Viscoelastic properties of fibrinogen adsorbed onto poly(ethylene terephthalate) surfaces by QCM-D

Structural changes of hemicellulose during pulping process and its interaction with nanocellulose

It is believed that hemicellulose plays a crucial role in binding cellulose and lignin in plant cells. It may provide significant implications through figuring out the interaction between hemicellulose and microfibers and gaining insights how the structure of hemicellulose affects its association with cellulose nanofibers. Herein, the hemicellulose and nanocellulose fractions from pulps obtained by controlling the H-factors of kraft pulping process were quantitatively evaluated for their adsorption behavior using QCM-D. The results showed that harsher cooking (corresponding to high H-factor) significantly affected the chemical composition of hemicellulose, leading to a decrease of its molecular weight and gradually turning it into a linear structure. Hemicellulose possesses a strong natural affinity for CNC-coated sensors. The hemicellulose from the pulp cooked by high H-factor process decreases its ability to adsorb onto nanocellulose, the adsorption rate also slows down, and the conformation of the adsorbed layer changes which makes the binding weak and reversible. In conclusion, the pulping process in high H-factor significantly changed the structure of hemicellulose, leading to a variation in the strength of its interaction with nanocellulose.

Amphiphilic Lignin Nanoparticles Made from Lignin-Acrylic Acid-Methyl Methacrylate Copolymers

In this study, a novel amphiphilic KL-AA-MMA nanoparticle was prepared through the graft copolymerization of kraft lignin (KL) with acrylic acid (AA) and methyl methacrylate (MMA), using potassium persulfate as an initiator in a water/dimethyl sulfoxide solvent medium, which was followed by the nanoprecipitation technique using dimethylformamide as a solvent and deionized water as an antisolvent. The successful graft polymerization was verified by ¹H-nuclear magnetic resonance (NMR), ³¹P-NMR, and Fourier transform infrared (FTIR) analyses; and the grafting yield of the generated KL-AA-MMA copolymer ranged from 68.2% to 96.5%. Transmission electron microscopy (TEM) observation revealed the formation of amorphous KL-AA-MMA nanoparticles. Additionally, KL-AA-MMA9 nanoparticles with the highest yield exhibited the minimum hydrodynamic diameter and polydispersity of 261 nm and 0.153, respectively. Moreover, the amphiphilicity of KL-AA-MMA nanoparticles was significantly improved by the grafting of MMA monomers. Finally, the adsorption performance of KL-AA-MMA nanoparticles at the xylene interface was evaluated by a quartz crystal microbalance with dissipation (QCM-D). The results demonstrated that the most amphiphilic sample, KL-AA-MMA9 nanoparticles, with the smallest hydrodynamic size displayed the highest adsorption on the oil/water interface. This product provides a wide range of applications in oil/water emulsions.

Polystyrene sulfonate is effective for enhancing biomass enzymatic saccharification under green liquor pretreatment in bioenergy poplar

BACKGROUND

Water-soluble lignin (particularly lignosulfonate, LS) has been well documented for its significance on enzymatic saccharification of lignocellulose, though the promotion mechanism has not been fully understood. Much attention has been paid to natural lignin or its derivatives. The disadvantage of using natural lignin-based polymers as promoting agents lies in the difficulty in tailor-incorporating functional groups due to their complex 3D structures. To further improve our understanding on the promotion mechanism of water-soluble lignin in the bioconversion of lignocellulose and to pursue better alternatives with different skeleton structures other than natural lignin, herein we reported a synthetic soluble linear aromatic polymer, sodium polystyrene sulfonate (PSS), to mimic LS for enhancing the efficiency of enzymatic saccharification.

