Showing papers in "Artificial Organs in 2007"

Electrically conductive biodegradable polymer composite for nerve regeneration: electricity-stimulated neurite outgrowth and axon regeneration.

Abstract: Normal and electrically stimulated PC12 cell cultures and the implantation of nerve guidance channels were performed to evaluate newly developed electrically conductive biodegradable polymer composites. Polypyrrole (PPy) doped by butane sulfonic acid showed a significantly higher number of viable cells compared with PPy doped by polystyrenesulfonate after a 6-day culture. The PC12 cells were left to proliferate for 6 days, and the PPy-coated membranes, showing less initial cell adherence, recorded the same proliferation rate as did the noncoated membranes. Direct current electricity at various intensities was applied to the PC12 cell-cultured conductive membranes. After 7 days, the greatest number of neurites appeared on the membranes with a current intensity approximating 1.7-8.4 microA/cm. Nerve guidance channels made of conductive biodegradable composite were implanted into rats to replace 8 mm of sciatic nerve. The implants were harvested after 2 months and analyzed with immunohistochemistry and transmission electron microscopy. The regenerated nerve tissue displayed myelinated axons and Schwann cells that were similar to those in the native nerve. Electrical stimulation applied through the electrically conductive biodegradable polymers therefore enhanced neurite outgrowth in a current-dependent fashion. The conductive polymers also supported sciatic nerve regeneration in rats.

Flow-induced platelet activation and damage accumulation in a mechanical heart valve: numerical studies.

Abstract: A model for platelet activation based on the theory of damage, incorporating cumulative effects of stress history and past damage (senescence) was applied to a three-dimensional (3-D) model of blood flow through a St. Jude Medical (SJM) bileaflet mechanical heart valve (MHV), simulating flow conditions after implantation. The calculations used unsteady Reynolds-averaged Navier-Stokes formulation with non-Newtonian blood properties. The results were used to predict platelet damage from total stress (shear, turbulent, deformation), and incorporate the contribution of repeated passages of the platelets along pertinent trajectories. Trajectories that exposed the platelets to elevated levels of stress around the MHV leaflets and led them to entrapment within the complex 3-D vortical structures in the wake of the valve significantly enhanced platelet activation. This damage accumulation model can be used to quantify the thrombogenic potential of implantable cardiovascular devices, and indicate the problem areas of the device for improving their designs.

Argatroban in Extracorporeal Membrane Oxygenation

Abstract: The objective of this study was to assess the required dose and anticoagulatory effect of argatroban (Mitsubishi, Pharma Deutschland GmbH, Dusseldorf, Germany), a direct thrombin inhibitor approved for anticoagulation in patients with heparin-induced thrombocytopenia (HIT) undergoing extracorporeal membrane oxygenation (ECMO). Nine consecutive patients undergoing ECMO for severe acute respiratory distress syndrome (ARDS) and presenting with suspected HIT were treated with a continuous argatroban infusion. Coagulation variables were measured and dose adjustments of argatroban were performed to target for an activated partial thromboplastin time (aPTT) of 50 to 60 s. The first patient received argatroban 2 microg/kg/min as recommended by the manufacturer. This resulted in excessive anticoagulation and severe bleeding. The consecutive eight patients received a 10-fold lower dose (0.2 microg/kg/min). This dose sufficiently increased aPTT time from 46 +/- 6 s to 65 +/- 14 s (P < 0.001) and thrombin time from 18 +/- 8 s to 45 +/- 11 s (P = 0.001). The maintenance dose averaged 0.15 microg/kg/min. Duration of argatroban infusion for ECMO averaged 4 +/- 1 days and no oxygenator or extracorporeal system clotting was observed. In three of nine patients (33%), HIT was confirmed. Argatroban is a feasible and effective anticoagulant for patients with suspected HIT undergoing ECMO. However, a dose 10-fold lower than that recommended by the manufacturer is sufficient to achieve appropriate anticoagulation in critically ill patients undergoing ECMO.

Combined Impella and Intra-aortic Balloon Pump Support to Improve Both Ventricular Unloading and Coronary Blood Flow for Myocardial Recovery: An Experimental Study

Abstract: Some patients in need of hemodynamic support do not respond to intra-aortic balloon pump (IABP) therapy. Hemodynamic stability can then be obtained by a more potent cardiac assist device, like the Impella catheter pump. Whether additional IABP support additional to Impella support can provide more optimal hemodynamic myocardial conditions is examined in this study. Seven sheep were implemented with IABP and Impella. An acute myocardial infarction was induced. Hemodynamic performance was assessed during baseline, during Impella support and IABP support individually, and during the combined Impella plus IABP support. The Impella support provided a reduction of afterload with 30% and an increase of coronary artery flow with 47%. The IABP increased coronary artery flow (13%), carotid artery flow (16%), and aortic ascending blood pressure (6%); a similar (but stronger) effect was provided when using the IABP support additional to Impella support and, respectively, increases of 33, 21, and 19% were established. The oxygen demand-supply ratio decreased by 25% due to the extra use of the IABP. A combination of IABP and Impella provides the most optimal hemodynamic myocardial conditions compared to either stand-alone support.

