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Gels, Volume 3, Issue 2 (June 2017) – 12 articles

Cover Story (view full-size image): Solvent evaporation from droplets can be used to guide dispersed colloidal particles into assembled superstructures, so-called supraparticles. If done on a super-repellant surface, these supraparticles are easily collected and isolated for further use. Due to the adaptive nature of this process, numerous kinds of materials can be easily combined to create complex functional devices with defined structures for various kinds of applications, such as photonics, catalysis, sensing, and many more. View the paper here.
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16029 KiB  
Article
Transcription of Nanofibrous Cerium Phosphate Using a pH-Sensitive Lipodipeptide Hydrogel Template
by Mario Llusar, Beatriu Escuder, Juan De Dios López-Castro, Susana Trasobares and Guillermo Monrós
Gels 2017, 3(2), 23; https://doi.org/10.3390/gels3020023 - 10 Jun 2017
Cited by 10 | Viewed by 5941
Abstract
A novel and simple transcription strategy has been designed for the template-synthesis of CePO4·xH2O nanofibers having an improved nanofibrous morphology using a pH-sensitive nanofibrous hydrogel (glycine-alanine lipodipeptide) as structure-directing scaffold. The phosphorylated hydrogel was employed as a template to [...] Read more.
A novel and simple transcription strategy has been designed for the template-synthesis of CePO4·xH2O nanofibers having an improved nanofibrous morphology using a pH-sensitive nanofibrous hydrogel (glycine-alanine lipodipeptide) as structure-directing scaffold. The phosphorylated hydrogel was employed as a template to direct the mineralization of high aspect ratio nanofibrous cerium phosphate, which in-situ formed by diffusion of aqueous CeCl3 and subsequent drying (60 °C) and annealing treatments (250, 600 and 900 °C). Dried xerogels and annealed CePO4 powders were characterized by conventional thermal and thermogravimetric analysis (DTA/TG), and Wide-Angle X-ray powder diffraction (WAXD) and X-ray powder diffraction (XRD) techniques. A molecular packing model for the formation of the fibrous xerogel template was proposed, in accordance with results from Fourier-Transformed Infrarred (FTIR) and WAXD measurements. The morphology, crystalline structure and composition of CePO4 nanofibers were characterized by electron microscopy techniques (Field-Emission Scanning Electron Microscopy (FE-SEM), Transmission Electron Microscopy/High-Resolution Transmission Electron Microscopy (TEM/HRTEM), and Scanning Transmission Electron Microscopy working in High Angle Annular Dark-Field (STEM-HAADF)) with associated X-ray energy-dispersive detector (EDS) and Scanning Transmission Electron Microscopy-Electron Energy Loss (STEM-EELS) spectroscopies. Noteworthy, this templating approach successfully led to the formation of CePO4·H2O nanofibrous bundles of rather co-aligned and elongated nanofibers (10–20 nm thick and up to ca. 1 μm long). The formed nanofibers consisted of hexagonal (P6222) CePO4 nanocrystals (at 60 and 250 °C), with a better-grown and more homogeneous fibrous morphology with respect to a reference CePO4 prepared under similar (non-templated) conditions, and transformed into nanofibrous monoclinic monazite (P21/n) around 600 °C. The nanofibrous morphology was highly preserved after annealing at 900 °C under N2, although collapsed under air conditions. The nanofibrous CePO4 (as-prepared hexagonal and 900 °C-annealed monoclinic) exhibited an enhanced UV photo-luminescent emission with respect to non-fibrous homologues. Full article
(This article belongs to the Special Issue Gels as Templates for Transcription)
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Graphical abstract
Full article ">Figure 1
<p>(<b>a</b>) TEM image of HCl-C12GA hydrogel (Pt-shadowing) formed in aqueous acidic medium (HCl vapors); (<b>b</b>–<b>d</b>) SEM images of H<sub>3</sub>PO<sub>4</sub>-C12GA hydrogel in aqueous NaH<sub>2</sub>PO<sub>4</sub> medium (lyophilized xerogel). The inset in (<b>d</b>) shows a representative EDX spectrum of the NaH<sub>2</sub>PO<sub>4</sub>-containing C12GA xerogel (average P/Na molar ratio = 1.19 ± 0.07).</p> Full article ">Figure 2
<p>XRD patterns of the NaH<sub>2</sub>PO<sub>4</sub>-based C12GA xerogel: (<b>a</b>) overall pattern; and (<b>b</b>) magnification of the low-angle region marked with the dashed rectangle. The peaks labelled with an asterisk correspond to the periodical arrangement of C12GA gelator molecules (the distances are shown in the magnification), and all the remaining peaks correspond to NaH<sub>2</sub>PO<sub>4</sub> phase (monoclinic P21/c space group, JCPDF number 70-0954) marked as <b>P</b> only in the low angle region; the Miller indexes and theoretical relative intensities of the three most intense peaks of NaH<sub>2</sub>PO<sub>4</sub> are indicated.</p> Full article ">Figure 3
<p>FTIR spectra of C12GA dried xerogels obtained in acidic media: HCl (dashed line), H<sub>3</sub>PO<sub>4</sub> (solid line): (<b>a</b>) 3500–2800 cm<sup>−1</sup>; (<b>b</b>) 2800–1800 cm<sup>−1</sup>; (<b>c</b>) 1800–1500 cm<sup>−1</sup>; (<b>d</b>) 1500–600 cm<sup>−1</sup>.</p> Full article ">Figure 4
<p>Energy-minimized structure models (MACROMODEL 7.0, AMBER* [<a href="#B98-gels-03-00023" class="html-bibr">98</a>]) for the packing of compound C12GA in phosphorylated xerogel (non-polar hydrogens are omitted for clarity in the bottom image).</p> Full article ">Figure 5
<p>FE-SEM images (<b>a</b>,<b>b</b>), and TEM images (<b>c</b>–<b>e</b>) of the as-prepared C12GA-templated nanofibrous CePO<sub>4</sub> (60 °C-dried and washed xerogel); (<b>f</b>) Representative energy-dispersive EDX spectrum of this CePO<sub>4</sub> xerogel (60 °C).</p> Full article ">Figure 6
<p>(<b>a</b>) HRTEM image of a representative nanofiber of as-prepared C12GA-templated nanofibrous CePO<sub>4</sub> (60 °C-dried and washed xerogel), the inset showing the corresponding digital diffraction pattern (DDP) of the region marked with an square, with indicated distances; (<b>b</b>) same DDP with indexed (<span class="html-italic">hkl</span>) values (taken along zone axis [uvw]: [010]); (<b>c</b>) Corresponding simulated kinetic diffraction diagram.</p> Full article ">Figure 7
<p>Differential thermal and thermogravimetric analysis (DTA-TGA) of as-prepared (60 °C-dried and washed) samples: (<b>a</b>) non-templated reference CePO<sub>4</sub>; and (<b>b</b>) templated CePO<sub>4</sub> xerogel.</p> Full article ">Figure 8
<p>XRD patterns with the evolution of crystalline phase in non-templated reference CePO<sub>4</sub> (bottom, red-colored) and C12GA-templated CePO<sub>4</sub> (up; dark-colored): (<b>a</b>) as-prepared 60 °C-dried samples; (<b>b</b>) 250 °C-annealed samples (air conditions); (<b>c</b>) 600 °C-annealed samples (air conditions).</p> Full article ">Figure 9
<p>(<b>a</b>) XRD patterns of: non-templated reference CePO<sub>4</sub> (a); and C12GA-templated CePO<sub>4</sub> (b) after annealing treatment at 900 °C under air atmosphere; (<b>b</b>) XRD patterns of templated CePO<sub>4</sub> after subsequent annealing treatments at: 250 °C (a), 600 °C (b), and 900 °C (c) under N<sub>2</sub> atmosphere.</p> Full article ">Figure 10
<p>FE-SEM images (<b>a</b>,<b>b</b>) and TEM images (<b>c</b>) of templated nanofibrous CePO<sub>4</sub> annealed at 600 °C (air conditions); (<b>d</b>) FE-SEM image of templated CePO<sub>4</sub> annealed at 900 °C (air conditions).</p> Full article ">Figure 11
<p>FE-SEM images corresponding to C12GA-templated nanofibrous CePO<sub>4</sub> annealed at 900 °C under N<sub>2</sub> conditions: (<b>a</b>) Well-preserved nanofibrous region (x 35000); (<b>b</b>) Higher magnification region (x 70000) showing thicker, more grown and aggregated nanofibers. Bar length: 100 nm.</p> Full article ">Figure 12
<p>(<b>a</b>–<b>e</b>) HRTEM images of a C12GA-templated CePO<sub>4</sub> annealed at 900 °C under N<sub>2</sub> conditions, the inset of (<b>e</b>) showing the corresponding digital diffraction pattern (DDP) of the region of the nanofiber marked with an square, with indicated distance; (<b>f</b>) same DDP with some indexed (<span class="html-italic">hkl</span>) values; (<b>g</b>) corresponding simulated kinetic diffraction diagram.</p> Full article ">Figure 13
<p>(<b>a</b>–<b>d</b>) STEM-HAADF images of C12GA-templated CePO<sub>4</sub> sample, as-prepared (<b>a</b> and <b>b</b>) and annealed at 600 °C/air (<b>c</b> and <b>d</b>); (<b>e</b>) Corresponding EELS spectra performed in a nanofiber of as-prepared and 600 °C-annealed templated CePO<sub>4</sub>; For comparison purposes, the electron energy loss near edge structure (ELNES) spectra of Ce<sup>3+</sup> and Ce<sup>4+</sup> ions are also shown as a reference [<a href="#B102-gels-03-00023" class="html-bibr">102</a>].</p> Full article ">Figure 14
<p>Absorbance spectra of: (<b>a</b>) reference and C12GA-templated as-prepared CePO<sub>4</sub> samples (60 °C-dried); and (<b>b</b>) reference and templated CePO<sub>4</sub> materials after annealing at 900 °C (under air or N<sub>2</sub> conditions), showing also the spectrum of 60 °C-dried templated sample for comparison purposes.</p> Full article ">Figure 15
<p>Photoluminiscence emission spectra corresponding to: (<b>a</b>) non-templated reference and C12GA-templated CePO<sub>4</sub> samples, as-prepared (60 °C) and after annealing at 900 °C/air; and (<b>b</b>) comparison of photoluminescence emission of as-prepared (60 °C) templated CePO<sub>4</sub> with respect to corresponding CePO<sub>4</sub> once annealed at 250, 600 and 900 °C (under N<sub>2</sub> atmosphere).</p> Full article ">Scheme 1
<p>Proposed scheme for the hierarchical self-assembly of lipodipeptide C12GA gelator (C<sub>17</sub>H<sub>32</sub>N<sub>2</sub>O<sub>4</sub>, <span class="html-italic">N</span>-Dodecanoyl-glycyl-<span class="html-small-caps">l</span>-alanine) in aqueous NaH<sub>2</sub>PO<sub>4</sub> media: gelator molecules self-assemble into lamellar-like elongated nanotapes (<b>I</b>). The single nanotapes merge into lamellar ribbons (<b>II</b>), which entangle and collapse forming the 3D-hidrogel (<b>III</b>).</p> Full article ">Scheme 2
<p>Transcription strategy (post-diffusion) for the mineralization of nanofibrous CePO<sub>4</sub>·H<sub>2</sub>O through the use of a preformed hydrogel template of phosphorylated C12GA.</p> Full article ">
5707 KiB  
Article
Cyclodextrin-Based Nanohydrogels Containing Polyamidoamine Units: A New Dexamethasone Delivery System for Inflammatory Diseases
by Monica Argenziano, Chiara Dianzani, Benedetta Ferrara, Shankar Swaminathan, Amedea Manfredi, Elisabetta Ranucci, Roberta Cavalli and Paolo Ferruti
Gels 2017, 3(2), 22; https://doi.org/10.3390/gels3020022 - 8 Jun 2017
Cited by 16 | Viewed by 5915
Abstract
Glucocorticoids are widely prescribed in treatment of rheumatoid arthritis, asthma, systemic lupus erythematosus, lymphoid neoplasia, skin and eye inflammations. However, well-documented adverse effects offset their therapeutic advantages. In this work, novel nano-hydrogels for the sustained delivery of dexamethasone were designed to increase both [...] Read more.
