| 1. |
- Al-Tikriti, Yassir, et al.
(author)
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Drug-Induced Phase Separation in Polyelectrolyte Microgels
- 2022
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In: Gels. - : MDPI AG. - 2310-2861. ; 8:1
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Journal article (peer-reviewed)abstract
- Polyelectrolyte microgels may undergo volume phase transition upon loading and the release of amphiphilic molecules, a process important in drug delivery. The new phase is "born" in the outermost gel layers, whereby it grows inward as a shell with a sharp boundary to the "mother" phase (core). The swelling and collapse transitions have previously been studied with microgels in large solution volumes, where they go to completion. Our hypothesis is that the boundary between core and shell is stabilized by thermodynamic factors, and thus that collapsed and swollen phases should be able to also coexist at equilibrium. We investigated the interaction between sodium polyacrylate (PA) microgel networks (diameter: 400-850 mu m) and the amphiphilic drug amitriptyline hydrochloride (AMT) in the presence of NaCl/phosphate buffer of ionic strength (I) 10 and 155 mM. We used a specially constructed microscopy cell and micromanipulators to study the size and internal morphology of single microgels equilibrated in small liquid volumes of AMT solution. To probe the distribution of AMT micelles we used the fluorescent probe rhodamine B. The amount of AMT in the microgel was determined by a spectrophotometric technique. In separate experiments we studied the binding of AMT and the distribution between different microgels in a suspension. We found that collapsed, AMT-rich, and swollen AMT-lean phases coexisted in equilibrium or as long-lived metastable states at intermediate drug loading levels. In single microgels at I = 10 mM, the collapsed phase formed after loading deviated from the core-shell configuration by forming either discrete domains near the gel boundary or a calotte shaped domain. At I = 155 mM, single microgels, initially fully collapsed, displayed a swollen shell and a collapsed core after partial release of the AMT load. Suspensions displayed a bimodal distribution of swollen and collapsed microgels. The results support the hypothesis that the boundary between collapsed and swollen phases in the same microgel is stabilized by thermodynamic factors.
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| 2. |
- Lopez-Sanchez, Patricia, 1977, et al.
(author)
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Impact of Glucose on the Nanostructure and Mechanical Properties of Calcium-Alginate Hydrogels
- 2022
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In: Gels. - : MDPI AG. - 2310-2861. ; 8:2
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Journal article (peer-reviewed)abstract
- Alginate is a polysaccharide obtained from brown seaweed that is widely used in food, pharmaceutical, and biotechnological applications due to its versatility as a viscosifier and gelling agent. Here, we investigated the influence of the addition of glucose on the structure and mechanical properties of alginate solutions and calcium-alginate hydrogels produced by internal gelation through crosslinking with Ca2+ . Using1H low-field nuclear magnetic resonance (NMR) and small angle neutron scattering (SANS), we showed that alginate solutions at 1 wt % present structural hetero-geneities at local scale whose size increases with glucose concentration (15–45 wt %). Remarkably, the molecular conformation of alginate in the gels obtained from internal gelation by Ca2+ crosslinking is similar to that found in solution. The mechanical properties of the gels evidence an increase in gel strength and elasticity upon the addition of glucose. The fitting of mechanical properties to a poroelastic model shows that structural changes within solutions prior to gelation and the increase in solvent viscosity contribute to the gel strength. The nanostructure of the gels (at local scale, i.e., up to few hundreds of Å) remains unaltered by the presence of glucose up to 30 wt %. At 45 wt %, the permeability obtained by the poroelastic model decreases, and the Young’s modulus increases. We suggest that macro (rather than micro) structural changes lead to this behavior due to the creation of a network of denser zones of chains at 45 wt % glucose. Our study paves the way for the design of calcium-alginate hydrogels with controlled structure for food and pharmaceutical applications in which interactions with glucose are of relevance.
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| 3. |
- Karim, Ali Naman, 1992, et al.
(author)
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Increasing Water Absorptivity of an Aerogel-Based Coating Mortar in Subsequent Wetting and Drying
- 2022
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In: Gels. - : MDPI AG. - 2310-2861. ; 8:12
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Journal article (peer-reviewed)abstract
- Aerogel-based coating mortars are energy-efficient composites with thermal conductivities of 30–50 mW/(m·K). They are useful when retrofitting uninsulated building envelopes, particularly in listed masonry buildings, as shown in studies. Meanwhile, the long-term reliability of their hygrothermal properties, typically declared after a single laboratory measurement, is not confirmed. To illustrate the latter and by combining experimental and numerical methods, this study shows that (1) the capillary water absorptivity of a commercially available aerogel-based coating mortar increases after repeated drying and wetting cycles, and (2) leads to a higher moisture content in a masonry wall. After the third cycle, the measured water absorption was more than five times higher than after the first one. Based on numerical simulations, the increasing capillary water absorptivity results in 36% higher relative humidity in the wall if the aerogel-based coating mortar is applied externally and exposed to driving rain. Future research should investigate the reasons behind the observed deviations in the capillary water absorptivity and whether it applies to other types of aerogel-based coating mortars.
