A new process for applying graduated marks on biomedical instruments is expected to improve the visual, mechanical, and biocompatibility nature of these important physician aids.

The marks on biomedical instruments show a physician the position of the device relative to the entry point, anatomical markers, or other devices in a patient — or to alert the doctor that he is nearing the travel limit of the device. Currently, guide wires, catheters, tubes, probes, mandrels, needles, and cannulas are available with these depth-of-insertion indicia. These instruments are typically manufactured from materials ranging from stainless steel or engineering plastics, then coated with fluorinated ethylene propylene (FEP) or polytetrafluoroethylene (PTFE) to reduce friction between sliding surfaces, smooth insertion and prevent sticking to body tissue.

For years, makers of these instruments have used laser etching, grinding, acid etching, paint and ink marking to create measurement indicia. None, however, has proven to be satisfactory, for a variety of reasons.

Marks produced by laser-ablating, grinding, and selective acid etching graduations on coated metal devices do not have high contrast, and users report that they are hard to read. Also, the interrupted surface has a saw-tooth affect that resists probe motion. This can cause tissue trauma as they are inserted and withdrawn. See figure below.

If the device is PTFE coated and the coating is selectively removed to create graduated marks, another problem involving the marking process is encountered. If lasers or abrasive processes remove the coatings, they can remove a small amount of the substrate material in the process of generating a notch, causing further disruption of the smooth coated surface. Now, the bare substrate is in contact with tissue, and the probe does not feed smoothly. As force is applied to overcome resistance of the notches, erratic motion occurs. This can lead to tissue trauma as the probe overshoots the intended target. In addition, there is a visual problem; the notches do not provide a pronounced contrasting color from the rest of the coating, and are harder to read in dim or very bright light, because of glare.

Another technique for marking probes involves applying paint or ink graduations to the part. But bonding high-friction paint to a slippery coating raises ridges on probes or wires that make insertion difficult. Also, paint or ink can slough off and become dislodged inside a patient.

No-change geometry

Orion Industries' VisiMark technology for creating permanent graduated marks on coated devices is a two-layer system. It is composed of a medical grade engineering polymer binder such as PTFE or PEEK (polyetherether ketone), color-shifting pigments, and a low-friction polymer such as PTFE or FEP.

When the coating is applied to a wire, probe, or other medical device, then cured at approximately 500° F, the low-friction component migrates to the upper surface to form a transparent layer. Color-shifting pigments remain within the binder layer, and next to the surface of the part. When a localized energy source is applied to the coating and heats it above the cure temperature, the color-shift pigments change color within the heat affected area.

These marks lie trapped within the low-friction coating — without removing or adding material, or raising ridges on the surface. The resulting graduations are precise, ruler-like divisions with a dimensional accuracy of ±0.001 in.

This coating can be permanently applied to create a wide array of narrow bands, stripes, and logos, letters, numbers, etc., of contrasting color with accurate positioning. Also, the color bands can be made to wrap fully around a round wire, or only part of it.

Because an array of coating colors — from light pastels to primary colors — is available, probes can be color-coded to designate various sizes or lengths. Devices can be coated with multiple colors with many VisiMark bands or markings.

Readability of the marks is much improved for two reasons: The matte finish of the coating cuts the glare in high-intensity lighting and the high-contrast matte colors of the marks also do not reflect light. In dimly lit areas, the high contrast marks are easily noted. Users report that they are able to read 2 mm bands on a 0.013-in. biopsy tube from 10 ft. away, and from any angle.

Currently, VisiMark technology is available for all metal substrates including stainless steel, nitonol, and some engineering polymers. Coding and identification marking is available for biopsy probes, needles, guide wires and similar probe and delivery devices.