Interrogating Cellular Functions with Designer Janus Particles

Features of Anisotropic Drug Delivery Systems

Natural materials are anisotropic. Delivery systems occurring in nature, such as viruses, blood cells, pollen, and many others, do have anisotropy, while delivery systems made artificially are mostly isotropic. There is apparent complexity in engineering anisotropic particles or capsules with micron and submicron sizes. Nevertheless, some promising examples of how to fabricate particles with anisotropic shapes or having anisotropic chemical and/or physical properties are developed. Anisotropy of particles, once they face biological systems, influences their behavior. Internalization by the cells, flow in the bloodstream, biodistribution over organs and tissues, directed release, and toxicity of particles regardless of the same chemistry are all reported to be factors of anisotropy of delivery systems. Here, the current methods are reviewed to introduce anisotropy to particles or capsules, including loading with various therapeutic cargo, variable physical properties primarily by anisotropic magnetic properties, controlling directional motion, and making Janus particles. The advantages of combining different anisotropy in one entity for delivery and common problems and limitations for fabrication are under discussion.

A Spatially Programmable DNA Nanorobot Arm to Modulate Anisotropic Gold Nanoparticle Assembly by Enzymatic Excision

Programmable assembly of gold nanoparticle superstructures with precise spatial arrangement has drawn much attention for their unique characteristics in plasmonics and biomedicine. Bio-inspired methods have already provided programmable, molecular approaches to direct AuNP assemblies using biopolymers. The existing methods, however, predominantly use DNA as scaffolds to directly guide the AuNP interactions to produce intended superstructures. New paradigms for regulating AuNP assembly will greatly enrich the toolbox for DNA-directed AuNP manipulation and fabrication. Here, we developed a strategy of using a spatially programmable enzymatic nanorobot arm to modulate anisotropic DNA surface modifications and assembly of AuNPs. Through spatial controls of the proximity of the reactants, the locations of the modifications were precisely regulated. We demonstrated the control of the modifications on a single 15 nm AuNP, as well as on a rectangular DNA origami platform, to direct unique anisotropic AuNP assemblies. This method adds an alternative enzymatic manipulation to DNA-directed AuNP superstructure assembly.

Development of Janus Particles as Potential Drug Delivery Systems for Diabetes Treatment and Antimicrobial Applications

Janus particles have emerged as a novel and smart material that could improve pharmaceutical formulation, drug delivery, and theranostics. Janus particles have two distinct compartments that differ in functionality, physicochemical properties, and morphological characteristics, among other conventional particles. Recently, Janus particles have attracted considerable attention as effective particulate drug delivery systems as they can accommodate two opposing pharmaceutical agents that can be engineered at the molecular level to achieve better target affinity, lower drug dosage to achieve a therapeutic effect, and controlled drug release with improved pharmacokinetics and pharmacodynamics. This article discusses the development of Janus particles for tailored and improved delivery of pharmaceutical agents for diabetes treatment and antimicrobial applications. It provides an account of advances in the synthesis of Janus particles from various materials using different approaches. It appraises Janus particles as a promising particulate system with the potential to improve conventional delivery systems, providing a better loading capacity and targeting specificity whilst promoting multi-drugs loading and single-dose-drug administration.

Janus Droplet Formation via Thermally Induced Phase Separation: A Numerical Model with Diffusion and Convection

Microscale Janus particles have versatile potential applications in many physical and biomedical fields, such as microsensor, micromotor, and drug delivery. Here, we present a phase-field approach of multicomponent and multiphase to investigate the Janus droplet formation via thermally induced phase separation. The crucial kinetics for the formation of Janus droplets consisting of two polymer species and a solvent component via an interplay of both diffusion and convection is considered in the Cahn-Hilliard-Navier-Stokes equation. The simulation results of the phase-field model show that unequal interfacial tensions between the two polymer species and the solvent result in asymmetric phase separation in the formation process of Janus droplets. This asymmetric phase separation plays a vital role in the establishment of the so-called core-shell structure that has been observed in previous experiments. By varying the droplet size, the surface tension, and the molecular interaction between the polymer species, several novel droplet morphologies are predicted in the development process of Janus droplets. Moreover, we stress that the hydrodynamics should be reckoned as a non-negligible mechanism that not only accelerates the Janus droplet evolution but also has great impacts on the coarsening and coalescence of the Janus droplets.

