Fractals support growing organs

Today scientists can regenerate tissue such as skin, but they are still figuring out how to grow replacement organs. The challenge is in coaxing cells from organs to grow into new organs rather than unstructured clusters of cells.

Researchers from Harvard Medical School, Massachusetts General Hospital and the Massachusetts Institute of Technology have found a way to impart structure to growing cells that may eventually allow for growth of entire organs.

If the method proves successful, "we can use [a] patient's own cells to create a living organ and this will remove the problems with organ rejections" and a shortage of donor organs, said Mohammed Kaazempur-Mofrad, a researcher at MIT and a senior research fellow at Harvard Medical School and Massachusetts General Hospital. This ultimate goal is still far away, he added.

Key to the method is supporting the growing cells with something akin to the circulatory system, which provides cells with oxygen and nutrients. "In order to make living replacements for large vital organs such as the liver and kidney, it is essential to integrate the creation of vasculature with the tissue engineering," said Kaazempur-Mofrad. And the growth of these vascular networks has to be highly controlled and precise, he said.

The researchers used computer-generated fractal patterns to fabricate a network of branching, microscopic tubes. Fractals are patterns that repeat at different scales. If, for instance, one portion of a fractal looks like a tree, zooming in on its branches and twigs will show that they also look like trees, and zooming further will show that their branches and twigs follow the same pattern.

These self-similar patterns are common in nature, including natural blood vessel networks, and can scale up or down in size. "Using [the] fractal concept will make it easier to mimic... nature and also to scale up our designs from one animal to another," said Kaazempur-Mofrad.

The researchers used computer chip manufacturing techniques to precisely etch the patterns onto silicon wafers to form a mold. "Microfabrication... provides a platform to generate such vascular networks with submicron, exquisite precision," Kaazempur-Mofrad said.

They used the patterned wafers to make microfluidic channels from biodegradable, biocompatible polymers, then stacked the networks to form a three-dimensional framework for growing cells.

The researchers' experiments using the prototypes showed that the frameworks can supply oxygen and nutrients to human kidney and liver cells. Ninety-six percent of the kidney cells were viable at the end of a one-week experiment and and 95 percent of the liver cells were viable at the close of a two-week experiment.

The work spans many disciplines -- it "brings together mechanical engineering, microfabrication, materials science and polymer processing, biotechnology, biology, and medicine," said Kaazempur-Mofrad.

The researchers are aiming to evaluate and characterize the method in animals within five years, said Kaazempur-Mofrad.

Kaazempur-Mofrad's research colleagues were Jeffrey T. Borenstein from Charles Stark Draper Laboratory, Wing S. Cheung, Lauren M. Hartman, Michael Y. Shin, and Joseph P. Vacanti of Harvard Medical School and Massachusetts General Hospital and Eli J. Weinberg of the Massachusetts Institute of Technology (MIT) and Charles Stark Draper Laboratory. They presented the research at the American Society for Microbiology (ASM) Conference on Bio-, Micro-, Nanosystems build in New York City on July 7 to 10. The research was funded by MIT and the Defense Advanced Research Projects Agency (DARPA).

Timeline:   5 years
Funding:   Government, University
TRN Categories:   Biotech; Materials Science and Engineering; Applied Technology
Story Type:   News
Related Elements:  Technical paper, "Microfabricated Microfluidic Biodegradable Systems for Vascularized Tissue Engineering of Vital Organs: Design, Modeling and Functional Testing," American Society for Microbiology (ASM) conference on Bio-, Micro-, Nanosystems, July 7-10, New York City.