Mixtures or adducts of N-heterocyclic carbenes with metal amides or metal alkoxides are effective catalysts for the polymerization of macrocyclic polyester oligomers. The front and side panels preferably are attached so that the side panels can be positioned from generally perpendicularly to the front panel in use to a folded position adjacent said front panel for storage or travel. An end of the outer layer is configured for receiving, in articulated engagement, an end of an adjoining bone. Application of an electric voltage between an inner and outer electrode on the piezoelectric thin film induces a lateral strain on the PZT thin film, thereby altering the curvature of the membrane, and thus its focal length. The injection head releasably connects to the soft tool and preferably uses a solenoid actuated injector to supply resin to the mold.