thiol-Michael Addition Click Research Articles

Light Switchable Bioorthogonal Reaction Manifold for Modulation of Hydrogel Properties.

Chemical reaction systems that can occur via multiple pathways in a controllable fashion are highly attractive for advanced materials applications and biological research. In this report, we introduce a bioorthogonal reaction manifold based on a chalcone pyrene (CPyr) moiety that can undergo either red-shifted photoreversible [2 + 2] cycloaddition or thiol-Michael addition click reaction. By coupling the CPyr to a water-soluble poly(ethylene glycol) end group, we demonstrate the efficient polymer dimerization and cleavage by blue light (λ = 450 nm) and UV light (λ = 340 nm), respectively. In the absence of light, CPyr rapidly reacts with thiols in aqueous environments, enabling fast and efficient polymer end-group functionalization. The chemical reaction manifold was further employed in polymer cross-linking for the preparation of hydrogels whose stiffness and morphology can be modulated by different photonic fields or the addition of a thiol cross-linker. The photoreversible cycloaddition and thiol-Michael addition click reaction can be used in conjunction for spatial and temporal conjugation of a streptavidin protein. Both cross-linking conditions are nontoxic to various cell lines, highlighting their potential in biomaterials applications.

Chitosan films synthesized via thiol-ene click chemistry: Toward safe and versatile platforms for packaging, cosmetics and biomedical applications

The first synthesis of chitosan-based films using bio-based reticulating agents via Thiol-Michael addition click reaction was described, along with their successful application in packaging, cosmetics, and biomedical fields. The impact of chitosan (CS) concentration and the type of synthesized bio-sourced biacids (GD) and triacids (GT and TT) on the physicochemical properties of these films were assessed. Films prepared with dibasic and tribasic acids (4%-CS) demonstrated superior mechanical properties and lower solubility compared to those containing 2% CS. The incorporation of the bio-sourced GD, GT, and TT acids led to a reduction of 53%, 60% and 60.4%, respectively, in the water vapor permeability (WVP) of 4% CS-based films compared to the control film. Remarkably, CS-TT-4% films exhibited the highest mechanical strength (TS), elongation at break (%E), elasticity, water vapor, and light barrier properties. Cytotoxicity tests performed on the NIH 3T3 fibroblast cell line showed that CS-GD-4% films exhibited the highest compatibility. The efficiency of these films as drug carriers was tested with challenging anticancer and cosmetic molecules, particularly etoposide (ETP) caffeine (Caf), showing very high drug loading with a progressive release of less than 20% after 72h of incubation. Moreover, ex-vivo permeation studies in rat skin revealed that the percutaneous absorption of Caf is significantly increased by a factor of 5.5 compared to that of CS-GD-4%-Caf films with no significant histological alterations of skin layers. Altogether, this work evidences the most suitable casting solvent for developing safe chitosan films, promising their potential applications in the cosmetic and biomedical fields.

ROS-Responsive 4D Printable Acrylic Thioether-Based Hydrogels for Smart Drug Release.

Reactive oxygen species (ROS) play a key role in several biological functions like regulating cell survival and signaling; however, their effect can range from beneficial to nondesirable oxidative stress when they are overproduced causing inflammation or cancer diseases. Thus, the design of tailor-made ROS-responsive polymers offers the possibility of engineering hydrogels for target therapies. In this work, we developed thioether-based ROS-responsive difunctional monomers from ethylene glycol/thioether acrylate (EGnSA) with different lengths of the EGn chain (n = 1, 2, 3) by the thiol-Michael addition click reaction. The presence of acrylate groups allowed their photopolymerization by UV light, while the thioether groups conferred ROS-responsive properties. As a result, smart PEGnSA hydrogels were obtained, which could be processed by four-dimensional (4D) printing. The mechanical properties of the hydrogels were determined by rheology, pointing out a decrease of the elastic modulus (G') with the length of the EG segment. To enhance the stability of the hydrogels after swelling, the EGnSA monomers were copolymerized with a polar monomer, 2-hydroxyethyl acrylate (HEA), leading to P[(EGnSA)x-co-HEAy] with improved compatibility in aqueous media, making it a less brittle material. Swelling properties of the hydrogels increased in the presence of hydrogen peroxide, a kind of ROS, reaching values of ≈130% for P[(EG3SA)7-co-HEA93] which confirms the stimuli-responsive properties. Then, the P[(EG3SA)x-co-HEAy] hydrogels were employed as matrixes for the encapsulation of a chemotherapeutic drug, 5-fluorouracil (5FU), which showed sustained release over time modulated by the presence of H2O2. Finally, the effect of the 5-FU release from P[(EG3SA)x-co-HEAy] hydrogels was tested in vitro with melanoma cancer cells B16F10, pointing out B16F10 growth inhibition values in the range of 40-60% modulated by the EG3SA percentage and the presence or absence of ROS agents, thus confirming their excellent ROS-responsive properties for the treatment of localized pathologies.

