Effects of controlled fibronectin surface orientation on subsequentStaphylococcus epidermidis adhesion

The role of plasma, albumin, and fibronectin in Staphylococcus epidermidis adhesion to polystyrene surface

The influence of soluble and immobilized plasma, albumin, and fibronectin (Fn) on the adhesion of three Staphylococcus epidermidis strains to polystyrene was investigated. Both soluble and immobilized plasma and albumin cause to 7-fold reduction of the amounts of adhered cells, regardless of the strain used. The soluble Fn exhibited the adhesion for one strain and did not affect the bacterial sorption for remaining strains, whereas on Fn-coated polystyrene two of the three strains showed about 1.5-fold increase in the number of adsorbed bacteria. The plasma- and albumin-coated surfaces became much more hydrophilic as the contact angle changed from 78 ± 2° for control to 18 ± 2° for plasma and 21 ± 3° for albumin. The ligand-receptor specific interactions strains S. epidermidis with Fn-coated surfaces were proved by measuring the adhesion forces between cell surface and Fn-coated AFM tip. The surface roughness measured using AFM after the plasma and proteins immobilization was changed within 10 nm and not correlate with changes in bacterial adhesion.

Adsorption behavior of human plasma fibronectin on hydrophobic and hydrophilic Ti6Al4V substrata and its influence on bacterial adhesion and detachment

Biomaterial implant-associated infections, a common cause of medical devices' failure, are initiated by bacterial adhesion to an adsorbed protein layer on the implant material surface. In this study, the influence of protein surface orientation on bacterial adhesion has been examined using three clinically relevant bacterial strains known to express specific binding sites for human plasma fibronectin (HFN). HFN was allowed to adsorb on hydrophobic Ti6Al4V and physically modified hydrophilic Ti6Al4V substrata. Ellipsometric data reveal that the characteristics of the adsorbed protein layers primary depend on solid surface tension and the initial protein concentration in solution. In particular, HFN molecules adopt a more extended conformation on hydrophobic than hydrophilic surfaces, an effect that is more pronounced at low than at high initial protein concentrations. Moreover, the extended conformation of the protein molecules on these surfaces likely facilitates the exposure of specific sites for adhesion, resulting in the higher bacterial-cell attachment observed regardless of the strain considered. Contact angle measurements and the analysis of the number of remaining adhering cells after being subjected to external forces further suggest that both specific and nonspecific (hydrophobic) interactions play an important role on bacterial attachment. This study is the first one to evaluate the influence of surface hydrophobicity on protein adsorption and its subsequent effect on bacterial adhesion using a material whose hydrophobicity was not modified using chemical treatments that potentially led to surface properties changes other than hydrophobicity.

Adhesion of Staphylococcus epidermidis to biomaterials is inhibited by fibronectin and albumin

Decades of contradictory results have obscured the exact role of adsorbed fibronectin in the adhesion of the bacterium, Staphylococcus epidermidis, to biomaterials. Here, the ability of adsorbed fibronectin (FN) or bovine serum albumin (BSA) to modulate S. epidermidis adhesion to various biomaterials is reported. FN or BSA was adsorbed in increasing surface densities up to saturated monolayer coverage onto various common biomaterials, including poly(ethylene terephthalate), fluorinated ethylene propylene, poly(ether urethane), silicone, and borosilicate glass. Despite the wide range of surface characteristics represented, adsorption isotherms varied only subtly between materials for the two proteins considered. S. epidermidis adhesion to the various protein-coated biomaterials was quantified in a static-fluid batch adhesion assay. Although slight differences in overall adherent cell numbers were observed between the various protein-coated substrata, all materials exhibited significant dose-dependent decreases in S. epidermidis adhesion with increasing adsorption of either protein (FN, BSA) to all surfaces. Results here indicate that S. epidermidis adhesion to FN-coated surfaces is not a specific adhesion (i.e., receptor: ligand) mediated process, as no significant difference in adhesion was found between FN- and BSA-coated materials. Rather, results indicate that increasing surface density of either FN or BSA actually inhibited S. epidermidis adhesion to all biomaterials examined.

