Phagocytic uptake by mouse peritoneal macrophages of microspheres coated with phosphocholine or polyethylene glycol phosphate-derived perfluoroalkylated surfactants

Selected physicochemical aspects of poly- and perfluoroalkylated substances relevant to performance, environment and sustainability-part one

The elemental characteristics of the fluorine atom tell us that replacing an alkyl chain by a perfluoroalkyl or polyfluorinated chain in a molecule or polymer is consequential. A brief reminder about perfluoroalkyl chains, fluorocarbons and fluorosurfactants is provided. The outstanding, otherwise unattainable physicochemical properties and combinations thereof of poly and perfluoroalkyl substances (PFASs) are outlined, including extreme hydrophobic and lipophobic character; thermal and chemical stability in extreme conditions; remarkable aptitude to self-assemble into sturdy thin repellent protecting films; unique spreading, dispersing, emulsifying, anti-adhesive and levelling, dielectric, piezoelectric and optical properties, leading to numerous industrial and technical uses and consumer products. It was eventually discovered, however, that PFASs with seven or more carbon-long perfluoroalkyl chains had disseminated in air, water, soil and biota worldwide, are persistent in the environment and bioaccumulative in animals and humans, raising serious health and environmental concerns. Further use of long-chain PFASs is environmentally not sustainable. Most leading manufacturers have turned to shorter four to six carbon perfluoroalkyl chain products that are not considered bioaccumulative. However, many of the key performances of PFASs decrease sharply when fluorinated chains become shorter. Fluorosurfactants become less effective and less efficient, provide lesser barrier film stability, etc. On the other hand, they remain as persistent in the environment as their longer chain homologues. Surprisingly little data (with considerable discrepancies) is accessible on the physicochemical properties of the PFASs under examination, a situation that requires consideration and rectification. Such data are needed for understanding the environmental and in vivo behaviour of PFASs. They should help determine which, for which uses, and to what extent, PFASs are environmentally sustainable.

Cellular uptake of nanoparticles as determined by particle properties, experimental conditions, and cell type

The increased application of nanoparticles (NPs) is increasing the risk of their release into the environment. Although many toxicity studies have been conducted, the environmental risk is difficult to estimate, because uptake mechanisms are often not determined in toxicity studies. In the present study, the authors review dominant uptake mechanisms of NPs in cells, as well as the effect of NP properties, experimental conditions, and cell type on NP uptake. Knowledge of NP uptake is crucial for risk assessment and is essential to predict the behavior of NPs based on their physical-chemical properties. Important uptake mechanisms for eukaryotic cells are macropinocytosis, receptor-mediated endocytosis, and phagocytosis in specialized mammalian cells. The studies reviewed demonstrate that uptake into nonphagocytic cells depends strongly on NP size, with an uptake optimum at an NP diameter of approximately 50 nm. Increasing surface charges, either positive or negative, have been shown to increase particle uptake in comparison with uncharged NPs. Another important factor is the degree of (homo-) aggregation. Results regarding shape have been ambiguous. Difficulties in the production of NPs, with 1 property changed at a time, call for a full characterization of NP properties. Only then will it be possible to draw conclusions as to which property affected the uptake.

In vitro assessments of nanomaterial toxicity

Nanotechnology has grown from a scientific interest to a major industry with both commodity and specialty nanomaterial exposure to global populations and ecosystems. Sub-micron materials are currently used in a wide variety of consumer products and in clinical trials as drug delivery carriers and imaging agents. Due to the expected growth in this field and the increasing public exposure to nanomaterials, both from intentional administration and inadvertent contact, improved characterization and reliable toxicity screening tools are required for new and existing nanomaterials. This review discusses current methodologies used to assess nanomaterial physicochemical properties and their in vitro effects. Current methods lack the desired sensitivity, reliability, correlation and sophistication to provide more than limited, often equivocal, pieces of the overall nanomaterial performance parameter space, particularly in realistic physiological or environmental models containing cells, proteins and solutes. Therefore, improved physicochemical nanomaterial assays are needed to provide accurate exposure risk assessments and genuine predictions of in vivo behavior and therapeutic value. Simpler model nanomaterial systems in buffer do not accurately duplicate this complexity or predict in vivo behavior. A diverse portfolio of complementary material characterization tools and bioassays are required to validate nanomaterial properties in physiology.

