Optimization of the IntraVascular Oxygenator Catheter Using Angular Oscillation.

We demonstrate a methodology which both improves oxygen transport and reduces or eliminates bubble formation in a novel hyperbaric membrane oxygenator catheter model system. Angular oscillations were introduced to a bundle of hollow fiber membranes (HFMs) supplied with hyperbaric 100% oxygen at average gauge pressures up to 0.35 barg. Oscillating bundles enabled delivery of an oxygen flux of up to 400 mL min-1 m-2 in an aqueous solution, a doubling over a previous non-oscillating setup. Similarly, the addition of angular oscillations facilitated a five-fold reduction in pressure to achieve similar oxygen flux. The increased angular speed of oscillation improved flux, while the addition of angular micro-oscillation variations resulted in flux reductions of 7-20% compared to continuous macro-oscillation only, depending on mixing conditions. However, semi-quantitative visual observation demonstrated that angular oscillations reduced or eliminated the instance of oxygen bubble formation on the HFMs. The modeled mass transfer coefficients indicated a quasi linear relationship between rotational velocity and flux, suggesting that faster oscillation speeds could further improve oxygen mass transport allowing for HFM bundles to maintain high oxygen fluxes while eliminating bubble formation. This encourages further development of our compact oxygenating catheter that could be used intravascularly.

Intravascular Gas Exchange: Physiology, Literature Review, and Current Efforts.

Acute respiratory failure with inadequate oxygenation and/or ventilation is a common reason for ICU admission in children and adults. Despite the morbidity and mortality associated with acute respiratory failure, few proven treatment options exist beyond invasive ventilation. Attempts to develop intravascular respiratory assist catheters capable of providing clinically important gas exchange have had limited success. Only one device, the IVOX catheter, was tested in human clinical trials before development was halted without FDA approval. Overcoming the technical challenges associated with providing safe and effective gas exchange within the confines of the intravascular space remains a daunting task for physicians and engineers. It requires a detailed understanding of the fundamentals of gas transport and respiratory physiology to optimize the design for a successful device. This article reviews the potential benefits of such respiratory assist catheters, considerations for device design, previous attempts at intravascular gas exchange, and the motivation for continued development efforts.

The Influence of Topical Vasodilator-Induced Pharmacologic Delay on Cutaneous Flap Viability and Vascular Remodeling.

BACKGROUND: Surgical delay is a well-described technique to improve survival of random and pedicled cutaneous flaps. The aim of this study was to test the topical agents minoxidil and iloprost as agents of pharmacologic delay to induce vascular remodeling and decrease overall flap necrosis as an alternative to surgical delay. METHODS: Seven groups were studied (n = 8 in each group), including the following: vehicle, iloprost, or minoxidil before treatment only; vehicle, iloprost, or minoxidil before and after treatment; and a standard surgical delay group as a positive control. Surgical flaps (caudally based modified McFarlane myocutaneous skin flaps) were elevated after 14 days of pretreatment, reinset isotopically, and observed at various time points until postoperative day 7. Gross viability, histology, Doppler blood flow, perfusion imaging, tissue oxygenation measurement, and vascular casting were performed for analysis. RESULTS: Pharmacologic delay with preoperative application of topical minoxidil or iloprost was found to have comparable flap viability when compared to surgical delay. Significantly increased viability in all treatment groups was observed when compared with vehicle. Continued postoperative treatment with topical agents had no effect on flap viability. The mechanism of improved flap viability was inducible increases in flap blood volume and perfusion rather than the acute vasodilatory effects of the topical agents or decreased flap hypoxia. CONCLUSIONS: Preoperative topical application of the vasodilators minoxidil or iloprost improved flap viability comparably to surgical delay. Noninvasive pharmacologic delay may reduce postoperative complications without the need for an additional operation. CLINICAL RELEVANCE STATEMENT: Preoperative use of topical vasodilators may lead to improved flap viability without the need for a surgical delay procedure. This study may inform future clinical trials examining utility of preoperative topical vasodilators in flap surgery.

Poly(lactide-co-ε-caprolactone) scaffold promotes equivalent tissue integration and supports skin grafts compared to a predicate collagen scaffold.

