Preparation and Drug-Release Kinetics of Porous Poly(L-lactic acid)/Rifampicin Blend Particles

Porous polymer spheres are promising materials as carriers for controlled drug release. As a new drug-carrier material, blend particles composed of poly(L-lactic acid) (PLLA) and rifampicin were developed using the freeze-drying technique. The blend particles exhibit high porosity with a specific surface area of 10–40？m2？g？1. Both the size and porosity of the particles depend on the concentration of the original solution and on the method of freezing. With respect to the latter, we used the drop method (pouring the original solution dropwise into liquid nitrogen) and the spray method (freezing a mist of the original solution). The release kinetics of rifampicin from the blend particles into water depends significantly on the morphology of the blend particles. The results show that the release rate can be controlled to a great extent by tuning the size and porosity of the blend particles, both of which are varied by parameters such as the solution concentration and the method of freezing. 1. Introduction Recently, microspheres and capsules for controlled drug release have been developed by using biodegradable and biocompatible polymers [1–3]. Highly porous polymeric spheres are often used as drug carriers because their high porosity allows for a high efficiency of drug loading and facilitates controllable release [4–7]. As carrier materials, poly(L-lactic acid) (PLLA), a typical biodegradable polymer, and its copolymer poly(lactic-co-glycolic acid) have been frequently studied [8–13]. Porous polymer spheres can be prepared using various techniques, among which freeze-drying from a dilute solution has been demonstrated to be a particularly excellent method [14, 15]. We have investigated the properties of highly porous poly(L-lactic acid) (PLLA) materials prepared using the freeze-drying technique (FDPLLA), which exhibit very high specific surface areas of 10–40？m2？g？1, and have found that they crystallize at a lower temperature and at a higher crystallization rate than bulk amorphous PLLA [15, 16]. The capability for controlled drug release from FDPLLA has been demonstrated using bovine serum albumin (BSA) as a model drug compound [11]. The immersion of FDPLLA in a BSA aqueous solution results in BSA-loaded FDPLLA via a simple adsorption mechanism, which shows an extremely high efficiency of loading (up to 79？wt% with respect to PLLA). It was also observed that the release kinetics strongly depends on the porosity of FDPLLA, which can be controlled by the concentration of the original solution and the rate of freezing. Such a simple adsorption method