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Gels, Volume 3, Issue 3 (September 2017) – 11 articles

Cover Story (view full-size image): Hydrogels based on polysaccharide and natural protein polymers are of great interest for innovative biomedical applications, as discussed in this review. Probably, the most recent and relevant advances concern: the design of shape memory hydrogels able to switch their form by external stimuli; the production of bioactive matrices with recognition characteristics; and the use of 3D printing technologies for the preparation of scaffolds based on important structural proteins. View this paper
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5280 KiB  
Article
Tuning the Size of Thermoresponsive Poly(N-Isopropyl Acrylamide) Grafted Silica Microgels
by Nils Nun, Stephan Hinrichs, Martin A. Schroer, Dina Sheyfer, Gerhard Grübel and Birgit Fischer
Gels 2017, 3(3), 34; https://doi.org/10.3390/gels3030034 - 17 Sep 2017
Cited by 20 | Viewed by 6310
Abstract
Core-shell microgels were synthesized via a free radical emulsion polymerization of thermoresponsive poly-(N-isopropyl acrylamide), pNipam, on the surface of silica nanoparticles. Pure pNipam microgels have a lower critical solution temperature (LCST) of about 32 °C. The LCST varies slightly with the [...] Read more.
Core-shell microgels were synthesized via a free radical emulsion polymerization of thermoresponsive poly-(N-isopropyl acrylamide), pNipam, on the surface of silica nanoparticles. Pure pNipam microgels have a lower critical solution temperature (LCST) of about 32 °C. The LCST varies slightly with the crosslinker density used to stabilize the gel network. Including a silica core enhances the mechanical robustness. Here we show that by varying the concentration gradient of the crosslinker, the thermoresponsive behaviour of the core-shell microgels can be tuned. Three different temperature scenarios have been detected. First, the usual behaviour with a decrease in microgel size with increasing temperature exhibiting an LCST; second, an increase in microgel size with increasing temperature that resembles an upper critical solution temperature (UCST), and; third, a decrease with a subsequent increase of size reminiscent of the presence of both an LCST, and a UCST. However, since the chemical structure has not been changed, the LCST should only change slightly. Therefore we demonstrate how to tune the particle size independently of the LCST. Full article
(This article belongs to the Special Issue Stimuli-Responsive Gels)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>(<b>a</b>) Scanning electron microscopy (SEM) image of silica particles (Si-2). The scale bar is 200 nm; (<b>b</b>) Fourier transformed infrared spectroscopy (FTIR) spectra of Si-2 before and after (Si-2+TPM) surface modification with TPM.</p> Full article ">Figure 2
<p>(<b>a</b>) Hydrodynamic radius of SiPN-1 for a heating (black cubes) and cooling cycle (red dots) with an empirical fitting function Equation (1); (<b>b</b>) Hydrodynamic radius for several heating and cooling cycles for SiPN-1. In red the temperature gradient is shown.</p> Full article ">Figure 3
<p>TEmicrograph of SiPN-1. Scale bar is 200 nm. Each particle has a darker core and a rough surface resulting from the dried microgel shell.</p> Full article ">Figure 4
<p>(<b>a</b>) Hydrodynamic radius of SiPN-2 as a function of temperature for heating and cooling; (<b>b</b>) TEmicrograph of SiPN-2. Scale bar is 200 nm.</p> Full article ">Figure 5
<p>(<b>a</b>) Hydrodynamic radius of SiPN-3 as a function of temperature for heating and cooling; (<b>b</b>) TEmicrograph of SiPN-3. Scale bar is 200 nm.</p> Full article ">Figure 6
<p>Different scenarios for the core-shell particles during the coil-to-globule transition. The silica core is shown as a grey sphere. The poly-(<span class="html-italic">N</span>-isopropyl acrylamide) (pNipam) chains are represented in purple and the crosslinking chains between two pNipam chains are visualized in green. The light blue circles indicate the hydrodynamic volume of the particles. Scenario (<b>a</b>): Below the lower critical solution temperature (LCST): The microgel particle is swollen with water and the pNipam chains are elongated. The pNipam chains are crosslinked from the inner to the outer shell. Above the LCST the pNipam shell collapses. Due to the internal crosslinking the pNipam shell homogeneously shrinks and the pNipam shell gets thinner due to the expulsion of water. Scenario (<b>b</b>): Below the LCST the pNipam chains are elongated and linked to the silica surface. Only near the surface of the silica particles are the pNipam chains crosslinked. Therefore, above the LCST the pNipam chains collapse into small spheres onto the surface of the silica particles. These small spheres we call microgel balls—we highlighted one with a black circle. Scenario (<b>c</b>): Below the LCST the microgel is swollen with water and the pNipam chains are elongated. By increasing the temperature the microgel structure expels water and shrinks. Due to external crosslinking the shell gets thinner like in scenario (<b>a</b>). However, since long not-crosslinked pNipam chains are also presented, these pNipam chains show up as microgel balls on the surface.</p> Full article ">Figure 7
<p>Hydrodynamic radius for several heating and cooling cycles for sample SiPN-2 (<b>a</b>) and SiPN-3c (<b>b</b>).</p> Full article ">
5249 KiB  
Review
Colloidal Dispersions of Gelled Lipid Nanoparticles (GLN): Concept and Potential Applications
by Mariana Carrancá Palomo, Victoria Martín Prieto and Plamen Kirilov
Gels 2017, 3(3), 33; https://doi.org/10.3390/gels3030033 - 10 Sep 2017
Cited by 19 | Viewed by 7011
Abstract
The interest in using colloidal dispersions of gelled lipid nanoparticles (GLN) for different fields of application has increased in recent years, notably in cosmetic, dermatology, and/or pharmaceutics due to their capacity to immobilize compounds with poor water solubility. The pharmaceutical field desires to [...] Read more.
