QCM-D studies of attachment and differential spreading of pre-osteoblastic cells on Ta and Cr surfaces

Determination of surface-induced platelet activation by applying time-dependency dissipation factor versus frequency using quartz crystal microbalance with dissipation

Platelet adhesion and activation rates are frequently used to assess the thrombogenicity of biomaterials, which is a crucial step for the development of blood-contacting devices. Until now, electron and confocal microscopes have been used to investigate platelet activation but they failed to characterize this activation quantitatively and in real time. In order to overcome these limitations, quartz crystal microbalance with dissipation (QCM-D) was employed and an explicit time scale introduced in the dissipation versus frequency plots (Df-t) provided us with quantitative data at different stages of platelet activation. The QCM-D chips were coated with thrombogenic and non-thrombogenic model proteins to develop the methodology, further extended to investigate polymer thrombogenicity. Electron microscopy and immunofluorescence labelling were used to validate the QCM-D data and confirmed the relevance of Df-t plots to discriminate the activation rate among protein-modified surfaces. The responses showed the predominant role of surface hydrophobicity and roughness towards platelet activation and thereby towards polymer thrombogenicity. Modelling experimental data obtained with QCM-D with a Matlab code allowed us to define the rate at which mass change occurs (A/B), to obtain an A/B value for each polymer and correlate this value with polymer thrombogenicity.

Quartz crystal microbalance with dissipation monitoring of supported lipid bilayers on various substrates

Supported lipid bilayers (SLBs) mimic biological membranes and are a versatile platform for a wide range of biophysical research fields including lipid-protein interactions, protein-protein interactions and membrane-based biosensors. The quartz crystal microbalance with dissipation monitoring (QCM-D) has had a pivotal role in understanding SLB formation on various substrates. As shown by its real-time kinetic monitoring of SLB formation, QCM-D can probe the dynamics of biomacromolecular interactions. We present a protocol for constructing zwitterionic SLBs supported on silicon oxide and titanium oxide, and discuss technical issues that need to be considered when working with charged lipid compositions. Furthermore, we explain a recently developed strategy that uses an amphipathic, alpha-helical (AH) peptide to form SLBs on gold and titanium oxide substrates. The protocols can be completed in less than 3 h.

Protein adsorption on derivatives of hyaluronic acid and subsequent cellular response

The modulation of biological interactions with artificial surfaces is a vital aspect of biomaterials research. Serum protein adsorption onto photoreactive hyaluronic acid (Hyal-N(3)) and its sulfated derivative (HyalS-N(3)) was analyzed to determine extent of protein interaction and protein conformation as well as subsequent cell adhesion. There were no significant (p < 0.01) differences in the amount of protein adsorbed to the two polymers; however, proteins were found to be more loosely bound on HyalS-N(3) compared with Hyal-N(3). Fibronectin was adsorbed onto HyalS-N(3) in such an orientation as to allow the availability of the cell binding region, while there was more restricted access to this region on fibronectin adsorbed onto Hyal-N(3). This was confirmed by reduced cell adhesion on fibronectin precoated Hyal-N(3) compared with fibronectin precoated HyalS-N(3). Minimal cell adhesion was observed on albumin and serum precoated Hyal-N(3). The quartz crystal microbalance confirmed that specific cell-surface interactions were experienced by cells interacting with the fibronectin precoated polymers and serum precoated HyalS-N(3).

Selective collection and detection of leukemia cells on a magnet-quartz crystal microbalance system using aptamer-conjugated magnetic beads

A novel method for selective collection and detection of human acute leukemia cells has been proposed using aptamer-conjugated magnetic beads (apt-MBs) and a magnet-quartz crystal microbalance (QCM) system. The sgc8c aptamer-conjugated MBs specifically binding to CCRF-CEM cells were used for target cell extraction from complex matrixes, and the magnet-QCM system was successfully applied for quantitative cell detection, requiring no further labeling of cells. The accumulation of MBs-conjugated CCRF-CEM cells on a quartz crystal gold electrode surface under a magnetic field resulted in decreased resonant frequency. A linear relationship between the frequency shift and cell concentration over the range of 1 x 10(4)-1.5 x 10(5)cells mL(-1) was obtained, with a detection limit of 8 x 10(3)cells mL(-1). The applicability of the method for target cell detection from cell mixture was satisfactory.

