Medical applications of shape memory alloys - SciELO · Medical applications of shape memory alloys ... SMA can be used in a large number of non-medical applications ... the biomedical

683

Braz J Med Biol Res 36(6) 2003

Medical applications of shape memory alloys

Medical applications of shapememory alloys

1Departamento de Engenharia Mecânica e de Materiais,Instituto Militar de Engenharia, Rio de Janeiro, RJ, Brasil2Departamento de Engenharia Mecânica, COPPE,Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, Brasil

L.G. Machado1

and M.A. Savi2

Abstract

Shape memory alloys (SMA) are materials that have the ability toreturn to a former shape when subjected to an appropriate thermome-chanical procedure. Pseudoelastic and shape memory effects are someof the behaviors presented by these alloys. The unique propertiesconcerning these alloys have encouraged many investigators to lookfor applications of SMA in different fields of human knowledge. Thepurpose of this review article is to present a brief discussion of thethermomechanical behavior of SMA and to describe their most prom-ising applications in the biomedical area. These include cardiovascu-lar and orthopedic uses, and surgical instruments.

CorrespondenceM.A. Savi

Departamento de EngenhariaMecânica

COPPE, UFRJ

Caixa Postal 68.503

21945-970 Rio de Janeiro, RJ

Brasil

E-mail: [email protected]

Research supported by CNPq.

Received July 3, 2002

Accepted December 4, 2002

Key words• Shape memory alloys• Biomaterials

Introduction

Shape memory alloys (SMA) constitute agroup of metallic materials with the ability torecover a previously defined length or a shapewhen subjected to an appropriate thermome-chanical load (1). When there is a limitationof shape recovery, these alloys promote highrestitution forces. Because of these proper-ties, there is a great technological interest inthe use of SMA for different applications.

Although a relatively wide variety of al-loys present the shape memory effect, onlythose that can recover from a large amount ofstrain or generate an expressive restitutionforce are of commercial interest. Particularlyimportant among them are alloys based onNi-Ti and on Cu, such as Cu-Zn-Al and Cu-Al-Ni (1). SMA based on Ni-Ti are the alloysmost frequently used in commercial applica-tions because they combine good mechani-

cal properties with shape memory.The remarkable properties of SMA have

been known since the 1930’s. In 1932, Changand Read noted the reversibility of the Au-Cd alloy not only by metallographic observa-tions, but also by the observation of changesin resistivity. In 1938, Greninger andMooradian observed the shape memory ef-fect in Cu-Zn and Cu-Sn alloys. Neverthe-less, it was only in the 1960’s that SMAattracted some technological interest. In 1962,Buehler and co-workers, of the U.S. NavalOrdnance Laboratory, discovered the shapememory effect in an equiatomic Ni-Ti alloywhich began to be known as Nitinol, as areference to the initials of the laboratory.Raychem developed the first industrial ap-plication of SMA for the aeronautic industryduring the 1960’s. In 1975, Andreasen, ofIowa University, made the first implant of asuperelastic orthodontic device (1,2). To-

Brazilian Journal of Medical and Biological Research (2003) 36: 683-691ISSN 0100-879X Review

684


L.G. Machado and M.A. Savi

day, these applications are being developedin different fields of science and engineering.

Basically, SMA present two well-definedcrystallographic phases, i.e., austenite andmartensite (3). Martensite is a phase that, inthe absence of stress, is stable only at lowtemperatures; in addition, it can be inducedby either stress or temperature. Martensite iseasily deformed, reaching large strains (~8%)(1). Depending on the type of transformationexperienced by these alloys, the crystal struc-ture of martensite can be either monoclinicor orthorhombic (4,5). When martensite isinduced by temperature, it is called twinnedmartensite. The twinned martensite has 24variants, i.e., 24 subtypes with different crys-tallographic orientations (6). On the otherhand, when martensite is induced by stress,these 24 variants of twinned martensite be-come only one variant. As a consequence,there is a crystallographic orientation, alignedwith the stress direction, which is calleddetwinned martensite. The austenite phase isstable only at high temperatures, having asingle variant with a body-centered cubiccrystal structure.

