Surface characteristics and mechanical properties of solid and porous polylactic acid: additive manufacturing versus compression molding

Additive manufacturing (AM) technologies such as material extrusion (MEX) enable the creation of design-driven internal architectures. In this study, 3D-printed polylactic acid (PLA) structures were systematically evaluated and compared with compression-molded PLA sheets to assess both surface and bulk material properties. An I-optimal design of experiments (DoE) was employed to investigate how the number of filaments per row and filament diameter—which together define pore size—affect scaffold porosity and mechanical properties. The eight DoE designs generated porosity values ranging from 60.4 ± 0.2% to 88.0 ± 0.1%, corresponding to Young’s modulus values between 13.9 ± 1.8 MPa and 6.0 ± 1.5 MPa. The modulus was found to be inversely correlated with porosity and was modeled using both empirical polynomial fits and statistical models generated in JMP® software. Furthermore, surface wettability was characterized using sessile drop contact angle measurements before and after argon plasma treatment. Plasma exposure led to a significant reduction in water contact angle—from 74.4 ± 3.8° to 34.9 ± 9.4° for 3D-printed samples and from 78.8 ± 6.6° to 19.8 ± 8.0° for compression-molded sheets— with stronger effects observed at higher power settings and longer treatment durations. Zisman plot analysis using water and diiodomethane estimated a surface energy of 41.3 mN/m for untreated compression-molded PLA; however, surface energy estimations after plasma treatment were not completely reliable due to wetting by both test liquids. These findings provide insights into how processing conditions and surface treatment could enhance the performance of PLA-based materials in applications such as tissue engineering scaffolds.