Surgeons often stop procedures in order to remove eschar (carbonized tissue) from the stainless steel cutting tips of their probes, even though the tips are coated with non-stick polytetrafluoroethylen (PTFE).

That, however, has changed because of an advanced PTFE-free, thin-film coating made of a hard, porcelain-like silicone based formulation that provides a more uniform release while serving as an effective insulator or conductor, depending on formulation.

The latter is critical because electrosurgery requires high-frequency AC energy. When probe are charged, current vaporizes fluid within nearby cells and converts it into an ionized plasma halo that cuts through tissue. A variant of this process, the “blend” technique, uses a staggered application of current to simultaneously cut and coagulate tissue, thus minimizing blood loss. This is the most common electrosurgical technique.

Addressing limitations

While PTFE remains the non-stick coating of choice for cookware and industrial applications, particularly where temperatures as high as 500°F are involved, PTFE has not eliminated the problem of eschar buildup in the OR.

Its limitation lies in the nature of the polymer. When cured at temperatures necessary to bond it to the metal substrate, PTFE sinters, causing molecules to draw together, leaving minute voids in between. The result is what is known as pinholes throughout the coating, Figure 1.

Pinholes are not a problem for numerous applications, even for products such as chemical valves where PTFE coatings serve as corrosion barriers; applicators simply overlap the valve with multiple layers of the coating, betting that the successive layers smother pinholes of the layers underneath.

Such a strategy is not possible on electrosurgical tips because the coating should be thin—on the order of 0.0004 to 0.001 in. Multiple overlapping coats are not feasible and can delaminate. In service, pinholes become vents for irregular bursts of energy which are often visible as sparking. Also, because there is little or no PTFE in or near the pinhole, they become attachment points for eschar, Figure 2.

When eschar builds up on a probe, it acts as an instant insulator, interfering with current flow from the probe. Cutting becomes irregular. Surgeons must stop the procedure to remove the eschar. In a one-hour procedure, a surgeon must stop repeatedly to clean the probe with an abrasive pad. This frequent scratching wears off the soft PTFE, and all benefit as a release agent is lost. Eventually, the probe has to be exchanged for a new one.

A second material—an RTV silicone—has also been tried on surgical tips, but it is soft and has to be applied in thick (0.004 in.) films that resist the electrical current.

Advanced continuous film provides continuous release

The problems associated with PTFE and soft RTV are being addressed via ElectroBond, a thin film that is a bonded layer of high-temperature, porcelain-like silicone matrix that cures into a solid, pinhole-free surface, Figure 3. Because there are no voids in the surface, release is uniform and continuous. The cutting/coagulation action of the ionized vapor is unimpeded and continuous, without flare-ups.

To demonstrate the effectiveness of the new coatings, engineers from Chicago-based Surface Solutions Group, maker of the material, simulated surgical conditions using calf liver (a standard test protocol). Blades were purchased with both PTFE and silicone RTV coatings and tested against the Electro- Bond. Each was used to make a total of 25 cuts at power levels of 20, 40, 60, 80, and 100 watts at the “blend” setting of the power supply. After each cut, the mass buildup of eschar on the individual blades was weighed to a tolerance of 0.0001g.

The results showed that the new film resists eschar buildup and outlasts the conventional PTFE and soft silicone RTV coatings by a factor of eight.

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