Atomic force microscopy evidence for conformational changes of fibronectin adsorbed on unmodified and sulfonated polystyrene surfaces

Enzymatic saccharification promotion for bioenergy poplar under green liquor pretreatment by fully sulfonated polystyrene: Effect of molecular weight

Water-soluble lignin and lignin derivatives are cited to promote the enzymatic saccharification of lignocellulose. Herein, a series of fully sulfonated polystyrene sulfonates (FSPSSs) with various molecular weights (MW) were synthesized through free radical polymerization (FRP) and atom transfer radical polymerization (ATRP) to serve as lignin analogues to boost the enzymatic saccharification of bioenergy poplar under green liquor pretreatment. The FRP-made polymers with MW 944.5 × 10³ to 123.6 × 10³ g/mol increased the enzymatic hydrolysis digestibility (SED) by 13 % to 18.8 %. On contrary, the ATRP-made polymers with lower MW (3.8 × 10³-12.2 × 10³ g/mol) showed a weak effect with<8 % improvement in SED. This can be explained the adsorption capacity and the conformation of cellulase-FSPSS complexes, which respond to the reducing nonproductive adsorption correlated to their MWs, due to the strong dependence of molecular conformation on the chain length of strong polyelectrolytes.

Characterization of plasmatic proteins adsorption on poly(styrene sodium sulfonate) functionalized silicone surfaces

Proteins adsorption occurs spontaneously on biomaterial upon insertion within the body. The resulting protein layer influences biomaterial biocompatibility through enhanced bio-integration or, on the contrary, adverse reactions. Furthermore, upon adsorption, proteins can undergo modifications of their structure and, ultimately, their physicochemical properties and activity. Hence, the understanding of protein adsorption on implanted materials appears essential, as exemplified by silicone breast prostheses that might lead to serious health issues. Surface modifications with a bioactive polymer, poly(styrene sodium sulfonate)-polyNaSS, on a hydrophobic silicone surface that composes breast implants, have been successfully performed under UV irradiation by a radical surface polymerization. This strategy enhances cell biocompatibility and antibacterial features. Although detailed insights related to the mechanism are still scarce, polyNaSS is supposed to promote changes in the conformation and/or orientation of adsorbed plasma proteins, reducing the odd for a biofilm to form. The present work addresses more in-depth structural investigations of the adsorbed state of two plasma proteins: Bovine Serum Albumin (BSA), as a model protein, and fibronectin (FN), for its role in cell adhesion. Using Atomic force microscopy (AFM), we report that polyNaSS showed no significant impact on the BSA structure conversely to the FN one. However, imaging findings with AFM clearly outlined a change in the structural organization of FN, going from a nano fibrillar assembly with an average length of 130 nm to a globular one when the surface was grafted. Thus, it is highlighted that polyNaSS interacts specifically with FN. In addition, cell spreading assay of L929 fibroblasts on FN-coated surfaces with optical microscopy indicated no significant impact of the change in FN structure upon fibroblasts adhesion, which displayed active elongated shapes. The present features are crucial for understanding the cell adhesion mechanism induced by surface modification.

Surface Free Energy of Titanium Disks Enhances Osteoblast Activity by Affecting the Conformation of Adsorbed Fibronectin

This study evaluated the influence of surface free energy (SFE) of titanium disks on the adsorption and conformation of fibronectin (FN) and the biological behavior of osteoblasts cultured on the FN-treated modified surfaces. High [H]-SFE titanium disks were irradiated by a 30 W UV light, while low (L)-SFE titanium disks received no treatment. The surface characteristics of the titanium disks were examined using scanning electron microscope, optical surface profilometer, X-ray photoelectron spectroscopy, and contact angle measurements. Adsorbed FN on different groups was investigated using attenuated total reflection-Fourier transform infrared spectroscopy. MG-63 cells were cultured on FN-treated titanium disks to evaluate the in vitro bioactivity. The experiment showed H-SFE titanium disks adsorbed more FN and acquired more ß-turn content than L-SFE group. MG-63 cells cultured on FN-treated H-SFE titanium disks showed better osteogenic responses, including adhesion, proliferation, alkaline phosphatase activity and mineralization than that on FN-treated L-SFE titanium disks. Compared to L-SFE titanium disks, integrin-β1, integrin-α5 and Rac-1 mRNA levels were significantly higher in MG-63 cells on FN-treated H-SFE after 3 h of culture. These findings suggest that the higher SFE of H-SFE compared to L-SFE titanium disks induced changes in the conformation of adsorbed FN that enhanced the osteogenic activity of MG-63 cells.

Fibronectin adsorption on polystyrene sulfonate-grafted polyester using atomic force microscope

Cell adhesion and growth over prostheses are strongly influenced by the adsorption and conformation of adhesive proteins from blood and extracellular matrix, such as fibronectin. This key behavior can be possibly exploited to develop a prosthetic ligament based on the surface bioactivation of biodegradable materials. In this work, surface functionalization was performed by grafting poly(sodium 4-styrene sulfonate) on polyethylene terephthalate and polycaprolactone using a thermal surface-initiated atom transfer radical polymerization grafting technique. The morphology and mechanical properties of the adsorbed fibronectin in the presence of albumin were studied by atomic force microscopy. The morphology of fibronectin on two kinds of polyester surfaces was similar. However, the study results showed a remarkable conformation change of fibronectin when adsorbed onto the nongrafted or grafted surface, leading to an increase in cell adhesion and organization in the second case. This research provided evidence of the relationship between the morphology change of fibronectin to the enhancement of the cell adhesion and spreading on the grafted surface of polyester.

