The design and production of efficient drug delivery systems (DDS) are of vital importance in tissue engineering and regenerative medicine. Various polymers, either synthetic or natural, have been exploited for the production of drug delivery systems. Among them the class of biodegradable compounds is of major interest. Polyhydroxyalkanoates (PHAs) are a family of natural biodegradable polyesters obtained by numerous bacteria through the fermentation of sugars, lipids, alkanes, alkenes and alkanoic acid, as a unique intracellular carbon and energy storage compounds and accumulated as granules in the cytoplasm of cells [1-3]. Poly(3-hydroxybutyrate) (PHB) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBHV) are the most studied natural polyesters and they are the first commercial thermoplastics from a bacterial source. This research paper is focused on the design of a delivery systems comprising polyhydroxyalkanoates nanoparticles (PHBHV) loaded with silymarin. Several approaches were employed to obtain an efficient DDS starting with oil in water emulsion and nanoprecipitation methods. PHBHV nanoparticles were characterized by FTIR and RAMAN. Morphological investigation of the particles was achieved through SEM and AFM techniques. Silymarin mass encapsulation in nanoparticle was determined from the amount of drug originally used and the amount remaining in the supernatant after harvesting. A validated spectrophotometric analysis method was used to assess encapsulation. In vitro release studies in PBS were performed in triplicate and the cumulative percentage release over time was plotted. Finally, biocompatibility of the nanoparticle system was assessed on human adipose stem cells (hASCs). References [1] S. Philip, T. Keshavarz and I. Roy, Review Polyhydroxyalkanoates: biodegradablepolymers with a range of applications, Journal of Chemical Technology and Biotechnology, 82, 2007,pp. 233–247 [2] Sang Yup Lee, Bacterial Polyhydroxyalkanoates, Biotechnology and Bioengineering, 49,1996, pp. 1-14 [3] Yu Ke, Yingjun Wang, Li Ren, Gang Wu, Wei Xue, Surface modification of PHBV films with different functional groups: Thermal properties and in vitro degradati