RESULTS

The role of PSS in enzymatic saccharification of pure cellulose and green liquor-pretreated poplar (GL-P) was explored by analyzing substrate enzymatic digestibility (SED) under different addition dosages and various pH media, along with LS for comparison. At the cellulase loading of 13.3 FPU/g-glucan, the glucose yield of GL-P increased from 53% for the control to 81.5% with PSS addition of 0.1 g/g-substrate. It outperformed LS with the addition of 0.2 g/g-substrate by 6.3%. In the pH range from 4.5 to 6, PSS showed a positive effect on lignocellulose saccharification with the optimum pH at 4.8, where the most pronounced SED of GL-P was achieved. The underlying mechanism was unveiled by measuring zeta potential and using Quartz Crystal Microbalance (QCM) and Multi-parametric Surface Plasmon Resonance (MP-SPR). The results confirmed that the complexes of cellulase and PSS were conjugated and the negatively supercharged complexes reduced non-productive binding effectively along with the improved saccharification efficiency. The thickness of PSS required to block the binding sites of cellulase film was less than half of that of LS, and the PSS adlayer on cellulase film is also more hydrated and with a much lower shear modulus than LS adlayer.

CONCLUSIONS

PSS as LS analogue is effective for enhancing the biomass enzymatic saccharification of GL-pretreated poplar. PSS exhibited a severer inhibition on the enzymatic saccharification of pure cellulose, while a more positive effect on bioconversion of lignocellulose (GL-P) than LS. In addition, a much lower dosage is required by PSS. The dynamic enzymatic hydrolysis indicated PSS could prolong the processive activity of cellulase. The valid data stemmed from QCM and SPR expressed that PSS bound to cellulases and the as-formed complexes reduced the non-productive adsorption of cellulase onto substrate lignin more efficiently than LS due to its flexible skeleton and highly hydrated structure. Therefore, PSS is a promising alternative promoting agent for lignocellulose saccharification. From another perspective, the synthetic lignin mimics with controllable structures enable us to reach an in-depth understanding of the promotion mechanism of soluble lignins on enzymatic saccharification.

Adsorption and Conformation Behavior of Lysozyme on a Gold Surface Determined by QCM-D, MP-SPR, and FTIR

The physicochemical properties of protein layers at the solid–liquid interface are essential in many biological processes. This study aimed to link the structural analysis of adsorbed lysozyme at the water/gold surface at pH 7.5 in a wide range of concentrations. Particular attention was paid to the protein’s structural stability and the hydration of the protein layers formed at the interface. Complementary methods such as multi-parameter surface plasmon resonance (MP-SPR), quartz crystal microbalance with energy dissipation (QCM-D), and infrared spectroscopy (FTIR) were used for this purpose. The MP-SPR and QCM-D studies showed that, during the formation of a monolayer on the gold surface, the molecules’ orientation changes from side-on to end-on. In addition, bilayer formation is observed when adsorbing in the high-volume concentration range >500 ppm. The degree of hydration of the monolayer and bilayer varies depending on the degree of surface coverage. The hydration of the system decreases with filling the layer in both the monolayer and the bilayer. Hydration for the monolayer varies in the range of 50–70%, because the bilayer is much higher than 80%. The degree of hydration of the adsorption layer has a crucial influence on the protein layers’ viscoelastic properties. In general, an increase in the filling of a layer is characterized by a rise in its rigidity. The use of infrared spectroscopy allowed us to determine the changes taking place in the secondary structure of lysozyme due to its interaction with the gold surface. Upon adsorption, the content of II-structures corresponding to β-turn and random lysozyme structures increases, with a simultaneous decrease in the content of the β-sheet. The increase in the range of β-turn in the structure determines the lysozyme structure’s stability and prevents its aggregation.

New insights into interaction of proteins in extracellular polymeric substances of activated sludge with ciprofloxacin using quartz crystal microbalance with dissipation

Proteins in extracellular polymeric substances play a vital role in adsorbing organic contaminants in biological wastewater treatment processes, but there is still lack of a fast and effective approach to monitor their interaction. Quartz crystal microbalance with dissipation (QCM-D) was used to investigate the binding and viscoelastic properties of ciprofloxacin (CIP) on extracellular proteins from activated sludge by a two-step sequential deposition method. A saturated viscoelastic monolayer of proteins was formed on the crystal by injecting 500 mg L^-1 extracellular proteins. Binding of CIP with the extracellular proteins film followed the pseudo-first-order kinetic equation and Langmuir model, with the maximum binding capacity of 172.4 mg g^-1. The binding mass, energy dissipation, and reaction rate constant increased with increasing CIP concentration. A strong binding was obtained at pH 5, suggesting electrostatic interactions as the dominating binding mechanism. Cations inhibited CIP binding with extracellular proteins, probably due to cations competition. Two binding periods were distinguished according to the viscoelastic properties of CIP layer: viscous binding in the initial period and elastic towards binding saturation. Results highlighted QCM-D as an effective and real-time technique to evaluate the role of extracellular proteins in contaminants removal.

