Electrohydrodynamic Co-jetting Research Articles

Chemically Orthogonal Three‐Patch Microparticles

Compared to two-dimensional substrates, only a few methodologies exist for the spatially controlled decoration of three-dimensional objects, such as microparticles. Combining electrohydrodynamic co-jetting with synthetic polymer chemistry, we were able to create two- and three-patch microparticles displaying chemically orthogonal anchor groups on three distinct surface patches of the same particle. This approach takes advantage of a combination of novel chemically orthogonal polylactide-based polymers and their processing by electrohydrodynamic co-jetting to yield unprecedented multifunctional microparticles. Several micropatterned particles were fabricated displaying orthogonal click functionalities. Specifically, we demonstrate novel two- and three-patch particles. Multi-patch particles are highly sought after for their potential to present multiple distinct ligands in a directional manner. This work clearly establishes a viable route towards orthogonal reaction strategies on multivalent micropatterned particles.

Synthesis, Characterization, and Directional Binding of Anisotropic Biohybrid Microparticles for Multiplexed Biosensing

Anisotropic microarchitectures with different physicochemical properties have been developed as advanced materials for challenging industrial and biomedical applications including switchable displays, multiplexed biosensors and bioassays, spatially-controlled drug delivery systems, and tissue engineering scaffolds. In this study, anisotropic biohybrid microparticles (MPs) spatio-selectively conjugated with two different antibodies (Abs) are first developed for fluorescence-based, multiplexed sensing of biological molecules. Poly(acrylamide-co-acrylic acid) is chemically modified with maleimide- or acetylene groups to introduce different targeting biological moieties into each compartment of anisotropic MPs. Modified polymer solutions containing two different fluorescent dyes are separately used for electrohydrodynamic co-jetting with side-by-side needle geometry. The anisotropic MPs are chemically stabilized by thermal imidization, followed by bioconjugation of two different sets of polyclonal Abs with two individual compartments via maleimide-thiol coupling reaction and Huisgen 1,3-dipolar cycloaddition. Finally, two compartments of the anisotropic biohybrid MPs are spatio-selectively associated with the respective monoclonal Ab-immobilized substrate in the presence of the antigen by sandwich-type immunocomplex formation, resulting in their ordered orientation due to the spatio-specific molecular interaction, as confirmed by confocal laser scanning microscopy. In conclusion, anisotropic biohybrid MPs capable of directional binding have great potential as a new fluorescence-based multiplexing biosensing system.

Amphiphilic Colloidal Surfactants Based on Electrohydrodynamic Co-jetting

A novel synthetic route for the preparation of amphiphilic Janus particles based on electrohydrodynamic cojetting has been developed. In this approach, selective encapsulation of hydrophobic fluorodecyl-polyhedral oligomeric silsesquioxane (F-POSS) in one compartment and a poly(vinyl alcohol) in the second compartment results in colloidal particles with surfactant-like properties including the self-organization at oil-water and air-water interfaces. Successful localization of the respective polymers in different compartments of the same particle is confirmed by a combination of fluorescence microscopy, vibrational spectroscopy, and ζ-potential measurements. We believe that this straightforward synthetic approach may lead to a diverse class of surface-active colloids that will have significant relevance ranging from basic scientific studies to immediate applications in areas, such as pharmaceutical sciences or cosmetics.

Controlled Microstructuring of Janus Particles Based on a Multifunctional Poly(ethylene glycol)

A novel water insoluble, multifunctional poly(ethylene glycol), poly(hydrazide ethylene glycol-co-benzyl glycidyl ether) (P(HZ-co-BnGE)), is synthesized via thiol-ene click reaction of poly(allyl glycidyl ether-co-benzyl glycidyl ether) (P(AGE-co-BnGE)). The base polymer P(AGE-co-BnGE) is previously prepared by anionic ring-opening copolymerization of the corresponding monomers. To demonstrate utility, bicompartmental microspheres and microcylinders containing P(HZ-co-BnGE) in one of the compartments are prepared via electrohydrodynamic (EHD) co-jetting. Next, spatially controlled surface reactivity toward sugars is demonstrated by selective binding of 2α-mannobiose to the P(HZ-co-BnGE) compartment only, as confirmed by a carbohydrate-lectin-binding assay. These sugar-reactive hydrazide-presenting microparticles have potential applications for glyco-targeted drug delivery.

