Assessment by finite element analysis modelling of tissue strains associated with the use of two different nasogastric tube securement devices.

OBJECTIVES: Nasogastric tube use can lead to pressure injury. Some nasogastric tube securement devices (NG-SD) include hard plastic components. In the current study, we assessed the differences in strain profiles for two NG-SD, one with hard segments and one without hard segments, using finite element analysis (FEA) to measure strain and deformation occurring at the nasogastric tube-tissue interface. METHODS: FEA in silico models of devices were based on device mechanical test data and clinically relevant placements. Peak strain values were determined by modelling different scenarios using Abaqus software whereby the tubing is moved during wear. RESULTS: The modelling showed peak strains ranging from 52% to 434% for the two NG-SD depending on the tubing placement and device type. Peak strain was always higher for the hard plastic device. Tissue strain energy was a minimum of 133.8 mJ for the NG-SD with no hard parts and a maximum of 311.6 mJ for the NG-SD with hard parts. CONCLUSIONS: This study provided evidence through in silico modelling that NG-SD without hard components may impart less strain and stress to tissues which may provide an option for tube securement that is less likely to cause medical device-related pressure injury.

Comparison of Medical Tape Performance Using Skin Response Quantitative Measurements on Healthy Volunteers.

BACKGROUND: Medical tapes can lead to skin damage upon removal in susceptible patients with fragile skin and at higher risk of developing tissue injury. PURPOSE: We compared the effect of medical tapes with silicone-based versus acrylate-based adhesives on the back or volar forearm stratum corneum using analytical techniques to assess skin condition and potential damage post product removal on 88 healthy volunteers. METHODS: Two studies were conducted in separate facilities (Study 1: 3M In-house Clinical Facility, St. Paul, Minnesota; Study 2: DermiCo, LLC, Broomall, Pennsylvania). Four commercially available tapes were the same in both studies, two for each type of adhesive. We evaluated adhesion to the skin, total proteins and corneocytes removed by the tapes, changes in transepidermal water loss (TEWL), and induction of the inflammatory cytokine interleukin-1 alpha (IL-1a). RESULTS: One of the silicone tapes displayed the strongest adhesion at 24 hours, and one of the acrylate tapes had the lowest adhesion, showing differences in performance within adhesive categories. The adhesion forces did not correlate with the amount of total protein or corneocytes removed. Silicone adhesives removed less total protein and corneocytes than acrylate adhesives. Silicone adhesives did not alter TEWL, whereas acrylate adhesives significantly raised TEWL. There were no differences in interleukin-1alpha induction. CONCLUSION: The silicone adhesive tapes were less disruptive to the skin barrier than the acrylate adhesive tapes, even in healthy volunteers whose skin is not as fragile as what is observed in typical patients. This type of data could guide clinical product usage decisions.

Biomimetic human skin model patterned with rete ridges.

Rete ridges consist of undulations between the epidermis and dermis that enhance the mechanical properties and biological function of human skin. However, most human skin models are fabricated with a flat interface between the epidermal and dermal layers. Here, we report a micro-stamping method for producing human skin models patterned with rete ridges of controlled geometry. To mitigate keratinocyte-induced matrix degradation, telocollagen-fibrin matrices with and without crosslinks enable these micropatterned features to persist during longitudinal culture. Our human skin model exhibits an epidermis that includes the following markers: cytokeratin 14, p63, and Ki67 in the basal layer, cytokeratin 10 in the suprabasal layer, and laminin and collagen IV in the basement membrane. We demonstrated that two keratinocyte cell lines, one from a neonatal donor and another from an adult diabetic donor, are compatible with this model. We tested this model using an irritation test and showed that the epidermis prevents rapid penetration of sodium dodecyl sulfate. Gene expression analysis revealed differences in keratinocytes obtained from the two donors as well as between 2D (control) and 3D culture conditions. Our human skin model may find potential application for drug and cosmetic testing, disease and wound healing modeling, and aging studies.

Finite Element Analysis Modelling of Negative Pressure Wound Therapy Drapes.

