The first cardiovascular device developed with shape memory was the Simon filter The Simon filter Figure 4 represents a new generation of devices that are used for blood vessel interruption in order to prevent pulmonary embolism. Persons who cannot take anticoagulant medicines are the major users of the Simon filter The purpose of this device is to filter clots that travel inside the bloodstream. The Simon filter traps these clots that in time are dissolved by the bloodstream The insertion of the filter inside the human body is done by exploiting the shape memory effect.
From its original shape in the martensitic state Figure 4 A the filter is deformed and placed on a catheter tip. Saline solution flowing through the catheter is used to keep a low temperature, while the filter is placed inside the body. When the catheter releases the filter, the flow of the saline solution is stopped. As a result, the bloodstream promotes the heating of the filter that returns to its former shape. This procedure can be seen in Figure 4 B The atrial septal occlusion device is employed to seal the atrial hole Figure 5 20, The atrial hole is located between the two upper heart chambers upon the surface that splits the upper part of the heart into the right and left atria.
The anomaly occurring when this hole is open can reduce life expectancy. The traditional surgery that fixes this anomaly is extremely invasive and dangerous.
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The thorax of the patient is opened and the atrial hole is sewn. Because of the intrinsic risks of this surgery, several problems might occur. The atrial septal occlusion device is an alternative to this surgery. This device is composed of SMA wires and a waterproof film of polyurethane As is the case for the Simon filter, the surgery to place this device exploits the shape memory effect, being much less invasive than the traditional one. First, one half of the device is inserted through a catheter by the vena cava up to the heart, in its closed form.
Then, it is placed on the atrial hole and opened, recovering its original shape. Next, the second half of the device is placed by the same route as the first one, and then both halves are connected. This procedure seals the hole, avoiding blood flow from one atrium to the other. It is expected that the device will stay in the heart for an indefinite period of time since the heart tissue regenerates Figure 6 A presents a scheme of the heart with the device in place.
Shape memory alloy engineering : for aerospace, structural and biomedical applications
Self-expanding stents, named after the dentist C. Stent, are another important cardiovascular application that is used to maintain the inner diameter of a blood vessel. Actually, these devices are used in several situations in order to support any tubular passage such as the esophagus and bile duct 27 , and blood vessels such as the coronary, iliac, carotid, aorta and femoral arteries In this type of application, a cylindrical scaffold with shape memory Figure 7 28 is placed, for example, inside a blood vessel through a catheter.
Initially, this scaffold is pre-compressed in its martensitic state. As the scaffold is heated, due to the body temperature, it tends to recover its original shape, expanding itself.
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This device can be used not only in the angioplasty procedure, in order to prevent another obstruction of a vessel, but also in the treatment of aneurysms for the support of a weakened vessel Figure 4. Simon filter. A , Filter in the recovery form. B , Filter release. Taken from Ref. Figure 5. Atrial septal occlusion device.
Figure 6. A , Scheme of the heart with the device in place. B , The first half of the device is placed in the left atrium. C , The second half of the device is placed in the right atrium. D , The catheter is withdrawn and the tissue begins its recovery. Figure 7. Shape memory self-expanding stents.
SMA have a large number of orthopedic applications. The spinal vertebra spacer Figure 8 is one. The insertion of this spacer between two vertebrae assures the local reinforcement of the spinal vertebrae, preventing any traumatic motion during the healing process. The use of a shape memory spacer permits the application of a constant load regardless of the position of the patient, who preserves some degree of motion This device is used in the treatment of scoliosis 2. Figure 8 shows spinal vertebrae and a shape memory spacer. On the left side, the spacer is in the martensitic state, and on the right side, the spacer is in its original shape, recovered by the pseudoelastic phenomenon.
Another application in the orthopedic area is related to the healing process of broken and fractured bones Several types of shape memory orthopedic staples are used to accelerate the healing process of bone fractures, exploiting the shape memory effect. The shape memory staple, in its opened shape, is placed at the site where one desires to rebuild the fractured bone. Through heating, this staple tends to close, compressing the separated part of bones. It should be pointed out that an external device performs this heating, and not the temperature of the body. The force generated by this process accelerates healing, reducing the time of recovery.
