Hydrogels that resist swelling enable 3D-printed soft implants that keep working in rats

What happened

Hydrogels are soft and water-rich like tissue, which makes them attractive for implants, but in the body they swell. Swelling weakens the encapsulation and breaks the conductive pathways. The researchers used a micellar self-assembly method to make soft, stretchable hydrogels that do not swell, and report that these provoked a smaller foreign-body reaction during long-term implantation than conventional swelling hydrogels and silicones.

They turned the material into both a supporting matrix and a two-phase conductive ink, allowing whole devices to be 3D printed inside the gel. The conductive hydrogel reached up to 4,000 S/cm and stretched beyond 1,300% strain before electrical failure when equilibrated in water. Printed devices included brain–computer interfaces, wirelessly powered optoelectronics and sciatic-nerve stimulators, which showed long-term stability and reliable operation after implantation in rats.

Why it matters

Hydrogel devices are meant to bridge biological and electronic systems, but only if they stay intact and conductive in wet tissue. A hydrogel that holds its shape and conductivity when wet, and can be printed into three-dimensional devices, addresses that obstacle.

Caveats

This entry is based on the abstract, which does not say how long "long-term" implantation was or how recording and stimulation performance compared with existing devices. All implant testing was in rats. The corresponding author Nanjia Zhou is also affiliated with a company, Enovate 3D (Hangzhou) Technology Development.