Advances in design and applications of polymer brush modified anisotropic particles

Current advancements in the creation of anisotropy in particles and their surface modification with polymer brushes have established a new class of hybrid materials termed polymer brush modified anisotropic particles (PBMAP). PBMAPs display unique property combinations, e.g., multi-functionality in multiple directions along with smart behavior, which is not easily achievable in traditional hybrid materials. Typically, anisotropic particles can be categorized based on three different factors, such as shape anisotropy (geometry driven), compositional anisotropy (functionality driven), and surface anisotropy (spatio-selective surface modification driven). In this review, we have particularly focused on the synthetic strategies to construct the various type of PBMAPs based on inorganic or organic core which may or may not be isotropic in nature, and their applications in various fields ranging from drug delivery to catalysis. In addition, superior performances and fascinating properties of PBMAPs over their isotropic analogues are also highlighted. A brief overview of their future developments and associated challenges have been discussed at the end.

Determination of the yield, mass and structure of silver patches on colloidal silica using multiwavelength analytical ultracentrifugation

Anisotropic nanoparticles offer considerable promise for applications but also present significant challenges in terms of their characterization. Recent developments in the electroless deposition of silver patches directly onto colloidal silica particles have opened up a simple and scalable synthesis method for patchy particles with tunable optical properties. Due to the reliance on patch nucleation and growth, however, the resulting coatings are distributed in coverage and thickness and some core particles remain uncoated. To support process optimization, new methods are required to rapidly determine patch yield, thickness and coverage. Here we present a novel approach based on multiwavelength analytical ultracentrifugation (MWL-AUC) which permits simultaneous hydrodynamic and spectroscopic characterization. The patchy particle colloids are produced in a continuous flow mixing process that makes use of a KM-type micromixer. By varying the process flow rate or metal precursor concentration we show how the silver to silica mass ratio distribution derived from the AUC-measured sedimentation coefficient distribution can be influenced. Moreover, through reasoned assumptions we arrive at an estimation of the patch yield that is close to that determined by arduous analysis of scanning electron microscopy (SEM) images. Finally, combining MWL-AUC, electrodynamic simulations and SEM image analysis we establish a procedure to estimate the patch thickness and coverage.

Flagellated Janus particles for multimodal actuation and transport

Catalytic Janus particles rely on chemical decomposition to self-propel and have displayed enormous potential for targeted drug delivery and cellular penetration. Catalytic propulsion mechanisms are limiting, however, with fuel requirements and specialized fluid properties being necessary to achieve propulsion. We have improved the dynamic propulsion of catalytic Janus particles by functionalizing flagellar filaments to one of their hemispheres. Flagellated Janus particles, torqued by rotating magnetic fields, swim along their rotation axis using the explicit chirality and flexibility of flagella, mimicking flagellar rotation of live bacteria. Depending on the working fluid, flagellated Janus particles can propel using either catalytic or swimming propulsion. We demonstrate experimentally that flagellated Janus particles behave predictably under the two actuation modes and can precisely follow trajectories under closed-loop feedback control. Flagellated Janus particles were demonstrated to swim in both Newtonian and shear-thickening fluids. These are the first Janus particles developed that can be propelled interchangeably between catalytic and flagellar swimming propulsion, allowing two distinct propulsion mechanisms for future use within in vivo operations.