In vivo cartilage tissue engineering using a cell-derived extracellular matrix scaffold.

Abstract: We have observed in our previous study that a cell-derived extracellular matrix (ECM) scaffold could assure the growth of a cartilage tissue construct in vitro. The purpose of the present study was to evaluate the feasibility of a chondrocyte-seeded cell-derived ECM scaffold by implanting it in vivo in nude mouse. A porous cell-derived ECM scaffold was prepared with a freeze-drying protocol using porcine chondrocytes. Rabbit articular chondrocytes were seeded onto the scaffold and cultured for 2 days in vitro, and then implanted into the nude mouse subcutaneously. They were retrieved at 1, 2, and 3 weeks postimplantation. Under macroscopic analysis, the cartilage-like tissue formation matured with time and developed a smooth, white surface. Contrary to the control (in which no cells were seeded), the size of the neocartilage tissue increased slightly by the third week and remained more stable. Total glycosaminoglycan (GAG) content and the GAG/DNA ratio increased significantly with time in the chemical analysis. The histology exhibited a sustained accumulation of newly synthesized sulfated proteoglycans. Immunohistochemistry, Western blot, and reverse transcriptase-polymerase chain reaction (RT-PCR) clearly identified type II collagen at all time points. Compressive strength of in vivo neocartilage increased from 0.45 +/- 0.06 MPa at 1 week to 1.18 +/- 0.17 MPa at 3 weeks. In conclusion, this study demonstrated that the cell-derived ECM scaffold could provide chondrocytes with favorable in vivo environment to produce a hyaline-like cartilage tissue.

Allogenous Bone Grafts Improved by Bone Marrow Stem Cells and Platelet Growth Factors: Clinical Case Reports

Abstract: In order to increase the amount of available bone where dental implants must be placed, the present study has associated platelet-rich plasma (PRP) and mono- nuclear cells (MNCs) from bone marrow aspirate and bone scaffold (BS) in 32 patients aged between 45 and 75 years old. The MNC attainment and the adherence to the BS were confirmed through histology, cell culture, and scan- ning electron microscopy. The clinical results, analyzed by computed tomography, have showed that the scaffolds were well integrated and adapted to the cortical bone. We can conclude that the process of healing observed in the patients was due to the presence of mesenchymal stem cell in MNC fraction in the bone grafts. KeyWords: Alveolar ridge augmentation—Blood platelets—Bone marrow cells—Dental implantation—Stem cell.

The Effect of Surface Roughness on Activation of the Coagulation System and Platelet Adhesion in Rotary Blood Pumps

Abstract: The surface roughness of left ventricular assist devices (LVADs) is important for the biocompatibility of blood pumps. However, little is known about the effect of surface roughness on the antithrombogenicity of the device. The present study investigated the effect of surface roughness on the activation of the coagulation system and platelet adhesion in an impeller-type blood pump. Three identical Baylor Gyro 710 centrifugal blood pumps (Baylor College of Medicine, Houston, TX, USA) were manufactured with impeller surface roughness of 0.05, 0.2, and 0.4 microm, respectively, as determined by a stylus profilometer and by scanning electron microscopy. Whole blood was anticoagulated (1-IU heparin/mL, ACT 250 s) and circulated for 60 min in an artificial circulatory system, simulating LVAD perfusion (5-L/min flow against 100 mm Hg). Enzyme-linked immunosorbent assays were developed to quantify fibrinogen- and von Willebrand factor (vWf) adsorption as well as platelet adhesion directly on the impellers of the pumps. Levels of prothrombin fragment F1.2 and thrombin-antithrombin (TAT) complex were measured in order to quantify activation of coagulation. Compared with the 0.05-microm surface, platelet adhesion was 40 and 76% higher on the 0.2- and 0.4-microm surface, respectively (P < 0.01). The evaluation of adsorbed fibrinogen and vWf showed significant higher protein antigen levels on the rougher surfaces (P < 0.01). Furthermore, nonpulsatile perfusion activated the coagulation system. By contrast, the surface roughness had no significant influence on plasma prothrombin F1.2 fragment- and TAT concentrations. Antithrombogenicity was significantly reduced in pumps with inferior metal-finishing quality.

