The evolution of surgical tools can be described as an epic. From the ancient barbaric era, through the era of copper and iron, to the widespread application of cutting-edge technologies such as high-frequency electric knives, ultrasonic knives, laser knives, and proton knives today, each change has promoted great progress in surgery. The speed of this development is breathtaking.
Among many surgical tools, ultrasonic scalpels stand out with their unique advantages. It not only has multiple functions such as cutting, hemostasis, separation and traction, but is also highly praised for its characteristics such as rapid cutting, less bleeding and less smoke. In surgery, it is like a knight in armor, waving a sword in his hand to eradicate pain for patients.
Next, we will explore in depth the working principle, clinical application, product structure and technical difficulties of ultrasonic scalpels, as well as technological innovation and future development directions. I hope that through this special research, we can have a more comprehensive understanding of the charm of ultrasonic scalpels and their indispensable position in surgery.
In 1967, Dr. Kelman developed the world's first ultrasonic emulsification device with the innovation of ultrasonic energy. This breakthrough invention provides strong support for the treatment of rupture and emulsification of the eye lens. With the advent of the 1980s, the application field of ultrasonic scalpels gradually expanded to the plastic surgery industry. In 1992, two American clinical experts were brave enough to innovate and took the lead in introducing Ultracision's ultrasonic scalpel products into laparoscopic surgery, thus opening up a broader market prospect for ultrasonic scalpels in the field of surgical operations. In order to meet different clinical needs, various forms of ultrasonic scalpel products have emerged, such as soft tissue ultrasonic scalpels, ultrasonic bone scalpels, and ultrasonic emulsification suction scalpels. This article will focus on the introduction of surgical soft tissue ultrasonic scalpels (abbreviated as "ultrasonic scalpels").
1.1 Energy conversion principle
The core function of ultrasonic power supply is to efficiently convert conventional AC electrical signals into ultrasonic frequency electrical signals as the basis for energy output. In this conversion process, the ultrasonic transducer plays a vital role. It is located in the ultrasonic vibration unit and can further convert ultrasonic frequency electrical signals into high-frequency mechanical vibrations. Subsequently, through the amplification of the ultrasonic horn, the blade head can output ultrasonic frequency mechanical vibration with a specific amplitude. This vibration is the key to the efficient cutting and coagulation of the ultrasonic knife.
1.2 Principle of cutting and coagulation
The ultrasonic blade head vibrates at a specific frequency. When it comes into contact with tissue cells, the liquid in the cells vaporizes, causing the protein hydrogen bonds to break, causing the cells to disintegrate and re-fuse. Subsequently, the tissue is cut in a coagulated state. In the process of cutting blood vessels, the mechanical vibration of the ultrasonic blade head interacts with tissue proteins to generate heat, thereby destroying the collagen structure in the tissue, achieving protein coagulation and blood vessel closure, and achieving the purpose of hemostasis.
(1) Mechanical effect
Under the action of ultrasound with moderate sound intensity, the tissue produces elastic vibration. As the sound intensity increases, when the mechanical vibration of the tissue exceeds its elastic limit, it will break or pulverize. When cutting soft tissue, the minimum amplitude required by the surgical blade head is 40μm, while in osteotomy, the blade head needs to output an amplitude of more than 100μm.
(2) Thermal effect
Heat is a key factor in achieving tissue coagulation and hemostasis. This includes the viscoelastic thermal energy inside the tissue and the heat generated by the friction between the blade and the tissue.
(3) Cavitation effect
Cavitation bubbles generate high temperature and high pressure in a very short time, while releasing strong shock waves and jets, which emulsify and fragment the tissue. When the high-frequency vibration end of the ultrasonic knife is placed on soft tissues such as adipose tissue and alveolar tissue, the temperature inside the soft tissue cells around the blade will increase significantly. Once the temperature reaches the boiling point of the water in the cell, the water in the cell will vaporize and increase in volume, causing the cell to rupture. The large amount of gas released after the cell rupture helps to expand the tissue layer, which facilitates the surgical operation under the concept of "membrane anatomy" of modern organs.
