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From a series of experimental measurements and supplemented by results from a computational model, we investigated the static and dynamic size dependent behaviors of a single-strand polycaprolactone (PCL) nanofiber. For the static bending, the fiber stiffness showed a dramatic increase as the fiber diameter is reduced and for the dynamic bending, the resonant frequency exhibited a very similar trend. Employing the strain gradient (SG) theory, we formulated a model that not only accurately captures the magnitude of the experimentally observed size dependent response but it is also, able to correctly predict the onset of the inverse square behavior. Both our experimental data and SG model results showed that the damping term is unaffected by the size-dependency. We introduced an experimentally calibrated fiber length scale parameter to predict the onset and rise of the size dependent response and an effective elastic modulus to characterize the stiffness increase. This understanding of the pronounced enhancement in nanofibers can be used to design a nanofibrous scaffold to keep its structural integrity intact against a sudden static pull of a seeded cell or when subjected to a dynamic loading environment from say, the pulsating peripheral blood. [ABSTRACT FROM AUTHOR]

The stiffness of a nano-fibrous scaffold is generally enhanced due to the size-dependency of the thin nanofibers contained in the scaffold. We proposed a model that incorporates size-dependency of single nanofibers to predict the scaffold effective modulus, in which the fibers' random or orientation distribution are considered. In the model the fiber segments between rigid fiber-fiber bonds can be stretching, shearing and bending. Using deformation energy equilibrium between sum of individual fibers and the plate of nano-fibrous scaffold, the scaffold effective modulus was derived explicitly. The model was verified via finite element analysis (FEA) and published experimental results. The parametric studies revealed that the fiber diameter is the dominant parameter to stiffen the scaffold beyond the fiber density and fiber aspect ratio when the fiber diameter is reduced below the onset value of size-dependencies. As a result, the scaffold stiffness can maintain its higher value and lower decrease rate because of the size-dependency with a decreasing diameter of the nanofiber as a result of biodegradation. This inspires the idea of selecting nanofibers near the onset value of size-dependency to obtain a controlled tuning of the scaffold stiffness in the design of novel nano-fibrous scaffolds. [ABSTRACT FROM AUTHOR]