Biomedical Engineering Reference
In-Depth Information
8
Biofunctional Hydrogels
8.1 Introduction ......................................................................................
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8.2 Synthetic Hydrogels..........................................................................
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Common Polymeric Hydrogel Materials •
In Situ
Gelation
8.3 Hydrogel Biofunctionality ...............................................................
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Engineering Cellular Adhesion • Presentation of Growth Factors
and Other Signaling Molecules • Cell-Mediated Hydrogel
Degradation • Incorporating Specific Biofunctionality into
Hydrogels
8.4 Importance of Physical Properties of Hydrogels .........................
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8.5 Design of Complex Biofunctional Hydrogels...............................
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8.6 Summary ..........................................................................................
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References ....................................................................................................
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Melissa K. McHale
Rice University
Jennifer L. West
Rice University
8.1 Introduction
Hydrogels are water-swollen matrices that are generally formed from hydrophilic polymers that
have been chemically or physically crosslinked to prevent dissolution. Perhaps the most recognizable
hydrogel material is the soft contact lens. Hydrogels are appropriate for this application because they
(1) generally exhibit excellent biocompatibility, (2) allow for transport of molecules (in this case pri-
marily gases) needed for tissue function and survival, and (3) possess appropriate mechanical prop-
erties for contact with soft tissue. Most synthetic hydrogel materials are relatively bioinert, resisting
protein adsorption and cell adhesion. Modification of bioinert hydrogels with bioactive sequences can
generate materials with biological functionalities such as biospecific cell adhesion, cell signaling, and
enzymatic reactivity.
The prototypical biofunctional hydrogel is the extracellular matrix (ECM) that surrounds the cells
of all tissues. This highly functional milieu is comprised of crosslinked proteins and polysaccharides
that act to provide cell adhesion and mechanical support to tissues while also guiding various cellular
processes. Rational design strategies for many cell- and tissue-interacting materials strive to emu-
late the functionality of the ECM. In addition, some components of the ECM, such as collagen and
hyaluronic acid, have been extensively studied as hydrogel materials for various biomedical applica-
tions, including cardiovascular tissue engineering (Masters et al. 2004) and stem-cell differentiation
(Chung and Burdick 2009). These naturally derived materials have advantages in that certain aspects
of their bioactivity are intrinsic and have evolved over the millennia for optimal cell-material inter-
actions. However, they suffer from difficulties associated with isolation and purification, and control
over mechanical properties is limited. Because many recent reviews (Nicodemus and Bryant 2008;
Tibbitt and Anseth 2009) and a chapter in this topic have provided an extensive look at these natural
biomaterials, this chapter will focus primarily on the incorporation of biofunctionality into synthetic
hydrogel materials.
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