1.3 Comparison of various types of scalpels
During the operation, it is crucial to choose the right scalpel. Next, we will compare different types of scalpels, including traditional scalpels, laser knives, microwave knives, and ultrasonic knives, to help you better understand their advantages and disadvantages.
From the perspective of clinical application, ultrasonic scalpels perform well in soft tissue cutting, especially in surgical scenarios that require precise control of bleeding and minimized thermal damage. It is often used to close blood vessels with a diameter of 3mm or less, and sometimes even can handle blood vessels with a diameter of 5mm or less. However, for blood vessels with a diameter of 5mm or more, doctors usually use large vessel closures, ligation clips or ligation sutures. In addition, ultrasonic scalpels are not only suitable for open surgery, but also widely used in laparoscopic surgery, and play an important role in various surgeries in multiple departments such as general surgery, gynecology, urology, thoracic surgery, head and neck surgery.
Common surgical ultrasonic scalpel products generally include a host and various accessories. Among these accessories, the transducer is a key component, which is responsible for converting electrical energy into ultrasonic energy. The ultrasonic scalpel head, as the part that directly contacts the tissue, its design covers key components such as the handle, waveguide rod and cannula. In addition, the foot switch and the manual control device on the scalpel head work together to achieve precise control of the output energy of the host.
The various handles of the ultrasonic scalpel head include clamp type, grip type and scissor type.
The standard length of the ultrasonic knife bar is usually 23cm, 36cm or 45cm. In addition, the tip of the blade has a variety of morphological structures, such as multi-purpose scissors, curved multi-purpose scissors, curved stripping knives, separation hooks and hemostatic balls. Doctors can flexibly choose the appropriate handle, blade length and blade shape according to the specific needs of the operation to adapt to different types of operations and patient groups, such as obese patients, conventional laparoscopic surgery, laparotomy and superficial surgery.
3.1 Ultrasonic generator (host)
The ultrasonic generator, also known as an ultrasonic power supply, is a device specially designed to generate and transmit ultrasonic frequency electrical signals to an ultrasonic transducer. According to its working principle, ultrasonic generators can be divided into two categories: analog circuits and digital circuits. At present, digital circuit ultrasonic generators have a dominant position in practical applications due to their excellent energy conversion efficiency.
As the core component of the ultrasonic system, the performance of the ultrasonic generator directly affects the operation effect of the entire system. According to different working principles, ultrasonic generators can be divided into two categories: analog circuits and digital circuits. In today's market, digital circuit ultrasonic generators have become the mainstream choice due to their excellent energy conversion efficiency and stability.
The core hardware modules of digital circuit ultrasonic generators include signal generators, power amplifier circuits, impedance matching circuits, and feedback circuits. During the operation of the ultrasonic transducer, impedance changes will inevitably occur, which involves dynamic adjustment of the impedance size and resonant frequency. In order to ensure that the load can obtain maximum power, the power supply impedance must be consistent with the load impedance. Therefore, the ultrasonic power supply needs to have the ability to track the operating frequency of the ultrasonic transducer and output a power signal of the corresponding frequency accordingly.
(2) Technical Challenges - Tissue Adaptation
During the operation, due to the difference in the texture of the cut and coagulated tissue, the load will change dynamically, which will cause the operating frequency and output amplitude of the ultrasonic transducer to change. If the power supply cannot track the frequency in time to reach the resonant state, the energy conversion efficiency of the transducer will be significantly reduced, causing the transducer to overheat, thereby affecting the efficiency of the operation. In addition, improper output power control of the ultrasonic power supply will also prolong the time it takes for the ultrasonic scalpel to cut tissue and reduce the hemostasis effect. Therefore, the frequency automatic tracking control technology of the ultrasonic power supply is crucial to maintaining its stability.
Tissue adaptation, that is, the output changes with the load impedance, is the core technology of the ultrasonic power supply host. Taking Johnson & Johnson's ultrasonic knife as an example, its host system adopts a one-button cutting and hemostasis mode, which can automatically operate various tissues with one button without the need for gear positions. After pressing the button, the system will output three energy segments of "high-low-high" over time. The output control method of each energy segment is different, and it will be intelligently adjusted according to the load impedance collected in real time. This technology can provide energy support continuously, intelligently and effectively.
