Autologous transplantation remains the golden standard for peripheral nerve repair.However, many drawbacks, such as the risk of reoperation or nerve injury remain associated with this method. To date, commercially available artificial nerve conduits comprise hollow tubes. By providing physical guiding and biological cues, tissue engineered conduits are promising for bridging peripheral nerve defects. The present study focuses on the preparation of artificial composite nerve conduits by 3D bio-printing. 3D-printed molds with a tubular cavity were filled with an Engelbreth-Holm-Swarm (EHS) Hydrogel mimicking the extracellular matrix (ECM) basement membrane. Chemically cross-linked gelatin methacryloyl (GelMA) was used to form the conduit backbone, while EHS Hydrogels improved nerve fiber growth while shortening repair time. Statistical significant difference had been found between the blank conduit and the composite conduit group on compound muscle action potential after 4 months. On the other hand, results between the composite conduit group and the autograft group were of no statistical differences.All results above showed that the composite conduit filled with EHS Hydrogel can promote the repair of peripheral nerve and may become a promising way to treat peripheral nerve defects.3D bioprint, chemical cross-link, ECM, GelMA, nerve repair Conduits were produced as described earlier (Hu et al., 2016). Briefly, the mold (Figure 1a,b) was modeled with the use of SolidWorks to create a tubular cavity prior to 3D printing. Based on the size of rat sciatic nerves, the inner and outer diameters were 2 and 4 mm, respectively (Zhao et al., 2016). Five percentage of GelMA (SE-3DP-0200, StemEasy Biotech, China) aqueous solution was prepared at 60 C. After complete dissolution, the solution was cooled to 15 C prior to the addition of 0.5% APS and 0.1% TEMED. The mixture was then poured into the mold and rapidly placed at −20 C. After 24 hr of solidification, the conduit was defrosted and unmolded, followed by intensive rinsing and freeze-drying.For EHS Hydrogel (SE-EHS-0100, StemEasy Biotech, China) filling, conduits were placed on precooled petri-dishes and 0.1 ml of EHS Hydrogel was poured into the cavity. Conduits were then immediately placed in an incubator. After 5 min, the EHS Hydrogel displayed a jellylike texture and the composite conduit was considered ready to use.According to the conventional method, the blank GelMA conduit was examined by scanning electron microscopy (SEM, Phenom ProX, Thermo fisher), and the images were analyzed by ImageJ to calculate the porosity. The blank conduits were immersed in saline in 37 C, and the swelling ratio was calculated by weighing before and after at different time points and calculated by the following formula (Zhao et al., 2016):Swelling ratio = wet weight− dry weight dry weight × 100%The mechanical properties of GelMA blank conduits were also evaluated by both compression and tensile tests using universal testing systems (5969, Instron, United States) equipped with a 50 N loa...