Construction of Skeletal Myoblast-Based Polyurethane Scaffolds for Myocardial Repair

Abstract: Intramyocardial transplantation of skeletal myoblasts augments postinfarction cardiac function. However, poor survival of injected cells limits this therapy. It is hypothesized that implantation of myoblast-based scaffolds would result in greater cell survival. Rat skeletal myoblasts were seeded on highly porous polyurethane (PU) scaffolds (7.5 x 7.5 x 2.0 mm). The effect of several scaffold pretreatments, initial cell densities, and culture periods was tested by DNA-based cell count and viability assessment. Seeded PU scaffolds were implanted on infarcted hearts and immunohistology was performed 4 weeks later. Precoating with laminin allowed the most favorable cell attachment. An initial inoculation with 5 x 10(6) cells followed by a 15-day culture period resulted in optimal myoblast proliferation. Four weeks after their implantation in rats, numerous myoblasts were found throughout the seeded patches although no sign of differentiation could be observed. This myoblast seeding technique on PU allows transfer of a large number of living myoblasts to a damaged myocardium.

Hemodynamic controller for left ventricular assist device based on pulsatility ratio.

Abstract: Hemodynamic control of left ventricular assist devices (LVADs) is generally a complicated problem due to diverse operating environments and the variability of the patients: both the changes in the circulatory and metabolic parameters as well as disturbances that require adjustment to the operating point. This challenge is especially acute with control of turbodynamic blood pumps. This article presents a pulsatility ratio controller for LVAD that provides a proper perfusion according to the physiological demands of the patient, while avoiding adverse conditions. It utilizes the pulsatility ratio of the flow through the pump and pressure difference across the pump as a control index and adjusts the pump speed according to the reference pulsatility ratio under the different operating conditions. The simulation studies were performed to evaluate the controller in consideration of the sensitivity to afterload and preload, influence of the contractility, and effect of suction sensitivity. The controller successfully adjusts the pump speed according to the reference pulsatility ratio, and supports the natural heart under diverse pump operating conditions. The resulting safe pump operations demonstrate the solid performance of the controller in terms of sensitivity to afterload and preload, influence of the contractility, and effect of suction sensitivity.

Suction due to left ventricular assist: implications for device control and management.

Abstract: Left ventricular assist device (LVAD) overpumping is associated with hemolysis, thrombus release, and tissue damage at the pump inlet. However, the impact of LVAD suction on pulmonary circulatory function remains unknown. We investigated LVAD suction as induced by pulmonary artery banding and overpumping in experimental animals and in a computer model. In six sheep, a rotary LVAD was implanted. Before inducing suction, partial support (40-60% of cardiac output) was established and characterized by measuring pressures and flows. In the animals, pulmonary artery occlusion (PAOC) elicited LVAD suction (left ventricular pressure was from -10 to -20 mm Hg) within 5-10 heartbeats. During suction, aortic pressure dropped to 50% and LVAD flow decreased significantly. After releasing the occlusion (20 s), the collapsed state persisted for another 20 s. A similar trend was obtained by simulating PAOC in the computer model. Additional simulations showed that pulmonary vascular resistance (PVR), volume status, and right ventricular (RV) contractility are exponentially related to the persistence of collapse after a suction event. Even modest increases in predisposing factors (elevated PVR, RV dysfunction, hypovolemia) caused sustained hemodynamic collapse lasting in excess of 15 min. Both in selected animals and the computer model, comparable suction-induced collapse was obtained by increasing LVAD speed by about 33%. Attempted compensation by simply decreasing speed was not effective, but temporarily shutting down the LVAD caused rapid reversal of collapse. In conclusion, rotary LVAD suction causes unfavorable conditions for effective unloading. The use of pump interventions appears a promising tool to detect suction and to avoid the associated hemodynamic depression.

The acute effect of intra-aortic balloon counterpulsation during extracorporeal life support: an experimental study.

Abstract: Hemodynamically unstable patients supported by an extracorporeal life support (ECLS) circuit often receive additional support by intra-aortic balloon pump (IABP). However, it is not established whether support of the failing heart is improved by adjunctive IABP in both peripheral cannulation (PC) and central cannulation (CC) settings. Seven sheep were supported by an IABP and an ECLS system which were cannulated centrally as well as peripherally. In each cannulation configuration, hemodynamic and cardiac function indices were measured at baseline, ECLS, and ECLS plus IABP. The primary variables were mean coronary artery flow (Qcor), diastolic pressure time index (DPTI), left ventricular (LV) pressure-volume area (PVA), and tension time index (TTI). Additional IABP with ECLS support (CC/PC) decreased LV afterload (LV systolic peak pressure -4%, P<0.05/-8%, P<0.02), as well as TTI -2%/-10% and PVA -10%/-12% (P<0.03). Coronary perfusion was increased by additional IABP: CC, Qcor, +9%, and DPTI, +18% (P<0.02); PC, Qcor,+6%, and DPTI, +11% (P<0.05). IABP augmented the myocardial oxygen supply/demand ratios (CC/PC): Qcor/(PVA.heart rate) (+21%/+22%, P<0.02) and DPTI/TTI (+27%/+24%, P<0.03). In case of low arterial pressure (<50 mm Hg) and reduced ECLS flow, the overall hemodynamic profile improved only with central cannulation. We conclude that in both central and peripheral ECLS cannulation settings, adjunctive IABP improves the myocardial oxygen supply demand balance. In case of low cardiac output and insufficient extracorporeal flow with PC, adjunctive IABP may be contraindicated.

