The role of protonation and conformational transition of polyamine grafts in platelet retention to polyamine-graft-PHEMA copolymer surfaces

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Abstract
Blood platelet retention on polyamine-graft-poly(2-hydroxyethyl methacrylate) (PHEMA) copolymer (HA) surface was investigated, focusing on pH and ionic strength of the surrounding medium to elucidate the nature of ionic interaction between platelets and HA copolymer surfaces. The conformational transition of polyamine graft chain in response to the protonation degree of amino groups was demonstrated to be an important factor influencing platelet retention on HA surfaces. When the polyamine graft chain exists in an extended conformation, protonated amino groups distribute from the matrix interface into the aqueous interior, resulting in the effective ionic interaction with platelets to increase their retention on HA copolymer surfaces. The number of protonated amino groups in polyamine portions crucially affected platelet retention. Worth noticing is that an introduction of a small but definite amount of cationic sites on the polymer surface led to significantly minimized platelet retention. It is considered that the surface property of PHEMA was drastically changed to a non-adhesive surface by introducing a small amount of protonated amino groups.