Engineering Helical Modular Polypeptide-Based Hydrogels as Synthetic Extracellular Matrices for Cell Culture.

Expanding the toolkit of modular and functional synthetic material systems for biomimetic extracellular matrices (ECMs) is needed for achieving more predictable and characterizable cell culture. In the present study, we engineered a synthetic hydrogel system incorporating poly(γ-propargyl-l-glutamate) (PPLG), an N-carboxy anhydride polypeptide with a unique α-helical secondary structure. PPLG macromers were cross-linked into poly(ethylene glycol) (PEG) networks to form hybrid polypeptide-PEG hydrogels. We compared the properties of PPLG-PEG to systems where the PPLG macromers were replaced with 8-arm PEG or poly(γ-propargyl-d,l-glutamate) (PPDLG), which has a flexible random-coil conformation. We evaluated each hydrogel system as synthetic ECMs for two-dimensional (2D) endothelial cell culture. Cells on PPLG-PEG displayed superior attachment and spreading at comparable adhesion ligand incorporation concentrations, demonstrating the unique benefit of combining the more rigid and hydrophobic α-helical PPLG within the more flexible and hydrophilic PEG matrix. The modular PPLG macromer is a promising building block for developing other types of PPLG-based hydrogels with favorable and tunable properties.

Electrochemiluminescence "turn-off" detection of curcumin via energy transfer using luminol-doped silica nanoparticles.

A method is presented for electrochemiluminescent (ECL) detection of the food additive curcumin via an energy transfer strategy and by using luminol-doped silica nanoparticles (luminol-NPs). The ECL emission of the luminol-NPs (peaking at 425 nm) is reduced in the presence of curcumin due to spectral overlap. The assay can be performed within 1 min, response is linear in the 0.1 to 100 µM curcumin concentration range, and the limit of detection is 32 nM. The method is selective over many ions, adenosine triphosphate, ascorbic acid, cysteine and folic acid. It was successfully applied to the determination of curcumin in spiked human serum and urine. The average recoveries range from 99.0 to 102.6%. Graphical abstract Electrochemiluminescence (ECL) "turn-off" detection of curcumin at levels as low as 32 nM via energy transfer using luminol-doped silica nanoparticles. No hydrogen peroxide (H2O2) is used in ECL detection which makes the luminol-NPs ECL system more stable than the conventional luminol-H2O2 ECL system.

Water-dispersed fluorescent silicon nanodots as probes for fluorometric determination of picric acid via energy transfer.

Water-dispersed fluorescent silicon nanodots (SiNDs) were synthesized by a one-pot hydrothermal method starting from tetraethyl orthosilicate (TEOS) as silicon source and trisodium citrate as reducing reagent. The method is simple and convenient. The SiNDs, with excitation/emission peaks at 347/440 nm and with fluorescence quantum yield of 18% are shown to be viable fluorescent probes for picric acid (PA). The SiNDs strongly bind PA, and their blue fluorescence is quenched. The distance between the donor and acceptor (R0 value) is calculated from fluorescence data to be 2.1 nm. A fluorometric method was worked out that has a linear response in the 8 nM to 50 µM PA concentration range and a 0.92 nM limit of detection. The method has a fast response (2 min) and is well selective over other nitroaromatic compounds and metal ions. The average recoveries from spiked lake water samples ranged between 98.4 and 100.8%. Graphical abstract Water-dispersed fluorescent silicon nanodots (SiNDs) are synthesized using tetraethyl orthosilicate (TEOS) and trisodium citrate. Based on spectral overlap of fluorescent spectrum of SiNDs and absorption spectrum of picric acid (PA), fluorometric determination of PA at concentrations as low as 0.92 nM is achieved.

Linear and Star Poly(ionic liquid) Assemblies: Surface Monolayers and Multilayers.

