Two days before New Year's Day of 2000, so December 30, 1999, Mrs. Graybeard and I left the house for a morning bike ride, as we did every morning over the Christmas break. It was a beautiful, clear morning; I don't recall the temperatures, but I don't recall wearing much in the way of cold weather clothing either. About 4 miles from home, so just far enough to be warmed up and settling in for a long ride, I looked in my rear view mirror. I saw a small pickup truck drifting into the bike lane and approaching behind us. As we usually rode, Mrs. Graybeard was behind me and I was in the lead to reduce the wind she'd get. I think I screamed something back at her but the next sensation I had was flying and tumbling onto the shoulder of the road, rolling over and coming to rest in the sparse grass. I looked toward the road and saw her lying in the street. In minutes, people were pulling their cars over to get out and help us.
There's no point in getting into too much detail here about a bike accident well over 17 years ago. I was lucky enough to walk out of the ER about four hours later, with a referral to see an orthopedic surgeon as soon as I could get in, because I had a broken vertebra in my back - L1. Mrs. Graybeard was not so lucky and while she also broke L1, hers was shattered. The problem was Y2K - the hospital wouldn't do anything except the most urgent of emergency procedures. She had to wait until January 2nd for surgery, which involved rebuilding the front part of the vertebra with donor cadaver bone. The massive surgery involved going in through her abdomen, repairing that bone and fastening it in place, then going in through her back and reinforcing her broken spine, adding (as we say) a pound of stainless steel in her back. Donor bone was made into a paste and used to cover and reinforce hardware, a paste that surgeons said would grow into a solid bone.
The point of this is to identify with the need for an improvement in how we do bone transplants. What if a compatible bone hadn't been available? A researcher at the University of British Columbia Okanagan's School of Engineering, Hossein Montazerian, has discovered a way to model and create artificial bone grafts that can be custom 3D printed.
“We have shown how porous bone replacements can be designed with the nature-inspired geometries and structures so that we provide cells strong, spacious and safe enough support to let them grow efficiently,” Montazerian said. “This technology allows the doctors and surgeons to design the patient-specific replacements so that they fit very well into the damaged bone area, instead of doing a secondary surgery and harvesting bone from other sites of the body for taking that replacement.”An interesting part of this story is that Montazerian analyzed the strength of 240 different ways of making these "biologically inspired" matrices to build bone out of.
In this study, numerical procedures were performed for a library of 240 TPMS-based unit cells (comprised of 10 volume fractions of 24 selected architectures) to explore the role of pore characteristics in determining normalized values stiffness, strength, and permeability. The associated design maps were developed based on which highly porous architectures with extreme properties were selected for experimental evaluations. Calcium sulfate scaffolds were designed based on the critical designs and 3D-printed (using a powder-based technique) in different cell sizes and size effects were addressed. The scaffolds were subjected to mechanical compression tests and the results were correlated with the computational data. [Note: TPMS = triply periodic minimal surfaces]
Besides the possibility of making bone available that the body won't reject and not waiting for a compatible donor, the ability to print bones on demand can help reduce the number of painful surgeries that some patients have to endure.
"When designing artificial bone scaffolds it's a fine balance between something that is porous enough to mix with natural bone and connective tissue, but at the same time strong enough for patients to lead a normal life," he said. "We've identified a design that strikes that balance and can be custom built using a 3D printer."I can anticipate doctors and old patients telling stories in 20 years or so about back when we used to actually use bone from a cadaver, or take bone from elsewhere in a person's body. What a bunch of savages!
Of those he printed, Montazerian tested them to determine how they would perform physically under real-world tension and weight loads.
"A few of the structures really stood out," he said. "The best designs were up to 10 times stronger than the others and since they have properties that are much more similar to natural bone, they're less likely to cause problems over the long term."