The initial host response to healthcare materials' surfaces after implantation is the adsorption of proteins from blood and interstitial fluids. This adsorbed protein layer modulates the biological/cellular responses to healthcare materials. This stresses the significance of the surface protein assembly for the biocompatibility and functionality of biomaterials and necessitates a profound fundamental understanding of the capability to control protein–surface interactions. This review, therefore, addresses this by systematically analyzing and discussing strategies to control protein adsorption on polymeric healthcare materials through the introduction of specific surface nanostructures. Relevant proteins, healthcare materials' surface properties, clinical applications of polymer healthcare materials, fabrication methods for nanostructured polymer surfaces, amorphous, semicrystalline and block copolymers are considered with a special emphasis on the topographical control of protein adsorption. The review shows that nanostructured polymer surfaces are powerful tools to control the amount, orientation, and order of adsorbed protein layers. It also shows that the understanding of the biological responses to such ordered protein adsorption is still in its infancy, yet it has immense potential for future healthcare materials. The review, which is—as far as it is known—the first one discussing protein adsorption on nanostructured polymer surfaces, concludes with highlighting important current research questions.

From the view of biomedical relevance, it is known that a specific arrangement of surface-immobilized human plasma fibrinogen (HPF) molecules is required to retain their biological functionality. Here, we demonstrate a topographical effect of chemically identical isotactic poly(butene-1) (iPB-1) semicrystalline nanostructures on the adsorption behavior, i.e., conformation change and orientation of HPF molecules. Using the distinct crystallization of iPB-1 under different shear conditions, polymer thin films consisting of needle-like crystals (NLCs) or shish-kebab crystals (SKCs) having lateral dimension, i.e., width, smaller than or comparable to the HPF major axis, respectively, were fabricated. The protein adsorption kinetic studies by quartz crystal microbalance with dissipation (QCM-D) revealed surface-dependent packing density and assembly configuration of HPF. High-resolution imaging disclosed a "side-on" protein adsorption and anisotropic network formation on the NLCs. With a 2-fold orientation analysis performed at both "single" protein and multiprotein levels, we quantitatively proved the preferential alignment of adsorbed HPF molecules with respect to the axial direction of the NLCs. Remarkably, the iPB-1 surface with SKCs perturbed the "end-to-end" protein-protein interactions and thus hindered the network formation. The distinguished adsorption behavior of HPF molecules on iPB-1 surfaces is explained by the physical effect of crystal width, which is additionally supported by the synergistic effect of crystal curvature and aspect ratio. Our studies provide fundamental insight into purely topography-controlled self-assembly of HPF molecules, which might be further exploited in creating topographically defined implant surfaces for preventing protein aggregation related disorders.

Creating and establishing proof of hybrid protein nanofibers (hPNFs), i.e., PNFs that contain more than one protein, is a currently unsolved challenge in bioinspired materials science. Such hPNFs could serve as universal building blocks for the bottom-up preparation of functional materials with bespoke properties. Here, inspired by the protein assemblies occurring in nature, we introduce hPNFs created via a facile self-assembly route and composed of human serum albumin (HSA) and human hemoglobin (HGB) proteins. Our circular dichroism results shed light on the mechanism of the proteins' self-assembly into hybrid nanofibers, which is driven by electrostatic/hydrophobic interactions between similar amino acid sequences (protein handshake) exposed to ethanol-triggered protein denaturation. Based on nanoscale characterization with tip-enhanced Raman spectroscopy (TERS) and immunogold labeling, our results demonstrate the existence and heterogenic nature of the hPNFs and reveal the high HSA/HGB composition ratio, which is attributed to the fast self-assembling kinetics of HSA. The self-assembled hPNFs with a high aspect ratio of over 100 can potentially serve as biocompatible units to create larger bioactive structures, devices, and sensors.

The conformational state of adsorbed human plasma fibrinogen (HPF) has been recognized as the determinant factor in platelet adhesion and thrombus formation on blood-contacting biomaterials. Studies have highlighted the ability to control the HPF conformation merely by tailoring surface nanotopographical features. However, a clear relationship between the conformational changes of adsorbed HPF and the degree of platelet adhesion and activation achieved with different surface nanotopographies is still unclear. Here, we examined HPF assembly characteristics on nanostructured polybutene-1 (PB-1) surfaces with nanosized lamellar crystals (LCs), needle-like crystals (NLCs), and a nanostructured high-density polyethylene (HDPE) surface with shish-kebab crystals (SKCs), at a biologically relevant HPF concentration. By exposing the nanostructured surfaces with preadsorbed HPF to human platelets, significant differences in platelet response on LCs/SKCs and NLCs were identified. The former presented a uniform monolayer in the advanced stage of activation, whereas the latter exhibited minimal adhesion and the early stage of activation. Distinct platelet response was related to the postadsorption conformational changes in HPF, which were confirmed by topography-dependent shifts of the amide I band in attenuated total reflection-Fourier transform infrared (ATR-FTIR) analysis. Supported by atomic force microscopy (AFM) characterization, we propose that the mechanism behind the nanotopography-induced HPF conformation is driven by the interplay between the aspect ratios of polymeric crystals and HPF. From the biomedical perspective, our work reveals that surface structuring in a nanoscale size regime can provide a fine-tuning mechanism to manipulate HPF conformation, which can be exploited for the design of thromboresistant biomaterials surfaces.

Surface nanostructures are increasingly more employed for controlled protein assembly on functional nanodevices, in nanobiotechnology, and in nanobiomaterials. However, the mechanism and dynamics of how nanostructures induce order in the adsorbed protein assemblies are still enigmatic. Here, we use single-molecule mapping by accumulated probe trajectories and complementary atomic force microscopy to shed light on the dynamic of in situ assembly of human plasma fibrinogen (HPF) adsorbed on nanostructured polybutene-1 (PB-1) and nanostructured polyethylene (PE) surfaces. We found a distinct lateral heterogeneity of HPF-polymer nanostructure interface (surface occupancy, residence time, and diffusion coefficient) that allow identifying the interplay between protein topographical nanoconfinement, protein diffusion mechanism, and ordered protein self-assembly. The protein diffusion analysis revealed high-diffusion polarization without correlation to the anisotropic friction characteristic of the polymer surfaces. This suggests that HPF molecules confined on the nanosized PB-1 needle crystals and PE shish-kebab crystals, respectively, undergo partial detachment and diffuse via a Sansetsukon-like nanocrawling mechanism. This mechanism is based on the intrinsic flexibility of HPF in the coiled-coil regions. We conclude that nanostructured surfaces that encourage this characteristic surface mobility are more likely to lead to the formation of ordered protein assemblies and may be useful for advanced nanobiomaterials.

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Graphene oxide deposited on thermoresponsive copolymer microspheres enhances their barrier diffusion properties and drug release performance.

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