Martensitic transformation explains theshape recovery in SMA. This transformationoccurs within a range of temperatures whichvaries according to the chemical content ofeach alloy (7). In general, four characteristictransformation temperatures can be defined:MS and MF, which are the temperatures atwhich the formation of martensite starts andends, respectively, and AS and AF, which arethe temperatures at which the formation ofaustenite starts and ends, respectively.

Recent studies have shown that, depend-ing on specific conditions, some SMA canpresent another crystallographic phase knownas R-phase. The R-phase transformation canappear before the martensitic transformationaccording to the following sequence: austenite→ R-phase → martensite. The crystal struc-ture of the R-phase is rhombohedric (4,5).

Because of their remarkable properties,SMA can be used in a large number of non-

medical applications (8-10). SMA can solveproblems in the aerospace industry, espe-cially those related to vibration control ofslender structures and solar panels, and non-explosive release devices (11,12). Microma-nipulators and robotic actuators have beenemployed in order to mimic the smooth move-ment of human muscles (13,14). SMA arecommonly used as external actuators or asSMA fibers embedded in a composite matrixso that they can alter the mechanical proper-ties of slender structures for the control ofbuckling and vibration (15).

Biomedical applications of SMA havebeen extremely successful because of thefunctional properties of these alloys, increas-ing both the possibility and the performanceof minimally invasive surgeries (2,16,17).The biocompatibility of these alloys is oneof the important points related to their bio-medical applications as orthopedic implants(18), cardiovascular devices (2), and surgi-cal instruments (16), as well as orthodonticdevices and endodontic files (19-21).

This article presents a brief discussion ofthe thermomechanical behavior of SMA, anda description of their main applications inthe biomedical field as cardiovascular andorthopedic devices and as surgical instru-ments.

Thermomechanical behavior

SMA present typical thermomechanicalbehaviors, like pseudoelasticity and shapememory effects (one-way and two-way). Thissection presents a short discussion of thesebehaviors, explaining the macroscopic phe-nomenological aspects related to each one(22).

Pseudoelasticity

Pseudoelasticity occurs whenever anSMA sample is at a temperature above AF(the temperature above which only the aus-tenitic phase is stable for a stress-free speci-

685



men). Thus, one can consider an SMA samplesubjected to a mechanical loading at a con-stant temperature above AF. The stress-straincurve (σ-ε) in Figure 1, left side, illustratesthe macroscopic behavior of SMA, showingthe pseudoelastic phenomenon.

A mechanical loading causes an elasticresponse until a critical value is reached,point A, when the martensitic transformation(austenite → martensite) arises, ending atpoint B. At this point, the crystal structure ofthe sample is totally composed of detwinnedmartensite. For higher stress values, SMApresents a linear response. During the un-loading process, the sample presents an elas-tic recovery (B → C). From point C to D onecan note the reverse martensitic transforma-tion (martensite → austenite). From point Don, the sample presents an elastic discharge.When the loading-unloading process is fin-ished, SMA have no residual strain. How-ever, since the path of the forward martensi-tic transformation does not coincide with thereverse transformation path, there is a hys-teresis loop associated with energy dissipa-tion.

Another way to observe the pseudoelasticeffect is indicated on the right side of Figure1. First, let us consider an SMA at a temper-ature above AF, . At this temperature, thereis only one phase, i.e., austenite. At a con-stant temperature, a mechanical loading isapplied promoting the appearance of thedetwinned martensite, . During the un-loading process, reverse transformation takesplace (detwinned martensite → austenite)and when load vanishes, , the sample pre-sents no residual strain.

Shape memory effect

The second thermomechanical behaviorthat can be observed in SMA is the shapememory effect. Figure 2, left side, shows thestress-strain curve of an SMA sample at alow temperature (less than MF, the tempera-ture below which only the martensitic phase

is stable) where the shape memory effect canbe noted. When the sample is subjected to amechanical loading, the stress reaches a criti-cal value, point A, when the transformationof the twinned martensite into the detwinnedmartensite begins, ending at point B. Whenthe loading-unloading process is finished,the SMA sample presents a residual strain(point C). This residual strain can be recov-ered by sample heating, which induces thereverse phase transformation. This is theshape memory effect, also known as one-way shape memory effect. This phenome-non can be understood from a motion of thehysteresis loop shown on the stress-straincurve in Figure 1. Since the temperaturegoes down, the hysteresis loop moves downas well.

