Hydrogel Probe Research Articles

Gemini Interfaces in Aqueous Lubrication with Hydrogels

The sliding interfaces found in the body—within the eyes, the digestive system, and the articulating joints, for example—are soft and permeable yet extremely robust, possessing low friction. The common elements among these systems are hydrophilic biopolymer networks that provide physical surfaces, elasticity, and fluid permeability. Stiff, impermeable probes are traditionally used to assess the frictional properties of most surfaces, including soft, permeable materials. However, both sides of physiological articulating interfaces are soft and hydrated. Measuring the friction response on just one-half of the cornea–eyelid interface or the cartilage–cartilage interface using a stiff, impermeable probe may not reproduce physiological lubrication. Here, we present lubricity measurements of the interface between two soft, hydrated, and permeable hydrogels. We explore the distinctions between the self-mated “Gemini” hydrogel interface and hydrogels sliding against hard impermeable countersurfaces. A rigid impermeable probe sliding against a soft permeable hydrogel exhibits strong frictional dependence on sliding speed, and a hydrogel probe sliding against flat glass shows a strong friction dependence on time in contact. The twin Gemini interface shows very low friction μ < 0.06, with little dependence on sliding speed or time in contact. This consistently low-friction Gemini interface emulates the physiological condition of two like permeable surfaces in contact, providing excellent lubricity.

An efficient Eu-based anion-selective chemosensor: Synthesis, sensing properties, and its use for the fabrication of fluorescent hydrogel probe

Abstract A novel Eu-complex Eu(TTA)2vinyl-phen has been designed and synthesized via simple reaction as an efficient fluorescent sensor for F−, CH3COO−, and H2PO4−. The anion-sensitivity of Eu-complex was evaluated using a series of anion in DMSO solution. On binding with F−, CH3COO−, or H2PO4−, fluorescence quenching of Eu-complex was easily observed, while no obvious fluorescence change could be observed in the presence of other anions. More importantly, the Eu-complex exhibited excellent selectivity and sensitivity for F− and H2PO4− in water/DMSO (5/5) solution. The titration results of UV–vis, fluorescence, and 1H NMR spectra indicated that the fluorescence quenching can be attributed to the strong hydrogen bonding interaction between anions and imidazole group of Eu-complex. To meet application requirements for biological and environmental detection in water, we successfully prepared a Eu-based fluorescent hydrogel probe using Eu(TTA)2vinyl-phen and N-isopropyl acrylamide (NIPAAm) as monomers through free radical copolymerization in DMF. Emission spectra titration experiments indicated that this hydrogel probe can effectively recognize H2PO4− (detection limit 10−5 M), but cannot recognize F− and CH3COO− in pure water. To the best of our knowledge, this is first report that Eu-based fluorescent hydrogel probe for H2PO4− detection in pure water. In addition, the emission of Eu-complex is also found to be sensitive to molecular oxygen through energy back-transfer mechanism.

Iontophoretic Treatment of Experimental Pseudomonas Keratitis in Rabbit Eyes Using Gentamicin-Loaded Hydrogels

To evaluate the efficacy of iontophoresis using a hydrogel probe containing gentamicin for the treatment of Pseudomonas keratitis in the rabbit cornea. Five groups (Groups 1-5) of 8 rabbits each were infected by injecting Pseudomonas aeruginosa into their corneas. Three dosings of corneal iontophoresis were performed, at intervals of 3.5 hours, using soft disposable gentamicin-loaded hydroxyethyl methacrylate hydrogel discs mounted on a portable iontophoretic device. Groups 1 and 2 were treated with corneal iontophoresis for 60 seconds and a current of 0.5 and 0.2 mA. Groups 3 and 4 were treated with hydrogel loaded with 0.9% NaCl solution, using a current of 0.2 mA and mock iontophoresis. Group 5 was treated with eye drops of 1.4% gentamicin every hour for 8 hours. One and a half hours after the last treatment, the animals were killed, and the corneas were excised and cultured for P. aeruginosa count after 24-hour incubation. After iontophoretic treatment of gentamicin with a current of 0.5 mA (Group 1), the logarithmic value of Pseudomonas colony-forming units (CFUs) was 2.96 +/- 0.45. After lower current iontophoretic treatment (Group 2), the logarithmic Pseudomonas count was 5.25 +/- 0.54 CFUs. At the control groups (Groups 3-5), the Pseudomonas counts were found to be much higher, 7.62 +/- 0.28, 7.22 +/- 0.29, and 6.29 +/- 0.45 CFUs, respectively. A short iontophoretic treatment using gentamicin-loaded hydrogels has potential clinical value in treating corneal infections.

