Effect of zinc-doped hydroxyapatite/graphene nanocomposite on the physicochemical properties and osteogenesis differentiation of 3D-printed polycaprolactone scaffolds for bone tissue engineering

Processing and composition can significantly affect the mechanobiology, biodegradability, and cellular behavior of polymer-based bone scaffolds to replace damaged bone tissue. In this research, hydroxyapatite (HA), zinc-doped HA (ZnHA), and ZnHA-graphene (ZnHA-rGO) nanoparticles are composed in a polycaprolactone (PCL) matrix. After compositing PCL with nanoparticles, 3D bone scaffolds were built by a custom-built 3D printing system. The characterization of nanoparticles was extensively investigated by TEM, EDX-MAP, XRD, and ATR-FTIR. Simultaneously, 3D-printed scaffolds with different compositions were studied in terms of structure, morphology, thermogravimetry, biodegradability, and mechanical behaviors. The FE-SEM images of the scaffolds showed a highly regular structure and good printability of the developed material system. Moreover, the stiffness modulus of the samples increased due to the presence of the nanoparticles, especially in the ZnHA-rGO nanocomposite. In vitro cell assessment of 3D bone scaffolds was investigated by cell viability tests, cell attachment, and alizarin red staining via mesenchymal stem cells (MSCs). For differentiation capacity of the developed scaffolds, stem cell osteogenesis differentiation was studied by RT-PCR to analyze the ALP, RUNX2, BMP2, TGFβ, and OCN genes. The cellular assessments revealed an increase in PCL scaffold's cell osteogenesis due to the HA nanoparticles in the scaffold matrix. Zinc doping in the HA nanoparticles and rGO addition significantly increased the osteogenesis of MSCs. In particular, the nanocomposite of ZnHA-rGO in PCL scaffold matrix significantly improved the osteogenic differentiation and, thus, it is a viable option for effective regeneration of damaged bone tissue.