Dissolution models

Fig. 8.2 Strain-generated active path mechanisms, (a) Often referred to as the film rupture model and (b) the slip step dissolution model. In both cases growth is by dissolution film rupture is the rate controlling step, not the mechanism of crack growth...

In vitro dissolution was virtually complete after 6-8 hr. Since the plot of cumulative drug release versus time is hyperbolic, the authors attempted to fit the data to the Higuchi matrix dissolution model (116,117), which predicts a linear correlation between cumulative drug release and the square root of time. Linearity occurred only between 20 and 70% release. 

Narasinham, B Peppas, N, A, The Physics of Polymer Dissolution Modeling Approaches and Experimental Behavior, Vol, 128, pp. 157-208,... 

The boundary conditions for this early dissolution model included saturated solubility for HA at the solid surface (Cha ) with sink conditions for both HA and A at the outer boundary of a stagnant film (Cha = Ca = 0). Since diffusion is the sole mechanism for mass transfer considered and the process occurs within a hypothesized stagnant film, these types of models are colloquially referred to as film models. Applying the simplifying assumption that the base concentration at the solid surface is negligible relative to the base concentration in the bulk solution (CB CB(o)), it is possible to derive a simplified scaled expression for the relative flux (N/N0) from HPWH s original expressions ... 

Other researchers used flow between two parallel plates as the experimental and theoretical system to incorporate diffusion plus convection into their dissolution modeling and avoid film model approximations [10]. Though they did not consider adding reactions to their model, these workers did show that convection was an important phenomenon to consider in the mass transfer process associated with solid dissolution. In fact, the dissolution rate was found to correlate with flow as... 

Figure 4 Dissolution model for multicomponent mixtures. (From Ref. 19.)...

In an effort to modernize the multicomponent dissolution HMD dissolution model, Neervannan, Dias, Southard, and Stella (NDSS) adopted the flow-... 

Figure 6 (a) Two-component noninteracting slab dissolution model, (b) Refined two-... 

Particle dissolution models, which presume spherical monodisperse particle size, inadequately depict the complexity of typical pharmaceutical powders. 

It is possible to derive a simple particle dissolution model where diffu-sional film thickness is not explicitly required. However, the boundary layer concentration profile derived from this model will extend for distances which cover an order of magnitude of the initial particle radius. 

ATK Lu, ME Frisella, KC Johnson. Dissolution modeling Factors affecting the dissolution rates of polydisperse powders. Pharm Res 10 1308-1314, 1993. 

The Johnson dissolution models described above postulate that h varies linearly with partide size up to a certain value, beyond which h remains unaltered. This assumption encompasses the differences in the release kinetics for both small and large particles. 

A dissolution model that takes in account the change in particle number and the polydisperse nature of the powder was proposed by de Almeida et al. [25]. The following dissolution equations were used to calculate the decrease in weight of solids with time ... 

Figure 7 (a) Sartorius absorption model (b) Sartorius dissolution model, a, Plastic syringe b, timer c, safety lock d, cable connector e, silicon tubes f, silicon-O-rings g, metal filter h, polyacryl reaction vessel. 

Figure 9 Scheme of in vitro dissolution model according to Strieker. Source From Ref. 28. 

This mechanism can be related to the formal dissolution model proposed by Gabrlelll et al (25) in terms of faradalc impedance. 

Origin of rounded forms Growth model Dissolution model... 

A more general theoretical approach for dissolution modeling called the Film-Model Theory was postulated by Nernst (1904) and expanded upon by Brunner (1904) in an effort to deconvo-lute the components of the dissolution constinIBoth Nernst and Brunner made the following assumptions ... 

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