Evaluating the Effects of Poly(ε-Caprolactone)-Nanohydroxyapatite Composition on 3D-Printed Scaffold Structural...

Bone tissue engineering scaffolds should be biocompatible, match the mechanical properties of native bone, and degrade at a rate that facilitates tissue regeneration. However, most scaffolds will excel in only one or two of these areas while sacrificing the others. This study aims to vary poly( $\epsilon$ -caprolactone) (PCL) molecular weight blend ratios (100:0, 70:30, and 50:50 25 kDa:14 kDa PCL) and nanohydroxyapatite (nHA) ceramic content (0, 30, and 40 wt%) to design 3D-printed scaffolds with tunable mechanical properties and degradation kinetics. Nine different 3D-printing inks were created, all of which exhibited similar thermal properties. While 40 wt% nHA fibers had a homogeneous distribution of nHA, 30 wt% nHA fibers exhibited significant differences in nHA radial distribution, as characterized by micro-computed tomography. PCL with blended molecular weights had the highest compressive moduli, whereas the 0 and 30 wt% nHA groups had the highest stress at yield and peak stress before becoming brittle like the 40 wt% nHA groups. An accelerated degradation study resulted in increased PCL mass loss in the presence of nHA, suggesting nHA promoted accelerated degradation of PCL. These findings demonstrate that blending polymer molecular weights and incorporating ceramic content provides an effective means of tailoring 3D-printing inks to produce scaffolds with application-specific mechanical and degradation properties. In summary, the key novel contributions of the present work are the blending of different PCL molecular weights, the incorporation of relatively high wt% nHA, and the quantification of radial nHA distribution in individual printed fibers.