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IBN Team Develops Thixotropic 3D Gel That Cultures HSCs, Controls Differentiation

Investigators at Singapore’s Institute of Bioengineering and Nanotechnology announced last week that they have developed a cell culture gel that can undergo thixotropy, or liquefy on demand when it is subjected to a moderate shear force, and can resolidify within one minute after that force is removed.
“When a shear stress is applied to the gel, for example by vortexing, the gel liquefies,” Andrew Wan, a team leader and principal scientist at IBN told CBA News this week via e-mail. “At this stage, cells can be added. Within a minute or so, the liquid reverts back to a solid state, and the cells are effectively trapped in 3D culture.”
The gel is synthesized at room temperature from a silica and polyethylene glycol composite, or PEG. According to the researchers, good permeability of gases and nutrients through the gel facilitates cell proliferation and viability for up to three weeks.
The gel is appropriate for culturing all types of cells, even those considered difficult to culture, such as stem cells. In addition, researchers were able to control the gel’s rheological properties, thus facilitating the differentiation of stem cells into specific cell types. Cells cultured in the PEG-silica gel secreted extracellular matrix proteins, in particular fibronectin and collagen. The secretion of ECM proteins increased matrix stiffness over time. 
The scientists, whose study appears in the Sept. 28 online edition of Nature Nanotechnology, reported that human mesenchymal stem cells cultured in stiffer gels developed “bone-like” behavior.
Unlike other matrices, the gel does not require chemical, enzymatic, or photo-crosslinking, or changes in ionic strength or temperature for gelation to occur, said Wan. Therefore, trypsin, a protease known to damage cells, and especially stem cells, is not required to detach the cultured cells from the solid media.  
Wan said his team is “open to both licensing and commercialization of this technology on our own or with a partner.”
A New Dimension
A number of research groups are looking to move cell culture in the direction of 3D. “The 3D environment is clearly the direction of the future” because nearly all cell types in nature are in 3D, Jonathan Dordick, director of the Center for Biotechnology & Interdisciplinary Studies at Rensselaer Polytechnic Institute, told CBA News this week via e-mail.
For example, last December, a team of researchers from Rensselaer Polytechnic Institute, the University of California at Berkeley, and Solidus Biosciences, including Solidus co-founder Dordick, announced that they had developed a miniaturized 3D cell culture array to enable high-throughput screening of drug candidates, cosmetics, and chemicals, as well as their cytochrome p450-generated metabolites (see CBA News, 12/21/07). The array is called the DataChip.
Last November, tissue engineering shop RegeneMed announced that it had developed a 3D liver tissue surrogate for ADME/Tox testing that could offer pharmaceutical companies long-term predictive cell life and human functionality (see CBA News, 11/9/07).
Scalability remains a concern, however. “At large scale, difficulty in transporting nutrients, including oxygen, to the cells in the middle may be limiting,” Dordick said. “On small scale (such as our 3D DataChip), the key is to integrate the 3D matrix with the support material.”
In terms of the future direction of the IBN investigators’ work, Wan said that they would like to develop applications for their gel, particularly in vitro models for drug development.
“We believe that the gel will make 3D cell culture a lot more convenient and help to popularize such assays for drug testing and development,” he said.

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