Immature dendritic cells (iDCs) were derived from human peripheral blood monocytes, and treated with 75:25 poly(lactic-co-glycolic acid) (PLGA) microparticles (MPs) or film to assess the resultant dendritic cell (DC) maturation as compared to positive control of lipopolysaccharide (LPS) treatment for DC maturation or negative control of untreated iDCs. The effect of PLGA contact on DC maturation was examined as one possible explanation for the PLGA adjuvant effect we have observed in the enhancement of an immune response to codelivered model antigen, as adjuvants act through the maturation of DCs. Culturing iDCs with PLGA MPs or PLGA film resulted in morphology similar to that of LPS-matured DCs and the association, or possible internalization, of PLGA MPs. Furthermore, biomaterial-treated iDCs demonstrated an increase in MHC class II and costimulatory molecule expression compared to iDCs but to a lower level than that of LPS-matured DCs. Direct iDC contact with PLGA MPs was necessary for maturation. Immature DCs exposed to PLGA MPs were stimulatory of allogeneic T-cell proliferation, whereas cells exposed to PLGA film were not. Further, PLGA MPs supported a moderate delayed type hypersensitivity reaction in mice indicative of in vivo DC maturation. Taken together, these results suggest that PLGA is a DC maturation stimulus and that the form of the biomaterial may influence the extent of DC maturation.

"Smart" materialsmaterials that respond to a stimulus or their environment to produce a dynamic and reversible change in critical propertieshave enabled progress in many areas, including display technologies, drug delivery, and self-healing materials for coating applications, among others. Many of the current examples of smart materials are biomimetic, since nature employs and depends on dynamic and rapid switching for critical functions such as vision, camouflage, and ion channel regulation. Despite progress in designing smart materials and surfaces, much work is still needed in this area to increase their implementation in useful applications. In this Perspective, the challenges and outlook in this field are highlighted, including the work of Balazs and co-workers found in this issue of ACS Nano.

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.

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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.

Electrified co-jetting of two aqueous polymer solutions followed by a thermal cross-linking step was used to create water-stable biphasic nanocolloids. For this purpose, aqueous solution mixtures of poly(acrylamide-co-acrylic acid) and poly(acrylic acid) were employed as jetting solutions. When the biphasic nanocolloids created by side-by-side electrified co-jetting were thermally treated, a cross-linking reaction occurred between amide groups and carboxylic groups to form stable imide groups. Infrared spectroscopy was employed to monitor the reaction. The quality and the integrity of the resulting biphasic nanocolloids were confirmed by confocal laser scanning microscopy, flow cytometry analysis, and dynamic light scattering. Selective encapsulation of two biomolecules in each phase of the biphasic colloids was maintained even after thermal reaction and suspension in aqueous environment. Well-dispersed spherical colloids with stable dye loadings in each hemisphere were kept intact without aggregation or dissolution for several weeks. Finally, biphasic nanocolloids were selectively surface-modified with a biotin-dextran resulting in water-stable particles to ensure binding of proteins only to a single hemisphere.

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A novel polymeric initiator coating for surface modification via atom transfer radical polymerization (ATRP) is reported. The synthetic approach involves the chemical vapor deposition of [2.2]paracyclophane‐4‐methyl 2‐bromoisobutyrate and can be applied to a heterogeneous group of substrates including stainless steel, glass, silicon, poly(dimethylsiloxane), poly(methyl methacrylate), poly(tetrafluoroethylene), and polystyrene. Surface analysis using X‐ray photoelectron spectroscopy and Fourier‐transformed infrared spectroscopy confirmed the chemical structure of the reactive initiator coatings to be consistent with poly[(p‐xylylene‐4‐methyl‐2‐bromoisobutyrate)‐co‐(p‐xylylene)]. Appropriate reactivity of the bromoisobutyrate side groups was confirmed by surface initiated atom transfer radical polymerization of a oligo(ethylene glycol) methyl ether methacrylate. After solventless deposition of the CVD‐based initiator coating, hydrogel films as thick as 300 nm could be conveniently prepared within a 24 h timeframe via ATRP. Moreover, the polymerization showed ATRP‐specific reaction kinetics and catalyst concentration dependencies. In addition, spatially controlled deposition of the initiator coatings using vapor‐assisted microstructuring in replica structures resulted in fabrication of spatially confined hydrogel microstructures. Both protein adsorption and cell adhesion was significantly inhibited on areas that were modified by surface‐initiated ATRP, when compared with unmodified PMMA substrates. The herein described initiator coatings provide a convenient access route to controlled radical polymerization on a wide range of different materials. While demonstrated only for a representative group of substrate materials including polymers, metals, and semiconductors, this method can be expected to be generically applicable – thereby eliminating the need for cumbersome modification protocols, which so far had to be established for each substrate material independently.