Integrating microneedles and sensing strategies for diagnostic and monitoring applications: The state of the art

Microneedles (MNs) offer minimally-invasive access to interstitial fluid (ISF) - a potent alternative to blood in terms of monitoring physiological analytes. This property is particularly advantageous for the painless detection and monitoring of drugs and biomolecules. However, the complexity of the skin environment, coupled with the inherent nature of the analytes being detected and the inherent physical properties of MNs, pose challenges when conducting physiological monitoring using this fluid. In this review, we discuss different sensing mechanisms and highlight advancements in monitoring different targets, with a particular focus on drug monitoring. We further list the current challenges facing the field and conclude by discussing aspects of MN design which serve to enhance their performance when monitoring different classes of analytes.

A Thiol-Michael Approach Towards Versatile Functionalized Cyclic Titanium-Oxo Clusters

In expanding our research activities of superlattice engineering, designing new giant molecules is the necessary first step. One attempt is to use inorganic transition metal clusters as building blocks. Efficient functionalization of chemically precise transition metal clusters, however, remains a great challenge to material scientists. Herein, we report an efficient thiol-Michael addition approach for the modifications of cyclic titanium-oxo cluster (CTOC). Several advantages, including high efficiency, mild reaction condition, capability of complete addition, high atom economy, as well as high functional group tolerance were demonstrated. This approach can afford high yields of fully functionalized CTOCs, which provides a powerful platform for achieving versatile functionalization of precise transition metal clusters and further applications.

Engineering the Properties of Transparent Hybrid Coating toward High Hardness, Excellent Flexibility, and Multifunction

Transparent functional coatings with glass-like hardness and polymer-like flexibility are highly desirable for flexible and foldable displays. Although several coatings have been developed toward this goal, achieving a functional coating with 9H pencil hardness and extremely low bending radius of curvature (r_c) remains a great challenge due to the inherent conflict between hardness and flexibility. To overcome this trade-off, a facile strategy is developed herein. The coating is an organic-inorganic hybrid nanocomposite that is prepared from thiol-acrylate polymerization of acrylo polyhedral oligomeric silsesquioxane and multifunctional thiols. The former provides the desired hardness, while the latter affords high flexibility and the maximum level of chemical bonding for organic-inorganic phases. Because of the good miscibility and varied functionality of monomers, we are able to manipulate the composition and internal structure of coating systematically, endowing it with high transparency (98%, 550 nm), super hardness (9H), excellent low modulus (1.85 GPa, the most flexible one to date), and the ability to withstand steel wool's abrasion and repeated bending (r_c = 0.8 mm) 10 000 times on PET film. On the final coating, both antifouling and antibacterial abilities are integrated without sacrificing its other properties after postfunctionalizing a zwitterionic layer. This work balances the hardness-flexibility conflict effectively and provides some useful protective coatings for next-generation displays.

The Use of the Thiol-Ene Addition Click Reaction in the Chemistry of Organosilicon Compounds: An Alternative or a Supplement to the Classical Hydrosilylation?

This review presents the main achievements in the use of the thiol-ene reaction in the chemistry of silicones. Works are considered, starting from monomers and ending with materials.The main advantages and disadvantages of this reaction are demonstrated using various examples. A critical analysis of the use of this reaction is made in comparison with the hydrosilylation reaction.

Determining Michael Acceptor Reactivity from Kinetic, Mechanistic, and Computational Analysis for the Base-catalyzed Thiol-Michael Reaction

A combined experimental and computational study of the reactivities of seven commonly used Michael acceptors paired with two thiols within the framework of photobase-catalyzed thiol-Michael reactions is reported. The rate coefficients of the propagation (kP), reverse propagation (k-P), chain-transfer (kCT), and overall reaction (koverall) were experimentally determined and compared with the well-accepted electrophilicity parameters of Mayr and Parr, and DFT-calculated energetics. Both Mayr's and Parr's electrophilicity parameters predict the reactivities of these structurally varying vinyl functional groups well, covering a range of overall reaction rate coefficients from 0.5 to 6.2 s-1. To gain insight into the individual steps, the relative energies have been calculated using DFT for each of the stationary points along this step-growth reaction between ethanethiol and the seven alkenes. The free energies of the individual steps reveal the underlying factors that control the reaction barriers for propagation and chain transfer. Both the propagation and chain transfer steps are under kinetic control. These results serve as a useful guide for Michael acceptor selection to design and predict thiol-Michael-based materials with appropriate kinetic and material properties.

