An initial project involved embedding one of the circuit boards inside a kids pajama suit that also has a couple breathing sensors built-in to address sudden infant death syndrome (SIDS). The entire package was ironed onto the suit, creating a comfortable yet smart pajamas that are able to detect pauses in breathing and warn parents of any danger. Moreover, the team is using their stretchable printed circuit boards to devise a better way for physicians to test their patients’ kidney function.
“The circuit board we have developed can be manufactured using routine industrial processes, meaning a high throughput and, consequently, good cost-efficiency,” says Manuel Seckel, scientist at the IZM. “Furthermore, components can be positioned on it just as precisely as on a standard board thanks to the stability of the stretchable substrate during processing. This stands in contrast to textile-based electronics, where one can expect an offset of up to five millimeters over a half-meter area.” However, the researchers had to overcome a number of challenges to achieve the high level of accuracy required. One of these was how to handle and process the polyurethane. “As with stretch fabric, PU PCBs are hard to machine manufacture because they tend to change shape. To counter this, we developed a support system on which we place the PU boards and machine process them before removing the support once more,” explains Seckel. The method is currently being tested by various industrial concerns.
The example of the romper suit is just one of many potential applications for flexible circuit boards. For instance, the technology could also be used to provide subtle lighting in the roof lining of cars – “stars” on the car roof, for example. Equally, it could be set to work in the pressure bandages applied to burn wounds. Here, PU plasters equipped with integrated sensors would help nurses find the optimal placement for the bandage.
The stretchable circuit board is also the basis for a plaster being developed by medical scientists from the University of Heidelberg in collaboration with the Fraunhofer researchers. In future, doctors will be able to use this plaster to test the kidney function of their patients. Up to now, the procedure has involved injecting a substance that only the kidney is able to break down, and then taking blood samples roughly every 30 minutes over a three-hour period. If a kidney is healthy, it will almost completely break down the substance within three hours; if it is diseased, it will only manage a slow reduction in concentration. Equipped with a PU circuit board plaster, a blue LED and a detector, in future doctors will be able to spare patients a lot of jabbing – and examine them with much more precision. As in the standard procedure, the investigation begins with the doctor injecting a substance, in this case an organic colorant. The blue LED causes this colorant to fluoresce, making it glow, a development in turn picked up by the detector located in the plaster. As the natural colorant is broken down by the kidney, the concentration of fluorescent radiation also decreases.