Evaluation and Method Development to Improve the Adhesion of Electrospun Fibres on Metals for Use in Medical Applications

The aim of this work is to develop an understanding of the adhesion mechanisms between ultrafine fibres and metallic substrates and a method for improving the adhesion at the interface. Electrospinning is used for producing ultrafine fibres, and peel force and resistance, according to DIN EN 29073-3, are used to evaluate the adhesion. Braided stents from nitinol are selected as a medical device, and thermoplastic polyurethane (TPU) for the ultrafine fibres. The stent structure is abstracted into a flat braid and a plate to investigate the influence of parameters such as effective width, surface struc-ture, or wraparound of fibres on adhesion. A fixture for peel tests on cylindrical structures is developed, and the corresponding test method is validated.
Pre-coating of stent structures leads to the highest peel resistance of 642 ± 120 cN/cm and is assessed as a suitable bonding method for producing ultrafine fibre-coated stents. The evaluation shows that interdiffusion is the best practice to increase adhesion, followed by increasing covalent bonds. The wrap-around of ultrafine fibres around stent struts exerts the greatest influence on adhesion. As validation of the results, pre-coated pulmonary stents are pre-coated with an ultrafine fibre coating, are crimped, placed into a catheter and deployed. No delamination or damaging of the interface or fibre coating occurred during the validation tests. Finally, the potential of the technology is evaluated in a business case regarding the development in publicly funded projects and the exploitation of a start-up company called StentCoat GmbH.