Davis Shawn P, Landis Benjamin J, Adams Zachary H, Allen Mark G, Prausnitz Mark R
School of Chemical & Biomolecular Engineering, 311 Ferst Drive, Georgia Institute of Technology, Atlanta, GA 30332-0100, USA.
J Biomech. 2004 Aug;37(8):1155-63. doi: 10.1016/j.jbiomech.2003.12.010.
As a hybrid between a hypodermic needle and transdermal patch, we have used microfabrication technology to make arrays of micron-scale needles that transport drugs and other compounds across the skin without causing pain. However, not all microneedle geometries are able to insert into skin at reasonable forces and without breaking. In this study, we experimentally measured and theoretically modeled two critical mechanical events associated with microneedles: the force required to insert microneedles into living skin and the force needles can withstand before fracturing. Over the range of microneedle geometries investigated, insertion force was found to vary linearly with the interfacial area of the needle tip. Measured insertion forces ranged from approximately 0.1-3N, which is sufficiently low to permit insertion by hand. The force required to fracture microneedles was found to increase with increasing wall thickness, wall angle, and possibly tip radius, in agreement with finite element simulations and a thin shell analytical model. For almost all geometries considered, the margin of safety, or the ratio of fracture force to insertion force, was much greater than one and was found to increase with increasing wall thickness and decreasing tip radius. Together, these results provide the ability to predict insertion and fracture forces, which facilitates rational design of microneedles with robust mechanical properties.
作为皮下注射针和透皮贴剂的结合体，我们利用微制造技术制作了微米级针阵列，这些针能够在不引起疼痛的情况下将药物和其他化合物输送穿过皮肤。然而，并非所有微针几何形状都能以合理的力插入皮肤且不会折断。在本研究中，我们通过实验测量并从理论上模拟了与微针相关的两个关键力学事件：将微针插入活体皮肤所需的力以及微针在断裂前所能承受的力。在所研究的微针几何形状范围内，发现插入力与针尖的界面面积呈线性变化。测量得到的插入力范围约为0.1 - 3N，这足够低以至于可以手动插入。发现微针断裂所需的力随着壁厚、壁角以及可能的针尖半径的增加而增大，这与有限元模拟和薄壳分析模型一致。对于几乎所有考虑的几何形状，安全系数，即断裂力与插入力的比值，远大于1，并且发现随着壁厚增加和针尖半径减小而增大。这些结果共同提供了预测插入力和断裂力的能力，这有助于合理设计具有稳健力学性能的微针。
