Mucoadhesive pickering nanoemulsions via dynamic covalent chemistry

HYPOTHESIS

Submicron oil droplets stabilized using aldehyde-functionalized nanoparticles should adhere to the primary amine groups present at the surface of sheep nasal mucosal tissue via Schiff base chemistry.

EXPERIMENTS

Well-defined sterically-stabilized diblock copolymer nanoparticles of 20 nm diameter were prepared in the form of concentrated aqueous dispersions via reversible addition-fragmentation chain transfer (RAFT) aqueous emulsion polymerization of 2,2,2-trifluoroethyl methacrylate (TFEMA) using a water-soluble methacrylic precursor bearing cis-diol groups. Some of these hydroxyl-functional nanoparticles were then selectively oxidized using an aqueous solution of sodium periodate to form a second batch of nanoparticles bearing pendent aldehyde groups within the steric stabilizer chains. Subjecting either hydroxyl- or aldehyde-functional nanoparticles to high-shear homogenization with a model oil (squalane) produced oil-in-water Pickering macroemulsions of 20-30 µm diameter. High-pressure microfluidization of such macroemulsions led to formation of the corresponding Pickering nanoemulsions with a mean droplet diameter of around 200 nm. Quartz crystal microbalance (QCM) experiments were used to examine adsorption of both nanoparticles and oil droplets onto a model planar substrate bearing primary amine groups, while a fluorescence microscopy-based mucoadhesion assay was developed to assess adsorption of the oil droplets onto sheep nasal mucosal tissue.

FINDINGS

Squalane droplets coated with aldehyde-functional nanoparticles adhered significantly more strongly to sheep nasal mucosal tissue than those coated with the corresponding hydroxyl-functional nanoparticles. This difference was attributed to the formation of surface imine bonds via Schiff base chemistry and was also observed for the two types of nanoparticles alone in QCM studies. Preliminary biocompatibility studies using planaria indicated only mild toxicity for these new mucoadhesive Pickering nanoemulsions, suggesting potential applications for the localized delivery of hydrophobic drugs.

Quercetin Loaded Cationic Solid Lipid Nanoparticles in a Mucoadhesive In Situ Gel-A Novel Intravesical Therapy Tackling Bladder Cancer

The study aim was to develop an intravesical delivery system of quercetin for bladder cancer management in order to improve drug efficacy, attain a controlled release profile and extend the residence time inside the bladder. Either uncoated or chitosan coated quercetin-loaded solid lipid nanoparticles (SLNs) were prepared and evaluated in terms of colloidal, morphological and thermal characteristics. Drug encapsulation efficiency and its release behaviour were assessed. Furthermore, cytotoxicity of SLNs on T-24 cells was evaluated. Ex vivo studies were carried out using bovine bladder mucosa. Spherical SLNs (≈250 nm) ensured good entrapment efficiencies (EE > 97%) and sustained drug release up to 142 h. Cytotoxicity profile revealed concentration-dependent toxicity recording an IC50 in the range of 1.6−8.9 μg/mL quercetin. SLNs were further dispersed in in situ hydrogels comprising poloxamer 407 (20%) with mucoadhesive polymers. In situ gels exhibited acceptable gelation temperatures (around 25 °C) and long erosion time (24−27 h). SLNs loaded gels displayed remarkably enhanced retention on bladder tissues relative to SLNs dispersions. Coated SLNs exhibited better penetration abilities compared to uncoated ones, while coated SLNs dispersed in gel (G10C-St-QCT-SLNs-2) showed the highest penetration up to 350 μm. Hence, G10C-St-QCT-SLNs-2 could be considered as a platform for intravesical quercetin delivery.

