(609f) Calcium-Phosphate Supraparticle Assembly Is Influenced By Both Intermolecular Forces and Fluid Dynamics

Authors: 
Caparco, A. A., Georgia Institute of Technology
Bommarius, A. S., Georgia Institute of Technology
Champion, J. A., Georgia Institute of Technology
The formation of hierarchical composite materials is ubiquitous in nature. Colloidal interactions between nanostructures can lead to complex micro- and macrostructures with internal pore networks, enhanced physical properties, and order on many scales. A mixture of calcium, phosphate, and protein leads to self-assembly of nanocomposites. However, these samples are often polydisperse and loosely ordered. We previously reported that an end-over-end rotation of such mixtures with contraction of the air-water interface can form microparticles with a regular structure. So-called supraparticles are composed of calcium-phosphate and a leucine zipper binding protein, which allows for the specific immobilization of proteins with the complementary binding domain.

Building off this work, we have uncovered the parameter space for the formation of uniform particles. Using microscopy and a specific binding assay, we sought to identify conditions for supraparticle formation to better understand the self-assembly process. The reaction medium composition was varied via component concentrations, ionic strength, and pH in a 3x3x3 Design of Experiment matrix. Once the conditions with supraparticle morphology were uncovered, the effects of additives such as DMSO and glycerol were tested, demonstrating the influence of viscosity and hydrogen bonding on the formation of supraparticles. With the ideal composition of reagents in the solution for particle formation, we elucidated the effects of tube geometry and flow regime on the output. Scalability of the synthesis procedure was considered using dimensional analysis. The supraparticles created here can be applied to immobilized enzyme systems, where a scalable material with predictable binding behavior would be preferred for a reactor.