A Facile Route Towards Inorganic Particles with Two Distinct Compartments Based on Electro‐Hydrodynamic Co‐Jetting

Inorganic Janus particles are prepared by electro-hydrodynamic (EHD) co-jetting of mixtures of organic polymers and inorganic precursors and are converted into inorganic particles by thermal calcination. Using this approach, bicompartmental SiO2 particles with iron oxide nanocrystals selectively loaded into one hemisphere are created. Moreover, bicompartmental particles composed of TiO2 and SiO2 are fabricated by EHD co-jetting.

Spontaneous shape reconfigurations in multicompartmental microcylinders

Nature's particles, such as spores, viruses or cells, are adaptive--i.e., they can rapidly alter major phenomenological attributes such as shape, size, or curvature in response to environmental changes. Prominent examples include the hydration-mediated opening of ice plant seeds, actuation of pine cones, or the ingenious snapping mechanism of predatory Venus flytraps that rely on concave-to-convex reconfigurations. In contrast, experimental realization of reconfigurable synthetic microparticles has been extremely challenging and only very few examples have been reported so far. Here, we demonstrate a generic approach towards dynamically reconfigurable microparticles that explores unique anisotropic particle architectures, rather than direct synthesis of sophisticated materials such as shape-memory polymers. Solely enabled by their architecture, multicompartmental microcylinders made of conventional polymers underwent active reconfiguration including shape-shifting, reversible switching, or three-way toggling. Once microcylinders with appropriate multicompartmental architectures were prepared by electrohydrodynamic cojetting, simple exposure to an external stimulus, such as ultrasound or an appropriate solvent, gives rise to interfacial stresses that ultimately cause reversible topographical reconfiguration. The broad versatility of the electrohydrodynamic cojetting process with respect to materials selection and processing suggests strategies for a wide range of dynamically reconfigurable adaptive materials including those with prospective applications for sensors, reprogrammable microactuators, or targeted drug delivery.

Differentially Degradable Janus Particles for Controlled Release Applications

Janus particles with differentially degradable compartments were prepared by electrohydrodynamic (EHD) co-jetting and subsequent controlled crosslinking. These bicompartmental particles are composed of an interpenetrating polymer network of poly(ethylene oxide) and poly(acrylamide-co-acrylic acid) in one hemisphere and a crosslinked copolymer of dextran and poly(acrylamide-co-acrylic acid) segments in the second compartment. The compositional anisotropy caused differential hydrolytic susceptibility: Although both compartments were stable at pH 3.0, selective degradation of the PEO-containing compartment pH 7.4 was observed within 5 days. Janus particles with differentially degradable polymer compartments may be of interest for a range of oral drug delivery applications because of their propensity for decoupled release profiles.

Multicompartmental Particles for Combined Imaging and siRNA Delivery

Multifunctional, multicompartmental particles can be fabricated by electrohydrodynamic co-jetting, capable of both imaging and siRNA delivery. These particles are able to sense and respond to the endosomal environment allowing for effective delivery of siRNA.

