Self-assembly Of Colloidal Particles Research Articles

Clustering and phase separation in mixtures of dipolar and active particles.

The self-assembly of colloidal particles in dynamic environments has become an important field of study because of potential applications in fabricating out-of-equilibrium materials. We investigate the phase behavior of mixtures of passive dipolar colloids and active soft spheres using Brownian dynamics simulations in two dimensions. The phase behaviors exhibited include dipolar percolated network, dipolar string-fluid, isotropic fluid, and a phase-separated state. We find that the clustering of dipolar colloids is enhanced in the presence of slow-moving active particles compared to the clustering of dipolar particles mixed with passive particles. When the active particle motility is high, the chains of dipolar particles are either broken into short chains or pushed into dense clusters. Motility-induced phase separation into dense and dilute phases is also present. The area fraction of particles in the dilute phase increases as the fraction of active particles in the system decreases, while the area fraction of particles in the dense phase remains constant. Our findings are relevant to the development of reconfigurable self-assembled materials.

Synthesis and characterization of nanometer-sized liposomes for encapsulation and microRNA transfer to breast cancer cells.

Introduction: The use of liposomes as a drug delivery carrier (DDC) for the treatment of various diseases, especially cancer, is rapidly increasing, requiring more stringent synthesis, formulation, and preservation techniques to bolster safety and efficacy. Liposomes otherwise referred to as phospholipid vesicles are self-assembled colloidal particles. When formed in either the micrometer or nanometer size range, they are ideal candidates as DDC because of their biological availability, performance, activity, and compatibility. Defining and addressing the critical quality attributes (CQAs) along the pharmaceutical production scale will enable a higher level of quality control for reproducibility. More specifically, understanding the CQAs of nanoliposomes that dictate its homogeneity and stability has the potential to widen applications in biomedical science.Methods: To this end, we designed a study that aimed to define synthesis, characterization, formulation (encapsulation), preservation, and cargo delivery and trafficking as the major components within a target product profile for nanoliposomes. A series of synthetic schemes were employed to measure physicochemical properties relevant to nanomaterial drug product development, including concentration gradients, probe versus bath sonication, and storage temperature measured by microscopy (electron and light) and dynamic light scattering.Results: Concentration was found to be a vital CQA as reducing concentrations resulted in nanometer-sized liposomes of <350 nm. Liposomes were loaded with microRNA and fluorescence spectroscopy was used to determine loading efficacy and stability over time. Lyophilization was used to create a dry powder formulation that was then assessed for stability for 6 months. Lastly, breast cancer cell lines were used to ensure efficacy of microRNA delivery and localization.Conclusion: We conclude that microRNA can be loaded into nanometer-sized liposomes, preserved for months in a dried form, and maintain encapsulation after extended time periods in storage.

Multifunctional approaches utilizing polymeric micelles to circumvent multidrug resistant tumors.

The concerns impeding the success of chemotherapy in cancer is descending efficacy of drugs due to the development of multiple drug resistance (MDR). The current efforts employed to overcome MDR have failed or are limited to only preliminary in-vitro investigations. Nanotechnology is at the forefront of the drug delivery research, playing pivotal role in chemotherapy and diagnosis, thereby providing innovative approaches for the management of the disease with minimal side effects. Recently, polymeric micelles (PMs) have witnessed significant developments in cancer therapy. PMs are self-assembled colloidal particles, with a hydrophilic head and a long hydrophobic tail, which enhance the solubility, permeability and bioavailability of drugs, due to the unique features of reaching higher concentration in the biological system, above critical micellar concentration. One of the effective approaches to improve the efficacy of chemotherapy and overcome drug resistance would be to employ multifunctional approach (combination of stimuli-responsive, utilization of drug resistance modulators and combination therapy) using PMs as drug delivery systems. Actively targeted, stimuli-sensitive and multifunctional approaches involve using single and/or combination of approaches (pH-responsive, temperature regulated, reduction-sensitive, ultrasound etc.) to combat drug resistant. The review will describe PMs, types of copolymers used in PMs, preparation and characterization of PMs. A comprehensive list of PMs tested in clinical trials is discussed. Lastly, this review covers stimuli-sensitive and multifunctional approaches to overcome MDR in cancer utilizing PMs.

