Quartz Crystal Microbalance With Dissipation Technique Research Articles

Interfacial adsorption dynamics of solid lipid particles at oil/water interfaces through QCM-D technique

The interfacial adsorption dynamics of solid particles are important processes in the formation of Pickering emulsion, and its stabilities and functionalities are critically dependent on the particle interfacial structures. In this study, we investigated the interfacial behaviors of solid lipid particles (SLPs) within six food-grade SLPs using the quartz crystal microbalance with dissipation (QCM-D) technique. These SLPs had been subjected to surface modification with varying emulsifier contents, specifically 1, 2, and 4 wt% of both Polysorbate 40 (T40) and sodium caseinate (Na-Cas), referred to as T40-SLPs and Na-Cas-SLPs. Two distinct interface behaviors have been identified: Type 1, characterized by with weak interfacial activity, which included the 1 and 2 wt% T40-SLPs, and Type 2, exhibiting stronger interfacial activity, encompassing the 4 wt% T40-SLPs as well as the 1, 2 and 4 wt% Na-Cas-SLPs. Subsequently, the mechanism through which the emulsifiers influenced the interfacial dynamic behaviors was established by correlating the interfacial behaviors with the properties of SLPs. Briefly, larger and more electronegative spherical Na-Cas-SLPs exhibited stronger interfacial activity, which facilitated the formation of smaller and more stable Pickering droplets. The interfacial films formed by the short plate-like T40-SLPs were not sufficiently consolidated, which led to instability of the hydrophobic interfaces. These results were confirmed with macrostability tests of the Pickering emulsions stabilized by the SLPs and are expected to provide basic information for the functionalization of multicomponent Pickering emulsions.

Detection of amyloid β oligomers toward early diagnosis of Alzheimer's disease

Amyloid β (Aβ) peptide accumulation in the brain is considered to be one of the hallmarks of Alzheimer's disease. Here, we compare two analytical techniques for detecting neurotoxic Aβ1-42 oligomers - Quartz Crystal Microbalance with Dissipation (QCM-D) and Single Molecule Array (Simoa). Both detection methods exploit a feature of the monoclonal antibody bapineuzumab, which targets N-terminal residues 1–5 of Aβ with high affinity and use it as both a capture and detection reagent. Assays developed with the two methods allow us to specifically recognize neurotoxic Aβ1-42 oligomers and higher aggregates such as fibrils but discriminate against Aβ1-42 monomer species. We find that for detection of Aβ1-42 oligomers, Simoa was roughly 500 times more sensitive than the QCM-D technique with limits of detection of 0.22 nM and 125 nM, respectively.

Effect of Temperature Changes on Serum Protein Adsorption on Thermoresponsive Cell-Culture Surfaces Monitored by A Quartz Crystal Microbalance with Dissipation.

Thermoresponsive cell-culture polystyrene (PS) surfaces that are grafted with poly(N-isopropylacrylamide) (PIPAAm) facilitate the cultivation of cells at 37 °C and the detachment of cultured cells as a sheet with an underlying extracellular matrix (ECM) by reducing the temperature. However, the ECM and cell detachment mechanisms are still unclear because the detachment of cells from thermoresponsive surfaces is governed by complex interactions among the cells/ECM/surface. To explore the dynamic behavior of serum protein adsorption/desorption, thermoresponsive surfaces that correspond to thermoresponsive tissue-culture PS dishes were formed on sensor chips for quartz crystal microbalance with dissipation (QCM-D) measurements. X-ray photoelectron spectroscopy (XPS) measurements and temperature-dependent frequency and dissipation shifts, Δf and ΔD, using QCM-D revealed that the thermoresponsive polymers were successfully grafted onto oxidized, thin PS films on the surfaces of the sensor chips. Increased amounts of adsorbed bovine serum albumin (BSA) and fibronectin (FN) were observed on the thermoresponsive polymer-grafted surfaces at 37 °C when compared with those at 20 °C because of enhanced hydrophobic interactions with the hydrophobic, thermoresponsive surface. While the calculated masses of adsorbed BSA and FN using QCM-D were 3–5 times more than those that were obtained from radiolabeling, the values were utilized for relative comparisons among the same substrate. More importantly, the thermoresponsive, dynamic behavior of serum protein adsorption/desorption was monitored using the QCM-D technique. Observations of this dynamic behavior revealed that the BSA and FN that were adsorbed at 37 °C remained on both surfaces after decreasing the temperature to 20 °C.