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| 4. |
- Miranda-Martinez, Andres, et al.
(author)
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Portable Quartz Crystal Resonator Sensor for Characterising the Gelation Kinetics and Viscoelastic Properties of Hydrogels
- 2022
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In: Gels. - : MDPI AG. - 2310-2861. ; 8:11, s. 718-
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Journal article (peer-reviewed)abstract
- Hydrogel biomaterials have found use in various biomedical applications partly due to their biocompatibility and tuneable viscoelastic properties. The ideal rheological properties of hydrogels depend highly on the application and should be considered early in the design process. Rheometry is the most common method to study the viscoelastic properties of hydrogels. However, rheometers occupy much space and are costly instruments. On the other hand, quartz crystal resonators (QCRs) are devices that can be used as low-cost, small, and accurate sensors to measure the viscoelastic properties of fluids. For this reason, we explore the capabilities of a low-cost and compact QCR sensor to sense and characterise the gelation process of hydrogels while using a low sample amount and by sensing two different crosslink reactions: covalent bonds and divalent ions. The gelation of covalently crosslinked mucin hydrogels and physically crosslinked alginate hydrogels could be monitored using the sensor, clearly distinguishing the effect of several parameters affecting the viscoelastic properties of hydrogels, including crosslinking chemistry, polymer concentrations, and crosslinker concentrations. QCR sensors offer an economical and portable alternative method to characterise changes in a hydrogel material's viscous properties to contribute to this type of material design, thus providing a novel approach.
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| 5. |
- Stjernholm, YV, et al.
(author)
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Progesterone Gel and Placebo Prolonged Pregnancy More Effectively Than Intravenous Tocolysis Alone in Women with Preterm Labor
- 2022
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In: Gels (Basel, Switzerland). - : MDPI AG. - 2310-2861. ; 8:5
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Journal article (peer-reviewed)abstract
- The aim of this trial was to evaluate the effect of progesterone gel compared to placebo in prolonging pregnancy among women with preterm labor. Methods: A randomized controlled trial in Sweden in 2009–18. Women with early preterm labor were randomized to daily doses of progesterone gel 90 mg (n = 28) or placebo (n = 30) after standard intravenous tocolytics. Women with intravenous tocolytics alone (n = 29) served as controls. Results: The median latency to delivery was 68 (range 28–88) days with progesterone and 72 (range 9–90) days with placebo (p = 0.84), compared to 1 (range 1–2) day in the control group (progesterone and placebo vs. control p < 0.001). The rate of preterm birth before 34 weeks was 32% after progesterone and 37 % after placebo (p = 0.32) compared to 100 % in the control group (p < 0.001, respectively). The composite neonatal morbidity (p = 0.65) and neonatal intensive care unit admission (p = 0.12) were comparable between the progesterone and placebo groups and lower in these groups compared with neonates in the control group (p < 0.001, respectively). Conclusions: Progesterone gel and placebo were equally effective in prolonging pregnancy among women with early preterm labor, and both treatments were more effective than standard intravenous tocolysis alone. We hypothesize that the acidic placebo gel reinforced the biochemical barrier at the uterine cervix, which counteracts ascending pathogen invasion and subsequent inflammation, and thereby prevented preterm labor.
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| 6. |
- Wanselius, Marcus, et al.
(author)
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Responsive Hyaluronic Acid-Ethylacrylamide Microgels Fabricated Using Microfluidics Technique
- 2022
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In: Gels. - : MDPI. - 2310-2861. ; 8:9
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Journal article (peer-reviewed)abstract
- Volume changes of responsive microgels can probe interactions between polyelectrolytes and species of opposite charges such as peptides and proteins. We have investigated a microfluidics method to synthesize highly responsive, covalently crosslinked, hyaluronic acid microgels for such purposes. Sodium hyaluronate (HA), pre-modified with ethylacrylamide functionalities, was crosslinked in aqueous droplets created with a microfluidic technique. We varied the microgel properties by changing the degree of modification and concentration of HA in the reaction mixture. The degree of modification was determined by H-1 NMR. Light microscopy was used to investigate the responsiveness of the microgels to osmotic stress in aqueous saline solutions by simultaneously monitoring individual microgel species in hydrodynamic traps. The permeability of the microgels to FITC-dextrans of molecular weights between 4 and 250 kDa was investigated using confocal laser scanning microscopy. The results show that the microgels were spherical with diameters between 100 and 500 mu m and the responsivity tunable by changing the degree of modification and the HA concentration. Microgels were fully permeable to all investigated FITC-dextran probes. The partitioning to the microgel from an aqueous solution decreased with the increasing molecular weight of the probe, which is in qualitative agreement with theories of homogeneous gel networks.
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