Biodegradable Elastomeric Polymers and MEMS in Tissue Engineering 35
Table 3.1 The controllable parameters from the key elements of the tissue
engineering paradigm.
Cells Scaffold Bioreactor
Source Architecture Nutrients/Oxygen Content
Type Materials Growth Factors
Density Pore Size/Shape Dynamic Flow Rate
Genetic Manipulation Bioactive Molecules Tension/Compression
Gene Expression Mechanical Properties Pulsatile Stress
Degradation Rate Shear Stress
the volume of cells that can be cultured in vitro, enhance mass transport, and add
mechanical cues to stimulate cell differentiation and growth.
Thus, controlling
the parameters from the key elements of the tissue engineering paradigm can
ultimately influence the outcome of a cell–scaffold–bioreactor system (Table 3.1).
Despite much of the recent success in tissue engineering, key challenges
remain to be addressed. Along with the difficulty in finding an appropriate cell
source, the lack of suitable scaffolding biomaterials and the current graft engineer-
ing design strategies challenge the success of the field. For example, one major
obstacle limiting the success of tissue engineering is compliance mismatch. The
current scaffolds cannot be fully integrated with their surrounding tissues because
of their incompliant molecular structures and mechanical properties. Thus, further
consideration in regards to matching scaffold mechanical properties to the native
tissues must be taken into consideration.
3.1.2 Mechanical Considerations for Tissue Engineering Scaffolds
All the tissue cells in the body are located in a unique 3-D extracellular ma-
trix (ECM) environment. The ECM supplies important biochemical signals and
functions, facilitates nutrient and waste exchange, guides cellular organization
and differentiation, and provides mechanical integrity to the cells.
In order to
sufficiently emulate the natural ECM, a successful scaffold design should include
several key requirements. The ideal scaffold should be biocompatible, biodegrad-
able, have an interconnected pore structure, possess a large surface area, allow
for adequate cell loading, encourage cell attachment and proliferation, facilitate
nutrient and waste exchange, and possess the appropriate mechanical properties
for the intended target application.
Materials used in scaffold fabrication can
be divided into four groups: metals, ceramics, polymers, and composites.
content of this discussion will be limited to synthetic polymers. Unlike other mate-
rials, synthetic polymers have received great attention because of their controllable
material properties such as strength, processability, degradation, microstructure,
and permeability.
Many of the soft tissues in the body have soft and elastomeric properties.
order to successfully engineer these tissues, the use of a mechanically compliant
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