Polyurethane nanoparticles formation

The formation of polyurethane nanoparticles from inverse nano-emulsions (W/O) has also been achieved. Interfacial polyaddition in inverse nano-emulsion is of special interest since this allows the encapsulation of hydrophilic active materials such as proteins or nucleic acids. Thus, taking advantage of the high reactivity of tolylene 2,4-diisocyanate with water molecules, polyurea lipid nanocapsules with aqueous cores obtained from W/O nano-emulsions and prepared by PIT method were designed. Polymer synthesis occurs by in situ interfacial polymerization after nano-emulsion formation. Volatile oils employed as the continuous phase were removed by evaporation and the nanocapsules were redispersed in water. These nanocapsules could be potentially used for encapsulation of both hydrophilic and lipophilic molecules simultaneously. 

Significant advances have been made in the design, formation, and characterization of polyurethane nanoparticles. Different approaches have been employed to synthesize polyurethane nanoparticles as carriers of imaging agents, as dmgs, or as copolymers to form different versatile matrices. The chemical reactivity and properties of these polymers make them suitable to bind peptides, nucleic acids, antibodies. 

Figure 7.1 Formation of different polyurethane nanoparticles (naked pol5nirethane, pegylated polyurethane, lysine-coated polyurea, biotinylated polyurethane-urea/pc DNA complex, and functionalized streptavidin-coated polyurethane-urea nanoparticles) obtained by interfacial polycondensation from OAV nano-emulsions (a) and transmission electron micrographs of polyurethane nanoparticles after being negatively stained with 1% v/v uranyl acetate (b).

In another study Escherichia coli cells treated by Ag nanoparticles were found damaged, showing formation of pits in the cell wall of the bacteria (59). Jain and Pradeep have studied the efficacy of silver nanoparticles as a drinking water filter where there is bacterial contamination of the surface water (60). Silver nanoparticles were utilized to make stable, silver-coated filters from common polyurethane (PU) foams. The performance of the material as an antibacterial water filter was checked and no bacterium was detected in the output water when the input water had a bacterial load of 1 X 10 colony-forming units (CPU) per miUditer. The antibacterial action was also checked inline for a flow rate of 0.5 L/min and no bacterium detected, which suggests that domestic use of this technology is possible. 

Hydrophilic materials can be encapsulated with the inverse minianulsions by using interfacial polymerization such as polyaddition and polycondensation, radical, or anionic polymerization. Crespy et al. reported that silver nitrate was encapsulated and subsequently reduced to give silver nanoparticles inside the nanocapsules. The miniemulsions were prepared by anulsilying a solution of amines or alcohols in a polar solvent with cyclohexane as the nonpolar continuous phase. The addition of suitable hydrophobic diisocyanate or diisothiocyanate monomers to the continuous phase allows the polycondensation or the cross-linking reactions to occur at the interface of the droplets. By using different monomers, polyurea, polythiourea, or polyurethane nanocapsules can be formed. The waU thickness of the capsules can be directly tuned by the quantity of the reactants. The nature of the monomers and the continuous phase are the critical factors for the formation of the hollow capsules, which is explained by the interfacial properties of the systan. The resulting polymer nanocapsules could be subsequently dispersed in water. 

The same investigators have successfully applied cryogel processing to prepare composite of a nitrocellulose gel (an energetic gel), polyurethane cross-linked nitrocellulose and the energetic material CL-20 [50]. Under those processing conditions, all of the components were initially in solution, which enabled the formation of nanoparticles of the... 

Morral-Ruiz G, Solans C, Luisa Garcia M, Jose Garcia-Celma M. Formation of pegylated polyurethane and lysine-coated pol5mrea nanoparticles obtained from O/W nano-emulsions. Langmuir April 17, 2012 28(15) 6256-64. 

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