Novel treatment of intracerebral hemorrhage with mechanical tissue resuscitation.

OBJECTIVE: The previous laboratory and clinical experience of the authors had demonstrated that application of controlled subatmospheric pressure directly to injured soft tissue can result in increased survival of compromised tissues. Mechanical tissue resuscitation (MTR) is a new concept evolving from these discoveries. The authors' recent studies have demonstrated that traumatic brain injury tissue can also be salvaged. The aim of this study was to examine the effects of MTR application to injuries from intracerebral hemorrhages (ICHs) in a swine model. METHODS: The ICHs in swine were simulated by infusion of autologous artery blood into the right frontal lobe. A specially designed silicone manifold device was introduced directly into the hematoma. Continuous negative pressure at -50 mm Hg was applied through this device. T2- and T2*-weighted MRI, histological H&E staining, and immunostaining were examined. RESULTS: After 1 week of treatment, MTR significantly decreased gross hematoma volume by more than 60%, from 472.62 ± 230.19 mm3 in the nontreated group to 171.25 ± 75.38 mm3 in the MTR-treated group (p < 0.05). Total hypointense volumes measured on T2*-weighted MR images decreased from 791.99 ± 360.47 mm3 in the nontreated group to 371.16 ± 105.75 mm3 in the MTR-treated group (p < 0.05). The hyperintense area on the T2-weighted MR image decreased significantly from 2656.23 ± 426.26 mm3 in the nontreated group to 1816.66 ± 525.26 mm3 in the MTR-treated group (p < 0.05). When ICHs were treated with MTR for 2 weeks, the gross hematomas were reduced by 94%, from 112.23 ± 66.21 mm3 in the nontreated group to 6.12 ± 10.99 mm3 in the MTR-treated group (p = 0.003). MTR significantly decreased the total necrotic tissue volume in H&E staining from 120.42 ± 48.35 mm3 in the nontreated group to 60.94 ± 38.99 mm3 in the MTR-treated group (p < 0.05). The total hypointense volumes on T2*-weighted MR images were significantly reduced, from 385.54 ± 93.85 mm3 in the nontreated group to 220.54 ± 104.28 mm3 in the MTR-treated group (p < 0.05), while their mean T2 hyperintense volume decreased significantly from 2192.83 ± 728.27 mm3 in the nontreated group to 1366.97 ± 463.36 mm3 in the MTR-treated group (p < 0.05). Histology revealed that the capillary diameter in the reactive tissue rim adjacent to the hematoma increased in both the 1- and 2-week MTR-treated groups. Both von Willebrand factor and CD31 signals were detectable in endothelial cells within the hematoma cavity of both MTR-treated groups. CONCLUSIONS: This study demonstrates that local continuous application of controlled subatmospheric pressure to an ICH can safely remove more than half of a clot in 1 week and more than 90% in 2 weeks.

Electrical stimulation via repeated biphasic conducting materials for peripheral nerve regeneration.

Improved materials for peripheral nerve repair are needed for the advancement of new surgical techniques in fields spanning from oncology to trauma. In this study, we developed bioresorbable materials capable of producing repeated electric field gradients spaced 600 µm apart to assess the impact on neuronal cell growth, and migration. Electrically conductive, biphasic composites comprised of poly (glycerol) sebacate acrylate (PGSA) alone, and doped with poly (pyrrole) (PPy), were prepared to create alternating segments with high and low electrically conductivity. Conductivity measurements demonstrated that 0.05% PPy added to PSA achieved an optimal value of 1.25 × 10-4 S/cm, for subsequent electrical stimulation. Tensile testing and degradation of PPy doped and undoped PGSA determined that 35-40% acrylation of PGSA matched nerve mechanical properties. Both fibroblast and neuronal cells thrived when cultured upon the composite. Biphasic PGSA/PPy sheets seeded with neuronal cells stimulated for with 3 V, 20 Hz demonstrated a 5x cell increase with 1 day of stimulation and up to a 10x cell increase with 3 days stimulation compared to non-stimulated composites. Tubular conduits composed of repeated high and low conductivity materials suitable for implantation in the rat sciatic nerve model for nerve repair were evaluated in vivo and were superior to silicone conduits. These results suggest that biphasic conducting conduits capable of maintaining mechanical properties without inducing compression injuries while generating repeated electric fields are a promising tool for acceleration of peripheral nerve repair to previously untreatable patients.

