Microplastic-Free Microcapsules Using Supramolecular Self-Assembly of Bis-Urea Molecules at an Emulsion Interface.

Encapsulation technology is well established for entrapping active ingredients within an outer shell for their protection and controlled release. However, many solutions employed industrially use nondegradable cross-linked synthetic polymers for shell formation. To curb rising microplastic pollution, regulatory policies are forcing industries to substitute the use of such intentionally added microplastics with environmentally friendly alternatives. This work demonstrates a one-pot process to make microplastic-free microcapsules using supramolecular self-assembly of bis-ureas. Molecular bis-urea species generated in-situ spontaneously self-assemble at the interface of an oil-in-water emulsion via hydrogen bonding to form a shell held together by noncovalent bonds. In addition, Laponite nanodiscs were introduced in the formulation to restrict aggregation observed during the self-assembly and to reduce the porosity of the shell, leading to well-dispersed microcapsules (mean Sauter diameter d [3,2] ∼ 5 µm) with high encapsulation efficiency (∼99%). Accelerated release tests revealed an increase in characteristic release time of the active by more than an order of magnitude after encapsulation. The mechanical strength parameters of these capsules were comparable to some of the commercial, nondegradable melamine-formaldehyde microcapsules. With mild operating conditions in an aqueous environment, this technology has real potential to offer an industrially viable method for producing microplastic-free microcapsules.

A review of artificial sebum formulations, their compositions, uses and physicochemical characteristics.

Sebum is a complex mixture of skin lipids responsible for lubrication, moisture retention and skin protection from external factors such as bacteria and fungi. The physicochemical properties of natural sebum are not well understood and are not easily accessible. Artificial sebum is widely used for sebum-related research such as dermal bioaccessibility, fingerprint production, dermatology, removal and sebum studies. It was found that the composition of artificial sebum affects the bioaccessibility of metals and drugs as well as the growth of some strains of bacteria. Squalene present in sebum was also found to be responsible for creating yellow stains on fabrics, whereas an increased concentration of fatty acids and triglycerides can lead to higher malodour of fabrics. Moreover, sebum and artificial sebum are poorly characterized with only 20 of 81 formulations characterized by certain techniques such as differential scanning calorimetry, nuclear magnetic resonance and thin-layer chromatography. This article reviews the artificial sebum formulations reported in the open literature between 1965 and 2023. We have discussed the compositions, uses and characterization techniques of artificial sebum used in the previous work and compared their properties to those of human sebum. A total of 81 artificial sebum formulations were found across the literature with 17 new formulations identified. The artificial sebum composition varies greatly between publications and there is no consistent formulation. There is a wide range of chemicals that are used as the main components of artificial sebum. We have highlighted the effect of chemical composition and individual compounds on the overall properties of the artificial sebum reported, and recommend that there is a great potential for creating personalized cosmetics and home care products once the characteristics of sebum are better understood.

Le sébum est un mélange complexe de lipides cutanés responsable de la lubrification, de la rétention d'humidité et de la protection de la peau contre des facteurs externes tels que les bactéries et les champignons. Les propriétés physico­chimiques du sébum naturel ne sont pas bien comprises et ne sont pas facilement disponibles. Le sébum artificiel est largement utilisé pour la recherche liée au sébum, comme la bioaccessibilité cutanée, la production d'empreintes digitales, la dermatologie, le retrait et les études sur le sébum. Il a été constaté que la composition du sébum artificiel affecte la bioaccessibilité des métaux et des médicaments ainsi que la croissance de certaines souches de bactéries. Le squalène présent dans le sébum s'est également avéré responsable de la formation de taches jaunes sur les tissus, tandis qu'une concentration accrue d'acides gras et de triglycérides peut entraîner une odeur désagréable plus élevée des tissus. En outre, le sébum et le sébum artificiel sont mal caractérisés avec seulement 20 formulations sur 81 caractérisées par certaines techniques telles que la calorimétrie à balayage différentiel, la résonance magnétique nucléaire et la chromatographie sur couche mince. Cet article examine les formulations de sébum artificiel rapportées dans la littérature ouverte entre 1965 et 2023. Nous avons discuté des compositions, des utilisations et des techniques de caractérisation du sébum artificiel utilisé dans l'ouvrage précédent et comparé leurs propriétés à celles du sébum humain. Au total, 81 formulations de sébum artificiel ont été trouvées dans la littérature, avec 17 nouvelles formulations identifiées. La composition du sébum artificiel varie considérablement d'une publication à l'autre et il n'existe pas de formulation cohérente. Il existe un large éventail de produits chimiques qui sont utilisés comme principaux composants du sébum artificiel. Nous avons souligné l'effet de la composition chimique et des composés individuels sur les propriétés globales du sébum artificiel rapporté, et nous soutenons qu'il existe un grand potentiel pour la création de produits cosmétiques et de soins à domicile personnalisés une fois que les caractéristiques du sébum seront mieux comprises.

