TY - JOUR

T1 - Design considerations for a novel shape-memory-plate osteosynthesis allowing for non-invasive alteration of bending stiffness

AU - Krämer, Manuel

AU - Müller, Christian W.

AU - Hermann, Maike

AU - Decker, Sebastian

AU - Springer, André

AU - Overmeyer, Ludger

AU - Hurschler, Christof

AU - Pfeifer, Ronny

N1 - Funding information: This work was supported by the “ Deutsche Forschungsgemeinschaft ” (DFG). The project is part of the collaborative research centre SFB599-D10 . The authors would like to thank the DFG for their support and the company Ingpuls for inspiring discussions regarding the behaviour of smart memory alloys and for providing DSC measurements of the SMA. Furthermore we would like to thank Dave Thomas for proof reading the article.

PY - 2017/8/23

Y1 - 2017/8/23

N2 - Biomechanical stimuli play a major role in fracture healing. Changing the fixation stiffness through the course of healing might accelerate bone healing and prevent healing complications. Shape memory alloy (SMA) based implants were developed to allow for non-invasive stiffness alteration during the fracture healing process. To gain a deeper understanding of the implant functionality based on the alloy characteristics and geometric design, the mechanical properties of different shape memory alloys where mechanically characterized. SMA bone plates were manufactured and the structural bending stiffness of the implants was determined at different temperatures and configurations. The temperature required for complete recovery of shape after deformation increased continuously with increasing pseudo-plastic deformation in SMA probes. Full recovery was observed at temperatures ranging from 38 °C to 52 °C after pseudo-plastic deformations ranging from 0.2% to 1.0% outer fibre strain, respectively. The small fragment inverse-dynamisation implants revealed bending stiffnesses ranging from 0.09 N m2 to 0.34 N m2 in the initial state and from 0.16 N m2 to 0.46 N m2 after shape alteration. Dependent on the design, a relative gain of the implant stiffness ranging from 18.8% to 115.0% could be observed. The large inverse-dynamisation implants revealed bending stiffnesses from 3.7 N m2 to 7.1 N m2 before and 4.1 N m2 to 12.6 N m2 after triggering the shape memory effect. Dependent on the design a gain in stiffness from 11.8% to 117.2% was observed. Warming the SMA implant to 40 °C for a short period of time, leads to a moderate increase in implant stiffness of up to 64.5%, while triggering the implant with 50 °C leads to a maximum increase in stiffness of up to 127.3%. The Nitinol shape memory bone plates have a huge potential for improving the treatment of long shaft fractures by allowing for the increase, decrease or incremental change of implant stiffness in fracture stabilization. However, the interaction between design, material properties, and manufacturing processes need to be carefully considered for each specific application to achieve optimum function of SMA-based, stiffness altering, fracture-fixation implants.

AB - Biomechanical stimuli play a major role in fracture healing. Changing the fixation stiffness through the course of healing might accelerate bone healing and prevent healing complications. Shape memory alloy (SMA) based implants were developed to allow for non-invasive stiffness alteration during the fracture healing process. To gain a deeper understanding of the implant functionality based on the alloy characteristics and geometric design, the mechanical properties of different shape memory alloys where mechanically characterized. SMA bone plates were manufactured and the structural bending stiffness of the implants was determined at different temperatures and configurations. The temperature required for complete recovery of shape after deformation increased continuously with increasing pseudo-plastic deformation in SMA probes. Full recovery was observed at temperatures ranging from 38 °C to 52 °C after pseudo-plastic deformations ranging from 0.2% to 1.0% outer fibre strain, respectively. The small fragment inverse-dynamisation implants revealed bending stiffnesses ranging from 0.09 N m2 to 0.34 N m2 in the initial state and from 0.16 N m2 to 0.46 N m2 after shape alteration. Dependent on the design, a relative gain of the implant stiffness ranging from 18.8% to 115.0% could be observed. The large inverse-dynamisation implants revealed bending stiffnesses from 3.7 N m2 to 7.1 N m2 before and 4.1 N m2 to 12.6 N m2 after triggering the shape memory effect. Dependent on the design a gain in stiffness from 11.8% to 117.2% was observed. Warming the SMA implant to 40 °C for a short period of time, leads to a moderate increase in implant stiffness of up to 64.5%, while triggering the implant with 50 °C leads to a maximum increase in stiffness of up to 127.3%. The Nitinol shape memory bone plates have a huge potential for improving the treatment of long shaft fractures by allowing for the increase, decrease or incremental change of implant stiffness in fracture stabilization. However, the interaction between design, material properties, and manufacturing processes need to be carefully considered for each specific application to achieve optimum function of SMA-based, stiffness altering, fracture-fixation implants.

KW - Fracture healing

KW - Inverse-dynamisation, osteosynthesis plate

KW - Nickel-titanium (NiTi)

KW - Shape memory alloy

KW - Stiffness alteration

UR - http://www.scopus.com/inward/record.url?scp=85028314599&partnerID=8YFLogxK

U2 - 10.1016/j.jmbbm.2017.08.024

DO - 10.1016/j.jmbbm.2017.08.024

M3 - Article

C2 - 28858665

AN - SCOPUS:85028314599

VL - 75

SP - 558

EP - 566

JO - Journal of the Mechanical Behavior of Biomedical Materials

JF - Journal of the Mechanical Behavior of Biomedical Materials

SN - 1751-6161

ER -