Functionalisation of implants by use of shape memory materials for temperature and force sensitive applications

形状记忆材料，尤其是镍钛诺，对于医学上的微创应用特别感兴趣。其独特的材料特性允许高度小型化和执行器功能的实现。然而，这种形状记忆作动器的设计过程复杂且控制不足。因此，到目前为止，钛钛诺在医学工程中的应用仅限于不需要精确的温度依赖行为或驱动运动可以慷慨而粗略地设计的应用。这是当转换温度可以选择大大低于或高于体温，或当周围组织足够坚固（例如，骨周围的压缩钉）的情况。当使用镍钛诺功能化人工耳蜗（CI）电极载体时，情况就不同了。将其形状从植入所需的直线形状改变为螺旋形状（适合耳蜗）表明使用了形状记忆材料。然而，一个尚未解决的挑战是同时保存内耳内功能重要的膜状结构。因此，依赖于温度的驱动运动和对周围组织的相应力必须非常精确地控制和调整。此外，狭窄的手术通道会导致来自周围组织的高热量输入，因此与温度相关的致动器的精确定时至关重要。因此，人工耳蜗作为临床应用的一个主要例子，既需要非常精确地调整执行器的热机械行为以适应临床条件，又需要足够的策略来控制热流。拟议的研究项目将解决使用细镍钛诺线作为执行元件应用于CI具体示例的特殊挑战。目的是为镍钛诺金属丝形状记忆执行器的尺寸制定一个健全的知识。因此，外力对热滞后的影响将通过对不同金属丝样品进行系统的热力学表征来量化。这将通过研究热-机械行为和临床前提条件（热：生理阈值，几何：解剖边界，机械：最大允许接触力）的相互依赖性来补充。此外，将开发适合于OR的冷却方法，并对主动加热（外部控制激活形状记忆效应）进行实验研究。由此产生的表面温度将通过使用热成像来量化。这项以应用为导向的基础研究将支持微型镍钛诺形状记忆驱动器在医疗技术中的更广泛应用。

Shape memory materials, above all Nitinol, are of particular interest for minimally invasive applications in medicine. Their unique material properties allow a high degree of miniaturization and the realization of actuator functions. However, the design process of such shape memory actuators is complex and insufficiently controlled. Therefore, the use of Nitinol in medical engineering is up to now restricted to applications which do not require an accurate temperature-dependent behavior or for which the actuation movement can be generously and coarsely designed. This is the case when the transformation temperatures can be chosen considerably below or above body temperature or when the surrounding tissues are sufficiently robust (e.g. bone around compression staples).The situation is different when functionalizing the electrode carrier of a cochlear implant (CI) by use of Nitinol. The desired change of its shape from a straight configuration required for implantation towards a spiral shape (adapted to the cochlea) suggests the use of shape memory materials. However, an unsolved challenge is the concurrent preservation of the functionally important, membranous structures inside the inner ear. Consequently, the temperature-dependent actuation movement and the corresponding forces on the surrounding tissue have to be controllable and adjusted very accurately. In addition, the narrow surgical access causes a high heat input from the surrounding tissues, so that a precise timing of the temperature-dependent actuator is crucial. Thus, the cochlear implant serves as a prime example of a clinical application that requires both a very accurate adjustment of the thermo-mechanical behavior of the actuator to the clinical conditions as well as sufficient strategies to control the heat flow.The proposed research project will address the special challenges of using thin Nitinol wires as actuator elements applied to the concrete example of the CI. The aim is to develop a sound knowledge for the dimensioning of wiry Nitinol shape memory actuators. Therefore, the influence of external forces on the thermal hysteresis will be quantified by a systematic thermo-mechanical characterization of different wire samples. This will be complemented by investigating the interdependence of the thermo-mechanical behaviour and the clinical preconditions (thermal: physiological threshold values, geometrical: anatomical boundaries, mechanical: maximum permissible contact forces). In addition, cooling methods suitable for the OR will be developed and active heating (externally controlled activation of the shape memory effect) will be experimentally investigated. Resulting surface temperatures will be quantified by use of thermography. This application-oriented basic research should support a broader utilization of miniaturized Nitinol shape memory actuators in medical technology.