A Giant Extracellular Matrix Binding Protein of Staphylococcus epidermidis Binds Surface-Immobilized Fibronectin via a Novel Mechanism

Although it is normally an innocuous part of the human skin microbiota, Staphylococcus epidermidis has emerged as a major nosocomial pathogen, and implanted foreign materials are an essential risk factor for the development of an infection. The extraordinary efficiency of S. epidermidis to colonize artificial surfaces is particularly related to the ability to form biofilms. Biofilm formation itself critically depends on stable pathogen binding to extracellular host matrix components, e.g. fibronectin (Fn), covering inserted devices in vast amounts. Extracellular matrix binding protein (Embp) and its subdomains referred to as the F-repeat and the FG-repeat are critical for adherence of S. epidermidis to surface-immobilized Fn. Embp-Fn interactions preferentially occur with surface-bound, but not folded, globular Fn via binding to the F3 domain. High-resolution structure analysis of F- and FG-repeats revealed that both repeats are composed of two tightly connected triple α-helix bundles, exhibiting an elongated but rather rigid structural organization in solution. Both F- and FG-repeat possess Fn-binding capacity via interactions with type III subdomain FN12, involving residues within the C and F β-sheet. FN12 essentially supports stability of the globular Fn state, and thus these findings reasonably explain why Embp-mediated interaction of S. epidermidis necessitates Fn surface immobilization. Thus, Embp employs an uncharacterized bacterial Fn-binding mechanism to promote staphylococcal adherence.IMPORTANCE Staphylococcus epidermidis is a leading pathogen in implant-associated hospital infections. The pathogenesis critically depends on bacterial binding to ECM components, specifically fibronectin (Fn). The cell surface-localized, 1-MDa extracellular matrix binding protein (Embp) is essentially characterized by 10 F- and 40 FG-repeats. These repetitive units, each characterized by two α-helical bundles, organize themselves in a rigid, elongated form. Embp binds preferentially to surface-localized but not soluble Fn, with both F- and FG-repeats being sufficient for Fn binding and resulting bacterial adherence. Binding preferentially involves Fn type III domain, specifically residues of FN12 β-sheets C and F. Both play key role in stabilizing the globular Fn conformation, explaining the necessity of Fn surface immobilization for a subsequent interaction with Embp. In comparison to many other bacterial Fn-binding proteins using the Fn N terminus, Embp employs a previously undescribed mechanism supporting the adhesion of S. epidermidis to surface-immobilized Fn.

Electrochemical modulation of plasma fibronectin surface conformation enables filament formation and control of endothelial cell–surface interactions

Electrochemical modulation of a gold surface charge induces conformational changes in fibronectin when immobilized on the surface. A negatively-charged surface yields an open and filamentous fibronectin which significantly improves endothelial cell adhesion.

Titanium alloy surface oxide modulates the conformation of adsorbed fibronectin to enhance its binding to α(5) β(1) integrins in osteoblasts

Our laboratory has previously demonstrated that heat (600°C) or radiofrequency plasma glow discharge (RFGD) pretreatment of a titanium alloy (Ti6Al4V) increased the net negative charge of the alloy's surface oxide and the attachment of osteoblastic cells to adsorbed fibronectin. The purpose of the current study was to investigate the biological mechanism by which these surface pretreatments enhance the capacity of fibronectin to stimulate osteoblastic cell attachment. Each pretreatment was found to increase the binding (measured by ELISA) of a monoclonal anti-fibronectin Ig to the central integrin-binding domain of adsorbed fibronectin, and to increase the antibody's inhibition of osteogenic cell attachment (measured by hexosaminidase assay). Pretreatments also increased the binding (measured by ELISA) of anti-integrin IgG's to the α(5) and β(1) integrin subunits that became attached to fibronectin during cell incubation. These findings suggest that negatively charged surface oxides of Ti6Al4V cause conformational changes in fibronectin that increase the availability of its integrin-binding domain to α(5) β(1) integrins.

Surface oxide net charge of a titanium alloy: modulation of fibronectin-activated attachment and spreading of osteogenic cells

In the current study, we have altered the surface oxide properties of a Ti6Al4V alloy using heat treatment or radiofrequency glow discharge (RFGD) in order to evaluate the relationship between the physico-chemical and biological properties of the alloy's surface oxide. The effects of surface pretreatments on the attachment of cells from two osteogenic cell lines (MG63 and MC3T3) and a mesenchymal stem cell line (C3H10T1/2) to fibronectin adsorbed to the alloy were measured. Both heat and RFGD pretreatments produced a several-fold increase in the number of cells that attached to fibronectin adsorbed to the alloy at a range of coating concentrations (0.001-10nM FN) for each cell line tested. An antibody (HFN7.1) directed against the central integrin binding domain of fibronectin produced a 65-70% inhibition of cell attachment to fibronectin-coated disks, indicating that cell attachment to the metal discs was dependent on fibronectin binding to cell integrin receptors. Both treatments also accelerated the cell spreading response manifested by extensive flattening and an increase in mean cellular area. The treatment-induced increases in the cell attachment activity of adsorbed fibronectin were correlated with previously demonstrated increases in Ti6Al4V oxide negative net surface charge at physiological pH produced by both heat and RFGD pretreatments. Since neither treatment increased the adsorption mass of fibronectin, these findings suggest that negatively charged surface oxide functional groups in Ti6Al4V can modulate fibronectin's integrin receptor activity by altering the adsorbed protein's conformation. Our results further suggest that negatively charged functional groups in the surface oxide can play a prominent role in the osseointegration of metallic implant materials.