Development of a five-axis printer for the fabrication of hybrid 3D scaffolds: From soft to hard phases and planar to curved surfaces

Abstract

Three-dimensional (3D) printing of hybrid scaffolds with material gradients, combining soft and hard phases, is an appealing frontier in additive manufacturing. However, most 3D printers are limited to either three-axis or mono-material capabilities, rendering them unsuitable for fabricating hybrid scaffolds. Additionally, printing on curved surfaces requires advanced printing capabilities. Our work aims to advance additive manufacturing by developing a hybrid piezoelectric inkjet-extrusion printer equipped with five-axis functionalities. The printer could be used to fabricate customized hybrid scaffolds, surpassing conventional mono-material or linear three-axis printing strategies. The soft phase comprises a low-viscosity photocurable resin and a high-viscosity peptide hydrogel, while the hard phase comprises 3D-printed polylactic acid and hydroxyapatite parts. To validate the system, we fabricated three hybrid scaffolding use cases, characterized by multi-material porous structures fabricated on planar, single-curved, and free-form surfaces. The scaffolds were subsequently analyzed using digital microscopy to assess their accuracy, particularly the feature sizes of pores and struts (i.e., 0.8–3.6 mm). In the first part of the study, we demonstrated the versatility of inkjet and extrusion printing by hybrid printing an interconnected network in the soft phase on top of a planar ceramic hard phase. A pore width and height deviation of 6% was achieved compared to the intended design. In the second part of the study, we evaluated the 3D inkjet printing of a multi-material porous scaffold on a single-curved surface for osteochondral defects. The circumferential pore width and radial pore height deviated by 0.8% and 2%, respectively. Finally, we inkjet-printed a mesh structure on a free-form surface, which acted as a membrane for palatal implants. In this case, the pore width deviations were -16% in the printing direction and 2% perpendicular to the printing direction.