Experimental Investigation on Z-A’s Behaviour Against the Amalgamation of Short Pulsed Laser and in-situ Prepared Environments for Surface Functionalization Aspects towards Biological Performances

Abstract

This research investigates the laser processing of tetragonal zirconia polycrystal-alumina (Z-A) composite, which exhibit its unique crack-clogging behaviour and exceptional mechanical robustness under stress. These properties make Z-A a promising material for load-bearing applications, particularly in the healthcare sector. Despite its potential, Z-A's intricate thermal properties and varying energy absorption rates present challenges for laser machining, particularly when processing thicker substrates. To address these challenges, the study explores the efficacy of step-down laser machining, comparing it to traditional laser machining, and evaluates its impact on ablation performance, surface morphology, and biological functionality. This work aims to bridge the gap between subtractive manufacturing and biomedical applications, offering a comprehensive exploration of advanced laser machining for Z-A. The research systematically examines four aspects: (i) a comparative analysis of traditional laser processing and step-down laser processing for thicker Z-A substrates, investigating the time-dependent ablation performance of short-pulse laser, shedding light on the mechanisms that differentiate these processes; (ii) the fabrication of a squircle pattern using laser step-down milling (LSDM) intended for potential use as a bone scaffold, while evaluating the influence of laser processing factors such as energy modulation and scan controller parameters under different environments (dry, gas, liquid, and solid); (iii) a detailed ceramography analysis of laser-ablated surfacesnto investigate surface morphology, polymorphic transformation, and crack behaviour; and (iv) an evaluation of the biological performance of LASs through in vitro tests, including apatite layer formation, wettability analysis, and cell proliferation studies. Key findings reveal that step-down laser processing outperformed traditional laser methods, achieving up to 36.14% higher ablation depth at specific energy levels, indicating its effectiveness for processing thicker Z-A substrates. The step-down approach also mitigated the narrowing effects of the Gaussian beam profile through scan track modulation. Among the auxiliary environments, dry, argon gas, and compressed air facilitated superior ablation efficiency and mechanical properties, while liquid and solid environments demonstrated reduced polymorphic transformations and preserved Z-A’s fundamental characteristics. Additionally, compared to all solid environment support in enhancing surface functionality by improving bioactivity, superior apatite layer formation, hydrophilicity, supporting factor for cell-surface interactions, cell proliferation, and fostered directional cell adhesion, increased proliferation, and higher metabolic activity compared to other conditions. The novelty of this research lies in its comprehensive exploration of LSDM under auxiliary environments, offering valuable insights into machining quality, surface characteristics, and biological assessments as a significant contributable aspect that bridges the gap between manufacturing and biomedical domains, providing a robust framework for leveraging laser-based subtractive manufacturing in healthcare industries by enabling its application in load-bearing implants and other healthcare solutions.