The invention provides sealants wherein biodegradable hydrogels that do not otherwise comprise protein-reactive groups for binding to membranes or tissue are provided said groups optionally through a linker. The linker may be biodegradable and may be biodegradable by an elimination reaction. The invention also provides multilayer gels for drug delivery wherein a porous gel in contact with a tissue or organ to which the drug is to be delivered is protected by a microporous layer from the surrounding bodily fluid.