Dermal scarring from motor vehicle accidents, severe burns, military blasts, etc. is a major problem affecting over 80 million people worldwide annually, many of whom suffer from debilitating hypertrophic scar contractures. These stiff, shrunken scars limit mobility, impact quality of life, and cost millions of dollars each year in surgical treatment and physical therapy. Current tissue engineered scaffolds have mechanical properties akin to unwounded skin, but these collagen-based scaffolds rapidly degrade over 2 months, premature to dampen contracture occurring 6-12 months after injury. This study demonstrates a tissue engineered scaffold can be manufactured from a slow-degrading viscoelastic copolymer, poly(ι-lactide-co-ε-caprolactone), with physical and mechanical characteristics to promote tissue ingrowth and support skin-grafts. Copolymers were synthesized via ring-opening polymerization. Solvent casting/particulate leaching was used to manufacture 3D porous scaffolds by mixing copolymers with particles in an organic solvent followed by casting into molds and subsequent particle leaching with water. Scaffolds characterized through SEM, micro-CT, and tensile testing confirmed the required thickness, pore size, porosity, modulus, and strength for promoting skin-graft bioincorporation and dampening fibrosis in vivo. Scaffolds were Oxygen Plasma Treatment and collagen coated to encourage cellular proliferation. Porosity ranging from 70% to 90% was investigated in a subcutaneous murine model and found to have no clinical effect on tissue ingrowth. A swine full-thickness skin wound model confirmed through histology and Computer Planimetry that scaffolds promote skin-graft survival, with or without collagen coating, with equal safety and efficacy as a commercially available tissue engineered scaffold. This study validates a scalable method to create poly(ι-lactide-co-ε-caprolactone) scaffolds with appropriate characteristics and confirms in mouse and swine wound models that the scaffolds are safe and effective at supporting skin-grafts. The results of this study have brought us closer towards developing an alternative technology that supports skin grafts with the potential to investigate long-term hypertrophic scar contractures.

Development of a novel intravascular oxygenator catheter: Oxygen mass transfer properties across nonporous hollow fiber membranes.

Despite hypoxic respiratory failure representing a large portion of total hospitalizations and healthcare spending worldwide, therapeutic options beyond mechanical ventilation are limited. We demonstrate the technical feasibility of providing oxygen to a bulk medium, such as blood, via diffusion across nonporous hollow fiber membranes (HFMs) using hyperbaric oxygen. The oxygen transfer across Teflon® membranes was characterized at oxygen pressures up to 2 bars in both a stirred tank vessel (CSTR) and a tubular device mimicking intravenous application. Fluxes over 550 ml min-1 m-2 were observed in well-mixed systems, and just over 350 ml min-1 m-2 in flow through tubular systems. Oxygen flux was proportional to the oxygen partial pressure inside the HFM over the tested range and increased with mixing of the bulk liquid. Some bubbles were observed at the higher pressures (1.9 bar) and when bulk liquid dissolved oxygen concentrations were high. High-frequency ultrasound was applied to detect and count individual bubbles, but no increase from background levels was detected during lower pressure operation. A conceptual model of the oxygen transport was developed and validated. Model parametric sensitivity studies demonstrated that diffusion through the thin fiber walls was a significant resistance to mass transfer, and that promoting convection around the fibers should enable physiologically relevant oxygen supply. This study indicates that a device is within reach that is capable of delivering greater than 10% of a patient's basal oxygen needs in a configuration that readily fits intravascularly.

Detection of flap tissue ischemia in a rat model: Real-time monitoring of changes in oxygenation and perfusion through injectable biosensors.

BACKGROUND: The success of surgical flaps is improved by timely correction of vascular compromise. Current monitoring methods are labor or cost intensive or have limited clinical benefit. We hypothesize that injectable oxygen sensors can identify acute vascular compromise. The purpose of this study was to use a long-term, real-time method of tissue oxygenation detection in a rat flap model with vascular manipulation. METHODS: Sensors incorporated benzo-porphyrin dye into a microporous hydrogel and were injected intradermally 1 day before flap elevation. Inspired oxygen was modulated between 100% and 12% to confirm sensor O2 sensitivity. Eight random flaps (4 cm wide, 8 cm long) were elevated. Sensor and clinical observation to temporary clamping of the flap vascular pedicle was recorded. Sodium fluorescein in saline was injected intraperitoneally on postoperative days 0, 3, and 7 with subsequent perfusion area analysis. RESULTS: Tissue oxygen tension measurements reflected the changes in inspired oxygen levels. Clinical observation of the flaps did not show any significant change in color or temperature with pedicle clamping. However, clamping of the pedicle resulted in a significant decrease in sensor tissue oxygen tension within 70 seconds. CONCLUSION: Oxygen monitoring of myocutaneous flaps is sensitive and can detect acute vascular occlusion. This technique is faster than current methods and offers a cost-effective and accurate means of monitoring surgical tissues.

