No abstract

Body tissues and organs have complex functions which undergo intrinsic changes during medical treatments. For the development of ideal drug delivery systems, understanding the biological tissue activities is necessary to be able to design materials capable of changing their properties over time, on the basis of the patient's tissue needs. In this study, a nanofibrous thermal‐responsive drug delivery system is developed. The thermo‐responsivity of the system makes it possible to self‐regulate the release of bioactive molecules, while reducing the drug delivery at early stages, thus avoiding high concentrations of drugs which may be toxic for healthy cells. A co‐axial electrospinning technique is used to fabricate core–shell cross‐linked copolymer poly(N‐isopropylacrylamide‐co‐N‐isopropylmethacrylamide) (P(NIPAAm‐co‐NIPMAAm)) hydrogel‐based nanofibers. The obtained nanofibers are made of a core of thermo‐responsive hydrogel containing a drug model, while the outer shell is made of poly‐l‐lactide‐co‐caprolactone (PLCL). The custom‐made electrospinning apparatus enables the in situ cross‐linking of P(NIPAAm‐co‐NIPMAAm) hydrogel into a nanoscale confined space, which improves the electrospun nanofiber drug dosing process, by reducing its provision and allowing a self‐regulated release control. The mechanism of the temperature‐induced release control is studied in depth, and it is shown that the system is a promising candidate as a “smart” drug delivery platform.

Over two decades ago the discovery of electrical conductivity in conjugated polymers spurred a tremendous amount of effort aimed at the development of practical conducting plastics. [1] One of the primary motivations was the hope of fabricating inexpensive, lightweight conducting materials. Those efforts have been coming to fruition in recent years with the development of polymer-based light-emitting diodes, [2] field-effect transistors, [3] elements for active matrix displays, [4] and all-polymer integrated circuits. [5] The synthesis and study of regioregular polythiophenes has produced conjugated polymers that self-assemble into well-defined superstructures and has furthered the use of these materials in the aforementioned applications. [6] Formation of ordered supermolecular structures in these regioregular materials correlates strongly with their excellent electrical conductivities (thousands or hundreds of S cm À1 in comparison with a few S cm À1 for regiorandom polymers). Nevertheless, regioregular polythiophenes still have poor mechanical and processing properties relative to typical flexible polymers.One approach to solving this problem is to synthesize block copolymers that contain conducting polymer or oligomer units. [7] Such a block copolymer [8] could self-assemble into a number of nanoscale morphologies, such as lamellar, spherical, cylindrical, and vesicular structures, which would lead to the possibility that new electronic/structural copolymers could be designed, synthesized, and assembled as components in new nano-devices. Here we present a very easy synthetic method to produce a large number of well-defined block copolymers and polyurethane elastomers containing regioregular polythiophenes. Despite having low percentages of regioregular polythiophenes, these new copolymers have very high conductivities (of the order of a few S cm À1 ) and form very well defined nanowires that reach lengths in the micron range. In addition, we have found that simply changing the solvent or evaporation conditions allows us to control the nanowire formation and the electrical conductivity of the block copolymer.The synthesis of diblock copolymers of head-to-tail-coupled poly(3-alkylthiophenes) (HT-PATs) can be accomplished by first preparing a well-defined PAT (polydispersity index (PDI) 1.2) with 95 % of its end groups [9] containing one proton and one bromine atom (2; Scheme 1). The method [10] shown in Scheme 1 is an important modification of methods previously published by our group. [6,11] The reaction was optimized and the polymer end groups were characterized by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS).Since PATs are chemically stable polymers, the ability to modify the end groups on one side of the polymer is similar to polymer-or bead-supported organic synthesis. Excess of reagents were used to drive the modification reactions to completion to give > 95 % yield for all of the steps subsequent to the synthesis of the HT-PHT. The purification of the products from all th...

A high-throughput optical screening method for the photocatalytic activity of a structurally diverse library of 1152 cationic iridium­(III) complexes ([Ir­(C^N)2(N^N)]+), corresponding to all combinations of 48 cyclometalating (C^N) and 24 ancillary (N^N) ligands, was developed. This rapid assay utilizes the colorimetric changes of a high contrast indicator dye, coumarin 6, to monitor the photo-induced electron transfer from a sacrificial amine donor to the metal complex excited state. The resulting [Ir­(C^N)2(N^N)]0 can then reduce an aryl bromide to form the highly reactive aryl radical intermediate. The rate of this reaction is dictated by the molecular structure of both coordinating ligands. Relative reaction rate constants determined via this method correlated closely with 19F NMR measurements obtained using a fluorinated substrate. A simple model that expresses the rate constant as a product of a single ″strength″ parameter assigned to each of the 72 ligands can well account for the 1152 measured rate constants. The best performing complexes exhibit much higher reactivity than the benchmark photocatalysts commonly used in photoredox transformations. The catalysts were also successfully tested for their chemoselectivity. The developed screening methodology can enable generation of the large data sets needed to use modern data science to extract structure–activity relationships.