Glucocorticoids are widely prescribed in treatment of rheumatoid arthritis, asthma, systemic lupus erythematosus, lymphoid neoplasia, skin and eye inflammations. However, well-documented adverse effects offset their therapeutic advantages. In this work, novel nano-hydrogels for the sustained delivery of dexamethasone were designed to increase both bioavailability and duration of the administered drug and reducing the therapeutic dose. Hydrogels are soft materials consisting of water-swollen cross-linked polymers to which the insertion of cyclodextrin (CD) moieties adds hydrophobic drug-complexing sites. Polyamidoamines (PAAs) are biocompatible and biodegradable polymers apt to create CD moieties in hydrogels. In this work, β or γ-CD/PAA nanogels have been developed. In vitro studies showed that a pretreatment for 24–48 h with dexamethasone-loaded, β-CD/PAA nanogel (nanodexa) inhibits adhesion of Jurkat cells to human umbilical vein endothelial cells (HUVEC) in conditions mimicking inflammation. This inhibitory effect was faster and higher than that displayed by free dexamethasone. Moreover, nanodexa inhibited COX-2 expression induced by PMA+A23187 in Jurkat cells after 24–48 h incubation in the 10−8–10−5 M concentration range, while dexamethasone was effective only at 10−5 M after 48 h treatment. Hence, the novel nanogel-dexamethasone formulation combines faster action with lower doses, suggesting the potential for being more manageable than the free drug, reducing its adverse side effects. Full article
(This article belongs to the Special Issue Micro- and Nanogels)
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Full article ">Figure 1
<p>FTIR spectra of β-CD and β-CD/PAA.</p> Full article ">Figure 2
<p>pH Dependence of β-CD/PAA and γ-CD/PAA nanogel swelling in aqueous media.</p> Full article ">Figure 3
<p>TEM image of blank (<b>A</b>) and dexamethasone-loaded nanogels (<b>B</b>) (scale bar 150 nm).</p> Full article ">Figure 4
<p>SEM image of blank (<b>A</b>) and dexamethasone-loaded nanogels (<b>B</b>) (scale bar 1 μm).</p> Full article ">Figure 5
<p>DSC thermograms of dexamethasone (<b>A</b>) and dexamethasone-loaded β-CD/PAA (<b>B</b>) and γ-CD/PAA (<b>C</b>) nanogels.</p> Full article ">Figure 6
<p>In vitro release kinetics of dexamethasone from β-CD/PAA (<b>A</b>) and γ-CD/PAA (<b>B</b>) nanogels at pH 7.4. Results are shown as means ± SEM from three independent experiments (<span class="html-italic">n =</span> 3).</p> Full article ">Figure 7
<p>Effect of HUVEC treatment with dexa and nanodexa on adhesiveness to Jurkat cells. HUVEC were pretreated or not with titrated amounts of dexa and nanodexa (10<sup>−9</sup>–10<sup>−5</sup> M) for 24 h (<b>a</b>) and 48 h (<b>b</b>), stimulated with IL-1β for 18 h, then incubated with Jurkat cells for 45 min. Data are expressed as mean ± SEM (<span class="html-italic">n</span> = 5) of the percentage of inhibition versus the control.* <span class="html-italic">p</span> ≤ 0.05 and ** <span class="html-italic">p</span> ≤ 0.01 nanodexa versus dexa (significance was assessed with Student’s <span class="html-italic">t</span>-test for paired varieties). <sup>§</sup> <span class="html-italic">p</span> &lt; 0.05; <sup>§§</sup> <span class="html-italic">p</span> &lt; 0.01, significantly different from untreated cells.</p> Full article ">Figure 8
<p>Fluorescent microscopy of Jurkat cells adherent to HUVECs that were not treated (<b>a</b>) or treated with dexa and nanodexa (<b>b</b>,<b>c</b>, respectively) (scale bar 10 μm; magnification 100×).</p> Full article ">Figure 9
<p>Effect of dexa or nanodexa on COX-2 expression in stimulated Jurkat. Jurkat were pretreated or not with titrated amounts of dexa or nanodexa (10<sup>−8</sup>–10<sup>−5</sup> M) for 24 h (<b>A</b>,<b>C</b>, respectively) and 48 h (<b>B</b>,<b>D</b>, respectively) and then stimulated with PMA+A23187 for 18 h. Then, cells were lysed, and COX-2 expression was analyzed by Western blot. The bar graphs show data (mean ± SEM) normalized to β-actin, expressed as the percentage of inhibition versus the control. * <span class="html-italic">p</span> ≤ 0.05 (significance was assessed with one-way ANOVA and the Dunnett test). Top: Western blot analysis from a representative experiment. Bottom: Densitometric analysis of COX-2 expression expressed in arbitrary units of three independent experiments.</p> Full article ">
10522 KiB  
Article
Temperature-Triggered Colloidal Gelation through Well-Defined Grafted Polymeric Surfaces
by Jan Maarten Van Doorn, Joris Sprakel and Thomas E. Kodger
Gels 2017, 3(2), 21; https://doi.org/10.3390/gels3020021 - 3 Jun 2017
Cited by 5 | Viewed by 5371
Abstract
Sufficiently strong interparticle attractions can lead to aggregation of a colloidal suspension and, at high enough volume fractions, form a mechanically rigid percolating network known as a colloidal gel. We synthesize a model thermo-responsive colloidal system for systematically studying the effect of surface [...] Read more.