Challenges associated with Quartz Crystal Microbalance with Dissipation (QCM-D) as a wettability screening tool

Wettability is an indispensable parameter in multiphase flow due to its profound effect in fluid phase distribution and flow properties in the oil reservoirs. One approach of unravelling the enigma associated with wettability characterization is to investigate oil adhesion onto reservoir rock surface during crude oil accumulation. This was accomplished using Quartz Crystal Microbalance with Dissipation (QCM-D) device. The QCM-D is a microbalance device that hinges on the changes in the frequency of a resonating crystal due to changes in the mass on sensor surface, precipitation, adsorption and desorption. However, this technique was confronted with numerous challenges during its early try-out. The objective of this study is to enumerate these challenges and how they were resolved. The piston-cell, valves, flow-lines and most of the experimental set-up were made from stainless steel. Hence, the high temperature coupled with high salinity brine resulted in the formation and deposition of corroded materials on the sensor. Due to the high sensitivity of the QCM-D technique, these corrosion deposits were detected via the high attenuation of the frequency signal as time elapsed during Formation Water (FW) injection. The second challenge was related to the dissolution of the thin sensor coatings (sensor etching) depicted by the relatively high increase in frequency signal with negligible changes in Dissipation (D). The third challenge was related to the trapping of fluids such as Stock Tank Oil (STO) inside the flow-cell. Finally, salt precipitation resulting from temperature variation during the initial experimental set-up was also observed. To resolve the corrosion challenge, all the stainless-steel components in the experimental set-up were replaced with titanium and non-metallic component such as peek materials. The sensor etching was also averted by injecting the brine through a packed column filled with similar mineral as the coatings on the sensor to attain equilibrium prior to injecting it onto the sensor. Geochemical simulation of the sensor etching was also confirmed using the geochemical simulator PHREEQ-C. Furthermore, the trapping of fluids inside the flow-cell was overcome by rotating the flow-cell to optimize the fluid displacement via capitalizing on their density contrast. Finally, the salt precipitation was avoided by conducting the experiment in a constant temperature experimental set-up. The QCM-D technique can be employed to estimate wettability by evaluating the tendency of the various minerals to adhere oil. The beauty of the QCM-D technique is that the surface interactions can be monitored on a real-time.

Interactions between fungal cellulases and films of nanofibrillar cellulose determined by a quartz crystal microbalance with dissipation monitoring (QCM-D)

Understanding the interactions between enzymes and substrates and the property changes of the substrates during the process is vital for efficiently producing fuels and chemicals from lignocellulosic biomass. In this manuscript, quartz crystal microbalance with dissipation (QCM-D) technique was employed as a tool to investigate the adsorption and hydrolysis behaviors of four fungal cellulases (Trichoderma reesei, Trichoderma viride, Aspergillus sp. and Aspergillus niger) on the substrate of nanofibrillar cellulose (NFC) film. The characterization of the cellulose films before and after enzymatic treatment was represented by atomic force microscopy. The results showed that four cellulases behaved quite differently. The cellulases from T. reesei and T. viride adsorbed onto NFC films and then the hydrolysis was carried out; and their trends represented by different overtones were similar and consistent. The cellulase from Aspergillus sp. adsorbed on the substrate to form a quite compact layer since substantial frequency changed with little dissipation variation. In term of the cellulase from A. niger, its frequency and dissipation overtones exhibited diverged behaviors. After viscoelastic modeling for cellulases except for Aspergillus sp using the multi-overtone data provided by QCM-D technique, the film properties of NFC film and adlayer were extracted and they could help to understand the interactions between cellulases and substrates.