Negative pressure wound therapy (NPWT) drape removal from the skin may be painful for patients and inadvertently cause skin damage during the length of therapy. Most NPWT drapes utilize an acrylate adhesive to achieve the seal. To improve the experience associated with NPWT drape removal, a novel hybrid drape was developed. This drape is composed of areas of acrylate adhesive and areas of silicone adhesive. To more fully understand how the removal of the hybrid drape versus the acrylate drape affects the skin, drape removal models were developed to assess the differences in strain profiles for acrylate versus hybrid NPWT drapes using finite element analysis (FEA) to measure the strain and deformation that occurs at the tissue interface with the NPWT drape. The FEA modeling showed that the maximum principal strain associated with the removal of the acrylate drape was 47.3%, whereas the maximum principal strain associated with the removal of the hybrid drape was 21.5%. The average peel force associated with the acrylate drape was 66.1 gf/in, while the peel force for the hybrid drape was 112.5 gf/in. NPWT drape removal may, in certain instances, be related to pain and periwound skin injury. The hybrid drape tested may provide clinicians with an option for NPWT that is gentler for the skin.

Theoretical and Pre-Clinical Models of Vacuum Assisted Closure.

Vacuum Assisted Closure (VAC) has changed how physicians treat complex and chronic wounds. For over 20 years, we have studied the mechanism of action of these devices in both an academic based research laboratory and in an industry-based laboratory.We performed a literature review of the theoretical and pre-clinical published studies from the two labs which related to the biomechanics of open pore reticulated polyurethane interfaces.The VAC device applies a direct mechanical interface to the wound surface. The interaction of the foam under suction with the wound surface causes surface deformation and cell stretch. The suction removes fluid from the tissues. There are increases in angiogenesis with better vessel morphology than standard dressings. The effect is dependent on the pore size of the foam, the pressure of application and the waveform of application. Undoubtedly, patient factors such as age, diabetes and radiation affect the response.Pre-clinical studies can help in the design and optimization of mechanical-based wound healing devices. Current work on the effects of these devices on lymphatics and scarring are areas of active investigation.

Comparing the physical performance of liquid barrier films.

BACKGROUND: Barrier films have been used for many years to protect skin from the damaging effects of excessive moisture and mechanical injury. The performance characteristics important for these protective effects are mainly product durability and its ability to reduce the force of adhesive removal. Additionally, the moisture vapor transmission rate through the film needs to be high enough that maceration is prevented. The current study was undertaken to investigate various physical performance characteristics of six commercially available barrier films. MATERIALS AND METHODS: Several bench tests were used to simulate performance features of the barriers on skin including barrier durability, breathability (moisture vapor permeability), and the effect on adhesive dressing force of removal. RESULTS: Results indicated that barrier films did not perform equivalently. However, Cavilon™ No Sting Barrier Film (NSB) was shown to have significantly greater durability in the barrier integrity test than all other barriers tested and was tied for highest breathability and highest reduction in peel force from steel. No other tested barrier film performed as consistently across the different tests. CONCLUSION: These results may provide mechanistic understanding of how barriers such as NSB may clinically assist with the prevention of adhesive- and moisture-related skin damage.

Finite Element Analysis Modeling of a Novel Silicone Dressing.

Introduction In the United States (US), pressure injuries are believed to affect over 2.5 million people. The prevalence of pressure ulcers in the European Union (EU) is believed to be 13.7%. Recent guidelines have recommended the consideration of polyurethane foam dressings as part of pressure injury prevention strategies. This study assesses the reduction in tissue strain and stresses associated with the use of a new silicone foam dressing.  Methods Finite element analysis (FEA) models were used to investigate the ability of silicone foam dressings to reduce tissue stress and strain energy density (SED) in the regions adjacent to the sacral bone. The loading modeled on the dressings was for combined compression and shear (modeling a patient lying in a 45° Fowler's position). Nine commercially available silicone foam dressings and a no-dressing control were modeled. Results FEA modeling showed that all silicone dressings tested, including Tegaderm™ Silicone Foam (TSF; 3M Health Care, St. Paul, MN) dressings, achieved reductions in tissue distortional stress and SED relative to no-dressing conditions. The use of silicone foam dressing results in a lower volume of tissue at higher stresses and deformation compared to no dressing. Conclusion The results presented indicate that TSF may provide an appropriate option for pressure ulcer prevention programs.

