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Method Article
This study presents a benchtop model designed to evaluate the compatibility of wound dressing materials with negative pressure wound therapy systems by assessing pressure and fluid collection over 72 h under continuous and intermittent pressure settings.
Negative pressure wound therapy (NPWT) systems facilitate wound healing by applying sub-atmospheric pressure to the wound bed, which promotes granulation tissue formation and reduces inflammation. Wound dressings can be used with these systems to enhance healing; however, the effects of dressings on NPWT device performance are challenging to assess. The purpose of this study was to develop a benchtop flesh analog model for testing the compatibility of wound dressing materials with NPWT devices. In this study, a chitosan-based advanced wound care device was evaluated for its effects on NPWT performance under maximum and minimum therapy pressures. The goal was to use the model to compare pressure readings and fluid collection for samples with and without the chitosan wound care device. The benchtop model was constructed using a plastic box connected to multiple pressure gauges. A circular defect was created on a piece of pork belly, used as the flesh analog, and inserted into the box. The defect was filled with standard NPWT foam or foam combined with the wound dressing. Simulated body fluid containing bovine serum was added to the box, which was then tested at either maximum (-200 mmHg) or minimum (-25 mmHg) pressures for 72 h. Pressure and fluid collection were recorded every 12 h. The NPWT system successfully maintained pressure over the 72 h test period, both with and without the test dressings. The addition of the wound dressings did not impact fluid collection. The test box proved effective as a benchtop model, as it could be sealed and maintained vacuum conditions over the 72 h testing period. This model successfully demonstrated its utility in evaluating the compatibility of wound dressing materials with NPWT systems.
Different therapeutic approaches exist to aid in the management and healing process of wounds. Such therapeutic approaches include advanced wound dressings, growth factors, hyperbaric oxygen therapy, skin substitutes, and negative pressure wound therapy (NPWT)1. NPWT refers to wound dressing systems that continuously or intermittently apply sub-atmospheric pressure to the system, which provides negative pressure to the surface of the wound. NPWT has become a popular treatment modality for the management of acute or chronic wounds2. The NPWT system consists of an open cell foam, adhesive wound dressing, a fluid collection system, and a suction pump3. The suction pump, or vacuum, is used to maintain a steady pressure on the wound, which helps increase blood flow and reduce the risk of infection4. NPWT promotes granulation tissue formation by removing fluid from the wound and reducing swelling1. Clinically, the amount of suction pressure used for wounds ranges from -20 mmHg to -200 mmHg, but the most relevant pressure tested is -125 mmHg5.
Ex vivo experiments of NPWT are a challenge due to a lack of adequate benchtop models for testing. Current methods for testing NPWT systems include finite element analysis (FEA) computer simulations, which have been used to test how NPWT affects incision sites6. Other models include benchtop agar-based wound models, which can be used to test fluid uptake7. In vivo, porcine models also have been used to examine wound healing8. These models have advantages such as being easy to simulate on a computer for predicting how a wound should heal in theory, as well as testing fluid being pulled through a model material. In vivo testing is definitive for determining whether the system works in live subjects8. These models all have disadvantages as well. A computer simulation may not accurately represent how a wound would heal in real life. An agar-based model may show good fluid collection being pulled through the wound but may not represent how fluid would be pulled through tissue and muscle7. In vivo models are expensive and require significant resources to complete a study. Also, it can be difficult to keep animals semi-immobile, so there may be challenges with them pulling at the system, which may have confounding results.
A benchtop model is needed for NPWT so that new materials can be tested for use with the system using actual tissue. The new model should be able to reflect how fluid collection is affected by tissue and muscle. The new model should also be able to provide pressure readings inside the wound bed to determine whether the wound was receiving as much pressure as the vacuum pump was supplying. New materials/devices may also be tested, such as additional wound dressings, different types of foam, and different adhesive dressings on top of the wound.
Certain wounds require additional wound dressings to aid in the healing process by reducing the risk of infection. Another reason additional wound dressing materials may be required is to prevent tissue ingrowth between the surface of the wound bed and the open-cell foam. This additional dressing reduces the risk of the wound bed adhering to the open-cell foam, which helps reduce damage and pain when stopping the NPWT system9. These additional dressings can be placed around the open-cell foam to act as a barrier membrane between the wound bed and the foam. Certain materials have been used as an interface between the wound bed and foam, such as paraffin or Vaseline-embedded gauze. Paraffin has shown positive potential as a wound dressing by not affecting the transfer of pressure from the system to the ound9. However, Vaseline-embedded gauze was reported to inhibit fluid collection and thus was not considered to be an appropriate additional material9.
Chitosan-based wound dressings may be a good additional dressing to add during NPWT due to their antimicrobial effects and biocompatibility10,11. Chitosan is an N-deacetylated derivative of chitin, which is a natural polysaccharide found in fungi and arthropods12,13. Chitosan has exhibited inherent antibacterial properties in a broad spectrum of gram-negative and gram-positive bacteria14. Therefore, chitosan membranes have become popular in the treatment of wounds because they can be easily produced, have a long shelf life, and show innate antimicrobial effects10. These membranes also show good biocompatibility biodegradation, and are non-toxic10.
