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Hello, good evening. Good afternoon. Good day, wherever you are in the world and welcome to the Black Belt Academy of Surgical Skills. My name is David o'regan. I'm a retired cardiac surgeon and immediate past director of the Faculty of Surgical Trainers with the Royal College of Surgeons of Edinburgh. And I'm a professor in the Medical Education Research and Development Unit in the Faculty of Medicine at the University of Malaya. Thank you very much for joining us this evening. If it's your first time, welcome. And if you're returning, thank you. Thanks to med O. We are now reaching 100 and 19 countries and this evening, we have registrations from 19 of those from America through to Australia, Colombia, Egypt, Jordan Kenya Maldives, Pakistan, Singapore to mention a few. Thank you very much indeed. And thank you for the feedback. I'm getting from many people. We did do a poll on the time of this right now. It's 2300 hours in Kuala Lumpur Gabriel who's doing the production in the background is in Lithuania and I believe is five hours behind and seven hours behind his fellow Sense. A Chris Caddy in Sheffield in the United Kingdom. It's very difficult to get the perfect time to meet everybody. But we are open to ideas. We recently did a poll and almost 60% of people preferred this time. I appreciate. It's four o'clock in the afternoon in the UK and doesn't meet everybody's requirements, but catch up is free. Thanks to me all. So, this evening, we're gonna be talking about the scalpel and sharp dissection is clean dissection. But have you ever considered what is sharp? I never wondered what the sharpest tool there is if it cuts it chop, right? But like most things, scientists have been trying to actually pin a definition of sharpness down. And one thing's for certain, they haven't found a universal definition and there are lots of ways to define it really, it's the eight pointedness or the narrowness of the blade. But actually, if you go down the, the blade pointed, in fact, it is. And that round is circumscribed by a circle that is given a and the smaller means that the edge is really, really sharp. And indeed, stone tools can be quite sharp, especially flint that can cut through PVC pipes, sapphire scalpel blades have a wedge angle of 2025 Newtons nanometer. So that's the radius then, so you've got a radius diameter. But if you put the two edges together, the ankle subtended by the two sides of the plate gives you an edge thickness. Again defining edge, you can imagine too thin, then it becomes rather fragile and anything less than 20 degrees is using a blade. But if it goes too thin, it becomes brittle and certainly very difficult to put through a sterilization process. I enjoyed while I started cardiac surgery, a set of diamond blades, they were perfect for cutting into the coronary vessels. But it was quite clear with the sterilization process that these will be blunt after a few cycles. And the way we looked after instruments was something to be desired. If you've ever an interest in it, I do recommend that you walk the process and have a look yourself. So what is the sharpest object ever made? Well, scientists at the University of Alberta took a tungsten needle, put it in an atmosphere of nitrogen with high voltage electricity and drew it out to a needle thickness, almost the tip being the thickness of an atom. And these tips are called nano tips. And they're used in scanning tunneling microscopy STM and used to reveal the surface of materials and give you atomic resolution. People have been using flint of stone for many years since the stone age for scraping and cutting and obsidian, which is a volcanic glass as the perfect blade for this. And indeed, they are still made by a Virginian archaeologist using a pressure flaking process. And these obsidian blades can use 10 to 20 times before they discard it, but they can be crafted into a wedge radius, that's the roundness at the top of three nanometer. So having something this sharp is very, very useful if you're making cuts into things which are quite squishy or full of fluid. The eye is the obvious example, these obsidian blades can actually cut cells in half under the microscope, but it doesn't quite end there because the geometry, the wedge angle and the radius does not describe how easy it is to cut something. Thank you, relax. When you will relax, it's the momentum and the force and the pivot and mech mechanics that bring the ax to life. And you will note that kitchen knives are of different sorts depending on how you cut a flat blade or round blade, but often used in that sort of action. You cousin and this is where you need to start understanding that cutting requires a force and behind that force, you need to understand there's a feel. So sharpness therefore, is not only the geometry or the mechanics, but also is the feel or the force that is required to make the cut gets complicated, doesn't it? But like many things are like the katana. I am told off by the sensei for putting too much force in my cutting. I'm chopping, I'm not cutting, I'm not letting the blade do the cut and doing the blade, doing the cut. He has pointed out my right leg bias and therefore the tilt my shoulders. So when I come overhead and bring my katana down. I do have it here. I was prompted, I'm going to get a, a live one. You've seen it. But when I do bring it down of the top, the technique is gotta be perfectly straight and that I'm slicing with this end of the blade, the round of the belly end and this is called the monoi, which consists of the kaki, the tip, the bashi just behind that and the hii there and that's what does the damage it slices. So the sharpness, the shape and the mechanics all come into the cut, think for example of the pizza knife, which is really a circle that you're willing across the pizza. Perfect for cutting pizzas as you will see in dominoes. So a sharp blade is really difficult to define and the definitions to be honest overlap, but to cut to the chase, excuse the pun. Yeah, feel it. And in order to be able to feel something you need to be. And this is where we come down to the uh Mr William Frederick South who told me and I see life like now how you hold a knife is described in the breaths in book of etiquette. But