Attenuated tissue damage with Mechanical Tissue Resuscitation in a pig model of spinal cord injury.

Our previous studies on the treatment of spinal cord injuries with Mechanical Tissue Resuscitation (MTR) in rats have demonstrated that it can significantly improve the locomotor recovery and BBB scores. MTR treatment also reduced fluid accumulations by T2-imaging and improved the mean neural fiber number and fiber length in injured sites by fiber tractography. Myelin volume was also significantly preserved by MTR treatment. For further clinical application, a large animal model is necessary to assess this treatment. This study examined the effects of application of MTR on traumatic spinal cord injury in a swine model. Traumatic spinal cord contusion injuries (SCI) in swine were created by controlled pneumatic impact device. Negative pressure at -75 mm Hg was continuously applied to the injured site through open cell silicone manifold for 7 days. In vivo MR imaging for T2 and GRE analysis employed a 3T machine, while a 7T machine was employed for diffusion tensor imaging (DTI) and fiber tractography. Histological HE and Luxol fast blue staining were examined. MTR significantly reduced the mean injured volumes over 46% by T2-imaging in the injured sites from 477.34±146.31 mm3 in non-treated group to 255.99±70.28 mm3 in MTR treated group (P<0.01). It also reduced fluid accumulations by relative T2 signal density in the epicenter of the SCI from 1.62±0.27 in non-treated group to 1.22±0.10 in the MTR treated group (P<0.05). The mean injured tissue volume measured by H&E staining was 303.71±78.21 mm3 in the non-treated group and decreased significantly to 162.16±33.0 mm3 in the MTR treated group (P<0.01). The myelin fiber bundles stained by Luxol blue were preserved much more in the MTR treated group (90±29.71 mm3) than in the non-treated group (33.68±24.99 mm3, P<0.01). The fractional anisotropy (FA) values processed by DTI analysis are increased from 0.203±0.027 in the untreated group to 0.238±0.029 in MTR treatment group (P<0.05). Fiber tractography showings the mean fiber numbers across the impacted area were increased over 112% from 327.0±99.74 in the non-treated group to 694.83±297.86 in the MTR treated group (P<0.05). These results indicates local application of MTR for seven days to spinal cord injury in a swine model decreased tissue injury, reduced tissue edema and preserved more myelin fibers as well as nerve fibers in the injured spinal cord. Keywords: Mechanical tissue resuscitation, Negative pressure treatment, Spinal cord injury, Diffusion tensor imaging, Nerve fiber tractography.

Age-dependent changes in brain hydration and synaptic plasticity.

Aging in humans and animals is associated with gradual and variable changes in some cognitive functions, but what causes them and explains individual variations remains unclear. Hydration decreases with aging but whether dehydration contributes to cognitive dysfunction is not known. The brain hydration of aging mice was determined by colloidosmotic-pressure titration. Dehydration increased with age from ∼76 mmHg at 6 weeks to ∼105 mmHg at 40 weeks, or a progressive ∼10 percent loss of brain water but seemed to level off afterward. When we adjusted dehydration in hippocampal slices of <8-week-old mice to the levels seen in mice 40 weeks and older, their basal synaptic responses were amplified at all stimulus voltages tested, but induction of late-phase long-term potentiation was impaired. Our results document progressive brain dehydration with age in inbred mice to levels at which in vitro synaptic plasticity appears dysregulated. They also suggest that dehydration contributes to some of the changes in synaptic plasticity observed with aging, possibly due to adjustments in neuronal excitation mechanisms.

