Enzyme-functionalized hydrogel film for extracorporeal uric acid reduction.

Enzyme replacement therapy for hyperuricemia treatment has been proven effective for critical state hyperuricemia patients. Still, direct administration of recombinant uricase can induce several fatal side effects. To circumvent this drawback, hydrogel protein carriers can be used in platforms for extracorporeal treatment such as microscale-based devices. In this work, calcium alginate and poly-(vinyl alcohol) hydrogel films were studied for their urate oxidase immobilization and uric acid reduction, which could be implemented in microscale-based extracorporeal devices. A mathematical model was developed in conjunction with uric acid reduction experiments to evaluate the influence of mass transfer and reaction parameters in the Michaelis-Menten kinetic expression. Alginate hydrogels prepared with crosslinker 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide and N-(hydroxysuccinimide) offered superior diffusivity of uric acid in the gel matrix at the maximum value of D g , UA ≈ $$ {D}_{\mathrm{g},\mathrm{UA}}\approx $$ 1.98 × 10-11 m2 /s compared with alginate prepared solely from ionic crosslinking with D g , UA ≈ $$ {D}_{\mathrm{g},\mathrm{UA}}\approx $$ 5.31 × 10-12 m2 /s at the same alginate concentration. The maximum value of νmax was experimentally determined at 7.78 × 10-5 mol/(m3 s). A 3% sodium alginate hydrogel with crosslinkers yielded the highest reduction of uric acid at 92.70%. The mathematical model demonstrated an excellent prediction of uric acid conversion suggesting potential use of the model for formulation and maximizing the therapeutic performance of functionalized hydrogels.

Longevity Demonstration of Methane to C2 via a Nonthermal Plasma Microreactor.

Hydrocarbon processing using plasmas has tremendous potential, yet there still exist many uncertainties pertaining to practical operation over long durations. Previously, it has been demonstrated that a nonthermal plasma operating in a DC glow regime can transform methane into C2 species (acetylene, ethylene, ethane) in a microreactor. Using a DC glow regime in a microchannel reactor allows for lower power consumption, at the expense of greater consequence of fouling. Since biogas can be a source of methane, a longevity study was undertaken to understand how the microreactor system would change over time with a feed mixture of simulated biogas (CO2, CH4) and air. Two different biogas mixtures were used, one of which contained 300 ppm H2S, while the other had no H2S. Potential difficulties observed from previous experiments included carbon deposition on the electrodes, which could interfere with the electrical characteristics of the plasma discharge as well as material deposition in the microchannel, which could affect gas flow. It was found that raising the temperature of the system to 120 °C helped prevent hydrocarbon deposition in the reactor. Purging the reactor periodically with dry air was also found to have positive effects as it removed carbon buildup on the electrodes themselves. Successful operation over a 50 h time period without any significant deterioration was demonstrated.

Effect of PEO coating on bubble behavior within a polycarbonate microchannel array: A model for hemodialysis.

Obstruction of fluid flow by stationary bubbles in a microchannel hemodialyzer decreases filtration performance and increases damage to blood cells through flow maldistribution. A polyethylene oxide (PEO)-polybutadiene (PB)-polyethylene oxide surface modification, previously shown to reduce protein fouling and water/air contact angle in polycarbonate microchannel hemodialyzers, can improve microchannel wettability and may reduce bubble stagnation by lessening the resistive forces that compete with fluid flow. In this study, the effect of the PEO-PB-PEO coating on bubble retention in a microchannel array was investigated. Polycarbonate microchannel surfaces were coated with PEO-PB-PEO triblock polymer via radiolytic grafting. Channel obstruction was measured for coated and uncoated microchannels after injecting a short stream of air bubbles into the device under average nominal water velocities of 0.9 to 7.2 cm/s in the channels. The presence of the PEO coating reduced obstruction of microchannels by stationary bubbles within the range of 1.8 to 3.6 cm/s, average nominal velocity. Numerical simulations based on the lattice Boltzmann method indicate that beneficial effects may be due to the maintenance of a lubricating, thin liquid film around the bubble. The determined effective range of the PEO coating for bubble management serves as an important design constraint. These findings serve to validate the multiutility of the PEO-PB-PEO coating (bubble lubrication, biocompatibility, and therapeutic loading). © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 941-948, 2016.

Preparation and evaluation of PEO-coated materials for a microchannel hemodialyzer.

The marked increase in surface-to-volume ratio associated with microscale devices for hemodialysis leads to problems with hemocompatibility and blood flow distribution that are more challenging to manage than those encountered at the conventional scale. In this work stable surface modifications with pendant polyethylene oxide (PEO) chains were produced on polydimethylsiloxane (PDMS), polycarbonate microchannel, and polyacrylonitrile membrane materials used in construction of microchannel hemodialyzer test articles. PEO layers were prepared by radiolytic grafting of PEO-polybutadiene-PEO (PEO-PB-PEO) triblock polymers to the material surfaces. Protein repulsion was evaluated by measurement of surface-bound enzyme activity following contact of uncoated and PEO-coated surfaces with ß-galactosidase. Protein adsorption was decreased on PEO-coated polycarbonate and PDMS materials to about 20% of the level recorded on the uncoated materials. Neither the triblocks nor the irradiation process was observed to have any effect on protein interaction with the polyacrylonitrile membrane, or its permeability to urea. This approach holds promise as a means for in situ application of safe, efficacious coatings to microfluidic devices for blood processing that will ensure good hemocompatibility and blood flow distribution, with no adverse effects on mass transfer.