Star-shaped polymers are attractive as drug carriers due to the integration of relatively easy synthesis compared to the preparation of hyper-branched dendrimers and their potential ability to form unimolecular nanoparticles with enhanced stability to survive the high dilution-associated deformation and subsequently premature drug release in the body fluids and blood during circulation. Clearly, the star structure exerts a significant effect on their bioproperties and potential applications. In this study, three star-shaped amphiphilic copolymers with the same polymer compositions but different star structures were synthesized to investigate the effect of star architecture on their properties as well as potential applications as drug carriers. Three different branched alcohols, 2-(hydroxymethyl) propane-1,3-diol, pentaerythritol and dipentaerythritol with 3, 4, and 6 respective hydroxyl groups were chosen as the starting core to generate the target star-shaped amphiphilic block copolymers composed of hydrophobic poly(ε-caprolactone) (PCL) and hydrophilic poly(oligoethyleneglycol methacrylate) (POEGMA) with 3, 4, and 6 corresponding star arms by a combination of ring-opening polymerization (ROP) and atom transfer radical polymerization (ATRP). Dynamic light scattering (DLS) measurements and pyrene fluorescence probe technique confirmed the capability of the resultant star-shaped amphiphilic copolymers to form unimolecular micelles with average diameters smaller than 50 nm in an aqueous phase. A comparison of the drug loading capacity revealed that the micelles of 4-star-PCL–POEGMA (4s-PCL–POEGMA) exhibited the highest drug loading content (DLC) of all the three formulations. More importantly, in vitro doxorubicin (DOX) release study showed unique pH-mediated drug release behaviors, i.e., dramatically accelerated release at pH 6.0 but a much slower profile at pH 7.4, from these generally recognized “pH-insensitive” 4-arm star-shaped micelles. An acid-triggered degradation and an acid–base titration were performed to further reveal that such interesting pH-responsive drug release behaviors were attributed primarily to the hydrophilic corona of OEG brushes. This study is believed to provide a new insight into the structure–bioproperties relationship of star-shaped polymers, thus should be useful for the future design and development of novel star-shaped polymers for controlled drug delivery.
The mixed surfactants of dodecyltrimethylammonium bromide (DTAB) and 1-dodecyl-3-methylimidazolium bromide (C 12 mimBr) in aqueous solutions were studied by measurement of electrical conductivity and isothermal titration microcalorimetry (ITC). The critical micelle concentrations (cmc) and the degree of dissociations of counter ions were determined for this system at various surfactant compositions, and the thermodynamic properties of micellization were evaluated. A one-parameter Margules equation was used to fit the cmc values to calculate the mole fraction, the activity coefficients of two surfactant components and the excess properties in mixed micelles.
The incorporation of hydroxy groups into long-chain quaternary ammonium surfactants can enhance their solubility and confer other desirable properties; however, the systematic investigation on the solution properties and the influence of molecular structures was less documented. In this work, two saturated C 18 -tailed quaternary ammonium surfactants with dual hydroxyethyl moieties, namely N , N -bis(2-hydroxyethyl)- N -methyloctadecan-1-aminium iodide (HEOAI) and N , N -bis(2-hydroxypropyl)- N -methyloctadecan-1-aminium iodide (HPOAI), were designed and synthesized. We investigated and compared their Krafft temperature ( T k ), surface activities, self-assembly behaviors, and rheological properties. Our findings demonstrate that the introduction of hydroxyethyl groups dramatically improves the solubility and surface activities. The T k of HEOAI and HPOAI is approximately 50 °C lower than that of the corresponding surfactant octadecyl trimethylammonium iodide. Both surfactants exhibit lower critical micelle concentration and equilibrium surface tension compared to those of corresponding conventional quaternary ammonium surfactant. This should be ascribed to the formation of hydrogen bonds between hydroxyl groups and water molecules. Moreover, HPOAI shows even better solubility and surface activities than HEOAI does. Additionally, the presence of two more methyl groups for HPOAI enhances its ability to form worm-like micelles in pure water. However, HEOAI shows better salt and temperature resistance for maintaining stability of worm-like micelles. A solution containing 50 mM HEOAI with 10 % NaCl exhibits temperature tolerance up to around 80 °C, indicating potential application as fracturing fluid for shallow and medium oil/gas reservoirs. These findings contribute to designing surfactants with improved solubility and diverse properties.
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