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As an emerging additive manufacturing (AM) technique, melt electrospinning writing (MEW) is used to fabricate three-dimensional (3D) submicron filament-based scaffolds with adjustable pore size and customized structure for bone regeneration. Poly(L-lactic acid) (PLLA) scaffold with excellent biodegradability and biocompatibility is first successfully manufactured using our self-assembled MEW device. However, the ultralow cell affinity and poor bioactivity severely hamper their practical applications in bone tissue engineering. These issues are caused by the severe inherent biologically inert, hydrophobicity as well as the smooth surface of the MEW PLLA filaments. In this study, a green and robust alkaline method is applied to modify the scaffold surface and to improve the bioactivity of the MEW PLLA scaffold. Without deterioration in mechanical property but robust surface hydrophilicity, the optimal MEW PLLA scaffold shows promoted surface roughness, enhanced filament tensile modulus (~ 2 folds of the as-prepared sample), and boosted crystallizability (ultrahigh WAXD intensity). Moreover, after being cultured with KUSA-A1 cells, the 0.5 M NaOH, 2 h treated MEW PLLA scaffold exhibits higher osteoinductive ability and increased immature bone tissue amounts (3 times of controlled scaffold). Thus, the flexible surface functionalization by the specific alkaline treatment was found to be an effective method for the preparation of bioactivated MEW PLLA scaffolds with promoted bone regeneration.

The thermally sensitive polymer, poly ( l -lactic acid) PLLA, is first printed to a high-resolution object using an advanced 3D printing technology, called melt electrowriting (MEW). The MEW processing conditions are systematically investigated to manufacture PLLA scaffolds with adjustable filament diameter and pore size for the application of bone tissue engineering. To this end, the relationships among the rheological behavior of the molten polymer, the electro-hydrodynamics of the jet, and the processing parameters (applied voltage, collection speed, and flow rate) are illuminated. The scaffold with relatively high deposition accuracy and crystallinity of PLLA is achieved when the printing speed was set slightly above the critical translation speed. The MEW PLLA scaffold with filament diameter of 40 μm and pore size of 200 μm is evaluated with KUSA-A1 cells to prove its in vitro potential. This is a milestone work for MEW since it supplies one of the best strategies to design and manufacture an essential biobased polymer for tissue engineering.