Prostheses Should Look Natural
Grützmann uses fine spatulas and knives to work out indentations, raised tendons and wrinkles. To make the hand look less artificial and more lifelike, the silicone is not uniformly colored. Instead, viscose flocks, chopped threads and some other tricks are incorporated to provide a degree of three-dimensionality. “Uniformly colored plastic dolls are not translucent, which is why they do not look alive,” says Andreas Leiniger, head of the Silicone department at Ottobock. “We use the material’s translucency to mimic the skin’s light permeability, which allows the different colors of adjacent tissue, veins and bones to influence each other.”
With the aid of photos and the cast of the remaining extremity, the employees at Ottobock – who truly are craftsmen – try to replicate the original as accurately as possible. This sometimes takes so long that the silicone compound begins to cure and can become too hard to work on. When that happens, the craftsmen in Leiniger’s department don pullovers and scarves and repair to the cold store, where the temperature of 17 °C prolongs the time available to work the material into a hand or foot. Once all the subtle details – from original hairs on the lower leg, age and liver spots, through to paintable acrylic fingernails – have been copied, the prosthesis is cured at 130 to 180 °C.
Even after 17 years – Leiniger, a qualified orthopedic technician who has been at Ottobock since 1997 and has expanded the Silicone department from two to 14 employees – never fails to be impressed by the natural appearance that silicone can produce. “A patient once got a fright when she saw her lower leg prosthesis for the first time,” he says with a smile. “The prosthesis looked so lifelike that at first she refused to put it on.” It took her a while to get used to it, but after that she was delighted with it, he adds.
These products are strongly resistant to heat and radiation, permeable to steam and gas, reliable, biocompatible, and considered harmless when used as intended. They are available as HTV solid and liquid silicone rubber grades, as well as RTV-1 and RTV-2 silicone rubber grades. SILPURAN® silicone rubber grades meet the healthcare industry's high safety standards. All products are checked in accordance with ISO 10993 and USP Class VI.
At Ottobock, silicone elastomers from WACKER are also used to make liners, a kind of stocking that acts as a link between the rigid carbon-fiber shaft of the prosthesis and the patient’s stump. These series products made up of a number of layers of silicone of different elasticity ensure that the lower arm or leg prosthesis fits tightly to the stump, without causing pressure points or rubbing. “In the past, two layers of leather and a piece of felt would have been used to cushion the pressure between the stump and a wooden or aluminum leg,” says Leiniger. “Plastics such as silicone offer a totally different level of comfort nowadays.” Silicone adheres well, is tolerated by the skin and easy to clean, and can be fixed to the shaft. It is also better at holding the vacuum that keeps prostheses attached to the stump for many types of shaft; this improves both blood circulation and hold.
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