Hydrophilic poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) and poly(2-hydroxyethyl methacrylate) (PHEMA) brush layers with different thicknesses and graft densities were prepared to construct ...a model surface to elucidate protein–surface interactions. In particular, we focused on the steric repulsion of hydrophilic polymer layers as one of the surface properties that strongly influence protein adsorption and employed force-versus-distance (f–d) curve measurements obtained via atomic force microscopy to quantitatively evaluate the steric repulsion force, which is also referred to as the “elastic repulsion energy.” We also analyzed direct interactions between the surface and proteins via the f–d curve, because these interactions trigger the protein-adsorption phenomenon. Protein–surface interactions were extremely suppressed at surfaces with high elastic repulsion energies and highly dense polymer brush structures, which is in contrast to those at surfaces with low elastic repulsion energies and low density of the grafted polymer layers. These results indicate that the elastic repulsion from the grafted polymer layer at the surface is an important parameter for controlling protein–surface interactions and protein adsorption phenomenon.
Amphiphilic diblock copolymers (M98En) composed of hydrophilic poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC, M) and hydrophobic poly(2-methoxyethyl acrylate) (PMEA, E) were prepared via ...controlled radical polymerization. The degree of polymerization (DP) of the PMPC block was 98, and the DP values of the PMEA block (=n) were 95 and 314. In water, M98En formed micelles with hydrophobic PMEA cores and hydrophilic PMPC shells. The size, density, and aggregation number of M98E314 were larger than those of M98E95 because the hydrophobic interactions became stronger with increasing PMEA block length. A hydrophobic anticancer agent, i.e., doxorubicin, was encapsulated into the core of the polymer micelles to assess the potential of these micelles as carriers in a drug delivery system. Micelles formed from M98En did not interact with proteins in the aqueous solution because the micelle surfaces were covered with biocompatible PMPC shells.Amphiphilic diblock copolymers (M98En) composed of hydrophilic poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) and hydrophobic poly(2-methoxyethyl acrylate) were synthesized via controlled radical polymerization. M98En formed micelles in water, which can encapsulate hydrophobic guest molecules into the core. The micelles did not interact with proteins in an aqueous solution due to the PMPC shells.
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A highly efficient methodology for preparing a poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) layer on the surface of poly(ether ether ketone) (PEEK) was examined by ...photoinduced and self-initiated graft polymerization. To enhance the polymerization rate, we demonstrated the effects of inorganic salt additives in the feed monomer solution on thickness of grafted PMPC layer. Photoinduced polymerization occurred and the PMPC graft layer was successfully formed on the PEEK surface, regardless of inorganic salt additives. Moreover, it was clearly observed that the addition of inorganic salt enhanced the grafting thickness of PMPC layer on the surface even when the photoirradiation time was shortened. The addition of inorganic salt additives in the feed monomer solution enhanced the polymerization rate of MPC and resulted in thicker PMPC layers. In particular, we evaluated the effect of NaCl concentration and how this affected the polymerization rate and layer thickness. We considered that this phenomenon was due to the hydration of ions in the feed monomer solution and subsequent apparent increase in the MPC concentration. A PMPC layer with over 100-nm-thick, which was prepared by 5-min photoirradiation in 2.5mol/L inorganic salt aqueous solution, showed good wettability and protein adsorption resistance compared to that of untreated PEEK. Hence, we concluded that the addition of NaCl into the MPC feed solution would be a convenient and efficient method for preparing a graft layer on PEEK.
Photoinduced and self-initiated graft polymerization on the PEEK surface is one of the several methodologies available for functionalization. However, in comparison with free-radical polymerization, the efficiency of polymerization at the solid-liquid interface is limited. Enhancement of the polymerization rate for grafting could solve the problem. In this study, we observed the acceleration of the polymerization rate of MPC in an aqueous solution by the addition of inorganic salt. The salt itself did not show any adverse effects on the radical polymerization; however, the apparent concentration of the monomer in feed may be increased due to the hydration of ions attributed to salt additives. We could obtain PMPC-grafted PEEK with sufficient PMPC thickness to obtain good functionality with only 5-min photoirradiation by using 2.5mol/L NaCl in the feed solution.
The biomimetic synthetic phospholipid polymer containing a phosphorylcholine group, 2-methacryloyloxyethyl phosphorylcholine (MPC), has improved the surface property of biomaterials. Both hydrophilic ...and anti-biofouling surfaces were prepared on polydimethylsiloxane (PDMS) with MPC grafted by surface-initiated photo-induced radical polymerization. Benzophenone was used as the photoinitiator. The quantity of the adsorbed initiator on PDMS was determined by UV absorption and ellipsometry. The poly(MPC)-grafted PDMS surfaces were characterized by XPS, ATR-FTIR and static water contact angle (SCA) measurements. The SCA on PDMS decreased from 115° to 25° after the poly(MPC) grafting. The in vitro single protein adsorption on the poly(MPC)-grafted PDMS decreased 50–75% compared to the unmodified PDMS. The surface friction of the poly(MPC)-grafted PDMS was lower than the unmodified PDMS under wet conditions. The oxygen permeability of the poly(MPC)-grafted PDMS was as high as the unmodified PDMS. The tensile property of PDMS was maintained at about 90% of the ultimate stress and strain after the poly(MPC) grafting. The surface-modified PDMS is expected to be a novel medical elastomer which possesses an excellent surface hydrophilicity, anti-biofouling property, oxygen permeability and tensile property.
