Macrophage activation can be modulated by biomaterial topography according to the biological scale (micrometric and nanometric range). In this study, we investigated the effect of fiber diameter and fiber alignment of electrospun poly(L-lactic) (PLLA) scaffolds on macrophage RAW 264.7 activation and secretion of proinflammatory cytokines and chemokines at 24 h and 7 days. Macrophages were cultured on four different types of fibrous PLLA scaffold (aligned microfibers, aligned nanofibers, random microfibers, and random nanofibers) and on PLLA film (used as a reference). Substrate topography was found to influence the immune response activated by macrophages, especially in the early inflammation stage. Secretion of proinflammatory molecules by macrophage cells was chiefly dependent on fiber diameter. In particular, nanofibrous PLLA scaffolds minimized the inflammatory response when compared with films and microfibrous scaffolds. The histological evaluation demonstrated a higher number of foreign body giant cells on the PLLA film than on the micro- and nanofibrous scaffolds. In summary, our results indicate that the diameter of electrospun PLLA fibers, rather than fiber alignment, plays a relevant role in influencing in vitro macrophage activation and secretion of proinflammatory molecules.

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Over the past six decades, engineered composite materials found wide ranging applications in land, sea and air transport vehicles, space exploration, military equipment and defense, storage, buildings and construction, chemical processing, electrical engineering, healthcare, and general engineering industries. Performance of engineered composites is tailored for an intended application by judiciously selecting the matrix and reinforcement materials, by modifying the fiber–matrix interface, and by controlling the architecture of fibers in the matrix. Most widely used reinforcement fibers are micron size diameter fibers. There is growing need for engineered composites with enhanced structural performance in newer applications as well as existing applications, which are expected to meet higher functional requirements and enhanced safety requirements. Moreover the global movement toward sustainable development is seeking engineered materials which are environmentally benign. Recently the electrospinning process has emerged as a viable industrial process to produce nanofibers from a variety of materials including naturally occurring polymers. This paper illustrates the benefits of using electrospun nanofibers in enhancing the structural performance of engineered composite materials. Copyright © 2010 John Wiley & Sons, Ltd.