Abstract
Additively manufactured biodegradable porous iron has been only very recently demonstrated. Two major limitations of such a biomaterial are very low biodegradability and incompatibility with magnetic resonance imaging (MRI). Here, we present a novel biomaterial that resolves both of those limitations. We used extrusion-based 3D printing to fabricate ex situ-alloyed biodegradable iron-manganese scaffolds that are non-ferromagnetic and exhibit enhanced rates of biodegradation. We developed ink formulations containing iron and 25, 30, or 35 wt% manganese powders, and debinding and sintering process to achieve Fe-Mn scaffolds with 69% porosity. The Fe25Mn scaffolds had the ε-martensite and γ-austenite phases, while the Fe30Mn and Fe35Mn scaffolds had only the γ-austenite phase. All iron-manganese alloys exhibited weakly paramagnetic behavior, confirming their potential to be used as MRI-friendly bone substitutes. The in vitro biodegradation rates of the scaffolds were very much enhanced (i.e., 4.0 to 4.6 times higher than that of porous iron), with the Fe35Mn alloy exhibiting the highest rate of biodegradation (i.e., 0.23 mm/y). While the elastic moduli and yield strengths of the scaffolds decreased over 28 days of in vitro biodegradation, those values remained in the range of cancellous bone. The culture of preosteoblasts on the porous iron-manganese scaffolds revealed that cells could develop filopodia on the scaffolds, but their viability was reduced by the effect of biodegradation. Altogether, this research marks a major breakthrough and demonstrates the great prospects of multi-material extrusion-based 3D printing to further address the remaining issues of porous iron-based materials and, eventually, develop ideal bone substitutes. Statement of significance3D printed porous iron biomaterials for bone substitution still encounter limitations, such as the slow biodegradation and magnetic resonance imaging incompatibility. Aiming to solve the two fundamental issues of iron, we present ex-situ alloyed porous iron-manganese scaffolds fabricated by means of multi-material extrusion-based 3D printing. Our porous iron-manganese possessed enhanced biodegradability, non-ferromagnetic property, and bone-mimicking mechanical property throughout the in vitro biodegradation period. The results demonstrated a great prospect of multi-material extrusion-based 3D printing to further address the remaining challenges of porous iron-based biomaterials to be an ideal biodegradable bone substitutes.
Highlights
Iron is one of the promising biodegradable metals
The optimum mixed powder loading and the shear-thinning behavior of the iron-manganese-containing ink (Fig. S3) allowed a smooth 3D printing process to create the scaffolds with a high aspect ratio and free-standing feature
The extrusion-based 3D printed porous iron-manganese scaffolds developed in this research exhibited a highly encouraging potential to meet most of the requirements for iron-based bone substitution, including (i) weak paramagnetic properties with a very low magnetic susceptibility, meaning that the synthesized materials successfully tackled the fundamental issue of the MRIincompatibility of pure iron, and (ii) significantly enhanced in vitro biodegradability (i.e., 0.20–0.23 mm/y) due to the addition of 30– 35 wt% manganese to iron
Summary
Iron is one of the promising biodegradable metals. Unlike magnesium, it has excellent processability [13,14] and its rate of biodegradation is slow enough to provide continued mechanical support while the bone regeneration process progresses. Iron is ferromagnetic by nature, which complicates the imaging procedure for the patients who are exposed to a strong magnetic field, typically in magnetic resonance imaging (MRI) [16]. To address both fundamental issues of iron, alloying of iron with manganese has been proposed [17]. As for the biocompatibility, despite naturally occurring in the human body, iron and manganese at high doses can be toxic [20,21]. Considering all these factors is of great importance in the design of iron-manganese alloys intended for bone substitution
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