Figure 9 presents an application of these staples during the healing process of a patient's foot fracture. With respect to the healing of fractured bones, one can also point out shape memory plates for the recovery of bones These plates are primarily used in situations where a cast cannot be applied to the injured area, i. They are placed on the fracture and fixed with screws, maintaining the original alignment of the bone and allowing cellular regeneration.
Because of the shape memory effect, when heated these plates tend to recover their former shape, exerting a constant force that tends to join parts separated by fractures, helping with the healing process 2. Figure 10 illustrates this device Orthopedic treatment also exploits the properties of SMA in the physiotherapy of semi-standstill muscles. Figure 11 shows gloves that are composed of shape memory wires on regions of the fingers These wires reproduce the activity of hand muscles, promoting the original hand motion.
The two-way shape memory effect is exploited in this situation.
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When the glove is heated, the length of the wires is shortened. On the other hand, when the glove is cooled, the wires return to their former shape, opening the hand. As a result, semi-standstill muscles are exercised. Research for obtaining porous SMA is currently underway. These alloys have a great potential application in orthopedic implants since their porosity enables the transport of body fluids from outside to inside the bone, which is in the healing process. This fact optimizes the treatment and also helps the fixation of the implant Figure 8. Spinal vertebrae A and shape memory spacers B in the martensitic state left and in the original shape right.
Figure 9. A , Orthopedic staples. B , Staples placed in a human foot. C , X-ray of a human foot. Figure Shape memory bone plates. A , Plates fixed upon a human jaw. B , Detail of the plate and the screw. Shape memory alloy glove. A , Low temperature position. B , High temperature position. In recent years, medicine and the medical industry have focused on the concept of less invasive surgical procedures Following this tendency, shape memory surgical instruments have been created and are becoming noticeable.
Among the advantages of these tools, one can emphasize their flexibility as well as their possibility to recover their former shape when heated. The SMA basket is used to remove kidney, bladder and bile duct stones This basket is inserted into the human body in the same way as the Simon filter. Figure 12 presents a sequence of pictures related to the basket opening as it is heated. The intra-aortic balloon pump Figure 13 is used to unblock blood vessels during angioplasty.
The device has an SMA tube whose diameter is reduced compared to polymer materials due to its pseudoelastic effect. Moreover, it also allows greater flexibility and torsion resistance when compared to the same tube made of stainless steel Laparoscopy is another procedure where SMA have been employed.
Figure 14 shows some surgical tools where the actions of grippers, scissors, tongs and other mechanisms are performed by SMA. These devices allow smooth movements tending to mimic the continuous movement of muscles. Moreover, these devices facilitate access to intricate regions. Sequence of opening of the shape memory basket.
Intra-aortic balloon pump. Laparoscopy tools. The actions of grippers, scissors, tongs and other mechanisms are performed by SMA. Applications of SMA to the biomedical field have been successful because of their functional qualities, enhancing both the possibility and the execution of less invasive surgeries. The biocompatibility of these alloys is one of their most important features. Different applications exploit the shape memory effect one-way or two-way and the pseudoelasticity, so that they can be employed in orthopedic and cardiovascular applications, as well as in the manufacture of new surgical tools.
Therefore, one can say that smart materials, especially SMA, are becoming noticeable in the biomedical field.
Probably, the adverse characteristic of biocompatibility of nickel is one of the most critical point concerning the spreading use of Ni-Ti alloys. Shape Memory Alloys, Metals Handbook. ASM International, Ohio, Mantovani D Shape memory alloys: Properties and biomedical applications. Journal of the Minerals, Metals and Materials Society , Recent developments on the research of shape memory alloys.
