Monitoring of adsorption behaviors of bovine serum albumin onto a stainless steel surface by the quartz crystal microbalance based on admittance analysis

Influence of titanium nanoscale surface roughness on fibrinogen and albumin protein adsorption kinetics and platelet responses

Biomaterials with nanoscale topography have been increasingly investigated for medical device applications to improve tissue-material interactions. This study assessed the impact of nanoengineered titanium surface domain sizes on early biological responses that can significantly affect tissue interactions. Nanostructured titanium coatings with distinct nanoscale surface roughness were deposited on quartz crystal microbalance with dissipation (QCM-D) sensors by physical vapor deposition. Physico-chemical characterization was conducted to assess nanoscale surface roughness, nano-topographical morphology, wettability, and atomic composition. The results demonstrated increased projected surface area and hydrophilicity with increasing nanoscale surface roughness. The adsorption properties of albumin and fibrinogen, two major plasma proteins that readily encounter implanted surfaces, on the nanostructured surfaces were measured using QCM-D. Significant differences in the amounts and viscoelastic properties of adsorbed proteins were observed, dependent on the surface roughness, protein type, protein concentration, and protein binding affinity. The impact of protein adsorption on subsequent biological responses was also examined using qualitative and quantitative in vitro evaluation of human platelet adhesion, aggregation, and activation. Qualitative platelet morphology assessment indicated increased platelet activation/aggregation on titanium surfaces with increased roughness. These data suggest that nanoscale differences in titanium surface roughness influence biological responses that may affect implant integration.

Real time monitoring and evaluation of the inhibition effect of fucoxanthin against α-amylase activity by using QCM-A

The main symptoms of diabetes are hyperglycemia and insulin resistance. The inhibition of the starch digestion enzymes could effectively regulate starch digestion and glucose absorption, thereby slowing or treating the symptoms of postprandial hyperglycemia. Herein, we used fucoxanthin isolated from Undaria pinnatifida stems, as α-amylase inhibitor, and monitored the interactions of both biomolecules by using quartz crystal microbalance-admittance (QCM-A) instrument. All the processes of α-amylase hydrolysis of starch were also dynamically tracked by using amylose-immobilized QCM technology. In our work, we found that the kinetic parameter (k off, k on, and k cat) values obtained by the QCM-A analysis were relatively consistent compared to the kinetic parameter values obtained by the conventional Michaelis-Menten analysis. For the inhibitory reactions, the results showed that fucoxanthin significantly reduced the activity of α-amylase in a dose-dependent manner. The QCM-A technology shown to be an excellent approach in obtaining comprehensive and accurate kinetic parameters, thereby providing real and accurate data for kinetic studies. It is helpful to clarify the mechanism of action of fucoxanthin on α-amylase, which further proved the potential of fucoxanthin to improve and treat postprandial hyperglycemia.

Label-Free Protein Detection by Micro-Acoustic Biosensor Coupled with Electrical Field Sorting. Theoretical Study in Urine Models

Diagnostic devices for point-of-care (POC) urine analysis (urinalysis) based on microfluidic technology have been actively developing for several decades as an alternative to laboratory based biochemical assays. Urine proteins (albumin, immunoglobulins, uromodulin, haemoglobin etc.) are important biomarkers of various pathological conditions and should be selectively detected by urinalysis sensors. The challenge is a determination of different oligomeric forms of the same protein, e.g., uromodulin, which have similar bio-chemical affinity but different physical properties. For the selective detection of different types of proteins, we propose to use a shear bulk acoustic resonator sensor with an additional electrode on the upper part of the bioliquid-filled channel for protein electric field manipulation. It causes modulation of the protein concentration over time in the near-surface region of the acoustic sensor, that allows to distinguish proteins based on their differences in diffusion coefficients (or sizes) and zeta-potentials. Moreover, in order to improve the sensitivity to density, we propose to use structured sensor interface. A numerical study of this approach for the detection of proteins was carried out using the example of albumin, immunoglobulin, and oligomeric forms of uromodulin in model urine solutions. In this contribution we prove the proposed concept with numerical studies for the detection of albumin, immunoglobulin, and oligomeric forms of uromodulin in urine models.

Hybrid Sensor Device for Simultaneous Surface Plasmon Resonance and Surface Acoustic Wave Measurements

Surface plasmon resonance (SPR) and Love wave (LW) surface acoustic wave (SAW) sensors have been established as reliable biosensing technologies for label-free, real-time monitoring of biomolecular interactions. This work reports the development of a combined SPR/LW-SAW platform to facilitate simultaneous optical and acoustic measurements for the investigation of biomolecules binding on a single surface. The system’s output provides recordings of two acoustic parameters, phase and amplitude of a Love wave, synchronized with SPR readings. We present the design and manufacturing of a novel experimental set-up employing, in addition to the SPR/LW-SAW device, a 3D-printed plastic holder combined with a PDMS microfluidic cell so that the platform can be used in a flow-through mode. The system was evaluated in a systematic study of the optical and acoustic responses for different surface perturbations, i.e., rigid mass loading (Au deposition), pure viscous loading (glycerol and sucrose solutions) and protein adsorption (BSA). Our results provide the theoretical and experimental basis for future application of the combined system to other biochemical and biophysical studies.

