Dynamics of insertion and extraction of hollow pyramidal microneedles: experiments and numerical modelling

The present study aimed to investigate the dynamics of HMNs' insertion and extraction utilising HMN fabrication, laboratory experiments and numerical simulations. In particular, the study aims to develop an experimentally validated mathematical model to investigate the mechanics of the insertion and extraction of hollow pyramidal MNs, considering the nonlinear material behaviour of HMNs and skin. This study reveals good consistency between the experimental and computational results, providing confidence on the validity of the developed mathematical model. The model was then used to conduct detailed numerical simulations of the insertion and extraction of hollow pyramidal MN within a multi-layered skin model under different conditions, allowing us to assess the impacts of several key parameters (e.g., the base radius, length, and tip radius of HMNs) on the insertion and extractions dynamics of the HMNs. Overall, the findings of this paper indicate that HMN length <600 µm, base diameter <300 µm, tip diameter <30 µm, needle spacing >800 µm, and number of HMNs <9 can significantly lower the forces required for insertion and extraction for the chosen pyramidal MN, while maintaining their mechanical and structural integrity.