The surface morphology and organization of poly(ionic liquid)s (PILs), poly[1-(4-vinylbenzyl)-3-butylimidazolium bis(trifluoromethylsulfonyl)imide] are explored in conjunction with their molecular architecture, adsorption conditions, and postassembly treatments. The formation of stable PIL Langmuir and Langmuir-Blodgett (LB) monolayers at the air-water and air-solid interfaces is demonstrated. The hydrophobic bis(trifluoromethylsulfonyl)imide (Tf2N-) is shown to be a critical agent governing the assembly morphology, as observed in the reversible condensation of LB monolayers into dense nanodroplets. The PIL is then incorporated as an unconventional polyelectrolyte component in the layer-by-layer (LbL) films of hydrophobic character. We demonstrate that the interplay of capillary forces, macromolecular mobility, and structural relaxation of the polymer chains influence the dewetting mechanisms in the PIL multilayers, thereby enabling access to a diverse set of highly textured, porous, and interconnected network morphologies for PIL LbL films that would otherwise be absent in conventional LbL films. Their compartmentalized internal structure is relevant to molecular separation membranes, ultrathin hydrophobic coatings, targeted cargo delivery, and highly conductive films.

A simple and universal gel permeation chromatography technique for precise molecular weight characterization of well-defined poly(ionic liquid)s.

Poly(ionic liquid)s (PILs) are an important class of technologically relevant materials. However, characterization of well-defined polyionic materials remains a challenge. Herein, we have developed a simple and versatile gel permeation chromatography (GPC) methodology for molecular weight (MW) characterization of PILs with a variety of anions. PILs with narrow MW distributions were synthesized via atom transfer radical polymerization, and the MWs obtained from GPC were further confirmed via nuclear magnetic resonance end group analysis.

A general strategy for the preparation of carbon nanotubes and graphene oxide decorated with PdO nanoparticles in water.

The preparation of carbon nanotube (CNT)/PdO nanoparticles and graphene oxide (GO)/PdO nanoparticle hybrids via a general aqueous solution strategy is reported. The PdO nanoparticles are generated in situ on the CNTs and GO by a one-step "green" synthetic approach in aqueous Pd(NO(3))(2) solution under ambient conditions without adding any additional chemicals. The production of PdO is confirmed by energy dispersive X-ray spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, and thermal gravimetric analysis. The morphologies of the resulting CNT/PdO and GO/PdO nanohybrids are characterized by transmission and/or scanning transmission electron microscopy. PdO nanoparticles with an average size of 2-3 nm in diameter are decorated evenly along the surfaces of CNTs and GO. This synthesis strategy is demonstrated to be compatible for 1) CNTs with different modifications, including pristine, oxidized, and polymer-functionalized CNTs; 2) different types of CNTs, including single-walled carbon nanotubes (SWCNTs), double-walled carbon nanotubes (DWCNTs), and multiwalled carbon nanotubes (MWCNTs); and 3) different shapes of carbon materials, including tubular CNTs and planar GO. The as-prepared CNT/PdO and GO/PdO nanohybrids can be transformed into CNT/Pd and GO/Pd nanohybrids by reduction with NaBH(4), and can then be used as a heterogeneous catalyst in the catalytic reduction of 4-nitrophenol.

Engineering PEG-based hydrogels to foster efficient endothelial network formation in free-swelling and confined microenvironments.

In vitro tissue engineered models are poised to have significant impact on disease modeling and preclinical drug development. Reliable methods to induce microvascular networks in such microphysiological systems are needed to improve the size and physiological function of these models. By systematically engineering several physical and biomolecular properties of the cellular microenvironment (including crosslinking density, polymer density, adhesion ligand concentration, and degradability), we establish design principles that describe how synthetic matrix properties influence vascular morphogenesis in modular and tunable hydrogels based on commercial 8-arm poly (ethylene glycol) (PEG8a) macromers. We apply these design principles to generate endothelial networks that exhibit consistent morphology throughout depths of hydrogel greater than 1 mm. These PEG8a-based hydrogels have relatively high volumetric swelling ratios (>1.5), which limits their utility in confined environments such as microfluidic devices. To overcome this limitation, we mitigate swelling by incorporating a highly functional PEG-grafted alpha-helical poly (propargyl-l-glutamate) (PPLGgPEG) macromer along with the canonical 8-arm PEG8a macromer in gel formation. This hydrogel platform supports enhanced endothelial morphogenesis in neutral-swelling environments. Finally, we incorporate PEG8a-PPLGgPEG gels into microfluidic devices and demonstrate improved diffusion kinetics and microvascular network formation in situ compared to PEG8a-based gels.

