Page 528 - IJB-10-3

International Journal of Bioprinting Mechanical responses of 3D-printed AFO

1. Introduction modeling (FDM), 15-19 multijet fusion (MJF), selective
20
laser sintering (SLS), 21,22 and stereolithography (SLA),
23
Gait deviations are a common problem in ambulant to manufacture AFOs. As presented in Figure 1b, the
children with cerebral palsy (CP) due to a combination fabrication processes of 3D-printed AFOs start with
of impaired motor control, movement disorders such as the acquisition of the patient-specific geometry using
spasticity, and secondary musculoskeletal deformities such 3D-scanning, microcomputed tomography (CT), or
as equinus contractures. Besides single-event multilevel
1
surgery, nonoperative management options to improve gait magnetic resonance imaging (MRI) data. Subsequently, a
2
impairments include physical therapy, pharmacological smooth foot-leg model can be reconstructed by repairing
3
and fitting raw scanning data. AFOs can be designed based
interventions (e.g., injections of botulinum toxin A),
4,5
and the use of an ankle-foot orthosis (AFO). AFOs on the foot-leg model according to clinical requirements
6-8
are externally applied devices encompassing the foot, using computer-aided design (CAD) software, followed
ankle, and leg from just below the knee. They are used to by converting the design to G-code compatible with the
compensate for impairments in the structure and function 3D printer for printing. Finally, the 3D-printed AFO can
of the neuromuscular and musculoskeletal systems. be inspected and delivered to the patient (Figure 1b).
7,9
Traditionally, patient-specific AFOs are handmade by Compared to traditional plaster molding techniques, 3D
experienced orthotists. The whole process includes six printing has the potential to eliminate several steps and
main steps and is labor-intensive, consuming about simplify the process, as well as provide repeatability and
6–8 h per device (Figure 1a). 10,11 The first step is taking design options that are not available through traditional
a negative impression of the foot, ankle, and leg using a methods. Table 1 compares the traditional plaster-molding
plaster bandage or fiberglass type. Then, a positive model is techniques and 3D printing techniques.
obtained by pouring plaster slurry into the negative model An important characteristic of AFOs that needs to be
and adding additional plaster to adjust the geometry. Once considered by clinicians is rotational stiffness, which is
the positive model is smoothed, a heated polypropylene (PP) determined by the resistance of AFOs against the ankle
sheet is wrapped around it, and vacuum is formed. Finally, the joint plantarflexion (PF) and dorsiflexion (DF) motions in
cooled plastic is cut to the AFO trimlines determined by the sagittal plane. 24-26 While the stiffness of AFOs can be
the orthotist and fitted to the patient. affected by the location of the trimline, base materials, and
With rapid advances in three-dimensional (3D) thickness, 27,28 evaluating this crucial property has received
printing techniques, complex geometry can be fabricated increasing attention from researchers. 29,30 Several testing
with exceptional quality using various metallic or systems, such as BRUCE, EMPIRE, and SMApp, have
33
32
31
12
polymeric materials for different applications. Recent been developed to measure the torque required to move
reviews indicate that it is feasible to produce AFOs using AFOs to a certain PF or DF angle for stiffness calculation.
3D printing techniques. 13,14 Researchers have considered In addition to experimental methods, attempts have
different 3D printing techniques, such as fused deposition also been made to develop finite element (FE) models to

Figure 1. Comparison between ankle-foot orthosis (AFO) fabrication processes: (a) traditional method and (b) 3D printing method.

Volume 10 Issue 3 (2024) 520 doi: 10.36922/ijb.3390