Direct Heat-Induced Patterning of Inorganic Nanomaterials

Patterning functional inorganic nanomaterials is an important process for advanced manufacturing of quantum dot (QD) electronic and optoelectronic devices. This is typically achieved by inkjet printing, microcontact printing, and photo- and e-beam lithography. Here, we investigate a different patterning approach that utilizes local heating, which can be generated by various sources, such as UV-, visible-, and IR-illumination, or by proximity heat transfer. This direct thermal lithography method, termed here heat-induced patterning of inorganic nanomaterials (HIPIN), uses colloidal nanomaterials with thermally unstable surface ligands. We designed several families of such ligands and investigated their chemical and physical transformations responsible for heat-induced changes of nanocrystal solubility. Compared to traditional photolithography using photochemical surface reactions, HIPIN extends the scope of direct optical lithography toward longer wavelengths of visible (532 nm) and infrared (10.6 μm) radiation, which is necessary for patterning optically thick layers (e.g., 1.2 μm) of light-absorbing nanomaterials. HIPIN enables patterning of features defined by the diffraction-limited beam size. Our approach can be used for direct patterning of metal, semiconductor, and dielectric nanomaterials. Patterned semiconductor QDs retain the majority of their as-synthesized photoluminescence quantum yield. This work demonstrates the generality of thermal patterning of nanomaterials and provides a new path for additive device manufacturing using diverse colloidal nanoscale building blocks.

Molecular and cellular cues governing nanomaterial-mucosae interactions: from nanomedicine to nanotoxicology

Mucosal tissues constitute the largest interface between the body and the surrounding environment and they regulate the access of molecules, supramolecular structures, particulate matter, and pathogens into it. All mucosae are characterized by an outer mucus layer that protects the underlying cells from physicochemical, biological and mechanical insults, a mono-layered or stratified epithelium that forms tight junctions and controls the selective transport of solutes across it and associated lymphoid tissues that play a sentinel role. Mucus is a gel-like material comprised mainly of the glycoprotein mucin and water and it displays both hydrophilic and hydrophobic domains, a net negative charge, and high porosity and pore interconnectivity, providing an efficient barrier for the absorption of therapeutic agents. To prolong the residence time, absorption and bioavailability of a broad spectrum of active compounds upon mucosal administration, mucus-penetrating and mucoadhesive particles have been designed by tuning the chemical composition, the size, the density, and the surface properties. The benefits of utilizing nanomaterials that interact intimately with mucosae by different mechanisms in the nanomedicine field have been extensively reported. To ensure the safety of these nanosystems, their compatibility is evaluated in vitro and in vivo in preclinical and clinical trials. Conversely, there is a growing concern about the toxicity of nanomaterials dispersed in air and water effluents that unintentionally come into contact with the airways and the gastrointestinal tract. Thus, deep understanding of the key nanomaterial properties that govern the interplay with mucus and tissues is crucial for the rational design of more efficient drug delivery nanosystems (nanomedicine) and to anticipate the fate and side-effects of nanoparticulate matter upon acute or chronic exposure (nanotoxicology). This review initially overviews the complex structural features of mucosal tissues, including the structure of mucus, the epithelial barrier, the mucosal-associated lymphatic tissues and microbiota. Then, the most relevant investigations attempting to identify and validate the key particle features that govern nanomaterial-mucosa interactions and that are relevant in both nanomedicine and nanotoxicology are discussed in a holistic manner. Finally, the most popular experimental techniques and the incipient use of mathematical and computational models to characterize these interactions are described.

Biodistribution and pharmacokinetics of thiolated chitosan nanoparticles for oral delivery of insulin in vivo

To improve the quality of life of diabetic patients, oral delivery of insulin would be better than subcutaneous injection, and the encapsulation of insulin for its oral delivery is a promising alternative one. In this study, we prepared an oral insulin delivery system using thiolated chitosan nanoparticles (TCNPs) loaded with insulin (Ins) and tested under in vitro and in vivo systems. TCNPs prepared from CS and pentaerythritol tetrakis (3-mercaptopropionate) (PETMP) at 4:1 ratio showed 220 ± 4 nm, 2.3 ± 1 mV, and 119 ± 4 μmol g^-1 in their size, charge and sulfhydryl content, respectively. There was a sustained release of insulin from the TCNPs at pH 5.3. TCNPs treatment did not alter cell viability in vitro and oral administration of TCNPs reached over the tip of the microvilli near the intestinal mucosa in vivo. There were increased and decreased the levels of insulin and glucose in the blood, respectively when Ins-TCNPs were orally administered in the diabetes induced rats. Thus, our results suggested that the insulin stays significantly for a prolonged period to make bio-distribution and bioavailability due to its interaction with the mucus of the intestine, thus offering a better oral insulin delivery system for diabetic patients.

