18 research outputs found
UV-Modulated Substrate Rigidity for Multiscale Study of Mechanoresponsive Cellular Behaviors
Mechanical properties of the extracellular matrix (ECM)
have profound
effects on cellular functions. Here, we applied novel photosensitive
polydimethylsiloxane (photoPDMS) chemistry to create photosensitive,
biocompatible photoPDMS as a rigidity-tunable material for study of
mechanoresponsive cellular behaviors. By modulating the PDMS cross-linker
to monomer ratio, UV light exposure time, and postexposure baking
time, we achieved a broad range of bulk Young’s modulus for
photoPDMS from 0.027 to 2.48 MPa. Biocompatibility of photoPDMS was
assayed, and no significant cytotoxic effect was detected as compared
to conventional PDMS. We demonstrated that the bulk Young’s
modulus of photoPDMS could impact cell morphology, adhesion formation,
cytoskeletal structure, and cell proliferation. We further fabricated
photoPDMS micropost arrays for multiscale study of mechanoresponsive
cellular behaviors. Our results suggested that adherent cells could
sense and respond to changes of substrate rigidity at a subfocal adhesion
resolution. Together, we demonstrated the potential of photoPDMS as
a photosensitive and rigidity-tunable material for mechanobiology
studies
Highly Efficient Enrichment of Radionuclides on Graphene Oxide-Supported Polyaniline
Graphene
oxide-supported polyaniline (PANI@GO) composites were
synthesized by chemical oxidation and were characterized by SEM, Raman
and FT-IR spectroscopy, TGA, potentiometric titrations, and XPS. The
characterization indicated that PANI can be grafted onto the surface
of GO nanosheets successfully. The sorption of UÂ(VI), EuÂ(III), SrÂ(II),
and CsÂ(I) from aqueous solutions as a function of pH and initial concentration
on the PANI@GO composites was investigated. The maximum sorption capacities
of UÂ(VI), EuÂ(III), SrÂ(II), and CsÂ(I) on the PANI@GO composites at
pH 3.0 and <i>T</i> = 298 K calculated from the Langmuir
model were 1.03, 1.65, 1.68, and 1.39 mmol·g<sup>–1</sup>, respectively. According to the XPS analysis of the PANI@GO composites
before and after EuÂ(III) desorption, nitrogen- and oxygen-containing
functional groups on the surface of PANI@GO composites were responsible
for radionuclide sorption, and that radionuclides can hardly be extracted
from the nitrogen-containing functional groups. Therefore, the chemical
affinity of radionuclides for nitrogen-containing functional groups
is stronger than that for oxygen-containing functional groups. This
paper focused on the application of PANI@GO composites as suitable
materials for the preconcentration and removal of lanthanides and
actinides from aqueous solutions in environmental pollution management
in a wide range of acidic to alkaline conditions
Adsorption of 4‑<i>n</i>‑Nonylphenol and Bisphenol‑A on Magnetic Reduced Graphene Oxides: A Combined Experimental and Theoretical Studies
Adsorption
of 4-<i>n</i>-nonylphenol (4-<i>n</i>-NP) and
bisphenol A (BPA) on magnetic reduced graphene oxides (rGOs)
as a function of contact time, pH, ionic strength and humic acid were
investigated by batch techniques. Adsorption of 4-<i>n</i>-NP and BPA were independent of pH at 3.0- 8.0, whereas the slightly
decreased adsorption was observed at pH 8.0–11.0. Adsorption
kinetics and isotherms of 4-<i>n</i>-NP and BPA on magnetic
rGOs can be satisfactorily fitted by pseudo-second-order kinetic and
Freundlich model, respectively. The maximum adsorption capacities
of magnetic rGOs at pH 6.5 and 293 K were 63.96 and 48.74 mg/g for
4-<i>n</i>-NP and BPA, respectively, which were significantly
higher than that of activated carbon. Based on theoretical calculations,
the higher adsorption energy of rGOs + 4-<i>n</i>-NP was
mainly due to π–π stacking and flexible long alkyl
chain of 4-<i>n</i>-NP, whereas adsorption of BPA on rGOs
was energetically favored by a lying-down configuration due to π–π
stacking and dispersion forces, which was further demonstrated by
FTIR analysis. These findings indicate that magnetic rGOs is a promising
adsorbent for the efficient elimination of 4-<i>n</i>-NP/BPA
from aqueous solutions due to its excellent adsorption performance
and simple magnetic separation, which are of great significance for
the remediation of endocrine-disrupting chemicals in environmental
cleanup
Interaction between Eu(III) and Graphene Oxide Nanosheets Investigated by Batch and Extended X-ray Absorption Fine Structure Spectroscopy and by Modeling Techniques
The interaction mechanism between EuÂ(III) and graphene
oxide nanosheets
