Time-Delayed Release of Bioencapsulates: A Novel Controlled Delivery Concept for Bone Implant Technologies

Vancomycin has been successfully entrapped into amino-polysiloxane matrixes via a one-step room-temperature sol−gel process, resulting in biodoped monolithic hybrid materials. The vancomycin-containing matrixes have been characterized by means of Fourier transform infrared (FTIR) and 29 Si magic angle spinning nuclear magnetic resonance ( 29 Si MAS NMR) solid-state spectroscopies, evidencing the effective encapsulation of the drug. In vitro swelling behavior and delivery tests carried out under physiological conditions (37 °C, pH 7.4) showed not only the absence of burst effect but also, and remarkably, a zero-release period, or lag time, where no vancomycin was released to the medium during the first hours of assay. Subsequently, there was a sustained release of vancomycin over a prolonged period of days. This lag time is an essential requirement for implantable bioceramics that would allow the surgeon to perform the surgical procedure with zero drug release. The delivery behavior has been also tested mimicking bone infection conditions (37 °C, pH 6.5), and the lag time and subsequent sustained release are comparable to those obtained at physiological conditions, despite of the decrease of pH. This research work opens new possibilities for the design of novel time-delayed controlled delivery systems for bioencapsulates, useful in bone implant technologies.