Biocompatibility of Plasma-Treated Polymeric Implants

Cardiovascular diseases are one of the main causes of mortality in the modern world. Scientist all around the world are trying to improve medical treatment, but the success of the treatment significantly depends on the stage of disease progression. In the last phase of disease, the treatment is possible only by implantation of artificial graft. Most commonly used materials for artificial grafts are polymer materials. Despite different industrial procedures for graft fabrication, their properties are still not optimal. Grafts with small diameters (<6 mm) are the most problematic, because the platelets are more likely to re-adhere. This causes thrombus formation. Recent findings indicate that platelet adhesion is primarily influenced by blood plasma proteins that adsorb to the surface immediately after contact of a synthetic material with blood. Fibrinogen is a key blood protein responsible for the mechanisms of activation, adhesion and aggregation of platelets. Plasma treatment is considered as one of the promising methods for improving hemocompatibility of synthetic materials. Another method is endothelialization of materials with Human Umbilical Vein Endothelial cells, thus forming a uniform layer of endothelial cells on the surface. Extensive literature review led to the conclusion that in this area, despite numerous studies there are no available standardized methods for testing the hemocompatibility of biomaterials. In this review paper, the most promising methods to gain biocompatibility of synthetic materials are reported; several hypotheses to explain the improvement in hemocompatibility of plasma treated polymer surfaces are proposed.

Synergistic effect of lignin incorporation into polystyrene for producing sustainable superadsorbent

Lignin has gained intensive interest as an excellent raw material for the generation of advanced green products. Polystyrene (PS) is known for its worldwide application in water purification processes. To induce a sustainable PS, kraft lignin (KL) and polystyrene were polymerized via free radical polymerization in a facile aqueous emulsion process. KL enhanced surface area and porosity of PS. The physicochemical properties of induced KL–PS were analyzed, and the fate of lignin in KL–PS was discussed fundamentally. Wettability and surface energy analyses were implemented to monitor the surface properties of KL, PS and KL–PS. Incorporation of KL in PS (40 wt%) boosted its surface energy and oxygen content, which led to KL–PS with better compatibility than PS with copper ions in aqueous systems. A quartz crystal microbalance with dissipation (QCM-D) confirmed the noticeably higher adsorption performance of copper ion on KL–PS than on PS and KL. The sorption mechanism, which was revealed by FTIR studies, was primarily attributed to the coordination of Cu(ii) and hydroxyl group of KL–PS as well as the quadrupolar system of KL–PS.

Lignin has gained intensive interest as an excellent raw material for the generation of advanced green products.

In situ viscoelastic properties and chain conformations of heavily hydrated carboxymethyl dextran layers: a comparative study using OWLS and QCM-I chips coated with waveguide material

Hydration, viscoelastic properties and dominant structure of thin polymer layers on the surface of waveguide material were evaluated using optical waveguide lightmode spectroscopy (OWLS) and quartz crystal microbalance (QCM) methods. The fundamentally different principles of the two applied label-free biosensors enable to examine analyte layers from complementary aspects, e.g. to determine the amount of bound water in hydrated layers. In this study, a new QCM instrument with impedance measurement (QCM-I) is introduced. Its specially designed sensor chips, covered by thin film of waveguide material, supply identical surface as used in OWLS sensors, thus enabling to perform parallel measurements on the same type of surface. Viscoelastic analysis of the measured data was performed by our evaluation code developed in MATLAB environment, using the Voinova's Voigt-based model. In situ deposition experiments on the ultrathin films of poly(L-lysine)-graft-poly(ethylene glycol) (PLL-g-PEG) were conducted for instrumental and code validation. Additionally, a novel OWLS-QCM data evaluation methodology has been developed based on the concept of combining hydration and viscoelastic data with optical anisotropy results from OWLS measurements. This methodology provided insight into the time-dependent chain conformation of heavily hydrated nano-scaled layers, resulting in unprecedented structural, hydration and viscoelastic information on covalently grafted ultrathin carboxymethyl dextran (CMD) films. The measured mass values as well as hydration and viscoelastic properties were compared with the characteristics of PLL-g-PEG layers.

