poly polymers bearing various ratios of a carboxylic acid containing sidegroup and an alkylamino , alkoxy , or alkoxy ether sidegroup are disclosed . these water - soluble macromolecules are cross - linked and allowed to absorb water to form hydrogels . because of their anionic character and high water content , the polymeric hydrogels are useful for a wide variety of biomedical applications including controlled drug delivery , biocompatible coatings , and ph sensitive membranes .