Local fluid transfer regulation in heart extracellular matrix

The interstitial myocardial matrix is a complex and dynamic structure that adapts to local fluctuations in pressure and actively contributes to the heart's fluid exchange and hydration. However, classical physiologic models tend to treat it as a passive conduit for water and solute, perhaps because local interstitial regulatory mechanisms are not easily accessible to experiment in vivo. Here, we examined the interstitial contribution to the fluid-driving pressure ex vivo. Interstitial hydration potentials were determined from influx/efflux rates measured in explants from healthy and ischemia-reperfusion-injured pigs during colloid osmotic pressure titrations. Adaptive responses were further explored by isolating myocardial fibroblasts and measuring their contractile responses to water activity changes in vitro. Results show hydration potentials between 5 and 60 mmHg in healthy myocardia and shifts in excess of 200 mmHg in edematous myocardia after ischemia-reperfusion injury. Further, rates of fluid transfer were temperature-dependent, and in collagen gel contraction assays, myocardial fibroblasts tended to preserve the micro-environment's hydration volume by slowing fluid efflux rates at pressures above 40 mmHg. Our studies quantify components of the fluid-driving forces in the heart interstitium that the classical Starling's equation does not explicitly consider. Measured hydration potentials in healthy myocardia and shifts with edema are larger than predicted from the known values of hydrostatic and colloid osmotic interstitial fluid pressures. Together with fibroblast responses in vitro, they are consistent with regulatory mechanisms that add local biological controls to classic fluid-balance models (AU)

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Local fluid transfer regulation in heart extracellular matrix.

The interstitial myocardial matrix is a complex and dynamic structure that adapts to local fluctuations in pressure and actively contributes to the heart's fluid exchange and hydration. However, classical physiologic models tend to treat it as a passive conduit for water and solute, perhaps because local interstitial regulatory mechanisms are not easily accessible to experiment in vivo. Here, we examined the interstitial contribution to the fluid-driving pressure ex vivo. Interstitial hydration potentials were determined from influx/efflux rates measured in explants from healthy and ischemia-reperfusion-injured pigs during colloid osmotic pressure titrations. Adaptive responses were further explored by isolating myocardial fibroblasts and measuring their contractile responses to water activity changes in vitro. Results show hydration potentials between 5 and 60 mmHg in healthy myocardia and shifts in excess of 200 mmHg in edematous myocardia after ischemia-reperfusion injury. Further, rates of fluid transfer were temperature-dependent, and in collagen gel contraction assays, myocardial fibroblasts tended to preserve the micro-environment's hydration volume by slowing fluid efflux rates at pressures above 40 mmHg. Our studies quantify components of the fluid-driving forces in the heart interstitium that the classical Starling's equation does not explicitly consider. Measured hydration potentials in healthy myocardia and shifts with edema are larger than predicted from the known values of hydrostatic and colloid osmotic interstitial fluid pressures. Together with fibroblast responses in vitro, they are consistent with regulatory mechanisms that add local biological controls to classic fluid-balance models.

Structural and mechanical characterization of bioresorbable, elastomeric nanocomposites from poly(glycerol sebacate)/nanohydroxyapatite for tissue transport applications.

