Nowadays people who suffer from deafness are able to hear again with the help of cochlear implants. Nevertheless, researchers work on enhancing this process focusing mainly on the optimization of the electrode-nerve contact in the inner ear. One option is to install biodegradable polymer fibers as an artificial nerve guidance on the surface of the implant. For this purpose polyglycolide (PGA) and poly-ε caprolactone (PCL) have already shown great potential in biomedical sciences. Firstly, the fibers are coated with components of the extracellular matrix (ECM), like laminin (LAM) or heparan sulfate (HS), to create a cell-friendly environment and to enhance the ingrowth of the implant after insertion. Heparan sulfate is well-known as an anticoagulant in clinical applications and is, for example, used in the eyedrops Cacicol® to regenerate and heal the cornea. Moreover, also cytokines, like the brain derived neurotrophic factor (BDNF), should be immobilized on the surface. Released BDNF from the fibers can stimulate the residual spiral ganglion neurons (SGNs) in the inner ear to grow neurites towards the implant, thus enhancing their interaction and finally the hearing process. It has already been shown, that BDNF is capable to improve neuronal outgrowth. In addition, the biomolecules of the ECM support the guidance of the neurites along the polymer fibers. As HS is able to bind growth factors, the fibers are coated with HS and BDNF simultaneously to mimic the natural function of the body.
In this work the polymer fibers are first functionalized with aminogroups via aminolysis using ethylenediamine. Afterwards the ECM molecules are linked covalently to the functionalized fibers using coupling and stabilizing agents. BDNF is then immobilized on the precoated fibers and released over time. It is detected via ELISA. Furthermore, cell culture investigations with fibroblasts and SGNs show promising results.
 YOO, H. S., KIM, T. G., PARK, T. G.; Adv. Drug Deliv. Rev.; 2009; 61; 12; 1033–1042.
 RABENSTEIN, D. L.; Nat. Prod. Rep.; 2002; 19; 1–4; 312–331.
 WARNECKE, A., SASSE, S., WENZEL, G. I., HOFFMANN, A., GROSS, G., PAASCHE, G., SCHEPER, V., REICH, U., ESSER, K. H., LENARZ, T., STÖVER, T., WISSEL, K.; Hear. Res.; 2012; 289; 1–2; 86–97.
 PIEPER, J. S., VAN WACHEM, P. B., VAN LUYN, M. J. a, BROUWER, L. a., HAFMANS, T., VEERKAMP, J. H., VAN KUPPEVELT, T. H.; Biomaterials; 2000; 21; 1689–1699.