a sorbent polymer is provided that interacts or reacts with aqueous urea to aid the regeneration of a dialysate liquid . the sorbent polymer may include one or more specific functional groups bonded thereto . such specific functional groups are selected from carboxylic acids , carboxylic acid esters , carboxylates , amides , dicarboxylic acids , dicarboxylic acid esters , and dicer boxylates to produce the desired urea sorbent .