Fully biobased PBA-DLA copolymer containing 70 wt% poly(butylene adipate) (PBA) as the hard segments and 30 wt% poly(dilinoleic adipate) (DLA) as the soft segments was successfully synthesized via two-step polycondensation in diphenyl ether using CALB as biocatalyst as presented in Figure . After synthesis, the material was recovered within a high reaction yield (88 %). To confirm the chemical structure of obtained copolymer 1 H NMR spectra were recorded based on which detailed structural analysis was conducted. Figure segments, a more detailed analysis was performed, on the basis of which the real ratio of hard to soft segments and number average molecular weight (Mn) were calculated following the method described in our previous work . According to data presented in Table , PBA-DLA is characterized by relatively high molecular weight, however, the calculated hard to soft segment ratio differs from values estimated theoretically, which may be related to the evaporation of 1,4-butanediol at the synthesis stage when the high vacuum was applied. Due to the potential application of copolymer as a drug delivery system (contact with the body), it was extremely important to verify material biocompatibility. Therefore, to assess any cytotoxic or growth-inhibitory effect of the PBA-DLA copolyester, an in vitro indirect contact assay was performed using L929 murine fibroblasts. Cells were incubated in the presence of extract from reference (PCL) and PBA-DLA samples for 24 h and viability was measured using an inverted light microscope and resazurin viability assay. After 24 hours of culture, a clear negative effect of PCL and PBA-DLA material was observed (Figure After receiving positive results from the cytotoxicity assessment, the manufacturing of PBA-DLA nanoparticles (NPs) via the nanoprecipitation method has been started. In this work, acetone was chosen as the solvent since it is widely used in the manufacturing of PNPs via nanoprecipitation, mainly due to the safety aspects, easy evaporation, and good miscibility with water (expressed by Hildebrand solubility parameter) which should be considered while performing nanoprecipitation since interactions between molecules of water and organic solvent are influencing polymer NPs size . According to the values obtained from DLS measurements presented in Table and Figure it was possible to obtain stabilizer-free NPs with a hydrodynamic diameter (HD) of 201.9 ± 0.2 characterized by a low dispersity index (DI). However, during the purification (centrifugation) step, problems related to the redispersion of NPs were encountered as evidenced by the size of NPs (421.9 ± 7.4) and significantly higher DI (0.282 ± 0.066). Part of the NPs also deposited and agglomerated on the walls of the vial and therefore, it was decided to use Pluronic F127 (PLUR) as a stabilizer in order to eliminate this drawback. Stabilizer used in the concentrations of 0.05 and 0.1 mg/ml allowed to obtain NPs with HD of 149.1 ± 0.4 and 190.2 ± 2.5, respectively, and DI of 0.017 ± 0.013 and 0.018 ± 0.010, respectively. Additionally, in both cases, it was possible to fully redisperse the NPs after purification steps, as evidenced by the comparable HD values and low DI (see Table ). Interestingly enough, it was clearly confirmed that the smallest NPs diameter (149.1 ± 0.4) is obtained at 0.05 mg/ml of PLUR concentration. Increase in the PLUR concentration to 0.1 mg/ml resulted in higher NPs size (190.2 ± 2.5) and most probably this is related to the fact, that higher PLUR concentration changed the aqueous solution parameters, affecting the reduced miscibility of the acetone phase with the aqueous phase and as a result particles with higher size were formed. Once the neat PBA-DLA NPs manufacturing process was optimized, work connected with α-tocopherol (α-TP) encapsulation started. In order to determine the role of α-TP amount on the NPs size and encapsulation efficiency, three different concentrations of α-TP were tested (2.5, 5, and 10 mg/ml). The average particle diameters and DI values were measured by DLS, and the results were summarized in Table . According to the collected data, the diameter of NPs permanently increases with increasing α-TP concentration (from 145.5 to 176.3 nm) (Figures and). This phenomenon may be related to the fact that part of α-TP is encapsulated in the core of PBA-DLA NPs, while the remaining part is located on the surface of the polymer shell. The increasing amount of α-TP in the acetone phase led to the NPs formation with a higher amount of the drug located on the surface, thus, NPs with higher diameter were formed.