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Random networks of semiflexible filaments play a crucial role in the mechanics of many systems, including the cell. To understand the response of semiflexible networks to stress, a strain-based measure of nonaffine deformation is introduced and used to probe the mechanics on various scales. This measure provides a unified description of nonaffinity in both strain and rotation and indicates that the level of nonaffinity in these quantities in a given system is comparable. The degree of nonaffinity decreases as the scale of observation increases. This scaling is a power law with different exponents for length scales smaller and larger than a characteristic length scale proportional to the fiber length. The fiber bending stiffness controls the scaling at small length scales, while the large length scale scaling exponent is independent of fiber density and stiffness.

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Bone healing can be significantly expedited by applying electrical stimuli in the injured region. Therefore, a three-dimensional (3D) ceramic conductive tissue engineering scaffold for large bone defects that can locally deliver the electrical stimuli is highly desired. In the present study, 3D conductive scaffolds were prepared by employing a biocompatible conductive polymer, ie, poly(3,4-ethylenedioxythiophene) poly(4-styrene sulfonate) (PEDOT:PSS), in the optimized nanocomposite of gelatin and bioactive glass. For in vitro analysis, adult human mesenchymal stem cells were seeded in the scaffolds. Material characterizations using hydrogen-1 nuclear magnetic resonance, in vitro degradation, as well as thermal and mechanical analysis showed that incorporation of PEDOT:PSS increased the physiochemical stability of the composite, resulting in improved mechanical properties and biodegradation resistance. The outcomes indicate that PEDOT:PSS and polypeptide chains have close interaction, most likely by forming salt bridges between arginine side chains and sulfonate groups. The morphology of the scaffolds and cultured human mesenchymal stem cells were observed and analyzed via scanning electron microscope, micro-computed tomography, and confocal fluorescent microscope. Increasing the concentration of the conductive polymer in the scaffold enhanced the cell viability, indicating the improved microstructure of the scaffolds or boosted electrical signaling among cells. These results show that these conductive scaffolds are not only structurally more favorable for bone tissue engineering, but also can be a step forward in combining the tissue engineering techniques with the method of enhancing the bone healing by electrical stimuli.

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