Fn Adsorption Research Articles

Mechanistic insights into the adsorption and bioactivity of fibronectin on surfaces with varying chemistries by a combination of experimental strategies and molecular simulations

Fibronectin (Fn) is significant to the performance of biomaterials, and the chemistry of biomaterial surface play important roles in Fn adsorption and subsequent cell behavior. However, the “molecular scale” mechanism is still unclear. Herein, we combined experimental strategies with molecular simulations to solve this problem. We prepared self-assembled monolayers with varying chemistries, i.e., SAMs-CH3, SAMs-NH2, SAMs-COOH and SAMs-OH, and characterized Fn adsorption and cell behaviors on them. Next, Monte Carlo method and all-atom molecular dynamics simulations were employed to reveal the orientation/conformation of Fn on surfaces. We found that SAMs-CH3 strongly adsorbed Fn via hydrophobic interactions, but show poor bioactivity as the low exposure of RGD/PHSRN motifs and the deformation of Fn. SAMs-NH2 and SAMs-COOH could adsorb Fn efficiently via vdW interactions, electrostatic interactions, hydrogen bonds and salt bridges. Fn exhibited excellent bioactivity for cell adhesion, proliferation and osteogenic differentiation as high exposure of bioactive motifs on SAMs-NH2, or as the activation of other inferior cell-binding motifs on SAMs-COOH. SAMs-OH showed poor Fn adsorption as the water film. However, the adsorbed Fn displayed non-negligible bioactivity due to high exposure of PHSRN motif and large degree of protein flexibility. We believe that the revealed mechanism presents great potential to rationally design Fn-activating biomaterials.

Fibronectin adsorption on carbonate-containing hydroxyapatite

Carbonate-containing hydroxyapatite (CO3-HAp) shows higher osteoconductivity than pure hydroxyapatite but the underlying mechanism is unclear. As specific adsorption of proteins on CO3-HAp may affect cellular responses and osteoconductivity, we examined the contribution of protein adsorption to the high osteoconductivity observed with CO3-HAp. We prepared CO3-HAp powders with different carbonate contents (0.3, 4.8, or 8.3 wt%) and investigated the adsorption behaviour of fibronectin (Fn) on the powders. We found that the Fn adsorption capacity of CO3-HAp decreased with increasing carbonate content. Although the Hill or Langmuir isotherm was the best-fit for the adsorption of Fn onto CO3-HAp with a carbonate content of 0.3 or 4.8 wt%, the Brunauer–Emmett–Teller isotherm was the best-fit for Fn adsorption on CO3-HAp with an 8.3 wt% carbonate content. These results show that the carbonate content of CO3-HAp influences the adsorption behaviour of Fn and suggest that its specific adsorption contributes to the high osteoconductivity of CO3-HAp. The findings do not affect the clinical application of CO3-HAp directly, but they might lead to the development of bone substitutes with high osteoconductivity.

QCM Analysis for Two‐Step Adsorption of Albumin and Fibronectin on Zirconia Surface

The adsorption of proteins on the dental implant surface is the first step in the key role of osseointegration. Many types of proteins exist in the living body and compete for adsorption on the material surface. As an implant material, partially stabilized zirconia (ZrO2) is currently an attractive alternative to titanium to overcome the shortcomings of titanium implants. In this study, we investigated the two‐step adsorption of fibronectin (Fn) and bovine serum albumin (Alb) on the ZrO2 surface using a 27‐MHz quartz crystal microbalance (QCM) method. A ZrO2 sensor was employed for the QCM measurements. Two‐step adsorptions were performed as follows. (1) Fn‐Alb series: first, the Fn solution was injected into the phosphate‐buffered saline (PBS) solution, followed by the Alb solution. (2) Alb‐Fn series: first, the Alb solution was injected, followed by the Fn solution. The decrease in frequency was monitored for 60 minutes after each protein injection. The adsorbed amounts of Fn or Alb were calculated by observing the decrease in frequency, and the apparent reaction rate, kobs, was obtained through the curve fitting of frequency shift against the adsorption time. No significant difference was observed in the adsorbed amounts of Fn and Alb between the Fn‐Alb and Alb‐Fn series (P > 0.05). The kobs, rate of protein adsorption, in the second step was significantly slower than that in the first step for both Fn and Alb adsorption (P < 0.05). There was no clear correlation between the amount of protein adsorbed on the ZrO2 sensor and the surface topography. It was concluded that the amount of protein adsorbed on the ZrO2 surface was not influenced by the two‐step adsorption series, but the adsorption rate of proteins in the second step was affected by the first‐step protein adsorption.