Effect of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) nanofiber matrices cocultured with hair follicular epithelial and dermal cells for biological wound dressing.

Abstract: We tested the effects on the early-stage wound healing of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) nanofiber matrices cultured with hair follicular cells. PHBV only, PHBV/collagen, and PHBV/gelatin at a 7/3 weight ratio were produced by electrospinning, and their in vitro cell culture and in vivo wound healing as biological dressings were examined. In cell attachment and growth on matrices, dermal sheath (DS) cells attached to hydrophilic PHBV/collagen and PHBV/gelatin faster than hydrophobic PHBV at the early incubation stage (up to 6 h). From 6- to 24-h incubation, PHBV/collagen showed the best results in cell culture. Furthermore, PHBV/collagen cocultured for 3-5 days with DS and epithelial outer root sheath (ORS) cells expressed more extracellular materials, such as type I collagen, elastin, and alpha-smooth muscle actin, than cocultured PHBV with the same cells. However, there was no significant difference between PHBV and PHBV/collagen in the amounts of cytokeratin 8 expressed. Grafting of PHBV and PHBV/collagen matrices cocultured with ORS/DS cells for 3-5 days showed that PHBV promoted wound closure and re-epithelization more obviously than PHBV/collagen in both cocultured matrices and matrices alone. Cocultured matrices would heal wounds better than the corresponding matrices alone. Thus, PHBV cocultured with ORS/DS cells could be used as a cell-seeded biological dressing, thereby reducing preparation time as well as regenerating the epidermis efficiently during the early stage of wound healing.

Cardiac magnetic resonance in Chagas' disease.

Abstract: American trypanosomiasis (Chagas' disease [CD]) caused by Trypanosoma cruzi is endemic in Latin America, where it is one of the leading causes of death. The involvement of the heart is crucial in the patients' prognosis. Besides lymphocytic myocarditis, cardiomyopathy is associated with several degrees of myocardial fibrosis (MF). Myocardial delayed enhancement by cardiac magnetic resonance (CMR) has been considered the most accurate method to detect MF in ischemic and nonischemic cardiomyopathy, including Chagas' heart disease. Additionally, CMR offers a wide variety of imaging tools to evaluate in detail morphology, the function and other tissue characterization abilities, such as detection of edema and fat. The present article aims to discuss the current clinical applicability of CMR to evaluate CD. We also discuss its future as a screening tool for very early myocardial involvement, which would allow the investigation of new therapeutic methods with potential influence in the natural history of CD.

Behavior of cardiomyocytes and skeletal muscle cells on different extracellular matrix components--relevance for cardiac tissue engineering.

Abstract: Myocardial cell transplantation in patients with heart failure is emerging as a potential therapeutic option to augment the function of remaining myocytes. Nevertheless, further investigations on basic issues such as ideal cell type continue to be evaluated. Therefore, the aim of our studies was to compare the performance of skeletal muscle cells and cardiomyocytes with respect to their proliferation rate and viability on different extracellular matrix components (EMCs). Rat cardiomyocytes (RCM) and rat skeletal muscle cells (RSMC) were cultured on EMCs such as collagen type I, type IV, laminin, and fibronectin. The components were used as "single coating" as well as "double coating." Proliferation rates were determined by proliferation assays on days 1, 2, 4, and 8 after inoculation of the cells. The most essential result is that collagen type I enhances the proliferation rate of RSMC but decreases the proliferation of RCM significantly. This effect is independent of the second EMC used for the double-coating studies. Other EMCs also influence cellular behavior, whereas the sequence of the EMCs is essential. Results obtained in our studies reveal the significant different proliferation behavior of RCM and RSMC under identical conditions. As skeletal muscle cells are also used in heart tissue engineering models, these results are essential and should be investigated in further studies to prove the applicability of skeletal muscle cells for heart tissue engineering purposes.

Enhancement of Peripheral Nerve Regeneration Using Bioabsorbable Polymer Tubes Packed With Fibrin Gel

Abstract: Nerve conduit tubes were developed using bioabsorbable polymer membranes, and the effects of tube shape--straight or bellows-shaped tubes--and the fibrin gel filling were investigated. The mechanical properties of the tubes were examined by in vitro tests, and their effectiveness for peripheral nerve regeneration was determined by grafting into experimentally transected sciatic nerves of rats. The bellows tube showed mechanically superior properties, and when used with the fibrin gel, it induced superior tissue formation of myelinated nerve fibers as compared to other tube types. The total area of myelinated axons regenerated in the fibrin-filled bellows tube was comparable to that of an isograft control, whereas those of the other tubes demonstrated inferior regeneration. This result suggests that the mechanically superior bellows tube filled with fibrin gel is an effective graft alternative for peripheral nerve regeneration.

