Chapter One
Introduction
M. Chiao
and J.-C. Chiao
Department of Mechanical Engineering, University of British C olumbia,
6250 Applied Science Lane, Vancouver, V6T 1Z4 Canada.
E-mail: muchiao@mech.ubc.ca
Department of Electrical Engineering, Nedderman 538, Box 19016,
University of Texas at Arlington, Arlington, TX 76019-0016, USA.
E-mail: jcchiao@uta.edu
Biomaterials have been used in biomedical industry to produce implantable devices
for the last several decades. Most of such devices have utilized conventional
manufacturing processes. MEMS (Microelectromechanical systems) uses microma-
chining techniques to build miniature devices and can enable novel applications.
Over the last decade, biomaterial-based MEMS devices have found applications
in medicine. However, due to the cross-disciplinary nature of the research that
often involves mechanical engineering, electrical engineering, chemistry, biology and
material science, review literatures on the subject that could lead scientists in a specific
field into the new biomaterial-based application world is often lacking. The goal of
this book is to provide a review on new micromachining techniques of biomaterials
and their applications.
1.1 INTRODUCTION
The definition of Biomaterial can be found in a Merriam-Webster’s dictionary,
dated 1966: A natural or synthetic material (as a metal or polymer) that is suitable
for introduction into living tissue especially as part of a medical device (as an artificial
joint). However, with the advances in technology, materials that are used ex vivo,
but interacting with living organisms can be arguably a biomaterial. For example,
blood contacting materials such as plasticized polyvinyl chloride (PVC) commonly
used in blood bags, may be considered as a type of biomaterial. More recently,
rapid diagnostic tools using miniaturized fluidic channels
1
combining with micro
mixers, valves and pumps have the potential to fundamentally change the ways
biochemical analysis have been performed. The materials involved in such devices
or systems include silicon, glass, metals and polymers. These materials, either
Biomaterials for MEMS, Edited b y M. Chiao and J.-C. Chiao
Copyright © 2011 by Pan Stanford Publishing Pte. Ltd.
www.panstanford.com
978-981-4241-46-5
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2 M. Chiao and J.-C. Chiao
used for the substrates, passive parts or active elements, need to interact with
biological components such as cells, proteins, DNAs, genes or reagents. The
interfacing mechanisms and reactions between the biological components and the
mechanical parts are not often discussed or taught in the curricula of conventional
MEMS courses in the departments of electrical or mechanical engineering. Thus,
the purpose of this book is to introduce biomaterials to engineers who are inter-
ested in MEMS and microfluidics, yet have no prior background in biomaterials.
Common biomaterials used in biomedical industries are summarized in
Table 1.1. It is clear that these materials cover a wide range from metals, ceramics
to polymers. Common factors need to be considered in biomaterial applications
include: toxicity, surface fouling and mechanical strength, besides their functional
characteristics and capabilities. For example, biomaterials used in dentistry need
to have satisfactory mechanical strength and also adequate biocompatibility. The
mechanical strength also has to be compatible with surrounding tissues to avoid
damages due to motions. In vivo or ex vivo microfluidic devices, either for drug
delivery implants or diagnostic tools, will have different biocompatibility con-
cerns. It is important to maintain certain flexibility and deformability of the in vivo
devices so the devices can stay inside the body without causing any tissue scarring.
However, the devices have to be rigid enough to maintain a proper internal
pressure or allow drug refill using a syringe. For ex vivo microfluidic platforms,
although the entire system does not have toxicity concerns, the interfacing parts
such as the substratum, channels and active sensing or actuation elements need
to maintain a proper environment for cell proliferation and movement. Another
example illustrates the importance of surface fouling. Long-term cardiovascular
catheters for intravenous drug delivery is critical for patients under chemotherapy.
However, sepsis as a result of bacterial contamination on the catheter walls, is a
major failure of the treatment. Surface fouling, initiated by protein adsorption
Table 1. 1 Common biomaterials and application fields.
Application Material
cardiovascular stainless steel; titanium; polyurethane;
polytetrafluoroethylene (PTFE);
polyethylene terephthalate (Dacron
TM
)
2
dentistry gold; calcium phosphate; porcelain; amalgam; glass ionomer
3
controlled drug delivery poly(D,L-lactide-co-glycolide) (PLGA);
4
ophthalmology silicone; hydrogel;
5
orthopedics titanium
6
urology polyurethane; silicone
7
neurology silicon
8
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