Sufficiently strong interparticle attractions can lead to aggregation of a colloidal suspension and, at high enough volume fractions, form a mechanically rigid percolating network known as a colloidal gel. We synthesize a model thermo-responsive colloidal system for systematically studying the effect of surface properties, grafting density and chain length, on the particle dynamics within colloidal gels. After inducing an attraction between particles by heating, aggregates undergo thermal fluctuation which we observe and analyze microscopically; the magnitude of the variance in bond angle is larger for lower grafting densities. Macroscopically, a clear increase of the linear mechanical behavior of the gels on both the grafting density and chain length arises, as measured by rheology, which is inversely proportional to the magnitude of local bond angle fluctuations. This colloidal system will allow for further elucidation of the microscopic origins to the complex macroscopic mechanical behavior of colloidal gels including bending modes within the network. Full article
(This article belongs to the Special Issue Colloid Chemistry)
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Full article ">Figure 1
<p>Controlled grafting density and chain length using surface initiated atom transfer radical polymer (ATRP) of poly(<span class="html-italic">N</span>-isopropylacrylamide) (pNIPAM).</p> Full article ">Figure 2
<p>Gel permeation chromatography (GPC) elution profiles for polymers with different degrees of polymerization; with the elution volume of the polymers being inversely proportional to their respective degree of polymerisation. DP = 10, Mn = 2.9 × 10<sup>2</sup> g/mol, Mw = 3.1 × 10<sup>2</sup> g/mol, PDI = 1.10; DP = 30, Mn = 3.1 × 10<sup>3</sup> g/mol, Mw = 3.6 × 10<sup>3</sup> g/mol, PDI = 1.2; DP = 100, Mn = 9.3 × 10<sup>3</sup> g/mol, Mw = 1.5 × 10<sup>4</sup> g/mol, PDI = 1.6.</p> Full article ">Figure 3
<p>Optical microscopy images for different grafting densities at 32 °C in 30 mM NaCl for DP = 100. (<b>A</b>) 0.1%; (<b>B</b>) 0.3%; (<b>C</b>) 1.0%; and (<b>D</b>) 3.0%.</p> Full article ">Figure 4
<p>Optical microscopy images for different chain lengths at 32 °C in 10 mM NaCl for a grafting density of 3.0%. (<b>A</b>) DP = 10; (<b>B</b>) DP = 30; and (<b>C</b>) DP = 100.</p> Full article ">Figure 5
<p>Bond angle fluctuations for samples of DP = 100 with 0.3% (<b>A</b>) and 3% (<b>B</b>) grafting density. The variance of the fluctuations are 6.7 <math display="inline"> <semantics> <mrow> <msup> <mrow> <mo>(</mo> <mi>deg</mi> <mo>)</mo> </mrow> <mn>2</mn> </msup> </mrow> </semantics> </math> and 19.2 <math display="inline"> <semantics> <mrow> <msup> <mrow> <mo>(</mo> <mi>deg</mi> <mo>)</mo> </mrow> <mn>2</mn> </msup> </mrow> </semantics> </math> respectively. Inset; schematic representation of bond angle calculation between neighboring particles.</p> Full article ">Figure 6
<p>Storage and loss moduli after heating dispersions at <math display="inline"> <semantics> <mrow> <mi mathvariant="sans-serif">ϕ</mi> <mo>=</mo> <mn>0.28</mn> </mrow> </semantics> </math> with 30 mM NaCl to 45 °C with green for DP = 10, gray for DP = 30, blue for DP = 100. All moduli are measured at 1 Hz and <math display="inline"> <semantics> <mrow> <mi mathvariant="sans-serif">γ</mi> <mo>&lt;</mo> <mn>0.03</mn> </mrow> </semantics> </math>.</p> Full article ">Figure 7
<p>Computer-reconstructed visualizations of a sample with particle coordinates obtained from three-dimensional confocal microscopy data. The field of view is 67 <math display="inline"> <semantics> <mi mathvariant="sans-serif">μ</mi> </semantics> </math>m × 67 <math display="inline"> <semantics> <mi mathvariant="sans-serif">μ</mi> </semantics> </math>m × 75 <math display="inline"> <semantics> <mi mathvariant="sans-serif">μ</mi> </semantics> </math>m. (<b>A</b>) a liquid dispersion of particles, <math display="inline"> <semantics> <mrow> <mi mathvariant="sans-serif">ϕ</mi> <mo>≈</mo> <mn>0.15</mn> </mrow> </semantics> </math>, at 25 °C in 50 wt % Sucrose with 10 mM NaCl; (<b>B</b>) a colloidal gel of the same dispersion at 50 °C; (<b>C</b>) calculated radial distribution functions normalized for particle size, <span class="html-italic">a</span>, for gel (red, <b>A</b>) and liquid dispersion (black, <b>B</b>).</p> Full article ">
2664 KiB  
Review
Bioengineering Microgels and Hydrogel Microparticles for Sensing Biomolecular Targets
by Edmondo Battista, Filippo Causa and Paolo Antonio Netti
Gels 2017, 3(2), 20; https://doi.org/10.3390/gels3020020 - 30 May 2017
Cited by 23 | Viewed by 9304
Abstract
Hydrogels, and in particular microgels, are playing an increasingly important role in a diverse range of applications due to their hydrophilic, biocompatible, and highly flexible chemical characteristics. On this basis, solution-like environment, non-fouling nature, easy probe accessibility and target diffusion, effective inclusion of [...] Read more.
Hydrogels, and in particular microgels, are playing an increasingly important role in a diverse range of applications due to their hydrophilic, biocompatible, and highly flexible chemical characteristics. On this basis, solution-like environment, non-fouling nature, easy probe accessibility and target diffusion, effective inclusion of reporting moieties can be achieved, making them ideal substrates for bio-sensing applications. In fact, hydrogels are already successfully used in immunoassays as well as sensitive nucleic acid assays, also enabling hydrogel-based suspension arrays. In this review, we discuss key parameters of hydrogels in the form of micron-sized particles to be used in sensing applications, paying attention to the protein and oligonucleotides (i.e., miRNAs) targets as most representative kind of biomarkers. Full article
(This article belongs to the Special Issue Micro- and Nanogels)
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Full article ">Figure 1
<p>Schemes for proteins and oligonucleotides detection implemented in microgels and hydrogel microparticles with optical fluorescence read-out. In (<b>a</b>) is depicted the recognition of the target by a ligand placed on the surface of the gel, in (<b>b</b>) the capture molecules are copolymerized inside the hydrogel network. In (<b>c</b>) is reported a scheme of recognition of two distinct regions on the target and a transduction mechanism of the capture based on volume phase changes or Förster resonance energy transfer (FRET) [<a href="#B16-gels-03-00020" class="html-bibr">16</a>].</p> Full article ">Figure 2
<p>Microgel and Hydrogel Particle production by batch synthesis and microfluidics. (<b>A</b>) Core/shell microgel synthesis by multistep combination of precipitation and seed polymerization: the formation mechanism of microgels from the aggregation of precursor nanoparticles to the realization of (<b>B</b>) a spectral encoding system on microgels by copolymerization in different compartments of two different dyes. Emulsification in microfluidics through Droplet Generation systems: (<b>C</b>) simple T-junction and flow-focusing; (<b>D</b>) combination of multiple flow-focusing to obtain poly(ethylene glycol) diacrylate (PEGDA)-based TMV Janus microparticles; (<b>E</b>) Continuous flow lithography for the realization complex shaped hydrogel microparticles; (<b>F</b>) Hydrogel microparticles obtained by droplet generation; (G) encoding by Janus PEGDA hydrogels microparticles; and (<b>H</b>) graphical and spectral encoding combination on PEGDA microparticles obtained by flow lithography approach. (<b>A</b>) reprinted with permission from [<a href="#B36-gels-03-00020" class="html-bibr">36</a>], copyright 2016 Wiley; (<b>B</b>) adapted with permission from [<a href="#B38-gels-03-00020" class="html-bibr">38</a>], copyright 2015 American Chemical Society; (<b>F</b>) adapted with permission from [<a href="#B39-gels-03-00020" class="html-bibr">39</a>], copyright 2016 Elsevier B.V.; (<b>D</b>,<b>G</b>) adapted with permission from [<a href="#B40-gels-03-00020" class="html-bibr">40</a>], copyright 2010 American Chemical Society; and (<b>E</b>,<b>H</b>) adapted with permission from [<a href="#B41-gels-03-00020" class="html-bibr">41</a>], copyright 2014 Springer Nature.</p> Full article ">Figure 2 Cont.
<p>Microgel and Hydrogel Particle production by batch synthesis and microfluidics. (<b>A</b>) Core/shell microgel synthesis by multistep combination of precipitation and seed polymerization: the formation mechanism of microgels from the aggregation of precursor nanoparticles to the realization of (<b>B</b>) a spectral encoding system on microgels by copolymerization in different compartments of two different dyes. Emulsification in microfluidics through Droplet Generation systems: (<b>C</b>) simple T-junction and flow-focusing; (<b>D</b>) combination of multiple flow-focusing to obtain poly(ethylene glycol) diacrylate (PEGDA)-based TMV Janus microparticles; (<b>E</b>) Continuous flow lithography for the realization complex shaped hydrogel microparticles; (<b>F</b>) Hydrogel microparticles obtained by droplet generation; (G) encoding by Janus PEGDA hydrogels microparticles; and (<b>H</b>) graphical and spectral encoding combination on PEGDA microparticles obtained by flow lithography approach. (<b>A</b>) reprinted with permission from [<a href="#B36-gels-03-00020" class="html-bibr">36</a>], copyright 2016 Wiley; (<b>B</b>) adapted with permission from [<a href="#B38-gels-03-00020" class="html-bibr">38</a>], copyright 2015 American Chemical Society; (<b>F</b>) adapted with permission from [<a href="#B39-gels-03-00020" class="html-bibr">39</a>], copyright 2016 Elsevier B.V.; (<b>D</b>,<b>G</b>) adapted with permission from [<a href="#B40-gels-03-00020" class="html-bibr">40</a>], copyright 2010 American Chemical Society; and (<b>E</b>,<b>H</b>) adapted with permission from [<a href="#B41-gels-03-00020" class="html-bibr">41</a>], copyright 2014 Springer Nature.</p> Full article ">Figure 3
<p>Hydrogels can be tuned in their physical and chemical properties to perform specific functions matching the need of the final applications: (<b>a</b>) tunable control of mesh size from polymerization reaction conditions; (<b>b</b>) versatile chemistry to allow the conjugation of capture molecule in different position; and (<b>c</b>) molecular sieving coupled to a specific capture of a given target obtained by changing the mesh size and cross-linking a ligand inside the hydrogel matrix.</p> Full article ">Figure 4
<p>(<b>A</b>) Hydrogel microparticles with Strep-Tag II copolymerized with PEGDA are realized by flow-focusing droplet generation approach; (<b>B</b>) the generated droplet photopolymerized inside the microfluidic channel provide monodisperse particle (diameter 88 μm, sd 5 μm) with uniformly distributed peptide sequence co-polymerized inside the gel (size bar is 20 μm); and (<b>C</b> and <b>D</b>) in the lower part of the figure are reported the isotherm binding curve of the Atto-425 Streptavidin captured on by Strep Tag II microparticles over a control in PBS and in serum (adapted with permission from [<a href="#B39-gels-03-00020" class="html-bibr">39</a>], copyright 2016 Elsevier B.V.).</p> Full article ">Figure 5
<p>Microgel platform for microRNA detection based on a strande displacement mechanism: (<b>b</b>) the building of the probe on an encoded microgel; (<b>a</b>) the strand displacement upon contact with target microRNA and fluorescence recovery on the particles; and (<b>c</b>) the distinct fluorescent channels for fluorescein and rhodamine for the encoding and Cy5 for the detection of binding; in the lower part is reported the titration curve of the recovered fluorescence in response to increasing amounts of microRNA (the inset show the limit of detection (LOD) = 2.6 fM) (adapted with permission from [<a href="#B38-gels-03-00020" class="html-bibr">38</a>]. Copyright 2015 American Chemical Society).</p> Full article ">Figure 6
<p>(<b>Upper</b>) Double encoded core/shell PEG microgels are imaged by fluorescence microscopy. Microgels are obtained by multistep synthesis allowing the realization of concentric shells with no spectral overlap between with the reporting system provided by suitable probe. (<b>Bottom</b>) The binding isotherms of ssDNA target of: (<b>a</b>) HIV; (<b>b</b>) SARS; and (<b>c</b>) HCV (Reproduced with permission from [<a href="#B55-gels-03-00020" class="html-bibr">55</a>], copyright 2016 The Royal Society of Chemistry).</p> Full article ">
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Article
A Controlled Antibiotic Release System for the Development of Single-Application Otitis Externa Therapeutics
by Bogdan A. Serban, Kristian T. Stipe, Jeremy B. Alverson, Erik R. Johnston, Nigel D. Priestley and Monica A. Serban
Gels 2017, 3(2), 19; https://doi.org/10.3390/gels3020019 - 17 May 2017
Cited by 15 | Viewed by 5476
Abstract
Ear infections are a commonly-occurring problem that can affect people of all ages. Treatment of these pathologies usually includes the administration of topical or systemic antibiotics, depending on the location of the infection. In this context, we sought to address the feasibility of [...] Read more.