Inconsistency of reported uremic toxin concentrations.

Abstract: Discrepancies in reported uremic toxin concentrations were evaluated for 78 retention solutes. For this analysis, 378 publications were screened. Up to eight publications per toxin were retained. The highest and the lowest reported concentrations, as well as the median reported concentration were registered. The ratio between the highest and the lowest (H/L) concentrations and, for some solutes, also the ratio between the highest and the median (H/M) concentrations were calculated. The compounds were arbitrarily subdivided into three groups based on their H/L ratio: group A, H/L 8.5 (n = 25). Solutes of groups A and B showed a low to intermediate scatter, suggesting a homogeneity of reported data. Group C showed a more substantial scatter. For at least 10 compounds of group C, extremely divergent concentrations were registered (H/M > 5.5) using scatter plot analysis. For all solutes of groups A and B, the highest reported concentration could be used as a reference. For some solutes of group C and for the compounds showing a divergent scatter analysis, however, more refined directives should be followed.

Study on decellularized porcine aortic valve/poly (3-hydroxybutyrate-co-3-hydroxyhexanoate) hybrid heart valve in sheep model.

Abstract: To overcome shortcomings of current heart valve prostheses, novel hybrid valves were fabricated from decellularized porcine aortic valves coated with poly (3-hydroxybutyrate-co-3-hydroxyhexanoate [PHBHHx]). In the mechanical test in vitro, the biomechanical performance of hybrid valve was investigated. In an in vivo study, hybrid valve conduits were implanted in pulmonary position in sheep without cardiopulmonary bypass. Uncoated grafts were used as control. The valves were explanted and examined histologically and biochemically 16 weeks after surgery. The hybrid valve conduits maintained original shapes, were covered by a confluent layer of cells, and had less calcification than uncoated control. The mechanical test in vitro revealed that PHBHHx coating improved tensile strength. The results in vivo indicated that PHBHHx coating reduced calcification and promoted the repopulation of hybrid valve with the recipient's cells resembling native valve tissue. The hybrid valve may provide superior valve replacement with current techniques.

Noninvasive average flow estimation for an implantable rotary blood pump: a new algorithm incorporating the role of blood viscosity.

Abstract: The effect of blood hematocrit (HCT) on a noninvasive flow estimation algorithm was examined in a centrifugal implantable rotary blood pump (iRBP) used for ventricular assistance. An average flow estimator, based on three parameters, input electrical power, pump speed, and HCT, was developed. Data were collected in a mock loop under steady flow conditions for a variety of pump operating points and for various HCT levels. Analysis was performed using three-dimensional polynomial surfaces to fit the collected data for each different HCT level. The polynomial coefficients of the surfaces were then analyzed as a function of HCT. Linear correlations between estimated and measured pump flow over a flow range from 1.0 to 7.5 L/min resulted in a slope of 1.024 L/min (R2=0.9805). Early patient data tested against the estimator have shown promising consistency, suggesting that consideration of HCT can improve the accuracy of existing flow estimation algorithms.

Air bubbles pass the security system of the dialysis device without alarming.

Abstract: During hemodialysis microembolic findings have been noted after the venous chamber (subclavian vein). The aim of this study was to evaluate if air could pass the venous chamber and, if so, if it passes the safety-system detector for air-infusion without triggering an alarm. Various in vitro dialysis settings were performed using regular dialysis devices. A dextran fluid was used instead of blood to avoid the risk of development of emboli. Optical visualization as well as recirculation and collection of eventual air into an intermediate bag were investigated. In addition, a specifically designed ultrasound monitor was placed after the venous air trap to measure the presence of eventual microbubbles. Speed of dialysis fluid was changed, as was the level of the fluid in the air trap. Thereby a fluid level was considered "high" if it was close to the top of the air trap and "low" if it was around the mid part of the air trap. By optical vision microbubbles were seen at the bottom of the air trap and could pass the air trap towards the venous line without alarming. During recirculation several mL of air were collected in an intermediate bag after the venous line. Ultrasound monitoring exhibited the presence of microbubbles of the size of approximately 5 microm upwards passing to the venous line in all runs performed. Amount of bubbles differed between devices and in general an increased fluid speed correlated significantly with the increased counts of microbubbles/min. No alarming of the detector occurred. A more concentrated fluid allowed higher counts/min when flow was increased to 600 mL/min. Data revealed that air passes the safety-sensor in the air trap without alarming. The presence of air increased in general with fluid speed and a lower fluid level in the air trap. Differences were present between devices. If this affects the patients has to be elucidated.

Numerical simulation of an axial blood pump.

