Multi-channel chitosan–polycaprolactone conduits embedded with microspheres for controlled release of nerve growth factor

Nerve growth factor (NGF)-loaded chitosan microspheres were prepared via emulsification method using sodium tripolyphosphate as a crosslinker. Some selected chitosan microspheres were embedded into chitosan–polycaprolactone (CH–PCL) multi-channel conduits that can potentially be used for long-gap nerve repair. PCL percentages in the CH–PCLs were optimized into a region changing from around 30 to 42   wt.% while the porosity and average channel diameter of the resulting multi-channel conduits were selected as about 80% and 200   μm, respectively. SEM images confirmed that the channels inside the conduits were longitudinally arrayed with an approximately parallel arrangement, and the NGF-loaded microspheres appeared to be embedded into the wall of channels without blocking. The compressive properties in wet state and in vitro degradation rates of CH–PCL multi-channel conduits were found to be mainly manipulated by the PCL content in the CH–PCLs whereas the cumulative amount of released NGF from the conduits could be independently regulated by altering the initial NGF load inside the embedded microspheres. The optimal microsphere-embedded CH–PCL multi-channel conduits with a dimension of around 6   mm in outer diameter and 30   mm in length were able to administrate bioactivity-preserved NGF release in a sustained and controlled manner without significant initial burst release, and the release rates of the conduits could be maintained with approximately linear characteristic over a period of time longer than 6   weeks.