Analysis of urokinase immobilization on the polytetrafluoroethylene vascular prosthesis

The blood compatibility challenge. Part 4: Surface modification for hemocompatible materials: Passive and active approaches to guide blood-material interactions

Biomedical devices in the blood flow disturb the fine-tuned balance of pro- and anti-coagulant factors in blood and vessel wall. Numerous technologies have been suggested to reduce coagulant and inflammatory responses of the body towards the device material, ranging from camouflage effects to permanent activity and further to a responsive interaction with the host systems. However, not all types of modification are suitable for all types of medical products. This review has a focus on application-oriented considerations of hemocompatible surface fittings. Thus, passive versus bioactive modifications are discussed along with the control of protein adsorption, stability of the immobilization, and the type of bioactive substance, biological or synthetic. Further considerations are related to the target system, whether enzymes or cells should be addressed in arterial or venous system, or whether the blood vessel wall is addressed. Recent developments like feedback controlled or self-renewing systems for drug release or addressing cellular regulation pathways of blood platelets and endothelial cells are paradigms for a generation of blood contacting devices, which are hemocompatible by cooperation with the host system. STATEMENT OF SIGNIFICANCE: This paper is part 4 of a series of 4 reviews discussing the problem of biomaterial associated thrombogenicity. The objective was to highlight features of broad agreement and provide commentary on those aspects of the problem that were subject to dispute. We hope that future investigators will update these reviews as new scholarship resolves the uncertainties of today.

Validation of an MPC Polymer Coating to Attenuate Surface-Induced Crosstalk between the Complement and Coagulation Systems in Whole Blood in In Vitro and In Vivo Models

Artificial surfaces that come into contact with blood induce an immediate activation of the cascade systems of the blood, leading to a thrombotic and/or inflammatory response that can eventually cause damage to the biomaterial or the patient, or to both. Heparin coating has been used to improve hemocompatibility, and another approach is 2-methacryloyloxyethyl phosphorylcholine (MPC)-based polymer coatings. Here, the aim is to evaluate the hemocompatibility of MPC polymer coating by studying the interactions with coagulation and complement systems using human blood in vitro model and pig in vivo model. The stability of the coatings is investigated in vitro and MPC polymer-coated catheters are tested in vivo by insertion into the external jugular vein of pigs to monitor the catheters' antithrombotic properties. There is no significant activation of platelets or of the coagulation and complement systems in the MPC polymer-coated one, which was superior in hemocompatibility to non-coated matrix surfaces. The protective effect of the MPC polymer coat does not decline after incubation in human plasma for up to 2 weeks. With MPC polymer-coated catheters, it is possible to easily draw blood from pig for 4 days in contrast to the case for non-coated catheters, in which substantial clotting is seen.

Endothelial Cell Transplantation

Endothelial cells line the lumenal surface of al) elements of the vascular system. These cells exhibit numerous metabolic functions necessary for the maintenance of homeostasis. The critical role of endothelium in maintaining normal blood vessel function is exemplified by the poor clinical performance of small diameter polymeric vascular grafts which fail due, in part, to the lack of a functional endothelium on the lumenal surface. Extensive research has explored the potentiality of transplanting endothelial cells onto polymeric vascular grafts to improve graft function. Several critical issues have been explored including the source of endothelial cells for transplantation, the interaction of endothelium with polymers and the healing process of endothelial cell transplanted grafts. The future of endothelial cell transplantation will also include the use of these cells as vehicles for genetic engineering.

Blood and cell compatibility of gelatin-carrageenan mixtures cross-linked by glutaraldehyde

Mixtures of gelatin and iota-carrageenan cross-linked by glutaraldehyde were prepared and their physical properties and blood and cell compatibility were compared to gelatin as a control material. According to scanning electron microscopic observation of fracture surfaces, the mixtures were composed of dispersed and continuous domains which might be generated by phase separation of carrageenan. The thermal degradation temperature of iota-carrageenan in the mixtures rose with increasing gelatin content. The swelling process in the mixtures proceeded slower than in gelatin. Tensile strengths of the mixtures, except that containing 50% iota-carrageenan, increased with increased amounts of iota-carrageenan in the mixtures. The iota-carrageenan contents at the surfaces of the mixtures were generally higher than those admixed originally. Static friction coefficients of the mixtures were lower than that of gelatin. Plasma recalcification times of the mixtures were longer than that of gelatin. Platelet adhesion of the mixtures was lower than that of gelatin, while cell adhesion and growth assays using Chinese hamster ovary cells showed that cell adhesion and growth were not dependent on adding iota-carrageenan. It was concluded that blood compatibility of the mixtures increased and cell compatibility did not decrease, compared to gelatin.

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.