Acrylated Eudragit® E PO as a novel polymeric excipient with enhanced mucoadhesive properties for application in nasal drug delivery

Eudragit® E PO (EPO) is a terpolymer based on N,N-dimethylaminoethyl methacrylate with methylmethacrylate and butylmethacrylate, produced by Evonik Industries AG as a pharmaceutical excipient. In this work, EPO was chemically modified through reaction with acryloyl chloride. The successful modification of EPO was confirmed by FTIR, NMR-spectroscopy, elemental and thermal analysis. The degree of acrylation was determined by permanganatometric titration. The slug mucosal irritation test was used to demonstrate non-irritant nature of EPO and its acrylated derivatives (AEPO). The mucoadhesive properties of EPO and AEPO were evaluated using freshly excised sheep nasal mucosa and it was demonstrated that acrylated polymers facilitated greater retention of sodium fluorescein on mucosal surfaces compared to solution mixture of this dye solution with EPO as well as free dye.

Chitosan/β-glycerophosphate in situ gelling mucoadhesive systems for intravesical delivery of mitomycin-C

The development of mucoadhesive in situ gelling formulations for intravesical application may improve the therapeutic outcomes of bladder cancer patients. In this work, chitosan/β-glycerophosphate (CHIGP) thermosensitive formulations have been prepared using three different chitosan grades (62, 124 and 370 kDa). Their ability to form in situ gelling systems triggered by changes in temperature upon administration to urinary bladder were evaluated using vial inversion and rheological methods. Texture analysis was used to study their mucoadhesive properties as well as syringeability through the urethral catheter. The retention of CHIGP formulations, with fluorescein sodium as the model drug, was studied on porcine urinary bladder mucosa ex vivo using the flow-through technique and fluorescent microscopy. CHIGP formulations containing mitomycin-C were prepared and drug release was studied using in vitro dialysis method. It was established that the molecular weight of chitosan influenced the thermogelling, mucoadhesive and drug release behaviour of the in situ gelling delivery systems. Formulations prepared from chitosan with greatest molecular weight (370 kDa) were found to be the most promising for intravesical application due to their superior gelling properties and in vitro retention in the bladder.

Electrosprayed cysteine-functionalized degradable amphiphilic block copolymer microparticles for low pH-triggered drug delivery

Fluorescent dye encapsulation and release using mucoadhesive degradable thiol-functionalized amphiphilic block copolymer microparticles prepared by electrospraying.

S-preactivated thiolated glycol chitosan useful to combine mucoadhesion and drug delivery

This work describes S-preactivated N-acetylcysteine (NAC)- and glutathione (GSH)-glycol chitosan (GC) polymer conjugates engineered as potential mucoadhesive platform. Preactivated thiomers (GC-NAC-MNA, GC-GSH-MNA) were synthesized by bond formation between GC-NAC or GC-GSH and 2-mercaptonicotinic acid (MNA) used as ligand. The presence of protected thiol moieties on this new class of thiolated GC made them not subject to oxidation. The structural modifications of the resulting derivatives were confirmed by proton Nuclear Magnetic Resonance (¹H NMR) and Size Exclusion Chromatography (SEC). The conjugates displayed 91.2% and 90.1% of S-preactivation for GC-NAC-MNA and GC-GSH-MNA, respectively. The polymers were tested in ex-vivo and in vitro for their mucoadhesive properties and toxicity. The results showed that the preactivation of GC-NAC and GC-GSH increased their mucoadhesive abilities compared to their thiolated precursors by 1.4-, 4.4-fold in time of adhesion evaluated using rotating cylinder method, 1.6-, 1.5-fold in total work of adhesion (TWA) and 2.0-, 1.3-fold in maximum detachment force (MDA) determined using tensile studies, respectively. Moreover, water-uptake studies showed an improved in weight indicating water-uptake strongly dependent on derivations, before erosion occurred, whereas disintegration took place for the thiolated polymers within the first hour. The S-preactivated modification did not affect the cell viability of Caco2 cells exposed to the polymers. The release of the model drug sodium naproxen from tablets prepared with a lyophilized mixture of drug and polymer was studied via dissolution apparatus revealing that the preactivation on GC-GSH and GC-NAC involves a slowdown in the drug release rate. The results shown that the novel preactivated thiolated GC-derivatives can be considered promising excipients for the development of mucoadhesive drug delivery systems.

