PHYSICOCHEMICAL PROPERTIES OF A RIFAMPICIN-RELEASING POLYDIMETHYLSILOXANE SHUNT

Infection of implanted polymeric devices is a major problem in modern medicine. Silicone shunts were modified in order to prevent microbial colonization by incorporating rifampicin. The release mechanism and th e altered properties of the silicone were studied. Release rates of ri fampicin out of the polymeric shunt material were measured in vitro fo r up to 60 d. For high velocity of rifampicin in the polymeric matrix and long-lasting controlled release rates, high compatibility of polym er and drug was required. Compatibility and therefore miscibility of d rug and polymer were estimated by reduced solubility and cohesion ener gy densities (Hansen parameter, solubility parameter delta). Mechanica l properties of the polymer were influenced by incorporation of small drug amounts, characterized by stress-strain curves. Differential scan ning calorimetry (DSC) measurements suggested thermodynamically contro lled interaction of the macromolecules with the incorporated substance . The physicochemical state of the drug in the internal phase and the surface of the polymer was studied by scanning electron micrography (S EM), showing homogeneous molecular dispersion of the drug in the polym eric material as well as crystalline structures on the surface. (C) 19 97 Elsevier Science Limited.