Photopolymerized Hydrogels

The structural complexity and functional diversity of the liver create challenges for the design and construction of an implantable, tissue-engineered liver construct. Important requirements for viable implantation include adequate transport of oxygen and nutrients and appropriate microenvironmental cues.

We have developed a method to create intricate, cell-laden 3-D architectures using photopolymerizable PEG-based hydrogels and microfabrication techniques . Hydrogels are water-swollen polymers that offer structural support and high tissue density while maintaining an in vivo-like environment for cells. By photocrosslinking layers of pre-polymer through a mask, hydrogels encapsulating living cells can be patterned into 3-D structures. Three layers of hybrid tissue consisting of PEG hydrogel containing mammalian cells are presented in the figure below. Panel c depicts a fluorescence image of a three-layer construct in which one layer contains red-labeled cells, one layer contains green-labeled cells, and all layers are counter-stained blue. Using this cell photoencapsulation technique, complex tissue-like structures can be created by including various cell types in different 3-D configurations. Furthermore, the chemical properties of polyethylene glycol (PEG)-based hydrogels allow for functionalization with biologically relevant molecules such as growth factors, degradable linkages, or peptides. We are exploring the use of functionalized hydrogels for hepatocyte photopatterning in collaboration with Jennifer West (Rice) to generate tissue-engineered constructs with improved transport properties and liver-specific function. Liu & Bhatia , 2002 .

We have also developed tools for organizing cells within photopolymerizable hydrogel scaffolds using dielectrophoresis , thereby allowing exploration of cell organization in three dimensions.   Albrecht et al (2005)

Hydrogels containing living cells can be patterned into 3-D structures by photocrosslinking each layer through a mask. These figures show two (a, b) and three (d, e) layered hydrogel patterns. The hydrogels in b, d, e all contain live cells. Using this technique, complex tissue-like structures can be created by including various cell types in different 3-D configurations. Liu et al (2002), Journal of Biomedical Microdevices.