Ear infections are a commonly-occurring problem that can affect people of all ages. Treatment of these pathologies usually includes the administration of topical or systemic antibiotics, depending on the location of the infection. In this context, we sought to address the feasibility of a single-application slow-releasing therapeutic formulation of an antibiotic for the treatment of otitis externa. Thixotropic hydrogels, which are gels under static conditions but liquefy when shaken, were tested for their ability to act as drug controlled release systems and inhibit Pseudomonas aeruginosa and Staphylococcus aureus, the predominant bacterial strains associated with outer ear infections. Our overall proof of concept, including in vitro evaluations reflective of therapeutic ease of administration, formulation stability, cytocompatibility assessment, antibacterial efficacy, and formulation lifespan, indicate that these thixotropic materials have strong potential for development as otic treatment products. Full article
(This article belongs to the Special Issue Hydrogels for Drug Delivery)
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<p>Tetraethyl orthosilicate (TEOS) hydrolysis. (<b>A</b>) Reaction scheme for the formation of the SiO<sub>2</sub> network due to TEOS hydrolysis; (<b>B</b>) Fourier-transformed infrared spectroscopy (FTIR) monitoring of TEOS hydrolysis indicating the apparition of the ethanol peak—a side product of the TEOS hydrolysis reaction; and (<b>C</b>) Proton nuclear magnetic resonance (<sup>1</sup>H-NMR) analysis and confirmation of TEOS hydrolysis. The upper spectrum corresponds to TEOS, while the bottom spectrum shows a shift in the –CH<sub>2</sub>– (methylene) peak from 3.8 to 3.4 ppm and –CH<sub>3</sub> (methyl) peak from 1.1 to 0.9 ppm, indicative of hydrolysis. The 2.0 ppm peak in the hydrolyzed TEOS spectrum corresponds to the methyl groups of the acetic acid used for hydrolysis.</p> Full article ">Figure 2
<p>Physical appearance and optical clarity of thixogels.</p> Full article ">Figure 3
<p>Rheological evaluation of hydrogel thixotropy during three stress cycles. All three formulations show stress-dependent gel-sol transitions. After the first cycle, for all formulations, the storage modulus (G′) values were higher, most likely due to polymeric network consolidation through solvent exclusion.</p> Full article ">Figure 4
<p>Evaluation of the temperature dependent behavior of the thixogels. A slight temperature dependence (approximately 10% increase in G′) is observed at temperatures above 60 °C, probably due to solvent loss.</p> Full article ">Figure 5
<p>Evaluation of the swelling behavior of thixogels in aqueous environments, indicating that the hydrogels minimally change their volumes (approximately 1%) in the presence of physiological fluids (no statistically significant differences were noted between the three formulations).</p> Full article ">Figure 6
<p>Thixogels cytocompatibility assessment. (<b>A</b>) LIVE/DEAD evaluation of cells on TXH indicating the presence of active intracellular esterases, intact cell membranes and some cytoplasmic vacuolation (circled); (<b>B</b>) evaluation of cellular metabolic activity via methyl tetrazolium salt (MTS) Cell-Titer assay, indicating reduced mitochondrial activity on TXL and TXH; (<b>C</b>) improvement of cellular metabolic activity through the addition on polyethylene glycol, molecular weight 600 Da (PEG600) to TXH; and (<b>D</b>) LIVE/DEAD evaluation of cells on TXH/PEG600 75% showing a more physiological spindle-like morphology with some cytoplasmic vacuolation (circled).</p> Full article ">Figure 7
<p>Evaluation of the controlled release capabilities of the thixogels by using fluorescein as a model drug. Lanolin—a compounding wax used for otic ointments—was used as a control. All three thixogels elicited controlled release properties for seven days.</p> Full article ">Figure 8
<p>Fluorescein release from thixogels indicating the controlled release capabilities of the hydrogels. (<b>A</b>) Evaluation of the effects of PEG200 addition, in different amounts, on the fluorescein release properties, compared to TXH; (<b>B</b>) evaluation of the effects of PEG600 addition, in different amounts, on the fluorescein release properties, compared to TXH; (<b>C</b>) comparison of TXH, TXH + PEG200 50%, and TXH + PEG600 50% release rates indicating that longer PEG chains decrease the release rates; and (<b>D</b>) assessment of the loading capacity of the thixogels with four different concentrations of fluorescein, indicating a consistent loading efficiency of ~70%.</p> Full article ">Figure 9
<p>Evaluation of the antibacterial activity of thixogels. (<b>A</b>) Evaluation of the effect of TEOS amounts (TXL versus TXH) on <span class="html-italic">S. aureus</span> growth; (<b>B</b>) evaluation of the effect of TEOS amounts (TXL versus TXH) on <span class="html-italic">P. aeruginosa</span> growth; (<b>C</b>) evaluation of TXH hydrogels with and without PEG on <span class="html-italic">S. aureus</span> growth; and (<b>D</b>) evaluation of TXH hydrogels with and without PEG on <span class="html-italic">P. aeruginosa</span> growth.</p> Full article ">Figure 10
<p>Evaluation of thixogel dehydration rates indicating that all formulations would gradually dry out to a small amount of dry material, and most likely would be naturally eliminated without causing hearing impairment.</p> Full article ">
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Article
Design of Hybrid Gels Based on Gellan-Cholesterol Derivative and P90G Liposomes for Drug Depot Applications
by Nicole Zoratto, Francesca Romana Palmieri, Claudia Cencetti, Elita Montanari, Chiara Di Meo, Maria Letizia Manca, Maria Manconi and Pietro Matricardi
Gels 2017, 3(2), 18; https://doi.org/10.3390/gels3020018 - 8 May 2017
Cited by 3 | Viewed by 5475
Abstract
Gels are extensively studied in the drug delivery field because of their potential benefits in therapeutics. Depot gel systems fall in this area, and the interest in their development has been focused on long-lasting, biocompatible, and resorbable delivery devices. The present work describes [...] Read more.
Gels are extensively studied in the drug delivery field because of their potential benefits in therapeutics. Depot gel systems fall in this area, and the interest in their development has been focused on long-lasting, biocompatible, and resorbable delivery devices. The present work describes a new class of hybrid gels that stem from the interaction between liposomes based on P90G phospholipid and the cholesterol derivative of the polysaccharide gellan. The mechanical properties of these gels and the delivery profiles of the anti-inflammatory model drug diclofenac embedded in such systems confirmed the suitability of these hybrid gels as a good candidate for drug depot applications. Full article
(This article belongs to the Special Issue Micro- and Nanogels)
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<p>Particle size (d) of the different hybrid gels measured with DLS. Results are reported as mean value (<span class="html-italic">n</span> = 3).</p> Full article ">Figure 2
<p>Viscosities of P90G/GeCH mixtures, obtained at 25 °C, 1 s<sup>−1</sup>, for the P90G and GeCH systems, at various concentrations (240–300 mg/g and 0–10 mg/mL, respectively). Results are reported as the mean value (<span class="html-italic">n</span> = 3).</p> Full article ">Figure 3
<p>Storage Modulus, G’, obtained by means of frequency sweep experiments (25 °C, 1 Hz) for the different hybrid gels. The data are reported as the mean value (<span class="html-italic">n</span> = 3).</p> Full article ">Figure 4
<p>(<b>a</b>) Representative mechanical spectra (<span class="html-italic">T</span> = 25 °C) and (<b>b</b>) strain sweep experiments (<span class="html-italic">T</span> = 25 °C) for hybrid gels prepared with different GeCH concentrations: P240-G1 (in orange), P240-G4 (in green), and P240-G10 (in purple). G’: full symbols; G”: empty symbols. The tests were performed in triplicate, and standard deviations always laid within 10% of the mean.</p> Full article ">Figure 4 Cont.
