Understanding protein adsorption phenomena at solid surfaces

Confinements of Thermoresponsive Dendronized Polymers to Proteins

Crowding environment created by host polymers plays crucial roles in manipulating interactions with proteins and modulating their bioactivity. Here, we report our investigation on interactions between polymers and proteins in...

Late stage of the formation of a protein corona around nanoparticles in biofluids

In biofluids containing various proteins, nanoparticles rapidly come to be surrounded by a nanometer-thick protein layer referred to as a protein corona. The late stage of this process occurs via replacement of proteins already bound to a nanoparticle by new ones. In the available kinetic models, this process is considered to include independent acts of protein detachment and attachment. It can, however, occur also at the level of protein pairs via exchange, i.e., concerted replacement of an attached protein by a newly arrived one. I argue that the exchange channel can be more important than the conventional one. To illustrate the likely specifics of the exchange channel, I present a kinetic model focused exclusively on this channel and based on the Evans-Polanyi-type relation between the activation energies of the protein-exchange steps and the protein binding energies. The corresponding kinetics were calculated for three qualitatively different distributions of proteins in solution over binding energy (with a maximum or monotonously decreasing or increasing, respectively) and are found to be similar, with relatively rapid replacement of weakly bound proteins and slow redistribution of strongly bound proteins. The ratio of the timescales characterizing the evolution of weakly and strongly bound proteins is found to depend on the type of the binding-energy distribution.

Long-term antibacterial properties of a nanostructured titanium alloy surface: An in vitro study

The demand for joint replacement and other orthopedic surgeries involving titanium implants is continuously increasing; however, 1%-2% of surgeries result in costly and devastating implant associated infections (IAIs). Pseudomonas aeruginosa and Staphylococcus aureus are two common pathogens known to colonise implants, leading to serious complications. Bioinspired surfaces with spike-like nanotopography have previously been shown to kill bacteria upon contact; however, the longer-term potential of such surfaces to prevent or delay biofilm formation is unclear. Hence, we monitored biofilm formation on control and nanostructured titanium disc surfaces over 21 days following inoculation with Pseudomonas aeruginosa and Staphylococcus aureus. We found a consistent 2-log or higher reduction in live bacteria throughout the time course for both bacteria. The biovolume on nanostructured discs was also significantly lower than control discs at all time points for both bacteria. Analysis of the biovolume revealed that for the nanostructured surface, bacteria was killed not just on the surface, but at locations above the surface. Interestingly, pockets of bacterial regrowth on top of the biomass occurred in both bacterial species, however this was more pronounced for S. aureus cultures after 21 days. We found that the nanostructured surface showed antibacterial properties throughout this longitudinal study. To our knowledge this is the first in vitro study to show reduction in the viability of bacterial colonisation on a nanostructured surface over a clinically relevant time frame, providing potential to reduce the likelihood of implant associated infections.

High Sensitivity Label-Free Quantitative Method for Detecting Tumor Biomarkers in Human Serum by Optical Microfiber Couplers

Label-free optical fiber immunosensors have attracted widespread attention in recent decades due to their high sensitivity. However, nonspecific adsorption in serum has remained a critical bottleneck in existing label-free fiber optic biosensors, which hinders their widespread use in diagnostics. In addition, individual differences in clinical human serum (HS) negatively impact biosensing results. In this work, the modified serum preadsorption strategy was applied to reduce nonspecific adsorption by forming a saturated antifouling interface on an optical microfiber coupler (OMC). Furthermore, to reduce the effect of the differences between individual HS samples, we proposed a new method where Sigma HS was used as a wavelength shift reference due to being close to clinical serum compared to other serums. Sigma HS was used first to reduce the differences in immune sensors before performing a clinical sample test in which quantitative detection was achieved based on the independent calibration of several sensors with wide dynamic ranges via dissociation processes. The individual differences in 25% HS were corrected by 30% Sigma HS. As a proof of concept, the label-free OMC immune sensor demonstrates good sensitivity and specificity for the detection of carcinoembryonic antigen (CEA) in 25% Sigma HS at different concentrations. The detection limit of CEA reached as low as 34.6 fg/mL (0.475 fM). Additionally, label-free quantitative detection of CEA using this OMC immune sensor was verified experimentally according to the calibration line, and the results agree well with clinical examination detection. To our knowledge, it is the first study to employ an OMC immune sensor in point-of-care label-free quantitative detection for clinical HS.

Fibronectin-Enriched Biomaterials, Biofunctionalization, and Proactivity: A Review

Modern innovation in reconstructive medicine implies the proposition of material-based strategies suitable for tissue repair and regeneration. The development of such systems necessitates the design of advanced materials and the control of their interactions with their surrounding cellular and molecular microenvironments. Biomaterials must actively engage cellular matter to direct and modulate biological responses at implant sites and beyond. Indeed, it is essential that a true dialogue exists between the implanted device and the cells. Biomaterial engineering implies the knowledge and control of cell fate considering the globality of the adhesion process, from initial cell attachment to differentiation. The extracellular matrix (ECM) represents a complex microenvironment able to meet these essential needs to establish a relationship between the material and the contacting cells. The ECM exhibits specific physical, chemical, and biochemical characteristics. Considering the complexity, heterogeneity, and versatility of ECM actors, fibronectin (Fn) has emerged among the ECM protagonists as the most pertinent representative key actor. The following review focuses on and synthesizes the research supporting the potential to use Fn in biomaterial functionalization to mimic the ECM and enhance cell–material interactions.

