Comparative Study of Porous Iron Foams for Biodegradable Implants: Structural Analysis and In Vitro Assessment

Abstract

Biodegradable metal systems are the future of modern implantology. This publication describes the preparation of porous iron-based materials using a simple, affordable replica method on a polymeric template. We obtained two iron-based materials with different pore sizes for potential application in cardiac surgery implants. The materials were compared in terms of their corrosion rate (using immersion and electrochemical methods) and their cytotoxic activity (indirect test on three cell lines: mouse L929 fibroblasts, human aortic smooth muscle cells (HAMSC), and human umbilical vein endothelial cells (HUVEC)). Our research proved that the material being too porous might have a toxic effect on cell lines due to rapid corrosion.

Keywords: biodegradable metals; corrosion; cytotoxic activity; iron; iron-based materials; porosity.

Figure 1

Scheme of the used heat treatment—temperature program; Two most essential processes: I—removal of the polymer template with the flow of gases; II—sintering of iron powder while preserving the template’s structure. (a) Process for Fe01; (b) Process for Fe02.

Figure 2

Comparison of the micro-structure of both iron scaffolds. (a–c) Images show sample Fe01 with increasing magnification. (d–f) Images showing sample Fe02 with increasing magnification.

Figure 3

Energy disperses spectroscopy (EDS) spectrum of synthesized material for (a) Fe01 and (b) Fe02.

Figure 4

Comparison of Raman spectra taken 24 h after the synthesis process for Fe01 (a) and Fe02 (b).

Figure 5

N₂ adsorption-desorption isotherm for Fe01 (red) and Fe02 (blue color) samples.

Figure 6

(a) Graph showing the loss of weight over time during immersion in a pseudo-physiological fluid at 37 °C, (b) Graph showing corrosion rate calculated form Equation (3).

Figure 7

Polarization curves of obtained samples, where (a-blue) Fe01; (b-black) Fe02.

Figure 8

The viability of human aortic smooth muscle cells (a), human umbilical vein endothelial cells (b) and murine fibroblast cell line L929 (c) stimulated with the extracts derived from the tested scaffolds. Cells were incubated for 24, 48 and 72 h with the extracts diluted in an appropriate culture medium using four dilution factors: 1:10, 1:6, 1:3 and 1. Cell viability was presented as a percentage ± S.E.M. of the control cells. Asterisks show statistical differences between the control cells (served as 100%; solid line) and the cells treated with the extracts (*** p < 0.001; ** p < 0.01; * p < 0.05). The dashed line presents the potential cytotoxicity when the cell viability decreases below 70% according to ISO norms.

Figure 9

Lactate dehydrogenase (LDH) release from human aortic smooth muscle cells (a), human umbilical vein endothelial cells (b) and murine fibroblast cell line L929 (c) stimulated with the extracts derived from the tested scaffolds. Cells were incubated for 24, 48 and 72 h with the extracts diluted in an appropriate culture medium using four dilution factors: 1:10, 1:6, 1:3 and 1. The results are expressed as the percentage ± S.E.M. of the cells stimulated with 0.8% Triton X-100 solution (served as 100%). Asterisks show statistically significant differences between the cells cultured in control media (culture medium) and the cells incubated with the corresponding diluted extracts (*** p < 0.001; ** p < 0.01; * p < 0.05).