Comparison of bovine serum albumin and chitosan effects on calcium phosphate formation in the presence of silver nanoparticles

The precipitation of calcium phosphates (CaPs) in the presence of more than one type of additive is of interest both from a fundamental point of view and as a possible biomimetic route for the preparation of multicomponent composites in which the activity of the components is preserved. In this study, the effect of bovine serum albumin (BSA) and chitosan (Chi) on the precipitation of CaPs in the presence of silver nanoparticles (AgNPs) stabilized with sodium bis(2-ethylhexyl)sulfosuccinate (AOT-AgNPs), poly(vinylpyrrolidone) (PVP-AgNPs), and citrate (cit-AgNPs) was investigated. In the control system, the precipitation of CaPs occurred in two steps. Amorphous calcium phosphate (ACP) was the first precipitated solid, which transformed into a mixture of calcium-deficient hydroxyapatite (CaDHA) and a smaller amount of octacalcium phosphate (OCP) after 60 min of ageing. Both biomacromolecules inhibited ACP transformation, with Chi being a stronger inhibitor due to its flexible molecular structure. As the concentration of the biomacromolecules increased, the amount of OCP decreased both in the absence and presence of AgNPs. In the presence of cit-AgNPs and two highest BSA concentrations, a change in the composition of the crystalline phase was observed. Calcium hydrogen phosphate dihydrate was formed in the mixture with CaDHA. An effect on the morphology of both the amorphous and crystalline phases was observed. The effect depended on the specific combination of biomacromolecules and differently stabilized AgNP. The results obtained suggest a simple method for fine-tuning the properties of precipitates using different classes of additives. This could be of interest for the biomimetic preparation of multifunctional composites for bone tissue engineering.

Can Differently Stabilized Silver Nanoparticles Modify Calcium Phosphate Precipitation?

Calcium phosphates (CaPs) composites with silver nanoparticles (AgNPs) attract attention as a possible alternative to conventional approaches to combating orthopedic implant-associated infections. Although precipitation of calcium phosphates at room temperatures was pointed out as an advantageous method for the preparation of various CaP-based biomaterials, to the best of our knowledge, no such study exists for the preparation of CaPs/AgNP composites. Motivated by this lack of data in this study we investigated the influence of AgNPs stabilized with citrate (cit-AgNPs), poly(vinylpyrrolidone) (PVP-AgNPs), and sodium bis(2-ethylhexyl) sulfosuccinate (AOT-AgNPs) in the concentration range 5-25 mg dm^-3 on the precipitation of CaPs. The first solid phase to precipitate in the investigated precipitation system was amorphous calcium phosphate (ACP). The effect of AgNPs on ACP stability was significant only in the presence of the highest concentration of AOT-AgNPs. However, in all precipitation systems containing AgNPs, the morphology of ACP was affected, as gel-like precipitates formed in addition to the typical chain-like aggregates of spherical particles. The exact effect depended on the type of AgNPs. After 60 min of reaction time, a mixture of calcium-deficient hydroxyapatite (CaDHA) and a smaller amount of octacalcium phosphate (OCP) formed. PXRD and EPR data point out that the amount of formed OCP decreases with increasing AgNPs concentration. The obtained results showed that AgNPs can modify the precipitation of CaPs and that CaPs properties can be fine-tuned by the choice of stabilizing agent. Furthermore, it was shown that precipitation can be used as a simple and fast method for CaP/AgNPs composites preparation which is of special interest for biomaterials preparation.

Particle Size Modulates Silver Nanoparticle Toxicity during Embryogenesis of Urchins Arbacia lixula and Paracentrotus lividus