Spatial and temporal changes in the morphology of preosteoblastic cells seeded on microstructured tantalum surfaces

It has been widely reported that surface morphology on the micrometer scale affects cell function as well as cell shape. In this study, we have systematically compared the influence of 13 topographically micropatterned tantalum surfaces on the temporal development of morphology, including spreading, and length of preosteoblastic cells (MC3T3-E1). Cells were examined after 0.5, 1, 4, and 24 h on different Ta microstructures with vertical dimensions (heights) of 0.25 and 1.6 mum. Cell morphologies depended upon the underlying surface topography, and the length and spreading of cells varied as a function of time with regard to the two-dimensional pattern and vertical dimension of the structure. Microstructures of parallel grooves/ridges caused elongated cell growth after 1 and 4 h in comparison to a flat, nonstructured, reference surface. For microstructures consisting of pillars, cell spreading was found to depend on the distance between the pillars with one specific pillar structure exhibiting a decreased spreading combined with a radical change in morphology of the cells. Interestingly, this morphology on the particular pillar structure was associated with a markedly different distribution of the actin cytoskeleton. Our results provide a basis for further work toward topographical guiding of cell function.

Probing mechanical properties of liposomes using acoustic sensors

Acoustic devices were employed to characterize variations in the mechanical properties (density and viscoelasticity) of liposomes composed of 1-oleoyl-2-palmitoyl- sn-glycero-3-phosphocholine (POPC) and cholesterol. Liposome properties were modified in three ways. In some experiments, the POPC/cholesterol ratio was varied prior to deposition on the device surface. Alternatively, the ratio was changed in situ via either insertion of cholesterol or removal of cholesterol with beta-cyclodextrin. This was done for liposomes adsorbed directly on the device surface and for liposomes attached via a biotin-terminated poly(ethylene glycol) linker. The acoustic measurements make use of two simultaneous time-resolved signals: one signal is related to the velocity of the acoustic wave, while the second is related to dissipation of acoustic energy. Together, they provide information not only about the mass (or density) of the probed medium but also about its viscoelastic properties. The cholesterol-induced increase in the surface density of the lipid bilayer was indeed observed in the acoustic data, but the resulting change in signal was larger than expected from the change in surface density. In addition, increasing the bilayer resistance to stretching was found to lead to a greater dissipation of the acoustic energy. The acoustic response is assessed in terms of the possible distortions of the liposomes and the known effects of cholesterol on the mechanical properties of the lipid bilayer that encloses the aqueous core of the liposome. To aid the interpretation of the acoustic response, it is discussed how the above changes in the lipid bilayer will affect the effective viscoelastic properties of the entire liposome/solvent film on the scale of the acoustic wavelength. It was found that the acoustic device is very sensitive to the mechanical properties of lipid vesicles; the response of the acoustic device is explained, and the basic underlying mechanisms of interaction are identified.

Quantifying blood platelet morphological changes by dissipation factor monitoring in multilayer shells

The ability of electrostatically driven layer-by-layer (LbL) assembly to adapt to the morphological features of a template was explored. Subtle cytoskeletal changes in blood platelets became traceable through energy dissipation monitoring in multilayered shells using microgravimetric measurements. This LbL coating was sequentially deposited on protein-modified chips onto which platelets were adhered. In addition to consequently improving the signal sensitivity, the LbL shell acted in synergy with the cell, allowing the determination and quantification of cytoskeletal changes induced by the specific cell adhesion to the protein-modified chip surface used with a quartz crystal microbalance with dissipation. The difference in cell morphology, as a result of the optimization of specific interactions between the protein layer and cell membrane integrins induced viscoelastic changes in the polyelectrolyte shell, thereby providing quantitative data on platelet conformational changes upon their adhesion to protein-modified chip surface.

