Influence of Infill Density on Bacterial Colonization and Mechanical Performance of 3D-Printed PETG Scaffolds

Polyethylene terephthalate glycol (PETG) is a versatile thermoplastic widely used in food packaging and biomedical applications owing to its excellent mechanical properties, chemical resistance, biocompatibility, and ease of processing. Porosity is a critical design parameter that governs the biological and mechanical performance of 3D-printed PETG structures by influencing cell attachment, nutrient transport, mechanical integrity, and microbial interactions. In this study, PETG scaffolds were fabricated at five nominal infill densities (20%, 40%, 60%, 80%, and 100%) using fused deposition modelling (FDM) to investigate the influence of printing-defined architecture on mechanical performance and bacterial colonization. Tensile testing revealed that decreasing infill density resulted in a progressive reduction in ultimate tensile strength and Young's modulus, demonstrating the trade-off between reduced material density and mechanical integrity. Bacterial interactions with the scaffolds were evaluated against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Staphylococcus epidermidis, and Salmonella typhimurium using optical density (OD) and ATP-based viability assays to quantify both planktonic and adherent bacterial populations. The results demonstrated that the influence of scaffold porosity was species-dependent. The results demonstrated species-dependent responses to scaffold architecture. Higher infill densities were generally associated with reduced attachment and metabolic activity for P. aeruginosa, S. epidermidis, and S. typhimurium, whereas E. coli exhibited relatively stable growth and metabolic activity across the tested infill conditions. S. aureus showed an intermediate response, with bacterial attachment and metabolic activity varying according to scaffold architecture. Overall, infill density exerted a greater influence on scaffold-associated bacteria than on planktonic populations, while simultaneously determining the mechanical performance of the printed structures. These findings demonstrate that controlling PETG infill architecture is important for balancing mechanical properties and bacterial colonization and provide design insights for future PETG-based biomedical and food-packaging applications.