Methods for reducing the electrode impedance of implantable biosensors by coating the surface of the biosensor with a uniform hydrogel which allows unimpeded water movement around the sensor are provided. The surface coatings are compositions which are biocompatible and are capable of water uptake of at least 120% of their weight, more preferably at least 200% of their weight. Upon the uptake of water, the hydrogels used in the present invention will also swell and provide a layer of water around the electrodes to which the hydrogels are attached. The hydrogels can be prepared from (a) a diisocyanate, (b) a hydrophilic polymer which is a hydrophilic diol, a hydrophilic diamine, or a combination thereof, and optionally, (c) a chain extender.