Non clamping anastomosis of the ascending and arch aneurysm using retrograde cerebral perfusion

Twelve consecutive patients requiring surgery for replacement of ascending aortic aneurysms (n = 3), ascending arch aortic aneurysms (n = 2), or type A aortic dissections (n = 7) were treated without aortic cross clamping. Retrograde cerebral perfusion (RCP) with circulatory arrest (mean RCP time: 46.0 +/- 15.9 minutes, range 20 to 65 minutes) and continuous retrograde cardioplegia (mean cardiac ischemic time: 134.4 +/- 39.7 minutes, range: 40 to 180 minutes) were employed. In the patients with aortic dissection, the intimal tear at the origin of the brachiocephalic artery (BCA) was resected completely, the aortic wall was trimmed and closed with Teflon felt. The distal anastomosis was created using an open technique. Air and debris were completely evacuated by returning blood from the cerebral vessels and femoral artery. Then the artificial graft was clamped, and cardiopulmonary bypass resumed. The proximal anastomosis was performed during rewarming. The operations were elective in seven cases, and emergent in five cases. Graft replacement of the ascending aorta was performed in ten patients (including two BCA reconstructions). The remaining two patients were treated by patch repair (n = 1), primary anastomosis (n = 1). There were no perioperative deaths. One patient had a transient neurological deficit. The distal false lumen was occluded completely in five of seven patients with aortic dissections. The other two patients had a secondary tears in the descending aorta. Thus retrograde cerebral perfusion and continuous retrograde cardioplegia without aortic cross clamping is an effective technique in the replacement of the ascending and arch aorta.     

Sliding wear evaluation of hot isostatically pressed thermal spray ceramet coatings

The principal aim of this study was to compare the sliding wear performance of as-sprayed and Hot Isostatically Pressed (HIPed) thermal spray cermet (WC-12Co) coatings. Results indicate that HIPing technique can be successfully applied to post-treat thermal spray cermet coatings for improved sliding wear performance, not only in terms of coating wear, but also in terms of the total volume loss for test couples. WC-12Co coatings sprayed by a HVOF system were deposited on SUJ-2 bearing steel substrate and then encapsulated and HIPed at 850 °C for one hour. A high frequency reciprocating ball on plate rig was used to measure the sliding wear resistance of these coatings in dry conditions under steel and ceramic contact configurations at two different loads. Results are discussed in terms of coating microstructure, microhardness, fracture toughness and residual stress evaluations. Microstructural investigations indicate fundamental changes in grain morphology, whereas x-ray diffraction revealed beneficial transformations in phase composition of these coatings during the HIPing post treatment. The effects of these microstructural changes on the physical properties and wear resistance are discussed.     

Rolling contact induced failures of siliconnitride

Nominally flat silicon nitride discs in contact with threeceramic balls were tested in the presence of various lubricatingfluids. Discs were attached to a stationary cup containinglubricant and the balls were driven by a spindle powered by anelectric motor. The balls were free to rotate and, as a resultof that, rolling contact fatigue conditions were created. Theresults obtained show that the type and nature of lubricatingliquid both have a significant effect on the failure modes ofceramic discs. For instance, base hydrocarbon oil producedfailure typical for surface fatigue whereas the failure mode in the case of a liquid containing acid additive suggests atribochemical type of wear.     

Programmable hierarchical three-component 2D assembly at a liquid-solid interface: recognition, selection, and transformation

Recognition and selection are of fundamental importance for the hierarchical assembly of supramolecular systems. Coronene induces the formation of a hydrogen-bonded isophthalic acid supramolecular macrocycle, and this well-defined heterocluster forces, in its turn, DBA1 to form a van der Waals stabilized honeycomb lattice, leading to a three-component 2D crystal containing nine molecules in the unit cell. The recognition and selection events enable efficient error correction and healing in redundant mixtures.     

