Microscale Liver and Bone Marrow Tissue Engineering

Many therapeutic applications of tissue engineering involve disease processes that might be prevented or treated if better drugs were available or if the processes could be better understood. Animal models, although they provide great insight into human disease, sometimes fall short of capturing the full spectrum of human pathologies and responses to therapy and are not readily adaptable to high throughput studies. Cell culture models, although high throughput, often fail to replicate physiological processes adequately. For example, liver cells lose their susceptibility to hepatitis infection and many aspects of drug metabolism when they are taken from the body and placed in culture. We are thus developing microscale 3D tissues in order to capture higher order physiological behavior of human tissues in vitro in a reasonably high throughput format.

One application area is development of physiological models of liver. The in vivo microenvironment of hepatocytes includes signaling mechanisms mediated by cell-cell and cell-matrix interactions, soluble factors, and mechanical forces. In an attempt to mimic key facets of the in vivo microenvironment, we have developed a microfabricated bioreactor system that fosters three dimensional tissue morphogenesis under continuous perfusion conditions. A key feature of the bioreactor is the distribution of cells into many tiny (~0.001 cm 3) tissue units that are relatively uniformly perfused with culture medium. The total mass of tissue in the system is readily adjusted for applications requiring only a few thousand cells to those requiring over a million cells by keeping the microenvironment the same and scaling the total number of tissue units. We are currently conducting fundamental studies characterizing cell dynamics and liver-specific gene expression as a function of several system parameters, and using and modifying the system for a range of applications including prediction of drug toxicity, evaluation of liver responses to environmental toxins, and models of cancer metastasis.

A second application area is development of in vitro models for assessment of toxicity in the hematopoietic system. Here, we are employing an in vitro erythropoiesis culture system developed by the Lodish lab, and attempting to build a quantitative model of responses to agents that damage DNA, such as chemotherapeutic drugs.