Mucoadhesion vs mucus permeability of thiolated chitosan polymers and their resulting nanoparticles using a quartz crystal microbalance with dissipation (QCM-D)

The aim of this present study was to evaluate the combination properties between mucoadhesion/mucus permeability of thiolated chitosans (TC) and their resulting nanoparticles using a quartz crystal microbalance with dissipation (QCM-D). The QCM-D experiments were conducted at pH 4 or 6.8 to assess the interaction between thiolated polymers, with low (TCL), medium (TCM) and high (TCH) contents of free thiol groups, and native porcine gastric mucin (NPGM). TCL was chosen for further carriers as it showed higher permeability into the NPGM layer compared to TCM and TCH. In this study, we describe a formulation of a novel carrier comprised by positively charged TCL, negatively charged DNA and degradable oligopeptide-modified poly(β-amino ester)s (PBAEs), which were employed in order to approach for tuning particle size and surface charge of complexes. TCL/PBAE complexes with or without DNA were characterized using dynamic light scattering. Mechanism of adsorption or permeation of the TCL/PBAE/DNA complexes into the NPGM barrier was investigated with QCM-D, which is a highly sensitive technique for studying nanomechanical (viscoelastic) changes of the substrates. This work might provide that the QCM-D technique would be a promising method to monitor the dynamic behaviour between complexes and NPGM.

ADSORPTION MECHANISM OF SODIUM OLEATE ON TITANIUM DIOXIDE COATED SENSOR SURFACE USING QUARTZ CRYSTAL MICROBALANCE WITH DISSIPATION

Quartz Crystal Microbalance with Dissipation (QCM-D) was firstly applied to investigate the adsorption mechanism of sodium oleate on TiO2 coated sensor surface. The effects of pH value, sodium oleate concentration, and temperature on TiO2 coated sensor surface were evaluated systematically using the QCM-D technique. Zeta potential, surface tension, adsorption isotherms, and adsorption thermodynamics were employed to characterize the adsorption process. The results showed the advantages of QCM-D on the investigation of the adsorption process. Additionally, the electrostatic equilibrium adsorption data was well matched to the Langmuir isotherm. Based on the thermodynamic analysis, adsorption was a spontaneous and endothermic physisorption process.

QCM-D for Haemostasis Assays: Current Status and Future: A Review

In recent years, modern technologies and devices for coagulation monitoring have demonstrated a multidisciplinary interest in assays and methods. Devices and equipment for point-of-care (POC) coagulation monitoring of whole blood or plasma could eliminate fundamental deficiencies of routine coagulation assays and tests. Quartz Crystal Microbalance with dissipation (QCM-D) is an emerging powerful biomedical device, and it has an outstanding potential in this perspective. This is 'first critical review' article' that focuses the applications of coagulation assays on QCM-D technique, and it covers the substantial scientific efforts from 2011 to January 2016. This article could provide baselines for coagulation assays on QCM-D technology for the future perspectives, ultra-refining the POC settings for laboratory and clinical methods levels in worldwide and far beyond.

A Simultaneous Monitoring of Coagulation Time and Fibrinogen via PiCT on QCM-D

‘Prothrombinase induced Clotting Time’ (PiCT) has potential to detect all anticoagulants in clinics. In the present study, PiCT has been used as a tool for anticoagulant detection in human plasma on quartz crystal microbalance with dissipation (QCM-D) technique. QCM-D technique enables monitoring of PiCT point, total coagulation and fibrinogen concentration from frequency and dissipation curves in single set of measurements. This is impossible on mechanical coagulometer (which is considered as 'gold standard') technique, and it cannot yield coagulation and fibrinogen concentration from a single set of measurements. It requires additional Clauss method or modified Clauss method to calculate fibrinogen by employing different reagents and experimental setups. Additionally, the present report utilizes the lowest sample volume (and each reagent volume) consumptions of 1.66 µL. The sample/reagent volume consumption of 1.66 µL on QCM-D is 30 times lower in comparison with mechanical coagulometer’s that uses 50 µL for laboratory experiments for PiCT. This element is crucial for application of spot test via QCM-D in laboratory and clinics for Point of Care (POC) settings. Different doses of anticoagulant in 20 human plasma samples on QCM-D technique have been studied and compared in parallel to ‘gold standard’. PiCT on QCM-D technique yielded precise and accurate data. Additionally, both techniques produced % RSD values between 3 and 8.5 with slight fluctuations on both sides for PiCT points. The %RSD data for both techniques has lower variability for danaparoid. Furthermore, QCM-D technique enables monitoring of substantial fibrinogen concentrations (i.e. 1 - 6 g/L) with outstanding R2 value of 0.99 on the calibration curve. PiCT-QCM-D technique proved superior at all concentrations of fibrinogen in standard reference plasma for PiCT range (precision) on comparing to that of 'gold standard'.

