To improve the electrode-nerve interface of cochlear implants (CI), the role of poly(L-lactide) (PLLA) and poly(4-hydroxybutyrate) (P(4HB)) as potential coating matrices for CI was assessed both in vitro and in vivo in terms of degradation behavior and effects on spiral ganglion neurons, the main target of the electrical stimulation with a CI. Growth rates of fibroblasts on the polymers were investigated and a direct-contact test with freshly isolated spiral ganglion cells (SGC) was performed. In addition, the effects of the polymer degradation inside the inner ear were evaluated in vivo. The polymer degradation was assessed by use of scanning electron microscopy in combination with an energy-dispersive X-ray analysis. In vitro, no influence of the polymers was detected on fibroblasts' viability and on SGC survival rate. In vivo, SGC density was decreased only 6 months after implantation in the basal and middle turns of the cochlea in comparison to normal-hearing animals but not between implanted groups (coated or uncoated). The analysis of the electrode models showed that in vivo P(4HB) is characterized by a gradual degradation completed after 6 months; whereas, the PLLA coatings burst along their longitudinal axis but showed only little degradation within the same time frame. In conclusion, both polymers seem to justify further evaluation as possible coating for CI electrodes. Of the two options, due to its excellent coating adhesion/stability and optimal degradation behavior, P(4HB) may prove to be the more promising biodegradable polymer for designing a drug delivery system from the surface of CI electrodes.

With the purpose to enhance spiral ganglion cell growth after cochlear implant insertion in order to preserve the residual hearing, we propose a polymer-based local drug delivery system for growth factor release. Therefore, the biodegradable natural poly(4-hydroxybutyrate) and the synthetic poly(L-lactide) were used as coatings matrices on the silicone-based electrode carrier material, and different surface activations were performed in order to enhance the effectiveness of surface attachment of brain-derived neurotrophic factor (BDNF) via absorption. Relating to this system it was shown that activation of the surface leads to an increased adsorption of BDNF. Furthermore, an in vitro degradation study of the used polymer matrices P(4HB) and PLLA under quasi-stationary conditions in human perilymph supplemented with enzymes was performed.

With the purpose to enhance spiral ganglion cell growth after cochlear implant (CI) insertion, we propose a biofunctionalization method allowing sustained BDNF release from poly(4-hydroxybutyrate) as a model biodegradable CI coating. Reaction efficiency of the crosslinker DSS with the polymer surfaces for covalent attachment of BDNF as well as its cleavage in aqueous medium as requirement for BDNF release were traced by LC-MS. Performed in vitro release studies, conducted in comparison to physically adsorbed BDNF, give indication of the successful immobilization of BDNF via hydrolyzable bonds.

In recent years novel implants in particular have already proven to contribute substantially to enhanced quality of life, higher efficacy of therapeutic approaches, as well as patient safety. With the purpose to optimize the implant-tissue interaction the focus of efforts is on implants with a controlled, site-selective drug release. Therefore, we develop within the REMEDIS consortium implant-associated local drug delivery (LDD) systems for different medical applications. Engineering and natural scientists together with medical experts from all over Germany work in close collaboration to develop such innovative implants which combine the function as medical device and as LDD system. These include vascular stents and stimulation electrodes for the circulatory system and the ears, glaucoma stents for the eyes as well as auditory tube stents for the ears. Through its efforts to combine a LDD system into the functionality of implants, REMEDIS provides cutting-edge research into such medical technology.