Implementation of mechanistic modeling and global sensitivity analysis (GSA) for design, optimization, and scale-up of a roller compaction process.

The pharmaceutical industry has been shifting towards the application of mechanistic modeling to improve process robustness, enable scale-up, and reduce time to market. Modeling approaches have been well-developed for processes such as roller compaction, a continuous dry granulation process. Several mechanistic models/approaches have been documented with limited application to high drug-loaded formulations.

Reduced Crystallization Temperature Methodology for Polymer Selection in Amorphous Solid Dispersions: Stability Perspective.

API-polymer interactions, used to select the right polymeric matrix with an aim to stabilize an amorphous dispersion, are routinely studied using spectroscopic and/or calorimetric techniques (i.e., melting point depression).

Effect of heating rate and kinetic model selection on activation energy of nonisothermal crystallization of amorphous felodipine.

The nonisothermal crystallization kinetics of amorphous materials is routinely analyzed by statistically fitting the crystallization data to kinetic models. In this work, we systematically evaluate how the model-dependent crystallization kinetics is impacted by variations in the heating rate and the selection of the kinetic model, two key factors that can lead to significant differences in the crystallization activation energy (Ea ) of an amorphous material. Using amorphous felodipine, we show that the Ea decreases with increase in the heating rate, irrespective of the kinetic model evaluated in this work.

Origin of two modes of non-isothermal crystallization of glasses produced by milling.

Purpose: To mechanistically explain the origin of two distinct non-isothermal crystallization modes, single-peak (unimodal) and two-peak (bimodal), of organic glasses.

Methods: Glasses of ten organic molecules were prepared by melt-quenching and cryogenic milling of crystals. Non-isothermal crystallization of glasses was monitored using differential scanning calorimetry and powder X-ray diffractometry.

Prediction of onset of crystallization in amorphous pharmaceutical systems: phenobarbital, nifedipine/PVP, and phenobarbital/PVP.

The aim of this work is to determine if a stability testing protocol based on the correlations between crystallization onset and relaxation time above the glass transition temperature (T(g)) can be used to predict the crystallization onsets in amorphous pharmaceutical systems well below their T(g). This procedure assumes that the coupling between crystallization onset and molecular mobility is the same above and below T(g). The stability testing protocol has been applied to phenobarbital, phenobarbital/polyvinylpyrrolidone (PVP) (95/5, w/w), and nifedipine/PVP (95/5, w/w).

Reduced pressure ice fog technique for controlled ice nucleation during freeze-drying.

A method to achieve controlled ice nucleation during the freeze-drying process using an ice fog technique was demonstrated in an earlier report. However, the time required for nucleation was about 5 min, even though only one shelf was used, which resulted in Ostwald ripening (annealing) in some of the vials that nucleated earlier than the others. As a result, the ice structure was not optimally uniform in all the vials.

Different measures of molecular mobility: comparison between calorimetric and thermally stimulated current relaxation times below Tg and correlation with dielectric relaxation times above Tg.

Stability of the amorphous state has been linked to molecular mobility of the matrix; however different techniques may capture different mobility substates. Our previous work suggested that two calorimetric techniques, Isothermal Microcalorimetry (TAM) and MDSC, measured different aspects of mobility with TAM measuring, in part, some faster modes of relaxation in addition to the modes mobilized at T(g). The aim of this work is to compare the relaxation times obtained using Thermally Stimulated Depolarization Current Spectroscopy (TSDC) with calorimetric mobility measured below T(g) and to determine if all measures of relaxation times below T(g) are consistent with relaxation times obtained above T(g) using Dielectric Spectroscopy (DRS).

Role of mechanical stress in crystallization and relaxation behavior of amorphous indomethacin.

Even within an amorphous state, high energy sites can be generated due to sample handling and variations in preparation techniques can result in variation in these high energy sites. Such small handling variations may result in changes in physical properties and physical stability. The aim of this work is to characterize the differences in crystallization tendencies of amorphous Indomethacin arising from minor variations in sample handling.

