The influence of 1‐hexene is examined on the kinetics of ethylene copolymerization with a metallocene catalyst in gas phase. A model is derived, which is able to describe a large reaction rate increase due to a small amount of incorporated comonomer. This complexation model describes the measured reaction rates for ethylene and 1‐hexene, and the co‐monomer incorporation. Polymer properties were analyzed, such as comonomer weight fraction. The density, melting point, and molecular weight of the produced polymer decreased with increase in 1‐hexene gas concentration. The in situ 1‐hexene sorption is estimated and follows Henry's law, but seems much higher than reported in the literature.
A pH‐sensitive polymer was synthesized by introducing the N‐Boc‐histidine to the ends of a PLGA‐PEG‐PLGA block copolymer. The synthesized polymer was confirmed to be biodegradable and biocompatible, well dissolved in water and forming micelles above the CMC. DOX was employed as a model anticancer drug. In vitro drug release from micelles of N‐Boc‐histidine‐capped PLGA‐PEG‐PLGA exhibited significant difference between pH = 6.2 and pH = 7.4, whereas DOX release from micelles composed of un‐capped virgin polymers was not significantly sensitive to medium pH. Uptake of DOX from micelles of the new polymer into MDA‐MB‐435 solid tumor cells was also observed, and pH sensitivity was confirmed. Hence, the N‐Boc‐histidine capped PLGA‐PEG‐PLGA might be a promising material for tumor targeting.
The preparation of a novel peptide/dendrimer hybrid is reported in which an elastin‐like oligopeptide is successfully assembled onto a poly(amidoamine) dendrimer surface (G4‐ELP), and its unique thermo‐responsive behavior is discussed. As a result, the G4‐ELP is found to exhibit LCST behavior in the pH range 3–10 including physiological temperature range under neutral‐pH conditions. Moreover, cooperative interplay between the folding state of the ELP shell and the ionization state of the dendrimer core enables the G4‐ELP to control its LCST widely by pH variation. This achievement provides a new insight for the design of dual‐responsive materials with a potential in biological applications.
The pH sensitivity of a series of PbAEs synthesized from primary amines and diacrylates is studied. By changing alkyl groups of the amine monomers, the pKb can be tuned across a broad range (from 3.5 to 7.2). Micelles formed from a PEG‐PbAE block copolymer retain the pH sensitivity of PbAE and can stably load hydrophobic molecules under neutral pH, while quickly dissociate and release their cargoes at pH ≈ 6.0. When the chemotherapy drug DOX is loaded, the micelles show efficient cell proliferation inhibition to HeLa cells and fast intracellular release. Thus, the primary‐amine‐based PbAEs are shown to be promising in the construction of intracellular targeting drug delivery systems.
A new approach to engineer a local drug delivery system with delayed release using nanostructured surface with nanotube arrays is presented. TNT arrays electrochemically generated on a titanium surface are used as a model substrate. Polymer micelles as drug carriers encapsulated with drug are loaded at the bottom of the TNT structure and their delayed release is obtained by loading blank micelles (without drug) on the top. The delayed and time‐controlled drug release is successfully demonstrated by controlling the ratio of blank and drug loaded‐micelles. The concept is verified using four different polymer micelles (regular and inverted) loaded with water‐insoluble (indomethacin) and water‐soluble drugs (gentamicin).
