Researchers Find New Method to Grow Tissues

Originally Published MDDI January 2004

R&D DIGEST

Erik Swain

Using a biodegradable polymer scaffold, engineers at the Massachusetts Institute of Technology (Cambridge, MA) say they have forged a new approach to tissue engineering. It could eventually lead to tissues being grown for therapeutic applications and replacement organs. 

The MIT team seeded human embryonic stem cells, which could eventually differentiate into various specialized cells, onto the scaffold. They then treated the structure with chemical cues known to stimulate the formation of specific cell types. These chemicals included retinoic acid, transforming growth factor, activin-A, and insulin-like growth factor. As a result, the stem cells formed tissues with characteristics of human cartilage, livers, nerves, and blood vessels. 

In a paper published on the on-line version of the Proceedings of the National Academy of Sciences, the team said this marked “the first time that polymer scaffolds ...promoted proliferation, differentiation, and organization of human embryonic cells into 3-D structures.”

Previously, researchers used one batch of stem cells to create a variety of cell types. They then would isolate the cell type of interest and grow the isolated cells on a polymer scaffold or other medium. 

What's different about the MIT project is that researchers seeded stem cells directly into the scaffold. “We found that with different growth factors, we could push them in different directions,” says project team member Shulamit Levenberg, a research associate in MIT's department of chemical engineering. “For me it was very exciting to see that these cells could move around and start to ‘talk' with one another, generating the different cell types common to a different tissue and organizing into that tissue.”

The technique could have implications for studying cell and developmental biology. “When you give cells a three-dimensional structure [on which to grow], it's really a lot more like what's happening in the embryo,” says Levenberg.

The team characterized the structures as “a supportive 3-D environment such as poly(lactic-co-glycolic acid)/poly(L- lactic acid) polymer scaffolds.” Their paper added that the scaffold “provides physical cues for cell orientation and spreading, and pores provide space for remodeling of tissue structures.”

Engineering the scaffolds was a major effort. “If the scaffold is too soft, it collapses under the cells' mechanical forces,” Levenberg says. She notes that the two polymers used degrade at different paces because “that gives cells room to grow while still retaining a support structure for them.”

Collaborating with Levenberg are Robert S. Langer, DSc., an MIT professor of chemical and biochemical engineering; Ngan F. Huang, a 2002 MIT alumna; Erin Lavik, PhD, assistant professor of biomedical and chemical engineering at Yale University (New Haven, CT); Arlin B. Rogers, DVM, PhD, of MIT's division of comparative medicine; and Joseph Itskovitz-Eldor, MD, D Sc., director of the obstetrics and gynecology department at Rambam Medical Center & The Faculty of Medicine, Technion (Haifa, Israel). 

The research has been supported by the National Institutes of Health, and the stem cells used in the experiments come from an NIH-approved line.

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