Shape Memory Alloys Manufacturing Processes

condition stock Alloys Manufacturing ProcessesSmart poppycocks reach been champion of the fastest growing cloths indispensable for health check device manufacturing. Smart materials, correspond to the McGraw-Hill Dictionary of Scientific Technical Terms, ar defined as Materials that behind importantly change their mechanical properties ( such(prenominal) as model, stiffness, and viscosity), or their thermal, optical, or electromagnetic properties, in a predictable or controlresearch laboratoryle manner in response to their environment. It is this property of changing according to its material that makes smart materials very valuable in manufacturing today. Perhaps one of the almost practice sessionful smart materials comes in the var. of reposition chassis perverts, specifically nitinol. remembrance board fabricate alloys con shew many applications in medical exam exam examination devices employ today. They argon mellowedly prized for their exceptional su perelasticity, their compel reminiscence, their strong vindication to fatigue and wear, and their relatively good biocompatibility. This makes them the perfect candidate for many in-vivo medical devices.OriginThe shape- holding make was first observed in copper-zinc and copper-tin alloys by Greninger and Mooradian in 1938, hardly it was whole in the early 1960s that Buehler and his colleagues discovered and secure nitinol, a atomic number 28- atomic weigh 22 alloy created in the Naval Ordnance Laboratory (NOL). This lab was formerly located in White Oak, Maryland and was the site of grand work that has had useful impact upon world technology. The White Oak site of NOL has now been taken over by the Food and Drug formation but has appease left its legacy in the name nitinol ( atomic number 28 + titanium + NOL- the initials of the Naval Ordinance Laboratory) (Gautam, et al. 2008). Their smart metal alloy, that, is 55% nickel by weight and may thus grow allergic, toxic , or carcinogenic effects. For short use, in-vitro and clinical data strongly support nitinol as a well(p) biomaterial which is at least as good as guilt little poise or titanium alloys also visible(prenominal) to designers. medical exam Applications of Shape Memory AlloysMuscles be the power of the consistence, used to turn energy into movement and motion. Shape memory alloys can be used to in their solid-state leg to make devices from muscle wires.Applications of shape memory alloys in the medical firmament argon numerous. Their flexibility at one temperature and one way shape memory effect when heated to their transformation temperature make these alloys key materials for conglomerate medical methods. The in business leader of shape memory materials to combine to early(a) metals requires some(prenominal) adaptation to be developed. A common material for this is nickel-titanium. Nickel-titanium has an excellent tortuousness transfer characteristic which is just one of the many reasons this material is used for fabricating medical equipment (Yoshida, et al. 2010). A few notable applications be catheters, medical excrete wires, bone plates and stents. Bone plates comprised of shape memory alloys, assist in repairing at sea bones by making use of the bodys natural temperature to contract and apply pressure for proper healing. (Georgia Inst. Of Tech, 2007)CathetersCatheters be used in a number of procedures such as therapeutics, diagnostics, and ablative procedures. Used in the medical range for administration of fluids, drainage, and provide a method to insert surgical instruments, catheters are tubes that can be regulated in a body cavity, vessel, or duct. In the case of blood vessels, the catheter must move around the caisson disease and angles to reach the desired destination. Stiff materials would not be flexible braggy for this procedure and may cause a rupture in the vessel. payable to heat restrictions and adventure of damage, on ly specific shape memory alloys can be used for many of these delicate processes. A solution for this enigma is provided by the R-phase transformation, which is a specific type of martensite transformation that occurs in veritable nickel- generative Ni-Ti alloys (Langelaar, et al. 2010). Travelling through the vessels is a difficult task, so a focus mechanism is implemented into a catheter to maneuver throughout the body.Currently catheters are equipped with integrated micro-actuators that allow controlled bending, which yields enhanced maneuverability compared to conventional catheters. Actuators inhabit of guide wires that bend when energy runs through them such as an voltaic occurrent that heat the shape memory material. The simplistic designs of the actuator allows for high strains and stresses emergencyed for a process. There are few actuating mechanisms which produce more than than useful work per unit volume than nitinol (Williams, et al. 1999). Guiding wires also cognise as pull wires or shaping wires, are located on the tube to allow for motion in many directions.Above This demonstrates that shape memory alloys are more effective in actuators than many of the current materials on the