The Science Behind the Image Contest Winners: Bovine Knees Are Beautiful

This year’s winning entry in the BPS Art of Sciences Image Contest was submitted by Chiara Peres, a postdoctoral student at the Istituto Italiano di Tecnologia in Genoa.  The image shows collagen fibers in a radial section of an ex vivo bovine knee meniscus, which based on the votes, was a crowd pleaser among the BPS Meeting attendees.  Peres took some time to provide some information about the image and the science it represents.

Peres-Chiara-1st-placeTo produce this image, I used a custom made microscope for Second Harmonic Generation (SHG) Microscopy, a label free technique that exploits a second order nonlinear coherent optical process to image macromolecules with non-centrosymmetric structure, like collagen fibers. The picture is a mosaic of false colored images given by the overlay of the Backward and Forward SHG signal from the not-stained collagen fibers. In particular the image shows the big long branches of radial “tie” collagen fibers which pack together circumferential fibers, perpendicularly aligned with respect to the plane of the image.

I submitted this image because I love the hierarchical structure of the collagen and the harmonious branched, natural organization of the collagen fibers in this section of the meniscus that makes it to look like a big tree in a forest. I love also the fact that this image is “natural” and staining independent, being an image taken with a label-free technique, just collecting and false coloring the endogenous Second Harmonic Generation signal and the Two-Photon autofluorescence of the collagen, without any modification of the sample.

I also like this image because it is a good example of my research activity: I am working to improve and develop new microscopy techniques for biological applications. In particular I am using SHG microscopy as an imaging tool for morphological characterization. This image gives us an easy and immediate means to visualize at a glance the hierarchical structure, organization and orientation of collagen fibers in different areas of the bovine meniscus, the final aim of this study.

When others look at the image, I hope that this image reminds them of an expressionist painting of a forest, as if they were looking at a “micro Van Gogh” being, at the same time, an important method of tissue imaging which connects structures at the micro-scale to macroscopic properties.

Supporting Scientific Information

The cartilage meniscus regeneration after an injury is rarely successful, because the soft scaffolds used lack the mechanical properties to withstand immediate loading. For this reason a strong effort is being done in tissue engineering area to design and to develop a new scaffold that mimics the original tissue, selecting an appropriate material and paying close attention at its mechanical and structural properties. We are studying ex vivo bovine meniscus to realize a proper model for a meniscus scaffold. Our work provides insights on the link between microscopic organization of collagen in different areas of meniscus and its biomechanical macroscopic functions. These results offer, for example, precious guidance for tissue engineers to evaluate the good outcome of the artificial tissues.

In addition to tissue engineering applications, our work can be useful for medical applications. In fact collagen is essential for the biomechanical integrity and the physical properties of various biological tissues and organs. In this context SHG microscopy can be used for ex-vivo imaging of different kinds of collagenous tissues that have a crucial structural and mechanical role in organism. Not only collagen, but also the myosin presents in muscle sarcomeres is another biological macromolecules which generates second harmonic. So SHG microscopy can be used to visualize the organization of these macromolecules in tissue, giving a powerful tool to monitor tissue development and pathology diagnosis.

To learn more about this research, visit my website or LinkedIn profile.


Ice-Tissue Interactions: Minimizing Damage

bpj_105_9_coverThe 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