Methacrylated chitosan as a polymer with enhanced mucoadhesive properties for transmucosal drug delivery

Chitosan is a cationic polysaccharide that exhibits mucoadhesive properties which allow it to adhere to mucosal tissues. In this work, we explored chemical modification of chitosan through its reaction with methacrylic anhydride to synthesise methacrylated derivative with the aim to improve its mucoadhesive properties. The reaction products were characterised using ¹H NMR, FTIR and UV-Vis spectroscopy. ¹H NMR and ninhydrin test were used to quantify the degree of methacrylation of chitosan. Turbidimetric analysis of the effect of pH on aqueous solubility of the polymers revealed that the highly methacrylated derivative remained turbid and its turbidity did not change from pH 3 to 9. However, solutions of native chitosan and its derivative with low methacrylation remained transparent at pH 6.5 and exhibited a rapid increase in turbidity at pH > 6.5. The mucoadhesive properties of chitosan and its methacrylated derivatives were evaluated using flow-through method combined with fluorescent microscopy with fluorescein sodium as a model drug. The retention of these polymers was evaluated on porcine bladder mucosa in vitro. The methacrylated derivatives exhibited greater ability to retain fluorescein sodium on the bladder mucosa compared to the parent chitosan. Toxicological studies using MTT assay with UMUC3 bladder cells show no significant differences in toxicity between chitosan and its methacrylated derivatives suggesting good biocompatibility of these novel mucoadhesive polymers.

Controlling the Size of Thiolated Organosilica Nanoparticles

Nanoparticle characteristics, including their size, are governed by the reagents employed and the reaction parameters. Here, we systemically vary the catalyst, oxygen content, temperature, and solvent to modify the size and zeta-potential of thiolated organosilica nanoparticles. The particles were synthesized by self-condensation of 3-mercaptopropyltrimethoxysilane in a range of organic solvents in contact with oxygen, with NaOH and other catalysts. The particle size increased with increasing reaction temperature (70 ± 1 nm at 50 °C; 50 ± 1 nm at room temperature) but decreased when air was bubbled through the reaction mixture compared to no bubbling. A significant decrease in the particle size was seen when increasing the dielectric constant of the solvent and when increasing the catalyst concentration; from these, we provide empirical equations that can be used to design particle sizes by manipulating the dielectric constant of the solvent (or cosolvents) or by varying the NaOH catalyst concentration when dimethylsulfoxide is the selected solvent.

Synthesis of thiolated, PEGylated and POZylated silica nanoparticles and evaluation of their retention on rat intestinal mucosa in vitro

In this study, we synthesised thiolated silica nanoparticles using 3-mercaptopropyltrimethoxysilane and functionalised them with either 5 kDa methoxy polyethylene glycol maleimide (PEG) or 5 kDa alkyne-terminated poly(2-ethyl-2-oxazoline) (POZ). The main objectives of this study are to investigate the effects of pH on the size and ξ-potential of these nanoparticles and evaluate their mucoadhesive properties ex vivo using rat intestinal mucosa. The sizes of thiolated, PEGylated and POZylated silica nanoparticles were 53 ± 1, 68 ± 1 and 59 ± 1 nm, respectively. The size of both thiolated and POZylated nanoparticles significantly increased at pH ≤ 2, whereas no size change was observed at pH 2.5-9 for both these two types of nanoparticles. On the other hand, the size of PEGylated nanoparticles did not change over the studied pH range (1.5-9). Moreover, thiolated nanoparticles were more mucoadhesive in the rat small intestine than both PEGylated and POZylated nanoparticles. After 12 cycles of washing (with a total of 20 mL of phosphate buffer solution pH 6.8), a significantly greater amount of thiolated nanoparticles remained on the intestinal mucosa than FITC-dextran (non-mucoadhesive polymer, p < 0.005) and both PEGylated and POZylated nanoparticles (p < 0.05 both). However, both PEGylated and POZylated nanoparticles showed similar retention to FITC-dextran (p > 0.1 for both). Thus, this study indicates that thiolated nanoparticles are mucoadhesive, whereas PEGylated and POZylated nanoparticles are non-mucoadhesive in the ex vivo rat intestinal mucosa model. Each of these nanoparticles has potential applications in mucosal drug delivery.