Multifunctional ferrofluid-infused surfaces with reconfigurable multiscale topography.

Developing adaptive materials with geometries that change in response to external stimuli provides fundamental insights into the links between the physical forces involved and the resultant morphologies and creates a foundation for technologically relevant dynamic systems1,2. In particular, reconfigurable surface topography as a means to control interfacial properties3 has recently been explored using responsive gels4, shape-memory polymers5, liquid crystals6-8 and hybrid composites9-14, including magnetically active slippery surfaces12-14. However, these designs exhibit a limited range of topographical changes and thus a restricted scope of function. Here we introduce a hierarchical magneto-responsive composite surface, made by infiltrating a ferrofluid into a microstructured matrix (termed ferrofluid-containing liquid-infused porous surfaces, or FLIPS). We demonstrate various topographical reconfigurations at multiple length scales and a broad range of associated emergent behaviours. An applied magnetic-field gradient induces the movement of magnetic nanoparticles suspended in the ferrofluid, which leads to microscale flow of the ferrofluid first above and then within the microstructured surface. This redistribution changes the initially smooth surface of the ferrofluid (which is immobilized by the porous matrix through capillary forces) into various multiscale hierarchical topographies shaped by the size, arrangement and orientation of the confining microstructures in the magnetic field. We analyse the spatial and temporal dynamics of these reconfigurations theoretically and experimentally as a function of the balance between capillary and magnetic pressures15-19 and of the geometric anisotropy of the FLIPS system. Several interesting functions at three different length scales are demonstrated: self-assembly of colloidal particles at the micrometre scale; regulated flow of liquid droplets at the millimetre scale; and switchable adhesion and friction, liquid pumping and removal of biofilms at the centimetre scale. We envision that FLIPS could be used as part of integrated control systems for the manipulation and transport of matter, thermal management, microfluidics and fouling-release materials.

Anisotropic Colloids: From Non-Templated to Patchy Templated Synthesis.

Self-assembly of colloidal particles is an important and challenging way to generate novel colloidal superstructures for new materials. Recent progress on syntheses of anisotropic colloids highlights opportunities for such self-assembly, particularly in defining new non-cubic superstructures. Both non-templated and templated synthesis play an important role in preparing anisotropic colloidal particles. In this article, we briefly summarize recent progress in anisotropic colloids by non-templated and conventional templated synthesis, and introduce a conceptual strategy of "patchy templated synthesis" that differs from the conventional approach. We illustrate this strategy with recent examples emanating from colloidal rings, and discuss the future opportunities with this strategy for the synthesis of other anisotropic colloids.

Bioinspired Photonic Pigments from Colloidal Self‐Assembly

The natural world is a colorful environment. Stunning displays of coloration have evolved throughout nature to optimize camouflage, warning, and communication. The resulting flamboyant visual effects and remarkable dynamic properties, often caused by an intricate structural design at the nano- and microscale, continue to inspire scientists to unravel the underlying physics and to recreate the observed effects. Here, the methodologies to create bioinspired photonic pigments using colloidal self-assembly approaches are considered. The physics governing the interaction of light with structural features and natural examples of structural coloration are briefly introduced. It is then outlined how the self-assembly of colloidal particles, acting as wavelength-scale building blocks, can be particularly useful to replicate coloration from nature. Different coloration effects that result from the defined structure of the self-assembled colloids are introduced and it is highlighted how these optical properties can be translated into photonic pigments by modifications of the assembly processes. The importance of absorbing elements, as well as the role of surface chemistry and wettability to control structural coloration is discussed. Finally, approaches to integrate dynamic control of coloration into such self-assembled photonic pigments are outlined.

Preparation of a novel lipid-core micelle using a low-energy emulsification method.