The interest in using colloidal dispersions of gelled lipid nanoparticles (GLN) for different fields of application has increased in recent years, notably in cosmetic, dermatology, and/or pharmaceutics due to their capacity to immobilize compounds with poor water solubility. The pharmaceutical field desires to achieve lipophilic drug formulations which are able to conserve their stability, although it is well-known that emulsions and solid lipid nanoparticles (SLN) present a lack of stability over time, leading to system destabilization. Furthermore, stable colloidal dispersions of gelled oil particles do not affect the properties of the molecule to be delivered, and they result as an alternative for the previously appointed systems. This review is an attempt to present the reader with an overview of colloidal dispersions of GLN, their concept, formulation methods, as well as the techniques used for their characterization. Moreover, various application fields of organogel dispersions have been illustrated to demonstrate the potential application range of these recent materials. Full article
(This article belongs to the Special Issue Organogels for Biomedical Applications)
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Graphical abstract
Full article ">Figure 1
<p>Examples of LMOG chemical structure: (<b>a</b>) n-octacosane; (<b>b</b>) 60-crown-20-macrocycle; (<b>c</b>) <span class="html-italic">N</span>-n-octyl-<span class="html-small-caps">d</span>-gluconamide; (<b>d</b>) 2-acryloylamide-dedecane-1-sulfonic acid (ADSA); (<b>e</b>) cyclic bis-urea gelator; (<b>f</b>) bis-(2-ethylhexyl) sodium sulfosuccinate (AOT); (<b>g</b>) palladium-CNC pincer bis(carbene).</p> Full article ">Figure 2
<p>Chemical structure and representation of intermolecular interactions of: (<b>a</b>) HSA molecules; <b>(b</b>) DBS molecules.</p> Full article ">Figure 3
<p>Schematic representation of gelled lipid nanoparticle (GLN) colloidal dispersion preparation process.</p> Full article ">Figure 4
<p>Organogel gelation–melting process representation.</p> Full article ">Figure 5
<p>Schematic representation of phase transition parameters of an LMOG organogel: (<b>a</b>) organogel liquefaction process (temperature increase); (<b>b</b>) organogel formation process (temperature decrease).</p> Full article ">Figure 6
<p>Schematic representation of GLN dispersion.</p> Full article ">Figure 7
<p>Chemical structure of common stabilizing agents used to prepare colloidal dispersions of GLN: (<b>a</b>) PEI; (<b>b</b>) AGS; (<b>c</b>) PVA; (<b>d</b>) SH; (<b>e</b>) CTAB; (<b>f</b>) P3HT.</p> Full article ">Figure 8
<p>Gel–sol phase transition parameter evolution of GLN dispersion: (<b>a</b>) Tmelt, Tsol, and gel–sol PTD value determination according to the temperature increase; (<b>b</b>) Tmelt value evolution according the organogelator wt % and the dynamic oil viscosity increase.</p> Full article ">Figure 9
<p>Electron microscopy pictures of GLN dispersion [<a href="#B4-gels-03-00033" class="html-bibr">4</a>]: (<b>a</b>) SEM micrograph; (<b>b</b>) TEM micrograph. Copyright Clearance Center’s RightsLink<sup>®</sup> service.</p> Full article ">Figure 10
<p>Representation of gelled sun protection nanoparticles (GSPN) and their photoprotection ability mechanism.</p> Full article ">Figure 11
<p>Chemical structure of immobilized chemical UV filter as GSPN: (<b>a</b>) octocrylene; (<b>b</b>) benzophenone-3 (BP-3); (<b>c</b>) 2-ethylhexyl-p-dimethylaminobenzoate (EHMAB); (<b>d</b>) avobenzone.</p> Full article ">Figure 12
<p>Representation of the drug delivery ability of GLN.</p> Full article ">Figure 13
<p>Representation of the medical treatment of skin cancers using photodynamic therapy (PDT).</p> Full article ">Figure 14
<p>Chemical structure of immobilized active substances: (<b>a</b>) chloroaluminum phthalocyanine (ClAlPc); <b>(b</b>) ketoconazole; (<b>c</b>) indomethacin.</p> Full article ">
2695 KiB  
Article
Fumed and Precipitated Hydrophilic Silica Suspension Gels in Mineral Oil: Stability and Rheological Properties
by Yoshiki Sugino and Masami Kawaguchi
Gels 2017, 3(3), 32; https://doi.org/10.3390/gels3030032 - 9 Aug 2017
Cited by 12 | Viewed by 9244
Abstract
Hydrophilic fumed silica (FS) and precipitated silica (PS) powders were suspended in mineral oil; increasing the silica volume fraction (φ in the suspension led to the formation of sol, pre-gel, and gel states. Gelation took place at lower φ values in the FS [...] Read more.
Hydrophilic fumed silica (FS) and precipitated silica (PS) powders were suspended in mineral oil; increasing the silica volume fraction (φ in the suspension led to the formation of sol, pre-gel, and gel states. Gelation took place at lower φ values in the FS than the PS suspension because of the lower silanol density on the FS surface. The shear stresses and dynamic moduli of the FS and PS suspensions were measured as a function of φ. Plots of the apparent shear viscosity against shear rate depended on φ and the silica powder. The FS suspensions in the gel state exhibited shear thinning, followed by a weak shear thickening or by constant viscosity with an increasing shear rate. In contrast, the PS suspensions in the gel state showed shear thinning, irrespective of φ. The dynamic moduli of the pre-gel and gel states were dependent on the surface silanol density: at a fixed φ, the storage modulus G′ in the linear viscoelasticity region was larger for the FS than for the PS suspension. Beyond the linear region, the G′ of the PS suspensions showed strain hardening and the loss modulus G″ of the FS and PS suspensions exhibited weak strain overshoot. Full article
(This article belongs to the Special Issue Rheology of Gels)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Visual appearance of the fumed silica (FS) suspensions in the sol, pre-gel, and gel states.</p> Full article ">Figure 2
<p>Plots of the transient shear stress for the FS suspension at the volume fraction of silica <span class="html-italic">φ</span> = 0.013 at the shear rates of 0.5 s<sup>−1</sup> (filled orange circle), 2 s<sup>−1</sup> (filled purple circle), 50 s<sup>−1</sup> (filled blue circle), 200 s<sup>−1</sup> (filled green circle), and 500 s<sup>−1</sup> (filled red circle) as a function of time.</p> Full article ">Figure 3
<p>Plots of the transient shear stress for the FS suspension at <span class="html-italic">φ</span> = 0.017 at the shear rates of 1 s<sup>−1</sup> (filled red circle), 2 s<sup>−1</sup> (filled orange circle), 10 s<sup>−1</sup> (filled purple circle), 50 s<sup>−1</sup> (filled blue circle), 200 s<sup>−1</sup> (filled green circle), and 500 s<sup>−1</sup> (filled black circle) as a function of time.</p> Full article ">Figure 4
<p>Plots of the transient shear stress for the precipitated silica (PS) suspension at <span class="html-italic">φ</span> = 0.030 at the shear rates of 0.5 s<sup>−1</sup> (filled red circle), 1 s<sup>−1</sup> (filled orange circle), 2 s<sup>−1</sup> (filled purple circle), 10 s<sup>−1</sup> (filled blue circle), 100 s<sup>−1</sup> (filled green circle), and 500 s<sup>−1</sup> (filled black circle) as a function of time.</p> Full article ">Figure 5
<p>Double-logarithmic plots of the apparent steady-state shear viscosities (<span class="html-italic">η</span><sub>a</sub>) for the FS suspensions at <span class="html-italic">φ</span> = 0.013 (open red circle), 0.017 (filled red circle), and 0.021 (filled blue square) as a function of the shear rate.</p> Full article ">Figure 6
<p>Double-logarithmic plots of the apparent steady-state shear viscosities for the PS suspensions at <span class="html-italic">φ</span> = 0.030 (open red circle) and 0.035 (filled red circle) as a function of the shear rate.</p> Full article ">Figure 7
<p>The relative viscosity values of the FS (open blue circle) and PS suspensions (filled blue circle) at the shear rate of 10<sup>3</sup> s<sup>−1</sup> as a function of <span class="html-italic">φ</span>. The dashed lines represent fit to the Krieger and Dougherty equation.</p> Full article ">Figure 8
<p>Double-logarithmic plots of the storage modulus (<span class="html-italic">G′</span>, filled circles) and the loss modulus (<span class="html-italic">G″</span>, open squares) for the FS suspensions at <span class="html-italic">φ</span> = 0.017 (red) and 0.035 (blue) as a function of strain.</p> Full article ">Figure 9
<p>Double-logarithmic plots of <span class="html-italic">G′</span> (filled circles) and <span class="html-italic">G″</span> (open circles) for the PS suspensions at <span class="html-italic">φ</span> = 0.035 (red) and 0.045 (blue) as a function of strain.</p> Full article ">Figure 10
<p>Double-logarithmic plots of the <span class="html-italic">G′</span> value in the linear region (<span class="html-italic">G′</span><sub>0</sub>, filled circles) and the critical oscillatory shear strain (<span class="html-italic">γ</span><sub>c</sub>, open circles) for the FS (red) and PS (blue) suspensions as a function of <span class="html-italic">φ</span>.</p> Full article ">Figure 11
<p>Double-logarithmic plots of <span class="html-italic">G′/G′</span><sub>0</sub> (filled circles) and <span class="html-italic">G″</span>/<span class="html-italic">G″</span><sub>0</sub> (open circles) for the FS suspensions at <span class="html-italic">φ</span> = 0.013 (red), 0.017 (red), 0.035 (orange), and 0.045 (green) as a function of strain. <span class="html-italic">G″</span><sub>0</sub> is the loss modulus in the linear region.</p> Full article ">Figure 12
<p>Double-logarithmic plots of <span class="html-italic">G′/G′</span><sub>0</sub> (filled circles) and <span class="html-italic">G″</span>/<span class="html-italic">G″</span><sub>0</sub> (open circles) for the PS suspensions at <span class="html-italic">φ</span> = 0.031 (red), 0.035 (red), 0.040 (orange), and 0.045 (green) as a function of strain.</p> Full article ">
2873 KiB  
Article
Hydrogel Microparticles as Sensors for Specific Adhesion: Case Studies on Antibody Detection and Soil Release Polymers
by Alexander Klaus Strzelczyk, Hanqing Wang, Andreas Lindhorst, Johannes Waschke, Tilo Pompe, Christian Kropf, Benoit Luneau and Stephan Schmidt
Gels 2017, 3(3), 31; https://doi.org/10.3390/gels3030031 - 8 Aug 2017
Cited by 10 | Viewed by 5777
Abstract
Adhesive processes in aqueous media play a crucial role in nature and are important for many technological processes. However, direct quantification of adhesion still requires expensive instrumentation while their sample throughput is rather small. Here we present a fast, and easily applicable method [...] Read more.
