Microbial bioink makes 3D printed materials
A team of researchers has genetically engineered bacteria to produce a bioink that can be 3D printed into a gel with special abilities, such as releasing drugs, removing toxins from the air and regulating its own growth.
“This is part of a general effort to replicate how biological organisms make materials, by engineering cells to do what we want them to,” says Neel Joshi, lead author of the study published this week in Nature Communications.
Biological systems like a tree or our own body can respond to their environment, for example by moving, growing or also self-regenerating, but the materials made by engineers today, like steel or paper, cannot do that. To make engineering living materials, scientists are trying to genetically programme biological cells to spontaneously produce substances that can respond to their environment.
“In this case, the starting point is the bacterium E. coli, commonly found in our intestines and in soil,” explains Joshi. His team at Northeastern University genetically programmed E. coli cells to make proteins that would join together to form fibers, which in turn would bundle up to form a viscous substance that could be used as an ink. Proteins are the building blocks of many biological tissues, like our muscles, and give structure to the ink.
The challenge was to design the ink so that it could be 3D printed. To do this, the researchers simulated the properties of toothpaste, which is firm enough to hold its own weight when resting, but will flow much like a liquid when you squeeze it. Similarly, the 3D printer applies pressure to the ink to squeeze it through the nozzle, but once the ink is resting, it will form a jelly-like substance that can hold its own weight.
This is a special gel with living cells embedded into it. The researchers demonstrated that these cells could secrete the drug Azurin, which has anticancer properties, or they could remove the pollutant Bisphenol A (BPA) from the surrounding air. More importantly, these cells could also be made to commit suicide, which shows that we can control and limit their spread. All these functions were genetically programmed into the E. coli bacteria used at the start of the process.
For the first time, the researchers managed to engineer the bacteria to produce all the proteins they needed to create the structure without the addition of any synthetic polymers. This means that the microbes can independently make the bioink in which the living cells are embedded.
“One area in which this could find application is extraterrestrial missions,” says Joshi. “It is impossible or cost prohibitive to ship materials to places like Mars, the Moon or international space stations, so we will need to find a way to produce materials locally.” The astronauts could instead bring some microbes with them and use those to 3D print the materials and structures they need to make buildings or other essential products.