High-energy methods for the manufacturing of nanomedicines are widely used; however, interest in low-energy methods is increasing due to their simplicity, better control over the process, and energy-saving characteristics during upscaling. Here, we developed a novel lipid-core micelle (LCM) as a nanocarrier to encapsulate a poorly water-soluble drug, nifedipine (NFD), by hot-melt emulsification, a low-energy method. LCMs are self-assembling colloidal particles composed of a hydrophobic core and a hydrophilic shell. Hybrid materials, such as Gelucire 44/14, are thus excellent candidates for their preparation. We characterized the obtained nanocarriers for their colloidal properties, drug loading and encapsulation efficiency, liquid state, stability, and drug release. The low-energy method hot-melt emulsification was successfully adapted for the manufacturing of small and narrowly dispersed LCMs. The obtained LCMs had a small average size of ~ 11nm and a narrow polydispersity index (PDI) of 0.228. These nanocarriers were able to increase the amount of NFD dispersible in water more than 700-fold. Due to their sustained drug release profile and the PEGylation of Gelucire 44/14, these nanocarriers represent an excellent starting point for the development of drug delivery systems designed for long circulation times and passive targeting.

Self-Assembly of Colloidal Particles

Colloidal dispersions are suspensions of micron-sized solid particles in a solvent like water or oil. Self-assembly is a widely used approach to create ordered structures of colloidal particles by engineering the inter-colloid potential. This article illustrates how entropy drives disorder to order transitions in a colloidal assembly.

Optimal Control of a Degenerate PDE for Surface Shape

Controlling the shapes of surfaces provides a novel way to direct self-assembly of colloidal particles on those surfaces and may be useful for material design. This motivates the investigation of an optimal control problem for surface shape in this paper. Specifically, we consider an objective (tracking) functional for surface shape with the prescribed mean curvature equation in graph form as a state constraint. The control variable is the prescribed curvature. We prove existence of an optimal control, and using improved regularity estimates, we show sufficient differentiability to make sense of the first order optimality conditions. This allows us to rigorously compute the gradient of the objective functional for both the continuous and discrete (finite element) formulations of the problem. Numerical results are shown to illustrate the minimizers and optimal controls on different domains.

Partitioning and self assembly of silica and hematite particles at grain boundaries of hexagonal liquid crystals: Implications on rheology

We investigate the rheological implications of partitioning and self-assembly of colloidal particles at the grain boundaries (GBs) of hexagonal (H1) liquid crystal (LC) phase as a function of particle loading, shape and phase transition kinetics. The rheology of spherical silica particles (SiO2, diameter = 140 nm)/H1 and irregular hematite particles (Fe2O3, size = 110 nm)/H1 composites is measured as the samples are cooled from an isotropic to H1 phase at 2 and 0.2 °C/min. At 2 °C/min, SiO2/H1 composites show a consistent increase in G′ as the particle loading increases from 0.5 to 7.5 wt. % while Fe2O3/H1 composites exhibit a small drop in G′ above 2.5 wt. % particle loading. On the other hand, SiO2/H1 and Fe2O3/H1 composites show a monotonic increase in G′ with particle loading at a cooling rate of 0.2 °C/min. Microscopy observations reveal that at 0.2 °C/min, both SiO2 and Fe2O3 particles aggregate at the H1 GBs. The different rheological responses of SiO2/H1 and Fe2O3/H1 composites at 2 °C/min are due...

Colloidal Surfaces with Boundaries, Apex Boojums, and Nested Elastic Self-Assembly of Nematic Colloids.

Self-assembly of colloidal particles is poised to become a powerful composite material fabrication technique, but remains challenged by a limited control over the ensuing structures. We develop a new breed of nematic colloids that are physical analogs of a mathematical surface with boundary, interacting with the molecular alignment field without inducing defects when flat. However, made from a thin nanofoil, they can be shaped to prompt formation of self-compensating defects that drive preprogramed elastic interactions mediated by the nematic host. To show this, we wrap the nanofoil on all triangular side faces of a pyramid, except its square base. The ensuing pyramidal cones induce point defects with fractional hedgehog charges of opposite signs, spontaneously align with respect to the far-field director to form elastic dipoles and nested assemblies with tunable spacing. Nanofoils shaped into octahedrons interact as elastic quadrupoles. Our findings may drive realization of low-symmetry colloidal phases.

Self-assembly of colloidal particles in deformation landscapes of electrically driven layer undulations in cholesteric liquid crystals.

