ArF-excimer laser as a potential tool for manufacturing of biomedical polymeric devices

The influence of excimer argon fluoride (ArF) laser cutting of poly(L-lactide) (PLLA) on its physicochemical properties was studied. The samples in the form of micro-bars of the size comparable to the width of typical vascular stents struts were fabricated in order to focus during the analysis on heat-affected zone and surfaces exposed to laser radiation and plasma. The threshold fluence and ablation rate of PLLA were measured. The ablated polymer's surface was analyzed using Scanning Electron Microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR-ATR). The produced microstructures with different laser repetition rates and beam size were analyzed using differential scanning calorimetry (DSC) and gel permeation chromatography (GPC) techniques. It allowed tracking the thermal history changes of PLLA, estimating the fraction of modified polymer within micro-bars, and determining the extent of the polymer degradation by observing the molecular weight changes. In many cases, DSC revealed no significant changes in the material's thermal history; however, GPC showed that each laser fabricated sample has a low molecular weight fraction resulting from multi-pulse exposition of the micro-bar walls to UV irradiation, laser-induced plasma, UV irradiation and heat. Nevertheless, most of the micro-bars preserve their original properties within the vast majority of their volume what gives the potential to use them in biomedical applications after cleaning the components from low molecular weight fragments localized at the cut walls.