Hybrid Electrospun Polycaprolactone Mats Consisting of Nanofibers and Microbeads for Extended Release of Dexamethasone.

PURPOSE: We designed electrospun polycaprolactone mats consisting of nanofibers and microbeads for extended delivery of dexamethasone. METHODS: Thin flexible dexamethasone loaded polycaprolactone mats were prepared by electrospinning. The solvents, polymer loading, voltage and tip-to-collector distance were varied to explore the effects on microstructure of the mats. The microstructure was determined by scanning electron microscope imaging; drug transport was measured and modeled, and X-ray diffraction was used to gauge the crystallinity. Drug transport and X-ray diffraction studies were also conducted with a spin cast film for comparison. RESULTS: Thin mats, about 10 µm in thickness, were prepared by electrospinning. By controlling the voltage and tip-to-collector distance, we achieved a hybrid structure comprising of nanorods (nanofibers) and microbeads. The release profiles were fitted to the diffusion equation to obtain the diffusivities in the spheres and the rods. The diffusivity in the electrospun nanofibers was significantly lower compared to the casted films due to increased crystallinity, which was estimated from X-ray diffraction analysis. The electrospun hybrid mats sustained drug release for the desired duration of a month, in spite of the small thickness of about 10 µm. By comparison, a ten-fold thicker cast film sustains release for about the same duration suggesting about 100-fold decrease in diffusivity in the electrospun mats due to increased crystallinity. CONCLUSIONS: Electrospun polycaprolactone mats are optimal for achieving long release durations due to increased crystallinity. Designing a hybrid structure by controlling the electrospinning parameters can be a useful approach to increase the release durations.

Scale of Carbon Nanomaterials Affects Neural Outgrowth and Adhesion.

Carbon nanomaterials have become increasingly popular microelectrode materials for neuroscience applications. Here we study how the scale of carbon nanotubes and carbon nanofibers affect neural viability, outgrowth, and adhesion. Carbon nanotubes were deposited on glass coverslips via a layer-by-layer method with polyethylenimine (PEI). Carbonized nanofibers were fabricated by electrospinning SU-8 and pyrolyzing the nanofiber depositions. Additional substrates tested were carbonized and SU-8 thin films and SU-8 nanofibers. Surfaces were O2-plasma treated, coated with varying concentrations of PEI, seeded with E18 rat cortical cells, and examined at 3, 4, and 7 days in vitro (DIV). Neural adhesion was examined at 4 DIV utilizing a parallel plate flow chamber. At 3 DIV, neural viability was lower on the nanofiber and thin film depositions treated with higher PEI concentrations which corresponded with significantly higher zeta potentials (surface charge); this significance was drastically higher on the nanofibers suggesting that the nanostructure may collect more PEI molecules, causing increased toxicity. At 7 DIV, significantly higher neurite outgrowth was observed on SU-8 nanofiber substrates with nanofibers a significant fraction of a neuron's size. No differences were detected for carbonized nanofibers or carbon nanotubes. Both carbonized and SU-8 nanofibers had significantly higher cellular adhesion post-flow in comparison to controls whereas the carbon nanotubes were statistically similar to control substrates. These data suggest a neural cell preference for larger-scale nanomaterials with specific surface treatments. These characteristics could be taken advantage of in the future design and fabrication of neural microelectrodes.