Hydrogels in Tissue Engineering

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					                             Hydrogels in Tissue Engineering
  Arthur Coury, Peter Jarrett, Robert Miller, Erika Johnston, Luis Avila, Kenneth
 Messier, Hildegard Kramer, Keith Greenawalt, Timothy Butler, Michael Philbrook,
  Li-Ping Yu, Grace Chang, Lauren Young, Rami El-Hayek, Aviva Shiedlin , Holly
        MacGregor, Kevin Skinner, Jude Colt, Jeffrey Kablik, James Burns

Genzyme Corporation, One Kendall Square, Cambridge, Massachusetts 02139, USA

We define “hydrogel” as: “A shape-retentive polymeric network swollen with a high
percentage of water.” It may or may not be fully swollen when applied and it may or may
not dissolve in more water. [1] Our working definition of tissue engineering is: “The
generation, regeneration, augmentation or limitation of the structure and function of living
tissues by the application of scientific and engineering principles.”[1] It is broad in scope,
encompassing many functional approaches beyond “cells in scaffolds” and, very basically,
involves controlling cells and matrices in tissues. A wide range of commercially successful
products falls within its scope. In this context, regenerative therapies comprise a subgroup
of tissue engineering. In the narrow interpretations of tissue engineering, which mandate
preparing cellular constructs outside the body, with or without scaffolds, and transplanting
them, topically or internally, tissue engineering products have not generally been financially
successful. Most commercial tissue engineering products have remained on the market,
however, and research and development continues at a significant level worldwide. [2]

 Hydrogels formed from natural or synthetic polymers find important applications in
medical devices and drug delivery. Early medical uses of hydrogels included soft contact
lenses and wound dressings, with the latter exemplifying one form of tissue engineering,
guided tissue regeneration, promoted by moist healing.[2] Subsequently, implantable
hydrogel products were developed, including surgical sealants, tissue adhesives, hemostats,
cell scaffolds and drug delivery systems.[1] Hydrogels induce beneficial tissue responses
based on their physical and chemical properties. Because of their high water content, they
are generally quite compatible with cells and may enter into specific or non-specific binding
with cell receptors. Proteins and polysaccharides that form hydrogels contain ligands for
specific binding to certain cells and form useful scaffolds for cell incorporation. Synthetic
hydrogels generally do not support the anchorage that matrix-forming cells require, but
encapsulate cells effectively, and can be modified for cell attachment and delivery. [3]

We have developed several cell and hydrogel-based products and have two proprietary
hydrogel platforms, one based on modified hyaluronan polysaccharide, the other comprised
of poly(oxyethylene)-based resorbable hydrogels. They have demonstrated features which
exemplify many of the broad-based manifestations of tissue engineering, providing realized
as well as potential commercial value. [2]

[1] A. Coury, R. Miller et al, “Bioresorbable Hydrogels for Medical Therapies,” Transactions of The
Knowledge Foundation Workshop: Polymeric Biomaterials for Medical Applications, Providence, Rhode
Island, October 9, 2002.
[2] A. Coury, “Tissue Engineering Products: Succeeding or Failing Depends on Interpretation of the
Definition,” Submitted to “Biomaterials,” (2006).
[3] K. Lee, D. Mooney et al, “Hydrogels for Tissue Engineering,” Chemical Reviews, 101, 7 1869-79 (2001).

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