Electrochemiluminescence resonance energy transfer immunoassay for alkaline phosphatase using p-nitrophenyl phosphate as substrate.

A sensitive electrochemiluminescent immunoassay for alkaline phosphatase (ALP) using p-nitrophenyl phosphate (PNPP) as substrate based on the electrochemiluminescence resonance energy transfer (ECRET) is developed. Luminol-doped silica nanoparticles (luminol-SiNPs) are prepared by water/oil (W/O) microemulsion method. PNPP convertes to p-nitrophenol (PNP) in the presence of ALP, which results in the absorption peak shifting from 360 nm to 450 nm. Herein the spectral overlap between absorption spectrum of PNP and electrochemiluminescence (ECL) spectrum of luminol-SiNPs (425 nm) makes energy transfer occur from luminol-SiNPs to PNP. In the optimized conditions, a linear relationship was obtained using this ECRET method at the concentration of ALP from 5 to 50 U/L (r = 0.9905) and with the limit of detection (LOD) of 0.8 U/L. This ECRET method exhibits sufficient specificity for ALP over other enzymes such as horseradish peroxidase, trypsin and lysozyme.

'Clicked' magnetic nanohybrids with a soft polymer interlayer.

We have developed a facile and efficient methodology to prepare magnetic nanohybrids from 'clickable' magnetic nanoparticles and polymer-coated nanomaterials by Cu(I)-catalyzed azide-alkyne cycloaddition 'click' chemistry.

Cubosomes from hierarchical self-assembly of poly(ionic liquid) block copolymers.

Cubosomes are micro- and nanoparticles with a bicontinuous cubic two-phase structure, reported for the self-assembly of low molecular weight surfactants, for example, lipids, but rarely formed by polymers. These objects are characterized by a maximum continuous interface and high interface to volume ratio, which makes them promising candidates for efficient adsorbents and host-guest applications. Here we demonstrate self-assembly to nanoscale cuboidal particles with a bicontinuous cubic structure by amphiphilic poly(ionic liquid) diblock copolymers, poly(acrylic acid)-block-poly(4-vinylbenzyl)-3-butyl imidazolium bis(trifluoromethylsulfonyl)imide, in a mixture of tetrahydrofuran and water under optimized conditions. Structure determining parameters include polymer composition and concentration, temperature, and the variation of the solvent mixture. The formation of the cubosomes can be explained by the hierarchical interactions of the constituent components. The lattice structure of the block copolymers can be transferred to the shape of the particle as it is common for atomic and molecular faceted crystals.

Synthetic Lift-off Polymer beneath Layer-by-Layer Films for Surface-Mediated Drug Delivery.

A broad range of biomaterials coatings and thin film drug delivery systems require a strategy for the immobilization, retention, and release of coatings from surfaces such as patches, inserts, and microneedles under physiological conditions. Here we report a polymer designed to provide a dynamic surface, one that first functions as a platform for electrostatic thin film assembly and releases the film once in an in vivo environment. Atom transfer radical polymerization (ATRP) was used to synthesize this polymer poly(o-nitrobenzyl-methacrylate-co-hydroxyethyl-methacrylate-co-poly(ethylene-glycol)-methacrylate) (PNHP), embedded beneath multilayered polyelectrolyte films. Such a base layer is designed to photochemically pattern negative charge onto a solid substrate, assist deposition of smooth layer-by-layer (LbL) polyelectrolyte in mildly acidic buffers and rapidly dissolve at physiological pH, thus lifting off the LbL films. To explore potential uses in the biomedical field, a lysozyme (Lys)/poly(acrylic acid) (PAA) multilayer film was developed on PNHP-coated silicon wafers to construct prototype antimicrobial shunts. Film thickness was shown to grow exponentially with increasing deposition cycles, and effective drug loading and in vitro release was confirmed by the dose-dependent inhibition of Escherichia coli (E. coli) growth. The efficacy of this approach is further demonstrated in LbL-coated microscale needle arrays ultimately of interest for vaccine applications. Using PNHP as a photoresist, LbL films were confined to the tips of the microneedles, which circumvented drug waste at the patch base. Subsequent confocal images confirmed rapid LbL film implantation of PNHP at microneedle penetration sites on mouse skin. Furthermore, in human skin biopsies, we achieved efficient immune activation demonstrated by a rapid uptake of vaccine adjuvant from microneedle-delivered PNHP LbL film in up to 37% of antigen-presenting cells (APC), providing an unprecedented LbL microneedle platform for human vaccination.

