Femtoseconde-laserbewerking en spuitgieten voor de productie van thermoplastische holle micronaaldjes

This thesis explores the development and manufacturing of polymer hollow microneedles (HMN) through femtosecond (fs) laser ablation and injection molding, integrating predictive modeling to address key challenges. HMNs present a promising alternative to traditional hypodermic needles, offering minimally invasive drug delivery and fluid sampling capabilities. However, their fabrication is hindered by challenges in achieving high sharpness, high replication fidelity, consistent performance, and cost-effective scalability. First, an experimental study evaluates the effects of laser cross-hatching strategies, injection molding settings, and polymer materials on HMN geometry and performance. The experiments demonstrate the influence of laser and injection molding parameters on HMN geometry and penetration behavior, and key findings reveal that tip angle, radius and wall thickness critically impact the penetration efficiency. Additionally, the dynamics of skin penetration are investigated, emphasizing the importance of HMN morphology and insertion speed in achieving reliable skin penetration. While this study provides valuable insights for the design and manufacturing of HMNs with fs laser ablation and injection molding, it also highlights the extensive trial-and-error associated with this process. Second, to address the experimental challenges associated with parameter optimization in the design and selection phase of HMN development, a three-dimensional predictive model for fs laser ablation in metals is presented. The fs laser ablation model is developed in three incremental steps with increasing complexity, including the local wall inclination, beam divergence and inclined ablation, and temperature-dependent material parameters. The validation is done for percussion drilled cavities, inclined grooves and parallel lines, and the results show that the simulations corresponds well with the experiments, with errors in the acceptable range for all three tested laser strategies. Third, the developed laser ablation prediction model is used for the simulation of the ablation of HMN cavities, and the results show that it accurately predicts their shape, depth, base width, and surface texture. This paves the way for a substantial reduction in the experimental effort required for parameter optimization of complex laser strategies. In addition to fs laser ablation modeling, injection molding simulations with Moldex3D are tailored to predict the replication fidelity of HMNs. High accuracy is achieved by incorporating customized boundary conditions for microscopic features such as entrapped air volume correction. Finally, the integration of both simulation tools reduces the active development time of HMNs by 70% and minimizes equipment needs, highlighting their potential to streamline the HMN design process. The results establish a robust framework for the efficient development of HMNs, combining experimental validation with computational insights. Future work is recommended to explore optimization algorithms, refine HMN designs, and develop lancing mechanisms for consistent skin penetration. These advancements will accelerate the adoption of HMNs in clinical and commercial settings, contributing to their widespread use in drug delivery, diagnostics, and beyond.