A redox responsive polymeric gel based on ionic crosslinking.

We report here an electrochemically responsive polymer hydrogel based on ionic crosslinking. The crosslinking by metal cations and anionic carboxylic acid side groups can be controlled by redox reactions. The crosslinks dissociate when the cation crosslinker is reduced to a lower oxidation state and reform following oxidation, which leads to a reversible and localized swelling-contraction. By choosing biocompatible components and miniaturization designs, the system has potential in microrobotic and biomedical applications.

Patterning poly(organophosphazenes) for selective cell adhesion applications.

Five polyphosphazenes with different hydrophilicites were synthesized and screened in vitro. The purpose was to identify unique types of polymeric substrates that distinctly favored or markedly prevented cellular adhesion. The SK-N-BE(2c) human neuroblastoma cell line, utilized for its electrogenic responses, was used to test this differential adhesion. In particular, the objective was to specifically culture this cell line in a highly selective pattern. Each candidate polymer was cast into films and plated with neuroblastoma cells for 3 days. The polyphosphazene materials which showed negative cellular adhesive properties (-CAPs) were poly[bis(trifluoroethoxy)phosphazene] (TFE) and poly[bis(methoxyethoxyethoxy)phosphazene] (MEEP). The polyphosphazenes which showed positive cellular adhesive properties (+CAPs) were poly[(methoxyethoxyethoxy)(1.0)(carboxylatophenoxy)(1.0)phosphazene] (PMCPP), poly[(methoxyethoxyethoxy)(1.0)(cinnamyloxy)(1.0)phosphazene] (PMCP), and poly[(methoxyethoxyethoxy)(1.0)(p-methylphenoxy)(1.0)phosphazene] (PMMP). To test cellular selectivity, films of -CAP and +CAP were copatterned onto glass substrates. The micropatterned films were plated with SK-N-BE(2c) neuroblastoma cells for one week. The results showed that neuroblastoma cells adhere selectively (over 60%) to the +CAP microfeatures. We also showed that multiple properties can be achieved with a single material and that we can use TFE as both a -CAP and an insulation layer and PMCP as a conductive +CAP layer.

Carboxylation and esterification of functionalized arylcopper reagents.

Functionalized arylcopper reagents have been produced in good yields at 25 degrees C from activated copper and the corresponding functionalized aryl iodides without the need of traditional organolithium or Grignard precursors. These organocopper compounds will undergo carboxylation with CO(2) to form the corresponding copper benzoates. In turn, these salts can be acidified to produce the functionalized aryl acids or treated with appropriate alkyl halides in the presence of a dipolar aprotic solvent to generate the corresponding aryl esters. This methodology permits the formation of functionalized organic acids and esters that could not be generated by the carboxylation of organomagnesium compounds.

Synthesis and self-association behavior of biodegradable amphiphilic poly[bis(ethyl glycinat-N-yl)phosphazene]- poly(ethylene oxide) block copolymers.

Amphiphilic diblock copolymers with varying compositions of hydrophilic poly(ethylene oxide) (PEO) and hydrophobic poly[bis(ethyl glycinat-N-yl)phosphazene] (PNgly) were synthesized via the controlled cationic-induced polymerization of a phosphoranimine (Cl(3)P=NSiMe(3)) at ambient temperature using a PEO-phosphoranimine macroinitiator. The aqueous-phase transition behavior of PEO-PNgly-3 (M(n) = 10,000) and micelle formation of both PEO-PNgly-3 and PEO-PNgly-4 (M(n) = 8,500) were investigated using fluorescence techniques and dynamic light scattering. The critical micelle concentrations (cmc's) of PEO-PNgly-3 and PEO-PNgly-4 were determined to be 3 and 12 mg/L with the mean diameters of micelles being 120 and 130 nm, respectively. The hydrolytic degradation of these diblock copolymers was also studied in solution. These studies coupled with the biodegradability of the poly[bis(ethyl glycinat-N-yl)phosphazene] block to give benign products make PEO-PNgly copolymers well-suited for a wide variety of biomedical applications including novel biodegradable drug-delivery systems.