Ordinarily, bioprinting is performed in a fashion much like regular 3D printing – an object is slowly built up as successive layers of material are deposited one on top of the other. This means that it can take hours or perhaps days to produce even a simple item.

Lately, though, scientists have been experimenting with a faster method of printing a variety of non-biological objects, which is known as volumetric printing. Working with colleagues at the Netherlands' Utrecht University, a team from the Swiss EMPA research institute has adapted that technology to produce body parts measuring up to several square centimeters in size – these parts have included a valve similar to a heart valve, a meniscus, and a complex-shaped section of femur.

The process involves projecting a laser beam down into a slowly-spinning tube that's filled with a stem cell-laden photosensitive hydrogel. By selectively focusing the light energy at specific locations within the tube, it's possible to solidify the gel in those places only, building up the desired three-dimensional object within a matter of seconds. The stem cells are unharmed in the process.