Michael E. Mullins

Creation of highly aligned electrospun poly-L-lactic acid fibers for nerve regeneration applications

Aligned, electrospun polymer fibers have shown considerable promise in directing regenerating axons in vitro and in vivo. However, in several studies, final electrospinning parameters are presented for producing aligned fiber scaffolds, and alignment where minimal fiber crossing occurs is not achieved. Highly aligned species are necessary for neural tissue engineering applications to ensure that axonal extension occurs through a regenerating environment efficiently. Axonal outgrowth on fibers that deviate from the natural axis of growth may delay axonal extension from one end of a scaffold to the other. Therefore, producing aligned fiber scaffolds with little fiber crossing is essential. In this study, the contributions of four electrospinning parameters (collection disk rotation speed, needle size, needle tip shape and syringe pump flow rate) were investigated thoroughly with the goal of finding parameters to obtain highly aligned electrospun fibers made from poly-L-lactic acid (PLLA). Using an 8 wt% PLLA solution in chloroform, a collection disk rotation speed of 1000 revolutions per minute (rpm), a 22 gauge, sharp-tip needle and a syringe pump rate of 2 ml h(-1) produced highly aligned fiber (1.2-1.6 microm in diameter) scaffolds verified using a fast Fourier transform and a fiber alignment quantification technique. Additionally, the application of an insulating sheath around the needle tip improved the rate of fiber deposition (electrospinning efficiency). Optimized scaffolds were then evaluated in vitro using embryonic stage nine (E9) chick dorsal root ganglia (DRGs) and rat Schwann cells (SCs). To demonstrate the importance of creating highly aligned scaffolds to direct neurite outgrowth, scaffolds were created that contained crossing fibers. Neurites on these scaffolds were directed down the axis of the aligned fibers, but neurites also grew along the crossed fibers. At times, these crossed fibers even stopped further axonal extension. Highly aligned PLLA fibers generated under optimized electrospinning conditions guided neurite and SC growth along the aligned fibers. Schwann cells demonstrated the bipolar phenotype seen along the fibers. Using a novel technique to determine fiber density, an increase in fiber density correlated to an increase in the number of neurites, but average neurite length was not statistically different between the two different fiber densities. Together, this work presents methods by which to produce highly aligned fiber scaffolds efficiently and techniques for assessing neurite outgrowth on different fiber scaffolds, while suggesting that crossing fibers may be detrimental in fostering efficient, directed axonal outgrowth.

Varying the diameter of aligned electrospun fibers alters neurite outgrowth and Schwann cell migration

Aligned, electrospun fibers have shown great promise in facilitating directed neurite outgrowth within cell and animal models. While electrospun fiber diameter does influence cellular behavior, it is not known how aligned, electrospun fiber scaffolds of differing diameter influence neurite outgrowth and Schwann cell (SC) migration. Thus, the goal of this study was to first create highly aligned, electrospun fiber scaffolds of varying diameter and then assess neurite and SC behavior from dorsal root ganglia (DRG) explants. Three groups of highly aligned, electrospun poly-l-lactic acid (PLLA) fibers were created (1325+383 nm, large diameter fibers; 759+179 nm, intermediate diameter fibers; and 293+65 nm, small diameter fibers). Embryonic stage nine (E9) chick DRG were cultured on fiber substrates for 5 days and then the explants were stained against neurofilament and S100. DAPI stain was used to assess SC migration. Neurite length and SC migration distance were determined. In general, the direction of neurite extension and SC migration were guided along the aligned fibers. On the small diameter fiber substrate, the neurite length was 42% and 36% shorter than those on the intermediate and large fiber substrates, respectively. Interestingly, SC migration did not correlate with that of neurite extension in all situations. SCs migrated equivalently with extending neurites in both the small and large diameter scaffolds, but lagged behind neurites on the intermediate diameter scaffolds. Thus, in some situations, topography alone is sufficient to guide neurites without the leading support of SCs. Scanning electron microscopy images show that neurites cover the fibers and do not reside exclusively between fibers. Further, at the interface between fibers and neurites, filopodial extensions grab and attach to nearby fibers as they extend down the fiber substrate. Overall, the results and observations suggest that fiber diameter is an important parameter to consider when constructing aligned, electrospun fibers for nerve regeneration applications.