Adhesive processes in aqueous media play a crucial role in nature and are important for many technological processes. However, direct quantification of adhesion still requires expensive instrumentation while their sample throughput is rather small. Here we present a fast, and easily applicable method on quantifying adhesion energy in water based on interferometric measurement of polymer microgel contact areas with functionalized glass slides and evaluation via the Johnson–Kendall–Roberts (JKR) model. The advantage of the method is that the microgel matrix can be easily adapted to reconstruct various biological or technological adhesion processes. Here we study the suitability of the new adhesion method with two relevant examples: (1) antibody detection and (2) soil release polymers. The measurement of adhesion energy provides direct insights on the presence of antibodies showing that the method can be generally used for biomolecule detection. As a relevant example of adhesion in technology, the antiadhesive properties of soil release polymers used in today’s laundry products are investigated. Here the measurement of adhesion energy provides direct insights into the relation between polymer composition and soil release activity. Overall, the work shows that polymer hydrogel particles can be used as versatile adhesion sensors to investigate a broad range of adhesion processes in aqueous media. Full article
(This article belongs to the Special Issue Colloid Chemistry)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Principle of the Johnson-Kendall-Roberts (JKR) adhesion measurements with colloidal probes and typical reflection interference contrast microscopy (RICM) images (<b>bottom</b>) right before and after SCP adhesion. The dark area in the middle signifies the soft colloidal probe (SCP) contact area with the solid support.</p> Full article ">Figure 2
<p>Sythetic route toward bovine serum albumin-fluoresceine isothiocyanate (BSA-FTIC) SCPs and cellubiose SCPs based on PEG-dAAm microgels.</p> Full article ">Figure 3
<p>Fluorescence microscopy of BSA-FITC SCPs without addition of antibodies (<b>left</b>) and after addition of antibodies (<b>right</b>). Reduction on fluorescence intensity is due to quenching upon antibody binding and signifies specific interaction of the antibody with the SCPs.</p> Full article ">Figure 4
<p>Toluidine blue (TBO) stained PEG SCPs before functionalization with crotonic acid (CA) (<b>left</b>). After CA functionalization PEG-CA SCPs bind TBO and acquire a dark color (<b>middle</b>). Reduced take-up of TBO after functionalization of CA groups with cellobiose (<b>right</b>).</p> Full article ">Figure 5
<p>Procedure of the SCP adhesion assay. First BSA-FITC SCPs are incubated in antibody solution. Then they are cleaned by centrifugation and washing (<b>a</b>). Next, the SCPs adhesion is measured on protein A slided (<b>b</b>). The micrographs show images of an untreated (<b>left</b>) and antibody treated BSA-FITC SCP (<b>right</b>). After measurement of the contact area, the JKR plots reveal the adhesion energies of the SCPs (<b>c</b>). Note that drawings in (<b>b</b>) are not to scale and are presenting an idealized orientation of the binding partners for clarity.</p> Full article ">Figure 6
<p>Results for SCPs adhesion assays for antibody detection. (<b>a</b>) Adhesion energies of BSA-FITC SCPs after incubation with antibodies (AB) on protein A slides. Measurements without antibody treatment were conducted as negative control. Measurements in presence and absence of 50 mg mL<sup>−1</sup> BSA were conducted to investigate the selectivity of the method. (<b>b</b>) Measurement of BSA-FITC SCPs treated in different concentrations of antibody solution show that the detection limit is on the order of 1 µg mL<sup>−1</sup> antibody.</p> Full article ">Figure 7
<p>Sketches of adhesion experiments with soil release polymers (<b>top</b>) and typical SCP contact areas (<b>bottom</b>). (<b>a</b>) adhesion of bare cellobiose SCPs on hydrophobic glass as reference; (<b>b</b>) in presence of polymer samples (antiredepostion experiment); (<b>c</b>) after removal of the polymers by centrifugation and washing (antiadhesive coating experiment); (<b>d</b>) direct binding of cellobiose SCPs on polymer surfaces (direct binding experiment). Scale bars: 2 µm.</p> Full article ">
5811 KiB  
Review
Gels Obtained by Colloidal Self-Assembly of Amphiphilic Molecules
by Paula Malo de Molina and Michael Gradzielski
Gels 2017, 3(3), 30; https://doi.org/10.3390/gels3030030 - 3 Aug 2017
Cited by 24 | Viewed by 8535
Abstract
Gelation in water-based systems can be achieved in many different ways. This review focusses on ways that are based on self-assembly, i.e., a bottom-up approach. Self-assembly naturally requires amphiphilic molecules and accordingly the systems described here are based on surfactants and to some [...] Read more.
Gelation in water-based systems can be achieved in many different ways. This review focusses on ways that are based on self-assembly, i.e., a bottom-up approach. Self-assembly naturally requires amphiphilic molecules and accordingly the systems described here are based on surfactants and to some extent also on amphiphilic copolymers. In this review we are interested in cases of low and moderate concentrations of amphiphilic material employed to form hydrogels. Self-assembly allows for various approaches to achieve gelation. One of them is via increasing the effective volume fraction by encapsulating solvent, as in vesicles. Vesicles can be constructed in various morphologies and the different cases are discussed here. However, also the formation of very elongated worm-like micelles can lead to gelation, provided the structural relaxation times of these systems is long enough. Alternatively, one may employ amphiphilic copolymers of hydrophobically modified water soluble polymers that allow for network formation in solution by self-assembly due to having several hydrophobic modifications per polymer. Finally, one may combine such polymers with surfactant self-assemblies and thereby produce interconnected hybrid network systems with corresponding gel-like properties. As seen here there is a number of conceptually different approaches to achieve gelation by self-assembly and they may even become combined for further variation of the properties. These different approaches are described in this review to yield a comprehensive overview regarding the options for achieving gel formation by self-assembly. Full article
(This article belongs to the Special Issue Colloid Chemistry)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Electron micrograph of (<b>A</b>) a sample of 1 mM CTAB/1 mM NaSal [<a href="#B24-gels-03-00030" class="html-bibr">24</a>] (With permission of Springer); (<b>B</b>) 50 mM CTAC/50 mM NaSal in 100 mM NaCl (scale bar: 100 nm) [<a href="#B27-gels-03-00030" class="html-bibr">27</a>]; (<b>C</b>) NaOleate solution containing 15 wt % octyltrimethyl ammonium bromide (OTAB) (scale bar: 50 nm), white arrows indicate branching points and black arrows the end-caps [<a href="#B25-gels-03-00030" class="html-bibr">25</a>].</p> Full article ">Figure 2