Machine Perfusion of Liver Grafts With Implantable Oxygen Biosensors: Proof of Concept Study in a Rodent Model.

BACKGROUND: Normothermic machine perfusion (NMP) is emerging as a novel preservation strategy in liver transplantation, but the optimal methods for assessing liver grafts during this period have not been determined. The aim of this study was to investigate whether implantable oxygen biosensors can be used to monitor tissue oxygen tension in liver grafts undergoing NMP. METHODS: Implantable phosphorescence-based oxygen sensors were tested in 3 different experimental groups: (1) in vivo during laparotomy, (2) during NMP of liver grafts with an acellular perfusate (NMP-acellular), and (3) during NMP with perfusate containing red blood cells (NMP-RBC). During in vivo experiments, intrahepatic oxygen tension was measured before and after occlusion of the portal vein (PV). In NMP experiments, intrahepatic oxygen tension was measured as a function of different PV pressure settings (3 vs 5 vs 8 mm Hg) and inflow oxygen concentration (95% O2 vs 6% O2). RESULTS: In vivo, intrahepatic oxygen tension decreased significantly within 2 minutes of clamping the PV (P < 0.05). In NMP experiments, intrahepatic oxygen tension correlated directly with PV pressure when high inflow oxygen concentration (95%) was used. Intrahepatic oxygen tension was significantly higher in the NMP-RBC group compared with the NMP-acellular group for all conditions tested (P < 0.05). CONCLUSIONS: Implantable oxygen biosensors have potential utility as a tool for real-time monitoring of intrahepatic oxygen tension during NMP of liver grafts. Further investigation is required to determine how intrahepatic oxygen tension during NMP correlates with posttransplant graft function.

Continuous monitoring of interstitial tissue oxygen using subcutaneous oxygen microsensors: In vivo characterization in healthy volunteers.

Measurements of regional tissue oxygen serve as a proxy to monitor local perfusion and have the potential to guide therapeutic decisions in multiple clinical disciplines. Transcutaneous oximetry (tcpO2) is a commercially available noninvasive technique that uses an electrode to warm underlying skin tissue and measure the resulting oxygen tension at the skin surface. A novel approach is to directly measure interstitial tissue oxygen using subcutaneous oxygen microsensors composed of a biocompatible hydrogel carrier platform with embedded oxygen sensing molecules. After initial injection of the hydrogel into subcutaneous tissue, noninvasive optical measurements of phosphorescence-based emissions at the skin surface are used to sense oxygen in the subcutaneous interstitial space. The object of the present study was to characterize the in vivo performance of subcutaneous microsensors and compare with transcutaneous oximetry (tcpO2). Vascular occlusion tests were performed on the arms of 7 healthy volunteers, with repeated tests occurring 1 to 10 weeks after sensor injection, yielding 95 total tests for analysis. Comparative analysis characterized the response of both devices to decreases in tissue oxygen during occlusion and to increases in tissue oxygen following release of the occlusion. Results indicated: (I) time traces returned by microsensors and tcpO2 were highly correlated, with the median (interquartile range) correlation coefficient of r = 0.93 (0.10); (II) both microsensors and tcpO2 sensed a statistically significant decrease in normalized oxygen during occlusion (p < 0.001 for each device); (III) microsensors detected faster rates change (p < 0.001) and detected overshoot during recovery more frequently (38% vs. 4% of tests); (IV) inter-measurement analysis showed no correlation of baseline values between microsensors and tcpO2 (r = 0.03), but comparison of integrated oxygen dynamics showed similar variation in the normalized response to occlusion between devices (p = 0.06), (V) intra-measurement analysis revealed that microsensors detect greater physiological fluctuations than tcpO2 (p < 0.001) and may provide enhanced sensitivity to processes such as vasomotion. Additionally, the functional response of microsensors was not significantly different across time groupings (per month) post-injection (p = 0.61). Although the compared devices have differences in the mechanisms used to sense oxygen, these findings demonstrate that subcutaneous oxygen microsensors measure changes in interstitial tissue oxygen in human subjects in vivo.