Direct Introduction of Single Protein Channels and Pores into Lipid Bilayers

We have developed a mechanical method for inserting single pores and channels into lipid bilayers. A hand-operated hydrogel probe, coated with a layer of proteins, is mechanically engaged with the lipid bilayer. The two major classes of membrane proteins (beta barrels and alpha-helix bundles) that can be inserted, thereby demonstrating the wide applicability of the approach. Recordings from the proteins show that they retain electrical properties that are the same as those of proteins inserted from solution. Protein-loaded probes can be used repeatedly, allowing individual pores to be rapidly screened one at a time. The method has implications for fundamental studies of cell membranes, array fabrication, and chemical screening.

Delivery of gentamicin to the rabbit eye by drug-loaded hydrogel iontophoresis.

To assess the corneal iontophoretic delivery of gentamicin by drug-loaded hydrogel probe, and to determine the resultant ocular disposition and elimination of the drug from the cornea and anterior chamber. Corneal iontophoresis of gentamicin sulfate was studied in healthy white rabbits by using drug-loaded disposable hydroxyethyl methacrylate (HEMA) hydrogel disk probes and a portable mini-ion device designed in the authors' laboratory. The iontophoretic treatment was performed with a current intensity of 1 mA for 60 seconds only. Three control groups were used: mock iontophoresis (no current) for 60 seconds, topical eye drops of fortified gentamicin (1.4%) every 5 minutes for 1 hour, and subconjunctival injection of 0.25 mL of 40 mg/mL gentamicin solution. The animals in the iontophoretic experimental groups were killed at predetermined time points. The gentamicin concentrations in the cornea and aqueous humor were assayed with a fluorescence polarization immunoassay. Analysis of the gentamicin eye pharmacokinetics was performed with a modeling approach. Peak gentamicin concentrations in the cornea (363.1 +/- 127.3 microg/g) and in the aqueous humor (29.4 +/- 17.4 microg/mL) were reached at 0 and 2 hours after the iontophoretic treatment, respectively. The peak gentamicin concentrations after a single iontophoresis treatment were 12 to 15 times higher than those obtained after gentamicin injection or after topical eye drop instillation, and much higher than in mock iontophoresis. The concentration versus time profile of gentamicin in the cornea and the anterior chamber after iontophoresis was appropriately described by applying a two-compartment pharmacokinetic model. A short iontophoretic treatment using gentamicin-loaded hydrogels has potential clinical value in increasing drug penetration to the anterior segments of the eye and maintaining therapeutic drug levels in the cornea for more than 8 hours.

Hydrogel probe for iontophoresis drug delivery to the eye

The aim of this study was to evaluate the use of a solid hydrogel loaded with a drug solution as a probe for ejecting drugs to the eye upon application of low current iontophoresis. Hydroxyethyl methacrylate (HEMA), cross-linked with ethylene glycol dimethacrylate (EGDMA), and cross-linked arabinogalactan or dextran were prepared to form solid hydrogels. The hydrogels were examined for their mechanical suitability, absorption of drug solution and in vitro release properties when applying an iontophoretic current through the drug-loaded hydrogel into a solid-agar surface. Transconjunctival and transscleral iontophoresis of gentamicin sulfate was studied in healthy rabbits using drug-loaded disposable HEMA hydrogel disc probes. Gentamicin concentrations in different eye segments were assayed using a fluorescence polarization immunoassay. Preliminary corneal toxicity was examined in rabbits using a current intensity of 2.5 and 5.1 mA/cm2 for 60 and 120 s. The most appropriate hydrogel is composed of HEMA, 2% EGDMA and 75% water. Iontophoresis onto agar gel was found indicative for the evaluation of iontophoretic activity of a hydrogel. Transscleral iontophoretic treatment resulted in high concentrations of drugs in the posterior segments of the eye. Application of iontophoresis onto the rabbit eye caused a reversible swelling of the cornea which lasted a few hours after application. Low current iontophoresis using drug-loaded hydrogel has a potential clinical value in obtaining high drug concentration at posterior segments of the eye.

Neonatal Thermal Care, Part II: Microbial Growth Under Temperature Probe Covers

To determine if temperature probe covers contribute to nosocomial infections by providing an environment for skin microbe colonization. Descriptive, comparative design with infants randomized into two groups: foam probe cover and hydrogel probe cover. Skin cultures were obtained 72 hours after cover placement. Bacterial growth was quantified after 24 and 48 hours. Skin integrity was assessed using visual irritations scores (VIS) every 5 minutes for 30 minutes following cover removal. ANOVA and ANOVA-RM were used to compare amounts of microbes and VIS scores between groups. Twenty-six medically stable infants, 29 to 34 weeks gestational age, less than 10 days postbirth, and in an incubator. Microbial growth and VIS. There were no statistically significant differences in microbial growth and VIS scores between groups (p > .05). Clinical significance was noted in VIS scores. Infants who had foam covers had more sustained irritation scores.