Pellet Crack Simulation Bison

In the domain of pharmaceutical formulation, computer simulation is a relatively new concept. This is not to say that it has not been attempted in the past. The mechanical modeling of the tablet compaction process with finite elements was first attempted in 1987 [69] and has been refined since [70, 71]. However, this methodology is based on the assumption that a tablet is a continuum, the properties of which can be defined by constitutive equations. It works well for tablet formulations comprising one ingredient but has little relevance to multicomponent formulations. Recently a combined finite-discrete element method for simulating multicomponent pharmaceutical powder tabletting has been proposed [72]. In this the irregular particle shapes and random sizes of powders are represented as a pseudoparticle assembly having a scaled-up geometry but based on the variations of real powder particles. The method is currently being evaluated and validated against experimental data, but initial results indicate that it does capture the characteristics of the pharmaceutical tableting process [73].

A prerequisite of tablet compaction is the initial filling of the tablet die with powder. Powder packing is one process that has received a great deal of attention, and commercial software for simulating this process is available (Macro Pac, Intelligensys Ltd., UK). This is software able to simulate the packing of multicomponent formulations of particles of any shape and size with a Monte Carlo technique. It is ideal for the simulation of the packing of pharmaceutical formulations into both tablet dies [72] and hard gelatin capsule shells [74]. A simulation of the packing of pellets into a hard gelatin capsule is shown in Figure 28.4.

Figure 28.4 A computer simulation of a size 0 capsule filled with pellets with a size distribution of 0.8 and 1.2 mm.

Pellet Crack Simulation Bison
Figure 28.5 A computer simulation of crack propagation in a tablet film coating containing one population of an inclusion.

Solid inclusions in the form of pigments are often added to tablet film coatings to improve their color and/or their opacity. A potential problem is that of localized cracking around the individual particles or aggregates compromising the release control of the active drug. A simulation of crack propagation in such systems has been developed [75, 76], allowing the investigation of such effects of the addition of a second population of pigments, pigment particle size and size distribution, polymer molecular weight, addition of plasticizers, and many other factors affecting the film coating formulation. Recently this simulation has been made available as MacroCrack from Intelligensys Ltd., UK. A computer simulation of a crack (black line) propagating through a pigmented film coating is shown in Figure 28.5.

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