Chitosan and Its Derivatives for Application in Mucoadhesive Drug Delivery Systems

Mucoadhesive drug delivery systems are desirable as they can increase the residence time of drugs at the site of absorption/action, provide sustained drug release and minimize the degradation of drugs in various body sites. Chitosan is a cationic polysaccharide that exhibits mucoadhesive properties and it has been widely used in the design of mucoadhesive dosage forms. However, its limited mucoadhesive strength and limited water-solubility at neutral and basic pHs are considered as two major drawbacks of its use. Chemical modification of chitosan has been exploited to tackle these two issues. In this review, we highlight the up-to-date studies involving the synthetic approaches and description of mucoadhesive properties of chitosan and chitosan derivatives. These derivatives include trimethyl chitosan, carboxymethyl chitosan, thiolated chitosan, chitosan-enzyme inhibitors, chitosan-ethylenediaminetetraacetic acid (chitosan-EDTA), half-acetylated chitosan, acrylated chitosan, glycol chitosan, chitosan-catechol, methyl pyrrolidinone-chitosan, cyclodextrin-chitosan and oleoyl-quaternised chitosan. We have particularly focused on the effect of chemical derivatization on the mucoadhesive properties of chitosan. Additionally, other important properties including water-solubility, stability, controlled release, permeation enhancing effect, and in vivo performance are also described.

Acrylated Chitosan Nanoparticles with Enhanced Mucoadhesion

The aim of this study was to investigate the effect of acrylate modification on the mucoadhesion of chitosan at the nanoscale. Nanoparticles were fabricated from acrylated chitosan (ACS) via ionic gelation with tripolyphosphate and were characterized in terms of size, zeta potential, stability, and nanoparticle yield. Chitosan (CS) nanoparticles, serving as a control, were fabricated using the same procedure. The mucoadhesion of the nanoparticles was evaluated using the flow-through method after different incubation periods. The retention percentages of ACS nanoparticles were found to be significantly higher than those of CS nanoparticles, for all studied time intervals. An additional indication for the increased mucoadhesion of ACS nanoparticles was the increase in particle size obtained from the mucin particle method, in which mucin and nanoparticles are mixed at different ratios. NMR data verified the presence of free acrylate groups on the ACS nanoparticles. Thus, the improved mucoadhesion could be due to a Michael-type addition reaction between the nanoparticles and thiol groups present in mucin glycoprotein, in addition to entanglements and hydrogen bonding. Overall, ACS nanoparticles exhibit enhanced mucoadhesion properties as compared to CS nanoparticles and could be used as vehicles for drug delivery systems.

