By now, we all know that 3D printing technology has many applications in the medical field, from manufacturing medical devices and prosthetics to printing patient-specific organ models and conducting valuable training and research. Recently, the Institute of Production Engineering and Machine Tools (IFW) at Leibniz University in Hannover, Germany, which focuses on all aspects of machining, was working on an R&D project for a tool that could cut bone without causing thermal-induced tissue damage. As of right now, the drilling process during surgery sounds pretty awful – it has to be interrupted multiple times to keep the temperature down, because fluid could enter the wound if the tool is removed to cool it. IFW needed help, and turned to the family-owned German toolcraft company, which specializes in manufacturing high-end precision components and parts.

Toolcraft utilizes a metal laser melting process, as it offers greater freedom of design and a broad range of applications and tough materials; it also saves customers time, because the parts are manufactured on the company’s Concept Laser M2 Cusing Machine in just a few days, with no tooling required after printing.

[Image: toolcraft]

Tissue damage during bone cutting occurs starting at temperatures of about 48°C, and conventional tools with cooling systems can’t be used during surgery because of the risk of fluid getting into the wound. Through use of metal additive manufacturing techniques like the one toolcraft uses, drills can be designed with their own integrated cooling ducts. These ducts allow the coolant to consistently flow along the helix inside the tool and back to its holder, without ever touching the open wound.

[Image: IFW]

Because the shape of the drill had to stay the same so users familiar with conventional drills would be comfortable with a new tool, the prototype was modeled on a traditionally manufactured bone drill. IFW and toolcraft also teamed up with Schmidt WFT for its CAD and simulation software services. The team had to figure out the drill’s cooling capacity, in terms of temperature, volumetric flow rate, and the coolant’s thermal capacity. Then, they determined a method to keep the tool stable while introducing a closed cooling circuit into its substrate, while also making sure the tool could perform the tasks it was required to perform.

Biocompatible 1.4404 material was used to 3D print the drill, as it can be tolerated by patients in surgery, and Schmidt WFT designed its shape, as well as its internal cooling ducts. Once the drill was off the print bed and machined to its actual size, IFW performed practical tests with the bone drill by drilling and measuring the process temperature, using both artificial and bovine bone, and water as a coolant. The researchers took reference temperature measurements at lower and higher feed rates, and also when the tool cooling system was turned on and off.

[Image: IFW]

To help keep the temperature consistently low, toolcraft also created a non-rotating pre-spindle attachment for the drill, which has an inflow and outflow function for the coolant. The attached tank and pump ensures a continuous supply of coolant, while continuous flow is made possible with a flow and return pipe. The thermal energy is moved away from the cutting edge by the drill’s internal circular cooling ducts, which each have a 1.2 mm diameter. Horizontally drilled holes link the cooling circuit to the drill, which help supply the coolant and take it away, and the manifold was attached with a circlip groove.

While we’ve seen 3D printed drills before, even a tiny one, this is certainly the first time I’ve heard of one being used to improve surgical processes, though metal laser melting and an M2 machine have been put to work to 3D print patient-specific craniomaxillofacial surgical implants. The tests of the 3D printed bone drill determined that its use had reduced the temperature produced by drilling up to 70%, thanks to the innovative internal cooling system’s ability to compensate for temperature increase. The technology could definitely have other applications than the medical field, such as manufacturing saws.

The German Federal Ministry for Economic Affairs and Energy funded IFW’s 3D printed bone drill project, as part of the Central Innovation Programme for SMEs (ZIM). Discuss in the 3D Printed Bone Drill forum at 3DPB.com.

[Sources: toolcraft, Today’s Medical Developments]

 

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