Engineering Nano-Therapeutics to Boost Adoptive Cell Therapy for Cancer Treatment

Although adoptive transfer of therapeutic cells to cancer patients is demonstrated with great success and fortunately approved for the treatment of leukemia and B-cell lymphoma, potential issues, including the unclear mechanism, complicated procedures, unfavorable therapeutic efficacy for solid tumors, and side effects, still hinder its extensive applications. The explosion of nanotechnology recently has led to advanced development of novel strategies to address these challenges, facilitating the design of nano-therapeutics to improve adoptive cell therapy (ACT) for cancer treatment. In this review, the emerging nano-enabled approaches, that design multiscale artificial antigen-presenting cells for cell proliferation and stimulation in vitro, promote the transducing efficiency of tumor-targeting domains, engineer therapeutic cells for in vivo imaging, tumor infiltration, and in vivo functional sustainability, as well as generate tumoricidal T cells in vivo, are summarized. Meanwhile, the current challenges and future perspectives of the nanostrategy-based ACT for cancer treatment are also discussed in the end.

Bioinspired Polymeric High Aspect Ratio Particles with Asymmetric Janus Functionalities

Polymeric particles with intricate morphologies and properties have been developed based on bioinspired designs for applications in regenerative medicine, tissue engineering, and drug delivery. However, the fabrication of particles with asymmetric functionalities remains a challenge. Janus polymeric particles are an emerging class of material with asymmetric functionalities; however, they are predominantly spherical in morphology, made from non-biocompatible materials, and made using specialized fabrication techniques. We therefore set out to fabricate nonspherical Janus particles inspired by high aspect ratio filamentous bacteriophage using polycaprolactone polymers and standard methods. Janus high aspect ratio particles (J-HARPs) were fabricated with a nanotemplating technique to create branching morphologies selectively at one edge of the particle. J-HARPs were fabricated with maleimide handles and modified with biomolecules such as proteins and biotin. Regioselective modification was observed at the tips of J-HARPs, likely owing to the increased surface area of the branching regions. Biotinylated J-HARPs demonstrated cancer cell biotin receptor targeting, as well as directional crosslinking with spherical particles via biotin-streptavidin interactions. Lastly, maleimide J-HARPs were functionalized during templating to contain amines exclusively at the branching regions and were dual-labeled orthogonally, demonstrating spatially separated bioconjugation. Thus, J-HARPs represent a new class of bioinspired Janus material with excellent regional control over biofunctionalization.

Bifunctional Janus Particles as Multivalent Synthetic Nanoparticle Antibodies (SNAbs) for Selective Depletion of Target Cells

Monoclonal antibodies (mAb) have had a transformative impact on treating cancers and immune disorders. However, their use is limited by high development time and monetary cost, manufacturing complexities, suboptimal pharmacokinetics, and availability of disease-specific targets. To address some of these challenges, we developed an entirely synthetic, multivalent, Janus nanotherapeutic platform, called Synthetic Nanoparticle Antibodies (SNAbs). SNAbs, with phage-display-identified cell-targeting ligands on one "face" and Fc-mimicking ligands on the opposite "face", were synthesized using a custom, multistep, solid-phase chemistry method. SNAbs efficiently targeted and depleted myeloid-derived immune-suppressor cells (MDSCs) from mouse-tumor and rat-trauma models, ex vivo. Systemic injection of MDSC-targeting SNAbs efficiently depleted circulating MDSCs in a mouse triple-negative breast cancer model, enabling enhanced T cell and Natural Killer cell infiltration into tumors. Our results demonstrate that SNAbs are a versatile and effective functional alternative to mAbs, with advantages of a plug-and-play, cell-free manufacturing process, and high-throughput screening (HTS)-enabled library of potential targeting ligands.

Facile synthesis of micron-size Janus particles by one-pot suspension polymerization and their functional modification

A novel strategy for preparing micron-size Janus particles with easily-functionalized surfaces was established by one-pot W/O/W-type suspension polymerization for the first time.