Poly(glycerol sebacate) (PGS)/nanohydroxyapatite (nHA) composites were assessed to develop new materials for closure via tissue transport for nonhealing defects (e.g., cleft palate and large skin wounds). The elastic shape memory polymer, PGS, was reinforced with nHA at 3 and 5% loading to increase the mechanical properties compared with the undoped PGS. Differential scanning calorimetry (DSC) was utilized to identify a glass transition temperature (Tg ) of -25°C. X-ray diffraction demonstrated a reduction in the amorphous nature of the material. The Fourier transform infrared photoacoustic spectral (FTIR-PAS) data showed decreased CO bonding and increased hydrogen bonding with increased nHA incorporation. Composites exhibited Young's moduli in the range of 0.25-0.5 MPa and tensile strength of 1.5-3 N. No significant difference in extension to break (∼50 mm) with addition of nHA was observed. The elastic modulus significantly increased for 5% PGS/nHA compared to 0 and 3% PGS/nHA and tensile strength significantly increased for 3% PGS/nHA compared to 0 and 5% PGS/nHA. Degradation of 5% nHA/PGS significantly increased during the second week compared to PGS 0 and 3% PGS/nHA. The accelerated degradation for 5% PGS/nHA coupled with decreased flexibility and tensile strength implies an interruption in crosslinking. By maintaining flexibility and extension while increasing tensile strength, the 3% PGS/nHA doped satisfied the force range desired for closure of soft tissue defects. Based on this work, PGS with 3% nHA shape memory polymers should serve as a good candidate for closure of nonhealing soft tissues. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 1366-1373, 2016.

Ameliorating Spinal Cord Injury in an Animal Model With Mechanical Tissue Resuscitation.

BACKGROUND: Traumatic spinal cord injury (SCI) is a major worldwide cause of mortality and disability with limited treatment options. Previous research applying controlled negative pressure to traumatic brain injury in rat and swine models resulted in smaller injuries and more rapid recovery. OBJECTIVE: To examine the effects of the application of a controlled vacuum (mechanical tissue resuscitation [MTR]) to SCI in a rat model under several magnitudes of vacuum. METHODS: Controlled contusion SCIs were created in rats. Vacuums of -50 and -75 mm Hg were compared. Analysis included open-field locomotor performance, magnetic resonance imaging (in vivo T2, ex vivo diffusion tensor imaging and fiber tractography), and histological assessments. RESULTS: MTR treatment significantly improved the locomotor recovery from a Basso, Beattie, and Bresnahan score of 7.8 ± 1.9 to 11.4 ± 1.2 and 10.7 ± 1.9 at -50- and -75-mm Hg pressures, respectively, 4 weeks after injury. Both pressures also reduced fluid accumulations > 10% by T2-imaging in SCI sites. The mean fiber number and mean fiber length were greater across injured sites after MTR treatment, especially with treatment with -50 mm Hg. Myelin volume was increased significantly by 60% in the group treated with -50 mm Hg. CONCLUSION: MTR of SCI in a rat model is effective in reducing edema in the injured cord, preserving myelin survival, and improving the rate and quantity of functional recovery. ABBREVIATIONS: BBB, Basso, Beattie, and BresnahanDTI, diffusion tensor imagingFA, fractional anisotropyMTR, mechanical tissue resuscitationMTR50, mechanical tissue resuscitation with 50-mm Hg subatmospheric pressureMTR75, mechanical tissue resuscitation with 75-mm Hg subatmospheric pressureROI, region of interestSCI, spinal cord injury.

Mechanical tissue resuscitation (MTR): a nonpharmacological approach to treatment of acute myocardial infarction.

BACKGROUND AND AIM: Myocardial ischemia-reperfusion injury is known to trigger an inflammatory response involving edema, apoptosis, and neutrophil activation/accumulation. Recently, mechanical tissue resuscitation (MTR) was described as a potent cardioprotective strategy for reduction of myocardial ischemia-reperfusion injury. Here, we further describe the protective actions of MTR and begin to define its therapeutic window. METHODS: A left ventricular, free-wall ischemic area was created in anesthetized swine for 85 minutes and then reperfused for three hours. Animals were randomized to two groups: (1) untreated controls (Control) and (2) application of MTR that was delayed 90 minutes after the initiation of reperfusion (D90). Hemodynamics and regional myocardial blood flow were assessed at multiple time points. Infarct size and neutrophil accumulation were assessed following the reperfusion period. In separate cohorts, the effect of MTR on myocardial interstitial water (MRI imaging) and blood flow was examined. RESULTS: Both groups had similar areas at risk (AAR), hemodynamics, and arterial blood gas values. MTR, even when delayed 90 minutes into reperfusion (D90, 29.2 ± 5.0% of AAR), reduced infarct size significantly compared to Controls (51.9 ± 2.7%, p = 0.006). This protection was associated with a 33% decrease in neutrophil accumulation (p = 0.047). Improvements in blood flow and interstitial water were also observed. Moreover, we demonstrated that the therapeutic window for MTR lasts for at least 90 minutes following reperfusion. CONCLUSIONS: This study confirms our previous observations that MTR is an effective therapeutic approach to reducing reperfusion injury with a clinically useful treatment window.

