Three-Dimensional Pulse-Based Modelling of Femtosecond Laser Ablation of Metals: Validation with Grooves.

The femtosecond (fs) laser ablation of metals is a precise method used to create microfeatures on the surface of the material with a minimized heat-affected zone (HAZ). Despite its many advantages, fs laser ablation often requires extensive trial-and-error experimentation before finding the optimal laser strategy for a desired geometry with minimal HAZ. The pulse-based two-temperature model (TTM) can significantly shorten this process by predicting the ablated geometry based on a set of material and laser parameters. However, this model has only been validated for percussion drilling and single lines. In this study, the pulse-based TTM is tested against parallel line experiments and subsequently modified to include geometry-dependent material parameters. More specifically, the threshold fluence and reflectivity of the material are modified to incorporate the temperature increase inside the standing features between parallel lines. The introduced geometry-dependent factors are fitted with experimental data and their inclusion in the model is shown to have a positive impact on the simulation results. The results show a clear amelioration in the shape and depth of the simulated profiles, with the error on the average depth and width of the modified TTM being lower than the average standard deviation on the experiments.

Comparing the Replication Fidelity of Solid Microneedles Using Injection Compression Moulding and Conventional Injection Moulding.

Polymer surfaces are increasingly being functionalized with micro- and nano- surface features using mass replication methods such as injection moulding. An example of these are microneedle arrays, which contain needle-like microscopic structures, which facilitate drug or vaccine delivery in a minimally invasive way. In this study, the replication fidelity of two types of solid polycarbonate microneedles was investigated using injection compression moulding and conventional injection moulding. Using a full factorial design of experiments for the injection moulding process, it was found that the volumetric injection rate had the largest positive effect on the replication fidelity. The mould temperature and holding pressure were also found to have a positive effect, while the effect of the melt temperature was found to be insignificant for the considered temperature range. For the injection compression moulding process, it was found that a larger compression stroke resulted in a better replication fidelity. A comparison between the replication fidelity for the injection moulding and injection compression moulding indicated that the injection compression moulding process resulted in a higher and more uniform replication fidelity. Using finite element flow simulations, a higher and more evenly distributed cavity pressure was observed compared to the conventional injection moulding process.

Ultrafast laser selective phase removal for surface modification of nanocomposite materials.

Ultrafast laser processing of zirconia/alumina nanocomposite ceramics, the current gold standard material for ceramic bearing components in orthopedics, was investigated. Instead of considering the substrate as a homogeneous material, as commonly assumed in laser micromachining, the damage behavior of different phases around the laser ablation threshold upon ultrafast laser irradiation was investigated. Under appropriate experimental conditions, the zirconia phase was selectively ablated while the alumina phase remained intact. The origin of this selective ablation behavior and its relationship with the material band gaps were discussed. Due to the nonlinear absorption mechanisms under ultrafast laser irradiation, the zirconia phase, with its band gap of 5.8 eV, can absorb more laser energy than the alumina phase which has a larger band gap of 8.8 eV. The negligible heat diffusion length ensures that the absorbed laser energy remains confined in the individual phases, leading to the selective ablation of zirconia phase under the given laser fluence. Based on this observation, an ultrafast laser selective phase removal method which can be used to modify the surface composition of nanocomposite materials consisting of phases with different band gaps was proposed.

Laser surface texturing of zirconia-based ceramics for dental applications: A review.

Laser surface texturing is widely explored for modifying the surface topography of various materials and thereby tuning their optical, tribological, biological, and other surface properties. In dentistry, improved osseointegration has been observed with laser textured titanium dental implants in clinical trials. Due to several limitations of titanium materials, dental implants made of zirconia-based ceramics are now considered as one of the best alternatives. Laser surface texturing of zirconia dental implants is therefore attracting increasing attention. However, due to the brittle nature of zirconia, as well as the metastable tetragonal ZrO2 phase, laser texturing in the case of zirconia is more challenging than in the case of titanium. Understanding these challenges requires different fields of expertise, including laser engineering, materials science, and dentistry. Even though much progress was made within each field of expertise, a comprehensive analysis of all the related factors is still missing. This review paper provides thus an overview of the common challenges and current status on the use of lasers for surface texturing of zirconia-based ceramics for dental applications, including texturing of zirconia implants for improving osseointegration, texturing of zirconia abutments for reducing peri-implant inflammation, and texturing of zirconia restorations for improving restoration retention by bonding.