Arthur Nedder

A bioinspired omniphobic surface coating on medical devices prevents thrombosis and biofouling.

Thrombosis and biofouling of extracorporeal circuits and indwelling medical devices cause significant morbidity and mortality worldwide. We apply a bioinspired, omniphobic coating to tubing and catheters and show that it completely repels blood and suppresses biofilm formation. The coating is a covalently tethered, flexible molecular layer of perfluorocarbon, which holds a thin liquid film of medical-grade perfluorocarbon on the surface. This coating prevents fibrin attachment, reduces platelet adhesion and activation, suppresses biofilm formation and is stable under blood flow in vitro. Surface-coated medical-grade tubing and catheters, assembled into arteriovenous shunts and implanted in pigs, remain patent for at least 8 h without anticoagulation. This surface-coating technology could reduce the use of anticoagulants in patients and help to prevent thrombotic occlusion and biofouling of medical devices.

In vivo monitoring of function of autologous engineered pulmonary valve

OBJECTIVES Clinical translation of tissue-engineered heart valves requires valve competency and lack of stenosis in the short and long term. Early studies of engineered valves showed promise, although lacked complete definition of valve function. Building on prior experiments, we sought to define the in vivo changes in structure and function of autologous engineered pulmonary valved conduits. METHODS Mesenchymal stem cells were isolated from neonatal sheep bone marrow and seeded onto a bioresorbable scaffold. After 4 weeks of culture, valved conduits were implanted. Valve function, cusp, and conduit dimensions were evaluated at implantation (echocardiography), at the experimental midpoint (magnetic resonance imaging), and at explant, at 1 day, and 1, 6, 12, or 20 weeks postoperatively (direct measurement, echocardiography). Histologic evaluation was performed. RESULTS Nineteen animals underwent autologous tissue-engineered valved conduit replacement. At implantation, valved conduit function was excellent; maximum transvalvular pressure gradient by Doppler echocardiography was 17 mm Hg; most valved conduits showed trivial pulmonary regurgitation. At 6 postoperative weeks, valve cusps appeared less mobile; pulmonary regurgitation was mild to moderate. At 12 weeks or more, valved conduit cusps were increasingly attenuated and regurgitant. Valved conduit diameter remained unchanged over 20 weeks. Dimensional measurements by magnetic resonance imaging correlated with direct measurement at explant. CONCLUSIONS We demonstrate autologous engineered tissue valved conduits that function well at implantation, with subsequent monitoring of dimensions and function in real time by magnetic resonance imaging. In vivo valves undergo structural and functional remodeling without stenosis, but with worsening pulmonary regurgitation after 6 weeks. Insights into mechanisms of in vivo remodeling are valuable for future iterations of engineered heart valves.

Respiratory, neuromuscular, and cardiovascular effects of neosaxitoxin in isoflurane-anesthetized sheep.

Background Neosaxitoxin (NeoSTX) is a potent site-1 sodium-channel blocker being developed as a local anesthetic. Doses of 100 &mgr;g have been used by local infiltration in anesthetized adult humans without adverse effect. We hypothesized that similar doses could cause significant respiratory, neuromuscular, and cardiovascular impairment and sought to test this hypothesis in sheep. Methods Procedures were approved by the Institutional Animal Care and Use Committee. In neuromuscular/respiratory experiments, 33 intubated, isoflurane-anesthetized sheep were randomized to 6 NeoSTX treatment groups: saline control, 1 &mgr;g/kg subcutaneous (SC), 1 &mgr;g/kg intravenous (IV), 2 &mgr;g/kg SC, 2 &mgr;g/kg SC with bupivacaine 0.25%, and 3 &mgr;g/kg SC. Primary outcome measures were doxapram-stimulated inspired volume (DSIV) and quantitative limb acceleration. In cardiovascular experiments, 8 sheep received escalating IV doses of NeoSTX (1, 2, and 3 &mgr;g), with hemodynamic and electrocardiographic measurements. Data were analyzed using repeated-measures analysis of variance with post hoc Bonferroni-corrected comparisons. Results NeoSTX 1 &mgr;g/kg IV and SC produced no significant reduction in DSIV or limb acceleration compared with baseline. NeoSTX 2 &mgr;g/kg SC produced clinically mild reduction in twitch and DSIV; animals recovered well postoperatively. Coadministration of bupivacaine did not worsen these effects. NeoSTX 3 &mgr;g/kg produced severe and prolonged impairment of DSIV and limb acceleration. Escalating IV doses of NeoSTX produced mild decrements in heart rate, systemic arterial pressure, and systemic vascular resistance; cardiac output was maintained. Transient interventricular conduction delay occurred without cardiac arrest or ventricular ectopy. Conclusions In our sheep model, neuromuscular, respiratory, and cardiovascular effects of NeoSTX were dose dependent and mild using the dose range anticipated for clinical use.

