112,728 research outputs found
Integrated 3D Hydrogel Waveguide Out-Coupler by Step-and-Repeat Thermal Nanoimprint Lithography: A Promising Sensor Device for Water and pH
Hydrogel materials offer many advantages for chemical and biological sensoring due to their response to a small change in their environment with a related change in volume. Several designs have been outlined in the literature in the specific field of hydrogel-based optical sensors, reporting a large number of steps for their fabrication. In this work we present a three-dimensional, hydrogel-based sensor the structure of which is fabricated in a single step using thermal nanoimprint lithography. The sensor is based on a waveguide with a grating readout section. A specific hydrogel formulation, based on a combination of PEGDMA (Poly(Ethylene Glycol DiMethAcrylate)), NIPAAm (N-IsoPropylAcrylAmide), and AA (Acrylic Acid), was developed. This stimulus-responsive hydrogel is sensitive to pH and to water. Moreover, the hydrogel has been modified to be suitable for fabrication by thermal nanoimprint lithography. Once stimulated, the hydrogel-based sensor changes its topography, which is characterised physically by AFM and SEM, and optically using a specific optical set-up
Sorption and spatial distribution of protein globules in charged hydrogel particles
We have theoretically studied the uptake of a non-uniformly charged
biomolecule, suitable to represent a globular protein or a drug, by a charged
hydrogel carrier in the presence of a 1:1 electrolyte. Based on the analysis of
a physical interaction Hamiltonian including monopolar, dipolar and Born
(self-energy) contributions derived from linear electrostatic theory of the
unperturbed homogeneous hydrogel, we have identified five different sorption
states of the system, from complete repulsion of the molecule to its full
sorption deep inside the hydrogel, passing through meta- and stable surface
adsorption states. The results are summarized in state diagrams that also
explore the effects of varying the electrolyte concentration, the sign of the
net electric charge of the biomolecule, and the role of including
excluded-volume (steric) or hydrophobic biomolecule-hydrogel interactions. We
show that the dipole moment of the biomolecule is a key parameter controlling
the spatial distribution of the globules. In particular, biomolecules with a
large dipole moment tend to be adsorbed at the external surface of the
hydrogel, even if like-charged, whereas uniformly charged biomolecules tend to
partition towards the internal core of an oppositely-charged hydrogel.
Hydrophobic attraction shifts the states towards internal sorption of the
biomolecule, whereas steric repulsion promotes surface adsorption for
oppositely-charged biomolecules, or the total exclusion for likely-charged
ones. Our results establish a guidance for the spatial partitioning of proteins
and drugs in hydrogel carriers, tuneable by hydrogel charge, pH and salt
concentration.Comment: 16 pages, 5 figure
An ultra melt-resistant hydrogel from food grade carbohydrates
© 2017 The Royal Society of Chemistry. We report a binary hydrogel system made from two food grade biopolymers, agar and methylcellulose (agar-MC), which does not require addition of salt for gelation to occur and has very unusual rheological and thermal properties. It is found that the storage modulus of the agar-MC hydrogel far exceeds those of hydrogels from the individual components. In addition, the agar-MC hydrogel has enhanced mechanical properties over the temperature range 25-85 °C and a maximum storage modulus at 55 °C when the concentration of methylcellulose was 0.75% w/v or higher. This is explained by a sol-gel phase transition of the methylcellulose upon heating as supported by differential scanning calorimetry (DSC) measurements. Above the melting point of agar, the storage modulus of agar-MC hydrogel decreases but is still an elastic hydrogel with mechanical properties dominated by the MC gelation. By varying the mixing ratio of the two polymers, agar and MC, it was possible to engineer a food grade hydrogel of controlled mechanical properties and thermal response. SEM imaging of flash-frozen and freeze-dried samples revealed that the agar-MC hydrogel contains two different types of heterogeneous regions of distinct microstructures. The latter was also tested for its stability towards heat treatment which showed that upon heating to temperatures above 120 °C its structure was retained without melting. The produced highly thermally stable hydrogel shows melt resistance which may find application in high temperature food processing and materials templating
Rain water transport and storage in a model sandy soil with hydrogel particle additives
We study rain water infiltration and drainage in a dry model sandy soil with