Control of Blood Coagulation by Hemocompatible Material Surfaces-A Review

Hemocompatibility of biomaterials in contact with the blood of patients is a prerequisite for the short- and long-term applications of medical devices such as cardiovascular stents, artificial heart valves, ventricular assist devices, catheters, blood linings and extracorporeal devices such as artificial kidneys (hemodialysis), extracorporeal membrane oxygenation (ECMO) and cardiopulmonary bypass. Although lower blood compatibility of materials and devices can be handled with systemic anticoagulation, its side effects, such as an increased bleeding risk, make materials that have a better hemocompatibility highly desirable, particularly in long-term applications. This review provides a short overview on the basic mechanisms of blood coagulation including plasmatic coagulation and blood platelets, as well as the activation of the complement system. Furthermore, a survey on concepts for tailoring the blood response of biomaterials to improve the hemocompatibility of medical devices is given which covers different approaches that either inhibit interaction of material surfaces with blood components completely or control the response of the coagulation system, blood platelets and leukocytes.

Adsorption of lysozyme into a charged confining pore

Several applications arise from the confinement of proteins on surfaces because their stability and biological activity are enhanced. It is also known that the way in which a protein adsorbs on the surface is important for its biological function since its active sites should not be obstructed. In this study, the adsorption properties of hen egg-white lysozyme, HEWL, into a negatively charged silica pore is examined by employing a coarse-grained model and constant-pH Monte Carlo simulations. The role of electrostatic interactions is taken into account via including the Debye-Hückel potentials into the Cα structure-based model. We evaluate the effects of pH, salt concentration, and pore radius on the protein preferential orientation and spatial distribution of its residues regarding the pore surface. By mapping the residues that stay closer to the pore surface, we find that the increase of pH leads to orientational changes of the adsorbed protein when the solution pH gets closer to the HEWL isoelectric point. Under these conditions, the pK_a shift of these important residues caused by the adsorption into the charged confining surface results in a HEWL charge distribution that stabilizes the adsorption in the observed protein orientation. We compare our observations to the results of the pK_a shift for HEWL available in the literature and to some experimental data.

Enhanced plasmonic processes in amino-rich plasma polymer films for applications at the biointerface

A new plasmonic biosensor was developed in a planar chip-based format by coupling the plasmonic properties of gold nanoparticles (Au NPs) with the mechanical and bioadhesive features of unconventional organic thin films deposited from plasma, namely primary amine-based plasma polymer films (PPFs). A self-assembled layer of spherical Au NPs, 12 nm in diameter, was electrostatically immobilized onto optically transparent silanised glass. In the next step, the Au NP layer was coated with an 18 nm polymeric thick PPF layer via the simultaneous polymerization/deposition of a cyclopropylamine (CPA) precursor performed by radio frequency discharge, both in pulsed and in continuous wave modes. The CPA PFF surface plays the dual role of an adsorbent towards negatively charged chemical species as well as an enhancer of plasmonic signals. The biosensor was tested in a proof-of-concept series of experiments of human serum albumin physisorption, and chosen as a model system for blood serum. The peculiar surface features of CPA PPF, before and after the exposure to buffered solution of fluorescein isothiocyanate-labelled human serum albumin (FITC-HSA), were investigated by a multi-technique approach, including UV-visible and X-ray photoelectron spectroscopies, atomic force microscopy, scanning electron microscopy, contact angle and surface free energy measurements. The results showed the very promising potentialities from both bioanalytical and physicochemical points of view in scrutinizing the macromolecule behavior at the biointerface.

Current knowledge in the field of algal organic matter adsorption onto activated carbon in drinking water treatment

The increasing occurrence of algal and cyanobacterial blooms and the related formation of algal organic matter (AOM) is a worldwide issue that endangers the quality of freshwater sources and affects water treatment processes. The associated problems involve the production of toxins or taste and odor compounds, increasing coagulant demand, inhibition of removal of other polluting compounds, and in many cases, AOM acts as a precursor of disinfection by-products. Previous research has shown that for sufficient AOM removal, the conventional drinking water treatment based on coagulation/flocculation must be often accompanied by additional polishing technologies such as adsorption onto activated carbon (AC). This state-of-the-art review is intended to serve as a summary of the most current research on the adsorption of AOM onto AC concerning drinking water treatment. It summarizes emerging trends in this field with an emphasis on the type of AOM compounds removed and on the adsorption mechanisms and influencing factors involved. Additionally, also the principles of competitive adsorption of AOM and other organic pollutants are elaborated. Further, this paper also synthesizes previous knowledge on combining AC adsorption with other treatment techniques for enhanced AOM removal in order to provide a practical resource for researchers, water treatment plant operators and engineers. Finally, research gaps regarding the AOM adsorption onto AC are identified, including, e.g., adsorption of AOM residuals recalcitrant to coagulation/flocculation, suitability of pre-oxidation of AOM prior to the AC adsorption, relationships between the solution properties and AOM adsorption behaviour, or AOM as a cause of competitive adsorption. Also, focus should be laid on continuous flow column experiments using water with multi-component composition, because these would greatly contribute to transferring the theoretical knowledge to practice.

Recent Advances in Emerging Metal- and Covalent-Organic Frameworks for Enzyme Encapsulation

Enzyme catalysis enables complex biotransformation to be imitated. This biomimetic approach allows for the application of enzymes in a variety of catalytic processes. Nevertheless, enzymes need to be shielded by a support material under challenging catalytic conditions due to their intricate and delicate structures. Specifically, metal-organic frameworks and covalent-organic frameworks (MOFs and COFs) are increasingly popular for use as enzyme-carrier platforms because of their excellent tunability in structural design as well as remarkable surface modification. These porous organic framework capsules that host enzymes not only protect the enzymes against harsh catalytic conditions but also facilitate the selective diffusion of guest molecules through the carrier. This review summarizes recent progress in MOF-enzyme and COF-enzyme composites and highlights the pore structures tuned for enzyme encapsulation. Furthermore, the critical issues associated with interactions between enzymes and pore apertures on MOF- and COF-enzyme composites are emphasized, and perspectives regarding the development of high-quality MOF and COF capsules are presented.

