05 Jan WP5 3D printed surgical instruments
In the domain of medical instruments, 3D printing is still in its infancy, although a few useful tools have already been developed. Examples include 3D printed steerable surgical forcipes suited for minimally-invasive bipolar electrosurgery at difficult-to-reach places in the human body (the DragonFlex, developed at BITE-group, TUD) and snake-like surgical devices for skull base surgery, 3D printed out of one single part and having clever intrinsic mechanical properties (stiff for torsion and axial compression, flexible for bending) due to the use of compliant helical structures, also developed by TUD.
Work Package 5 has been designed to revolutionize the application of 3D printing in the medical field, by focusing on three key challenges:
– The creation of miniature high-precision surgical instrumentation (Activity 5.1);
– The development of complex surgical devices that can be printed out of one single part (Activity 5.2);
– Easy manufacture of surgical instrumentation adaptable to individual patient needs (Activity 5.3).
During Activity 5.1, a state-of-the-art review on miniature, high precision 3D printing applications within the medical and technical design domains was presented. The report generated scientific knowledge on the existing 3D printing methodologies, in order to cope with tight tolerances and high precision in the development of miniature 3D printed devices.
The trocar system is used as key-example for Activity 5.1. The trocar system includes a handpiece with the inserter to create the incision for the trocar cannula. The trocar cannula creates a working channel for the insertion of instruments used to operate inside the eye. When no instrument is inserted is important the channel remains closed, this is ensured by the presence of a silicone valve.
A series of 3D printed valves were made using two different additive manufacturing techniques (Low Force Stereolitography and Digital Light Processing) and five different materials. An advantage of 3D printing is the ability to change geometrical parameters easily and get a prototype quickly. Knowing this, different valve geometries were created changing, for example, the thickness of the valve and the shape of the cut. Among the different prototypes, the valves made with Elastic material, characterized by high elongation properties, were performing the best when compared to the original trocar valve. Additionally, a 25G trocar cannula has been successfully 3D printed using low force stereolithography (Form3 printer) and manual drilling to remove the residual non-cured resin into the channel and make it completely open.
During Activity 5.2, a state-of-the-art review on existing methods to generate non-assembly 3D printed mechanisms was presented. This report is used as basis for the rest of the work that will be performed within this activity. The vitrectome is used as key-example for Activity 5.2. This instrument is used during vitrectomy to to remove the vitreous from the eye. The vitrectome has a closed and blunt shaft with an aspiration opening (port) which contains the cutter. Inside this shaft is the inner knife that cuts the vitreous gel. The vitrectome mechanism contains many parts currently assembled manually. This is a time-consuming process and not always very accurate. In the future the current manufacturing and assembly of the vitrectome could change thanks to additive manufacturing. The goal of this activity is to design a novel vitreous cutter that could be 3D printed without any assembly step. A diaphragm actuator was selected to drive the mechanism based on the limitations of additive manufacturing, the requirements of the new device, and examples found in the scientific literature. A concept design containing two diaphragms was chosen to develop further in a 3D printed prototype. Polyjet 3D printing technique was selected because allows to create parts using multiple materials. In this way, the housing could be printed with rigid material and the diaphragm with flexible material. The vitrectome mechanism was successfully 3D printed in one step, however the performance is still far from the original vitrectome. To improve the current prototype additional investigation on material selection for the diaphragm is necessary, as well as additional analysis on the diaphragm geometry.