Most people judge a liposuction cannula by what they can see: the tip, the vents, the shine on the shaft. The part you can't see gets far less attention. The lumen is a long, narrow tube that carries tissue and fluid during every case, and it has to be cleaned and reprocessed afterwards. How that inner surface was made, finished and checked tells you a lot about the instrument.
Where residue and burrs come from
Every vent in a cannula is a hole cut through the wall of a steel tube. On many instruments those holes are made by traditional milling or drilling. Both work by pushing a cutting tool through metal, and that leaves something behind. A burr is the thin, raised lip of metal that forms at the edge of a cut. When the cut breaks through into a tube, part of that burr, along with fine metal particles, can end up on the inside wall.
On the outside of a cannula, a burr is easy to spot and deburr. Inside a lumen that may be under a millimetre across, it's a different story. Residue there is hard to see and hard to reach, and a rough edge or a loose particle gives debris another place to sit. That's why the inside deserves as much attention as the outside.
Cutting the vents with specialty CNC lasers
CLINIMED cannula vents and holes are cut on specialty CNC laser cutting machines. A programmed laser shapes each feature precisely and repeatably, so the same vent geometry comes out the same way on every tube, without a cutting tool being forced through the wall. Cutting still leaves microscopic edges and residue, though, which is where the later finishing steps come in.
What electropolishing actually does
Electropolishing is often described as "reverse plating", and that's a fair shorthand. The steel part is placed in an electrolyte bath and connected to a power supply so that it becomes the positive electrode. When current flows, metal is removed from the surface atom by atom rather than being added to it.
The useful bit is where the metal comes off. Current concentrates on high points, so microscopic peaks and sharp edges dissolve faster than the valleys around them. The result is a microscopically thin layer removed from the whole wetted surface, with the peaks smoothed down and leftover particles and residue from cutting dissolved away. It isn't a coating and it doesn't add anything; it takes a little away, evenly, and leaves a smoother surface behind.
Unlike buffing, which can only reach the outside, electropolishing can also treat the inside of the lumen. Every diameter in the CLINIMED range is electropolished inside and out.
What Ra means, in plain terms
Surface finish is usually given as Ra, the roughness average. Imagine running a very fine stylus along a surface and tracing its tiny hills and dips. Ra is the average height of those hills and dips measured from the middle line. A smaller number means a smoother surface.
The units are small. One micrometre (µm) is a thousandth of a millimetre, and you'll also see microinches (µin), common in the US. Here are the figures for a CLINIMED cannula tube:
| Surface | Finish | Ra |
|---|---|---|
| Outside of the tube | Hand-buffed No. 8 true mirror, then electropolished | ≤ 0.05 µm |
| Inside the lumen | Electropolished | ≤ 0.38 µm (15 µin) |
The lumen figure isn't arbitrary. Ra ≤ 0.38 µm (15 µin) is the electropolished-finish benchmark used for pharmaceutical process tubing under ASME BPE. To be clear, it's a benchmark we finish to, not a certification. It gives buyers a recognised, measurable reference point.
Cleaning and looking inside
After finishing, every cannula is ultrasonically cleaned. In an ultrasonic bath, high-frequency sound waves create tiny bubbles in the cleaning fluid that form and collapse against the metal, loosening material from places a brush or rinse would struggle to reach, including the inside of a narrow tube.
Then each one is inspected inside with a borescope, a slim optical scope that goes into the lumen and lets the inspector see the inner wall and the inside edges of the vents directly. This is done across the whole range, from Ø0.64 mm up to Ø5.0 mm.
The five steps, in order
- Specialty CNC laser-cut: vents and holes are cut precisely and repeatably.
- Hand-buffed: the outside is buffed to a No. 8 true-mirror finish.
- Electropolished: outside and inside the lumen, removing a microscopically thin layer and dissolving cutting residue.
- Ultrasonically cleaned: to loosen anything left on the surfaces.
- Borescope inspected: the inside of every cannula is checked visually.
You can see the sequence on the homepage in how our cannulas are made, and the same details are set out in the downloadable brochures, available in seven languages.
Keeping the lumen clean in use
A well-finished lumen still needs proper reprocessing. Because every CLINIMED cannula is a 2-part system, the cannula comes off its handle, so a brush and rinse water can pass straight through the lumen from the hub. That matters most on long cannulas. Cannula lumen brushes and flexible picks are in the product care collection. For cleaning agents, sterilisation methods and cycle parameters, always follow the manufacturer's IFU.
Questions to ask your supplier
If you're comparing cannulas, or reviewing an existing supplier, these questions get to the point quickly:
- How are the vents and holes cut: laser, milling or drilling?
- Is the inside of the lumen electropolished, or only the outside?
- What Ra figures do you give for the outside and the lumen, and in what units?
- Are all diameters finished the same way, including the smallest?
- Is every cannula ultrasonically cleaned before it ships?
- Is the inside of every cannula inspected, and with what?
A supplier who can answer each of these with a number or a named process is telling you how the instrument was made.
Frequently asked questions
What is an electropolished liposuction cannula?
It's a cannula whose steel surface has been smoothed by an electrochemical process that removes a microscopically thin layer of metal. On CLINIMED cannulas this is done on the outside and inside the lumen, which also dissolves microscopic edges and residue left by cutting.
What is a good surface finish Ra for a cannula lumen?
A useful reference is Ra ≤ 0.38 µm (15 µin), the electropolished-finish benchmark used for pharmaceutical process tubing under ASME BPE. CLINIMED electropolishes every lumen to that figure.
How do I keep a cannula lumen clean?
Separate the cannula from its handle, pass a correctly sized lumen brush and rinse water through from the hub, and then follow the manufacturer's IFU for cleaning and sterilisation. Lumen brushes are in the product care collection.
Why do burrs form inside a cannula?
Milling and drilling push a cutting tool through the tube wall, which can leave a raised lip of metal and fine particles on the inside. Laser cutting followed by electropolishing addresses these edges and residue.
Is electropolishing the same as mirror polishing?
No. Mirror polishing is mechanical buffing of the outer surface, while electropolishing is electrochemical and also reaches inside the tube. CLINIMED cannulas get both: a No. 8 mirror finish outside, then electropolishing inside and out.