MSE Ph,D. Defense - Mengdi Luo

MSE Grad Presentation
Event Date:
Friday, November 7, 2014 - 2:15pm to 4:00pm
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%.