8872 universal test machine

To assess the strength of 3DP-WHOs in wrist sagittal movements, a three-point bending test method was chosen. The orthoses were installed on two supports (in the forearm zone and in the palm/fingers zone) with self-locking nylon cable zip ties, leaving the wrist zone unsupported (Figure 5a). Attention was paid to ensure a similar tightening for all WHOs by measuring the free-end length of the zip ties. The load was applied on the orthoses in the wrist region, with the deflection points being separated at 100 mm.
The Instron 8872 Universal Test Machine (Instron Inc., Norwood, MA, USA) was used for the mechanical tests. Three samples of 3DP-WHO1 and three samples of 3DP-WHO2 were subjected to three-point bending tests, and the results were comparatively analyzed. Moreover, 3DP-WHO2s were subjected to a fatigue bending test using tension–compression cyclic loads (Figure 5b) and the dummy forearm (presented in Section 2.1) as the interior support. Each sample underwent 2000 cycles (equivalent to an active wearing of the splint for around three–four weeks [24 (link)]) at 0.5 Hz frequency and ± 2.5 mm displacements (flexion–extension).

The tensile specimens were immersed in disinfectant until saturation. Methylene blue was added in the solution for evaluating the fluid penetration depth by observing the coloring of the fracture surfaces. Specimens were tested using an Instron 8872 Universal Test Machine (Instron Inc., Kawasaki, Japan) equipped with a load cell of 25 kN. The testing speed was set at a rate of 1 mm/min and the extensometer gauge length was 25 mm.
Phenom ProX scanning electron microscope (SEM) (Phenom World, Eindhoven, The Netherlands) was used for investigating if the specimens fracture surfaces show any specific features which might be caused by the disinfectant action.

For the absorption tests, the cubes were repeatedly immersed in disinfectant at room temperature (22–24 °C) and their mass was measured. The first measurement was performed on dry specimens and the second measurement was made 10 min after by removing the cubes from the solution and placing them on a dry cloth for eliminating the excess of disinfectant. In the first two and a half hours, the cubes were weighed every half an hour. Then, the measurements were performed after 5 h, 7 h, 10 h, 24 h, 30 h, 48 h, 72 h, and 7 days. In total, the samples were weighed fifteen times (minutes: 0, 10, 30, 60, 90, 120, 150, 300, 420, 600, 1440, 1800, 2880, 4320, and 10,080).
The compression testing was performed on saturated specimens using an Instron 8872 Universal Test Machine (Instron Inc., Noorwood, MA, USA) with a constant compression velocity of 1 mm/min until the specimens’ fracture.