Laser processing of polymers for surface energy control of biomedical implants

Poly (etheretherketone) (PEEK) is a high-performance rigid polymer that combines excellent chemical resistance, mechanical strength, and dimensional stability. PEEK is mostly used in the biomedical field for the manufacture of implants. However, the inherently bioinert PEEK surface poses a challenge in terms of adhesion at the implant-tissue interface. Effective enhancement of the adhesive properties of PEEK can be achieved by modifications of surface wettability and free energy. Although many studies investigate the influence of laser parameters on wettability and topography of PEEK, there is scarce information in literature on surface treatment with CO₂ laser of neat PEEK. Furthermore, there is no detailed literature report on impact of various laser parameters on the biomechanical properties of PEEK relevant for implants. Therefore, this work focuses on enhancing surface functionality of PEEK through surface energy control. Samples treated at various laser power, fluence, beam pitch and number of passes were characterized with 3D profilometry, Rockwell hardness test, compression tests and contact-angle measurements. Generally, CO₂ laser treatment of PEEK did not result in unfavorable changes in its bulk mechanical properties, namely, yield strength and elastic modulus only above the ablation threshold. At a fluence of 14 J/cm², a significant reduction in hardness (98.03 HRM) was recorded with a single-pass processing. A positive correlation was observed between roughness parameters, groove geometries and laser fluence. More intense surface changes were achieved via ablative mechanism with single-pass processes at a lower total fluence in comparison to double-pass ones. Overall, all increases in roughness resulting from non-ablative processes led to improved wettability.