Electrospun Scaffolds are Not Necessarily Always Made of Nanofibers as Demonstrated by Polymeric Heart Valves for Tissue Engineering

In the last 30 years, there are ≈60 000 publications about electrospun nanofibers, but it is still unclear whether nanoscale fibers are really necessary for electrospun tissue engineering scaffolds. The present report puts forward this argument and reveals that compared with electrospun nanofibers, microfibers with diameter of ≈3 µm (named as "oligo-micro fiber") are more appropriate for tissue engineering scaffolds owing to their better cell infiltration ability caused by larger pores with available nuclear deformation. To further increase pore sizes, electrospun poly(ε-caprolactone) (PCL) scaffolds are fabricated using latticed collectors with meshes. Fiber orientation leads to sufficient mechanical strength albeit increases porosity. The latticed scaffolds exhibit good biocompatibility and improve cell infiltration. Under aortic conditions in vitro, the performances of latticed scaffolds are satisfactory in terms of the acute systolic hemodynamic functionality, except for the higher regurgitation fraction caused by the enlarged pores. This hierarchical electrospun scaffold with sparse fibers in macropores and oligo-micro fibers in filaments provides new insights into the design of tissue engineering scaffolds, and tissue engineering may provide living heart valves with regenerative capabilities for patients with severe valve disease in the future.