superabsorbent hydrogel particle additives by measuring the mass of retained
water for non-ponding rainfall using a self-built 3D laboratory set-up. In the
pure model sandy soil, the retained water curve measurements indicate that
instead of a stable horizontal wetting front that grows downward uniformly, a
narrow fingered flow forms under the top layer of water-saturated soil. This
rain water channelization phenomenon not only further reduces the available
rain water in the plant root zone, but also affects the efficiency of soil
additives, such as superabsorbent hydrogel particles. Our studies show that the
shape of the retained water curve for a soil packing with hydrogel particle
additives strongly depends on the location and the concentration of the
hydrogel particles in the model sandy soil. By carefully choosing the particle
size and distribution methods, we may use the swollen hydrogel particles to
modify the soil pore structure, to clog or extend the water channels in sandy
soils, or to build water reservoirs in the plant root zone
Larval therapy for leg ulcers (VenUS II) : randomised controlled trial
Objective To compare the clinical effectiveness of larval therapy with a standard debridement technique (hydrogel) for sloughy or necrotic leg ulcers. Design Pragmatic, three armed randomised controlled trial. Setting Community nurse led services, hospital wards, and hospital outpatient leg ulcer clinics in urban and rural settings, United Kingdom. Participants 267 patients with at least one venous or mixed venous and arterial ulcer with at least 25% coverage of slough or necrotic tissue, and an ankle brachial pressure index of 0.6 or more. Interventions Loose larvae, bagged larvae, and hydrogel. Main outcome measures The primary outcome was time to healing of the largest eligible ulcer. Secondary outcomes were time to debridement, health related quality of life (SF-12), bacterial load, presence of meticillin resistant Staphylococcus aureus, adverse events, and ulcer related pain (visual analogue scale, from 0 mm for no pain to 150 mm for worst pain imaginable). Results Time to healing was not significantly different between the loose or bagged larvae group and the hydrogel group (hazard ratio for healing using larvae v hydrogel 1.13, 95% confidence interval 0.76 to 1.68; P=0.54). Larval therapy significantly reduced the time to debridement (2.31, 1.65 to 3.2; P<0.001). Health related quality of life and change in bacterial load over time were not significantly different between the groups. 6.7% of participants had MRSA at baseline. No difference was found between larval therapy and hydrogel in their ability to eradicate MRSA by the end of the debridement phase (75% (9/12) v 50% (3/6); P=0.34), although this comparison was underpowered. Mean ulcer related pain scores were higher in either larvae group compared with hydrogel (mean difference in pain score: loose larvae v hydrogel 46.74 (95% confidence interval 32.44 to 61.04), P<0.001; bagged larvae v hydrogel 38.58 (23.46 to 53.70), P<0.001). Conclusions Larval therapy did not improve the rate of healing of sloughy or necrotic leg ulcers or reduce bacterial load compared with hydrogel but did significantly reduce the time to debridement and increase ulcer pain. Trial registration Current Controlled Trials ISRCTN55114812 and National Research Register N0484123692
Patterning porosity in hydrogels by arresting phase separation
Poly (ethylene glycol) (PEG) hydrogels have been used extensively in biological and tissue engineering, because of their outstanding biocompatibility and processability. However, it is not yet possible to process soft materials like PEG hydrogels with the requisite precision and throughput needed to recapitulate macroscopic biological tissue with control over every hierarchical scale. In this study, porous PEG hydrogels are processed by a phase separation method and patterned in a single photolithographic step. The thermodynamics of the temperature triggered spinodal decomposition of a ternary mixture of water, salt, and polymer are studied resulting in a ternary phase diagram and a spinodal temperature plot. Importantly, the state of porosity can be frozen by exposing the hydrogel to UV light to form a crosslinked hydrogel network. The average pore size can be tuned by changing delay between the application of heat and UV exposure. By utilizing grey-scale photomasks, a single process can be used to define regions of pure hydrogel, porous hydrogel with a programmed average pore size, and blank substrate with no hydrogel. In addition to representing a combination of a top-down and a bottom-up processes that enables the realization of complex samples, the simplicity of this process and the versatility of the resultant patterns could provide a useful capability for the definition of hydrogel samples for the development of advanced biomaterials
