Extrusion-based 3D printed biodegradable porous iron

N.E Putra,M.A Leeflang,M Minneboo,P Taheri,L.E Fratila-Apachitei,J.M.C Mol,J Zhou,A.A Zadpoor

doi:10.1016/j.actbio.2020.11.022

N.E Putra, M.A Leeflang + Show 6 more

Open Access

https://doi.org/10.1016/j.actbio.2020.11.022

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Journal: Acta Biomaterialia	Publication Date: Nov 20, 2020
Citations: 54	License type: cc-by

Affiliation: Delft University of Technology

Abstract

Extrusion-based 3D printing followed by debinding and sintering is a powerful approach that allows for the fabrication of porous scaffolds from materials (or material combinations) that are otherwise very challenging to process using other additive manufacturing techniques. Iron is one of the materials that have been recently shown to be amenable to processing using this approach. Indeed, a fully interconnected porous design has the potential of resolving the fundamental issue regarding bulk iron, namely a very low rate of biodegradation. However, no extensive evaluation of the biodegradation behavior and properties of porous iron scaffolds made by extrusion-based 3D printing has been reported. Therefore, the in vitro biodegradation behavior, electrochemical response, evolution of mechanical properties along with biodegradation, and responses of an osteoblastic cell line to the 3D printed iron scaffolds were studied. An ink formulation, as well as matching 3D printing, debinding and sintering conditions, was developed to create iron scaffolds with a porosity of 67%, a pore interconnectivity of 96%, and a strut density of 89% after sintering. X-ray diffracometry confirmed the presence of the α-iron phase in the scaffolds without any residuals from the rest of the ink. Owing to the presence of geometrically designed macropores and random micropores in the struts, the in vitro corrosion rate of the scaffolds was much improved as compared to the bulk counterpart, with 7% mass loss after 28 days. The mechanical properties of the scaffolds remained in the range of those of trabecular bone despite 28 days of in vitro biodegradation. The direct culture of MC3T3-E1 preosteoblasts on the scaffolds led to a substantial reduction in living cell count, caused by a high concentration of iron ions, as revealed by the indirect assays. On the other hand, the ability of the cells to spread and form filopodia indicated the cytocompatibility of the corrosion products. Taken together, this study shows the great potential of extrusion-based 3D printed porous iron to be further developed as a biodegradable bone substituting biomaterial.

Highlights

Owing to its abundance in nature, ease of manufacturing, and high mechanical performance, iron-based materials have been extensively used as structural materials and potentially to be used as biodegradable materials for bone substitution [6]
Iron acts as a catalyst for the formation of reactive oxygen species (ROS) and an appropriate ROS level has been reported to regulate a pathway in osteoblast differentiation [9]
It is important to note that the reported in vivo corrosion rates are extremely low with no significant changes in the mass of iron-based materials implanted in the bulk [14] and foam forms [15], which may lead to the longer-than-expected longevity of such iron-based implants

Summary

Introduction

Owing to its abundance in nature, ease of manufacturing, and high mechanical performance, iron-based materials have been extensively used as structural materials and potentially to be used as biodegradable materials for bone substitution [6]. It is important to note that the reported in vivo corrosion rates are extremely low with no significant changes in the mass of iron-based materials implanted in the bulk (after 52 weeks) [14] and foam (after 6 weeks) forms [15], which may lead to the longer-than-expected longevity of such iron-based implants (within a few years [16]). It is still an open research question whether the biocompatibility of iron-based materials remains favorable enough when their biodegradation rates are enhanced to match the rate of bone tissue healing. The ferromagnetic nature of iron, causing complications during magnetic resonance imaging (MRI), is another issue, which has been addressed by alloying with 28 wt% or more manganese to retain the austenite phase and change the alloy to be non-ferromagnetic [17]

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