Technological Advancement for Health Roma, 21-22/06/2017

Transcription

1 BIO-MEDICAL APPLICATIONS OF NITI SHAPE MEMORY ALLOYS Girolamo Costanza, Maria Elisa Tata Department of Industrial Engineering, University of Rome Tor Vergata, Italy PhD Industrial Engineering 1

2 Shape Memory Alloys (SMA): alloys able to recover a preset shape just upon heating above the critical transformation temperature PhD Industrial Engineering 2

3 PhD Industrial Engineering 3

4 One-way Shape Memory Effect Two-way Shape Memory Effect PhD Industrial Engineering 4

5 Two sides of the same coin: Shape Memory Effect (SME) and SuperElasticity (SE) SME: T< Mf SE: T> Af PhD Industrial Engineering 5

6 Most common SMA: NiTi Cu-based Fe-Mn NiTi properties: Excellent corrosion-fatigue-resistance Bio-compatibility High ductility High strain recovery (up to 8%) Excellent magnetic resonance compatibility Excellent computer tomography compatibility MAIN APPLICATIONS Sensors Actuators Aerospace Biomedical Orthopedic Orthodontic Safety devices Fire Protection Active surfaces PhD Industrial Engineering 6

7 History 1932: A. Olander discovered the superelastic behaviour of the Au-Cd alloy; 1938: Greninger & Mooradian observed phase changes by decreasing and increasing the temperature in a Cu-Zn alloy; 1960: The U.S. Naval Ordnance Laboratory developed a new material that exhibited shape memory effect, whence the name NiTiNOL. Number of publication by year on SMA PhD Industrial Engineering 7

8 SMA Patent geographic distribution PhD Industrial Engineering 8

9 First 50 patent holders on SMA PhD Industrial Engineering 9

10 1975: first application in the biomedical field. Dr. Andreasen from Iowa University made the first implantation of an orthodontic device exploiting the superelastic property of the alloy (plateau on shape recovery during unloading, 5). As the recovery is prevented, a constant and lower force acts on the teeth. PhD Industrial Engineering 10

11 Results in 3 weeks PhD Industrial Engineering 11

12 SMA wires inserted into steel palatal arches: Superelasticity allows the device to apply lower and constant force in comparison with steel arches PhD Industrial Engineering 12

13 At the end of 80s a great improvement in the technique was given by introducing NiTi in the endodontic (rotating) file: high flexibility, recovery of deformation, limitation of the applied force. PhD Industrial Engineering 13

14 Orthopedic field The stress generated by the SMA when the shape recovery is constrained during heating is exploited for fracture treatment by using orthopedic plates (a) or staples (b). a) NiTi plate for mandible fracture Staples before and after distraction b) Staple for fixing frontozygomatic fracture PhD Industrial Engineering 14

15 Orthopedic field: Intramedullary nail for fractured elongate bones Two-way shape memory effect is used for inserting and subsequently removing the intramedullary nail in fractured elongate bones. The nail shows some SMA elements positioned along the stem in suitable seats. These elements can, by varying the temperature, assume two different configurations: an open position, where they stick out of the stem, and a closed position where they are retracted in the stem. PhD Industrial Engineering 15

16 Orthopedic treatments for physiotherapy Gloves for promoting the movements of hands were developed by positioning SMA wires in correspondence of the fingers. The two-way shape memory effect is exploited; heating or cooling, the wires contract or stretch and accordingly the hand is closed or opened. PhD Industrial Engineering 16

17 Orthopedic field The Shape Memory Effect has been employed for the design of a spinal vertebrae spacer with a rounded shape to be used on behalf of the damaged intervertebral disc. NiTi rods are also inserted in devices for scoliosis correction. PhD Industrial Engineering 17

18 Orthopedic field: porous NiTi Devices for spinal fusion and for lumbar and cervical vertebrae have been developed due to the higher stimulus for bone tissue growth and a bone deposit velocity two orders of magnitude higher than traditional materials (Ti, stainless steels, Cr-Co). PhD Industrial Engineering 18

19 Vascular field The introduction of the shape memory alloys boosted the development of mini-invasive techniques where the pathology is treated by the percutaneous insertion of the device rather than surgical intervention The first vascular SMA application was the venous Simon filter used to prevent emboli in patients unable to tolerate anticoagulants The device is produced in the open configuration with a NiTi alloy having Af equal to the body temperature, which depicts it in the martensitic phase at room temperature PhD Industrial Engineering 19

