Nanoporous silica nanoparticles (NPSNPs) have already offered their great potential as delivery platforms in previous studies due to their advantageous properties. The properties include a high surface area, a high porosity (up to 50%) and the amenability for surface modification, because the silanol groups at the internal and external surface can be used to adjust the surface properties. Moreover, NPSNPs have shown a good biocompatibility and are biodegradable.[1,2] Our approach is the application of such delivery systems on the surface of implants, e.g. on the cochlear implant. Cochlear implants are required to treat sensorineural deafness, which is caused by damage of hair cells followed by ongoing degeneration of spiral ganglion neurons (SGNs). The establishment of delivery systems for neuroprotective factors on the silicon surface of the cochlear implant can promote different cell processes like differentiation or proliferation. Previous studies have demonstrated that the brain-derived neurotrophic factor (BDNF) is a promising agent due to its ability to improve the survival and growth of SGNs. For that reason we investigated the delivery of BDNF by NPSNPs.
NPSNPs were prepared via sol-gel process from alkaline aqueous solution. Cetyltrimethylammonium bromide (CTAB) acted as structure directing agent to build up the porous system. The particle surface was modified with different trialkoxysilanes to equip the surface with various functional groups. We investigated the immobilization of BDNF on the surface of the NPSNPs and its release. The immobilized and released amounts of BDNF were determined by using an ELISA. The cytocompatibility of the NPSNPs was investigated with fibroblasts and the neuroprotective effect of immobilized and released BDNF was studied with SGNs.
The NPSNPs were successfully used as delivery system for BDNF. They exhibit a good cytocompatibility with fibroblasts and the delivered amounts of BDNF increased the survival rate of SGNs.
This work was supported by the Cluster of Excellence Hearing4all.
 F. Tang et al., Adv. Mater., 2012, 24, 1504-1534.
 Y. Wang et al., Nanomedicine: NBM, 2015, 11, 313-327.
 A. Warnecke et al., PLOS One, 2014, 9, 1-10.
 Q. Huo et al., Chem. Mater., 2009, 21, 3823-3829.