Publications

Abstract Soft nanomaterials can form stimuli-responsive self-assembled structures with significant potential for pharmaceutical and biomedical applications. Polymer/surfactant (P/S) solutions and hydrogels, in particular, have drawn great interest for the development of effective delivery systems, yet molecular insight into these systems and their mechanisms of action is still needed. Here, we examine the colloidal properties of mixtures comprising the amino acid-derived surfactant 14Lys10 and the amphiphilic triblock copolymers Pluronic F127 and P84, which have distinct hydrophobic/hydrophilic balances. We hypothesized that the two F127/14Lys10 and P84/ 14Lys10 systems would show strong, complex associative behavior and this was indeed observed. Combined data from light and electron microscopy, differential scanning microcalorimetry, rheology and surface tension provide a comprehensive picture. At room temperature, the bio-inspired surfactant forms a gel network of entangled nano and micro-tubes that transitions into vesicles at 33 degrees C. The polymers form micelles upon heating. When mixed, the polymer significantly decreases the strength of the tube network and lowers the tube-to-vesicle transition temperature, with the effect strongly dependent on polymer concentration and hydrophobic/hydrophilic balance. Upon tube disassembly, evidence indicates the formation of mixed vesicles coexisting with mixed micelles. Molecular-level insights into the interactions and self-assembly phenomena are provided. This study opens avenues for rationally designing hybrid soft materials as advanced functional biomaterials in nano-medicine and pharmaceutics.

Abstract Catanionic mixtures, composed of cationic and anionic surfactants, spontaneously form robust self-assembled aggregates whose morphology, size, and surface charge can be tailored by adjusting the surfactant mixing ratio. This straightforward and scalable approach, based on easily obtainable components, offers a versatile and simple platform with high potential for drug delivery. However, developing viable nanocarriers also requires a favorable cytotoxicity profile, high drug loading, and strong bioactivity-features that catanionic vesicles often lack. Here, we present a systematic study of pH-sensitive catanionic vesicles composed of mixtures of the biocompatible, FDA-approved anionic surfactant sodium lauroyl sarcosinate (SLSar) and various cationic double-tailed surfactants (didodecyldimethylammonium bromide and bis-quat 12-s-12 gemini surfactants). The different vesicle systems form spontaneously at low critical aggregation concentrations (approximate to 3-30 mu mol kg-1), and exhibit a broad range of size distributions, high surface charge (positive and negative), and long-term colloidal stability. Cytotoxicity screening in healthy L929 fibroblasts enabled the selection of highly biocompatible compositions, with gemini/SLSar systems showing superior doxorubicin (DOX) encapsulation efficiency. These vesicles exhibit enhanced DOX release at acidic pH (approximate to 6.0), mimicking tumor microenvironments, and demonstrate rapid and efficient uptake in lung carcinoma cells within 30 min, increasing over 3 h. Remarkably, DOX-loaded vesicles achieve potent cytotoxicity at only 5 nM DOX-well below the IC50 of free drug-highlighting enhanced therapeutic efficacy and potential for reduced systemic toxicity. Overall, SLSar-based catanionic vesicles constitute a simple, stable, and tunable nanocarrier platform with significant potential for pH-responsive, low-dose cancer chemotherapy.

Abstract The efficient delivery of nucleic acids (NAs) remains a major challenge in gene therapy due to their poor stability and limited cellular uptake. Even though non-viral vectors have been pivotal to overcoming some of these challenges, significant barriers, such as intracellular digestion of NAs and limited endosomal escape, still remain. Here, we developed novel stimuli-responsive lipoplexes integrating a 2-hydroxychalcone-based cationic amphiphile (CnNCh, with 4 or 6 carbons in their alkyl chains, n = 4 or 6) and monoolein (MO). This combination leverages the photoisomerization and pH-sensitivity of chalcone derivatives, along with the fusogenic capabilities of MO, to achieve enhanced transfection efficiency via light irradiation. To reach this goal, we first assessed the cytotoxicity of the cationic amphiphiles in healthy and tumor cells. We then prepared mixtures with varying CnNCh/MO molar ratios, yielding net cationic vesicles with long-term colloidal stability. Subsequently, NAs were efficiently compacted into lipoplexes at N/P ratios (positively charged nitrogen/negatively charged phosphate) higher than 1, attaining near-complete compaction. Light and pH stimuli induce the formation of the expected products, but without compromising lipoplex stability or activating premature NA release. Vesicles with different CnNCh/MO molar ratios do not induce the loss of viability of normal fibroblasts for concentrations up to 50 mu M. Crucially, siRNA-lipoplex mixtures having C4NCh/MO molar ratios of 1/1 and 2/1 (N/P = 6) achieve significant GFP knockdown after irradiation, indicative of successful siRNA delivery and biological effects. Using biomimicking endosomal membranes, we show that photoactivation enhances membrane fusion, suggesting a mechanism entailing light-mediated endosomal escape. Our study provides proof-of-concept for a light-switch mechanism offering precise spatiotemporal control over gene silencing, a highly desirable feature in therapeutic applications.