Correlation between molecular mobility and crystal growth of amorphous phenobarbital and phenobarbital with polyvinylpyrrolidone and L-proline.

The aim of the present study is to determine if the correlation between molecular mobility and crystallization growth rates exists over a broad temperature range from temperatures below the glass transition (T(g)) to temperatures above the glass transition. Phenobarbital and solid dispersions of phenobarbital with PVP and L-proline were studied in this research. Relaxation times below and above the T(g) were measured.

Prediction of onset of crystallization from experimental relaxation times. II. Comparison between predicted and experimental onset times.

Unlabelled: Given a good correlation between onsets of crystallization and mobility above T(g), one might be able to predict crystallization onsets at a temperature of interest far below T(g) from this correlation and measurement of mobility at a temperature below T(g). Such predictions require that: (a) correlation between crystallization onset and mobility is the same above and below T(g), and (b) techniques used to measure mobility above and below T(g) measure the same kind of mobility [(b) demonstrated previously using dielectric and calorimetric techniques]. The objective of present work is to determine whether crystallization onset times couple with relaxation times determined above T(g), and if so to verify predictions made below T(g) (from data above T(g)) with experimental data.

Role of thermodynamic, molecular, and kinetic factors in crystallization from the amorphous state.

Though there is an advantage in using the higher solubility amorphous state in cases where low solubility limits absorption, physical instability poses a significant barrier limiting its use in solid oral dosage forms. Unlike chemical instability, where useful accelerated stability testing protocols are common, no methodology has been established to predict physical instability. Therefore, an understanding of the factors affecting crystallization from the amorphous state is not only important from a scientific perspective but also has practical applications.

Prediction of the onset of crystallization of amorphous sucrose below the calorimetric glass transition temperature from correlations with mobility.

The objective of the present work is to determine if crystallization onset observed for an amorphous solid correlate with relaxation time at temperatures above and below the calorimetric glass transition (T(g)). Crystallization onset of spray-dried and freeze-dried amorphous sucrose were measured calorimetrically. Relaxation times measured in two temperature ranges by different techniques (isothermal calorimetry, dielectric spectroscopy) followed the expected modified Vogel-Tammann-Fulcher (VTF) behavior when extrapolated to a temperature near T(g).

Predictions of onset of crystallization from experimental relaxation times I-correlation of molecular mobility from temperatures above the glass transition to temperatures below the glass transition.

Purpose: Predicting onsets of crystallization at temperatures below T (g), from data above T (g), would require that the correlation between crystallization onset and mobility is same above and below T (g), and the techniques being used to measure mobility above and below T (g) are measuring essentially the same kind of mobility. The aim of this work is to determine if the relaxation times obtained using different techniques (DSC, TAM) below T (g) correlate with relaxation time obtained above T (g) using dielectric spectroscopy.

Methods: Model compounds for this work were chosen based on their varied DeltaH (f), DeltaC (p)(T (g)) and H-bonding in crystalline state vs.

The nonsteady state modeling of freeze drying: in-process product temperature and moisture content mapping and pharmaceutical product quality applications.

Introduction: Theoretical models of the freeze-drying process are potentially useful to guide the design of a freeze-drying process as well as to obtain information not readily accessible by direct experimentation, such as moisture distribution and glass transition temperature, Tg, within a vial during processing. Previous models were either restricted to the steady state and/or to one-dimensional problems. While such models are useful, the restrictions seriously limit applications of the theory.

Heat and mass transfer scale-up issues during freeze drying: II. Control and characterization of the degree of supercooling.

This study aims to investigate the effect of the ice nucleation temperature on the primary drying process using an ice fog technique for temperature-controlled nucleation. In order to facilitate scale up of the freeze-drying process, this research seeks to find a correlation of the product resistance and the degree of supercooling with the specific surface area of the product. Freeze-drying experiments were performed using 5% wt/vol solutions of sucrose, dextran, hydroxyethyl starch (HES), and mannitol.