Nitinol alloy by different processing of these two characteristics, each has its own characteristics, the application of this characteristic to the medical field, will be made into surgical suture, can be in accordance with the clinical suture required, no damage within the muscle and skin suture, need setting temperature available memory metal suture line, do not need to shapes of super elastic metal sutures are available, and wound healing after take out the wire, no foreign bodies in the human body, make the wound will not be hard edges, adverse circumstance, such as pinhole is a noninvasive medical products after the operation.
Special properties of Nitinol alloy:
1. Shapememory's shapememory is that when the parent phase of a certain shape is cooled from above Af temperature to below Mf temperature to form martensite, the martensite is deformed at temperature below Mf and heated to below Af temperature. With the reverse phase transformation, the material will automatically recover its shape in the parent phase. In fact, the shape memory effect is a thermally induced phase change in Nitinol alloys.
The so-called superelastic phenomenon refers to the phenomenon that the strain of the sample under the action of external forces is much larger than the strain of the elastic limit strain, and the strain can recover automatically when unloading. In other words, under the condition of parent phase, the stress-induced martensitic transformation occurs due to the action of applied stress, so that the mechanical behavior of the alloy is different from that of ordinary materials, its elastic limit is far greater than that of ordinary materials, and it no longer obeys hooke's law. In contrast to shape memory properties, hyperelasticity has no thermal involvement. In a word, hyperelasticity means that the stress does not increase with the increase of strain in a certain deformation range. Hyperelasticity can be divided into linear hyperelasticity and nonlinear hyperelasticity. In the former, the relationship between stress and strain is almost linear. Nonlinear hyperelasticity refers to the results of stress-induced martensitic phase transition and its inverse phase transition during loading and unloading at a certain temperature range above Af. Therefore, nonlinear hyperelasticity is also called phase transition pseudo-elasticity. The pseudo-elasticity of Nitinol alloy can reach about 8%. The superelasticity of Nitinol alloy can be changed with the change of heat treatment conditions. When the bow wire is heated to more than 400oC, the superelasticity begins to decrease.
3. Sensitivity to temperature changes in the oral cavity: the orthodontic power of stainless steel wire and CoCr alloy orthodontic wire is basically not affected by the oral cavity temperature. The orthodontic force of hyperelastic Nitinol dental orthodontic wire varies with the change of oral temperature. When the deformation is constant. As the temperature increases, the orthodontic force increases. On the one hand, it can accelerate the movement of the teeth, because the temperature change in the mouth will stimulate the blood flow to the stagnant area caused by the capillary stagnation caused by the orthodontic devices, thus enabling the repair cells to get sufficient nutrition during the tooth movement and maintain their vitality and normal function. On the other hand, the orthodontist cannot precisely control or measure the orthodontic force in the oral environment.
Recently, there is a non-invasive cosmetic skin suture needle. The needle features a nitinol memory alloy wire as the suture line at the end of the suture needle and is coated with zinc. As the memory alloy wire has temperature memory, when it reaches the original set temperature, it forms a straight line, showing the elastic property of the metal material, which is not possessed by the general metal material. This method of skin suture makes the healing of the surgical wound more ideal.
To achieve the suture setting, muscle binding, suture setting, muscle binding is the use of all kinds of suture needles mentioned above, the use of suture and live knot binding, like a straight line to heal the wound of the wire out, so that no foreign body. The ability to pull a wire out of the metal is characterized by the metal's temperature memory and hyperelasticity independent of temperature.