Silver nanoparticles represent a threat to biota and have been shown to cause harm through a number of mechanisms, using a wide range of bioassay endpoints. While nanoparticle concentration has been primarily considered, comparison of studies that have used differently sized nanoparticles indicate that nanoparticle diameter may be an important factor that impacts negative outcomes. In considering this, the aim of the present study was to determine if different sizes of silver nanoparticles (AgNPs; 10, 20, 40, 60 and 100 nm) give rise to similar effects during embryogenesis of Mediterranean sea urchins Arbacia lixula and Paracentrotus lividus, or if nanoparticle size is a parameter that can modulate embryotoxicity and spermiotoxicity in these species. Fertilised embryos were exposed to a range of AgNP concentrations (1−1000 µg L−1) and after 48 h larvae were scored. Embryos exposed to 1 and 10 µg L−1 AgNPs (for all tested sizes) showed no negative effect in both sea urchins. The smaller AgNPs (size 10 and 20 nm) caused a decrease in the percentage of normally developed A. lixula larvae at concentrations ≥50 µg L−1 (EC50: 49 and 75 μg L−1, respectively) and at ≥100 µg L−1 (EC50: 67 and 91 μg L−1, respectively) for P. lividus. AgNPs of 40 nm diameter was less harmful in both species ((EC50: 322 and 486 μg L−1, for P. lividus and A. lixula, respectively)). The largest AgNPs (60 and 100 nm) showed a dose-dependent response, with little effect at lower concentrations, while more than 50% of larvae were developmentally delayed at the highest tested concentrations of 500 and 1000 µg L−1 (EC50(100 nm); 662 and 529 μg L−1, for P. lividus and A. lixula, respectively. While AgNPs showed no effect on the fertilisation success of treated sperm, an increase in offspring developmental defects and arrested development was observed in A. lixula larvae for 10 nm AgNPs at concentrations ≥50 μg L−1, and for 20 and 40 nm AgNPs at concentrations >100 μg L−1. Overall, toxicity was mostly ascribed to more rapid oxidative dissolution of smaller nanoparticles, although, in cases, Ag+ ion concentrations alone could not explain high toxicity, indicating a nanoparticle-size effect.

Deciphering the origin of the melting profile of unilamellar phosphatidylcholine liposomes by measuring the turbidity of its suspensions

The elucidation of the thermal properties of phosphatidylcholine liposomes is often based on the analysis of the thermal capacity profiles of multilamellar liposomes (MLV), which may qualitatively disagree with those of unilamellar liposomes (LUV). Experiments and interpretation of LUV liposomes is further complicated by aggregation and lamellarization of lipid bilayers in a short time period, which makes it almost impossible to distinguish the signatures of the two types of bilayers. To characterize independently MLV and LUV of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), the latter were prepared with the addition of small amounts of 1,2-dipalmitoyl-sn-glycero-3-phosphatidylglycerol (DPPG) which, due to the sterical hindrance and negative charge at a given pH value, cause LUV repellence and contribute to their stability. Differential scanning calorimetry curves and temperature-dependent UV/Vis spectra of the prepared MLV and LUV were measured. Multivariate analysis of spectrophotometric data determined the phase transition temperatures (pretransition at T_p and the main phase transition at T_m), and based on the changes in turbidities, the thickness of the lipid bilayer in LUV was determined. The obtained data suggested that the curvature change is a key distinguishing factor in MLV and LUV heat capacity profiles. By combining the experimental results and those obtained by MD simulations, the interfacial water layer was characterized and its contribution to the thermal properties of LUV was discussed.

New spirit of an old technique: Characterization of lipid phase transitions via UV/Vis spectroscopy

One of the advantages of investigating lipid phase transitions by thermoanalytical techniques such as DSC is manifested in the proportionality of the signal strength on a DSC curve, attributed to a particular thermotropic event, and its cooperativity degree. Accordingly, the pretransition of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) is less noticeable than its main phase transition; as a matter of fact, when DSC measurements are performed at low heating rate, such low-cooperativity phase transition could go (almost) unnoticed. The aim of this work is to present temperature-dependent UV/Vis spectroscopy, based on a temperature-dependent change in DPPC suspension turbidity, as a technique applicable for determination of lipid phase transition temperatures. Multivariate analyzes of the acquired UV/Vis spectra show that phase transitions of the low-cooperativity degree, such as pretransitions, can be identified with the same certainty as transitions of a high-cooperativity degree.

