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With regard to the periodontal pocket application of in situ forming systems, the understanding the phase behavior after solidification owing to solvent movement could verify the deformability of specimen and its capacity to reside in the artificial periodontal pocket. The aim of this research was to investigate the phase behavior by determining mechanical properties as hardness and elasticity/plasticity ratio with texture analyzer for matrices obtained from drug-free and doxycycline hyclate (DX)-incorporated bleached shellac (BS) in situ forming gel (isg) and –microparticle (ism) after solvent exchange. The solvents for dissolving BS were 2-pyrrolidone (PYR), N-methyl pyrrolidone (NMP) and dimethyl sulfoxide (DMSO). The matrix from isg was less rough and bulge than that of isg. The order of mechanical hardness of transformed system prepared with different solvents was presented as PYR > NMP > DMSO, influenced by phase separation rate and porosity. The systems prepared with NMP and DMSO were more likely plastic or able to adapt its geometry to dynamic changes while that prepared with PYR was elastic. DX-incorporated ism matrix was still governed by the oil in external phase; thus, its consequence was reasonably plastic instead. XRD pattern indicated that the solvent type had no effect on the crystallinity of remained BS after solvent movement. SEM topography revealed sponge-like structure of isg prepared with DMSO and NMP whereas that prepared with PYR exhibited only initiated diminutive pores. The size and density of pores increased by time of isg using different solvents as following DMSO > NMP > PYR, whereas ism matrices had less pore density. The level of porosity of each matrix reflected the mechanical strength that a higher porous structure collapsed easily but a dense matrix considerably resisted to a compression.

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Ascorbic acid (AA) is a general antioxidant used in aqueous pharmaceutical formulations. However, in aqueous solutions, AA is unstable and easily oxidized when exposed to air, light and/or heat. Cyclodextrins are well known for their ability to form inclusion complexes with various compounds to improve their solubility and stability. Previous studies demonstrate that cyclodextrins preserve the antioxidant capacity of AA but data for γ-cyclodextrin (γCD) have not been reported. Poly(vinyl alcohol) (PVA) is a hydrophilic polymer widely used as a drug matrix in various pharmaceutical fields, but its application for drug stabilization is limited. This study aimed to investigate the protective ability of γCD on AA through the formation of ternary complexes with PVA. Binary (i.e., AA/γCD, AA/PVA and γCD/PVA) and ternary (i.e., AA/γCD/PVA) complexes were first confirmed. It was reported that those complexes were formed through interactions between the heterocyclic ring of AA, hydroxyl group of PVA and hydrophobic cavity of γCD. The hydrodynamic diameter of complexes was then studied. It was found that the diameter of γCD/PVA complexes increased with respect to the concentration of γCD. Higher γCD concentrations also resulted in increasing hydrodynamic diameters of the ternary complex. The presence of AA in ternary complexes interfered with the aggregation tendency of γCD/PVA binary complexes. Furthermore, the antioxidant capacity of AA in binary and ternary complexes was investigated. It was found that the presence of γCD preserved the antioxidant activity of AA, whereas PVA showed a contrasting effect. The influence of γCD and PVA concentration on antioxidant capacity was then studied through central composite design (CCD). Even though the concentration of γCD significantly affected the inhibition efficiency of the ternary complex, the insignificant influence of PVA could not be ignored. A promising protective ternary complex should consist of an optimized concentration of PVA and a high concentration of γCD.