The latest Biophysical Journal cover image represents an important milestone in a lengthy scientific investigation into the causes of damage to multicellular tissue during freezing. My laboratory is elucidating the mechanisms of deleterious ice-tissue interactions, with the ultimate goal of making possible minimally damaging cryopreservation procedures for tissue engineered devices constructed from living cells. Our recent studies have focused on understanding how ice pervades tissue, and in particular, why the intracellular water crystallizes more readily in intact tissue (i.e., when cells are in contact with each other) than in cell suspensions (in which cells are isolated from each other). The work reported in our paper used adherent cell pairs as a simple model system, allowing us to investigate the effects of cell-cell interactions.  Through a combination of experimental and theoretical techniques, we were able to show that extracellular ice crystals can invade tissue constructs via paracellular pathways, and that such paracellular ice penetration is a precursor to intracellular freezing.

The cover image depicts the moment that the ice invades a microscale compartment at the cell-cell interface, by breaching a tight junction barrier.  The artwork was created in collaboration with medical illustrator Scott Leighton (Medicus Media), and is based on a detail from a larger illustration that he prepared for our paper. Coming up with an effective visual depiction of the hypothesized paracellular ice penetration mechanism was challenging, because the key events occur inside a three-dimensional volume that is obscured on all six sides (being surrounded by the two apposing cell membranes, by the culture substrate, by the extracellular ice, and by the intercellular junction proteins). We ultimately decided on a view that is a cross-sectional plane, cutting through the cell-cell interface. The rendering of the network of tight junction strands was inspired by scanning electron microscopy images from the literature. Because the morphology of transiently growing nanoscale ice is actually not known, the shape chosen for the growing ice bud is based on the appearance of larger (i.e., micrometer scale) ice dendrites that can be observed by cryomicroscopy.  We incorporated a subtle yellow gradient in front of the ice crystal interface to represent solutes in the liquid, which, together with the interfacial curvature, determine the temperature at which the crystal protrusion can advance. For the journal cover, I selected a zoomed-in view, in which the Biophysical Journal logotype would be balanced within the block of color representing ice.  Another aspect of the composition that I liked was the contrast between the symmetry of the upper part of the image and the asymmetry in the lower part.

My co-author (Adam Higgins, Oregon State University) and I are honored to have our work showcased on the cover of one of the top journals in the field.  We hope that the cover art will spur some curiosity about the complex biophysical processes that govern the response of cells and tissue to freezing.  Interested readers can learn more about this research at the web site of the Biothermal Sciences Laboratory at Villanova University.

--Jens Karlsson, Villanova University