Cellulose Diacetate-g-poly(p-dioxanone) Co-polymer: Synthesis, Properties and Microsphere Preparation
A novel biodegradable graft co-polymer based on cellulose diacetate (CDA) and poly(p-dioxanone) was synthesized by ring-opening polymerization of p-dioxanone (PDO). The molecular structure of co-polymers was characterized by one- and two-dimensional NMR. The graft co-polymers with different lengths of PPDO side-chains could be controllably synthesized by changing the in-feed ratio of CDA/PDO. It was found that the PPDO content had great effect on the thermal transition behavior, crystallization ability and thermal stability of the graft co-polymer. The in vitro degradation rates of CDA-g-PPDO were higher than that of linear PPDO due to their lower crystallinity. Moreover, porous microspheres of graft co-polymers with a diameter of about 5 μm, prepared through the solvent evaporation of water-in-oil emulsion (W/O), indicated it may have potential applications in drug-delivery systems.
Polydioxanone-based bio-materials for tissue engineering and drug/gene delivery applications.
Since the commercialization of polydioxanone (PDX) as a biodegradable monofilament suture by Ethicon in 1981, the polymer has received only limited interest until recently. The limitations of polylactide-co-glycolide (PLGA) coupled with the growing need for materials with enhanced features and the advent of new fabrication techniques such as electrospinning have revived interest for PDX in medical devices, tissue engineering and drug delivery applications. Electrospun PDX mats show comparable mechanical properties as the major structural components of native vascular extracellular matrix (ECM) i.e. collagen and elastin. In addition, PDX's unique shape memory property provides rebound and kink resistance when fabricated into vascular conduits. The synthesis of methyl dioxanone (MeDX) monomer and copolymers of dioxanone (DX) and MeDX have opened up new perspectives for poly(ester-ether)s, enabling the design of the next generation of tissue engineering scaffolds for application in regenerating such tissues as arteries, peripheral nerve and bone. Tailoring of polymer properties and their formulation as nanoparticles, nanomicelles or nanofibers have brought along important developments in the area of controlled drug or gene delivery. This paper reviews the synthesis of PDX and its copolymers and provides for the first time an exhaustive account of its applications in the (bio)medical field with focus on tissue engineering and drug/gene delivery.
Effects of the mineral phase and valence of vanadium on vanadium extraction from stone coal
The influence of roasting on the leaching rate and valence of vanadium was evaluated during vanadium extraction from stone coal. Vanadium in stone coal is hard to be leached and the leaching rate is less than 10% when the raw ore is leached by 4 mol/L H2SO4 at 90°C for 2 h. After the sample is roasted at 900°C for 2 h, the leaching rate of vanadium reaches the maximum, and more than 70% of vanadium can be leached. The crystal of vanadium-bearing mica minerals decomposes and the content of V(V) increases with the rise of roasting temperature from 600 to 900°C, therefore the leaching rate of vanadium increases significantly with the decomposition of the mica minerals. Some new phases, anorthite for example, form when the roasting temperature reaches 1000°C. A part of vanadium may be enwrapped in the sintered materials and newly formed phases, which may impede the oxidation of low valent vanadium and make the leaching rate of vanadium drop dramatically. The leaching rate of vanadium is not only determined by the valence state of vanadium but also controlled by the decomposition of vanadium-bearing minerals and the existence state of vanadium to a large extent.