Effect of Protein Adsorption on Air Plastron Behavior of a Superhydrophobic Surface

Protein fouling on critical biointerfaces causes significant public health and clinical ramifications. Multiple strategies, including superhydrophobic (SHP) surfaces and coatings, have been explored to mitigate protein adsorption on solid surfaces. SHP materials with underwater air plastron (AP) layers hold great promise by physically reducing the contact area between a substrate and protein molecules. However, sustaining AP stability or lifetime is crucial in determining the durability and long-term applications of SHP materials. This work investigated the effect of protein on the AP stability using model SHP substrates, which were prepared from a mixture of silica nanoparticles and epoxy. The AP stability was determined using a submersion test with real-time visualization. The results showed that AP stability was significantly weakened by protein solutions compared to water, which could be attributed to the surface tension of protein solutions and protein adsorption on SHP substrates. The results were further examined to reveal the correlation between protein fouling and accelerated AP dissipation on SHP materials by confocal fluorescent imaging, surface energy measurement, and surface robustness modeling of the Cassie-Baxter to Wenzel transition. The study reveals fundamental protein adsorption mechanisms on SHP materials, which could guide future SHP material design to better mitigate protein fouling on critical biointerfaces.

Application of Tamm Plasmon Polaritons and Cavity Modes for Biosensing in the Combined Spectroscopic Ellipsometry and Quartz Crystal Microbalance Method

Low-cost 1D plasmonic photonic structures supporting Tamm plasmon polaritons and cavity modes were employed for optical signal enhancement, modifying the commercially available quartz crystal microbalance with dissipation (QCM-D) sensor chip in a combinatorial spectroscopic ellipsometry and quartz microbalance method. The Tamm plasmon optical state and cavity mode (CM) for the modified mQCM-D sample obtained sensitivity of ellipsometric parameters to RIU of Ψ_TPP = 126.78 RIU^-1 and Δ_TPP = 325 RIU^-1, and Ψ_CM = 264 RIU^-1 and Δ_CM = 645 RIU^-1, respectively. This study shows that Tamm plasmon and cavity modes exhibit about 23 and 49 times better performance of ellipsometric parameters, respectively, for refractive index sensing than standard spectroscopic ellipsometry on a QCM-D sensor chip. It should be noted that for the optical biosensing signal readout, the sensitivity of Tamm plasmon polaritons and cavity modes are comparable with and higher than the standard QCM-D sensor chip. The different origin of Tamm plasmon polaritons (TPP) and cavity mode (CM) provides further advances and can determine whether the surface (TPP) or bulk process (CM) is dominating. The dispersion relation feature of TPP, namely the direct excitation without an additional coupler, allows the possibility to enhance the optical signal on the sensing surface. To the best of our knowledge, this is the first study and application of the TPP and CM in the combinatorial SE-QCM-D method for the enhanced readout of ellipsometric parameters.

Emerging Challenges and Innovations in Surfactant-mediated Stabilization of Biologic Formulations

Biologics may be subjected to various destabilizing conditions during manufacturing, transportation, storage, and use. Therefore, biologics must be appropriately formulated to meet their desired quality target product profiles. In the formulations of protein-based biologics, one critical component is surfactant. Polysorbate 80 and Polysorbate 20 remain the most commonly used surfactants. Surfactants can stabilize proteins through different mechanisms and help the proteins withstand destabilization stresses. However, the challenges associated with surfactants, for instance, impurities, degradation, and potential triggering of adverse immune responses, have been encountered. Therefore, there are continued efforts to develop novel surfactants to overcome these challenges associated with traditional surfactants. Meanwhile, surfactants have also found their use in formulations of newer and novel modalities, namely, antibody-drug conjugates, bispecific antibodies, and adeno-associated viruses (AAV). This review provides an updated in-depth discussion of surfactants in the above-mentioned areas, namely mechanism of action of surfactants, a critical review of challenges with surfactants and current mitigation approaches, and emerging technologies to develop novel surfactants. In addition, gaps, current mitigations, and future directions have been presented to trigger further discussion and research to facilitate the use and development of novel surfactants.

Separation of charge variants of a monoclonal antibody by overloaded ion exchange chromatography

A procedure for adjusting the content of charge variants of monoclonal antibody by ion exchange chromatography has been developed. The band splitting phenomenon was utilized to split the protein load into two parts, i.e., the flowthrough and bound fractions, which were either enriched or depleted with some of variants. The phenomenon was triggered by thermodynamic effects resulting from oversaturation of the resin binding sites at high column loadings as well as from kinetic effects arising from limited rates of mass transport. Cation exchange chromatography (CEX) and anion exchange chromatography (AEX) separations were examined, with the reverse order of the variant elution: acidic, main, basic in CEX, and basic, main, acidic in AEX, and the corresponding reverse enrichment tendency in the collected fractions. The separations were performed by pH gradient, whose course was simplified to two stages: isocratic loading and washing at mild pH to load and partly elute the protein, followed by a rapid pH change towards non-binding conditions to desorb the remains of the protein load. To improve yield of the operation, possibility of recycling of waste fractions was considered. To predict the process performance, a dynamic model was developed, which accounted for both adsorption kinetics and thermodynamics.

Surface Effect of Nano-Roughened Yttria-Doped Zirconia on Salivary Protein Adhesion

Biocompatibility of yttria (3 mol%) stabilized zirconia ceramics, 3Y-TZP, was affected to a large degree as a result of protein adsorption from human saliva that in turn depends on materials surface properties. Variable nano-roughness levels in 3Y-TZP discs were characterized and tested for specificity and selectivity with respect to size and uptake for human salivary protein.

Predicting the In Vivo Performance of Cardiovascular Biomaterials: Current Approaches In Vitro Evaluation of Blood-Biomaterial Interactions

The therapeutic efficacy of a cardiovascular device after implantation is highly dependent on the host-initiated complement and coagulation cascade. Both can eventually trigger thrombosis and inflammation. Therefore, understanding these initial responses of the body is of great importance for newly developed biomaterials. Subtle modulation of the associated biological processes could optimize clinical outcomes. However, our failure to produce truly blood compatible materials may reflect our inability to properly understand the mechanisms of thrombosis and inflammation associated with biomaterials. In vitro models mimicking these processes provide valuable insights into the mechanisms of biomaterial-induced complement activation and coagulation. Here, we review (i) the influence of biomaterials on complement and coagulation cascades, (ii) the significance of complement-coagulation interactions for the clinical success of cardiovascular implants, (iii) the modulation of complement activation by surface modifications, and (iv) in vitro testing strategies.