We study elastic interactions between colloidal particles and deformation landscapes of undulations in a cholesteric liquid crystal under an electric field applied normal to cholesteric layers. The onset of undulation instability is influenced by the presence of colloidal inclusions and, in turn, layers' undulations mediate the spatial patterning of particle locations. We find that the bending of cholesteric layers around a colloidal particle surface prompts the local nucleation of an undulations lattice at electric fields below the well-defined threshold known for liquid crystals without inclusions, and that the onset of the resulting lattice is locally influenced, both dimensionally and orientationally, by the initial arrangements of colloids defined using laser tweezers. Spherical particles tend to spatially localize in the regions of strong distortions of the cholesteric layers, while colloidal nanowires exhibit an additional preference for multistable alignment offset along various vectors of the undulations lattice. Magnetic rotation of superparamagnetic colloidal particles couples with the locally distorted helical axis and undulating cholesteric layers in a manner that allows for a controlled three-dimensional translation of these particles. These interaction modes lend insight into the physics of liquid crystal structure-colloid elastic interactions, as well as point the way towards guided self-assembly of reconfigurable colloidal composites with potential applications in diffraction optics and photonics.

Electrophoretic deposition of colloidal particles on Mg with cytocompatibility, antibacterial performance, and corrosion resistance.

Biomedical Mg metals have been considered as promising biodegradable implants because of their intended functions, such as cytocompatibility, antibacterial, and biodegradable properties. However, rapid corrosion in physiological environment limits their clinical applications. Alloying and surface coatings have been used to reduce the degradation rate. But this would compromise other excellent performance of Mg samples, including antibacterial and anti-inflammatory activity. Thus, while the rapid degradation of Mg samples must be solved, good antibacterial property and acceptable cytocompatibility are also necessary. In this study, polymer-based coatings were fabricated on Mg surfaces by electrophoretic deposition of poly(isobornyl acrylate-co-dimethylaminoethyl methacrylate)/tannic acid (P(ISA-co-DMA)/TA) colloidal particles. It suggested that the coating materials effectively improved the biocompatibility, antimicrobial behavior, and corrosion resistance of biomedical Mg.

Photonic Crystals with an Eye Pattern Similar to Peacock Tail Feathers

A facile fabrication of photonic crystals (PCs) with an eye pattern similar to peacock tail feathers has been demonstrated by self-assembly of colloidal particles in a sandwich mode. The sandwich mode is formed by superhydrophilic flat substrate sandwiching the poly(styrene-methyl methacrylate-arylic acid) (Poly(St-MMA-AA)) latex suspension (2 wt%) by the hydrophobic one. The patterns are characterized by optical microscopy images, reflection spectra, and the relative scanning electronic microscope images. This work will provide beneficial help for the understanding of the self-assembly process of colloidal crystals.

Dual-responsive supramolecular colloidal microcapsules from cucurbit[8]uril molecular recognition in microfluidic droplets

Thermal and light dual-responsive supramolecular colloidal microcapsules have been successfully prepared by combining cucurbit[8]uril-based host–guest recognition with the self-assembly of colloidal particles within microfluidic droplets.

Self-assembled colloidal particles with pH sensing property

Self-assembled colloidal particles with pH sensing property

Microscopic characterisation of self-assembled colloidal particles in electrohydrodynamic convection of a low-birefringence nematic liquid crystal

ABSTRACTElectrokinetics of small particles immersed in anisotropic fluids is attracting attention in recent years. Here we focus on microscopic appearance of single as well as self-assembled particles moving in the electrohydrodynamic convection (EHC) of a nematic liquid crystal with low birefringence. Characterisation of the birefringent properties is made by polarised light microscopy under different illumination conditions. Because of the small optical anisotropy, the director distortion around the particles clearly exhibits distinctive colours on both sides depending on the height in the cell. The observation can be explained as the change in the net phase retardation of the light. It is also found that a caterpillar-like motion is possible by tuning temperature, although the horizontal size of the EHC rolls is relatively narrow.

