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Piston rings learn to walk

iglidur® - highest convenience and safety in knee joint prostheses


  • What was needed: Slotted piston ring for use in a prosthetic knee joint with pneumatic cylinder
  • Manufacturing process: Injection moulding
  • Requirements: Piston ring must absorb radial forces and allow easy, low-friction guidance of the piston
  • Material: iglidur J
  • Success for the customer: Reduction of assembly and service costs by simple and quick clip on. Functionality, quality and service life of the knee joint were increased, along with improved sliding and wear properties

Only materials and components that can be relied upon are used for prostheses. Especially for leg prostheses, it is important that the user can trust his prosthesis when he is running and standing with it. Therefore, Otto Bock SE & Co. KGaA, the world market leader in technical orthopaedics, has been relying on iglidur plain bearings made of high-performance polymers for more than 20 years.  When caring for a patient, it is very important that the prosthesis is individually adapted to the wearer and supports his or her body in the most motorically demanding tasks, such as running. In order to perform these tasks in a natural way and as pleasingly as possible for the prosthesis user, Otto Bock has been continuously developing innovative products for many years.


Some of the bearing points in prosthetic knee joints were fitted with bronze bearings.  Otto Bock SE & Co KGaA was looking for an alternative for these bearing points.  It turned out that fretting corrosion can occur at the bearing points during small pivoting movements. As a result, knee joints can become stiff and pose a risk to the wearer of the prosthesis.  With increasing clearance of the bronze bearings, noises were also generated.  


By using corrosion-free iglidur plain bearings, the fretting corrosion problem was solved. Due to their low wear values, the plain bearings were also impressive during tests in Otto Bock's in-house laboratory.  Further advantages of iglidur plain bearings: Dirt and dust deposits do not affect the plain bearings and thus do not impair the function of the prosthetic knee joints. Their quiet operation also contributes to the comfort of the prostheses.   

"The lack of lubrication means that the prosthetic knee joints are not as susceptible to dirt. This means that no cover caps or additional sealing elements are required to protect the bearing points from dirt and water".
Andreas Schuh, Expert for Fluidic Control Systems, Otto Bock SE & Co. KGaA

Individually manufactured components made of high-performance polymers

In addition to numerous standard parts, which are available in a large selection of materials for a wide variety of applications, igus also manufactures individual components according to customer requirements. The benefits of this service have also beenalready recognised by Otto Bock SE & Co. KGaA. The 3R78 prosthetic knee joint, one of the most sought-after mechanical joints with pneumatic control system, uses a piston ring that, due to its special geometry, is not available in the standard range from igus. For such cases, igus offers a variety of manufacturing processes to initially produce cost-effective prototypes, which can then be manufactured in quantities of 1 up to several million. Depending on the application, the selection of the optimum material can be adapted to achieve the best possible results in operation.
Quality for Life – This is the motto of Otto Bock, which stands for reliable products. To cope with this, Otto Bock SE & Co. KGaA operates an in-house test laboratory. It not only tests its own developments, but also components from suppliers, such as the igus polymer plain bearings. Only in this way can Otto Bock provide prosthesis users with the quality, reliability and stability they need.


Knee joint prosthesis 3R78 with iglidur® piston rings  

Further application reports

Made of bar stock: special bearings for highest precision in ophthalmology

iglidur® bar stock is used to manufacture a microscope arm for eye examinations. The reason: it can be machined to produce customised plain bearings down to sizes measured in μm to ensure the necessary precision for examinations.  

Machined from bar stock: durable and wear-resistant plain bearings for finger prosthesis

This prosthesis is an electrically powered finger. The joint at the base of the finger is moved directly via a gear motor, which carries along the middle joint via a flexible connection. All axes involved in this movement are mounted through plastic bushes made of the material iglidur® J. Altogether, 8 bearings are integrated in one finger.

Printed in 3D: maintenance-free gripper for the packaging industry

Fast availability at a low price and use under hygienic conditions were important prerequisites for this 3D-printed gripper. It is used to package cosmetic products and has the special advantage of working without additional lubrication, hence fulfilling hygienic requirements.

Manufactured by injection moulding: plain bearings for heavy-duty agriculture

Using iglidur plain bearings, Lemken GmbH and Co. KG save maintenance costs and lubricants on a daily basis. The plain bearings made of high-performance polymers easily withstand the high loads on the bearing points of the intensive cultivator and are also very durable. For Lemken it is pretty clear: The igus plastic plain bearings made of iglidur material will also be used in the future to avoid the annoying maintenance time.  

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Here you can find further interesting applications from very different areas of use