Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2004. / "September 2004." / Includes bibliographical references. / (cont.) biochemical and morphological properties in the pretreated group. Finally, in order to mimic capillary structure cardiac fibroblasts and myocytes were co-cultured on a scaffold with a parallel channel array that was perfused with culture medium supplemented with synthetic oxygen carrier (PFC emulsion). Presence of the PFC emulsion resulted in significantly higher cell density and improved contractile properties compared to the constructs cultivated in the culture medium alone, by increasing total oxygen content and effective diffusivity. / Heart disease is the leading cause of death in the Western world. Tissue engineering may offer alternative treatment options or suitable models for studies of normal and pathological cardiac tissue function in vitro. Current tissue engineering approaches have been limited by diffusional oxygen supply, lack of physical stimuli and absence of multiple cell types characteristic of the native myocardium. We hypothesized that functional, clinically sized (1-5 mm thick), compact cardiac constructs with physiologic cell densities can be engineered in vitro by mimicking cell microenvironment present in the native myocardium in vivo. Since cardiac myocytes have limited ability to proliferate we developed methods of seeding cells at high densities while maintaining cell viability. Cultivation of cardiac constructs in the presence of convective-diffusive oxygen transport in perfusion bioreactors, maintained aerobic cell metabolism, viability and uniform distribution of cells expressing cardiac markers. To improve cell morphology and tissue assembly cardiac constructs were cultivated with electrical stimulation of contraction in a physiologically relevant regime. Electrical stimulation enabled formation of tissue with elongated cells aligned in parallel and with organized ultrastructure remarkably similar to the one present in the native heart. To investigate the effect of multiple cell types on the properties of engineered cardiac tissue cardiac fibroblasts and cardiac myocytes were cultivated synchronously, separately or serially (pretreatment of scaffolds with fibroblasts followed by the addition of myocytes). Presence of fibroblasts remarkably improved contractile response of the engineered cardiac constructs with the superior / by Milica Radisic. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1997. / Includes bibliographical references. / by Russell Clay. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, February 2010. / Cataloged from PDF version of thesis. / Includes bibliographical references. / Ink jet printing is a demanding application that requires carefully formulated inks in order to quickly and reliably produce high-quality printed images. Although ink jet inks are currently produced via an aqueous process, supercritical fluids (SCF) and gas-expanded liquids (GXL) present alternative processing media for particle coating operations that may offer significant benefits with respect to the production of polymer-encapsulated pigment particles for these inks. The main thesis objective is the demonstration and analysis of a particle size reduction and encapsulation process which takes place in CO₂-expanded acetone and produces colloidal carbon black particles. These particles should be uniformly coated with functionalized hydrophobic resins such that they are easily redispersed in water or solvent to form stable nanoparticle dispersions suitable for use in ink jet inks. A prototype size reduction and encapsulation system has been constructed based on a high-pressure stirred reaction vessel designed to operate at pressures up to 200 bar (3000 psi). The prototype vessel has a fluid volume of 1 liter with a multidisc agitator capable of rotating at more than 3400 RPM. Pigment particles are initially milled in a solution of non-aqueous solvent and dissolved dispersing resin. Size reduction is achieved within the apparatus via the grinding action of 1.2 mm spherical ceramic media contacting the micron-size pigment particles. As milling progresses, high-pressure CO₂ is slowly introduced to the vessel; the CO₂ acts as an anti-solvent, lowering polymer solubility and driving adsorption of the dispersing resin onto the pigment particles as new surface area is exposed. / (cont.) After encapsulation is complete, the system is flushed with CO₂ and the product particles are retained as a dry powder in a high-pressure filter. The solvent-free particles are then recovered by venting the system to atmospheric pressure, and subsequently re-dispersed in water for analysis in inks. The apparatus under investigation provides a new process approach to particle size reduction and coating that affords greater freedom in ink formulation, while offering a path to improved ink quality and possible cost savings in a highly competitive market. Specifically, the use of CO₂-expanded liquids enables the deposition of hydrophobic polymers on the surface of particles for use in aqueous inks, thus significantly increasing the variety of polymers that are available for use in these systems. A representative model system of carbon black pigment and benzyl methacrylate/methacrylic acid (BzMA/MAA) copolymer dispersing resins of varying monomer compositions (BzMA/MAA mass ratio = 85/15, 80/20, and 75/25) has been studied in order to assess the feasibility of the high-pressure milling and encapsulation process for ink jet applications. These components have been successfully employed in high-pressure coating operations to produce encapsulated carbon