Development of novel carriers and optimization of their design parameters has led to significant advances in the field of targeted drug delivery. Since carrier shape has recently been recognized as an important design parameter for drug delivery, we sought to investigate how carrier shape influences their flow in the vasculature and their ability to target the diseased site. Idealized synthetic microvascular networks (SMNs) were used for this purpose since they closely mimic key physical aspects of real vasculature and at the same time offer practical advantages in terms of ease of use and direct observation of particle flow. The attachment propensities of surface functionalized spheres, elliptical/circular disks and rods with dimensions ranging from 1 µm to 20 µm were compared by flowing them through bifurcating SMNs. Particles of different geometries exhibited remarkably different adhesion propensities. Moreover, introduction of a bifurcation as opposed to the commonly used linear channel resulted in significantly different flow and adhesion behavior, which may have important implications in correlating these results to in vivo behavior. This study provides valuable information for design of carriers for targeted drug delivery.

We have designed a series of versatile lipopolyamines which are amenable to chemical modification for in vivo delivery of small interfering RNA (siRNA). This report focuses on one such lipopolyamine (Staramine), its functionalized derivatives and the lipid nanocomplexes it forms with siRNA. Intravenous (i.v.) administration of Staramine/siRNA nanocomplexes modified with methoxypolyethylene glycol (mPEG) provides safe and effective delivery of siRNA and significant target gene knockdown in the lungs of normal mice, with much lower knockdown in liver, spleen, and kidney. Although siRNA delivered via Staramine is initially distributed across all these organs, the observed clearance rate from the lung tissue is considerably slower than in other tissues resulting in prolonged siRNA accumulation on the timescale of RNA interference (RNAi)-mediated transcript depletion. Complete blood count (CBC) analysis, serum chemistry analysis, and histopathology results are all consistent with minimal toxicity. An in vivo screen of mPEG modified Staramine nanocomplexes-containing siRNAs targeting lung cell-specific marker proteins reveal exclusive transfection of endothelial cells. Safe and effective delivery of siRNA to the lung with chemically versatile lipopolyamine systems provides opportunities for investigation of pulmonary cell function in vivo as well as potential treatments of pulmonary disease with RNAi-based therapeutics.

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Objective Particle adhesion in vivo is dependent on microcirculation environment which features unique anatomical (bifurcations, tortuosity, cross-sectional changes) and physiological (complex hemodynamics) characteristics. The mechanisms behind these complex phenomena are not well understood. In this study, we used a recently developed in vitro model of microvascular networks, called Synthetic Microvascular Network, for characterizing particle adhesion patterns in the microcirculation. Methods Synthetic microvascular networks were fabricated using soft lithography processes followed by particle adhesion studies using avidin and biotin-conjugated microspheres. Particle adhesion patterns were subsequently analyzed using CFD based modeling. Results Experimental and modeling studies highlighted the complex and heterogeneous fluid flow patterns encountered by particles in microvascular networks resulting in significantly higher propensity of adhesion (>1.5X) near bifurcations compared to the branches of the microvascular networks. Conclusion Bifurcations are the focal points of particle adhesion in microvascular networks. Changing flow patterns and morphology near bifurcations are the primary factors controlling the preferential adhesion of functionalized particles in microvascular networks. Synthetic microvascular networks provide an in vitro framework for understanding particle adhesion.

The therapeutic application of commercially available polyethylenimines (e.g., PEI 25 kD) is marred by substantial toxicity. The benefit of using lower molecular weight polyethylenimines (<25 kD) has not been fully explored because of limited availability and high molecular heterogeneity (e.g., degree of branching) among the available few. We have synthesized a series of low molecular weight linear polyethylenimines (LPEI; 2.5-25 kD) with a single synthesis scheme to minimize molecular heterogeneity. DNA formulation with the newly synthesized linear polyethylenimines resulted in the formation of stable nanoparticles (100-150 nm) of positive zeta potential. Addition of these nanoparticles onto COS-1 and HEK 293 cell cultures led to transgene expression the efficiency and cytotoxicity of which varied with the LPEI size. The lowest molecular weight LPEI (LPEI 2.5 kD) gave the smallest level of gene expression and did not exert any cytotoxicity. The transfection activity exponentially increased with higher molecular weight LPEIs reaching maximal level with 7.5 kD LPEI and was accompanied with some cytotoxicity. The transfection activity of 7.5 kD LPEI was equal to that of the higher molecular weight LPEIs including 25 kD LPEI, but caused less cytotoxicity. To achieve high transfection efficiency without substantial increase in cytotoxicity, we cross-linked LPEI 3.6 kD with a biodegradable linkage to form a multi-block copolymer (BD3.6K) of approximately 8 kD. The multi-block copolymer, BD3.6K, expressed 20-fold higher transfection activity than that of the monomer block and produced significantly lower cytotoxicity than 25 kD PEI in vitro. Following intravenous administration, plasmid/BD3.6K complexes elicited significant gene transfer in lungs, while complexes prepared with monomer block did not yield discernable transfection activity. The transfection efficiency of the systemically administered plasmid/BD3.6K complexes was 2.5-times and 70-times higher than that of linear and branched 25 kD PEI, respectively. Transfection complexes prepared with BD3.6K exhibited better tolerability than complexes prepared with 25 kD PEIs. These results demonstrate that: (1) the lower molecular weight linear polyethylenimines (<10 kD) are more suitable for gene delivery than the commercially available higher molecular weight polyethylenimines (25 kD) and (2) the cross-linking of the non-toxic low molecular weight polyethylenimines via biodegradable linkage is a viable approach to improving PEI transfection efficiency without significantly increasing the cytotoxicity.