In-situ interfacial compatibilization via edge-sulfurated few layer graphene during the formation of crosslinked graphene-rubber nanocomposites.

Herein, we report various physico-chemical approaches to probe the nature of the interface between few layers graphene (FLG) and carboxylated nitrile rubber (XNBR) nanocomposites prepared through efficient blending of XNBR latex with an aqueous dispersion of FLG. The extent of physical interaction between FLG and XNBR was investigated using Lorentz-Park and Cunneen-Russell models. The chemical interface between FLG and sulfur crosslinked XNBR was studied using model reactions between sulfur and graphene in presence of zinc 2-mercaptobenzothiazole (ZMBT). We propose that an edge sulfurated FLG is formed, which could chemically bond with XNBR during the vulcanization process. Density Functional Theory (DFT) was employed to unravel the mechanistic insights, which support this hypothesis and suggest a kinetically favorable sulfuration of both XNBR and FLG. The formation of a chemical bond between edge-FLG and XNBR through the proposed intermediacy of sulfurated FLG leads to the observed improvement in mechanical properties of the nanocomposites.

Cytotoxicity of Formulated Graphene and Its Natural Rubber Nanocomposite Thin Film in Human Vaginal Epithelial Cells: An Influence of Noncovalent Interaction.

Graphene family materials (GFMs) are extensively explored for various biomedical applications due to their unique physical properties. The prime challenge is to establish a conclusive safety profile of these nanomaterials and their respective products or devices. Formulating GFMs with appropriate ingredients (e.g., surfactant/compatibilizer) will help to disperse them homogeneously (i.e., within the polymer matrix in the case of polymer-graphene nanocomposites) and aid in good interfacial interaction to achieve the desired properties. However, no cytotoxicity report is available on the effects of the additives on graphene and its incorporated materials. Here, we report in vitro cytotoxicity of formulated FLG (FLG-C), i.e., a mixture of FLG, melamine, and sodium poly(naphthalene sulfonate) (SPS), along with natural rubber (NR) latex and FLG-C-included NR latex nanocomposite (FLG-C-NR) thin films on human vaginal epithelial (HVE) cells. FLG-C shows reduced cellular proliferation (∼55%) only at a longer exposure time (72 h) even at a low concentration (50 µg/mL). It also displays significant down- and upregulation in mitochondrial membrane potential (MMP) and reactive oxygen species (ROS), respectively, whereas no changes are observed in lactate dehydrogenase (LDH), propidium iodide (PI), uptake, and cell cycle analysis at 48 h. In vitro experiments on NR latex and FLG-C-NR latex thin films demonstrate that the incorporation of FLG-C does not compromise the biocompatibility of the NR latex. Further substantiation from the in vivo experiments on the thin films recommends that FLG-C could be suitable to prepare a range of biocompatible rubber latex nanocomposites-based products, viz., next-generation condoms (male and female), surgical gloves, catheters, vaginal rings, bladder-rectum spacer balloon, etc.

Aphrodisiac properties of hydro-alcoholic extract of Cassia auriculata flower in male rats.

Cassia auriculata is a commonly found plant in Asia, widely used in Ayurveda and Siddha medicines as a tonic, astringent and in general for diabetes. Herbal tea made from this plant has been marketed as a product for restoring sexual vitality, to increase sperm count and counteract ejaculatory disorders. However, the scientific evidences are scarce to prove this concept. Here, we examined the effect of hydro-alcoholic extract obtained from C. auriculata flower upon the expression of male Wistar albino rat's sexual behaviour. Sildenafil was used as a positive control. Penile erection index (PEI), mount latency (ML), intromission latency (IL), ejaculation latency (EL), mounting frequency (MF), intromission frequency (IF), ejaculation frequency (EF) and post-ejaculatory interval (PEjI) were recorded for days 0, 7, 14 and 28 and also after the withdrawal of the treatment on days 7 and 15. Significant reduction in ML, IL and PEjI, and increment in EL, PEI, MF, IF and EF were observed (p < 0.05, <0.01). However, neither extract nor sildenafil sustains the effect after withdrawal of the treatment. The present finding demonstrates the aphrodisiac potential of hydro-alcoholic extract of C. auriculata flower in vivo and lends support to the traditional utilisation as a sexual stimulating agent.

Facile, environmentally benign and scalable approach to produce pristine few layers graphene suitable for preparing biocompatible polymer nanocomposites.

