Elastomeric polymers such as polydimethylsiloxane (PDMS) and polyurethane (PU) unite a broad range of beneficial properties, as a result they can be both, compliant and resilient. Their mechanical robustness, especially towards wear and abrasion, and flexibility at the same time, would make them great candidates for tribological applications. In combination with their good biocompatibility, they appear very well suitable for demanding applications in the human body where space is limited, and varying loads and repeated deformations occur. However, such applications are often limited by the bad frictional performance of PDMS and PU.
To mitigate this undesired behaviour, we apply different bio-macromolecular coatings and combine them with suitable bio-macromolecular lubricants to assess their influence on the friction response of the materials. We compare a facile, non-covalent, dopamine-assisted coating approach to a multi-step, covalent coating strategy employing carbodiimide chemistry and investigate different macromolecules as top-layers.
In a bespoke reciprocating tribology setup, we compare the direct friction response of the coatings under various conditions (varying load, interrupted load, short-term and long-term performance) as well as the friction performance of the coated materials after different application-oriented treatments (after e.g., prolonged storage, sterilizations procedures). To support the findings of these examinations, wear analysis, surface zeta potential measurements, and examinations of the autohesive behaviour, of the flexibility, and of the transparency of uncoated and coated foils are conducted.
We find that the employed coatings, applied via either coating strategy, i.e., dopamine-based or carbodiimide-mediated, clearly improve the friction response of the examined polymers, even over long-term evaluations running for up to one million cycles. However, the dopamine-based coatings appear to suffer distinctly by the applied application-oriented procedures since (mostly) no continuously smooth movement of the dopamine-coated samples could be maintained in the tribological examinations.
In conclusion, we not only provide a detailed comparison of the tribological performance of two (in the biomedical field) frequently applied coating strategies, but also show that such coatings could broaden the medical application range of elastomeric devices. Moreover, the findings presented here can also prove valuable for the development of various (medical) devices, such as bio-sensors, membranes/scaffolds, or nanoparticles, which frequently employ coatings and require sterility and durability for their indented applications while remaining functional.