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3D bioprinting, or the 3D printing of implantable, living tissue, can certainly be considered the Holy Grail of 3D printing.

Various ongoing research projects throughout the world are currently competing to reach the finish line first, though it is expected that it will take a few more years before patients can benefit from custom-made 3D printed organ implants. But we might not have to wait so long for 3D printed bone and cartilage structures, as the ‘Tissue Factory’ of the University Medical Center Utrecht is having a lot of success with their custom hydrogel structures. As project coordinator and associate professor Jos Malda revealed, they are now performing tests with a 3D bioprinted rabbit shoulder implant.

The ‘Tissue Factory’ is actually a research facility that has been developed by Utrecht Life Sciences, a Dutch open innovation network that involves Utrecht University, the University Medical Center Utrecht, as well as various government agencies and commercial businesses. Consisting of two laboratories with 3D bioprinters and cell culture facilities, the facility opened its doors in 2014 and have been especially focused on 3D printing bone and cartilage structures.

One of the driving forces behind the facility is bioprocessing biologist Jos Malda, who caught the 3D printing bug a few years ago. Under his guidance, this biofabrication facility have previously developed a very potent hydrogel. Made from specific polymers, these gels have the ability to retain large amounts of moisture, making it a perfect carrier substance for cells used in regenerative treatment. While cell therapy is already commonly used in various hospitals for the treatment of damaged cartilage, this hydrogel can be used for much larger surfaces through 3D printing. “Our reinforced hydrogels are firmer and more elastic than most cell carriers and with this we can eventually perhaps restore larger parts of a joint,” Malda said of the substance.

These hydrogels have been extensively tested, and are with growth factors and stem cells, cartilage-forming cells, or a combination of both. Most importantly, it creates the ideal environment for cells to survive the 3D printing process and continue living in the new structure. “The hydrogel is a bit soft, almost like gelatin,” Malda tells reporters. “Not exactly good enough to support the human body, but we have been trying to combine that with other materials to enhance its strength.”

The Utrecht team first 3D printed it onto a framework of thick fibers, which Malda compared to reinforced concrete. Though strong enough for the human body, it removed any flexibility from the test implants. “Fortunately, we succeeded in decreasing the size of the fibers, to a point where they are comparable to the fibers of polar fleece. Those thin fibers were not very strong, but worked very well in combination with the hydrogel. The forces the gel applied to the fibers held the whole construction together. In this case, one plus one wasn’t two, but fifty,” Malda said.

Malda and his team are currently working on implants made from a combination of thicker and thinner fibers, with the thicker fibers being perfect for bone, and the thinner ones perfect for cartilage. By combining those materials with support structures, a wide range of shapes, such as discs and tubes, are already possible. All that progress has even led to the development of the very first test: replacing a rabbit’s entire shoulder with a 3D printed implant.

Images: University Medical Center Utrecht

While the test results are being evaluated over the coming months, the research is promising. According to Malda, they are also increasingly understanding how stem cells become specific types of tissue cells, such as bone or muscle cells. “We are learning more and more about those processes. But unfortunately, we cannot yet force stem cells to become bone structures in every situation we put them in,” Malda says. But as the team has enough funds to continue their research for the next five years, the future looks good for the Utrecht Tissue Factory.