<p>Sketch of different types of densely packed vesicle gels. (<b>A</b>) made up from unilamellar vesicles (ULVs); (<b>B</b>) made up from multilamellar vesicles (MLVs); (<b>C</b>) densely packed deformed vesicles at high concentration.</p> Full article ">Figure 3
<p>(<b>A</b>) Freeze-fracture transmission electron microscopy (FF-TEM) image of densely packed ULV in the system 182 Na isostearate/567 mM 1-octanol (the aqueous solution contained 20 wt % glycrol to facilitate the FF preparation (size bar: 200 nm) [<a href="#B41-gels-03-00030" class="html-bibr">41</a>]; (<b>B</b>) cryo scanning electron microscopy (cryo-SEM) image of a C<sub>18</sub>–C<sub>8</sub> gemini vesicle gel (size bar: 66.7 nm) [<a href="#B46-gels-03-00030" class="html-bibr">46</a>].</p> Full article ">Figure 4
<p>FF-TEM micrographs of the systems: (<b>A</b>) 90 mM TDMAO/10 mM TTABr/220 mM 1-hexanol (Reproduced (“Adapted” or “in part”) from [<a href="#B49-gels-03-00030" class="html-bibr">49</a>] with permission of The Royal Society of Chemistry.); (<b>B</b>) 360 mM TDMAO/40 mM TTABr/780 mM 1-hexanol/700 mM NaCl.</p> Full article ">Figure 5
<p>(<b>A</b>): FF-TEM micrographs of the system 90 mM TDMAO/10 mM TTABr/220 mM 1-hexanol: (<b>a</b>) immediately after shearing the sample for 1.5 h at a shear rate of 200 s<sup>−1</sup>; (<b>b</b>) 2000 s<sup>−1</sup>; (<b>c</b>) 4000 s<sup>−1</sup>; (<b>d</b>) after allowing the system depicted in (<b>c</b>) to relax under stirring for 12 days; (<b>B</b>): Shear modulus G<sub>0</sub> (□) and electric conductivity during shear in vorticity direction (×) versus shear rate of the pre-shear for the same system. The vesicle solution was sheared at the given shear rate until the apparent shear viscosity indicated a steady state. Then, shearing was stopped and the modulus was measured in an oscillation experiment (Original in [<a href="#B51-gels-03-00030" class="html-bibr">51</a>]).</p> Full article ">Figure 6
<p>Storage modulus G′ as a function of total concentration for vesicles gels composed of Brij30 (technical grade C<sub>12</sub>E<sub>4</sub>) and 4 mol % DTAB, solid line: G′(1 Hz) = A × (c − c<sub>0</sub>)<sup>x</sup>; c<sub>0</sub> = 76 mM, x = 1.87.</p> Full article ">Figure 7
<p>Schematic representation of (<b>A</b>) the polymer architecture of linear and low functionality telechelic polymers and comb-type hydrophobically modified polymers; association of telechelic polymers in (<b>B</b>) aqueous solutions and (<b>C</b>) with microemulsions as a function of the polymer concentration.</p> Full article ">Figure 8
<p>Schematic representation of the interaction potential between micelles (microemulsions) that are decorated and bridged by a telechelic polymer. The interaction has an effective attractive interaction between the micelles, due to the bridging, and a repulsive interaction, due to the steric repulsion between the micelles induced by the presence of the water soluble polymer that decorates the micelles.</p> Full article ">Figure 9
<p>Effect of sodium dodecyl sulfate (SDS) concentration on the zero-shear viscosity of aqueous hydrophobically modified polyacrylamide (HMPAM) solutions of different concentration C [<a href="#B126-gels-03-00030" class="html-bibr">126</a>].</p> Full article ">Figure 10
<p>Zero-shear viscosity η<sub>0</sub> at 25 °C of the mixtures of a microemulsion (100 mM TDMAO/35 mM decane in water) as a function of the concentration of C<sub>18</sub>-EO<sub>150</sub>-C<sub>18</sub> measured with a capillary viscometer until a concentration of 2 wt % and with the instrument AR-G2 above this concentration. Solid line: η<sub>0</sub> = 0.0016((1.54 − c)/wt %)<sup>−0.7</sup>. Dashed line: η<sub>0</sub> = 3.6((c − 1.54)/wt %)<sup>1.7</sup> ([<a href="#B136-gels-03-00030" class="html-bibr">136</a>]—Published by The Royal Society of Chemistry).</p> Full article ">Figure 11
<p>Schematic representation of the (<b>A</b>) association of telechelic polymers and vesicles leading to the formation of decorated vesicles and vesicle networks; and (<b>B</b>) anchoring of hydrophobically modified polymers of different architectures to vesicle membranes.</p> Full article ">
11010 KiB  
Article
Assembly of a Tripeptide and Anti-Inflammatory Drugs into Supramolecular Hydrogels for Sustained Release
by Marina Kurbasic, Chiara D. Romano, Ana M. Garcia, Slavko Kralj and Silvia Marchesan
Gels 2017, 3(3), 29; https://doi.org/10.3390/gels3030029 - 3 Aug 2017
Cited by 25 | Viewed by 6879
Abstract
Supramolecular hydrogels offer interesting opportunities for co-assembly with drugs towards sustained release over time, which could be achieved given that the drug participates in the hydrogel nanostructure, and it is not simply physically entrapped within the gel matrix. dLeu-Phe-Phe is an attractive [...] Read more.
Supramolecular hydrogels offer interesting opportunities for co-assembly with drugs towards sustained release over time, which could be achieved given that the drug participates in the hydrogel nanostructure, and it is not simply physically entrapped within the gel matrix. dLeu-Phe-Phe is an attractive building block of biomaterials in light of the peptide’s inherent biocompatibility and biodegradability. This study evaluates the assembly of the tripeptide in the presence of either of the anti-inflammatory drugs ketoprofen or naproxen at levels analogous to commercial gel formulations. Fourier-transformed infrared (FT-IR), circular dichroism, Thioflavin T fluorescence, transmission electron microscopy (TEM), and oscillatory rheometry are used. Drug release over time is monitored by means of reverse-phase high performance liquid chromatography, and shows different kinetics for the two drugs. Full article
(This article belongs to the Special Issue Hydrogels for Drug Delivery)
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<p>Chemical structures of drug model compounds evaluated for co-assembly with the peptide <sup><span class="html-small-caps">d</span></sup>Leu-Phe-Phe in previous studies (<b>top</b>) and this study (<b>bottom</b>). <b>*</b> denotes the chiral centre of the racemic mixture that composes ketoprofen.</p> Full article ">Figure 2
<p>Oscillatory rheometry analysis of hydrogels (<b>a</b>–<b>c</b>) frequency sweeps; (<b>d</b>–<b>f</b>) time sweeps; (<b>g</b>–<b>i</b>) stress sweeps.</p> Full article ">Figure 3
<p>TEM micrographs of (<b>a</b>) peptide hydrogel, (<b>b</b>) peptide hydrogel with ketoprofen, and (<b>c</b>) peptide hydrogel with naproxen. Scale bar = 50 nm.</p> Full article ">Figure 4
<p>CD spectra of hydrogels; (<b>a</b>–<b>c</b>) kinetics over 60 min, (<b>d</b>–<b>f</b>) heating ramps up to 80 °C.</p> Full article ">Figure 5
<p>Thioflavin T fluorescence assay.</p> Full article ">Figure 6
<p>Drug release study for naproxen (<b>a</b>,<b>b</b>) and ketoprofen (<b>c</b>,<b>d</b>).</p> Full article ">
5328 KiB  
Review
Hydrogels for Biomedical Applications: Cellulose, Chitosan, and Protein/Peptide Derivatives
by Luís J. Del Valle, Angélica Díaz and Jordi Puiggalí
Gels 2017, 3(3), 27; https://doi.org/10.3390/gels3030027 - 17 Jul 2017
Cited by 161 | Viewed by 21236
Abstract
Hydrogels based on polysaccharide and protein natural polymers are of great interest in biomedical applications and more specifically for tissue regeneration and drug delivery. Cellulose, chitosan (a chitin derivative), and collagen are probably the most important components since they are the most abundant [...] Read more.
