Engineered tissues and organs have been grown with varying degrees of success in labs for many years. Many of them have used a scaffolding approach where cells are seeded onto biodegradable supportive structures that provide the underlying architecture of the organ or tissue desired.
However, scaffolds can be problematic. They should degrade and disappear but timing decomposition to coincide with the maturation of the organ is challenging and sometimes degradation by-products can be toxic. Scaffolds also can interfere with the development of cell-to-cell connections, which are important for the formation of functional tissues.
A research team led by Eben Alsberg, the Richard and Loan Hill Professor of Bioengineering and Orthopaedics at the University of Illinois at Chicago, has just developed a process that enables 3D printing of biological tissues without scaffolds using "ink" made up of only stem cells. They reported their results in the journal Materials Horizons.
“Our cell only printing platform allows for the 3D printing of cells without a classical scaffold support using a temporary hydrogel bead bath in which printing takes place,” said Alsberg. “The hydrogel bead bath has unique properties which allow for both printing of the cell-only bioink in complex architectures, and subsequent temporary stabilisation of these cell-only structures to allow for cell-cell junctions to form. Using chemistry we can then regulate when the beads go away.”
Researchers used stem cells, which can differentiate into a wide variety of other cell types. They used the stem cells to 3D print a cartilage ear and a rodent-sized "femur" in the hydrogel bead bath. The cells they printed were able to form stable, cell-cell connections through specialized proteins. These have a number of exciting potential uses.
“For the first time, cell-only constructs can be printed in intricate forms that are made up of different cell types without a hydrogel carrier or traditional scaffold that can then be stabilised for a period of a day to weeks,” said Alsberg. “We've demonstrated that cell aggregates can be organised 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.”