6 research outputs found
Static and Dynamic Permeability Assay for Hydrophilic Small Molecules Using a Planar Droplet Interface Bilayer
Because
numerous drugs are administered through an oral route and
primarily absorbed at the intestine, the prediction of drug permeability
across an intestinal epithelial cell membrane has been a crucial issue
in drug discovery. Thus, various <i>in vitro</i> permeability
assays have been developed such as the Caco-2 assay, the parallel
artificial membrane permeability assay (PAMPA), the phospholipid vesicle-based
permeation assays (PVPA) and Permeapad. However, because of the time-consuming
and quite expensive process for culturing cells in the Caco-2 assay
and the unknown microscopic membrane structures of the other assays,
a simpler yet more accurate and versatile technique is still required.
Accordingly, we developed a new platform to measure the permeability
of small molecules across a planar freestanding lipid bilayer with
a well-defined area and structure. The lipid bilayer was constructed
within a conventional UV spectrometer cell, and the transport of drug
molecules across the bilayer was recorded by UV absorbance over time.
We then computed the permeability from the time-dependent diffusion
equation. We tested this assay for five exemplary hydrophilic drugs
and compared their values with previously reported ones. We found
that our assay has a much higher permeability compared to the other
techniques, and this higher permeability is related to the thickness
of the lipid bilayer. Also we were able to measure the dynamic permeability
upon the addition of a membrane-disrupting surfactant demonstrating
that our assay has the capability to detect real-time changes in permeability
across the lipid bilayer
Structural Determinants of Chirally Selective Transport of Amino Acids through the α‑Hemolysin Protein Nanopores of Free-Standing Planar Lipid Membranes
Despite the importance of the enantioselective
transport
of amino
acids through transmembrane protein nanopores from fundamental and
practical perspectives, little has been explored to date. Here, we
study the transport of amino acids through α-hemolysin (αHL)
protein pores incorporated into a free-standing lipid membrane. By
measuring the transport of 13 different amino acids through the αHL
pores, we discover that the molecular size of the amino acids and
their capability to form hydrogen bonds with the pore surface determine
the chiral selectivity. Molecular dynamics simulations corroborate
our findings by revealing the enantioselective molecular-level interactions
between the amino acid enantiomers and the αHL pore. Our work
is the first to present the determinants for chiral selectivity using
αHL protein as a molecular filter
Fluorescence Recovery after Merging a Surfactant-Covered Droplet: A Novel Technique to Measure the Diffusion of Phospholipid Monolayers at Fluid/Fluid Interfaces
We
present a novel technique to measure diffusion coefficients
of insoluble surfactant monolayers.
We merge a surfactant-coated droplet with a fluorescently labeled
planar monolayer. During the merging process, a monolayer on a droplet
displaces the existing planar monolayer, leaving a dark area when
viewed under a fluorescence microscope. We measure fractional intensities
as the dyes recover, which allows diffusion coefficients to be computed.
We validate this technique with the two most common phospholipid monolayers
(DPPC and DOPC) and study the diffusion of their mixtures. The proposed
technique has several advantages over the FRAP technique and is potentially
capable of measuring the diffusion of any soluble/insoluble surfactant
monolayers
Removal Analysis of Residual Photoresist Particles Based on Surface Topography Affected by Exposure Times of Ultraviolet and Developer Solution
Particle removal from the surface of a substrate has
been an issue
in numerous fields for a long time. In semiconductor processes, for
instance, the formation of clean surfaces by removing photoresist
(PR) must be followed in order to create neat patterns. Although PR
removal has been intensively investigated recently, little is known
about how ultraviolet (UV) and developer solutions alter the PR resin
(and in what manner) near the surface. While varying the exposure
times of UV and developer solution, we investigated the topographic
changes on the surfaces of PR resin films and particles. The measured
surface properties were then correlated with the detachment force
determined using films, and eventually with the residual PR particle
removal percentages obtained in a microchannel. Using a positive PR
and a base developer solution, we demonstrated that UV causes the
surface of PR resin to become hydrophilic and wavy, whereas the developer
solution produces a surface with a larger degree of roughness by swelling
and partially dissolving the resin. Ultimately, the increased roughness
decreased the effective contact area between PR resins, hence decreasing
the detachment force and increasing the particle removal percentages.
We anticipate that our findings will help understand residual particle
issues, particularly on the removal mechanism of PR resins based on
surface topography
Thermally Fast-Curable, “Sticky” Nanoadhesive for Strong Adhesion on Arbitrary Substrates
Demand
of adhesives that are strong but ultrathin with high flexibility,
optical transparency, and long-term stability has been rapidly growing
recently. Here, we suggest a thermally curable, “sticky”
nanoadhesive with outstanding adhesion strength accomplished by single-side
deposition of the nanoadhesive on arbitrary substrates. The sticky
nanoadhesive is composed of an ionic copolymer film generated from
two acrylate monomers with tertiary amine and alkyl halide functionalities,
formed by a solvent-free method, initiated chemical vapor deposition
(iCVD). Because of the low glass transition temperature (<i>T</i><sub>g</sub>) of the copolymer (−9 °C), the ionic copolymer
shows a viscoelastic behavior that makes the adhesive attachable to
various substrates, regardless of the substrate materials. Moreover,
the copolymer film is thermally curable via a cross-linking reaction
between the alkyl halide and tertiary amine functionalities, which
substantially increased the adhesion strength of the 500 nm thick
nanoadhesive greater than 25 N/25 mm within 5 min of curing at 120
°C. The adhesive thickness can further be reduced to 50 nm to
achieve greater than 35 N/25 mm within 30 min at 120 °C. The
nanoadhesive layer can form uniform adhesion in a large area substrate
(up to 130 × 100 mm<sup>2</sup>) with the deposition of the adhesive
only on one side of the substrates to be laminated. Because of its
ultrathin nature, the nanoadhesive is also optically transparent as
well as highly flexible, which will play a critical role in fabrication
and the lamination of future flexible/wearable devices
Thermally Fast-Curable, “Sticky” Nanoadhesive for Strong Adhesion on Arbitrary Substrates
Demand
of adhesives that are strong but ultrathin with high flexibility,
optical transparency, and long-term stability has been rapidly growing
recently. Here, we suggest a thermally curable, “sticky”
nanoadhesive with outstanding adhesion strength accomplished by single-side
deposition of the nanoadhesive on arbitrary substrates. The sticky
nanoadhesive is composed of an ionic copolymer film generated from
two acrylate monomers with tertiary amine and alkyl halide functionalities,
formed by a solvent-free method, initiated chemical vapor deposition
(iCVD). Because of the low glass transition temperature (<i>T</i><sub>g</sub>) of the copolymer (−9 °C), the ionic copolymer
shows a viscoelastic behavior that makes the adhesive attachable to
various substrates, regardless of the substrate materials. Moreover,
the copolymer film is thermally curable via a cross-linking reaction
between the alkyl halide and tertiary amine functionalities, which
substantially increased the adhesion strength of the 500 nm thick
nanoadhesive greater than 25 N/25 mm within 5 min of curing at 120
°C. The adhesive thickness can further be reduced to 50 nm to
achieve greater than 35 N/25 mm within 30 min at 120 °C. The
nanoadhesive layer can form uniform adhesion in a large area substrate
(up to 130 × 100 mm<sup>2</sup>) with the deposition of the adhesive
only on one side of the substrates to be laminated. Because of its
ultrathin nature, the nanoadhesive is also optically transparent as
well as highly flexible, which will play a critical role in fabrication
and the lamination of future flexible/wearable devices