Winston-Salem - US bioengineers have developed new type of bioprinter that prints living implants in size that would be needed to replace skull bones, lower jaws, ears or muscles in humans. The living models presented in Nature Biotechnology (2016; doi: 10.1038 / nbt.3413) also had sufficient stability.
The attempts to produce human tissue with 3D printer are not new. The results have so far been disappointing, however, because the cells did not survive the printing process, or because the tissue was not mechanically resilient or could not be sufficiently perfused with nutrients. The “Integrated Tissue and Organ Printing System” that team led by Anthony Atala from the Wake Forest Institute for Regenerative Medicine in Winston-Salem is now presenting seems to have overcome these initial difficulties.
The living cells that will later fill the implant with life and integrate it into the organism are packed in hydrogel that protects them during the printing process. In the following weeks, the hydrogel dissolves. The space released is formed by the extracellular tissue that the transplanted cells release. Apparently, one difficulty was to make the hydrogel so stable in the meantime that the hair-thin tubules through which oxygen and nutrients get into the interior of the transplant do not collapse. Because without sufficient blood circulation, it is not possible to produce larger implants in which living tissue gradually develops, which in the end completely replaces the implant with the body's own tissue. The external shape of the implant was given by plastic-like tissue that is also biodegradable.
The researchers first produced part of the human lower jaw with their bioprinter. The dimensions were calculated from the results of CT examination. After 28 days, bone tissue had formed. This experiment was limited to the laboratory phase. The tissue was not implanted.
Then the researchers printed part of the skullcap for rat. The implant was placed in the animal's skull, where it was gradually converted into fully perfused part of the skull bone. After five months it was completely integrated into the skull roof.
The third project was an ear. It was printed from the cartilage cells of rabbits, but was the size and shape of human ear. The ear was implanted under the skin of mice, where it gradually transformed into normal ear with cartilage tissue and blood vessels.
Finally, the researchers created small muscle. This time the hydrogel contained myoblasts. New muscle fibers were formed after just few days. The muscle was provided with nerve that actually formed motor end plates and thus established connection to the nervous system. The muscle later reacted to electrical stimuli.
However, it is still unclear whether the muscle could do useful work in the body. It is also unclear how the immune system would react to the foreign body. According to the researchers, number of animal studies are necessary before it can be used in humans.