Effect of Three-Dimensional Printing With Nanotubes on Impact and Fatigue Resistance

Abstract

The types of biomedical devices that can be three-dimensional printed (3DP) are limited by the mechanical properties of the resulting materials. As a result, much research has been focused on adding carbon nanotubes (CNT) to these photocurable polymers to make them stronger. The objective of this study was to expand the use of 3DP to prosthetics by testing the hypothesis that adding CNTs to a stereolithographic (SLA) photocurable resin will result in a cured polymer with increased impact and fatigue resistance. For impact testing, twenty-six total specimens, 13 with nanotubes and 13 without nanotubes, were printed on a Form2 SLA printer. Once all the specimens were printed, washed, and cured, the impact resistance was quantified using a pendulum impact tester using a notched Izod configuration. Similarly, twelve R. R. Moore fatigue specimens were printed, washed, and cured. The specimens with SWCNTs (0.312 ± 0.036 ft lb/in.) had a significantly lower impact resistance compared to the non-SWCNT specimens (0.364 ± 0.055 ft lb/in.), U = 34.0, p = 0.004. Adding SWCNTs also reduced the short cycle fatigue life (i.e., 103) from 3.1 × 5 to 8.8 × 3 psi and increased the endurance limit from 0.4 to 3.0 × 3 psi. If used for creating a foot prosthetic, the non-SWCNT polymer would last 2919 cycles while the SWCNT mixture would last <1 cycle. Therefore, SLA polymers do not yet have the impact and fatigue resistance capabilities to be used for prosthetic feet.