<p>(<b>a</b>) Representative mechanical spectra (<span class="html-italic">T</span> = 25 °C) and (<b>b</b>) strain sweep experiments (<span class="html-italic">T</span> = 25 °C) for hybrid gels prepared with different GeCH concentrations: P240-G1 (in orange), P240-G4 (in green), and P240-G10 (in purple). G’: full symbols; G”: empty symbols. The tests were performed in triplicate, and standard deviations always laid within 10% of the mean.</p> Full article ">Figure 5
<p>Release profiles of free DCF, DCF-loaded within the liposomes and DCF-loaded within the hybrid gels. Results were obtained through dialysis in water at 37 °C. Curves represent the release of DCF from: water solution, as control (black), P240 hybrid gels (P240-G0, P240-G7, and P240-G10 light pink, pink, and purple, respectively), and P300 hybrid gels (P300-G0, P300-G7, and P300-G10 light blue, blue, and dark blue, respectively).</p> Full article ">Scheme 1
<p>Schematic description of the procedure for the hybrid gels preparation.</p> Full article ">
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Review
The Potential of Stimuli-Responsive Nanogels in Drug and Active Molecule Delivery for Targeted Therapy
by Marta Vicario-de-la-Torre and Jacqueline Forcada
Gels 2017, 3(2), 16; https://doi.org/10.3390/gels3020016 - 8 May 2017
Cited by 72 | Viewed by 10125
Abstract
Nanogels (NGs) are currently under extensive investigation due to their unique properties, such as small particle size, high encapsulation efficiency and protection of active agents from degradation, which make them ideal candidates as drug delivery systems (DDS). Stimuli-responsive NGs are cross-linked nanoparticles (NPs), [...] Read more.
Nanogels (NGs) are currently under extensive investigation due to their unique properties, such as small particle size, high encapsulation efficiency and protection of active agents from degradation, which make them ideal candidates as drug delivery systems (DDS). Stimuli-responsive NGs are cross-linked nanoparticles (NPs), composed of polymers, natural, synthetic, or a combination thereof that can swell by absorption (uptake) of large amounts of solvent, but not dissolve due to the constituent structure of the polymeric network. NGs can undergo change from a polymeric solution (swell form) to a hard particle (collapsed form) in response to (i) physical stimuli such as temperature, ionic strength, magnetic or electric fields; (ii) chemical stimuli such as pH, ions, specific molecules or (iii) biochemical stimuli such as enzymatic substrates or affinity ligands. The interest in NGs comes from their multi-stimuli nature involving reversible phase transitions in response to changes in the external media in a faster way than macroscopic gels or hydrogels due to their nanometric size. NGs have a porous structure able to encapsulate small molecules such as drugs and genes, then releasing them by changing their volume when external stimuli are applied. Full article
(This article belongs to the Special Issue Micro- and Nanogels)
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<p>A thermo-responsive nanogel in its swollen state (T &lt; VPTT) and in its collapsed state (T &gt; VTPP) (Reprinted with permission from reference [<a href="#B1-gels-03-00016" class="html-bibr">1</a>]. VPTT = volume phase transition temperature. Copyright 2014 ACS).</p> Full article ">Figure 2
<p>Schematic representation of a multi-stimuli nanogel particle with encapsulated magnetic nanoparticles sensitive to pH, temperature, and magnetic field. (Reprinted with permission from reference [<a href="#B54-gels-03-00016" class="html-bibr">54</a>]. Copyright 2016 Wiley).</p> Full article ">Figure 3
<p>Average hydrodynamic particle size as a function of temperature at different pH and in a buffered solution (ionic strength of 150 mM). pH 6.0 (<span class="html-fig-inline" id="gels-03-00016-i001"> <img alt="Gels 03 00016 i001" src="/gels/gels-03-00016/article_deploy/html/images/gels-03-00016-i001.png"/></span>); pH 6.5 (<span class="html-fig-inline" id="gels-03-00016-i002"> <img alt="Gels 03 00016 i002" src="/gels/gels-03-00016/article_deploy/html/images/gels-03-00016-i002.png"/></span>), pH 6.9 (<span class="html-fig-inline" id="gels-03-00016-i003"> <img alt="Gels 03 00016 i003" src="/gels/gels-03-00016/article_deploy/html/images/gels-03-00016-i003.png"/></span>), pH 7.5 (<span class="html-fig-inline" id="gels-03-00016-i004"> <img alt="Gels 03 00016 i004" src="/gels/gels-03-00016/article_deploy/html/images/gels-03-00016-i004.png"/></span>) and pH 7.9 (<span class="html-fig-inline" id="gels-03-00016-i005"> <img alt="Gels 03 00016 i005" src="/gels/gels-03-00016/article_deploy/html/images/gels-03-00016-i005.png"/></span>). (Reprinted with permission from reference [<a href="#B25-gels-03-00016" class="html-bibr">25</a>]. Copyright 2014 Wiley).</p> Full article ">Figure 4
<p>Schematic picture of multi-functional hybrid nanogel (NG) containing a bimetallic Ag-Au core coated with poly(ethylene glycol) (PEG) network and surface-decorated with hyaluronic acid (HA) molecules as targeting ligands. (Reprinted with permission from reference [<a href="#B76-gels-03-00016" class="html-bibr">76</a>]. Copyright 2010 ACS).</p> Full article ">Figure 5
<p>Cell viabilities of 16-day “in vitro” cultured rat primary neuronal cells after incubating for (<b>a</b>) 24 and (<b>b</b>) 72 h at three concentrations of nanoparticles (1%, 0.3%, and 0.1%). (Reprinted with permission from reference [<a href="#B110-gels-03-00016" class="html-bibr">110</a>]. Copyright 2010 Wiley).</p> Full article ">Figure 6
<p>Degradation mechanisms for (<b>a</b>) highly cross-liked nanogel synthesized with a high degree of substitution and high molecular weight dextran-methacrylate macro-cross-linker and (<b>b</b>) slightly cross-linked nanogel synthesized with a low degree of substitution and low molecular weight dextran-methacrylate macro-cross-linker. (Reprinted with permission from reference [<a href="#B120-gels-03-00016" class="html-bibr">120</a>]. Copyright 2013 RSC).</p> Full article ">Figure 7
<p>(<b>1</b>) In vivo near-infrared (NIR) fluorescence imaging of fluorescent Dox-loaded HA-based NG IV administered in induced tumor mice by injection of H22 tumor cells. The fluorescence intensities are represented by different colors according to color histogram. Red circles on the images display the localization of the tumor; (<b>2</b>) Tumor growth inhibition in H22 tumor-bearing mice that received as treatment Dox-loaded HA-NGs, free Dox, unloaded HA-NGs and saline solution; (<b>3</b>) Uptake of Dox-loaded HA NGs by cells with high CD44 and CD168 receptor expression (<b>A</b>) A549 and (<b>C</b>) H22 and low receptor expression cells (<b>B</b>) NIH3T3. Fluorescent HA NGs are green-colored in the confocal laser scanning microscope images indicating uptake by HA-receptor cells. The scale bar = 10 μm, (<b>D</b>) Flow cytometry analysis of HA NGs incubated with A549, NIH3T3 and H22 cells for 4 h; (<b>4</b>) Biodistribution of Dox for Dox-loaded HA NGs in H22 tumor-bearing mice at various time points after intravenous injection. (Reprinted with permission from reference [<a href="#B147-gels-03-00016" class="html-bibr">147</a>]. Copyright 2015 Elsevier).</p> Full article ">Figure 8
<p>Co-localization of Pc4 loaded MBA-functionalized triple responsive expansile NGs (TRN) (red) in lysosome and mithocondria at 2, 3 and 21 h respectively for (<b>A</b>); (<b>B</b>) and (<b>C</b>). Scale bar in (<b>C</b>) is 10 µm. (<b>F</b>) Biodistribution of MBA-Pc4-TRN before and 72 h after injection in induced tumor mice; (<b>G</b>) “Ex vivo” images 96 h after MBA-Pc4-TRN according to color scale. (Reprinted with permission from reference [<a href="#B148-gels-03-00016" class="html-bibr">148</a>]. Copyright 2014 Elsevier).</p> Full article ">Figure 9
<p>Schematic picture of glucose sensitivity of a double-layered nanogel composed by glycol chitosan/sodium alginate(SA)-poly(<span class="html-small-caps">l</span>-glutmate-<span class="html-italic">co</span>-<span class="html-italic">N</span>-3-<span class="html-small-caps">l</span>-glutamylphenylboronic acid) (PGGA) encapsulating insulin and releasing it in the presence of glucose by complexation between PBA derivative and glucose. (Reprinted with permission from reference [<a href="#B152-gels-03-00016" class="html-bibr">152</a>]. Copyright 2015 RSC).</p> Full article ">
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Article
Nanoparticulate Poly(glucaramide)-Based Hydrogels for Controlled Release Applications
by Erik R. Johnston, Tyler N. Smith and Monica A. Serban
Gels 2017, 3(2), 17; https://doi.org/10.3390/gels3020017 - 6 May 2017
Cited by 1 | Viewed by 4713
Abstract
In 2004, D-Glucaric acid (GA) was identified as one of the top value-added chemicals from renewable feedstocks. For this study, a patented synthetic method was used to obtain gel forming polymers through the polycondensation of GA and several aliphatic diamines. The first time [...] Read more.
