Abstract
Summary
Metal Injection Molding could provide cost saving of about 20–50% for implantable medical device manufacturing and hence healthcare public spending. Corrosion behaviour and biocompatibility of the new manufactured alloy were studied and showed similar behaviour compared to the traditional one.
Introduction
The growing trend for total joint arthroplasties could raise healthcare costs in the near future. Metal Injection Molding (MIM) is a near net shape manufacturing technology and allows the production of finite prosthesis components saving the machining step, and so resources, up to 20–50%. In order to apply such process to the production of actual devices, the bulk material have to show biocompatibility and corrosion behaviour similar to the traditional one. (ASTM F2083, ISO 21536) The aim of this work was to compare cast and forged CoCrMo alloy with the MIM one from the electrochemical point of view and cytocompatibility.
Material and Methods
Metallographic observations by optical microscopy and SEM were taken to better understand the electrochemical behaviour. This evaluation was performed through potentiodynamic tests on MIM and forged (FOR) samples with polished and sandblasted surfaces (as the actual devices), in ASTM G5 cell with saline solution simulating the body environment, graphite counter electrodes and Ag/AgCl 0.15M NaCl reference electrode. Linear polarization, open circuit potential measurements and potentiostatic tests at +335 mV vs SCE were also performed during 10 days to have direct information on the corrosion resistance and ion release. Cell viability were also assessed through MTT test on polished MIM and cast (CAS) elutes, after 2 and 7 days contact periods, following ISO 10993 directions. Static ion release in H2O at 2, 4 and 8 weeks were also performed.
Results
MIM showed coarser grains, free of boundary carbide but with lots of circular porosities and stacking faults, in comparison with CAS structure, which presented many carbides and typical dendritic grain. Electrochemical tests exhibited analogue behaviour for the MIM and FOR CoCrMo alloys. The slightly lower passive current density and transpassive potential values obtained could be ascribed to a passive oxide layer on the MIM sample less protective than FOR CoCrMo one, as inferable from the OCP measurements, but these facts had no visible influence on polarization resistance and ion release. Such good corrosion behaviour was reflected also in static ion release results and MTT viability results, which were comparable, not only to CAS samples but also to the control medium.
Conclusions
From such preliminary results MIM technology showed to have good possibility for the production of implantable medical devices with CoCrMo alloy. Corrosion resistance and biocompatibility seemed not to be affected by the different manufacturing technique. Further studies will be needed to asses also the equivalence of mechanical properties. From the metallographic observations the absence of second phases and the homogeneous microstructure suggests a better fatigue performance for this kind of alloy, even if some concerns arise from the widespread porosity observed.