Facile and Powerful In Situ Polymerization Strategy for Sulfur-Based All-Solid Polymer Electrolytes in Lithium Batteries.

All-solid-state polymer electrolytes can improve the safety of lithium batteries. However, the common Bellcore polymer electrolyte technology faces several issues such as wasting a mass of solvent, high manufacturing cost, and poor interfacial compatibility between polymer electrolytes and electrodes. Herein, we propose an in situ polymerization technique to synthesize all-solid-state polymer electrolytes by a thiol-Michael addition click reaction. The alternating copolymer is made from the Michael addition reaction of ethylene glycol dimethacrylate (EGDMA) and 1,2-ethane dithiol (EDT). At ambient temperature, the obtained composite polymer electrolyte displays an ionic conductivity of 3.02 × 10-5 S/cm, an electrochemical window of 4.5 V, and a lithium-ion transference number of 0.45. In light of this unique polymerization process, the traditional fabrication method of liquid electrolyte-based lithium batteries can be adopted in the current study for the preparation of all-solid-state Li/LiFePO4 batteries. It was found that the assembled all-solid-state Li/LiFePO4 batteries exhibited superior charging/discharging performance and preferable safety. Thus, this facile and powerful in situ polymerization strategy may open up a new approach for the design and fabrication of all-solid-state batteries with desirable performances.

Encapsulation of murine hematopoietic stem and progenitor cells in a thiol-crosslinked maleimide-functionalized gelatin hydrogel

Biomaterial platforms are an integral part of stem cell biomanufacturing protocols. The collective biophysical, biochemical, and cellular cues of the stem cell niche microenvironment play an important role in regulating stem cell fate decisions. Three-dimensional (3D) culture of stem cells within biomaterials provides a route to present biophysical and biochemical stimuli through cell-matrix interactions and cell-cell interactions via secreted biomolecules. Herein, we describe a maleimide-functionalized gelatin (GelMAL) hydrogel that can be crosslinked via thiol-Michael addition click reaction for the encapsulation of sensitive stem cell populations. The maleimide functional units along the gelatin backbone enables gelation via the addition of a dithiol crosslinker without requiring external stimuli (e.g., UV light, photoinitiator), thereby reducing reactive oxide species generation. Additionally, the versatility of crosslinker selection enables easy insertion of thiol-containing bioactive or bioinert motifs. Hematopoietic stem cells (HSCs) and mesenchymal stem cells (MSCs) were encapsulated in GelMAL, with mechanical properties tuned to mimic the in vivo bone marrow niche. We report the insertion of a cleavable peptide crosslinker that can be degraded by the proteolytic action of Sortase A, a mammalian-inert enzyme. Notably, Sortase A exposure preserves stem cell surface markers, which are an essential metric of hematopoietic activity used in immunophenotyping. This novel GelMAL system enables a route to produce artificial stem cell niches with tunable biophysical properties, intrinsic cell-interaction motifs, and orthogonal addition of bioactive crosslinks. Statement of significanceWe describe a maleimide-functionalized gelatin hydrogel that can be crosslinked via a thiol-maleimide mediated click reaction to form a stable hydrogel without the production of reactive oxygen species typical in light-based crosslinking. The mechanical properties can be tuned to match the in vivo bone marrow microenvironment for hematopoietic stem cell culture. Additionally, we report inclusion of a peptide crosslinker that can be cleaved via the proteolytic action of Sortase A and show that Sortase A exposure does not degrade sensitive surface marker expression patterns. Together, this approach reduces stem cell exposure to reactive oxygen species during hydrogel gelation and enables post-culture quantitative assessment of stem cell phenotype.

Engineering Modular Half-Antibody Conjugated Nanoparticles for Targeting CD44v6-Expressing Cancer Cells.