Abstract Malaria is one of the big three global infectious diseases, having caused above two hundred million cases and over half a million deaths in 2020. The continuous demand for new treatment options prioritizes the cost-effective development of new chemical entities with multi-stage antiplasmodial activity, for higher efficacy and lower propensity to elicit drug-resistant parasite strains. Following up on our long-term research towards the rescue of classical antimalarial aminoquinolines like chloroquine and primaquine, we have developed new organic salts by acid-base pairing of those drugs with natural bile acids. These antimalarial drug-derived bile salts were screened in vitro against the hepatic, blood and gametocyte stages of Plasmodium parasites, unveiling chloroquine bile salts as unprecedented triple-stage antiplasmodial hits. These findings pave a new pathway for drug rescuing, even beyond anti-malarial and other anti-infective drugs. Malaria is one of the big three global infectious diseases, with the heaviest toll on human lives in low-to-middle income countries. Cost-effective antimalarial drugs with multi-stage action remain an unmet and urgent need in global healthcare.

Abstract Cationic gemini surfactants have emerged as potential gene delivery agents as they can co-assemble with DNA due to a strong electrostatic association. Commonly, DNA complexation is enhanced by the inclusion of a helper lipid (HL), which also plays a key role in transfection efficiency. The formation of lipoplexes, used as non-viral vectors for transfection, through electrostatic and hydrophobic interactions is affected by various physicochemical parameters, such as cationic surfactant:HL molar ratio, (+/-) charge ratio, and the morphological structure of the lipoplexes. Herein, we investigated the DNA complexation ability of mixtures of serine-based gemini surfactants, (nSer)2N5, and monoolein (MO) as a helper lipid. The micelle-forming serine surfactants contain long lipophilic chains (12 to 18 C atoms) and a five CH2 spacer, both linked to the nitrogen atoms of the serine residues by amine linkages. The (nSer)2N5:MO aggregates are non-cytotoxic up to 35-90 mu M, depending on surfactant and surfactant/MO mixing ratio, and in general, higher MO content and longer surfactant chain length tend to promote higher cell viability. All systems efficaciously complex DNA, but the (18Ser)2N5:MO one clearly stands as the best-performing one. Incorporating MO into the serine surfactant system affects the morphology and size distribution of the formed mixed aggregates. In the low concentration regime, gemini-MO systems aggregate in the form of vesicles, while at high concentrations the formation of a lamellar liquid crystalline phase is observed. This suggests that lipoplexes might share a similar bilayer-based structure.

Abstract Mixtures of cationic and anionic surfactants often originate bilayer structures, such as vesicles and lamellar liquid crystals, that can be explored as model membranes for fundamental studies or as drug and gene nanocarriers. Here, we investigated the aggregation properties of two catanionic mixtures containing biomimetic surfactants derived from serine. The mixtures are designated as 12Ser/8-8Ser and 14Ser/10-10Ser, where mSer is a cationic, single-chained surfactant and n-nSer is an anionic, double-chained one (m and n being the C atoms in the alkyl chains). Our goal was to investigate the effects of total chain length and chain length asymmetry of the catanionic pair on the formation of catanionic vesicles, the vesicle properties and the vesicle/micelle transitions. Ocular observations, surface tension measurements, video-enhanced light microscopy, cryogenic scanning electron microscopy, dynamic and electrophoretic light scattering were used to monitor the self-assembly process and the aggregate properties. Catanionic vesicles were indeed found in both systems for molar fractions of cationic surfactant >= 0.40, always possessing positive zeta potentials (zeta = +35-50 mV), even for equimolar sample compositions. Furthermore, the 14Ser/10-10Ser vesicles were only found as single aggregates (i.e., without coexisting micelles) in a very narrow compositional range and as a bimodal population (average diameters of 80 and 300 nm). In contrast, the 12Ser/8-8Ser vesicles were found for a wider sample compositional range and as unimodal or bimodal populations, depending on the mixing ratio. The aggregate size, pH and zeta potential of the mixtures were further investigated. The unimodal 12Ser/8-8Ser vesicles (<D-H> approximate to 250 nm, pH approximate to 7-8, zeta approximate to +32 mV and a cationic/anionic molar ratio of approximate to 2:1) are particularly promising for application as drug/gene nanocarriers. Both chain length asymmetry and total length play a key role in the aggregation features of the two systems. Molecular insights are provided by the main findings.