Novel nanofiber-based material for endovascular scaffolds.

Conventional collagen-based heart valves eventually fail because of insufficient replacement of graft material by host tissue. In this study, type I collagen was blended with silk fibroin and the synthetic elastic polymer poly (glycerol-sebacate) (PGS) in varying proportions to create multifunctional electrospun nanofibrous materials tailored for use as endovascular scaffolds such as heart valve replacement. Depending on the blended material the elastic moduli ranged from 2.3 to 5.0 Mpa; tensile stresses ranged from 0.8 to 1.5 Mpa; and strains ranged from 30% to 70%. Electrospun materials with a weight ratio of 4.5:4.5:1 (collagen, fibroin, and PGS) (termed PFC mats) were the most similar to native heart valves. In vitro degradation of PFC mats was 0.01% per week. Endothelial cells adhered to, proliferated, and formed cell-cell junctions on PFC mats. Compared with collagen hydrogels and electrospun collagen mats respectively 220-290% less platelet adhesion was observed for PFC mats. The study demonstrates that PFC material has superior mechanical properties, low degradation, and reduced thrombogenic potential and suggests that further investigation of this biomaterial for cardiovascular applications is warranted.

Mechanical tissue resuscitation at the site of traumatic brain injuries reduces the volume of injury and hemorrhage in a swine model.

BACKGROUND: Traumatic brain injuries (TBIs) continue to be a devastating problem with limited treatment options. Previous research applying controlled vacuum to TBI in a rat model resulted in smaller injuries and more rapid recovery. OBJECTIVE: To examine the effects of the application of a controlled vacuum (mechanical tissue resuscitation) to TBI in a large-animal model. The magnitude of vacuum, length of application, and length of delay between injury and the application of mechanical tissue resuscitation were investigated. METHODS: Localized, controlled cortical injuries were created in swine. Vacuums of -50 and -100 mm Hg were compared. Mechanical tissue resuscitation for 3 or 5 days was compared. Delays of 0, 3, or 6 hours between the creation of the TBI and the initiation of mechanical tissue resuscitation were examined. Analysis included histological assessments, computed tomographic perfusion, and magnetic resonance imaging (T2, proton magnetic spectra). RESULTS: A -100 mm Hg vacuum resulted in significantly smaller mean contused brain and hemorrhage volumes compared with -50 mm Hg and controls. Magnetic resonance spectra of treated animals returned to near baseline values. All 10 animals with 5-day mechanical tissue resuscitation treatment survived. Three of 6 animals treated for 3 days died after the discontinuation of treatment. A 3-hour delay resulted in similar results as immediate treatment. A 6-hour delay produced significant, but lesser responses. CONCLUSION: Application of mechanical tissue resuscitation to TBI was efficacious in the large-animal model. Application of -100 mm Hg for 5 days resulted in significantly improved outcomes. Delays of up to 3 hours between injury and the initiation of treatment did not diminish the efficacy of the mechanical tissue resuscitation treatment.

Interstitial-matrix edema in burns: mechanistic insights from subatmospheric pressure treatment in vivo.