Control of the hydration layer states on phosphorus-containing mesoporous silica films and their reactivity evaluation with biological fluids.

Transparent phosphorus-containing MPS (PMPS) films were synthesized by the introduction and reaction of phosphoric acid into the silica framework during the sol-gel reaction. We then investigated the hydration layer structures formed on the PMPS films and achieved the selective adsorption of fibronectin (Fn). In particular, the surface analyses indicated that the P atom was distributed at the outermost surfaces of the PMPS films. The PMPS films exhibited a high transparency (e.g., averaged transmittance value in the visible light region: 79%), and the haze value (0.14%) decreased with the increasing P/Si molar concentration. Solid-state 29Si-NMR and Fourier transform infrared spectroscopy (FT-IR) spectra indicated the formation of Si-O-P bonds, suggesting that the condensation reaction between the Si-O- and P-O- groups effectively occurs in the silica framework. The larger amount of P-O- and P[double bond, length as m-dash]O groups at the Si-O-P bonding site on the films affects the water molecular adsorption states (i.e., formation of the hydration layer), which was supported by the Brunauer-Emmett-Teller (BET) surface areas of N2 and water vapor, leading to enhancement of the hydrogen bondability of the PMPS films with the increased formation of Si-O-P bonds. The deconvolution results of the FT-IR spectra demonstrated that the ratio of free water to bonding water increased significantly with an increase in the formation of Si-O-P bonding, and the resulting O-H stretching vibration in the hydration layer became more asymmetric. It is suggested that the water molecules are irregularly hydrogen-bonded with the different functional groups of Si-O-, P-O- and P[double bond, length as m-dash]O. In the immersion experiment of the PMPS films in phosphate buffer, the resultant P/Si molar concentration of the PMPS film decreased upon increasing the immersion time and the mesostructures were preserved. The amount of Fn adsorption significantly increased as the O-H stretching vibration of the water molecules became more asymmetric, whereas the adsorption of fibrinogen was completely suppressed by the films. Therefore, we found that the addition of phosphoric acid in the MPS film synthesis significantly affects the hydration layer structures on the film surfaces to provide the possibility of selective protein adsorption.

Fibronectin Adsorption on Hydroxyapatite Nanosensors and the Effect of Fibronectin Preadsorption on Biological Apatite Growth.

In this study, hydroxyapatite (HA) nanoparticles were prepared at 30 °C by the chemical precipitation method. The adsorption behavior of fibronectin (Fn) on Au and HA surfaces at different Fn concentrations (50, 100, and 200 μg mL-1 and the effect of fibronectin preadsorption on the apatite growth process were investigated by the quartz crystal microbalance technique. The surface properties of Au and HA were characterized by atomic force microscopy and field emission scanning electron microscopy. Fn adsorption experiments show that the adsorption capacity of Fn on Au and HA surfaces is in the order Au-Fn200> Au-Fn100≈ HA-Fn100≈ HA-Fn200> HA-Fn50> Au-Fn50, where the number after Fn corresponds to the concentration of the Fn solution. The order of the viscoelasticity of the adsorbed layer is HA-Fn200> HA-Fn100> Au-Fn200> HA-Fn50> Au-Fn50> Au-Fn100. These results suggest that the Fn concentration and the chemical composition and topography of the substrate surface affect Fn adsorption and the viscoelasticity of the adsorbed Fn layer. A high Fn concentration is not conducive to Fn adsorption on the HA surface and formation of a viscoelastic Fn layer. Based on the experimental results, the states and orientations of Fn adsorbed on Au and HA are rationally discussed. Mineralization experiments show that the order of the mass of the apatite layer is HA > HA-Fn50 > Au-Fn50» Au. The apatite growth rate on the Au surface is essentially zero, whereas the apatite growth rate on the Au-Fn50 surface linearly increases. For the HA and HA-Fn50 surfaces, the apatite growth rate can be divided into several stages. An adsorbed Fn layer affects apatite nucleation on both the Au and HA surfaces and decreases the apatite growth rate on the HA surface.