Cationic disulfide-functionalized worm gels

The recent development of polymerization-induced self-assembly (PISA) has facilitated the rational synthesis of a range of diblock copolymer worms, which hitherto could only be prepared via traditional post-polymerization processing in dilute solution. Herein we explore a new synthetic route to aqueous dispersions of cationic disulfide-functionalized worm gels. This is achieved via the PISA synthesis of poly[(glycerol monomethacrylate-stat-glycidyl methacrylate)]-block-poly(2-hydroxypropyl methacrylate) (P(GMA-stat-GlyMA)-PHPMA) block copolymer worms via reversible addition-fragmentation chain transfer (RAFT) aqueous dispersion polymerization of HPMA. A water-soluble reagent, cystamine, is then reacted with the pendent epoxy groups located within the P(GMA-stat-GlyMA) stabilizer chains to introduce disulfide functionality, while simultaneously conferring cationic character via formation of secondary amine groups. Moreover, systematic variation of the cystamine/epoxy molar ratio enables either chemically cross-linked worm gels or physical (linear) primary amine-functionalized disulfide-based worm gels to be obtained. These new worm gels were characterized using gel permeation chromatography, 1H NMR spectroscopy, transmission electron microscopy, dynamic light scattering, aqueous electrophoresis and rheology. In principle, such hydrogels may offer enhanced mucoadhesive properties.

Systematic evaluation of oligodeoxynucleotide binding and hybridization to modified multi-walled carbon nanotubes

BACKGROUND

In addition to conventional chemotherapeutics, nucleic acid-based therapeutics like antisense oligodeoxynucleotides (AS-ODN) represent a novel approach for the treatment of bladder cancer (BCa). An efficient delivery of AS-ODN to the urothelium and then into cancer cells might be achieved by the local application of multi-walled carbon nanotubes (MWCNT). In the present study, pristine MWCNT and MWCNT functionalized with hydrophilic moieties were synthesized and then investigated regarding their physicochemical characteristics, dispersibility, biocompatibility, cellular uptake and mucoadhesive properties. Finally, their binding capacity for AS-ODN via hybridization to carrier strand oligodeoxynucleotides (CS-ODN), which were either non-covalently adsorbed or covalently bound to the different MWCNT types, was evaluated.

RESULTS

Pristine MWCNT were successfully functionalized with hydrophilic moieties (MWCNT-OH, -COOH, -NH2, -SH), which led to an improved dispersibility and an enhanced dispersion stability. A viability assay revealed that MWCNT-OH, MWCNT-NH2 and MWCNT-SH were most biocompatible. All MWCNT were internalized by BCa cells, whereupon the highest uptake was observed for MWCNT-OH with 40% of the cells showing an engulfment. Furthermore, all types of MWCNT could adhere to the urothelium of explanted mouse bladders, but the amount of the covered urothelial area was with 2-7% rather low. As indicated by fluorescence measurements, it was possible to attach CS-ODN by adsorption and covalent binding to functionalized MWCNT. Adsorption of CS-ODN to pristine MWCNT, MWCNT-COOH and MWCNT-NH2 as well as covalent coupling to MWCNT-NH2 and MWCNT-SH resulted in the best binding capacity and stability. Subsequently, therapeutic AS-ODN could be hybridized to and reversibly released from the CS-ODN coupled via both strategies to the functionalized MWCNT. The release of AS-ODN at experimental conditions (80 °C, buffer) was most effective from CS-ODN adsorbed to MWCNT-OH and MWCNT-NH2 as well as from CS-ODN covalently attached to MWCNT-COOH, MWCNT-NH2 and MWCNT-SH. Furthermore, we could exemplarily demonstrate that AS-ODN could be released following hybridization to CS-ODN adsorbed to MWCNT-OH at physiological settings (37 °C, urine).

CONCLUSIONS

In conclusion, functionalized MWCNT might be used as nanotransporters in antisense therapy for the local treatment of BCa.

Spray-dried mucoadhesives for intravesical drug delivery using N-acetylcysteine- and glutathione-glycol chitosan conjugates