New perfluorinated polycationic dimerizable detergents for the formulation of monomolecular DNA nanoparticles and their in vitro transfection efficiency

We describe the synthesis of new perfluorinated dimerizable detergents which contain a tricationic or tetracationic (linear or branched spermine, respectively) polar head, and report on their cmc, their ability to condense DNA into cationic monomolecular DNA nanoparticles as well as on the in vitro transfection efficiency of these nanoparticles. Such cationic nanoparticles were prone to display efficient cell transfection properties as a result of increased contact to the anionic cell surface and internalization by endocytosis, low size compatible with improved intracellular diffusion and nuclear pore crossing, and the presence of amine function of low pK(a) for their endosomal escape. The challenge was to design polymerizable polycationic detergents that display a cmc high enough for the monomer to perform monomolecular DNA condensation (as cationic particles) and low enough for the dimer to form stable nanoparticles capable of efficient cell transfection. Although we succeeded in formulating small-sized cationic monomolecular DNA nanoparticles (<40 nm) with these dimerizable perfluorinated spermine-based detergents for N/P ratios of up to 5 (N=number of detergent amine equivalents/P=number of DNA phosphate equivalents), these small-sized cationic nanoparticles proved to be poor non-specific transfection agents in vitro, even in the presence of chloroquine. Their poor transfection potential could be due more likely to Brownian motion which prevents these very small-sized particles from sedimentation and adsorption onto the adherent cell monolayer, and, consequently, from proteoglycan-triggered endocytosis.

Opsonization of polyethylene wear particles regulates macrophage and osteoblast responses in vitro

The cellular reaction to wear debris may result in the failure of an artificial joint's fixation to the skeleton. The influence of debris opsinization on cell activity has received little attention. This study seeks to establish whether different proteinaceous culture environments may invoke variant cellular responses to debris challenge. Consideration of the zeta potential of a low density polyethylene particle group and an ex vitro ultrahigh molecular weight polyethylene particle group revealed that the nature of the protein adsorbants is related to the concentration of the proteins in solution. Furthermore, the composition of the adsorbed layer was shown to vary with the spectra of proteins in solution. In standard cell culture conditions zeta potential approached zero, indicating the high probability of particle agglomeration. Cell challenge studies with U937 macrophages showed that BSA and FCS protein adsorption mediated increased cell adhesion, while bovine IgG showed little change over control values. No changes in behavior of osteoblastic cells were observed in similar experiments.

Cosurfactant effect of a semifluorinated alkane at a fluorocarbon/water interface: impact on the stabilization of fluorocarbon-in-water emulsions

Previous work has demonstrated that semifluorinated alkanes CnF2n+1CmH2m+1 (FnHm diblocks), when used in conjunction with phospholipids, strongly stabilize fluorocarbon (FC)-in-water emulsions destined to be used as oxygen carriers. Although the presence of FnHm diblocks in the emulsion's interfacial phospholipid film was suggested to account for the observed stabilization, no direct proof of the diblock's location has been provided so far. We now report definite experimental evidence of the diblock's presence at the interfacial film, both on a macroscopic level by investigating the FC/water interface using the pendant drop method and directly on emulsions by monitoring their stability for various phospholipid chain lengths. We first establish that F8H16 has a strong cosurfactant effect with phospholipids [dimyristoylphosphatidylcholine (DMPC), dilaurylphosphatidylcholine (DLPC), dioctanoylphosphatidylcholine (PCL8)] at a perfluorooctyl bromide (PFOB)/water interface, as evidenced by a dramatic F8H16-concentration-dependent decrease of the interfacial tension. Where FC emulsions are concerned, we show that the stabilization effect, which consists of a decrease of the rate of molecular diffusion of the FC, depends strongly on the length of the phospholipid's fatty chain as compared to the length of the hydrocarbon segment, Hm, of the diblock. Stabilization is maximized when the Hm length is similar to that of the phospholipid's fatty chains. A strong mismatch between Hm and the phospholipid chain length can actually destabilize the emulsion. A different destabilization mechanism is then at work: coalescence. The presence of F8H16 at the interfacial film is further supported by the fact that perfluorodecyl bromide, a heavy analogue of PFOB that stabilizes PFOB emulsions by lowering the solubility and diffusibility of the emulsion's dispersed FC phase, exercises its stabilizing effect similarly for all the phospholipids investigated.

