In-situ re-melting and re-solidification treatment of selective laser sintered polycaprolactone lattice scaffolds for improved filament quality and mechanical properties

Selective laser sintering (SLS) is a promising additive manufacturing technique that produces biodegradable tissue-engineered scaffolds with highly porous architectures without additional supporting. However, SLS process inherently results in partially melted microstructures which significantly impair the mechanical properties of the resultant scaffolds for potential applications in tissue engineering and regenerative medicine. Here, a novel post-treatment strategy was developed to endow the SLS-fabricated polycaprolactone (PCL) scaffolds with dense morphology and enhanced mechanical properties by embedding them in dense NaCl microparticles for in-situ re-melting and re-solidification. The effects of re-melting temperature and dwelling time on the microstructures of the SLS-fabricated filaments were studied. The results demonstrated that the minimum requirements of re-melting temperature and dwelling time for sufficient treatment were 65 °C and 5 min respectively and the size of the SLS-fabricated filaments was reduced from 683.3 ± 28.0 μm to 601.6 ± 17.4 μm. This method was also highly effective in treating three-dimensional (3D) PCL lattice scaffolds, which showed improved filament quality and mechanical properties after post-treatment. The treated PCL scaffolds with an initial compressive modulus and strength of 3027.8 ± 204.2 kPa and 208.8 ± 14.5 kPa can maintain their original shapes after implantation in vivo for 24 weeks. Extensive newly-grown tissues were found to gradually penetrate into the porous regions along the PCL filaments. Although degradation occurred, the mechanical properties of the implanted constructs stably maintained. The presented method provides an innovative, green and general post-treatment strategy to improve both the filament quality and mechanical properties of SLS-fabricated PCL scaffolds for various tissue engineering applications.