Electrically Responsive Surfaces: Experimental and Theoretical Investigations.

Stimuli-responsive surfaces have sparked considerable interest in recent years, especially in view of their biomimetic nature and widespread biomedical applications. Significant efforts are continuously being directed at developing functional surfaces exhibiting specific property changes triggered by variations in electrical potential, temperature, pH and concentration, irradiation with light, or exposure to a magnetic field. In this respect, electrical stimulus offers several attractive features, including a high level of spatial and temporal controllability, rapid and reverse inducement, and noninvasiveness. In this Account, we discuss how surfaces can be designed and methodologies developed to produce electrically switchable systems, based on research by our groups. We aim to provide fundamental mechanistic and structural features of these dynamic systems, while highlighting their capabilities and potential applications. We begin by briefly describing the current state-of-the-art in integrating electroactive species on surfaces to control the immobilization of diverse biological entities. This premise leads us to portray our electrically switchable surfaces, capable of controlling nonspecific and specific biological interactions by exploiting molecular motions of surface-bound electroswitchable molecules. We demonstrate that our self-assembled monolayer-based electrically switchable surfaces can modulate the interactions of surfaces with proteins, mammalian and bacterial cells. We emphasize how these systems are ubiquitous in both switching biomolecular interactions in highly complex biological conditions while still offering antifouling properties. We also introduce how novel characterization techniques, such as surface sensitive vibrational sum-frequency generation (SFG) spectroscopy, can be used for probing the electrically switchable molecular surfaces in situ. SFG spectroscopy is a technique that not only allowed determining the structural orientation of the surface-tethered molecules under electroinduced switching, but also provided an in-depth characterization of the system reversibility. Furthermore, the unique support from molecular dynamics (MD) simulations is highlighted. MD simulations with polarizable force fields (FFs), which could give proper description of the charge polarization caused by electrical stimulus, have helped not only back many of the experimental observations, but also to rationalize the mechanism of switching behavior. More importantly, this polarizable FF-based approach can efficiently be extended to light or pH stimulated surfaces when integrated with reactive FF methods. The interplay between experimental and theoretical studies has led to a higher level of understanding of the switchable surfaces, and to a more precise interpretation and rationalization of the observed data. The perspectives on the challenges and opportunities for future progress on stimuli-responsive surfaces are also presented.

Switching specific biomolecular interactions on surfaces under complex biological conditions.

Herein, electrically switchable mixed self-assembled monolayers based on oligopeptides have been developed and investigated for their suitability in achieving control over biomolecular interactions in the presence of complex biological conditions. Our model system, a biotinylated oligopeptide tethered to gold within a background of tri(ethylene glycol) undecanethiol, is ubiquitous in both switching specific protein interactions in highly fouling media while still offering the non-specific protein-resistance to the surface. Furthermore, the work demonstrated that the performance of the switching on the electro-switchable oligopeptide is sensitive to the characteristics of the media, and in particular, its protein concentration and buffer composition, and thus such aspects should be considered and addressed to assure maximum switching performance. This study lays the foundation for developing more realistic dynamic extracellular matrix models and is certainly applicable in a wide variety of biological and medical applications.

Glucose selective surface plasmon resonance-based bis-boronic acid sensor.

Saccharides - a versatile class of biologically important molecules - are involved in a variety of physiological and pathological processes, but their detection and quantification is challenging. Herein, surface plasmon resonance and self-assembled monolayers on gold generated from bis-boronic acid bearing a thioctic acid moiety, whose intramolecular distance between the boronic acid moieties is well defined, are shown to detect d-glucose with high selectivity, demonstrating a higher affinity than other saccharides probed, namely d-galactose, d-fructose and d-mannose.

Different formation kinetics and photoisomerization behavior of self-assembled monolayers of thiols and dithiolanes bearing azobenzene moieties.