Development of an Ovine Model of Pediatric Complete Heart Block

BACKGROUND Complete heart block is a significant clinical problem that can limit the quality of life in affected children. To understand the pathophysiology of this condition and provide for development of novel therapies, we sought to establish a large animal model of permanent, pacemaker-dependent atrioventricular block (AVB) that mimics the size and growth characteristics of pediatric patients. MATERIALS AND METHODS We utilized nine immature lambs weighing 10.5 ± 1.4 kg. After implantation of dual-chamber pacemaker devices with fixed leads, AVB was produced by interrupting His-bundle conduction using radio-frequency ablation at the base of the non-coronary cusp of the aortic valve. Ablations (30 to 60 s in duration) were performed under fluoroscopic guidance with electrophysiological monitoring. Interrogation of pacemakers and electrocardiography (ECG) determined the persistence of heart block. Ovine hearts were also examined immunohistochemically for localization of conduction tissue. RESULTS AVB was produced in eight animals using an atypical approach from the left side of the heart. One animal died due to ventricular fibrillation during ablation proximal to the tricuspid annulus and one lamb was sacrificed postoperatively due to stroke. Four sheep were kept for long-term follow-up (109.8 ± 32.9 d) and required continuous ventricular pacing attributable to lasting AVB, despite significant increases in body weight and size. CONCLUSIONS We have created a large animal model of pediatric complete heart block that is stable and technically practicable. We anticipate that this lamb model will allow for advancement of cell-based and other innovative treatments to repair complete heart block in children.

Visualization and Analysis of the Deforming Piglet Femur and Hip Following Experimentally Induced Avascular Necrosis of the Femoral Head

Childhood avascular necrosis (AVN) of the femoral head leads to its progressive deformation and compensatory changes of the adjacent acetabulum. To simulate this disease for laboratory study, we used an AVN model of the hip in a skeletally immature piglet. The 3-D visualization and analysis of this piglets deforming femur and hip form the basis for this paper. In particular, the data for this analysis were generated via serial CT images of bilateral femurs and acetabula of a piglet at regular time intervals following experimental unilateral induction of femoral head AVN. The contralateral femur and acetabulum served as the control. We applied a shape analysis technique that effectively captured not only the temporal shape changes of the femurs and acetabula, but also their codependencies. The resulting computational framework not only confirmed the widely accepted deformational changes of the femoral head following AVN; it also revealed the underappreciated compensatory changes of the surrounding acetabulum. The 3-D visualization of these dynamically changing structures provided a visual understanding of the shape changes associated with the AVN and control models. By quantitatively mapping the deformation trajectory of these shapes over time, we created an objective tool for clinical decision making.

Sunitinib reduces recurrent pelvic adhesions in a rabbit model

BACKGROUND Adhesions represent a major problem after abdominal and pelvic procedures. The purpose of the present study was to determine the effect of sunitinib (Sutent, SU11248), a Food and Drug Administration-approved receptor tyrosine kinase inhibitor, on recurrent pelvic adhesion formation after pelvic adhesiolysis in a rabbit model. MATERIALS AND METHODS A total of 20 New Zealand white rabbits underwent a uterine abrasion procedure, followed by an adhesiolysis procedure 4 weeks later. Before adhesiolysis, the rabbits were randomized to sunitinib at 10 mg/kg/d or placebo. These were administered as 1 dose preoperatively followed by 10 doses postoperatively. The rabbits were killed 30 d after the adhesiolysis procedure. At death, the adhesions were scored, and a total adhesion score (presented as the median and interquartile range [IQR]) was calculated according to the percentage of uterine involvement and the tenacity of the adhesions. RESULTS All the rabbits survived the operative procedures without complications. The sunitinib-treated rabbits (n = 10) had a significantly lower uterine involvement score (median 2.0, IQR 1.0-3.0) than the placebo-treated rabbits (median 4.0, IQR 3.0-4.0; P = 0.02). The sunitinib-treated rabbits also had median tenacity score of 3.0 (IQR 3.0-4.0) compared with a median of 4.0 (IQR 4.0-4.0; P = 0.04) in the placebo-treated rabbits (n = 10). The median total score in the sunitinib-treated rabbits was 5.0 (IQR 4.0-6.25) compared with 8.0 (IQR 6.75, 8.0) in the placebo-treated rabbits (P = 0.01). CONCLUSIONS Sunitinib treatment might be an efficacious strategy to reduce recurrent adhesion formation after pelvic procedures.

Effect of sunitinib on functional reproductive outcome in a rabbit model.

