3D printed implants

The 3D printer is a catalyst for industry 4.0. Researchers at the Institute of Medical and Analytical Technology are demonstrating that it is also opening up entirely new directions for implantology. They are developing the complete process chain, from implant design, to manufacturing, to quality management of 3D printed implants. The research groups are testing the potential of a wide range of materials and developing new production techniques; their vision is that in the not too distant future doctors will design implants in the hospital.

3D printers are revolutionising production technology. They enable the large-scale production of objects with significantly more complex three- dimensional structures than is possible with conventional production methods. At the HLS, Erik Schkommodau and Ralf Schumacher are making sure that medical technology also benefits from these advances. For them, the advantages of 3D printing for implantology are clear. Schkommodau, the head of the Institute for Medical and Analytical Technology, explains: “ In future, and in some cases even today, doctors can create 3D- printed implants for patient- specific bony structures, for example in the face. We have been working on this technology for about 15 years. Ralf Schumacher, who heads the HLS spin-off Mimedis in addition to his teaching and research activities in the field of 3D printing and medicine, has a clear vision: “We want to develop 3D printing systems which doctors can use to design implants themselves in the clinic.” To this end the two researchers are developing complete processes, from the implant design software, through to production and quality management. This vital work goes hand in hand with their research into new materials for the next generation of implants.

Applications in the human body place high demands on materials: they must not be toxic or otherwise harmful, they need to be very strong where necessary and in some cases should also interact with the body, e.g. dissolve over time or allow bone cells to grow through them. To meet these requirements, HLS researchers are working with both metals and ceramic materials. Titanium and its alloys have been the state of the art in implantology for many years. Over the last three years the Institute has established a quality management system for the manufacture of implants using 3D printers, according to EU guidelines. External medical technology firms can thus outsource implant production to the HLS and audit them as a supplier. The HLS laboratories can provide these firms with special implants and help to cure patients with complex bone defects.

One printing process for metallic implants is Selective Laser Melting. The printer holds a layer of metal powder a few microns thick, which is melted by a laser at predetermined points. “In this way, the bone structure, its pores and hence its biomechanical properties can be replicated very precisely. It is also possible to give an implant different elastic properties”, explains Schumacher. “Artificial joint sockets can be modelled in such a way that they are dense near the joint gap and open-pore near the bone. Bone cells can then grow through the pores, strengthening the anchoring of the implant.” In addition to traditional implant materials, the scientists are researching NiTinol, an alloy containing nickel. Not only is it more flexible than conventional titanium alloys, it also has good mechanical damping properties and has form memory. The HLS researchers have even succeeded in maintaining this form memory at body temperature: 3D printed NiTinol forms can be changed at low temperatures so that they can easily be introduced into the body; they then resume their original shape when heated in the body.

Ceramic implants that break down in the body are also being investigated. However, they are not bonded with a laser but rather with a chemical binding agent which is applied by a print head to the powder layer. The ceramics used, hydroxylapatite and tricalcium phosphate, make up the bulk of the extracellular matrix of the bone and give it its strength. However, bone also contains biopolymers such as collagen which give it flexibility. These are difficult to add to the artificial production process, since the ceramics are brittle after printing and being baked in an oven at 1200 to 1400 degrees Celsius. Working with the Paul Scherrer Institute, the researchers are taking a different approach, using crystalline nanoparticles instead of biopolymers; the print head applies these nanoparticles with the binder. First results have shown a very promising stabilization of the implants. With all the different materials and the need to establish quality management systems for them, the HLS researchers are taking ambitious steps into the future: “Standard printers are rather limited and we do not have the range of possibilities we need. Therefore we are now developing our own printers.”

Methods

Computer Aided Design (CAD)
Free-form surface modelling
Material and process development for 3D printing
Antibacterial tests
Electrochemical surface treatment

Infrastructure

3D printing technologies: MultiJet printing for plastics, Selective Laser Melting for metals, Binder-in-Bed printing for bioceramics, Fused Deposit Modelling, Bio-Plotter
Metallographic laboratory (SEM, EDX, μ-CT, confocal microscopy)
Mechanical test laboratory (tribology, hydropulser, tracking, optical 3D scanner)
Plasma cleaner
Dynamic differential calorimetry