Nanoscale double emulsions stabilized by single-component block copolypeptides.

Water-in-oil-in-water emulsions are examples of double emulsions, in which dispersions of small water droplets within larger oil droplets are themselves dispersed in a continuous aqueous phase. Emulsions occur in many forms of processing and are used extensively by the foods, cosmetics and coatings industries. Because of their compartmentalized internal structure, double emulsions can provide advantages over simple oil-in-water emulsions for encapsulation, such as the ability to carry both polar and non-polar cargos, and improved control over release of therapeutic molecules. The preparation of double emulsions typically requires mixtures of surfactants for stability; the formation of double nanoemulsions, where both inner and outer droplets are under 100 nm, has not yet been achieved. Here we show that water-in-oil-in-water double emulsions can be prepared in a simple process and stabilized over many months using single-component, synthetic amphiphilic diblock copolypeptide surfactants. These surfactants even stabilize droplets subjected to extreme flow, leading to direct, mass production of robust double nanoemulsions that are amenable to nanostructured encapsulation applications in foods, cosmetics and drug delivery.

Amino Acid Block Copolymers with Broad Antimicrobial Activity and Barrier Properties.

Antimicrobial properties of a long-chain, synthetic, cationic, and hydrophobic amino acid block copolymer are reported. In 5 and 60 min time-kill assays, solutions of K100 L40 block copolymers (poly(l-lysine·hydrochloride)100 -b-poly(l-leucine)40 ) at concentrations of 10-100 µg mL-1 show multi-log reductions in colony forming units of Gram-positive and Gram-negative bacteria, as well as yeast, including multidrug-resistant strains. Driven by association of hydrophobic segments, K100 L40 copolymers form viscous solutions and self-supporting hydrogels in water at concentrations of 1 and 2 wt%, respectively. These K100 L40 preparations provide an effective barrier to microbial contamination of wounds, as measured by multi-log decreases of tissue-associated bacteria with deliberate inoculation of porcine skin explants, porcine open wounds, and rodent closed wounds with foreign body. Based on these findings, amino acid copolymers with the features of K100 L40 can combine potent, direct antimicrobial activity and barrier properties in one biopolymer for a new approach to prevention of wound infections.

Highly reactive heterogeneous Heck and hydrogenation catalysts constructed through 'bottom-up' nanoparticle self-assembly.

Polymer-mediated self-assembly of functionalized Pd and SiO2 nanoparticles provides highly active hydrogenation and Heck coupling catalysts.

Nonionic Block Copolypeptide Micelles Containing a Hydrophobic racemic-Leucine Core.

Block copolymer micelles have been used extensively as carriers for therapeutic drugs and diagnostic molecules. Here, we report the synthesis of nonionic, block copolypeptides, K(P) (x)(rac-L)(y), which have a "reversed" rod-coil structure composed of a hydrophilic, rod-like, α-helical segment attached to a disordered, racemic hydrophobic segment. The self assembly of these block copolypeptides in water was studied, and their compositions were optimized to identify a sample, K(P) (100)(rac-L)(10), which is able to form well defined micelles that are very stable against dilution, high temperatures, and various media. Micelle structure was determined using a combination of electron microscopy and dynamic light scattering measurements. The potential of these micelles as drug delivery carriers was evaluated by encapsulation of the anticancer drug camptothecin. The drug containing micelles were found to be stable.