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Methods for the evaluation of melanin as a sunscreen agent


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Bleasel, Martin Daniel 1999 , 'Methods for the evaluation of melanin as a sunscreen agent', PhD thesis, University of Tasmania.

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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” 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

Item Type: Thesis - PhD
Authors/Creators:Bleasel, Martin Daniel
Keywords: melanin synthesis, melanin characterisation, pseudo-mass spectra, NIST, diffuse reflectance, colour, pseudo-double beam, in vitro SP, Bleasel
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