Protein Adsorption to Titanium and Zirconia Using a Quartz Crystal Microbalance Method.

Protein adsorption onto titanium (Ti) or zirconia (ZrO2) was evaluated using a 27 MHz quartz crystal microbalance (QCM). As proteins, fibronectin (Fn), a cell adhesive protein, and albumin (Alb), a cell adhesion-inhibiting protein, were evaluated. The Ti and ZrO2 sensors for QCM were characterized by atomic force microscopy and electron probe microanalysis observation, measurement of contact angle against water, and surface roughness. The amounts of Fn and Alb adsorbed onto the Ti and ZrO2 sensors and apparent reaction rate were obtained using QCM measurements. Ti sensor showed greater adsorption of Fn and Alb than the ZrO2 sensor. In addition, amount of Fn adsorbed onto the Ti or ZrO2 sensors was higher than that of Alb. The surface roughness and hydrophilicity of Ti or ZrO2 may influence the adsorption of Fn or Alb. With regard to the adsorption rate, Alb adsorbed more rapidly than Fn onto Ti. Comparing Ti and ZrO2, Alb adsorption rate to Ti was faster than that to ZrO2. Fn adsorption will be effective for cell activities, but Alb adsorption will not. QCM method could simulate in vivo Fn and Alb adsorption to Ti or ZrO2.

Effect of fibronectin adsorption on osteoblastic cellular responses to hydroxyapatite and alumina

Initial cellular responses following implantation are important for inducing osteoconduction. We investigated cell adhesion, spreading, proliferation and differentiation of mouse MC3T3-E1 osteoblastic cells on untreated or fibronectin (Fn)-coated discs of hydroxyapatite (HAp) or alpha-type alumina (α-Al2O3). Fn coating significantly enhanced adhesion and spreading of MC3T3-E1 cells on HAp, but did not affect MC3T3-E1 cell proliferation and differentiation on HAp or α-Al2O3. Fn-coated HAp likely does not stimulate pre-osteoblast cells to initiate the process of osteoconduction; however, Fn adsorption might affect the response of inflammatory cells to the implanted material or, in conjunction with other serum proteins, stimulate pre-osteoblast cell proliferation and differentiation. Further studies on the effect of serum proteins in cell culture and the efficacy of Fn-coated HAp and α-Al2O3in vivo are warranted.

Fibronectin adsorption on surface-modified polyetherurethanes and their differentiated effect on specific blood elements related to inflammatory and clotting processes.

After the introduction of a medical device into the body, adhesive proteins such as fibronectin (Fn) will adsorb to the surface of the biomaterial. Monocytes (MCs) will interact with these adsorbed proteins, and adopt either a proinflammatory and/or prowound healing phenotype, thereby influencing many blood interaction events including thrombogenesis. In this work, Fn adsorption as well as subsequent MC response and thrombus formation were investigated on two surfaces-modified polyetherurethanes (PEUs) using different surface modifiers: an anionic/dihydroxyl oligomeric (ADO) additive, known to enable cell adhesion, and a fluorinated polypropylene oxide oligomer (PPO), known to reduce platelet adhesion. Results indicated that at 24 h of MC culture, PEU-ADO and PEU-PPO promoted an anti-inflammatory character relative to the base PEU. Longer clotting times, based on a free hemoglobin assay, were also found on the two surface-modified PEUs relative to the native one, suggesting their potential for the reduction of thrombus formation. In presence of a Fn monolayer, the surface-modified PEUs conserved a lower thrombogenic character than the base PEU, and was however significantly decreased when compared to prior protein adsorption. Furthermore, Fn coatings increased the MC production levels of tumor necrosis factor-α and interleukin-10 at 24 h, while not affecting the anti-inflammatory effect of the modifications relative to the base PEU. This finding was most prominent on PEU-PPO, suggesting that the interaction of the adsorbed Fn with blood cells was different for the two additives. Hence, the results highlighted differentiating effects of Fn adsorption on specific blood activating processes related to inflammatory and thrombotic responses.