The right side of Figure 2 presents analternative way to observe the shape memoryeffect. At first, the SMA sample is at atemperature above AF, . At this tempera-ture, the sample has only the austenitic phase.When the temperature of the SMA sample

σ

ε0

AB

C

AF

AS

MS

MFTem

pera

ture

1

32

4

Figure 2. Shape memory effect. For abbreviations, see legend to Figure 1. See text forexplanation of process.

σ

σ

ε0

A B

C

D

AF

AS

MS

MFTem

pera

ture

1

3

2σ

Figure 1. Pseudoelasticity. AS, AF and MS and MF = temperature at which the formation ofaustenite and martensite starts and ends, respectively. σ-ε = stress-strain curve. See textfor explanation of process.

686



decreases and crosses the line related to MS,the phase transformation begins to take placeand the twinned martensite replaces the aus-tenite. This transformation is concluded whenthe sample temperature is below MF, .Under a constant temperature, a mechanicalloading is applied ( → ), promoting theappearance of the detwinned martensite.When this load vanishes the sample presentsa residual strain, . The former shape of thesample can be recovered through a heatingprocess ( → ) which causes the reversemartensitic transformation (detwinned mar-tensite → austenite).

Two-way shape memory effect

Another phenomenon concerning mar-tensitic transformation is the two-way shapememory effect. The primary characteristicof the two-way effect is associated with thepresence of a specific phase in a specificsetting. In this way, the sample has a shape inthe austenitic state and another in the mar-tensitic state. The change of temperatureproduces a change in sample shape withoutany mechanical loading.

In order to obtain the two-way effect, it isnecessary that the SMA sample be trained.Typically, there are two training procedures(23): shape memory effect cycling (cycles ofshape memory effect) and the training throughthe appearance of the detwinned martensite,the stress-induced martensite training. Bothinduce considerable plastic strains.

Figure 3 shows a schematic presentationof the two-way effect. First of all, let usconsider that a trained SMA sample is at a

temperature above AF, . Sample coolingpromotes a phase change (austenite → mar-tensite), which leads to a change in shape,

. When the temperature is increased aboveAF, the sample experiences another phasetransformation ( → ), recovering its ori-ginal shape, . Another cooling returns thesample to its low temperature shape, . Itshould be pointed out that, in contrast to theone-way shape memory effect, it is not nec-essary to apply mechanical loading in orderto alter the sample’s shape at low tempera-ture.

Biocompatibility of shape memoryalloys - Ni-Ti

Biocompatibility is the ability of a mate-rial to remain biologically innocuous duringits functional period inside a living creature(24). This is a crucial factor for the use ofSMA devices in the human body (25). Abiocompatible material does not produce al-lergic reactions inside the host, and also doesnot release ions into the bloodstream. Theperiod during which a biomaterial remainsinside the human body is an important aspectto be considered concerning its use.

Generally, the biocompatibility of a ma-terial is strongly related to allergic reactionsbetween the material surface and the inflam-matory response of the host. Several aspectscan contribute to these reactions such aspatient’s characteristics (health, age, immu-nological state, and so on), and materialcharacteristics (rugosity and porosity of thesurface and individual toxic effects of theelements present in the material) (25).

Several investigations have been con-ducted in order to establish the biocompati-bility of Ni-Ti-based alloys, and to excludeintrinsic hazards involved in their applica-tions (24,25). The analysis of aspects relatedto the biocompatibility of these alloys isperformed by assessing each of their ele-ments, nickel and titanium, separately.

Nickel, although necessary to life, is a

AF

AS

MS

MFTem

pera

ture

1 3

2 4

Figure 3. Two-way shapememory effect. For abbrevia-tions, see legend to Figure 1.See text for explanation of pro-cess.

