3D Printed driving mechanism design for a high-speed reciprocating needle used during vitrectomy

Abstract

Vitrectomy is an often performed procedure during eye surgery and requires a high-precision vitreous cutter. The production of these precise and lightweight vitreous cutters sets high demands on the manufacturing process. Trained technicians must assemble the device step by step and continuously check and validate the manufacturing process. Additive manufacturing on the contrary allows for non-assembly mechanisms that can be printed at once without requiring any post-assembling steps. However, a high-speed vitreous cutter design suitable for 3D Printing is not yet presented. This research aimed to deliver a 3D Printed driving mechanism design for a high-speed reciprocating needle used during vitrectomy that does not require post assembly steps from trained technicians. It was established that the driving mechanism should reciprocate two concentric needles by air pressure to cut vitreous. Currently used actuators are investigated and a prior attempt for a non-assembly vitreous cutter is analysed. The diaphragm and bellow-based design were considered a potential solution path. A suitable design for both potential solution paths is made. The bellow design consists of an inner and outer bellow to allow the passage of the needle. The diaphragm concept is already used for the first and only attempt to produce a non-assembly vitreous cutter. This prior attempt is further analysed and it became clear the damping of the diaphragm needed to be decreased to increase the speed of the backward motion. Therefore, a planar spring is added to the dual flat diaphragm design. Finally, the spring-reinforced dual flat diaphragm concept is selected for continuation and tested by using PolyJet prototypes. Tests are executed to determine if the requirements could be met, especially focussing on the speed and force requirements. Different spring shapes and thicknesses are tested. It became clear that the behaviour of the spring-reinforced diaphragms is suboptimal. The return time is higher than preferred and damping is still present in a large extent due to hysteresis. To improve the design it was decided to continue with tests where the start position is relocated to form a pretension and overcome the damping seen especially at the last part of the return stroke. Pretension appeared successful and showed a 98% decrease in return time, but the requirements for the speed could not be obtained. Altering the thickness of the spring led to a sufficient high backward force but did not show direct influence on the speed of the backward motion. Overall, a non-assembly vitreous cutter driving mechanism is made but not all requirements could be met. Exploring design directions which do have some drawbacks should be considered to offer a solution in the near future. Designing a driving mechanism that also requires 3D Printed flexible material, first requires a thoroughly material investigation to identify the mechanical properties and time-dependent behaviour such that a trustworthy design optimization can be made. However, a design for a non-assembly high-speed vitreous cutter is made and with the upcoming developments in the 3D Printing techniques and materials the design might form the basis of a high-speed vitreous cutter. This research tested the most ideal case and gave further insight bringing us a step closer towards a non-assembly high-speed vitreous cutter.