Ultrasound is by far the most widely used clinical tool for disease screening or examination. When a patient comes to the ultrasound department of a hospital for an ultrasound examination, the examination site is always coated with a light blue or transparent gel that is sticky: to the ultrasonographer, this gel is an important tool for a smooth ultrasound examination and is really mundane; however, to the patient it is familiar but quite unfamiliar. There are always patients who are resistant to this and ask: What is this stuff that is applied to the body? Why do we have to use it for ultrasonography? Is it dirty? Is it toxic? Can it be washed off? First of all, let’s understand why this gel is used for ultrasound. People who have studied physics should know that when ultrasound waves are shot to the dividing surface of two different media, there will be a reflection, resulting in less ultrasound energy into the other media. The degree of reflection of ultrasound is related to a certain indicator of the two media, this indicator is the acoustic impedance, acoustic impedance indicates the ability of a medium to impede the propagation of ultrasound. Of course, different media will have different acoustic impedance, from a physical point of view, when the difference between the acoustic impedance of the two media, the greater the reflection. Therefore, in the ultrasound examination, if the ultrasound probe and the skin in direct contact, there must be a cavity filled with air between the two, which is equivalent to the formation of an interface between the ultrasound probe and the air, due to the existence of large differences in acoustic impedance, when the ultrasound probe emitted ultrasound travels to the air interface, there will be a strong reflection effect, resulting in the ultrasound basically can not enter the human body, can not achieve diagnostic examination or treatment purposes. Therefore, according to this physical principle, this time there is an urgent need for a substance can be filled between the surface of the ultrasound probe and the skin surface to exclude the interference of air, so that the ultrasound can pass smoothly and minimize the loss of sound waves, in order to maximize access to the human body, this substance is the ultrasound doctor for ultrasound examination before the commonly used medical ultrasound coupling agent. Of course, in addition to such an important role, ultrasound coupling agent has another role, many patients often comment that “this stuff is oily”, indicating that the coupling agent also plays the role of lubricant, otherwise without it, ultrasound doctors need to spend more effort, the patient’s skin will be more friction damage. Through the above analysis of physical principles, our requirements for ultrasound coupling agent are also very simple: it is required to be approximately equal to the acoustic impedance of human tissue to reduce reflection loss; the attenuation coefficient should be small to minimize the attenuation loss of ultrasound; it should be better filled between the probe and the skin surface to completely exclude air; it can be kept for a longer time without drying as well as remaining viscous for a longer period of time so that the probe slides smoothly Sweeping; not to irritate the skin, not to produce damage to the skin; easy to clean, etc. Medical ultrasound couplant also has a unique history. Since the early days of medical ultrasound was used to detect injuries, the early days mainly used mineral oil (including petroleum jelly, butter), vegetable oil, silicone oil, etc. as coupling agent. However, due to its poor acoustic properties, it is difficult to obtain high-quality ultrasound images, and easy to irritate the skin, damage the probe, dirty clothing, not easy to clean, etc., gradually not accepted by doctors and patients. With the development of modern ultrasound medicine, there was an urgent need for a safe and effective ultrasound coupling agent to be introduced, and eventually researchers first chose a polymer gel-type preparation. As early as in the early 1980s, China began to burst the mouth ultrasound instruments, following the equipment together with the medical ultrasound coupling agent, its main component is carbomer resin, and add neutralizer, wetting agent, preservative, coloring agent and other preparations. Those who have studied chemistry should know that carbomer resin is a polyacrylic acid cross-linking compound, which can form a high-viscosity gel at a very low concentration, so it is widely used in the research and production of cosmetics and pharmaceuticals, and if you look carefully at the composition list of some gel cosmetics and pharmaceuticals, it is easy to find the figure of carbomer resin. The domestic use of medical ultrasound coupling agent is accompanied by ultrasound technology in the clinical application of the beginning. Because the patent technology is restricted, and the imported ultrasound coupling agent is expensive, most domestic hospitals in a long time are their own preparation of ultrasound coupling agent, there are hospitals use paste as coupler, but its preservation time and physical properties are far from meeting the needs of ultrasound examination. Only in the mid-1990s, the domestic development and production of carbomer gel type couplant began. At present, the products officially produced in China are all carbomer gel type, but the product variety is relatively monotonous and difficult to adapt to a variety of clinical needs. Since the skin of most patients’ examination sites is intact and unbroken, the healthy and intact skin itself is a barrier to external germ attack, therefore clinical diagnosis or treatment of ultrasound examination for such patients does not require skin disinfection, and in principle, non-sterile type couplant is used, which is the ordinary type couplant normally used by ultrasound doctors. However, with the increasing concern and attention to the hygiene and cross-infection of clinical examination at home and abroad, the demand for special (sterile, sterilized, etc.) medical ultrasound couplants is gradually increasing. For example, the Canadian health department clearly requires: “For all invasive operations with devices through the tissue (such as aspiration with a needle, positioning with a needle and tissue biopsy), all operations involving a sterile environment and on non-intact skin, infants in the infant care unit, must use sterile type gels. For operations performed on intact mucous membranes (e.g., esophageal mucosa, gastric mucosa, rectal mucosa, vaginal mucosa), it is also appropriate to consider the use of aseptic-type gels or antibacterial gels.” Domestic “medical ultrasound coupling agent” standard (YY0299-2008) stipulates that for other characteristics (such as sterile, sterilization) of the product, the manufacturer should supplement its corresponding requirements, and currently there are already “sterilization type” of medical ultrasound coupling agent into the market and hospitals. Of course, for examinations or operations with traumatic nature, most domestic ultrasound doctors or clinicians use sterile saline or sterile iodine, which can basically meet the clinical needs, but because sterile saline or sterile iodine is easy to dry and evaporate and has poor adhesion, it needs constant refilling, which is time-consuming and laborious. At present, the sterilization type coupling agent on the market is not made by sterilizing the existing carbomer resin type preparation directly, but adding some ingredients with antibacterial or antimicrobial. At present, some bactericides and naturally extracted antimicrobial agents (such as triclosan, polysaccharide, aloe vera, mint, lavender, lemon antimicrobial agent, eucalyptus, etc.) that meet the requirements of cosmetic hygiene standards and are safe and non-toxic have been used by famous medical coupling agents at home and abroad manufacturers at home and abroad have been applied to the antibacterial type (sterilization type, disinfection type) coupling agent, whose main feature is biodegradable and bio-eliminable. In addition, in view of the adverse effect of air bubbles contained in the coupling agent on the therapeutic effect, some companies also manufacture and sell a special bubble-free dosage form for extracorporeal shock wave lithotripsy.