The impact of first-aid dressing design on healing of porcine partial thickness wounds.

Literature describes that a well-maintained moist wound healing environment leads to faster healing by preventing scabbing and drying of the wound. A moist wound speeds healing by allowing for unimpeded movement of newly dividing epidermal cells in the wound. Contrary to what is described in literature and practiced by clinicians, first-aid dressings used at home by consumers advertise breathability and absorptivity as benefits. This manuscript examines the effects of dressing breathability and highly absorptive pads on healing and wound appearance in a porcine dermatome wound model, designed to mimic an abrasion injury. Partial thickness wounds were covered with an experimental silicone-polymer film dressing and various over-the-counter bandages for time frames ranging from 4 to 11 days. The progression of healing was quantified by histology and wound-size reduction measurements. The thickness and persistence of a scab or serocellular crust (SCC) over the injury was measured using both pixel density and optical coherence tomography to supplement visual observations, demonstrating new tools for quantification of SCC over wounds. The results of the experiments illustrate the impact of dressing features on the rate of wound reepithelialization and the formation of SCC. Both a low moisture vapor transmission rate (MVTR) and the absence of an absorptive layer were important in speeding wound healing. Surprisingly, use of a dressing with a low MVTR and a highly absorptive pad healed significantly more slowly than a comparative dressing with a low MVTR and no absorptive pad, even though both dressings had very little scab formation over the wound. This study shows that breathability and absorbency of dressings play independent roles in providing an optimal healing environment, and that these properties can vary widely among commercially available dressings.

Use of a powered coverlet for moisture removal, skin temperature reduction, odor, and bacteria control.

PURPOSE: The purpose of this study was to assess the ability of a powered coverlet (PCL) to control moisture, reduce skin temperature, and help control odor and microbial growth at the skin/support-surface interface. SUBJECTS AND SETTING: A human torso was simulated using a water temperature-regulated loading gauge. The PCL is a 3-tier coverlet composed of vapor-permeable, liquid-impermeable layers with a foam spacer inbetween and a fan blower to draw moisture and heat away from the patient's skin through the spacer. METHODS: A fabric moisture reservoir simulated sweating skin. It was placed between the simulated human torso and pressure redistribution support surface. A change in moisture reservoir weight was used to calculate moisture vapor transfer rate; temperature and relative humidity at the support surface interface were recorded as a function of time. To test for odor control, a malodorous compound was applied daily to the coverlet with and without power for 30 days in a laboratory setting. In a separate test, both a PCL and a standard hospital sheet were inoculated with Staphylococcus aureus and incubated at 32°C to observe the PCL's ability to mitigate microbial growth. RESULTS: Results indicated a higher moisture vapor transfer rate with the PCL as compared to a standard hospital bed sheet (129.5 g/m/h vs 34.1 g/m/h, P < .005). The PCL also had a larger reduction in skin temperature (1.1ºC vs 0.7ºC, P = .13) when compared to control. Gas chromatography analysis showed that the PCL helped control odor better than a non-PCL (P < .05). At 24 hours, the PCL showed greater than 2 log difference of S aureus over the standard hospital sheet (P < .05). CONCLUSIONS: These studies indicate the potential ability of the PCL to remove moisture at the patient/support-surface interface, thus creating a microenvironment with improved moisture management and reduction in odor and microbial growth.

Comparison of tissue damage, cleansing and cross-contamination potential during wound cleansing via two methods: lavage and negative pressure wound therapy with instillation.

The use of lavage was compared to negative pressure wound therapy (NPWT) with instillation (NPWTi) to assess extent of soft tissue damage, debris removal and environmental cross-contamination susceptibility in three distinct models. Scanning electron microscopy in an ex vivo model showed increased visible tissue trauma from lavage treatment at low and high pressures versus NPWTi, with the degree of trauma relative to the pressure of the irrigant. These results were corroborated in granulating full-thickness excisional swine wounds coated with dextran solution to simulate wound debris. Both low-pressure lavage and NPWTi demonstrated effective cleansing in this model, reducing debris by >90%. However, using three-dimensional photography to evaluate tissue damage by measuring immediate tissue swelling (changes in wound volume and depth) showed significantly greater (P < 0.05) swelling in low-pressure lavage-treated wounds compared with NPWTi-treated wounds. Lastly, bench top wound models were inoculated with fluorescent bacterial particles to assess environmental cross-contamination potential and collected at measured distances after treatment with low-pressure lavage and NPWTi. No evidence of cross-contamination was found with NPWTi, whereas one-half of the particles became 'aerosolised' during low-pressure lavage (P < 0.05). Collectively, these studies demonstrate the effective wound cleansing capabilities of NPWTi without the tissue damage and environmental contamination associated with lavage.

