Cauchi Marija, Grech Ivan, Mallia Bertram, Mollicone Pierluigi, Sammut Nicholas
Department of Mechanical Engineering, Faculty of Engineering, University of Malta, MSD 2080 Msida, Malta.
Department of Microelectronics and Nanoelectronics, Faculty of Information and Communication Technology, University of Malta, MSD 2080 Msida, Malta.
Micromachines (Basel). 2019 Feb 28;10(3):167. doi: 10.3390/mi10030167.
Microelectromechanical systems (MEMS) have established themselves within various fields dominated by high-precision micromanipulation, with the most distinguished sectors being the microassembly, micromanufacturing and biomedical ones. This paper presents a horizontal electrothermally actuated 'hot and cold arm' microgripper design to be used for the deformability study of human red blood cells (RBCs). In this study, the width and layer composition of the cold arm are varied to investigate the effects of dimensional and material variation of the cold arm on the resulting temperature distribution, and ultimately on the achieved lateral displacement at the microgripper arm tips. The cold arm widths investigated are 14 μ m, 30 μ m, 55 μ m, 70 μ m and 100 μ m. A gold layer with a thin chromium adhesion promoter layer is deposited on the top surface of each of these cold arms to study its effect on the performance of the microgripper. The resultant ten microgripper design variants are fabricated using a commercially available MEMS fabrication technology known as a silicon-on-insulator multi-user MEMS process (SOIMUMPs)™. This process results in an overhanging 25 μ m thick single crystal silicon microgripper structure having a low aspect ratio (width:thickness) value compared to surface micromachined structures where structural thicknesses are of the order of 2 μ m. Finite element analysis was used to numerically model the microgripper structures and coupled electrothermomechanical simulations were implemented in CoventorWare ® . The numerical simulations took into account the temperature dependency of the coefficient of thermal expansion, the thermal conductivity and the electrical conductivity properties in order to achieve more reliable results. The fabricated microgrippers were actuated under atmospheric pressure and the experimental results achieved through optical microscopy studies conformed with those predicted by the numerical models. The gap opening and the temperature rise at the cell gripping zone were also compared for the different microgripper structures in this work, with the aim of identifying an optimal microgripper design for the deformability characterisation of RBCs.
微机电系统（MEMS）已在以高精度微操作为主导的各个领域中确立了自身地位，其中最突出的领域是微装配、微制造和生物医学领域。本文提出了一种水平电热驱动的“冷热臂”微夹钳设计，用于研究人类红细胞（RBC）的变形能力。在本研究中，改变冷臂的宽度和层组成，以研究冷臂的尺寸和材料变化对所得温度分布的影响，并最终对微夹钳臂尖端处实现的横向位移的影响。研究的冷臂宽度为14μm、30μm、55μm、70μm和100μm。在这些冷臂的每一个顶面上沉积一层带有薄铬粘附促进层的金层，以研究其对微夹钳性能的影响。使用一种称为绝缘体上硅多用户MEMS工艺（SOIMUMPs）™的商用MEMS制造技术制造出了十种微夹钳设计变体。与结构厚度约为2μm的表面微机械加工结构相比，该工艺产生了一个悬垂的25μm厚的单晶硅微夹钳结构，其具有较低的纵横比（宽度：厚度）值。使用有限元分析对微夹钳结构进行数值建模，并在CoventorWare®中进行耦合电热机械模拟。数值模拟考虑了热膨胀系数、热导率和电导率特性的温度依赖性，以获得更可靠的结果。制造的微夹钳在大气压下驱动，通过光学显微镜研究获得的实验结果与数值模型预测的结果相符。在这项工作中，还比较了不同微夹钳结构在细胞抓取区域的间隙开口和温度升高情况，目的是确定一种用于RBC变形能力表征的最佳微夹钳设计。
