First Generation: One-to-One 3D Printed “Replacement Parts” Made with Polymers and Other Medically Safe Materials
Progress in 3D printing technology for medical use has been dramatic, but the story behind the headlines is as much about advances in conceptual design as it is about technological progress.
What we might call the first-generation usage of 3D printing in the medical field focused on replicating existing biological structures on a 1:1 basis –mimicking the approach initially taken by mechanical engineers and product designers when 3D printing first became available.
A great example of this is the world’s first 3D-printed artificial bladder, which was implanted in a young spina bifida patient at Boston Children’s Hospital in 2004.
3D-printed teeth have also proven to be a viable solution for dental implants. 3D printing allows biomedical engineers to create composite structures that more accurately match the original human teeth, including matching the interior structural strength as well as simulating the hard exterior enamel surface.
Artificial 3D-printed bone structures are also gaining ground in healthcare. Initially, the focus was on creating smaller custom-shaped bone grafts that could be surgically implanted, providing a scaffold for natural bone to grow onto.
However, in 2021, lab researchers in Australia demonstrated it was possible to 3D print bone structures made from calcium phosphate ceramic-based ink, which happens to be the primary mineral in natural human bone and teeth.
Immediately before surgery, this artificial bone is soaked in a gelatinous solution of living cells, allowing the living cells to form colonies of tissue networks, mimicking the natural bone-building process.
Second Generation: Growing Living Cells (Organoids) in the Laboratory, Useful for Scientific Research and Animal-Free Drug Testing
The second generation of 3D printing in the medical context is printing directly with living cells to create “living” organs on a laboratory slide, often called organoids or “organs on a chip.”
One of the most important applications for organoids is drug testing. They reduce the need for using live animals in testing products such as cosmetics – where a “cruelty-free” label is a significant commercial advantage.
Organoids also have precision medicine applications – such as creating a living lung cell structure from a patient to evaluate a proposed cancer therapy before treatment on the live patient.
However, replicating complicated cell structures, such as blood vessels or nerve networks, remains a challenge when using traditional 3D printing technology.
Researchers in Canada and Brazil were able to sidestep this issue by using a laser technique (known as Laser-Induced Side Transfer or LIST) to work at the microscopic level to print functioning mouse brain cells, fabricating the tissue-like structures of dorsal root ganglion neurons layer-by-layer.
Third Generation: 3D Printing with Living “Bio Ink” to Build Novel Structures That Could Lead to Growing Replacement Organs for Human Transplant
Unfortunately, this LIST approach is time-consuming, and critics worry it would not scale up well to create larger organ structures.
The solution may come from a philosophical shift in what we are calling the third-generation approach to printing organs.
In this approach, the basic structure is 3D printed using “bioink” – a living ink – that creates a simplified large-scale structure (scaffold) that allows the bioink to grow into a living organism that develops the necessary small-scale details, such as vascular or neural connections, without direct human intervention.
Looking to the future, this approach could not only help solve the scalability problem (e.g. allow for the creation of complex organs, such as a kidney or a human heart) but also avoid the auto-immune rejection problem that makes transplanting organs from one person to another so difficult.
If the original bioink cells are sourced from a patient during a simple biopsy, they could be grown into organs in the lab, thus avoiding rejection by their immune system when the organ is later surgically transplanted into their body.
Researchers at Stanford University are using this approach of letting the bioink cells do the hard work, such as creating blood vessels, in their experiments in creating a living heart pump designed to help patients who were not born with the proper number of working heart ventricles.
The researchers are harvesting inducible pluripotent stem cells (IPSCs) from a patient to create the bioink; these naturally occurring stem cells can, in turn, create different organs and structures, such as heart muscle. In their experiments, the Stanford researchers found that they could print a soft, donut-like 3D structure (with the consistency of toothpaste), then use a printer nozzle to inject nutrients into the center of the growing cell culture, allowing it to develop into a working heart muscle structure.
This implantable living heart pump, if successful, would be an important steppingstone in the goal of creating full-size organs, such as a human heart, for transplantation.
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