New ways to grow human “mini bones”

Main ingredients for tissue engineering

To grow the “mini bones”, De Wildt needed four important parts. First, he needed specialized stem cells, called parental cells. Unlike pluripotent stem cells, which are cells that can become any type of cell in the body, parent cells can only become osteoblasts or osteoclasts. De Wildt: “These parental cells must receive the correct biochemical signals to transform into osteoclasts and osteoblasts.”

Secondly, de Wildt needed a structure on which the bone cells could fuse into the “mini bone”. “We used silk from silkworms for this, because it is a material with favorable mechanical properties, it is biocompatible and human cells can grow on the material in three dimensions,” says De Wildt.

Third, cells need an environment in which to grow and thrive. “The cells are placed in an incubator kept at a temperature of 37 degrees Celsius, which also contains oxygen and CO_2-content and moisture, “says De Wildt.

Finally, to mimic bone as closely as possible, the bone cells are placed in a bioreactor, which is then placed in the incubator. De Wildt: “The bioreactor circulates a nourishing fluid and mimics the mechanical load of bone in the human body. If a ‘minibot’ is to be representative of real bone, the cells must be challenged to resist these forces.”

“Together, these are essential prerequisites for tissue engineering, which has been used in regenerative medicine since the 1990s to grow implants for the body,” says De Wildt. “Recently, however, tissue engineering has become accustomed to in vitro versions of human bones, which are versions of bones grown outside the human body. “