Faster blood tests possible thanks to 3D printed gears

A lightweight and wear-resistant gear to increase the resolving power of a stepper motor system. It also need to be low-maintenance and lubrication-free due to the hospital environment.

A blood test is based on what is known as SPR spectroscopy. A concentration of troponin in the critical range of 1 to 100ng/L indicates an increased risk of a heart attack. In the technology used by Cor.Sync, a stepper motor with a troponin concentration of 1ng/L is said to produce an angular fluctuation of approx. 0.009 degrees. Therefore, the available 0.9-degree stepper motor was coupled with two gearboxes in series. Each gearbox has a 100:1 transmission ratio, allowing for 0.00009 degrees of offset angles. However, metal gears are not suitable for such an application because they are too heavy in relation to the torque achieved by the stepper motor.

To enable the troponin concentration in the blood to be recorded accurately, a 0.9 degree stepper motor was coupled in series with two gears, both of which have a transmission ratio of 100:1. What still stood in the way of the resulting resolution of 0.00009 degrees was the increased inertia of the system due to the metal gears. A lighter material was needed so that the torque of the stepper motor could overcome the inertia of the system.

In addition, a hospital environment requires special operating conditions. Adjusting the device for maintenance could cost some patients their lives. This means, among other things, that the gears needed to be lubrication-free as lubrication pose a biological hazard during blood tests. As far as the gears are concerned, Cor.Sync initially tested several metal models. Once a suitable device had been found, a lubrication-free implementation option was sought.

The 3D printing of the gear from the wear-resistant iglidur ® i3 plastic fulfilled every requirement. Thanks to the 3D printing service from igus®, the desired design could be realised with minimal inertia. In addition, the system's freedom from maintenance was guaranteed thanks to the self-lubricating polymer gear.

In hospital environments, the use of lubricants is avoided, as these can become a favourable environment for the spread of infectious agents. For this reason, not only the self-lubricating iglidur® i3 gears were used, but also other lubrication-free igus® components in other parts of the device. The optical system, for example, consists of laser diodes and photodiodes, among other things, which have to be aligned with each other. For this purpose, the optical elements were mounted on the drylin® W cam slides, which slide over the drylin® W double rail, thus ensuring the concentricity and alignment of the optical system.