Enhanced Drug Delivery to the Skin Using Liposomes.

BACKGROUND: Enhancing drug delivery to the skin has importance in many therapeutic strategies. In particular, the outcome in vascularized composite allotransplantation mainly depends on systemic immunosuppression to prevent and treat episodes of transplant rejection. However, the side effects of systemic immunosuppression may introduce substantial risk to the patient and are weighed against the expected benefits. Successful enhancement of delivery of immunosuppressive agents to the most immunogenic tissues would allow for a reduction in systemic doses, thereby minimizing side effects. Nanoparticle-assisted transport by low temperature-sensitive liposomes (LTSLs) has shown some benefit in anticancer therapy. Our goal was to test whether delivery of a marker agent to the skin could be selectively enhanced. METHODS: In an in vivo model, LTSLs containing doxorubicin (dox) as a marker were administered intravenously to rats that were exposed locally to mild hyperthermia. Skin samples of the hyperthermia treated hind limb were compared with skin of the contralateral normothermia hind limb. Tissue content of dox was quantified both via high-performance liquid chromatography and via histology in skin and liver. RESULTS: The concentration of dox in hyperthermia-treated skin was significantly elevated over both normothermic skin and liver. (P < 0.02). CONCLUSIONS: We show here that delivery of therapeutics to the skin can be targeted and enhanced using LTSLs. Targeting drug delivery with this method may reduce the systemic toxicity seen in a systemic free-drug administration. Development of more hydrophilic immunosuppressants in the future would increase the applicability of this system in the treatment of rejection reactions in vascularized composite allotransplantation. The treatment of other skin condition might be another potential application.

Antibiotic-induced changes in the microbiota disrupt redox dynamics in the gut.

How host and microbial factors combine to structure gut microbial communities remains incompletely understood. Redox potential is an important environmental feature affected by both host and microbial actions. We assessed how antibiotics, which can impact host and microbial function, change redox state and how this contributes to post-antibiotic succession. We showed gut redox potential increased within hours of an antibiotic dose in mice. Host and microbial functioning changed under treatment, but shifts in redox potentials could be attributed specifically to bacterial suppression in a host-free ex vivo human gut microbiota model. Redox dynamics were linked to blooms of the bacterial family Enterobacteriaceae. Ecological succession to pre-treatment composition was associated with recovery of gut redox, but also required dispersal from unaffected gut communities. As bacterial competition for electron acceptors can be a key ecological factor structuring gut communities, these results support the potential for manipulating gut microbiota through managing bacterial respiration.

Characterization of the Foreign Body Response to Common Surgical Biomaterials in a Murine Model.

BACKGROUND: Implanted biomaterials are subject to a significant reaction from the host, known as the foreign body response (FBR). We quantified the FBR to five materials following subcutaneous implantation in mice. MATERIALS AND METHODS: Polyvinyl alcohol (PVA) and silicone sheets are considered highly biocompatible biomaterials and were cut into 8mm-diameter disks. Expanded PTFE (ePTFE)and polypropylene are also widely used biocompatible biomaterials and were cut into 2cm-long cylinders. Cotton was selected as a negative control material that would invoke an intense FBR, was cut into disks and implanted. The implants were inserted subcutaneously into female C57BL/6 mice. On post-implantation days 14, 30, 60, 90 and 180, implants were retrieved. Cellularity was assessed with DAPI stain, collagen with Masson's trichrome stain. mast cells with toluidine-blue, macrophages with F4/80 immunohistochemical-stain, and capsular thickness and foreign body giant cells with hematoxylin & eosin. RESULTS: DAPI revealed a significantly increased cellularity in both PVA andsilicone, and ePTFE had the lowest cell density. Silicone showed the lowest cellularity at d14 and d90 whereas ePTFE showed the lowest cellularity at days 30, 60, and 180. Masson's trichrome staining demonstrated no apparent difference in collagen. Toluidine blue showed no differences in mast cells. There were, however, fewer macrophages associated with ePTFE. On d14, PVA had highest number of macrophages, whereas polypropylene had the highest number at all time points after d14. Giant cells increased earlier and gradually decreased later. On d90, PVA exhibited a significantly increased number of giant cells compared to polypropylene and silicone. Silicone consistently formed the thinnest capsule throughout all time points. On d14, cotton had formed the thickest capsule. On d30 polypropylenehas formed thickest capsule and on days 60, 90 and 180, PVA had formed thickest capsule. CONCLUSION: These data reveal differences in capsule thickness and cellular response in an implant-related manor, indicating that fibrotic reactions to biomaterials are implant specific and should be carefully considered when performing studies on fibrosis when biomaterials are being used.