The preparation and analysis of zeolite ZSM-5 membranes on porous alumina supports

Abstract Zeolite ZSM-5 particles formed in the synthesis solution assume a negative charge due to electrical double layer effects. Therefore, we investigated the use of electrophoretic techniques in addition to the hydrothermal synthesis method to attract the zeolite particles to the substrate surface before they precipitate out of the solution. This electrophoretic driving force produces a thin, continuous zeolite ZSM-5 membrane on the porous substrate. This research was conducted in order to produce zeolite membranes on a tubular support that could effect continuous gas phase separations. The thickness of membranes can be controlled by varying the precursor concentration, applied potential, and synthesis time. The selectivity of n -butane over iso -butane is observed on every membrane. The membranes were characterized by using scanning electron microscopy (SEM), X-ray diffractometry (XRD), and energy dispersive X-ray spectrometry (EDX).

The effect of carbon morphology on the combustion synthesis of titanium carbide

Titanium carbide may be readily produced in high purity via direct reaction between the solid phases of titanium and carbon in the process of combustion synthesis, also known as self-propagating high-temperature synthesis (SHS). The high temperatures generated by this exothermic reaction (

An overview of compiling, critically evaluating, and delivering reliable physical property data from AIChE DIPPR® Projects 911 and 912

Abstract The goal of AIChE DIPPR® Projects 911 and 912 is to develop a comprehensive, consolidated database of physical properties for those chemical species which are regulated by various agencies of the US government, and are important to the chemical process industry. Environmental, safety and health (ESH) properties are the prime focus of the data collection and validation efforts of the two projects. Project 911, a database compilation effort, collects data for 700 chemicals and 55 physical properties. These properties include aqueous solubility, viscosity, vapor pressure, flash point, octanol–water partition coefficient, and bioconcentration factor. Project 912 is a complementary effort which focuses on the review of existing physical property prediction techniques and developing new estimation algorithms where none exist. Limited mixture data (e.g., infinite dilution vapor/liquid equilibrium measurements) are also being researched. Work is continuing on the critical assessment of the quality of data within the Project 911 database. Available literature data are compiled and categorized according to quality. Recommended data values and correlation statistics are provided as part of the Project 911 software product. To automate the data evaluation effort, a computerized Statistical Process Control (SPC) data review system has been designed. The Project 911 database is being developed to support engineering and regulatory calculations and to work in tandem with the estimation protocols established by Project 912 to predict properties for chemicals not readily available through literature sources.

Henry's law constants derived from equilibrium static cell measurements for dilute organic-water mixtures

Abstract The relationship of pressure and composition in the Henry’s law regime has been experimentally measured in an equilibrium static cell for a set of binary organic–water mixtures. The solutes range from hydrophilic materials, such as alcohol to extremely hydrophobic components, such as toluene and 1,2-dichloroethane. The goal of this study is to determine the effective concentration range over which Henry’s law reasonably approximates the gas–liquid partitioning. With the goal of obtaining accurate values of Henry’s law constant, several methodologies are critically compared for the aqueous solutes examined experimentally. The apparatus employed can determine gas–liquid partitioning coefficients through a variety of methods including direct phase concentration ratios, equilibrium partitioning in closed systems (EPICS), and application of the coexistence equation for γ ∞ . Results to date indicate a more complex d P /d x behavior in the dilute region than previously assumed; and Henry’s law constant may not strictly apply to hydrophobic materials until the solute concentration is so low that analytical detection is problematic.