Chemically Controlled Bending of Compositionally Anisotropic Microcylinders

Soft materials that can undergo mechanical actuation in response to external stimuli, such as changes in temperature, light, pH value, or ionic strength, have attracted increasing attention because of their potential use as thinfilm actuators, smart sutures, and soft robots. These materials typically require specialty polymers, such as shape-memory polymers or use macroscopically layered films. In layered films, the anisotropic distribution of two polymers, or a polymer and a metal, is essential. This creates a mismatch in mechanical properties that gives rise to a defined bending. In principle, this concept is not limited to macroscopic multilayer films, but can be achieved with colloidal materials, as long as the required anisotropy can be realized and different parts of the colloidal object will respond differently to the external stimulus. In recent years, compositionally anisotropic microand nanoparticles have been devised using a range of different synthesis methods including microfluidic and lithographic techniques, particle replication in low surface energy templates, selective crosslinking of polybutadiene segments in terpolymers, lithographic patterning of microspheres, electrochemical and photochemical reduction, templating of porous membranes and nanotubes, surfactant aided growth, graft polymerization, and processes based on controlled surface nucleation. Alternatively, electrohydrodynamic co-jetting is a method to prepare particles and fibers with multiple compartments by transferring fluids through a set of capillaries that can process dissimilar materials. In the past, electrohydrodynamic co-jetting has resulted in particles with multiple compartments that contain different polymer blends, dyes, low-molecular weight additives, reactive molecules and even inorganic nanoparticles. If a reactive additive, such as a functionalized polymer, is added to one of the compartments, selective surface modification is possible and can result in spatially controlled immobilization of proteins or peptides. Because different compartments can be loaded with dissimilar materials, entirely new sets of functions can arise from unique synergistic effects, not just from the addition of the properties of the individual compartments. Herein, we report a new type of compositionally anisotropic microcylinders, where defined compartments within the same microcylinder undergo differential expansion due to the site-selective growth of a surface layer. The asymmetric expansion creates surface stresses resulting in significant and controllable bending of the microcylinders, which depends on the particle geometry and the architecture of the surface layers. Using finite element simulations, we verify the observed bending trends and derive a family of performance curves that predict a wide-range tunability of the actuation stroke based on the cylinder geometry and the amount of swelling. The microcylinders are fabricated based on electrohydrodynamic co-jetting followed by microsectioning. In brief, an electric field is applied to a compound droplet comprising two or more polymer solutions generated by laminar flow from a side-by-side arrangement of capillary needles. We have previously demonstrated the synthesis of particles and fibers from chloroform-based solutions of lactic acid polymers. In the case of fibers, high viscosities, combined with high solvent volatility and low charge-to-volume ratios, can result in an extremely linear and controlled jet migration without the bending and whipping instabilities commonly observed in charged jets. This situation enables the production of multicompartmental microfibers, which not only exhibit monodispersity with respect to diameter, but can also be aligned on rotating collectors. Such highly aligned fiber scaffolds can then be cut into monodisperse microcylinders. Importantly, particle diameters are controlled by altering the solution and process parameters during electrohydrodynamic co-jetting, while control over cylinder length is achieved by the microsectioning step. Spatioselective functionalization of one or more compartments of the cylinders has been achieved by incorporation of poly(lactide-co-propargyl glycolide) as an additive during fabrication of the microcylinders, and subsequent modification with biotin and streptavidin by click chemistry. As shown in the Supporting Information, Figure S1, we incorporated a poly[lactide-co[*] Dr. S. Saha, N. Clay, A. Donini, Prof. J. Lahann Department of Chemical Engineering University of Michigan, Ann Arbor, MI 48109 (USA) E-mail: lahann@umich.edu

Recent Progress in Nano‐biotechnology: Compartmentalized Micro‐ and Nanoparticles via Electrohydrodynamic Co‐jetting

Compartmentalized particles enable co-presentation of dissimilar sets of properties, thereby offering a broad design space for multifunctional particles. Electrohydrodynamic co-jetting is a simple, yet versatile fabrication technique that can be used to prepare such multicompartmental particles and fibers. Processing conditions are summarized for co-jetting of aqueous and organic polymer solutions as well as nanoparticle suspensions. Because particles can comprise distinct polymers in different compartments, selective surface modification becomes possible. The latter can result in unidirectional interactions with cells or may pave new routes towards targeted drug delivery.

Engineering, Characterization and Directional Self‐Assembly of Anisotropically Modified Nanocolloids

Along with traditional attributes such as the size, shape, and chemical structure of polymeric micro-objects, control over material distribution, or selective compartmentalization, appears to be increasingly important for maximizing the functionality and efficacy of biomaterials. The fabrication of tri- and tetracompartmental colloids made from biodegradable poly(lactide-co-glycolide) polymers via electrohydrodynamic co-jetting is demonstrated. The presence of three compartments is confirmed via flow cytometry. Additional chemical functionality is introduced via the incorporation of acetylene-functionalized polymers into individual compartments of the particles. Direct visualization of the spatioselective distribution of acetylene groups is demonstrated by confocal Raman microscopy as well as by reaction of the acetylene groups with azide-biotin via 'click chemistry'. Biotin-streptavidin binding is then utilized for the controlled assembly and orientation of bicompartmental particles onto functionalized, micropatterned substrates prepared via chemical vapor deposition polymerization.

