Description of the component:
Walking aids, such as forearm crutches in accordance with DIN EN ISO 11334-1, are often still mass-produced items with limited adaptability to the user. However, additive manufacturing is ideal for the production of one-offs and therefore individual fittings. The additive manufacturing laboratory at Landshut University of Applied Sciences therefore developed a forearm crutch that was individually adapted to a test subject. The fused filament fabrication (FFF) process was used as the additive manufacturing method.
Challenge:
For cost reasons, the upper parts of forearm crutches (handle and cuff) are manufactured using plastic injection molding. The lower part usually consists of an aluminum telescopic tube. Due to the high cost of producing conventional injection molds, upper parts with individual geometries cannot be produced economically. In addition, the injection molds impose restrictions on the geometric design. Demolding directions and angles must be taken into account and undercuts must be avoided. This severely restricts load-compliant lightweight construction and individual design.
Based on the premise that life expectancy is increasing and people are living alone for longer, crutches will not only be used for short periods in the future, but also to maintain mobility into old age. However, in order to increase acceptance, the image of the forearm crutch must change from a "crutch" to an accessory and offer a high level of comfort.
The former can be achieved through an attractive design that can be chosen by the user. However, a high level of comfort can only be achieved if the geometry is tailored as precisely as possible to the user's individual physical characteristics. In addition, strength decreases with age, which means that the weight of the crutch must be kept as low as possible. Thanks to the high degree of design freedom offered by additive manufacturing processes, attractive design, individual geometry and lightweight construction can be combined.
Solution:
Despite standardization, there is a lot of leeway in the design of forearm crutches. A completely additively manufactured, one-piece crutch would be ideal. For economic reasons, a compromise between 3D-printed and purchased parts was sought in the developed concept in order to realize the individualization as cost-effectively as possible.
The upper part was specially adapted to a test person with the help of CAD and topology optimization programs and printed from ABS (acrylonitrile butadiene styrene) using the FFF process. It includes a handle carrier, the arm cuff and, as a functional enrichment, mounts for the front and rear lights. A soft 3D-printed handle made of TPU (thermoplastic polyurethane), individually molded from the person, and other padding elements can be attached separately. The lower part consists of a purchased carbon tube and a standard walking support rubber cap. The connections of the individual parts are designed as press fits or adhesive connections.
Due to its size, the upper part can still be produced in many conventional 3D printers in a moderate amount of time. Complex lattice structures, which cannot be realized by injection moulding, ensure sufficient load-bearing capacity with low weight and an attractive design.
The use of additive manufacturing makes it possible to customize the shape and color of the upper part. In terms of shape, the limits are somewhat narrower due to the function to be fulfilled. However, the surface and color open up many possibilities through the choice of printing material, subsequent surface treatments or coatings (e.g. lacquering or colored upholstery). Further customization options include the integration of additional functions, such as lamps that make it easier to see and be seen in dark environments. Sensors for monitoring vital parameters, fall detection or localization can be further useful additions.
A conventional forearm crutch weighs approx. 500 to 550 g. The 3D-printed prototype adapted to the test subject weighs 445 g without or 472 g with lamps. The prototype was developed by Veronika Selmaier as part of her bachelor's thesis at Landshut University of Applied Sciences. The work was supervised by Prof. Dr.-Ing. Raimund Kreis and produced in the additive manufacturing laboratory with the support of Prof. Dr.-Ing.
Conclusion:
By creating a prototype for a test subject, it was possible to show that 3D printing makes it technically possible to customize forearm crutches. It is therefore conceivable that orthopaedic technicians (possibly in cooperation with manufacturing or design service providers) will be able to customize forearm crutches for patients in the future. However, fatigue and drop tests in accordance with DIN EN ISO 11334-1 still need to be carried out to validate additive manufacturing.