Fluid extraction or filtration device, associated materials and methods

A fluid extraction or filtration device (1) for removing fluid from a body, the device comprising an array of microneedles (6) for contacting fluid in said body and an absorbent gel matrix (3) in fluid communication with said array of microneedles. There is further provided a combined fluid extraction and sampling device and methods employing the device (s), for example in determining the level of a target species in a sample of fluid, transdermal dialysis and renal replacement therapy. There is further provided an absorbent gel matrix for use in the treatment of uraemia and a haemodialysis filter comprising an absorbent gel matrix. Use of such a matrix is described in the context of methods including haemodialysis, transdermal dialysis and gastrointestinal dialysis.