Most of the attention surrounding 3D printers in medicine has focused on patching up our outsides, whether it’s making skin to heal wounds or restoring theuse of limbs. The Wake Forest Institute for Regenerative Medicine has just detailed a technique that could go considerably deeper. By mixing natural gel put through an inkjet printer with thin and porous polymer threads coming from an electrospinner, researchers have generated constructs that could be ideal for cartilage implants: they encourage cell growth in and around an implant while remaining durable enough to survive real-world abuse. Early tests have been confined to the lab, but the institute pictures a day when doctors can scan a body part to produce an implant that’s a good match. If the method is ultimately refined for hospital use, patients could recover from joint injuries faster or more completely — and 3D printers could become that much more integral to health care.