Light is a Game-Changer
The use of visible light can preserve these properties and through experimentation, Lim has developed specific bio-resin and hydrogel chemistries that respond to visible light, making 3D DLP bioprinting of tissues more practical in the surgical theater, dental applications, and more. This allows for a much broader range of light intensity, from 1 mW/cm2
all the way up to 100 mW/cm2, which is much safer for cells (controlling for heat, of course).
Oxygen inhibition is also a challenge that Lim has worked to overcome. From a polymer standpoint, it’s quite easy to crosslink in the absence of oxygen, but in living tissue, oxygen is ubiquitous. By varying multiple factors, including photoinitiators, their concentration, light intensity, and material chemistry in a systematic approach, Lim has been able to adapt his strategies to overcome oxygen inhibition and produce viable, functional tissue.
Finally, Lim and his team have also experimented with the impact of wavelength on bio-functionality. Most scientists have traditionally used 365nm wavelength, primarily because there is a popular photoinitiator that absorbs this well. But in a 3D hydrogel at that wavelength, cytocompatibility is preserved but functionality is not—the cells don’t remodel the matrix or make new tissue as well as they do at 450nm. So, Lim and his team have adapted their materials to tolerate various wavelengths, including 405nm, to optimize tissue build.