A large number of RPENSs have been developed for bone regeneration by using natural and synthetic resorbable polymers such as chitosan, collagen, alginate, PCL, PLA, PLGA, and their mixtures with other substances [
154,
155]. Bone tissue engineering involves scaffolds, cells and growth factors to promote the regeneration of fractured or damaged bones with efficient mineralization. The ideal bone repair scaffolds have suitable mechanical properties and appropriate osteogenic differentiation ability. Therefore, bioactive substances such as inorganics (hy-droxyapatite and
etc.) and/or growth factors (bone morphogenetic protein-2 and
etc.) have been applied to be combined with RPENSs for bone regenerations. The application of RPENSs for bone tissue engineering can be classified into three types: (i) Bioactive substances are loaded into the nanofibers. Generally, bioactive substances are mixed with polymers and then the mixed polymer solution is applied for the electrospinning process. The bioactive substances are uniformly distributed into the nanofibers. The bioactive substances can be gradually delivered at the implanta-tion sites in the human body with the degradation of RPENSs. It is especially useful for the long-term treatment of bone injury. This is the most explored way to fabricate biomaterials for bone tissue engineering. Typical examples include hydroxyapatite-blended chitosan RPENSs [
156], hydroxyapatite-blended collagen RPENSs [
157], hydroxyapatite-blended gelatin RPENSs [
158], hydroxyapa-tite-blended poly(lactic acid) RPENSs [
159]. For the bioactive substance, nanoparticle encapsulation prior to the electrospinning processs is an efficient way to increase their stability. (ii) Bioactive substances are immobilized onto the nanofibers. RPENSs are firstly fabricated by the electrospinning process and then the bioactive substances are immobilized onto the RPENSs [
160]. Ngiam
et al. [
161] prepared nano-hydroxyapatite on PLGA and PLGA/collagen nanofibers by a chemical deposition method. The fabricated RPENSs had a positive modulation on early osteoblast capture on the scaffolds. Cho
et al. [
162] prepared BMP-2 immobilized PLLA RPENSs inspired by polydopamine for bone regeneration. BMP-2 is immobilized on PLLA RPENSs by polydopamine-mediated chemi-cal modification. (iii) The bioactive substances are encapsulated into nano- and micro-materials prior to scaffolds fabrication. The encapsulation can increase the stability of the bioactive sub-stances. Li
et al. [
163] prepared BMP-2-cencapsulated bovine serum albumin nanoparticles, and then the mixture solution of the nanoparticles, dexamethasone, and polymers was applied to prepare RPENSs for bone repair. Ding
et al. [
163] developed a RPENS-microbeads alternating multilayer scaffolds for bone repair. Stem cells and BMP2 are simultaneously loaded into the microbe-ads. The composite scaffold showed an outstanding osteogenic effect
in vitro and
in vivo. (iii) Bioactive substances are encapsulat-ed by RPENSs. RPENs are fabricated into a balloon shape and the bioactive substances are encapsulated into the balloon-shape RPENs. Sun
et al. [
68] designed a balloon-shape P(DLLA-CL) RPENS for the treatment of vertebral compression fractures (
Fig. 2). The RPENSs can be inflated by injecting calcium phosphate cement to restore the height of fractured vertebral body. Moreover, the shortcomings of calcium phosphate cement such as water-induced collapsibility and cement leakage could be prevented. Further-more, their team comprehensively compared the
in vitro and
in vivo behaviors of the balloon-shape RPENS for the treatment of vertebral compression fractures [
164]. The balloon-shape RPENS could satisfy the clinical needs and had good biodegradability and bioavailability. These researches showed the RPENS had a promising potential for the clinical application for the treatment of vertebral compression fractures.