This study deals with the synthesis and in vitro osteocompatibility evaluation of two novel alanine-containing biodegradable ester polyphosphazenes as candidates to form self-setting composites with hydroxyapatite (HAp) precursors. The two novel biodegradable polyphosphazenes synthesized were poly[(ethyl alanato)1.0(ethyl oxybenzoate)1.0 phosphazene] (PN-EA/EOB) and poly[(ethyl alanato)1.0(propyl oxybenzoate)1.0 phosphazene] (PN-EA/POB). The polymers were characterized by multinuclear magnetic resonance (NMR), differential scanning calorimetry (DSC), and gel permeation chromatography (GPC). Biodegradability and percentage water absorption of the polymers were evaluated by following the mass change in phosphate buffer (pH 7.4) at 37 degrees C. PN-EA/POB underwent faster degradation and showed higher water absorption compared to PN-EA/EOB. Both polymers became insoluble in common organic solvents following hydrolysis presumably due to crosslinking reactions accompanying the degradation process. Osteoblast cell adhesion and proliferation on PN-EA/EOB and PN-EA/POB was followed by scanning electron microscopy (SEM) and by using a biochemical assay. Both PN-EA/EOB and PN-EA/POB supported the adhesion and proliferation of primary rat osteoblast cells in vitro. Furthermore, the enzymatic activity of the osteoblast cells cultured on the polymers was confirmed by the alkaline phosphatase activity. Thus, these biodegradable amino-acid-based polyphosphazenes are promising new materials for forming self-setting bone cements.

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 swellingcontraction. By choosing biocompatible components and miniaturization designs, the system has potential in microrobotic and biomedical applications.

Polyphosphazenes that bear both methoxyethoxyethoxy and cinnamyl side groups were synthesized and evaluated for use as hydrogels incorporated into micrometer-scale biosensor arrays. Polymers with the general formula [NPR x R‘ y ] n where R = OCH2CH2OCH2CH2OCH3 and R‘ = OCHCHCH2Ph (x = y = 1; x = 2, y = 0) were synthesized. The polymers were cross-linked to form hydrogels by exposure to ultraviolet radiation (λ = 320−480 nm) in the presence of a photoinitiator. Hydrogel microstructures in the size range 50−500 μm were fabricated using standard photolithographic techniques. The resolution and dimensions of these microstructures were examined by optical microscopy, scanning electron microscopy, and profilometry. The resultant three-dimensional hydrogel microstructures were used to encapsulate enzymes for biosensor applications. The enzymatic activity of encapsulated horseradish peroxidase (HRP) was examined as a model system. The HRP catalyzed reaction between H2O2 and Amplex Red to produce a fluorescent product, resorufin, was confirmed by fluorescence microscopy.

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.

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