Assessment of a Virtual Functional Prototyping Process for the Rapid Manufacture of Passive-Dynamic Ankle-Foot Orthoses

Abstract

Passive-dynamic ankle-foot orthosis (PD-AFO) bending stiffness is a key functional characteristic for achieving enhanced gait function. However, current orthosis customization methods inhibit objective premanufacture tuning of the PD-AFO bending stiffness, making optimization of orthosis function challenging. We have developed a novel virtual functional prototyping (VFP) process, which harnesses the strengths of computer aided design (CAD) model parameterization and finite element analysis, to quantitatively tune and predict the functional characteristics of a PD-AFO, which is rapidly manufactured via fused deposition modeling (FDM). The purpose of this study was to assess the VFP process for PD-AFO bending stiffness. A PD-AFO CAD model was customized for a healthy subject and tuned to four bending stiffness values via VFP. Two sets of each tuned model were fabricated via FDM using medical-grade polycarbonate (PC-ISO). Dimensional accuracy of the fabricated orthoses was excellent (average 0.51 ± 0.39 mm). Manufacturing precision ranged from 0.0 to 0.74 Nm/deg (average 0.30 ± 0.36 Nm/deg). Bending stiffness prediction accuracy was within 1 Nm/deg using the manufacturer provided PC-ISO elastic modulus (average 0.48 ± 0.35 Nm/deg). Using an experimentally derived PC-ISO elastic modulus improved the optimized bending stiffness prediction accuracy (average 0.29 ± 0.57 Nm/deg). Robustness of the derived modulus was tested by carrying out the VFP process for a disparate subject, tuning the PD-AFO model to five bending stiffness values. For this disparate subject, bending stiffness prediction accuracy was strong (average 0.20 ± 0.14 Nm/deg). Overall, the VFP process had excellent dimensional accuracy, good manufacturing precision, and strong prediction accuracy with the derived modulus. Implementing VFP as part of our PD-AFO customization and manufacturing framework, which also includes fit customization, provides a novel and powerful method to predictably tune and precisely manufacture orthoses with objectively customized fit and functional characteristics.

Additive manufacturing of custom orthoses and prostheses—A review

“…9 Examples of AM AFOs, produced by: (a) Faustini et al [21], (b) Mavroidis et al [22], (c) Schrank et al [23], (d) Telfer et al [17], (e) Creylman et al [24], (f) Schrank et al [25], (g) Chen et al [26], and (h) Harper et al [27].…”

“…9(e)) on eight subjects with unilateral drop foot gait, evaluated gait performance and concluded that SLS AFOs had at least equivalent performances as conventional AFOs. Schrank et al [25] integrated the CAD model parameterization and FEM analysis to quantitatively tune, predict and experimentally validate the bending stiffness of AFOs made by FDM. AFOs with different stiffness levels were fabricated ( Fig.…”

Experimental and computational analysis of composite ankle-foot orthosis

“…In the field of prosthetics and orthotics, FEA has been used to evaluate and design a variety of devices [10–13]. FEA can also predict stress distribution and material deformation patterns [5–6,8,14] and can determine the orthosis dimensions needed to mimic design characteristics of commercial orthoses [15]. FEA of fully parameterized CAD models may hold great potential for rapidly identifying optimal PLS AFO functional characteristics, such as bending stiffness.…”

The use of a low cost 3D scanning and printing tool in the manufacture of custom-made foot orthoses: a preliminary study

“…Three-dimensional (3D) printing, one of the most recent forms of CAM, has proven efficacy in the fabrication of ankle foot orthoses (AFO) with reports of excellent dimensional accuracy, good manufacturing precision, and performance that is at least equivalent to hand-crafted AFO’s [7-9]. Recent studies report positive subjective comfort ratings and similar biomechanical gait parameters with the use of orthoses manufactured using 3D printing in comparison to orthoses fabricated using traditional means [1,6,10].…”