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 Serviços 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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