Extracellular matrix remodelling during cell adhesion monitored by the quartz crystal microbalance

A cell's ability to remodel adsorbed protein layers on surfaces is influenced by the nature of the protein layer itself. Remodelling is often required to accomplish cellular adhesion and extracellular matrix formation which forms the basis for cell spreading, increased adhesion and expression of different phenotypes. The adhesion of NIH3T3 (EGFP) fibroblasts to serum protein (albumin or fibronectin) precoated tantalum (Ta) and oxidised polystyrene (PS(ox)) surfaces was examined using the quartz crystal microbalance with dissipation (QCM-D) monitoring and fluorescence microscopy. The cells were either untreated or treated with cycloheximide to examine the contribution of endogenous protein production during cell adhesion to the QCM-D response over a period of 2h. Following adsorption of albumin onto Ta and PS(ox) there was no difference detected between the response to seeding untreated and cycloheximide treated cells. The QCM-D was able to detect differences in the untreated cellular responses to fibronectin versus serum precoated Ta and PS(ox) substrates, while cycloheximide treatment of the cells produced the same QCM-D response for fibronectin and serum precoatings on each of the materials. This confirmed that the process of matrix remodelling by the cells is dependent on the underlying substrate and the preadsorbed proteins and that the QCM-D response is dominated by changes in the underlying protein layer. Changes in dissipation correspond to the development of the actin cytoskeleton as visualised by actin staining.

Recombinant single-chain variable fragment and single domain antibody piezoimmunosensors for detection of HIV1 virion infectivity factor

In this paper recombinant single-chain fragments (scFv-4BL), and single domain antibodies (4BL-V(H)) and (4BL-V(H)D) generated against HIV1 virion infectivity factor (Vif) are used to develop piezoimmunosensors for HIV1 recognition. Mixed self assembled monolayers were generated at the surface of gold coated crystal sensors to which scFv-4BL, 4BL-V(H), or 4BL-V(H)D were immobilized. Impedance analysis was used to discriminate interfering signals from frequency variation data and to increase the sensor sensitivity. The elimination of interfering signals enabled the quantification of the amount of immobilized protein and gave some indication on the viscoelasticity of immobilized biofilms. All the modified sensors were able to specifically recognize HIV1 Vif in liquid samples. The results indicate that lower sensitivities are obtained with 4BL-V(H) single domain antibodies, possibly due to its higher hydrophobic character. The sensitivity obtained when using scFv-4BL was reestablished when using the more hydrophilic 4BL-V(H)D single domain. 4BL-V(H)D piezoimunosensors were effective in recognizing HIV1 Vif from protein mixtures and from cell extracts of human embryonic kidney cells expressing HIV1 Vif. The results presented in this paper demonstrate the potential applicability of the developed piezoimmunosensors to monitor HIV1 infection evolution.

Critical assessment of the Quartz Crystal Microbalance with Dissipation as an analytical tool for biosensor development and fundamental studies: Metallophthalocyanine–glucose oxidase biocomposite sensors

