This CAREER Award by the Biomaterials program in the Division of Materials Research, and co-funded by the Nano-Biosensors Program in the Division of Chemical, Bioengineering, Environmental and Transport Systems (ENG/CBET) to the University of Pennsylvania, is to study the self-assembly of a class of proteins found in molluscan animals. Mollusks are animals such as squids, octopuses, slugs, clams and oysters. Many of these animals are strikingly iridescent, and this iridescence is used for camouflage, for signaling, and in the case of giant clams, for optimization of photosynthesis with symbiotic algae. This project seeks to understand the evolution of these iridescent structures, and to understand how their structures emerge from the proteins that make them. To do this, the PI will use a unique combination of insights from oceanographic animal collections, materials characterization techniques, and molecular dynamics modeling. The hierarchically ordered complexity of these structures often far exceeds the current capabilities of synthetic fabrication, so understanding how animals make these optical materials will provide insight into fabrication of materials with hierarchical length scales smaller than a micron. The education and research activities of this project are well integrated with the PI playing a leading role in developing an introductory physics for life sciences curriculum (IPLS) which is a core need in the Department of Physics at UPenn. Graduate students will receive highly interdisciplinary training in cutting-edge materials characterization techniques as well as biochemistry and biological field work. This award will also fund summer internship for high school students in the Philadelphia public schools who have been identified as scientifically talented via their participation in the University of Pennsylvania's summer physics camp. The goal of these internships is to provide opportunities for research experiences and practical knowledge that help make these students competitive for admission to highly selective colleges and universities. The ultimate goal is to be able increase the number of students interested in STEM careers.
Molluscan animals such as squids, octopuses and clams build an array of living optical devices of astounding optical/photonic sophistication and complexity, such as structural camouflaging coatings, graded index lenses, solar radiance distributors, and wavelength-specific light guides. Unlike the iridescent structures in fish, butterflies and birds, the "iridocytes" in molluscs are formed from still-living cells, with the high-index portions generated by dense assemblies of protein in the active cytoplasm. These optically resonant cells seem to be allowed more structural diversity than systems in other taxa, and have evolved to solve a wider array of evolutionary optical problems than in any other animal group, such as underwater vision, emissive camouflage, reflective camouflage, and distribution of light for efficient photosynthesis. Several new observations about reflectin proteins and S-crystallins from squids show that "patchy colloids" is the most informative theoretical paradigm for understanding assembly of these living photonic systems. This project will use molecular dynamics modeling, structural characterization, and oceanographic collection to describe whether and how the constituent reflectin proteins making these living photonic systems self-assemble into the observed biophotonic structures.
