Bioinks containing stem cells are being used to 3-D print living tissues that can be inserted into the body and provoke a damaged joint to heal itself. This could reduce the discomfort and pain of ten percent of the people who will suffer from arthritis over their lifetime. However, new cartilage could be bioprinted on demand using the patients’ own cells as the building blocks.

As part of a project called 3-D-JOINT, Professor Jos Malda, Head of Research at the Department of Orthopaedics, University Medical Center Utrecht and the Department of Equine Sciences, University of Utrecht, is working to make bioprinted tissues that can be implanted into a living joint to replace the damaged part. These would eventually mature into a tissue that is the same as the original healthy cartilage.

Already, stem cells can be deposited by 3-D printers according to a precise blueprint, creating complex tissues layer by layer. Yet that doesn’t mean they can instantly transform into new organs or body parts. “Printing is not the last step in biofabrication, since printing something in the shape of a heart does not make it a heart,” said Prof. Malda. “The printed construct needs time and the correct chemical and biophysical cues to mature into a functional tissue.”

One challenge is maintaining the right conditions for the cellular building material. Traditional 3-D printing uses plastics, which are flexible enough to be pushed through a printer nozzle, but are also solid enough to keep their shape afterwards. But because bioinks contain living cells, scientists are having to develop new solutions. One option is to use a hydrogel — a type of material that consists of networks of large molecules known as polymers, swollen with water. “For bioprinting, the material has to be able to keep cells alive. This demands aqueous conditions and processing under a relatively low temperature, which makes hydrogel-based materials ideal candidates,” Prof. Malda said. But while the squishy nature of such hydrogels makes them very good at delivering cells, it is also their weakness. They are unable to withstand the mechanical load certain tissues undergo in the body.

To solve that, Prof. Malda and his team are experimenting with additive materials, which can make the hydrogels strong enough to act as replacement cartilage. “Reinforcing the hydrogel makes it stronger – just like steel rods are combined with soft cement to create the reinforced concrete that makes the foundations of our homes,” he explained.

His team is using melt electrowriting, a 3-D-printing technique that combines melted polycaprolactone, a type of polyester, with an electrical field that creates fibres as thin as a hair. Using these microfibres, the team creates scaffolding to be combined with the cell-containing hydrogel – already with good results. “The combination of the hydrogel with the fibres acts in synergy, increasing the strength of the composite over 50 times while still allowing the cells to generate extracellular matrix and mature into a cartilage-like tissue,” Prof. Malda said.

Source: This article was first published in Horizon: The EU Research & Innovation Magazine. Read the full article here.