Evaluation of in vitro corrosion resistance and in vivo osseointegration properties of a FeMnSiCa alloy as potential degradable implant biomaterial

Extrusion-based 3D printing of biodegradable, osteogenic, paramagnetic, and porous FeMn-akermanite bone substitutes

The development of biodegradable Fe-based bone implants has rapidly progressed in recent years. Most of the challenges encountered in developing such implants have been tackled individually or in combination using additive manufacturing technologies. Yet not all the challenges have been overcome. Herein, we present porous FeMn-akermanite composite scaffolds fabricated by extrusion-based 3D printing to address the unmet clinical needs associated with Fe-based biomaterials for bone regeneration, including low biodegradation rate, MRI-incompatibility, mechanical properties, and limited bioactivity. In this research, we developed inks containing Fe, 35 wt% Mn, and 20 or 30 vol% akermanite powder mixtures. 3D printing was optimized together with the debinding and sintering steps to obtain scaffolds with interconnected porosity of 69%. The Fe-matrix in the composites contained the γ-FeMn phase as well as nesosilicate phases. The former made the composites paramagnetic and, thus, MRI-friendly. The in vitro biodegradation rates of the composites with 20 and 30 vol% akermanite were respectively 0.24 and 0.27 mm/y, falling within the ideal range of biodegradation rates for bone substitution. The yield strengths of the porous composites stayed within the range of the values of the trabecular bone, despite in vitro biodegradation for 28 d. All the composite scaffolds favored the adhesion, proliferation, and osteogenic differentiation of preosteoblasts, as revealed by Runx2 assay. Moreover, osteopontin was detected in the extracellular matrix of cells on the scaffolds. Altogether, these results demonstrate the remarkable potential of these composites in fulfilling the requirements of porous biodegradable bone substitutes, motivating future in vivo research. STATEMENT OF SIGNIFICANCE: We developed FeMn-akermanite composite scaffolds by taking advantage of the multi-material capacity of extrusion-based 3D printing. Our results demonstrated that the FeMn-akermanite scaffolds showed an exceptional performance in fulfilling all the requirements for bone substitution in vitro, i.e., a sufficient biodegradation rate, having mechanical properties in the range of trabecular bone even after 4 weeks biodegradation, paramagnetic, cytocompatible and most importantly osteogenic. Our results encourage further research on Fe-based bone implants in in vivo.

Progress in manufacturing and processing of degradable Fe-based implants: a review

Biodegradable metals have gained vast attention as befitting candidates for developing degradable metallic implants. Such implants are primarily employed for temporary applications and are expected to degrade or resorbed after the tissue is healed. Fe-based materials have generated considerable interest as one of the possible biodegradable metals. Like other biometals such as Mg and Zn, Fe exhibits good biocompatibility and biodegradability. The versatility in the mechanical behaviour of Fe-based materials makes them a better choice for load-bearing applications. However, the very low degradation rate of Fe in the physiological environment needs to be improved to make it compatible with tissue growth. Several studies on tailoring the degradation behaviour of Fe in the human body are already reported. Majority of these works include studies on the effect of manufacturing and processing techniques on biocompatibility and biodegradability. This article focuses on a comprehensive review and analysis of the various manufacturing and processing techniques so far reported for developing biodegradable iron-based orthopaedic implants. The current status of research in the field is neatly presented, and a summary of the works is included in the article for the benefit of researchers in the field to contextualise their research and effectively find the lacunae in the existing scholarship.

Stress-Induced Dual-Phase Structure to Accelerate Degradation of the Fe Implant

Fe is considered as a potential candidate for implant materials, but its application is impeded by the low degradation rate. Herein, a dual-phase Fe30Mn6Si alloy was prepared by mechanical alloying (MA). During MA, the motion of dislocations driven by the impact stress promoted the solid solution of Mn in Fe, which transformed α-ferrite into γ-austenite since Mn was an austenite-stabilizing element. Meanwhile, the incorporation of Si decreased the stacking fault energy inside austenite grains, which tangled dislocations into stacking faults and acted as nucleation sites for ε-martensite. Resultantly, Fe30Mn6Si powder had a dual-phase structure composed of 53% γ-austenite and 47% ε-martensite. Afterward, the powders were prepared into implants by selective laser melting. The Fe30Mn6Si alloy had a more negative corrosion potential of -0.76 ± 0.09 V and a higher corrosion current of 30.61 ± 0.41 μA/cm² than Fe and Fe30Mn. Besides, the long-term weight loss tests also proved that Fe30Mn6Si had the optimal degradation rate (0.25 ± 0.02 mm/year).

