Surface Assembly Configurations and Packing Preferences of Fibrinogen Mediated by the Periodicity and Alignment Control of Block Copolymer Nanodomains
The ability to control the specific adsorption and packing behaviors of biomedically important proteins by effectively guiding their preferred surface adsorption configuration and packing orientation on polymeric surfaces may have utility in many applications such as biomaterials, medical implants, and tissue engineering. Herein, we investigate the distinct adhesion configurations of fibrinogen (Fg) proteins and the different organization behaviors between single Fg molecules that are mediated by the changes in the periodicity and alignment of chemically alternating nanodomains in thin films of polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) block copolymer (BCP). Specifically, the adsorption characteristics of individual Fg molecules were unambiguously resolved on four different PS-b-PMMA templates of dsa PS-b-PMMA, sm PS-b-PMMA, com PS-b-PMMA, and PS-r-PMMA. By direct visualization through high resolution imaging, the distinct adsorption and packing configurations of both isolated and interacting Fg molecules were determined as a function of the BCP template-specific nanodomain periodicity, domain alignment (random versus fully aligned), and protein concentration. The three dominant Fg adsorption configurations, SP¥, SP¥, and TP, were observed and their occurrence ratios were ascertained on each PS-b-PMMA template. During surface packing, the orientation of the protein backbone was largely governed by the periodicity and alignment of the underlying PS-b-PMMA nanodomains whose specific direction was explicitly resolved relative to the polymeric nanodomain axis. The use of PS-b-PMMA with a periodicity much smaller than (and comparable to) the length of Fg led to a Fg scaffold with the protein backbone aligned parallel (and perpendicular) to the nanodomain major axis. In addition, we have successfully created fully Fg-decorated BCP constructs analogous to two-dimensional Fg crystals in which aligned protein molecules are arranged either side-on or end-on, depending on the BCP template. Our results demonstrate that the geometry and orientation of the protein can be effectively guided during Fg self-assembly by controlling the physical dimensions and orientations of the underlying BCP templates. Finally, the biofunctionality of the BCP surface-bound Fg was assessed and the Fg/BCP construct was successfully used in the Ca-P nanoparticle nucleation/growth and microglia cell activation.