Challenges on the road to 3D bioprinted organs
Juil 24, 2017 Dr Nadia Tsao
In IDTechEx Research's report 3D Bioprinting 2017 - 2027: Technologies, Markets, Forecasts, we predict that the regenerative medicine market has the potential to be the largest application for 3D bioprinting, and that the replacement of damaged and failing organs by 3D bioprinting is not limited to science fiction after all. But how far away is this future? We forecast that the market for regenerative medicine products only begins to become significant in the long term, and this article will highlight some issues faced by the industry.
One of the limits in achieving 3D bioprinted organs for transplant is size. Currently, researchers can create miniaturized tissue resembling natural tissue, but many of these constructs are not capable of achieving therapeutic impact due to their small size. There are several hurdles to creating large 3D bioprinted tissues, as follows:
Though there are a variety of methods to deposit cells in 3D bioprinting, the most popular techniques, and also those available commercially, are still inkjet and extrusion. Both types of printheads feature nozzles, and for that reason, the viscosity of cell-laden bioink must remain low. Cells are sensitive to mechanical stress, which can become significant when cell-laden bioinks are forced through a small orifice such as the printing nozzle. Thus, bioinks are usually shear-thinning, to ensure that cells can be deposited with high viability.
This need for low viscosity during the deposition process is directly in contradiction with the printing of large constructs. To ensure that large structures are appropriately supported, each layer must maintain its shape when printed. However, this is almost impossible with low viscosity bioinks, as they quickly flow and spread after ejection from the nozzle.
Currently, numerous materials and strategies are being explored to cover the conflicting needs of viscosity. A popular strategy is to use biocompatible polymers capable of crosslinking, and research efforts are focused on increasing the speed, reliability, and biocompatibility of the crosslinking step. The majority of the research in this area focuses on developing novel functional side groups for existing bioink polymers.
A second hurdle to the fabrication of large 3D bioprinted constructs is the speed at which the tissue can be built. Due to the high resolution of 3D bioprinting, of which droplets can be as small as 20 μm in diameter, large constructs may require hours, if not days to complete. The problem here is in maintaining the cells in a physiological environment throughout the long printing process. This involves strict control over the temperature and humidity of the printed construct, as cells are fragile and sensitive to changes in their environment. Therefore, there is a need for both advancements in 3D bioprinters to support the construct, but also in increasing the printing speed.
A third hurdle, and one that is the most often cited, is the need for vasculature in large tissues. Without vasculature to bring nutrients and oxygen to the centre of large tissues, and similarly, to remove the waste, the size of the tissue is limited to the diffusion limit of oxygen, which is approximately 150 μm. There are several 3D bioprinting techniques to create artificial vasculature, such as using coaxial nozzles to create tubular structures with sacrificial cores, but it is the complex design of vasculature throughout organ that may prove difficult to replicate through 3D bioprinting.
For more on 3D bioprinting join Dr. Tsao for a free webinar on the topic, Introduction to 3D Bioprinting, on Thursday 27 July. We will be hosting the same webinar twice in one day, so please join which ever session is the most convenient for you. Spaces are limited so sign up today! Registration and full details at www.IDTechEx.com/webinars