Self-healing boronic acid-based hydrogels for 3D co-cultures.

Synthetic hydrogels have been widely adopted as well-defined matrices for three-dimensional (3D) cell culture, with increasing interest in systems that enable the co-culture of multiple cell types for probing both cell-matrix and cell-cell interactions in studies of tissue regeneration and disease. We hypothesized that the unique dynamic covalent chemistry of self-healing hydrogels could be harnessed for not only the encapsulation and culture of human cells but also the subsequent construction of layered hydrogels for 3D co-cultures. To test this, we formed hydrogels using boronic acid-functionalized polymers and demonstrated their self-healing in the presence of physiologically-relevant cell culture media.

Cross-Linked Aptamer-Lipid Micelles for Excellent Stability and Specificity in Target-Cell Recognition.

The specific binding ability of DNA-lipid micelles (DLMs) can be increased by the introduction of an aptamer. However, supramolecular micellar structures based on self-assemblies of amphiphilic DLMs are expected to demonstrate low stability when interacting with cell membranes under certain conditions, which could lead to a reduction in selectivity for targeting cancer cells. We herein report a straightforward cross-linking strategy that relies on a methacrylamide branch to link aptamer and lipid segments.

Efficiency of Biodegradable and pH-Responsive Polysuccinimide Nanoparticles (PSI-NPs) as Smart Nanodelivery Systems in Grapefruit: In Vitro Cellular Investigation.

Biodegradable pH-responsive polysuccinimide nanoparticles (PSI-NPs) are synthesized for directly delivering agrochemicals to plant phloem to improve their efficacy. The PSI-NPs have an average size of 20.6 nm with negative charge on the surface.

Photoinduced Electron Transfer in Naphthalene Diimide End-Capped Thiophene Oligomers.

A series of linear thiophene oligomers containing 4, 6, 8, 10, and 12 thienylene units were synthesized and end-capped with naphthalene diimide (NDI) acceptors with the objective to study the effect of oligomer length on the dynamics of photoinduced electron transfer and charge recombination. The synthetic work afforded a series of nonacceptor-substituted thiophene oligomers, T, and corresponding NDI end-capped series, TNDI (where n is the number of thienylene repeat units). This paper reports a complete photophysical characterization study of the T and TNDI series by using steady-state absorption, fluorescence, singlet oxygen sensitized emission, two-photon absorption, and nanosecond-microsecond transient absorption spectroscopy.

Radical Ring-Opening Copolymerization of Cyclic Ketene Acetals and Maleimides Affords Homogeneous Incorporation of Degradable Units.

Radical copolymerization of donor-acceptor (D-A) monomer pairs has served as a versatile platform for the development of alternating copolymers. However, due to the use of conventional radical polymerization, the resulting copolymers have generally been limited to nondegradable vinyl polymers. By combining radical D-A copolymerization with radical ring-opening polymerization (rROP), we have synthesized an alternating copolymer with a high incorporation of degradable backbone units.

Polymer Chromophore-Catalyst Assembly for Solar Fuel Generation.

A polystyrene-based chromophore-catalyst assembly (poly-2) has been synthesized and assembled at a mesoporous metal oxide photoanode. The assembly contains water oxidation catalyst centers based on [Ru(trpy) (phenq)] (Ru-Cat) and [Ru(bpy)] derivatives (Ru-C) as chromophores (trpy= 2,2';6,2″- terpyridine, phenq = 2-(quinol-8'-yl)-1,10-phenanthroline and bpy = 2,2'-bipyridine). The photophysical and electrochemical properties of the polychromophore-oxidation catalyst assembly were investigated in solution and at the surface of mesoporous metal oxide films.

Effect of Conjugation Length on Photoinduced Charge Transfer in π-Conjugated Oligomer-Acceptor Dyads.

A series of π-conjugated oligomer-acceptor dyads were synthesized that feature oligo(phenylene ethynylene) (OPE) conjugated backbones end-capped with a naphthalene diimide (NDI) acceptor. The OPE segments vary in length from 4 to 8 phenylene ethynene units (PEn-NDI, where n = 4, 6 and 8). Fluorescence and transient absorption spectroscopy reveals that intramolecular OPE → NDI charge transfer dominates the deactivation of excited states of the PEn-NDI oligomers.

Star Architecture Promoting Morphological Transitions during Polymerization-Induced Self-Assembly.

Polymerization-induced self-assembly (PISA) via reversible addition-fragmentation chain transfer (RAFT) dispersion polymerization is an effective method to produce block copolymer nano-objects of various morphologies at high solids. However, current PISA formulations have been limited to linear block copolymers. We report the synthesis of AB star block copolymers via RAFT aqueous dispersion polymerization of diacetone acrylamide using a poly(ethylene glycol) methyl ether bearing two chain transfer agents as the difunctional macromolecular chain transfer agent (macro-CTA), which was efficiently synthesized using 2,4,6-trichloro-1,3,5-triazine and activated esters to afford a high end functionality (97%).

Catalyst-Free Photoinduced End-Group Removal of Thiocarbonylthio Functionality.

