An adsorption chromatography assay to probe bulk particle transport through hydrogels

Biopolymer-based hydrogels such as mucus and the basal lamina play a key role in biology, where they control the exchange of material between different compartments. They also pose a barrier that needs to be overcome for successful drug delivery. Characterizing the permeability properties of such hydrogels is mandatory for the development of suitable drug delivery vectors and pharmaceutics. Here, we present an experimental method to measure bulk particle transport through hydrogels. We validate our assay by applying it to mucin hydrogels and show that the permeability properties of these mucin hydrogels can be modulated by polymer density and pH, in agreement with previous results obtained from single particle tracking. The method we present here is easy to handle, inexpensive, and high-throughput compatible. It is also a suitable platform for the design and screening of drugs that aim at modifying the barrier properties of hydrogels. This system can also aid in the characterization and development of synthetic gels for a range of biomedical applications.National Institutes of Health (U.S.) (Grant P50-GM068763)National Institutes of Health (U.S.) (Grant P30-ES002109

Filling an Emulsion Drop with Motile Bacteria

We have measured the spatial distribution of motile Escherichia coli inside spherical water droplets emulsified in oil. At low cell concentrations, the cell density peaks at the water-oil interface; at increasing concentration, the bulk of each droplet fills up uniformly while the surface peak remains. Simulations and theory show that the bulk density results from a `traffic' of cells leaving the surface layer, increasingly due to cell-cell scattering as the surface coverage rises above $\sim 10\%$. Our findings show similarities with the physics of a rarefied gas in a spherical cavity with attractive walls.Comment: 5 pages, 4 figures, Supporting Information (5 pages, 5 figures

Comparing Skill Acquisition Under Varying Onsets of Differential Reinforcement: A Preliminary Analysis

The purpose of the current study was to evaluate the effect of implementing differential reinforcement at different times relative to the onset of teaching new skills to learners with autism spectrum disorder. Specifically, we first determined the most efficient differential reinforcement arrangement for each participant. Using the most efficient arrangement, we evaluated if differential reinforcement from the immediate onset, early onset, or late onset is the most efficient for learners to acquire a new skill. Three children diagnosed with autism spectrum disorder who have a history of receiving intervention based on the principles of applied behavior analysis participated in this study. The immediate onset of differential reinforcement resulted in the most efficient instruction in 6 of 7 comparisons. The results are discussed in light of previous studies and suggestions for future research are provided