About shape memory metals

The Siberian Research Institute of Medical Materials and Shape Memory Implantates (RUSSIA) is a world leader in the field of physics of metals with shape memory. Progress of the Institute is conditioned by the following achievements of fundamental and applied character:

• for the first time  a general mechanism in behavior of organism tissues and other biological systems was ascertained - the law of delay which established that under the conditions of applying load and unloading organism tissues and other living biological systems hysteresis dependence between the amounts of the load and deformity exists. It is manifested in superelastic behavior and return of deformity (over 2%) into the initial state. In this case width of hysteresis and the extent of the reversible deformity are the most important individual characteristics of tissues;

• biocompatible materials based on TiNi(Mo,Fe) close to organism tissues in their behaviour are created. The nature of deformation of such materials, methods of controlling the properties are revealed and a technology of their production is worked out;

• superelastic materials permeable by the organism tissues   with shape memory, capable of substituting for the defects of organism tissues, are created. The mechanism of filling of such materials with the organism tissues was established.

• using superelastic materials with shape memory methods of operative treatment in surgery, traumatology, orthopedics, stomatology, vertebrology and other field of medicine  wonderful for their efficiency were worked out. For the first time in vascular surgery, ophthalmology, neurosurgery, gynecology, urology the implantates new by shape and by functional possibilities were suggested.

The phenomena of reversible inelastic change of the shape or effects of shape memory and superelasticity are known for a long time. However the real "boom" in the scientific world has been caused by detection of effect of memorizing shape in alloys of titanium nickelide. According to the chemical formula - TiNi these alloys are called "titanium nickelide". For the inquisitive and experienced reader we give some publications at the end of this page, where the laws of physics and characteristics of these alloys are elucidated in detail. Here we shall tell about manifestation of these effects briefly with the purpose of explanation of methods for musculoskeletal system correction.

The TiNi-alloy is a bright metal like steel under usual conditions. Such an alloy is elastic at a room temperature. However the cooling approximately up to 0�� transforms it in an amazingly flexible and inelastic material, which easily changes the shape under an effect of rather small efforts. But when the metal is heated up to the same room temperature it  completely returns the originally given shape. The initial shape is set by heating the alloy to temperature 300-800��.

But the superelasticity property of such materials is not less important than shape memory property. Just this property allows to set the constant directed effort. The property of plasticity allows to set any shape to a metal bar or wire which will correspond to the shape of a body or limb. It means that the orthopedist is not restricted in choice of the shape of a corset (bandage, tutor) as this material is extremely convenient for similar constructions.  

It is necessary to mark that the correcting effort which is achieved with the help of units and constructions made of TiNi-alloys qualitatively differs from efforts which would be possible to achieve with the help of elastic steel slices and springs or rubber extensions. The elastic steel as well as any extension gives maximum effort in an extreme point of deformation. In the process of deformation decrease the elastic effort falls in any case. If you use elastic units you should update them rather frequently to set constant effort. Effort created by the shape memory metal is always permanent at all stages of restoring the shape. It is necessary to  notice that the installation of elastic units in  complex constructions of the correctors is rather labour-consuming and simply impossible to be done frequently.

For the last years many countries including the USA, Germany, Canada, France, England, China, Japan, India show the large interest in developments made in Russia in the field of creation and application of the new class of medical materials - alloys with effects of shape memory and superelastic properties, similar to the properties of organism tissues. The production of implantates with shape memory today makes more than 200 thousand constructions per one year. The development of physical, technical, technological and medical problems of creation and application of shape memory materials for medicine in Russia occupies more than 300 high quality experts including more than 60 doctors of sciences and 120 candidates of sciences.

Literature:
1) Medical Materials and Implants with Shape Memory. Tomsk State University, 1998 (rus.)
2) Superelastic Shape Memory Materials and Implants in   Medicine. Proceeding of  The International Conference, June 25-26, 1998 Tomsk, Russia