The present invention provides a water-soluble crosslinkable polyurea prepolymer. The crosslinkable polyurea prepolymer of the invention is prepared by reacting an amine- or isocyanate-capped polyurea with a multifunctional compound having at least one one ethylenically unsaturated group and a function group coreactive with the capping amine or isocyanate groups of the amine- or isocyanate-capped polyurea. The amine- or isocyanate-capped polyurea is a copolymerization production of: (a) at least one poly(oxyalkylene)diamine, (b) optionally at least one organic di- or poly-amine, (c) optionally at least one diisocyanate, and (d) at least one polyisocyanate. The crosslinkable polyurea prepolymer of the invention can find use in economically producing contact lenses which have durable, highly elastic soft contact lenses with desired physical properties. In addition, the present invention provides method for making a medical device, preferably an ophthalmic device, more preferably a contact lens.