Scientists 3D-print biological tissue without using scaffolds
Although it may be hard to believe that there is already an "established" method of doing something such as 3D-printing biological tissue, there does indeed seem to be one. It involves using microscale scaffolds, but a newly-developed technique overcomes some of the shortcomings of this approach by using hydrogel instead.
Ordinarily, the "bioprinting" of bodily tissue (including organs) involves seeding cells into a material with a scaffolding-like microstructure. That material provides a three-dimensional home for the cells to nest within, and then subsequently reproduce. Eventually, the cells take over as the host material biodegrades, until nothing remains but biotissue in the desired physical form.
According to scientists from the University of Illinois at Chicago, however, the process does have its drawbacks. For one thing, it can be tricky getting the timing just right, so that the scaffolding disappears at the same time the tissue reaches maturation. Additionally, the biodegradation of the material can produce toxic by-products, and the scaffolding can interfere with cell-to-cell communication – the latter is essential for the proper formation of tissue.
As an alternative, a team led by Prof. Eben Alsberg has developed a system which uses a block of hydrogel made up of microscopic beads. A printing nozzle is lowered into that gel, where it moves back and forth – vertically and horizontally – depositing a "bioink" consisting of stem cells. That bioink is held in place by the microbeads, staying where it was deposited within three-dimensional space.
The whole hydrogel bead matrix is then exposed to ultraviolet light, causing the beads to cross-link with one another, so that the shape holds. Over the next several weeks, the cells proceed to reproduce and freely communicate with each other. As they do so, technicians add a nutrient-bath solution, which easily flows through the cross-linked beads to reach the tissue.
Once that biotissue has reached maturation, the beads can be removed either by gently agitating the matrix, or by allowing them to harmlessly biodegrade – the rate of degradation can be chemically-determined. What's left behind is nothing but the fully-formed organ or other tissue. So far, the researchers have used the technique to produce a rodent-sized femur, and a cartilage ear.
"We've demonstrated that cell aggregates can be organized and assembled using this strategy to form larger functional tissues, which may be valuable for tissue engineering or regenerative medicine, drug screening and as models to study developmental biology," says Alsberg.
A paper on the research was recently published in the journal Materials Horizons. The process is used to bioprint a letter C, in the video below.