Distribution assessment comparing continuous and periodic wound instillation in conjunction with negative pressure wound therapy using an agar-based model.

Negative pressure wound therapy (NPWT) is a widely accepted and effective treatment for various wound types, including complex wounds. Negative pressure with instillation was initially used as a gravity-fed system whereby reticulated, open-cell foam in the wound bed was periodically exposed to cycles of soaking with instillation solution followed by NPWT. Recent publications have alluded to positive outcomes with continuous instillation, where fluid is delivered simultaneously with negative pressure. To evaluate the distribution of instillation solutions to wound beds in conjunction with negative pressure, agar-based models were developed and exposed to coloured instillation solutions to identify exposure intensity via agar staining. This model allowed comparison of continuous- versus periodic-instillation therapy with negative pressure. Continuous instillation at a rate of 30 cc/hour with negative pressure showed isolated exposure of instillation fluid to wound beds in agar wound models with and without undermining and tunnelling. In contrast, periodic instillation illustrated uniform exposure of the additive to the entire wound bed including undermined and tunnel areas, with increased staining with each instillation cycle. These findings suggest that periodic instillation facilitates more uniform exposure throughout the wound, including tunnels and undermining, to instillation solutions, thereby providing therapy consistent with the clinician-ordered treatment.

The effects of normal saline instillation in conjunction with negative pressure wound therapy on wound healing in a porcine model.

UNLABELLED: Acute and chronic wounds impact the lives of millions of patients. Since its introduction, negative pressure wound therapy using reticulated open cell foam (NPWT/ROCF) has significantly improved the healing outcome for many of these wounds. METHODS: The effects of intermittent instillation of normal saline in conjunction with NPWT were investigated to determine if instillation therapy provides additional benefits in wound healing. Conventional NPWT/ROCF as delivered by V.A.C.® Therapy was compared to V.A.C. Instill® Therapy with normal saline in the treatment of porcine full-thickness excisional wounds. Wounds were treated with NPWT/ROCF or NPWT/ROCF with instillation therapy at approximately 4 cycles of normal saline instillation per day and dwell times of either 5 or 60 minutes for the instilled saline on the wound bed. RESULTS: Instillation therapy with normal saline at either dwell time elicited a faster rate of wound filling with granulation tissue that contained an increase in total collagen content compared to continuous NPWT/ROCF alone. Analyses of wound contraction and the hydration state of the treated tissue exhibited no apparent differences between the experimental instillation therapy groups and the control NPWT/ROCF group. CONCLUSION: Collectively, these data suggest that instillation therapy with normal saline may lead to wound fill with higher quality granulation tissue composed of increased collagen following wounding of cutaneous tissue compared to the use of NPWT/ROCF alone.  .

Effects of negative pressure wound therapy on cellular energetics in fibroblasts grown in a provisional wound (fibrin) matrix.

Negative pressure wound therapy (NPWT) using reticulated open cell foam dressing (ROCF) is effective for treatment of recalcitrant wounds; however, the effects of this therapy on cellular metabolism remain to be elucidated. The effect of two different subatmospheric pressure applications on the cell energetics of human fibroblasts grown in a 3D fibrin matrix was studied using two different pressure-manifolding materials, an ROCF or gauze under suction (GUS). It was found that levels of cytochrome c oxidase, energy charge, and adenosine triphosphate/adenosine diphosphate were significantly increased following the application of NPWT using ROCF vs. GUS (p<0.05). Increases in these parameters likely reflect an improved energetic status. In addition, levels of transforming growth factor-beta and platelet-derived growth factor (alpha and beta isoforms) were significantly increased (80 and 53%, respectively; p<0.05) over static control cultures following treatment with NPWT using ROCF but not following GUS. These growth factors are known to be important during wound healing. Clearly, both the material used as the dressing to manifold the subatmospheric pressure and the pressure used have a dramatic effect on cellular response.

