At present, most of the 3D printed cartilage scaffolds are homogeneous or isotropic, which is still quite different from the unique structure of natural articular cartilage. In this study, a multilayer cartilage scaffold with gradient pore size and directional arrangement structure was constructed using 3D bio-printing and template-freezing orientation technology to achieve a high degree of mimicry of natural cartilage structure at macroscopic and microscopic levels. Moreover, gelatin (Gt) and sodium alginate (Alg) were selected as the base materials for 3D printing bioinks to realize the mimicry of the main components of natural articular cartilage. For structural and performance comparison, we prepared three multilayer cartilage scaffolds: uniform non-oriented group, uniform oriented group and gradient-oriented group, and evaluated their performances respectively. The results showed that the gradient-oriented multilayer scaffolds had more desirable microstructure, more suitable physicochemical properties, better biological properties and excellent mechanical properties than the other two groups. For example, the maximum strength is 432.75kPa under 10 cycles of compression at 80% strain, and the creep deformation is 0.578mm under 10N load within 1 hour. Finally, the cartilage repair ability of the three scaffolds was investigated in a rabbit cartilage defect model, and the results further showed that the gradient-oriented multilayer scaffolds were more effective in promoting cartilage tissue repair and regeneration. In conclusion, this 3D printed multilayer gradient-oriented biomimetic cartilage scaffold has a good application potential in the repair and regeneration of articular cartilage tissue.
The structure design of the anode catalyst layer (ACL) is crucial to the performance of the proton exchange membrane water electrolyzer (PEMWE). In this work, a novel ACL structure is designed using the pore-forming agents (PF) in catalyst ink. The performance of PEMWE is systematically investigated by controlling the pore in inner layer and outer layer of ACL by adding PF. Scanning electron microscope (SEM) shows that the surface pores of the ACL are significantly regulated using PF. At the current density of 3 A cm −2 , the cell voltage of the optimized gradient ACL is 2.063 V, 154 mV lower than the 2.217 V in single-layer ACL. An electrolysis efficiency of PEMWE of 86.10 %@1 A cm −2 is achieved. Electrochemical impedance spectroscopy (EIS) results shows that the ohmic resistance of the optimized gradient ACL is 141.31 mΩ cm 2 , which is 18.23 % lower than that of the single-layer ACL. Furthermore, the distribution function of relaxation times exhibits a significant decrease in mass transfer impedance. These results confirms that the ACL structure with gradient pore size distribution greatly improves mass transfer in PEMWE. Therefore, the ACL structural design strategy is efficient to the widespread adoption of PEMWE for clean hydrogen production.
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