Design and fabrication considerations, numerical modelling, and testing of a MEMS microgripper

Microgrippers play an important role in the manipulation of biological cells and tissues. This paper presents a horizontal electrothermally actuated microgripper that is designed for the handling and deformability characterization of human red blood cells (RBCs). Pathological alterations in the mechanical properties of RBCs have been associated with a number of specific diseases. This has accentuated the significance of analysing the deformability characteristics of RBCs within the biomedical field. A polysilicon microgripper structure was designed and fabricated according to the dimensional specifications imposed by the commercial PolyMUMPsTM fabrication process. The microgripper design was developed and numerically modelled using finite element analysis where coupled electrothermomechanical simulations were carried out in CoventorWare®. The fabrication method is presented in this paper, together with details of the experimental set-up used for the actuation testing. The tip displacement of the microgripper arm when electrothermally actuated is compared with that obtained by means of numerical simulations. Results show that the microgripper arm deflected as designed when electrothermally actuated, with good agreement obtained between simulation and experimental results. This paper also proposes critical design and fabrication considerations that were implied from the experimental campaign performed in this work and that take into account out-of-plane buckling of the hot arm, fracture of the arms in the vicinity of the anchored probe pads, residual stresses, and device stiction. Such considerations are regarded as an important outcome of this work, and they must be thoroughly investigated to mitigate the malfunction or failure of the microgripper.