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.

Science supporting negative pressure wound therapy with instillation.

A new method (V.A.C.ULTA Therapy System, KCI USA, Inc., San Antonio, TX) combines the benefits of negative pressure wound therapy (NPWT; V.A.C. Therapy, KCI USA, Inc.) with regulated, periodic instillation of user-selected topical wound solutions (V.A.C. VeraFlo Therapy, KCI USA, Inc.). In simulated wound model studies comparing solution distribution using NPWT with and without a soak phase, the instillation soak phase allowed for uniform solution distribution across the wound bed, whereas continuous (no soak) irrigation resulted in uneven coverage. Additional in vitro work illustrated that bacterial particle aerosolisation during wound cleansing was significantly decreased using NPWT with instillation (NPWTi) versus commercially available low-pressure wound cleansers (P < 0·05). In porcine studies, NPWT with saline instillation induced 43% more granulation tissue versus NPWT (P < 0·05) and was as effective at wound cleansing as pulsed lavage. These studies have demonstrated that NPWTi may be an effective wound management therapy that provides both wound cleansing and NPWT benefits.

Mechanoporation is a potential indicator of tissue strain and subsequent degeneration following experimental traumatic brain injury.

BACKGROUND: An increases in plasma membrane permeability is part of the acute pathology of traumatic brain injury and may be a function of excessive membrane force. This membrane damage, or mechanoporation, allows non-specific flux of ions and other molecules across the plasma membrane, and may ultimately lead to cell death. The relationships among tissue stress and strain, membrane permeability, and subsequent cell degeneration, however, are not fully understood. METHODS: Fluorescent molecules of different sizes were introduced to the cerebrospinal fluid space prior to injury and animals were sacrificed at either 10 min or 24 h after injury. We compared the spatial distribution of plasma membrane damage following controlled cortical impact in the rat to the stress and strain tissue patterns in a 3-D finite element simulation of the injury parameters. FINDINGS: Permeable cells were located primarily in the ipsilateral cortex and hippocampus of injured rats at 10 min post-injury; however by 24 h there was also a significant increase in the number of permeable cells. Analysis of colocalization of permeability marker uptake and Fluorojade staining revealed a subset of permeable cells with signs of degeneration at 24 h, but plasma membrane damage was evident in the vast majority of degenerating cells. The regional and subregional distribution patterns of the maximum principal strain and shear stress estimated by the finite element model were comparable to the cell membrane damage profiles following a compressive impact. INTERPRETATION: These results indicate that acute membrane permeability is prominent following traumatic brain injury in areas that experience high shear or tensile stress and strain due to differential mechanical properties of the cell and tissue organization, and that this mechanoporation may play a role in the initiation of secondary injury, contributing to cell death.

Genomic and proteomic evaluation of tissue quality of porcine wounds treated with negative pressure wound therapy in continuous, noncontinuous, and instillation modes.

OBJECTIVE: Negative pressure wound therapy with instillation (NPWTi-d) combines NPWT with automated delivery and removal of topical wound treatment solutions. This porcine study compared genomic and proteomic responses of wounds treated with NPWTi-d with saline to wounds treated with NPWT in continuous and noncontinuous modes. METHODS: Full-thickness porcine dorsal excisional wounds were treated with continuous NPWT, intermittent NPWT, dynamic NPWT, or NPWTi-d with saline (n = 10 wounds per group). On day 7, animals were euthanized and tissues collected. Real-time quantitative polymerase chain reaction arrays profiled expression of 84 genes including extracellular matrix remodeling factors, inflammatory cytokines and chemokines, and growth factors and major signaling molecules. Concentrations of proteins associated with angiogenesis, extracellular matrix components, and cellular energetics were analyzed via enzyme-linked immunosorbent assays. RESULTS: Gene expression profiles for NPWTi-d with saline and continuous NPWT were similar. There were 5 upregulated and 18 downregulated genes overexpressed in NPWTi-d compared to NPWT wounds. Protein content was comparable in all treatment groups and similar to unwounded tissue. CONCLUSIONS: Previous preclinical studies have reported an increased rate of granulation tissue formation with NPWTi-d with saline compared to NPWT in continuous and noncontinuous modes. This evaluation of gene and protein expression suggests that the granulation tissue in these wounds has a similar quality. This first look at the differences in gene expression, particularly in genes related to remodeling, cell adhesion, inflammation, and growth factors, could help to clarify the observed differences in granulation rates.