Estimation of Henry's constants for aqueous systems at elevated temperatures

Abstract The treatment and removal of dilute organic contaminants from water require methods for estimating the vapor–liquid equilibrium behavior of these mixtures. Highly hydrophobic solutes may exhibit a maximum in Henrys law constant that is difficult to predict using traditional activity coefficient models. This paper examines the application of an activity coefficient model fitted specifically for dilute aqueous systems (UNIFAC-ENV) to make predictions for the infinite dilution activity coefficients at ambient conditions. The use of activity coefficient based mixing rules for equations of state to extend the range of the UNIFAC-ENV predictions to the temperatures typical for steam stripping conditions (80–140°C) is also evaluated. Application of this approach to Henrys law data for trichloroethylene in water indicates that these models require temperature dependent interaction coefficients to accurately predict the highly non-ideal solution behavior observed.

Quantitative review and delivery of reliable physical property data: development of DIPPR® Environ 2001™ database and estimation software

Abstract The goal of American Institute of Chemical Engineers Design Institute for Physical Property Data (AIChE DIPPR ® ) Project 911 has been to develop a comprehensive database of physical properties for chemicals that are regulated by various agencies of the United States government, and are important to the chemical process industry. Project 911 collects and quantitatively reviews environmental, safety and health (ESH) data for over 1000 chemicals and 56 physical properties. Project 912 analyzes and uses published estimation methods and develops new algorithms to generate predicted values where experimental data do not exist. Physical properties within Project 911 include aqueous solubility, octanol–water partition coefficients, vapor pressure, aquatic toxicity, bioconcentration factor, flash point, and activity coefficients at infinite dilution. Data are reviewed qualitatively for purity of chemicals and type of experiment, reported precision of measured data, and agreement with other investigators. An extensive quantitative review of the Project 911 database uses statistical quality control (SQC) techniques, where individual data points are compared to the highest rated data value from the qualitative review. The SQC review also tests data values using thermodynamic relationships. Recommended data values and estimation techniques are delivered to the user by a new Visual Basic™ software product, Environ 2001™. Results to date show an error rate of 1.5% for nearly 130,000 data values in the Project 911 database.

Gelation Point In Borosilicate Sols From Rheological Experiments

Dynamic oscillatory experiments are used to monitor the gelation of the borosilicate systems prepared through the sol-gel process from metal alkoxides. The rheological experiments show that tan δ = G”/G’ is independent of frequency at the gel point in agreement with the results of others on organic gelling systems. The dynamic moduli at the gel point followed power-law behavior with respect to frequency. The power-law exponent is found to be ∼0.70. The apparent fractal dimension, dp, of the network cluster at the gel point is determined. The d F values for the samples ranged from 2.5 to 3.8 depending on the final structure of the evolved products at the gel point. The large values (d F > 3) exclude a simple geometric interpretation of the results. The effect of processing parameters, such as composition of reactants and temperature, on the resulting microstructures near the gel point is discussed.

Optical waveguides using PDMS-metal oxide hybrid nanocomposites

Development of passive and active polymer based optical materials for high data rate waveguide routing and interconnects has gained increased attention because of their excellent properties such as low absorption, cost savings, and ease in fabrication. However, optical polymers are typically limited in the range of their refraction indices. Combining polymeric and inorganic optical materials provides advantages for as development of nano-composites with higher refractive indices with the possibility of being used as an active optical component. In this paper a new composite material is proposed based on polymer-metal oxide nano-composites for use as optical wave guiding structures and components. PDMS (Polydimethylsiloxane) is utilized for the polymer portion while the inorganic material is titanium dioxide. Refraction indices as high as 1.74 have been reported using these composites. For PDMS-TiO2 hybrids, the higher the ratio of titanium dioxide to PDMS, the higher the resulting refractive index. The index of refraction as a function of the PDMS:TiO2 ratio is reported with an emphasis on use as optical waveguide devices. Absorption spectrum of the nano-composites is measured showing low absorption at 850 nm and high absorption in the UV regime for direct UV laser/light curing. Prototype multimode waveguides are fabricated using soft imprint embossing that is compatible with the low viscosity nano-composite material. Cross dimensional shape and profile show the potential for full scale development utilizing the material set.