Tensile properties and thermoformability of 3D-printed PLA/TPE hybrid laminate orthoses under environmental stress

Three-dimensional (3D) printing enables rapid, patient-specific production of lightweight and cost-effective orthotic devices. However, clinical adoption remains limited due to uncertainties in material durability, bonding reliability, and environmental resistance. Hybrid laminates combining Polylactic Acid (PLA) for stiffness and Thermoplastic Elastomer (TPE) for comfort offer a promising solution. This study investigates the mechanical behaviour, environmental sensitivity, and re-thermoformability of 3D-printed PLA/TPE laminates for wrist-hand orthoses. Specimens were fabricated using FFF (Fused Filament Fabrication) and bonded with three different adhesives. Peel testing was employed as a simple comparative screening method to identify suitable bonding approaches for hybrid laminates. Cyanoacrylate showed the most favourable behaviour, consistently resulting in substrate-dominated failure and maintaining bond integrity after thermoforming and environmental conditioning. Tensile testing revealed that increasing PLA thickness improved strength and stiffness, while normalized values confirmed PLA's dominant role in load-bearing behaviour. Environmental conditioning, including thermoforming, temperature variation, moisture, and chemical exposure, was assessed using a Taguchi design. Thermoforming had the most significant impact on stiffness, reducing it without noticeably affecting stress, while chlorinated water and ethanol reduced stiffness and increased variability of stiffness results. A prototype orthosis demonstrated good ergonomic fit, bonding integrity, and re-thermoformability. These findings provide practical guidance for adhesive selection, material configuration, and post-processing strategies, supporting the integration of 3D-printed hybrid orthoses into clinical practice.