The application of modern manufacturing processes

Pre-clinical evaluation of novel socket materials Brian McLaughlin, David Simpson & Arjan Buis

Traditional socket production

Wrap casting Appling pressure to predetermined areas

Traditional socket production

Remove the cast from the patient Fill wrap cast with plaster of Paris slurry Remove bandages from the cast ~ destroys the original data Rectify cast

Traditional socket production

This process creates a model which is not the same

shape as the stump but which has been modified by artisan techniques ~ no record is available of these changes.

Traditional socket production Remove plaster model from • socket Destroys the modified data.

Traditional socket production This method of design and fabrication is able to produce comfortable sockets. However, the process has drawbacks. – No permanent record of the patient’s stump geometry nor the rectified cast. – both the wrap cast and the positive mould are destroyed during the process.

CAD-CAM Scanning with a variety of scanners A digital model of the stump shape is stored On-screen rectification

CAD-CAM The file is usually sent to a central fabrication facility. Blank is cut by a milling machine.

BUT the socket is still produced in the usual way using artisan methods and techniques.

But Considerable variability in the quality of sockets produced by different central fabrication facilities.

Sanders et al CAD/CAM transtibial prosthetic sockets. JRRD, 44, 3 2007

Rapid Manufacture RM is a relatively new class of manufacturing technology Has the potential to create a prosthetic socket directly from the CAD data.

Rapid Manufacture Material is deposited in thin

horizontal sections to form the finished component.

Rapid Manufacture

Stereolithography

Selective Laser Sintering 3D Printing Fused Deposition Modelling

Fused Deposition Modelling Price of this equipment has fallen and it is becoming affordable. Strength of ABS is claimed to be similar to some materials that are currently used for socket fabrication. Our intention was to test this material against existing socket materials.

Specimen Preparation ABS

Dimension Elite

ABS

M30

Polycarbonate Pre & Post draped Copolymer polypropylene Fibre reinforced acrylic resin (Blatchford trans-tibial lay-up)

Tensile Testing Five samples of each material were tested in an Instron tensile testing machine. Strain rate of 5mm/minute for all specimens. Stress was calculated using the dimensions at the point of fracture as measured prior to testing.

Results Material

Maximum Strain

Maximum Stress (Nmm-2)

ABS – M30

0.12

30.2

ABS+ Dim EL

0.06

28.7

Polycarbonate

0.09

60

Undraped Copolymer

0.5

27.3

Draped Copolymer

0.5

28.1

Laminated Resin

0.07

262.5

Laminated Resin

Undraped Copolymer

Draped Copolymer

300

250

Stress Nmm-2

200

150

100

50

0 0

0.01

0.02

0.03

0.04

0.05 Strain

0.06

0.07

0.08

0.09

0.1

Undraped Copolymer ABS+ Dim EL Polycarbonate

Draped Copolymer ABS-M30

70 60

Stress Nmm-2

50 40 30 20 10 0 0

0.02

0.04

0.06

0.08 Strain

0.1

0.12

0.14

Summary The laminated resins are considerably stronger than the other materials tested – are they too strong? The draping process appears not to affect the strength of copolymer polypropylene. ABS+ and ABS-M30 materials have been shown to be of similar strength to copolymer.

Polycarbonate seems to be twice as strong as copolymer and therefore the most appropriate material to continue evaluating.

Future Work Further evaluation of polypropylene as a suitable socket material Produce polycarbonate sockets for testing to the ISO standards

Produce sockets for clinical trials, subject to ethical approval

The End

Thanks to Laser Lines for supplying the FDM test samples