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 U­(VI), Eu­(III), Sr­(II), and Cs­(I) from aqueous solutions as a function of pH and initial concentration on the PANI@GO composites was investigated. The maximum sorption capacities of U­(VI), Eu­(III), Sr­(II), and Cs­(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^–1, respectively. According to the XPS analysis of the PANI@GO composites before and after Eu­(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 Eu­(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 Eu­(III) adsorption on GONS were evaluated. The results indicated that ionic strength had no effect on Eu­(III) adsorption on GONS. The maximum adsorption capacity of Eu­(III) on GONS at pH 6.0 and <i>T</i> = 298 K was calculated to be 175.44 mg·g^–1, much higher than any currently reported. The thermodynamic parameters calculated from temperature-dependent adsorption isotherms suggested that Eu­(III) adsorption on GONS was an endothermic and spontaneous process. Results of EXAFS spectral analysis indicated that Eu­(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 >SOEu²⁺ and binuclear bidentate (>SO)₂Eu₂(OH)₂²⁺ 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 U­(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 U­(VI) were GOs > HOOC-GOs > rGOs, whereas the desorbed amounts of U­(VI) were rGOs > GOs > HOOC-GOs by desorption kinetics. According to EXAFS analysis, inner-sphere surface complexation dominated the adsorption of U­(VI) on GOs and HOOC-GOs at pH 4.0, whereas outer-sphere surface complexation of U­(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^···UO₂]²⁺ (8.1 kcal/mol) was significantly lower than those of [HOOC-GOs^···UO₂]²⁺ (12.1 kcal/mol) and [GOs-O^···UO₂]²⁺ (10.2 kcal/mol), suggesting the physisorption of UO₂²⁺ on rGOs. Such high binding energy of [GOs-COO^···UO₂]⁺ (50.5 kcal/mol) revealed that the desorption of U­(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 U­(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 Sr­(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 Sr­(II) on magnetic PANI/GO composites was observed with increasing ionic strength at pH <5.0, whereas no effect of ionic strength on Sr­(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 Sr­(II) on magnetic PANI/GO composites at pH 3.0 due to the similarity to the EXAFS spectra of Sr²⁺ in aqueous solutions, but the Sr­(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 Sr­(II) on magnetic PANI/GO composites was well simulated using a diffuse layer model with an outer-sphere complex (SOHSr²⁺ species) and two inner-sphere complexes (i.e., (SO)₂Sr­(OH)⁻ and SOSr⁺ 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 U­(VI) and Eu­(III) on carbonaceous nanofibers (CNFs) was investigated using batch, IR, XPS, XANES, and EXAFS techniques. The pH-dependent adsorption indicated that the adsorption of U­(VI) on the CNFs was significantly higher than the adsorption of Eu­(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 U­(VI) and Eu­(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 U­(VI) and Eu­(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 U­(VI) adsorption. In addition, the remarkable reducing agents of the R-CH₂OH groups were responsible for the highly efficient adsorption of U­(VI) on the CNFs. The adsorption mechanism of U­(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)­precipitate (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⁺ 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⁺ and Oct⁻ 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_eff</i> = 1.92 kPa) and rigid (<i>E_eff</i> = 1,218.4 kPa) PDMS micropost arrays. Scale bar, 50 µm. (<i>E</i>) Bar plot of percentage of Oct⁺ 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⁺ and Oct⁻ hESCs.

<p>(<i>A</i>) Quantification of subcellular traction forces for single Oct⁺ (top row) and Oct⁻ (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⁺ and Oct⁻ 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⁺; right: Oct⁻), 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⁺) and differentiated (Oct⁻) hESC colonies on soft (<i>E_eff</i> = 1.92 kPa) and rigid (<i>E_eff</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_eff</i> = 1.92 kPa) and rigid (<i>E_eff</i> = 1,218.4 kPa) PDMS micropost arrays. Scale bar, 50 µm. (<i>C</i>) Bar plot of percentage of Oct⁺ 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