Mass Transport of Cryoprotectants in a Tissue Engineered Pancreatic Substitute

Vitrification, an ice-free cryopreservation approach utilizing high concentrations of cryoprotectants (CPAs), has the potential to be more effective than ice-assisted conventional freezing. The characterization of CPA transport through tissues is critical for finding the balance between equilibration and exposure time. Adequate CPA equilibration confers protection during freezing; however, excessive exposure results in cytotoxic death. In this work, a two-compartment mathematical diffusion model was developed to incorporate solute transport through the tissue matrix and across the cell membrane. In particular, this was carried out for a spherical construct that describes CPA transport of a single component through a model tissue engineered pancreatic substitute consisting of murine insulinomas (bTC-tet cells) encapsulated in alginate beads. CPA loading and removal were simulated in a stepwise manner to minimize the cytotoxic effects of CPAs to cells as well as to keep the cell volume excursions within their osmotic tolerances. Currently, a more thorough mathematical model is being developed that uses the Maxwell-Stefan equation to incorporate multi-component CPA diffusion through 3-D tissues (e.g., cartilage plugs and blood vessels) for long-term storage by vitrification.