Shortened 'Thrombin Time' Monitoring on QCM-D: A Better Substitute of 'Gold Standard'

Thrombin is the central enzyme in the coagulation cascade. Recently, modern technologies for thrombin generation measurement have shown a multidisciplinary interest in methods and assays. This is first report to recognize and optimize for human plasma application of 'thrombin time' (TT) assay for quartz crystal microbalance with dissipation (QCM-D) technique. QCM-D technique has been studied comparatively with mechanical coagulometer (which is regarded as 'gold standard' for coagulation assays). The optimized protocol for TT has been applied for plasma samples (n=54) on both platforms. Thrombin times (TTs) on QCM-D platform versus those of 'gold standard' yielded a promising correlation line with R2 value of 0.86. For TT assay, QCM-D platform proved superior as compared to 'gold standard' platform due to following four edges. Firstly, QCM-D platform provides whole kinetic information, including monitoring of total coagulation on its measurement curve. 'Gold standard' cannot yield this information because it picks one point during coagulation. Secondly, TTs on QCM-D platform are 30% shorter as compared to those of 'gold standard'. Thirdly, TTs on QCM-D technique produced 16% lower %RSD demonstrating lower variability. Lastly, a historical lowest sample volume consumption of 2.50 µl has been applied on QCM-D platform. ‘Gold standard’ employs 40 times greater sample volume consumption for laboratory experiments of TT. Additionally, 40 times lower reagent volume consumption has been employed on QCM-D platform in comparison to its counterpart’s. These advantageous features are substantial support for point of care (POC) settings for TT assay via QCM-D technique.

APTT: 1st Recognition for Human Whole Blood on QCM-D Platform

Activated partial thromboplastin time (aPTT) assay for whole blood on quartz crystal microbalance with dissipation (QCM-D) platform has been recognized for the first time. QCM-D platform is studied in parallel with ‘gold standard’ mechanical coagulometer in the perspective of anticoagulant bio-sensing. In this report, the lowest sample volume application of 1.66 µL of human whole blood for aPTT has been demonstrated. Mechanical coagulomter uses 60 times higher whole blood (and each reagent) volume application of 100 µL for aPTT laboratory experiments. This study is important in the terms of its robustness due to direct whole blood method and its cost-effectiveness due to lowest sample (and reagents) volume application. This could be fundamental support for spot test application by employing QCM-D in laboratory and sergry. Anticoagulant doses in 20 blood samples have been measured on QCM-D platform in comparison to ‘gold standard’. Each technique yielded relative standard deviation values between 7 and 15 depending on different doses of anticoagulant. Furthermore, QCM-D technique is advantageous over 'gold standard’ for additional monitoring of the whole kinetics of coagulation. It displays total coagulation recognition from frequency and dissipation shifts, which is impossible on 'gold standard’.

