Sutapa Ghosh

Use of glycidyl methacrylate monomers for developing cross-linkable pressure sensitive adhesives

Abstract Emulsion copolymers based on glycidyl methacrylate and butylacrylate (or 2-ethylhexylacrylate) were prepared and evaluated as pressure sensitive adhesives. These emulsions were characterised by their non-volatile content, viscosity, mechanical stability, swelling behaviour, IR spectroscopy, differential scanning calorimetry and scanning electron microscopy. The pressure sensitive adhesive tapes were prepared with flexible backings and the peel strengths between flexible–flexible and flexible–rigid surfaces were determined. The swelling properties of these copolymers before and after curing were also studied.

Palladium nanoparticles on β-cyclodextrin functionalised graphene nanosheets: a supramolecular based heterogeneous catalyst for C–C coupling reactions under green reaction conditions

The use of functional properties of native cyclodextrins in palladium nanoparticle–β-cyclodextrin–graphene nanosheet (Pd@CD–GNS) catalyzed carbon–carbon (C–C) coupling reactions have been investigated under green reaction conditions. The supramolecular catalyst was prepared by deposition of Pd nanoparticles (Pd NPs) on CD–GNS using ethanol as the greener solvent and in situ reducing agent. The catalyst was characterised by FTIR, XRD, RAMAN, UV-Vis spectroscopy, TEM, SAED, XPS and ICP-AES. The catalytic activity of these catalysts is investigated in C–C coupling reactions such as Suzuki–Miyaura and Heck–Mizoroki reactions of aryl bromides and aryl chlorides containing functional groups under green reaction conditions i.e. in water, under phosphine free and aerobic conditions. This catalyst afforded excellent selectivities for the products in good to excellent yields under low Pd loadings (0.2–0.05 mol%), while ensuring the recovery and reusability of the catalysts. The reused catalyst was characterized by FTIR, TEM, XPS and ICP-AES. The CD supramolecular mediators loaded on GNS act as stabilising agents for the Pd NPs. The excellent catalytic activity of this system was attributed to the presence of CDs, excellent dispersibility in water, hydrophobic nature of the GNS support for the accumulation of organic substrates in water, “Breslow effect”, the presence of PTC to overcome the mass transfer limitation onto the surface of GNS and formation of ternary CD/substrate/additive complexes on the Pd–GNS surface.

Proliferation and Differentiation Potential of Human Adipose-Derived Stem Cells Grown on Chitosan Hydrogel

Applied tissue engineering in regenerative medicine warrants our enhanced understanding of the biomaterials and its function. The aim of this study was to evaluate the proliferation and differentiation potential of human adipose-derived stem cells (hADSCs) grown on chitosan hydrogel. The stability of this hydrogel is pH-dependent and its swelling property is pivotal in providing a favorable matrix for cell growth. The study utilized an economical method of cross linking the chitosan with 0.5% glutaraldehyde. Following the isolation of hADSCs from omentum tissue, these cells were cultured and characterized on chitosan hydrogel. Subsequent assays that were performed included JC-1 staining for the mitochondrial integrity as a surrogate marker for viability, cell proliferation and growth kinetics by MTT assay, lineage specific differentiation under two-dimensional culture conditions. Confocal imaging, scanning electron microscopy (SEM), and flow cytometry were used to evaluate these assays. The study revealed that chitosan hydrogel promotes cell proliferation coupled with > 90% cell viability. Cytotoxicity assays demonstrated safety profile. Furthermore, glutaraldehyde cross linked chitosan showed < 5% cytotoxicity, thus serving as a scaffold and facilitating the expansion and differentiation of hADSCs across endoderm, ectoderm and mesoderm lineages. Additional functionalities can be added to this hydrogel, particularly those that regulate stem cell fate.

Preparation and properties of uv-curable polyurethane methacrylate cationomers and their use as adhesives

Cationomeric polyurethanes (containing methacrylic functionality) were prepared from a diisocyanate [toluene diisocyanate (TDI), hexamethylene diisocyanate (HDI), or isophorone diisocyanate (IPDI)], polyethylene glycol (PEG 200, PEG 400, or PEG 1000), 2-hydroxyethyl methacrylate (HEMA), N-methyldiethanolamine (N-MDEA), and dimethyl sulfate (DMS), using dibutyltin dilaurate (DBTDL) as a catalyst. The ultraviolet (UV) curable aqueous cationomeric emulsions were then made with these reactive polyurethane oligomers (having hydrophilic groups), water, and photoinitiator [1-(4-isopropylphenyl)-2-hydroxy-2-methyl propane-1-one]. The effects of PEG chain length and different diisocyanates on properties of the emulsions were studied. The effect of concentration of cationomers on the thermal stability of these systems was also studied. These emulsion systems were evaluated as adhesives before and after curing under UV light. With decrease in PEG molecular weight, the glass transition temperature of the polymers increased and the storage modulus, tensile strength, and peel strength also increased, but the percentage of elongation decreased. Polymer containing TDI was found to have the highest glass transition temperature, storage modulus, peel strength, and tensile strength when compared to the polymer containing HDI or IPDI.