Effect of the Materials Properties of Hydroxyapatite Nanoparticles on Fibronectin Deposition and Conformation.

Hydroxyapatite (HAP, Ca10(PO4)6(OH)2) nanoparticles with controlled materials properties have been synthesized through a two-step hydrothermal aging method to investigate fibronectin (Fn) adsorption. Two distinct populations of HAP nanoparticles have been generated: HAP1 particles had smaller size, plate-like shape, lower crystallinity, and more negative ζ potential than HAP2 particles. We then developed two-dimensional platforms containing HAP and Fn and analyzed both the amount and the conformation of Fn via Förster resonance energy transfer (FRET) at various HAP concentrations. Our FRET analysis reveals that larger amounts of more compact Fn molecules were adsorbed onto HAP1 than onto HAP2 particles. Additionally, our data show that the amount of compact Fn adsorbed increased with increasing HAP concentration due to the formation of nanoparticle agglomerates. We propose that both the surface chemistry of single nanoparticles and the size and morphology of HAP agglomerates play significant roles in the interaction of Fn with HAP. Collectively, our findings suggest that the HAP-induced conformational changes of Fn, a critical mechanotransducer protein involved in the communication of cells with their environment, will ultimately affect downstream cellular behaviors. These results have important implications for our understanding of organic–inorganic interactions in physiological and pathological biomineralization processes such as HAP-related inflammation.

Use of precisely sculptured thin film (STF) substrates with generalized ellipsometry to determine spatial distribution of adsorbed fibronectin to nanostructured columnar topographies and effect on cell adhesion

Sculptured thin film (STF) substrates consist of nanocolumns with precise orientation, intercolumnar spacing, and optical anisotropy, which can be used as model biomaterial substrates to study the effect of homogenous nanotopogrophies on the three-dimensional distribution of adsorbed proteins. Generalized ellipsometry was used to discriminate between the distributions of adsorbed FN either on top of or within the intercolumnar void spaces of STFs, afforded by the optical properties of these precisely crafted substrates. Generalized ellipsometry indicated that STFs with vertical nanocolumns enhanced total FN adsorption two-fold relative to flat control substrates and the FN adsorption studies demonstrate different STF characteristics influence the degree of FN immobilization both on top and within intercolumnar spaces, with increasing spacing and surface area enhancing total protein adsorption. Mouse fibroblasts or mouse mesenchymal stem cells were subsequently cultured on STFs, to investigate the effect of highly ordered and defined nanotopographies on cell adhesion, spreading, and proliferation. All STF nanotopographies investigated in the absence of adsorbed FN were found to significantly enhance cell adhesion relative to flat substrates; and the addition of FN to STFs was found to have cell-dependent effects on enhancing cell–material interactions. Furthermore, the amount of FN adsorbed to the STFs did not correlate with comparative enhancements of cell–material interactions, suggesting that nanotopography predominantly contributes to the biocompatibility of homogenous nanocolumnar surfaces. This is the first study to correlate precisely defined nanostructured features with protein distribution and cell–nanomaterial interactions. STFs demonstrate immense potential as biomaterial surfaces for applications in tissue engineering, drug delivery, and biosensing.

Adsorption of plasma proteins and fibronectin on poly(hydroxylethyl methacrylate) brushes of different thickness and their relationship with adhesion and migration of vascular smooth muscle cells.

