Skip to 0 minutes and 12 secondsSo now we'll pick up on a real challenge-- the ability to create, to print 3D structures containing living cells. Now we must match the actual properties of the material with the living cell to provide protection during the printing process and to provide the mechanical robustness after the printing process. Coupled with that, the fact we will need to deliver biologically active molecules to sustain those living cells in the structure during the printing process. And we have quite a complex, multi-dimensional challenge for 3D printing. Steve, how do we confront a challenge like this where we need to have materials that can actually protect the cells during printing and then create the mechanical robustness we need after printing?
Skip to 0 minutes and 59 secondsSo in this case we need to develop a new form of printing technique. We need to take the benefits of extrusion printing and couple that with materials developments in how we protect the cells during the actual extrusion process. One approach that we've taken in doing this is coaxial extrusion. Using coaxial printing, we can build complex structures containing two materials. A special nozzle is used to feed one type of material inside another. The core may contain sensitive components, such as living cells. The shell material is designed to hold the structure together and protect those delicate entities contained within. The ability to distribute biologically active molecules within these 3D printed structures also means that we can control their accessibility.
Skip to 1 minute and 48 secondsWe can control when cells can access those molecules during the development process. In biological terms, we are engineering controlled delivery system, controlled delivery systems for biologically active molecules. This is also the basis of other applications in releasing anti-inflammatories, immunosuppressant agents as required for medical implants. Would materials like gelatin still be appropriate for printing, but printing with living cells? Absolutely. So we can formulate the materials so that it is tailored to maintain the cell viability. So now our choice of materials takes on an extra challenge. The material has at least three roles to play. It must keep the cells suspended in the ink reservoir during the printing process. It must protect the cell during the printing.
Skip to 2 minutes and 41 secondsAnd afterwards, it must provide enough mechanical robustness so that we can create 3D structures with these cells strategically distributed throughout the structure that we want to create.
Putting the 'bio' in bioprinting
Inkjet printing is a process with incredible resolution when compared with other techniques such as pneumatic extrusion.
Using modified commercial two-dimensional printers, researchers and surgeons are now developing inks containing tissue engineering polymers and living cells to build tissues in three dimensions. The placement of multiple cell types in synergistic formation could allow for the survival of these cells in scaffolds in culture with a close representation of the anatomy of the bladder.
The cells could then be accelerated to differentiate along the correct lineage before implantation. This is now being tested by Professor Atala, Director of the Wake Forest Institute for Regenerative Medicine, and his associates - who successfully registered a patent in 2009 for this strategy. However there are a whole host of researchers globally who are working to create these bioinks and to deliver reportedly, over 20 different kinds of living human ‘neo-tissue’.
These custom bioinks are formulated and loaded into the reservoirs of the cartridges. At the base of each cartridge, a series of piezoelectric crystals (materials that expand under applied electrical bias) or miniature heating elements are positioned to regulate the flow of material through an ultrafine deposition head. In the case of thermal inkjet printing, a tiny current vaporises the solvent into a tiny steam bubble, forcing an ink droplet out of the nozzle. For inks where this heating will still damage the cells, a piezoelectric option is preferred. This all happens within thousandths to tens of thousandths of a second.
Now imagine this en masse. An array of hundreds of nozzles all controlled independently and at the discretion of the software. This is the magic of inkjet printing. Each two-dimensional slice fed into the firmware is dissected, delegated out to each of the nozzles and jetted into the pattern observed. Computer numerical control of the stage enables building these structures upwards in 3D, as well as in 2D, and then the precursors of a tissue are set for growth.
© University of Wollongong, 3D Bioprinting: Printing parts for bodies, 2014, Wallace, G.G., Cornock, R.C., O’Connell, C.D., Beirne, S., Dodds, S., Gilbert, F.