On the degradation properties of electrospun fibers based on PLLA: The effect of a drug model modification

In this work, the features of electrospun fibers based on poly(L-lactide) (PLLA) containing drug model molecules, which were modified as to render them more dispersible in the polymer matrix and potentially capable of tuning the PLLA degradation, were investigated. Indeed, the above compounds, constituted by a pyrene terminal group attached to a short chain of poly(D-lactide) (Pyr-D) or PLLA (Pyr-L), were synthesized by employing 1-pyremethanol (Pyr-OH), a widely applied hydrophobic model drug, as the initiator of the ring opening polymerization (ROP) of L- or D-lactide.1H NMR measurements allowed to calculate the oligomer molecular masses, which resulted to be in satisfactory agreement with the theoretical value. With the aim at verifying the influence of the synthesized compounds on the material final properties, electrospun fibers characterized by different compositions were prepared, that is fibers based on neat PLLA, PLLA with Pyr-OH, PLLA with Pyr-L, PLLA with Pyr-D and PLLA with Pyr-OH and Pyr-D, by adding an amounts of the various additives in order to obtain the same pyrene content. The morphological characterization, accomplished by means of FE-SEM, evidenced that the addition of the above compounds did not significantly influence the morphology of the fibers. Conversely, the fluorescent microscopy measurements demonstrated a different dispersion of the pyrene-based additives in the various samples, namely an aggregation of Pyr-OH and a homogeneous distribution of Pyr-L as well as Pyr-D. The fiber thermal properties were investigated by DSC measurements. In general, the annealing treatment, accomplished at 80 °C for 4 h, turned out to increase the system crystallinity. Furthermore, as confirmed also by X-ray diffraction analysis, the fibers containing the Pyr-D additive were found to be characterized by a partial stereocomplexation resulting from the combination of the PDLA chain of Pyr-D with those of PLLA matrix. Enzymatic degradation tests, conducted on both annealed and non-annealed samples, indicated that the thermal treatment as well as the addition of Pyr-D significantly decreased the rate of the fiber degradation. As such, the release of pyrene, followed in time by UV measurements, was related to the system degradation and stereocomplexation, it being much slower in the fibers containing Pyr-D.