Fate and transformation of silver nanoparticles in different biological conditions

The exploitation of silver nanoparticles (AgNPs) in biomedicine represents more than one third of their overall application. Despite their wide use and significant amount of scientific data on their effects on biological systems, detailed insight into their in vivo fate is still lacking. This study aimed to elucidate the biotransformation patterns of AgNPs following oral administration. Colloidal stability, biochemical transformation, dissolution, and degradation behaviour of different types of AgNPs were evaluated in systems modelled to represent biological environments relevant for oral administration, as well as in cell culture media and tissue compartments obtained from animal models. A multimethod approach was employed by implementing light scattering (dynamic and electrophoretic) techniques, spectroscopy (UV-vis, atomic absorption, nuclear magnetic resonance) and transmission electron microscopy. The obtained results demonstrated that AgNPs may transform very quickly during their journey through different biological conditions. They are able to degrade to an ionic form and again reconstruct to a nanoparticulate form, depending on the biological environment determined by specific body compartments. As suggested for other inorganic nanoparticles by other research groups, AgNPs fail to preserve their specific integrity in in vivo settings.

Interaction of Differently Sized, Shaped, and Functionalized Silver and Gold Nanoparticles with Glycosylated versus Nonglycosylated Transferrin

Exposure of nanomaterials (NMs) to biological medium results in their direct interaction with biomolecules and the formation of a dynamic biomolecular layer known as the biomolecular corona. Despite numerous published data on nano-biointeractions, the role of protein glycosylation in the formation, characteristics, and fate of such nano-biocomplexes has been almost completely neglected, although most serum proteins are glycosylated. This study aimed to systematically investigate the differences in interaction of metallic NPs with glycosylated vs nonglycosylated transferrin. To reach this aim, we compared interaction mechanisms between differently sized, shaped, and surface-functionalized silver NMs and gold NMs to commercially available human transferrin (TRF), a glycosylated protein, and to its nonglycosylated recombinant form (ngTRF). Bovine serum albumin (BSA) was also included in the study for comparative purposes. Characterization of NMs was performed using transmission electron microscopy and dynamic and electrophoretic light scattering techniques. Fluorescence quenching and circular dichroism methods were used to evaluate protein binding constants on the nanosurface and conformational changes after the protein-NM interactions, respectively. Competitive binding of TRF, ngTRF, and BSA to the surface of different NMs was evaluated by separating them after extraction from protein corona by gel electrophoresis following quantification with a commercial protein assay. The results showed that the binding strength between NMs and transferrin and the changes in the secondary protein structure largely depend not only on NM physicochemical properties but also on the protein glycosylation status. Data gained by this study highlight the relevance of protein glycosylation for all future design, development, and efficacy and safety assessment of NMs.

Tailoring the stability/aggregation of one-dimensional TiO2(B)/titanate nanowires using surfactants

The increased utilization of one-dimensional (1D) TiO2 and titanate nanowires (TNWs) in various applications was the motivation behind studying their stability in this work, given that stability greatly influences both the success of the application and the environmental impact. Due to their high abundance in aqueous environments and their rich technological applicability, surfactants are among the most interesting compounds used for tailoring the stability. The aim of this paper is to determine the influence of surfactant molecular structure on TNW stability/aggregation behavior in water and aqueous NaBr solution by dynamic and electrophoretic light scattering. To accomplish this, two structurally different quaternary ammonium surfactants (monomeric DTAB and the corresponding dimeric 12-2-12) at monomer and micellar concentrations were used to investigate TNW stability in water and NaBr. It was shown that TNWs are relatively stable in Milli-Q water. However, the addition of NaBr induces aggregation, especially as the TNW mass concentration increases. DTAB and 12-2-12 adsorb on TNW surfaces as a result of the superposition of favorable electrostatic and hydrophobic interactions. As expected, the interaction of TNWs with 12-2-12 was stronger than with DTAB, due to the presence of two positively charged head groups and two hydrophobic tails. As a consequence of the higher adsorption of 12-2-12, TNWs remained stable in both media, while DTAB showed an opposite behavior. In order to gain more insight into changes in the surface properties after surfactant adsorption on the TNW surface, a surface complexation model was employed. With this first attempt to quantify the contribution of the surfactant structure on the adsorption equilibrium according to the observed differences in the intrinsic log K values, it was shown that 12-2-12 interacts more strongly with TNWs than DTAB. The modelling results enable a better understanding of the interaction between TNWs and surfactants as well as the prediction of the conditions that can promote stabilization or aggregation.