20 Vascular field Device to close ventricular septal defects as atrial hole between the two low-pressure chambers of the hearth. The surgical method includes an invasive and hazardous approach by thoracotomy and manual suture of the hole. The alternative of using a minimally-invasive approach (SMA wires, impermeable polyurethane membrane) is appealing. Both Superelastic and Shape Memory Effect can be used. PhD Industrial Engineering 20

21 Vascular field: self-expandable stents Stents are metallic nets which open a stenotic vessel (obstructed by atherosclerotic deposits), therefore allowing restoration of the blood stream Carotid Femoral Coronary The advantage of the selfexpandable stent with respect to the stainless steel one is that it does not need balloon expansion which possess the risks of further damage of the vascular tissue due to its inflation Self-expandable stents are used to treat atherosclerotic lesions in the coronary arteries, the carotid arteries, and in the peripheral arteries, such as the iliac and femoral arteries PhD Industrial Engineering 21

22 Vascular field Percutaneous insertion of stent-graft for the treatment of the abdominal aortic aneurism The stentgraft is easily crimpable on a catheter, sufficiently flexible during the insertion phase, and able to recover its original shape anchoring to the aorta once it has been positioned correctly (Superelastic effect) PhD Industrial Engineering 22

23 Vascular field: stenotic and regurgitant cardiac valves 1/2 In the surgical valve replacement with a mechanical or biological valvular prosthesis a thoractomy is present with possible surgical complications. The use of mini-invasive techniques allows the surgeon to reduce the risks of the procedure. Many Companies are developing percutaneous devices to treat mitral, pulmonary, and aortic valvular diseases Corevalve (Aortic): biological prosthesis made with bovine pericardium mounted and sutured on a selfexpandable stent. PhD Industrial Engineering 23

24 Vascular field: stenotic and regurgitant cardiac valves 2/2 Corevalve The stent shape obtained from a laser-cut NiTi tube: the superior part (highly expanded) allows for the anchoring of the prosthesis to the aortic walls; the central portion supports the valves, which in turn determines the diameter; the inferior part anchors the prosthesis to the aortic annulus. PhD Industrial Engineering 24

25 Vascular field: percutaneous aortic valve Prosthesis where the valve is manufactured with 10 μm NiTi membranes and the stent exploits the superelastic properties of the SMA These membranes called enitinol are sufficiently flexible to be used in a semilunar valve The membranes allow long life as a mechanical valve, but without the necessity of anticoagulant therapy PhD Industrial Engineering 25

26 Neurosurgical field: self-expandible stent Stents are also used for the treatment of intracranial atherosclerotic disease. The stent treatment aims to recover the original blood flow where there is a narrowed lumen. The major difficulty of the treatment is allowing the navigation of the system stent + catheter, which is relatively rigid, through tortuous anatomy up to the cerebral vessel. For this reason, SMA self-expandable stents are preferred. PhD Industrial Engineering 26

27 Surgical instruments The ability of SMA to remember highly deformed shapes and the presence of the plateau in the stress-strain curve, which assures a limitation in the force transmitted by the device thereby avoiding excessive damage of the tissues, has allowed the production of effective, mini-invasive surgical instruments, which are useful in many interventional and endoscopic procedures. PhD Industrial Engineering 27

28 Sport: pressure regulator on shock absorber The transitional stages of suspension system behaviour can be managed by SMA component to control shock absorption at a given temperature. PhD Industrial Engineering 28

29 Sport: Inserts The ability of absorption and rebound can be exploited to improve the behaviour at the time of ball bounce. PhD Industrial Engineering 29

30 Sport: Structural elements Superelastic reinforcement can be used to lighten, reliable or simplify the assembly-disassembly. PhD Industrial Engineering 30

31 Sport: Textile - Safety The integration of very thin memory or superelastic wires modifies significantly the behaviour of textile for clothes, shoes or others. PhD Industrial Engineering 31

32 Conclusions There is still a lot of room for new ideas able to enlarge the range of SMA applications or to optimize the existing SMA devices. There are different aspects that can be approached to develop or improve a NiTi medical product: a new design can be studied, a new alloy can be developed (changing the composition of nickel and titanium or alloying the nickel-titanium with other elements), melting practices can be improved, and heat treatment and mechanical processing of the alloy can be optimized. These results underline an important aspect related to biomedical applications of shape memory alloys: the complexity of the material and application requires a strict collaboration between clinicians, engineers, physicists, and chemists for accurately defining the problem, finding the best solution in terms of device design, and, accordingly, optimizing the NiTi alloy properties. PhD Industrial Engineering 32