The overall goal of this paper was to develop poly(lactic-co-glycolic acid) nanoparticles (PLGA-NPs) of curcumin (CUR), named CUR-PLGA-NPs, and to study the effect and mechanisms enhancing the oral bioavailability of CUR. CUR-PLGA-NPs were prepared according to a solid-in-oil-in-water (s/o/w) solvent evaporation method and exhibited a smooth and spherical shape with diameters of about 200 nm. Characterization of CUR-PLGA-NPs showed CUR was successfully encapsulated on the PLGA polymer. The entrapment efficiency and loading rate of CUR were 91.96 and 5.75%, respectively. CUR-PLGA-NPs showed about 640-fold in water solubility relative to that of n-CUR. A sustained CUR release to a total of approximately 77% was discovered from CUR-PLGA-NPs in artificial intestinal juice, but only about 48% in artificial gastric juice. After oral administration of CUR-PLGA-NPs, the relative bioavailability was 5.6-fold and had a longer half-life compared with that of native curcumin. The results showed that the effect in improving oral bioavailability of CUR may be associated with improved water solubility, higher release rate in the intestinal juice, enhanced absorption by improved permeability, inhibition of P-glycoprotein (P-gp)-mediated efflux, and increased residence time in the intestinal cavity. Thus, encapsulating hydrophobic drugs on PLGA polymer is a promising method for sustained and controlled drug delivery with improved bioavailability of Biopharmaceutics Classification System (BCS) class IV, such as CUR.

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The QCD quark cyclobutadiene (ring-like), a new color structure of tetraquark system, is proposed and studied in the flux-tube model with a multi-body confinement interaction. Numerical calculations show that the light tetraquark systems (u, d, s only) with cyclobutadiene, diquark-antidiquark flux-tube structures have similar energies and they can be regarded as QCD isomeric compounds. The energies of some tetraquark states are close to the masses of some excited mesons and so in the study of these mesons, the tetraquark components should be taken into account. There are also some meson states, σ, κ(800), f0(980), f0(1500), π1(1400), π1(1600), f2(1430) and K * (1410), where tetraquark components might be dominant. The meson states with exotic quantum numbers are studied as the tetraquark states. The multi-body confinement interaction reduces the energy of the tetraquark state in comparison with the usual additive two body confinement interaction model.

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