(GONS) was investigated by batch and extended X-ray absorption fine
structure (EXAFS) spectroscopy and by modeling techniques. The effects
of pH, ionic strength, and temperature on EuÂ(III) adsorption on GONS
were evaluated. The results indicated that ionic strength had no effect
on EuÂ(III) adsorption on GONS. The maximum adsorption capacity of
EuÂ(III) on GONS at pH 6.0 and <i>T</i> = 298 K was calculated
to be 175.44 mg·g<sup>–1</sup>, much higher than any currently
reported. The thermodynamic parameters calculated from temperature-dependent
adsorption isotherms suggested that EuÂ(III) adsorption on GONS was
an endothermic and spontaneous process. Results of EXAFS spectral
analysis indicated that EuÂ(III) was bound to ∼6–7 O
atoms at a bond distance of ∼2.44 Å in the first coordination
shell. The value of Eu–C bond distance confirmed the formation
of inner-sphere surface complexes on GONS. Surface complexation modeling
gave an excellent fit with the predominant mononuclear monodentate
>SOEu<sup>2+</sup> and binuclear bidentate (>SO)<sub>2</sub>Eu<sub>2</sub>(OH)<sub>2</sub><sup>2+</sup> complexes. This paper
highlights
the application of GONS as a suitable material for the preconcentration
and removal of trivalent lanthanides and actinides from aqueous solutions
in environmental pollution management
Adsorption and Desorption of U(VI) on Functionalized Graphene Oxides: A Combined Experimental and Theoretical Study
The adsorption and desorption of
UÂ(VI) on graphene oxides (GOs),
carboxylated GOs (HOOC-GOs), and reduced GOs (rGOs) were investigated
by batch experiments, EXAFS technique, and computational theoretical
calculations. Isothermal adsorptions showed that the adsorption capacities
of UÂ(VI) were GOs > HOOC-GOs > rGOs, whereas the desorbed amounts
of UÂ(VI) were rGOs > GOs > HOOC-GOs by desorption kinetics.
According
to EXAFS analysis, inner-sphere surface complexation dominated the
adsorption of UÂ(VI) on GOs and HOOC-GOs at pH 4.0, whereas outer-sphere
surface complexation of UÂ(VI) on rGO was observed at pH 4.0, which
was consistent with surface complexation modeling. Based on the theoretical
calculations, the binding energy of [G<sup>···</sup>UO<sub>2</sub>]<sup>2+</sup> (8.1 kcal/mol) was significantly lower
than those of [HOOC-GOs<sup>···</sup>UO<sub>2</sub>]<sup>2+</sup> (12.1 kcal/mol) and [GOs-O<sup>···</sup>UO<sub>2</sub>]<sup>2+</sup> (10.2 kcal/mol), suggesting the physisorption
of UO<sub>2</sub><sup>2+</sup> on rGOs. Such high binding energy of
[GOs-COO<sup>···</sup>UO<sub>2</sub>]<sup>+</sup> (50.5
kcal/mol) revealed that the desorption of UÂ(VI) from the −COOH
groups was much more difficult. This paper highlights the effect of
the hydroxyl, epoxy, and carboxyl groups on the adsorption and desorption
of UÂ(VI), which plays an important role in designing GOs for the preconcentration
and removal of radionuclides in environmental pollution cleanup applications
Decontamination of Sr(II) on Magnetic Polyaniline/Graphene Oxide Composites: Evidence from Experimental, Spectroscopic, and Modeling Investigation
The
interaction of SrÂ(II) on magnetic polyaniline/graphene oxide
(PANI/GO) composites was elucidated by batch, EXAFS, and surface complexation
modeling techniques. The batch experiments showed that decreased uptake
of SrÂ(II) on magnetic PANI/GO composites was observed with increasing
ionic strength at pH <5.0, whereas no effect of ionic strength
on SrÂ(II) uptake was shown at pH >5.0. The maximum uptake capacity
of magnetic PANI/GO composites derived from the Langmuir model at
pH 3.0 and 293 K was 37.17 mg/g. The outer-sphere surface complexation
controlled the uptake of SrÂ(II) on magnetic PANI/GO composites at
pH 3.0 due to the similarity to the EXAFS spectra of Sr<sup>2+</sup> in aqueous solutions, but the SrÂ(II) uptake at pH 7.0 was inner
sphere complexation owing to the occurrence of the Sr–C shell.
According to the analysis of surface complexation modeling, uptake
of SrÂ(II) on magnetic PANI/GO composites was well simulated using
a diffuse layer model with an outer-sphere complex (SOHSr<sup>2+</sup> species) and two inner-sphere complexes (i.e., (SO)<sub>2</sub>SrÂ(OH)<sup>−</sup> and SOSr<sup>+</sup> species). These findings are
crucial for the potential application of magnetic nanomaterials as
a promising candidate for the uptake of radionuclides for environmental
remediation
Macroscopic and Microscopic Investigation of U(VI) and Eu(III) Adsorption on Carbonaceous Nanofibers
The adsorption mechanism of UÂ(VI)
and EuÂ(III) on carbonaceous nanofibers
(CNFs) was investigated using batch, IR, XPS, XANES, and EXAFS techniques.