Self-assembled monolayers (SAMs) containing azobenzene moieties are very attractive for a wide range of applications, including molecular electronics and photonics, bio-interface engineering and sensoring. However, very little is known about the aggregation and photoswitching behavior that azobenzene units undergo during the SAM formation process. Here, we demonstrate that the formation of thiol-based SAMs containing azobenzenes (denoted as AzoSH) on gold surfaces is characterised by a two-step adsorption kinetics, while a three-step assembly process has been identified for dithiolane-based SAMs containing azobenzenes (denoted AzoSS). The H-aggregation on the AzoSS SAMs was found to be remarkably dependent on the time of self-assembly, with less aggregation as a function of time. While photoisomerization of the AzoSH was suppressed for all different assembly times, the reversible trans-cis photoisomerization of AzoSS SAMs formed over 24 hours was clearly observed upon alternating UV and Vis light irradiation. We contend that detailed information on formation kinetics and related optical properties is of crucial importance for elucidating the photoswitching capabilities of azobenzene-based SAMs.

Multicomponent synthetic polymers with viral-mimetic chemistry for nucleic acid delivery.

The ability to deliver genetic material for therapy remains an unsolved challenge in medicine. Natural gene carriers, such as viruses, have evolved sophisticated mechanisms and modular biopolymer architectures to overcome these hurdles. Here we describe synthetic multicomponent materials for gene delivery, designed with features that mimic virus modular components and which transfect specific cell lines with high efficacy. The hierarchical nature of the synthetic carriers allows the incorporation of membrane-disrupting peptides, nucleic acid binding components, a protective coat layer, and an outer targeting ligand all in a single nanoparticle, but with functionality such that each is utilized in a specific sequence during the gene delivery process. The experimentally facile assembly suggests these materials could form a generic class of carrier systems that could be customized for many different therapeutic settings.

Determination of the shell permeability of microcapsules with a core of oil-based active ingredient.

An experimental and theoretical methodology is proposed to calculate the permeability of microcapsules that contain a core of oil-based active ingredient. Theoretical analysis is performed considering the polydispersity of the measurable capsule size, which allows the estimation of the permeability polydispersity via three different methods. The models proposed were applied in order to determine the permeability of melamine-formaldehyde microcapsules with hexyl salicylate as core oil. Release experiments were performed with four different co-solvents (ethanol, propan-1-ol, propan-2-ol and 1,3-butanediol) of different concentration. Permeability values were found to be constant, despite a two order magnitude of difference in the solubility concentrations.

Direct electron-beam writing of highly conductive wires in functionalized fullerene films.

This work demonstrates the patterning of thin films (approximately 25 nm) of a newly synthesized fullerene derivative by direct-write electron-beam lithography to produce highly conducting carbon microstructures. Scanning electron microscopy and atomic force microscopy are used to characterize the resulting microstructure morphology, whilst the resistivities of the structures are probed using four-point probe electrodes deposited on the microstructures by lift-off. The microstructures have a resistivity of approximately 9.5 x 10(-3) Omega cm after exposure to an electron dose of 0.1 C cm(-2). The method may have applications in the generation and electrical contacting of organic electronics, organic photovoltaics, and lab-on-a-chip devices.

Spatially controlled assembly of nanomaterials at the nanoscale.

A molecular monolayer of 4-nitrothiophenol ongold electrodes is reduced electrochemically when its nitro groups are converted into amino groups by potentiometric scans. The protonated amine with its NH3+ functions can be employed to induce the self-assembly of gold nanoparticles at the surface of the electrodes. The electrochemical reaction and the induced assembly process can be controlled at the nanoscale level on the electrodes with a high degree of selectivity. The technology opens up the possibility of fabricating complex multi-nanomaterial nanostructures on the basis of a two-step electrochemical assembly process.

(LYS)(16)-based reducible polycations provide stable polyplexes with anionic fusogenic peptides and efficient gene delivery to post mitotic cells.

