Examining the Flexural Behavior of Thermoformed 3D-Printed Wrist–Hand Orthoses: Role of Material, Infill Density, and Wear Conditions

Abstract

This paper examined the mechanical properties of wrist–hand orthoses made from polylactic acid (PLA) and polyethylene terephthalate glycol (PETG), produced through material extrusion with infill densities of 55% and 80%. These orthoses, commonly prescribed for wrist injuries, were 3D-printed flat and subsequently thermoformed to fit the user’s hand. Experimental and numerical analyses assessed their mechanical resistance to flexion after typical wear conditions, including moisture and long-term aging, as well as their moldability. Digital Imaging Correlation investigations were performed on PLA and PETG specimens for determining the characteristics required for running numerical analysis of the mechanical behavior of the orthoses. The results indicated that even the orthoses with the lower infill density maintained suitable rigidity for wrist immobilization, despite a decrease in their mechanical properties after over one year of shelf life. PLA orthoses with 55% infill density failed at a mean load of 336 N (before aging) and 215 N (after aging), while PETG orthoses did not break during tests. Interestingly, PLA and PETG orthoses with 55% infill density were less influenced by aging compared to their 80% density counterparts. Additionally, moisture and aging affected the PLA orthoses more, with thermoforming, ongoing curing, and stress relaxation as possible explanations related to PETG behavior. Both materials proved viable for daily use, with PETG offering better flexural resistance but posing greater thermoforming challenges.

Keywords

• 3D printing
• wrist–hand orthosis
• thermoforming
• PLA
• PETG
• infill density