One of the challenges in electrochemical biosensor design is gaining a fundamental knowledge of the processes underlying immobilisation of the molecules onto the electrode surface. This is of particular importance in biocomposite sensors where concerns have arisen as to the nature of the interaction between the biological and synthetic molecules immobilised. We examined the use of the Quartz Crystal Microbalance with Dissipation (QCM-D) as a tool for fundamental analyses of a model sensor constructed by the immobilisation of cobalt(II) phthalocyanine (TCACoPc) and glucose oxidase (GOx) onto a gold-quartz electrode (electrode surface) for the enhanced detection of glucose. The model sensor was constructed in aqueous phase and covalently linked the gold surface to the TCACoPc, and the TCACoPc to the GOx, using the QCM-D. The aqueous metallophthalocyanine (MPc) formed a multi-layer over the surface of the electrode, which could be removed to leave a monolayer with a mass loading that compared favourably to the theoretical value expected. Analysis of frequency and dissipation plots indicated covalent attachment of glucose oxidase onto the metallophthalocyanine layer. The amount of GOx bound using the model system compared favourably to calculations derived from the maximal amperometric functioning of the electrochemical sensor (examined in previously-published literature, Mashazi, P.N., Ozoemena, K.I., Nyokong, T., 2006. Electrochim. Acta 52, 177-186), but not to theoretical values derived from dimensions of GOx as established by crystallography. The strength of the binding of the GOx film with the TCACoPc layer was tested by using 2% SDS as a denaturant/surfactant, and the GOx film was not found to be significantly affected by exposure to this. This paper thus showed that QCM-D can be used in order to model essential processes and interactions that dictate the functional parameters of a biosensor.

Piezoelectric biosensors for biorecognition analysis: application to the kinetic study of HIV-1 Vif protein binding to recombinant antibodies

In this work three piezoelectric sensors modified with anti-HIV-1 Vif (virion infectivity factor) single fragment antibodies (4BL scFV), single domains (VH) and camelized single domains (VHD) were constructed and used to detect HIV1 Vif in liquid samples. Dithio-bis-succinimidyl-undecanoate (DSU) and 11-hydroxy-1-undecanethiol (HUT) mixed self assembled monolayers (SAM) were generated at the sensors surface onto which the antibodies were immobilized. All sensors detected specifically the target HIV1-Vif antigen in solution and no unspecific binding was monitored. Impedance analysis was performed to quantify electroacoustic and viscoelastic interferences during antibody immobilization and antigen recognition. The elimination of such interferences enabled the quantitative use of the piezoelectric immunosensors to estimate the antibody surface density as well as antigen binding and equilibrium constants. In spite of the possible limitation regarding mass transport and other related molecular phenomena, which were not considered in the binding model used, this work demonstrates the usefulness of piezoelectric biosensors in biorecognition analysis and evidences the advantages on using simultaneous impedance analysis to bring analytical significance to measured data, and thus to improve piezoelectric sensors sensitivity and applicability.

Influence of electrolytes in the QCM response: Discrimination and quantification of the interference to correct microgravimetric data

In this work we demonstrate that the presence of electrolytes in solution generates desorption-like transients when the resonance frequency is measured. Using impedance spectroscopy analysis and Butterworth-Van Dyke (BVD) equivalent electrical circuit modeling we demonstrate that non-Kanazawa responses are obtained in the presence of electrolytes mainly due to the formation of a diffuse electric double layer (DDL) at the sensor surface, which also causes a capacitor like signal. We extend the BVD equivalent circuit by including additional parallel capacitances in order to account for such capacitor like signal. Interfering signals from electrolytes and DDL perturbations were this way discriminated. We further quantified as 8.0+/-0.5 Hz pF-1 the influence of electrolytes to the sensor resonance frequency and we used this factor to correct the data obtained by frequency counting measurements. The applicability of this approach is demonstrated by the detection of oligonucleotide sequences. After applying the corrective factor to the frequency counting data, the mass contribution to the sensor signal yields identical values when estimated by impedance analysis and frequency counting.

Digital imaging of stem cells by electron microscopy

This chapter deals with basic techniques of scanning and transmission electron microscopy applicable to stem cell imaging. It is sometimes desirable to characterize the fine structure of embryonic and adult stem cells to supplement the images obtained by phase-contrast and confocal immunofluorescent microscopy to compare with the microstructure of cells and tissues reported in the literature. This would help confirm their true identity whilst defining their surface and internal morphology. The intention is to put a face on stem cells during their differentiation.