If you have ever had a kidney stone removed the hard way, you will know how important it is that certain things in life are made as small as possible.
And that’s just why research engineers at the Lawrence Livermore National Laboratory have developed a very small silicon microgripper that is actuated by shape memory alloy (SMA) thin films. The microgripper device can be used for remote manipulation in small areas via access through small holes or catheters.
This device can also be used in conjunction with other microtools to go through a singular trocar in laparoscopic procedures and reduce the amount of incisions required, and cut down on the exchange of tools. The microgripper generates a large gripping force, has a relatively rigid structural body and is designed with small cross-sectional areas to facilitate entry through small holes.
The microgripper is fabricated by alignment and selective eutectic bonding of two preprocessed silicon wafers. After bonding, the individual microgripper structures are formed by bulk silicon etching with double-sided alignment and precision depth-controlled sawing.
The fabrication process allows the designer some flexibility in shaping the gripping jaws to match the object being gripped. Also, batch fabrication allows for highly automated processing and reduces manufacturing costs. Ni-Ti-Cu SMA films developed at LLNL are deposited to generate high actuation force (500MPa) with low applied temperature gradients (30° C- 70° C).
The stress induced can open each side of the microgripper by up to 55 mm for a total gripping motion of 110 mm. Due to hysteresis, the SMA must reach 70C initially. The gripper will remain open if the temperature is immediately (within milliseconds) lowered to 55C. Further reduction in temperature closes the gripper. Preliminary tests indicate the gripper uses about 0.1 W in air and 0.2 W in water.
The Microtechnology Center at LLNL is developing a variety of microtools for use in biomedical applications, and is pursuing industrial partners for commercialising these devices.
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Abraham Lee, Ph.D.Microtechnology CenterLawrence Livermore National LaboratoryPO Box 808, L-222Livermore, CA 94551510-423-4524E-mail:firstname.lastname@example.org