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Future developments in pacemakers are being directed toward better coupling of power to the heart muscle, better energy sources that will work for an indefinite period of time, and better prosthetic materials for implantation. Artificial joints have been in use for many years, primarily as hip prostheses. These devices have been a challenge to metallurgical engineers, who have had to produce strong, non-brittle, ductile, noncorrosive, nonfatigable materials that do not irritate tissue. The material used in a hip-joint prosthesis, for example, must be able to withstand high stresses caused by forces ranging up to three to four times body weight.

Their proponents recognize the liabilities and even some dangers in their use. Artificial heart valves, for example, permit replacement of valves diseased by arteriosclerosis and rheumatic fever, but formation of blood clots on prosthetic surfaces has been a problem and infection around the valve is nearly always fatal. Currently useful artificial heart valves are numerous, but it is surprising that few act physiologically or appear anatomically the same as natural valves.

Investigators at Baylor University used prosthetic implants on 45 persons with prior unsuccessful corneal transplants and achieved success in all but two instances. It is of interest to speculate that if permanent optical correction can be built into plastic grafts and if uniform success can be obtained, persons now nearly Blind from corneal lesions might receive plastic corneal grafts with total correction of their vision.