Ph.D. Defense by Mengdi Luo

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PTFE PhD Defense — Mengdi Luo

Title: Materials and Microfabrication Approaches for Completely
Biodegradable Wireless Micromachined Sensors

Date: Friday, November 7, 2014
Time: 2:10 pm
Location: MRDC 3515 (Hightower Conference Room)

Dr. Mark G. Allen, ECE (Advisor)
Dr. Oliver Brand, ECE
Dr. Zhiqun Lin, MSE
Dr. Preet Singh, MSE
Dr. Donggang Yao, MSE


Implantable sensors have been extensively investigated to facilitate
diagnosis or to provide a means to generated closed loop control of therapy
by yielding in vivo measurements of physical, chemical and biological
signals. MEMS technology has demonstrated significant value in this
application mainly due to their micro-scale size, low weight, low power
consumption, potential for low fabrication cost, superior functionality or
performance, and can be combined with biotechnology and molecular biology.
Among those, biodegradable sensors which degrade gradually after they are no
longer functionally needed exhibit great potential in the acute or
shorter-term medical diagnosing and sensing due to the advantages of (a)
exclude the need to a secondary surgery for sensor removal, and (b) reduce
the risk of long-term infection.

The objective of this research is by investigating the biodegradable
materials and developing proper fabrication process, to design and
characterize microfabricated RF wireless pressure sensors that are made of
completely biodegradable materials and degrade at time-controlled manner. In
order to do that, we explore this study in four areas: (1) designing the
sensors that operate wirelessly made of biodegradable materials; (2)
investigating the biodegradable materials in the application of implantable
biodegradable wireless sensors to achieve different degradation life time;
(3) developing a new fabrication process that allow handling delicate
biodegradable materials; and (4) testing the pressure response functionality
and studying the degradation behavior of the wireless biodegradable pressure

In this work, two categories of completely biodegradable pressure sensors
are fabricated and characterized. (1) Slow degradation sensor that made of
poly(L-lactic acid) (PLLA) and zinc(Zn) or zinc/iron (Zn/Fe)-couple; (2)
rapid degradation sensors that utilizes poly(lactic-co-glycolic acid)/poly
(vinyl alcohol) (PLGA/PVA) “shell-core” structure as the dielectrics and Zn
or Zn/Fe couple as the conductors. All the sensors show three stages of
behavior in vitro: equilibration stage, functional lifetime, and performance
degradation. During the functional life time, most successful sensors
exhibit fully stable functionality: relatively steady resonant frequency and
slight decrease of quality factor with zero applied pressure, as well as
comparable sensitivities at different time points. The slow degradation
sensors which demonstrate functional lifetimes of 4 to 15 days, are expected
to fully degrade after 2 years based on the degradation of the polymer
package. The rapid degradation sensors exhibit functional lifetimes of
approximately 1 day and degrade completely with 26 days, demonstrating a
higher functional time ratio of 4%.


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