Highly Porous Magnetic Janus Microparticles with Asymmetric Surface Topology

Monodispersed magnetic Janus particles composed of a porous polystyrene portion and a nonporous poly(vinyl acetate) portion with embedded oleic acid-coated magnetic nanoparticles were generated using microfluidic emulsification followed by two distinct phase separation events triggered by solvent evaporation. The template droplets were composed of 2 wt % polystyrene, 2 wt % poly(vinyl acetate), and 0.5-2 wt % n-heptane-based magnetic fluid dissolved in dichloromethane (DCM). The porosity of polystyrene compartments was the result of phase separation between a nonvolatile nonsolvent (n-heptane) and a volatile solvent (DCM) within polystyrene-rich phase. The focused ion beam cross-sectioning and scanning electron microscopy (SEM) imaging revealed high surface porosity of polystyrene compartments with negligible porosity of poly(vinyl acetate) parts, which can be exploited to increase the wettability contrast between the two polymers and enhance bubble generation in bubble-driven micromotors. The porosity of the polystyrene portion was controlled by varying the fraction of n-heptane in the dispersed phase. The particle composition was confirmed by scanning electron microscopy-energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, and differential scanning calorimetry. The fabricated particles were successfully magnetized when subjected to an external magnetic field, which led to their aggregation into regular 2D assemblies. The particle clusters composed of two to four individual particles could be rotated with a rotating magnetic field. Microfluidic generation of highly porous Janus particles with compositional, topological, and magnetic asymmetry provides a cost-effective, easy-to-implement yet highly robust and versatile strategy for the manufacturing of multifunctional smart particles.

Morphological Transitions in Patchy Nanoparticles

Nanoparticles (NPs) decorated with topographically or chemically distinct surface patches are an emerging class of colloidal building blocks of functional hierarchical materials. Surface segregation of polymer ligands into pinned micelles offers a strategy for the generation of patchy NPs with controlled spatial distribution and number of patches. The thermodynamic nature of this approach poses a question about the stability of multiple patches on the NP surface, as the lowest energy state is expected for NPs carrying a single patch. In the present work, for gold NPs end-grafted with thiol-terminated polymer molecules, we show that the patchy surface morphology is preserved under conditions of strong grafting of the thiol groups to the NP surface (i.e., up to a temperature of 40 °C), although the patch shape changes over time. At higher temperatures (e.g., at 80 °C), the number of patches per NP decreases, due to the increased lateral mobility and coalescence of the patches as well as the ultimate loss of the polymer ligands due to desorption at enhanced solvent quality. The experimental results were rationalized theoretically, using a scaling approach. The results of this work offer insight into the surface science of patchy nanocolloids and specify the time and temperature ranges of the applications of patchy NPs.

Probing the morphology evolution of chemically anisotropic colloids prepared by homopolymerization- and copolymerization-induced phase separation

Chemically anisotropic colloids prepared by polymerization-induced phase separation during seeded emulsion polymerization with non-crosslinked seeds reveals tunability in both surface and interior properties based on the morphology evolution.

Learning from Solar Energy Conversion: Biointerfaces for Artificial Photosynthesis and Biological Modulation

Three seemingly distinct directions of nanomaterials research, photovoltaics, biofuel production, and biological modulation, have been sequentially developed over the past several decades. In this Mini Review, we discuss how the insights gleaned from nanomaterials-based solar energy conversion can be adapted to biointerface designs. Because of their size- and shape-dependent optical properties and excellent synthetic control, nanomaterials have shown unique technological advantages as the light absorbers or energy transducers. Biocompatible nanomaterials have also been incorporated into biological systems including biomolecules, bacteria, and eukaryotic cells for a large collection of fundamental studies and applications. For the photocatalytic biofuel production, either isolated bacterial enzymes or the entire bacteria have been hybridized with the nanomaterials, where functions from both parts are synergistically integrated. Likewise, interfacing nanomaterials with eukaryotic systems, whether in individual cells or tissues, has enabled optical modulation of cellular behavior and the construction of active cellular materials. Here we survey different approaches in which nanomaterials are used to elicit electrical or mechanical changes in single cells or cellular assemblies via photoelectrochemical or photothermal processes. We end this Mini Review with the discussion of future nongenetic modulation at the intracellular level.

Nanoparticle heterogeneity: an emerging structural parameter influencing particle fate in biological media?

