New polymer alloy dialysis membranes with varying permeabilities and sievings.

The superstructure of polymer alloys that is responsible for their function is best controlled by varying the polymers, polymer blend ratio, solvents, temperature, or all four. Dialysis membranes made of polymer alloys can have varying pure water and solute permeabilities, pore sizes, pore size distributions, and mechanical strengths when wet. Resistance to heat and mass transfer can also vary. The optimal superstructure design of a polymer alloy dialysis membrane enables it to remove efficiently newly identified uremic toxins with higher molecular weights from patients on hemodialysis. The authors prepared new hollow fiber dialysis membranes using a polyethersulfone/polyacrylate (PEPA) polymer alloy, and evaluated pure water and solute permeabilities and reflection coefficients that are dependent upon the superstructure of the PEPA membranes. The new PEPA membranes are asymmetric, with skin layers on either side. The values for pure water permeability and overall mass transfer coefficients for urea, creatinine, and vitamin B12 are quite adequate for hemodialysis. The reflection coefficients for substances with molecular weights greater than 3,000 are strongly dependent upon the conditions under which the membranes were prepared. The values for cytochrome C permeability ranged from 0.42 to 0.71 microns/s.