Sterilization Effects and Reuse Potential of Additively Manufactured Material Systems: a Multiscale Thermo–Mechanical, Surface–Sterility Evaluation Framework

Abstract

Additive manufacturing (AM) is rapidly expanding from prototyping into end-use biomedical and industrial products, yet the sustainability of polymer AM remains uncertain as service life ultimately governs waste generation and environmental exposure. In healthcare, the challenges of sustainable polymer AM are particularly apparent. Utilization of polymer AM for medical devices can reduce assembly requirements, enable customization, and lower cost, but many AM polymer devices are treated as single-use because reprocessing and sterilization can degrade performance, and because AM process artifacts like layer interfaces, trapped material, surface roughness, cure history, and porosity complicate cleaning and sterility assurance. Motivated by a growing concern over plastic persistence and microplastics exposure for both humans and the environment, this dissertation investigates and establishes process-structure-performance relationships for reuse-oriented AM and quantifies how multi-scale material distribution, macroscale component morphology, and repeated sterilization jointly impact mechanical durability, thermal evolution, surface damage, and microbial inactivation. Aim 1 establishes structure–performance relationships for voxel-scale multi-material jetting (MMJ) polymeric composites by systematically varying both volumetric ratio and spatial distribution of rigid and soft constituent materials across layered, suspended, and voxel-scale mixtures. Monotonic tensile testing and deformation modeling show that distribution and interface density can shift stiffness-strength-ductility tradeoffs at fixed composition, and that custom voxel-scale material distributions enable a broader and more controllable property range than existing composite distributions. Aim 2 extends to cross-process comparison of relevant porous architectures by fabricating sheet-based (TPMS gyroid) and strut-based (octet) lattices across multiple designed porosity levels and six AM process technologies (SLM, SLS, FFF, MJF, MMJ, and VPP). Mechanical behavior in tension, torsion, and compression is normalized by process-matched solid baselines to decouple bulk material capability from material distribution and morphology effects, revealing technology-dependent porosity realization and defect-limited failure modes that dominate ductility and toughness, even when stiffness scaling appears to be porosity-controlled. Finally, Aim 3 treats sterilization as a coupled aging and sterility problem by subjecting representative polymers and metals to repeated UV-C (UV) and steam autoclave (AC) cycles while tracking mass change, tensile property retention, bulk thermal-state evolution, observed surface evolution, and microbial inactivation. AC sterilization achieves complete microbial eradication across cycles but induces material- and process-specific mechanical damage in susceptible polymers, whereas UV sterilization presented more variability across material surfaces and cycles. These phenomena are hypothesized to be strongly dependent on the bacterial growth phase and the formation of biofilms due to their proven ability to enhance bacterial resistance and prevent UV light penetration. Collectively, this work provides multiscale evidence that reuse potential in AM is governed by the interaction of polymer chemistry with process-imprinted structure and evolving surface condition, and it offers a unified experimental foundation and practical guidance for selecting AM technologies, material classes, and architectures for reusable, sterilizable products that reduce single-use plastic burden without compromising mechanical function or sterility assurance.