Collagen gel combined with mesoporous nanoparticles loading nerve growth factor as a feasible therapeutic three-dimensional depot for neural tissue engineering

Three-dimensional matrices with controllable and sustainable delivery capacity of neurotrophic factors are promising platforms for neural tissue engineering. Here we developed a nerve growth factor (NGF) delivering cell culture system involving mesoporous silica nanoparticles (MSNs) combined with collagen hydrogel. Particularly for the loading of large protein molecules, the mesopores of MSNs were exploited to a size as large as about 16 nm with the help of an auxiliary surfactant. Loading of proteins was confirmed within the enlarged mesopores with a high loading capacity. The NGF-loaded MSNs were combined with collagen hydrogel by a temperature-mediated gelation which was used as the delivery system of NGF as well as the culture matrix for neural cells. The NGF loaded onto MSN was shown to release sustainably for over a week. When the NGF-loaded MSN was embedded within a collagen gel, the release amount of NGF was more sustained and followed the release pattern of NGF from MSN. A model study to examine the biological efficacy of the NGF release was performed using PC12 cells with culturing cells either outside or within the hydrogel. When cultured outside of the system, the neurite outgrowth of cells was significantly improved, confirming biological action of the NGF delivered from the MSN-NGF loaded collagen. Gene expression of growth-associated protein, GAP43, was significantly up-regulated, demonstrating the system is effective in delivering NGF to elicit biological activity of the growth factor. Furthermore, when cultured within the MSN-NGF-collagen hydrogel matrix, cells were stimulated to undergo neuritogenesis while preserving the cell viability, confirming the effectiveness for neural tissue engineering. The novel delivery system of NGF utilizing enlarged-pored MSNs in combination with collagen hydrogel may be potentially useful as therapeutic neural engineering matrices and the concept can also be extended to other growth factor delivering systems.