Summary: PVA Gelling Fiber Dressings Demonstrate Key Clinical Performance Criteria for Chronic and Cavity Wounds

Chronic wounds, in particular, have a marked negative impact on patients’ overall well-being and represent a major burden on health care cost around the world. While these wounds may have varying etiologies, including venous leg ulcers, diabetic foot ulcers (DFU), pressure injuries (PI), among others, clinicians are faced with similar challenges in treating them all. Typically, chronic wounds are those that become stalled in the inflammatory stage of healing. If a wound were to progress toward the proliferative stage, exudate levels would begin to decrease as new epithelium develops. But stalled wounds face continuous exudate with an excess of proteases, which are associated with dissolution of the extracellular matrix, and thus a risk of maceration to surrounding skin.

Many of the wound types mentioned above are also prone to cavities, which are often defined as wounds that extend beyond the layers of the dermis or more than 2 cm in depth from the edge of the wound to the wound bed. Cavity wounds are particularly difficult to assess and manage, and pooling of exudate in the wound bed is a common problem that can lead to bacterial proliferation. As such, it is crucial that wound dressings effectively absorb and retain exudate, even under the load of mechanical forces. An ideal dressing will keep the wound warm and moist, not wet, and be impermeable to outside fluids and pathogens while still allowing gas exchange between the wound and the environment. In the case of cavity wounds, where exudate pooling is a serious concern, fiber dressings are typically used as a primary dressing, facilitating the transfer of exudate to an absorbent secondary dressing.

In an in-depth article published in 2021, researchers examined 2 new gelling fiber dressings—1 containing silver and 1 without—both made from polyvinyl alcohol (PVA) fibers with unique properties to determine the dressings’ absorption and retention capacities, management of exudate transfer from primary to secondary dressings, and structural integrity, as well as antimicrobial effects and wound healing. This work comprised a range of in vitro studies as well as in vivo animal and clinical studies.

Absorption and retention capacity
To assess the PVA dressings’ absorption capacities, the dressings were tested with a free swell absorption method, weighing each dressing sheet before and after placing it in a dish of test solution. Absorption was also tested in continuous flow, under pressure, at varying inclines, and using fluids of various viscosities. To determine fluid retention, the dressing was subjected to the equivalent of 40 mm Hg of pressure for 30 seconds after absorption and then weighed again to calculate a percentage of fluid retained. These results showed that the non-silver–containing gelling fiber dressing was able to retain up to 23% more absorbed fluid than a carboxymethylcellulose (CMC)-based fiber dressing.

Dressing sorptivity
Dressing sorptivity, or ability to transfer exudate, was tested using a robotic phantom model built to mimic an exuding wound. Researchers were able to simulate cavity wound beds resembling a sacral PI as well as a heel DFU. These models were both anatomically and pathophysiologically realistic, reflecting the real-world impact of forces applied to the dressing via patient body weight and dressing removal and application, as well as assessing dressing performance based on time between dressing changes and realistic physical, chemical, and biological properties of exudate. In these tests, the PVA gelling fiber dressing with silver was found to transfer 49% of its absorbed fluid to a secondary dressing, while a market-leading, silver-containing CMC-based comparator transferred only 31% of fluid to a secondary dressing.

Fluid retention
Robotic phantom-based testing was also employed to assess the performance of the gelling fiber dressing under bodyweight forces, such as those experienced in a non-offloaded DFU. Combined function of primary and secondary dressings were measured in both standing and supine positions. In both postures, the gelling fiber dressing retained approximately 97% of fluid, only losing 3% of fluid absorbed, while the comparator dressing lost 13% of fluid in the transition from supine to standing. Researchers also compared fluid retention after remaining in each simulated position for a period of 5 hours. During this period in the standing test, the PVA gelling fiber dressing retained 39% of its fluid, while transferring the remaining 61% to the secondary dressing. The tested comparator dressing (CMC-based) was able to transfer only 36% of its fluid to a secondary dressing. Similarly, in the supine position, the PVA gelling fiber dressing retained 26% of the fluid while transferring 74% to the secondary dressing, whereas the CMC-based comparator dressing transferred only 37% to a secondary dressing.

