Taiji Yakushiji

Effects of fluid flow on elution of hydrophilic modifier from dialysis membrane surfaces

When uremic blood flows through dialyzers during hemodialysis, dialysis membrane surfaces are exposed to shear stress and internal filtration, which may affect the surface characteristics of the dialysis membranes. In the present study, we evaluated changes in the characteristics of membrane surfaces caused by shear stress and internal filtration using blood substitutes: water purified by reverse osmosis and 6.7 wt% dextran70 solution. We focused on the levels of a hydrophilic modifier, polyvinylpyrrolidone (PVP), on the membrane surface measured by attenuated total reflectance Fourier transform infrared spectroscopy. Experiments involving 4 h dialysis, 0–144 h shear-stress loading, and 4 h dead-end filtration were performed using polyester-polymer alloy (PEPA) and polysulfone (PS) membranes. After the dialysis experiments with accompanying internal filtration, average PVP retention on the PEPA membrane surface was 93.7% in all areas, whereas that on the PS membrane surface was 98.9% in all areas. After the shear-stress loading experiments, PVP retention on the PEPA membrane surface decreased as shear-stress loading time and the magnitude of shear stress increased. However, with the PS membrane, PVP retention scarcely changed. After the dead-end filtration experiments, PVP retention decreased in all areas for both PEPA and PS membranes, but PVP retention on the PEPA membrane surface was lower than that on the PS membrane surface. PVP on the PEPA membrane surface was eluted by both shear stress and internal filtration, while that on the PS membrane surface was eluted only by internal filtration.

Computational Evaluation of Dialysis Fluid Flow in Dialyzers With Variously Designed Jackets

Dialyzer performance strongly depends on the flow of blood and dialysis fluid as well as membrane performance. It is necessary, particularly to optimize dialysis fluid flow, to develop a highly efficient dialyzer. The objective of the present study is to evaluate by computational analysis the effects of dialyzer jacket baffle structure, taper angle, and taper length on dialysis fluid flow. We modeled 10 dialyzers of varying baffle angles (0, 30, 120, 240, and 360 degrees ) with and without tapers. We also modeled 30 dialyzers of varying taper lengths (0, 12.5, 25.0, and 50.0 mm) and angles (0, 2, 4, and 6 degrees ) based on technical data of APS-SA dialyzers having varying surface areas of 0.8, 1.5, and 2.5 m(2) (Rexeed). Dialysis fluid flow velocity was calculated by the finite element method. The taper part was divided into 10 sections of varying fluid resistances. A pressure of 0 Pa was set at the dialysis fluid outlet, and a dialysis fluid flow rate of 500 mL/min at the dialysis fluid inlet. Water was used as the dialysis fluid in the computational analysis. Results for dialysis fluid flow velocity of the modeled dialyzers indicate that taper design and a fully surrounded baffle are important in making the dialysis fluid flow into a hollow-fiber bundle easily and uniformly. However, dialysis fluid flow channeling occurred particularly at the outflowing part with dialyzers having larger taper lengths and angles. Optimum design of dialysis jacket structure is essential to optimizing dialysis fluid flow and to increasing dialyzer performance.

Technical evaluation of dialysate flow in a newly designed dialyzer.

Rexeed was developed by Asahi Kasei Medical using wave-shaped hollow fibers, a full baffle, and a short taper housing to improve dialysate flow. The present study is clarifies improvement in dialysate flow with Rexeed-15 compared with that of a conventional dialyzer. Dialysate flow was evaluated by the pulse-response method. Dialysate pressure and tracer concentration were measured at a blood-side flow rate (Q&Bgr;) of 200 ml/min, a dialysate-side flow rate (QD) of 500 ml/min, and a net filtration rate (QF) of 0 ml/min using needles placed in the test dialyzer. Dialyzer performance was evaluated by measuring urea and vitamin B12 clearance at QB = 200 and 400 ml/min, QD = 300–800 ml/min, and QF = 0 ml/min. In the conventional dialyzer, dialysate channeling was observed. In contrast, Rexeed-15 had a uniform dialysate flow. Urea and vitamin B12 clearance with Rexeed-15 was slightly sensitive to QD. The overall mass transfer coefficient for urea with Rexeed-15 was more than 50% higher than that of the conventional dialyzer, indicating the possibility of reduced dialysate usage with Rexeed. Rexeed has a highly optimal dialysate flow, due to the wave-shaped hollow fibers and the new housing, and gives increased clearance for lower-molecular-weight substances.

Development of a device for chemiluminescence determination of superoxide generated inside a dialysis hollow-fiber membrane

Reactive oxygen species (ROS) generated during hemodialysis treatment cause dialysis complications because of the high reactivity of ROS. To prevent dialysis complications caused by oxidative stress, it is important to evaluate the generation and dismutation of ROS during hemodialysis treatment. In this study, our aim was to develop a device to determine superoxide (O2−) generated inside a dialysis hollow fiber, and also to examine whether this device could detect O2− separated from plasma using hollow fibers. Experimental apparatus was set up so that hypoxanthine (HX) solution flowed inside the hollow fibers and 2-methyl-6-p-methoxyphenylethynyl-imidazopyrazinone (MPEC) solution flowed outside the hollow fibers. Then, xanthine oxidase (XOD) solution was added to the HX solution to generate O2−, and chemiluminescence resulting from the reaction of O2− with MPEC was measured with an optical fiber. Chemiluminescence intensity was measured at different HX concentrations, and the peak area of relative luminescence intensity yielded a first-order correlation with the HX concentration. Based on the relationship between HX and O2− concentrations determined by the cytochrome c reduction method, the relative luminescence intensity measured by this device was linearly dependent on the O2− concentration inside the hollow fibers. After modifications were made to the device, XOD solution injection into plasma including HX resulted in an increase in the relative luminescence intensity. We concluded that this novel device based on chemiluminescence is capable of determining aqueous O2− generated inside a hollow fiber and also of detecting O2− in plasma.

Biomedical Engineering. Design of Thermo-Responsive Surfaces for Temperature-Regulated Hydrophobic Chromatography and Separation of Steroids.

本研究では, 固体表面に修飾したポリ (N-イソプロピルアクリルアミド) (PIPAAm) の構築構造が温度に応答したぬれ特性, ステロイドとの相互作用に与える影響を検討し, クロマト担体としての特性を追究した.PIPAAm共重合体を固体表面と多点で結合させた表面, さらにこの表面に片末端アミノ化PIPAAmを導入し自由末端鎖構造を有するグラフト表面をそれぞれ作製した.PIPAAm導入表面は温度に応答して親水性/疎水性の変化を示すが, その挙動は2つの表面で大きく異なっていた.自由末端鎖導入表面はPIPAAm分子が水中で示す相転移温度 (305K) で大きな変化を示したが, 多点で結合した表面ではより低温側になった.この表面特性の相違は, ステロイドとの相互作用にも認められ, 自由末端鎖導入表面は高温側でより強い疎水性相互作用を示すことが明らかとなった.温度上昇にしたがい表面の疎水性は次第に増大し, ステロイドの溶離時間を大幅に延長することができた.修飾高分子の構築構造制御により溶質との相互作用を変化できる新しいクロマト担体を実現した.