Gastric cancer (GC) remains a major cause of death worldwide mainly because of the late detection in advanced stage. Recently, we proposed CD44v6 as a relevant marker for early detection of GC, opening new avenues for GC-targeted theranostics. Here, we designed a modular nanoscale system that selectively targets CD44v6-expressing GC cells by the site-oriented conjugation of a new-engineered CD44v6 half-antibody fragment to maleimide-modified polystyrene nanoparticles (PNPs) via an efficient bioorthogonal thiol-Michael addition click chemistry. PNPs with optimal particle size (200 nm) for crossing a developed biomimetic CD44v6-associated GC stromal model were further modified with a heterobifunctional maleimide crosslinker and click conjugated to the novel CD44v6 half-antibody fragment, obtained by chemical reduction of full antibody, without affecting its bioactivity. Collectively, our results confirmed the specific targeting ability of CD44v6-PNPs to CD44v6-expressing cells (1.65-fold higher than controls), highlighting the potential of CD44v6 half-antibody conjugated nanoparticles as promising and clinically relevant tools for the early diagnosis and therapy of GC. Additionally, the rational design of our nanoscale system may be explored for the development of several other nanotechnology-based disease-targeted approaches.

Modification of graphene oxide with acrylate phosphorus monomer via thiol-Michael addition click reaction to enhance the anti-corrosive performance of waterborne epoxy coatings

To develop a convenient way to functionalize graphene oxide (GO) for corrosion protective coatings, a commercial acrylate phosphorus functional monomer (SIPOMER PAM100) was used to modify thiol-terminated GO via thiol-Michael addition click reaction. Subsequently, PAM100 modified GO (PGO) was introduced to waterborne epoxy coating as a nanofiller for anticorrosion reinforcement. The anticorrosive performance of PGO/WEP nanocomposite coatings was evaluated by electrochemical impedance spectroscopy (EIS). Results obtained from FT-IR, XRD, Raman, SEM and SEM-EDS show that PAM100 is successfully grafted to the surface of GO using γ-Mercaptopropyl triethoxysilane (KH-580) as a bridge molecule. It is clear that PGO distributes homogenously within WEP matrix from SEM images. After 40-day exposure to 3.5 wt.% NaCl solution, the |Z|0.01Hz of blank WEP suffers a serious decrease (from 9.83 × 107 Ω·cm2 to 4.93 × 106 Ω·cm2) while PGO/WEP has a relatively smaller change in |Z|0.01Hz (from 1.35 × 108 Ω·cm2 to 2.91 × 107 Ω·cm2). It demonstrated that PGO/WEP coating presents a superior corrosion resistance performance.

Fabrication of micropatterned gold nanoparticles on graphene oxide nanosheet via thiol-Michael addition click chemistry

Here, the micropatterned gold nanoparticles (AuNPs) on graphene oxide (GO) nanosheet (AuNPs@GO) was fabricated via thiol-Michael addition click reaction under ultraviolet (UV) light. First, AuNPs and GO were both functionalized by acrylamide and dithiothreitol, respectively, which were characterized by transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), dynamic light scattering (DLS) and ultraviolet–visible spectroscopy (UV–vis). The size of acrylamide modified AuNPs increased to 52.8 ± 16.5 nm compared to bare AuNPs (44.1 ± 14.5 nm). The AuNPs@GO could be fabricated under the UV-light, and the UV–vis signal varied depending on the concentration of AuNPs. Also, the micropatterned structure of AuNPs@GO nanosheet was accomplished by using a designed mask, which showed a high potential for cancer diagnosis and therapy.

Injectable Shape-Holding Collagen Hydrogel for Cell Encapsulation and Delivery Cross-linked Using Thiol-Michael Addition Click Reaction.

Injectable hydrogels based on extracellular matrix-derived polymers show much promise in the field of tissue engineering and regenerative medicine. However, the hydrogels reported to date have at least one characteristic that limits their potential for clinical use, such as excessive swelling, complicated and potentially toxic cross-linking process, or lack of shear thinning and self-healing properties. We hypothesized that a collagen hydrogel cross-linked using thiol-Michael addition click reaction would be able to overcome these limitations. To this end, collagen was modified to introduce thiol groups, and hydrogels were prepared by cross-linking with 8-arm polyethylene glycol-maleimide. Rheological measurements on the hydrogels revealed excellent shear-thinning and self-healing properties. Additionally, only minimal swelling (6%) was observed over a period of 1 month in an aqueous buffer solution. Finally, tests using mesenchymal stromal cells and endothelial cells showed that the hydrogels are cell-compatible and suitable for cell encapsulation and delivery. Thus, the reported thiolated-collagen hydrogel cross-linked using thiol-Michael addition click reaction overcomes most of the challenges in the injectable hydrogel design and is an excellent candidate for cell delivery in regenerative medicine and tissue engineering applications. The hydrogel reported here is the first example of a self-healing hydrogel containing covalent cross-links.

Building Covalent Molecular Capsules by Thiol-Michael Addition Click Reaction.