Shape memory behavior of high strength NiTiHfPd polycrystalline alloys

Systematic characterization of the shape memory properties of a quaternary Ni_45.3–Ti_29.7–Hf₂₀–Pd₅ (at.%) polycrystalline alloy was performed in compression after selected aging treatments. Precipitation characteristics were revealed by transmission electron microscopy. The effects of aging temperature and time on transformation temperatures, recoverable and residual strains, and temperature and stress hystereses were determined by differential scanning calorimetry, constant-load thermal cycling experiments and isothermal strain cycling (superelasticity) tests. The crystal structure and lattice parameters of the transforming phases were determined from X-ray diffraction analysis. It was revealed that precipitation hardening significantly improved the shape memory properties of the NiTiHfPd alloy. Under optimum aging conditions, shape memory strains of up to 4% under 1 GPa were possible, and superelasticity experiments resulted in full strain recovery without any plastic deformation, even at stress levels as high as 2 GPa. The NiTiHfPd polycrystalline alloy exhibited very high damping capacity/absorbed energy (30–34 J cm^?3) and work output (30–35 J cm^?3), which were attributed to the ability to operate at high stress levels without significant plastic deformation and to a high mechanical hysteresis (>900 MPa) at temperatures ranging from 20 °C to 80 °C.     

Influence of counter material on friction and wear performance of PTFE–metal binary coatings

The study presented in this paper concerns the influence of the counter materials on wear and friction performance of polytetrafluoroethylene (PTFE) reservoirs arranged in distinct patterns on coated surfaces. Al-bronze and Mo coatings were deposited on a mild steel substrate using an atmospheric plasma spray process. Three patterns of PTFE reservoirs were used. Pins, which served as counter surface, were made of three different materials. Wear tests were carried out in a pin-on-disc test rig at room temperature and under dry contact conditions. The tests were carried out at a constant pressure of 10 MPa. An average linear speed of the test disc was 0.036 m/s. The importance of appropriately matched hardness of two surfaces in sliding contact is emphasised. Due to inadequate hardness of the counter material, performance of Mo coating was adversely affected and expected beneficial action of PTFE reservoirs severely hindered. Al-bronze coating proved to be performing far better than Mo coating. Serious deterioration of Mo coating occurred faster than that for Al-bronze coating.     

A long-term course of experimentally produced choroidal neovascularization in the rat

We studied morphologically a long-term course of experimental choroidal neovascularization (ChNV) induced by krypton laser photocoagulation in the rat retina. Fifty-two weeks after photocoagulation, ChNV was enveloped completely by the retinal pigment epithelium. Vascular endothelial cells of ChNV were thin, with many fenestrations and wide lumen. The ChNV maintained the morphological characteristics of mature leaky capillaries similar to choriocapillaris. The lumen of the neovascularizations tended to be compressed by massive collagen fibers produced by the retinal pigmented epithelium. We found that experimental ChNV in the rat retina retains the characteristics of leaky capillaries for a long time unlike that in the monkey ChNV.     

Characterization of the hemorrhagic reaction caused by Vibrio vulnificus metalloprotease, a member of the thermolysin family

Vibrio vulnificus is an opportunistic human pathogen causing wound infections and septicemia, characterized by hemorrhagic and edematous damage to the skin. This human pathogen secretes a metalloprotease (V. vulnificus protease [VVP]) as an important virulence determinant. When several bacterial metalloproteases including VVP were injected intradermally into dorsal skin, VVP showed the greatest hemorrhagic activity. The level of the in vivo hemorrhagic activity of the bacterial metalloproteases was significantly correlated with that of the in vitro proteolytic activity for the reconstituted basement membrane gel. Of two major basement membrane components (laminin and type IV collagen), only type IV collagen was easily digested by VVP. Additionally, the immunoglobulin G antibody against type IV collagen, but not against laminin, showed sufficient protection against the hemorrhagic reaction caused by VVP. Capillary vessels are known to be stabilized by binding of the basal surface of vascular endothelial cells to the basement membrane. Therefore, specific degradation of type IV collagen may cause destruction of the basement membrane, breakdown of capillary vessels, and leakage of blood components including erythrocytes.