Injectable Phosphorescence-based Oxygen Biosensors Identify Post Ischemic Reactive Hyperoxia.

Novel injectable biosensors were used to measure interstitial oxygenation before, during, and after transient ischemia. It is well known that reactive hyperemia occurs following a period of ischemia. However, increased blood flow does not necessarily mean increased oxygen tension in the tissue. Therefore, the purpose of this study was to test the hypothesis that tissue reactive hyperoxia occurs following release of hind-limb tourniquet occlusions. Rats were injected with bilateral hind-limb biosensors and were simultaneously subjected to a unilateral femoral vessel ligation. After approximately one and three months, the rats underwent a series of oxygenation challenges, including transient hind-limb tourniquet occlusion. Along with the biosensors, near infrared spectroscopy was used to measure percent oxyhemoglobin in capillaries and laser Doppler flowmetry was used to measure blood flow. Post-occlusion reactive hyperemia was observed. It was accompanied by tissue reactive hyperoxia, affirming that the post-occlusion oxygen supply must have exceeded the expected increased oxygen consumption. The measurement of the physiologic phenomenon of reactive hyperoxia could prove clinically beneficial for both diagnosis and optimizing therapy.

Tissue-Integrating Oxygen Sensors: Continuous Tracking of Tissue Hypoxia.

We describe a simple method of tracking oxygen in real-time with injectable, tissue-integrating microsensors. The sensors are small (500 µm × 500 µm × 5 mm), soft, flexible, tissue-like, biocompatible hydrogel s that have been shown to overcome the foreign body response for long-term sensing. The sensors are engineered to change luminescence in the presence of oxygen or other analytes and function for months to years in the body. A single injection followed by non-invasive monitoring with a hand-held or wearable Bluetooth optical reader enables intermittent or continuous measurements. Proof of concept for applications in high altitude, exercise physiology, vascular disease, stroke, tumors, and other disease states have been shown in mouse, rat and porcine models. Over 90 sensors have been studied to date in humans. These novel tissue-integrating sensors yield real-time insights in tissue oxygen fluctuations for research and clinical applications.

Stiffness of Protease Sensitive and Cell Adhesive PEG Hydrogels Promotes Neovascularization In Vivo.

Materials that support the assembly of new vasculature are critical for regenerative medicine. Controlling the scaffold's mechanical properties may help to optimize neovascularization within implanted biomaterials. However, reducing the stiffness of synthetic hydrogels usually requires decreasing polymer densities or increasing chain lengths, both of which accelerate degradation. We synthesized enzymatically-degradable poly(ethylene glycol) hydrogels with compressive moduli from 2 to 18 kPa at constant polymer density, chain length, and proteolytic degradability by inserting an allyloxycarbonyl functionality into the polymer backbone. This group competes with acrylates during photopolymerization to alter the crosslink network structure and reduce the hydrogel's stiffness. Hydrogels that incorporated (soft) or lacked (stiff) this group were implanted subcutaneously in rats to investigate the role of stiffness on host tissue interactions. Changes in tissue integration were quantified after 4 weeks via the hydrogel area replaced by native tissue (tissue area fraction), yielding 0.136 for softer vs. 0.062 for stiffer hydrogels. Including soluble FGF-2 and PDGF-BB improved these responses to 0.164 and 0.089, respectively. Softer gels exhibited greater vascularization with 8.6 microvessels mm-2 compared to stiffer gels at 2.4 microvessels mm-2. Growth factors improved this to 11.2 and 4.9 microvessels mm-2, respectively. Softer hydrogels tended to display more sustained responses, promoting neovascularization and tissue integration in synthetic scaffolds.

A medical-toxicological view of tattooing.

