Structural mechanics of 3D-printed poly(lactic acid) scaffolds with tetragonal, hexagonal and wheel-like designs.

While various porous scaffolds have been developed, the focused study about which structure leads to better mechanics is rare. In this study, we designed porous scaffolds with tetragonal, hexagonal and wheel-like structures under a given porosity, and fabricated corresponding poly(lactic acid) (PLA) scaffolds with three-dimensional printing. High-resolution micro-computed tomography was carried out to calculate their experimental porosity and confirm their high interconnectivity. The theoretical and experimental compressive properties in the longitudinal direction were characterized by finite element analysis method and electromechanical universal testing system, respectively. Thereinto, the scaffold with the tetragonal structure exhibited higher mechanical strength both theoretically and experimentally. Creep and stress relaxation behaviors of the scaffolds revealed that the tetragonal scaffold had less significant viscoelasticity. Immersion dynamic mechanical analysis was performed to test their cycle-loading fatigue behaviors in the simulated body fluid at 37 °C; the tetragonal scaffold exhibited the latest fatigue beginning point at 4400 cycles, which indicated a better anti-fatigue performance; the hexagonal and wheel-like ones exhibited the middle and earliest fatigue beginning points at 3200 and 2500 cycles, respectively. What is more, cytocompatibility and histocompatibility of the scaffolds with all of the structures were confirmed by cell counting kit-8 assay in vitro and three-month subcutaneous implantation in rats in vivo. Hence, the key property difference of the three examined structures comes from their mechanics; the tetragonal structure exhibited better mechanics in the longitudinal direction examined in this study, which could be taken into consideration in design of a porous scaffold for tissue engineering and regeneration.