Thermal injury disrupts fluid homeostasis and hydration, affecting hemodynamics and local interstitial fluid-driving forces, leading rapidly to edema. This study explores local mechanisms in vivo, after deep partial-thickness burns in the dermal matrix. Heat-damaged skin was obtained from pig corpses, byproducts of unrelated burn treatment protocols approved by the Institutional Animal-Care-and-Use Committee. Hydration potential and flow rates were measured by osmotic stress techniques at 4 and 37 °C, and collagen folding/unfolding was examined by differential scanning calorimetry and diffusion tensor magnetic resonance imaging. Kinetic and equilibrium hydration parameters differed in heat-damaged and undamaged skin; the mean hydration potential and initial flow rates of damaged skin were negative at 37 but positive at 4 °C, in contrast to the positive mean at either temperature of explants taken from undamaged skin sites on the same animals. After subatmospheric pressure treatment (125 mmHg), parameters in damaged reversed to values similar to those of undamaged, whereas the proportion of folded collagen and unidirectional resistance to water diffusion increased. Together, results support interfacial rather than colloidosmotic fluid transfer mechanisms in burns and confirm in vivo the relevance of collagen folding/unfolding, further suggesting collagen structural transitions as potential therapeutic targets and models for engineered biomimetic materials.

Mechanical tissue resuscitation protects against myocardial ischemia-reperfusion injury.

BACKGROUND AND AIM: Reperfusion injury is a complex inflammatory response involving numerous mechanisms and pathways. Mechanical tissue resuscitation is a newly described therapeutic strategy that reduces reperfusion injury. This study further investigates potential mechanisms for the protective effects of mechanical tissue resuscitation while utilizing a bio-absorbable matrix. METHODS: Anesthetized swine were subjected to 80 minutes of coronary ischemia and three hours of reperfusion. An absorbable matrix was used to cover the ischemic-reperfused myocardium and apply the mechanical tissue resuscitation (-50 mmHg) throughout reperfusion. Infarct size, myocardial blood flow (microspheres), apoptosis, edema, and hemodynamics were analyzed. RESULTS: Both control and treated groups displayed similar hemodynamics and physiologic parameters. Mechanical tissue resuscitation significantly reduced early infarct size (16.6 ± 3.8% vs. 27.3 ± 2.5% of area at risk, p < 0.05). This reduction of infarct size was accompanied by reduced edema formation in both epicardial (27% reduction) and endocardial (58% reduction) samples. Histological examination of both epicardial and endocardial tissues also revealed a reduction in apoptosis (80% and 44% reductions) in MTR-treated hearts. CONCLUSIONS: Treatment with mechanical tissue resuscitation during reperfusion reduces both early cell death and the delayed, programmed cell death after ischemia-reperfusion. This cardioprotection is also associated with a significant reduction in interstitial water. Additional cardioprotection may be derived from mechanical tissue resuscitation-induced increased blood flow. Mechanical tissue resuscitation, particularly with a resorbable device, is a straightforward and efficacious mechanical strategy for decreasing cardiomyocyte death following myocardial infarction as an adjunctive therapy to surgical revascularization.

Properties of single electrospun poly (diol citrate)-collagen-proteoglycan nanofibers for arterial repair and in applications requiring viscoelasticity.

Single nanofibers with chemical and functional properties consistent with artery extracellular matrix nanofibers were produced by electrospinning. Using weight ratios to mimic artery extracellular matrix, five materials were tested: (1) Collagen type I, (2) Collagen type I + Collagen type III, (3) Collagen type I + poly (diol citrate), (4) Collagen type I + Collagen type III + poly (diol citrate), and (5) Collagen type I + poly (diol citrate) + Decorin + Aggrecan. Fiber sizes for all materials ranged from 50 nm to 600 nm and random fiber mats had pore sizes from 21 to 40 = m(2) and porosities of 72-84%. Human embryonic palatal mesenchymal cells fibroblasts adhered to all fibers and proliferated over a 7-day study period. Mechanical properties of single fibers were investigated using a combined atomic force/optical microscope. Materials containing poly (diol citrate) showed elasticity increased 3.2 fold greater than composites without poly (diol citrate). Maximum stress was within functional range in comparison to decellularized artery extracellular matrix fibers. By incorporating poly (diol citrate) and proteoglycan along with collagen, a viscoelastic nanofibrous material was produced for use in tissues such as artery where viscoelasticity and tensile strength are required.