The pH-dependent adsorption indicated that the adsorption of UÂ(VI)
on the CNFs was significantly higher than the adsorption of EuÂ(III)
at pH < 7.0. The maximum adsorption capacity of the CNFs calculated
from the Langmuir model at pH 4.5 and 298 K for UÂ(VI) and EuÂ(III)
were 125 and 91 mg/g, respectively. The CNFs displayed good recyclability
and recoverability by regeneration experiments. Based on XPS and XANES
analyses, the enrichment of UÂ(VI) and EuÂ(III) was attributed to the
abundant adsorption sites (e.g., −OH and −COOH groups)
of the CNFs. IR analysis further demonstrated that −COOH groups
were more responsible for UÂ(VI) adsorption. In addition, the remarkable
reducing agents of the R-CH<sub>2</sub>OH groups were responsible
for the highly efficient adsorption of UÂ(VI) on the CNFs. The adsorption
mechanism of UÂ(VI) on the CNFs at pH 4.5 was shifted from inner- to
outer-sphere surface complexation with increasing initial concentration,
whereas the surface (co)Âprecipitate (i.e., schoepite) was observed
at pH 7.0 by EXAFS spectra. The findings presented herein play an
important role in the removal of radionuclides on inexpensive and
available carbon-based nanoparticles in environmental cleanup applications
Matrix mechanic-mediated behaviors of single hESCs on PDMS micropost arrays with different rigidities.
<p>(<i>A</i>) Bar plot of percentage of Oct<sup>+</sup> cells for single hESCs plated on the PDMS micropost arrays with different rigidities. (<i>B&C</i>) Traction force per cell area (<i>B</i>) and total traction forces per cell (<i>C</i>) for both Oct<sup>+</sup> and Oct<sup>−</sup> cells as a function of the PDMS micropost array rigidity. (<i>D</i>) Phase contrast and immunofluorescence images of hESCs treated with or without blebbistatin on both soft (<i>E<sub>eff</sub></i> = 1.92 kPa) and rigid (<i>E<sub>eff</sub></i> = 1,218.4 kPa) PDMS micropost arrays. Scale bar, 50 µm. (<i>E</i>) Bar plot of percentage of Oct<sup>+</sup> cells for blebbistatin treated hESCs and untreated controls as a function of the PDMS micropost array rigidity. Data in <i>E</i> was normalized to the value for untreated hESCs plated on the rigid micropost array under the 24-hr treatment condition. Data in <i>A</i>–<i>C</i> and <i>E</i> represents the means ± s.e.m from 3 independent experiments. *: <i>p</i><0.05; **: <i>p</i><0.01; <i>NS</i>: <i>p</i>>0.05.</p
Differential cytoskeleton contractility and FA distribution for single Oct<sup>+</sup> and Oct<sup>−</sup> hESCs.
<p>(<i>A</i>) Quantification of subcellular traction forces for single Oct<sup>+</sup> (top row) and Oct<sup>−</sup> (bottom row) hESCs using the PDMS micropost array. (<i>B&C</i>) Bar plots of total traction forces per cell (<i>B</i>) and traction force per cell area (<i>C</i>) for both single Oct<sup>+</sup> and Oct<sup>−</sup> hESCs. Data represents the means ± s.e.m from 3 independent experiments. **, <i>p</i><0.01. (<i>D</i>) Immunofluorescence images showing FA distributions in single hESCs (left: Oct<sup>+</sup>; right: Oct<sup>−</sup>), as indicated by vinculin staining. Scale bar, 20 µm.</p
E-cadherin expression of hESCs modulated by substrate rigidity.
<p>(<i>A</i>) Immunofluorescence images taken for undifferentiated (Oct<sup>+</sup>) and differentiated (Oct<sup>−</sup>) hESC colonies on soft (<i>E<sub>eff</sub></i> = 1.92 kPa) and rigid (<i>E<sub>eff</sub></i> = 1,218.4 kPa) PDMS micropost arrays, as indicated. Differentiated hESC colonies were marked with an arrow. Scale bars, 50 µm. (<i>B</i>) Phase contrast and immunofluorescence images of hESCs treated with or without DECMA-1 on both soft (<i>E<sub>eff</sub></i> = 1.92 kPa) and rigid (<i>E<sub>eff</sub></i> = 1,218.4 kPa) PDMS micropost arrays. Scale bar, 50 µm. (<i>C</i>) Bar plot of percentage of Oct<sup>+</sup> cells for DECMA-1 treated hESCs and untreated controls as a function of the PDMS micropost rigidity. Data represents the means ± s.e.m from 3 independent experiments. *: <i>p</i><0.05; **: <i>p</i><0.01.</p