5 research outputs found
Highly Stretchable and Transparent Microfluidic Strain Sensors for Monitoring Human Body Motions
We report a new class of simple microfluidic strain sensors with
high stretchability, transparency, sensitivity, and long-term stability
with no considerable hysteresis and a fast response to various deformations
by combining the merits of microfluidic techniques and ionic liquids.
The high optical transparency of the strain sensors was achieved by
introducing refractive-index matched ionic liquids into microfluidic
networks or channels embedded in an elastomeric matrix. The microfluidic
strain sensors offer the outstanding sensor performance under a variety
of deformations induced by stretching, bending, pressing, and twisting
of the microfluidic strain sensors. The principle of our microfluidic
strain sensor is explained by a theoretical model based on the elastic
channel deformation. In order to demonstrate its capability of practical
usage, the simple-structured microfluidic strain sensors were performed
onto a finger, wrist, and arm. The highly stretchable and transparent
microfluidic strain sensors were successfully applied as potential
platforms for distinctively monitoring a wide range of human body
motions in real time. Our novel microfluidic strain sensors show great
promise for making future stretchable electronic devices
Polymer Brushes Patterned with Micrometer-Scale Chemical Gradients Using Laminar Co-Flow
We
present a facile microfluidic method for forming narrow chemical
gradients in polymer brushes. Co-flow of an alkylating agent solution
and a neat solvent in a microfluidic channel forms a diffusion-driven
concentration gradient, and thus a gradient in reaction rate at the
interface of the two flows, leading to a quaternization gradient in
the underlying polyÂ(2-(dimethylamino)Âethyl methacrylate) polymer brush.
The spatial distribution of the quaternized polymer brush is characterized
by confocal Raman microscopy. The quaternization gradient length in
the polymer brush can be varied with the injection flow rate and the
distance from the co-flow junction. A chemical gradient in the polymer
brush as narrow as 5 μm was created by controlling these parameters.
The chemical gradient by laminar co-flow is compared with numerical
calculations that include only one adjustable parameter: the reaction
rate constant of the polymer brush quaternization. The calculated
chemical gradient agrees with the experimental data, which validates
the numerical procedures established in this study. Flow of multiple
laminar streams of reactive agent solutions enables single-run fabrication
of brush gradients with more than one chemical property. As one example,
four laminar streamsî—¸neat solvent/benzyl bromide solution/propargyl
bromide solution/neat solventî—¸generate multistep gradients
of aromatic and alkyne groups. Because the alkyne functional group
is a click-reaction available site, the alkyne gradient could allow
small gradient formation with a wide variety of chemical properties
in a polymer brush
Cytotoxicity of Gallium–Indium Liquid Metal in an Aqueous Environment
Eutectic gallium–indium alloy
(EGaIn) liquid metal is highly conductive, moldable, and extremely
deformable and has attracted significant attention for many applications,
ranging from stretchable electronics to drug delivery. Even though
EGaIn liquid metal is generally known to have low toxicity, the toxicity
of the metal, rather than a salt form of Ga or In, has not been systematically
studied yet. In this paper, we investigate the time-dependent concentration
of the ions released from EGaIn liquid metal in an aqueous environment
and their cytotoxicity to human cells. It is observed that only the
Ga ion is dominantly released from EGaIn when no external agitation
is applied, whereas the concentration of the In ion drastically increases
with sonication. The cytotoxicity study reveals that all human cells
tested are viable in the growth media with naturally released EGaIn
ions, but the cytotoxicity becomes significant with sonication-induced
EGaIn releasates. On the basis of the comparative study with other
representative toxic elements, that is, Hg and Cd, it could be concluded
that EGaIn is reasonably safe to use in an aqueous environment; however,
it should be cautiously handled when any mechanical agitation is applied
General Method for Forming Micrometer-Scale Lateral Chemical Gradients in Polymer Brushes
We report a general diffusion based
method to form micrometer-scale
lateral chemical gradients in polymer brushes via selective alkylation.
A quaternized brush gradient is derived from a concentration gradient
of alkylating agent formed by diffusion in permeable media around
a microchannel carrying the alkylating agent. Polymer brushes containing
both charge and aromatic gradients are formed using the alkylating
agents, methyl iodide and benzyl bromide, respectively. The gradients
are quantitatively characterized by confocal Raman spectroscopy and
qualitatively by fluorescence microscopy. The length and gradient
strength can be controlled by varying the diffusion time, concentrations,
and solvents of the alkylating agent solutions. This microfluidic
brush gradient generation method enables formation of 2-D chemical
potential gradients with a diversity of shapes
Autonomic Molecular Transport by Polymer Films Containing Programmed Chemical Potential Gradients
Materials which induce
molecular motion without external input
offer unique opportunities for spatial manipulation of molecules.
Here, we present the use of polyacrylamide hydrogel films containing
built-in chemical gradients (enthalpic gradients) to direct molecular
transport. Using a cationic tertiary amine gradient, anionic molecules
were directionally transported up to several millimeters. A 40-fold
concentration of anionic molecules dosed in aerosol form on a substrate
to a small region at the center of a radially symmetric cationic gradient
was observed. The separation of mixtures of charged dye molecules
was demonstrated using a boronic acid-to-cationic gradient where one
molecule was attracted to the boronic acid end of the gradient, and
the other to the cationic end of the gradient. Theoretical and computational
analysis provides a quantitative description of such anisotropic molecular
transport, and reveals that the gradient-imposed drift velocity is
in the range of hundreds of nanometers per second, comparable to the
transport velocities of biomolecular motors. This general concept
of enthalpy gradient-directed molecular transport should enable the
autonomous processing of a diversity of chemical species