687



highly poisonous element (2). Studies haveshown that persons having systematic con-tact with nickel present problems such aspneumonia, chronic sinusitis and rhinitis,nostril and lung cancer, as well as dermatitiscaused by physical contact.

Unlike nickel, titanium and its compoundsare highly biocompatible; moreover, due totheir mechanical properties, they are usuallyemployed in orthodontic and orthopedic im-plants (2). The oxidation reaction of tita-nium produces an innocuous layer of TiO2which surrounds the sample. This layer isresponsible for the high resistance to corro-sion of titanium alloys, and the fact that theyare harmless to the human body.

Inquiries concerning the biocompatibili-ty of Ni-Ti alloys began shortly after theirdiscovery in 1968. Corrosion analyses haveshown that this alloy is easily changed to thepassive condition in physiological solutions;moreover, its corrosion resistance is greaterthan that of stainless steel (24). In general,one can say that the properties of titaniumconfer good biocompatibility to Ni-Ti al-loys.

Applications of shape memory alloys

As mentioned earlier, the remarkableproperties of SMA have promoted severalinvestigations related to their applications indifferent fields of human knowledge. In thissection we present a discussion of the bio-medical applications of SMA. Cardiovascu-lar applications are presented first, followedby orthopedic applications and the use ofSMA in surgical instruments.

Cardiovascular applications

The first cardiovascular device devel-oped with shape memory was the Simonfilter (25). The Simon filter (Figure 4) repre-sents a new generation of devices that areused for blood vessel interruption in order toprevent pulmonary embolism. Persons who

cannot take anticoagulant medicines are themajor users of the Simon filter (26). Thepurpose of this device is to filter clots thattravel inside the bloodstream. The Simonfilter traps these clots that in time are dis-solved by the bloodstream (16). The inser-tion of the filter inside the human body isdone by exploiting the shape memory effect.From its original shape in the martensiticstate (Figure 4A) the filter is deformed andplaced on a catheter tip. Saline solution flow-ing through the catheter is used to keep a lowtemperature, while the filter is placed insidethe body. When the catheter releases thefilter, the flow of the saline solution isstopped. As a result, the bloodstream pro-motes the heating of the filter that returns toits former shape. This procedure can be seenin Figure 4B (16).

The atrial septal occlusion device is em-ployed to seal the atrial hole (Figure 5)(20,26). The atrial hole is located betweenthe two upper heart chambers upon the sur-face that splits the upper part of the heart intothe right and left atria. The anomaly occur-ring when this hole is open can reduce life

1 2 3 4 5

Figure 4. Simon filter. A, Filter in the recovery form. B, Filter release. Taken from Ref. 26(http://www.nmtmedical.com).

A B

Figure 5. Atrial septal occlusion device. Taken from Ref. 26 (http://www.nmtmedical.com).

688



Rightatrium

Catheter

Vein

Septum

Leftatrium

Valve

Septum

PFO

Catheter

Tissue

1

3

B

A

2

CardioSEAL

expectancy. The traditional surgery that fixesthis anomaly is extremely invasive and dan-gerous. The thorax of the patient is openedand the atrial hole is sewn. Because of theintrinsic risks of this surgery, several prob-lems might occur. The atrial septal occlusiondevice is an alternative to this surgery. Thisdevice is composed of SMA wires and awaterproof film of polyurethane (16). As isthe case for the Simon filter, the surgery toplace this device exploits the shape memoryeffect, being much less invasive than thetraditional one. First, one half of the device

is inserted through a catheter by the venacava up to the heart, in its closed form. Then,it is placed on the atrial hole and opened,recovering its original shape. Next, the sec-ond half of the device is placed by the sameroute as the first one, and then both halvesare connected. This procedure seals the hole,avoiding blood flow from one atrium to theother. It is expected that the device will stayin the heart for an indefinite period of timesince the heart tissue regenerates (26). Fig-ure 6A presents a scheme of the heart withthe device in place.

