52 research outputs found
Self-Propelled Metal–Polymer Hybrid Micromachines with Bending and Rotational Motions
Two
self-propelled micromachines were fabricated with gold/platinum
micromotors that exhibit simple translational motion in a fuel solution.
In each one, two micromotors were connected with a joint of polymer
tube formed by stacking cationic poly(allylamine hydrochloride) (PAH)
and anionic poly(acrylic acid) (PAA) using a layer-by-layer technique.
A bent structure was created by making one longitudinal side of the
joint more swellable with alkaline treatment. The joint containing
fewer PAA/PAH bilayers was flexible and allowed a larger range of
Brownian angular fluctuation. In the fuel solution, bending and stable
rotation were observed for the micromotors tethered with soft and
rigid angled joints, respectively. The radius and angular velocity
of the rotation depended on the angle of the joint. Such tethered
micromotors can be used to realize sophisticated micro/nanomachines
for microscale surgery and drug delivery
Falling test apparatus.
<p>(a) Custom-made apparatus consisting of drop object, guide pipe, and polyethylene sheet. (b) Temporal acceleration profiles of the object dropped from different heights (0.1−1.0 m) measured by the commercial accelerometer.</p
Schematics of the fluidic based impact sensor.
<p>(a) Schematic overview of the basic structure of the sensor. (b, c) Working principle of the sensor based on which impacts are detected depending on different combinations of immiscible working fluids.</p
Fluorescence micrographs showing two successive rounds of vesicle fusion (mixing), reaction, and budding/fission (aliquoting).
<p>The 5-µm scale bar in panel (a) also applies to panel (b) and to panels (e)–(h), whereas the 10-µm scale bar in panel (c) also applies to panel (d).</p
Stochasticity in Gene Expression in a Cell-Sized Compartment
The gene expression in a clonal cell
population fluctuates significantly,
and its relevance to various cellular functions is under intensive
debate. A fundamental question is whether the fluctuation is a consequence
of the complexity and redundancy in living cells or an inevitable
attribute of the minute microreactor nature of cells. To answer this
question, we constructed an artificial cell, which consists of only
necessary components for the gene expression (<i>in vitro</i> transcription and translation system) and its boundary as a microreactor
(cell-sized lipid vesicle), and investigated the gene expression noise.
The variation in the expression of two fluorescent proteins was decomposed
into the components that were correlated and uncorrelated between
the two proteins using a method similar to the one used by Elowitz
and co-workers to analyze the expression noise in <i>E. coli</i>. The observed fluctuation was compared with a theoretical model
that expresses the amplitude of noise as a function of the average
number of intermediate molecules and products. With the assumption
that the transcripts are partly active, the theoretical model was
able to well describe the noise in the artificial system. Furthermore,
the same measurement for <i>E. coli</i> cells harboring
an identical plasmid revealed that the <i>E. coli</i> exhibited
a similar level of expression noise. Our results demonstrated that
the level of fluctuation found in bacterial cells is mostly an intrinsic
property that arises even in a primitive form of the cell
Result of the impact sensors with different neck diameter <i>d</i><sub>neck</sub>.
<p>(a) Fraction of responded sensors versus peak acceleration values with <i>d</i><sub>neck</sub> = 1.5−3.0 mm. Insets show typical images of responded states after droplet falls. Blue dashed lines represent the fitted curves based on the use of the sigmoidal function. (b) Plot showing the dependence of <i>g</i><sub>th</sub> on <i>d</i><sub>neck</sub>.</p
State diagram of the response of the sensor as a function of <i>Ar</i> and <i>Bo</i>.
<p>Filled symbols represent sensors that “responded,” while open symbols represent sensors that “did not respond.” Circle: water, cross: ethanol 10%, star: ethanol 40%, square: sucrose 45 wt%, diamond: sucrose 65 wt%, pentagon: sucrose 70 wt%, triangle: glycerol 60 wt%, inverse triangle: glycerol 90 wt%, and hexagon: glycerol. Straight and dashed lines represent the results obtained with <i>d</i><sub>neck</sub> = 3.0 mm and 2.0 mm, respectively.</p
Deformation Modes of Giant Unilamellar Vesicles Encapsulating Biopolymers
The
shapes of giant unilamellar vesicles (GUVs) enclosing polymer
molecules at relatively high concentration, used as a model cytoplasm,
significantly differ from those containing only small molecules. Here,
we investigated the effects of the molecular weights and concentrations
of polymers such as polyethylene glycol (PEG), bovine serum albumin
(BSA), and DNA on the morphology of GUVs deflated by osmotic pressure.
Although small PEG (MW < 1000) does not alter the mode of shape
transformation even at >10% (w/w), PEG with MW > 6000 induces
budding
and pearling transformation at above 1% (w/w). Larger PEG frequently
induced small buddings and tubulation from the membrane of mother
GUVs. A similar trend was observed with BSA, indicating that the effect
is irrelevant to the chemical nature of polymers. More surprisingly,
long strands of DNA (>10<sup>5</sup> bp) enclosed in GUVs induced
budding transformation at concentrations as low as 0.01–0.1%
(w/w). We expect that this molecular size dependency arises mainly
from the depletion volume effect. Our results showed that curving,
budding, and tubulation of lipid membranes, which are ubiquitous in
living cells, can result from simple cell-mimics consisting of the
membrane and cytosolic macromolecules, but without specific shape-determining
proteins
Result of the impact sensor with different oil phase.
<p>(a) Fraction of responded sensors versus peak acceleration tested using different oil viscosities. (b) Comparison of <i>g</i><sub>th</sub> for fluorocarbon oils with different viscosities.</p
Programmed Transport and Release of Cells by Self-Propelled Micromotors
Autonomous
transport and release of bacterial cells by self-propelled
micromotors were achieved. The motors consisted of zinc and platinum
hemispheres formed on polystyrene beads and moved as a result of simultaneous
redox reactions occurring on both metal ends. The highly negative
redox potential of zinc enabled the selection of a wide variety of
organic redox compounds as fuels, such as methanol and <i>p</i>-benzoquinone. The movement of motors was observed in solutions of
fuels. To realize autonomous capture, transport, and release of cargo,
a self-assembled monolayer (SAM) was formed on the platinum part of
the motor. This SAM could be desorbed by coupling the reaction with
the dissolution of zinc, which could also be controlled by adjusting
the concentration of Zn<sup>2+</sup> ions. <i>Escherichia coli</i> (<i>E. coli</i>) cells were captured by the motor (due
to hydrophobic interactions), transported, and released following
SAM desorption at the mixed potential
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