This work focuses on the development of electrically conducting porous nanocomposite structures by the incorporation of multiwalled carbon nanotubes (MWNT) into electrospun poly(ethylene oxide) (PEO) nanofibers. Electron microscopy confirmed the presence of individual aligned MWNT encapsulated within the fibers and showed fiber morphologies with diameters of 100-200 nm. Electrical conductance measurements of the random nanofiber mats showed that by increasing the concentration of MWNT we were able to produce porous nanocomposite structures with dramatically improved electrical conductivity. Above a percolation threshold of 0.365 ( 0.09 MWNT weight percent (wt %) in PEO the conductance increased by a factor of 10 12 and then became approximately constant as the concentration of MWNT was further increased. Because of this percolation threshold, for a 1 wt % loading of MWNT, the conductivity is essentially maximized. Mechanical testing confirmed that the tensile strength did not change, and there was a 3-fold increase in the Young's modulus when comparing a 1 wt % MWNT loading to the pure electrospun PEO. Thus, the optimal MWNT concentration for PEO nanofiber mats with enhanced mechanical and electrical properties is ∼1 wt %.

Articular cartilage lesions, which can progress to osteoarthritis, are a particular challenge for regenerative medicine strategies, as cartilage function stems from its complex depth-dependent microstructural organization, mechanical properties, and biochemical composition. Fibrous scaffolds offer a template for cartilage extracellular matrix production; however, the success of homogeneous scaffolds is limited by their inability to mimic the cartilage's zone-specific organization and properties. We fabricated trilaminar scaffolds by sequential electrospinning and varying fiber size and orientation in a continuous construct, to create scaffolds that mimicked the structural organization and mechanical properties of cartilage's collagen fibrillar network. Trilaminar composite scaffolds were then compared to homogeneous aligned or randomly oriented fiber scaffolds to assess in vitro cartilage formation. Bovine chondrocytes proliferated and produced a type II collagen and a sulfated glycosaminoglycan-rich extracellular matrix on all scaffolds. Furthermore, all scaffolds promoted significant upregulation of aggrecan and type II collagen gene expression while downregulating that of type I collagen. Compressive testing at physiological strain levels further demonstrated that the mechanical properties of trilaminar composite scaffolds approached those of native cartilage. Our results demonstrate that trilaminar composite scaffolds mimic key organizational characteristics of native cartilage, support in vitro cartilage formation, and have superior mechanical properties to homogenous scaffolds. We propose that these scaffolds offer promise in regenerative medicine strategies to repair articular cartilage lesions.

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