Abstract Interactions between polymers (P) and surfactants (S) in aqueous solution lead to interfacial and aggregation phenomena that are not only of great interest in physical chemistry but also important for many industrial applications, such as the development of detergents and fabric softeners. Here, we synthesized two ionic derivatives-sodium carboxymethylcellulose (NaCMC) and quaternized cellulose (QC)-from cellulose recycled from textile wastes and then explored the interactions of these polymers with assorted surfactants-cationic (CTAB, gemini), anionic (SDS, SDBS) and nonionic (TX-100)-commonly used in the textile industry. We obtained surface tension curves of the P/S mixtures by fixing the polymer concentration and then increasing the surfactant concentration. In mixtures where polymer and surfactant are oppositely charged (P-/S+ and P+/S-), a strong association is observed, and from the surface tension curves, we determined the critical aggregation concentration (cac) and critical micelle concentration in the presence of polymer (cmc(p)). For mixtures of similar charge (P+/S+ and P-/S-), virtually no interactions are observed, with the notable exception of the QC/CTAB system, which is much more surface active than the neat CTAB. We further investigated the effect of oppositely charged P/S mixtures on hydrophilicity by measuring the contact angles of aqueous droplets on a hydrophobic textile substrate. Significantly, both P-/S+ and P+/S- systems greatly enhance the hydrophilicity of the substrate at much lower surfactant concentrations than the surfactant alone (in particular in the QC/SDBS and QC/SDS systems).

Abstract Inspired by previous disclosure of room-temperature ionic liquids derived from primaquine and cinnamic acids, which displayed slightly enhanced blood-stage activity compared to the parent drug, we have now combined this emblematic antimalarial with natural fatty acids. This affords surface-active ionic liquids whose liver-stage antiplasmodial activity is either retained or slightly enhanced, while revealing blood-stage antiplasmodial activity at least one order of magnitude higher than that of the parent compound. These findings open new perspectives towards the cost-effective recycling of classical drugs that are either shelved or in decline, and which is not limited to antimalarial agents.

Abstract While surfactants and polymers have been independently investigated as agents to separate, disperse and stabilize carbon nanotubes (CNTs) in water, mixed polymer/surfactant (P/S) systems have been far less studied for those ends. In this work, we investigated the ability of various types of P/S mixtures to effectively separate multiwalled carbon nanotubes (MWNTs) in water, using rigorously controlled processing conditions. Two types of mixtures were explored: i) nonionic polymer (PVP, polyvinylpyrrolidone) and ionic surfactant (sodium dodecylbenzene sulfonate, SDBS, or cetyltrimethylammonium bromide, CTAB); and ii) ionic polymer (poly(diallyl dimethyl ammonium chloride), PDDA, and sodium polyacrylate, PAS) and nonionic surfactant (TX-100). Detailed, high precision dispersibility curves (concentration of dispersed nanotubes vs. total P/S concentration, at fixed S concentration) are presented for four P/S mixtures (PVP/SDBS, PVP/CTAB, PDDA/TX-100 and PAS/TX-100) and their respective individual components. Quantitative metrics extracted from the dispersibility curves allow for reliable comparisons between the systems. In all P/S mixtures, beneficial (synergistic) effects in nanotube dispersibility are observed compared to the individual components, with the exception of the PDDA/TX-100 one for which a detrimental (antagonistic) effect occurs. Morphological characterization of the as-obtained dispersions by scanning electron microscopy (SEM) shows a significant degree of nanotube separation by the P/S systems. Surface tension and zeta potential measurements provide further information on the interactions at play between the MWNTs and the P/S mixtures, allowing to conceive plausible mechanisms for the synergistic effects observed. P/S association may not only offer conditions for an enhanced dispersibility of CNTs but also expand the types of noncovalent, reversible functionalization required in many applications, such as the development of nanocomposite particles, films and coatings.

Abstract Aqueous surfactant/polymermixtures form colloidal structures of great fundamental interest and practical relevance, such as nanostructured hydrogels for biomedical and pharmaceutical uses. In this work, we investigated the phase behavior, structure and cytotoxicity of mixtures of a double-tailed lysine-based surfactant, 16Lys12, and two hydroxyethyl cellulose (HEC) derivatives, JR400 and LM200. The surfactant, S-, is anionic and self-assembles into tubular structures at room temperature, undergoing a tubule-to-vesicle transition at approximate to 44 degrees C. JR400 is a cationic homopolymer, P+, longer and more densely charged than LM200, a closely related hydrophobically modified polymer, HMP+. Electrostatic and hydrophobic interactions play a crucial role in the observed phase behavior and resulting colloidal structures. Both the S-/P+ and S-/HMP+ mixtures show three main phase regions: at surfactant charge excess, bluish dispersions containing mixed polymer/tubular aggregates and, upon heating, polymer/vesicle clusters; a white precipitate near charge equimolarity, coexisting with either a solution or a gel; and highly viscous hydrogels, at polymer charge excess. In the bluish dispersions, the S-/P+ and S-/HMP+ systems show relevant differences in thermal behavior and type of aggregates present. Cryogenic scanning electron microscopy shows that the hydrogels consist of honeycomb-like structure of surfactant and polymer moieties. Cytotoxicity assays in the bluish dispersion region indicate good levels of cytocompatibility for both types of surfactant/polymer systems. Overall, these dispersions and hydrogels can be further explored for the encapsulation and temperature-triggered release of biomolecules.