Pseudoelastic NiTiNOL in Orthopaedic Applications
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SPECIAL ISSUE: A TRIBUTE TO PROF. DR. GUNTHER EGGELER, INVITED PAPER
Pseudoelastic NiTiNOL in Orthopaedic Applications David Safranski1 • Kenneth Dupont1 • Ken Gall2,3
Ó ASM International 2020
Abstract Pseudoelastic NiTiNOL presents an attractive material option for devices used in clinical orthopaedic applications. The capacity of the material to exert sustained compression during shape recovery aligns well with the mechanobiological factors associated with bone healing, particularly in applications such as fracture healing and joint fusion. Orthopaedic medical devices which have incorporated NiTiNOL are increasing in number, with two noted examples including staples and intramedullary nails. Early NiTiNOL devices utilized shape memory NiTiNOL, but the logistical difficulties with maintaining a cold state in the clinic or limited force-generation for materials warmed from room temperature to body temperature have led to pseudoelastic NiTiNOL devices dominating clinical usage. Both pre-clinical biomechanical and clinical studies have shown that these devices do exert sustained compression beyond the abilities of competing static devices, and largely have resulted in superior clinical outcomes, such as higher fusion rates and faster times to fusion. Given these results, continued adoption of existing NiTiNOL
This invited article is part of a special issue of Shape Memory and Superelasticity to honor Prof. Dr.-Ing. Gunther Eggeler. This special issue was organized by Prof. Hu¨seyin Sehitoglu, University of Illinois at Urbana-Champaign, and Prof. Dr.-Ing. Hans Ju¨rgen Maier, Leibniz Universita¨t Hannover. & Ken Gall [email protected] 1
MedShape, Inc., Atlanta, GA, USA
2
Department of Mechanical Engineering and Materials Science, Duke University, Durham, NC, USA
3
Department of Biomedical Engineering, Duke University, Durham, NC, USA
devices and future development of new orthopaedic devices utilizing the material should continue. Keywords Pseudoelastic NiTiNOL Orthopaedic Arthrodesis Foot and ankle Staple Intramedullary nail Sustained compression
History of NiTiNOL for Medical Applications In the early 1960s, William Buehler at the Naval Ordnance Lab was experimenting with metal alloys synthesized from nickel (Ni) and titanium (Ti). He noticed that when combining Ni and Ti in nearly equal amounts the bars seemed to have very low stiffness, and when he dropped one of them on the ground, it made a distinct ‘‘thud’’ compared to the high pitched ‘‘ting’’ a normal metal resonates when it hits the ground. Buehler also noticed that bent bars could be realigned with minimal heating to their original straight shapes. Buehler was observing the shape memory effect and the thud from the bar was a signature of dissipation from the phase transformation now widely known to govern the deformation of shape memory alloys. Buehler called this newfound material NiTiNOL after Nickel-Titanium-Naval-Ordnance-Laboratory. In the years that followed, many researchers began studying NiTiNOL as the applications of the mater
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