3D Printing: Another Path-Breaking Invention for On-Demand Bones

A hyperelastic bone in the shape of a section of the human spine, 3-D printed using an ink developed at Northwestern University. Credit: Adam E. Jakus
A hyperelastic bone in the shape of a section of the human spine, 3-D printed using an ink developed at Northwestern University. Credit: Adam E. Jakus

3D printing is gaining copious amounts of attention and rightly so, it is a revolution churning its way through the field of healthcare and replacement surgeries. Developments are being made to produce and market 3D-printed products by reputed companies; prominent ones being GE, Aurora Flight Sciences, and upcoming ones like BioBots, GeSim and Next21.

Bone replacements invite meticulous attention owing to its structural complexity and ethical concerns for implantation in humans. This did not stop researchers from being optimistic with respect to a “hyperelastic bone” that has the ability of being manufactured on demand. As of today, it is said to be a potentially faithful step forward for quick amendment of injuries varying from bones affected by cancer to broken/cracked skulls. This seems to be a positive reinforcement for a generation of bone replacements.

In the current era, there are a variety of methods today for replacing cracked and shattered bones.

An autograft is a method in which a patient’s bone from another part of their own body (commonly hip or rib) is used as a replacement for implanting in the required area as a part of the skeleton. An autograft is preferred by surgeons alike due to the bone that has stem cells giving rise to healthy bone cells, providing support to the new bone member. Stem cells are useful in the way an existing bone can direct it, to grow at a particular location and to a desired type. One of the major highs of an autograft is that there is no risks of an immune rejection of the replaced bone part since the bone is from a patient’s own body. An autograft comes with its own issues of availability of bone, along with painful surgery and recovery of the patient.

One of the other options for replacement is growing a synthetic or natural scaffold for the bone to grow on. These scaffolds are latched on by stem cells which then grow and differentiate. The resulting cells build the bone brick-by-brick much like the idea behind the construction of a building. This method is unlike the autograft process where the stem cells might not grow into the required bone or cartilage. On the other hand, a scaffold can be manipulated materially. Materials like calcium phosphate have been used as bases for stem cell growth but they turn out to be brittle and tight. This makes implantation an issue and may cause the immune system rejecting them owing to the “foreign” attack to the body.

The above issues are being worked upon by researchers at Northwestern University, Evanston, Illinois to create a suitable material in the form of a hyperelastic bone. This bone is a type of scaffold that comprises of hydroxyapatite (a mineral in bones and teeth), polycaprolactone (a biocompatible polymer), and a solvent. The polymer provides flexibility while the solvent sticks to the resulting 3D layers whilst evaporating through the printing process. The main takeaway from this idea is that a patient with a broken bone only has to undergo an x-ray for a 3D-printed hyperelastic bone scaffold and it can be obtained the same day. This overcomes the problem of a painful autograft surgery and the waiting time for a custom-made scaffold.

These researchers tested the 3D-printed scaffold on rats by fusing spinal vertebrae in them. The objective behind this experiment was to gauge whether their created material could juxtapose two vertebrae in place and other scaffolds that are commonly used for treating spinal injury patients. Eight weeks after the hyperelastic bone implantation, new blood vessels were found to have grown in their scaffold (for keeping the bone-forming tissue alive) and calcified bone was formed from the existing stem cells of the rats. The fusion of the vertebrae was more efficient than their controls (these received a bone graft from a donor or nothing at all) as reported in Science Translational Medicine.

In addition, this hyperelastic bone was used for the repair of a macaque monkey’s damaged skull. Post four weeks after the implant, the scaffold was again found to be grown in blood vessels along with some calcified bone. The highlight of this experiment was that the monkey was unharmed from any adverse biological effects.

Jos Malda (not involved in the research), a biomaterials engineer from Utrecht University in Netherlands, expressed that a material like hydroxyapatite is commonly used as a part of biomedical engineering laboratories and hence, it would be cheap-effective to print. Ramille Shah (Material Science Engineer & co-author on this study) says, “The sky’s the limit for this material’s applications”. This is true to its meaning as was shown by the researchers in creating the scaffolds at a lightning speed (less than 5 hours for each) as compared to conventional 3D-printing standards. The future could shape up to print scaffolds with exact specifications and be utilized for facial reconstructions.

Shah imagines that hospitals may one day have 3-D printers, where customized implants can be printed while the patient waits.

“The turnaround time for an implant that’s specialized for a customer could be within 24 hours,” Shah said. “That could change the world of craniofacial and orthopaedic surgery, and, I hope, will improve patient outcomes.”

As with any scientific research, this work needs to be tested repetitively before taking a step towards humans. All in all, this could be a blessing for patients and would be a huge growth in engineering medicine foreseeing the fact that implants could be quickly printed and customized!

The original article can be found here.