<p>Bioresorbable iron-manganese
(Fe-Mn) alloys are considered as a new class of biomaterials for the
development of orthopedic fixation devices due to their promising mechanical
properties, comparable to the human cortical bone, and the ability to degrade in
the physiological environment and release small quantities of metallic
ions/particles that are absorbable by the host. The greatest challenge for
developing an ideal resorbable Fe-Mn alloy is to increase the degradation rate
of the alloy without compromising the alloy biocompatibility, that is, causing
zero or minimal local and systemic toxicity to the tissue. Another challenge is
to improve osteo-integration through inducing a cascade of events leading to
tissue ingrowth.</p>
<p> </p>
<p>The incorporation of porosity into the Fe-Mn alloys aimed to
increase the corrosion rate and to provide the three-dimensional structure for cellular
activity and nutrient transport. The Fe-30wt.%Mn alloys with 0-, 5-, 10-, and
60-volume percent porosity were produced through the space holder
technique in powder metallurgy.
The space-holder material, ammonium bicarbonate (NH<sub>4</sub>HCO<sub>3</sub>),
was sieved to a particle size ranging 355~500 µm. The microstructures and
mechanical properties of the alloys, as well as the influence of the degree of porosity
on the alloy corrosion rates comparing to the concentrations of the degraded
metal ions were
investigated. Although the Fe-30Mn alloys containing 60-vol% porosity exhibited
the lowest average ultimate compressive strength of 381 MPa among the tested
groups, they were still mechanically stronger than a typical human wet compact
bone. Furthermore, the alloys had the highest average corrosion rate of 0.98 ± 0.20
mm/year, compared to 0.13 ± 0.07 mm/year for the non-porous Fe-30Mn alloys. Nevertheless,
the extract from the 60%-pore group had a cytotoxicity effect to the bone
marrow stem cells (BMSCs) at an average normalized cell viability of 58%, which
was below the standard viability of 70%, considered as cytotoxic in the
indirect cytotoxicity study. The cytotoxicity study also corresponded to the
highest level of transition metal ions Mn<sup>2+</sup> released into the media for
the 60%-pore group at an average ion released rate of 7 mg/day, compared to the
other groups presenting similar Mn<sup>2+</sup> released rates about 4 mg/day
after 1 day of incubation. The extreme case of the 60%-pore group demonstrated
the tradeoff between the corrosion rates and biocompatibility. On the other
hand, the 10%-pore group showed an average ultimate compressive strength of 737
MPa comparable to the stainless steel 316L, an average corrosion rate of 0.260
± 0.09 mm/year, which was 2-fold higher than the non-porous group, and
an average cell viability of 86% close to the non-porous group. It is promising
based on the above results,
however, the osteo-integration of the 10%-pore group in terms of cell-to-cell
and alloy-to-cell interactions was not ideal. </p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/8279498 |
| Date | 05 August 2019 |
| Creators | Sabrina M Huang (6843719) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/INVESTIGATION_OF_BIODEGRADABLE_IRON-MANGANESE_ALLOYS_WITH_VARIOUS_POROSITY/8279498 |
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