The surface-grafted poly(hydroxylethyl methacrylate) (PHEMA) molecules were demonstrated to show a brush state regardless of their molecular length (molecular weight). Adsorption of proteins from 10% fetal bovine serum (FBS), fibronectin (Fn) and bovine serum albumin (BSA) was quantified by ellipsometry, revealing that the amounts of FBS and Fn decreased monotonously along with the increase of PHEMA thickness, whereas not detectable for BSA when the PHEMA thickness was larger than 6 nm. Radio immunoassay found that the adsorption of Fn from 10% FBS had no significant difference regardless of the PHEMA thickness. However, ELISA results showed that the Arg-Gly-Asp (RGD) activity of adsorbed Fn decreased with the increase of PHEMA thickness. By comparison of cellular behaviors of vascular smooth muscle cells (VSMCs) being cultured in vitro in the normal serum-containing medium and the Fn-depleted serum-containing medium, the significant role of Fn on modulating the adhesion and migration of VSMCs was verified. Taking account all the results, the Fn adsorption model and its role on linking the biomaterials surface to the VSMCs behaviors are proposed.

Adsorption of fibronectin on salt-etched polyelectrolyte multilayers and its roles in mediating the adhesion and migration of vascular smooth muscle cells.

Protein adsorption on biomaterials strongly mediates the subsequent cell responses. Here adsorption of fibronectin (Fn) on salt-treated PEI(PSS/PDDA)7 multilayers was characterized. The amounts of adsorbed Fn increased linearly along with the increase of thickness of multilayers pretreated with 1 M and 5 M NaCl solutions (Multilayer-1M and 5M), but was independent on the thickness of Multilayer-3M. The normalized relative RGD activity of Fn were significantly higher on the Multilayer-3M than on others. By comparison of cellular behaviors of VSMCs being cultured in the normal and Fn-depleted serum-containing medium, the significant role of Fn on modulating the behaviors of VSMCs was verified. The Fn adsorption model and its role on linking the biomaterials surface to the VSMCs behaviors are proposed.

Impact of selective fibronectin nanoconfinement on human dental pulp stem cells

In this study, it was aimed to investigate the combinatory effect of biophysical and biochemical factors on human dental pulp stem cells’ (hDPSCs) behavior. For this purpose, well-defined nanotopography of nanowells with two different pitch size of 109nm and 341nm were prepared on polyhydroxymethylsiloxane (PHMS) by using colloidal particles nanofabrication. The nanopatterned PHMS surfaces (PHMS/109 and PHMS/341) were subsequently used for fibronectin (Fn) adsorption. With this approach, nanotopographical details were combined with biochemical signals from Fn. Depending upon the size of cavities created by the nanowells, Fn molecules followed a site-selective adsorption. While they adsorbed both inside and outside the nanowells of PHMS/341, they preferred to adsorb outside the cavities of PHMS/109 surfaces. Human dental pulp stem cells were cultured on nanopatterned PHMS with or without Fn adsorption in the presence and absence of serum. Scanning electron microscopy and fluorescence microscopy analyses showed the interaction of cells was dependent on nanotopography size especially in serum-free medium. Furthermore, hDPSCs’ morphology and cytoskeletal organization changed in correlation with preferential Fn adsorption. On Fn adsorbed PHMS/109 surfaces, cells displayed stretched bundles whereas, they showed extensive spreading and followed the Fn adsorbed sites inside the cavities of PHMS/341 surfaces. The observed effects are interpreted in terms of the preferential exposure of different Fn epitopes occurring on PHMS/109 and PHMS/341 as a consequence of the different hydrophilic/hydrophobic adsorbing surface.

A correlation study of protein adsorption and cell behaviors on substrates with different densities of PEG chains