Pickering emulsions stabilized by self-assembled colloidal particles of amphiphilic branched random poly(styrene- co -acrylic acid)

Amphiphilic branched random poly(styrene-co-acrylic acid) (BPSAA) is facilely synthesized by a one-pot atom transfer radical copolymerization of styrene and tert-butyl acrylate with 1-(chloromethyl)-4-ethenylbenzene as chain transfer monomer followed by hydrolysis of ester groups. Then the self-assembled colloidal particles of BPSAA are prepared by a selective solvent method and used to stabilize Pickering emulsions. The influences of pH, branching degree, and salinity on the structure and emulsifying performance of the colloidal particles are investigated. The results show that the BPSAA colloidal particles exhibit pH responsiveness. They can stabilize O/W emulsions effectively at strongly alkaline conditions rather than acidic or weakly alkaline conditions. It is probably due to the random distribution of hydrophobic and hydrophilic microdomains in the colloidal structure restrains the ionization of carboxyl groups and leads to high pKa. The branched structure of the copolymer plays an important role in the colloidal structure and emulsification. The colloidal particles of the BPSAA copolymer with higher degree of branching exhibit higher ionization of carboxyl groups at same pH condition, thus better hydrophilicity and emulsifying performance. In addition, a high NaCl salinity can reduce the electrostatic repulsion among the colloidal particles significantly by shielding effect, to make the colloidal particles flocculate. The formed flocs show an enhanced emulsifying performance. This study may contribute to understand the relationship between the structure and emulsifying performance of polymeric self-assembled colloidal particles.

Controlled release and corrosion protection by self-assembled colloidal particles electrodeposited onto magnesium alloys.

We report a potential example of using surface functionalization to provide magnesium alloys (Mg-Ca) with controlled release and corrosion resistance properties. A key feature of this approach is to treat the Mg-Ca surfaces with nanoparticles via electrodeposition that can stably load and controllably release bioactive agents or drugs. These photo-cross-linkable and nano-scale particles were prepared by the self-assembly of an amphiphilic poly(γ-glutamic acid)-g-7-amino-4-methylcoumarin (γ-PGA-g-AMC) with encapsulation of a vitamin; moreover, the size and morphology of the resulting particles were studied. Fluorescence microscopy analysis indicated that Vm was effectively incorporated into the γ-PGA-g-AMC particles. Scanning electron microscopy (SEM) images showed that the colloidal particles could be uniformly electrodeposited on the Mg-Ca alloys. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analyses confirmed the successful anchoring of the particles. After the surface electrodeposition of self-assembled colloidal particles, the in vitro degradation results show that deposition of the particles was found to reduce the degradation rate of the magnesium alloys; moreover, the vitamin was controllably released for up to 20 days. Furthermore, the Mg-Ca substrate functionalized with colloidal particles containing a vitamin significantly promoted the attachment, proliferation and spread of NIH-3T3 normal cells. The entire strategy may be used in various medical devices to create coatings for improved biomedical performance.

One-step electrodeposition of self-assembled colloidal particles: a novel strategy for biomedical coating.

A novel biomedical coating was prepared from self-assembled colloidal particles through direct electrodeposition. The particles, which are photo-cross-linkable and nanoscaled with a high specific surface area, were obtained via self-assembly of amphiphilic poly(γ-glutamic acid)-g-7-amino-4-methylcoumarin (γ-PGA-g-AMC). The size, morphology, and surface charge of the resulting colloidal particles and their dependence on pH, initial concentrations, and UV irradiation were successfully studied. A nanostructured coating was formed in situ on the surface of magnesium alloys by electrodeposition of colloidal particles. The composition, morphology, and phase of the coating were monitored using Fourier transform infrared spectroscopy, energy-dispersive X-ray spectroscopy, scanning electron microscopy, and X-ray diffraction. The corrosion test showed that the formation of the nanostructured coating on magnesium alloys effectively improved their initial anticorrosion properties. More importantly, the corrosion resistance was further enhanced by chemical photo-cross-linking. In addition, the low cytotoxicity of the coated samples was confirmed by MTT assay against NIH-3T3 normal cells. The contribution of our work lies in the creation of a novel strategy to fabricate a biomedical coating in view of the versatility of self-assembled colloidal particles and the controllability of the electrodeposition process. It is believed that our work provides new ideas and reliable data to design novel functional biomedical coatings.