A hard-sphere model of protein corona formation on spherical and cylindrical nanoparticles

A nanoparticle (NP) immersed in biological media rapidly forms a corona of adsorbed proteins, which later controls the eventual fate of the particle and the route through which adverse outcomes may occur. The composition and timescale for the formation of this corona are both highly dependent on both the NP and its environment. The deposition of proteins on the surface of the NP can be imitated by a process of random sequential adsorption, and, based on this model, we develop a rate-equation treatment for the formation of a corona represented by hard spheres on spherical and cylindrical NPs. We find that the geometry of the NP significantly alters the composition of the corona through a process independent of the rate constants assumed for adsorption and desorption of proteins, with the radius and shape of the NP both influencing the corona. We further investigate the roles of protein mobility on the surface of the NP and changes in the concentration of proteins.

Molecular Mechanistic Insights into the Ionic-Strength-Controlled Interfacial Behavior of Proteins on a TiO2 Surface

By adjusting the ionic strengths through changing the concentration of the buffer ions, the molecular force and the interfacial behavior of cytochrome c (Cyt c) and TiO₂ are systematically studied. The molecular forces determined by combining the adhesion force and adsorption capacity are found to first increase and then decrease with the increasing ionic strength, with a peak obtained at an ionic strength between 0.8 and 1.0 M. The mechanism is explained based on the dissociation and hydration of ions at the interfaces, where the buffer ions could be completely dissociated at ionic strengths of <0.8 M but were partially associated when the ionic strength increased to a high value (>1.2 M), and the strongest hydration was observed around 1.0 M. The hydrodynamic size and the zeta potential value representing the effective contact area and protein stability of the Cyt c molecule, respectively, are also affected by the hydration and are proportional to the molecular forces. The interfacial behavior of Cyt c molecules on the TiO₂ surface, determined through surface-enhanced Raman scattering (SERS), is extremely affected by the ionic strength of the solution as the ion dissociation and hydration also increase the electron transfer ability, where the best SERS enhancement is observed at the ionic strength of around 1.0 M, corresponding to the largest molecular force. Our results provide a detailed understanding at the nanoscale on controlling the protein interfacial behavior with solid surfaces, adjusted by the buffer ions.

Immunomodulatory bioactive glasses for tissue regeneration

The regulatory functions of the immune response in tissue healing, repair, and regeneration have been evidenced in the last decade. Immune cells play central roles in immune responses toward inducing favorable tissue regenerative processes. Modulating and controlling the immune cell responses (particularly macrophages) is an emerging approach to enhance tissue regeneration. Bioactive glasses (BGs) are multifunctional materials exhibiting osteogenic, angiogenic, and antibacterial properties, being increasingly investigated for various tissue regeneration scenarios, including bone regeneration and wound healing. On the other hand, the immunomodulatory effects of BGs in relation to regenerating tissues have started to be understood, and key knowledge is emerging. This is the first review article summarizing the immunomodulatory effects of BGs for tissue repair and regeneration. The immune response to BGs is firstly introduced, discussing potential mechanisms regarding the immunomodulation effects induced by BGs. Moreover, the interactions between the immune cells involved in the immunomodulation process and BGs (dissolution products) are summarized in detail. Particularly, a well-regulated and timely switch of macrophage phenotype from pro-inflammatory to anti-inflammatory is crucial to constructive tissue regeneration through modulating osteogenesis, osteoclastogenesis, and angiogenesis. The influence of BG characteristics on macrophage responses is discussed. We highlight the strategies employed to harness macrophage responses for enhanced tissue regeneration, including the incorporation of active ions, surface functionalization, and controlled release of immunomodulatory molecules. Finally, we conclude with our perspectives on future research challenges and directions in the emerging field of immunomodulatory BGs for tissue regeneration. STATEMENT OF SIGNIFICANCE: Immunomodulatory effects of bioactive glasses (BGs) in relation to bone regeneration and wound healing have started to be understood. We summarize those studies which have focused on immunomodulatory BGs for tissue regeneration. We first introduce the potential mechanisms of the immunomodulation effects induced by BGs. Interactions between the cells involved in immunomodulation processes and BGs (and their dissolution products, biologically active ions) are elaborated. We highlight the strategies employed to modulate macrophage responses for enhancing tissue regeneration, including incorporation of active ions, surface functionalization, and controlled release of immunomodulatory agents. This is the first review article summarizing and outlining the immunomodulatory effects of BGs for tissue regeneration. We anticipate that increasing research efforts will start to emerge in the area of immunomodulatory BGs.

Kinetic investigation of protein adsorption into polyelectrolyte brushes by quartz crystal microbalance with dissipation: The implication of the chromatographic mechanism

With the growing concerns of polymer-grafted ion-exchange chromatography, the importance of protein adsorption on charged polymer-grafted surfaces cannot be stressed enough. However, a full understanding in adsorption in polymer brushes is still a great challenge due to the lack of in situ characterization technique. In this work, we use quartz crystal microbalance with dissipation to in situ investigate adsorption kinetics of γ-globulin and recombinant human lactoferrin on poly(3-sulfopropyl methacrylate) (pSPM) sensors prepared via atom transfer radical polymerization. With an increase of chain length and grafting density, great increasing amounts of proteins on pSPM-grafted sensors revealed that protein underwent a transition from monolayer to multilayer adsorption. It was attributed to direct protein binding into charged brushes, in which more binding sites involved and more coupled water lost. However, such a strong binding and rigid structure of proteins limited the protein transport in pSPM brushes and "chain delivery" effect. With an increase in grafting density, moreover, denser brushes hindered adjustment in protein conformation in pSPM brushes and further exacerbated protein transport in pSPM brushes. Furthermore, the influence of buffer pH and salt concentration further validated the ion exchange characteristics of protein adsorption into pSPM brushes. The research provided a variety of in situ evidence of protein binding and conformation evolution in pSPM brushes and elucidated mechanism of protein adsorption in pSPM brushes.