Hydrogels based on polysaccharide and protein natural polymers are of great interest in biomedical applications and more specifically for tissue regeneration and drug delivery. Cellulose, chitosan (a chitin derivative), and collagen are probably the most important components since they are the most abundant natural polymers on earth (cellulose and chitin) and in the human body (collagen). Peptides also merit attention because their self-assembling properties mimic the proteins that are present in the extracellular matrix. The present review is mainly focused on explaining the recent advances on hydrogels derived from the indicated polymers or their combinations. Attention has also been paid to the development of hydrogels for innovative biomedical uses. Therefore, smart materials displaying stimuli responsiveness and having shape memory properties are considered. The use of micro- and nanogels for drug delivery applications is also discussed, as well as the high potential of protein-based hydrogels in the production of bioactive matrices with recognition ability (molecular imprinting). Finally, mention is also given to the development of 3D bioprinting technologies. Full article
(This article belongs to the Special Issue Colloid Chemistry)
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<p>(<b>a</b>) Scheme of the linear molecular chain (green box), the syndiotactic repeat unit (garnet), the establishment of glycosylic bonds between glucose rings (violet ellipsoid) and intra and intermolecular hydrogen bonding interactions; (<b>b</b>) TEM micrograph of cellulose nanowhiskers (left), scheme and SEM micrograph of nanofibers derived from a fiber of cellulose (middle) and TEM micrograph of bacterial cellulose (right). Reproduced with permission from [<a href="#B19-gels-03-00027" class="html-bibr">19</a>], copyright 2007 ACS; and reproduced from [<a href="#B20-gels-03-00027" class="html-bibr">20</a>].</p> Full article ">Figure 2
<p>Preparation of a physically crosslinkinked injectable hydrogel based on chitosan and hydroxyapatite. Reproduced with permission from [<a href="#B87-gels-03-00027" class="html-bibr">87</a>], copyright 2017 Elsevier.</p> Full article ">Figure 3
<p>Scheme showing the synthesis of chitosan-<span class="html-italic">g</span>-aniline (<b>a</b>), PEGS-FA copolymers (<b>b</b>) and the structure of the hydrogel derived from both copolymers (<b>c</b>). Photographs showing the corresponding solutions (<b>d</b>) and flexible behavior of the hydrogel under bending and pressing efforts (<b>e</b>). Reproduced with permission from [<a href="#B89-gels-03-00027" class="html-bibr">89</a>], copyright 2017 Elsevier.</p> Full article ">Figure 4
<p>Preparation of hollow structures (e.g., cup and tube) from CS/gelatin hydrogels based on a controllable ion crosslinking process. Reproduced with permission from [<a href="#B113-gels-03-00027" class="html-bibr">113</a>], copyright 2017 Elsevier.</p> Full article ">Figure 5
<p>Typical structures of different self-assembled peptides: RADA-like SAPs, complementary coassembling peptides, peptide amphiphiles, cyclo-SAPs, and functionalized SAPs. Reproduced with permission from [<a href="#B121-gels-03-00027" class="html-bibr">121</a>], copyright 1995 Elsevier.</p> Full article ">Figure 6
<p>(<b>a</b>) Scheme showing the hydrophobic (blue) and hydrophilic (orange) regions of a cyclohexane-based hydrogelator having amino acids (AA) with hydrophobic side groups; (<b>b</b>) a single strand formed through the multiple hydrogen bonds that each single molecule can establish. Reproduced with permission from [<a href="#B127-gels-03-00027" class="html-bibr">127</a>], copyright 2004 Wiley.</p> Full article ">Figure 7
<p>Schematic representation of the culture of fibroblast or endothelial cells in enantiomeric nanofibrous hydrogels (<span class="html-italic">d</span>, <span class="html-italic">l</span> right-handed and left-handed helices, respectively). Reproduced with permission from [<a href="#B144-gels-03-00027" class="html-bibr">144</a>], copyright 2014 Wiley.</p> Full article ">Figure 8
<p>Scheme showing the different preparation methods applied for the production of micro/nanogel particles. Reproduced with permission from [<a href="#B147-gels-03-00027" class="html-bibr">147</a>], copyright 2017 Elsevier.</p> Full article ">Figure 9
<p>Scheme showing the different preparation methods applied for the production microgel networks. Reproduced with permission from [<a href="#B147-gels-03-00027" class="html-bibr">147</a>], copyright 2017 Elsevier.</p> Full article ">Figure 10
<p>Mechanism of SSMHs: A crosslinked hydrogel can be deformed under an external stress and the temporary shape fixed by an external stimulus that induces the establishment of reversible interactions. A second stimulus may break the interactions and the material reverts to its permanent shape. Reproduced with permission from [<a href="#B173-gels-03-00027" class="html-bibr">173</a>], copyright 2017 RSC.</p> Full article ">Figure 11
<p>Scheme showing the different steps involved in the molecular imprinting process: Mixing of the appropriate template molecule and the selected functional monomer(s) and cross-linker(s) in a solvent; the polymerization of the formed complex; and finally the removal of the template, unreacted monomer, and cross-linker molecules. Adapted from [<a href="#B179-gels-03-00027" class="html-bibr">179</a>].</p> Full article ">Figure 12
<p>Main 3D bioprinting strategies: (<b>A</b>) laser-assisted; (<b>B</b>) injet-based and (<b>C</b>) extrusion-based. Examples of bioprinting tissues correspond to skin prepared by laser printing (<b>D</b>); branched vasculature obtained by inkjet printing (<b>E</b>) and heart aortic valve by extrusion bioprinting (<b>F</b>). Reproduced with permission from [<a href="#B194-gels-03-00027" class="html-bibr">194</a>], copyright 2016 Wiley.</p> Full article ">
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Article
Exploration of Dynamic Elastic Modulus Changes on Glioblastoma Cell Populations with Aberrant EGFR Expression as a Potential Therapeutic Intervention Using a Tunable Hyaluronic Acid Hydrogel Platform
by Hemamylammal Sivakumar, Roy Strowd and Aleksander Skardal
Gels 2017, 3(3), 28; https://doi.org/10.3390/gels3030028 - 13 Jul 2017
Cited by 17 | Viewed by 5542
Abstract
Glioblastoma (GBM) is one of most aggressive forms of brain cancer, with a median survival time of 14.6 months following diagnosis. This low survival rate could in part be attributed to the lack of model systems of this type of cancer that faithfully [...] Read more.