This work describes N-acetylcysteine (NAC)- and glutathione (GSH)-glycol chitosan (GC) polymer conjugates engineered as potential platform useful to formulate micro-(MP) and nano-(NP) particles via spray-drying techniques. These conjugates are mucoadhesive over the range of urine pH, 5.0-7.0, which makes them advantageous for intravesical drug delivery and treatment of local bladder diseases. NAC- and GSH-GC conjugates were generated with a synthetic approach optimizing reaction times and purification in order to minimize the oxidation of thiol groups. In this way, the resulting amount of free thiol groups immobilized per gram of NAC- and GSH-GC conjugates was 6.3 and 3.6mmol, respectively. These polymers were completely characterized by molecular weight, surface sulfur content, solubility at different pH values, substitution and swelling degree. Mucoadhesion properties were evaluated in artificial urine by turbidimetric and zeta (ζ)-potential measurements demonstrating good mucoadhesion properties, in particular for NAC-GC at pH 5.0. Starting from the thiolated polymers, MP and NP were prepared using both the Büchi B-191 and Nano Büchi B-90 spray dryers, respectively. The resulting two formulations were evaluated for yield, size, oxidation of thiol groups and ex-vivo mucoadhesion. The new spray drying technique provided NP of suitable size (<1μm) for catheter administration, low degree of oxidation, and sufficient mucoadhesion property with 9% and 18% of GSH- and NAC-GC based NP retained on pig mucosa bladder after 3h of exposure, respectively.

STATEMENT OF SIGNIFICANCE

The aim of the present study was first to optimize the synthesis of NAC-GC and GSH-GC, and preserve the oxidation state of the thiol moieties by introducing several optimizations of the already reported synthetic procedures that increase the mucoadhesive properties and avoid pH-dependent aggregation. Second, starting from these optimized thiomers, we studied the feasibility of manufacturing MP and NP by spray-drying techniques. The aim of this second step was to produce mucoadhesive drug delivery systems of adequate size for vesical administration by catheter, and comparable mucoadhesive properties with respect to the processed polymers, avoiding thiolic oxidation during the formulation. MP with acceptable size produced by spray-dryer Büchi B-191 were compared with NP made with the apparatus Nano Büchi B-90.

Adhesion of thiolated silica nanoparticles to urinary bladder mucosa: Effects of PEGylation, thiol content and particle size

Intravesical drug administration is used to deliver cytotoxic agents through a catheter to treat bladder cancer. One major limitation of this approach is poor retention of the drug in the bladder due to periodic urine voiding. Mucoadhesive dosage forms thus offer significant potential to improve drug retention in the bladder. Here, we investigate thiolated silica nanoparticles retention on porcine bladder mucosa in vitro, quantified through Wash Out50 (WO50) values, defined as the volume of liquid necessary to remove 50% of the adhered particles from a mucosal tissue. Following irrigation with artificial urine solution, the thiolated nanoparticles demonstrate significantly greater retention (WO50 up to 36mL) compared to non-mucoadhesive dextran (WO50 7mL), but have weaker mucoadhesive properties than chitosan (WO50 89mL). PEGylation of thiolated silica reduces their mucoadhesion with WO50 values of 29 and 8mL for particles decorated with 750 and 5000Da PEG, respectively. The retention of thiolated silica nanoparticles is dependent on their thiol group contents and physical dimensions.

Off-stoichiometry improves the photostructuring of thiol-enes through diffusion-induced monomer depletion

Thiol-enes are a group of alternating copolymers with highly ordered networks and are used in a wide range of applications. Here, "click" chemistry photostructuring in off-stoichiometric thiol-enes is shown to induce microscale polymeric compositional gradients due to species diffusion between non-illuminated and illuminated regions, creating two narrow zones with distinct compositions on either side of the photomask feature boundary: a densely cross-linked zone in the illuminated region and a zone with an unpolymerized highly off-stoichiometric monomer composition in the non-illuminated region. Using confocal Raman microscopy, it is here explained how species diffusion causes such intricate compositional gradients in the polymer and how off-stoichiometry results in improved image transfer accuracy in thiol-ene photostructuring. Furthermore, increasing the functional group off-stoichiometry and decreasing the photomask feature size is shown to amplify the induced gradients, which potentially leads to a new methodology for microstructuring.

A new approach for the synthesis of sulfur-bridged polysiloxanes via thiol–ene “click” reaction and their post-functionalization to obtain luminescent materials

A novel polymerization method for preparing well defined sulfur containing siloxane polymers.

Maleimide-bearing nanogels as novel mucoadhesive materials for drug delivery

Novel class of mucoadhesive polymers has been developed via polymerisation of 2,5-dimethylfuran-protected 3-maleimidoethyl butylacrylate in the presence of presynthesised poly(N-vinylpyrrolidone) nanogel scaffolds. The resulting maleimide-bearing nanogels were capable of forming covalent linkages with mucosal membranes.