Adsorption of organic matter on titanium surfaces with nano- and micro-scale roughness studied with the electrochemical quartz crystal microbalance dissipation technique

Adsorption of calf serum organic matter from a phosphate-buffered solution was studied using the electrochemical quartz crystal microbalance with additional dissipation measurements. Two types of crystal surfaces were used: one rough with micrometer-range surface features and one with roughness in the low nanometer range. The results showed that the adsorption of the organic material was about 1.5 orders of magnitude larger on the rough surface and almost independent of serum concentration in the electrolyte. The adsorption rates were found to increase with increasing serum concentration. For rough crystals, the adsorption kinetics were interpreted with the Johnson-Mehl-Avrami-Kolmogorov model, indicating an initial growth phase according to the tⁿ-law, followed by a slower growth as the nucleation sites fill up. This study suggests that specific surface sites are critical to promote adsorption of proteins on a titanium surface.

A Critical Review on the Multiple Roles of Manganese in Stabilizing and Destabilizing Soil Organic Matter

Manganese (Mn) is a biologically important and redox-active metal that may exert a poorly recognized control on carbon (C) cycling in terrestrial ecosystems. Manganese influences ecosystem C dynamics by mediating biochemical pathways that include photosynthesis, serving as a reactive intermediate in the breakdown of organic molecules, and binding and/or oxidizing organic molecules through organo-mineral associations. However, the potential for Mn to influence ecosystem C storage remains unresolved. Although substantial research has demonstrated the ability of Fe- and Al-oxides to stabilize organic matter, there is a scarcity of similar information regarding Mn-oxides. Furthermore, Mn-mediated reactions regulate important litter decomposition pathways, but these processes are poorly constrained across diverse ecosystems. Here, we discuss the ecological roles of Mn in terrestrial environments and synthesize existing knowledge on the multiple pathways by which biogeochemical Mn and C cycling intersect. We demonstrate that Mn has a high potential to degrade organic molecules through abiotic and microbially mediated oxidation and to stabilize organic molecules, at least temporarily, through organo-mineral associations. We outline research priorities needed to advance understanding of Mn-C interactions, highlighting knowledge gaps that may address key uncertainties in soil C predictions.

Adsorption of lysozyme on gold surfaces in the presence of an external electric potential

Adsorbed protein films consist of essential building blocks of many biotechnological and biomedical devices. The electrostatic potential may significantly modulate the protein behaviour on surfaces, affecting their structure and biological activity. In this study, lysozyme was used to investigate the effects of applied electric potentials on adsorption and the protein structure. The pH and the surface charge determine the amount and secondary structure of adsorbed lysozyme on a gold surface. In-situ measurements using polarization modulation infrared reflection absorption spectroscopy indicated that the concentration of both the adsorbed anions and the lysozyme led to conformational changes in the protein film, which was demonstrated by a greater amount of aggregated β-sheets in films fabricated at net positive charges of the Au electrode (E_ads > E_pzc). The changes in secondary structure involved two parallel processes. One comprised changes in the hydration/hydrogen-bond network at helices, leading to diverse helical structures: α-, 3₁₀- and/or π-helices. In the second process β-turns, β-sheets, and random coils displayed an ability to form aggregated β-sheet structures. The study illuminates the understanding of electrical potential-dependent changes involved in the protein misfolding process.

Adsorption Behavior of Arabinogalactan-Proteins (AGPs) from Acacia senegal Gum at a Solid-Liquid Interface

Adsorption of five different hyperbranched arabinogalactan-protein (AGP) fractions from Acacia senegal gum was thoroughly studied at the solid-liquid interface using a quartz crystal microbalance with dissipation monitoring (QCM-D), surface plasmon resonance (SPR), and atomic force microscopy (AFM). The impact of the protein/sugar ratio, molecular weight, and aggregation state on the adsorption capacity was investigated by studying AGP fractions with different structural and biochemical features. Adsorption on a solid surface would be primarily driven by the protein moiety of the AGPs through hydrophobic forces and electrostatic interactions. Increasing ionic strength allows the decrease in electrostatic repulsions and, therefore, the formation of high-coverage films with aggregates on the surface. However, the maximum adsorption capacity was not reached by fractions with a higher protein content but by a fraction that contains an average protein quantity and presents a high content of high-molecular-weight AGPs. The results of this thorough study highlighted that the AGP surface adsorption process would depend not only on the protein moiety and high-molecular-weight AGP content but also on other parameters such as the structural accessibility of proteins, the molecular weight distribution, and the AGP flexibility, allowing structural rearrangements on the surface and spreading to form a viscoelastic film.

Lipid bilayer coatings for rapid enzyme-linked immunosorbent assay

The enzyme-linked immunosorbent assay (ELISA) is a widely used method for protein detection and relies on the specific capture of target proteins while minimizing the nonspecific binding of other interfering proteins and biomolecules. To prevent nonspecific binding events, blocking agents such as bovine serum albumin (BSA) protein, mixtures of proteins in media such as milk or serum, and/or surfactants are typically added to ELISA plates after probe attachment and before analyte capture. Herein, we developed a streamlined ELISA strategy in which readily prepared lipid nanoparticles are utilized as the blocking agent and are added together with the probe molecule to the ELISA plate, resulting in fewer processing steps, quicker protocol time, and superior detection performance compared to conventional BSA blocking. These measurement capabilities were established for coronavirus disease-2019 (COVID-19) antibody detection in saline and human serum conditions and are broadly applicable for developing rapid ELISA diagnostics.

