Scientists have some interesting news about advances in human “spare parts.”
Soon it may be possible to replace damaged human bones with synthetic, customized bones created on a 3-D printer.
This “hyperelastic” bone will be produced with an “ink” made from a natural calcium found in human bone.
In a significant advance over current methods, scientists say the custom-printed bones could rapidly induce bone regeneration and growth.
That could make medical procedures more effective, less painful, and longer-lasting.
Applications could include the repair of craniofacial, dental, spinal, and other bone and sports medicine injuries.
Scientists at Northwestern University published their findings last month in the journal Science Translational Medicine.
Ramille Shah, Ph.D., who led the research team, is an assistant professor of materials science and engineering at Northwestern’s McCormick School of Engineering, and an assistant professor of surgery at Northwestern’s Feinberg School of Medicine.
Shah describes hyperelastic bone as “a highly versatile, growth factor–free, osteoregenerative, scalable, and surgically friendly biomaterial.”
The scientists created hyperelastic bone to perform a spinal fusion in a rat and to repair a skull defect in a rhesus monkey. The animal trials will continue.
Shah and her team believe human trials of their synthetic bone could begin within five years.
Shah, who heads the Shah Tissue Engineering and Additive Manufacturing Lab at Northwestern, said in a Healthline interview that the goal of her team of scientists and clinicians was “to develop a 3-D printable biomaterial for bone tissue regeneration in children.”
Pediatric patients suffering from bone defects from trauma or birth could benefit significantly from this technology.
“The current materials surgeons use for craniofacial defects are metallic plates and screws, and polymers, but not degradable ones, for facial work,” Shah said. “The primary way now is take pieces of bone from the patient’s ribs or hips and do an ‘auto-graft’ — shape the pieces to fit the defect space they want to reshape. But this method can cause problems elsewhere in the body. Auto-grafts are used especially with children, because you do not want to use ‘foreign bodies’ in pediatric patients.”
Bone implantation surgery is painful and complicated for children, she said. Bone harvesting for an auto-graft can lead to other complications and pain. Metallic implants are sometimes used, but this is not a permanent fix for growing children.
“Adults have more options when it comes to implants,” Shah said. “Pediatric patients do not. If you give them a permanent implant, you have to do more surgeries in the future as they grow. They might face years of difficulty.”
The right ingredients
Natural bone component is critical to success.
The main constituent of Shah’s biomaterial is hydroxyapatite, a phosphate of calcium that is the chief structural element (90 percent by weight) of natural vertebrate bone.
Shah and her colleagues mix 90 percent hydroxyapatite with 10 percent biocompatible, biodegradable medical polymer in a solvent that makes the texture more like a liquid than a solid.
“The consistency is like Elmer’s glue,” Shah said.
The mixture is called “ink” because it is used in a 3-D printer.
Once the mixture is extruded, the main solvent immediately evaporates and solidifies the material. The structure of the material is porous and can be used at room temperature.
“High porosity is critical because cells and blood vessels must infiltrate the structural scaffold to enhance tissue integration,” Shah explained.
In addition, the high concentration of hydroxyapatite creates an environment that induces rapid bone regeneration.
“The [hyperelastic bone] is designed to degrade and remodel into natural bone, and therefore can grow with the patient,” Shah said. “This eliminates the need for future surgeries, as is done with metallic plates or implants.”
A versatile product
Hyperelastic bone is versatile and can be printed in varying strengths.
That includes highly elastic bones, ones that can withstand significant loads as well as those that are more hollow or dense. These mechanical properties are determined by the architecture of the 3-D printed object, Shah said.
Synthetic bone could be customized for each patient.
The variety of applications includes repairs for spine fractures, sports medicine injuries, and ACL and rotator cuff injuries that require soft-tissue-to-bone healing, Shah said.
In craniofacial and dental applications, and for facial deformities, the replacement bone can be printed “to perfectly fit the symmetry and anatomy of the patient, especially in cases where there is an aesthetic component important to the patient outcome,” she said.
“The material is highly elastic, too, and surgeons can manipulate it,” Shah said. “The materials available now are very flexible, and not hard to cut and shape. When surgeons heard about this, they were very excited.”
Important in head, face surgeries
The properties of hyperelastic bone are particularly crucial in repairing bones in the head and face.
“In craniofacial defects, we can create an object that fixes or covers the defect, allowing us to maintain facial symmetry,” Shah said. ‘We can print something that is patient-specific. The material will go through the scaffold. This is important, because if you don’t have blood vessels within the defect, you can have tissue necrosis [tissue death]. In the scaffold, cells will deposit new bone material. With permanent implants, you have to replace them over time. This new material grows with the patient and is noninvasive.”
Antibiotics could be added to control infection.
The researchers perform the 3-D printing process at room temperature, which allows them to add other elements, such as antibiotics, to the ink.
“We can incorporate antibiotics to reduce the possibility of infection after surgery,” Shah said. “We also can combine the ink with different types of growth factors, if needed, to further enhance regeneration. It’s really a multifunctional material.”
Surgeons using Shah’s synthetic bone material would be able to scan the patient’s body and create personalized replacement bone on a 3-D printer.
The flexible mechanical properties of the biomaterial allow physicians to easily cut and shape it to size during a surgical procedure. Not only is this faster, Shah said, but also less painful compared with using auto-graft material.
When she began her research in 2009, Shah received faculty start-up funding and has had ongoing support from the National Institutes of Health (NIH).
She hopes to obtain government and corporate funding, and recently founded a start-up enterprise at Northwestern to explore applications for her work.
Shah looks forward to a day when “the turnaround time for an implant that’s specialized for a customer could be within 24 hours. That could change the world of craniofacial and orthopedic surgery, and, I hope, will improve patient outcomes.”