SESSION 8

CRYOBIOLOGY - II

Chairman: H. Ishiguro


A MODEL OF LOW-TEMPERATURE WATER TRANSPORT FOR
HEPATOCYTE SPHEROIDS1

Brian Korniski and Allison Hubel2

Biomedical Engineering Center, Department of Laboratory Medicine and Pathology, University of Minnesota, Minneapolis, MN 55455, USA

ABSTRACT

Spheroids are multicellular aggregates that exhibit a more tissue- like morphology and function when compared to monolayer cultures of the same cells. Hepatocyte spheroids are presently under investigation for use in an artificial liver. The ability to cryopreserve hepatocyte spheroids is essential for their clinical and commercial application. A multicompartment model was formulated to predict water content as a function of temperature during freezing. The theoretical predictions of water transport indicate that there will be spatial differences in water content of the spheroid during freezing and that due to the rapid decrease in water transport with decreasing temperature, the undercooling of the intracellular solution during freezing will increase steadily. These results indicate that conventional freezing of hepatocyte spheroids will be difficult to accomplish due to transport limitations in the spheroids.


1 This work was supported in part by a grant from the National Institutes of Health (GM-54886). B.K. was supported by an NSF training grant (BIR-9413241).
2 Address for correspondence: Department of Laboratory Medicine & Pathology, Box 609 UMHC, 420 Delaware Street SE, Minneapolis, MN 55455. Phone, 612/626-4451;
fax 612/625-1121; e-mail, hubel001@tc.umn.edu

NETWORK THERMODYNAMIC MODEL OF COUPLED TRANSPORT
IN A MULTICELLULAR TISSUE - THE ISLET OF LANGERHANS

Robson C. de Freitas1, Kenneth R. Diller, Charles A. Lachenbruch and Fatima A. Merchant2
The University of Texas at Austin, Biomedical Engineering Program, Austin, Texas 78712-1084
1currently with Enron Servišos do Brasil Ltda., Sao Paulo, Brazil
2currently with Perceptive Scientific Instruments, Inc, League City, Texas

ABSTRACT

Network thermodynamic modeling via bond graphs was used to describe the water and cryoprotectant (CPA) transport in a multicellular tissue. The model is presented as a tool to understand the osmotic behavior of the islets of Langerhans when exposed to ternary aqueous solutions containing an electrolyte and a CPA. It accounts for the positioning of cells within the tissue and an interstitial matrix, plus differential permeabilities to water and CPA. The interstitial matrix was assumed to be a porous medium able to store the chemical species being transported. Controlled osmotic stress experiments were conducted on isolated rat pancreas islets to measure the transient volumetric response to step-wise changes in DMSO concentrations. The model provides a tool for predicting the transient volumetric response of peripheral and interior cells ,and of interstitial compartments as well as the build up of internal solute concentrations during addition and removal of CPAs and freezing and thawing protocols. Inverse solutions methods were applied to determine values for standard cell membrane permeability parameters Lp, w and s as well as for the interstitial flow conductivities KW and Kp .

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