Owing to their reputation as safe materials and their biodegradability, aliphatic polyesters are primarily used as biocompatible and biodegradable carriers in many types of implantable or injectable drug-delivery systems for both human and veterinary use. Examples of implantable drug delivery systems include rods, cylinders, tubing, films, fibers, pellets, and beads. Examples of injectable drug-delivery systems include microcapsules, microspheres, nanoparticles, and liquid injectable controlled-release systems such as gel formulations.