An initiator- and catalyst-free method for polymer end-group modification has been designed. Under long-wave ultraviolet irradiation, polymers with thiocarbonylthio end groups undergo photolytic cleavage to reveal an active macroradical capable of irreversible termination with a suitable hydrogen source. This straightforward method was successfully demonstrated by the removal of a range of end groups that commonly result from reversible addition-fragmentation chain transfer or photoiniferter polymerizations, including trithiocarbonate, dithiobenzoate, xanthate, and dithiocarbamate mediating agents.

Pyrophosphate Sensor Based on Principal Component Analysis of Conjugated Polyelectrolyte Fluorescence.

The pyrophosphate anion (PPi) plays an important role in biochemical processes. Therefore, a simple but reliable analytical technique is essential for selective detection of PPi in biochemical systems. Here, we present a principal component analysis (PCA) method for analytical determination of PPi concentration using a fluorescent conjugated polyelectrolyte (CPE) combined with a polyamine modifier.

Role of Macromolecular Structure in the Ultrafast Energy and Electron Transfer Dynamics of a Light-Harvesting Polymer.

Ultrafast energy and electron transfer (EnT and ET, respectively) are characterized in a light-harvesting assembly based on a π-conjugated polymer (poly(fluorene)) functionalized with broadly absorbing pendant organic isoindigo (iI) chromophores using a combination of femtosecond transient absorption spectroscopy and large-scale computer simulation. Photoexcitation of the π-conjugated polymer leads to near-unity quenching of the excitation through a combination of EnT and ET to the iI pendants. The excited pendants formed by EnT rapidly relax within 30 ps, whereas recombination of the charge-separated state formed following ET occurs within 1200 ps.

Radical Departure: Thermally-Triggered Degradation of Azo-Containing Poly(β-thioester)s.

The design and synthesis of a new class of thermally-labile poly(β-thioester)s is reported. Aliphatic azo linkages were incorporated into the main chain of the polymers to allow for degradation to lower molecular weights upon heating. These polymers displayed a temperature-dependent degradation profile with a significant increase in decomposition rate as the temperature was raised from 60 to 95 °C.

Effect of Oligomer Length on Photophysical Properties of Platinum Acetylide Donor-Acceptor-Donor Oligomers.

We report a systematic study that explores how the triplet excited state is influenced by conjugation length in a series of benzothiadiazole units containing donor-acceptor-donor (DAD)-type platinum acetylide oligomers and polymer. The singlet and triplet excited states for the series were characterized by an array of photophysical methods including steady-state luminescence spectroscopy and femtosecond-nanosecond transient absorption spectroscopy. In addition to the experimental work, a computational study using density functional theory was conducted to gain more information about the structure, composition, and energies of the frontier molecular orbitals.

Triplet excited state properties in variable gap π-conjugated donor-acceptor-donor chromophores.

A series of variable band-gap donor-acceptor-donor (DAD) chromophores capped with platinum(ii) acetylide units has been synthesized and fully characterized by electrochemical and photophysical methods, with particular emphasis placed on probing triplet excited state properties. A counter-intuitive trend of increasing fluorescence quantum efficiency and lifetime with decreasing excited state energy (optical gap) is observed across the series of DAD chromophores. Careful study of the excited state dynamics, including triplet yields (as inferred from singlet oxygen sensitization), reveals that the underlying origin of the unusual trend in the fluorescence parameters is that the singlet-triplet intersystem crossing rate and yield decrease with decreasing optical gap.

Efficient Light-Driven Oxidation of Alcohols Using an Organic Chromophore-Catalyst Assembly Anchored to TiO2.

The ligand 5-PO3H2-2,2':5',2″-terthiophene-5-trpy, T3 (trpy = 2,2':6',2″-terpyridine), was prepared and studied in aqueous solutions along with its metal complex assembly [Ru(T3)(bpy)(OH2)](2+) (T3-Ru-OH2, bpy = 2,2'-bipyridine). T3 contains a phosphonic acid group for anchoring to a TiO2 photoanode under aqueous conditions, a terthiophene fragment for light absorption and electron injection into TiO2, and a terminal trpy ligand for the construction of assemblies comprising a molecular oxidation catalyst. At a TiO2 photoanode, T3 displays efficient injection at pH 4.

Effect of Selenium Substitution on Intersystem Crossing in π-Conjugated Donor-Acceptor-Donor Chromophores: The LUMO Matters the Most.

This study explores the effect of substitution of selenium (Se) for sulfur (S) on the photophysical properties of a series of π-conjugated donor-acceptor-donor chromophores based on 4,7-bis(2-thienyl)-2,1,3-benzothiadiazole (TBT). The effect of Se substitution is studied systematically, where the substitution is in the thiophene donors only, the benzothiadiazole acceptor only, and in all of the positions. The fluorescence quantum yield decreases with an increase in Se substitution.

Enhanced Photovoltaic Performances of Dye-Sensitized Solar Cells by Co-Sensitization of Benzothiadiazole and Squaraine-Based Dyes.

