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

Abstract

Passivedynamic anklefoot orthosis (PDAFO) bending stiffness is a key functional characteristic for achieving enhanced gait function. However, current orthosis customization methods inhibit objective premanufacture tuning of the PDAFO 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 PDAFO, which is rapidly manufactured via fused deposition modeling (FDM). The purpose of this study was to assess the VFP process for PDAFO bending stiffness. A PDAFO 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 medicalgrade polycarbonate (PCISO). Dimensional accuracy of the fabricated orthoses was excellent (average 0.51 آ±â€‰0.39 mm). Manufacturing precision ranged from 0.0 to 0.74 Nm/deg (average 0.30 آ±â€‰0.36 Nm/deg). Bending stiffness prediction accuracy was within 1 Nm/deg using the manufacturer provided PCISO elastic modulus (average 0.48 آ±â€‰0.35 Nm/deg). Using an experimentally derived PCISO elastic modulus improved the optimized bending stiffness prediction accuracy (average 0.29 آ±â€‰0.57 Nm/deg). Robustness of the derived modulus was tested by carrying out the VFP process for a disparate subject, tuning the PDAFO model to five bending stiffness values. For this disparate subject, bending stiffness prediction accuracy was strong (average 0.20 آ±â€‰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 PDAFO 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.