Researchers print electronics directly on the skin

The University of Minnesota has developed a method of 3D printing onto human skin for medical applications and advanced biological sensors. In a new study, researchers used a customised, low-cost 3D printer to print electronics on a real hand for the first time. The technology could be used by soldiers on the battlefield to print temporary sensors on their bodies to detect chemical or biological agents or solar cells to charge essential electronics.

The researchers also successfully printed biological cells on the skin wound of a mouse. The technique could lead to new medical treatments for wound healing and direct printing of grafts for skin disorders.

The ability to 3D print different materials has expanded in recent years. 3D-printed metals used to seem like a ludicrous concept, and now it is one of the leading 3D printing-associated industries.

The research was published in the academic journal Advanced Materials in April.

Conventional 3D-printing technologies typically rely on open‐loop, calibrate‐then‐print operation procedures. The new technique uses adaptive 3D printing, a closed‐loop method that combines real‐time feedback control and direct ink writing of functional materials onto moving free-form surfaces. The hybrid fabrication procedure combines 3D printing of electrical connects with automatic pick‐and‐placing of surface‐mounted electronic components. Using this same approach, the team was also able to successfully print biological cell‐laden hydrogels cells on the skin wound of a mouse.

“We are excited about the potential of this new 3D-printing technology using a portable, lightweight printer costing less than $400,” said Michael McAlpine, the study's lead author. “We imagine that a soldier could pull this printer out of a backpack and print chemical sensor or other electronics they need, directly on the skin.”

For the new technique to work, the team devised a way for the 3D printer to adjust to small movements of the body during printing. The system uses temporary markers, which are placed on the skin, to scan the surface during printing. The printer uses computer vision to make adjustments based on the surface movement in real time.

“No matter how hard anyone would try to stay still when using the printer on the skin, a person moves slightly and every hand is different,” said McAlpine. “This printer can track the hand using the markers and adjust in real time to the movements and contours of the hand, so printing of the electronics keeps its circuit shape.”

The 3D-printing technique uses a specialised ink made of silver flakes that cure and conduct at room temperature. Other 3D-printing inks need to cure at high temperatures of up to 100°C that would burn the skin. To remove the 3D-printed features from the skin, the user can simply peel them off with tweezers or wash them off with water.

The team partnered with the University of Minnesota Department of Pediatrics to print cells on living tissue. Doctor and medical school Dean Jakub Tolar, a world-renowned expert in treating rare skin diseases, helped the team print bioink cells on a mouse skin wound. This could lead to advanced treatments for patients suffering from skin diseases.

“I'm fascinated by the idea of printing electronics or cells directly on the skin,” McAlpine said. “It is such a simple idea and has unlimited potential for important applications in the future.”

Image credit: McAlpine Group, University of Minnesota.