Prothrombin Time (PT) for Human Plasma on QCM-D Platform: A Better Alternative to 'Gold Standard'

Measurements of hemostasis parameters such as Prothrombin time (PT) are substantial in various clinical cases of extensive surgery, dialysis or innate hemostasis disorders. This is the first study of recognition of PT assay for human plasma on quartz crystal microbalance with dissipation (QCM-D) platform. QCM-D technique has been compared in parallel with ‘gold standard’ mechanical coagulometer in the terms of anticoagulant monitoring in 20 plasma samples. In this report the shortest sample volume consumption of 2.66 µl of human plasma for PT has been demonstrated on QCM-D platform. This also demonstrates the shortest reagent (thromborel) volume consumption employed ever for PT. 'Gold standard' employs 38 folds higher plasma as well as reagent volume consumption. Additionally, QCM-D technique proved superior to 'gold standard’ for monitoring of the whole process of plasma coagulation kinetics. It yielded total coagulation information from frequency and dissipation shifts, which are impossible on 'gold standard’. Furthermore, QCM-D platform offers the calculation of fibrinogen concentration along with PT and total coagulation monitoring in single set of measurements. Fibrinogen concentration can be calculated from calibration curves having R2 values of 0.99. This is promising support for Point of Care (POC) settings in the perspective that it covers the extreme range of fibrinogen from 1.0 to 6 g/L. PT based QCM-D platform for plasma application proved better alternative to that of 'gold standard' and it paves the path towards routine laboratory method.

Real-time QCM-D monitoring of cancer cell death early events in a dynamic context

Since a few years, the acoustic sensing of whole cell is the focus of increasing interest for monitoring the cytoskeletal cellular response to morphological modulators. We aimed at illustrating the potentialities of the quartz crystal microbalance with dissipation (QCM-D) technique for the real-time detection of the earliest morphological changes that occur at the cell-substrate interface during programmed cell death. Human breast cancer cells (MCF-7) grown on serum protein-coated gold sensors were placed in dynamic conditions under a continuous medium flow. The mass and viscoelasticity changes of the cells were tracked by monitoring the frequency and dissipation shifts during the first 4h of cell exposure to staurosporine, a well-known apoptosis inducer. We have identified a QCM-D signature characteristic of morphological modifications and cell detachment from the sensing surface that are related to the pro-apoptotic treatment. In particular, for low staurosporine doses below 1µM, we showed that recording the dissipation shift allows to detect an early cell response which is undetectable after the same duration by the classical analytical techniques in cell biology. Furthermore, this sensing method allows quantifying the efficiency of the drug effect in less than 4h without requiring labeling and without interfering in the system, thus preventing any loss of information. In the actual context of targeted cancer therapy development, we believe that these results bring new insights in favor of the use of the non invasive QCM-D technique for quickly probing the cancer cell sensitivity to death inducer drugs.

Vesicle deposition and subsequent membrane–melittin interactions on different substrates: A QCM-D experiment

Quartz crystal microbalance with dissipation (QCM-D) technique is one of the most effective methods to monitor the dynamic behaviors of a layer on a solid surface. Moreover, it has been reported recently that it is able to provide a fingerprint for the peptide–membrane interactions. In this work, QCM-D technique combined with computer simulations was employed to investigate the deposition and transformation of vesicles, as well as the subsequent membrane–melittin interactions on different substrates. A range of substrate surfaces, i.e. naked SiO2 without or with Au/polyelectrolyte coating, were produced. The nature of the substrate determined whether the adsorbed vesicles were present as a high-quality supported bilayer or an assembled vesicle matrix, which consequently influenced the membrane–melittin interactions. It was indicated by the related computer simulations that the lipid packing state of the membrane was a key factor to determine the mechanism of membrane–peptide interactions. Furthermore, this work might be a good example of the application of QCM-D for the exploration of membrane-active peptides.

