Bioengineering Single Crystal Growth

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Non-technical abstract: Optimized during hundreds of millions of years of evolution, biomineralized tissues frequently display an extraordinary level of performance. Bone, for example, displays high toughness at low weight and is capable of self-repair; some invertebrate teeth self-sharpen despite continuous wear. Organisms typically form these materials under mild conditions through environmentally sustainable processes, making them appealing targets for bio-inspired or bio-enabled syntheses. Despite the abundance of such materials in nature, many biological mechanisms that allow the organism to control their formation remain poorly understood. As a model organism, sea urchins exert remarkable control over mineralization, creating smoothly curving and branched, yet single crystalline endoskeletal spicules of calcium carbonate (CaCO3). Previously, the team designed an in vitro culture system of sea urchin embryo primary mesenchyme cells (PMCs) to control the growth of these spicules in the laboratory. They discovered that a signaling protein, VEGF, controls the shape of spicules deposited by PMCs. The team will next probe the roles of a number of proteins that have been identified as potential crystal growth regulators in transcriptomics experiments. Techniques include, proteomics, in vitro assays in microfluidic droplet reactors, and knock-down experiments in vivo. In combination, these studies will lead to an improved understanding of biologically controlled mineralization. Poised at the intersection of molecular biology, materials science, and bioengineering, this research has the potential to inform a wealth of new technologies, from bio-inspired and bio-enabled materials to materials for carbon dioxide sequestration. The team will to leverage the interdisciplinary potential of this research to train undergraduate and graduate students from a broad range of backgrounds. An undergraduate research assistant will learn fundamental biological laboratory skills while also using advanced materials characterization techniques. Finally, the team will utilize instrumentation developed as part of a NSF Major Research Instrumentation grant to help undergraduate students visualize phase transformations in seawater, thus broadening the project?s reach to fundamental materials science education.Technical abstract: The proposed activities address gaps in the understanding of how living organisms control crystal growth processes, with the long-term objective to develop bio-inspired and bio-enabled materials. In prior work, the team discovered the role of VEGF signaling in branching of endoskeletal single crystals of calcite that are deposited by primary mesenchyme cells (PMCs) of the sea urchin embryo. Going forward, the team will use quantitative proteomics to confirm proteins that have been identified by transcriptomics as candidates involved in crystal growth control. Selected proteins will be produced recombinantly, and recombinant antibodies (rAbs) will be raised against them. rAbs will be used to map proteins across the spicule deposition vesicle and the spicule itself. In parallel, the team will use existing microfluidic devices to dissect the impact of native and recombinant proteins, individually and collectively on nucleation, polymorph selection, and crystal growth. Finally, the team will complement these experiments with functional analyses in vivo. Taken together, the team expects to develop a detailed mechanistic understanding of how expression of the relevant proteins, localization in the spicule matrix, and impact on nucleation kinetics and crystal growth may be connected. This is an important first step towards translating key molecular players into a system that is more easily engineered and scaled up, using the tools of synthetic biology for materials processing. The team will thereby address all four challenges in hard materials identified in the Report on the 2012 NSF Biomaterials Workshop. Complementary to the proposed research objectives, the team will engage undergraduates in research, incorporate research outcomes into undergraduate laboratory modules, and host high school interns through Northwestern University's Science in Society program.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.