In 2004, D-Glucaric acid (GA) was identified as one of the top value-added chemicals from renewable feedstocks. For this study, a patented synthetic method was used to obtain gel forming polymers through the polycondensation of GA and several aliphatic diamines. The first time characterization and a potential practical application of such hydrogels is reported herein. Our findings indicate that the physical properties and gelling abilities of these materials correlate with the chemical structure of the precursor diamines used for polymerization. The hydrogels appear to have nanoparticulate nature, form via aggregation, are thermoresponsive, and appear suitable as controlled release systems for small molecules. Overall, this study further highlights the versatility of GA as a building block for the synthesis of sustainable materials, with potential for a wide array of applications. Full article
(This article belongs to the Special Issue Hydrogels Based on Dynamic Covalent Chemistry)
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<p>Syntheses of poly(glucaramide)s. (<b>A</b>) reaction scheme for the formation of polymerization precursors for the synthesis of poly(glucaramide)s. Monopotassium glucarate (1) is acidified to glucaric acid (2), which is then reacted with a diamine of choice to produce a diammonium <span class="html-small-caps">d</span>-glucarate salt (3) (<b>B</b>) reaction scheme for the synthesis of poly(glucaramide)s. Diammonium <span class="html-small-caps">d</span>-glucarate salts (3) are esterified in methanolic HCl then neutralized with sodium methoxide to form diamine poly(glucaramide)s (4) via polycondensation.</p> Full article ">Figure 2
<p>Physical appearance of poly(glucaramide) gels obtained from C4C6 and C6 polymer solutions, respectively, ranging from 1% <span class="html-italic">w/w</span> (<b>left</b>) to 10% <span class="html-italic">w/w</span> (<b>right</b>). C4C6 mixed poly(glucaramide)s formed gels at concentrations ≥2.5% <span class="html-italic">w/w</span>, while C6 polymers formed gels at concentrations ≥1% <span class="html-italic">w/w</span>. C4 polymer solutions did not form gels in the 1–10% <span class="html-italic">w/w</span> concentration range tested.</p> Full article ">Figure 3
<p>SEM analyses of poly(glucaramide) hydrogels. (<b>A</b>) micrographs of lyophilized 2.5%, 5% and 10% <span class="html-italic">w/w</span> C4C6 gels. For the 2.5% <span class="html-italic">w/w</span> C4C6 samples the structural hierarchy appears to indicate the formation of nanoparticle blocks (<b>top right</b>) while at higher concentrations the nanoparticulate nature of the samples appears more homogeneous; (<b>B</b>) micrographs of lyophilized 1%, 2.5% and 5% <span class="html-italic">w/w</span> C6 gels indicative of the nanoparticulate nature of the samples. The scale bar is 1 μm.</p> Full article ">Figure 4
<p>Particle analyses of the poly(glucaramide) solutions. Particle size distribution in water at 0, 1 and 3 h for the C4 (<b>left</b>), C4C6 (<b>middle</b>) and C6 (<b>right</b>) polymer solutions as observed by dynamic light scattering (DLS). All solutions were prepared at non-gelling concentrations (0.5% <span class="html-italic">w/w</span>) to allow the observation of the nanoparticles and their behavior in solution. Axes information: <span class="html-italic">x</span>—Intensity (%); scale: 0–30%; <span class="html-italic">y</span>—Size (d. nm); scale: 0–10,000 nm. Insets—Visual appearance of poly(glucaramide) solutions after 24 h illustrating the absence of aggegation or precipitation in C4 solutions (<b>top left</b>), aggregation and pre-gellation in C4C6 solutions (<b>top middle</b>) and precipitation in C6 solutions (<b>top right</b>).</p> Full article ">Figure 5
<p>Concentration dependent viscoelastic properties of C4C6 (<b>top</b>) and C6 (<b>bottom</b>) hydrogels, indicating a gel-like behavior for all tested samples (G’ &gt; G”). Maroon symbols indicate G’ (storage modulus), grey symbols indicate G” (loss modulus).</p> Full article ">Figure 6
<p>Gel-to-liquid transition temperature (<span class="html-italic">T</span><sub>G<b>→</b></sub><sub>L</sub>) determination for 5% <span class="html-italic">w/w</span> C4C6 (<b>top</b>) and 5% <span class="html-italic">w/w</span> C6 (<b>bottom</b>) hydrogels. C4C6 samples transitioned from a gel to a liquid state between 100–107 °C, while C6 sample transitioned from a gel to a liquid state between 85–101 °C, indicating that the nature of the diamine in the poly(glucaramide)s influences the structural stability of the hydrogels. No solvent loss occurred during the testing process. The experimental temperature range was 25–110 °C. Maroon symbols indicate G’ (storage modulus), grey symbols indicate G” (loss modulus).</p> Full article ">Figure 7
<p>Thermoreversibility of C4C6 and C6 hydrogels. C4C6 (<b>top</b>) and C6 (<b>bottom</b>) were tested across three cycles of heating/cooling. The data indicates that upon cooling the solutions revert to gels with storage moduli similar to the initial values. The experimental temperature range was 25–110 °C. Maroon symbols indicate G’ (storage modulus), grey symbols indicate G” (loss modulus). The concentration of the hydrogels tested was 5% <span class="html-italic">w/w</span>.</p> Full article ">Figure 8
<p>Slow release of Sodium Tripolyphosphate (STPP) from C4C6 hydrogels (the high error bars for the 10% hydrogel are due to the rapid gelation of the samples during casting, creating some inconsistencies). (<b>A</b>) STPP release rates represented as percent (%) released/day; (<b>B</b>) STPP released, represented as amount (mg) released/day. The data indicates that the C4C6 systems are capable of controlled release of small molecules.</p> Full article ">Figure 9
<p>Illustration of potential STPP loading mechanisms in the poly(glucaramide) hydrogels with the small molecules either encapsulated in the nanoparticles (<b>right</b>) or entrapped in the hydrogel network (<b>left</b>).</p> Full article ">Figure 10
<p>STPP concentration dependent release from C4C6 hydrogels. (<b>A</b>) hydrogels (2.5% <span class="html-italic">w/w</span>) loaded with different amounts of STPP (30, 40 and 120 mg STPP/g gel) showed identical release rates; (<b>B</b>) hydrogels (2.5% <span class="html-italic">w/w</span>) loaded with different amounts of STPP (30, 40 and 120 mg STPP/g gel) released the small molecule in amounts proportional to the loading concentration (the lowest amounts were detected for the 30 mg STPP/g gel while the highest released amounts were observed for the 120 mg STPP/g gel).</p> Full article ">
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Review
Droplets, Evaporation and a Superhydrophobic Surface: Simple Tools for Guiding Colloidal Particles into Complex Materials
by Marcel Sperling and Michael Gradzielski
Gels 2017, 3(2), 15; https://doi.org/10.3390/gels3020015 - 4 May 2017
Cited by 29 | Viewed by 10353
Abstract
The formation of complexly structured and shaped supraparticles can be achieved by evaporation-induced self-assembly (EISA) starting from colloidal dispersions deposited on a solid surface; often a superhydrophobic one. This versatile and interesting approach allows for generating rather complex particles with corresponding functionality in [...] Read more.
