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

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 inkjetextrusion 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 multimaterial 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.