Abstract: The axial blood pump with a magnetically suspended impeller is superior to other artificial blood pumps because of its small size. In this article, the distributions of velocity, path line, pressure, and shear stress in the straightener, the rotor, and the diffuser of the axial blood pump, as well as the gap zone were obtained using the commercial software, Fluent (version 6.2). The main focus was on the flow field of the blood pump. The numerical results showed that the axial blood pump could produce 5.14 L/min of blood at 100 mm Hg through the outlet when rotating at 11 000 rpm. However, there was a leakage flow of 1.06 L/min in the gap between the rotor cylinder and the pump housing, and thus the overall flow rate the impeller could generate was 6.2 L/min. The numerical results showed that 75% of the scalar shear stresses (SSs) were less than 250 Pa, and 10% were higher than 500 Pa within the whole pump. The high SS region appeared around the blade tip where a large variation of velocity direction and magnitude was found, which might be due to the steep angle variation at the blade tip. Because the exposure time of the blood cell at the high SS region within the pump was relatively short, it might not cause serious damage to the blood cells, but the improvement of blade profile should be considered in the future design of the axial pump.

Implantation of decellularized small-caliber vascular xenografts with and without surface heparin treatment

Abstract: Heparin treatment of decellularized xenografts has been reported to reduce graft thrombogenicity. However, little is known about the in vivo comparison of heparin-treated with non-heparin-treated xenografts, especially for small-caliber vascular implants. We implanted either a heparin-treated or a non-heparin-treated canine carotid artery as bilateral carotid xenograft in rabbits (n = 24). Small-caliber xenografts (3 similar to 4 mm) were decellularized by enzymatic and detergent extraction and were further covalently linked with heparin. During implantation, thrombosis rate was 4% in the heparin-treated xenografts and 25% in the non-heparin-treated xenografts after 3 weeks (P <0.05). After 6 months, it was 8 versus 58%, respectively (P <0.01). Both heparin-treated and non-heparin-treated xenografts harvested at the end of 3 and 6 months showed a satisfactory cellular reconstruction of either smooth muscle cells or endothelial cells. These results indicate that heparin treatment of the small-caliber decellularized xenograft reduces the in vivo thrombogenicity. Both heparin-treated and non-heparin-treated xenografts seem to undergo a similar cellular remodeling process up to 6 months.

Deformability of red blood cells and its relation to blood trauma in rotary blood pumps.

Abstract: In this study, mechanical trauma to red blood cells was evaluated by conventional hemolysis test and a newly developed cyclically reversing shear flow generator. The fresh porcine blood obtained from a local slaughterhouse was subjected to the conventional hemolysis test using a commercial centrifugal blood pump for the duration of 8 h. The measurements consisted of (i) plasma-free hemoglobin based on the standard optical measurement and (ii) the deformability of red blood cells (RBCs) using a cyclically reversing shear flow generator and microscope image acquisition system. The deformability of RBCs was expressed by the L/W value where L and W were the longer and shorter axes of the elongated RBCs' images. Although the plasma-free hemoglobin level increased with the pumping duration, the L/W remained unchanged for the duration of 8 h of pumping to indicate no alteration in the deformability. It was speculated that (i) although RBCs might have been circulated for so many times through the test pump, after each exposure to mechanical stress, RBCs might have recovered, and net effect due to shear stress-exposure time might have been small; and (ii) RBCs' deformability might be maintained near normal until sudden burst or membrane rupture, or the hemoglobin might have continuously leaked through the pores of the thinned membrane created by the mechanical stress. The deformability testing under a fluctuating shear flow could be a new method to quantify subhemolytic mechanical damage that has been accumulated in the RBCs' membrane and that may not be assessed by the conventional hemolysis test.

Effect of Osteogenic Induction on the in Vitro Differentiation of Human Embryonic Stem Cells Cocultured With Periodontal Ligament Fibroblasts

Abstract: Osteogenesis is one of the principal components of periodontal tissue development as well as regeneration. As pluripotent cells with unlimited proliferative potential and differentiation ability to all germ layer representatives, embryonic stem cells also hold the promise to become a cell source in bone tissue engineering. Our aim was to investigate osteogenic differentiation potential of human embryonic stem cells (hESCs) under the inductive influence of human periodontal ligament fibroblast (hPDLF) monolayers. After being expanded and characterized morphologically and immunohistochemically, hESCs (HUES-9) were cocultured with hPDLFs for 28 days. Two groups were established: (i) osteogenic induction group with ascorbic acid, β-glycerophosphate, and dexamethasone containing hESC differentiation medium; and (ii) spontaneous differentiation group cultured in hESC differentiation medium. Morphological shift in cells was analyzed under an inverted microscope, and immunohistochemistry was performed on fixed specimens at days 1 and 28 using antibodies against alkaline phosphatase, osteonectin, osteopontin, bone sialoprotein (BSP), and osteocalcin (OSC). Reverse transcription–polymerase chain reaction was utilized for the detection of octameric binding protein-4, BSP, and OSC expression at mRNA level. Mineralization was assessed using alizarin red, and the surface topology shift in colonies was demonstrated with scanning electron microscopy. Results indicate the feasibility of osteogenic differentiation of hESCs in coculture, and suggest a role of periodontal ligament fibroblasts in their differentiation patterns. Advances in the field could allow for potential utilization of hESCs in periodontal tissue engineering applications involving regeneration of bone in periodontal compartment lost as a result of destructive periodontal diseases.

