Behind the Cover: June 2021

Each month, Physics Today editors explore the research and design choices that inspired the latest cover of the magazine.

The research: In our bodies, cell migration is crucial to immune response and tissue self-renewal. During embryo development, for instance, cells move in groups to properly position organs and tissues. And well after birth, those movements continue to shape organs and facilitate wound healing. Collective cell migration may be most dramatic in the inner surface of the gut—the fastest self-renewing tissue in mammals.

The light micrograph on this month’s cover shows a thin cross section of finger-like projections—villi—in the duodenum, the uppermost part of the intestine. The duodenum renews itself every three to five days, as epithelial cells move from the bottom of the villi to the top. Once there, they detach themselves and enter the intestine.

The villi increase the intestine’s surface area so the digestive tract can absorb nutrients. In the columnar epithelium of the villi’s outer surfaces (blue) are goblet cells (yellow) that secrete mucus to lubricate the nutrient particles and prevent their self-digestion. The central core of the villi houses the blood supply that transports the products of digestion. So-called Brunner’s glands sit below the villi and secrete an alkaline fluid that protects the intestine’s mucus membrane from acidic stomach contents entering the duodenum. For more on collective cell migration in living tissue, see the article by Ricard Alert and Xavier Trepat.

Cover design: The editorial and art teams sought an image for the June cover to highlight the issue’s special focus on biophysics (see the box). They selected a micrograph that not only relates to a topic in Alert and Trepat’s article on collective cell migration but also evokes that cellular motion. What’s more, the image offers visual variety: Multiple layers of cells are shown in a range of vibrant, albeit false, colors. Because the top of this month’s cover was white, it gave the art team the opportunity to match the lettering of the Physics Today logotype to part of the villi. For the main cover line, “Collective cell migration,” the art team paired bold and demi Adobe Rift Soft fonts in different sizes to echo the shapes, densities, and layers in the image.