Composition-dependent mechanical properties and viscoelastic behavior of a 3D-printable polyurethane-acrylate soft...

The long-term clinical performance of conventional soft denture liners is limited by microbial colonization, poor adhesion, and plasticizer leaching. This study developed a polyurethane-acrylate soft denture liner enabling moldless fabrication through digital photolithography-based 3D printing. Two urethane-acrylate oligomers with different molecular weights (1K: 12900 g/mol, 2K: 18500 g/mol) were synthesized and mixed in five different ratios to investigate compositional effects on mechanical and viscoelastic behavior. Increasing the proportion of the 2K oligomer enhanced tensile strength and elongation, with compositions ≥1:1 (GR-C) showing mechanical performance comparable to conventional silicone-based soft liners. Dynamic mechanical analysis showed storage modulus values (0.50-0.65 MPa) within the oral mucosal elastic range (0.37-5.93 MPa), indicating damping capacity. Shore A hardness of all compositions remained within the extra-soft range after 30 days, satisfying ISO 10139-2. Under compressive loading, higher 1K content increased resistance to deformation, while GR-C demonstrated intermediate compressive stress at 10-30% strain. In terms of dimensional accuracy, GR-A and GR-D showed greater deviations than the other groups, with higher deviations along the x- and y-axes compared to the z-axis, and group- and axis-dependent patterns were observed. Optical rheometry revealed that increasing the 2K oligomer content reduced the storage modulus while increasing the loss modulus and loss tangent, indicating enhanced viscous behavior. Water sorption (13.1-14.9 μg/mm³) was within previously reported ranges, whereas solubility (12.3-16.2 μg/mm³) was comparatively higher. Near-surface degree of conversion approached 100% after post-polymerization. GR-C was selected as the optimized formulation and showed no cytotoxicity in an L929 cell assay. In the printability assessment using a novel digital workflow, GR-C exhibited a root-mean square (RMS) deviation of 0.619 mm. These results demonstrate that controlled oligomer composition enables tunable tensile, compressive, and viscoelastic properties in 3D-printable polyurethane-acrylate soft denture liners.