[Inhibition of Staphylococcus epidermidis adhesion on titanium surface with bioactive water-soluble copolymers bearing sulfonate, phosphate or carboxylate functions]

Implanted prostheses are sometimes subject to bacterial infections, which can threat their benefit rule on a long-term basis. Various methods are studied to fight against these infections. Among them, the grafting of bioactive polymers onto the prosthesis surface shows up as a promising way to the problem of infections. This work presents the influence of various water-soluble bioactive polymers on the inhibition of the Staphylococcus epidermidis adhesion on the titanium samples surfaces initially preadsorbed with various proteins. Whatever the studied protein is, it is shown that the bioactive polymer containing sulfonate functions generates an inhibition of the adhesion of Staphylococcus epidermidis. For a plasma preadsorption, the inhibition rate rises up to 68% when the concentration of sulfonate function is 2.5μmol/L. Titanium surfaces grafted with the bioactive polymer were also tested. We find an inhibitive activity of the adhesion close to that of the previous case. These preliminary results can point up a clinical interest in the fight against the medical devices infection, because they highlight a clear local effect of S. epidermidis adhesion inhibition. Copolymers containing other functional groups (phosphate or carboxylate) were dissolved in a bacterial suspension to monitor the influence of the composition on the adhesion inhibition. Their inhibition rates are not significantly lower than those of pNaSS homopolymers, as much as the sulfonate function proportion remains higher than 50%. Thus, the sulfonate function is the main responsible for the inhibition of the S. epidermidis adhesion.

Effect of adsorbed fibronectin on the differential adhesion of osteoblast-like cells and Staphylococcus aureus with and without fibronectin-binding proteins

The influence of fibronectin (Fn) coated surfaces patterned with poly(ethylene glycol) microgels having inter-gel spacings between 0.5 and 3.0 μm on the adhesion of Staphylococcus aureus strains with and without Fn-binding proteins and cellular adhesion/spreading was investigated. Quantitative force measurements between a S. aureus cell and a patterned surface showed that the adhesion force between the bacterium and the patterned surface increased substantially after Fn adsorption, regardless of the strain used, but decreased with decreasing inter-gel spacing. In flow-chamber experiments, the Fn-binding strain adhered at a higher rate after Fn adsorption than the strain lacking Fn-binding proteins. In both cases, the adhesion rates decreased with decreasing inter-gel spacing. Osteoblast-like cells could bind to patterned surfaces despite the microgels, and adsorbed Fn substantially amplified this effect. Even under highly non-adhesive conditions associated with closely spaced microgels, adsorbed Fn preserves a window of inter-gel spacing around 1 μm where the adhesion of staphylococcal cells is hindered while cells can still adhere and spread.

Multivalent artificial opsonin for the recognition and phagocytosis of Gram-positive bacteria by human phagocytes

Hospital-acquired infections (HAIs) remain a leading cause of death in the United States. Unfortunately, treatment of HAIs is complicated by the emergence of antibiotic-resistant bacterial strains. In an effort to enhance the body's natural immune response to infection, we have developed an artificial opsonin to promote the recognition, phagocytosis, and destruction of pathogenic bacteria by human phagocytes. The artificial opsonin is constructed from multivalent conjugates of poly(L-lysine)-graft-poly(ethylene glycol) with vancomycin and human IgG-Fc. Our approach utilizes vancomycin's inherent ability to bind to D-Ala-D-Ala terminated peptides present in the cell wall of Gram-positive bacteria. Here, we show that conjugation of vancomycin to PLL-g-PEG prevents its action as an antibiotic and allows vancomycin to function solely as a recognition molecule. Human IgG-Fc antibody fragment serves as a phagocyte recognition molecule and is recognized by the Fcγ cell surface receptors expressed on professional human phagocytes. Using flow cytometry, we found that a polysaccharide-encapsulated, methicillin-resistant strain of Staphylococcus epidermidis is efficiently recognized by the artificial opsonin (nearly 100% of cells were opsonized) and that opsonin binding is specific since it can be inhibited by the soluble cell wall peptide analog acetyl-Lys-D-Ala-D-Ala. Opsonization of S. epidermidis resulted in an approximate 2-fold increase in phagocytosis by a human neutrophil cell line. Notably, Enterococcus faecalis VanB, a bacterial strain with inducible vancomycin resistance, was used to show that the artificial opsonin does not unintentionally induce antibiotic resistance mechanisms.