Self-expanding stents, named after thedentist C.T. Stent, are another important car-diovascular application that is used to main-tain the inner diameter of a blood vessel.Actually, these devices are used in severalsituations in order to support any tubularpassage such as the esophagus and bile duct(27), and blood vessels such as the coronary,iliac, carotid, aorta and femoral arteries (16).In this type of application, a cylindrical scaf-fold with shape memory (Figure 7) (28) isplaced, for example, inside a blood vesselthrough a catheter. Initially, this scaffold ispre-compressed in its martensitic state. Asthe scaffold is heated, due to the body tem-perature, it tends to recover its original shape,expanding itself. This device can be used notonly in the angioplasty procedure, in order toprevent another obstruction of a vessel, butalso in the treatment of aneurysms for thesupport of a weakened vessel (16).

Orthopedic applications

SMA have a large number of orthopedicapplications. The spinal vertebra spacer (Fig-ure 8) is one. The insertion of this spacerbetween two vertebrae assures the local rein-forcement of the spinal vertebrae, prevent-ing any traumatic motion during the healingprocess. The use of a shape memory spacerpermits the application of a constant loadregardless of the position of the patient, whopreserves some degree of motion (29). This

Figure 6. Atrial septal occlusion device. 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 isplaced in the right atrium. D, The catheter is withdrawn and the tissue begins its recovery.PFO = patent foramen ovale. Taken from Ref. 26 (http://www.nmtmedical.com).

Figure 7. Shape memory self-ex-panding stents. Taken from Ref.28 (http://www.raychem.com).

C D

689



device is used in the treatment of scoliosis(2). Figure 8 shows spinal vertebrae and ashape memory spacer. On the left side, thespacer is in the martensitic state, and on theright side, the spacer is in its original shape,recovered by the pseudoelastic phenomenon.

Another application in the orthopedic areais related to the healing process of brokenand fractured bones (30). Several types ofshape memory orthopedic staples are used toaccelerate the healing process of bone frac-tures, exploiting the shape memory effect.The shape memory staple, in its opened shape,is placed at the site where one desires torebuild the fractured bone. Through heating,this staple tends to close, compressing theseparated part of bones. It should be pointedout that an external device performs thisheating, and not the temperature of the body.The force generated by this process acceler-ates healing, reducing the time of recovery.Figure 9 presents an application of thesestaples during the healing process of apatient’s foot fracture.

With respect to the healing of fracturedbones, one can also point out shape memoryplates for the recovery of bones (31). Theseplates are primarily used in situations wherea cast cannot be applied to the injured area,i.e., facial areas, nose, jaw and eye socket.They are placed on the fracture and fixedwith screws, maintaining the original align-ment of the bone and allowing cellular re-generation. Because of the shape memoryeffect, when heated these plates tend to re-cover their former shape, exerting a constantforce that tends to join parts separated byfractures, helping with the healing process(2). Figure 10 illustrates this device (31).

Orthopedic treatment also exploits theproperties of SMA in the physiotherapy ofsemi-standstill muscles. Figure 11 showsgloves that are composed of shape memorywires on regions of the fingers (32). Thesewires reproduce the activity of hand muscles,promoting the original hand motion. Thetwo-way shape memory effect is exploited in

Figure 11. Shape memory alloy glove. A, Low temperature position. B, High temperatureposition. Taken from Ref. 32 (http://www.amtbe.com).

A B

Ventral view

Atlas (C1)Axis (C2)

Left lateralview

Dorsal view

Atlas (C1)Axis (C2)

Thoracicvertebrae

C7T1

Sacrum(S1-5)

Coccyx

Sacrum(S1-5)

T12

L1

L5L5

T12

T1C7

L1

Atlas (C1)Axis (C2)

Sacrum(S1-5)

CoccyxCoccyx

T1C7

T12L1

L5

Cervicalvertebrae

Lumbarvertebrae

Figure 8. Spinal vertebrae (A) and shape memory spacers (B) in the martensitic state (left)and in the original shape (right). Taken from Ref. 20 with permission.

A

A

B

Figure 10. Shape memory bone plates. A, Plates fixed upon a human jaw. B, Detail of theplate and the screw. Taken from Ref. 31 (http://database.cs.ualberta.ca/MEMS/sma_mems).

