3D-Printed Polymer Scaffolds for Vascularized Bone Regeneration Using Mineral and Extracellular Matrix Deposition

Abstract

Abstract Purpose Trauma, injury, disease, infection, congenital deformities, and non-union after a fracture can lead to significant loss of bone tissue resulting in large bone defects. If left untreated, this can lead to decreased bone strength, stability, and function as well as long-term malformations. We present a novel, pre-vascularized 3D-printed biodegradable scaffold mimicking the architecture of native bone as a bone graft alternative to promote vascularized bone regeneration. Methods Scaffolds with a highly porous central trabecular section surrounded by an outer cortical section modeled after the bone’s osteons were 3D printed in polylactic acid (PLA). Hydroxyapatite (HA) posts were incorporated to improve mechanical strength. A soak-freeze technique was used to introduce additional porosity to support the recruitment, proliferation, and differentiation of stem cells. Scaffolds were mineralized to provide cues for osteoconduction and osteoinduction. They were also pre-vascularized to promote the differentiation of stem cells along the vascular lineage. Results Compression mechanical testing showed the addition of HA posts improved mechanical strength. Using the soak-freeze technique, micropores in the range of 0–10 µm were introduced. Osteogenic differentiation capability of the scaffolds was verified in vitro through the estimation of osteocalcin (OC) produced by the cells seeded on them and by staining for alkaline phosphatase. Differentiation of stem cells along the vascular lineage within the scaffold was confirmed via the estimation of vascular endothelial growth factor (VEGF-A) and by staining for CD31, a marker for vascular differentiation. Conclusion This novel scaffold incorporated with cues necessary to promote the regeneration of bone and its vasculature shows promise as an alternative to currently used bone grafts. Lay Summary Significant bone loss caused by trauma, infection, or disease results in large defects that are currently treated using bone grafts—autografts (taken from the same patient), allografts and xenografts (donor tissue), or synthetic grafts. We have developed a tissue-engineered alternative that mimics the architecture of natural bone and has cues to promote both the regeneration of bone and its vasculature. These are fabricated using 3D printing (3DP) technology, providing cost-effective, customizable alternatives to conventional bone grafts.