Three-dimensional culture of human nucleus pulposus cells in fibrin clot: Comparisons on cellular proliferation and matrix synthesis with cells in alginate

Abstract: Regeneration of nucleus pulposus (NP) tissue may stop or reverse early intervertebral disk (IVD) degeneration. Cellular proliferation and matrix synthesis can be promoted by incorporation of cells and bioscaffolds. However, insertion of preshaped solid bioscaffolds may damage remaining IVD integrity. Fibrin clots can be introduced in a minimally invasive manner with polymerization in desired three-dimensional shape and retention of cells. In this study, we investigated the cellular proliferation and matrix synthesis of human NP cells in the fibrin clots in vitro. Monolayer-expanded cells were embedded in fibrin clot or alginate and were cultivated in vitro for 2 weeks. Increased DNA content and decreased expression of apoptosis stimulating fragment (Fas)-associated death-domain protein in fibrin scaffolds suggested higher cellular proliferation and reduced apoptosis. Superior proteoglycan synthesis was found in fibrin scaffolds. As expression of collagens I and X increased and SOX9 expression decreased, fibrin scaffolds tended to promote fibrotic transformation and inhibit chondrogenesis. Adjustments of fibrin preparations are needed to make it more suitable for IVD regeneration.

Left Ventricular Pressure–Volume Loop Analysis During Continuous Cardiac Assist in Acute Animal Trials

Abstract: For better understanding of the interaction between left ventricle and continuous cardiac assist, the effect of different working conditions and support levels on left ventricular pressure-volume (PV) loop was investigated in acute animal experiments. A MicroMed-DeBakey ventricular assist device (MicroMed Cardiovascular Inc., Houston, TX, USA) was implanted in seven healthy sheep (102 +/- 20 kg). Measurements of hemodynamic variables were taken with clamped graft, on minimum, medium, and maximum support, and in pump-off condition (backflow). Each pump condition was studied for different heart rates, central venous pressures, and under pharmacologically altered contractility. End-systolic and end-diastolic volume normalized by the body surface area (BSA) (end systolic volume index [ESVI] and end diastolic volume index [EDVI]) showed significant correlation both within each sheep and in the pooled data. The linear regression for the pooled data was ESVI = 0.845 x EDVI - 15.21, R(2) = 0.924, P < 0.0001, n = 200. EDVI and stroke volume (SV) normalized by BSA (stroke volume index [SVI]) also showed a lower but significant correlation: SVI = 0.155 x EDVI + 15.21, R(2) = 0.291, P < 0.0001, n = 200. An increase of preload due to infusion caused, in the clamped graft condition, an increase in end diastolic volume of 22%, no significant increase in SV, a decrease both of systemic vascular resistance of 30% and ventricular contractility (maximum elastance [E(max)] and peak rate of rise of ventricular pressure [dP/dt(max)] decreasing 38 and 21%, respectively). PV loop analysis in continuous cardiac assist reveals that the ESVI and the EDVI are strongly correlated and that ESVI varies considerably with preload. SVI becomes slightly dependent on EDVI, which may be due to autoregulatory mechanisms.

Effect of Cannula Shape on Aortic Wall and Flow Turbulence: Hydrodynamic Study During Extracorporeal Circulation in Mock Thoracic Aorta

Abstract: This study was designed to analyze flow pattern, velocity, and strain on the aortic wall of a glass aortic model during extracorporeal circulation, and to elucidate the characteristics of flow pattern in four aortic cannulas. Different patterns of large vortices and helical flow were made by each cannula. The high-velocity flow (0.6 m/s) was observed in end-hole cannula, causing high strain rate tensor (0.3~0.4 without unit) on the aortic arch. In dispersion cannula, a decreased strain rate tensor (less than 0.1) was found on the outer curvature of the aortic arch. In Soft-flow cannula (3M Cardiovascular, Ann Arbor, MI, USA), further decreased flow velocity (0.2 m/s) and strain (less than 0.2) were observed. In Select 3D cannula (Medtronic, Inc., Minneapolis, MN, USA), a high strain (0.4~0.5) was observed along the inner curvature of the aortic arch. In conclusion, end-hole cannula should not be used in atherosclerotic aorta. Particular attention should be paid both for selection of cannulas and cannulation site based on this result.

Tissue engineering of trachea-like cartilage grafts by using chondrocyte macroaggregate: experimental study in rabbits.

