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

目前，超声切割装置由附接到切割刀片的朗之万压电换能器组成，所述朗之万压电换能器和切割刀片均被调谐为在通常在20-50 kHz范围内的低超声频率下以纵向模式谐振。超声波切割装置已成功地用于多个行业，尤其是食品行业，并且最近已被设计用于涉及软组织的各种外科手术，并且甚至最近用于切割骨。因为超声刀是调谐部件，所以其长度必须是驱动频率下的半波长或半波长的倍数。此外，由于朗之万传感器只能传递几微米的振动幅度，因此必须仔细设计刀片轮廓，以提供足够的振动幅度增益，以满足待切割材料的要求。这两个几何形状的要求可以是非常限制性的设备的设计;在一个低的超声波频率的半波长导致相当大的切割设备和高增益的配置导致非常高的stresss.This新的研究建议调查适应弯张换能器功率超声应用。弯张换能器由粘结到两个端盖的压电环组成。当环在AC电压下径向收缩时，端盖挠曲，提供垂直于盖表面的放大的纵向运动。对于所提出的应用，切割刀片将连接到其中一个振动端盖上，对操作频率的影响很小。因此，叶片将几乎表现为刚性体，而不需要是装置的调谐部件。巨大的好处是，切割刀片设计可以更密切地关注刀片和骨之间的最佳相互作用，以提供高度准确的切割，并且超声设备可以被简化，以允许设计用于涉及最小进入手术的精密骨科手术的设备。需要研究超声切割刀片和骨之间的相互作用，以便理解超声振动如何能够实现精确的高质量切割。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。骨超声切割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，例如速度、振动幅度、频率以及刀片切割边缘的几何形状。这将为切割刀片的设计提供有价值的输入。本研究项目中设计的切割装置将在人类尸体材料和动物研究中进行试验。这些研究的结果将提供有价值的模拟验证以及深入评估的设备在骨的性能，为广泛的骨科手术programmes.The研究计划汇集了三个学术机构在英国研究功率超声穿透到骨。参与的三个研究小组在功率超声器械和超声骨切割（格拉斯哥）、超声加工和骨钻孔的多尺度计算建模（拉夫堡）以及超声切割器械和矫形工程的试验（爱丁堡）方面具有特殊的专业知识和良好的记录。为了提供一个商业重点的研究和获得专业知识的超声设备设计和制造，两个工业合作伙伴，Mectron医疗和声波系统，是支持该计划。

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.