25 research outputs found
Effect of Mechanical Instability of Polymer Scaffolds on Cell Adhesion
The
adhesion of fibroblast on polymer bilayers composed of a glassy
polystyrene (PS) prepared on top of a rubbery polyisoprene (PI) was
studied. Since the top PS layer is not build on a glassy, or firm,
foundation, the system becomes mechanically unstable with decreasing
thickness of the PS layer. When the PS film was thinner than 25 nm,
the number of cells adhered to the surface decreased and the cells
could not spread well. On a parallel experiment, the same cell adhesion
behavior was observed on plasma-treated PS/PI bilayer films, where
in this case, the surface was more hydrophilic than that of the intact
films. In addition, the fluorescence microscopic observations revealed
that the formation of F-actin filaments in fibroblasts attached to
the thicker PS/PI bilayer films was greater than those using the thinner
PS/PI bilayer films. On the other hand, the thickness dependence of
the cell adhesion behavior was not observed for the PS monolayer films.
Taking into account that the amount of adsorbed protein molecules
evaluated by a quartz crystal microbalance method was independent
of the PS layer thickness of the bilayer films, our results indicate
that cells, unlike protein molecules, could sense a mechanical instability
of the scaffold
Aggregation States of Polymers at Hydrophobic and Hydrophilic Solid Interfaces
Aggregation states of polystyrene
(PS) and poly(methyl methacrylate)
(PMMA) at hydrophobic deuterated-octadecyltrichlorosilane (OTS-<i>d</i>) and hydrophilic SiO<sub>x</sub> interfaces are discussed,
focusing on the interaction strength between polymer and substrate.
Sum-frequency generation spectroscopy revealed that PS exhibited oriented
phenyl groups along the normal direction at the interface in a spin-coated
film because of the centrifugal force generated during the film solidification
process, whereas it did not in a solvent-cast film. This result was
common for both hydrophobic and hydrophilic substrates. That is, the
aggregation states of PS depended little on which kind of substrate
was used. This is because the interaction between PS and the surfaces
is weak. In the case of a PMMA film on the hydrophobic OTS-<i>d</i> substrate, the interfacial local conformation was also
dependent on the method of film preparation. PMMA at the hydrophilic
SiO<sub>x</sub> interface, however, exhibited oriented ester methyl
groups along the direction normal to the interface, regardless of
the film preparation method. This is due to a stronger interaction
via hydrogen bonding between carbonyl groups of PMMA and the substrate
surface
The Impact of Polymer Dynamics on Photoinduced Carrier Formation in Films of Semiconducting Polymers
A better understanding of the carrier
formation process in photosemiconducting
polymers is crucial to design and construct highly functionalized
thin film organic photodevices. Almost all studies published focus
on the effect of structure on the photoinduced carrier formation process.
Here, we study the dynamics of polymer chain impacts on the carrier
formation process for a series of poly(3-alkylthiophene)s (P3ATs)
with different alkyl side-chain lengths. The formation of polarons
(<b>P</b>) from polaron pairs (<b>PP</b>) was accelerated
at a temperature at which the twisting motion of thiophene rings occurs.
Among all P3ATs employed, in P3AT with hexyl groups, or poly(3-hexylthiophene)
(P3HT), it was easiest to twist the thiophene rings and generate <b>P</b> from <b>PP</b>. The activation energy for <b>P</b> formation was proportional to that of thiophene ring motion. This
makes it clear that chain dynamics, in addition to the crystalline
structure, is a controlling factor for the carrier formation process
in photosemiconducting polymers
Design of a Well-Defined Polyrotaxane Structure on a Glassy Polymer Surface
The
polymer dynamics at the water interface play a crucial role
in the manifestation of biorelated functions. One of the strategies
for this is to form inclusion complexes of polymer chains with cyclic
compounds. However, such an idea has been limited to bulk materials
so far. Here we propose a preparation pathway for a polyrotaxane structure
composed of poly(ethylene oxide) (PEO) and α-cyclodextrin (CD)
at the outermost surface of a glassy poly(methyl methacrylate) film
on the basis of the combination of a click reaction and the Langmuir–Blodgett
method. The chain motion of PEO at the water interface could be regulated
by threading of CD molecules on PEO and thereby the biological responses
such as protein adsorption and platelet adhesion altered depending
on the extent of complexation
Dynamics of Water-Induced Surface Reorganization in Poly(methyl methacrylate) Films
At the outermost surface, aggregation states of polymers
generally
tend to alter to their most stable ones in response to their surrounding
environment. We here apply a time-resolved contact angle measurement
to study the rate of the surface reorganization of poly(methyl methacrylate)
(PMMA) in water. By doing these measurements at various temperatures,
it is possible to determine the apparent activation energy of the
surface dynamics based on the relation of the surface relaxation time
and temperature. Also, the sum-frequency generation spectroscopy revealed
that the surface reorganization involves the conformational changes