Toxicity and safety study of silver and gold nanoparticles functionalized with cysteine and glutathione

This study was designed to evaluate the nano-bio interactions between endogenous biothiols (cysteine and glutathione) with biomedically relevant, metallic nanoparticles (silver nanoparticles (AgNPs) and gold nanoparticles (AuNPs)), in order to assess the biocompatibility and fate of nanoparticles in biological systems. A systematic and comprehensive analysis revealed that the preparation of AgNPs and AuNPs in the presence of biothiols leads to nanoparticles stabilized with oxidized forms of biothiols. Their safety was tested by evaluation of cell viability, reactive oxygen species (ROS) production, apoptosis induction and DNA damage in murine fibroblast cells (L929), while ecotoxicity was tested using the aquatic model organism Daphnia magna. The toxicity of these nanoparticles was considerably lower compared to their ionic metal forms (i.e., Ag⁺ and Au³⁺). The comparison with data published on polymer-coated nanoparticles evidenced that surface modification with biothiols made them safer for the biological environment. In vitro evaluation on human cells demonstrated that the toxicity of AgNPs and AuNPs prepared in the presence of cysteine was similar to the polymer-based nanoparticles with the same core material, while the use of glutathione for nanoparticle stabilization was considerably less toxic. These results represent a significant contribution to understanding the role of biothiols on the fate and behavior of metal-based nanomaterials.

Surface coating affects uptake of silver nanoparticles in neural stem cells

The rapid development and widespread applications of nanotechnology necessitates the design towards safe nanoparticles. Surface structure is among the most important physicochemical characteristics of metallic nanoparticles affecting their mode of action in certain biological or environmental compartments. This study aimed to investigate how different surface coatings affect the cytotoxicity and cellular uptake of silver nanoparticles (AgNPs) in murine neural stem cells (mNSCs). Different AgNPs were prepared by stabilisation with surface coatings encompassing sodium bis(2-ethylhexyl)-sulfosuccinate (AOT), cetyltrimethylammonium bromide (CTAB), poly(vinylpyrrolidone) (PVP), poly-l-lysine (PLL), and bovine serum albumin (BSA). The obtained results revealed that AgNPs stabilized with different surface coating caused different cytotoxicity effects and internalization pattern in mNSCs. Macropinocytosis was determined as the main uptake mechanism in mNSCs for all of the tested AgNP types. These findings contribute to the overall knowledge essential to the safety assessment of novel nanomaterials.

How protein coronas determine the fate of engineered nanoparticles in biological environment

Nanomedicine is a booming medical field that utilises nanoparticles (NPs) for the development of medicines, medical devices, and diagnostic tools. The behaviour of NPs in vivo may be quite complex due to their interactions with biological molecules. These interactions in biological fluids result in NPs being enveloped by dynamic protein coronas, which serve as an interface between NPs and their environment (blood, cell, tissue). How will the corona interact with this environment will depend on the biological, chemical, and physical properties of NPs, the properties of the proteins that make the corona, as well as the biological environment. This review summarises the main characteristics of protein corona and describes its dynamic nature. It also presents the most common analytical methods to study the corona, including examples of protein corona composition for the most common NPs used in biomedicine. This knowledge is necessary to design NPs that will create a corona with a desired efficiency and safety in clinical use.

Cytokinin response in pepper plants (Capsicum annuum L.) exposed to silver nanoparticles

The increasing development of different nanomaterials, such as silver nanoparticles (AgNPs), and their practical use in agriculture and biotechnology has created a strong need for elucidations of biological effects and risk assessments of AgNPs in plants. This study was aimed to investigate AgNPs effects on metal uptake and their biodistribution in pepper plants as well as on morphological parameters and hormonal responses of the isoprenoid cytokinin (CK) family. In addition, the comparison of effects silver form, nanoparticles vs. ionic, has also been examined. To the best of our knowledge, this is the first study describing CK responses in plants exposed to metallic NPs. The obtained results indicate that both AgNPs and Ag⁺ ions significantly increased total content of Ag⁺ in pepper tissues in a dose-dependent manner and affected on plant development by decreasing both plant height and biomass in a similar way. This study evidenced for the first time the role of CKs in abiotic stress in plants caused by AgNPs. The hormonal analysis, conducted by an ultra-high performance liquid chromatography-electrospray tandem mass spectrometry, revealed a significant increase in total CKs in the leaves and also highlighted the importance of cis-zeatin type CKs in plants treated with AgNPs. Our observations suggest potential risks of AgNPs on plant ecosystems upon their release into the environment.

