Porous silicon-poly(ε-caprolactone) film composites: evaluation of drug release and degradation behavior.

This work focuses on an evaluation of novel composites of porous silicon (pSi) with the biocompatible polymer ε-polycaprolactone (PCL) for drug delivery and tissue engineering applications. The degradation behavior of the composites in terms of their morphology along with the effect of pSi on polymer degradation was monitored. PSi particles loaded with the drug camptothecin (CPT) were physically embedded into PCL films formed from electrospun PCL fiber sheets. PSi/PCL composites revealed a release profile of CPT (monitored via fluorescence spectroscopy) in accordance with the Higuchi release model, with significantly lower burst release percentage compared to pSi microparticles alone. Degradation studies of the composites, using gravimetric analysis, differential scanning calorimetry (DSC), and field emission scanning electron microscopy (FESEM), carried out in phosphate-buffered saline (PBS) under simulated physiological conditions, indicated a modest mass loss (15%) over 5 weeks due to pSi dissolution and minor polymer hydrolysis. DSC results showed that, relative to PCL-only controls, pSi suppressed crystallization of the polymer film during PBS exposure. This suppression affects the evolution of surface morphology during this exposure that, in turn, influences the degradation behavior of the polymer. The implications of the above properties of these composites as a possible therapeutic device are discussed.

First-principle study of structure and stability of nickel carbides.

Computational studies of nickel carbides, particularly Ni(2)C, are scarce. A systematic density functional theory study is reported for Ni(2)C, along with NiC and Ni(3)C, to understand the stability and electronic structure of nickel carbides of varying stoichiometry. A comprehensive study was executed that involved 28 trial structures of varying space group symmetry for Ni(2)C. An analysis of the electronic structure, geometry and thermodynamics of Ni(2)C is performed, and compared with that for Ni(3)C and NiC as well as several defect structures of varying composition. It is found that the most stable ground state arrangement of Ni(2)C exists within a simple orthorhombic lattice and that it has metallic character. The calculated formation energies (kcal mol(-1)) of NiC, Ni(2)C, and Ni(3)C are 48.6, 7.9 and 6.4, respectively.