Understanding Three Hydration-Dependent Transitions of Zwitterionic Carboxybetaine Hydrogel by Molecular Dynamics Simulations
In this work, molecular dynamics simulations were
performed to study a carboxybetaine methacrylate (CBMA) hydrogel under various swelling states. The water content in this study ranged from 28% to 91% of the total weight of the hydrogel. Three transitions of the CBMA hydrogel were observed as the water content increased. The first transition occurs when the water content increases from 33%
to 37%. The observed kink in the self-diffusion coefficient of water indicates that the hydration of the polymer network of the hydrogel is saturated; the further added water is in a less confined state. The second transition was found to be related to the physical cross-links of
the polymer network. As the water content rises to above 62%, the lifetime of the physical cross-links decreases significantly. This abrupt change in the lifetime indicates that the transition represents the equilibrium swelling state of the hydrogel. Finally, the third transition was observed when the water content goes above 81%. The significant increases in the bond and angle energies of the
polymer network indicate that the hydrogel reaches its upper limit swelling state at this transition. These results are comparable to previously published experimental studies of similar zwitterionic hydrogels
Exploitation of a pH-sensitive hydrogel for CO2 detection
In this paper is described how hydrogel is exploited as sensor material for the \ud
detection of carbon dioxide (CO2). A pH-sensitive hydrogel disc, which swells and deswells in response to pH changes, was clamped between a pressure sensor membrane and a porous metal screen together with a bicarbonate solution. Bicarbonate reacts with CO2 resulting in a pH change. The enclosed hydrogel will generate pressure as a response to the pH change. This pressure is a measure for the partial pressure of CO2. The main advantage of this sensor principle is the lack of a reference electrode as required for potentiometric sensors
Fabrication of salt–hydrogel marbles and hollow-shell microcapsules by an aerosol gelation technique
We designed a new method for preparation of liquid marbles by using hydrophilic particles. Salt–hydrogel marbles were prepared by atomising droplets of hydrogel solution in a cold air column followed by rolling of the collected hydrogel microbeads in a bed of micrometre sized salt particles. Evaporation of the water from the resulting salt marbles with a hydrogel core yielded hollow-shell salt microcapsules. The method is not limited to hydrophilic particles and could potentially be also applied to particles of other materials, such as graphite, carbon black, silica and others. The structure and morphology of the salt–hydrogel marbles were analysed by SEM and their particle size distributions were measured. We also tested the dissolution times of the dried salt marbles and compared them with those of table salt samples under the same conditions. The high accessible surface area of the shell of salt microcrystals allows a faster initial release of salt from the hollow-shell salt capsules upon their dissolution in water than from the same amount of table salt. The results suggest that such hollow-shell particles could find applications as a table salt substitute in dry food products and salt seasoning formulations with reduced salt content without the loss of saltiness
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Injectable and Spatially Patterned Microporous Annealed Particle (MAP) Hydrogels for Tissue Repair Applications.
Spatially patterned hydrogels are becoming increasingly popular in the field of regenerative medicine and tissue repair because of their ability to guide cell infiltration and migration. However, postfabrication technologies are usually required to spatially pattern a hydrogel, making these hydrogels difficult to translate into the clinic. Here, an injectable spatially patterned hydrogel is reported using hyaluronic acid (HA)-based particle hydrogels. These particle hydrogels are sequentially loaded into a syringe to form a pattern and, once injected, they maintain the pattern. The applicability of this hydrogel in a wound healing skin model, a subcutaneous implant model, as well as a stroke brain model is examined and distinct patterning in all models tested is shown. This injectable and spatially patterned hydrogel can be used to create physical or biochemical gradients. Further, this design can better match the scaffold properties within the physical location of the tissue (e.g., wound border vs wound center). This allows for better design features within the material that promote repair and regeneration
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