Comparison of the Effects of Different Negative Pressure Wound Therapy Modes-Continuous, Noncontinuous, and With Instillation-on Porcine Excisional Wounds.

OBJECTIVE: Negative pressure wound therapy (NPWT) can be delivered in continuous or noncontinuous modes, while NPWT with instillation (NPWTi) couples NPWT with automated delivery and removal of topical wound treatment solutions and suspensions. This porcine study compared granulation response of NPWTi (instillation foam dressing with saline) to NPWT (standard foam dressing) in continuous and noncontinuous modes. METHODS: Full-thickness dorsal excisional wounds in pigs were treated with continuous NPWT, intermittent NPWT, dynamic (controlled variable) NPWT, and NPWTi with saline (n = 10 per group). Wound dimensions were determined from 3D images collected on days 0, 2, 5, and 7. On day 7, animals were euthanized and specimens were harvested for histopathological review. RESULTS: Average granulation thickness was not statistically different among continuous (3.29 ± 0.33 mm), intermittent (3.03 ± 0.47 mm), and dynamic (3.40 ± 0.34 mm) NPWT wounds at day 7. Average granulation thickness of NPWTi wounds (4.75 ± 0.54 mm), however, was statistically greater (P < .05) by 44%, 57%, and 40%, respectively, than that of wounds treated with continuous, intermittent, and dynamic NPWT. Analysis of 3D images revealed a greater reduction in wound area and perimeter in NPWTi wounds compared to all NPWT wounds (P < .05). In addition, the average wound fill rate for NPWTi wounds was faster than that for continuous (40%; P < .05), intermittent (25%; P > .05), and dynamic (65%; P < .05) NPWT wounds. CONCLUSIONS: Although not confirmed in humans, these porcine data suggest that NPWTi with saline may stimulate a faster rate of wound granulation than NPWT in continuous and noncontinuous modes.

Collagen-dependent neurite outgrowth and response to dynamic deformation in three-dimensional neuronal cultures.

In vitro models of brain injury that use thick 3-D cultures and control extracellular matrix constituents allow evaluation of cell-matrix interactions in a more physiologically relevant configuration than traditional 2-D cultures. We have developed a 3-D cell culture system consisting of primary rat cortical neurons distributed throughout thick (>500 microm) gels consisting of type IV collagen (Col) conjugated to agarose. Neuronal viability and neurite outgrowth were examined for a range of agarose (AG) percentages (1.0-3.0%) and initial collagen concentrations ([Col](i); 0-600 microg/mL). In unmodified AG, 1.5% gels supported viable cultures with significant neurite outgrowth, which was not found at lower (< or =1.0%) concentrations. Varying [Col](i )in 1.25% AG revealed the formation of dense, 3-D neurite networks at [Col](i) of 300 microg/mL, while neurons in unmodified AG and at higher [Col](i) (600 microg/mL) exhibited significantly less neurite outgrowth; although, neuronal survival did not vary with [Col](i). The effect of [Col](i) on acute neuronal response following high magnitude, high rate shear deformation (0.50 strain, 30 s(-1) strain rate) was evaluated in 1.5% AG for [Col](i) of 30, 150, and 300 microg/mL, which supported cultures with similar baseline viability and neurite outgrowth. Conjugation of Col to AG also increased the complex modulus of the hydrogel. Following high rate deformation, neuronal viability significantly decreased with increasing [Col](i), implicating cell-matrix adhesions in acute mechanotransduction events associated with traumatic loading. These results suggest interrelated roles for matrix mechanical properties and receptor-mediated cell-matrix interactions in neuronal viability, neurite outgrowth, and transduction of high rate deformation. This model system may be further exploited for the elucidation of mechanotransduction mechanisms and cellular pathology following mechanical insult.