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3D-printed splint for mallet finger injury
considering both maximum stress and deflection in an Instron 300LX (Instron, High Wycombe,
values while reducing the heat trapped around UK) to measure the average maximum deflection
the finger by a significant amount. This splint is of the three splints from each design. The
simpler to print than lower percentage mass splints comparison results, shown in Figure 14B, imply
that can require more printing support structures. good agreement of the experimental findings with
It was found that inevitably reducing the amount the simulations.
of material in a load-bearing finger splint would Surface finish and appearance are important
increase the deflection of it. However, when the considerations in comfort and appeal to the user.
distribution of that material is chosen to optimize The parameters that optimize the quality of 3D
the stiffness in that situation, the deflection value printing need to be explored in this area to compete
was low enough to justify its use. with the thermoplastic hand molded thermoplastic
For verifying the simulation results, some splints. There are some complications on achieving
experiments were carried out to find the maximum more strength of splints through print orientations
deflection that occurred at the tip of the 3D-printed on the expense of losing the surface finish quality,
splints. A set up, as shown in Figure 14A, was used which could be the subject for future work.
Investigation in the future needs to be undertaken
into the duration of time before PLA splints begin
to experience mechanical property decline. It
should be investigated at what point in the lead
up to hydrolysis does mechanical performance
decline. Fatigue testing should be investigated in
the future. Cyclic loading of a finger splint with
sub-maximal loads may place a more realistic
loading pattern on the splint than one large one
off-load. In the day-to-day wearing of a finger
splint, the user would apply small repeat loads into
the splint. This over the course of the 6 – 8-week
recovery period may cause degradation or decline
Figure 13. A trade-off among deflection, stress, in mechanical properties of the splint.
and heat dissipation of three-dimensional-printed Measurements of the finger were taken
splints. with calipers. Taking seven dimensions of the

A B

Figure 14. (A) A topology optimized three-dimensional-printed splint under deflection test; (B) comparison
of experiments versus simulations of splints deflection.

26 International Journal of Bioprinting (2020)–Volume 6, Issue 2