Nick Virgilio

Towards ultraporous poly(L-lactide) scaffolds from quaternary immiscible polymer blends.

Ultraporous poly(l-lactide) (PLLA) scaffolds were prepared by melt-processing quaternary ethylene propylene diene rubber/poly(epsilon-caprolactone)/polystyrene/poly(l-lactide) (EPDM/PCL/PS/PLLA) 45/45/5/5 %vol. polymer blends modified with a PS-b-PLLA diblock copolymer. The morphology consists of a PS+PLLA+copolymer sub-blend layer forming at the interface of the EPDM and PCL phases. Quiescent annealing and interfacial modification using the block copolymer are used to control the blend microstructure. The ultraporous structure is subsequently obtained by selectively extracting the EPDM, PS and PCL phases. The PLLA scaffolds modified with the PS-b-PLLA copolymer present themselves as fully interconnected porous networks with asymmetric channel walls, one side being smooth while the other is covered with an array of submicron-sized PLLA droplets. They are prepared with a high degree of control over the pore size, with averages ranging from 5microm to over 100microm and a specific surface from 9.1 to 23.1m(2)/g of PLLA, as annealing is carried out from 0 to 60min. The void volume reaches values as high as 95% and in all cases the shape and dimensions of the scaffolds are maintained with a high level of integrity. The proposed method represents a comprehensive approach towards the design and generation of porous PLLA scaffolds based on complex morphologies from melt-processed multiphase polymer systems.

Sodium alginate-grafted submicrometer particles display enhanced reversible aggregation/disaggregation properties

In this article, we demonstrate that submicrometer particles with surface-grafted sodium alginate (SA) display enhanced and reversible aggregation/disaggregation properties in aqueous solution. 300 nm silica particles were first functionalized with an aminosilane coupling agent, followed by the grafting of pH-sensitive SA, as confirmed by zeta potential, XPS and FTIR analyses. The SA-modified particles show enhanced aggregation properties at acidic pH compared to unmodified silica, with a 10 times increase in average aggregate diameter. The process is reversible, as the aggregates can be broken and dispersed again when the pH is increased back to 7.0. As a result, the sedimentation rate of SA-modified particles at pH 3.0 is both significantly faster and complete compared to the unmodified particles. This enhanced aggregation is most likely due to the formation of intermolecular hydrogen bonds between neighboring SA-modified particles. This work illustrates how surface-grafted macromolecules of natural origins can be used to tune interparticle interactions, in order to improve separation processes.

Tailored Macroporous Hydrogels with Nanoparticles Display Enhanced and Tunable Catalytic Activity

This work demonstrates that a model system of poly( N-isopropylacrylamide) (PNIPAam) macroporous hydrogels, with tailored microstructures and comprising gold (Au) or silver (Ag) nanoparticles, display enhanced and tunable catalytic activity. These nanocomposites are prepared using polymer templates obtained from melt-processed cocontinuous polymer blends. The reaction rate, controlled by both hydrogel porosity and the PNIPAam lower critical solution temperature, increases by more than an order of magnitude as compared to nonporous gels, and is comparable to micro- or nanocarrier-based systems, with easier catalyst recovery. The fabrication process is scalable, and is compatible with broad choices of polymer blend, gel, and nanoparticle chemistries.