Glioblastoma (GBM) is one of most aggressive forms of brain cancer, with a median survival time of 14.6 months following diagnosis. This low survival rate could in part be attributed to the lack of model systems of this type of cancer that faithfully recapitulate the tumor architecture and microenvironment seen in vivo in humans. Therapeutic studies would provide results that could be translated to the clinic efficiently. Here, we assess the role of the tumor microenvironment physical parameters on the tumor, and its potential use as a biomarker using a hyaluronic acid hydrogel system capable of elastic modulus tuning and dynamic elastic moduli changes. Experiments were conducted to assess the sensitivity of glioblastoma cell populations with different mutations to varying elastic moduli. Cells with aberrant epithelial growth factor receptor (EGFR) expression have a predilection for a stiffer environment, sensing these parameters through focal adhesion kinase (FAK). Importantly, the inhibition of FAK or EGFR generally resulted in reversed elastic modulus preference. Lastly, we explore the concept of therapeutically targeting the elastic modulus and dynamically reducing it via chemical or enzymatic degradation, both showing the capability to reduce or stunt proliferation rates of these GBM populations. Full article
(This article belongs to the Special Issue Hydrogels Based on Dynamic Covalent Chemistry)
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<p>Tuning of hydrogel formulations by cross-linker manipulation. The three elastic moduli (100, 1000 and 2000 Pa) employed in S1, S2, and S3 hydrogels are obtained by modulating ratios of linear versus four-arm PEG-based cross-linkers. The elastic modulus corresponding to an environment less than normal brain elastic modulus (S1), normal brain elastic modulus (S2), and the brain tumor microenvironment (S3). Statistical significance: * <span class="html-italic">p</span> &lt; 0.01 between hydrogel groups.</p> Full article ">Figure 2
<p>Cell proliferation rates as an effect of elastic moduli. U373 cells (<b>A</b>), A172 cells (<b>B</b>), U87 (<b>C</b>), and U87 EGFRvIII cells (<b>D</b>). * denotes <span class="html-italic">p</span> value is less than 0.05 when S1 and S3 values were compared. &amp; denotes <span class="html-italic">p</span> value is less than 0.05 when values of S2 and S3 were compared and # denotes when <span class="html-italic">p</span> value is less than 0.05 when S1 and S2 values where compared.</p> Full article ">Figure 3
<p>Focal adhesion kinase (FAK) expression increases with elastic modulus. (<b>A</b>) Immunofluorescent staining for phosphorylated FAK in U373 cells, A172 cells and U87EGFRvIII cells at S1, S2, and S3. Scale bars—100 μm; (<b>B</b>) Increased resolution imaging of FAK expression at S3. Scale bars—50 μm. (<b>C</b>–<b>F</b>) Proliferation of glioblastoma (GBM) cell types on varying elastic moduli under inhibition of FAK phosphorylation with defactinib: U373 cells (<b>C</b>), A172 cells (<b>D</b>), U87 (<b>E</b>) and U87 EGFRvIII cells (<b>F</b>). * denotes <span class="html-italic">p</span>-value was less than 0.05 when S1 and S3 values were compared, &amp; denotes <span class="html-italic">p</span>-value was less than 0.05 when values of S2 and S3 were compared, and # denotes when the <span class="html-italic">p</span>-value was less than 0.05 when S1 and S2 values were compared.</p> Full article ">Figure 4
<p>Proliferation of GBM cell types on varying elastic moduli under inhibition of epidermal growth factor receptor (EGFR) inhibitors: U373 cells with erlotinib (<b>A</b>), A172 cells with dacomitinib (<b>B</b>), U87 with erlotinib (<b>C</b>) and U87 EGFRvIII cells with dacomitinib (<b>D</b>). * denotes <span class="html-italic">p</span>-value was less than 0.05 when S1 and S3 values were compared, &amp; denotes <span class="html-italic">p</span>-value was less than 0.05 when values of S2 and S3 were compared, and # denotes when <span class="html-italic">p</span>-value was less than 0.05 when S1 and S2 values were compared.</p> Full article ">Figure 5
<p>(<b>A</b>) The integration of a double sulfide bond in the cross-linker, which can then be broken on demand and thereby decrease the elastic modulus of the hydrogels on demand; (<b>B</b>) The elastic modulus reduction experiment modified to suit in vivo conditions, in which hydrogels without the breakable cross-linker are partially digested using collagenase/hyaluronidase to decrease the elastic modulus; (<b>C</b>,<b>D</b>) Rheological data demonstrating NAC treatment reduction PEGSSDA cross-linked hydrogels and collagenase/hyaluronidase treatment reduction of S3 hydrogels, respectively. Statistical significance: * <span class="html-italic">p</span> &lt; 0.01.</p> Full article ">Figure 6
<p>Targeting elastic modulus by using <span class="html-italic">N</span>-Acetyl-<span class="html-small-caps">l</span>-Cysteine to break disulfide bonds in PEGSSDA cross-linked hydrogels, and resulting proliferation rates: (<b>A</b>) U373 cells; (<b>B</b>) A172 cells; (<b>C</b>) U87 cells and (<b>D</b>) U87 EGFRvIII cells. Targeting elastic modulus with collagenase/hyaluronidase to degrade the hyaluronic acid (HA) and gelatin components in S3 hydrogels: (<b>E</b>) U373 cells; (<b>F</b>) A172 cells; (<b>G</b>) U87 cells and (<b>H</b>) U87 EGFR viii cells. * Denotes <span class="html-italic">p</span> value is less than 0.05.</p> Full article ">Figure 7
<p>Biocompatibility assays of cells with <span class="html-italic">N</span>-Acetyl-<span class="html-small-caps">l</span>-cysteine (<b>A</b>) U373 cells; (<b>B</b>) A172 cells; (<b>C</b>) U87 cells and (<b>D</b>) U87 EGFRvIII cells. Biocompatibility assays of cells with collagenase/hyaluronidase; (<b>E</b>) U373 cells; (<b>F</b>) A172 cells; (<b>G</b>) U87 cells and (<b>H</b>) U87 EGFRvIII cells. Other than the case of U373 cells under collagenase treatment (* <span class="html-italic">p</span> &lt; 0.05), control and treated conditions are not significantly different, indicating that the NAC and collagenase/hyaluronidase treatments do not contribute to a reduction in cell proliferation in the <b><span class="html-italic">E’</span></b> reduction studies.</p> Full article ">
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Article
A Bioactive Hydrogel and 3D Printed Polycaprolactone System for Bone Tissue Engineering
by Ivan Hernandez, Alok Kumar and Binata Joddar
Gels 2017, 3(3), 26; https://doi.org/10.3390/gels3030026 - 6 Jul 2017
Cited by 65 | Viewed by 8973
Abstract
In this study, a hybrid system consisting of 3D printed polycaprolactone (PCL) filled with hydrogel was developed as an application for reconstruction of long bone defects, which are innately difficult to repair due to large missing segments of bone. A 3D printed gyroid [...] Read more.
In this study, a hybrid system consisting of 3D printed polycaprolactone (PCL) filled with hydrogel was developed as an application for reconstruction of long bone defects, which are innately difficult to repair due to large missing segments of bone. A 3D printed gyroid scaffold of PCL allowed a larger amount of hydrogel to be loaded within the scaffolds as compared to 3D printed mesh and honeycomb scaffolds of similar volumes and strut thicknesses. The hydrogel was a mixture of alginate, gelatin, and nano-hydroxyapatite, infiltrated with human mesenchymal stem cells (hMSC) to enhance the osteoconductivity and biocompatibility of the system. Adhesion and viability of hMSC in the PCL/hydrogel system confirmed its cytocompatibility. Biomineralization tests in simulated body fluid (SBF) showed the nucleation and growth of apatite crystals, which confirmed the bioactivity of the PCL/hydrogel system. Moreover, dissolution studies, in SBF revealed a sustained dissolution of the hydrogel with time. Overall, the present study provides a new approach in bone tissue engineering to repair bone defects with a bioactive hybrid system consisting of a polymeric scaffold, hydrogel, and hMSC. Full article
(This article belongs to the Special Issue Hydrogels in Tissue Engineering)
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<p>Digital pictures of 3D printed mesh (<b>a</b>), honeycomb (<b>b</b>), and gyroid (<b>c</b>) structures of identical dimensions.</p> Full article ">Figure 2
<p>Scanning electron microscope (SEM) images of freeze-dried polycaprolactone (PCL)-gel samples (<b>a</b>). A high magnification image confirmed the highly porous nature of the hydrogel with interconnected pores. The pore shape and pore wall thickness are marked with a cross-arrow and a rectangular box, respectively (<b>b</b>). A magnified image of region marked with rectangular box in (<b>a</b>) showed complete adherence of hydrogel on the scaffold, which is expected to provide a bioactive coating to the otherwise bioinert surface of PCL (<b>c</b>). The PCL scaffold was characterized by surface micro-roughness and non-homogeneity (<b>d</b>).</p> Full article ">Figure 3
<p>A comparison of X-ray diffraction (XRD) data of hybrid PCL/hydrogel scaffolds with alginate, and gelatin confirmed the presence of semi-crystalline phases of alginate and gelatin in the hydrogel loaded in the PCL scaffold (∇). The diffraction data also confirmed the presence of PCL (•) and hydroxyapatite (HA) (◊) in its monolithic phase.</p> Full article ">Figure 4
<p>The dissolution study carried out in simulated body fluid (SBF) for 3, 6, and 12 days showed the continuous dissolution of hydrogel with time, with decrease in dissolution rate after 3 days. A plateau region after 6 days can either be associated with significant decrease in degradation rate of hydrogel or predominant apatite deposition from the SBF (see <a href="#gels-03-00026-f005" class="html-fig">Figure 5</a>).</p> Full article ">Figure 5
<p>Low magnification SEM images of freeze-dried PCL-gel samples without SBF (<b>a</b>) and with SBF treatment for 3 (<b>b</b>), 6 (<b>c</b>), and 12 days (<b>d</b>). The SBF treated samples showed homogenous apatite layer over the hydrogel as well as PCL struts with an increasing amount of apatite deposition with time. A crack in apatite layer in (<b>c</b>,<b>d</b>) is due the strain generated due to drying of the samples.</p> Full article ">Figure 6
<p>High magnification SEM images of freeze-dried PCL/ hydrogel samples after 3 (<b>a</b>,<b>d</b>,<b>g</b>), 6 (<b>b</b>,<b>e</b>,<b>h</b>), and 12 days (<b>c</b>,<b>f</b>,<b>i</b>) of immersion in SBF. The (<b>g</b>), (<b>h</b>), and (<b>i</b>) are the magnified images of regions marked in micrographs (<b>d</b>), (<b>e</b>), and (<b>f</b>), respectively. Results showed the deposition of apatite on both PCL as well hydrogel (<b>a</b>,<b>d</b>) in the initial period (3 days) of SBF immersion. A lower amount of apatite on PCL struts than hydrogel after 6 and 12 days may be due to the dissolution of deposited apatite from PCL. Scale bar for (<b>a</b>–<b>c</b>,<b>g</b>–<b>i</b>) is 3 μm and for (<b>d</b>–<b>f</b>) 20 μm.</p> Full article ">Figure 7
<p>Representative fluorescence images of PCL-gel samples seeded with pre-stained human mesenchymal stem cells showed the presence of cells (green) in the hydrogel (<b>a</b>,<b>b</b>) as well as on the PCL struts (<b>a</b>). The white-colored broken line shows the boundary between the PCL scaffold and hydrogel. The cells are marked with red circles within both the hydrogel and scaffold areas. Images (<b>c</b>,<b>d</b>) are the magnified images of micrographs (<b>a</b>,<b>b</b>), respectively. Scale bar for (<b>a</b>,<b>b</b>) is 500 μm and for (<b>c</b>,<b>d</b>) is 100 μm.</p> Full article ">
18837 KiB  
Review
Polymeric Hydrogels as Technology Platform for Drug Delivery Applications
by Alejandro Sosnik and Katia P. Seremeta
Gels 2017, 3(3), 25; https://doi.org/10.3390/gels3030025 - 3 Jul 2017
Cited by 71 | Viewed by 15101
Abstract
Hydrogels have become key players in the field of drug delivery owing to their great versatility in terms of composition and adjustability to various administration routes, from parenteral (e.g., intravenous) to non-parenteral (e.g., oral, topical) ones. In addition, based on the envisioned application, [...] Read more.