Reversible Changes in Cell Morphology due to Cytoskeletal Rearrangements Measured in Real-Time by QCM-D

The mechanical properties and responses of cells to external stimuli (including drugs) are closely connected to important phenomena such as cell spreading, motility, activity, and potentially even differentiation. Here, reversible changes in the viscoelastic properties of surface-attached fibroblasts were induced by the cytoskeleton-perturbing agent cytochalasin D, and studied in real-time by the quartz crystal microbalance with dissipation (QCM-D) technique. QCM-D is a surface sensitive technique that measures changes in (dynamically coupled) mass and viscoelastic properties close to the sensor surface, within a distance into the cell that is usually only a fraction of its size. In this work, QCM-D was combined with light microscopy to study in situ cell attachment and spreading. Overtone-dependent changes of the QCM-D responses (frequency and dissipation shifts) were first recorded, as fibroblast cells attached to protein-coated sensors in a window equipped flow module. Then, as the cell layer had stabilised, morphological changes were induced in the cells by injecting cytochalasin D. This caused changes in the QCM-D signals that were reversible in the sense that they disappeared upon removal of cytochalasin D. These results are compared to other cell QCM-D studies. Our results stress the combination of QCM-D and light microscopy to help interpret QCM-D results obtained in cell assays and thus suggests a direction to develop the QCM-D technique as an even more useful tool for real-time cell studies.

Watching cellulose grow – Kinetic investigations on cellulose thin film formation at the gas–solid interface using a quartz crystal microbalance with dissipation (QCM-D)

The conversion of trimethylsilyl cellulose (TMSC) to cellulose films via acid vapor hydrolysis is investigated at the gas solid interface in situ, in real time and under ambient conditions using the QCM-D technique. For this purpose, a permanent flow of gaseous HCl is employed which reacts with TMSC spun on QCM sensors to form cellulose films. The kinetics behind this reaction is elucidated and reveals first order. This desilylation reaction proceeds via a fast first phase (k=3.01×10−3s−1) and a second slower phase (k=6.29×10−5s−1) where less accessible silyl groups are cleaved off. Besides kinetics, film thicknesses have been determined using the QCM method. Moreover, the influence of the acid concentration on the kinetics and layer thickness was studied. A comparison between the materials synthesized in the QCM chamber with those obtained by classical vapor phase hydrolysis does not show any differences in the surface characteristics and composition as proven by X-ray photoelectron spectroscopy, atomic force microscopy, and wettability studies.

生体セラミックスの表面機能化技術の開発

Hydroxyapatite [Ca10(PO4)6(OH)2, HAp] is a major inorganic component of bone and teeth tissues and has the excellent biocompatibility and high osteoconductivity. The interactions between HAp and protein or cell have been studied. The HAp related bioceramics such as bone substitute, coating substance of metal implants, inorganic-polymer composites, and cell culture. We described two methods; (1) surface modification of HAp using organosilane; (2) fabrication of HAp ultra-thin layer on gold surface for protein adsorption analyzed with QCM-D technique. The interfacial interaction between collagen and HAp in a nano-region was controlled by depositing the organosilane of n-octadecyltrimethoxysilane (ODS: -CH3) or aminopropyltriethoxysilane (APTS: -NH2) with a chemical vapor deposition method. The morphologies of collagen adsorbed on the surfaces of HAp and HAp deposited with APTS were similar, however that of the surface with ODS was apparently different, due to the hydrophobic interaction between the organic head group of -CH3 and residual groups of collagen. We present a method for coating gold quartz crystal microbalance with dissipation (QCM-D) sensor with ultra-thin layer of hydroxyapatite nanocrystals evenly covering and tightly bound to the surface. The hydroxyapatite sensor operated in liquid with high stability and sensitivity. The in-situ adsorption mechanism and conformational change of fibrinogen on gold, titanium and hydroxyapatite surfaces were investigated by QCM-D technique and Fourier-transform infrared spectroscopy. The study indicates that the hydroxyapatite sensor is applicable for qualitative and conformational analysis of protein adsorption.