Cerebral blood flow quantification in swine using pseudo-continuous arterial spin labeling.

PURPOSE: To develop quantitative cerebral blood flow (CBF) imaging using pseudo-continuous arterial spin labeling (PCASL) in swine, accounting for their cerebrovascular anatomy and physiology. MATERIALS AND METHODS: Five domestic pigs (2.5-3 months, 25 kg) were used in these studies. The orientation of the labeled arteries, T1bl , M0bl , and T1gm were measured in swine. Labeling parameters were tuned with respect to blood velocity to optimize labeling efficiency based on the data collected from three subjects. Finally, CBF and arterial transit time (ATT) maps for two subjects were created from PCASL data to determine global averages. RESULTS: The average labeling efficiency over measured velocities of 5-18 cm/s was 0.930. The average T1bl was 1546 ms, the average T1gm was 1224 ms, and the average blood-to-white matter ratio of M0 was 1.25, which was used to find M0bl . The global averages over the subjects were 54.05 mL/100 g tissue/min CBF and 1261 ms ATT. CONCLUSION: This study demonstrates the feasibility of PCASL for CBF quantification in swine. Quantification of CBF using PCASL in swine can be further developed as an accessible and cost-effective model of human cerebral perfusion for investigating injuries that affect blood flow.

Collagen unfolding accelerates water influx, determining hydration in the interstitial matrix.

In the interstitial matrix, collagen unfolding at physiologic temperatures is thought to facilitate interactions with enzymes and scaffold molecules during inflammation, tissue remodeling, and wound healing. We tested the hypothesis that it also plays a role in modulating flows and matrix hydration potential. After progressively unfolding dermal collagen in situ, we measured the hydration parameters by osmotic stress techniques and modeled them as linear functions of unfolded collagen, quantified by differential scanning calorimetry after timed heat treatment. Consistent with the hypothetical model, the thermodynamic and flow parameters obtained experimentally were related linearly to the unfolded collagen fraction. The increases in relative humidity and intensity of T(2) maps were also consistent with interfacial energy contributions to the hydration potential and the hydrophobic character of the newly formed protein/water interfaces. As a plausible explanation, we propose that increased tension at interfaces formed during collagen unfolding generate local gradients in the matrix that accelerate water transfer in the dermis. This mechanism adds a convective component to interstitial transfer of biological fluids that, unlike diffusion, can speed the dispersion of water and large solutes within the matrix.

A new method for modulating traumatic brain injury with mechanical tissue resuscitation.

BACKGROUND: Traumatic brain injuries remain a treatment enigma with devastating late results. As terminally differentiated tissue, the brain retains little capacity to regenerate, making early attempts to preserve brain cells after brain injury essential. OBJECTIVE: To resuscitate damaged tissue by modulating edema, soluble cytokines, and metabolic products in the "halo" of damaged tissue around the area of central injury that progressively becomes compromised. By re-equilibrating the zone of injury milieu, it is postulated neurons in this area will survive and function. METHODS: Mechanical tissue resuscitation used localized, controlled, subatmospheric pressure directly to the area of controlled cortical impact injury and was compared with untreated injured controls and with sham surgery in a rat model. Functional outcome, T2 magnetic resonance imaging hyperintense volume, magnetic resonance imaging spectroscopy metabolite measurement, tissue water content, injury cavity area, and cortical volume were compared. RESULTS: There were significant differences between mechanical tissue resuscitation treated and untreated groups in levels of myoinositol, N-acetylaspartate, and creatine. Treated animals had significantly less tissue swelling and density than the untreated animals. Nonviable brain tissue areas were smaller in treated animals than in untreated animals. Treated animals performed better than untreated animals in functional tests. Histological analysis showed the remaining viable ipsilateral cerebral area was 58% greater for treated animals than for untreated animals, and the cavity for treated animals was 95% smaller than for untreated animals 1 month after injury. CONCLUSION: Mechanical tissue resuscitation with controlled subatmospheric pressure can significantly modulate levels of excitatory amino acids and lactate in traumatic brain injury, decrease the water content and volume of injured brain, improve neuronal survival, and speed functional recovery.