OBJECTIVE To determine the effect of sunitinib (Sutent; SU11248; Pfizer), a US Food and Drug Administration-approved receptor tyrosine kinase inhibitor previously shown to reduce de novo pelvic adhesion formation, on reproductive function after surgical uterine abrasion in a rabbit model. DESIGN Randomized placebo-controlled study. SETTING Large animal facility within an academic hospital. ANIMAL(S) Thirty New Zealand White adult female rabbits (2.2-3.0 kg). INTERVENTION(S) Administration of 11 doses (one preoperative and 10 postoperative) of oral sunitinib (10 mg/kg/d) or placebo. MAIN OUTCOME MEASURE(S) Effect of short-term postoperative sunitinib administration on reproductive function after surgical uterine abrasion. RESULT(S) All animals were impregnated and survived until designated euthanasia. Sunitinib-treated animals had a larger average litter size (7.7 ± 1.9 vs. 5.6 ± 2.7 kits) and offspring viability (7.1 ± 2.7 vs. 3.5 ± 3.2 kits) compared with placebo-treated animals. There was no difference in gestational length or aberration in the maintenance of fertility. There were no gross abnormalities, detectable birth defects, or growth disparity in offspring from sunitinib versus placebo-treated mothers. The adhesion burden identified at euthanasia after parturition was lower in sunitinib compared with placebo-treated animals (N = 10/group). CONCLUSION(S) Sunitinib ameliorated adhesion-induced reproductive aberrations after surgical uterine abrasion and may be an efficacious strategy to reduce postoperative pelvic adhesions.

Bi-layer Silk Fibroin Grafts Support Functional Tissue Regeneration in a Porcine Model of Onlay Esophagoplasty

Partial circumferential, full thickness defects of the esophagus can occur as a result of organ perforation or tumour resection, or during surgical reconstruction of strictured segments. Complications associated with autologous tissue flaps conventionally utilized for defect repair necessitate the development of new graft options. In this study, bi‐layer silk fibroin (BLSF) scaffolds were investigated for their potential to support functional restoration of partial circumferential defects in a porcine model of esophageal repair. Onlay thoracic esophagoplasty with BLSF matrices (~3 x 1.5 cm) was performed in adult swine (N = 6) for 3 months of implantation. All animals receiving BLSF grafts survived with no complications and were capable of solid food consumption. Radiographic esophagrams revealed preservation of organ continuity with no evidence of contrast extravasation or strictures. Fluoroscopic analysis demonstrated peristaltic contractions. Ex vivo tissue bath studies displayed contractile responses to carbachol, electric field stimulation, and KCl while isoproterenol produced tissue relaxation. Histological and immunohistochemical evaluations of neotissues showed a stratified, squamous epithelium, a muscularis mucosa composed of smooth muscle bundles, and a muscularis externa organized into circular and longitudinal layers, with a mix of striated skeletal muscle fascicles interspersed with smooth muscle. De novo innervation and vascularization were observed throughout the graft sites and consisted of synaptophysin‐positive neuronal boutons and vessels lined with CD31‐positive endothelial cells. The results of this study demonstrate that BLSF scaffolds can facilitate constructive remodeling of partial circumferential, full thickness esophageal defects in a large animal model. Copyright

Vascular Endothelial Growth Factor Enhances Compensatory Lung Growth in Piglets

Background: Vascular endothelial growth factor has been found to accelerate compensatory lung growth after left pneumonectomy in mice. The aim of this study was to determine the natural history and the effects of vascular endothelial growth factor on compensatory lung growth in a large animal model. Methods: To determine the natural history of compensatory lung growth, female Yorkshire piglets underwent a left pneumonectomy on days of life 10–11. Tissue harvest and volume measurement of the right lung were performed at baseline (n = 5) and on postoperative days 7 (n = 5), 14 (n = 4), and 21 (n = 5). For pharmacokinetic studies, vascular endothelial growth factor was infused via a central venous catheter, with plasma vascular endothelial growth factor levels measured at various time points. To test the effect of vascular endothelial growth factor on compensatory lung growth, 26 female Yorkshire piglets underwent a left pneumonectomy followed by daily infusion of vascular endothelial growth factor at 200 &mgr;g/kg or isovolumetric 0.9% NaCl (saline control). Lungs were harvested on postoperative day 7 for volume measurement and morphometric analyses. Results: Compared with baseline, right lung volume after left pneumonectomy increased by factors of 2.1 ± 0.6, 3.3 ± 0.6, and 3.6 ± 0.4 on postoperative days 7, 14, and 21, respectively. The half‐life of VEGF ranged from 89 to 144 minutes. Lesser doses of vascular endothelial growth factor resulted in better tolerance, volume of distribution, and clearance. Compared with the control group, piglets treated with vascular endothelial growth factor had greater lung volume (P < 0.0001), alveolar volume (P = 0.001), septal surface area (P = 0.007) and total alveolar count (P = 0.01). Conclusion: Vascular endothelial growth factor enhanced alveolar growth in neonatal piglets after unilateral pneumonectomy.

Changes in tissue oxygen tension, venous saturation, and Fick-based assessments of cardiac output during hyperoxia

Hyperoxemia (arterial oxygen tension >100 mm Hg) may occur in critically ill patients and have effects on mixed venous saturation (SvO2) and on Fick‐based estimates of cardiac output (CO). We investigated the effect of hyperoxemia on SvO2 and on assessments of CO using the Fick equation.