Mechanism Analysis And Instrument Design In Variable Stiffness Structure

With the development of medical technologies,the form of surgical operations has evolved steadily.Multi-port minimally invasive surgery was gradually developed based on the traditional open surgery,and then single-port minimally invasive surgery and natural orifice transluminal endoscopic surgery came into being.Corresponding to the development of surgical forms,surgical instruments were also developed and updated simultaneously.In the process of single-port minimally invasive surgery and natural orifice transluminal endoscopic surgery,surgical instruments and tools have to be able to vary the stiffness to achieve complicated surgical movements which are required by the surgical operations.According to the stiffness control requirements for different surgical instrument parts,this paper conducted researches from several aspects including mechanism analysis,mechanical performance test,structural design,operational feasibility experiment and so on.The specific researches are as follows:First of all,the surgical mode of minimally invasive surgery and the structure of surgical instruments were studied,and the instrument design method and parameter specification were elaborated with the natural lumen surgical instruments as an example.Besides,the natural lumen surgical instrument prototype developed by our laboratory was used for resection.Combined with the requirements of surgical operation and based on the current operating situation of surgical instruments,it can be considered that surgical instruments,especially the supporting part of the executing end of surgical instruments,need to be designed with variable stiffness.Secondly,the mechanism of variable stiffness is elaborated.One of reasons is the swelling effect of polyvinyl formal(PVF)sponge after contacting with water.The physical cross-linking points of PVF sponge dominate the stiffness of the structure,and the dissolution and reconstruction of the physical cross-linking points which are realized by the combination and separation with water control the change of the stiffness.The other is a two-component mechanism of a mixed material in which an open-cell structure sponge is filled with a low-melting material.The low melting point material in the mixed material can respond to temperature stimuli and can be dissolved in water and some organic solvents to change the stiffness of the mixed material.When the low melting point material is in the solid state,it dominates the stiffness of the mixed material and can fix the transient shape of the mixed material.When the low-melting material is melted or dissolved,the deformation recovery force of the open-cell structure sponge causes the shape recovery of the mix material.Then,the designs of the different surgical instrument parts are carried out.The structure consisting of PVF sponge and stainless steel spring is used as supporting structure of the operating end in surgical instrument to realize the rigidity control of the operating end in the surgical instrument.The traditional articular snake structure is replaced by the integrated snake structure to make actuator with more flexible movements and easier operations.An implantable embolization tool was designed based on a mix material in which open-cell sponge(polyurethane sponge)is filled with low-melting materials to meet the surgical needs of special cases at small scales(such as aneurysms).Finally,the operational feasibilities of the new proposed schemes are verified separately,and in vitro demonstration experiments are carried out to evaluate the actual use effects.According to the experimental results,the new designed schemes are highly feasible and have remarkable improvements in performances of the surgical instruments and surgical tools.