3D printed bio-dough for your custom skeleton

3D printed skeletal parts can be a lifesaver. Replacement skulls made from transparent plastic can now be made to order and fitted in no time. Although there may be some benefits to using artificial materials for skulls, for many applications real bone is still the best option. The problem is that there really is no good way to feed calcium, phosphate, and protein into a printer and have living bone come out.

One way around this dilemma is to print a material that cells can do something with. That way the body can better integrate with the material, and perhaps even replace it over time with its own stock. This would be particularly important for the meshwork of spongy tissue (known as trabeculae) that is typically found in the core of the spinal vertebral bodies, and long bones of the limbs. A potential substitute for this ‘cancellous bone’ has recently been reported in the journal Biofabrication. This bone is not only structural, but also provides unique niches for the production of various kinds of blood cells.

The researchers combined two commonly used biomaterials into a thermoresponsive blend that could be printed and then quickly cured into a solid at 37 degrees Celsius. The main component, poly(lactic-co-glycolic acid) (PLGA), is the go to material for biodegradable applications. When stabilized with polyethylene glycol (PEG) and extruded through a print head, a porous solid with properties similar to cancellous bone can be made. Mechanically speaking that amounts to tolerating yield stresses up to 1.22 MPa and having a Young’s moduli of up to 57.3 MPa.

Incidentally, you may have heard of PEG before. It happens to be the ‘magic ingredient’ that is being touted for use in the allegedly forthcoming head transplant surgery.

The researchers were also able to embed microspheres laced with proteins that could be released over time. Although they just used a common protein (lysozyme) here for testing purposes, the idea is probably to incorporate a bone-morphogenic protein like BMP that could aid in regrowth. To remove any doubt that the new material was biofriendly, the researchers also did the essential experiment of incubating it together with human mesenchymal stem cells obtained from bone marrow.

We covered the 3D printed ‘total skull’ replacement operation over a year ago. The 22-year-old patient seems to be doing well and there is even a video (below) of the operation that has been released in the time since. While that is all very encouraging, having a lining of the real thing may still have much to offer, particularly for the skeletal bones.

More than just bone is probably going to be needed for any significant repair or major augmentation of the skeletal system. Fortunately, researchers are also coming up with ways to print other important elements like cartilage. Not only that, but they can potentially do it in less than an hour while you wait. Soon we might expect that if your hospital is not advertising its own state-of-the-art machine shop, you may may want to go somewhere else. One obvious place for a custom preformed cartilage insert would be for the meniscus of the knee.

That is exactly the spot for a new implant (see pic above) made of a material called Samsonium. Scientists at Swansea University-UK have FDM printed this nylon titanium powder into a meniscus with the right degree of cushion and slipperiness to do the job. Reportedly ten times stronger than ABS or PLA filament, the material is described as ‘the purest form of a delta transition of nylon 6/9 with an optimized crystallinity.’

We’re not sure exactly what that means, but it sounds like the next time you have a major accident, you might want to at least ask about some of these goodies. To temper all this optimism we should probably leave you with at least one sobering dose of reality from the world of bone cements and materials: beware of off-label usage and make sure everything has been thoroughly vetted.