Engineering colloidal assembly via biological adhesion
Abstract
Due to highly specialized recognition properties, biological receptor-ligand interactions offer valuable tools for engineering the assembly of novel colloidal materials. A unique sub-class of these macromolecules, called selectins, was exploited to develop binary suspensions where particles are programmed to associate reversibly or irreversibly via specific biomolecular cross-linking. Flow cytometry and videomicroscopy were used to examine factors controlling suspension assembly and structure, including biomolecular affinity and density, and individual and total particle volume fractions. By functionalizing small (RA = 0.47 μm) and larger (RB = 2.75 μm) particles with high surface densities of complementary E-selectin/sialyl Lewis X (sLeX ) carbohydrate chemistry, a series of structures, from colloidal micelles (large particle coated with smaller particles) and clusters, to rings and elongated chains, was synthesized by decreasing the number ratio, NA /NB , of small (A) to large (B) particles (2 ≤ NA /NB ≤ 200) at low total volume fraction (10-4 ≤ [straight phi]T ≤ 10-3 ). Using significantly lower surface densities, the low affinity binding between E-selectin and sLeX was exploited to create particles that interact reversibly, and average particle interaction lifetimes were tuned from minutes down to single selectin-carbohydrate bond lifetimes ([approximate]1 s) by reducing sLeX density, a significant step toward assembling ordered microstructures. Particle binding lifetimes were analyzed with a receptor-ligand binding model, yielding estimates for molecular parameters, including on rate, 10-2 s-1 < kon < 10-1 s-1 , and unstressed off rate, 0.25 s-1 ≤ [Special characters omitted.] ≤ 1.0 s-1 , that characterize the docking dynamics of particles. Finally, at significantly higher volume fraction ([straight phi] T ≥ 10-1 ) and low number ratio, the rheology of space-filling networks crosslinked by high affinity streptavidin-biotin chemistry was probed to acquire knowledge on bulk properties of biocolloidal suspensions. Flow curves (apparent viscosity (η) versus shear rate ([Special characters omitted.] )) exhibited non-Newtonian behavior, and the viscosity and extent of shear thinning increased with an increase in total volume fraction. Micrographs suggest that shear thinning originated from a breakdown of the binary network into smaller flocs, and ultimately a fluid-like suspension, with increasing shear rate. With such remarkable control over particle interactions, biologically-mediated colloidal assembly holds promise for engineering new materials with biophysically tunable properties and applications.
Subject Area
Chemical engineering,Materials science,Biomedical research
Recommended Citation
Amy Lynn Hiddessen,
"Engineering colloidal assembly via biological adhesion"
(January 1, 2003).
Dissertations available from ProQuest.
Paper AAI3087411.
http://repository.upenn.edu/dissertations/AAI3087411
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