Miniature Ultrasonic Cutting Devices for High Precision Minimal Access Orthopaedic Surgical Procedures

目前，超声波切割设备由连接在切割刀片上的朗之万压电换能器组成，这两个换能器都可以在低频(通常在20-50 kHz范围内)以纵向模式共振。超声波切割设备被成功地应用于几个行业，特别是食品行业，最近被设计用于各种涉及软组织的外科手术，最近甚至被设计用于切割骨骼。由于超声波叶片是一个调谐元件，在驱动频率下，其长度必须是半波长或半波长的倍数。此外，由于朗之万式传感器只能提供几微米的振动幅度，因此叶片外形必须经过精心设计，以提供足够的振动幅度增益，以满足被切割材料的要求。这两个几何要求在器件设计中可能是非常严格的；在低超声频率下的半波长会导致相当大的切割设备，而高增益的仿形会导致非常高的应力。这项新的研究建议研究如何将弯拉换能器应用于功率超声应用。弯拉换能器由压电环连接在两个端盖上组成。当环在交流电压下径向收缩时，端盖弯曲，提供垂直于盖表面的放大的纵向运动。对于拟议的应用，切割刀片将安装在其中一个振动端盖上，而对工作频率几乎没有影响。因此，叶片的行为将几乎像一个刚体，而不需要是设备的调谐组件。巨大的好处是，切割刀片的设计可以更紧密地专注于提供刀片和骨骼之间的最佳交互，以提供高度精确的切割，并且超声波设备可以被微型化，以允许设计用于涉及最小进入手术的精细矫形手术的设备。此外，需要研究超声波切割刀片和骨骼之间的相互作用，以了解超声波振动如何能够实现准确的高质量切割。由于骨是一种复杂的分层材料，具有许多不同组成的层，多尺度建模方法将允许模拟振动冲击下骨渗透的微观和宏观效应。超声波切割骨骼的模拟还将允许进行参数研究，以研究各种参数对切割的影响，如速度、振动幅度、频率以及刀片刃口的几何形状。这将为切割刀片的设计提供有价值的输入。在这个研究项目中设计的切割装置将在人类身体材料上和动物实验中进行试验。这些研究的结果将为这些模拟提供有价值的验证，并深入评估这些设备在各种骨科手术中的性能。研究计划将英国三个学术机构聚集在一起，研究超声波对骨的穿透能力。参与的三个研究小组在功率超声设备和超声骨切割(格拉斯哥)、超声波加工和骨钻孔的多尺度计算模型(拉夫堡)以及超声波切割设备和整形外科工程的试验(爱丁堡)方面拥有特殊的专业知识和良好的记录。为了将重点放在研究和获得超声波设备设计和制造方面的专业知识上，两个工业合作伙伴--美创医疗和Sonic Systems--正在支持该计划。

Currently, ultrasonic cutting devices consist of a Langevin piezoelectric transducer attached to a cutting blade both tuned to resonate in a longitudinal mode at a low ultrasonic frequency, usually in the 20-50 kHz range. Ultrasonic cutting devices are successfully used in several industries, especially the food industry, and have recently been designed for a variety of surgical procedures involving soft tissue, and even more recently for cutting of bone. Because the ultrasonic blade is a tuned component its length must be a half-wavelength or a multiple of the half-wavelength at the driving frequency. Also, because Langevin transducers can only deliver a few microns of vibration amplitude, the blade profile must be carefully designed to provide sufficient vibration amplitude gain to meet the requirements of the material to be cut. These two geometry requirements can be very restrictive in the design of devices; a half-wavelength at a low ultrasonic frequency leads to quite a large cutting device and profiling for high gain leads to very high stresses.This new research proposes to investigate adapting flextensional transducers for power ultrasonics applications. A flextensional transducer consists of piezoelectric rings bonded to two endcaps. When the ring contracts radially under an AC voltage, the endcaps flex providing an amplified longitudinal motion normal to the cap surfaces. For the proposed application a cutting blade will be attached to one of the vibrating endcaps with little effect on the operational frequency. Thus, the blade will behave nearly as a rigid body, without the need to be a tuned component of the device. The enormous benefit is that the cutting blade design can focus more closely on delivering the best interaction between the blade and bone to provide a highly accurate cut, and also the ultrasonic device can be miniaturised to allow the design of devices for delicate orthopaedic procedures involving minimal access surgery.Complementary to this work, it is required to investigate the interaction between the ultrasonic cutting blade and bone in order to understand how the ultrasonic vibrations enable accurate high quality cuts to be achieved. As bone is a complex hierarchical material with many layers of very different composition, a multi-scale modelling approach will allow both the micro and macro effects of bone penetration under vibro-impacts to be simulated. The simulations of ultrasonic cutting of bone will also allow parametric studies to be carried out to research the effects on cutting of various parameters, such as speed, vibration amplitude, frequency and also the geometry of the cutting edge of the blade. This will provide valuable input in to the design of the cutting blade. The cutting devices designed in this research project will be trialled both on human cadaver material and in animal studies. The results of these studies will provide valuable validations of the simulations as well as in depth assessments of the performance of the devices in bone for a wide range of orthopaedic surgical procedures.The research programme brings together the three academic institutions in the UK researching power ultrasonic penetration into bone. The three research groups involved have particular expertise and strong track records in power ultrasonic devices and ultrasonic bone cutting (Glasgow), multi-scale computational modelling of ultrasonic machining and bone drilling (Loughborough), and trialling of ultrasonic cutting devices and orthopaedic engineering (Edinburgh). To provide a commercial focus to the research and access to expertise in ultrasonic device design and manufacture, two industrial partners, Mectron Medical and Sonic Systems, are supporting the programme.