in the main chain part as well as the side chains. Hence, the dynamics
observed here may reflect the segmental motion at the outermost region
of the PMMA film, in which water plays as a plasticizer
Simple Surface Treatment of Cell-Culture Scaffolds with Ultrafine Bubble Water
We
propose a novel method to treat polymeric scaffold surfaces
for cell culture with water containing nanobubbles, called ultrafine
bubbles (UFBs), with typical diameters less than 1 μm. A thin
film of polystyrene (PS) prepared on a solid substrate was exposed
to UFB water for 2 days at room temperature. The PS surface was characterized
by X-ray photoelectron spectroscopy (XPS), static contact angle measurements
in water, and atomic force microscopy (AFM). The surface chemical
composition and wettability of PS films remained unchanged after treatment,
so that aggregation states of PS at film surfaces remained unaltered
by UFB water. On the other hand, after treatment, many UFBs were adsorbed
on hydrophobic PS surfaces. To study the effect of UFBs on scaffold
properties, the adsorption behavior of fibronectin, which is a typical
extracellular matrix protein involved in cell adhesion and proliferation,
was examined. While the effect on the adsorption was unclear, the
structural denaturation of fibronectin was enhanced after UFB treatment,
so that the proliferation of fibroblast cells on PS surfaces was promoted
Design of a Dynamic Polymer Interface for Chiral Discrimination
Enantioselective wetting of a chiral
polymer film was demonstrated.
The contact angle of chiral liquids on the film was strongly dependent
on their chirality although their physical properties including surface
tension were identical. Such wetting behavior resulted from the enantioselective
surface reorganization involving local conformational change of the
polymer chains at the liquid interface. The concept of “dynamic
interface for chiral discrimination” has possible potential
for the development of materials capable of chiral sensing, optical
resolution, and asymmetric synthesis
Load-Induced Frictional Transition at a Well-Defined Alkane Loop Surface
Self-assembled
monolayers (SAMs) have attracted considerable attention
as a tool to confer desirable properties on material surfaces. So
far, molecules used for the SAM formation are generally limited to
linear ones and thus chain ends dominate the surface properties. In
this study, we have successfully demonstrated unique frictional properties
of a SAM composed of alkane loops from cyclic alkanedisulfide on a
gold substrate, where both sulfurs are bound to gold. The frictional
response was proportional to the load. However, once the load went
beyond a threshold value, the frictional response became more dominant.
Such a frictional transition was reversible and repeatable and was
not discerned for a corresponding SAM composed of <i>n</i>-alkyl chains. The load-induced change in the frictional response
from the alkane loops could be associated with the conformational
change of the alkane loops. The present results differ from most studies,
in which the surface properties are designed on the basis of functional
chain end groups
Mesoscopic Heterogeneity in Pore Size of Supramolecular Networks
There
has been a considerable interest in developing new types
of gels based on a network of fibrous aggregate composed of low molecular
weight gelators, also known as supramolecular gels (SMGs). Unlike
conventional polymer gels with chemical cross-linking, the network
formation in SMGs does not involve any covalent bonds. Thus, the network
in SMGs has been often regarded as homogenous or less heterogeneous
in comparison with that in chemically cross-linked polymer gels. In
this study, we have experimentally verified the existence of the network
heterogeneity even in SMGs. The thermal motion of probe particles
in SMGs, which were prepared from aqueous dispersions of gelators
having a different number of peptide residues, PalGH, PalG<sub>2</sub>H, and PalG<sub>3</sub>H, was tracked. The gels were spatially heterogeneous
in terms of the network pore size, as evidenced by the variation in
the particle motion depending on the location, at which a particle
existed. With varying particle size, it was found that the characteristic
length scale of the heterogeneity was in the order of (sub)micrometers
and was smaller in the order of the PalG<sub>2</sub>H, PalG<sub>3</sub>H, and PalGH gels
Glass Transition Behavior in Thin Polymer Films Covered with a Surface Crystalline Layer
Thin amorphous poly(ethylene terephthalate)
(PET) films covered
with/without a crystallized surface layer were prepared onto silicon
wafers. In the former and latter cases, the surface mobility in the
film was depressed and enhanced, respectively. The glass transition
temperature (<i>T</i><sub>g</sub>) of the amorphous PET
film decreased with the reduction of the film thickness, exhibiting
a remarkable nanoconfinement effect. However, once the surface region
of the thin film was crystallized, or frozen in terms of the segmental
motion, <i>T</i><sub>g</sub> of the films recovered to that
of the bulk. Concurrently, the apparent activation energy of the segmental
motion in the surface-crystallized film was in good accordance with
the bulk value as well. These results make it clear that the mobility
in the surface region plays an essential role in the glass transition
of the thin films