Dye-sensitized solar cells (DSSCs) based on a donor-acceptor-donor oligothienylene dye containing benzothiadiazole (T4BTD-A) were cosensitized with dyes containing cis-configured squaraine rings (HSQ3 and HSQ4). The cosensitized dyes showed incident monochromatic photon-to-current conversion efficiency (IPCE) greater than 70% in the 300-850 nm wavelength region. The individual overall conversion efficiencies of the sensitizers T4BTD-A, HSQ3, and HSQ4 were 6.

Reusable nanoengineered surfaces for bacterial recruitment and decontamination.

Biofouling, or accumulation of unwanted biofilms, on surfaces is a major concern for public health and human industry. Materials either avoiding contamination (fouling resistant) and/or directly killing attached microbes (biocidal) have thus far failed to achieve the goal of eliminating biofouling; fouling resistant surfaces eventually foul and biocidal surfaces accumulate debris that eventually decrease their efficacy. Combined biocidal and fouling release materials offer the potential for both killing and removing debris and are promising candidates for reducing biofouling on manufactured materials.

Photo-PISA: Shedding Light on Polymerization-Induced Self-Assembly.

Herein we report an aqueous photoinitiated polymerization-induced self-assembly (photo-PISA) for the preparation of a remarkably diverse set of complex polymer nanoparticle morphologies (e.g., spheres, worms, and vesicles) at room temperature.

π-Conjugated Organometallic Isoindigo Oligomer and Polymer Chromophores: Singlet and Triplet Excited State Dynamics and Application in Polymer Solar Cells.

An isoindigo based π-conjugated oligomer and polymer that contain cyclometalated platinum(II) "auxochrome" units were subjected to photophysical characterization, and application of the polymer in bulk heterojunction polymer solar cells with PCBM acceptor was examined. The objective of the study was to explore the effect of the heavy metal centers on the excited state properties, in particular, intersystem crossing to a triplet (exciton) state, and further how this would influence the performance of the organometallic polymer in solar cells. The materials were characterized by electrochemistry, ground state absorption, emission, and picosecond-nanosecond transient absorption spectroscopy.

Photophysics and Nonlinear Absorption of Gold(I) and Platinum(II) Donor-Acceptor-Donor Chromophores.

A series of Au(I) and Pt(II) acetylide complexes of a π-conjugated donor-acceptor-donor (D-A-D) chromophore were studied to develop quantitative structure-property relationships for their photophysical and nonlinear optical properties. The D-A-D chromophore consists of a "TBT" unit, where T = 3-hexyl-2,5-thienylene and BTD = 2,1,3-benzothiadiazole, capped with ethynylene groups. The D-A-D chromophore is functionalized with Au(I)PR3 (R = -Me and -Ph) and trans-Pt(II)(PR3)2-CCPh (R = -Me and -Bu) "auxochromes".

Role of Polymer Architecture on the Activity of Polymer-Protein Conjugates for the Treatment of Accelerated Bone Loss Disorders.

Polymers of similar molecular weights and chemical constitution but varying in their macromolecular architectures were conjugated to osteoprotegerin (OPG) to determine the effect of polymer topology on protein activity in vitro and in vivo. OPG is a protein that inhibits bone resorption by preventing the formation of mature osteoclasts from the osteoclast precursor cell. Accelerated bone loss disorders, such as osteoporosis, rheumatoid arthritis, and metastatic bone disease, occur as a result of increased osteoclastogenesis, leading to the severe weakening of the bone.

Conjugated Polyelectrolyte-Sensitized TiO2 Solar Cells: Effects of Chain Length and Aggregation on Efficiency.

Two sets of conjugated polyelectrolytes with different molecular weights (Mn) in each set were synthesized. All polymers feature the same conjugated backbone with alternating (1,4-phenylene) and (2,5-thienylene ethynylene) repeating units, but different linkages between the backbone and side chains, namely, oxy-methylene (-O-CH2-) (P1-O-n, where n = 7, 9, and 14) and methylene (-CH2-) (P2-C-n, n = 7, 12, and 18). They all bear carboxylic acid moieties as side chains, which bind strongly to titanium dioxide (TiO2) nanoparticles.

Surface Modification of Multiwalled Carbon Nanotubes with Cationic Conjugated Polyelectrolytes: Fundamental Interactions and Intercalation into Conductive Poly(methyl methacrylate) Composites.

This research investigates the modification and dispersion and of pristine multiwalled carbon nanotubes (MWCNTs) through a simple solution mixing technique based on noncovalent interactions between poly(phenylene ethynylene)-based conjugated polyelectrolytes functionalized with cationic imidazolium solubilizing groups (PIM-2 and PIM-4) and MWCNTs. Spectroscopic studies demonstrated the ability of PIMs to strongly interact with and efficiently disperse MWCNTs in different solvents, mainly due to π interactions between the PIMs and the MWCNTs. Transmission electron microscopy and atomic force microscopy revealed the coating of the polyelectrolytes on the walls of the nanotubes.