Hydrogels have become key players in the field of drug delivery owing to their great versatility in terms of composition and adjustability to various administration routes, from parenteral (e.g., intravenous) to non-parenteral (e.g., oral, topical) ones. In addition, based on the envisioned application, the design of bioadhesive or mucoadhesive hydrogels with prolonged residence time in the administration site may be beneficial. For example, hydrogels are used as wound dressings and patches for local and systemic therapy. In a similar way, they can be applied in the vaginal tract for local treatment or in the nasal cavity for a similar goal or, conversely, to target the central nervous system by the nose-to-brain pathway. Overall, hydrogels have demonstrated outstanding capabilities to ensure patient compliance, while achieving long-term therapeutic effects. The present work overviews the most relevant and recent applications of hydrogels in drug delivery with special emphasis on mucosal routes. Full article
(This article belongs to the Special Issue Hydrogels for Drug Delivery)
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<p>Hydrogels and tissue engineering. Schematic diagram of the use of hydrogels in (<b>A</b>) microencapsulation and (<b>B</b>) tissue-engineering scaffold. (Reprinted with permission from reference [<a href="#B16-gels-03-00025" class="html-bibr">16</a>]. Copyright 2014 Elsevier).</p> Full article ">Figure 2
<p>Preparation of alginate hydrogels coated with chitosan for wound dressing. (Reprinted from reference [<a href="#B20-gels-03-00025" class="html-bibr">20</a>]).</p> Full article ">Figure 3
<p>(<b>a</b>,<b>b</b>) Microscopic images of mesenchymal stromal cells (MSC) cultured for seven days in control culture medium after crystal violet staining; (<b>c</b>,<b>d</b>) microscopic images of MSC cultured for seven days in 0.1% chitosan hydrochloride culture medium after crystal violet staining. (Reprinted from reference [<a href="#B20-gels-03-00025" class="html-bibr">20</a>]).</p> Full article ">Figure 4
<p>Schematic representations of Pluronic<sup>®</sup> F127 micelles: (<b>a</b>) single micelle with spherical core-shell geometry; (<b>b</b>) single 2D hexagonally packed layer of micelles; (<b>c</b>) two 2D hexagonally packed layers of micelles (AB); and (<b>d</b>) three layers with ABC (or Faced Centered Cubic, FCC) stacking sequence structure. (<b>b</b>–<b>d</b>) correspond to the radial geometry. (Reprinted with permission from reference [<a href="#B32-gels-03-00025" class="html-bibr">32</a>]. Copyright 2007 American Chemical Society).</p> Full article ">Figure 5
<p>Tetracycline release profiles from poloxamer (- - -) and monoglyceride (―) based gels. Kinetics were determined by equilibrium dialysis. The reported values represent the average of five independent experiments, bars = S.D. (Reprinted with permission from reference [<a href="#B34-gels-03-00025" class="html-bibr">34</a>]. Copyright 1996 Elsevier).</p> Full article ">Figure 6
<p>Correlation between in vitro pilocarpine release and pupillary constriction obtained in vivo. A linear correlation is evident with an <span class="html-italic">R</span><sup>2</sup> of 0.97. As the amount of pilocarpine available for absorption decreases, a corresponding increase in pupil diameter is observed. Data are reported as mean ± SEM. Solid line indicates the best-fit line and dashed line indicates the 95% confidence interval. (Reprinted with permission from reference [<a href="#B1-gels-03-00025" class="html-bibr">1</a>]. Copyright 2009 Elsevier).</p> Full article ">Figure 7
<p>Hematoxylin and Eosin staining to visualize the histology of CEES and NM-exposed corneas treated for 24 h with doxycycline in solution or in a hydrogel. The damaged area is where the epithelium meets the stroma. The wound-healing efficacy of doxycycline solution was close to the doxycycline hydrogel for CEES exposed corneas, as the extent of damage was comparatively mild. However, a superior wound healing efficacy was observed with hydrogels over solutions when harshly damaged NM-exposed corneas were treated with doxycycline. CEES: half mustard; NM: mustard; DOXY: doxycycline. (Reprinted with permission from reference [<a href="#B45-gels-03-00025" class="html-bibr">45</a>]. Copyright 2010 Elsevier).</p> Full article ">Figure 8
<p>Concept behind hydrogels of poly[(propylenesulfide) (PPS)-(<span class="html-italic">N</span>,<span class="html-italic">N</span>-dimethylacrylamide) (DMA)-(<span class="html-italic">N</span>-isopropylacrylamide) (PNIPAAM) that undergo reversible gelation at 37 °C and degrade upon exposure to ROS. (Reprinted with permission from reference [<a href="#B26-gels-03-00025" class="html-bibr">26</a>]. Copyright 2014 American Chemical Society).</p> Full article ">Figure 9
<p>Schematic of aFGF-heparin (HP) thermo-sensitive hydrogels enhance the recovery of spinal cord injury (SCI). The protection of aFGF-HP containing blood-spinal cord barrier (BSCB) protection, neuroprotection, remyelination, attenuation of astrogliosis, axon elongation in three different stages after SCI, which are the main obstacles to recovery of SCI. (Reprinted with permission from reference [<a href="#B50-gels-03-00025" class="html-bibr">50</a>]. Copyright 2017 American Chemical Society).</p> Full article ">Figure 10
<p>Representative TEM micrographs for the aqueous dried AgNPs (100 μg AgNPs/mL): (<b>A</b>) uncoated AgNPs; (<b>B</b>) SDS-coated AgNPs; (<b>C</b>) PEG-coated AgNPs (×100,000); (<b>D</b>) β-CD-coated AgNPs (×140,000) with sizes = 15.7 ± 4.8, 13 ± 4, 19.2 ± 3.6, and 14 ± 4.4 nm, respectively (<span class="html-italic">n</span> = 50, bar represents 100 nm). Insets indicate histograms of AgNPs size distribution. Abbreviations: TEM, transmission electron microscopy; AgNPs, silver nanoparticles; SDS, sodium dodecyl sulfate; PEG, polyethylene glycol; β-CD, β-cyclodextrin. (Reprinted from reference [<a href="#B52-gels-03-00025" class="html-bibr">52</a>]).</p> Full article ">Figure 11
<p>Successive images of representative mice skin abrasion wounds infected with MRSA at different time intervals. Two groups were treated with 0.1% silver nanoparticles (AgNPs) hydrogel and 1% silver sulfadiazine cream. The two other groups were the blank hydrogel-treated group and control untreated mice. Abbreviations: MRSA, methicillin-resistant <span class="html-italic">Staphylococcus aureus</span>; AgNPs, silver nanoparticles. (Reprinted from reference [<a href="#B52-gels-03-00025" class="html-bibr">52</a>]).</p> Full article ">Figure 12
<p>(<b>A</b>) Schematic illustration of the preparation of pectin/starch hydrogels encapsulated <span class="html-italic">Lactobacillus plantarum</span> (<span class="html-italic">L. plantarum</span>) cells. (<b>B</b>) Release profile of encapsulated cells in buffered solution with pH 1.2 and pH 7.4; Values shown are means ± standard deviations (<span class="html-italic">n</span> = 3). (Reprinted with permission from reference [<a href="#B57-gels-03-00025" class="html-bibr">57</a>]. Copyright 2017 Elsevier).</p> Full article ">Figure 12 Cont.