Abstract We investigated the production of free radicals on a poly(ether-ether-ketone) (PEEK) substrate under ultraviolet (UV) irradiation. The amount of the ketyl radicals produced from the ...benzophenone (BP) units in the PEEK molecular structure initially increased rapidly and then became almost constant. Our observations revealed that the BP units in PEEK acted as photoinitiators, and that it was possible to use them to control the graft polymerization of poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC). This “self-initiated surface graft polymerization” method is very convenient in the absence of external photoinitiator. We also investigated the effects of the monomer concentration and UV irradiation time on the extent of the grafted PMPC layer. Furthermore, as an application to improving the durability of artificial hips, we demonstrated the nanometer-scale photoinduced grafting of PMPC onto PEEK and carbon fiber-reinforced PEEK (CFR-PEEK) orthopedic bearing surfaces and interfaces. A variety of test revealed significant improvements in the water wettability, frictional properties, and wear resistance of the surfaces and interfaces.
A random copolymer ((U/A10)165) bearing pendent ureido groups and a small amount (10 mol %) of primary amino groups exhibits an upper critical solution temperature (UCST). We prepared a diblock ...copolymer (PMPC20P(U/A10)165) composed of water-soluble poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) and (U/A10)165 blocks via reversible addition–fragmentation chain-transfer radical polymerization with postmodification reaction. The subnumbers are the degrees of polymerization of each block. Although in water PMPC20P(U/A10)165 dissolves as a unimer above the UCST phase transition temperature (T p), it forms polymer micelles composed of dehydrated (U/A10)165 cores and hydrophilic PMPC shells. A nanogel was prepared by cross-linking the pendent primary amines in the micelle core using (hydroxymethyl)phosphonium chloride below T p. NMR and light-scattering data indicated that the nanogel core shrinks upon dehydration below T p and swells upon hydration above T p. The nanogel can encapsulate guest molecules such as hydrophobic fluorescence probes and bovine serum albumin (BSA) below T p mainly owing to hydrophobic interactions in the core. Encapsulated BSA can be held in the nanogel core below T p and subsequently released above T p.
Intermediate filaments (IF) bind to various proteins and regulate cell function in the cytoplasm. Recently, IFs were found to regulate gene expression by acting as capture scaffolds for ...transcription-related proteins and preventing their translocation into the nucleus. To reveal such transcriptional regulatory mechanisms controlled by IFs, a method to analyze the interaction between IFs and transcription-related proteins is necessary. Although there are many methods to observe interactions in living cells, it is still challenging to measure protein-protein interactions in living cells in their unmodified and native state. In this study, we utilized a nanoneedle that can access the cytosol by insertion into the cell. Modification of antibody recognizing transcription-related proteins allows the needle to detect mechanical force required to unbind the interaction between antibody and target proteins interacting with IFs during retraction of the needle from the cell. We focused on IF vimentin, a marker of epithelial-mesenchymal transition, to mechanically detect transcription-related proteins trapped by vimentin filaments. Prohibitin 2 (PHB2), a transcription-related factor, was selected as the candidate vimentin-binding protein. We conducted mechanical detection of PHB2 using atomic force microscopy and anti-PHB2 antibody-modified nanoneedles in vimentin-expressing mouse breast cancer and vimentin-knockout (VKO) cells. Significantly larger unbinding forces were detected in the vimentin-expressing cells than in the VKO cells. The results demonstrate that this method is useful for in-cell mechanical detection of IF-binding proteins.
The self-assembly of pH-responsive random and block copolymers composed of 2-(
-diisopropylamino)ethyl methacrylate and 2-methacryloyloxyethyl phosphorylcholine was investigated in aqueous media. ...Their pH-responsive behaviors were investigated in aqueous media by dynamic light scattering (DLS) and fluorescence measurements using a pyrene hydrophobic fluorescence probe. In an acidic environment, these copolymers existed as single polymer chains that did not interact with each other. In contrast, upon increasing the pH of the solution above the critical value of ~8, separated micelles were formed in the mixture, which was indicated by bimodal distribution in DLS results with radius of 4.5 and 10.4 nm, corresponding to the random and block copolymer micelles, respectively. Fluorescence resonance energy transfer efficiencies were near to zero in the mixture of the donor labeled block and acceptor labeled random copolymers under both acidic and basic pH. These results demonstrated the coexistence of two distinct micelles.
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