From space to earth: shape memory alloys, a material in good health!

6 December 2016

Shape memory alloys were discovered in the 1930s, but it was only in the 1960s that the first applications saw the light of day thanks to the discovery of shape recovery properties for nickel titanium (50/50). Very quickly these alloys caught the interest of scientists across the world and numerous applications were developed by using the nickel titanium alloy.
Nevertheless, another property of these materials was also discovered which has widened the field of possible applications of SMAs. SMAs are known to change their shape following a rise in temperature, but they also present the characteristic of being extremely elastic in their austenitic crystal form, which is highly superior to standard materials. This super-elasticity allows them to undergo significant changes in shape, up to 8-10% without any residual deformation.
Since nickel titanium is biocompatible, this super-elastic characteristic is of great interest to a completely different sector, i.e. the medical sector.
The best known applications are orthodontic thread and spacers, endodontic files, stents, pins and orthopedic staples which shut at body temperature as well as extraction baskets for retrieving kidney stones, thereby making it the N°1 sector for nickel titanium.
The current tendency in surgery is what is called mini-invasive surgery, i.e. the use of natural holes or an incision of several centimetres to reach the target organ. This technique reduces post operation trauma. The super-elasticity of nickel titanium is ideal, giving the surgeon access to organs through winding tubes or maintaining an opening under strong pressure.
Nimesis Technology develops and manufactures these applications using shape memory alloys. Traditionally, the company produces memory actuators for satellite antenna aperture controls and solar panels, but over the past few years it has recognized the opportunity of offering high added-value technological innovations made of nickel titanium for the medical sector. The nickel titanium stents which are currently on the market are manufactured from tubes which are cut by laser. These cuts leave sharp edges and damage the material. In addition, the removal of these stents is very complicated and risks damaging the surrounding organic tissue.
Nimesis has therefore developed a wide range of ”single-strand, braided stents with an open and closed mesh”. They present the unique feature of having neither a soldering nor crimping device. The single-strand design of the stent leads to a perfect integration of the two ends of the strand in the braid. This characteristic minimalizes the risk of interaction between different types of elements and of solderings whose reliability is difficult to monitor in a continuous industrial process.
The second advantage of this kind of stent is its capacity to be repositioned in situ. In fact, the majority of stents cannot be moved once they are put in place by the surgeon. The single-strand, braided stent can be reintroduced numerous times into its sheath to adjust its position.
This type of stent retains its tubular shape inside whatever the angle of the curve. Practically no crushing effect is observed when it is deformed or bent.
After two years of development Nimisis now offers a wide range of standard and made-to-measure stents which can be adapted to the specific needs of the customer.

tony Paulino
project manager