Polyethylene/hydrophilic polymer blends for biomedical applications.

Polyethylene blends with poly(2-hydroxyethyl methacrylate) [poly(HEMA)] or poly(2,3-dihydroxypropyl methacrylate) [poly(DHPMA)] were prepared by swelling polyethylene with HEMA or 2,3-epoxypropyl methacrylate (EPMA) and by polymerization of the respective monomers. Poly(EPMA) in blends was hydrolysed to poly(DHPMA) with acetic acid. The blends had similar surface and bulk compositions. Swelling with water and surface wettability were proportional to the content of the hydrophilic component; at the same content the polyethylene/poly(DHPMA) blends appeared more hydrophilic than those of polyethylene/poly(HEMA). Thrombus formation in contact with blood examined ex vivo and in vivo was considerably slower on the blends than on unmodified polyethylene. The tests indicated optima in composition; the best biological response was achieved with the blends containing about 14% poly(HEMA) or 16% poly(DHPMA).

In vitro and in situ intercellular adhesion molecule-1 (ICAM-1) expression by endothelial cells lining a polyester fabric.

In order to improve long-term patency of vascular grafts, the promising concept of endothelial cell seeding is actually under investigation. Our laboratory tested a polyester coated with albumin and chitosan which permits a rapid colonization by human umbilical vein endothelial cells (HUVEC) and it seems relevant to test in vitro the expression of adhesive molecules expressed by cells with regard to the inflammatory process. We studied intercellular adhesion molecule-1 (ICAM-1) expression and focused our work on the determination of ICAM-1 sites expressed per adherent cell lining the biomaterial, thus in situ, in comparison to control HUVEC on plastic wells: the results obtained by binding experiments were correlated to flow cytometry analyses and showed that the polyester does not induce a proinflammatory state and that HUVEC covering the structure are able to respond to a stimulus.

Comparative assessment of hepatic Glisson's capsule and bovine pericardium in heart valve bioprostheses.

BACKGROUND AND AIM OF THE STUDY: The optimal material for heart valve bioprostheses remains disputable. This investigation was initiated to compare the properties of hepatic Glisson's capsule, clinical experience of which in cardiovascular surgery is minimal, with those of bovine pericardium. METHODS: Hepatic Glisson's capsule was harvested from bull calves and used to create composite pulmonary arterial monocusp grafts and bioprostheses. Comparison of the strength and elastic properties of Glisson's capsule and bovine pericardium, as well as the hydrodynamic characteristics of valves made from these materials, was performed. Late results of operations using these materials were estimated echocardiographically. RESULTS: Although Glisson's capsule tissue is thinner than the bovine pericardium, its elasticity modulus is greater. However, the hydrodynamic characteristics of heart valves made from either tissue are similar. Moreover, valves made from Glisson's capsule have a lower systolic pressure gradient on the prosthesis and a higher effective orifice area. Composite pulmonary arterial xenopericardial grafts with a monocusp of Glisson's capsule were used in 30 patients during tetralogy of Fallot repair. Glisson's capsule was also used for tricuspid valve reconstruction and as a bioprosthesis in six patients with Ebstein's anomaly. At 1-2 years after surgery, the Glisson's capsule tissue remained thin and flexible, with no calcification. CONCLUSIONS: Although the hydrodynamic properties of hepatic Glisson's capsule and the bovine pericardium are similar, the capsule tissue is thinner and has a greater elasticity modulos. Thus, Glisson's capsule may be used for bioprosthesis construction both independently and in combination with bovine pericardium.

[Hydrodynamics of disk artificial heart valves with different design characteristics]. / Gidrodinamika diskovykh iskusstvennykh klapanov serdtsa s razlichnymi konstruktivnymi kharakteristikami.

