Toshiaki Masuda

Effects of internal filtration on the solute removal efficiency of a dialyzer.

To improve solute removal efficiency, several types of dialyzers with enhanced internal filtration were introduced for clinical application. In these dialyzers, enhanced internal filtration increased convective transport of the solute, in addition to diffusive transport. In this study, the effects of internal filtration on solute removal efficiency were examined by both analytic and experimental studies. Internal filtration is affected by blood (QB) and dialysate (QD) flow rates; the patient’s hematocrit and plasma level of total protein; and the effective length (Leff), inner diameter (D), and density ratio (DR) of the hollow fibers. An analytic model was introduced for the estimation of the changes in mass and momentum along the dialyzer. It clarified the effects of these parameters on maximum internal filtration flow rate (QIF) and clearance (K) of urea (60 daltons), vitamin B12 (1,355), and myoglobin (17,000). As a result of the analytic study, QIF was increased, resulting in a smaller D, a longer Leff, and a larger DR value. Several types of dialyzers with the same cellulose triacetate membrane, produced by Toyobo Co, Ltd., Ohtsu, Japan, and Nissho Corporation, Kusatsu, Japan, were used for the experimental study. An in vitro evaluation using myoglobin solution showed the same trends as found in the analytic study. For example, a dialyzer with 150 &mgr;m of D has a 72.0 ml/min myoglobin K value, much higher than that of 53.7 ml/min for a dialyzer with 200 &mgr;m of D under constant QB (300 ml/min) and DR (50%) values. Development of a dialyzer with enhanced internal filtration, however, should take the patient’s safety into account, and hemolysis and endotoxin invasion from the dialysate to the patient should be avoided.

Cellulose triacetate as a high-performance membrane.

The cellulose triacetate membrane is one of the typical high-performance membranes. Cellulose triacetate is a plastic material manufactured from cellulose. The hydroxyl group of cellulose is chemically substituted for the carboxyl group. Therefore, its characteristics are quite different from cellulose. The cellulose triacetate membrane has a homogeneous membrane structure. It can be produced with a wide range of permeability, from low-flux performance to super high-flux performance. Because the thickness of the membrane is thin, and flow distribution of the dialysate (due to the moiré structure) is uniform, this enables the development of a dialyzer with high diffusive efficiency. Recently, this new product, improved through a sieving process, produced a uniform pore size distribution. As for the dialyzer, through sterilization by γ-rays with the absence of oxygen, now enables long-term safety of the product. Several clinical improvements have been reported, such as high antithrombus, the improvement of lipid metabolism and the reduction of biomarkers. Thus, continuous membrane development is desired, made of safe and stable cellulose triacetate material.

Fundamental Characteristics of the Newly Developed ATA™ Membrane Dialyzer.

BACKGROUNDnDialysis membranes are often made from synthetic polymers, such as polysulfone. However, membranes made from cellulose triacetate have superior biocompatibility and have been used since the 1980s. On-line hemodiafiltration treatment accompanied by massive fluid replacement is increasingly being used in Europe and Japan, but cellulose triacetate is not suitable for this treatment.nnnSUMMARYnOur newly developed asymmetric triacetate membrane, the ATA™ membrane, substantially improved the filtration properties and blood compatibility because of the asymmetric structure and smooth surface of this cellulose acetate membrane. Key Message: The ATA membrane maintains its high permeability even after massive filtration and shows less temporal variation in its permeation performance, lower protein adsorption, and superior biocompatibility compared with conventional membranes.