Thiol-Ene Photopolymerization: Scaling Law and Analytical Formulas for Conversion Based on Kinetic Rate and Thiol-Ene Molar Ratio

Kinetics and analytical formulas for radical-mediated thiol-ene photopolymerization were developed in this paper. The conversion efficacy of thiol-ene systems was studied for various propagation to chain transfer kinetic rate-ratio (R_K), and thiol-ene concentration molar-ratio (R_C). Numerical data were analyzed using analytical formulas and compared with the experimental data. We demonstrated that our model for a thiol-acrylate system with homopolymerization effects, and for a thiol-norbornene system with viscosity effects, fit much better with the measured data than a previous model excluding these effects. The general features for the roles of R_K and R_C on the conversion efficacy of thiol (C_T) and ene (C_V) are: (i) for R_K = 1, C_V and C_T have the same temporal profiles, but have a reversed dependence on R_C; (ii) for R_K >> 1, C_T are almost independent of R_C; (iii) for R_K << 1, C_V and C_T have the same profiles and both are decreasing functions of the homopolymerization effects defined by k_CV; (iv) viscosity does not affect the efficacy in the case of R_K >> 1, but reduces the efficacy of C_V for other values of R_K. For a fixed light dose, higher light intensity has a higher transient efficacy but a lower steady-state conversion, resulting from a bimolecular termination. In contrast, in type II unimolecular termination, the conversion is mainly governed by the light dose rather than its intensity. For optically thick polymers, the light intensity increases with time due to photoinitiator depletion, and thus the assumption of constant photoinitiator concentration (as in most previous models) suffers an error of 5% to 20% (underestimated) of the crosslink depth and the efficacy. Scaling law for the overall reaction order, defined by [A]^m[B]ⁿ and governed by the types of ene and the rate ratio is discussed herein. The dual ratio (R_K and R_C) for various binary functional groups (thiol-vinyl, thiol-acrylate, and thiol-norbornene) may be tailored to minimize side effects for maximal monomer conversion or tunable degree of crosslinking.

Thiol-Michael addition in polar aprotic solvents: nucleophilic initiation or base catalysis?

The thiol-Michael addition of ethanethiol to ethyl acrylate, methyl vinylsulfone and maleimide initiated by ethyl-, diethyl-, triethylamine and triethylphosphine in tetrahydrofuran (THF) is investigated at room temperature.

Tube-graft-Sheet Nano-Objects Created by A Stepwise Self-Assembly of Polymer-Polyoxometalate Hybrids

In this work, we report the preparation of complex nano-objects by means of a stepwise self-assembly of two polymer-polyoxometalate hybrids (PPHs) in solution. The PPHs are designed and synthesized by tethering two linear poly(ε-caprolactone)s (PCL) of different molecular weights (MW) on a complex of a Wells-Dawson-type polyoxometalate (POM) cluster and its countraions. The higher MW PCL-POM self-assembled into nanosheets, while the lower MW PCL-POM assembled into nanotubes just by altering the ratio of water in the DMF-water mixed solvent system. The two nano-objects have a similar membrane structure in which a PCL layer is sandwiched by the two POM-based complex layers. The PCL layer in the nanosheets is semicrystalline, while the PCL layer in the nanotubes is amorphous. We further exploited this MW-dependence to self-assemble the nanotubes on the nanosheet edges to create complex tube-graft-sheet nano-objects. We found that the nanotubes nucleate on the four {110} faces of the PCL crystal and then further grow along the crystallographic b-axis of the PCL crystal. Our findings offer hope for the further development of nano-objects with increasing complexity.

POSS-functionalized polyphosphazene nanotube: preparation and effective reinforcement on UV-curable epoxy acrylate nanocomposite coatings

This study presents an efficient method of preparing functionalized poly(cyclotriphosphazene-co-4,4′-sulfonyldiphenol) (PZS) nanotube reinforced UV-curable materials.

Unexpected fluorescence from maleimide-containing polyhedral oligomeric silsesquioxanes: nanoparticle and sequence distribution analyses of polystyrene-based alternating copolymers

Unusual fluorescent polyhedral oligomeric silsesquioxane (POSS)-containing polymers lacking any common fluorescent units because of the crystallinity and clustering of locked CO groups of POSS units.

Facile and Efficient Synthesis of Carbosiloxane Dendrimers via Orthogonal Click Chemistry Between Thiol and Ene

A combination of a thiol-Michael addition reaction and a free radical mediated thiol-ene reaction is employed as a facile and efficient approach to carbosiloxane dendrimer synthesis. For the first time, carbosiloxane dendrimers are constructed rapidly by an orthogonal click strategy without protection/deprotection procedures. The chemoselectivity of these two thiol-ene click reactions leads to a design of a new monomer containing both electron-deficient carbon-carbon double bonds and unconjugated carbon-carbon double bonds. Siloxane bonds are introduced as the linker between these two kinds of carbon-carbon double bonds. Starting from a bifunctional thiol core, the dendrimers are constructed by iterative thiol-ene click reactions under different but both mild reaction conditions. After simple purification steps the fifth dendrimer with 54 peripheral functional groups is obtained with an excellent overall yield in a single day. Furthermore, a strong blue glow is observed when the dendrimer is excited by a UV lamp.

Thiol-Michael addition miniemulsion polymerizations: functional nanoparticles and reactive latex films

Thiol-Michael addition polymerization is successfully implemented in a miniemulsion polymerization system.

Precision synthesis of macrocyclic giant surfactants tethered with two different polyhedral oligomeric silsesquioxanes at distinct ring locations via four consecutive “click” reactions

Cyclic polymers tethered with two different nanoparticles at distinct ring locations were precisely achieved via the multiple sequential “click” strategy.

Modular construction of macrocycle-based topological polymers via high-efficient thiol chemistry

Tadpole-, spiro-shaped, fused-dicyclic tadpole and other complex macrocycle-based topological polymers were modularly constructed via thiol-X chemistry.