Use of simple and complex in vitro models for multiparameter characterization of human blood-material/device interactions

Medical devices, intended for blood contacting applications, undergo extens ive in vitro testing followed by animal and clinical feasibility studies. B esides the use of materials known to be intrinsically blood-compatible, the surface of such devices is often modified with a coating in order to impro ve the performance characteristics during blood exposure. In vitro evaluati on of blood-device interactions accompanies the product development cycle f rom the early design phase using basic material geometries until final fini shed-product testing. Specific test strategies can vary significantly depen ding on the end application, the particular study objectives and variables of interest, and cost. To examine the degree to which findings derived from two different in vitro approaches complement one another, this report cont rasts findings from a simple multipass loop model with findings from a simu lated cardiopulmonary bypass (CPB) model. The loop model consists of tubular test materials, with and without surface modification, formed into valved Chandler loops. The CPB model has an oxyg enator with and without surface modification connected to a reservoir and a blood pump. The surface modifications studied in this report are the Carme da(R) BioActive Surface and Duraflo(R) II heparin coatings. Common blood pa rameters in the categories of coagulation, platelets, hematology, and immun ology were monitored in each model. Ideal models employ the optimal level of complexity to study the design var iables of interest and to meet practical cost considerations. in the case o f medical device design studies; such models should also be predictive of p erformance. In the more complex and realistic simulated CPB model, experime ntal design and cost factors prevented easy/optimum manipulation of critica l variables such as blood donor (use of paired samples) and heparin level. Testing in the simpler loop model, on the other hand, readily offered manip ulation of these variables, and produced findings which overlapped with obs ervations from the more complex CPB model. Thus, the models described here complimented one another. Moreover, conclusions from consistent findings, s uch as favorable responses associated with the heparin coatings, between th e two models were considered to be more robust.