Drug nanocarriers' surface chemistry is often presumed to be uniform. For instance, the polymer surface coverage and distribution of ligands on nanoparticles are described with averaged values obtained from quantification techniques based on particle populations. However, these averaged values may conceal heterogeneities at different levels, either because of the presence of particle sub-populations or because of surface inhomogeneities, such as patchy surfaces on individual particles. The characterization and quantification of chemical surface heterogeneities are tedious tasks, which are rather limited by the currently available instruments and research protocols. However, heterogeneities may contribute to some non-linear effects observed during the nanoformulation optimization process, cause problems related to nanocarrier production scale-up and correlate with unexpected biological outcomes. On the other hand, heterogeneities, while usually unintended and detrimental to nanocarrier performance, may, in some cases, be sought as adjustable properties that provide NPs with unique functionality. In this review, results and processes related to this issue are compiled, and perspectives and possible analytical developments are discussed.

Biodegradable Anisotropic Microparticles for Stepwise Cell Adhesion and Preparation of Janus Cell Microparticles

The biomimetic anisotropic particles have different physicochemical properties on the opposite two sides, enabling diverse applications in emulsion, photonic display, and diagnosis. However, the traditional anisotropic particles have a very small size, ranging from submicrons to a few microns. The design and fabrication of anisotropic macron-sized particles with new structures and properties is still challenging. In this study, anisotropic polycaprolactone (PCL) microparticles well separated with each other were prepared by crystallization from the dilute PCL solution in a porous 3D gelatin template. They had fuzzy and smooth surfaces on each side, and a size as large as 70 μm. The fuzzy surface of the particle adsorbed significantly larger amount of proteins, and was more cell-attractive regardless of the cell types. The particles showed stronger affinity toward fibroblasts over hepatocytes, which paved a new way for cell isolation merely based on the surface morphology. After a successive seeding process, Janus cell microparticles with fibroblasts and endothelial cells (ECs) on each side were designed and obtained by making use of the anisotropic surface morphology, which showed significant difference in EC functions in terms of prostacyclin (PGl2) secretion, demonstrating the unique and appealing functions of this type of anisotropic microspheres.

Enabling the synthesis of homogeneous or Janus hairy nanoparticles through surface photoactivation

Nanoparticles (NPs) homogeneously covered with polymer chains or with chains of two different polymers segregated in distinct domains ("Janus" particles) possess remarkable features. Their unique colloidal properties can be finely tuned by the grafted polymers while the characteristics of the nano-core remain unaffected. Herein, a simple and robust photochemical approach is reported to synthesize, from 50 nm cores, homogeneous and Janus "hairy" nanoparticles with hydrophilic and amphiphilic properties, respectively. This is achieved by using a surface-anchored bis(acyl)phosphane oxide photoinitiator which allows a spatially controlled surface-initiated photopolymerization at room temperature. Homogeneous and Janus hairy nanoparticles dispersed in water have very different interaction behaviours which are directly visualized by in situ liquid cell transmission electron microscopy and confirmed by small angle X-ray scattering from a statistically relevant number of particles.

Rapid Production of Internally Structured Colloids by Flash Nanoprecipitation of Block Copolymer Blends

Colloids with internally structured geometries have shown great promise in applications ranging from biosensors to optics to drug delivery, where the internal particle structure is paramount to performance. The growing demand for such nanomaterials necessitates the development of a scalable processing platform for their production. Flash nanoprecipitation (FNP), a rapid and inherently scalable colloid precipitation technology, is used to prepare internally structured colloids from blends of block copolymers and homopolymers. As revealed by a combination of experiments and simulations, colloids prepared from different molecular weight diblock copolymers adopt either an ordered lamellar morphology consisting of concentric shells or a disordered lamellar morphology when chain dynamics are sufficiently slow to prevent defect annealing during solvent exchange. Blends of homopolymer and block copolymer in the feed stream generate more complex internally structured colloids, such as those with hierarchically structured Janus and patchy morphologies, due to additional phase separation and kinetic trapping effects. The ability of the FNP process to generate such a wide range of morphologies using a simple and scalable setup provides a pathway to manufacturing internally structured colloids on an industrial scale.