The formation of complexly structured and shaped supraparticles can be achieved by evaporation-induced self-assembly (EISA) starting from colloidal dispersions deposited on a solid surface; often a superhydrophobic one. This versatile and interesting approach allows for generating rather complex particles with corresponding functionality in a simple and scalable fashion. The versatility is based on the aspect that basically one can employ an endless number of combinations of components in the colloidal starting solution. In addition, the structure and properties of the prepared supraparticles may be modified by appropriately controlling the evaporation process, e.g., by external parameters. In this review, we focus on controlling the shape and internal structure of such supraparticles, as well as imparted functionalities, which for instance could be catalytic, optical or electronic properties. The catalytic properties can also result in self-propelling (supra-)particles. Quite a number of experimental investigations have been performed in this field, which are compared in this review and systematically explained. Full article
(This article belongs to the Special Issue Colloid Chemistry)
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<p>Hypothetical qualitative estimation of the value-to-price ratio for different products gathered by colloidal assembly. Adapted with permission from [<a href="#B4-gels-03-00015" class="html-bibr">4</a>] (p. 7), Copyright 2009 Wiley.</p> Full article ">Figure 2
<p>Scheme describing the contact angle (CA) <span class="html-italic">θ</span> of the liquid droplet on a solid substrate and its relation to the different interfacial tensions between the solid (<span class="html-italic">s</span>), liquid (<span class="html-italic">l</span>) and gas (<span class="html-italic">g</span>) phase, as related to each other by Equation (1).</p> Full article ">Figure 3
<p>Blood samples dried on a glass surface from: (<b>a</b>) 27-year-old healthy woman; (<b>b</b>) a person with anemia; (<b>c</b>) a 31-year-old healthy man; (<b>d</b>) a person with hyperlipidemia. Adapted with permission from [<a href="#B30-gels-03-00015" class="html-bibr">30</a>] (p. 90). Copyright 2011 Cambridge University Press.</p> Full article ">Figure 4
<p>(<b>a</b>) SEM image of dried drops for a ratio of silica NPs (diameter: 10 nm)/DNA (20,000 bp) ratio 1:0.5. The scale bar is 200 µm; (<b>b</b>) HR-SEM images of dried drops for an NP/dsDNA ratio of 1:0.5. The scale bar is 2 µm. Adapted with permission from [<a href="#B32-gels-03-00015" class="html-bibr">32</a>] (p. 3663). Copyright 2014 Springer Nature.</p> Full article ">Figure 5
<p>Schematic description of the different modes observed for a drying droplet on a solid substrate, with the mass flow of cooled water (blue arrows) and that due to the interfacial tension gradients (Marangoni flow; red arrows) being indicated for: (<b>a</b>) constant contact angle (CCA) mode, as observed on most superhydrophobic surfaces; (<b>b</b>) constant contact radius (CCR) mode.</p> Full article ">Figure 6
<p>Wetting of superhydrophobic surfaces: (<b>a</b>) Cassie state with entrapped air within the surface grooves; (<b>b</b>) Wenzel state with liquid filling the grooves. Dynamic wetting strongly depends on the prevailing mode of (<b>a</b>) versus (<b>b</b>): (<b>c</b>) the difference of advancing <math display="inline"> <semantics> <mrow> <mrow> <mo>(</mo> <mrow> <msub> <mi>θ</mi> <mi>A</mi> </msub> </mrow> <mo>)</mo> </mrow> </mrow> </semantics> </math> and receding <math display="inline"> <semantics> <mrow> <mo stretchy="false">(</mo> <msub> <mi>θ</mi> <mi>R</mi> </msub> </mrow> </semantics> </math>) CA is the measure of the surface hysteresis and droplet adhesion.</p> Full article ">Figure 7
<p>Typical examples for supraparticles prepared by drying of aqueous droplets containing polystyrene (PS) latex particles dispersed in fluorinated oil. Spherical supraparticles are formed showing different color patterns based on the size of the PS latex particles: (<b>a</b>) 270 nm and (<b>b</b>) 320 nm, scale bars = 500 µm. These patterns arise from light-diffraction due to long-range ordering of the particles as shown in (<b>c</b>) at the surface and (<b>d</b>) along the vertically-broken edge of a similar supraparticle; scale bars = 1 µm. Adapted with permission from [<a href="#B25-gels-03-00015" class="html-bibr">25</a>] (p. 2241). Copyright 2000 Science.</p> Full article ">Figure 8
<p>Top: Illustration of the evaporation-induced formation of “doughnut” supraparticles; the inset is showing an SEM of the particle lattice built by 330-nm diameter silica particles. Bottom: Optical micrographs of the final supraparticle from top- (left) and side-view; scale bars are 500 µm. Adapted with permission from [<a href="#B92-gels-03-00015" class="html-bibr">92</a>] (p. 192). Copyright 2010 Wiley.</p> Full article ">Figure 9
<p>Examples for anisometric supraparticles obtained from drying fumed silica (FS) suspensions (from left to right 1.75%, 3.50%, 5.25% <span class="html-italic">w</span>/<span class="html-italic">v</span>) for an initial ionic strength of (<b>a</b>) 0.001 mM and (<b>b</b>) 25 mM using NaCl; the last image on the right side shows a side-view perspective. The scale bars are 500 µm. Adapted with permissions from [<a href="#B93-gels-03-00015" class="html-bibr">93</a>,<a href="#B96-gels-03-00015" class="html-bibr">96</a>] (pp. 587, 598). Copyright 2014 Wiley.</p> Full article ">Figure 10
<p>Controlled supraparticle orientation after drying: (<b>a</b>) anisotropic evaporation due to the surface bending. This allows for the creation of patchy anisometric particles with defined location of magnetic components (Fe<sub>3</sub>O<sub>4</sub>) by appropriately placing external magnets: (<b>b</b>) along the transversal or (<b>c</b>) longitudinal diameter of the ellipsoid. In (<b>b</b>) and (<b>c</b>), the images on the right side present zoomed-in excerpts; scale bars = 0.5 mm; other scale bars are 1 mm. Composed with permission from [<a href="#B108-gels-03-00015" class="html-bibr">108</a>] (p. 5). Copyright 2016 Wiley.</p> Full article ">Figure 11
<p>Optical microscopy of anisometric photonic crystals (PC) obtained by using mixtures of water and ethanol with varying compositions: (<b>a</b>) 2; (<b>b</b>) 4; (<b>c</b>) 6 and (<b>d</b>) 8 vol % of EtOH; scale bars are 800 µm. The systematic dependency of aspect ratios, i.e., anisometry values, is given in (<b>e</b>). Adapted with permission from [<a href="#B109-gels-03-00015" class="html-bibr">109</a>] (p. 22647). Copyright 2015 American Chemical Society.</p> Full article ">Figure 12
<p>Assembly of (multi-)patched supraparticles in drying sessile droplets on a superhydrophobic surface: (<b>a</b>) single- (<b>b</b>) bi- and (<b>c</b>) tri-patched; scale bars are 500 µm. Altered with permission from [<a href="#B92-gels-03-00015" class="html-bibr">92</a>] (p. 193). Copyright 2010 Wiley.</p> Full article ">Figure 13
<p>Optical microscopy images of patchy supraparticles assembled by EISA using variably-sized polystyrene (PS) latex nano-/micro-particles in suspension droplets generating highly light diffracting “opal balls”. The gold nanoparticles are 22 nm in size. Reprinted with permission from [<a href="#B97-gels-03-00015" class="html-bibr">97</a>] (p. 4266). Copyright 2008 Wiley.</p> Full article ">Figure 14
<p>Optical microscopy images of patchy supraparticles assembled by EISA using differently-sized polystyrene (PS) latex microparticles in suspension droplets, thereby generating these highly light-diffracting “opal balls”. Reprinted with permission from [<a href="#B97-gels-03-00015" class="html-bibr">97</a>] (p. 4266). Copyright 2008 Wiley.</p> Full article ">Figure 15
<p>Colloidal photonic crystals (supraparticles) embedded in an elastomeric matrix in: (<b>a</b>) free; (<b>b</b>) contracted; (<b>c</b>) stretched state. Photographs of the resulting films are shown in (<b>d</b>–<b>f</b>) with supraparticles made of differently-sized PS particles. The reflected color is independent of the observing angle and strain on the films. The scale bars are 1 cm. Reprinted with permission from [<a href="#B116-gels-03-00015" class="html-bibr">116</a>] (p. 1587). Copyright 2015 Royal Society of Chemistry.</p> Full article ">Figure 16
<p>Magnetic Janus supraparticles (<b>a</b>) switched using the different hemispheres at different light intensities: upwards directed (<b>b</b>) PS hemisphere at low light intensity or (<b>c</b>) Fe<sub>3</sub>O<sub>4</sub>-TMPTA hemisphere under strong light intensity; scale bars are 500 µm. Adapted with permission from [<a href="#B117-gels-03-00015" class="html-bibr">117</a>] (p. 9435). Copyright 2014 Royal Society of Chemistry.</p> Full article ">Figure 17
<p>Resulting droplets for a 30-min incubation time and containing anti-rabbit IgG antibody functionalized gold nanoparticles at different concentrations of antigen (rabbit IgG); left to right: 0, 1.0, 10.0, 100.0 µg/mL. Reprinted with permission from [<a href="#B119-gels-03-00015" class="html-bibr">119</a>] (p. 6). Copyright 2007 AIP Publishing.</p> Full article ">Figure 18
<p>Oscillating elevator supraparticle in a wt % aqueous H<sub>2</sub>O<sub>2</sub> solution. Starting at the top left, the elevator releases the oxygen bubble and falls down to the left bottom. After producing an oxygen bubble, it gets attracted by the bottom right magnet, following this attraction to the right during the way up. Having reached the surface meniscus, the left magnet pulls the elevator supraparticle back to its starting position, restarting the movement cycle; the scale bar is 1 cm. Reprinted with permission from [<a href="#B94-gels-03-00015" class="html-bibr">94</a>] (p. 6). Copyright 2016 Wiley.</p> Full article ">
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Article
Impact of Chitosan Molecular Weight and Attached Non-Interactive Chains on the Formation of α-Lactalbumin Nanogel Particles
by Juan Du, Young-Hee Cho, Ryan Murphy and Owen Griffith Jones
Gels 2017, 3(2), 14; https://doi.org/10.3390/gels3020014 - 26 Apr 2017
Cited by 4 | Viewed by 4198
Abstract
Thermal treatment of protein–polysaccharide complexes will form nanogel particles, wherein the polysaccharide controls nanogel formation by limiting protein aggregation. To determine the impact of the chitosan molecular weight and non-interactive chains on the formation of nanogels, mixtures of α-lactalbumin were prepared with selectively-hydrolyzed [...] Read more.
