Multizone polymer membrane and dialyzer

Abstract

Membranes are made from polymers and heat treated so that they have at least two zones with pores of different sizes. Pores with a smaller size have a lower molecular weight cut off than pores with a larger size. Zones with pores of different sizes may also be made by coating portions of membranes with polymer coatings. Membranes with pores of different sizes may be used in dialyzers for hemofiltration, hemodiafiltration, and other hemodialysis procedures. The membranes may also be used in other separation processes.

What is claimed is: 
     
         1 . A multizone polymer membrane, comprising:
 a first zone comprising a first plurality of pores of a first size having an average molecular weight cut-off of about 50,000 Daltons; and   a second zone comprising a second plurality of pores of a second size, the second size less than the first size, wherein the first plurality is formed at a first temperature and the second plurality is formed at a second temperature greater than the first temperature, and wherein the pores of the first size and the pores of the second size are arranged along a longitudinal axis of the membrane.   
     
     
         2 . The multizone polymer membrane according to  claim 1 , wherein the first plurality is formed by immersion in an air atmosphere or liquid atmosphere at a first temperature and the second plurality is formed by immersion in the air atmosphere or the liquid atmosphere at a second temperature greater than the first temperature. 
     
     
         3 . The multizone polymer membrane according to  claim 1 , further comprising a third zone having a third plurality of pores, wherein a size of the third plurality of pores is smaller than the size of the second plurality of pores. 
     
     
         4 . The multizone polymer membrane according to  claim 1 , further comprising a coating on the first or second zone forming the first or second plurality of pores. 
     
     
         5 . The multizone polymer membrane according to  claim 1 , wherein the membrane is selected from the group consisting of polyethersulfone, polyarylethersulfone, cellulose acetate, and derivatives of cellulose. 
     
     
         6 . The multizone polymer membrane according to  claim 1 , wherein the membrane further comprises a third zone formed at a third temperature higher than the second temperature, wherein pores in the third zone are smaller than pores of the second zone. 
     
     
         7 . A plurality of multizone polymer membranes according to  claim 1 , wherein the plurality of multizone membranes comprises a bundle, and further comprising:
 a first tubesheet to which a first end of each of the plurality of multizone membrane is sealed;   a second tubesheet to which a second end of each of the plurality of multizone membranes is sealed; and   a housing containing the bundle and the tubesheets, the housing further comprising a blood inlet and a blood outlet, and a dialyzer inlet and a dialyzer outlet.   
     
     
         8 . The multizone polymer membrane according to  claim 1 , wherein the membrane is a sheet membrane. 
     
     
         9 . A multizone polymer membrane for hemodialysis, comprising:
 a first zone comprising a first plurality of pores of a first size having an average molecular weight cut-off of about 50,000 Daltons, the first plurality formed at a first temperature; and   a second zone comprising a second plurality of pores of a second size, the second size smaller than the first size, the second plurality formed at a second temperature greater than the first temperature, wherein the membrane and the first and second pluralities are suitable for hemodialysis, and wherein the pores of the first size and the pores of the second size are arranged along a longitudinal axis of the membrane.   
     
     
         10 . The membrane for hemodialysis of  claim 9 , wherein the membrane is made from a polymer selected from the group consisting of polyethersulfone, polyarylethersulfone, cellulose acetate, and derivatives of cellulose. 
     
     
         11 . The membrane for hemodialysis of  claim 9 , wherein the second zone comprises pores with a molecular weight cut off (MWCO) of about 10,000 Daltons. 
     
     
         12 . The membrane for hemodialysis of  claim 9 , wherein the membrane is formed as a continuum in a form of a hollow fiber. 
     
     
         13 . The membrane for hemodialysis of  claim 9 , wherein the first zone has a lower molecular weight cut off (MWCO) than the second zone. 
     
     
         14 . A multizone polymer membrane, comprising:
 a unitary polymer membrane formed at a first temperature and comprising a longitudinally-spaced first zone and a second zone, the first zone comprising a first plurality of pores of a first size having an average molecular weight cut-off of about 50,000 Daltons; and   a second zone comprising a second plurality of pores of a second size, the pores of the second zone formed by immersing the second zone into an environment at a temperature greater than the first temperature, the pores of the second size less than the first size, and wherein the second zone further comprises a coating, the coating effectively reducing the size of the pores of the second zone, and wherein the pores of the first size and the pores of the second size are arranged along a longitudinal axis of the membrane.   
     
     
         15 . The multizone polymer membrane of  claim 14 , wherein the membrane is in the form of a hollow fiber or a sheet.