Effect of Protein Corona on Silver Nanoparticle Stabilization and Ion Release Kinetics in Artificial Seawater

In parallel with the growing use of nanoparticle-containing products, their release into the environment over the coming years is expected to increase significantly. With many large population centers located in near-coastal areas, and increasing evidence that various nanoparticles may be toxic to a range of organisms, biota in estuarine and coastal waters may be particularly vulnerable. While size effects may be important in cases, silver nanoparticles have been found to be toxic in large part due to their release of silver ions. However, there is relatively little data available on how nanoparticle coatings can affect silver ion release in estuarine or marine waters. We have found that albumin, as a model for biocorona-forming macromolecules which nanoparticles may encounter in wastewater streams, stabilizes silver colloids from agglomeration in high salinity marine waters by electrosteric repulsion for long time periods. A minimum mass ratio of about 130 for albumin:silver nanoparticles (40 nm) was required for stable dispersion in seawater. Increasing albumin concentration was also found to reduce dissolution of nanoparticles in seawater with up to 3.3 times lower concentrations of silver ions noted. Persistent colloids and slow sustained ion release may have important consequences for biota in these environmental compartments.

Interplay of Noncovalent Interactions in Ionic Liquid/Sodium Bis(2-ethylhexyl) Sulfosuccinate Mixtures: From Lamellar to Bicontinuous Cubic Liquid Crystalline Phase

Phase transitions in mixtures of imidazolium based ionic liquid ([C₁₂mim]Br) and anionic double tail surfactant, sodium bis(2-ethylhexyl) sulfosuccinate (AOT), were studied using a multitechnique approach. The system was primarily chosen for its expected ability to form a variety of lamellar and nonlamellar liquid crystalline phases which can transform into each other via different mechanisms. Depending on the bulk composition and total surfactant concentration, mixed micelles, coacervates, and lamellar and inverse bicontinuous cubic liquid crystalline phase were observed. Along with electrostatic attractions and geometric packing constraints, additional noncovalent interactions (hydrogen bonding, π-π stacking) enhanced attractive interactions and stabilized low curvature aggregates. At stoichiometric conditions, coexistence of coacervates and vesicles was found at lower, while bicontinuous cubic phase and vesicles were present at higher total surfactant concentrations. The phase transitions from a dispersed lamellar to inverse cubic bicontinuous phase occur as a consequence of charge shielding and closer packing of oppositely charged headgroups followed by a change in bilayer curvature. Transition is continuous with both phases coexisting over a relatively broad range of concentrations and very likely involves a sponge-like phase as a structural intermediate. To the best of our knowledge, this type of phase transition has not been observed before in surface active ionic liquid/surfactant mixtures.

Surface coating affects behavior of metallic nanoparticles in a biological environment

Silver (AgNPs) and maghemite, i.e., superparamagnetic iron oxide nanoparticles (SPIONs) are promising candidates for new medical applications, which implies the need for strict information regarding their physicochemical characteristics and behavior in a biological environment. The currently developed AgNPs and SPIONs encompass a myriad of sizes and surface coatings, which affect NPs properties and may improve their biocompatibility. This study is aimed to evaluate the effects of surface coating on colloidal stability and behavior of AgNPs and SPIONs in modelled biological environments using dynamic and electrophoretic light scattering techniques, as well as transmission electron microscopy to visualize the behavior of the NP. Three dispersion media were investigated: ultrapure water (UW), biological cell culture medium without addition of protein (BM), and BM supplemented with common serum protein (BMP). The obtained results showed that different coating agents on AgNPs and SPIONs produced different stabilities in the same biological media. The combination of negative charge and high adsorption strength of coating agents proved to be important for achieving good stability of metallic NPs in electrolyte-rich fluids. Most importantly, the presence of proteins provided colloidal stabilization to metallic NPs in biological fluids regardless of their chemical composition, surface structure and surface charge. In addition, an assessment of AgNP and SPION behavior in real biological fluids, rat whole blood (WhBl) and blood plasma (BlPl), revealed that the composition of a biological medium is crucial for the colloidal stability and type of metallic NP transformation. Our results highlight the importance of physicochemical characterization and stability evaluation of metallic NPs in a variety of biological systems including as many NP properties as possible.