Extracellular stability, endocytic escape, intracellular DNA release and nuclear translocation of DNA are all critical properties of non-viral vector/DNA particles. We have evaluated a (Lys)(16)-based linear, reducible polycation (RPC) in combination with an acid-dependent, anionic fusogenic peptide for gene delivery to dividing and post-mitotic cells. The RPC was formed from Cys(Lys)(16)Cys monomers. Molecular weight was 24,000 Da, corresponding to an average of 10.5 peptide monomers per RPC. Non-reducible polylysine (PLL) (27,000 Da) and monomeric (Lys)(16) peptide were evaluated for comparison. (Lys)(16)/DNA particles were disrupted at fusogenic peptide concentrations well below those used for gene delivery. By contrast, RPC/DNA an PLL/DNA particles were stable in the presence of high concentrations of the anionic peptide. Addition of 10% serum virtually abolished the transfection ability of (Lys)(16)/DNA/fusogenic peptide particles, but had little effect on RPC/DNA/fusogenic peptide particles. RPC/DNA/fusogenic peptide particles were highly effective for gene delivery to both cell lines and post-mitotic corneal endothelium. PLL/DNA/fusogenic peptide particles were moderately effective on cell lines, but gave no gene delivery with corneal endothelial cells. We conclude that (Lys)(16)-based RPC/DNA/fusogenic peptide particles provide a gene delivery system which is potentially stable in the extracellular environment and, on reductive depolymerisation, can release DNA plasmids for nuclear translocation.

Processing and characterization of gold nanoparticles for use in plasmon probe spectroscopy and microscopy of biosystems.

Noble metal nanoparticles have great potential for applications in biochemical sensing and biological imaging because of their unique optical properties originating from the excitation of local surface plasmon resonances. We investigated gold nanoparticles with controlled size, shape, and passivating agents, along with a new process of guided self-assembly to create two-dimensional nanostructures from such nanoparticles.

Interaction between manufactured gold nanoparticles and naturally occurring organic macromolecules.

The increasing exploitation of nanomaterials into many consumer and other products is raising concerns as these nanomaterials are likely to be released into the environment. Due to our lack of knowledge about the environmental chemistry, transport and ecotoxicology of nanomaterials, it is of paramount importance to study how natural aquatic colloids can interact with manufactured gold nanoparticles as these interactions will determine their environmental fate and behaviour. In this context, our work aims to quantify the effect of naturally occurring riverine macromolecules--International Humic Substances Society (IHSS) Suwannee River Humic Acid Standard (SRHA)--on citrate- and acrylate-stabilized gold nanoparticles. The influence of SRHA on the stability of the gold colloids was studied as a function of pH by UV-visible absorption spectroscopy, dynamic light scattering (DLS) and transmission electron microscopy (TEM). At high ionic strengths (0.1 M), extensive and rapid aggregation occurred, while more subtle effects were observed at lower ionic strength values. Evidence was found that SRHA enhances particle stability at extreme pH values (ionic strength<0.01 M) by substituting and/or over-coating the original stabilizer on the gold nanoparticle surface, thus affecting surface charge and chemistry. These findings have important implications for the fate and behaviour of nanoparticles in the environment and their ecotoxicity.

Novel encapsulation of water soluble inorganic or organic ingredients in melamine formaldehyde microcapsules to achieve their sustained release in an aqueous environment.

A novel type of melamine formaldehyde microcapsule with a desirable barrier has been used to encapsulate water soluble ingredients, including potassium chloride (KCl) and allura red (dye) as models of an inorganic salt and organic molecule, respectively, via a facile method, and it has shown a sustained release of KCl and allura red for 12 h and 10 days in aqueous environment, respectively.

On-Demand Electrical Switching of Antibody-Antigen Binding on Surfaces.

The development of stimuli-responsive interfaces between synthetic materials and biological systems is providing the unprecedented ability to modulate biomolecular interactions for a diverse range of biotechnological and biomedical applications. Antibody-antigen binding interactions are at the heart of many biosensing platforms, but no attempts have been made yet to control antibody-antigen binding in an on-demand fashion. Herein, a molecular surface was designed and developed that utilizes an electric potential to drive a conformational change in surface bound peptide moiety, to give on-demand control over antigen-antibody interactions on sensor chips. The molecularly engineered surfaces allow for propagation of conformational changes from the molecular switching unit to a distal progesterone antigen, resulting in promotion (ON state) or inhibition (OFF state) of progesterone antibody binding. The approach presented here can be generally applicable to other antigen-antibody systems and meets the technological needs for in situ long-term assessment of biological processes and disease monitoring on-demand.

A chemically amplified fullerene-derivative molecular electron-beam resist.

Current lithographic resists depend on large polymeric materials, which are starting to limit further improvements in line-width roughness and feature size. Fullerene molecular resists use much smaller molecules to avoid this problem. However, such resists have poor radiation sensitivity. Chemical amplification of a fullerene derivative using an epoxy crosslinker and a photoacid generator is demonstrated. The sensitivity of the material is increased by two orders of magnitude, and 20-nm line widths are patterned.

A versatile reducible polycation-based system for efficient delivery of a broad range of nucleic acids.