Intermetallics , 7: Recent development of TiNi-based shape memory alloys in Twain. Materials Chemistry and Physics , Funakubo H Shape Memory Alloys. Shape Memory Applications, Inc. Shape memory materials: state of art and requirements for future applications. Journal de Physique IV , 7: Non-medical applications of shape memory alloys. Materials Science and Engineering A , Schetky LMcD The industrial applications of shape memory alloys in North America. Materials Science Forum , Advanced smart structures flight experiments for precision spacecraft.
Acta Astronautica , Modeling and simulation of a shape memory release device for aerospace applications. Adaptive control of shape memory alloy actuators for underwater biomimetic applications. AIAA Journal , Rogers CA Intelligent materials. Scientific American , September: Birman V Theory and comparison of the effect of composite and shape memory alloy stiffeners on stability of composite shells and plates. Consequently, SMA actuation is typically asymmetric, with a relatively fast actuation time and a slow deactuation time. A number of methods have been proposed to reduce SMA deactivation time, including forced convection,  and lagging the SMA with a conductive material in order to manipulate the heat transfer rate.
Novel methods to enhance the feasibility of SMA actuators include the use of a conductive " lagging ". This heat is then more readily transferred to the environment by convection as the outer radii and heat transfer area are significantly greater than for the bare wire.
Shape Memory Alloys - SMA | ARQUIMEA
This method results in a significant reduction in deactivation time and a symmetric activation profile. As a consequence of the increased heat transfer rate, the required current to achieve a given actuation force is increased. SMA is subject to structural fatigue — a failure mode by which cyclic loading results in the initiation and propagation of a crack that eventually results in catastrophic loss of function by fracture. The physics behind this fatigue mode is accumulation of microstructural damage during cyclic loading.
This failure mode is observed in most engineering materials, not just SMAs. As a result of cyclic loading both mechanical and thermal , the material loses its ability to undergo a reversible phase transformation. For example, the working displacement in an actuator decreases with increasing cycle numbers. The physics behind this is gradual change in microstructure—more specifically, the buildup of accommodation slip dislocations.
This is often accompanied by a significant change in transformation temperatures. SMA actuators are typically actuated electrically by Joule heating. If the SMA is used in an environment where the ambient temperature is uncontrolled, unintentional actuation by ambient heating may occur. Such a variable area fan nozzle VAFN design would allow for quieter and more efficient jet engines in the future.
In and , Boeing conducted successful flight testing of this technology. SMAs are being explored as vibration dampers for launch vehicles and commercial jet engines. The large amount of hysteresis observed during the superelastic effect allow SMAs to dissipate energy and dampen vibrations. These materials show promise for reducing the high vibration loads on payloads during launch as well as on fan blades in commercial jet engines, allowing for more lightweight and efficient designs.
There is also strong interest in using SMAs for a variety of actuator applications in commercial jet engines, which would significantly reduce their weight and boost efficiency. A variety of wing-morphing technologies are also being explored. The Chevrolet Corvette became the first vehicle to incorporate SMA actuators, which replaced heavier motorized actuators to open and close the hatch vent that releases air from the trunk, making it easier to close. A variety of other applications are also being targeted, including electric generators to generate electricity from exhaust heat and on-demand air dams to optimize aerodynamics at various speeds.
There have also been limited studies on using these materials in robotics , for example the hobbyist robot Stiquito and "Roboterfrau Lara"  , as they make it possible to create very lightweight robots. Recently, a prosthetic hand was introduced by Loh et al. Other biomimetic applications are also being explored. Weak points of the technology are energy inefficiency, slow response times , and large hysteresis. SMAs find a variety of applications in civil structures such as bridges and buildings.
These wires can sense cracks and contract to heal micro-sized cracks. Another application is active tuning of structural natural frequency using SMA wires to dampen vibrations. The first consumer commercial application was a shape-memory coupling for piping, e. The second high volume application was an autofocus AF actuator for a smart phone.
There are currently several companies working on an optical image stabilisation OIS module driven by wires made from SMAs [ citation needed ]. Shape-memory alloys are applied in medicine, for example, as fixation devices for osteotomies in orthopaedic surgery , in dental braces to exert constant tooth-moving forces on the teeth, and in Capsule Endoscopy they can be used as a trigger for biopsy action.