Long perceived as a form of exotic self-expression in some social fringe groups, tattoos have left their maverick image behind and become mainstream, particularly for young people. Historically, tattoo-related health and safety regulations have focused on rules of hygiene and prevention of infections. Meanwhile, the increasing popularity of tattooing has led to the development of many new colours, allowing tattoos to be more spectacular than ever before. However, little is known about the toxicological risks of the ingredients used. For risk assessment, safe intradermal application of these pigments needs data for toxicity and biokinetics and increased knowledge about the removal of tattoos. Other concerns are the potential for phototoxicity, substance migration, and the possible metabolic conversion of tattoo ink ingredients into toxic substances. Similar considerations apply to cleavage products that are formed during laser-assisted tattoo removal. In this Review, we summarise the issues of concern, putting them into context, and provide perspectives for the assessment of the acute and chronic health effects associated with tattooing.

Porous, Dexamethasone-loaded polyurethane coatings extend performance window of implantable glucose sensors in vivo.

Continuous glucose sensors offer the promise of tight glycemic control for insulin dependent diabetics; however, utilization of such systems has been hindered by issues of tissue compatibility. Here we report on the in vivo performance of implanted glucose sensors coated with Dexamethasone-loaded (Dex-loaded) porous coatings employed to mediate the tissue-sensor interface. Two animal studies were conducted to (1) characterize the tissue modifying effects of the porous Dex-loaded coatings deployed on sensor surrogate implants and (2) investigate the effects of the same coatings on the in vivo performance of Medtronic MiniMed SOF-SENSOR™ glucose sensors. The tissue response to implants was evaluated by quantifying macrophage infiltration, blood vessel formation, and collagen density around implants. Sensor function was assessed by measuring changes in sensor sensitivity and time lag, calculating the Mean Absolute Relative Difference (MARD) for each sensor treatment, and performing functional glucose challenge test at relevant time points. Implants treated with porous Dex-loaded coatings diminished inflammation and enhanced vascularization of the tissue surrounding the implants. Functional sensors with Dex-loaded porous coatings showed enhanced sensor sensitivity over a 21-day period when compared to controls. Enhanced sensor sensitivity was accompanied with an increase in sensor signal lag and MARD score. These results indicate that Dex-loaded porous coatings were able to elicit an attenuated tissue response, and that such tissue microenvironment could be conducive towards extending the performance window of glucose sensors in vivo. STATEMENT OF SIGNIFICANCE: In the present article, a coating to extend the functionality of implantable glucose sensors in vivo was developed. Our study showed that the delivery of an anti-inflammatory agent with the presentation of micro-sized topographical cues from coatings may lead to improved long-term glucose sensor function in vivo. We believe that improved function of sensors treated with the novel coatings was a result of the observed decreases in inflammatory cell density and increases in vessel density of the tissue adjacent to the devices. Furthermore, extending the in vivo functionality of implantable glucose sensors may lead to greater adoption of these devices by diabetic patients.

Scaffold-free, Human Mesenchymal Stem Cell-Based Tissue Engineered Blood Vessels.

Tissue-engineered blood vessels (TEBV) can serve as vascular grafts and may also play an important role in the development of organs-on-a-chip. Most TEBV construction involves scaffolding with biomaterials such as collagen gel or electrospun fibrous mesh. Hypothesizing that a scaffold-free TEBV may be advantageous, we constructed a tubular structure (1 mm i.d.) from aligned human mesenchymal cell sheets (hMSC) as the wall and human endothelial progenitor cell (hEPC) coating as the lumen. The burst pressure of the scaffold-free TEBV was above 200 mmHg after three weeks of sequential culture in a rotating wall bioreactor and perfusion at 6.8 dynes/cm(2). The interwoven organization of the cell layers and extensive extracellular matrix (ECM) formation of the hMSC-based TEBV resembled that of native blood vessels. The TEBV exhibited flow-mediated vasodilation, vasoconstriction after exposure to 1 µM phenylephrine and released nitric oxide in a manner similar to that of porcine femoral vein. HL-60 cells attached to the TEBV lumen after TNF-α activation to suggest a functional endothelium. This study demonstrates the potential of a hEPC endothelialized hMSC-based TEBV for drug screening.

In vivo detection of SERS-encoded plasmonic nanostars in human skin grafts and live animal models.

