The Application of Computational Modeling to Pharmaceutical Materials Science
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10/31/2006
3:12 PM
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The Application of
Computational Modeling to Pharmaceutical Materials Science
Carl Wassgren and Jennifer Sinclair Curtis Abstract Computational modeling is a ubiquitous technique in materials science, but until recently this approach has not been widely applied to the drug development process. The formation of particles, their kinematics, and their response to processing stresses are increasingly being studied using computational techniques (computational fluid dynamics and discrete element analysis). These computational techniques can be predictive tools to guide scientists who are designing pharmaceutical dosage forms with specific macroscopic properties. This article gives an overview of the types of computational methods that are used in pharmaceutical materials science and provides examples of their application to some problems from the literature and the authors’ own work. Keywords: biomedical, particle, powder, simulation.
Introduction Particle processes pervade the pharmaceutical industries. Many of these processes have significant opportunities for optimization and productivity enhancements. Reliable modeling and simulation tools can improve critical understanding and design of particle processes, and thus accelerate the achievement of substantial process improvements. Because of dramatic improvements in computer hardware, there has been a rapid global increase in the use of modeling and simulation in the process industries. Improved user interfaces are another factor driving this increase in the application of computational modeling. Thus, commercial simulation packages now require less training so that relatively inexperienced users can use them to good effect. Computational fluid dynamics (CFD) is one such simulation tool.1 CFD is a computational technology that enables the study of flow dynamics, often coupled
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with heat or mass transfer. In CFD, a computational grid is constructed that represents the system or device being analyzed, mathematical equations (mass, momentum, and energy balances) are solved numerically, and the CFD software generates a prediction of the fluid dynamics associated with the system being analyzed. The dynamics of a dispersed particle phase (e.g., a pharmaceutical powder) in conjunction with the fluid can also be modeled. CFD software has been available for more than 20 years, and many commercial CFD packages have been developed. CFD is now an easy-to-use tool with much widespread, global, successful application. For example, a case study on the economic benefits of using CFD in one engineering company concluded that during a six-year period, the benefits achieved generated approximately a sixfold return on the company’s total investment in CFD.2
A more recent approach to modeling pharmaceutical powders employs the discrete element method (DEM).3 In DEM, the fluid phase is typically neglected and the dynamics of individual powder particles are described rather than treating the powder as a continuum. DEM models are especially useful for
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