The late s saw the commercial introduction of Nitinol as an enabling technology in a number of minimally invasive endovascular medical applications. While more costly than stainless steel, the self expanding properties of Nitinol alloys manufactured to BTR Body Temperature Response , have provided an attractive alternative to balloon expandable devices in stent grafts where it gives the ability to adapt to the shape of certain blood vessels when exposed to body temperature.
These frames are usually made out of shape-memory alloys that have their transition temperature set below the expected room temperature. This allows the frames to undergo large deformation under stress, yet regain their intended shape once the metal is unloaded again. The very large apparently elastic strains are due to the stress-induced martensitic effect, where the crystal structure can transform under loading, allowing the shape to change temporarily under load. This means that eyeglasses made of shape-memory alloys are more robust against being accidentally damaged.
Memory metal has been utilized in orthopedic surgery as a fixation-compression device for osteotomies , typically for lower extremity procedures. The device, usually in the form of a large staple, is stored in a refrigerator in its malleable form and is implanted into pre-drilled holes in the bone across an osteotomy.
As the staple warms it returns to its non-malleable state and compresses the bony surfaces together to promote bone union. The range of applications for SMAs has grown over the years, a major area of development being dentistry. One example is the prevalence of dental braces using SMA technology to exert constant tooth-moving forces on the teeth; the nitinol archwire was developed in by orthodontist George Andreasen. Andreasen's alloy has a patterned shape memory, expanding and contracting within given temperature ranges because of its geometric programming.
Harmeet D. Walia later utilized the alloy in the manufacture of root canal files for endodontics. Traditional active cancellation techniques for tremor reduction use electrical, hydraulic, or pneumatic systems to actuate an object in the direction opposite to the disturbance. However, these systems are limited due to the large infrastructure required to produce large amplitudes of power at human tremor frequencies.
SMAs have proven to be an effective method of actuation in hand-held applications, and have enabled a new class active tremor cancellation devices. Experimental solid state heat engines, operating from the relatively small temperature differences in cold and hot water reservoirs, have been developed since the s, including the Banks Engine, developed by Ridgway Banks. German scientists at Saarland University have produced a prototype machine that transfers heat using a nickel-titanium "nitinol" alloy wire wrapped around a rotating cylinder.
As the cylinder rotates, heat is absorbed on one side and released on the other, as the wire changes from its "superelastic" state to its unloaded state. According to a recent article released by Saarland University, the efficiency by which the heat is transferred appears to be higher than that of a typical heat pump or air conditioner. Almost all air conditioners and heat pumps in use today employ vapor-compression of refrigerants. Over time, some of the refrigerants used in these systems leak into the atmosphere and contribute to global warming.
If the new technology, which uses no refrigerants, proves economical and practical, it might offer a significant breakthrough in the effort to reduce climate change. A variety of alloys exhibit the shape-memory effect. Alloying constituents can be adjusted to control the transformation temperatures of the SMA. Some common systems include the following by no means an exhaustive list :. Media related to Memory effect at Wikimedia Commons.
From Wikipedia, the free encyclopedia. Please add a reason or a talk parameter to this template to explain the issue with the section. February Play media. Applying a stress to detwin the martensite. Heating the martensite to reform austenite, restoring the original shape. Cooling the austenite back to twinned martensite. This section needs attention from an expert in Medicine.
WikiProject Medicine may be able to help recruit an expert. Bibcode : JOM Le Journal de Physique IV. ASM International. Metal Science and Heat Treatment. Bibcode : MSHT Periodica Polytechnica Ser Mech Eng. Otsuka; C. Wayman, eds. Cambridge University Press. Collings eds.
Materials Properties Handbook: Titanium Alloys. American Society for Metals. Scripta Metallurgica et Materialia. Mechanical behavior of materials 2nd ed. Boston: McGraw Hill. July Progress in Materials Science. Retrieved Retrieved on Bibcode : Natur. Mathematical Problems in Engineering.
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