January 19, 2014

Although 3D printing is used in nearly every modern product development process, it is still rare for the actual final product to be produced commercially using 3D printing methods.  Despite this, any industry that has previously had to replace tools or otherwise put them through an extensive process to make them usable again has been seeing an increasing amount of success in using additive manufacturing for creating new prints for each job.

Among other applications where 3D printing new products for each use has proven to be successful is in the medical industry – or to be more specific – instruments used during surgical procedures.

The high costs associated with not only acquiring the necessary tools but also maintaining them and sterilizing them from patient to patient leaves a lot to be desired.  While some commonly-used medical instruments will probably never be 3D printed, there are quite a few where it makes sense.

One such example was presented last week by biomechanical engineer Filip Jelínek, who wanted to improve upon the design of an existing medical instrument with one that would be easy to replicate from patient-to-patient and at a fraction of the cost.

Upscaled plastic DragonFlex prototype demonstrating tip opening and pivoting in two DOF; and a close-up picture highlighting the striking size difference between the 5mm & 15mm thick prototype tips. Image:ASME

The DragonFlex, which Jelínek developed as a part of his PhD thesis at TU Delft, is a steerable medical instrument for keyhole operations.

Modeled after the EndoWrist, a surgical tool that is engineered to act similar to the human wrist and be able to be used through small incisions, the aim of Jelínek’s research was to demonstrate a design of a structurally simple handheld steerable laparoscopic grasping forceps free from cable fatigue, while attaining sufficient bending stiffness for surgery.  Additionally, Jelínek wanted to improve upon the original EndoWrist’s maneuverability and dimensions.

Real-scale DragonFlex prototype components additive manufactured from a ceramic-filled epoxy resin.Image: ASME

“Despite its success, e.g. in prostatectomy, da Vinci’s steerable grasper EndoWrist from Intuitive Surgical has a complex design prone to steel cable fatigue, potential sterilization issues and high associated costs, all of which insinuate a need for an alternative,” said Jelínek in his thesis.

While the tip of the EndoWrist uses multiple parts of various materials in order to mimic the joint functionality that is similar to a human’s wrist, the DragonFlex’s instrument tip contains just for parts that are driven and bound by two cables that are mechanically fixed in the handle.

Real-scale ceramic DragonFlex prototype allowing seven DOF control by only seven structural components. Image: ASME

Image credit: Informa Healthcare

Two orthogonal planar joints utilize a rolling link mechanism that allow for the cables to follow circular arc profiles at a diameter that is 1.5 times larger than the width of the instrument shaft.  The rolling link feature equalizes the force requirements on both cables throughout the joint rotation which, in turn, makes the handling of the 3D printed tool feel fluid and effortless.  Additionally, the mechanism ensures that the cables are able to be used for longer durations of time.  The final smart joint design and instrument construction enable a surgeon to have full control of seven degrees of freedom while only using two cables.

Jelínek explained to that “the orange prototype was printed by TNO (Eindhoven, The Netherlands) using a Perfactory SXGA+ Mini Multi Lens rapid prototype manufacturing system in EnvisionTEC NanoCure RCP 30, a ceramicfilled epoxy resin. It was printed at 30μm resolution and 50μm layer thickness.”

And the clear prototype was 3D printed by PROFORM AG (Marly, Switzerland) using 3D Systems Viper si2 SLA System in 3D Systems Accura 60 material. And it was printed at 75±15μm resolution and 2.5μm layer thickness.

“[The] DragonFlex concept sheds new light on the possibilities of additive manufacturing of surgical instruments, allowing for a feature-packed design, simple assembly, suitability for disposable use and potential MRI compatibility,” concluded Jelínek.



Posted in 3D Printing Applications


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