Abstract
Microneedles (MNs) are playing an increasingly important role in biomedical applications, where minimally invasive methods are being developed that require imperceptible tissue penetration and drug delivery. To improve the integration of MNs in microelectromechanical devices, a high‐resolution 3D printing technique is implemented. A reservoir with an array of hollow MNs is produced. The flow rate through the MNs is simulated and measured experimentally. The mechanical properties of the 3D printed material, such as elasticity modulus and yield strength, are investigated as functions of printing parameters, reaching maximum values of 1750.7 and 101.8 MPa, respectively. Analytical estimation of the MN buckling, fracture, and skin penetration forces is presented. Penetration tests of MNs into a skin‐like material are conducted, where the piercing force ranges from 0.095 to 0.115 N, confirming sufficient stability of MNs. Furthermore, 200 and 400 μm‐long MN arrays are used to successfully pierce and deliver into mouse skin with an average penetration depth of 100 and 180 μm, respectively. A biocompatibility assessment is performed, showing a high viability of HCT 116 cells cultured on top of the MN's material, making the developed MNs a very attractive solution for many biomedical applications.
Highlights
The finite element method (FEM) was used to simulate the volumetric flow rate for the different designs (Table 1), and the modeling was implemented in SolidWorks Flow Simulation (Dassault Systèmes SolidWorks Corporation, MA, USA)
To test the MNs on a material that has skin-like mechanical properties, PDMS samples were created with an elasticity modulus
The experimental flow rates were lower than the results found by FEM
Summary
MNs used for transdermal delivery have to overcome the skin’s mechanical resistance by piercing the stratum corneum and penetrate up to the dermis layer without mechanical failure In this regard, the prediction of the forces applied to the MNs is a critical design aspect. The estimation of the fracture force was based on the assumptions that the failure or fracture of the MN is caused by axial forces applied to the MN tip, which means that shear forces are neglected and that the MN fracture is mainly due to an applied pressure higher than the ultimate stress of the material Based on these assumptions, the MN fracture force can be modeled by Equation S(2), Supporting Information. The fracture toughness Gp of the human skin ranges from Gp1 1⁄4 30.1 kJ mÀ2 (hard skin) to Gp2 1⁄4 20 kJ mÀ2 (soft skin), as reported by Davis et al and Khanna et al, respectively.[37,38]
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