Early Stage Researcher (PhD Year 1) X Post-Doctoral Researcher/Senior Researcher/PI

Entry for the Engineers Ireland Biomedical Research Medal

Corresponding author has completed PhD and would like to review BinI abstract submissions

Please place an X in any appropriate categories

INTRODUCTION

Microneedle patches are a minimally invasive, painless, self-administered transdermal drug delivery system that overcome the limitation of conventional hypodermic needles [1]. However, not all microneedle geometries and materials are able to insert into skin with reasonable force and without breaking or buckling. Microneedle patch designs and the best ways of predicting how they will perform in clinical use are yet to be fully optimised. While quantifying Penetration efficiency (PE) achieved is a non-trivial task, it has become accepted in the literature that full MN penetration will often not be obtained (<50% [2, 3]). Consequently, this limits the functionality of the MN patch designs and often leads to novel MN designs falling short of their specified performance when tested in vivo. Considering the challenges involved in experimentally measuring the mechanical interaction of microneedles patches and skin, a validated computational model can be used to investigate many parameters regarding the microneedle mechanical interaction with skin.

MATERIALS AND METHODS

A 3D finite element model (Abaqus) will be used for in silico comparison of microneedle patch performance during skin penetration and adhesion. Solid microneedle arrays designed by the UCD Medical Device Design are chosen as the base design for future experimental validation. In the initial model, each microneedle is designed to have 2.24 mm height, 600 μm base and 0.018 mm tip radius. Needle-to-needle distance was set at 1mm. In these simulations of stainless steel solid microneedles, the microneedle is modelled as a rigid body.

A multilayered skin model is proposed [4]. A Von Mises stress criterion coupled with element deletion to simulate the failure of the skin during the insertion process is employed [5]. The Neo-Hookean material model was used here to simulate the stratum corneum and the dermis, and a simple linear elastic material model simulated the hypodermis. The optimal material properties were determined and validated by Kong et.al [4]. Hex elements (C3D8) were chosen for Skin Tissue to prevent the generation of artificial strain (using full integration to avoid hourglassing issues).

RESULTS

The insertion speed for the microneedle penetration into the skin was applied at range from 1 to 2 mm/s and the insertion angle was applied at 90o and 26.5o. During the

insertion process, the maximum stresses are located at the tip area and around the maximum cross-section of the MN which pierces the dermis, as seen in Fig.1. In addition, increasing the insertion velocity leads to smaller penetration force, and oblique insertion needs greater penetration force and pull-out force.

Figure 1 Stress distribution in the skin during the penetration processing (a) with MN (b) without MN at insertion velocity of 2mm/s and at insertion angle of 90o.

DISCUSSION

It is challenging to capture the dynamic skin behaviour during and after insertion of microneedles. This study contributes to the development of a state-of-the-art skin tissue model, that provides quantitative analysis of microneedle mechanical interaction with skin that can ultimately lead to improved microneedle design. The viscoelastic nature of skin causes skin to appear stiffer at higher insertion velocity, which results in an increased maximum penetration force in our models. Upon further model development, we will validate the results obtained with corresponding experimental assessment of microneedle penetration and drug delivery.

REFERENCES

[1]. Larran ̃eta (et al.), Materials Science and Engineering R 104, pp. 1–32, 2016.

[2]. Park (et al.), J Control Release, 104(1):51-66, 2005.

[3]. Ahmad(et al.), Frontiers in Nanoscience and Nanotechnology, DOI:10.15761/FNN.1000169, 2018.

Bioengineering in Ireland26, January 17-18, 2020

Computational Modelling of Microneedle Mechanical Interaction with Skin

Shu, W.T., O'Cearbhaill, E.D., Ní Annaidh A.UCD Centre for Biomedical Engineering, School of Mechanical and Materials Engineering, University

College Dublin, Engineering Building Belfield Dublin 4, Dublin, Irelandemail: eoin.ocearbhaill@ucd.ie

Early Stage Researcher (PhD Year 1) X Post-Doctoral Researcher/Senior Researcher/PI

Entry for the Engineers Ireland Biomedical Research Medal

Corresponding author has completed PhD and would like to review BinI abstract submissions

Please place an X in any appropriate categories[4]. Kong (et al.), Computer Methods in Biomechanics

and Biomedical Engineering 14.9, pp. 827–835. issn: 1025-5842, 1476-8259, 2011.

[5]. Nı ́Annaidh, The mechanics of stabbing: a combined experimental and numeri- cal study of sharp force injury, University College, Dublin, 2012, Ph.D. Thesis.

Bioengineering in Ireland26, January 17-18, 2020