In-vivo biodegradation of extruded lipid implants in rabbits

In-vitro studies with twin-screw extruded triglyceride based implants showed promising erosion behavior. However, little is known about the behavior of such systems in-vivo and therefore a degradability study was performed in a rabbit model. Four formulations were used to prepare tsc-extrudates and implanted in rabbits and mass loss of the implants was measured after one, three and six months. Samples were additionally assessed by differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). A time dependent in-vivo erosion of the triglyceride matrices was detected and only 24% (± 17%) of the matrix material was recovered after 6 months of incubation (n=9). The application of a pore forming agent resulted in higher mass loss and an accelerated degradation rate. Exchange of the type of low melting triglyceride during preparation resulted in a better preservation of the porous implant structure, explained by a higher melting point of the alternate low-melting lipid. The good in-vivo degradability of tsc-extrudates was explained by the composition of the implants and the application of a low melting lipid which allowed partial melting of the implant at body temperature and rendered the implants more susceptible to degradation processes (e.g. lipolyses).