Mixing liposomes with hydrophilic particles will induce fusion of the liposome onto the particle surface. Such supported bilayers have been extensively studied as a model for the cell membrane, while its application in drug delivery has not been pursued. In this communication, we report the use of phospholipids to achieve synergistic loading and encapsulating of a fluorescent dye (calcein) in mesoporous silica nanoparticles, and its delivery into mammalian cells. We found that cationic lipid DOTAP provides the highest calcein loading with the concentration inside silica ∼110× higher than that in the solution under experimental conditions. Compared to some other nanoparticle systems, protocells provide a simple construct for loading, sealing, delivering and releasing, and should serve as a useful system in nanomedicine.One of the major challenges in nanomedicine is to engineer nanostructures and materials that can efficiently encapsulate drugs at high concentration, cross the cell membrane, and controllably release the cargo at the target site over a prescribed period of time. 1 Recently, inorganic nanoparticles, including gold, silica, and carbon nanotubes have emerged as a new generation of drug/therapy delivery vehicles in nanomedicine. 2,3 Mesoporous silica nanoparticles are particularly attractive in this regard, because of their biocompatibility and their precisely defined nanoporosity. 4-7 With uniform, tunable pore diameters, ranging from ∼2-5-nm and surfaces areas of 700-1500 m 2 /g, drugs and other components can be loaded by adsorption or capillary filling, and the release profiles adjusted by the combination of pore size and pore surface chemistry. 8 Very recently, elegant gating methods, employing coumarin, 9 azobenzene, 10,11 rotaxane, 12 polymers, 13,14 or small nanoparticles, 15,16 have been established to seal the cargo within the particle and allow its triggered release according to an optical or electrochemical stimulus. Here we describe a synergistic system where liposome fusion on a mesoporous silica particle core simultaneously loads and seals the cargo, creating a 'protocell' construct useful for delivery across the cell membrane (Fig. 1B). We observe that fusion of a positively charged liposome on a negatively charged mesoporous silica core serves to load the core with a negatively charged dye (excluded from the mesopores without lipid) to concentrations that can exceed 100x those in solution. Sealed within the protocell, this membrane impermeable dye can be transported across the cell membrane and slowly released within the cell. Compared to other nanoparticle delivery systems, the protocell is simple and takes advantage of the low toxicity and immunogenicity of liposomes along with their ability to be PEGylated or conjugated to extend circulation time and effect targeting. Compared to liposomes, however, the protocell is more stable and takes advantage of the mesoporous core to control both loading and release. As noted in many other relevant papers the mesoporous E-mail: cjbrink...

Silica nanoparticle supported cationic lipids can effectively bind plasmid DNAs and transfect mammalian cells with an efficiency that depends on both the particle size and lipid composition; here the gene delivery and expression process has been confirmed by confocal fluorescence microscopy.Gene delivery to mammalian cells has gained significant attention due to its importance in gene therapy. [1][2][3] Genes embedded in plasmid DNAs provide a stable source for therapeutic proteins and RNAs. Naked DNAs by themselves cannot cross the cell membrane barrier and are easily degraded by nucleases in biological fluids. 4 As a result, delivery vehicles are needed for efficient transfection. 5 Due to the intrinsic toxicity and immunogenicity of viral vectors, current research focus has shifted to the development of nonviral carriers. [6][7][8][9][10][11][12] Cationic lipids and liposomes are quite effective in gene delivery. 13,14 However, highly negatively charged DNAs can induce fusion of such liposomes to generate large particles, which may reduce the transfection efficiency and increase toxicity. 15 To minimize this problem, crosslinked or PEGylated liposomes have been tested. 15,16 Crosslinked liposomes, however, may have biodegradation problems in vivo. We have recently explored the use of silica nanoparticle (NP) supported lipid bilayers for drug delivery applications. 17,18 Such supported bilayers have higher stability compared to empty liposomes and the lipid layers are unlikely to fuse with each other due to the presence of a solid core. On the other hand, the lipids are not covalently linked and can still exchange and fuse with cellular lipids and be metabolized. Herein we report the use of supported lipid bilayers for gene delivery to Chinese hamster ovary cells (CHO). One of the advantages of the supported bilayer system is that both the silica core size and lipid composition of the shell can be systematically varied, which provides us a useful system to tune and understand the gene delivery process.Pure silica is negatively charged at pH 7 and thus requires charge reversal to bind DNA. We employed silica NPs with sizes ranging from 8 to 130 nm, and tested their interactions with cationic liposomes and DNA. Silica NPs with a diameter of 8 nm appear transparent in solution. Addition of a small amount of cationic DOTAP liposomes resulted in a white suspension, suggesting the formation of larger NP assemblies that scattered light strongly (Fig 1A). These larger NPs showed a negative surface charge by zeta-potential measurement (Fig 2A). This is consistent with the formation of liposome-supported, sub-20-nm diameter NPs as reported by Zhang and Granick. 19 Further addition of DOTAP led to the formation of gel-like large aggregates, suggesting the crosslinking of supported particles by liposomes ( Fig 1A). Since these very small particles gave either a negative surface charge or very large aggregates when mixed with cationic lipids, they are not suitable for binding negatively charged DNA and are therefor...

We are developing a novel computer simulation game based on authentic engineering practices to give first-year engineering undergraduates a more complete and accurate understanding of the engineering profession. The game is student-focused in that it is tailored to the newest generation of engineering students who are more computer literate, electronically connected, and simulation game-oriented than any prior generation. The game also is epistemic frame-based in that it seeks to teach and assess the degree to which students acquire the skills, knowledge, values, identity, and epistemology (i.e., the epistemic frame) of the engineering profession. We anticipate that this approach will be highly engaging to first-year undergraduate engineering students and help promote the development of their engineering epistemic frame.