Blood interactions with noble metals: coagulation and immune complement activation

Noble metals are interesting biomaterials for a number of reasons, e.g., their chemical inertness and relative mechanical softness, silver's long known antimicrobial properties, and the low allergenic response shown by gold. Although important for the final outcome of biomaterials, little is reported about early events between pure noble metals and blood. In this article, we used whole blood in the "slide chamber model" to study the activation of the immune complement activation, generation of thrombin/antithrombin (TAT) complexes, and platelet depletion from blood upon contact with silver (Ag), palladium (Pd), gold (Au), titanium (Ti), and Bactiguard, a commercial nanostructured biomaterial coating comprised of Ag, Pd, and Au. The results show the highest TAT generation and platelet depletion on Ti and Au and lower on Pd, Ag, and the Bactiguard coating. The immune complement factor 3 fragment (C3a) was generated by the surfaces in the following order: Ag > Au > Pd > Bactiguard > Ti. Quartz crystal microbalance adsorption studies with human fibrinogen displayed the highest deposition to Ag and the lowest onto the Bactiguard coating. The adsorbed amounts of fibrinogen did not correlate with thrombogenicity in terms of TAT formation and platelet surface accumulation in blood. The combined results suggest, hence, that noble metal chemistry has a different impact on the protein adsorption properties and general blood compatibility. The low thrombogenic response by the Bactiguard coating cannot be explained by any of the single noble metal properties but is likely a successful combination of the nanostructure, nanogalvanic effects, or combinatory chemical and physical materials properties.

Adhesion forces between Staphylococcus epidermidis and surfaces bearing self-assembled monolayers in the presence of model proteins

Self-assembled monolayers (SAMs) are being developed into coatings to reduce microbial biofilm formation on biomaterials. To test anti-adhesion properties, SAMs can be easily constructed on gold, and used to represent a coated biomaterial. However, coatings that prevent bacterial adhesion must also resist protein adsorption. We explored the competitive effects of bacteria and protein for adsorption to SAMs, choosing fetal bovine serum (FBS) to represent protein non-specific binding, and fibronectin (FN) to evaluate ligand/receptor binding. Staphylococcus epidermidis were immobilized on an atomic force microscope (AFM) tip and used as a force probe to detect the interaction forces between bacteria and gold-coated SAMs. The SAMs tested were alkanethiol molecules terminating in isophthalic acid (IPA) or isophthalic acid with silver (IAG). While S. epidermidis showed weak interactions with FBS, the bacteria showed strong adhesion with FN, due to ligand/receptor binding. Bacterial retention and viability experiments were correlated with the force measurements. S. epidermidis interacting with IAG SAMs showed a loss of viability, due to the mobility of silver ions. For most substrata, there was a link between high adhesion forces with bacteria and a high percentage of dead cells being retained on that substratum (even in the absence of a specific biocidal effect, such as silver). This may suggest that high adhesion forces can cause stress to the bacteria which contributed to their death. The relationship between highly adhesive SAMs and bacterial inactivation may be useful in future biomaterial design. When evaluating coatings for biomaterials, it is important to consider the interplay between bacteria, proteins, and the coating material.

