Electron photomicrographs of the xiphoid cartilage defect area in 45-day-old male rats. A-C: Control group; D-F: group submitted to microcurrent stimulation (20 μA/5 min). Specimens were collected 7 (A and D), 21 (B and E), and 35 (C and F) days after experimental injury. The samples were fixed by the addition of 0.1% tannic acid. (*) Fibroblastic cell; (▸) fibrillar matrix; (→) secretory vesicle. Bar, 2 μm.