INTRODUCTION: The first off-Earth fused deposition modeling (FDM) 3D printer is investigating acrylonitrile butadiene styrene (ABS) thermoplastic manufacturing applications for long-duration space missions. This study assessed the feasibility of FDM 3D printing ABS thermoplastic customized mallet splints on site for Mars analogue crewmembers.METHODS: Seven caliper measurements were taken of the right ring finger of 13 healthy Mars Desert Research Station mission crewmembers. These measurements were input into a free 3D modeling software program to create customized digital splint models. These digital files were uploaded to a desktop FDM 3D printer and custom splints were printed on site with ABS thermoplastic. Splint fit was assessed via subject feedback. Joint active range of motion was recorded when the splint was worn briefly.RESULTS: The time it took the software program to digitally render each splint model was less than 2 min and 30 s. The print duration for the splints ranged from 21 to 29 min. All 13 subjects reported that their 3D printed custom mallet splints fit securely and comfortably. All splints permitted full active range of motion of the proximal interphalangeal joint (0–100°) while maintaining the distal interphalangeal joint in extension.DISCUSSION: It is feasible to 3D print functional ABS thermoplastic custom mallet splints on site for Mars analogue crewmembers. This technology could be used clinically in the future when a custom mallet splint is required in a remote, resource-constrained setting.Wong JY. On-site 3D printing of functional custom mallet splints for Mars analogue crewmembers. Aerosp Med Hum Perform. 2015; 86(10):911–914.