Cranial implants today are primarily manufactured from materials such as titanium and PEEK. The patient’s bone may grow into and bond with these materials, but there are other options that more actively encourage new bone growth so that the implant becomes fully integrated. In this episode, we look at how 3D printing is enabling the development of cranial implants made from hydroxyapatite (HA), a ceramic also known as bone mineral that makes up around 70% of human bone by weight. The body recognizes this material and is more likely to produce new bone cells when it is present. We explore how Lithography-Based Ceramic Manufacturing (LCM) makes it possible to 3D print patient-adapted implants with this material, and the way forward for such medical devices. | This episode of The Cool Parts Show is sponsored by Carpenter Additive

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Related Resources

• Our previous episode with Lithoz, developer of Lithography-Based Ceramic Manufacturing (LCM)
• More on LCM 
• An episode on a PEEK implant that makes use of hydroxyapatite’s osseointegration properties as a coating.
• More on 3D printing with ceramics.

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Transcript

Stephanie Hendrixson

Today on the show, we’re going to be talking about medical implants, specifically cranial implants and the use of 3D printing to produce patient-adapted implants like this one from a very interesting material.

Pete Zelinski

So this model obviously represents a patient with a very serious condition. Maybe this is an injury, the result of a blow or trauma. Maybe the skull had to be opened up as part of a surgery to relieve pressure. In either case, the value of 3D printing is clear for producing a geometry precisely mated to this hole in the patient and a personalized implant of exactly the right shape and contour.

But geometry isn’t actually the most significant value of 3D printing in this case. Because, in this case, 3D printing also makes it possible to work with a material that is very well suited to success in this procedure.

Stephanie Hendrixson

So, as we said in the cold open, the material used here is a ceramic called hydroxyapatite. We’re going to learn more about that material in a moment. But first let’s talk a little bit more about the kinds of situations that might cause a patient to need an implant like this, and how those conditions have been treated up until now.

I want to introduce Dr. Christophe Staudigl. He is an attending physician in the Cranio-Maxillofacial Department at the Kepler University Clinic, located in Linz, Austria.

Christoph Staudigl - Department of Cranio-Maxillofacial Surgery, Kepler University

The part you’re holding is the cranial implant to reconstruct parts of the cranium. Cranium is the part of the skull that covers the brain, basically the brain case, so to say. There are some conditions, especially when the pressure inside of the brain rises, you need to relieve the pressure. And to do this, you remove part of the skull. That’s called an osteoclastic trepanation.

And, as soon as the swelling has gone down and the underlying medical condition has been resolved, usually you replant the piece of the bone to cover the part of the skull. In some cases, about 30%, this doesn't work because the body doesn’t accept the transplant or let’s say the part of the bone that’s been removed, or because there’s some sort of infection. And these kinds of cranial implants that you see here are a possible solution for this problem.

The current standard of care, well the gold standard right now is autologous bone, meaning the bone of the patient that’s been removed during the first surgery. If this does not work, currently there are some materials that we can use. The next best thing to the patient’s own bone is either titanium or PEEK, a polymer.

Pete Zelinski

So, if the patient’s own bone is not available, then the alternative is typically PEEK or titanium. The question there relates to the body’s acceptance of that material. The strength of this repair is greater to the extent that the patient’s remaining bone around the implant is able to grow into and fuse tightly with that implant.

Bone integration, osseointegration is the issue we’re talking about. And the very best case is a material that is just like bone — that bone wants to naturally grow into and fuse with. Bone is mostly made out of a mineral, hydroxyapatite. So why not make an implant out of that material?

Christoph Staudigl

This material, hydroxyapatite, is a great material for the body. The body already knows this, so it’s highly biocompatible. It’s nontoxic. Under the right conditions, it can get resorbed and it leads to the ingrowth of bone cells.

These properties are called osteoinduction, [which] means that this material can lead to the production of new bone on the implant site, as well as osteoconduction, which means that boney cells and boney matrix grow along the surface of the same plant. And this whole process leads to osseointegration.

Stephanie Hendrixson

So osseointegration, that is the goal. And hydroxyapatite will get you most of the way there. But how do we actually make implants from this material? How do we adapt them to the size and shape needed for the patient’s specific situation and injury? How do we 3D print with this ceramic? In this case, Christoph is collaborating with a company also located in Austria called Lithoz.

We’ve actually covered them on the show before in an episode about a more experimental type of implant. But they have developed a 3D printing process that is specifically for printing ceramic materials. So I want to introduce, for the second time in the show, Dr. Daniel Bomze. He is the director for Medical Solutions at Lithoz.

Daniel Bomze - Lithoz

So we have been working with Dr. Staudigl for a lot of years already. The Kepler University Clinic, where Dr. Staudigl works, is known for their specialty in training maxillofacial surgery, which again is a surgical area where Lithoz can contribute a lot too.

So we just successfully finished a research project which is called INKplant, where we could quite successfully show what can be done in combination of different kinds of biocompatible ceramic materials. And we are currently already setting up a follow-up project.