Bench tests for 38 models of artificial heart valves (AHV) with different design parameters allowed us to decide in favour of the valves with reduced eccentricity (compared to the serial AHV of the EMAHV type) according to its resistance in the constant flow. Out of the compatibility checks of the design parameters tested it was concluded that the disk did not make the complete calculated angle when rotated. The dependence of AHV resistance on the disk rotation angle showed that there is no necessity to increase that angle more than 70 degrees for the mitral valve and more than 75 degrees for the aortic AHV.

[Analysis of the causes of potential wear and breakdown of elements of artificial heart valves of the disk type]. / Analiz prichin vozmozhnogo iznosa i razrusheniia élementov iskusstvennykh klapanov serdtsa diskovogo tipa.

The reliability analysis of the artificial cardiac valve and experiments made it possible to establish that the ACV reliability is ensured by the physical and mechanical properties of the material, technology observance and thorough control over each operation during the manufacturing process. The accelerated testing of the new MX disk valve made in the USSR showed a satisfactory degree of the disk wear and the absence of breaks-down after 400 million working cycles which is equivalent to ten-years' work in a human body.

[Pressure distribution on the surface of the cut-off elements of artificial heart valves]. / Raspredelenie davleniia na poverkhnosti zapiraiushchikh élementov iskusstvennykh klapanov serdtsa.

With hydroaerodynamic investigations into pressure distribution on the surface of blocking components in artificial cardiac valves in the shape of a sphere, semisphere, lens and a disc opening at an angle serving as a basis a quantitative evaluation of the arrangement for the flow separation, evacuation peak regions and congestion zones is given. The highest velocity, greatest evacuation and shear stress occur in a flow-past of a valve having a shape of the lens. The disc valve opening at an angle, as concerns its hydrodynamic characteristics, is superior to the valves of all the other designs considered in the present work.

[Functional characteristics of flexible supporting structures for heart valve bioprosthesis]. / Issledovanie funktsional'nykh kharakteristik gibkikh opornykh bioprotezov klapanov serdtsa.

Hydraulic characteristics of heart valve bioprostheses mounted on supporting structures of various rigidity have been studied under physiologic conditions. An actual mobility of the supporting structures made of different polymers is determined. Static and dynamic components of the support displacements have been shown to develop as the bioprosthesis is under the load, the dynamic component being strongly dependent upon the rigidity of fastening the bioprosthesis on the axis. It is noted that considerable improvements in hydraulic characteristics of bioprostheses are achieved through the use of flexible supporting structures.

[Evaluation of the function of the left heart ventricle during the modeling of right ventricular hyperfunction using a pulsatile pump]. / Otsenka funktsii levogo zheludochka serdtsa pri modelirovanii pravozheludochkovoi giperfunktsii s pomoshch'iu pul'siruiushchego nasosa.

Left ventricular function was studied in 11 acute experiments on dogs during right ventricular hyperfunction modelling using an artificial heart ventricle (AHV). The right ventricle was excluded from circulation and replaced by AHV. First the baseline condition with regard to the cardiac index was recovered. The right ventricle was considered to be completely functionally replaced when no hemodynamic changes were observed. When the AHV output increased by 26% there were no considerable changes in hemodynamics and the functional condition of the left ventricle remained adequate. If the output was 56% higher certain hemodynamic changes and a tendency towards deterioration of the left ventricular function have been observed. The final stage of the experiments was characterized by twice as high ANV output, as compared to the initial one, which caused considerable hemodynamic changes and greater left ventricular weakness.

An in vivo comparative study of the e-polytetrafluoroethylene vascular prostheses: Vitaflon and Gore-Tex.

A comparative study was performed in order to validate new Russian e-PTFE vascular prostheses Vitaflon (St. Petersburg, Russia). The Gore-Tex prostheses were chosen as a referential model. The prostheses were implanted in the venous and arterial positions in 13 dog experiments. After the implantation time was over a comprehensive histological and histochemical examination of excized specimens was performed. It was demonstrated that there is no difference in healing and functional properties between the two studied prostheses.

