To the Editor,

I want to thank Mrs Joel Bradley, Raymond Chiu, and Robert Asmus for taking the time to respond to my article, "An Ex Vivo Comparison of 2 Cyanoacrylate Skin Protectants" from the January/February issue of Journal of Wound, Ostomy and Continence Nursing (JWOCN).

DESCRIPTION OF THE MIXED POLYMER PRODUCT

The article explicitly describes the noncyanoacrylate portion of the mixed polymer product, which is described as "acrylic polymer" in the cited document, as paint-like. Acrylic polymers are used to create hard rigid plastics like Plexiglas and are less viscous products like acrylic paints. The paint-like metaphor was chosen since it is a product that most individuals outside of organic chemistry are familiar with.

FILM THICKNESS AND MECHANICS

The flexural rigidity formula cited describes an increase in rigidity for a material with changing thickness, which the letter's authors admit is only appropriate if the same material is used. It is known a priori and acknowledged by the letter's authors that the 2 materials subject to this comparison are not chemically the same at the start. As such, they would not cure to a similar final chemistry either. Even if they were chemically equivalent, an increase in rigidity due to changes in thickness does not change a material from ductile to brittle and would therefore not affect how the material failed (sheering vs flaking/fracture). For simplicity, the cited passage was describing the necessary properties for a skin protectant. Neither of the skin protectants flaked off, so regardless of the potential variation in flexural rigidity, that anticipated difference did not make a difference.

PRODUCT APPLICATION

The "Methods" section clearly describes that "[w]e tested commercially available, off-of-the shelf versions of the product, packaged and labeled for sale. The solely cyanoacrylate-based product was an enclosed ampule with beveled tip applicator, while the mixed polymer product was the thumb lever activated, rectangular sponge applicator." This clearly conveys that the applicator sponge used was the only one made available. What was not explicitly stated, but inferable from the passage above, is that the skin protectants were used following the included instructions for use. Since the time to dryness (30 seconds per the IFU), application angle, and the others questioned by the letter's authors are not variables end users are controlling, they were not manipulated in this comparative analysis. In short, the films shared in the results shown are a consequence of the device design, chemistry chosen, and instructions for use by the respective product manufacturers.

INITIAL AMOUNT OF MATERIAL PRESENT ON THE SURFACE

Again, the letter's authors seem to question the application of the products despite the method of application being to follow the instructions for use of the product as sold. The film was applied by snapping the thumb-activated lever and then covering the area to be protected with a minimally overlapping pattern. There is evidence of complete coverage over the sampled area, which is clearly provided in Figure 1 (see Figure 1, page 33, JWOCN January/February 45.1), but that same level of coverage was absent when methods of direct visualization were utilized. The lack of capacity to fill in the skin's creases when used as directed indicates a thinner initial layer. However, the most important fact is that that the film was evidenced to still be present after mild hydration by the fact that it remained tremendously adhesive 2 hours after application. This yet-to-be contested finding severely outweighed any comparison of film thickness or barrier effect.

SUBSTANTIALLY DIFFERENT PERFORMANCE

The primary data supporting the claim of substantially different performance are not cited by the letter's authors once, nor are they disputed by the letter's authors. The maintained adhesiveness of the mixed polymer product is sufficient to recapitulate tape stripping/desquamation of skin, and this by itself is more than sufficient to support the claim of drastic differences between the products. The statements that I made are typical for any published article in that no comparison will cover all tests, nor will it lead to complete characterization. The still-adhesive layer of mixed polymer product may still be a barrier and might explain their cited clinical success. Though the cited success is still contingent upon the eventual validation of the unvalidated method used to support the claims of success. The key issue remains, that this potential barrier may have been attained at an unacceptable cost. The finding of substantial tissue removal due to the mixed polymer product is clinically important and therefore was sufficient for sharing with the readers of this journal. Together, your previous clinical work paired with the shortcomings revealed by the work in mine will allow clinicians to balance the risks and chose which approach is best for their patients.

SUMMARY

The mechanics of the films will be affected first by their differing chemistries and only secondly by the thickness of the resulting film. Even then, the thickness will not make a ductile material brittle. The thickness of the film may in fact be due to choices in applicator design and due to the usage instructed, but neither of these are variables that the clinicians can control. The manufacturer's choice of ingredients should be revisited due to the evidence that the potentially polyanionic polymer chosen (depending on the nature of the acrylic polymer chosen) was evidenced both to be not well retained on the skin in the face of hydration stresses and more importantly the formulation's propensity to form tighter bonds with other wound care-relevant materials leading to removal of tissue. The letter's authors are implored to consider biological constraints, like the net negative charge of the skin, when choosing their formula's components. Also, I and other readers eagerly await validation of the method used to evidence the clinical value of skin protectants so that we can use it to compare current and future technologies and approaches. Finally, I implore the letter's authors to more thoroughly test their product, following the instructions for use, in biologically relevant models as opposed to relying on analytic approaches. Doing so would have easily revealed the residual tackiness of the mixed polymer product.

Again, I appreciate the thoughtful comments from Mrs Joel Bradley, Raymond Chiu, and Robert Asmus and the editors for giving me an opportunity to clarify my work.

Sincerely,

Daniel J. Gibson, PhD

Assistant Professor

University of Florida, Institute for Wound Research

Gainesville

[email protected]