Rheological and thermodynamic properties of Pluronic F127 copolymer and Pluronic-g-PAA have been studied as a function of temperature and concentration. A combination of rheometry and DSC was employed to examine the gelation behavior of F127 and F127-g-PAA. The viscosity of F127 is extremely sensitive to temperature when the polymer concentration exceeds 10 wt%. But significant increase of viscosity has been observed for 1.0 wt%F127-PAA aqueous solution as a function of temperature. This could be due to the PAA grafts, acting as cross-links attached to the F127 backbone. / Singapore-MIT Alliance (SMA)

Non-viral delivery vectors have potential advantages over the viral systems that currently are used extensively for delivering therapeutic genes of interest. However, non-viral gene therapy has low efficiencies in vivo, in part due to the aggregation of the particles in the delivery system associated with serum proteins and other components of the blood. An effective technique for overcoming this problem to use PluronicTM block copolymers to cover the surfaces of the particles in the delivery system with polyethylene oxide, which decreases their charge density and reduces their interactions with the serum proteins. The objectives of this project were to characterize a Pluronic-gemini surfactant system to be used as non-viral vectors for gene therapy. Five Pluronics (L44, F68, F87, F108, and F127) were evaluated by studying their physiochemical properties, including particle size and zeta potential. Also, these systems were evaluated in OVCAR-3 cell culture for gene expression and cell viability. The in vitro systems showed small particle sizes (approximately 200 nm) for all Pluronics. The particle sizes in the systems were increased dramatically (up to 2000 nm) by adding dioleylphosphatidylethanolamine (DOPE) to the systems. The zeta potential of these systems shifted the negative zeta potential of DNA (-43 mV) to a positive value (+35 mV). The addition of DOPE had very little effect on zeta potential. The in vitro transfection efficiency in OVCAR-3 showed that all of the Pluronics were able to transfect OVCAR-3 at various DNA/gemini surfactant ratios. The highest transfection efficiency was obtained with Pluronics L44, F87 and F108. PluronicF127 demonstrated the lowest transfection efficiency among the five Pluronics. Adding DOPE did not improve the transfection efficiency in any of the pluronic-gemini surfactant systems. The viabilities of the cells in these systems were high, and there were greater than the positive control (Lipofectamine 2000). The greatest cell viability (about 60%) was observed when the DNA to gemini surfactant ratio was 1:2. After adding DOPE, the cell viability decreased in all of the Pluronics except for Pluronic F68. The results of this investigation indicated that Pluronic block copolymers can transfect OVCAR-3 cell cultures in vitro and that they had a low level of cytotoxicity.

Class of 2009 Abstract / OBJECTIVES: The primary objective of this experiment was to characterize the pH stability range of 20% Pluronic lecithin organogel (PLO). We intended to determine the viscosity at varying pHs. We prepared six samples of 20% PLO. METHODS: An initial rheological reading of each sample was recorded by a dynamic stress rheometer. Each sample was titrated drop-wise with citric acid or KOH in 0.5 pH increments. When the desired pH was obtained, a 0.5 mL sample was analyzed with a dynamic stress rheometer, RS-200, using Rheos software. RESULTS: Since PLO is a non-Newtonian substance, viscosity changed relative to shear stress and we were not able to examine a correlation of pH with viscosity. Instead we inputted the data into Microsoft Excel® and plotted a shear stress versus viscosity curve for each sample to identify trends. CONCLUSIONS: We were unable to achieve our primary objective of determining the viscosity characterization of 20% PLO at varying pHs due to the non-Newtonian nature of the material. Subjectively, we determined the viscosity of 20% PLO is not substantially affected by pH. Other factors such as temperature, excess liquid, and surfactant ability may influence viscosity and need to be examined in the future.

Described in this report is stimulated echo pulsed field gradient (STE-PFG) 1H nuclear magnetic resonance (NMR) diffusion on neutral and negatively charged magnetically aligned bicelles incorporating the Pluronic tri-block copolymer F68. Bicelles are model lipid membrane systems composed of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and 1,2-dihexanoyl-sn-glycero-3-phosphocholine (DHPC). Pluronic F68 incorporated into neutral bicellar mixtures (q= [DMPC]/[DHPC]= 4.5) exhibited resonance intensity decays that are non-exponential and diffusion-time dependent., i.e. non-Gaussian diffusion. In contrast, Pluronic F68 incorporated in negatively charged bicellar mixtures, containing 1 mol% 1,2-dimyristoyl-sn-glycero-3-phosphoglycerol (DMPG), showed the F68 intensity decays that are exponential and diffusion-time independent, viz., Gaussian diffusion. The implication may be that neutral bicellar mixtures incorporating Pluronic F68 consist of extended lamellae composed of meshed ribbon structures, while negatively charged bicellar mixtures incorporating Pluronic F68 consist of perforated lamellae. Pluronic F68 incorporated into the bicelles reports these morphological differences through its diffusion.

