Digital light processing stereolithography of hydroxyapatite scaffolds with bone-like architecture, permeability, and mechanical properties

This work deals with the additive manufacturing and characterization of hydroxyapatite scaffolds mimicking the trabecular architecture of cancellous bone. A novel approach was proposed relying on stereolithographic technology, which builds foam-like ceramic scaffolds by using three-dimensional (3D) micro-tomographic reconstructions of polymeric sponges as virtual templates for the manufacturing process. The layer-by-layer fabrication process involves the selective polymerization of a photocurable resin in which hydroxyapatite particles are homogeneously dispersed. Irradiation is performed by a dynamic mask that projects blue light onto the slurry. After sintering, highly-porous hydroxyapatite scaffolds (total porosity ~0.80, pore size 100-800 µm) replicating the 3D open-cell architecture of the polymeric template as well as spongy bone were obtained. Intrinsic permeability of scaffolds was determined by measuring laminar airflow alternating pressure wave drops and was found to be within 0.75-1.74 × 10−9m2, which is comparable to the range of human cancellous bone. Compressive tests were also carried out in order to determine the strength (~1.60 MPa), elastic modulus (~513 MPa) and Weibull modulus (m = 2.2) of the scaffolds. Overall, the fabrication strategy used to print hydroxyapatite scaffolds (tomographic imaging combined with digital mirror device [DMD]-based stereolithography) shows great promise for the development of porous bioceramics with bone-like architecture and mass transport properties.