Effective graphical displays

A graph is a visual display of data to achieve an understanding of the underlying patterns and interrelationships of the data. Such visual representations of data often form the basis for inferences and decisions. However, a poorly chosen graphical form can lead to erroneous inferences. In this paper previously published graphs depicting biopharmaceutical, drug metabolism, formulation, and pharmacokinetic data are recast using alternate display methods in an attempt to better clarify the data structure. The display methods used include dot plots and trellis plots.

Interfacial adsorption of polymers and surfactants: implications for the properties of disperse systems of pharmaceutical interest

This review considers basic aspects of the interfacial adsorption of polymers and surfactants, with particular reference to the relevance of these processes for the formulation of pharmaceutical disperse systems. First, we discuss different approaches to the interpretation of adsorption isotherms, paying particular attention to systems containing more than one adsorbate. Second, we consider the implications of adsorption for the properties of suspensions, emulsions, and colloidal systems, particularly as regards the use of polymers and surfactants for stabilizing disperse systems, for controlling flocculation, and for modifying the biopharmaceutical behavior of colloidal drug carriers. Finally, we present a number of representative examples of the importance of adsorption of macromolecules in pharmaceutical systems.

Highly fluorinated amphiphiles and colloidal systems, and their applications in the biomedical field. A contribution

Fluorocarbons and fluorocarbon moieties are uniquely characterized by very strong intramolecular bonds and very weak intermolecular interactions. This results in a combination of exceptional thermal, chemical and biological inertness, low surface tension, high fluidity, excellent spreading characteristics, low solubility in water, and high gas dissolving capacities, which are the basis for innovative applications in the biomedical field. Perfluoroalkyl chains are larger and more rigid than their hydrogenated counterparts. They are considerably more hydrophobic, and are lipophobic as well. A large variety of well-defined, modular fluorinated surfactants whose polar head groups consist of polyols, sugars, sugar phosphates, amino acids, amine oxides, phosphocholine, phosphatidylcholine, etc, has recently been synthesized. Fluorinated surfactants are significantly more surface active than their hydrocarbon counterparts, both in terms of effectiveness and of efficiency. Despite this, they are less hemolytic and less detergent. Fluorosurfactants appear unable to extract membrane proteins. Fluorinated chains confer to surfactants a powerful driving force for collecting and organizing at interfaces. As compared to non-fluorinated analogs, fluorosurfactants have also a much stronger capacity to self-aggregate into discrete molecular assemblies when dispersed in water and other solvents. Even very short, single-chain fluorinated amphiphiles can form highly stable, heat-sterilizable vesicles, without the need for supplementary associative interactions. Sturdy microtubules were obtained from non-chiral, non-hydrogen bonding single-chain fluorosurfactants. Fluorinated amphiphiles can be used to engineer a variety of colloidal systems and manipulate their morphology, structure and properties. Stable fluorinated films, membranes and vesicles can also be prepared from combinations of standard surfactants with fluorocarbon/hydrocarbon diblock molecules. In bilayer membranes made from fluorinated amphiphiles the fluorinated tails segregate to form an internal teflon-like hydrophobic and lipophobic film that increases the stability of the membrane and reduces its permeability. This fluorinated film can also influence the behavior of fluorinated vesicles in a biological milieu. For example, it can affect the in vivo recognition and fate of particles, or the enzymatic hydrolysis of phospholipid components. Major applications of fluorocarbons currently in advanced clinical trials include injectable emulsions for delivering oxygen to tissues at risk of hypoxia; a neat fluorocarbon for treatment of acute respiratory failure by liquid ventilation; and gaseous fluorocarbon-stabilized microbubbles for use as contrast agents for ultrasound imaging. Fluorosurfactants also allow the preparation of a range of stable direct and reverse emulsions, microemulsions, multiple emulsions, and gels, some of which may include fluorocarbon and hydrocarbon and aqueous phases simultaneously. Highly fluorinated systems have potential for the delivery of drugs, prodrugs, vaccines, genes, markers, contrast agents and other materials.