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.

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.

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.

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.

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.

Reduction of myocardial ischemia-reperfusion injury by mechanical tissue resuscitation using sub-atmospheric pressure.

BACKGROUND: Reperfusion-induced injury after myocardial infarction is associated with a well-defined sequence of early and late cardiomyocyte death. Most present attempts to ameliorate this sequence focus on a single facet of the complex process in an attempt to salvage cardiomyocytes. We examined, as proof of concept, the effects of mechanical tissue resuscitation (MTR) with controlled negative pressure on myocardial injury following acute myocardial infarction. METHODS: Anesthetized swine were subjected to 75 minutes of left coronary artery occlusion and three hours of reperfusion. Animals were assigned to one of three groups: (A) untreated control; treatment of involved myocardium for 180 minutes of MTR with (B) -50 mmHg, or (C) -125 mmHg. RESULTS: All three groups were subjected to equivalent ischemic stress. Treatment of the ischemic area with MTR for 180 minutes significantly (p < 0.001) reduced infarct size (area of necrosis/area at risk) in both treatment groups compared to control: 9.3 +/- 1.8% (-50 mmHg) and 11.9 +/- 1.2% (-125 mmHg) versus 26.4 +/- 2.1% (control). Total area of cell death was reduced by 65% with -50 mmHg treatment and 55% in the -125 mmHg group. CONCLUSIONS: Treatment of ischemic myocardium with MTR, for a controlled period of time during reperfusion, successfully reduced the extent of myocardial death after acute myocardial infarction. These data provide evidence that MTR using subatmospheric pressure may be a simple, efficacious, nonpharmacological, mechanical strategy for decreasing cardiomyocyte death following myocardial infarction, which can be delivered in the operating room.

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.

Loxoscelism and negative pressure wound therapy (vacuum-assisted closure): a clinical case series.

Brown recluse spider (Loxosceles sp) bites continue to be a significant challenge to manage clinically. Sequelae from these lesions range from chronic necrotic ulcers that persist for months to an acute life-threatening course of sepsis. Negative pressure wound therapy using vacuum-assisted closure (VAC) has been described for use in both acute and chronic wounds. We present a novel application for the use of this therapy in a retrospective review of eight clinical cases treated with the VAC.

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.

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.

Acceleration of Integra incorporation in complex tissue defects with subatmospheric pressure.

In an effort to accelerate vascularization and simplify the care of Integra (Ethicon, Inc., Somerville, N.J.), topical subatmospheric pressure was used for eight patients (age range, 2 to 60 years) with complex wounds. Bone was exposed in 62.5 percent of cases, joint in 50 percent, tendon in 37.5 percent, and bowel in 25 percent. The estimated Integra take rate was 96 percent. Split-thickness skin grafting was performed at 4 to 11 days (mean, 7.25 days), with a 93 percent take rate. No adverse side effects were observed with this technique. Application of subatmospheric pressure improved the take rate and time to vascularization of Integra, compared with previous published results, even with complicated wounds. This technique may be a practical alternative to flap closure.

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.

Vacuum-assisted closure: state of basic research and physiologic foundation.

A tremendous amount of research has been conducted in recent years investigating the mechanisms of action by which the application of subatmospheric pressure to wounds increases the rate of healing. Similarly, numerous studies have also been conducted examining the physiologic response of wounds to the applied subatmospheric pressure. However, many more need to be conducted. A series of basic studies examining the use of subatmospheric pressure to treat wounds is presented, including the original studies upon which the vacuum-assisted closure device was based (on blood flow, granulation tissue formation, bacterial clearance, and survival of random-pattern pedicle flaps). Subsequent studies analyzing removed fluids, envenomation/extravasation, burns, grafts, and in vitro tissue culture studies are also reviewed. Two broad mechanisms of action are proposed: removal of fluid and mechanical deformation. Fluid removal both decreases edema--thus decreasing interstitial pressure and shortening distances of diffusion--and removes soluble factors that may affect the healing process (both positively and negatively). The relationship of mechanical deformation to increased growth is well known to plastic surgeons, as it is the basis of tissue expansion. While much has been done, a great deal more needs to be done to elucidate the mechanisms of action responsible for the dramatic response seen clinically.

Vacuum-assisted closure: state of clinic art.

Treatment of wounds has been the cornerstone of plastic surgery since its inception. Vacuum-assisted closure provides a new paradigm that can be used in concert with a wide variety of standard existing plastic surgery techniques. It was originally developed as an alternative treatment for debilitated patients with chronic wounds. It has rapidly evolved into a widely accepted treatment of chronic and acute wounds, contaminated wounds, burns, envenomations, infiltrations, and wound complications from failed operations. The ease of technique and a high rate of success have encouraged its adaptation by thoracic, general, trauma, burn, orthopedic, urologic, as well as plastic surgeons. This article discusses multidisciplinary advances in the use of the vacuum-assisted closure technique over the past 10 years and its status as of 2006. Creative surgeons continue to regularly adapt the system to difficult problems. This technique in trained surgical hands greatly enhances the scope and safety of wound treatment.

Management of an acute thermal injury with subatmospheric pressure.

OBJECTIVE: This article reports the first application of subatmospheric pressure management to a deep, partial-thickness human thermal burn. METHODS: After cleaning the wound, the decision was made to treat the hand and distal forearm with subatmospheric pressure (V.A.C., KCI, Inc, San Antonio, Tex). The sponge was applied directly to the burned skin without additional interface at approximately 6 hours after injury. The dressing was maintained at a continuous negative pressure of 125 mm Hg over the next 40 hours, with interruption only for routine clinical evaluation at 5, 16, and 24 hours after initiation of treatment. This was accomplished by opening the dressing without completely changing it. The treatment was tolerated well by the patient, requiring no excessive pain medication. After the subatmospheric pressure treatment was stopped, the wound appeared to be of indeterminate depth and the patient was started on twice daily applications of silver sulfadiazine. RESULTS: The clinical impression at this time was that the hand burn had not progressed but had stabilized and had minimal edema. He was followed as an outpatient and returned to work by 8 weeks. At approximately 4 weeks postinjury, his skin not only was functional but also appeared more normal, with less hyperemia than adjacent areas treated with topical antibacterials. CONCLUSION: The present case does not prove that subatmospheric pressure treatment prevents burn wound progression. However, when combined with the previously reported laboratory studies it suggests the need for further research. Currently, a prospective, randomized, blinded, controlled multicenter trial is underway to evaluate the clinical importance of these observations.

The effect of externally applied subatmospheric pressure on serum myoglobin levels after a prolonged crush/ischemia injury.

BACKGROUND: Patients with injuries that cause significant muscle death often develop rhabdomyolysis. The subsequent release and entry of myoglobin into the systemic circulation leads to myoglobinuria, renal injury, and potentially acute renal failure. METHODS: Large (5 kg) adult rabbits (n = 8) were anesthetized and a 15-kg weight placed on the posterior compartment for 4 hours. After this time, the weight was removed and releasing incisions were made. Subatmospheric pressure (125 mm Hg) was continuously applied to the wounds of four rabbits. Systemic serum samples were obtained at the time of weight removal and at 2, 4, and 8 hours postremoval, and were analyzed for myoglobin content. RESULTS: Serum myoglobin levels were similar for both groups at the time of weight removal. Serum myoglobin levels demonstrated a progressive increase with time in nontreated animals, and were significantly elevated compared with subatmospheric pressure-treated animals at all time points (p < 0.001). CONCLUSION: This study shows that application of subatmospheric pressure to an affected body part is associated with lower serum myoglobin levels.