"It's amazing, absolutely beautiful," says Doris Taylor, describing the latest addition to an array of tiny thumping hearts that sit in her lab, hooked up to an artificial blood supply.
The rat hearts beat just as if there were inside a live animal, but even more remarkable is how each one has been made: by coating the stripped-down "scaffolding" of one rat's heart with tissue grown from another rat's stem cells.
The idea is fairly simple: take an organ from a human donor or animal, and use a mild detergent to strip away flesh, cells and DNA so that all is left is the inner "scaffold" of collagen, an "immunologically inert" protein. Add stem cells from the relevant patient to this naked shell of an organ and they will differentiate into all the cells the organ needs to function without inducing an immune response after transplant, or any new infections.
Although Taylor only added stem cells to the hearts, these cells differentiated into many different cells, in all the correct places, which is the best part of using decellularised scaffolds. The stem cells transformed into endothelial cells in the ventricles and atria, for example, and into vascular and smooth-muscle cells in the spaces for blood vessels, just as in a natural heart. Taylor thinks this happened because she pumped blood and nutrients through the organ, producing pressure in each zone which helps to determine how cells differentiate there.
But chemical, as well as mechanical, cues seem to have guided differentiation. Taylor has evidence that growth factors and peptides remained anchored to the scaffold even after the flesh was washed off. These chemicals likely signalled to the stem cells, indicating how many should migrate to which areas and what to change into in each zone. "Our mantra is to give nature the tools and get out of the way," she says.
The idea to team stem cells with contact lenses came from an observation that stem cells from the cornea stick to contact lenses. To obtain the stem cells, Dr Watson took less than a millimeter of tissue from the side of each patients' cornea. Working with colleagues at POWH and UNSW, he cultured stem cells from the tissue in extended wear contact lenses.
Within 10 to 14 days the stem cells began to attach to the cornea, replenishing damaged cells. Satisfied that the stem cells were doing their job, Dr Watson removed the lenses and the patients have been seeing with new eyes for the last 18 months.