Reversible Thermal-responsive Drug Delivery And Morphology Control Of （PUA/PSS）₄Layer By Layer Assembly Microcapsules

The reversible thermal-responsive microcapsules which could be used as drugdelivery systems were prepared by layer-by-layer self-assembly technique usingpH-/thermal-responsive aliphatic poly(urethane-amine)(PUA) and sodiumpoly(styrene sulfonate)(PSS) as shell materials, the assembly drivers were based onthe electrostatic interaction and hydrogen bonding under weak-acid conditionbetween aliphatic PUA and PSS. In addition, we controlled the morphology of(PUA/PSS)4microcapsules to study its effect on the smart responsibily. There arethree major sections in this paper:In the first part,(PUA/PSS)4hollow microcapsules made of PSS and rapidthermal-responsive PUA which was catalysised by (salen)-MnCl were successfullyfabricated via LbL technique. The reversible thermal-responsive behavior and smartresponsive drug release properties of microcapsules were studied. TEM and EDXcharacterization confirmed the successfully preparation of hollow microcapsules. Theζ-potential and FT-IR results confirmed the electrostatic interaction and hydrogenbonding between PUA and PSS. SEM results showed that the microcapsules hadreversible thermal-responsibility both at pH7.4and4.5, and more obvious at pH4.5.The drug release results demonstrated that the microcapsules were pH-and thermal-dual responsive. The pH response was attributed to the changes of the interactionbetween PUA and PSS varied with pH, and the thermal response was attributed to theshrinkage and precipitation of the PUA chains above its LCST.In the second part, the influence of ionic strength on the morphology andproperties of (PUA/PSS)4hollow microcapsules was conducted. SEM results showedthat the morphology of microcapsules was gradually changing from flat tothree-dimensional spherical with increasing salt treatment time, which showed thatthe strength of microcapsules was gradually improved. In addition, the morphology ofmicrocapsules could be changed by different salt solution, especially by the calciumchloride solution. The drug release results of the enhanced microcapsules after salttreatment showed that the enhanced microcapsules were still pH-and thermal- responsive, and could reduce drug release effectively.In the third part, biomimetic mineralization was used to improve the strength andstability of (PUA/PSS)4hollow microcapsules. SEM and EDX results showed thatHAp inorganic layer was successfully grown on the surface of microcapsules and thestrength of microcapsules was improved significantly which was manifested by thechange of its morphology from flat to three-dimensional spherical after drying. Inaddition, the thickness of HAp inorganic layer could be controlled by adjusting themineralization conditions such as concentration, pH, and etc.