An Investigation of the Antimicrobial Efficacy of a Nonwoven CMC PHMB Dressing and the Ability of the Dressing to Absorb Wound Slough

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Wound exudate presents in various forms, from thin and runny to thick and viscous. Consisting of water, white blood cells, electrolytes, MMPs, and growth factors, exudate comprises a complex mixture of compounds.¹ Typically, wound exudate viscosity increases with the presence of increased protein, white blood cells, and bacteria.² If not appropriately handled, excess exudate may lead to maceration and create an environment for bacterial growth.³

A large majority of chronic wounds contain this viscous tissue (slough) that can make it difficult for clinicians to accurately assess the wound bed. A chronic wound is a wound that does not progress through the normal stages of healing in a timely manner.⁴ Chronic wounds are also at increased risk of infection with the potential to lead to a more serious infection, such as biofilm formation.⁵ Biofilm is present in approximately 80% of chronic wounds, and it is crucial that the infection be treated effectively when necessary.⁵ Additional factors associated with chronic wounds are increased pain, longer healing times, and increased costs and other financial implications.^4-6 Thus, appropriate and safe removal of slough and infection are essential elements of wound healing.

Advanced wound care dressings are used with compression therapy as part of the treatment plan in patients with chronic wounds. Use of a dressing that can effectively address desloughing and exudate management and that can be used under compression is key to promoting wound healing.

A high-absorbing gelling fiber dressing composed of CMC fibers and PHMB has been developed (Dressing A [Advanced Medical Solutions]) (Figure 1). The product is indicated for moderately to heavily exuding wounds due to its highly absorbent capability, whereby the product can absorb high amounts of fluid while retaining its integrity by gelling. The objective of this study was to assess the dressing's ability to absorb and retain thick and viscous solutions (representing slough removal) and its antimicrobial efficacy performance under simulated compression.

Slough absorption and retention was performed in accordance with an industry standard, BS EN13726-1:2002.⁷ The majority of the in vitro absorbency data currently available are based on use of a solution consisting of sodium chloride and calcium chloride, which has a thin viscosity similar to water.⁸ Limited data are available on the capability of wound care dressings to absorb and retain thicker, more viscous solutions, which can be representative of wound slough. In the current study, the test solution was modified using a thickening agent (guar gum) to assess the dressing's ability to absorb solutions of different viscosities.

Furthermore, the dressing's ability to retain viscous solutions was investigated by applying a weight to simulate compression conditions. Other nonwoven competitor products currently on the market were assessed as well.

Antimicrobial efficacy testing was performed to determine the dressing's sustained antimicrobial activity over a 7-day challenge period and against a range of clinically relevant microorganisms. This test method was based on AATCC TM100: Assessment of Antibacterial Finishes on Textile Materials guidelines with the addition of a compression element.⁹

As stated by Philippe,¹⁰ secondary dressings are essential because they have an impact on the efficacy of the primary dressing. As Dressing A is indicated for use with secondary dressings, it was important to assess the performance of the product under simulated compression to confirm that compression did not compromise the antimicrobial efficacy. This was achieved by applying a pressure of approximately 55 mm Hg to each dressing using a weight with a specific mass to represent conditions of compression to a primary product.

Figure 2 shows that Dressing A effectively absorbed more viscous solution than the 5 other dressings tested: Dressing B (Aquacel Ag Advantage; ConvaTec), Dressing C (Durafiber; Smith & Nephew), Dressing D (Durafiber Ag), Dressing E (Exufiber; Mölnlycke Health Care), and Dressing F (Exufiber Ag). On average, Dressing A absorbed 33 g/100 cm² per sample, or 28% more viscous solution than other products. Additionally, Dressing A absorbed 33% more than the market leader, Dressing B. Dressing A also retained the viscous solution when subjected to compression. Dressing A retained 24% more slough compared with the next best product (Dressing C) and retained 29% more slough than Dressing B. These in vitro data are a promising sign of the product's potential for slough removal.

Antimicrobial efficacy testing has successfully shown the ability of the CMC PHMB gelling fibers to remain effective while under simulated compression. A greater than or equal to 6-log reduction of all microorganisms tested was achieved within 168 hours (Figure 3). Dressing A performed consistently across a range of species: gram-positive/-negative bacteria, yeast, and mold.

Figure 3 shows that the antimicrobial performance of the dressing was not affected with extra pressure applied. Even under compression the dressing achieved total eradication of all tested microorganisms.

The in vitro data demonstrate that Dressing A (the CMC PHMB gelling fiber dressing) absorbs 33% more viscous solution than the other products tested. The highest amount of solution retained (28 g/100 cm²) was achieved by Dressing A, which demonstrates that the dressing can absorb and retain viscous solutions. Additionally, the antimicrobial efficacy of this dressing remains effective while under compression, with total eradication achieved within 168 hours.

The absorbency and retention data are based on 1 viscosity solution type, equivalent to thick slough. Thus, additional testing using a range of viscocities is recommended to further evaluate the dressing's ability to absorb and retain varying wound exudate compositions.

The CMC PHMB gelling fiber dressing has the ability to handle larger amounts and differing types of exudate, retain wound fluid within the dressing, and maintain antimicrobial efficacy while under compression compared with other dressings. This dressing could have a positive effect on wounds requiring compression therapy as well as on other chronic wounds, thereby affecting wound progression and wound healing.

Authors: Cerys Griffiths, BSc (hons)¹; Emily Oakes, MSc²; Daniel Cook, BSc¹; Lynne Salmon¹; and Alex Lawton, MMATH³

Affiliations: ¹Research & Development, Advanced Medical Solutions, Winsford, Cheshire, United Kingdom; ²Sustaining Engineering, Advanced Medical Solutions, Winsford, Cheshire, United Kingdom; ³Marketing, Advanced Medical Solutions, Winsford, Cheshire, United Kingdom

Disclosure: The authors are full-time employees of Advanced Medical Solutions. Data reported in this article were presented at the 2023 Symposium on Advanced Wound Care Fall, Las Vegas, Nevada.

Correspondence: Cerys Griffiths, BSc (hons); Advanced Medical Solutions, Research & Development, Premiere Park, 33 Road One, Winsford Industrial Estate, Winsford, Cheshire CW7 3RT United Kingdom; alexis.harding@admedsol.com

Manuscript Accepted: January 17, 2024