Mechanistic Investigation of Peptide Sorption and Acylation in Poly(lactic-co-glycolic acid).

The aim of this dissertation is to understand peptide sorption to PLGA, with the goal of stabilizing octreotide against acylation within PLGA. These studies describe the first detailed investigations of peptide sorption to low Mw free-acid PLGA. A new class of inhibitors of the sorption and acylation of a model peptide, octreotide, has been described. Long-term sorption studies indicated that CaCl2 and MnCl2 disrupt peptide sorption to PLGA with the inorganic divalent cation inhibitors translates to inhibition of peptide acylation. The octreotide-PLGA interactions are mostly irreversible in aqueous solution and strongly increase solubility of octreotide in acetonitrile. Only the addition of solvent or 5% SDS resulted in a substantial desorption from PLGA, strongly suggesting the irreversibility is due to hydrophobic interactions or hydrogen-bonding between the peptide and PLGA. The kinetics of peptide sorption to PLGA was studied and well described using a biexponential model. Sorption is reduced at low octreotide concentrations, high ionic strength and low temperature, suggesting polymer mobility plays a critical role in the sorption interaction. Although irreversible, peptide sorption follows Langmuir behavior. Sorption of octreotide decreased as the pH of the solutions tested was decreased toward the pKa of PLGA carboxylates. Reducing the number of total acid end-groups by increasing the PLGA molecular weight also decreased octreotide sorption. These results indicate the critical role of ionized PLGA acid end-groups during the peptide sorption pathway. Quantification of the maximal amount of peptide sorbed at high solution concentration showed this value to be similar to the total number of PLGA acid end-groups for RG502H and RG503H. The low amount of sorption to the higher molecular-weight RG504H is also consistent with peptide partitioning into the polymer phase. Film sectioning after peptide sorption showed a proportional decrease in peptide remaining in the polymer with fraction of film removed. Hence, these results suggest both multilayer adsorption and absorption of peptide to free-acid PLGA.Ph.D.Chemical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/64668/1/asophocl_1.pd

Towards continuously programmable networks

While programmability has been a feature of network devices for a long time, the past decade has seen significant enhancement of programming capability for network functions and nodes, spearheaded by the ongoing trend towards softwarization and cloudification. In his context, new design principles and technology enablers are introduced (Section 7.2) which reside at: (i) service/application provisioning level, (ii) network and resource management level, as well as (iii) network deployment and connectivity level

A parametric model for the changes in the complex valued conductivity of a lung during tidal breathing

Classical homogenization theory based on the Hashin-Shtrikman coated ellipsoids is used to model the changes in the complex valued conductivity (or admittivity) of a lung during tidal breathing. Here, the lung is modeled as a two-phase composite material where the alveolar air-filling corresponds to the inclusion phase. The theory predicts a linear relationship between the real and the imaginary parts of the change in the complex valued conductivity of a lung during tidal breathing, and where the loss cotangent of the change is approximately the same as of the effective background conductivity and hence easy to estimate. The theory is illustrated with numerical examples, as well as by using reconstructed Electrical Impedance Tomography (EIT) images based on clinical data from an ongoing study within the EU-funded CRADL project. The theory may be potentially useful for improving the imaging algorithms and clinical evaluations in connection with lung EIT for respiratory management and monitoring in neonatal intensive care units

Localized Hydration in Lyophilized Myoglobin by Hydrogen–Deuterium Exchange Mass Spectrometry. 2. Exchange Kinetics

Solid-state hydrogen–deuterium exchange with mass spectrometric analysis (ssHDX) is a promising method for characterizing proteins in amorphous solids. Though analysis of HDX kinetics is informative and well-established in solution, application of these methods to solid samples is complicated by possible heterogeneities in the solid. The studies reported here provide a detailed analysis of the kinetics of hydration and ssHDX for equine myoglobin (Mb) in solid matrices containing sucrose or mannitol. Water sorption was rapid relative to ssHDX, indicating that ssHDX kinetics was not limited by bulk water transport. Deuterium uptake in solids was well-characterized by a biexponential model; values for regression parameters provided insight into differences between the two solid matrices. Analysis of the widths of peptide mass envelopes revealed that, in solution, an apparent EX2 mechanism prevails, consistent with native conformation of the protein. In contrast, in mannitol-containing samples, a smaller non-native subpopulation exchanges by an EX1-like mechanism. Together, the results indicate that the analysis of ssHDX kinetic data and of the widths of peptide mass envelopes is useful in screening solid formulations of protein drugs for the presence of non-native species that cannot be detected by amide I FTIR

Localized Hydration in Lyophilized Myoglobin by Hydrogen–Deuterium Exchange Mass Spectrometry. 1. Exchange Mapping

The local effects of hydration on myoglobin (Mb) in solid matrices containing mannitol or sucrose (1:1 w/w, protein:additive) were mapped using hydrogen–deuterium exchange with mass spectrometric analysis (HDX–MS) at 5 °C and compared to solution controls. Solid powders were exposed to D₂O­(g) at controlled activity (<i>a</i>_w) followed by reconstitution and analysis of the intact protein and peptides produced by pepsin digestion. HDX varied with matrix type, <i>a</i>_w, and position along the protein backbone. HDX was less in sucrose matrices than in mannitol matrices at all <i>a</i>_w while the difference in solution was negligible. Differences in HDX in the two matrices were detectable despite similarities in their bulk water content. The extent of exchange in solids is proposed as a measure of the hydration of exchangeable amide groups, as well as protein conformation and dynamics; pepsin digestion allows these effects to be mapped with peptide-level resolution