4 research outputs found
Stochastic electrotransport selectively enhances the transport of highly electromobile molecules
Nondestructive chemical processing of porous samples such as fixed biological tissues typically relies on molecular diffusion. Diffusion into a porous structure is a slow process that significantly delays completion of chemical processing. Here, we present a novel electrokinetic method termed stochastic electrotransport for rapid nondestructive processing of porous samples. This method uses a rotational electric field to selectively disperse highly electromobile molecules throughout a porous sample without displacing the low-electromobility molecules that constitute the sample. Using computational models, we show that stochastic electrotransport can rapidly disperse electromobile molecules in a porous medium. We apply this method to completely clear mouse organs within 1â3 days and to stain them with nuclear dyes, proteins, and antibodies within 1 day. Our results demonstrate the potential of stochastic electrotransport to process large and dense tissue samples that were previously infeasible in time when relying on diffusion.Simons Foundation. Postdoctoral FellowshipLife Sciences Research FoundationBurroughs Wellcome Fund (Career Awards at the Scientific Interface)Searle Scholars ProgramMichael J. Fox Foundation for Parkinson's ResearchUnited States. Defense Advanced Research Projects AgencyJPB FoundationNational Institutes of Health (U.S.)National Institutes of Health (U.S.) (Grant 1-U01-NS090473-01
Study of the AirâWater Interfacial Properties of Biodegradable Polyesters and Their Block Copolymers with Poly(ethylene glycol)
It has been reported that the surface pressureâarea
isotherm
of polyÂ(d,l-lactic acid-<i>ran</i>-glycolic
acid) (PLGA) at the airâwater interface exhibits several interesting
features: (1) a plateau at intermediate compression levels, (2) a
sharp rise in surface pressure upon further compression, and (3) marked
surface pressureâarea hysteresis during compressionâexpansion
cycles. To investigate the molecular origin of this behavior, we conducted
an extensive set of surface pressure and AFM imaging measurements
with PLGA materials having several different molecular weights and
also a polyÂ(d,l-lactic acid-<i>ran</i>-glycolic acid-<i>ran</i>-caprolactone) (PLGACL) material
in which the caprolactone monomers were incorporated as a plasticizing
component. The results suggest that (i) the plateau in the surface
pressureâarea isotherm of PLGA (or PLGACL) occurs because of
the formation (and collapse) of a continuous monolayer of the polymer
under continuous compression; (ii) the PLGA monolayer becomes significantly
resistant to compression at high compression because under that condition
the collapsed domains become large enough to become glassy (such behavior
was not observed in the nonglassy PLGACL sample); and (iii) the isotherm
hysteresis is due to a coarsening of the collapsed domains that occurs
under high-compression conditions. We also investigated the monolayer
properties of PEG-PLGA and PEG-PLGACL diblock copolymers. The results
demonstrate that the tendency of PLGA (or PLGACL) to spread on water
allows the polymer to be used as an anchoring block to form a smooth
biodegradable monolayer of block copolymers at the airâwater
interface. These diblock copolymer monolayers exhibit protein resistance
Water Is a Poor Solvent for Densely Grafted Poly(ethylene oxide) Chains: A Conclusion Drawn from a Self-Consistent Field Theory-Based Analysis of Neutron Reflectivity and Surface PressureâArea Isotherm Data
By use of a combined experimental and theoretical approach,
a model
polyÂ(ethylene oxide) (PEO) brush system, prepared by spreading a polyÂ(ethylene
oxide)âpolyÂ(<i>n</i>-butyl acrylate) (PEOâPnBA)
amphiphilic diblock copolymer onto an airâwater interface,
was investigated. The polymer segment density profiles of the PEO
brush in the direction normal to the airâwater interface under
various grafting density conditions were determined by using the neutron
reflectivity (NR) measurement technique. To achieve a theoretically
sound analysis of the reflectivity data, we used a data analysis method
that utilizes the self-consistent field (SCF) theoretical modeling
as a tool for predicting expected reflectivity results for comparison
with the experimental data. Using this data analysis technique, we
discovered that the effective FloryâHuggins interaction parameter
of the PEO brush chains is significantly greater than that corresponding
to the θ condition in FloryâHuggins solutions (i.e.,
Ď<sub>PEOâwater</sub>(brush chains)/Ď<sub>PEOâwater</sub>(θ condition) â 1.2), suggesting that contrary to what
is more commonly observed for PEO in normal situations (Ď<sub>PEOâwater</sub>(free chains)/Ď<sub>PEOâwater</sub>(θ condition) â 0.92), the PEO chains are actually not
âhydrophilicâ when they exist as polymer brush chains,
because of the many body interactions that are forced to be effective
in the brush situation. This result is further supported by the fact
that the surface pressures of the PEO brush calculated on the basis
of the measured Ď<sub>PEOâwater</sub> value are in close
agreement with the experimental surface pressureâarea isotherm
data. The SCF theoretical analysis of the surface pressure behavior
of the PEO brush also suggests that even though the grafted PEO chains
experience a poor solvent environment, the PEO brush layer exhibits
positive surface pressures, because the hydrophobicity of the PEO
brush chains (which favors compression) is insufficient to overcome
the opposing effect of the chain conformational entropy (which resists
compression)