<p>(<b>A</b>) Schematic illustration of the preparation of pectin/starch hydrogels encapsulated <span class="html-italic">Lactobacillus plantarum</span> (<span class="html-italic">L. plantarum</span>) cells. (<b>B</b>) Release profile of encapsulated cells in buffered solution with pH 1.2 and pH 7.4; Values shown are means ± standard deviations (<span class="html-italic">n</span> = 3). (Reprinted with permission from reference [<a href="#B57-gels-03-00025" class="html-bibr">57</a>]. Copyright 2017 Elsevier).</p> Full article ">Figure 13
<p>Percentages of paracetamol release from the hydroxyethylacryl chitosan (HC)/sodium alginate (SA) hydrogels after immersing in simulated gastric fluid (SGF) for 2 h followed by simulated intestinal fluid (SIF) for 6 h at 37 °C: (<b>a</b>) varying ratios of HC to SA and (<b>b</b>) HC50SA50 with varying cross-linker types). (Reprinted with permission from reference [<a href="#B61-gels-03-00025" class="html-bibr">61</a>]. Copyright 2017 Elsevier).</p> Full article ">
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Article
Metal Oxide/TiO2 Hybrid Nanotubes Fabricated through the Organogel Route
by Masahiro Suzuki, Keita Tanaka, Yukie Kato and Kenji Hanabusa
Gels 2017, 3(3), 24; https://doi.org/10.3390/gels3030024 - 22 Jun 2017
Cited by 6 | Viewed by 4846
Abstract
Titanium dioxide (TiO2) nanotube and its hybrid nanotubes (with various metal oxides such as Ta2O5, Nb2O5, ZrO2, and SiO2) were fabricated by the sol-gel polymerization in the ethanol gels formed [...] Read more.
Titanium dioxide (TiO2) nanotube and its hybrid nanotubes (with various metal oxides such as Ta2O5, Nb2O5, ZrO2, and SiO2) were fabricated by the sol-gel polymerization in the ethanol gels formed by simple l-lysine-based organogelator. The self-assembled nanofibers (gel fibers) formed by the gelator functioned as a template. The different calcination temperatures gave TiO2 nanotubes with various crystalline structures; e.g., anatase TiO2 nanotube was obtained by calcination at 600 °C, and rutile TiO2 nanotube was fabricated at a calcination temperature of 750 °C. In the metal oxide/TiO2 hybrid nanotubes, the metal oxide species were uniformly dispersed in the TiO2 nanotube, and the percent content of metal oxide species was found to correspond closely to the feed ratio of the raw materials. This result indicated that the composition ratio of hybrid nanotubes was controllable by the feed ratio of the raw materials. It was found that the metal oxide species inhibited the crystalline phase transition of TiO2 from anatase to rutile. Furthermore, the success of the hybridization of other metal oxides (except for TiO2) indicated the usefulness of the organogel route as one of the fabrication methods of metal oxide nanotubes. Full article
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Full article ">Figure 1
<p>FE-SEM images of TiO<sub>2</sub> nanotubes (<b>A</b>,<b>B</b>) and TEM (transmission electron microscope ) images of gel fibers, prepared from ethanol gel of gelator 1 (<b>C</b>) and TiO<sub>2</sub> nanotubes (<b>D</b>). Scale bars are 10 μm (<b>A</b>); 1.2 μm (<b>B</b>); 0.5 μm (<b>C</b>); and 50 nm (<b>D</b>). The TiO<sub>2</sub> nanotubes were calcined at 600 °C.</p> Full article ">Figure 2
<p>FE-SEM images of surfaces of TiO<sub>2</sub> nanotubes, fabricated at various calcination temperatures (500–900 °C). Scale bars are 600 nm for 500–650 and 800 °C, and 300 nm for 700, 750 and 900 °C.</p> Full article ">Figure 3
<p>Powder XRD patterns of TiO<sub>2</sub> nanotubes fabricated at various calcination temperatures.</p> Full article ">Figure 4
<p>FE-SEM (<b>upper</b>) and TEM (<b>lower</b>) images of Ta<sub>2</sub>O<sub>5</sub>, ZrO<sub>2</sub>, Nb<sub>2</sub>O<sub>5</sub>, and SiO<sub>2</sub> fabricated in ethanol gels. Scale bars are 5 μm for Ta<sub>2</sub>O<sub>5</sub>, ZrO<sub>2</sub> and Nb<sub>2</sub>O<sub>5</sub>; 5 μm for SiO<sub>2</sub> in SEM; and 0.2 μm in TEM images.</p> Full article ">Figure 5
<p>FE-SEM images of Ta<sub>2</sub>O<sub>5</sub>/TiO<sub>2</sub> hybrid nanotubes fabricated in ethanol gels. The ratios of Ti and Ta are 9:1, 8:2, 7:3, and 6:4 from left. Calcination temperature is 600 °C. Scale bars are 3 μm.</p> Full article ">Figure 6
<p>TEM images of metal oxide/TiO<sub>2</sub> hybrid nanotubes (<b>a</b>–<b>d</b>: Zr, <b>e</b>–<b>h</b>: Nb, and <b>i</b>–<b>l</b>: Si). Ti:Zr = 9:1 (<b>a</b>); 8:2 (<b>b</b>); 7:3 (<b>c</b>) and 6:4 (<b>d</b>); Ti:Nb = 9:1 (<b>e</b>), 8:2 (<b>f</b>), 7:3 (<b>g</b>) and 6:4 (<b>h</b>); Ti:Si = 9:1 (<b>i</b>), 8:2 (<b>j</b>), 7:3 (<b>k</b>) and 6:4 (<b>l</b>). Scale bars are 0.2 μm.</p> Full article ">Figure 7
<p>FE-SEM images of hybrid nanotubes of ZrO<sub>2</sub>/SiO<sub>2</sub> (8:2), ZrO<sub>2</sub>/Ta<sub>2</sub>O<sub>5</sub> (8:2), ZrO<sub>2</sub>/Nb<sub>2</sub>O<sub>5</sub> (8:2), Ta<sub>2</sub>O<sub>5</sub>/SiO<sub>2</sub> (8:2), Nb<sub>2</sub>O<sub>5</sub>/SiO<sub>2</sub> (8:2), and Ta<sub>2</sub>O<sub>5</sub>/Nb<sub>2</sub>O<sub>5</sub> (8:2). Scale bars are 5 μm.</p> Full article ">Scheme 1
<p>Chemical structure of Gelator 1.</p> Full article ">
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