Chapter Three
Biodegradable Elastomeric Polymers
and MEMS in Tissue Engineering
Richard Tran, Jagannath Dey, Dipendra Gyawali,
Yi Zhang and Jian Yang
Department of Bioengineering, University of Texas at Arlington, 501 West First Street,
Arlington, Texas 76019, USA
E-mail: jianyang@uta.edu
3.1 INTRODUCTION
Within the past decade, researchers in the field of tissue engineering have recog-
nized the need for new materials with soft and elastic properties. As a result, many
groups have focused on the synthesis, characterization, and application of materi-
als with a wide range of biodegradable and elastomeric properties.
1
The combina-
tion of these polymers with Micro–Electro–Mechanical Systems (MEMS) technolo-
gies has sparked a new area of research with increasing practical applications.
2
The following chapter discusses important design criteria for creating polymers
with elastomeric properties, recently researched biodegradable elastomers, and the
use of MEMS in combination with biodegradable elastomers in tissue engineering
applications.
3.1.1 Tissue Engineering
Currently, the only effective and permanent treatment to restore lost tissue func-
tion is transplantation. Although the success rate for organ replacement ther-
apy has improved, the number of patients awaiting transplantation continues
to increase, and the supply of transplantable organs does not meet the current
demand.
3
In addition, complications can occur from chronic immune rejection and
the required life–long immunosuppressive drug regimen. Due to the growing
demand for transplantable organs, a heavy burden is placed on the healthcare
industry and the national economy. For example, patients suffering from liver
failure cost the United States over $9 billion annually since 1992.
4
Biomaterials for MEMS, Edited by 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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34 R. Tran et al.
Better alternatives need to be developed that are less invasive and more
cost effective to provide the needed tissue.
5
As defined by Langer and Vacanti,
tissue engineering, or regenerative medicine, is “an interdisciplinary field that
applies the principles and methods of engineering and life sciences toward the
understanding and development of biological substitutes to restore, maintain, and
improve human tissue functions.” By combining the fundamental principles and
methods from chemistry, engineering, and biological sciences, the major goal of
tissue engineering is to restore damaged or diseased tissue.
1
The field of tissue engineering has progressed for almost 30 years. Due to the
great potential of this field, much attention has been attracted to help overcome
major healthcare needs.
6
Research groups in the field have attempted to recreate
a variety of mammalian tissue. For example, ectodermal-, endodermal-, and
mesodermal-derived tissue such as the nerve, cornea, skin, liver, pancreas, carti-
lage, bone, muscle, urethra, bladder, and blood vessels have been investigated.
715
The foundation of tissue engineering relies on four key elements: cells, scaf-
folds, signals, and bioreactors.
16,17
In the general scheme for tissue engineering,
cells are seeded onto a three–dimensional (3D) scaffold, a tissue is cultivated
in vitro, then proper signals are supplemented to the system, and finally the
construct is implanted into the body as a prosthesis.
17
The general scheme for the
key elements involved in the tissue engineering paradigm is illustrated in Fig. 3.1.
The cells used in tissue engineering applications can be isolated from either
an autologous, allogenic, or xenogenic source. The cells may be tissue specific,
stem cells, or progenitor cells. Scaffolds, which provide a substrate for cell growth,
can be composed of either a natural or synthetic material, and fabricated into a
fibrous, foam, hydrogel, or capsule architecture. Signals can be introduced to
enhance cell proliferation, differentiation, and vascularization of the construct.
Bioreactors mimic the conditions inside the body, and provide many benefits
towards a successful design. For example, bioreactors allow for an increase in
Figure 3.1. The key elements involved in the classic tissue engineering paradigm. For
color reference, see page 255.
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