Abstract
Rapid Prototyping is becoming an accessible manufacturing method but before clinical adoption can occur, the safety of treatments needs to be established. Previous studies have evaluated the static strength of traditional sockets using ultimate strength testing protocols outlined by the International Organization for Standardization (ISO). To carry out a pilot test in which 3D printed sockets will be compared to traditionally fabricated sockets, by applying a static ultimate strength test. 36 sockets were made from a mold of a transtibial socket shape,18 for cushion liners with a distal socket attachment block and 18 for locking liners with a distal 4-hole pattern. Of the 18 sockets, 6 were thermoplastic, 6 laminated composites & 6 3D printed Polylactic Acid. Sockets were aligned in standard bench alignment and placed in a testing jig that applied forces simulating individuals of different weight putting force through the socket both early and late in the stance phase. Ultimate strength tests were conducted in these conditions. If a setup passed the ultimate strength test, load was applied until failure. All sockets made for cushion liners passed the strength tests, however failure levels and methods varied. For early stance, thermoplastic sockets yielded, laminated sockets cracked posteriorly, and 3D printed socket broke circumferentially. For late stance, 2/3 of the sockets failed at the pylon. Sockets made for locking liners passed the ultimate strength tests early in stance phase, however, none of the sockets passed for forces late in stance phase, all broke around the lock mechanism. Thermoplastic, laminated and 3D printed sockets made for cushion liners passed the ultimate strength test protocol outlined by the ISO for forces applied statically in gait. This provides initial evidence that 3D printed sockets are statically safe to use on patients and quantifies the static strength of laminated and thermoplastic sockets. However, all set-ups of sockets made for locking liners failed at terminal stance. While further work is needed, this suggests that the distal reinforcement for thermoplastic, laminated and 3D printed sockets with distal cylindrical locks may need to be reconsidered.
Highlights
A prosthetic socket is the interface connecting a person’s limb to the prosthetic components they use to interact with the environment
Previous studies have evaluated the static strength of traditional sockets using ultimate strength testing protocols outlined by the International Organization for Standardization (ISO)
Prostheses, Rapid Prototyping, Prosthesis Design,3D Printing, Three Dimensional Printing, Transtibial, Socket Strength, Transtibial Socket, Thermoplastic, Lamination, Rapid Additive Manufacturing, Lower-limb Prostheses, CONCLUSION: Thermoplastic, laminated and 3D printed sockets made for cushion liners passed the ultimate strength test protocol outlined by the ISO for forces applied statically in gait. This provides initial evidence that 3D printed sockets are statically safe to use on patients and quantifies the static strength of laminated and thermoplastic sockets
Summary
A prosthetic socket is the interface connecting a person’s limb to the prosthetic components they use to interact with the environment. Sockets are manufactured from a plaster mold of a person’s limb which is modified to create an optimized shape.[1] The socket is fabricated over the mold using materials including thermoplastics and laminated composites. 3D scanning systems are an alternate method to digitize the patient’s limb and modify the shape.[1] Often, the optimized shape is milled by a computer numerically controlled (CNC) milling machine and the socket is fabricated using traditional methods.[1]. RP involves sectioning the digital 3D socket design into thin slices, and sending it to a 3D printer that builds the shape layer by layer.[1] Over the past three decades, several groups have begun to create prosthetic sockets using rapid prototyping techniques.[2,3,4]. Previous studies have evaluated the static strength of traditional sockets using ultimate strength testing protocols outlined by the International Organization for Standardization (ISO)
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