Electrospinning is a technique employed for preparing polymer fibers having diameters in the range of 10 μm–10 nm using high electrostatic field. In this letter, we report the formation of aligned polymer fibers, several centimeters in length, with separation between the fibers in the range of 5–100 μm. Achieving alignment is an important step toward the exploitation of these fibers in applications. We have employed about 4500 V and a separation distance of about 1–3 cm between the electrodes. Smaller distance between electrodes, we believe, provides better control on the formation of the fibers.

Electrospinning produces polymeric fibers with diameters in the range of 10μm–10nm by accelerating a charged polymer jet under a high electric field. We report the preparation of conducting nanocomposite fibers of poly(methyl methacrylate) (PMMA) and multiwalled carbon nanotubes (MWCNTs) by electrospinning. The fibers obtained are long and well aligned. The carbon nanotubes are found to be oriented along the fiber axis. The room temperature dc electrical conductivity of a single fiber with MWCNT (0.05% w/w) shows about a ten orders of magnitude improvement from the pure PMMA. The conductivity increases with MWCNT concentration.

Concentration gradient of diffusible bioactive chemicals assumes many important roles in regulating cellular behavior. Among the many factors influencing functional recovery after nerve injury, such as topographical and biochemical signals, concentration gradients of neurotrophic factors provide chemotactic cues for neurite outgrowth and targeted renervation. In this study, a concentration gradient of nerve growth factor (NGF, 0-250 μg/ml) was incorporated throughout the thickness of poly(ε-caprolactone)-poly(ethylene glycol) coaxial electrospun nanofibrous scaffolds (∼700 μm thick with ∼800 nm average fiber diameter). The existence of the protein gradient upon protein release was demonstrated using a customized under-agarose-PC12 neurite outgrowth assay. When exposed to scaffolds endowed with NGF concentration gradient (NGF-CG), a significant difference in the percentage of cells bearing neurite outgrowth was observed (7.1 ± 1.9% vs. 0.8 ± 0.3% for cells exposed to high vs. low concentration surface, respectively; p < 0.05). In contrast, no significant difference was observed when cells were exposed to scaffolds that encapsulated a fixed concentration of NGF. Direct culture of PC12 cells on the substrates demonstrated the cytocompatibility and the effect of diffusible NGF gradient on neurite outgrowth. A significant difference in the percentage of cells with neurite extensions was observed when PC12 cells were seeded on NGF-CG scaffolds (21.2 ± 3.6% vs. 10.4 ± 1.3% on high vs. low concentration surface, respectively; p < 0.05). Furthermore, Z-stack confocal microscopy tracking of neurite extensions revealed the chemotatic guidance effect of NGF concentration gradient. Directed and enhanced neurite penetration into the scaffolds towards increasing NGF concentration was observed. In vitro release study indicated that the encapsulated NGF was released in a sustained manner for at least 30 days (80.4 ± 3.6% released). Taken together, this study demonstrates the feasibility of incorporating concentration gradient of diffusible bioactive chemicals in nanofibrous scaffolds via the coaxial electrospinning technique.