Biodegradable implants constitute a new generation of biomedical materials that are being developed to assist in tissue healing processes and gradually degrade in vivo after their function is fulfilled. In recent years, Fe-Mn alloys have been studied as potential candidates for biodegradable implant materials because of their excellent mechanical properties and improved corrosion rate. In addition, the incorporation of antimicrobial elements, such as Ag and ZnO, is being studied to develop a material with antibiofilm properties that will lead to a decreased risk of implant-associated infections. In this thesis, porous equiatomic Fe-Mn alloy disks were fabricated via powder metallurgy by ball-milling and vacuum sintering. The first field of study covered the incorporation of antibacterial Ag into the Fe50Mn50 base alloy by the mechanical alloying of metallic powders to form uniformly dispersed Ag-rich precipitates within the FeMn matrix. The second field of study covered the deposition of a ZnO coating onto the porous FeMn disk by the dip-coating method. The addition of Ag and ZnO was aimed at accelerating the degradation rate and simultaneously decreasing the biofilm formation. A variety of methods were employed to characterize the properties of the synthesized materials, including scanning electron microscopy, transmission electron microscopy, and X-ray diffraction for microstructural characterization, while nanoindentation and compression tests were used to assess the mechanical properties. Biodegradability was investigated by immersing the specimens in Hank's Balanced Salt Solution (HBSS). The release of Fe, Mn and Ag/Zn ions was quantified to assess the degradation rate. The magnetic properties were studied using vibrating sample magnetometry before and after immersion in HBSS. Studies on cytocompatibility towards Saos-2 cells, inflammatory cytokine responses, and biofilm formation of Staphylococcus aureus have also been conducted. The results revealed that porous, non-cytotoxic, FeMn-based biomaterials can be fabricated by powder metallurgy. The phase composition of porous FeMn(-xAg) alloys changes with increasing Ag content from fully austenitic to a dual phase comprising austenite and martensite, which also leads to a higher mechanical strength of the Ag-containing alloys. The immersion tests, conducted up to 84 days for FeMn(-xAg) samples revealed that Mn release is higher than that of Fe. Formation of degradation products enriched in O, Ca, P and Cl was observed. The deposition of ZnO coatings significantly improved the degradation rate of the FeMn alloys, with a significant increase in ion release up to 28 days of immersion. Formation of secondary phases during the fabrication process was observed, which contributed to accelerating degradation. Both groups of materials showed good cytocompatibility towards Saos-2 cells. Moreover, the addition of both Ag and ZnO lead to a reduction in S. aureus biofilm formation when compared to the base FeMn alloy.
Fabrication and characterization of FeMn alloys with antibiofilm properties for biodegradable implant applications
Bartkowska ., A. (Author). 9 Nov 2023
Student thesis: Doctoral thesis
Student thesis: Doctoral thesis