reduced the release rates, and cl osely approached the zero order release kinetics for at least five days. In this study we also showed that ESCA could be used as a powerful tool to ex plain the release behavior of molecules through the plasma-deposited films (PDFs). (C) 1999 Elsevier Science B.V. All rights reserved.