Thermal treatment of protein–polysaccharide complexes will form nanogel particles, wherein the polysaccharide controls nanogel formation by limiting protein aggregation. To determine the impact of the chitosan molecular weight and non-interactive chains on the formation of nanogels, mixtures of α-lactalbumin were prepared with selectively-hydrolyzed chitosan containing covalently-attached polyethylene glycol chains (PEG) and heated near the protein’s isoelectric point to induce formation of nanogels. Turbidity of heated mixtures indicated the formation of suspended aggregates, with greater values observed at higher pH, without attached PEG, and among samples with 8.9 kDa chitosan. Mixtures containing 113 kDa chitosan-PEG formed precipitating aggregates above pH 5, coinciding with a low-magnitude colloidal charge and average hydrodynamic radii > 400 nm. All other tested mixtures were stable to precipitation and possessed average hydrodynamic radii ~100 nm, with atomic force microscopy showing homogeneous distributions of spherical nanogel aggregates. Over all of the tested conditions, attached PEG led to no additional significant changes in the size or morphology of nanogels formed from the protein and chitosan. While PEG may have interfered with the interactions between protein and the 113 kDa chitosan, prompting greater aggregation and precipitation, PEG did not indicate any such interference for shorter chitosan chains. Full article
(This article belongs to the Special Issue Micro- and Nanogels)
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<p>Effect of pH on turbidity of heated α-lac complexes at different <span class="html-italic">r</span>-values for mixtures with (<b>a</b>) CH<sub>113</sub>, (<b>b</b>) CH<sub>76</sub>, (<b>c</b>) CH<sub>8.9</sub>, (<b>d</b>) CH<sub>113</sub>PEG, (<b>e</b>) CH<sub>76</sub>PEG, and (<b>f</b>) CH<sub>8.9</sub>PEG. Note that datapoints are not shown for α-lac/CH<sub>113</sub>PEG for <span class="html-italic">r</span> = 10 at pH 5.3 and 5.8 due to formation of precipitates.</p> Full article ">Figure 2
<p>Effect of pH on the ζ-potential of heated α-lac mixtures (<span class="html-italic">r</span> = 10) with (<b>a</b>) CH<sub>XX</sub> and (<b>b</b>) CH<sub>XX</sub>PEG.</p> Full article ">Figure 3
<p>Effect of pH and <span class="html-italic">r</span>-value on hydrodynamic radii of heated α-lac mixtures with (<b>a</b>) CH<sub>113</sub> or (<b>b</b>) CH<sub>113</sub>PEG.</p> Full article ">Figure 4
<p>Images describing the topographical height of surface-deposited samples taken from heated α-lac mixtures (<span class="html-italic">r</span> = 2, pH 4.8) with (<b>a</b>) CH<sub>113</sub> or (<b>b</b>) CH<sub>113</sub>PEG. Z-axis scale shown to right of (<b>b</b>).</p> Full article ">
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Article
Tacticity-Dependent Interchain Interactions of Poly(N-Isopropylacrylamide) in Water: Toward the Molecular Dynamics Simulation of a Thermoresponsive Microgel
by Gaio Paradossi and Ester Chiessi
Gels 2017, 3(2), 13; https://doi.org/10.3390/gels3020013 - 19 Apr 2017
Cited by 8 | Viewed by 5962
Abstract
The discovery that the lower critical solution temperature (LCST) of poly(N-Isopropylacrylamide) (PNIPAM) in water is affected by the tacticity opens the perspective to tune the volume phase transition temperature of PNIPAM microgels by changing the content of meso dyads in the [...] Read more.
The discovery that the lower critical solution temperature (LCST) of poly(N-Isopropylacrylamide) (PNIPAM) in water is affected by the tacticity opens the perspective to tune the volume phase transition temperature of PNIPAM microgels by changing the content of meso dyads in the polymer network. The increased hydrophobicity of isotactic-rich PNIPAM originates from self-assembly processes in aqueous solutions also below the LCST. The present work aims to detect the characteristics of the pair interaction between polymer chains, occurring in a concentration regime close to the chain overlap concentration, by comparing atactic and isotactic-rich PNIPAM solutions. Using atomistic molecular dynamics simulations, we successfully modelled the increased association ability of the meso-dyad-rich polymer in water below the LCST, and gain information on the features of the interchain junctions as a function of tacticity. Simulations carried out above the LCST display the PNIPAM transition to the insoluble state and do not detect a relevant influence of stereochemistry on the structure of the polymer ensemble. The results obtained at 323 K provide an estimate of the swelling ratio of non-stereocontrolled PNIPAM microgels which is in agreement with experimental findings for microgels prepared with low cross-linker/monomer feed ratios. This study represents the first step toward the atomistic modelling of PNIPAM microgels with a controlled tacticity. Full article
(This article belongs to the Special Issue Micro- and Nanogels)
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<p>(<b>a</b>) Illustration of the meso and racemo dyads within the poly(<span class="html-italic">N</span>-Isopropylacrylamide) (PNIPAM) chain. (<b>b</b>) Chemical structure of the stereoisomers and nomenclature of side chain atoms.</p> Full article ">Figure 2
<p>Number of inter-chain contacts in the PNIPAM solutions. Hydrophobic contacts for the atactic and isotactic-rich stereoisomers are displayed in pink and green, respectively. Contacts between N and O atoms for the atactic and isotactic-rich stereoisomers are displayed in red and blue, respectively: (<b>a</b>) <span class="html-italic">T</span> = 283 K; (<b>b</b>) <span class="html-italic">T</span> = 323 K.</p> Full article ">Figure 3
<p>Time behaviour of the radius of gyration of the two-chain ensemble. Red and blue curves refer to atactic and isotactic-rich PNIPAM, respectively. (<b>a</b>) <span class="html-italic">T</span> = 283 K; (<b>b</b>) <span class="html-italic">T</span> = 323 K.</p> Full article ">Figure 4
<p>Time behaviour of the solvent surface accessible area of the two-chain ensemble. Red and blue curves refer to atactic and isotactic-rich PNIPAM, respectively, at <span class="html-italic">T</span> = 283 K. Green and pink curves refer to atactic and isotactic-rich PNIPAM, respectively, at <span class="html-italic">T</span> = 323 K.</p> Full article ">Figure 5
<p>Inter-residues contact map at 283 K in the interval 200–202 ns. The top-left and bottom-right regions across the diagonal refer to atactic and isotactic-rich PNIPAM, respectively.</p> Full article ">Figure 6
<p>Snapshot at 202 ns of the trajectory of the atactic (<b>top</b>) and isotactic-rich (<b>bottom</b>) PNIPAM ensemble at 283 K. Water and hydrogen atoms are omitted. The blue dots display the solvent accessible surface.</p> Full article ">Figure 7
<p>Snapshot at about 130 ns of the trajectory of the isotactic-rich PNIPAM at 283 K. Water and hydrogen atoms are omitted. The backbone atoms are coloured in red and blue for chain A and B, respectively. The pink circles highlight the junctions.</p> Full article ">Figure 8
<p>Inter-residues contact map at 323 K in the interval 200–202 ns. The top-left and bottom-right regions across the diagonal refer to atactic and isotactic-rich PNIPAM, respectively.</p> Full article ">Figure 9
<p>Snapshot at 202 ns of the trajectory of the atactic (<b>left</b>) and isotactic-rich (<b>right</b>) PNIPAM ensemble at 323 K. Water and hydrogen atoms are omitted. The blue dots display the solvent accessible surface.</p> Full article ">
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Article
Ultrasound- and Temperature-Induced Gelation of Gluconosemicarbazide Gelator in DMSO and Water Mixtures
by Mothukunta Himabindu and Aruna Palanisamy
Gels 2017, 3(2), 12; https://doi.org/10.3390/gels3020012 - 18 Apr 2017
Cited by 15 | Viewed by 6462
Abstract
We have developed amphiphilic supramolecular gelators carrying glucose moiety that could gel a mixture of dimethyl sulfoxide (DMSO) and water upon heating as well as ultrasound treatment. When the suspension of gluconosemicarbazide was subjected to ultrasound treatment, gelation took place at much lower [...] Read more.
We have developed amphiphilic supramolecular gelators carrying glucose moiety that could gel a mixture of dimethyl sulfoxide (DMSO) and water upon heating as well as ultrasound treatment. When the suspension of gluconosemicarbazide was subjected to ultrasound treatment, gelation took place at much lower concentrations compared to thermal treatment, and the gels transformed into a solution state at higher temperatures compared to temperature-induced gels. The morphology was found to be influenced by the nature of the stimulus and presence of salts such as KCl, NaCl, CaCl2 and surfactant (sodium dodecyl sulphate) at a concentration of 0.05 M. The gel exhibited impressive tolerance to these additives, revealing the stability and strength of the gels. Fourier transform infrared spectroscopy (FTIR) revealed the presence of the intermolecular hydrogen bonding interactions while differential scanning calorimetry (DSC) and rheological studies supported better mechanical strength of ultrasound-induced (UI) gels over thermally-induced (TI) gels. Full article
(This article belongs to the Special Issue Organogels for Biomedical Applications)
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<p>Digital photographs of sol gel transition of ultrasound- and thermally-induced gels.</p> Full article ">Figure 2
<p>FTIR spectrum of sol, thermally-induced (TI) gel and ultrasound-induced (UI) gel of the gelator in dimethyl sulfoxide (DMSO)/water mixtures (80/20 <span class="html-italic">v</span>/<span class="html-italic">v</span>) at a concentration of 30 mg/mL.</p> Full article ">Figure 3
<p>Thermogram of UI-gel and TI-gel in DMSO/water (80/20 <span class="html-italic">v</span>/<span class="html-italic">v</span>) at 30 mg/mL concentration.</p> Full article ">Figure 4
<p>SEM images of xerogels of Gluconosemicarbazide gelator in DMSO/water mixture at a concentration of 30 mg/mL under different stimuli: (<b>A</b>) thermally-induced (1 µm); (<b>B</b>) SDS (100 nm); (<b>C</b>) KCl (1 μm); (<b>D</b>) NaCl (100 nm); (<b>E</b>) CaCl<sub>2</sub> (100 nm); (<b>F</b>) ultrasound-induced (1 µm).</p> Full article ">Figure 5
<p>Storage modulus <span class="html-italic">G</span>′ and loss modulus <span class="html-italic">G</span>″ as a function of (<b>a</b>) angular frequency; (<b>b</b>) shear stress for gels at a concentration of 30 mg/mL.</p> Full article ">Figure 6
<p>X-ray diffraction spectrum of xerogels of (<b>a</b>) thermally-induced gel and (<b>b</b>) ultrasound-induced gel.</p> Full article ">Figure 7
<p>Schematic route to synthesize gluconosemicarbazide gelator.</p> Full article ">
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