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

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.

Effect of Three-dimensional Printing with Nanotubes on Impact Resistance

The types of biomedical devices that can be three-dimensional printed (3DP) is limited by the mechanical properties of the resulting materials. As a result, much research has focused on adding carbon nanotubes (CNT) to these photocurable polymers to make them stronger. However, there is little to no data on how CNTs affect the impact resistance of these polymers, an important property when designing and manufacturing lower limb prosthetics. 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 resistance. 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 in a notched Izod configuration. Contrary to the hypothesis, 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. This decreased impact resistance may be due to voids in the printed polymer around the aggregated nanotubes. Thus, SLA polymers still do not have the impact strength needed to be used for a full lower limb prosthetic.

Morphology and Mechanical Properties of Natural Rubber-PCL Core-Shell/PLA Composites

Natural rubber (NR)/Polycaprolactone (PCL) core-shell (NR-ad-PCL), from admicellar polymerization, was as an impact modifier for the composites. PLA was mixed with NR-ad-PCL with different NR-ad-PCL contents at 5, 10, 15 and 20 wt%. PLA-based composites were prepared by co-rotating twin screw extruder. The morphology of the composites was observed by Field emission scanning electron microscope (FE-SEM). Mechanical properties of the composites were investigated by dynamic mechanical analyzer and pendulum impact tester. The impact strength of the PLA filled with NR-ad-PCL increased while modulus of the PLA composites decreased with increasing rubber contents.