The Center for Alternatives to Animal Testing is an academic center affiliated with the Division of Toxicological Sciences in the Department of Environmental Health Sciences of the Johns Hopkins University Bloomberg School of Public Health.

 

Johns Hopkins School of Public Health

Commemorative Booklet for CAAT 20th Anniversary Symposium

Tissue Engineering Liver in a Novel Multi-coaxial Hollow-Fiber Bioreactor

Jeffrey M. Macdonald1, Stephen P. Wolfe1, Edward Hsu1, Bhupender Gupta2, Ajit Moghe2 and Lola M. Reid3
1University of North Carolina, Chapel Hill; 2North Carolina State University, Raleigh; 3Duke University, Durham

We are tissue engineering liver using the body's natural tissue-replacing cells, progenitors, for toxicity testing. Tissue engineering is a new field combining cell biology and engineering. The liver is the organ primarily responsible for metabolizing toxicants and is the main port of entry for toxicants and especially drugs. We combine concepts in stem cell biology and cell signal pathways (hormones, paracrine, and autocrine factors), with a bioengineering analytical tool (magnetic resonance spectroscopy (MRS)) and a bioengineered device (a hollow-fiber bioreactor).

We isolate progenitors and culture them in a multi-coaxial hollow-fiber bioreactor perfused with media and extracellular matrix containing the molecules that elicit signal pathways common to progenitors in vivo.

A multi-coaxial bioreactor is composed of four tubes of increasing diameter placed one inside the other, creating four spatially isolated compartments. Liver acinar structure and physiological parameters are mimicked by sandwiching cells in the space between the two innermost semi-permeable tubes, or hollow fibers, and creating radial flow of media from an outer compartment (ECC), through the cell mass compartment, and to an inner compartment (ICC). The outermost compartment is created by gas permeable tubing and the housing; it is used to oxygenate the perfusion media in the ECC to periportal levels.

The coaxial fibers mimic the very small physiological unit of the liver, the liver lobule. Therefore, we call this a "bioartificial liver lobule." The theoretical optimum hydraulic permeability for the two innermost semi-permeable membranes was determined based on physiological hepatic sinusoidal blood flow and pressures. Experimental studies using flow-rate and pressure-monitoring systems in conjunction with phase-contrast, velocity-encoded MRI confirmed theoretical results. Dead-ended and cross-flow configurations were compared, and the latter was best in minimizing membrane fouling. Novel woven vascular tubes with optimum hydraulic permeability are presently being investigated for culturing hepatocytes in the multicoaxial bioreactor.