Electrodeposition of Calcium Phosphate Coatings on Metallic Substrates for Bone Implant Applications: A Review

This review summaries more than three decades of scientific knowledge on electrodeposition of calcium phosphate coatings. This low-temperature process aims to make the surface of metallic bone implants bioactive within a physiological environment. The first part of the review describes the reaction mechanisms that lead to the synthesis of a bioactive coating. Electrodeposition occurs in three consecutive steps that involve electrochemical reactions, pH modification, and precipitation of the calcium phosphate coating. However, the process also produces undesired dihydrogen bubbles during the deposition because of the reduction of water, the solvent of the electrolyte solution. To prevent the production of large amounts of dihydrogen bubbles, the current density value is limited during deposition. To circumvent this issue, the use of pulsed current has been proposed in recent years to replace the traditional direct current. Thanks to breaking times, dihydrogen bubbles can regularly escape from the surface of the implant, and the deposition of the calcium phosphate coating is less disturbed by the accumulation of bubbles. In addition, the pulsed current has a positive impact on the chemical composition, morphology, roughness, and mechanical properties of the electrodeposited calcium phosphate coating. Finally, the review describes one of the most interesting properties of electrodeposition, i.e., the possibility of adding ionic substituents to the calcium phosphate crystal lattice to improve the biological performance of the bone implant. Several cations and anions are reviewed from the scientific literature with a description of their biological impact on the physiological environment.

Biologically modified implantation as therapeutic bioabsorbable materials for bone defect repair

For decades, researches have concentrated on the mechanical properties, biodegradation, and biocompatibility of implants used in the therapy of large size bone defect. In vivo studies demonstrate that bioabsorbable bone substitute materials can reduce the risk of common symptoms such as inflammation and osteonecrosis caused by bio-inert materials after long-term implantation. Several organic, inorganic, and composite materials have been approved for clinical application, based on their unique characteristics and advantages. Although some artificial bioabsorbable bone substitute materials have been used for years, there are still some disadvantages existing, such as low mechanical strength, high brittleness, and low degradation rate. Therefore, novel bioabsorbable composite materials biomaterials have been developed for bone defect repair. In this review, we provide an overview of the development of artificial bioabsorbable bone substitute materials and highlight the advantages and disadvantages. Furthermore, recent advances in bioabsorbable bone substitute materials used in bone defect repair are outlined. Finally, we discuss current challenges and further developments in the clinical application of bioabsorbable bone substitute materials.

Biodegradable shape memory alloys: Progress and prospects

Shape memory alloys (SMAs) have a wide range of potential novel medical applications due to their superelastic properties and ability to restore and retain a 'memorised' shape. However, most SMAs are permanent and do not degrade in the body when used in implantable devices. The use of non-degrading metals may lead to the requirement for secondary removal surgery and this in turn may introduce both short and long-term health risks, or additional waste disposal requirements. Biodegradable SMAs can effectively eliminate these issues by gradually degrading inside the human body while providing the necessary support for healing purposes, therefore significantly alleviating patient discomfort and improving healing efficiency. This paper reviews the current progress in biodegradable SMAs from the perspective of biodegradability, mechanical properties, and biocompatibility. By providing insights into the status of SMAs and biodegradation mechanisms, the prospects for Mg- and Fe-based biodegradable SMAs to advance biodegradable SMA-based medical devices are explored. Finally, the remaining challenges and potential solutions in the biodegradable SMAs area are discussed, providing suggestions and research frameworks for future studies on this topic.

Evolution of the ε and γ phases in biodegradable Fe-Mn alloys produced using laser powder-bed fusion

The key feature of Fe-Mn alloys is gradual degradability and non-magneticity, with laser power bed fusion (LPBF) parameters influencing the microstructure and chemical composition. Our study focuses on biodegradable Fe-Mn alloys produced by mechanically mixing pure metal feedstock powders as part of the LPBF process. The Mn content and, consequently, the γ-ε phase formation in LPBF samples are directly correlated with an adapted energy-density (E) equation by combining the five primary LPBF parameters. We varied laser power (P) in a range of 200-350 W and scanning speed at 400 and 800 mm/s, and a comprehensive study was performed on samples with similar E. The study also showed an almost linear correlation between the LPBF's laser power and the material's hardness and porosity. The corrosion resistance was significantly reduced (from 13 to 400 μm/year) for the LPBF samples compared to a conventionally produced sample due to the dual-phase microstructure, increased porosity and other defects. The static immersion test showed that the process parameters greatly influence the quantity of oxides and the distribution of their diameters in the LPBF samples and, therefore, their corrosion stability. The most challenging part of the study was reducing the amount of ε phase relative to γ phase to increase the non-magnetic properties of the LPBF samples.

Biodegradable Iron-Based Materials-What Was Done and What More Can Be Done?

Iron, while attracting less attention than magnesium and zinc, is still one of the best candidates for biodegradable metal stents thanks its biocompatibility, great elastic moduli and high strength. Due to the low corrosion rate, and thus slow biodegradation, iron stents have still not been put into use. While these problems have still not been fully resolved, many studies have been published that propose different approaches to the issues. This brief overview report summarises the latest developments in the field of biodegradable iron-based stents and presents some techniques that can accelerate their biocorrosion rate. Basic data related to iron metabolism and its biocompatibility, the mechanism of the corrosion process, as well as a critical look at the rate of degradation of iron-based systems obtained by several different methods are included. All this illustrates as the title says, what was done within the topic of biodegradable iron-based materials and what more can be done.