The thiol-Michael addition (TMA) is a powerful methodology to click several fragments together, despite having been underestimated in the synthesis of complex systems for supramolecular chemistry. Herein, a very fast and efficient method has been developed to make covalent molecular capsules by taking advantage of the TMA click reaction. Several scaffolds commonly used in supramolecular chemistry, such as calixarenes, CTV, or cavitands, have been used to quickly obtain covalent cages. Additionally, a ' click&click' procedure has been also developed, by sequential combination of TMA and CuAAC click reaction, as an easy and quick way to build complex molecular structures.

Charge-Controlled Synthetic Hyaluronan-Based Cell Matrices.

The extracellular matrix (ECM) represents a highly charged and hydrated network in which different cells in vertebrate tissues are embedded. Hydrogels as minimal ECM mimetics with a controlled chemistry offer the opportunity to vary material properties by varying the negative network charge. In this paper, a synthetic biology model of the ECM based on natural and highly negatively charged polyelectrolyte hyaluronic acid (HA) is characterized with specific emphasis on its charge-related bioactivity. Therefore, the thiol-Michael addition click reaction is used to produce HA hydrogels with defined network structure and charge density. The presented hydrogels show enzymatic degradability and cell attachment. These properties depend on both covalent and electrostatic interactions within the hydrogel network. Furthermore, no unspecific or specific attachment of proteins to the presented hydrogels is observed. In addition, these fundamental insights into charge-related ECM behavior and the influence of electrostatic properties could also lead to innovations in existing biomedical products.

Construction of a 3D multiple network skeleton by the thiol-Michael addition click reaction to fabricate novel polymer/graphene aerogels with exceptional thermal conductivity and mechanical properties

Novel porous polymer/graphene composite aerogels with a multiple network structure, enhanced compressive properties and high thermal conductivity are first fabricated by adsorbing water vapour, reduction, and freeze-drying procedures.

Functionalised type-I collagen as a hydrogel building block for bio-orthogonal tissue engineering applications.

In this study, we derivatized type I collagen without altering its triple helical conformation to allow for facile hydrogel formation via the Michael addition of thiols to methacrylates without the addition of other crosslinking agents. This method provides the flexibility needed for the fabrication of injectable hydrogels or pre-fabricated implantable scaffolds, using the same components by tuning the modulus from Pa to kPa. Enzymatic degradability of the hydrogels can also be easily fine-tuned by variation of the ratio and the type of the cross-linking component. The structural morphology reveals a lamellar structure mimicking native collagen fibrils. The versatility of this material is demonstrated by its use as a pre-fabricated substrate for culturing human corneal epithelial cells and as an injectable hydrogel for 3-D encapsulation of cardiac progenitor cells.

Facile Synthesis of Thiol‐Functionalized Long‐Chain Highly Branched ROMP Polymers and Surface‐Decorated with Gold Nanoparticles

The synthesis of thiol-functionalized long-chain highly branched polymers (LCHBPs) has been accomplished in combination of ring-opening metathesis polymerization (ROMP) and thiol-Michael addition click reaction. A monotelechelic polymer with a terminal acrylate and many pendent thiol groups is first prepared through adding an internal cis-olefin terminating agent to the reaction mixture immediately after the completion of the living ROMP, and then utilized as an ABn -type macromonomer in subsequent thiol-ene reaction between acrylate and thiol, yielding LCHBPs as the reaction time prolonged. Au nanoparticles are then covalently conjugated onto the surface of thiol-functionalized LCHBP to fabricate novel hybrid nanostructures, which is shown as one interesting application of such functionalized metathesis polymers. This facile approach can be extended toward the fabrication of novel nanomaterials with sophisticated structures and tunable multifunctionalities.

Cyclic polyphosphoesters synthesized by acyclic diene metathesis polymerization and ring closing metathesis

This article describes the synthesis of cyclic polyphosphoester (PPE) by the ring-closing metathesis (RCM) of different difunctional linear PPEs. Linear PPE precursors were prepared through a selective head-to-tail acyclic diene metathesis polymerization of phenyl dienephosphate monomer using 2-hydroxyethyl acrylate as a selective chain terminator, followed by the transformation of the terminal acrylate functional group into a hydroxyl group utilizing a thiol-Michael addition click reaction. These products were then reacted with the corresponding acyl chloride containing a vinyl end group. The subsequent end-to-end intramolecular coupling reaction was performed under highly dilute conditions. The successful transformation of the linear PPE precursors to cyclic PPE was confirmed by NMR spectroscopy and gel permeation chromatography. The thermal and flame retardant properties of linear and cyclic PPEs were investigated, and their thermal degradation and flame retardance were evaluated, as these are important features for future applications.