After long-term clinical data accumulation and optimization, Johnson & Johnson's ultrasonic knife has shown better performance than domestic brands.
3.2 Ultrasonic transducer
The ultrasonic transducer, as the core of the ultrasonic vibration unit, is responsible for efficiently converting ultrasonic frequency electrical energy into high-frequency mechanical energy. This process further amplifies the amplitude and gathers energy through the amplitude rod, and finally accurately transmits the energy to the knife head. At present, the mainstream ultrasonic transducers on the market can be divided into two categories: piezoelectric transducers and magnetostrictive transducers.
With the popularization of piezoelectric ceramic materials, magnetostrictive transducers have gradually been replaced by piezoelectric ultrasonic transducers, and are still used only in some special fields. At present, piezoelectric transducers have become the mainstream choice in the market. Next, we will explore the core principles and structures of piezoelectric transducers in depth.
(1) Working principle of piezoelectric transducers - piezoelectric effect
When piezoelectric materials are deformed by mechanical stress, the special arrangement of atoms in their lattice will lead to the emergence of polarization, thereby generating a measurable potential difference in the entire material, which is called the positive piezoelectric effect. On the contrary, if a voltage is applied to the surface of a piezoelectric material, the material will be deformed by the electric field, which is called the inverse piezoelectric effect. The size and direction of the deformation depend on the direction of the electric field, the polarization direction of the material, and the connection method with the adjacent structure. This means that piezoelectric materials have the function of converting mechanical energy into electrical energy and converting electrical energy back into mechanical energy. In ultrasonic scalpels, this characteristic enables piezoelectric crystals to efficiently convert electrical energy into mechanical energy through the inverse piezoelectric effect.
(2) Structural analysis of piezoelectric transducers
Next, we will further understand the internal structure of piezoelectric transducers.
Taking the sandwich piezoelectric ceramic ultrasonic transducer as an example, its core components include piezoelectric ceramic sheets, metal front cover, metal back cover, metal electrode sheets and prestressed bolts. In terms of design, the front cover is usually made of light metal to improve the forward transmission efficiency of ultrasonic waves, while the back cover is made of heavy metal to ensure the stability of the transducer.
(3) Piezoelectric materials
Piezoelectric materials can be divided into two categories: inorganic piezoelectric materials and organic piezoelectric materials. Among them, inorganic piezoelectric materials are further divided into piezoelectric crystals (such as piezoelectric single crystals) and piezoelectric ceramics (synthetic materials). Piezoelectric ceramics have excellent mechanical properties, chemical inertness and simple manufacturing. They can be flexibly made into various shapes and sizes, and the polarization direction can be freely selected, making them an ideal choice for transducer manufacturing. For this reason, piezoelectric ceramics have been widely used in the field of transducers.
The main raw materials for making piezoelectric ceramics include barium titanate, lead zirconate titanate, and lithium niobate. These materials show higher power generation capacity than many natural materials. Among them, lead zirconate titanate (PZT) is the most commonly used raw material in the manufacture of piezoelectric ceramics. It is synthesized from lead and zirconium under high temperature. Commercial ultrasonic knife manufacturers, such as Johnson & Johnson, usually use PZT-8 piezoelectric ceramics. However, different companies will choose P8 materials with different performance parameters (such as relative dielectric constant, dielectric loss, and electromechanical coupling coefficient) according to the characteristics of their own transducers.
(4) Technical challenges
The cutting and coagulation speed of ultrasonic knives are affected by many factors, including the electroacoustic conversion efficiency of the transducer, the mechanical loss and transmission efficiency of the ultrasonic waveguide, and the output stability of the ultrasonic knife system. Improving the core indicators of the transducer and ensuring that the ultrasonic energy can be efficiently and stably transmitted to the tip of the blade is the key to optimizing the mechanical system of the ultrasonic knife. High-performance piezoelectric ceramic materials play a vital role in this process.
