Patent ID: 8114157

Claim:
A method of making a shear-reversible polyurethane gel suitable for use in treatment of a medical or cosmetic condition, the method comprising the steps of: a) providing a polyisocyanate prepolymer, the prepolymer having a polyalkylene oxide backbone comprising one or more copolymers having on average about 65 to about 95 mole % ethylene oxide monomers and at least about 5 to about 35 mole % propylene oxide monomers, and less than about 5% of any other monomer, having an average functionality of greater than 2 active isocyanate groups per prepolymer molecule; b) providing a reaction-supporting solvent, selected from a solution consisting essentially of water, a solution consisting essentially of a dry non-aqueous water-miscible organic solvent in which the prepolymer will dissolve, and a mixture thereof; c) shearing said reaction-supporting solvent so as to provide a known rate of shear; and d) either i) when said reaction-supporting solvent contains water, infusing said prepolymer, optionally diluted with a dry non-reactive organic solvent, into said water solution at a rate slow enough to prevent the formation of macroscopic gel particles; or ii) dissolving said prepolymer in said dry non-aqueous water-miscible organic solvent, and infusing one of water, and a mixture of water and solvent, into said solution of prepolymer in a dry non-aqueous water-miscible organic solvent, at a rate slow enough to prevent the formation of macroscopic gel particles; and e) allowing said prepolymer solution to finish reacting, thereby producing a reversibly gelling polyurethane (RGP) polymer solution; characterized in that the polyurethane solution gels when it is not sheared, and becomes fluid under shear.