Additive Manufacturing Strategies

Cost Sensitivity Analysis Performed for 3D Printed, Open Source Infant Clubfoot Brace

ST Medical Devices

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Congential talipes equinovarus (CTEV), perhaps better known as clubfoot, is one of the most common congenital physical deformities, as it occurs at least once every 1,000 births. In countries like the US, CTEV is diagnosed at birth and treated while the patient is still a young child, using a method of weekly manipulation and casting, followed by an Achilles tenotomy. Then a foot abduction orthosis (FAO) is worn until the patient is about four years old so that the deformity will not reoccur. Unfortunately, these types of treatment options are not as readily available, or affordable, in developing countries like East Africa, where clubfoot can occur up to eight times every 1,000 births.

However, 3D printing, which has been used in the past to help treat CTEV, can help democratize the manufacture of these FAOs for more sustainable development, in addition to bringing the cost down. A new paper, titled “Open-Source Three-Dimensional Printable Infant Clubfoot Brace,” was recently published in the Journal of Prosthetics and Orthotics by a team of researchers, including open source advocate Dr. Joshua Pearce, from Michigan Technological University (MTU).

The researchers explain that inexpensive, open source RepRap 3D printers have helped expand access to the technology, while also keeping costs down.

Angle brackets reversed to allow for increased leg motion.

“To investigate the potential of distributed manufacturing of an FAO for clubfoot patients in the developing world, this study makes a careful investigation of the use of RepRap 3-D printers to fabricate an open-source clubfoot brace,” the researchers wrote.

“The methodology includes first selecting among the various commercial 3-D printing materials based on material properties and cost, developing an open-source design using only open-source tools, and describing the open-source 3-D printer used and the settings to fabricate the clubfoot brace. Then, the brace’s features were examined to ensure that it met the required features for foot abduction orthoses designed for treating clubfoot. Finally, this brace was then examined by doing a cost and functionality comparison with existing designs.”

The team designed their 3D printable clubfoot brace using free, open source FreeCAD software, in order to “enable customization.” The design was optimized for easy printing, with minimal overhangs, and was “created with the intent of being able to meet criteria collected from the literature.” The most important features in the brace are:

  • the ability to maintain foot positioning in order to prevent relapses
  • the ability to adjust the angle of abduction
  • the ability to dorsiflex the feet

Additionally, by making sure the width of the FAO between the feet is adjustable, the brace will need to be replaced less, thus making it more cost-effective.

“The ability of the foot pads to move independently and attach and detach from the abduction bar increases comfort and encourages proper usage,” the researchers explained.

Bill of Materials: all 3D printed components laid out and labeled

Due to its strength and low cost, the researchers chose to 3D print the brace, and its 13 assembly components, out of biodegradable PLA. Cura software was used to slice the CAD models, and the brace was printed, at a speed of 40 mm/second, on a MOST delta RepRap 3D printer with an infill density of 80%, 0.2 mm layer height, and a 1 mm shell thickness.

Then the team ran a cost analysis on the three main variables – labor, filament, and electricity – that would drive the cost of manufacturing the brace locally in Kenya, where CTEV is “especially prevalent.” Labor costs in the country varied from $0 for volunteers, or employees who simply monitor the 3D printer and assemble the brace, up to the government-dictated wage of $1.30/hour for a Kenyan machinist in an urban area. Three commercial filament sources are available, while electricity costs run from $0/kWh for running a solar-powered 3D printer to $0.2029/kWh – the highest standardized rate for electricity in Kenya based on data from January of 2017.

Cost sensitivity analysis: Cost of manufacturing brace vs percentage change in variable costs.

The researchers found that the total material cost of the clubfoot brace was $11.08. However, it should be noted that the variable with the most potential to effect the overall cost is the labor, though electricity and filament costs can also vary.

The base of the FAO consists of top and bottom sliders held together by two carriage bolts, a closing bracket, and two nuts. By loosening and tightening the knobs, the feet width of the brace can be adjusted for a growing child.

Attachment of the footpads to the assembly via angle brackets with interlocking ridges to lock footpads into place.

“Due to the simplicity of the assembly, the infant’s shoes can be first attached to the footpad via Velcro straps before attaching the footpad to the bar,” the researchers explained. “The shoes employed should be “low rise” at the heel to allow observation that the heel remains against the foot pad, which is lost if a “high top” shoe is employed.”

This FAO offers more functionality at lower cost, and also has a lower environmental impact, as it only requires a partial infill and no shipping is required when it’s 3D printed locally. The team made the STL files and FreeCAD models for its infant clubfoot brace available for free at the Open Science Framework under a GNU General Public License 3.0.

The researchers concluded, “The results show that the open-source clubfoot brace matches or surpasses the physical features and mechanical degrees of freedom of all commercial- and non-profit-developed brace designs while substantially reducing the costs of the braces to hospitals and families.”

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