Wound repair and proliferation of bronchial epithelial cells regulated by CTNNAL1

Adhesion molecules play vital roles in airway hyperresponsiveness (AHR) or airway inflammation. Our previous study indicated that adhesion molecule catenin alpha-like 1 (CTNNAL1) is relevant closely to asthma susceptibility, but its biological function or significance is still unclear. In the present study, we observed the temporal and spatial distribution of CTNNAL1 expression in mouse lung tissue with the OVA-sensitized asthma model and found that the level of CTNNAL1 mRNA showed a prominent negative correlation with pulmonary resistance (R(L)). To study the function of CTNNAL1 in airway, effects of CTNNAL1 on proliferation and wound repair activity of human bronchial epithelial cells (HBEC) was investigated with antisense oligonucleotide (ASO) technique. The results showed that: (1) CTNNAL1 ASO could decelerate the repairing velocity and proliferation of HBEC; (2) CTNNAL1 expression was increased on the edge cells of mechanic wounded area in culture; (3) extracellular matrix component fibronectin (Fn) obviously promoted wound repair activity and proliferation of HBEC, which could be blocked by CTNNAL1 ASO; (4) Western blot showed that Fn could promote FAK phosphorylation, which also be inhibited by CTNNAL1 ASO. In conclusion, the level of CTNNAL1 mRNA expression is highly correlated to airway resistance; CTNNAL1 may contribute to the wound repair and proliferation of HBEC. Furthermore, it may serve to Fn mediated cell-extracellular adhesion and its signal transduction.

Medical biofilms

For more than two decades, Biotechnology and Bioengineering has documented research focused on natural and engineered microbial biofilms within aquatic and subterranean ecosystems, wastewater and waste-gas treatment systems, marine vessels and structures, and industrial bioprocesses. Compared to suspended culture systems, intentionally engineered biofilms are heterogeneous reaction systems that can increase reactor productivity, system stability, and provide inherent cell:product separation. Unwanted biofilms can create enormous increases in fluid frictional resistances, unacceptable reductions in heat transfer efficiency, product contamination, enhanced material deterioration, and accelerated corrosion. Missing from B&B has been an equivalent research dialogue regarding the basic molecular microbiology, immunology, and biotechnological aspects of medical biofilms. Presented here are the current problems related to medical biofilms; current concepts of biofilm formation, persistence, and interactions with the host immune system; and emerging technologies for controlling medical biofilms.

Influence of the substrate's hydrophilicity on thein vitro Schwann cells viability

A series of polymeric biomaterials including poly (methyl acrylate) (PMA), chitosan (CHT), poly(ethyl acrylate) (PEA), poly(hydroxyethyl acrylate) (PHEA), and a series of random copolymers containing ethyl acrylate and hydroxyethyl acrylate monomeric units were tested in vitro as culture substrates and compared for their impact on the proliferation and expansion of Schwann cells (SCs). Immunocytochemical staining assay and scanning electron microscopy techniques were applied to perform a quantitative analysis to determine the correct maintenance of the cultured glial cells on the different biomaterials. The results strongly suggest that cell attachment and proliferation is influenced by the substrate's surface chemistry, and that hydrophobic biomaterials based on PMA, PEA, and the copolymers PEA and PHEA in a narrow composition window are suitable substrates to promote cell attachment and proliferation of SCs in vitro.

Survival and differentiation of embryonic neural explants on different biomaterials

Biomaterials prepared from polyacrylamide, ethyl acrylate (EA), and hydroxyethyl acrylate (HEA) in various blend ratios, methyl acrylate and chitosan, were tested in vitro as culture substrates and compared for their ability to be colonized by the cells migrating from embryonic brain explants. Neural explants were isolated from proliferative areas of the medial ganglionic eminence and the cortical ventricular zone of embryonic rat brains and cultured in vitro on the different biomaterials. Chitosan, poly(methyl acrylate), and the 50% wt copolymer of EA and HEA were the most suitable substrates to promote cell attachment and differentiation of the neural cells among those tested. Immunofluorescence microscopy analysis showed that progenitor cells had undergone differentiation and that the resulting glial and neuronal cells expressed their intrinsic morphological characteristics in culture.