Described in this report is stimulated echo pulsed field gradient (STE-PFG) 1H nuclear magnetic resonance (NMR) diffusion on neutral and negatively charged magnetically aligned bicelles incorporating the Pluronic tri-block copolymer F68. Bicelles are model lipid membrane systems composed of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and 1,2-dihexanoyl-sn-glycero-3-phosphocholine (DHPC). Pluronic F68 incorporated into neutral bicellar mixtures (q= [DMPC]/[DHPC]= 4.5) exhibited resonance intensity decays that are non-exponential and diffusion-time dependent., i.e. non-Gaussian diffusion. In contrast, Pluronic F68 incorporated in negatively charged bicellar mixtures, containing 1 mol% 1,2-dimyristoyl-sn-glycero-3-phosphoglycerol (DMPG), showed the F68 intensity decays that are exponential and diffusion-time independent, viz., Gaussian diffusion. The implication may be that neutral bicellar mixtures incorporating Pluronic F68 consist of extended lamellae composed of meshed ribbon structures, while negatively charged bicellar mixtures incorporating Pluronic F68 consist of perforated lamellae. Pluronic F68 incorporated into the bicelles reports these morphological differences through its diffusion.

Microfluidics refers to devices and methods for controlling and manipulating fluid flows at length scales less than a millimeter. Miniaturization of a laboratory to a small device, usually termed as lab-on-a-chip, is an advanced technology that integrates a microfluidic system including channels, mixers, reservoirs, pumps and valves on a micro scale chip and can manipulate very small sample volumes of fluids. While several flow control concepts for microfluidic devices have been developed to date, here flow control concepts based on thermally responsive polymer solutions are presented. In particular, flow control concepts base on the thermally triggered reversible phase change of aqueous solutions of the polymer Pluronic will be discussed. Selective heating of small regions of microfluidic channels, which leads to localized gel formation in these channels and reversible channel blockage, will be used to control a membrane valve that controls flow in a separate channel. This new technology will allow generating inexpensive portable bioanalysis tools where microvalve actuation occurs simply through heaters at a constant pressure source without a need for large external pressure control systems as is currently the case. Furthermore, a concept for controlled cross-channel transport of particles and potentially cells is presented that relies on the continuous regeneration of a gel wall at the diffusive interface of two co-streaming fluids in a microfluidic channel.

Microfluidics refers to devices and methods for controlling and manipulating fluid flows at length scales less than a millimeter. Miniaturization of a laboratory to a small device, usually termed as lab-on-a-chip, is an advanced technology that integrates a microfluidic system including channels, mixers, reservoirs, pumps and valves on a micro scale chip and can manipulate very small sample volumes of fluids. While several flow control concepts for microfluidic devices have been developed to date, here flow control concepts based on thermally responsive polymer solutions are presented. In particular, flow control concepts base on the thermally triggered reversible phase change of aqueous solutions of the polymer Pluronic will be discussed. Selective heating of small regions of microfluidic channels, which leads to localized gel formation in these channels and reversible channel blockage, will be used to control a membrane valve that controls flow in a separate channel. This new technology will allow generating inexpensive portable bioanalysis tools where microvalve actuation occurs simply through heaters at a constant pressure source without a need for large external pressure control systems as is currently the case. Furthermore, a concept for controlled cross-channel transport of particles and potentially cells is presented that relies on the continuous regeneration of a gel wall at the diffusive interface of two co-streaming fluids in a microfluidic channel.

Microfluidics refers to devices and methods for controlling and manipulating fluid flows at length scales less than a millimeter. Miniaturization of a laboratory to a small device, usually termed as lab-on-a-chip, is an advanced technology that integrates a microfluidic system including channels, mixers, reservoirs, pumps and valves on a micro scale chip and can manipulate very small sample volumes of fluids. While several flow control concepts for microfluidic devices have been developed to date, here flow control concepts based on thermally responsive polymer solutions are presented. In particular, flow control concepts base on the thermally triggered reversible phase change of aqueous solutions of the polymer Pluronic will be discussed. Selective heating of small regions of microfluidic channels, which leads to localized gel formation in these channels and reversible channel blockage, will be used to control a membrane valve that controls flow in a separate channel. This new technology will allow generating inexpensive portable bioanalysis tools where microvalve actuation occurs simply through heaters at a constant pressure source without a need for large external pressure control systems as is currently the case. Furthermore, a concept for controlled cross-channel transport of particles and potentially cells is presented that relies on the continuous regeneration of a gel wall at the diffusive interface of two co-streaming fluids in a microfluidic channel. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

No description available.

No description available.