Optimization of femtosecond laser micromachining of polylactide and PLLA/HAp composite

摘要

This paper presents results of poly(L-lactide) (PLLA) and poly(L-lactide)/hydroxyapatite (PLLA/HAp) composite cutting optimization using second harmonic of femtosecond fiber laser. There are several limitations regarding the use of femtosecond lasers for processing of heat-sensitive medical grade polymers such as PLLA. Improper use of ultrashort pulse laser may lead to heat load into surrounding material causing its melting and cracking when excessive energy is deposited and pulse repetition frequency is too high. The optimization of laser parameters is necessary not only because of heat accumulation but also due to reflection and scattering of incident light in high aspect ratio V-shaped groove resulting in decrease of ablation rate with an increasing number of repetitions. This problem is especially important in case of polymer foils thicker than 200 μm and the beam spot size around 15 - 30 urn which is typical in commercial systems. In this work we present threshold fluence and ablation rates for three types of material: amorphous PLLA, crystalline PLLA and PLLA/HAp composite. For those materials in form of thick foils (～400 μm) we performed cutting optimization. Significant improvement of cutting efficiency in case of thick foils was made by applying a method of multiple, overlapped cuts.