Multifunctional Hydrogels with Reversible 3D Ordered Macroporous Structures.

Three-dimensionally ordered macroporous (3DOM) hydrogels prepared by colloidal crystals templating display highly reversible shape memory properties, as confirmed by indirect electron microscopy imaging of their inverse replicas and direct nanoscale resolution X-ray microscopy imaging of the hydrated hydrogels. Modifications of functional groups in the 3DOM hydrogels result in various materials with programmed properties for a wide range of applications.

Synthesis of High Molecular Weight Polymethacrylates with Polyhedral Oligomeric Silsesquioxane Moieties by Atom Transfer Radical Polymerization.

A new polyhedral oligomeric silsesquioxane (POSS) methacrylate monomer, 1-(3-(methacryloyloxy)propyl)dimethylsiloxy-3,5,7,9,11,13,15-hepta(isobutyl)pentacyclo-[9.5.1.13,9.15,15.17,13]octasiloxane ((i-Bu)7POSS-OSiMe2-MA, 1), with a flexible spacer between the cubic POSS cage and methacrylate group was synthesized to reduce steric strain and thus achieve polymethacrylates (poly(POSS-MA)s) with high molecular weight (MW). Atom transfer radical polymerization (ATRP) of 1 at high monomer concentration (1 M, corresponding to ca. 85 wt % of 1) led to polymers with the absolute number-average MW, determined by multiangle laser light scattering, Mn,MALLS = 2 350 000 (and apparent MW, measured by gel permeation chromatography with linear poly(methyl methacrylate) (PMMA) standards, Mn,GPC = 550 000). Optimization of the reaction conditions, including the ATRP catalyst, targeted degrees of polymerization, monomer concentrations, as well as a monomer feeding, resulting in the first well-defined high MW polymers with POSS moieties.

Biologically derived soft conducting hydrogels using heparin-doped polymer networks.

The emergence of flexible and stretchable electronic components expands the range of applications of electronic devices. Flexible devices are ideally suited for electronic biointerfaces because of mechanically permissive structures that conform to curvilinear structures found in native tissue. Most electronic materials used in these applications exhibit elastic moduli on the order of 0.1-1 MPa. However, many electronically excitable tissues exhibit elasticities in the range of 1-10 kPa, several orders of magnitude smaller than existing components used in flexible devices. This work describes the use of biologically derived heparins as scaffold materials for fabricating networks with hybrid electronic/ionic conductivity and ultracompliant mechanical properties. Photo-cross-linkable heparin-methacrylate hydrogels serve as templates to control the microstructure and doping of in situ polymerized polyaniline structures. Macroscopic heparin-doped polyaniline hydrogel dual networks exhibit impedances as low as Z = 4.17 Ω at 1 kHz and storage moduli of G' = 900 ± 100 Pa. The conductivity of heparin/polyaniline networks depends on the oxidation state and microstructure of secondary polyaniline networks. Furthermore, heparin/polyaniline networks support the attachment, proliferation, and differentiation of murine myoblasts without any surface treatments. Taken together, these results suggest that heparin/polyaniline hydrogel networks exhibit suitable physical properties as an electronically active biointerface material that can match the mechanical properties of soft tissues composed of excitable cells.