Development of a biodegradable foam for use in negative pressure wound therapy.

Treatment of wounds using negative pressure wound therapy (NPWT) uses a nondegradable polyvinyl alcohol (PVA) foam in the application of negative pressures typically for 1-3 days. The purpose of this study was to construct and test biodegradable poly(ε-caprolactone) (PCL) foam as a substitute for the PVA foam. Such a foam would be left within the wound until healing was achieved and form a biodegradable matrix into which tissue would grow. The use of such foam would obviate the need for any serial foam changes and a final foam removal, thus making patient care much easier and more economical. PCL foams were prepared by salt leaching and phase separation. Morphological and mechanical properties of the foams were characterized and compared to PVA foam. PCL and PVA foams were tested on the uncut surface of a pig liver maintained in a hydration chamber continuously replenished with saline under the conditions of negative pressure of 50 mm Hg for 72 h. The results demonstrated that PCL foam made from phase separation had the similar properties and function as the PVA foam. The results demonstrate that PCL foam is an appropriate substitute for currently used nondegradable PVA foam in NPWT applications.

The local pathology of interstitial edema: surface tension increases hydration potential in heat-damaged skin.

The local pathogenesis of interstitial edema in burns is incompletely understood. This ex vivo study investigates the forces mediating water-transfer in and out of heat-denatured interstitial matrix. Experimentally, full-thickness dermal samples are heated progressively to disrupt glycosaminoglycans, kill cells, and denature collagen under conditions that prevent water loss/gain; subsequently, a battery of complementary techniques including among others, high-resolution magnetic resonance imaging, equilibrium vapor pressure and osmotic stress are used to compare water-potential parameters of nonheated and heated dermis. The hydration potential (HP) determined by osmotic stress is a measure of the total water-potential defined empirically as the pressure at which no net water influx/efflux into/from the dermis is detected. Results show that after heat denaturation, the HP, the intensity of T2-weighed magnetic resonance images, and the vapor pressure increase indicating higher water activity and necessarily, smaller contributions from colloidosmotic forces to fluid influx in burned relative to healthy dermis. Concomitant increases in HP and in water activity implicate local changes in interfacial and metabolic energy as the source of excess fluid-transfer potential. These ex vivo findings also show that these additional forces contributing to abnormal fluid-transfer in burned skin develop independently of inflammatory and systemic hydrodynamic responses.

Loxoscelism and negative pressure wound therapy (vacuum-assisted closure): an experimental study.

Brown recluse spider (Loxosceles) bites cause lesions ranging from chronic necrotic ulcers to acute life-threatening sepsis. Based on our experience in treating acute and chronic wounds with negative pressure, we postulated that vacuum-assisted closure (VAC) would be valuable in this application. Chester pigs were procured and injected with purified brown recluse spider venom, 1 µl of venom in two anterior sites and 0·1 µl of venom in two posterior sites on their dorsum. For each concentration of venom, treatment consisted of either VAC or dry, non adherent dressings (control group). Each day, the wounds were inspected and measured. For wounds receiving 1·0 µl of venom, the control wounds decreased in surface area to 50% of initial size after 7 days and none had healed, whereas VAC-treated wounds were less than 50% after 48 hours and completely healed and reepithelialised after 8 days. Wounds with 0·1 µl of venom had 50% reduction after 5 days with no complete healing for control wounds, and the VAC wounds were 50% after 48 hours and all had closed and reepithelialised after 5 days. Our experimental study showed an accelerated healing time in the animals treated with the VAC as compared with controls.