In situ kinetic study of zinc sulfide activation using a quartz crystal microbalance with dissipation (QCM-D)

We have studied the activation kinetics of zinc sulfide (ZnS) using silver as an activator by a quartz crystal microbalance with dissipation (QCM-D). The zinc sulfide coating on QCM-D sensor was shown to have similar crystallographic structure, composition, and surface properties as nature sphalerite through the characterization of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and xanthate adsorption measurement using QCM-D. The activation of ZnS sensor by silver was confirmed by the mass increase in ZnS sensor coupled with subsequent xanthate adsorption during QCM-D measurement, the change of surface wettability, and the presence of Ag2S on the surface. Two distinct stages on the silver uptake vs. time curve were identified and fitted well by a logarithmic function for the initial stage and a parabolic law in the later stage, which agrees with the two-stage zinc–silver reaction kinetics reported previously. Argon sputtering followed by XPS measurement on the ZnS surface demonstrated the penetration of silver into the bulk ZnS after activation. The present study is the first of its kind to apply the QCM-D technique to investigate sphalerite activation, which introduces a new in situ approach to investigate surface adsorption and activation in many mineral processes and surface modifications.

Competitive adsorption of fibronectin and albumin on hydroxyapatite nanocrystals

Competitive adsorption of two-component solutions containing fibronectin (Fn) and albumin (Ab) on hydroxyapatite (HAp) nanocrystals was analyzed in situ using the quartz crystal microbalance with dissipation (QCM-D) technique. Adsorption of the one-component protein (Fn or Ab) and the two-component proteins adjusted to different molar ratios of Fn to Ab at a fixed Fn concentration was investigated. The frequency shift (Δf; Hz) and the dissipation energy shift (ΔD) were measured with the QCM-D technique, and the viscoelastic changes of adlayers were evaluated by the saturated ΔD/Δf value and the Voigt-based viscoelastic model. For the adsorption of the one-component protein, the Fn adlayer showed a larger mass and higher viscoelasticity than the Ab adlayer, indicating the higher affinity of Fn on HAp. For the adsorption of the two-component proteins, the viscoelastic properties of the adlayers became elastic with increase in Ab concentration, whereas the adsorption mass was similar to that of Fn in the one-component solution regardless of the Ab concentration. The specific binding mass of the Ab antibody to the adlayers increased with increase in Ab concentration, whereas that of the Fn antibody decreased. Therefore, Fn preferentially adsorbs on HAp and Ab subsequently interacts with the adlayers, indicating that the interfacial viscoelasticity of the adlayers was dominated by the interaction between Fn and Ab.

Detection of Interfacial Phenomena with Osteoblast-like Cell Adhesion on Hydroxyapatite and Oxidized Polystyrene by the Quartz Crystal Microbalance with Dissipation

The adhesion process of osteoblast-like cells on hydroxyapatite (HAp) and oxidized polystyrene (PSox) was investigated using a quartz crystal microbalance with dissipation (QCM-D), confocal laser scanning microscope (CLSM), and atomic force microscope (AFM) techniques in order to clarify the interfacial phenomena between the surfaces and cells. The interfacial viscoelastic properties (shear viscosity (η(ad)), elastic shear modulus (μ(ad)), and tan δ) of the preadsorbed protein layer and the interface layer between the surfaces and cells were estimated using a Voigt-based viscoelastic model from the measured frequency (Δf) and dissipation shift (ΔD) curves. In the ΔD-Δf plots, the cell adhesion process on HAp was classified as (1) a mass increase only, (2) increases in both mass and ΔD, and (3) slight decreases in mass and ΔD. On PSox, only ΔD increases were observed, indicating that the adhesion behavior depended on the surface properties. The interfacial μ(ad) value between the material surfaces and cells increased with the number of adherent cells, whereas η(ad) and tanδ decreased slightly, irrespective of the surface. Thus, the interfacial layer changed the elasticity to viscosity with an increase in the number. The tan δ values on HAp were higher than those on PSox and exceeded 1.0. Furthermore, the pseudopod-like structures of the cells on HAp had periodic stripe patterns stained with a type I collagen antibody, whereas those on PSox had cell-membrane-like structures unstained with type I collagen. These results indicate that the interfacial layers on PSox and HAp exhibit elasticity and viscosity, respectively, indicating that the rearrangements of the extracellular matrix and cytoskeleton changes cause different cell-surface interactions. Therefore, the different cell adhesion process, interfacial viscoelasticity, and morphology depending on the surfaces were successfully monitored in situ and evaluated by the QCM-D technique combined with other techniques.