Preparation of polymeric nanoscale networks from cylindrical molecular bottlebrushes.

The design and control of polymeric nanoscale network structures at the molecular level remains a challenging issue. Here we construct a novel type of polymeric nanoscale networks with a unique microporous nanofiber unit employing the intra/interbrush carbonyl cross-linking of polystyrene side chains for well-defined cylindrical polystyrene molecular bottlebrushes. The size of the side chains plays a vital role in the tuning of nanostructure of networks at the molecular level. We also show that the as-prepared polymeric nanoscale networks exhibit high specific adsorption capacity per unit surface area because of the synergistic effect of their unique hierarchical porous structures. Our strategy represents a new avenue for the network unit topology and provides a new application for molecular bottlebrushes in nanotechnology.

Supraparamagnetic, conductive, and processable multifunctional graphene nanosheets coated with high-density Fe3O4 nanoparticles.

The amazing properties of graphene are triggering extensive interests of both scientists and engineers, whereas how to fully utilize the unique attributes of graphene to construct novel graphene-based composites with tailor-made, integrated functions remains to be a challenge. Here, we report a facile approach to multifunctional iron oxide nanoparticle-attached graphene nanosheets (graphene@Fe(3)O(4)) which show the integrated properties of strong supraparamagnetism, electrical conductivity, highly chemical reactivity, good solubility, and excellent processability. The synthesis method is efficient, scalable, green, and controllable and has the feature of reduction of graphene oxide and formation of Fe(3)O(4) nanoparticles in one step. When the feed ratios are adjusted, the average diameter of Fe(3)O(4) nanoparticles (1.2-6.3 nm), the coverage density of Fe(3)O(4) nanoparticles on graphene nanosheets (5.3-57.9%), and the saturated magnetization of graphene@Fe(3)O(4) (0.5-44.1 emu/g) can be controlled readily. Because of the good solubility of the as-prepared graphene@Fe(3)O(4), highly flexible and multifunctional films composed of polyurethane and a high content of graphene@Fe(3)O(4) (up to 60 wt %) were fabricated by the solution-processing technique. The graphene@Fe(3)O(4) hybrid sheets showed electrical conductivity of 0.7 S/m and can be aligned into a layered-stacking pattern in an external magnetic field. The versatile graphene@Fe(3)O(4) nanosheets hold great promise in a wide range of fields, including magnetic resonance imaging, electromagnetic interference shielding, microwave absorbing, and so forth.

Covalent layer-by-layer functionalization of multiwalled carbon nanotubes by click chemistry.

The covalent functionalization of multiwalled carbon nanotubes (MWNTs) by layer-by-layer (LbL) click chemistry is reported. The clickable polymers of poly(2-azidoethyl methacrylate) and poly(propargyl methacrylate) were synthesized at first by atom transfer radical polymerization (ATRP) of 2-azidoethyl methacrylate and reverse addition-fragmentation chain transfer (RAFT) polymerization of propargyl methacrylate, respectively. The two polymers were then alternately coated on alkyne-modified multiwalled carbon nanotubes using Cu(I)-catalyzed click reaction of Huisgen 1,3-dipolar cycloaddition between azides and alkynes. Thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) measurements confirm that the quantity and thickness of the clicked polymer shell on MWNTs can be well controlled by adjusting the cycles or numbers of click reaction and the polymer shell is uniform and even. X-ray photoelectron spectroscopy (XPS) and Fourier tranform infrared (FTIR) measurements showed that there were still a great amount of residual azido groups on the surfaces of the functionalized MWNTs after clicking three layers of polymers. Furthermore, alkyne-modified rhodamine B and monoalkyne-terminated polystyrene were subsequently used to functionalize the clickable polymer grafted MWNTs, giving rise to fluorescent carbon nanotubes (CNTs) and CNT-based polystyrene brushes, respectively. It demonstrates that the residual azido groups on the surfaces of MWNTs are available for further click reaction with various functional molecules.