Four-hole, 2-mm miniplate Miniscrew, 2 mm

A B

Figure 9. A, Orthopedic staples. B, Staples placed in a human foot. C, X-ray of a human foot.Taken from Ref. 30 (http://www.labosite.com/anglais/pages/summary.html).

A B C

690



this situation. When the glove is heated, thelength of the wires is shortened. On the otherhand, when the glove is cooled, the wiresreturn to their former shape, opening thehand. As a result, semi-standstill muscles areexercised.

Research for obtaining porous SMA is

currently underway. These alloys have a greatpotential application in orthopedic implantssince their porosity enables the transport ofbody fluids from outside to inside the bone,which is in the healing process. This factoptimizes the treatment and also helps thefixation of the implant (33).

Applications to surgical instruments

In recent years, medicine and the medicalindustry have focused on the concept of lessinvasive surgical procedures (29). Follow-ing this tendency, shape memory surgicalinstruments have been created and are be-coming noticeable. Among the advantagesof these tools, one can emphasize their flex-ibility as well as their possibility to recovertheir former shape when heated.

The SMA basket is used to remove kid-ney, bladder and bile duct stones (20). Thisbasket is inserted into the human body in thesame way as the Simon filter. Figure 12presents a sequence of pictures related to thebasket opening as it is heated.

The intra-aortic balloon pump (Figure13) is used to unblock blood vessels duringangioplasty. The device has an SMA tubewhose diameter is reduced compared to poly-mer materials due to its pseudoelastic effect.Moreover, it also allows greater flexibilityand torsion resistance when compared to thesame tube made of stainless steel (16).

Laparoscopy is another procedure whereSMA have been employed. Figure 14 showssome surgical tools where the actions ofgrippers, scissors, tongs and other mechan-isms are performed by SMA. These devicesallow smooth movements tending to mimicthe continuous movement of muscles. More-over, these devices facilitate access to intri-cate regions.

Final remarks

Applications of SMA to the biomedicalfield have been successful because of their

Figure 12. Sequence of opening of the shape memory basket. Taken from Ref. 34 (http://smet.tomsk.ru/eng/prod.htm).

Figure 13. Intra-aortic balloonpump. Taken from Ref. 16 withpermission.

Figure 14. Laparoscopy tools.The actions of grippers, scissors,tongs and other mechanisms areperformed by SMA. Taken fromRef. 16 with permission.

691



functional qualities, enhancing both the pos-sibility and the execution of less invasivesurgeries. The biocompatibility of these al-loys is one of their most important features.Different applications exploit the shapememory effect (one-way or two-way) andthe pseudoelasticity, so that they can be em-ployed in orthopedic and cardiovascular ap-

plications, as well as in the manufacture ofnew surgical tools. Therefore, one can saythat smart materials, especially SMA, arebecoming noticeable in the biomedical field.Probably, the adverse characteristic of bio-compatibility of nickel is one of the mostcritical point concerning the spreading useof Ni-Ti alloys.

References

1. Hodgson DE, Wu MH & Biermann RJ (1990). Shape Memory Alloys,Metals Handbook. Vol. 2. ASM International, Ohio, 897-902.

2. Mantovani D (2000). Shape memory alloys: Properties and biomedi-cal applications. Journal of the Minerals, Metals and Materials Socie-ty, 52: 36-44.

3. Shape Memory Alloy Research Team (Smart) (2001). http://smart.tamu.edu

4. Otsuka K & Ren X (1999). Recent developments on the research ofshape memory alloys. Intermetallics, 7: 511-528.

5. Wu SK & Lin HC (2000). Recent development of TiNi-based shapememory alloys in Twain. Materials Chemistry and Physics, 64: 81-92.

6. Funakubo H (1987). Shape Memory Alloys. Gordon & Bleach, NewYork, NY, USA.

7. Shape Memory Applications, Inc. (2001). http://www.sma-inc.com8. van Humbeeck J (1997). Shape memory materials: state of art and

requirements for future applications. Journal de Physique IV, 7: 3-12.

