Thrombogenesis molecular motions

The effect and interrelationship between primary (segmental backbone) and secondary (side chain) molecular motions on thrombogenesis, independent of morphological order/dis-order, crystallinity, and/or associated water, were elucidated using an amorphous hydrophobic polymer of poly[(trifluoro-ethoxy) (fluoroalkoxy)phosphazene]. The results indicated that for an amorphous hydrophobic polymer, thrombogenesis was sensitive, and depended on the degrees and types of primary and secondary molecular motions at the polymer interface. 

Therefore, this chapter presents preliminary evidence indicating the effect and interrelationship between primary and secondary molecular motions on thrombogenesis, independent of morphological order and/or crystallinity. The polymer selected for this study was an amorphous elastomeric hydrophobic polymer of poly[(trifluoroethoxy) (fluoroalkoxy)phosphazene] (PNF) I (5, 6). The salient aspects of this polymer are that (1) the onset of the secondary molecular motions occurs between -160° and - 120°C (2) the side chain motion can be altered by irradiation (ultraviolet, electron beam, or gamma) (3) no apparent ultrastructure morphology exists (4) the side chains can be derivatized (5) and (5) the polymer can be readily coated onto our extracorporeal test shafts (7) and irradiated accordingly. Additionally, contact angle measurements of the homopolymer (8) and the PNF (9), 19.7 and 15.0 dyn/cm2, respectively, indicated that the fluorinated side chains comprised the surface to be interfaced in the extracorporeal blood studies. 

To study selectively the effect of primary and secondary molecular motions on thrombogenesis, the PNF was subjected to low-dose ultraviolet irradiation the same dose rate as used in the extracorporeal studies. It was anticipated that this low-dose treatment would selectively cross-link the pendant side chains intramolecularly, followed by intramolecular/intermo-lecular cross-linking at higher dose rates. 

Therefore, in conclusion, these results indicate that an initial effect of molecular motions on thrombogenesis occurs independent of morphological order/disorder, crystallinity, and/or associated water (at the 0.01 mg bound water/mg polymer level). At higher levels of bound water (0.05 mg bound water/mg polymer), the effect of molecular motions on thrombogenesis is complexed by the presence of the bound water, as evidenced by the increased thrombogenic response. 

A semiempirical/theoretical ionic model was derived to cor-relate and interrelate the ultrastructure morphology, surface charge, surface chemistry, and surface molecular motions of a model semicrystalline hydrophobic triblock copolymer to thrombogenesis. This chapter addresses the aspects of ultra-structure order vs. disorder, primary and secondary molecular motions, surface and side chain chemistry, thrombogenesis, and the resultant ionic model. This model can be extrapolated to predict the relative thrombogenic responses of various crystalline and semicrystalline hydrophobic polymeric substrates. 

At this step, then, the differences between the effects of surface chemistry and secondary molecular motions as dictated by morphological order can be observed on thrombogenesis. In the case of the sterically ordered substrate, in conjunction with the subsurface cationic array, the sorbed pro-tein(s) can assume a paracrystalline state, and subsequently be subjected to further pertubations. However, in the case of the disordered substrate, the sorbed proteins can not assume a paracrystalline state and, therefore, will not, per se, be subjected to any further conformational changes. 

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