Basic considerations in the dermatokinetics of topical formulations

Assessing the bioavailability of drug molecules at the site of action provides better insight into the efficiency of a dosage form. However, determining drug concentration in the skin layers following topical application of dermatological formulations is a great challenge. The protocols followed in oral formulations could not be applied for topical dosage forms. The regulatory agencies are considering several possible approaches such as tape stripping, microdialysis etc. On the other hand, the skin bioavailability assessment of xenobiotics is equally important for topical formulations in order to evaluate the toxicity. It is always possible that drug molecules applied on the skin surface may transport thorough the skin and reaches systemic circulation. Thus the real time measurement of molecules in the skin layer has become obligatory. In the last two decades, quite a few investigations have been carried out to assess the skin bioavailability and toxicity of topical/dermatological products. This review provides current understanding on the basics of dermatokinetics, drug depot formation, skin metabolism and clearance of drug molecules from the skin layers following application of topical formulations

Development of GMR eddy current sensors for high temperature applications and imaging of corrosion in thick multi-layer structures

Detection and quantification of corrosion damage in aircraft structures is essential for condition based maintenance strategies and for the extension of the life of the aircraft. The eddy current technique was found to be one of the most favorable methods for the determination of thickness loss due to corrosion because this technique is capable of detecting corrosion in several layers of a multi-layer structure. A limitation for the eddy current technique is the eddy current penetration depth. Decreasing the analyzing frequency can increase the eddy current penetration depth. Giant Magneto Resistive sensors are highly sensitive magnetic field sensors, they have better signal to noise ratio for very low frequencies than conventional coils systems. Moreover these sensors are very efficient over a broad frequency range. Hence they allow the use of the multifrequency concept for multi-layer structures of higher thickness. Images of corrosion damage can be generated separately for different layers of a multi-layer structure by using deep penetrating GMR based eddy current probes and data acquired from the multi-frequency eddy current testing. This paper describes the design of deep penetrating GMR based eddy current probes and their application for generating images of corrosion in different layers with the help of a MAUS scanner