Fabrication of highly ordered willemite/PCL bone scaffolds by 3D printing: Nanostructure effects on compressive strength and in vitro behavior

Abstract

In this study, first willemite (Zn₂SiO₄) micro and nano-powders were synthesized by the sol-gel method. X-ray diffraction (XRD), transmission electron microscopy (TEM), and dynamic light scattering (DLS) were applied to characterize the crystalline phases and particle size of powders. Then polycaprolactone (PCL) polymer scaffolds containing 20 wt% willemite were successfully fabricated by the DIW 3D printing (direct ink writing) method. The effects of willemite particle size on compressive strength, elastic modulus, degradation rate, and bioactivity of the composite scaffolds were investigated. The results showed that nanoparticle willemite/PCL (NW/PCL) scaffolds had 33.1% and 58.1% higher compressive strength and the elastic modulus of NW/PCL were 1.14 and 2.45 times better compared to micron size willemite/PCL (MW/PCL) and pure PCL scaffolds, respectively. Scanning electron microscopy (SEM) images and Energy-dispersive X-ray spectroscopy map (EDS map) results indicated that willemite nanoparticles, unlike microparticles, were smoothly embedded in the scaffold struts. In vitro tests also revealed an improvement in bone-like apatite formation ability and an increase in the degradation rate up to 2.17% by decreasing the willemite particle size to 50 nm. In addition, NW/PCL rendered significant enhancement in cell viability and cell attachment during the culture of MG-63 human osteosarcoma cell line. Nanostructure had also a positive effect on ALP activity and biomineralization in vitro.

Keywords: 3D printing; Bone tissue engineering; Nanocomposite; PCL matrix composite; Scaffolds; Willemite.