How to Cleave Surgical Fibers

How to Cleave Laser Surgical Fibers

Purpose:        Provide simple instructions for reprocessing flat tip bare fibers for laser surgery.

Summary:    Clean cut and flat optical faces are necessary for surgical efficacy in laser surgery. Badly cut fibers deliver energy to target tissue less efficiently and degrade more quickly than properly cut fibers. Step-by-step instructions….

Rationale:      A.A. Griffith developed the first theoretical model for fractures during WWI, inaugurating the Science of Fracture Mechanics. As luck would have it, Griffith studied glass fibers. Telecommunications fibers are made of fused silica -- just like laser surgical fibers -- and more telecom fibers are cut each day using techniques based in based in the science of fracture mechanics than all the surgical fibers cut in a year.

1 -- Fiber cuts are controlled fractures within bulk amorphous materials, propagating from an induced defect -- the score line.

 2 -- The smaller the defect, the more force that is needed to initiate the fracture and the flatter that fracture will be across the fiber face.

 3 -- Multiple score lines favor multiple fracture planes.

 4 -- Mode 1 cracks (opening mode, i.e. cuts) propagate normal to applied stress.

Safety:            Wear safety glasses and disposable gloves or finger cots while doing this. The bits of glass involved will rarely cut you, but a fragment in the eye really, really hurts. Tefzel® is slippery; rubber helps you grip the fiber securely, particularly where you’re averse to cutting large lengths off of your fiber.

 Suggested Supplies:   

Safety glasses or goggles

Rubber or nitrile gloves or finger cots

Scoring wafer, Sapphire™ brand wafer, diamond, sapphire or ruby blade

Fiber stripper, e.g. MicroStrip™

Alcohol wipes

Laser or 30X loupe (preferably both)

 Procedure:   

Prepare your work area. If it is possible to do so, making the cut on a clean, hard surface will produce better and more reproducible results. 

1. Strip a few centimeters of the fiber buffer (blue) from the fiber using the appropriate stripper tool (please refer to “Laser Fiber Stripper Instructions for Use” for important safety information). It is best practice to test the stripped section for possible stripper damage by bending the fiber about the parting line in full rotation. Be advised that the end of the fiber may be sharp so perform this test with care, particularly where working with larger fibers.
2. Regardless of what tool you may be using, the goal is to produce a tiny (submicron) flaw in the glass wall of the fiber where the flaw is orthogonal to the capillary axis. There are 10 to 30 microns of fluoropolymer coating, aka hard clad (HC) between you and your target. 
3. It is helpful to know the dimensions and construction of the fiber that you are cutting to avoid mistakes. Laser fibers are generally all made with the same type of optical fiber with a low water content fused silica core, a fluorine doped fused silica cladding, the fluoropolymer coating and a blue Tefzel® buffer (see below).  

4.  Regardless of what labels say, the most common fiber sizes are:

a. 150 µm core with a 15 µm thick layer of doped silica cladding = 180 µm glass OD

b. 200 µm core with a 20 µm thick layer of doped silica cladding = 240 µm glass OD

c. 242 µm core with a 20 µm thick layer of doped silica cladding = 290 µm glass OD

d. 273 µm core with a 13.5 µm thick layer of doped silica cladding = 300 µm glass OD

e. 365 µm core with a 17.5 µm thick layer of doped silica cladding = 400 µm glass OD

f. 550 µm core with a 25 µm thick layer of doped silica cladding = 600 µm glass OD

g. 910 µm core with a 45 µm thick layer of doped silica cladding = 1 mm glass OD

5. All alumina scoring wafers have two sides where the four edges are either serrated or smooth. Only the smooth side should be used to score a surgical fiber. One may discern the sides by comparing the feel of dragging a fingernail along the edge but this won’t work in the OR. Accordingly, ProFlex branded scoring wafers are printed with a QR code on one side that directs you to these instructions on innovaquartz.com. If your thumb is on the QR code, the smooth edges are away from you, toward the fiber, as it should be.

6.  Regardless of which scoring tool is used, the sharp edge should address the fiber core at about 90 degrees. For Sapphire™ branded scoring wafers and other sharp fiber cleavers, holding the tool at 90 degrees accomplishes this well enough. For the easily sterilized ProFlex™ brand 2” wafer, hold a smooth edge at roughly 45 degrees to the fiber.

7. 13.5 µm to 45 µm is not much glass thickness and you do not want to score into the fiber core, so it is best to just touch the scoring wafer to the fiber coating, pressing it slightly to pass through to nick the glass cladding of the fiber. Do not drag the blade across the fiber to make a score line because doing so gouges out a huge valley of glass and may well cut into the core.

8. Do not fold over the fiber at the score point to produce the fracture. Fractures propagate normal to the applied force. The flaw you made will start the fracture in the desired direction – at right angles to the fiber axis – but a bending force competes with this directionality, pulling the fracture plane off of orthogonal.

9. Pull the fiber apart: this is where the gloves come in handy. If it doesn’t ‘open’ (break), you failed to produce a flaw in the glass or the flaw is too small. This is a problem because we don’t want this score line opening up in surgery. Strip the fiber again so that your next try will be behind the first one. This way the first (potential) flaw will be discarded with the scrap.

10. INSPECT THE CUT END with 30X, minimum magnification (40X to 50X is preferred for smaller fibers). Proper technique may occasionally produce a few glass shards. Large glass shards can cut the fiber again while passing the working cannel, so get them off. Look for tangs protruding from the cut plane. If you see a tang, start over because tangs will badly gouge working channel liners. If the cut end is nice and flat and has no chips or cracks in the glass the fiber will produce a nice round spot with the aiming beam. If you see a flare from the spot the cut is bad.

Wipe the fiber with an alcohol wipe or cloth to remove any small fragments of glass.

 Additional Information:

Preserving your tools:

If you press too hard with a sharpened blade of any kind -- ruby, diamond, or sapphire – the blade will chip and render that portion useless for future cuts. It is far simpler to apply a reproducible force when the fiber is on a flat, hard surface than it is if you have to hold the fiber section in your hand.

Sterilization:

Scoring wafers are 98% microcrystalline alumina with alumina binder: basically synthetic sapphire. The material is similar to the heat shield tiles on the Space Shuttle. They are non-porous and extremely stable in solvents, acids, bases, oxidizers, steam, temperatures above 1000°C, ionizing radiation, etc.

 IQ has validated ProFlex brand wafer compatibility with EtO and Autoclave sterilization but there is no chemical or microbiological reason that ANY sterilization method cannot be used: H₂O₂, acetic acid, CO, gamma…