Molecular-weight-engineered PLA composite inks for room-temperature 3D printing of high-fidelity osteogenic scaffolds

This study presents a molecular-weight-engineered strategy for room-temperature 3D printing of osteogenic PLA/PCL/n-HA scaffolds, where PLA's molecular weight (M_w) governs printability and structural fidelity. We demonstrate that low-M_w PLA (LPLA, ∼9.0 × 10⁴ g mol^-1) leads to mechanical instability with filament collapse and nozzle clogging due to insufficient chain entanglement (5.9 × 10³ mol mm^-3), while medium- (MPLA, 4.7 × 10⁵ g mol^-1) and high-M_w PLA (HPLA, 5.9 × 10⁵ g mol^-1) achieve stable extrusion and complex architectures (overhangs/grids) through enhanced entanglement densities (7.16 × 10³ and 12.1 × 10³ mol mm^-3, respectively). Dynamic mechanical analysis reveals HPLA's superior performance, maintaining a storage modulus (E') of 8.1 MPa at 100 °C versus LPLA's 2.8 MPa, with residual E' post-glass transition following LPH < MPH < HPH, directly correlating with entanglement density. This molecular design enables precise control over extrusion dynamics and filament strength, eliminating the need for high-temperature processing. The optimized HPH composite ink (HPLA/PCL/n-HA) exhibits shear-thinning behavior, rapid solidification, and self-supporting porosity (>65%), while n-HA incorporation ensures bone-mimetic mechanics (Young's modulus ∼9 MPa) and osteoconductivity (∼20% new bone volume in vivo at 12 weeks). By establishing PLA M_w as a critical parameter for balancing extrudability and mechanical stability, this work advances solvent-based composite inks for room-temperature fabrication of patient-specific scaffolds, with broad implications for precision tissue engineering.