market. Guide wires provide flexibility, shape memory, and pseudoelasticity. When a grander stiffness is required, the thickness of the wire may be increased to meet performance standards. Shape memory alloys allow for the catheter to return to its original geometry when the tension in the wire is removed. One adaptation formed due to the lack of metallurgical joining is a stainless stigma sleeve, known as a crimp sleeve, to hold the wires to the catheter (Stoeckel, 2010). The sleeve brings up the problem of increasing the diam of the catheter. To prevent breakage in a material, more flexibility and ductileness is ideal. In medical applications, nitinol has higher ductility allowing more plastic twisting without fracturing due to the temperature of the serviceman body.At body temperature (310K), nitinol result have a high percentage of strain at low stress moment more ductility.StentsOne of the outsizest medical uses for shape memory alloys is in stents. A stent is a tube that is inserted into an artery to hold it open. Stents are needed when the walls of the artery are not strong enough to remain open and need support to ensure that blood is able to flow. The stent is put in place during a procedure called an angioplasty (Stent Facts, 2010). In order to get the stent into the artery, it ineluctably to be collapsed and inserted into a catheter. Shape memory alloys allow doctors to collapse the stent to a much littler diameter, and have it return to its original shape after passing the catheter inside the artery. The original use of shape memory alloys in stents was in the form of a simple roster. The bowl was tightly wound in the catheter and past expanded at a quantify it was inserted into the artery and warmed. The ex panded size of the coil is chosen to be slightly larger than the inner diameter of the aspire vessel, which means the coil will not be able to richly expand inside the artery. The shape memory alloy, in its warmed state, will continue to attempt to expand, which will put a continuous external pressure on the walls of the artery. This will ensure that the artery remains open. In more recent times, simple coil stents are used more for non-vascular applications such as preventing bladder obstruction. The simple coil stents that are unruffled in use today are used in vascular cases where easy retrieval is required. The shape memory alloy allows the stent to hold its form in the body, but still be easy to deform covering to a straight wire for removal (Sutou, et al. 2006).More modern shape memory alloy stents are made in forms early(a) than a coil. The shape memory alloy can be formed into a braided or knitted coil. The downside of this is that the points where the wires cross for m thicker walls, which are unwanted in a stent. Although the braided and knitted shape memory alloy stents were a step up in functionality from the simple coils, the thicker walls made them unsuitable for many cases. The next level of shape memory alloy stents occurred once scientists determined how to make the alloys in flat sheets rather than just wire. laser cutting a pattern into a flat sheet of the alloy, then rolling and welding it at various points creates a stent with no coincide wires at the walls. Sheet mode stents are thin, but also structurally supportive when heated to body temperature. This gives them more flexibility than the simple coil models and is a better use of the shape memory alloys characteristics (Sutou, et al. 2006).An older way coil stent in both its compressed and expanded formsExamples of sheet style stents Top- Jostent SelfX (made by Jomed), Bottom- Dynalink (made by Guidant)Examples of braided style stents Left- ZA Stent (made by Cook), Right- Symp hony Stent (made by Boston Scientific)General HazardsGeneral hazards of inhaling Nitinol include irritation, coughing, and shortness of breath. If ingested gastrointestinal disorders are assertable. Skin contact and eye contact include irritation with possible redness and pain. None of these side effects are chronic. (SMDS 2008)Complications of Nickel-Titanium in Medical ApplicationsOf the wide range of alloys that contain the properties of shape memory alloys, nickel-titanium and copper-based alloys hold the most value commercially. Nickel-titanium, also known as nitinol, is an equi-atomic mixture of the deuce metals. Concerns have risen over this alloy for the fear of nickel being released into the body (Williams, et al. 1999). It is important in medical equipment for the materials to be bio harmonious, or the ability of the material to perform with a necessary response. In most medical procedures no response is typically desired. To determine if nitinol meets these criteria, th e properties of titanium, nickel, and the conspiracy of the both can be looked at.Titanium is a metal with a high resistivity to corrosion. It is not particularly reactive and therefore is effective for medical uses where the device needs to be in the human body for an extended period of time (Lagoudas, 2010). It contains no characteristics of toxicity. Titanium is also a very strong material, however it is rarer and more difficult to manufacture than