black particles which were recovered as a dry, flowable powder. Dry product particles were redispersed in water to obtain stable aqueous dispersions with a number average particle size of 135-190 nm. / (cont.) In order to guide the selection of appropriate process conditions for the encapsulation system, the high-pressure solid-liquid-vapor phase equilibrium of ternary CO₂-solvent-polymer systems has been probed experimentally and modeled with the PC-SAFT equation of state. Precipitation of BzMA/MAA copolymers generally required a larger overall CO 2 mole fraction - and thus a higher system pressure - for more dilute polymer solutions; however, a minimum in the precipitation pressure was observed for all polymer compositions and temperatures near a CO₂-free polymer mass fraction of 0.03. The ternary systems were characterized by a rapid reduction in polymer solubility over a relatively narrow range of pressure (between 200 psig and 400 psig, depending on the polymer and system temperature); the precipitation pressure increased with increasing temperature and BzMA mass fraction (per polymer mass unit). The PC-SAFT EOS was successfully employed to correlate the phase behavior data by adjusting only two binary interaction parameters; the average relative error associated with the predictions of precipitation pressure for each polymer was 3.7%. Characterization of the encapsulation process also requires knowledge of the thermodynamics and kinetics of polymer adsorption onto particle surfaces from CO₂- expanded solvents. To this end, interactions with the particle surface have been investigated through the collection and correlation of experimental adsorption isotherm data. / (cont.) Adsorption of 85/15 and 75/25 BzMA/MAA polymers onto carbon black from CO₂-expanded acetone was measured at 35°C and pressures between 0 psig and 300 psig over a range of mixture compositions relevant to particle coating operations. Pressurization with CO₂ to pressures up to 200 psig caused a decrease in the amount of polymer adsorbed on particle surfaces, but further increases in pressure resulted in higher polymer loadings. In the case of 75/25 BzMA/MAA polymer, the polymer loading increased significantly between 200 psig and 300 psig as the solubility limit was approached or exceeded. Our results are valuable not only in providing quantitative data to facilitate process optimization, but also in offering a more fundamental understanding of interactions among the pigment particles, the dispersant resin, and the gas-expanded liquid media. Such information is important to both process and product design. / by Scott M. Paap. / Ph.D.

Thesis (Sc.D.) Massachusetts Institute of Technology. Dept. of Chemical Engineering, 1946. / Bibliography: leaves 141-143. / by Charles Nelson Satterfield. / Sc.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1996. / Includes bibliographical references (v. 2, leaves 815-882). / by Vikki J. Vlastnik. / Ph.D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemical Engineering, 2015. / Cataloged from student-submitted PDF version of thesis. / Includes bibliographical references (pages 198-214). / Crystallization is a key unit operation in the pharmaceutical industry. Control of crystallization processes can be challenging when undesirable phenomena such as particle attrition and breakage occur. This thesis describes the controlled crystallization of pharmaceuticals and amino acids for more efficient manufacturing processes and better efficacy of products. Crystallization equipment is designed so that (1) the undesirable phenomena do not occur at all, and/or (2) the phenomena that do occur are carefully controlled. One key strategy is to exploit dual-impinging jets and multiphase flow to decouple nucleation and growth so that they can be individually controlled. Various configurations of micromixers were designed to provide controlled nucleation. Based on the dual-impinging-jet (DIJ) configuration, a physical explanation was provided for the discovery that a cooling micromixer can generate small crystals of uniform size and shape. An alternative design replaces the micromixing with the application of ultrasonication to decouple nucleation and flow rates. Based on these nucleation methods, a novel continuous crystallizer is designed where the slurry flow is combined with an air flow to induce a multiphase hydrodynamic instability that spontaneously generates slugs where the crystals continue to grow. These slugs are well-mixed without having the mixing blades in traditional crystallizer designs that induce undesirable uncontrolled crystallization phenomena. Another key strategy is to increase the degrees of freedom in the dynamic operation of the crystallizers. In the slug-flow continuous crystallizer, extra degrees of freedom for control of the crystal growth are created by spatially varying the temperature profile along the tube. In a semi-continuous crystallizer configuration, continuous seeding using a DIJ mixer is combined with growth rate control in a stirred tank to experimentally demonstrate the manufacture of uniform-sized crystals. In addition, temperature-cycling experiments are designed in batch crystallizers to substantially change crystal shape with only a small number of cycles. Experimental validation confirms that the proposed crystallizer designs reduce production time and equipment cost by orders of magnitude while suppressing secondary nucleation, attrition, and aggregation/agglomeration-dominant but undesired phenomena that worsen the ability to control the properties of crystals produced by most existing crystallizer designs. / by Mo Jiang. / Ph. D.

Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1930. / Includes bibliographical references (leaves 224-227). / by Victor Claude Smith. / Sc.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1986. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Bibliography: leaves 156-158. / by Ali Nadim. / Ph.D.

Massachusetts Institute of Technology. Dept. of Chemical Engineering. Thesis. 1965. Sc.D. / Sc.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2006. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Includes bibliographical references (p. [137]-143). / Tracking the Brownian motion of colloids was first used about a hundred years ago to demonstrate the molecular nature of matter. Today's colloidal scientists perform particle tracking experiments to assess the structural and mechanical properties of complex materials at a micron length scale. Indeed, the dynamics of micron sized probe particles embedded in a material can be related to the local mechanical response of the system. This probing technique, called microrheology, has received much interest in the last few decades due to the importance of a materials local properties in its function and its macro-scale characteristics. These new assessments are especially relevant in soft matter sciences such as biophysics. Video microscopy particle tracking is an easy technique to implement experimentally. Movies of the fluctuating particles in a sample are recorded and analyzed off-line using custom algorithms. For this reason, it is widely used in studies of soft matter properties and in fluid dynamics. However, behind this apparent simplicity lie a number of subtle limitations that can alter significantly the validity of the measurements. The focus of the parts of this thesis is an exhaustive characterization of the errors incurred in the standard video microscopy particle tracking setup. / (cont.) Detailed understanding of these errors led to new methods to circumvent some of the intrinsic limitations. The trajectories extracted from particle tracking are used to compute the means-squared displacement that characterizes the dynamics of the probe particles. This measurement suffers from two kinds of limitations: the finite spatial resolution in the particle localization and statistical uncertainties. The source of localization errors was separated into two separate contributions. A "static error" arises in the position measurements of immobilized particles. A "dynamic error" comes from the particle motion during the finite exposure time that is required for visualization. We calculated the propagation of these errors on the mean-squared displacement and examined the impact of our analysis on theoretical model fluids used in biorheology. These theoretical predictions were verified for purely viscous fluids using simulations and a multiple particle tracking technique performed with video microscopy. We showed that the static contribution could be confidently eling the sampling design, we derived estimators for the mean and variance of particle's dynamics that are independent, under well-efined conditions, of the peculiar statistics of the measurement output. / (cont.) These estimators serve to quantify a material heterogeneity. Having gained a full characterization of the technique, we applied video multiple particle tracking to study a complex time-evolving system of self-assembling peptides. This material undergoes a transition from a purely viscous solution to an elastic hydrogel through the molecular assembly of the peptides into a fibrous network. We used the oligo-peptide KFE8 as a model self-assembling peptide and assessed the dependency of the gelation kinetics with the pH of the solution. We were able to develop a theoretical model for this dependency by using the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory for the interaction between the peptides. / by Thierry Savin. / Ph.D.