Responsive hybrid microcapsules by the one-step interfacial thiol-ene photopolymerization

Synthesis and characterization of tetrathiol-substituted double-decker or ladder silsesquioxane nano-cores

Tetra(3-mercaptopropyl)-silsesquioxanes with double-decker (DDSQ) or ladder nano-cores were easily prepared from the corresponding tetraallyl derivatives through fast and convenient thiol-ene reactions. An additional tetrathiol-DDSQ with more flexible arms was also synthesized in high yield from the corresponding tetrachloro-DDSQ derivative. The three novel tetrathiol silsesquioxanes described represent versatile building blocks for the preparation of hybrid organic-inorganic materials.

Droplet nucleation in miniemulsion thiol–ene step photopolymerization

Reaction parameters, such as droplet size, initiator solubility and monomer solubility, which are important in favouring droplet nucleation in a miniemulsion thiol–ene step polymerization are reviewed.

Fabrication of antibody-loaded microgels using microfluidics and thiol-ene photoclick chemistry

Reducing burst effects, providing controlled release, and safeguarding biologics against degradation are a few of several highly attractive applications for microgels in the field of controlled release. However, the incorporation of proteins into microgels without impairing stability is highly challenging. In this proof of concept study, the combination of microfluidics and thiol-ene photoclick chemistry was evaluated for the fabrication of antibody-loaded microgels with narrow size distribution. Norbornene-modified eight-armed poly(ethylene glycol) with an average molecular mass of 10,000 Da, 20,000 Da, or 40,000 Da were prepared as macromonomers for microgel formation. For functionalization, either hydrolytically cleavable ester or stable amide bonds were used. A microfluidic system was employed to generate precursor solution droplets containing macromonomers, the cross-linker dithiothreitol and the initiator Eosin-Y. Irradiation with visible light was used to trigger thiol-ene reactions which covalently cross-linked the droplets. For all bond-types, molecular masses, and concentrations gelation was very rapid (<20 s) and a plateau for the complex shear modulus was reached after only 5 min. The generated microgels had a rod-like shape and did not show considerable cellular toxicity. Stress conditions during the fabrication process were simulated and it could be shown that fabrication did not impair the activity of the model proteins lysozyme and bevacizumab. It was confirmed that the average hydrogel network mesh size was similar or smaller than the hydrodynamic diameter of bevacizumab which is a crucial factor for restricting diffusion and delaying release. Finally, microgels were loaded with bevacizumab and a sustained release over a period of 30 ± 4 and 47 ± 7 days could be achieved in vitro.

Recyclable cross-linked hydroxythioether particles with tunable structures via robust and efficient thiol-epoxy dispersion polymerizations

Thiol-epoxy reactions were first exploited as a simple method for the preparation of recyclable cross-linked hydroxythioether particles with tunable structures.

Light-Mediated Thiol-Ene Polymerization in Miniemulsion: A Fast Route to Semicrystalline Polysulfide Nanoparticles

Historically, the synthesis of aqueous polymer dispersions has focused on radical chain-growth polymerization of low-cost acrylate or styrene emulsions. Herein, we demonstrate the potential of UV-initiated thiol-ene step-growth radical polymerization, departing from a nontransparent difunctional monomer miniemulsion based on ethylene glycol dithiol and diallyl adipate. Performed without solvent and at ambient conditions, the photopolymerization process is energy-effective, environmentally friendly, and ultrafast, leading to full monomer consumption in 2 s, upon irradiating a miniemulsion contained in a 1 mm thick quartz cell microreactor. The resultant linear poly(thioether ester) particles have an average diameter of 130 nm. After water evaporation, they yield a clear elastomeric film combining chemical resistance and high degree of crystallinity (55%).

One-step interfacial thiol-ene photopolymerization for metal nanoparticle-decorated microcapsules (MNP@MCs)

We herein reported a one-step strategy to prepare the noble metal nanoparticle-decorated microcapsules (MNP@MCs) through the interfacial thiol-ene photopolymerization. In the presence of amphiphlic polyhedral oligomeric silsesquioxane (POSS) containing thiol groups (PTPS) as a reactive surfactant and trimethylolpropane triacrylate (TMPTA) as a cross-linker, the oil phase of toluene dissolved with a photoinitiator was emulsified into a water phase containing a metal precursor to form an oil-in-water (O/W) emulsion. Upon irradiation of ultraviolet (UV) light, the thiol-ene photoploymerization and photoreduction at the interface of toluene/water lead to the formation of the cross-linked wall and metal nanoparticles, respectively. A series of gold, silver, and platinum nanoparticle-decorated microcapsules (AuNP@MC, AgNP@MC, and PtNP@MC) were prepared through this one-step interfacial thiol-ene photopolymerization and were characterized carefully by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM). The results revealed that the obtained MNP@MCs were 2.2-2.7 μm in diameter with a wall of 40-70 nm in thickness, which was covered with the metal nanoparticles. The size and amount of metal nanoparticles increased with the increasing concentration of the metal precursor in water. Furthermore, the catalyst performance of AuNP@MC was studied by reduction of aromatic nitro compounds and exhibited the enhanced catalytic activity and good stability in the reduction of hydrophobic nitrophenol. It is believed that this robust, convenient, simple strategy based on the one-step interfacial thiol-ene photopolymerization will provide an important alternative to fabricate the functional metal nanoparticle-modified microcapsules.

Polyhedral oligomeric silsesquioxane-F68 hybrid vesicles for folate receptor targeted anti-cancer drug delivery

Polyhedral Oligomeric Silsesquioxane (POSS)-F68 hybrid vesicles with an average diameter of 700 nm are produced using a stable solution of heterofunctional POSS having 3-aminopropyl and vinyl groups and pluronic F68 in ethanol-water mixture. Thermogram and zeta potential values evidence the spontaneous self-assembly of POSS into bilayers through H-bonding interaction between the aminopropyl groups, and the effective stabilization of the POSS-bilayers by amphiphilic F68 during solvent-evaporation to form the vesicles. The vesicles are noncytotoxic and dispersible in aqueous solvents through steric stabilization provided by the hydrophilic F68. A highly facile coinclusion method has been used for making doxorubicin and folic acid loaded vesicles. Doxorubicin loaded in the vesicles exhibits a controlled release profile in phosphate buffered saline. Confocal microscopic and flow cytometric studies on the endocytosis of the vesicles by HeLa and HOS cells prove that a noncovalent entrapment of excess folic acid in the vesicles through H-bonding is sufficient to enhance the uptake significantly. POSS-F68 vesicles in combination with folic acid and a chemotherapeutic can have potential for targeted intracellular anti-cancer drug delivery.

Thiol–ene “click” reactions and recent applications in polymer and materials synthesis: a first update

This contribution serves as an update to a previous review (Polym. Chem.2010,1, 17–36) and highlights recent applications of thiol–ene ‘click’ chemistry as an efficient tool for both polymer/materials synthesis as well as modification.