Pete Zelinski

So biocompatible ceramics, hydroxyapatite is a mineral our bones are made of. It is arguably a ceramic. An additive manufacturing process that is very effective with ceramics, lithography-based ceramic manufacturing — a DLP process (digital light processing) involves a liquid polymer resin. The ceramic material is suspended in that to create a slurry. Light is used to solidify that slurry layer by layer, by layer by layer to build the form. When the liquid is removed, when the form is sintered, the result is this dense, solid, hard completed ceramic part.

Daniel Bomze

This implant is made of hydroxyapatite or, more specifically, of LithaBone HA 480 — which is a material used in 3D printing of ceramics. So LithaBone HA 480 is a suspension of hydroxyapatite powder in a photocurable binder system. We call that a slurry. So this slurry is 3D printed within the lithography-based ceramic manufacturing process, which is also known as LCM.

After the printing, the part is cleaned of excess slurry and baked at high temperature. This temperature treatment will remove the photocurable binder thermally so it’s broken down into small molecules by the heat and then burned off. This process is also called debinding. And, as it says, it means removal of the binder.

Thereafter, the residual ceramic part is consolidated by further increasing the temperature up to a sintering temperature. This sintering converts a chalk-like, off-white, brittle intermediate part to its final properties.

So during this process, the part shrinks to its final dimension and also it develops its properties — like being biocompatible, being stable and, in the case of hydroxyapatite for example, it changes from off-white to some light blue color.

Stephanie Hendrixson

So, lithography-based ceramic manufacturing (LCM) brings a lot of the advantages that we’ve come to expect from additive manufacturing. So the ability to build porosity or lattice work into an implant like this, again, kind of opens up, makes space for those bone cells to grow in.

It’s also allowing these implants to be sized and shaped correctly for each individual patient. Cranial implants are less common than, say, spine implants or hip implants. And so, there’s not really a need to standardize them. Instead, implants like this will be designed to be adapted, to be tailored a little bit to each individual patient.

That means that before the 3D printing can happen, there are some other steps that are needed to capture the patient’s anatomy to make those design decisions before actually printing the final implant.

Christoph Staudigl

We schedule a CT scan. The CT scan has to have some special parameters in order to get an accurate representation of the boney structures.

Daniel Bomze

From the CT, the surgeon can then upload that medical imaging data to a platform typically provided by the medical implant manufacturer, where the surgeon or the team of surgeons can then, together with a team of biomedical engineers, design the implant itself and plan the whole surgery, including how will the patient look like or move like after the successful treatment.

Christoph Staudigl

And as soon as we are satisfied with the implant design, it goes into production.

Pete Zelinski

Is it possible now to receive a 3D printed hydroxyapatite cranial implant? No, but we’re not far from that. The idea of the personalized implant, that is established — a cranial implant tailored to the specific patient. The new elements that need to be validated are the manufacturing process, this new material. Christoph is in Austria, so keep in mind he’s talking about Europe. But here is the way forward that he sees.

Christoph Staudigl

Most manufacturers go the so-called patient-matched route. That means it’s not a completely custom implant. There is a design envelope, like a minimal thickness and some certain standardized material properties that we have to work and plan around.

For 3D printed cranial maxillofacial implants, we are currently finishing up the INKplant project. It’s been an EU-funded project where we assessed, together with some of our consortium partners, including Lithoz, new materials for these implants. And the results are really positive. We want to go ahead with a clinical trial with a new implant design in the next couple of months.

Pete Zelinski

All right. I think we got this.

Stephanie Hendrixson

All right. This is a 3D printed cranial implant made from hydroxyapatite — a ceramic material that’s already present in our bones. It was 3D printed with lithography-based ceramic manufacturing, a process developed by Lithoz that allows for printing a solid hydroxyapatite implant, and also makes it possible to customize the size and shape of each implant for the specific patient.

Pete Zelinski

So 3D printing is already the most effective process for quickly, reliably creating a tailor-made implant. But add to that the fact that there is an effective 3D printing process for ceramics means we can print with a ceramic material that is very close to the same material that our bones are made of. The patient’s remaining natural bone is going to want to bond with this implant that it sees as more bone.

Stephanie Hendrixson

One issue around patient-adapted implants like this that we didn’t get into in this episode is, where they should be manufactured? Should they continue to be made by off-site producers as they are now, or should they be 3D printed maybe on-site at the hospital? Daniel had more to say about this in a segment that we shared with our All Access subscribers, but you can sign up for free to see that segment as well just by going to TheCoolPartsShow.com/AllAccess.

Pete Zelinski

In addition, Christoph, our surgeon, when we were talking to him, he kind of took us down a side road of the history of osseointegration. The discovery of this phenomenon, how it was discovered. We couldn’t use it in the episode, but it was super interesting. We were interested. We think you will be, too. Our All Access members can see that too at TheCoolPartsShow.com/AllAccess.