Abstract: Treatment and management of tracheal defects remain challenges in head and neck surgery. The purposes of this study were to explore a novel strategy to fabricate tissue-engineered trachea by using chondrocyte macroaggregate, and evaluate the feasibility of creating tracheal cartilage equivalents grown in the shape of cylindrical structure without scaffold. Chondrocytes from rabbit cartilage were expanded and seeded into a culture dish at high density to form mechanically stable chondrocyte macroaggregate. Once the chondrocyte macroaggregate was harvested by scrapping technique, it was wrapped around a silicon tube and implanted subcutaneously into the cell donor rabbit. Eight weeks later, specimens were harvested and analyzed for gross appearance, and histological, biochemical, and biomechanical properties. These values were compared with native rabbit cartilage. It was found that expanded chondrocytes could be harvested as a coherent cellular macroaggregate and could be fabricated into a tubelike graft. After in vivo implantation, cartilage-like tissue with cylindrical structure was regenerated successfully. Histological analysis showed engineered trachea cartilage consisted of evenly spaced lacunae embedded in a matrix rich in proteoglycans; type II collagen was also highly expressed in this engineered trachea cartilage. In a conclusion, based on the chondrocyte macroaggregate strategy, tracheal cartilage equivalents with cylindrical shape could be successfully reconstructed. This construct has advantages of high cell-seeding efficiency, good nutritional perfusion, and minimal inflammatory reaction, which provided a highly effective cartilage graft substitute and could be useful in many situations of trachea-cartilage loss encountered in clinical practice.

The adsorption of vancomycin by polyacrylonitrile, polyamide, and polysulfone hemofilters.

Abstract: The aim of this study was to characterize vancomycin adsorption by polyacrylonitrile (PAN), polyamide, and polysulfone hemofilters using an in vitro model of hemofiltration. Vancomycin (36 mg) was added to a blood-crystalloid mixture of known volume (target concentration of 50 mg/L) and pumped around a closed circuit. Adsorption, which was calculated from the fall in concentration over 120 min, was significantly greater by 0.6-m(2) PAN filters (10.08 +/- 2.26 mg) than by 0.6-m(2) polyamide (5.20 +/- 1.82 mg) or 0.7-m(2) polysulfone (4.80 +/- 2.40 mg) filters (P < 0.05). Cumulative adsorption was not changed by the addition of 500-mL lactated Ringer's solution (to reduce the circulating vancomycin concentration). These data show that although adsorption of vancomycin by PAN, polyamide, and polysulfone hemofilters occurs, the absolute adsorption is small. Adsorption is dependent on filter material and is not reversed by a decrease in circulating concentration.

Wound healing effect of acellular artificial dermis containing extracellular matrix secreted by human skin fibroblasts.

Abstract: In this study, an acellular artificial dermis, composed of human collagen and glycosaminoglycan (GAG) secreted by cultured human fibroblasts on a bovine collagen sponge, was developed. Much of the newly secreted extracellular matrix (ECM) remained after the cell removal process. The main theme of this study focused on the matrix, rather than the viable cell components of the skin, as the major dermal deficit in the wound. Both the acellular artificial and bioartificial dermises, containing viable cells with ECM, were significantly less soluble than the collagen sponge, and the relative GAG content in the bioartificial and acellular artificial dermises was approximately 115-120% of the chondroitin-6-sulfate (CS) content found in the collagen sponge. In the group receiving the collagen sponge, the wound area gradually decreased to approximately 10% of its original area, while in the groups receiving the bioartificial and acellular artificial dermises, the wound area also gradually decreased to approximately 60 and 50%, respectively, of the original size over the 5 weeks after grafting. Both the bioartificial and acellular artificial dermises formed thicker, denser collagen fibers; more new blood vessel formation was observed in both cases. The basement membrane of the regenerated epidermal-dermal junction was thicker and more linear in the acellular artificial dermis graft than in the collagen sponge graft. In conclusion, the wound healing effects of acellular artificial dermis are no less than those of the bioartificial dermis, and much better than the collagen sponge graft with respect to wound contraction, angiogenesis, collagen formation, and basement membrane repair.

Investigation on wear of knee prostheses under fixed kinematic conditions.

Abstract: Although polyethylene components have been used in the human joint for over 30 years, wear simulation studies are fundamental to assess wear resistance of total joint replacements. This assessment will help to obtain quality control and acquire further knowledge of the tribological processes that involve joint prostheses. As a result, the risk of implant failure of innovative prostheses will be reduced. The aim of the present study was to investigate the influence on wear of the polyethylene tibial inserts against metallic femoral components using a knee simulator following a standardized kinematics protocol (ISO/CD 14243-3.2). Four intact "small" size specimens of the tibial MP 913 were tested in a four-station knee wear simulator for two million cycles. The volumetric weight loss for the ultra-high-molecular-weight-polyethylene (UHMWPE) tibial inserts was 44 +/- 2, 45 +/- 3, and 47 +/- 3 mg for the specimens #1-3, respectively. This study demonstrated a good repeatability among the stations of the knee simulator obtaining weight loss values congruent with those found by other authors using similar test conditions.