The surface bonded, covalently crosslinked urokinase synthetic surface. In vitro and chronic in vivo studies

Haemocompatibility of invasive sensors

In recent years the importance and utilisation of invasive chemical sensors have increased, especially in respect to their function and behaviour in a biological environment. This review aims to highlight the development of various sensors and reflect on the problems which can occur when the sensors come into contact with blood. Thus their haemocompatibility is a key area of importance. A clear understanding of their interaction with plasma proteins at the point of interface is fundamental as this determines their ultimate capability to function safely and effectively. There is also an overview of various techniques that have been developed, together with a broad summary of inherent problems which may arise when aiming to improve the haemocompatibility of invasive sensors for in vivo applications.

Effect of controlled local acetylsalicylic acid release on in vitro platelet adhesion to vascular grafts

Thrombosis is the most serious acute problem for small diameter arterial bypass grafts. In this research, small diameter expanded polytetrafluoroethylene (e-PTFE) vascular grafts were coated with acetylsalicylic acid (ASA) loaded poly (d,l-lactide) (PLA) by a solvent casting method. The feasibility and efficacy of this approach were evaluated by ASA release studies and platelet adhesion tests. First, the ASA release kinetics were evaluated from the ASA/PLA coated vascular grafts in an in vitro steady flow loop model. ASA release was measured by a spectrophotometric technique. Finally, the efficacy of local ASA release to reduce in vitro canine platelet adhesion to grafts was determined with epifluorescent video microscopy and quantitative image analysis. The steady state release rates from the 5%, 10%, and 15% ASA/PLA coated grafts were 13.2 x 10(-5), 32.0 x 10(-5), and 41.5 x 10(-5) micrograms/cm2.sec, respectively. Platelet adhesion to 10% and 15% ASA/PLA coated grafts was reduced with respect to the control and 5% grafts for 10 days. Platelet adhesion to 5% ASA/PLA coated grafts was reduced with respect to controls at 2 and 10 days, but not initially.

New small-caliber antithrombotic vascular prosthesis: experimental study

Vascular prostheses with the inner diameter smaller than 1 mm were implanted to the common carotid artery of rats, and their patency was examined. Four types of tubes were prepared for this purpose in Experiment 1: polyethylene (PE), poly-(acrylic acid)-grafted polyethylene (PE-AA), polyacrylamide-grafted polyethylene (PE-AAm), and poly(vinyl alcohol) (PVA) tubes. Comparative studies made using nonsuture anastomosis revealed that the PE-AAm and PVA tubes were antithrombotic, although disconnection was noted at the anastomotic sites within 1 week and 1 month, respectively. Thereafter in Experiment 2, the PVA tubes were implanted to the common carotid artery of 20 rats using conventional anastomosis. Neither anticoagulants nor fibrinolytic agents were used in both series of experiments. Patency of the PVA tubes was 80% after 1 week and 70% after 1 month. In patent cases after 1 month, the luminal surfaces of the prostheses and the host arteries were examined using scanning electron microscopy. The lumen of the arteries and anastomotic sites was covered with endothelial cells, while the lumen of the PVA tubes was free from thrombi and there was no neointima formation. So far, there has been reported no manmade material that has completely antithrombotic property in vivo. However, our studies disclosed that PVA is antithrombotic and one of the most promising materials for the inner surface of small vascular prostheses.

Thoraco-abdominal bypass as a method of evaluating vascular grafts in the dog

Seven Vasculour d grafts, five Gore-Tex grafts and seven Solco-graft, 8 mm by 30 cm, implanted as thoraco-abdominal bypasses in dogs. Sixteen were retrieve at two months. Graft size was assessed angiographically in representative dogs of each group prior to sacrifice. Initial examination of the retrieved specimens revealed pannus extensions at both anastomoses on all graft types, and a variable midgraft appearance from smooth and glistening to partially thrombus coated. Histological assessment of graft segments revealed widely differing healing responses on the three graft types. Tissue attachment to both graft surfaces and varying degrees of tissue incorporation were observed in the Vasculour D and Gore-Tex prostheses. The Solco-graft specimens showed no evidence of tissue incorporation of the wall at two months. Tissue on the graft surfaces remains loosely attached and unincorporated. Pannus extensions were thickest on the Solco-graft. Variably thin fibrin is scattered over the luminal surface of the three graft types. Vascularization of the wall particularly the internal capsulae was noted in the Vasculour D grafts. Although biological responses in the dog are difficult to extrapolate to man, the types of comparison testing allowed by the use of the thoraco-abdominal by-pass procedure can provide valuable information of degree of dilation, relative tissue attachment, tissue incorporation into various types of prostheses and kidney infarcts study. The greatest value of the thoraco-abdominal by-pass lies in graft sizes and length without special regard for patency: assessment of graft size post-implantation and structural changes is then made possible.

Urokinase immobilized on medical polymeric materials: fundamental and clinical studies

One of the methods of preparing an antithrombogenic material is to immobilize a fibrinolytic enzyme on the surface of a carrier. The clinical trial of such a material must be subject to not only a basic study on the quality of a carrier, the technique of immobilization, and the method of disinfection, but also an in vivo study on its antithrombotic effect. Reported herein is the evaluation of the fibrinolytic ability, at fundamental and clinical levels, of the urokinase that was immobilized on the surface of various polymeric materials. The results were favorable.

Antithrombogenicity of immobilized urokinase and its clinical significance

Urokinase (UK), a plasminogen activator was immobilized on nylon surface by application of a newly devised technique. When applied clinically, this new preparation proved to have excellent thromboresistance.

Blood compatibility of silicone rubber chemically coated with cross-linked albumin

A new method is reported for chemically coating cross-linked albumin onto silicone rubber in an attempt to improve the blood compatibility of the material. Promising results were obtained in an evaluation using both vena cava and renal embolus antithrombogenicity tests ondogs. Coated silicone rubber rings induced much less renal emboli than uncoated ones after one week implantation.