More insight into tandem ROMP and ADMET polymerization for yielding reactive long-chain highly branched polymers and their transformation to functional polymer nanoparticles

Tandem chain transfer ring-opening metathesis polymerization (ROMP-CT) and acyclic diene metathesis (ADMET) polymerization were carried out in a controlled one-pot procedure, and behaved noticeable differences in polymerization of monomers by different ruthenium catalysts, whereas there indeed had been two distinctly polymerization stages. In the first one, ROMP-CT of functional monomers was conducted in the presence of a symmetrical multi-olefin as chain transfer agent within various reaction time scales, yielding linear telechelic polymers. Next, ADMET polymerization of telechelic polymers was performed and generated a series of reactive long-chain highly branched polymers (LCHBPs) with acrylate and/or azobenzene groups having molecular weights of 8.5–47.9 kDa under varied conditions. LCHBPs were fully characterized by several techniques, and interestingly, UV–vis analysis displayed the specific peak at 278 nm, which offered a new evidence for the existence of internal acrylate structure on the LCHBP backbone, and supported the highly branched architecture of polymers. LCHBP containing a number of pendent acrylate groups was readily converted, by thiol-Michael addition click reaction, to novel thiol-functionalized intra-molecular crosslinked unimolecular polymer nanoparticles with diameter of 40–60 nm, which provided a facile method for post-functionalization of branched polymers.

Preparation of a Rapidly Forming Poly(ferrocenylsilane)‐Poly(ethylene glycol)‐based Hydrogel by a Thiol‐Michael Addition Click Reaction

The synthesis of a rapidly forming redox responsive poly(ferrocenylsilane)-poly(ethylene glycol) (PFS-PEG)-based hydrogel is described, achieved by a thiol-Michael addition click reaction. PFS bearing acrylate side groups (PFS-acryl) was synthesized by side group modification of poly(ferrocenyl(3-iodopropyl)methylsilane) (PFS-I) and characterized by (1) H NMR, (13) C NMR, and FT-IR spectroscopy. The equilibrium swelling ratio, morphology, rheology, and redox responsive properties of the PFS-PEG-based hydrogel are reported.

04/02053 Exergy losses in refrigerating systems. A study for performance comparisons in compressor and condenser: Stegou-Sagia, A. and Paignigiannis, N. International Journal of Energy Research, 2003, 27, (12), 1067–1078

Biomaterial platforms are an integral part of stem cell biomanufacturing protocols. The collective biophysical, biochemical, and cellular cues of the stem cell niche microenvironment play an important role in regulating stem cell fate decisions. Three-dimensional (3D) culture of stem cells within biomaterials provides a route to present biophysical and biochemical stimuli through cell-matrix interactions and cell-cell interactions via secreted biomolecules. Herein, we describe a maleimide-functionalized gelatin (GelMAL) hydrogel that can be crosslinked via thiol-Michael addition click reaction for the encapsulation of sensitive stem cell populations. The maleimide functional units along the gelatin backbone enables gelation via the addition of a dithiol crosslinker without requiring external stimuli (e.g., UV light, photoinitiator), thereby reducing reactive oxide species generation. Additionally, the versatility of crosslinker selection enables easy insertion of thiol-containing bioactive or bioinert motifs. Hematopoietic stem cells (HSCs) and mesenchymal stem cells (MSCs) were encapsulated in GelMAL, with mechanical properties tuned to mimic the in vivo bone marrow niche. We report the insertion of a cleavable peptide crosslinker that can be degraded by the proteolytic action of Sortase A, a mammalian-inert enzyme. Notably, Sortase A exposure preserves stem cell surface markers, which are an essential metric of hematopoietic activity used in immunophenotyping. This novel GelMAL system enables a route to produce artificial stem cell niches with tunable biophysical properties, intrinsic cell-interaction motifs, and orthogonal addition of bioactive crosslinks.We describe a maleimide-functionalized gelatin hydrogel that can be crosslinked via a thiol-maleimide mediated click reaction to form a stable hydrogel without the production of reactive oxygen species typical in light-based crosslinking. The mechanical properties can be tuned to match the in vivo bone marrow microenvironment for hematopoietic stem cell culture. Additionally, we report inclusion of a peptide crosslinker that can be cleaved via the proteolytic action of Sortase A and show that Sortase A exposure does not degrade sensitive surface marker expression patterns. Together, this approach reduces stem cell exposure to reactive oxygen species during hydrogel gelation and enables post-culture quantitative assessment of stem cell phenotype.