Influence of mineral coatings on fibroblast behaviour: The importance of coating formulation and experimental design

Mineral coatings manipulate surface properties such as roughness, porosity, wettability and surface energy. Properties that are known to determine cell behaviour. Therefore, mineral coatings can potentially be used to manipulate cell fate. This paper studies mineral-cell interactions through coatings in a stacked cell culture platform. Minerals were chosen according to their influence on Human Dermal Fibroblasts (HDFs): calcium carbonate, calcium sulphates, and kaolin. Mineral coatings were formulated with the additives latex, sorbitol, polyvinyl alcohol (PVOH) and TEMPO-oxidised cellulose nanofibrils (CNF-T). The coatings were placed as a bottom or top of the device, for a direct or indirect interaction with HDFs, respectively. Cells were seeded, in various densities, to the bottom of the device; and cell density and confluency were monitored in time. Overall, results show that the coating interaction is influenced at first by the cell seeding density. Scarce cell seeding density limits adaptability to the new environment, while an abundant one encourages confluency in time. In between those densities, coating formulation plays the next major role. Calcium carbonate promoted HDFs growth the most as expected, but the response to the rest of minerals depended on the coating additive. CNF-T encouraged proliferation even for kaolin, a mineral with long-term toxicity to HDFs, while PVOH induced a detrimental effect on HDF growth regardless of the mineral. At last, the placement of the coated layer provided insights on the contact-dependency of each response. This study highlights the importance of the experimental design, including coating formulation, when investigating cellular response to biomaterials.

The Early Adhesion Effects of Human Gingival Fibroblasts on Bovine Serum Albumin Loaded Hydrogenated Titanium Nanotube Surface

The soft tissue sealing at the transmucal portion of implants is vital for the long-term stability of implants. Hydrogenated titanium nanotubes (H₂-TNTs) as implant surface treatments were proved to promote the adhesion of human gingival fibroblasts (HGFs) and have broad usage as drug delivery systems. Bovine serum albumin (BSA) as the most abundant albumin in body fluid was crucial for cell adhesion and was demonstrated as a normal loading protein. As the first protein arriving on the surface of the implant, albumin plays an important role in initial adhesion of soft tissue cells, it is also a common carrier, transferring and loading different endogenous and exogenous substances, ions, drugs, and other small molecules. The aim of the present work was to investigate whether BSA-loaded H₂-TNTs could promote the early adhesion of HGFs; H₂-TNTs were obtained by hydrogenated anodized titanium dioxide nanotubes (TNTs) in thermal treatment, and BSA was loaded in the nanotubes by vacuum drying; our results showed that the superhydrophilicity of H₂-TNTs is conducive to the loading of BSA. In both hydrogenated titanium nanotubes and non-hydrogenated titanium nanotubes, a high rate of release was observed over the first hour, followed by a period of slow and sustained release; however, BSA-loading inhibits the early adhesion of human gingival fibroblasts, and H₂-TNTs has the best promoting effect on cell adhesion. With the release of BSA after 4 h, the inhibitory effect of BSA on cell adhesion was weakened.

Biomaterial and cellular implants:foreign surfaces where immunity and coagulation meet

Exposure of blood to a foreign surface in the form of a diagnostic or therapeutic biomaterial device or implanted cells or tissues, elicits an immediate, evolutionarily conserved thrombo-inflammatory response by the host. Primarily designed to protect against invading organisms following an injury, this innate response features instantaneous activation of several blood-borne, highly interactive and well-orchestrated cascades and cellular events that limit bleeding, destroy and eliminate the foreign substance/cells, and promote healing and a return to homeostasis via delicately balanced regenerative processes. In the setting of blood-contacting synthetic or natural biomaterials and implantation of foreign cells/tissues, innate responses are robust, albeit highly context-specific. Unfortunately, they tend to be less than adequately regulated by the host's natural anti-coagulant/anti-inflammatory pathways, thereby jeopardizing the functional integrity of the device, as well as the health of the host. Strategies to achieve biocompatibility with a sustained return to homeostasis, particularly while the device remains in situ and functional, continue to elude scientists and clinicians. In this review, some of the complex mechanisms by which biomaterials and cellular transplants provide a "hub" for activation and amplification of coagulation and immunity - thrombo-inflammation - will be discussed, with a view toward the development of innovative means of overcoming the innate challenges.

Sustainable One-Pot Immobilization of Enzymes in/on Metal-Organic Framework Materials

The industrial use of enzymes generally necessitates their immobilization onto solid supports. The well-known high affinity of enzymes for metal-organic framework (MOF) materials, together with the great versatility of MOFs in terms of structure, composition, functionalization and synthetic approaches, has led the scientific community to develop very different strategies for the immobilization of enzymes in/on MOFs. This review focuses on one of these strategies, namely, the one-pot enzyme immobilization within sustainable MOFs, which is particularly enticing as the resultant biocomposite Enzyme@MOFs have the potential to be: (i) prepared in situ, that is, in just one step; (ii) may be synthesized under sustainable conditions: with water as the sole solvent at room temperature with moderate pHs, etc.; (iii) are able to retain high enzyme loading; (iv) have negligible protein leaching; and (v) give enzymatic activities approaching that given by the corresponding free enzymes. Moreover, this methodology seems to be near-universal, as success has been achieved with different MOFs, with different enzymes and for different applications. So far, the metal ions forming the MOF materials have been chosen according to their low price, low toxicity and, of course, their possibility for generating MOFs at room temperature in water, in order to close the cycle of economic, environmental and energy sustainability in the synthesis, application and disposal life cycle.

