OTWorld 2018Lecture Scientific/Practical [6739] Abstract [2230] | Topic: Prosthetics

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Referent/inOpitz, Manuel (München DE)Mecuris GmbH - Production

TitelWorld’s 1st 3D-printed prosthetic feet - ISO-tested & certified up to K4

Coauthors

Breuninger J., Gundlack F., Taubmann C.

Zusammenfassung

This study aims at proving the mechanical durability of 3D-printed prosthetic feet in various

configurations: K3/adults vs. K4/children, everyday vs. water-proof. The goal was achieved

by using a combination of ISO 10328:2016 tests up to 1 metric ton and computer-based

simulations.

Einführung

Digital tailoring of patient aids offers the advantages to 3D-print patient specific designs even

for very special patient requests (e.g. pediatrics, low-profile, water sports) and thanks to digital

simulation with predictable durability even for unknown new features. 3D printing allows 100%

bespoke patient aids in terms of a custom fit, functionality and look.

In 2015, the first 3D-printed prosthetic foot passed ISO 10328:2006 level P4 [1]. However,

industrial 3D-printing methods like selective laser sintering (SLS) are still questioned in

prosthetics regarding their mechanical properties [2], despite being widely used in critical

applications in aerospace (turbine parts, interior frames) and medical (joint replacements, dental

implants) [3].

This study aims at proving the mechanical durability of 3D-printed prosthetic feet according to

ISO 10328:2016 level P6 and higher. In parallel, a Finite Element Analysis (FEA) is used to

predict potential material failure or design weaknesses.

Methodik

Test foot samples: 2 samples with max length (300mm) + min width (97mm), 2 samples with

standard length (270mm), 2 samples with minimal length (pediatrics)

Physical testing: DIN EN ISO 10328:2016 at load level P6 (patients up to 125kg), dynamic load

1.580N over 2 Mio cycles at 1.1 Hz, heel + toe load 4.880N (P6 Upper Level), maximum load

OTWorld 2018Lecture Scientific/Practical [6739] Abstract [2230] | Topic: Prosthetics

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tests of up to 1 metric ton, load levels for pediatric prosthetics were derived from adult norm +

K4 safety factor

Simulation of ISO 10328: Finite Element Analysis (FEA) using ANSYS, high density mesh,

simplified material behavior

Patient evaluation: 4 male + 3 female, weight 10-90kg, age 3-62 years, 2 amputated since birth

(pediatrics) + 3 amputated when grown-ups (15-20 years ago) + 2 wearers of ortho-prosthetics

since birth (congenital fibula defect), high mobility levels (K3/K4)

Prosthetic foot design: body printed from PA12 (“Nylon”, EOS PA2200), glass fiber element for

higher energy return (heel 88.0%/ toe 84.8%), SACH adaptor, 2 damper elements

Ergebnisse

Physical testing (cf. attached figure ISO 10328 dynamic test): In a pre-test, forefoot was tested

up to Fmax at 6.000N (P8) with no visible or internal signs of material failure. In main test, 2

samples showed no visible sign of damage after 2 Mio cycles of dynamic testing. Both samples

were then tested up to P6 Upper Level, still no material failure visible. In later static tests,

loads of up to 1 metric ton (10.000 N) were applied to forefoot and heel, without visible signs of

material failure. For pediatrics, adults (>80kg) walked up some stairs and jumped on children

prosthetics.

Simulation: Temporary deformations of the heel and forefoot were simulated correctly.

However, FEA predicted a material failure before reaching P8 (pre-test), but samples was more

durable than simulated.

Patient evaluation: Supervised by 7 independent German CPOs, the 7 patients evaluated the

foot. Field testing still continues with longest duration of wearing a 3D-printed prosthetic foot

currently standing at 11 months of continuous everyday use.

Schlußfolgerung

In conclusion, the study confirms and adds to Fraunhofer’s results from 2015. It proofs that

industrially 3D-printed (SLS) prosthetic feet fulfil the requirements of ISO 10328:2016 of load

level P6 and higher. Temporary deformations can be predicted using FEA, however exact

critical failure not yet.

OTWorld 2018Lecture Scientific/Practical [6739] Abstract [2230] | Topic: Prosthetics

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These results enable medical approval of 3D-printed prosthetics (CE marking). The advantages

of digital tailoring of bespoke patient aids will offer new possibilities for prosthetists in terms of

custom fit and functionality. Special requests like salt water resistance can be included more

easily. Last but not least, patient compliance is boosted by a co-creation of the prosthetic’s look.

In outlook, these results need further investigation like:

- Dynamic test up to P8 (static already passed up to 10.000N)

- Full tests according to ISO 22675

- A validated simulation to robustly predict material failure

- Long-term patient evaluation (3 years)

- Tests of maximum prosthetic foot size (norm: 320mm)

Literaturreferenzen

[1] Fraunhofer Institute for Manufacturing Engineering and Automation IPA, Stuttgart

[2] Auer V., Opitz M.; “Meinungsforschung Orthopädietechnik - Umfrage zur Zukunft der

Orthopädietechnik & 3D-Druck”, n>90, Technikum Wien, Mecuris, 2017

[3] Breuninger J., Becker R., Wolf A., Rommel S., Verl A.; “Generative Fertigung mit

Kunststoffen - Konzeption und Konstruktion für Selektives Lasersintern”, Springer, 2013

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Image: Figure ISO 10328 dynamic test_2230.jpg