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Imagine if doctors could precisely print miniature capsules capable of delivering cells needed for tissue repair exactly where they are needed inside a beating heart. A team of scientists led by Caltech has taken a significant step toward that ultimate goal, having developed a method for 3D printing polymers at specific locations deep within living animals. The technique relies on sound for localization and has already been used to print polymer capsules for selective drug delivery as well as glue-like polymers to seal internal wounds.

Previously, scientists have used infrared light to trigger polymerization, the linking of the basic units, or monomers, of polymers within living animals. “But infrared penetration is very limited. It only reaches right below the skin,” says Wei Gao, professor of medical engineering at Caltech and a Heritage Medical Research Institute Investigator. “Our new technique reaches the deep tissue and can print a variety of materials for a broad range of applications, all while maintaining excellent biocompatibility.”

Gao and his colleagues report their new in vivo 3D-printing technique in the journal Science. Along with bioadhesive gels and polymers for drug and cell delivery, the paper also describes the use of the technique for printing bioelectric hydrogels, which are polymers with embedded conductive materials for use in the internal monitoring of physiological vital signs as in electrocardiograms (ECGs). The lead author of the study is Elham Davoodi, an assistant professor of mechanical engineering at the University of Utah, who completed the work while a postdoctoral scholar at Caltech.