Dendrimers have emerged as topical microbicides to treat vaginal infections. This study explores the in-vitro, in-vivo antimicrobial activity of PAMAM dendrimers, and the associated mechanism. Interestingly, topical cervical application of 500 µg of generation-4 neutral dendrimer (G4-PAMAM-OH) showed potential to treat the Escherichia coli induced ascending uterine infection in guinea pig model of chorioamnionitis. Amniotic fluid collected from different gestational sacs of infected guinea pigs post treatment showed absence of E. coli growth in the cultures plated with it. The cytokine level [tumor necrosis factor (TNFα) and interleukin (IL-6 and IL-1β)] in placenta of the G4-PAMAM-OH treated animals were comparable to those in healthy animals while these were notably high in infected animals. Since, antibacterial activity of amine-terminated PAMAM dendrimers is known, the activity of hydroxyl and carboxylic acid terminated PAMAM dendrimers was compared with it. Though the G4-PAMAM-NH2 shows superior antibacterial activity, it was found to be cytotoxic to human cervical epithelial cell line above 10µg / mL, while the G4-PAMAM-OH was non cytotoxic upto 1mg / mL concentration. Cell integrity, outer (OM) and inner (IM) membrane permeabilization assays showed that G4-PAMAM-OH dendrimer efficiently changed the OM permeability, while G4-PAMAM-NH2 and G3.5-PAMAM-COOH damaged both OM and IM causing the bacterial lysis. The possible antibacterial mechanism are; G4-PAMAM-NH2 acts as polycation binding to the polyanionic lipopolysaccharide in E. coli, the G4-PAMAM-OH forms hydrogen bonds with the hydrophilic O-antigens in E. coli membrane and the G3.5-PAMAM-COOH acts as a polyanion, chelating the divalent ions in outer cell membrane of E. coli. This is the first study which shows that G4-PAMAM-OH dendrimer acts as an antibacterial agent.

The effect of primary particle shape on the porosity, mechanical strength, and luminescence intensity of metal chalcogenide aerogels was probed by comparison of CdSe aerogels prepared from spherical and rod-shaped particles. Rod-shaped particles yield aerogels with polymeric morphologies in contrast to the colloidal morphology obtained from spherical particles. Relative to the colloidal analogues, the polymeric CdSe aerogels exhibit twice the surface area, a doubling of the complex viscosity for 5 wt % aerogel-PDMS composites, and a 25-fold increase in emission intensity. Altering the shape of the building block from which nanostructured networks are assembled is an effective way to tune the basic properties of metal chalcogenide semiconducting aerogels.

Achieving clay dispersion and improving clay−polymer interactions are keys to producing superior nanocomposites. A supercritical CO2 (scCO2) processing method was utilized to prepare high molecular weight polystyrene (PS)/Cloisite 10A nanocomposites with significant dispersion and rheological enhancement. The effects of scCO2 processing, presence of cosolvent, and clay weight fraction on clay dispersion and polymer−clay interactions in nanocomposites were investigated. Rheology, WAXD, and TEM of the nanocomposites indicate that substantial improvements in the rheological properties of scCO2 nanocomposites are the result of increased dispersion and polymer−clay interactions. At low frequencies, the elastic plateau modulus of the scCO2-processing nanocomposites (5 wt % clay loading) is more than 40-fold higher than benchmark solution-blended samples. Our results suggest that the substantial contacting with scCO2, followed by rapid depressurization, produces a combination of disorder and dispersion of this “as-received” clay, and the presence of the cosolvent enables more intimate contact of the high molecular weight PS and clay.

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