solution fig2 to form a coating 30 thereon fig3 because the solvent is a solvent of polycarbonate it caused the rigid polycarbonate surface of the cannula 10 to soften and swell facilitating the penetration of polyurethane into the polycarbonate thereafter the coating 30 was allowed to cure and the thf being volatile was released via off gassing perhaps accelerated with heat leaving behind the polyurethane bonded to and coating the polycarbonate of the cannula 10 because of the good compatibility of polycarbonate and polyurethane resulting from this process the interface of polycarbonate and polyurethane had good strength by virtue of the coating 30 the joint surface of the cannula was altered to be a material which is weldable and comprises polyurethane the same material from which the balloon dissector 40 to be welded thereto is made this simple process enables the dissimilar materials of the polycarbonate of the cannula 10 and the tpu of the balloon dissector 40 to be rf welded together resulting in a weld with a good joint strength fig4 another embodiment of the method of the invention involves using aliphatic polycarbonate based tpu such as carbothane u00ae produced by noveon inc carbothane u00ae consists of both polycarbonate segments and tpu segments this unique structure can be.