Cell and Protein Fouling Properties of Polymeric Mixtures Containing Supramolecular Poly(ethylene glycol) Additives

Fouling properties of new biomaterials are important for the performance of a material in a biological environment. Here, a set of three supramolecular polymeric additives consisting of ureidopyrimidinone (UPy)-functionalized poly(ethylene glycol) (UPyPEG) were formulated with UPy-modified polycaprolactone into thin supramolecular material films. The antifouling properties of these material films were determined by investigation of the relation of cell adhesion and protein adsorption on these materials films. The presence of the UPyPEG additives at the surface of the films was evident by an increased hydrophilicity. Adhesion of human epithelial and endothelial cells was strongly reduced for two of the UPyPEG-containing films. Analysis of adsorption of the first three proteins from the Vroman series, albumin, γ-globulin, and fibrinogen, using quartz crystal microbalance with dissipation in combination with viscoelastic modeling, revealed that the surfaces containing the UPyPEG additives had a limited effect on adsorption of these proteins. Despite a limited reduction of protein adsorption, UPyPEG-containing mixtures were non-cell-adhesive, which shows that non-cell-adhesive properties of supramolecular polymer surfaces are not always directly correlated to protein adsorption.

Degradation of Albumin on Plasma-Treated Polystyrene by Soft X-ray Exposure

Thin films of human serum albumin (HSA) were immobilized on polystyrene (PS) substrates previously functionalized either with polar or nonpolar functional groups. The functionalization was performed by treatment with cold gaseous plasma created in pure oxygen and tetrafluoromethane (CF₄) plasmas, respectively. Samples were examined with soft X-rays in the photon energy range of 520 to 710 eV in the ANTARES beam line at SOLEIL Synchrotron. NEXAFS spectra of O K-edge and F K-edge were collected at different spots of the sample, and measurements at each spot were repeated many times. A strong degradation of the HSA protein was observed. The weakly irradiated samples exhibited strong absorption at 531.5 eV associated with the O 1s→π*_amide transitions, and a broad non distinctive peak at 540 eV was attributed to the O 1s→σ*_C–O transitions. Both peaks decreased with increasing irradiation time until they were completely replaced by a broad non-distinctive peak at around 532 eV, indicating the destruction of the original protein conformation. The shortage of the amide groups indicated breakage of the peptide bonds.

Utilisation of Quartz Crystal Microbalance Sensors with Dissipation (QCM-D) for a Clauss Fibrinogen Assay in Comparison with Common Coagulation Reference Methods

The determination of fibrinogen levels is one of the most important coagulation measurements in medicine. It plays a crucial part in diagnostic and therapeutic decisions, often associated with time-critical conditions. The commonly used measurement is the Clauss fibrinogen assay (CFA) where plasma is activated by thrombin reagent and which is conducted by mechanical/turbidimetric devices. As quartz crystal microbalance sensors with dissipation (QCM-D) based devices have a small footprint, can be operated easily and allow measurements independently from sample transportation time, laboratory location, availability and opening hours, they offer a great opportunity to complement laboratory CFA measurements. Therefore, the objective of the work was to (1) transfer the CFA to the QCM-D method; (2) develop an easy, time- and cost-effective procedure and (3) compare the results with references. Different sensor coatings (donor’s own plasma; gold surface) and different QCM-D parameters (frequency signal shift; its calculated turning point; dissipation signal shift) were sampled. The results demonstrate the suitability for a QCM-D-based CFA in physiological fibrinogen ranges. Results were obtained in less than 1 min and in very good agreement with a standardized reference (Merlin coagulometer). The results provide a good basis for further investigation and pave the way to a possible application of QCM-D in clinical and non-clinical routine in the medical field.

