Type of Document	Dissertation
Author	Snyder, Trevor Arnoult
URN	etd-04062006-102142
Title	Preclinical Biocompatibility Assessment of Cardiovascular Devices
Degree	Doctor of Philosophy
Program	Bioengineering
School	School of Engineering
Advisory Committee	Advisor Name Title William R. Wagner Committee Chair Franklin A. Bontempo Committee Member Harvey S. Borovetz Committee Member James F. Antaki Committee Member Robert L. Kormos Committee Member William J. Federspiel Committee Member
Keywords	coatings biomaterials mechanical circulatory support flow cytometry thrombosis
Date of Defense	2006-03-31
Availability	unrestricted
Abstract Bleeding and thromboembolism remain major complications of ventricular assist device (VAD) support. The amount of biocompatibility information that may be collected during preclinical studies is limited due to a lack of available assays, leaving the evaluation of investigational devices incomplete. To address these issues, flow cytometric assays were developed to quantify bovine circulating activated platelets, platelet microaggregates, platelet-leukocyte aggregates, and monocytes expressing tissue factor. Platelet lifespan was determined using an ex vivo biotinylation technique. These assays were applied in 50 animals receiving the Nimbus/Heartmate II axial flow VAD, 29 receiving the SunMedical EVAHEART centrifugal VAD, over 20 animals receiving a variety of other cardiovascular devices, and eight animals that underwent a sham VAD implantation procedure. The results demonstrated significantly increased circulating activated platelets and leukocytes, and cell aggregates following VAD implantation, which then usually declined to a lower but still significantly elevated level. Deviations from this pattern were observed in several pumps with obstructive thrombi in the blood flow path. Platelet life span decreased and platelet consumption correspondingly increased. The sham studies demonstrated that the effects of the implant procedure abated within three weeks. Thus, the ongoing platelet and leukocyte activation and aggregation, and decreased platelet life span could be attributed to the VADs, even while accounting for surgical effects. To identify the potential causes of the observed cellular activation, VAD surface modifications, revolutions per min increases, and anticoagulant regimen changes were evaluated in vivo. Two blood-shearing devices were constructed to investigate the effects of the supraphysiologic shear field within rotary VADs, although heat generation and sealing issues limited their effectiveness. Flow visualization of the Heartmate II VAD revealed vortices developed at low flow rates, frequently encountered in vivo. In conclusion, the propensity of cardiovascular devices to activate platelets and leukocytes was quantified, while accounting for the effects of the implant procedure. Through in vivo and in vitro investigations, it was demonstrated that the blood-contacting surface and adverse flow effects each contributed to the observed cellular activation. Thus, applying novel biocompatibility assays to preclinical studies, including those evaluating design enhancements and refinements, may be used to develop safer cardiovascular devices.
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