In this study, Foundation DRS, a chitosan and glycosaminoglycan advanced wound care device, was examined to determine its biocompatibility with NPWT. Foundation DRS is a biodegradable dermal regeneration scaffold manufactured for ideal handling characteristics and porosity to promote cellular invasion and neo-angiogenesis in wounds. This device is advantageous for healing in a range of different injuries and uses. It was created for intended use in a wide range of wounds, such as pressure ulcers, diabetic foot ulcers, first-degree burns, trauma wounds, dehisced wounds, and surgical wounds10,11. Foundation DRS is a good option for use in NPWT due to its manufacturing process, which prevents the device from turning into a hydrogel when it is wet. This device maintains an open pore structure when wetted, which should allow fluid to flow during the application of NPWT12,13.
The objective of this study was to develop a benchtop flesh analog model that could be used to test the compatibility of wound dressing materials with NPWT devices. Clinically, pressures range from -80 mmHg to -125 mmHg for most NPWT applications4. To simulate worst-case clinical use conditions, a higher and lower pressure setting were used (-25 mmHg and -200 mmHg). Another objective of this study was to determine if the addition of the chitosan wound care device interfered with the pressure readings and fluid collection of the NPWT. Disruptions in fluid collection or losses of pressure during NPWT could lead to poor wound healing and clinical outcomes. The fluid collection should be similar to the test groups with and without the chitosan wound care device. Pressure readings should also be similar across the test groups over 72 h. In clinical settings, the wound dressing is changed every 48-72 h, so each sample was tested for 72 h in this study3. During testing, the pressure readings should be observed to ensure there is not a drop in pressure.
The details of the reagents and the equipment used in this study are listed in the Table of Materials.
1. Creation of the test box
2. Flesh analog preparation
3. Loading of the test chamber
4. Creation of the simulated body fluid
5. Test conditions
6. Statistical analysis
The goal of the study was to develop a benchtop model for NPWT that uses a tissue analog and to use the model to investigate the compatibility of wound dressing materials with a negative pressure wound therapy machine. The model was used to study if the NPWT machine was able to maintain pressure over time with the addition of a wound care device. The model was also used to determine if the pressure generated and fluid collected by the NPWT machine in the presence of a wound care device were different as compared to the a...
There are a few benchtop models for NPWT, but they have significant limitations. Loveluck et al. developed an FEA computer model to determine how NPWT affected sutured incision sites but did not account for additional wound dressing materials6. Rycerz et al. developed agar-based models to evaluate instillation solution distribution to wounds during NPWT7. While the agar provided a medium for assessing the distribution of water-soluble materials/dyes in the different models,...
This work was supported by a grant from Bionova Medical, Inc. (Germantown, TN).
This research was made possible with the help of the University of Memphis Department of Biomedical Engineering and Bionova Medical.
Name | Company | Catalog Number | Comments |
100x antibiotics/mycotics | Gibco | 15240062 | This is the 100X antibiotics/antimycotics used in the simulated body fluid |
3 M KCI ACTIV.A.C Therapy System | KCI Mdical Products | VFTR006619 | This is the vacuum pump used in the study. |
3 M KCI InfoV.A.C Canister w/Gel 500 mL | eSutures.com | M8275063 | These are the fluid collection canisters used in the study |
3 M KCI V.A.C GranuFoam Medium Dressing Kit, SensaT.R.A.C | eSutures.com | M8275052 | These are the wound dressing packs with the vacuum nozzle including the open cell foam. |
Bovine Serum | Gibco | 16170086 | This was used to mix with the simulated body fluid and the antibiotics/antimycotics |
Calcium Chloride | Fisher Scientific | C614-500 | This was used to create the simulated body fluid |
Excel/Powerpoint | Microsoft Office | N/A | This was used to run the statistics and create the schematic for Figure 1 |
Foundation DRS Solo | BioNova Medical | N/A | This is the advanced chitosan wound care device used in the study. |
Hydrochloric Acid | Fisher Scientific | SA54-1 | This was used to create the simulated body fluid |
Magensium Chloride | Fisher Scientific | M33-500 | This was used to create the simulated body fluid |
Phosphate buffered saline | Thermo Scientific | J62036.K3 | This was used to dilute the 100x antibiotic/antimycotic to 10x |
Potassium Chloride | SIGMA | P-3911 | This was used to create the simulated body fluid |
Potassium Phosphate Dibasic | Fisher BioReagents | BP363-500 | This was used to create the simulated body fluid |
PRM Vacuum Gauge 0 to -10 in Hg | PRM Filtration | PGCNBTY630652J10HG | Two pressure gauges are needed for the testing chamber. |
Salted Pork Belly | Hormel Food Corporations | UPC: 0003760037988 | Salted pork belly can be bought from Kroger. It cannot be sliced. It is best to pick samples that have less fat, and more muscle. |
Sodium Bicarbonate | SIGMA | S5761-500G | This was used to create the simulated body fluid |
Sodium Chloride | Fisher Scientific | S640-500 | This was used to create the simulated body fluid |
Sodium Sulfate | Fisher Scientific | BP166-100 | This was used to create the simulated body fluid |
Tris(hydroxymethyl) aminomethane | Fisher Scientific | BP152-500 | This was used to create the simulated body fluid |
Tupperware Brands Corp, Kissimmee , FL | Tupperware | N/A | This is the box used as the testing chamber. |
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