Protein-targeted corona phase molecular recognition

Corona phase molecular recognition (CoPhMoRe) uses a heteropolymer adsorbed onto and templated by a nanoparticle surface to recognize a specific target analyte. This method has not yet been extended to macromolecular analytes, including proteins. Herein we develop a variant of a CoPhMoRe screening procedure of single-walled carbon nanotubes (SWCNT) and use it against a panel of human blood proteins, revealing a specific corona phase that recognizes fibrinogen with high selectivity. In response to fibrinogen binding, SWCNT fluorescence decreases by >80% at saturation. Sequential binding of the three fibrinogen nodules is suggested by selective fluorescence quenching by isolated sub-domains and validated by the quenching kinetics. The fibrinogen recognition also occurs in serum environment, at the clinically relevant fibrinogen concentrations in the human blood. These results open new avenues for synthetic, non-biological antibody analogues that recognize biological macromolecules, and hold great promise for medical and clinical applications.

Corona phase molecular recognition (CoPhMoRe) involves the deposition of a heteropolymer onto a nanoparticle surface, providing a recognition site for a given analyte. Here, the authors show that CoPhMoRe can be used to selectively detect proteins (fibrinogen) with high selectivity, including in a complex serum environment.

Fibrinogen adsorption mechanisms at the gold substrate revealed by QCM-D measurements and RSA modeling

Adsorption kinetics of fibrinogen at a gold substrate at various pHs was thoroughly studied using the QCM-D method. The experimental were interpreted in terms of theoretical calculations performed according to the random sequential adsorption model (RSA). In this way, the hydration functions and water factors of fibrinogen monolayers were quantitatively evaluated at various pHs. It was revealed that for the lower range of fibrinogen coverage the hydration function were considerably lower than previously obtained for the silica sensor [33]. The lower hydration of fibrinogen monolayers on the gold sensor was attributed to its higher roughness. However, for higher fibrinogen coverage the hydration functions for both sensors became identical exhibiting an universal behavior. By using the hydration functions, the fibrinogen adsorption/desorption runs derived from QCM-D measurements were converted to the Γd vs. the time relationships. This allowed to precisely determine the maximum coverage that varied between 1.6mgm(-2) at pH 3.5 and 4.5mgm(-2) at pH 7.4 (for ionic strength of 0.15M). These results agree with theoretical eRSA modeling and previous experimental data derived by using ellipsometry, OWLS and TIRF. Various fibrinogen adsorption mechanisms were revealed by exploiting the maximum coverage data. These results allow one to develop a method for preparing fibrinogen monolayers of well-controlled coverage and molecule orientation.

Interactions of hyaluronan grafted on protein surfaces studied using a quartz crystal microbalance and a surface force balance

Vocal folds are complex and multilayer-structured where the main layer is widely composed of hyaluronan (HA). The viscoelasticity of HA is key to voice production in the vocal fold as it affects the initiation and maintenance of phonation. In this study a simple layer-structured surface model was set up to mimic the structure of the vocal folds. The interactions between two opposing surfaces bearing HA were measured and characterised to analyse HA's response to the normal and shear compression at a stress level similar to that in the vocal fold. From the measurements of the quartz crystal microbalance, atomic force microscopy and the surface force balance, the osmotic pressure, normal interactions, elasticity change, volume fraction, refractive index and friction of both HA and the supporting protein layer were obtained. These findings may shed light on the physical mechanism of HA function in the vocal fold and the specific role of HA as an important component in the effective treatment of the vocal fold disease.

