Effect of packing density of hollow fibers on solute removal performances of dialyzers.

Solute removal performances of dialyzers are dependent not only on the solute permeabilities of the membrane but also on the module design. We have investigated how the packing density of hollow fiber (PDF) affects the solute removal performances. A series of 4 polyester polymer alloy membrane test dialyzers were assembled with varying PDFs of 29.6%, 35.3%, 44.1%, and 53.1%. Clearances (C(L)) were measured in vitro for creatinine (MW113), vitamin B(12) (MW1355), and chymotrypsin (MW25300) with various Q(B)=100 to 400 and Q(D)=350 to 650 mL/min in the absence of net ultrafiltration. When Q(B) was <or=300 mL/min, no significant changes were found in creatinine C(L) with the increase of PDF up to 35.3%. A slightly greater increase was found in C(L) when Q(B)=400 mL/min. Clearances for vitamin B(12), however, increased with the increase of PDF in the range of 29.6% to 35.3%. The effects of PDF on C(L) were greater with larger Q(B). More importantly, an abrupt increase of C(L) was found when PDF was increased from 44.1% to 53.1%. According to a rigorous mathematical model, this may be caused by the internal filtration, which is reverse ultrafiltration occurring in a dialyzer at any given time. No significant increase was found in chymotrypsin C(L) when the PDF was <or=35.3%, which suggested that C(L) for large molecules was strongly dependent on the solute permeability rather than the conditions of flow patterns. A very steep increase was also found in C(L) for chymotrypsin when the PDF was >44.1%, which was also considered to be due to the internal filtration. Packing density of hollow fiber can be optimized in terms of solute removal performances when the target solute and therapeutic conditions are specified.