Further testing carried out by Professor Amit Gefen, PhD, of Tel Aviv University showed that this silver-containing PVA gelling fiber dressing was able to transfer as much as 1.5 times and 2 times the amount of fluid to a secondary foam dressing compared to a market alternative CMC-based primary dressing when tested over 10 and 15 hours, respectively, in a simulated cavity wound.

Structural integrity
Structural integrity is another crucial facet of a gelling wound dressing, as any particulate or debris left behind from a dressing may lead to a prolonged inflammatory response in the wound. In this study, the PVA fiber-based dressing was tested against a CMC-based primary dressing product via uniaxial stretching performed by a materials testing machine. Here, the PVA gelling fiber dressing was shown to have mechanical endurance approximately 5 times more than that of the comparator dressing after exposing each dressing to the exudate environment of the phantom sacral PI model and 1.7 times greater after use in the DFU model.

Dressing removal
This portion of the study also included testing the removal of the PVA dressing from the simulated wound to assess how well the dressing would remain intact. The PVA gelling fiber dressing showed a distinct advantage, as it does not have a directional stiffness or strength preference, helping it to resist pull-out forces, while the other CMC-based dressing tested displayed a seam pattern or directionality in its fibers, affecting its ability to be removed effectively in the direction of maximal mechanical strength under realistic conditions.

Microbiological studies
Regarding microbiological effects, the silver-containing PVA gelling fiber dressing displayed an antimicrobial effect against common pathogens, including gram-negative bacteria, gram-positive bacteria, and fungal species using a direct contact method. This effect was sustained for up to 8 days and reduced the test organisms by at least 4 logarithmic units at days 4 and 8. It also showed a rapid antimicrobial effect, with logarithmic reductions of microorganisms evident within 3 hours. The dressing was also shown to have an antimicrobial effect against Pseudomonas aeruginosa, methicillin-resistant Staphylococcus aureus (MRSA), and Candida albicans.

In vitro and in vivo studies
Meanwhile, in vitro testing using the collagen gel method showed the PVA gelling fiber dressing was able to reduce S aureus bacterial count by roughly 5 logarithmic units compared to the control over 24 hours, indicating the effectiveness of the dressing’s silver contents against bacterial load. And in vivo testing in a porcine model showed a significant reduction in P aeruginosa and MRSA on days 3, 5, and 7 postinfection using a silver-containing dressing.

Clinical studies
Finally, a summary of clinical studies was included in the article, which involved a multicenter randomized controlled trial performed across 35 centers in Europe, where the PVA gelling fiber dressing was compared with a CMC fiber-based dressing. Over 6 weeks, the study group treated with the gelling fiber dressing saw a 50% wound area reduction, compared with 42% for the comparator group. Another study over 4 weeks demonstrated the silver-containing PVA fiber dressing was excellent in managing exudate, with more than half of the sample group requiring only 1 weekly dressing change; all patients in this group progressed toward wound healing.

The original paper also includes 4 case studies, including an abscess, 2 DFUs, and a leg ulcer. Each of these wounds showed significant area reduction, no signs of wound infection, and excellent exudate management after treatment with the gelling fiber dressings.

Conclusion
Because wounds in real-world settings are so varied in their etiologies, healing stages, and exudate levels and types, it is essential that clinicians have appropriate preclinical and clinical data on each wound dressing available on the market to select the best product for each wound. Extensive preclinical testing, such as that outlined here, demonstrates that PVA gelling fiber dressings exhibit adequate fluid absorption, retention, and sorptivity, as well as mechanical durability and antimicrobial effects. The use of robotic phantom wound models particularly reinforces the evidence that the dressing will perform as intended in real-world settings, potentially saving researchers significant time and money, ensuring the product is worth clinical testing before those resources are put forth. In this case, both the preclinical and clinical data show that PVA gelling fiber dressings perform exceptionally well in chronic and cavity wounds where exudate management is key to the progression of healing.

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Reference: Gefen A, Timmons J, Carlsson E, Wendel M, Hamberg K, Rook S. Exufiber® and Exufiber® Ag+: a review of the scientific and clinical evidence. Wounds Int. 2021(Special Edition):1-25