A method of forming an implantable biomaterial comprising the steps of providing a polyether-diisocyanate prepolymer, reacting the prepolymer with one or more chain extender molecules to form a mouldable polymer selected from a polyurethane or polyurethane-urea polymer or a polyurethane-urea block copolymer； placing the mouldable polymer into an implantable biomaterial shaped mould, and shaping and curing the mouldable polymer in the implantable biomaterial shaped mould to form the implantable biomaterial. An implantable biomaterial such as a heart valve leaflet is also disclosed.
