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Comparison of cytotoxicity between 99.5 and 99.95% iron for use in cardiovascular stents produced by powder metallurgy


Biodegradable materials are promising candidates to be used in cardiovascular stents because they provide a provisional framework for the vessel and avoid long-term clinical problems such as vessel restenosis. Biodegradable metallic materials (BMMs) have been proposed nowadays as it is expected to corrode gradually in vivo after providing the structural support to the tissue during it regeneration and healing processes.
Most of medical devices including BMMs are produced from metallic ingots fabricated using both casting and thermomechanical treatment. Recently, the use of new processes in the fabrication of biodegradable metallic stents, such as powder metallurgy, has been investigated.
Among the metals, iron has been proposed as a material in the manufacture of stents because its mechanical properties are similar to Stain Steel 316L, the golden standard. However, it is still unclear what level of impurity concentration is to be considered tolerable, and thus may be left in the material to maintain the device properties.

Objetivos - Metodologia - Resultados - Discussão dos Resultados/Objectives - Methodology - Results - Discussion of Results/Objetivos - Metodología - Resultados - Discusión de los resultados

In the present study we investigated the biocompatibility in vitro of the iron in two in two different purities and conformations with ADSCs (Adipose Derived Stem Cells) to evaluate their biomedical applicability.
For this purpose, samples with 99.5% and 99.95% iron were tested in the powdered state before and after the sintering process via powder metallurgy. The fabrication process included: Powder mixing (Fe and 1.5% wt % Zn-stearet), compacting (P=600 MPa,) and solid-state sintering (T=1150C; t=1h; atmosphere: Ar-5%). ADSCs were isolated from human adipose tissue (CEP-ISCMPA 882968), tested to verify their capacity to differentiate into adipogenic, chondrogenic and osteogenic cells and characterized by immunophenotyping on the flow cytometer using the antibodies anti CD44, CD105, CD45, CD14 and CD34 proteins. The samples of powdered and sintered iron were sterilized in an ultraviolet light irradiator. Sintered iron discs and their correspondent mass in powder were incubated, separately in accordance with the EN ISO 10993:12, for 48h. At end, it was collected and sterilized in 0.22 μm membrane for use in the indirect culture.
After direct and indirect culture with 99.5 and 99.95% powdered and sintered iron during 48h, ADSCs viability was evaluated by MTT assay and Trypan exclusion method. The morphological analysis was perfomed by labeling the nucleus and actin cytoskeleton in order to verify the biocompatibility of the tested biomaterial with ADSCs. Genotoxic damages were identified by comet alkaline assay.
It was observed that the cells maintained their viability when treated directly or indirectly with the iron powder, but decreased viability when exposed to high concentration of 99.5% iron powder. However, Fe after sintering by powder metallurgy proved to be cytotoxic, reducing the viability of the cells submitted to indirect contact and causing the death of the cells cultured in direct contact with the biomaterial. Genotoxic damages were observed in cells that were cultured indirectly with the powdered and sintered iro

Considerações Finais/Final considerations/Consideraciones finales

The previous results showed that the sintering of the metal caused a reduction in the viability of the tested cells, requesting a readjustment in the process. Further studies are needed to determine the toxicity threshold of an orthosis of Fe, considering its biodegradability in the body.

Palavras-chave/Key words/Palabras clave

Adipose Derived Stem Cells, Powder Metallurgy, Biocompatibility, Iron Stent, Biodegradable metallic materials




THAIS CASAGRANDE PAIM, Cristiano Rodrigues, Liliana Sous Naasani, Vinícius Martins, Diego Pacheco Wermuth, André Carvalho Tavares, Marcia Rosângela Wink