Identifier

etd-07112006-070802

Degree

Master of Science in Mechanical Engineering (MSME)

Department

Mechanical Engineering

Document Type

Thesis

Abstract

There is an ever expanding interaction between the fields of micro-electromechanical systems (MEMS) and biology to develop devices to monitor, control and act on living systems. Particularly in the field of cryobiology, there is a need to monitor and control temperature at the cellular level. An important step towards achieving this aim is to fabricate an array of microscale thermoelectric actuators. As a first step for towards achieving such localized control of temperatures in cells and tissues, an array of individually addressable micro-thermoelectric coolers (µTECs) were modeled, characterized, and fabricated. Prefabrication experimentation and modeling were carried out to understand the behavior of the device. Two mathematical models, the lumped parameter model and finite element model, were used to identify important device parameters and dimensions. The organization of the proposed device was an array of 4 x 4 microscale (~10 ìm) thermoelectric actuators, each of which was separated by a distance of 50 ìm center-to-center and dimensioned so that each µTEC could measure or modulate the temperature in the neighborhood of a single cell. The prefabrication experiments showed that it was feasible to produce the TECs required for fabrication of the device through electrodeposition. Bismuth-telluride was electrodeposited to form the n-type and p-type leg elements of µTEC and the deposition was achieved by varying the cathodic potential. The material deposition development could focus on a single material system, yielding both n-type, and p-type pellets of TEC. The prototype devices were successfully fabricated with a modified multi-step LIGA (Lithographie, Galvanoformung and Abformung) technique wherein a patterned positive photoresist and photomasks defined the geometry of the device. This enables high-density wiring required for the device. In future, these µTECs will be embedded in Polymethylmethacrylate (PMMA) matrix to improve insulation. An artificial tissue (AT) system composed of Normal Human Dermal Fibroblast (NHDF) cells from stem cells will be grown on the device for experimentation wherein a PMMA sheet will act as an interface between the cooler and the embedded cells. The thermoelectric micro device thus developed will result in the unique capability of temperature manipulation and control on cellular scales (micrometers).

Date

2006

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Ram V. Devireddy

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