The invention relates to electrospun three-dimensional (3D) nanofibrous scaffolds (with controllable porosities as high as about 96%) and methods of preparing the same. The electrospun 3D scaffolds possess interconnected and hierarchically structured pores with sizes ranging from tens of nanometers to hundreds of micrometers. In embodiments, the 3D scaffolds can be biocompatible and/or biodegradable. In some embodiments, the 3D scaffolds can be conductive. In some embodiments, the 3D scaffolds can contain bioactive species.