Surface-enhanced Raman scattering (SERS)-active plasmonic nanomaterials have become a promising agent for molecular imaging and multiplex detection. Among the wide variety of plasmonics-active nanoparticles, gold nanostars offer unique plasmon properties that efficiently induce strong SERS signals. Furthermore, nanostars, with their small core size and multiple long thin branches, exhibit high absorption cross sections that are tunable in the near-infrared region of the tissue optical window, rendering them efficient for in vivo spectroscopic detection. This study investigated the use of SERS-encoded gold nanostars for in vivo detection. Ex vivo measurements were performed using human skin grafts to investigate the detection of SERS-encoded nanostars through tissue. We also integrated gold nanostars into a biocompatible scaffold to aid in performing in vivo spectroscopic analyses. In this study, for the first time, we demonstrate in vivo SERS detection of gold nanostars using small animal (rat) as well as large animal (pig) models. The results of this study establish the usefulness and potential of SERS-encoded gold nanostars for future use in long-term in vivo analyte sensing.

A novel immune competent murine hypertrophic scar contracture model: a tool to elucidate disease mechanism and develop new therapies.

Hypertrophic scar (HSc) contraction following burn injury causes contractures. Contractures are painful and disfiguring. Current therapies are marginally effective. To study pathogenesis and develop new therapies, a murine model is needed. We have created a validated immune-competent murine HSc model. A third-degree burn was created on dorsum of C57BL/6 mice. Three days postburn, tissue was excised and grafted with ear skin. Graft contraction was analyzed and tissue harvested on different time points. Outcomes were compared with human condition to validate the model. To confirm graft survival, green fluorescent protein (GFP) mice were used, and histologic analysis was performed to differentiate between ear and back skin. Role of panniculus carnosus in contraction was analyzed. Cellularity was assessed with 4',6-diamidino-2-phenylindole. Collagen maturation was assessed with Picro-sirius red. Mast cells were stained with Toluidine blue. Macrophages were detected with F4/80 immune. Vascularity was assessed with CD31 immune. RNA for contractile proteins was detected by quantitative real-time polymerase chain reaction (qRT-PCR). Elastic moduli of skin and scar tissue were analyzed using a microstrain analyzer. Grafts contracted to ∼45% of their original size by day 14 and maintained their size. Grafting of GFP mouse skin onto wild-type mice, and analysis of dermal thickness and hair follicle density, confirmed graft survival. Interestingly, hair follicles disappeared after grafting and regenerated in ear skin configuration by day 30. Radiological analysis revealed that panniculus carnosus doesn't contribute to contraction. Microscopic analyses showed that grafts show increase in cellularity. Granulation tissue formed after day 3. Collagen analysis revealed increases in collagen maturation over time. CD31 stain revealed increased vascularity. Macrophages and mast cells were increased. qRT-PCR showed up-regulation of transforming growth factor beta, alpha smooth muscle actin, and rho-associated protein kinase 2 in HSc. Tensile testing revealed that human skin and scar tissues are tougher than mouse skin and scar tissues.

Bioburden after Staphylococcus aureus inoculation in type 1 diabetic rats undergoing internal fixation.

SUMMARY: Fracture stabilization in the diabetic patient is associated with higher complication rates, particularly infection and impaired wound healing, which can lead to major tissue damage, osteomyelitis, and higher amputation rates. With an increasing prevalence of diabetes and an aging population, the risks of infection of internal fixation devices are expected to grow. Although numerous retrospective clinical studies have identified a relationship between diabetes and infection, currently there are few animal models that have been used to investigate postoperative surgical-site infections associated with internal fixator implantation and diabetes. The authors therefore refined the protocol for inducing hyperglycemia and compared the bacterial burden in controls to pharmacologically induced type 1 diabetic rats after undergoing internal fracture plate fixation and Staphylococcus aureus surgical-site inoculation. Using an initial series of streptozotocin doses, followed by optional additional doses to reach a target blood glucose range of 300 to 600 mg/dl, the authors reliably induced diabetes in 100 percent of the rats (n = 16), in which a narrow hyperglycemic range was maintained 14 days after onset of diabetes (mean ± SEM, 466 ± 16 mg/dl; coefficient of variation, 0.15). With respect to their primary endpoint, the authors quantified a significantly higher infectious burden in inoculated diabetic animals (median, 3.2 × 10 colony-forming units/mg dry tissue) compared with inoculated nondiabetic animals (7.2 × 10 colony-forming units/mg dry tissue). These data support the authors' hypothesis that uncontrolled diabetes adversely affects the immune system's ability to clear Staphylococcus aureus associated with internal hardware.