System overview and sensors for an external fixator model. (A) System overview of sensor embedded in a mouse tibia fracture, where the injury is stabilized with an external fixator. Image created by the Ella Maru Studio. (B) 0.25 mm diameter sensor fabricated on an FR4 substrate, with gold (Au) surface electrodes and large vias outside the leg to connect to measurement hardware. Sensors were implanted in externally-fixed mice tibias with 0.5 mm and 2 mm defects. (C) Photograph of open surgery performed to implant 0.25 mm sensor in the external fixator model. Surgical site was closed following sensor placement. (D) Fluoroscopy image of implanted 0.25 mm sensor in a 2 mm defect. (E) 56 µm diameter sensor assembled using platinum (Pt) wire, with recording sites exposed by a CO2 laser and coils added to provide strain relief. (F) Photograph of open surgery performed to implant 56 µm sensor in the external fixator model. Surgical site was closed following sensor placement. (G) Fluoroscopy image of implanted 56 µm sensor in a 0.5 mm defect.