Self-Assembly of siRNA/PEG- b-Catiomer at Integer Molar Ratio into 100 nm-Sized Vesicular Polyion Complexes (siRNAsomes) for RNAi and Codelivery of Cargo Macromolecules.

Vesicular polyion complexes (PICs) were fabricated through self-assembly of rigid cylindrical molecules, small interfering RNAs (siRNAs), with flexible block catiomers of poly(ethylene glycol) (2 kDa) and cationic polyaspartamide derivative (70 units) bearing a 5-aminopentyl side chain. 100 nm-sized siRNA-assembled vesicular PICs, termed siRNAsomes, were fabricated in specific mixing ranges between siRNA and block catiomer. The siRNAsome membrane was revealed to consist of PIC units fulfilling a simple molar ratio (1:2 or 2:3) of block catiomer and siRNA. These ratios correspond to the minimal integer molar ratio to maximally compensate the charge imbalance of PIC, because the numbers of charges per block catiomer and siRNA are +70 and -40, respectively. Accordingly, the ζ-potentials of siRNAsomes prepared at 1:2 and 2:3 were negative and positive, respectively. Cross-section transmission electron microscopic observation clarified that the membrane thicknesses of 1:2 and 2:3 siRNAsomes were 11.0 and 17.2 nm, respectively. Considering that a calculated long-axial length of siRNA is 5.9 nm, these thickness values correspond to the membrane models of two (11.8 nm) and three (17.7 nm) tandemly aligned siRNAs associating with one and two block catiomers, respectively. For biological application, siRNAsomes were stabilized through membrane-cross-linking with glutaraldehyde. The positively charged and cross-linked siRNAsome facilitated siRNA internalization into cultured cancer cells, eliciting significant gene silencing with negligible cytotoxicity. The siRNAsome stably encapsulated dextran as a model cargo macromolecule in the cavity by simple vortex mixing. Confocal laser scanning microscopic observation displayed that both of the payloads were internalized together into cultured cells. These results demonstrate the potential of siRNAsomes as a versatile platform for codelivery of siRNA with other cargo macromolecules.

Fabrication of polyion complex vesicles with enhanced salt and temperature resistance and their potential applications as enzymatic nanoreactors.

Integrating catalytic functions into polymeric vesicles through enzyme entrapment is appealing for bioreactor fabrication, yet there are critical issues regarding the regulation of solute transport through membranes and enzyme loading without denaturation. Polyion complex vesicles (PICsomes) with semipermeable membranes and the propensity to form in water can overcome these issues; however, cross-linking is required for sufficient physiological stability. Herein, we report the first successful fabrication of non-cross-linked PICsomes with sufficient stability at physiological salinity and temperature by tuning the hydrophobicity of the aliphatic side chains in the pendant group of the constituent polyelectrolytes. Dynamic light scattering and transmission electron microscopy revealed that the intervesicular fusion and disintegration of the PICsomes was prevented and a narrow distribution was maintained at physiological salinity and temperatures. Furthermore, their application as enzymatic nanoreactors was verified even in the presence of proteases. As such, the potential utility of the PICsomes in biomedical fields was established.

Monodispersed polymeric nanocapsules: spontaneous evolution and morphology transition from reducible hetero-PEG PICmicelles by controlled degradation.

In this communication, a novel "self-templating" strategy was used to prepare uniform and biocompatible nanocapsules by the addition of a reduction agent (i.e., DTT) into a solution of highly monodispersed PICmicelles bearing a heterodetachable PEG corona. PEG chains were released from PICmicelle shells following disulfide reduction which leads a spontaneous and drastic morphology evolution from micelles to vesicles induced by the decrease of the PEG weight fraction. Formation of uniform nanocapsules with controllable capsule size was achieved by careful control of the micelle composition and molecular weight of homo-P[Asp(DET)].