9. van Humbeeck J (1999). Non-medical applications of shape memoryalloys. Materials Science and Engineering A, 273-275: 134-148.

10. Schetky LMcD (2000). The industrial applications of shape memoryalloys in North America. Materials Science Forum, 327-328: 9-16.

11. Denoyer KK, Erwin RS & Ninneman RR (2000). Advanced smartstructures flight experiments for precision spacecraft. ActaAstronautica, 47: 389-397.

12. Pacheco PMCL & Savi MA (2000). Modeling and simulation of ashape memory release device for aerospace applications. Revista deEngenharia e Ciências Aplicadas.

13. Webb G, Wilson L, Lagoudas DC & Rediniotis O (2000). Adaptivecontrol of shape memory alloy actuators for underwater biomimeticapplications. AIAA Journal, 38: 325-334.

14. Rogers CA (1995). Intelligent materials. Scientific American, Sep-tember: 122-127.

15. Birman V (1997). Theory and comparison of the effect of compositeand shape memory alloy stiffeners on stability of composite shellsand plates. International Journal of Mechanical Sciences, 39: 1139-1149.

16. Duerig TM, Pelton A & Stöckel D (1999). An overview of nitinolmedical applications. Materials Science and Engineering A, 273-275:149-160.

17. Pelton AR, Stöckel D & Duerig TW (2000). Medical uses of nitinol.Materials Science Forum, 327-328: 63-70.

18. Chu Y, Dai K, Zhu M & Mi X (2000). Medical application of NiTi shapememory alloy in China. Materials Science Forum, 327-328: 55-62.

19. Airoldi G & Riva G (1996). Innovative materials: The NiTi alloys inorthodontics. Bio-Medical Materials and Engineering, 6: 299-305.

20. Lagoudas DC, Rediniotis OK & Khan MM (1999). Applications ofshape memory alloys to bioengineering and biomedical technology.Proceedings of the 4th International Workshop on MathematicalMethods in Scattering Theory and Biomedical Technology, Perdika,Greece, October 8-10, 1999.

21. Jordan L, Goubaa K, Masse M & Bouquet G (1991). Comparativestudy of mechanical properties of various Ni-Ti based shape memoryalloys in view of dental and medical applications. Journal de Phy-sique IV, 1: 139-144.

22. Savi MA, Paiva A, Baêta-Neves AP & Pacheco PMCL (2002). Phe-nomenological modeling and numerical simulation of shape memoryalloys: A thermo-plastic-phase transformation coupled model. Jour-nal of Intelligent Material Systems and Structures, 13: 261-273.

23. Zhang XD, Rogers CA & Liang C (1992). Modeling of the two-wayshape memory effect. Philosophical Magazine A, 65: 1199-1215.

24. Shabalovskaya SA (1995). Biological aspects of TiNi alloys surfaces.Journal de Physique IV, 5: 1199-1204.

25. Ryhänen J (1999). Biocompatibility evolution of nickel-titanium shapememory alloy. Academic Dissertation, Faculty of Medicine, Univer-sity of Oulu, Oulu, Finland.

26. NMT Medical, Inc. (2001). http://www.nmtmedical.com27. Medical Devicelink (2001). http://www.devicelink.com28. Raychem (2001). http://www.raychem.com29. Duerig TM, Pelton A & Stöckel D (1996). The use of superelasticity

in medicine. Metall, 50: 569-574.30. TECHNOSITE MEDICAL (2001). http://www.labosite.com/anglais/

pages/summary.html31. SMA/MEMS Research Group (2001). http://database.cs.ualberta.ca/

MEMS/sma_mems32. @medical technologies (2001). http://www.amtbe.com33. Li B, Rong L, Li Y & Gjunter VE (2000). A recent development in

producing porous NiTi shape memory alloys. Intermetallics, 8: 881-884.

34. SMET (2001). http://smet.tomsk.ru/eng/prod.htm

Documents

Medical applications of shape memory alloys - SciELO · Medical applications of shape memory alloys ... SMA can be used in a large number of non-medical applications ... the biomedical