other materials. This makes titanium overpriced compared to other alternatives.Nickel is a metal which is extremely reactive. Nickel is toxic to the human body and may cause massive inflammation and interaction with proteins. These properties urge on questions on whether nitinol alloy is safe for medical uses. The benefits of using nickel in medical devices is that nickel increases flexibility and lowers the expense when debase with more high-ticket(prenominal) materials such as titanium (Langelaar, et. al. 2010 ).The properties when nickel and titanium are alloyed together usually take on those of titanium. During the manufacturing process an outer class of titanium oxide forms. Although some nickel will still exist on the exterior, the toxicity is greatly reduced. When choosing a material for medical instruments, a risk/benefit analysis controls which alloy will be used. Nitinol is chosen because it holds great benefits and is very safe to use. Extensive testing of this material has been done and is still occurring to limit complications (Yoshida, et al. 2010).Safety During Medical ApplicationWhen considering the use of shape memory alloys (such as nitinol), in medical applications, it go bads necessary to evaluate the safety of the materials for use in the human body. Biocompatibility and corrosion are two factors that come into gaming when considering placement into humans. Properly treated nitinol implants are corrosion resistant and compatible in humans. These implants form a aerofoil oxide layer that protects the base material from most corrosion. There are some concerns of the nickel content licentiousness from the Nitinol and causing adverse affects. However, other alloys containing high levels of nickel, such as MP35N or three hundred series stainless brace, have been used in orthodontics, orthopedics, and cardiovascular applications, all the while displaying good biocompatibility. (Stoeckel, et al. 2003)Studies have shown that in vitro dissolution of nitinol alveolar archwires in saliva released an average of 13.05 mg/day nickel. This number is significantly lower than the average dietary intake of 200-300 mg/day. There was no increase in the nickel blood level throughout the study. A comparative in vitro cell destination study was performed to measure nickel release from nitinol and 316L stainless steel in fibroblast and osteoblast cell culture media. The nickel content was higher in the nitinol group for the first day, but rapidly decreased over time to achieve s imilar levels as the stainless steel. The nickel content never reached toxic levels in the nitinol and did not interfere with the cell growth. It was found that samples fain by mechanical polish released higher meats of Ni-ions than those prepared by electropolishing. In order to evaluate the effect of polishing on nickel release, mechanically polished and electropolished samples of nitinol, MP35N, and 316L stainless steel were immersed in solution for a period of over degree centigrade0 hours. Samples prepared by electropolishing released smaller amounts of Ni-ions than those with mechanical polishing. The electropolishing process removes excess nickel from the surface and forms an enriched layer of titanium. (Stoechel, et al. 2003)A study on blood compatibility was conducted on nitinol and stainless steel stents using an ex vivo, AV-shunt porcine model. It was concluded that nitinol is significantly less thrombogenic than stainless steel, meaning that when used in the human bo dy it has a much lower chance of causing blood clots. It is thought that the titanium-oxide rich surface layer on the nitinol prevents denaturation of fibrinogen and minimizes platelet-rich thrombus formation within the stent after implantation. (Thierry, et al. 2000)Comparison of Shape Memory Alloy Nickel-Titanium to Stainless SteelThe ability of shape memory alloys to return to their original position after large strains are induced is similar to that of rubber. However, unlike rubber, shape memory alloys are strong and noncorrosive much like stainless steel. Both nickel-titanium and stainless steel have long fatigue life. many another(prenominal) stainless steels contain nickel to maintain an austenitic structure. Higher nickel content guarantees superior resistance to corrosive cracking. Stainless steel has a relatively lower court compared to nitinol mainly due to larger production numbers. Only about two hundred tons were produced in 1998 compared to a few hundred kelvin to ns of stainless steel (Lagoudas, 2010). Alloying a metal raises the production disbursement but changes the tensile and shear strength of the initial metals. The properties of shape memory alloys are better than those of stainless steel and therefore are the chosen material for certain applications.Above Shape memory alloys have two phases, each with a different crystal structure andproperties. One is the high temperature phase, called austenite, and the other is the low temperature phase, martensite. Each martensitic crystal formed can have a different orientation direction, called a variant. The assembly of martensitic variants can exist in two forms. Twinned