The realised evaluation of the energetic and electrokinetic characterization of the modified tetraether lipid coatings revealed in particular on the substrate glass a limited range of the parameters. The characteristic properties hydrophilic/hydrophobic or negative/positive charged were not reached in the expected dimension. On the substrate silicone a significant variation can only be achieved concerning the surface charge. This limited range of variation is attributed either to the insufficient number or the reduced functionality of the coupled functional molecules.
Nevertheless the analysis of the antifouling potential of the tetraether lipid coatings and their modifications can be summarized in a positive summary. The reached reduction of the bacterial adhesion in in vitro laboratoy tests is promising. In particular in the field test a clearly improved antifouling of the new layers was presented.
The pure tetraether lipid coating of the materials already shows a continuous reduction of bioadhesion. In the laboratory adhesion reductions are reached of up to 40% in river and drinking water, while in the waste water only a decrease of the adhesion of 20-25% was determined. The different functionalizations lead in the three water models to a varying order of rank in antifouling. For the samples TL PEG, TL negative, TL positive as well as unmodified lipid can be drawn in all aqueous media a positive balance. In contrast to this the samples TL PC and TL CF lead to a successful antifouling result in the infection model. Unmodified TL and the sample TL PEG possess again promising results. The functionalized silicone surfaces confirm the result as far as possible. The sample SIK TL Combi led on silicone to the best antifouling property.
The analysis of the adhesion measurement with single organisms served for the development of a close-to-reality biological model and clarifies a competitive adhesion of several organisms in the mixed culture.
The adhesion potential of the bacteria varies drastically. These differences become additionally interpretable by the strong differences in the surface properties of the bacteria. It is shown that with increasing thickness of surrounding sime layer the number of the adhered bacteria decreases, i.e.
attractively effective physicochemical interactions or protein functions are masked.
The comparative analysis of the results of the laboratory experiments and the field test confirms the acceptance that the selected methodology of in vitro bioadhesion evaluation represents a strong test condition which does not exist in the natural conditions.
In the context of the discussion of the individual surface parameters comparatively the results from the literature and own views of correlation were opposite placed. The result clarifies that the hydrophobicity of the substrate material affects the bacterial adhesion only insignificantly. The only exception are media with high ion strength e.g. peritoneal dialysis liquid, in which hydrophobic interactions increase. The electrostatically effective repulsion becomes more clear on the negatively charged glass surface. The lipid coating of the substrate does not show a relation, which is supported by the leveling of the zeta potentials of the lipid coated and modified substrates.
The experimentally based correlation analysis were supplemented by the representation of the interactions in the form of energy distance functions on the basis of thermodynamically colloid-chemical model conceptions. An own organization of the interaction energies serving in this thesis for the discussion of the bioadhesion took place in the concept identification. This aimed to estimation interactions apart from the classical DLVO theory, acid-base-model as well as steric interaction energy.
The interpretation of the reached antifouling demonstrated that the contribution of van der Waals interactions is comparatively small and independent from the functionalization of the tetraether lipid film.
Compared with van der Waals interactions the effect of electrostatic energgies is somewhat larger and of higher range. While the selected media affect the height of the energy barrier, the functionalization of the tetraether lipids determines the range of the electrostatic interaction. In summary the represented antifouling is not derivable from the DLVO concept by itself. The view of the hydrophobic attraction and the hydrophilic repulsion permits likewise the statement that the prevention of the hydrophobic attraction e.g. by the lipid coating of the silicone surface cannot be interpreted as an effective principle of the antifouling. In contrast to this hydrophilic effects play a more substantial role caused by the lipid coating and its functionalization. The determined repulsion however only works in small distances. On the other
hand the interpretation of the steric interactions reveals a high potential for the antifouling by the example of the functionalized tetraether lipid layers. The selected polyethylene glycol represents as the optimally defined size for the repulsive steric effect. Both effects: the long sterically active polymer chain and the formation of a water barrier with medium chain lengths, combined with functional groups, could be described effectively at the modified glass and silicone. The quantification of the steric interactions illustrates additionally the influence of this energy under the condition of an optimal conformation of the polymers.
In summary and in principle concerning the theoretical description of the bioadhesion it is confirmed that none of the thermodynamic models describes the complex situation satisfyingly and comprehensively.
Finally the specific situation is justified and models are optimized. Regardless it was clearly pointed out that the reduction of the initial bioadhesion can be attributed to acid-base-interaction in particular its hydrophilic and steric energy contribution and thus the creation of a sterically effective water barrier represents an promising antifouling concept.
With respect to the technical application of the tetraether lipid films among other things a patent application was developed. In accordance to the technical goal of the work the successful examination of selected optimized lipid coatings in field tests under material application environments, e.g. in a drinking water dam and a local purification plant took place. Additionally a good biocompatibility and compatibility as implant material could be proven in the context of the necessary functionality examination.
In preparation of the technological scale-up of the coating technology a prototype plant was developed for the coating of tubes. First coating attempts underlined the functionality of the coating principle in the laboratory dimension.
The development of biomimetic surface coatings on the basis of new archaean tetraether lipids represents a promising lipid chemical approach for the establishment of a long-term-stable and biomimetic antifouling concept. The reduction of the initial bioadhesion and thus the reduced biofilm formation is attributed to repulsive hydrophilic and steric nonDLVO interactions. Due to their adjustable specific interactions with the respective medium and the covalent fixability on technical surfaces they can be applied field and process-suited.