Elastic formulation evaluation

A suitable animal model can be used for in vivo pharmacokinetic assessment of a topically applied elastic liposome formulation. Rats and mice are most common but tend to provide an over-estimate compared to human skin as the skin is more permeable. Piglets provide a closer approximation to human skin permeability and have been used for some evaluations of elastic liposomes (9, 34). Appropriate animal ethics committee approval is required. A generalised protocol is outlined in the following section but there can be considerable variation depending on the complexity of information sought, i.e., if the determination of distribution into tissues is required in addition to absorption into the circulation ... 

Measurement of C requires more sophisticated and expensive rheometers and more involved experimental procedures. It must be remembered that experiments have to he carried out below the critical strain value (see Sec II), or in [he region of linear viscoelastic behavior. This region is determined by measuring the complex modulus G as a function of the applied strain at a constant oscillation frequency (usually 1 Hz). Up to 7, G does not vary with the strain above Yr, G tends to drop. The evaluation of oscillatory parameters is more often restricted to product formulation studies and research. However, a controlled-fall penetrometer may be used to compare the degree of elasticity between different samples. Creep compliance and creep relaxation experiments may be obtained by means of this type of device. In fact, a penetrometer may be the only way to assess viscoeIa.sticity when the sample does not adhere to solid surfaces, or adheres too well, or cures to become a solid or semisolid. This is the case of many dental products such as fillings, impression putties, sealants, and cements. 

The present study shows that It is possible to evaluate the variability of statically determinate and statically indeterminate structures due to spatial variation of elastic properties without resort to finite element analysis. If a Green s function formulation is used, the mean square statistics of the indeterminate forces are obtained in a simple Integral form which is evaluated by numerical methods in negligible computer time. It was shown that the response variability problem becomes a problem Involving only few random variables, even if the material property is considered to constitute stochastic fields. The response variability was estimated using two methods, the First-Order Second Moment method, and the Monte Carlo simulation technique. 

Cohesive failure was shown to arise for currently-used commercial PU sealants under extreme conditions of combined water and heat. A formulation was developed for a two-component PU sealant which was resistant to cohesive failure under prolonged exposure to combined water and heat. The newly-developed sealant exhibited retention of TS, hardness and elastic recovery after prolonged 70C water immersion. A test package was designed for evaluation of cohesion under these conditions. 12 refs. 

In one study, the formulation efficiency of several direct compression materials was evaluated using instrumented press methodology.It was found that subtle changes in the structure of the component particles could lead to the observation of significantly different behaviors upon compression. The tablet hardness and compressibility of differently sourced sucrose materials, obtained at comparable compressional forces, was found to vary significantly with the source of the compound. To quantitative the results, an elastic recovery index was defined, and it was found that the indices of direct compressible materials were lower than those of poorly compressible powders. 

S.P. Harvinder, U. Puneet, K.T. Ashok, J. Subheet, Elastic hposomal formulation for sustained dehvery of colchicine In vitro characterization and in vivo evaluation of anti-gout actiwity, AAPS PharmSci. Tech., 11 54-64,2009. 

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