Towards Designer Microparticles: Simultaneous Control of Anisotropy, Shape, and Size

Biodegradable, compositionally anisotropic microparticles with two distinct compartments that exhibit controlled shapes and sizes are fabricated. These multifunctional particles are prepared by electrohydrodynamic co-jetting of poly(lactide-co-glycolide) polymer solutions. By varying different solution and process parameters, namely, concentration and flow rate, a variety of non-equilibrium bicompartmental shapes, such as discoid and rod-shaped microparticles are produced in high yields. Optimization of jetting parameters, combined with filtration, results in near-perfect, bicompartmental spherical particles in the size range of 3-5 microm. Simultaneous control over anisotropy, size, shape, and surface structure provides an opportunity to create truly multifunctional microparticles for a variety of biological applications, such as drug delivery, diagnostic assays, and theranostics.

Compartmentalization of Gold Nanocrystals in Polymer Microparticles using Electrohydrodynamic Co‐Jetting

Polymer particles with micro- and nanoscale anisotropy have received increasing interest for their ability to simultaneously present different physical- and chemical properties. In this communication, we demonstrate that gold nanocrystals (NCs) can be selectively incorporated into one compartment of anisotropic polymer particles. Stable bicompartmental particles were prepared via electrohydrodynamic co-jetting of aqueous nanoparticle suspensions followed by thermal cross-linking. Bicompartmental particle populations with different NC densities were obtained by varying the NC concentration in the jetting suspension. While NC-loaded polymer particles showed different optical properties depending on the NC density, they still maintained discrete interfaces between two compartments. Moreover, the fraction of the bicompartmental particles was higher than 98% based on flow cytometry. This study delineates a new approach for preparation of inorganic/organic composite particles with precisely engineered, anisotropic nanoparticle distributions and may contribute to further developments in emerging scientific areas, such as smart materials or particle-based diagnostics.

Anisotropic hybrid particles based on electrohydrodynamic co-jetting of nanoparticle suspensions

Electrohydrodynamic co-jetting of two different nanocrystal suspensions can result in anisotropic nanocomposite particles. Using this approach, we are able to prepare submicron-sized, spherical Janus particles (464 ± 242 nm), which are not only comprised of two chemically distinct compartments, but are also morphologically anisotropic. Specifically, multifunctional hybrid particles have been derived, which are composed of a crosslinked copolymer, poly(acrylamide-co-acrylic acid) (p(AAm-co-AA)), and compartmentalized with respect to two metal oxides, i.e. titanium dioxide (TiO(2)) and magnetite (Fe(3)O(4)). Due to size as well as optical color differences between the Fe(3)O(4) (∼10 nm) and TiO(2) (<100 nm) loadings, the surface morphology of the two compartments are significantly different and the particles display magnetic, optical, and interfacial anisotropy. Magnetic anisotropy of the particles has been utilized to control the particles' positioning in an external magnetic field, which--with further work--may lead to magnetically switchable surfaces for display applications.

Biocompatible Polymers: Structurally Controlled Bio-hybrid Materials Based on Unidirectional Association of Anisotropic Microparticles with Human Endothelial Cells (Adv. Mater. 48/2009).

Biocompatible anisotropic polymer particles with bipolar affinity towards human endothelial cells are a novel type of building blocks for microstructured biohybrid materials, report Joerg Lahann and co-workers on p. 4920. Functional polarity due to two biologically distinct hemispheres has been achieved by synthesis of anisotropic particles via electro-hydrodynamic co-jetting of two different polymer solutions and subsequent selective surface modification.

Structurally Controlled Bio-hybrid Materials Based on Unidirectional Association of Anisotropic Microparticles with Human Endothelial Cells.

Biocompatible anisotropic polymer particles with bipolar affinity towards human endothelial cells are a novel type of building blocks for microstructured bio-hybrid materials. Functional polarity due to two biologically distinct hemispheres has been achieved by synthesis of anisotropic particles via electro-hydrodynamic co-jetting of two different polymer solutions and subsequent selective surface modification.