The success of developing graphene based biomaterials depends on its ease of synthesis, use of environmentally benign methods and low toxicity of the chemicals involved as well as biocompatibility of the final products/devices. We report, herein, a simple, scalable and safe method to produce defect free few layers graphene using naturally available phenolics i.e. curcumin/tetrahydrocurcumin/quercetin, as solid-phase exfoliating agents with a productivity of ∼45 g/batch (D/G ≤ 0.54 and D/D' ≤ 1.23). The production method can also be employed in liquid-phase using a ball mill (20 g/batch, D/G ≤ 0.23 and D/D' ≤ 1.12) and a sand grinder (10 g/batch, D/G ≤ 0.11 and D/D∼ ≤ 0.78). The combined effect of π-π interaction and charge transfer (from curcumin to graphene) is postulated to be the driving force for efficient exfoliation of graphite. The yielded graphene was mixed with the natural rubber (NR) latex to produce thin film nanocomposites, which show superior tensile strength with low modulus and no loss of % elongation at break. In-vitro and in-vivo investigations demonstrate that the prepared nanocomposite is biocompatible. This approach could be useful for the production of materials suitable in products (gloves/condoms/catheters), which come in contact with body parts/body fluids.

Poly(glycerol sebacate)-Based Polyester-Polyether Copolymers and Their Semi-Interpenetrated Networks with Thermoplastic Poly(ester-ether) Elastomers: Preparation and Properties.

Poly(glycerol sebacate) (PGS), produced from renewable monomers such as sebacic acid and glycerol, has been explored extensively for various biomedical applications. However, relatively less attention has been paid to explore PGS as sustainable materials in applications such as elastomers and rigid plastics, primarily because of serious deficiencies in physical properties of PGS. Here, we present two new approaches for enhancing the properties of PGS; (i) synthesizing block copolymers of PGS with poly(tetramethylene oxide)glycol (PTMO) and (ii) preparing a blend of PGS-b-PTMO with a poly(ester-ether) thermoplastic elastomer. The consequence of molar ratio (hard and soft segments) and M n of soft segment on tensile properties of the material was investigated. The PGS-b-PTMO with 25:75 mole ratios of hard and soft segments and having a medium M n soft segment (5350 g mol-1) exhibits an appreciable increase in percentage of elongation that is from 32% for PGS to 737%. Blends of PGS-b-PTMO and a thermoplastic polyester elastomer, Hytrel 3078, form a semi-interpenetrated polymer network, which exhibits increased tensile strength to 2.11 MPa and percentage of elongation to 2574. An elongation of such magnitude is unprecedented in the literature for predominantly aliphatic polyesters and demonstrates that the simple polyester can be tailored for superior performance.

Thermally conductive thin films derived from defect free graphene-natural rubber latex nanocomposite: Preparation and properties.

Commercially useful rubber products viz. gloves, condoms, tyres, and rubber hoses used in high temperature environments, etc., require efficient thermal conductivity, which increases the lifetime of these products. Graphene can fetch this property, if it is effectively incorporated into the rubber matrix. The great challenge in preparing graphene-rubber nanocomposites is formulating a scalable method to produce defect free graphene and its homogeneous dispersion into polymer matrices through an aqueous medium. Here, we used a simple method to produce defect free few layer (2-5) graphene, which can be easily dispersed into natural rubber (NR) latex without adversely affecting its colloidal stability. The resulting new composite showed large increase in thermal conductivity (480-980%) along with 40% increase in tensile properties and 60% improvement in electrical conductivity. This study provides a novel and generalized approach for the preparation of graphene based thermally conductive rubber nanocomposites.

An orthogonal click-chemistry approach to design poly(glycerol monomethacrylate)-based nanomaterials for controlled immunostimulation.

A versatile approach is proposed for the synthesis of novel immunoactive nanomaterials based on biocompatible poly(glycerol monomethacrylate) (PGMMA). Propargyl-terminated PGMMA is synthesized via atom transfer radical polymerization and then modified through the introduction of dangling acrylate groups, at controlled degree of functionalisation. Acrylates are then able to react quantitatively with thiols, such as immunoactive thiomannose, through Michael-type addition under mild conditions and at a physiologically acceptable pH. The terminal propargyl group can be modified independently with azide end-capping groups and it is utilized to graft the macromolecules to a fluorescent dye. The resulting mannose-linked PGMMAs confirm a safe cytotoxic profile and are able to stimulate cytokine production (TNFα), membrane protein expression (CD40), and cellular uptake in bone marrow derived dendritic cells. Cell stimulation is dependent on the mannose content and enhanced by serum proteins, suggesting a role for mannose-binding receptors and/or complement receptors in the cell membrane.