In Vitro Bactericidal Efficacy of Nanostructured Ti6Al4V Surfaces is Bacterial Load Dependent

The demand for medical implants globally has increased significantly due to an aging population amongst other reasons. Despite the overall increase in the survivorship of Ti6Al4V implants, implant infection rates are increasing due to factors such as diabetes, obesity, and bacterial resistance to antibiotics. Two commonly found bacteria implicated in implant infections are Staphylococcus aureus and Pseudomonas aeruginosa. Based on prior work that showed nanostructured surfaces might have potential in passively killing these bacterial species, we developed a hierarchical, hydrothermally etched, nanostructured titanium surface. To evaluate the antibacterial efficacy of this surface, etched and as-received surfaces were inoculated with S. aureus or P. aeruginosa at concentrations ranging from 10² to 10⁹ colony-forming units per disc. Live/dead staining revealed there was a 60% decrease in viability for S. aureus and greater than a 98% decrease for P. aeruginosa on etched surfaces at the lowest inoculum of 10² CFU/disc, when compared to the control surface. Bactericidal efficiency decreased with increasing bacterial concentrations in a stepwise manner, with decreases in bacterial viability noted for S. aureus above 10⁵ CFU/disc and above 10⁶ CFU/disc for P. aeruginosa. Surprisingly, biofilm depth analysis revealed a decrease in bacterial viability in the 2 μm layer furthest from the nanostructured surface. The nanostructured Ti6Al4V surface developed here holds the potential to reduce the rate of implant infections.

Biopatterning: The Art of Patterning Biomolecules on Surfaces

Patterning biomolecules on surfaces provides numerous opportunities for miniaturizing biological assays; biosensing; studying proteins, cells, and tissue sections; and engineering surfaces that include biological components. In this Feature Article, we summarize the themes presented in our recent Langmuir Lecture on patterning biomolecules on surfaces, miniaturizing surface assays, and interacting with biointerfaces using three key technologies: microcontact printing, microfluidic networks, and microfluidic probes.

In Situ Label-Free Study of Protein Adsorption on Nanoparticles

Improving the design of nanoparticles for use as drug carriers or biosensors requires a better understanding of the protein-nanoparticle interaction. Here, we present a new tool to investigate this interaction in situ and without additional labeling of the proteins and/or nanoparticles. By combining nonresonant second-harmonic light scattering with a modified Langmuir model, we show that it is possible to gain insight into the adsorption behavior of blood proteins, namely fibrinogen, human serum albumin, and transferrin, onto negatively charged polystyrene nanoparticles. The modified Langmuir model gives us access to the maximum amount of adsorbed protein, the apparent binding constant, and Gibbs free energy. Furthermore, we employ the method to investigate the influence of the nanoparticle size on the adsorption of human serum albumin and find that the amount of adsorbed protein increases more than the surface area per nanoparticle for larger diameters.

Salt-dependent passive adsorption of IgG1κ-type monoclonal antibodies on hydrophobic microparticles

Understanding how antibodies adsorb on solid surfaces is essential for developing effective approaches to control this process. In this study, passive adsorptions on the hydrophobic solid surface of a polystyrene microparticle (MP) of two highly similar IgG1 κ-type monoclonal antibodies (mAbs), rituximab, and trastuzumab, were examined in the presence of Hofmeister salts. Except of kosmotropic salts, the screening of electrostatic interactions using salts reduces the passive adsorption of mAbs on MP. To better understand the ion-specific adsorption process, salt-dependent Langmuir isotherm parameters were obtained and correlated for two mAbs. We find that while their maximum adsorption capacities to MPs are highly correlated (r > 0.9), the salt-dependent profiles of adsorption binding constants, Kobs, differ substantially. For rituximab, Kobs increases >10-fold in an ion-specific manner; for trastuzumab, Kobs remains constant. We conclude that even minor sequence variations among the mAbs can affect the adsorption, as well as the molecular forces attracting proteins to a solid surface. This difference might originate from the heterogeneous orientation of the adsorbed mAbs.

Modelling the adsorption of proteins to nanoparticles at the solid-liquid interface

HYPOTHESIS

We developed a geometrical model to determine the theoretical maximum number of proteins that can pack as a monolayer surrounding a spherical nanoparticle. We applied our new model to study the adsorption of receptor binding domain (RBD) of the SARS-CoV-2 spike protein to silica nanoparticles. Due to its abundance and extensive use in manufacturing, silica represents a reservoir where the virus can accumulate. It is therefore important to study the adsorption and the persistence of viral components on inanimate surfaces.

EXPERIMENTS

We used previously published datasets of nanoparticle-adsorbed proteins to validate the new model. We then used integrated experimental methods and Molecular Dynamics (MD) simulations to characterise binding of the RBD to silica nanoparticles and the effect of such binding on RBD structure.

FINDINGS

The new model showed excellent fit with existing datasets and, combined to new RBD-silica nanoparticles binding data, revealed a surface occupancy of 32% with respect to the maximum RBD packing theoretically achievable. Up to 25% of RBD's secondary structures undergo conformational changes as a consequence of adsorption onto silica nanoparticles. Our findings will help developing a better understanding of the principles governing interaction of proteins with surfaces and can contribute to control the spread of SARS-CoV-2 through contaminated objects.

Isoelectric Point of Proteins at Hydrophobic Interfaces

Structural and colloidal stability of proteins at different surfaces and interfaces is of great importance in many fields including medical, pharmaceutical, or material science. Due to their flexibility, proteins tend to respond to their environmental conditions and can undergo structural and conformational changes. For instance, alterations in physiological factors such as temperature, ions concentration, or pH as well as the adsorption to an interface can initiate protein aggregation. Therefore, at different surfaces and interfaces the characterization of the structural and colloidal stability of proteins, which is mainly influenced by their electrostatic and hydrophobic interactions, is of fundamental importance. In this study, we utilized sum frequency generation (SFG) spectroscopy to assess the role of solution pH on the polarity and magnitude of the electric field within the hydration shell of selected model proteins adsorbed to a hydrophobic surface. We used polystyrene (PS) as a model hydrophobic surface and determined the isoelectric point (IEP) of four structurally different model proteins. Comparing the measured IEP of proteins at the PS/solution or air/solution interface with that determined in the bulk solution via zeta potential measurement, we found significant similarities between the IEP of surface adsorbed proteins and those in the bulk aqueous phase. The pH dependence behavior of proteins was correlated to their amino acid composition and degree of hydrophobicity.