High-quality piezoelectric ceramic materials should have high mechanical quality factor, high piezoelectric coefficient, high electromechanical coupling coefficient, low dielectric loss, and stable performance (such as temperature and frequency stability). Through doping modification, multi-component development and optimization of the preparation process of ceramic materials, fine control of material properties can be achieved. At present, most manufacturers choose to purchase piezoelectric ceramics from upstream manufacturers at home and abroad, but some manufacturers also have the ability to develop their own research.
3.3 Amplitude Transformer
In the ultrasonic vibration system, the amplitude transformer plays a vital role. Since the vibration amplitude generated by the radiating surface of the ultrasonic transducer is small, usually at an operating frequency of 20kHz, its amplitude is only a few microns, which is far from enough to meet actual needs. Therefore, the amplitude transformer is introduced, which can effectively amplify the displacement and movement speed of the mechanical vibration particles, concentrate the ultrasonic energy in a small area, and thus achieve the energy gathering effect. In addition, the amplitude transformer also acts as a mechanical impedance transformer, matching the impedance between the transducer and the load to ensure that the ultrasonic energy can be efficiently transmitted from the transducer to the load end.
3.4 Ultrasonic scalpel head
The ultrasonic scalpel head, a key component, consists of precision components such as a handle, a waveguide rod (i.e., a shank) and a sleeve. Among them, the shank is the core of the scalpel head, and its material selection and process level are directly related to the risk of scalpel breakage. At present, titanium alloys are favored for their low acoustic impedance, high tensile strength and light weight, and TC4 (Ti-6Al-4V) alloy is the best among them. TC4 titanium alloy not only has the advantages of both α and β titanium alloys - excellent plasticity and thermal strength, but also can work for a long time at 400°C, and has excellent resistance to seawater corrosion. In addition, its production process is simple, and it can be strengthened by welding, hot and cold forming, quenching and aging treatment, making the shank both strong and durable. However, the high cost of imported titanium alloy materials is still a challenge, and manufacturers are actively seeking domestic alternatives to reduce production costs.
4.1 Key performance indicators
In clinical applications, the performance indicators of ultrasonic scalpels have received widespread attention. These indicators cover aspects such as vascular closure effect, cutting closure efficiency, thermal damage range, fine cutting and separation ability, clamping force, and anti-adhesion. Among them, cutting efficiency and vascular closure effect are regarded as the most core indicators, which directly affect the surgical effect and safety. At the same time, industry standards and relevant guidelines also provide clear evaluation methods and standards for these performance indicators.
4.2 Common clinical problems
In clinical applications, we found that the ultrasonic scalpel products on the market generally have the following problems: First, the coagulation effect is often not ideal; second, the soft tissue at the incision is easily damaged by heat, resulting in failure to close normally, cutting failure or blade breakage; in addition, there is a risk that foreign matter may be left in the body, such as tissue pad shedding or internal components of the product shedding. These problems occur for a variety of reasons, usually related to the coordinated work of multiple components of the ultrasonic scalpel system. In addition to improper clinical operation, technical or process defects of any component may affect the overall performance of the ultrasonic scalpel.
In clinical applications, we often face the following risks brought by ultrasonic scalpel products: first, due to poor coagulation effect, postoperative bleeding may occur; second, the soft tissue at the incision may not be able to close normally due to thermal damage, which may lead to serious consequences such as cutting failure or blade breakage; in addition, there is a potential risk that foreign matter may be left in the body, such as tissue pad detachment or
In clinical applications, we often face the following risks brought by ultrasonic scalpel products: First, due to poor coagulation effect, postoperative bleeding may occur; second, the soft tissue at the incision may not be closed normally due to thermal damage, which may lead to serious consequences such as cutting failure or broken scalpel; in addition, there is a potential risk that foreign matter may be left in the body, such as tissue pads falling off or internal components of the product falling off. The existence of these risks not only affects the clinical application effect of ultrasonic scalpels, but also may threaten the safety of patients.
Therefore, in clinical operations, we need to be particularly vigilant about these risks and take corresponding preventive measures to ensure the safety of patients and the smooth progress of the operation.