Designing a Bioinert Surface by Simple Coating with Cholesterol End-Modified Poly(ethylene glycol)

A bioinert surface has been designed by simple coating with cholesterol end-modified poly(ethylene glycol), Chol-U-Pr-mPEG, using a cholesterol anchor. A poly(propylene) (PP) surface was immersed into the Chol-U-Pr-mPEG aqueous solution, where control mPEGs without cholesterol were not suitable for the design of bioinert surfaces. The resulting surfaces coated with Chol-U-Pr-mPEG above and below its critical micelle concentration were swollen and less swollen, respectively. Chol-U-Pr-mPEG with a molecular weight of 2000, Chol-U-Pr-mPEG (2k), formed a swollen layer with a thickness of 10-15 nm and adhered to the PP surface with an estimated K_d value of 4.4×10^-7 M. The resulting Chol-U-Pr-mPEG (2k)-coated surface with the swollen layer suppressed the adsorption of γ-globulin proteins and the adhesion of platelets in plasma. Although the PP surface coated with Chol-U-Pr-mPEG with a molecular weight of 5000, Chol-U-Pr-mPEG (5k), also suppressed the adsorption of γ-globulin proteins, the Chol-U-Pr-mPEG (5k)-coated PP surface did not suppress the adhesion of the platelets in plasma despite the existence of a swollen layer with a thickness of 20-25 nm. These results suggest that the Chol-U-Pr-mPEG-coated PP surface with an optimized swollen layer has been established as a bioinert surface by a facile method.

Radial Wicking of Biological Fluids in Paper

In this study, we analyze stain growth kinetics from droplets of biological fluids such as blood, plasma, and protein solutions on paper both experimentally and numerically. The primary difference of biological fluids from a simple fluid is a significant wetting/dewetting hysteresis in paper. This becomes important in later stages of droplet wicking, after the droplet has been completely absorbed into paper. This is shown by anomalous power dependence of area with time in the later stages of radial wicking. At early stages, current numerical wicking models can predict stain growth of biological fluids. However, at later stages, the introduction of hysteresis complicates modeling significantly. We show that the cause of the observed hysteresis is due to contact angle effects and that this is the dominant mechanism that leads to the anomalous stain growth kinetics measured uniquely in biological fluids. Results presented will streamline the design process of paper-based diagnostics, allowing a modeling approach instead of a trial and error method.

Stirring rate affects thermodynamics and unfolding kinetics in isothermal titration calorimetry

Isothermal titration calorimetry (ITC) directly provides thermodynamic parameters depicting the energetics of intermolecular interactions in solution. During ITC experiments, a titration syringe with a paddle is continuously rotating to promote a homogeneous mixing. Here, we clarified that the shape of the paddles (flat, corkscrew and small-pitched corkscrew) and the stirring rates influence on the thermodynamic parameters of protein-ligand interaction. Stirring with the flat paddle at lower and higher rate both yielded a lower exothermic heat due to different reasons. The complete reaction with no incompetent fractions was achieved only when the stirring was performed at 500 or 750 rpm using the small-pitched corkscrew paddle. The evaluation of the protein solution after 1,500 rpm stirring indicated that proteins in the soluble fraction decreased to 94% of the initial amount, among which 6% was at an unfolded state. In addition, a significant increase of micron aggregates was confirmed. Furthermore, a new approach for the determination of the unfolding kinetics based on the time dependence of the total reaction heat was developed. This study demonstrates that a proper stirring rate and paddle shape are essential for the reliable estimation of thermodynamic parameters in ITC experiments.

End Point Versus Backbone Specificity Governs Characteristics of Antibody Binding to Poly(ethylene glycol) Brushes

End-grafted poly(ethylene glycol) (PEG) brushes are widely used in order to suppress undesired protein adsorption to surfaces exposed to blood or other biological fluids. The specific adsorption of antibodies (Abs) to PEG brushes associated with PEG's antigenicity is drawing increasing attention because it can affect clinical applications. Here, the adsorption to PEG brushes of two Ab types, specifically binding the polymer backbone and the polymer endpoints, is structurally characterized by neutron reflectometry. The measurements yield volume fraction profiles of PEG and of the adsorbed Abs with sub-nanometer resolution perpendicular to the surface. For all brush parameters in terms of grafting density and polymerization degree, the Ab profiles clearly differ between backbone binders and endpoint binders. The adsorbed Ab amount per unit area is substantial for both Ab types and for all brush parameters investigated, even for dense brushes, which impose a considerable osmotic barrier to Ab insertion. The results therefore indicate that variation of brush parameters alone is insufficient to prevent undesired Ab adsorption. Instead, our work motivates further efforts in the search for nonantigenic brush chemistry.

Neutron Reflectometry Elucidates Protein Adsorption from Human Blood Serum onto PEG Brushes

Poly(ethylene glycol) (PEG) brushes are reputed for their ability to prevent undesired protein adsorption to material surfaces exposed to biological fluids. Here, protein adsorption out of human blood serum onto PEG brushes anchored to solid-supported lipid monolayers was characterized by neutron reflectometry, yielding volume fraction profiles of lipid headgroups, PEG, and adsorbed proteins at subnanometer resolution. For both PEGylated and non-PEGylated lipid surfaces, serum proteins adsorb as a thin layer of approximately 10 Å, overlapping with the headgroup region. This layer corresponds to primary adsorption at the grafting surface and resists rinsing. A second diffuse protein layer overlaps with the periphery of the PEG brush and is attributed to ternary adsorption due to protein-PEG attraction. This second layer disappears upon rinsing, thus providing a first observation of the structural effect of rinsing on protein adsorption to PEG brushes.