Facile Fabrication of Polymerizable Ionic Liquid Based-Gel Beads via Thiol-ene Chemistry

Multipurpose gel beads prepared from natural or synthetic polymers have received significant attention in various applications such as drug delivery, coatings, and electrolytes because of their versatility and unique performance as micro- and nanocontainers.1 However, comparatively little work has been done on poly(ionic liquid)-based materials despite their unique ionic characteristics. Thus, in this contribution we report the facile preparation of polymerizable ionic liquid-based gel beads using thiol-ene click chemistry. This novel system incorporates pentaerythritol tetra (3-mercaptopropionate) (PETKMP) and 1,4-di(vinylimidazolium) butane bisbromide in a thiol-ene-based photopolymerization to fabricate the gel beads. Their chemical structure, thermal and mechanical properties have been investigated using Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and dynamic mechanical analysis (DMA). The gel beads possess low Tg and their ionic functionalities attribute self-healing properties and their ability to uptake small molecules or organic compounds offers their potential use as pH sensing material and macrocontainers.

Functional, sub-100 nm polymer nanoparticles via thiol–ene miniemulsion photopolymerization

Thiol–ene photopolymerization in miniemulsion under non-stoichiometric conditions offers a facile route to functionalized polymer nanoparticles.

Water-borne thiol–isocyanate click chemistry in microfluidics: rapid and energy-efficient preparation of uniform particles

A nucleophile-catalyzed thiol–isocyanate reaction has been exploited as an efficient route to fabricate uniform particles in a water-borne system.

Cytotoxic metabolites from the endophytic fungus Penicillium chermesinum: discovery of a cysteine-targeted Michael acceptor as a pharmacophore for fragment-based drug discovery, bioconjugation and click reactions

A novel tetracyclic polyketide uniquely spiro-attached with a γ-lactone ring and a potent cytotoxic agent possessing a thiol-reactive pharmacophore were isolated from the mangrove endophytic fungus Penicillium chermesinum.

Synthesis of mucoadhesive thiol-bearing microgels from 2-(acetylthio)ethylacrylate and 2-hydroxyethylmethacrylate: novel drug delivery systems for chemotherapeutic agents to the bladder

Thiol-bearing microgels have been synthesised from copolymerisation of 2-(acetylthio)ethylacrylate and 2-hydroxyethylmethacrylate, and subsequent deprotection using sodium thiomethoxide.

Functionalized mesoporous silica nanoparticles with mucoadhesive and sustained drug release properties for potential bladder cancer therapy

The synthesis of a series of β-cyclodextrin modified mesoporous silica nanoparticles with hydroxyl, amino, and thiol groups was described. A comparison of their mucoadhesive properties and potential as a drug delivery system for superficial bladder cancer therapy was made. The thiol-functionalized nanoparticles exhibit significantly higher mucoadhesivity on the urothelium as compared to the hydroxyl- and amino-functionalized nanoparticles. This is attributed to the formation of disulfide bonds between the thiol-functionalized nanoparticles and cysteine-rich subdomains of mucus glycoproteins. An anticancer drug, doxorubicin, was loaded into the mesopores of the thiol-functionalized nanoparticles, and sustained drug release triggered by acidic pH was achieved. The present study demonstrates that thiol-functionalized mesoporous silica nanoparticles are promising as a mucoadhesive and sustained drug delivery system for superficial bladder cancer therapy.

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.

Spontaneous assembly and synchronous scan spectra of gold nanoparticle monolayer Janus film with thiol-terminated polystyrene

This communication presents a facile method for preparing ordered hydrophilic metal nanoparticles into gold nanoparticle monolayer Janus film. It also reveals the enhanced light source spectrum properties of the gold nanoparticle film.

Fast and facile fabrication of porous polymer particles via thiol–ene suspension photopolymerization

The porous particles were fabricated via thiol–ene click chemistry within 5 minutes under mild conditions.