Methods for the evaluation of melanin as a sunscreen agent

This thesis outlines the development of four new procedures (1) to synthesise melanins reproducibly, (2) to objectively determine the degree of structural similarity between melanins (3) to use diffuse reflectance to objectively measure skin colour and (4) to evaluate the SPF of melanin and other sunscreen formulations using in vitro methods. 1) Reproducible synthesis of melanins Melanins were synthesised from the precursors adrenaline, dopamine and DL-dopa under controlled conditions. The synthesis procedure outlined was simple and inexpensive and the variables were easily monitored and controlled. The method also allowed for the synthesis of multiple batches of melanin simultaneously in a reproducible fashion. 2) Characterisation of melanin The synthesised melanins were characterised by objective comparison of pyrograms. This was achieved by conversion of the pyrograms to pseudo-mass spectra‚ÄövÑvp and objective comparison using NIST software that us readily and widely available for the comparison of mass spectra. The method indicated that the melanin batches, synthesised by the methods outlined in this thesis and later analysed by the methods described, were synthesised in a reproducible manner. 3) Measurement of skin colour by diffuse reflectance A commercially available spectrophotometer was modified to objectively characterise skin colour and changes in skin colour by the determination of the diffuse reflectance of the skin. This device developed compares favourably with similar devices described in the literature in terms of reproducibility and has the advantages of shorter scan times and a higher resolution. It was simple to construct and at about A$600 was approximately one tenth the cost of similar commercial devices.4) In vitro evaluation of topical sunscreens The aim of this work was to develop an improved technique for the in vitro determination of SPF values of sunscreens. The method outlined differs from other in vitro techniques in that it utilises a standard spectrophotometer operated in a pseudo-double beam mode. The pseudo-double beam mode compared detector responses taken at different gains in single beam mode, and was used to increase the linear range of the spectrophotometer detector, allowing the measurement of SPF values greater than 30 which is difficult using standard in vitro techniques. In theory, SPF values greater than > 1000 could be measured by this method. The value of this technique was subsequently demonstrated when it correctly measured the SPF value of a commercially available sunscreen that had been assigned an incorrect SPF value from earlier in vivo testing. The corrected value was subsequently confirmed by independent in vivo testing.