The adsorption of proteins, in particular fibronectin (Fn), was studied on poly(ethylene glycol) (PEG, 5kDa)-grafted surfaces, and was correlated with the adhesion behaviors of smooth muscle cells (SMCs). The PEG molecules were covalently grafted on aldehyde-activated substrates with different densities of amino groups. The thickness of PEG layer increased nearly 10 fold in a hydrated state, reaching to 27nm on the surface of highest PEG chain density with a brush configuration. On the lower PEG-grafted surfaces, however, the PEG molecules adopted a mushroom configuration. The adsorption of Fn without and with the competition of bovine serum albumin (BSA) and serum was studied by using ellipsometry, fluorescence microscopy and radio-labeling techniques. The adsorption amount of Fn in serum decreased initially with increased PEG chain density until 0.12chains/nm2 PEG, and then slightly increased on the 0.29chains/nm2 PEG. A series of protein preadsorption experiments were carried out under different conditions before SMCs culture in vitro. Compared with those substrates without Fn preadsorption, the cell adhesion and spreading were significantly enhanced on all the PEG surfaces preadsorbed with Fn and serum, although they overall decreased along with the increase of PEG grafting density. The adhesion force of Fn decreased monotonously with the increase of PEG grafting density, which was in accordance with the cell adhesion force. The correlation between the PEG-grafted surfaces, Fn adsorption, and cellular behaviors is finally suggested.

Effects of human fibronectin and human serum albumin sequential adsorption on preosteoblastic cell adhesion.

Fibronectin (Fn) is widely reported to promote cell adhesion and spreading, and recent reports attest to the synergistic effect of coadsorbed albumin (unexpected due to the passivating character of the latter protein). In this study, the sequential adsorption of fibronectin and albumin, and the morphology of cultured MC3T3-E1 preosteoblastic cells are investigated on three important biomaterial surfaces: silicon oxide, poly(styrene) (PS), and hydroxyapatite (HA). Using quartz crystal microgravimetry with dissipation analysis, the adsorbed protein composition and mechanics are determined. Interestingly, cell morphological changes correlate neither with the amount of Fn nor the rigidity of the protein layer. On the PS surface, Alb is seen to significantly diminish cell spreading, possibly due to Alb aggregation with a partially denatured initially placed Fn layer. HA appears to be a particularly favorable substrate for osteoblast adhesion, despite having low Fn adsorption and protein layer rigidity.

Effect of 3D microgroove surface topography on plasma and cellular fibronectin of human gingival fibroblasts

ObjectivesFibronectin (FN), an extracellular matrix (ECM) glycoprotein, is a key factor in the compatibility of dental implant materials. Our objective was to determine the optimal dimensions of microgrooves in the transmucosal part of a dental implant, for optimal absorption of plasma FN and expression of cellular FN by human gingival fibroblasts (HGFs). MethodsMicrogroove titanium surfaces were fabricated by photolithography with parallel grooves: 15μm, 30μm, or 60μm in width and 5μm or 10μm in depth. Smooth titanium surfaces were used as controls. Surface hydrophilicity, plasma FN adsorption and cellular FN expression by HGFs were measured for both microgroove and control samples. ResultsWe found that narrower and deeper microgrooves amplified surface hydrophobicity. A 15-μm wide microgroove was the most hydrophobic surface and a 60-μm wide microgroove was the most hydrophilic. The latter had more expression of cellular FN than any other surface, but less absorption of plasma FN than 15-μm wide microgrooves. Variation in microgroove depth did not appear to effect FN absorption or expression unless the groove was narrow (∼15 or 30μm). In those instances, the shallower depths resulted in greater expression of cellular FN. ConclusionsOur microgrooves improved expression of cellular FN, which functionally compensated for plasma FN. A microgroove width of 60μm and depth of 5 or 10μm appears to be optimal for the transmucosal part of the dental implant.

Cell Adhesion on a POEGMA-Modified Topographical Surface

It is well known that adsorbed proteins play a major role in cell adhesion. However, it has also been reported that cells can adhere to a protein-resistant surface. In this work, the behavior of L02 and BEL-7402 cells on a protein-resistant, 3D topographical surface was investigated. The topographical gold nanoparticle layer (GNPL) surfaces were prepared by chemical gold plating, and the topography was described by roughness parameters acquired from a multiscale analysis. Both smooth Au and GNPL surfaces were modified with POEGMA polymer brushes using surface-initiated ATRP. The dry and hydrated thicknesses of POEGMA brushes on both smooth and rough surfaces were measured by AFM using a nanoindentation method. Protein adsorption experiments using (125)I radiolabeling revealed similarly low levels of protein adsorption on smooth and GNPL surfaces modified with POEGMA, thus allowing an investigation of the effects of topography on cell behavior under conditions of minimal protein adsorption. The roles of VN and FN adsorption in both L02 cells and BEL-7402 cells adhesion were investigated using cell culturing with and without a serum supplement. It was found that initial cell adhesion occurred via proteins adsorbed from the cell culture medium, whereas subsequent durable cell adhesion could be attributed to the topographical structure of the surface. Although cell spreading on protein-resistant surfaces was constrained because of the lack of adsorbed proteins, we found that cells adherent to topographical surfaces were more firmly attached and thus were more durable compared to those on smooth surfaces. In general, however, we conclude that topography is more important for cell adhesion on a protein-resistant surface.