Multicompartmental Materials by Electrohydrodynamic Cojetting

While multicomponent microand nanoscale structures and even atomically blended materials have been in use for centuries in various bulk forms ranging from metal-nanoparticle-doped glasses to crystalline alloys, recent advances in top-down and bottom-up fabrication processes have allowed for improved control over the structure of microand nanoscale multicomponent materials. These multicomponent microstructured materials are important in imaging, drug delivery, sensing, and tissue engineering. A simple example of such a material is the core–shell particle, where the shell could improve the compatibility with the surrounding environment in imaging applications, provide for a controlled release profile in drug delivery, or give tuneable absorption properties in plasmonic particles. While the core–shell configuration has its utility, there is ample room for more complex configurations. In drug delivery and diagnostics, for example, it would be attractive to have a platform where multiple compartments of a microstructured material could be used to: 1) target the desired cells, 2) deliver the desired drug(s) at the desired rate(s) for the required duration(s), and 3) label the treated cells for diagnostic evaluation. Various techniques have been utilized to fabricate multicomponent microstructured materials with core–shell, nested, Janus, and/or granular architecture. Figure 1 depicts examples of multiphase microstructures patterned by various techniques, including the microfluidic sheath flow of granular Janus particles (Figure 1a), laser direct writing of a trapped colloidal fluid (Figure 1b), electrospinning of inorganic– organic hybrid materials in core–sheath and side-by-side configurations (Figure 1c and d), and the electrospray and cellular uptake of water-stable Janus particles (Figure 1e). While the solution-phase syntheses of particles can be scaled up readily, they have not been well suited for the arbitrary placement of multiple components on the microscale. Stan-

Macromol. Rapid Commun. 19/2009

Front Cover: Electrohydrodynamic co-jetting can result in microfibers with defined compartments. Here, the selective surface modification of bicompartmental microfibers is reported. This novel technology has the potential to address a so-far unmet requirement of tissue engineering: how to pattern cells in a three-dimensional scaffold framework. Further details can be found in the article by S. Mandal, S. Bhaskar, and J. Lahann* on page 1638.

Environmentally Responsive Core/Shell Particles via Electrohydrodynamic Co‐Jetting of Fully Miscible Polymer Solutions

Herein it is demonstrated that electrohydrodynamic co-jetting is not limited to Janus-type particles, but can also be used for the preparation of core/shell particles. Using side-by-side flow of miscible polymer solutions, electrohydrodynamic co-jetting offers an elegant and scalable route towards preparation of core/shell particles with otherwise difficult-to-prepare particle architectures, including particles with hydrophilic shell and core. Throughout this study, electrohydrodynamic co-jetting of aqueous solutions consisting of a mixture of PAAm-co-AA and PAA is used, and a range of different types of particles with distinct compartments are observed. Transition from Janus particles to core/shell particles appears to be caused by changes in the relative conductivity of the two jetting solutions. After crosslinking, the core/shell particles are stable in aqueous solution and exhibit reproducible swelling behavior while maintaining the original core/shell geometry. In addition, the pH-responsiveness of the particles is demonstrated by repeatedly switching the environmental pH between 1.3 and 12. Moreover, the core/shell particles show surprising uptake selectivity. For instance, a 450% increase in uptake of 6-carboxyfluorescein over rhodamine B base is found.

Compartmentalized, multiphasic nanocolloids with potential applications in drug delivery and biomedical imaging

AbstractNanoparticles are excellent candidates for drug delivery or biomedical imaging, because they often exhibit superb tuneability of critical properties, such as size, surface characteristics, degradation rate, and therefore drug release rates. We have recently developed a route towards fabrication of sub‐micron particles that relies on electrohydrodynamic co‐jetting. In this process, fluid manipulation in an electrical field is used to fabricate large quantities of multi‐compartment particles, where individual compartments can be independently loaded with different drugs or selectively surface‐modified. In this contribution, aspects of multifunctional particles for biomedical applications are reviewed and a specific focus is given to recent progress with compartmentalized, multiphasic nanocolloids in our laboratory.