martensite, which is formed by a combination of self-accommodated martensitic variants and detwinned or reoriented martensite in which a specific variant is dominant (Lagoudas, 2010). be of Shape Memory Alloys such as Nickel-TitaniumAlloys such as nitinol have poor formability in the manufacturing process which increases the production be of such materials. The heterogeneous behavior of the material makes the development of shape memory alloys adaptive structures a challenging task. In this case, it is generally accepted that systematic, model-based design approaches and design optimisation techniques can be of great assistance (Langelaar et al. 2010). However, as more applications for these materials are needed, the price will decrease.Currently, shape memory alloys are commercially available from a limited number of producers. When more production of these alloys begins, production bell will reduce. World production is small in contrast to other metal commodities. Competition drives prices lower in a market. Newer technology in manufacturing will also make the production more effective. Prices for shape memory alloys were over one dollar per gram of material in the 1990s. Today, the costs are roughly ninety percent lower.Whatever the cost may be, shape memory alloys such as nickel-titanium are on e of the only materials capable of such miniscule instrumentation with the desired properties. Shape memory alloys are effective for their cost due to reliability and multiple functions (Stoeckel, 2010). Many applications of shape memory alloys only require a small amount of material. With prices around that of similar steels, shape memory alloys are gaining more tutelage in a variety of applications.Above The best material lies towards the stop number left corner as it corresponds to low material costfor the aforementioned(prenominal) output work (Lagoudas, 2010). It indicates that CuZnAl is the best, while Ni-Ti is the least. However, it may be more beneficial to use Ni-Ti because of reduced voltage requirements due to much higher resistivity, which results in cheaper equipment in cyclic applications. Copper based alloys are less enduring and more brittle than Ni-Ti. Although less expensive, copper based alloys have found little approval for applications.Future TrendsCurrent studies at the University of OULU have been conducted in order to demonstrate that bone modeling can be controlled by using a functional implant such as a NiTi nail which can be used to bend a design shaft of the long bone. The method could also be applied inversely, such as straightening a deformed bone. Fractures and especially frequent fractures lead to angular deformity and bowing of long bones. Operative treatment has usually consisted of cortical osteotomies with cast, internal fixation, or external fixation (Kujala, 2003). However, these are relatively large operations with much postoperative pain and a risk for complications. nidation of a bending rod would be a much smaller operation for the patient with reduced postoperative recovery. It might even be possible to insert the nails using minimally invasive techniques which would require a minute incision. Thus, the functional nail presented might provide an easier, quicker, cheaper, and less galling way to correct such bo ne deformities in the future.In addition, model piping in nuclear reactors has been wound with pre-stretched Ni-Ti wire, which leaves very high compressive stresses in the pipe. Tennis racket strings have been tested in china and the USA with both countries claiming performance superior to existing string materials (Deurig, 1995). Furthermore, a variety of damping applications are being examined including such motivated projects as dragoon wheel tires and damping mechanisms for suspension bridges.Moreover, the maximum Ms temperature achieved in Ni-Ti binary alloys is 100 degrees Celsius and for several years scientists have searched extensively for ways to increase this. Ms temperature or Martensite start temperature is the temperature at which the transformation from austenite to martensite begins on cooling. Until just two years ago the only alloys display hope were extremely expensive alloys such as Ti- Pd-Ni and Ti-Pt-Ni. Recently, however two new alloys are showing a great deal of promise, Ni-Ti-Hf and Ni-Ti-Zr31. These alloys prove that transformation temperatures of over 300 degrees C are possible (Deurig, 1995). However, it is too early to know what the cost of the alloys will be and if other properties will be as good as the original alloys. Luckily, these first indications seem positive. One advantage if such an Ms temperature is possible would include the use of nitinol in circuit breaker and in automotive applications.ConclusionShape memory alloys are quickly becoming a common material used in medical applications today. The adverse uses of alloys, such as nitinol, allow for improved stents, catheters, bone plates, medical procedures, and more. These advanced materials are helping to shape medical technology for the future. by dint of their durability and unusual prowess for changing shape they have become the future of medical material.