Covalent Polyisobutylene-Paclitaxel Conjugates for Controlled Release from Potential Vascular Stent Coatings.

The development of covalent polyisobutylene (PIB)-paclitaxel (PTX) conjugates as a potential approach to controlling drug release from vascular stent coatings is described. PIB-PTX materials containing ∼24 and ∼48 wt % PTX, conjugated via ester linkages, were prepared. The PTX release profiles were compared with those of physical mixtures of PTX with carboxylic acid-functionalized PIB and with the triblock copolymer polystyrene-b-PIB-b-polystyrene (SIBS). Covalent conjugation led to significantly slower drug release. Atomic force microscopy imaging of coatings of the materials suggested that the physical mixtures exhibited multiple domains corresponding to phase separation, whereas the materials in which PTX was covalently conjugated appeared homogeneous. Coatings of the conjugated materials on stainless steel surfaces suffered less surface erosion than the physically mixed materials, remained intact, and adhered well to the surface throughout the thirty-five day study. Tensile testing and rheological studies suggested that the incorporation of PTX into the polymer introduces similar physical changes to the PIB as the incorporation of a glassy polystyrene block does in SIBS. Cytotoxicity assays showed that the coatings did not release toxic levels of PTX or other species into a cell culture medium over a 24 h period, yet the levels of PTX in the materials were sufficient to prevent C2C12 cells from adhering to and proliferating on them. Overall, these results indicate that covalent PIB-PTX conjugates have promise as coatings for vascular stents.

Functional polymer laminates from hyperthermal hydrogen induced cross-linking.

The use of a hyperthermal hydrogen induced cross-linking process to prepare laminates comprising polypropylene, poly(isobutylene-co-isoprene), and poly(vinyl acetate) is described. In this new, milder alternative to conventional plasma techniques, neutral molecular hydrogen projectiles were used to create carbon radicals on impacted surfaces by collision-induced dissociation of C-H bonds, and this process was used to cross-link polymers on a polypropylene surface. It was demonstrated that multiple layers of cross-linked materials could be added, creating polymer laminates with each layer introducing new functionalities and properties. In particular, the present work shows that the process is largely nondestructive toward ester functionalities. First, the esters were grafted to become nonleachable. Then, the esters were subsequently hydrolyzed to convert the surface from hydrophobic to hydrophilic. Afterward, the esters could be recovered by simple esterification demonstrating that further chemical transformations were possible.

Ultrathin gold nanoframes through surfactant-free templating of faceted pentagonal silver nanoparticles.

Ultrathin gold nanoframes (up to 1.6 nm) were prepared via templating upon well-defined faceted silver morphologies. Starting with silver decahedra, small quantities of gold (1-10 mol% relative to the amount of silver) were selectively deposited on the nanoparticle edges under optimized reducing conditions. Silver dissolution in hydrogen peroxide yielded well-defined gold frames that retained their structural integrity in the ultrathin nanowire regime below 2 nm. The frame formation protocol was also successfully applied to other silver nanoparticle shapes featuring pentagonal twinning and (111) facets (e.g., pentagonal faceted rods and icosahedra). The demonstrated approach can be applied in the controlled preparation of ultrathin metal nanowires complementary to lithography and in the production of ultrafine noble-metal nanostructures for catalytic applications.

Synthesis of size-controlled faceted pentagonal silver nanorods with tunable plasmonic properties and self-assembly of these nanorods.

Monodisperse size-controlled faceted pentagonal silver nanorods were synthesized by thermal regrowth of decahedral silver nanoparticle (AgNPs) in aqueous solution at 95 degrees C, using citrate as a reducing agent. The width of the silver nanorods was determined by the size of the starting decahedral particle, while the length was varied from 50 nm to 2 mum by the amount of new silver added to the growth solution. Controlled regrowth allowed us to produce monodisperse AgNPs with a shape of elongated pentagonal dipyramid (regular Johnson solid, J(16)). Faceted pentagonal particles exhibited remarkable optical properties with sharp plasmon resonances precisely tunable across visible and NIR. Due to the narrow size distribution, faceted pentagonal silver nanorods readily self-assembled into the 3-D arrays similar to smectic mesophases. Hexagonal arrangement in the array completely overrode five-fold symmetry of the nanorods. Overall, our findings highlight the importance of pentagonal symmetry in metal nanoparticles and offer a facile method of the preparation of monodisperse AgNPs with controlled dimensions and plasmonic properties that are promising for optical applications and functional self-assembly.

Direct structural transformation of silver platelets into right bipyramids and twinned cube nanoparticles: morphology governed by defects.

Silver platelets can undergo quantitative conversion to right bipyramids and twinned cubes by regrowth with silver in conditions that preserve original 2-D structural defects in resulting 3-D morphologies.