Synthesis and characterization of poly(dimethylsiloxane)-poly(ethylene oxide)-heparin CBABC type block copolymers

Sung Wan Kim - Early events in blood/material interactions

Sung Wan Kim's initial efforts as an independent investigator were focused on improving the understanding of the early events in blood/material interactions with the goal to develop blood compatible materials for application in medical devices and prostheses. These initial efforts were centered around blood protein adsorption on biomaterials and related mechanisms of thrombus formation (thrombosis). Ultimately, Sung Wan's efforts were expanded to studies of the non-thrombogenic nature of heparinized biomaterials, prostaglandin biomaterials, and block copolymer systems. These studies were supported by two NIH grants for 22 and 19 years, respectively, and a NIH Career Development Award. Moreover, these studies resulted in over 140 peer-reviewed publications and training of many students and postdoctoral scientists. The intent of this paper is to identify key concepts, papers, and contributions by Sung Wan and his colleagues that fall within the four aforementioned research categories. In this context, many of Sung Wan's early efforts contributed directly to Utah's biomaterials efforts and the Total Artificial Heart program at the time, while providing the foundation for the productive international Triangle Collaboration as well as his following work in polymer-controlled drug releasing systems.

Creating molecular barriers to acute platelet deposition on damaged arteries with reactive polyethylene glycol

We report here a novel method for blocking acute platelet deposition at the site of vessel injury by molecularly masking thrombogenic vascular wall proteins with covalently attached polyethylene glycol (PEG). To evaluate this technique, blood containing 111In-labeled platelets was perfused over damaged human placental arteries for 2 min at a wall shear rate of 200 s-1. Denuded vessel segments were incubated for 30, 15, 5, and 1 min with a solution of either reactive PEG-diisocyanate (PEG-ISO) or nonreactive PEG-dihydroxyl (PEG-OH). Vessels treated with PEG-ISO for 1 min exhibited 87 +/- 12% less platelet deposition (p < 0.01) than untreated control vessels, and this reduction did not vary significantly among treatment times, indicating that this reaction occurs rapidly enough to be clinically applicable. To investigate the duration of this thrombotic barrier, denuded pig carotid arteries were treated with reactive PEG-ISO for 1 min, perfused with plasma for 30 min, and then perfused with blood containing radiolabeled platelets. PEG-ISO-treated arteries exhibited 84 +/- 9% less platelet deposition (p < 0.05) than untreated controls. These data demonstrate that damaged arterial surfaces can be rendered resistant to platelet deposition after short contact periods with reactive PEG. Molecular PEG barriers ultimately might find application following vascular procedures to sterically inhibit blood cell interaction with damaged vascular surfaces.

Does polyethylene oxide possess a low thrombogenicity?

Because of the 'bland' nature of polyethylene oxide towards proteins and cells, considerable effort has been devoted to preparing surfaces rich in polyethylene oxide, using block copolymers, surface immobilization or other methods. It is clear that these modifications result in reduced levels of cell (including platelet) adhesion and protein adsorption, when compared to unmodified and typically hydrophobic substrates. It is far less clear whether the reduced adhesion or adsorption is due specifically to the thermodynamic effects of polyethylene oxide or to the increase in surface hydrophilicity after its immobilization. Even more so, it is unclear whether the reduction in such parameters is evidence of a reduced thrombogenicity.