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.

Protein adsorption and cytocompatibility of poly(L‐lactic acid) surfaces modified with biomacromolecules

AbstractSurface modification of biomaterials has been adopted over the years in order to improve their biocompatibility. In this study, heparin, hyaluronic acid and chondroitin sulfate were used to modify the surface of poly(L‐lactic acid) (PLLA) films by an entrapment method to promote its biocompatibility and to introduce natural recognition sites to the surface of PLLA films. The surface properties of PLLA films before and after modification were characterized by using water contact angle measurement, scanning electron microscope (SEM) and X‐ray photoelectron spectroscopy (XPS). Subsequently, the protein adsorption behavior of radiolabeled (125I) fibronectin (Fn) was evaluated on the modified PLLA surfaces, including adsorption kinetics, isotherm adsorption, competitive adsorption with bovine serum albumin (BSA) or serum. The cytocompatibility of the modified PLLA films was further investigated by testing osteoblasts‐like compatibility, including cell attachment, cell proliferation, alkaline phosphatase activity and cell cycle. Experimental results indicated that the hydrophilicity of the modified PLLA films was improved by the enriched biomacromolecules. In the study of protein absorption, the entrapment of the biomacromolecules on PLLA surface could decrease and reduce Fn adsorption speed and capacity, while the three biomacromolecules had almost the same adsorption capacity. Addition of BSA or serum had great effect on the adsorption of Fn on the modified PLLA surfaces. Moreover, the modifications could significantly promote osteoblasts‐like compatibility of PLLA films. The biomacromolecules modified PLLA films, combining their individual advantages such as good mechanical property and excellent cytocompatibility, are promising candidates for tissue engineering. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Effects of Plasma Proteins on <i>Staphylococcus epidermidis</i> RP62A Adhesion and Interaction with Platelets on Polyurethane Biomaterial Surfaces

Plasma proteins influence the initial adhesion of bacteria to biomaterials as well as interactions between bacteria and blood platelets on blood-contacting medical devices. In this paper, we study the effects of three human plasma proteins, albumin, fibrinogen (Fg), and fibronectin (Fn), on the adhesion of Staphylococcus epidemidis RP62A to polyurethane biomaterial surfaces, and also address how these three proteins affect bacterial interactions with human platelets on materials. Measurements of bacterial adhesion on polymer surfaces pre-adsorbed with a variety of proteins demonstrate that Fn leads to increased bacterial adhesion, with the order of effectiveness being Fn 》Fg > albumin. Immuno-AFM (atomic force microscopy) was used to assess the Fn adsorption/activity on surfaces and bacterial cell membranes by looking at molecular scale events. A correlation between molecular scale Fn adsorption and macroscale bacterial adhesion was observed, with an increased numbers of Fn-receptor recognition events measured on cell surfaces as compared to Fg-receptor recognition events, suggesting Fn is an important protein in bacterial adhesion. Monoclonal antibodies recognizing either the carboxyl-terminus or amino-terminus of Fn were coupled to AFM probes and used to assess the orientation of Fn adsorbed on a surface, with an increased amount of Fn carboxyl-terminus availability corresponding to higher bacterial adhesion. Interactions between bacteria and platelets were demonstrated with fluorescence and AFM imaging on the polyurethane surfaces, with albumin inhibiting bacteria-platelet interaction and platelet activation, and both Fg and Fn promoting adhesion of bacteria to platelets and apparent platelet activation, resulting in bacteria/platelet aggregation.