[A new approach to the creation of heart valve xenograft bioprostheses resistant to calcification]. / Novyi podkhod k sozdaniiu ksenobioprotezov klapanov serdtsa, rezistentnykh k kal'tsifikatsii.

The calcium binding activity of xenograft tissue in stages of modification with papain, diphosphonates, and heparin was studied on a model of accelerated calcification in subcutaneous implantation of cusps of pig's aortic bioprostheses to 42 rats. In immobilization of 3-amino-1-oxypropylidendiphosphonic acid and xydiphon the amount of calcium in the implants reduced 50 times as compared to the control. The first stage of ion-covalent heparin immobilization--treatment with albumin--increased the calcium-binding activity of the biomaterial, but subsequent heparinization reduced again the calcium content in the cusp tissue to the level attained in the stage of diphosphonate immobilization. The results of the chemical analysis correlated with the findings of morphological examination. Besides, the new method of treatment made it possible to increase the strength of the biological tissue by 20%. This method of storage of bioprostheses is promising for clinical approbation.

[Clinical characteristics of the Soviet low-profile heart valve prostheses EMIKS and LIKS]. / Klinicheskaia kharakteristika otechestvennykh nizkoprofil'nykh protezov klapanov serdtsa EMIKSA i LIKS.

The present work is devoted to the clinical assessment of the Soviet-made cardiac valve prostheses 'EMIKS' and 'LIKS'. From 1983 to May 1, 1988, 632 prostheses were implanted to 508 patients. A group of 348 patients were assessed: 139 after mitral (M) replacement, 130 after aortal (A) replacement, and 79 after mitral-aortal (M+A) replacement. Hospital mortality rate was: in M group--4.3 per cent, in A group--5.3 per cent, in M+A group--8.8 per cent. Survival rate on the fifth postoperative year was: in M group--89.5 +/- 9.2 per cent, in a group--90.0 +/- 4.2 per cent, in M+A group--91.0 +/- 6.2 per cent, the stability of the good results being 85.5 +/- 7.2, 79.5 +/- 6.2, and 75.0 +/- 9.1 per cent, respectively. At year 5 of the follow-up, patient numbers without thromboembolic complications amounted to 95.0 +/- 4.7 per cent in M group, 95.5 +/- 4.2 per cent in A group, and 85.0 +/- 9.1 in M+A group. 95.1 per cent patients belong to functional classes I and II. In mitral replacement, the mean 'EMIKS' gradient was 4.2 +/- 0.58 mm Hg, the 'LIKS' one--4.58 +/- 0.62 mm Hg. Intravascular hemolysis was not observed. The 'EMIKS' and 'LIKS' prostheses match the models produced in other countries. No significant differences between the two models were found.

[Studies and clinical experiences in the use of domestic blood vessel prostheses with increased thromboresistance]. / Issledovaniia i klinicheskii opyt primeneniia novykh otechestvennykh sosudistykh protezov s povyshennoi tromborezistentnost'iu.

The experimental and clinical data on the use of new native grafts with increased thromboresistance--the Vitlan and heparinized ones are presented. In all the acute and chronic experiments, the increased thromboresistance of both types of the grafts versus the common Fluorlon-Lavsan ones, and well-formed neointima with sufficient vascularization by the year 1 and 5 of follow-up were revealed. Complete organization of the external and internal capsules of the grafts was noted 5 mos later, no tissue reaction to Vitlan and heparinized grafts was revealed. The Vitlan grafts were used in 19 patients. Good immediate and long-term results were obtained in reconstruction of the aorto-femoral, aorto-pulmonary and femoro-popliteal segments with the grafts of 10 and 8 mm in diameter. All the Vitlan shunts of the femoro-popliteal segment with 6 mm diameter were thrombosed 1-6 mos after the operation. The heparinized grafts with 8 mm diameter at the femoro-popliteal position were used in 28 patients, good long-term results were noted in 27.