Proteome difference among the salivary proteins adsorbed onto metallic orthodontic brackets and hydroxyapatite discs

The aim of this study was to investigate the atomic composition and the proteome of the salivary proteins adsorbed on the surface of orthodontic metallic bracket. For this, the atomic composition of orthodontic metallic brackets was analyzed with X-ray Photoelectron Spectroscopy (XPS). The acquired bracket pellicle was characterized after brackets were immersed in human whole saliva supernatant for 2 hours at 37°C. Hydroxyapatite (HA) discs were used as a control. Acquired pellicle was harvested from the HA discs (n = 12) and from the metallic brackets (n = 12). Proteomics based on mass spectrometry technology was used for salivary protein identification and characterization. Results showed that most of the proteins adsorbed on the surface of orthodontic metallic brackets and on the HA discs were identified specifically to each group, indicating a small overlapping between the salivary proteins on each study group. A total of 311 proteins present on the HA discs were unique to this group while 253 proteins were unique to metallic brackets, and only 45 proteins were common to the two groups. Even though most proteins were unique to each study group, proteins related to antimicrobial activity, lubrication, and remineralization were present in both groups. These findings demonstrate that the salivary proteins adsorbed on the bracket surface are dependent on the material molecular composition.

Innovative fouling-resistant materials for industrial heat exchangers: a review

Fouling of heat exchangers (HEs) has become a major concern across the industrial sector. Fouling is an omnipresent phenomenon but is particularly prevalent in the dairy, oil, and energy industries. Reduced energy performance that results from fouling represents significant operating loss in terms of both maintenance and impact on product quality and safety. In most industries, cleaning or replacing HEs are currently the only viable solutions for controlling fouling. This review examines the latest advances in the development of innovative materials and coatings for HEs that could mitigate the need for costly and frequent cleaning and potentially extend their operational life. To better understand the correlation between surface properties and fouling occurrence, we begin by providing an overview of the main mechanisms underlying fouling. We then present selected key strategies, which can differ considerably, for developing antifouling surfaces and conclude by discussing the current trends in the search for ideal materials for a range of applications. In our presentation of all these aspects, emphasis is given wherever possible to the potential transfer of these innovative surfaces from the laboratory to the three industries most concerned by HE fouling problems: food, petrochemicals, and energy production.

Effect of Recombinant Human Perlecan Domain V Tethering Method on Protein Orientation and Blood Contacting Activity on Polyvinyl Chloride

Surface modification of biomaterials is a promising approach to control biofunctionality while retaining the bulk biomaterial properties. Perlecan is the major proteoglycan in the vascular basement membrane that supports low levels of platelet adhesion but not activation. Thus, perlecan is a promising bioactive for blood-contacting applications. This study furthers the mechanistic understanding of platelet interactions with perlecan by establishing that platelets utilize domains III and V of the core protein for adhesion. Polyvinyl chloride (PVC) is functionalized with recombinant human perlecan domain V (rDV) to explore the effect of the tethering method on proteoglycan orientation and bioactivity. Tethering of rDV to PVC is achieved via either physisorption or covalent attachment via plasma immersion ion implantation (PIII) treatment. Both methods of rDV tethering reduce platelet adhesion and activation compared to the pristine PVC, however, the mechanisms are unique for each tethering method. Physisorption of rDV on PVC orientates the molecule to hinder access to the integrin-binding region, which inhibits platelet adhesion. In contrast, PIII treatment orientates rDV to allow access to the integrin-binding region, which is rendered antiadhesive to platelets via the glycosaminoglycan (GAG) chain. These effects demonstrate the potential of rDV biofunctionalization to modulate platelet interactions for blood contacting applications.

Polydopamine-assisted immobilization of silk fibroin and its derived peptide on chemically oxidized titanium to enhance biological activity in vitro

Biochemical modification can endow the surface of implants with superior biological activity. Herein, silk fibroin (SF) protein and its anionic derivative peptides (Cs) were covalently immobilized onto a titanium implant surface via a polydopamine layer. The successful conjugation of SF and Cs was revealed by X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), and contact angle measurements. The addition of Cs prevented the conformational transition of silk fibroin to silk II. The deposition of apatite on its surface was significantly accelerated, and the bioactive composite coating was observed to enhance protein adsorption and cell proliferation. More importantly, it also promoted the osteogenic differentiation of bone marrow stem cells (BMSCs) for the quantitative and qualitative detection of alkaline phosphatase (ALP) and alizarin red (ARS). Overall, the stable performance and enhanced osteogenic property of the composite coating promote an extensive application for clinical titanium-based implants.

Waveguide Enhanced Raman Spectroscopy for Biosensing: A Review

Waveguide enhanced Raman spectroscopy (WERS) utilizes simple, robust, high-index contrast dielectric waveguides to generate a strong evanescent field, through which laser light interacts with analytes residing on the surface of the waveguide. It offers a powerful tool for the direct identification and reproducible quantification of biochemical species and an alternative to surface enhanced Raman spectroscopy (SERS) without reliance on fragile noble metal nanostructures. The advent of low-cost laser diodes, compact spectrometers, and recent progress in material engineering, nanofabrication techniques, and software modeling tools have made realizing portable and cheap WERS Raman systems with high sensitivity a realistic possibility. This review highlights the latest progress in WERS technology and summarizes recent demonstrations and applications. Following an introduction to the fundamentals of WERS, the theoretical framework that underpins the WERS principles is presented. The main WERS design considerations are then discussed, and a review of the available approaches for the modification of waveguide surfaces for the attachment of different biorecognition elements is provided. The review concludes by discussing and contrasting the performance of recent WERS implementations, thereby providing a future roadmap of WERS technology where the key opportunities and challenges are highlighted.