BACKGROUND: There is no any mature and complete system to repair nerve tissue after segmental injury due to particularity of nerve tissue regeneration. Using tissue-engineering technique to solve this problem is difficult and challenged.OBJECTIVE: To research an artificial nerve bridging substance in application of repairing nerve injury on clinic and obverse its microcosmic spatial structure at the same time.DESIGN: Open experiment.SETTING: Orthopaedic Research Institute, Xijing Hospital of the Fourth Military Medical University of Chinese PLA.MATERTALS: The experiment was carried out in the Orthopaedic Research Institute, Xijing Hospital of the Fourth Military Medical University of Chinese PLA from November 2001 to January 2003. CollagenⅠ, collagen Ⅳ and gelatin were provided by Sigma-aldrich Company, USA.METHODS: Establishment of bridging substance: Collagen Ⅰ (65.53%) and collagen Ⅳ (32.77%) were added into 0.05 mol/L acetic acid solution, respectively; and then, two suspensions were mixed together and stirred at 4℃. The suspension of collagen and heparin sulfate was pumped, held still and poured into silica gel tube with bore of 3 mm.Continuously, two ends of tube were enclosed and suffered from cold drench and mold at five various speeds. General observation was done. Composites were intercepted cross section, vertical section and 45° section for observation by optic microscope at different speeds of 10×10-5 m/s, 5×10-5 m/s, 2.5×10-5 m/s, 1.0×10-5 m/s and 1.0×10-6 m/s; meanwhile, interior structure of microtubule was observed with scanning electron microscope. Interior diameter of microtubule was calculated as the following formula: actual aperture = (magnification × area of microtubule) ÷ (length of guage × perimeter of aperture).MAIN OUTCOME MEASURES: ① General observation; ② observation with microscope; ③ observation with scanning electron microscope and interior diameter of microtubule.RESULTS: ① General observation: Models were regular cylinders and had symmetrical features. Flexility was wonderful,texture was well-proportioned, and elasticity was strong. ② Results of optic microscope: Structure of external surface was completely blocking without any poricidal dehiscence. Surface was smooth and had good continuity. ③ Results of electron microscope: External surface shaped like terrace tile; asides, interior structure of microtubule was average and its courser was coincident and parallel to each other. Microtubules with longitudinal courser were independence on each other. The structure was blocking and did not connect to each other. This was as the same as courser of nerve fibrous bands of organis. Cross section of interior microtubule was general round and regular, and the diameter was average. Interior microtubule had groat continuity without breaks or transection. Trabeculae of microtubule also had groat continuity,and its surface was smooth. Interior diameter of microtubule ranged from 197.3 μm to 258.8 μm.CONCLUSION: Nerve bridging substance is made of collagen and gelatin which are characterized by groat compatibility and degradation after mixture, lysis and cold drench, It has singly longitudinal microtubule and microstructure of high imitation by normal nerves, so nerve bridging substance can be used in basic researches and repair nerve injury on clinic.