Rosette-induced separation of T cells by acoustophoresis.

Breakthrough cell therapies for the treatment of cancers require the separation of specific cells, such as T cells, from the patient's blood. Current cell therapy processes rely on magnetic separation, which adds clinical risk and requires elevated manufacturing controls due to the added foreign material that constitutes the magnetic beads. Acoustophoresis, a method that uses ultrasound for cell separation, has demonstrated label-free enrichment of T cells from blood, but residual other lymphocytes limit the ultimate purity of the output T cell product. Here, to increase the specificity of acoustophoresis, we use affinity reagents to conjugate red blood cells with undesired white blood cells, resulting in a cell-cell complex (rosette) of increased acoustic mobility. We achieve up to 99% purity of T cells from blood products, comparable to current standards of magnetic separation, yet without the addition of separation particles.

Spinodal decomposition in a model colloid-polymer mixture in microgravity.

We study phase separation in a deeply quenched colloid-polymer mixture in microgravity on the International Space Station using small-angle light scattering and direct imaging. We observe a clear crossover from early-stage spinodal decomposition to late-stage, interfacial-tension-driven coarsening. Data acquired over 5 orders of magnitude in time show more than 3 orders of magnitude increase in domain size, following nearly the same evolution as that in binary liquid mixtures. The late-stage growth approaches the expected linear growth rate quite slowly.

Time-dependent strength of colloidal gels.

Colloidal silica gels are shown to stiffen with time, as demonstrated by both dynamic light scattering and bulk rheological measurements. Their elastic moduli increase as a power law with time, independent of particle volume fraction; however, static light scattering indicates that there are no large-scale structural changes. We propose that increases in local elasticity arising from bonding between neighboring colloidal particles can account for the strengthening of the network, while preserving network structure.

Limits to gelation in colloidal aggregation.

We show that the dynamics of large fractal colloid aggregates are well described by a combination of translational and rotational diffusion and internal elastic fluctuations, allowing both the aggregate size and internal elasticity to be determined by dynamic light scattering. The comparison of results obtained in microgravity and on Earth demonstrates that cluster growth is limited by gravity-induced restructuring. In the absence of gravity, thermal fluctuations ultimately inhibit fractal growth and set the fundamental limitation to the lowest volume fraction which will gel.