Silastic Artificial Hearts Constructed on Wax Molds
STEPHEN R. TOPAZ, B.S.M.E.
Department of Artificial Internal Organs
ARTIFICIAL heart ventricles are currently made of Silastic,* a silicone rubber, in the following manner. At the factory, sheets of Silastic are calendered around dacron fabric. These sheets are then layered around a mold in the form of a heart ventricle; the seams are reinforced by Silastic. The Silastic on the cast is vulcanized in an autoclave at a temperature of 270 F. for five minutes; next it is cured by heating in an air oven at a temperature of 350 F. for four hours. The result is an odorless, whitish plastic that is remarkably inert.
After the complex Silastic parts are constructed by layering, the mold must be removed. Therefore mold material should not only have a good surface finish, but it should be able to be broken out, melted out, or dissolved out.
Glass is an excellent material for a mold, however, delivery from the factory cannot always be prompt. The chief disadvantage of plaster molds is that they do not have a good surface finish. Wax is a good material from which complicated forms can be cast easily (Fig. 1), and a smooth surface finish can be obtained. The drawback with some waxes, particularly those containing flame retarders, is that in affecting the vulcanizing agent they affect the curing of the Silastic.
After appropriate experimentation it was found that vulcanization of the Silastic in an autoclave with steam could be performed at temperatures of approximately 270 F. even with wax molds that have a melting point of. . .