Synthetic vectors based on reducible polycations consisting of histidine and polylysine residues (HIS RPCs) were evaluated for their ability to deliver nucleic acids. Initial experiments showed that RPC-based vectors with at least 70% histidine content mediated efficient levels of gene transfer without requirement for the endosomolytic agent chloroquine. Significant gene transfer was observed in a range of cell types achieving up to a 5-fold increase in the percentage of transfected cells compared to 25 kDa PEI, a gold standard synthetic vector. In contrast to 25 kDa PEI, HIS RPCs also mediated efficient transfer of other nucleic acids, including mRNA encoding green fluorescent protein in PC-3 cells and siRNA directed against the neurotrophin receptor p75(NTR) in post-mitotic cultures of rat dorsal root ganglion cell neurons. Experiments to elevate intracellular glutathione and linear profiling of cell images captured by multiphoton fluorescent microscopy highlighted that parameters such as the molecular weight and rate of cleavage of HIS RPCs were important factors in determining transfection activity. Altogether, these results demonstrate that HIS RPCs represent a novel and versatile type of vector that can be used for efficient cytoplasmic delivery of a broad range of nucleic acids. This should enable different or a combination of therapeutic strategies to be evaluated using a single type of polycation-based vector.

Hysteresis of charge tunneling in assemblies of carboxylic acid-modified gold nanoparticles.

We report on charge transport measurements through laterally contacted assemblies of Au nanoparticles capped with 11-mercaptoundecanoic acid ligands. Both alternating- and direct-current data indicate that although the nanoparticles behave as electrically isolated metallic islands, there is a significant influence from the nanoparticle environment, indicating the existence of a slow reorganization process linked to charge transport. On the basis of the observation of temperature-dependent hysteresis of charge tunneling, we propose that this process is due to proton transfer between the carboxylic acid tails of the ligands.

Selective glycoprotein detection through covalent templating and allosteric click-imprinting.

Many glycoproteins are intimately linked to the onset and progression of numerous heritable or acquired diseases of humans, including cancer. Indeed the recognition of specific glycoproteins remains a significant challenge in analytical method and diagnostic development. Herein, a hierarchical bottom-up route exploiting reversible covalent interactions with boronic acids and so-called click chemistry for the fabrication of glycoprotein selective surfaces that surmount current antibody constraints is described. The self-assembled and imprinted surfaces, containing specific glycoprotein molecular recognition nanocavities, confer high binding affinities, nanomolar sensitivity, exceptional glycoprotein specificity and selectivity with as high as 30 fold selectivity for prostate specific antigen (PSA) over other glycoproteins. This synthetic, robust and highly selective recognition platform can be used in complex biological media and be recycled multiple times with no performance decrement.

Luminescent gold surfaces for sensing and imaging: patterning of transition metal probes.

Luminescent transition metal complexes are introduced for the microcontact printing of optoelectronic devices. Novel ruthenium(II), RubpySS, osmium(II), OsbpySS, and cyclometalated iridium(III), IrbpySS, bipyridyl complexes with long spacers between the surface-active groups and the metal were developed to reduce the distance-dependent, nonradiative quenching pathways by the gold surface. Indeed, surface-immobilized RubpySS and IrbpySS display strong red and green luminescence, respectively, on planar gold surfaces with luminescence lifetimes of 210 ns (RubpySS·Au) and 130 and 12 ns (83%, 17%) (IrbpySS·Au). The modified surfaces show enhancement of their luminescence lifetime in comparison with solutions of the respective metal complexes, supporting the strong luminescence signal observed and introducing them as ideal inorganic probes for imaging applications. Through the technique of microcontact printing, complexes were assembled in patterns defined by the stamp. Images of the red and green patterns rendered by the RubpySS·Au and IrbpySS·Au monolayers were revealed by luminescence microscopy studies. The potential of the luminescent surfaces to respond to biomolecular recognition events is demonstrated by addition of the dominant blood-pool protein, bovine serum albumin (BSA). Upon treatment of the surface with a BSA solution, the RubpySS·Au and IrbpySS·Au monolayers display a large luminescence signal increase, which can be quantified by time-resolved measurements. The interaction of BSA was also demonstrated by surface plasmon resonance (SPR) studies of the surfaces and in solution by circular dichroism spectroscopy (CD). Overall, the assembly of arrays of designed coordination complexes using a simple and direct µ-contact printing method is demonstrated in this study and represents a general route toward the manufacture of micropatterned optoelectronic devices designed for sensing applications.