Binding Interactions of Keratin-Based Hair Fiber Extract to Gold, Keratin, and BMP-2

Hair-derived keratin biomaterials composed mostly of reduced keratin proteins (kerateines) have demonstrated their utility as carriers of biologics and drugs for tissue engineering. Electrostatic forces between negatively-charged keratins and biologic macromolecules allow for effective drug retention; attraction to positively-charged growth factors like bone morphogenetic protein 2 (BMP-2) has been used as a strategy for osteoinduction. In this study, the intermolecular surface and bulk interaction properties of kerateines were investigated. Thiol-rich kerateines were chemisorbed onto gold substrates to form an irreversible 2-nm rigid layer for surface plasmon resonance analysis. Kerateine-to-kerateine cohesion was observed in pH-neutral water with an equilibrium dissociation constant (KD) of 1.8 × 10(-4) M, indicating that non-coulombic attractive forces (i.e. hydrophobic and van der Waals) were at work. The association of BMP-2 to kerateine was found to be greater (KD = 1.1 × 10(-7) M), within the range of specific binding. Addition of salts (phosphate-buffered saline; PBS) shortened the Debye length or the electrostatic field influence which weakened the kerateine-BMP-2 binding (KD = 3.2 × 10(-5) M). BMP-2 in bulk kerateine gels provided a limited release in PBS (~ 10% dissociation in 4 weeks), suggesting that electrostatic intermolecular attraction was significant to retain BMP-2 within the keratin matrix. Complete dissociation between kerateine and BMP-2 occurred when the PBS pH was lowered (to 4.5), below the keratin isoelectric point of 5.3. This phenomenon can be attributed to the protonation of keratin at a lower pH, leading to positive-positive repulsion. Therefore, the dynamics of kerateine-BMP-2 binding is highly dependent on pH and salt concentration, as well as on BMP-2 solubility at different pH and molarity. The study findings may contribute to our understanding of the release kinetics of drugs from keratin biomaterials and allow for the development of better, more clinically relevant BMP-2-conjugated systems for bone repair and regeneration.

Amyloid aggregation and deposition of human islet amyloid polypeptide at membrane interfaces

Amyloid deposition of human islet amyloid polypeptide (hIAPP) within the islets of Langerhans is a pathological feature of type 2 diabetes mellitus. Substantial evidence indicates that the membrane-mediated aggregation and subsequent deposition of hIAPP are linked to dysfunction and death of pancreatic β-cells, but the molecular processes of hIAPP deposition are poorly understood. In this study, we examined the membrane-mediated aggregation and deposition of hIAPP at supported planar lipid bilayers with and without raft components (i.e. cholesterol and sphingomyelin) to provide insight into hIAPP-induced membrane dysfunction. The adsorption of hIAPP onto the bilayers was studied using a quartz crystal microbalance with dissipation monitoring, which showed enhanced accumulation of the peptide onto the bilayer containing raft components. Microscope observations demonstrated the growth of the aggregates formed from the membrane-adsorbed hIAPP. The examination of the membrane interfaces revealed that hIAPP aggregates retained the ability to associate with the membranes during the aggregation process, resulting in insertion of the aggregates into the bilayers. We also report the inhibitory effect of insulin on the hIAPP deposition. These findings demonstrate the aggregation of hIAPP at the membrane interfaces leading to amyloid deposits associated with the membrane and suggest a role for insulin in hIAPP deposition. A presumed mechanism regulating hIAPP deposition at the membrane interfaces is discussed.

Protein adsorption on various plasma-treated polyethylene terephthalate substrates

Protein adhesion and cell response to plasma-treated polymer surfaces were studied. The polymer polyethylene terephthalate (PET) was treated in either an oxygen plasma to make the surface hydrophilic, or a tetrafluoromethane CF₄ plasma to make the surface hydrophobic. The plasma source was radiofrequency (RF) discharge. The adsorption of albumin and other proteins from a cell-culture medium onto these surfaces was studied using a quartz crystal microbalance (QCM), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The cellular response to plasma-treated surfaces was studied as well using an MTT assay and scanning electron microscopy (SEM). The fastest adsorption rate was found on the hydrophilic oxygen plasma-treated sample, and the lowest was found on the pristine untreated sample. Additionally, the amount of adsorbed proteins was higher for the oxygen-plasma-treated surface, and the adsorbed layer was more viscoelastic. In addition, cell adhesion studies support this finding because the best cell adhesion was observed on oxygen-plasma-treated substrates.