Comparative analysis of global gene expression profiles between diabetic rat wounds treated with vacuum-assisted closure therapy, moist wound healing or gauze under suction.

How differential gene expression affects wound healing is not well understood. In this study, Zucker diabetic fatty (fa/fa) male inbred rats were used to investigate gene expression during wound healing in an impaired wound-healing model. Whole genome microarray surveys were used to gain insight into the biological pathways and healing processes in acute excisional wounds treated with vacuum-assisted closure (V.A.C.). Therapy, moist wound healing (MWH) or gauze under suction (GUS). Global gene expression analyses after 2 days of healing indicated major differences with respect to both number of genes showing fold changes and pathway regulation between the three different wound treatments. Statistical analysis of expression profiles indicated that 5072 genes showed a >1.6-fold change with V.A.C. Therapy compared with 3601 genes with MWH and 3952 genes with GUS. Pathways and related genes associated with the early phases of wound healing diverged between treatment groups. For example, pathways involving angiogenesis, cytoskeletal regulation and inflammation were associated with elevated gene expression following V.A.C. Therapy. This study is the first to assess wound healing by whole genome interrogation in a diabetic rat model treated with different healing modalities.

Effects of negative pressure wound therapy on fibroblast viability, chemotactic signaling, and proliferation in a provisional wound (fibrin) matrix.

Vacuum Assisted Closure brand Negative Pressure Wound Therapy (V.A.C. NPWT) has been shown to be an effective therapeutic option for the treatment of recalcitrant wounds; however, the mechanism of action at the cellular level remains to be elucidated. Here, we examined the effects of negative pressure wound therapy, manifolded with two different dressings, on fibroblast viability, chemotactic signaling, and proliferation in a fibrin clot matrix. Fibroblasts were grown in a three-dimensional fibrin matrix and were treated for 48 hours with either V.A.C. NPWT and GranuFoam Dressing, or with gauze under suction, or as static controls without negative pressure or dressings. Cells treated by gauze under suction showed significantly greater cell death and stimulated less migration and proliferation than static and V.A.C. NPWT-treated cells (p<0.05). Apoptosis was also significantly higher in gauze under suction than in static treatments. These results indicate that the dressing material has a significant effect on cell response following negative pressure wound therapy. The ability to support cell growth, stimulate chemotaxis, and proliferation without increasing apoptosis may provide an insight into the mechanisms of action of V.A.C. NPWT.

Bioreactor for application of subatmospheric pressure to three-dimensional cell culture.

Vacuum-assisted closure (VAC) negative pressure wound therapy (NPWT) is a highly successful and widely used treatment modality for wound healing, although no apparatus exists to monitor the effects of subatmospheric pressure application in vitro. Such an apparatus is desirable to better understand the biological effects of this therapy and potentially improve upon them. This article describes the development and validation of a novel bioreactor that permits such study. Tissue analogues consisting of 3-dimensional fibroblast-containing fibrin clots were cultured in off-the-shelf disposable cell culture inserts and multi-well plates that were integrated into the bioreactor module. Negative pressure dressings, commercialized for wound therapy, were placed on top of the culture, and subatmospheric pressure was applied to the dressing. Cultures were perfused with media at controlled physiologic wound exudate flow rates. The design of this bioreactor permits observation of the culture using an inverted microscope in brightfield and fluorescence modes and sustained incubation of the system in a 5% carbon dioxide atmosphere. This closed-system mimics the wound micro-environment under VAC NPWT. Matrix compression occurs as the subatmospheric pressure draws the dressing material down. At the contact zone, surface undulations were clearly evident on the fibroblast-containing tissue analogues at 24 h and appeared to correspond to the dressing microstructure. The bioreactor design, consisting of sterilizable machined plastics and disposable labware, can be easily scaled to multiple units. Validation experiments show that cell survival in this system is comparable with that seen in cells grown in static tissue culture. After application of VAC NPWT, cell morphology changed, with cells appearing thicker and with an organized actin cytoskeleton. The development and validation of this new culture system establishes a stable platform for in vitro investigations of subatmospheric pressure application to tissues.