Melanin Made by Dopamine Oxidation: Thin Films and Interactions with Polyelectrolyte Multilayers

Dissertation / Doktorarbeit von Falk Bernsmann

Introduction:

The present thesis is situated in the field of biomaterial science. In this field, the chemical and physical properties of materials of biological origin like mussel feet, nacre or bone are investigated to understand the relationship between their structure and function. The obtained knowledge can be used to create bioinspired or biomimetic materials in all fields of engineering science and especially in biomedical engineering to design for example artificial soft tissue, implants or drug delivery systems. Due to the immense variety of materials found in nature with properties often superior to man-made materials, biomaterial science has an important influence on technological development. The laboratory Biomatériaux et Ingénierie Tissulaire of Inserm (Institut National de la Santé et de le Recherche Médicale), where this thesis was prepared, is focused on surface modifications for biomedical applications using most often the technique of layer-by-layer (LbL) deposition of polyelectrolytes. Multiple studies have been carried out to characterise the growth of LbL films, to functionalise them by incorporation of biologically active molecules and to control their physical properties. In spite of their versatility, LbL coatings have not found any industrial applications, because as a multi-step procedure their application is very slow and needs sophisticated automation equipment. Hence there is a need to find simple one-step procedures to obtain functional coatings of controlled thickness. One possible method is the deposition of a polymer made by spontaneous oxidation of dopamine as first described by Lee and others. A further examination of this method in the present thesis will reveal that the deposits are made of melanin, a material with several interesting properties:

- Monotonous absorption from the ultraviolet to the infrared and efficient conversion of electromagnetic radiation into heat make melanin a candidate for photodetection, photoprotection or photothermal applications.

- The ability to capture and reduce metal cations can be used to build metal particles, for example for chemical catalysis.

- Melanin plays a role in innate immunity and in neurodegenerative diseases.

- Despite huge efforts, the macromolecular structure of melanin remains unclear.

- Melanin films can easily be formed on virtually any kind of substrate by a biocompatible method.

- These films can be used as a versatile platform for further functionalisation or to build melanin capsules.

Different protocols will be established to build melanin thin films by dopamine oxidation, and the properties of the obtained films will be examined. Furthermore melanin will also be formed in poly(L-lysine)-hyaluronate LbL films leading to an important enhancement of the films' strength by a biocompatible method.

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