Physicochemical and mechanical properties of CO2 laser-modified biodegradable polymers for medical applications

Abstract

Poly(lactic acid)/polylactide (PLA), poly(glycolic acid)/polyglycolide (PGA), and their copolymers poly(lactide-co-glycolide) (PLGA) [1,2] are one of the most widely used biopolymers in medicine. Beside unique biodegradability and biocompatibility, PLA and PLGA possess other advantages, such as good mechanical properties and easy processability [3]. The physicochemical and mechanical properties of polyesters can be altered by bulk and/or surface modifications during processing such as laser modifications. Beside microstructural modification, laser irradiation can influence the surface morphology, determining changes in cell affinity, roughness, and surface wettability [30–32]. However photochemical and photothermal effects occurring during laser irradiation are causes various degradation processes. The goal of this study was to investigate the influence of surface modification of amorphous and semicrystalline poly(L-lactide) and poly(L-lactide-co-glycolide) by CO2 laser irradiation. This study investigated the physicochemical properties of polymers, with special emphasis on the mechanical properties, in relation to different process parameters. Two different morphologies of PLLA (amorphous poly(L-lactide) and semicrystalline poly(L-lactide)), as well as the PLGA sample, were investigated. The materials were modified using a CO2 laser (λ = 10.6 μm) and irradiated with three different values of accumulated laser fluencies. Based on the DSC profiles and FTIR spectra the changes in physicochemical properties of the materials were determined. The mechanical properties were tested in a static uniaxial tensile test according to ISO 527-1. The CO2 laser surface modification of the polylactide-based polymers are noticeable in the results of the mechanical properties and DSC and FTIR investigations. The greatest influence on the mechanical parameters was observed for amorphous samples (PLGA, PLLAAMO), where, along with an increase of fluence, there is a gradual but a clear decline in the values of all mechanical parameters. For the vast majority of samples after the modification, the FTIR spectra show the occurrence of bands related to the presence of vinyl groups, indicating the presence of thermal degradation. The data are confirmed by the results of DSC, where the presence of cold crystallization peaks at a lower temperature was recorded, responsible for low molecular weight fraction, which had been created due to thermal degradation.