Fundamental Interactions Between MPC Polymers and Proteins

Protein adsorption on material surfaces causes serious biological reactions such as, for example, thrombus formation, immune response, and complement activation, capsulation (Brash and Horbett 1987; Horbett and Brash 1995). To understand the blood compatibility of surfaces, it is necessary not only to determine the amount of adsorbed protein but also the species

Fig. 10. Amount of protein adsorbed on polymer surfaces from human plasma. Poly(BMA) poly(butyl methacrylate), Poly(HEMA) poly(2-hydroxyethyl methacrylate), PMB poly(MPC-co-n-butyl methacrylate). Number after PMB is molar percent of MPC in the coplymer

of the protein. Therefore, the effects of MPC units on protein adsorption were investigated. Figure 10 shows the amount of protein adsorbed on PMB, poly(HEMA), and poly(butyl methacrylate) (BMA) after contact with plasma for 60 min (Ishihara et al. 1992). On poly(BMA), many more proteins were adsorbed than on either poly(HEMA) or PMB. The amount of proteins adsorbed on PMB decreased with increases in the ratio ofthe MPC composition of the polymer. The species and distribution of the protein adsorbed on PMB were also determined by gold-colloid and radiolabeled immunoassay (Ishihara et al. 1991b). From these experiments, it was clarified that the PMB could reduce plasma protein adsorption nonspecifically. Thrombus formation on conventional polymeric materials occurred through the multilayers of plasma proteins denatured by contact with the surfaces. The secondary structures of BSA and BPF adsorbed onto the PMB were evaluated by circular dichroism (CD) spectroscopy (Ishihara et al. 1991a, 1998). Figure 11 shows the CD spectra of BSA in phosphate-buffered saline (PBS) and that adsorbed on the polymer surface. For BSA in PBS, the mean molecular residual ellipticity had a large negative value at 222 nm. The CD spectrum of BSA adsorbed onto PMB was almost the same as that in PBS. The negative ellipticity at 222 nm of BSA adsorbed on the MPC polymers increased as the ratio of MPC decreased, then became almost zero for BSA adsorbed on poly(HEMA). The authors found the same tendency in the case of BPF. Calculation of the a-helix contents of BSA and BPF revealed that the PMB could effectively suppress the conformational change of proteins even when the proteins were adsorbed on the surface (Ishihara et al. 1991,1998).

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Fig. 11. Circular dichroism spectra of BSA in PBS and of that adsorbed on polymer surfaces. A poly(HEMA), B PMB10, C PMB30, D BSA/PBS. Mol. Ellip. Molar ellipticity

In contrast, the a-helix content of both proteins adsorbed on poly(HEMA) decreased significantly. The protein-adsorption-resistant properties of the MPC polymer have also been determined by other researchers (Campbell et al. 1994; Chang et al. 1998; Sugiyama et al. 1997).

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