Biological surfaces show a enormous variety of functional, three-dimensional structures in the micro-dimension. On plant surfaces epicuticular waxes form hydrophobic, crystalline structures in form of e.g. thin layers, tubules, threads or platelets. Most plant waxes are complex mixtures, composed of aliphatic components as primary or secondary alcohols, aldehydes and fatty acids (1).
However, in most waxes only one- or two compounds are responsible for the building of the 3-D structures. For the development of microstructured technical surfaces with non-toxic biomaterial we used different single wax compounds and compound mixtures, and their ability to build 3-D structures by self-assembly. Different substrate characters (polarity and crystallinity) were used to influence the preferred crystal growth direction and the pattern of crystal arrangement.
SEM and AFM have been used to characterise the structures. Waxes have been separated from plant surfaces by dissolving them in chloroform, followed by chemical analysis and re-crystallisation from the solution on different substrates. Additionally wax recrystallisation on technical surfaces was studied after applying waxes by physical vapour deposition. The later method resulted in homogenous distributions of the wax structures on the substrates. Single compound crystals, e.g. of octacosan-1-ol were successfully recrystallized, whereas tubules, which are composed of two different compounds did not reassemble with this technique. This problem was overcome by heating of the substrates, approximately 10° C below the specific melting point of the substances, to mobilise the deposited molecules for reorganisation.
Microstructured surfaces could be used as templates for the development of technical biomimetic surfaces. The range of application includes also some lab on a chip applications. Recrystallisation of natural plant waxes resulted in systems of defined substrates and plant waxes, in the same morphology and chemical composition as know from the plant surfaces. These defined systems could be used for e.g. analysis of efficiency in plant nutrients application performed under controlled and reproduce able conditions.
(1) For literature see: www. nees.uni-bonn.de
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