Biodegradation of implanted gold in human tissue. TEM images reveal markedly biodegradation of implanted gold and re-crystallization of dissolved gold as nanoparticle of different size, shape and crystallinity. Highly crystalline icosahedral Au nanoparticle and the corresponding power spectrum are shown on top.
Background: Despite the importance of biodegradation for the durability of metal prosthesis and the widely use of gold implants, there exist a lack of knowledge regarding the stability of pure gold in tissue.
Methods: We studied biodegradation of grids of pure gold, nickel, and copper as well as middle ear prosthesis of gold, platinum or titanium. Metals were implanted into rat skin and humans. Dissolution and re-crystallization process of the metals was analysed using SEM, TEM, power spectra as well as elemental analysis by EDX and EELS/ESI.
Results: Biodegradation of gold was detected, presumably by solving and re-precipitation of gold around implants. Gold cluster, nanoparticles, and mesostructures were detected, formed by dissolution and re-crystallization process. This process results into a migration of gold into the farer off tissue. Cellular filaments as biomolecular templates facilitate the formation of mesostructures. Loss of function of middle ear prosthesis by biodegradation is caused by chronic inflammation and fibrosis. Indeed, similar processes were detected with platinum, but in a very lower level.
Conclusion: Noble metal implants undergo biodegradation in oxidative environment in tissue. The dissolution – recrystallization process can be explained by enzyme catalysed redox processes comprising reactive oxygen species and reduction agents as ascorbic acid present in cells and body tissue. Enymes like myeloperoxidase inside lysosomes of inflammatory cells produce hypochloride ions and H2O2 which can dissolve the gold.
General significance: The crucial role of the specific chemical environments of gold implants in tissue for their chemical stability and durability of function has been demonstrated. Due to widely use and importance of gold implants, this finding is of general interes.
Stems of Santalum album (Sandalwood), Mangiferra indica (Mango wood), and Tinospora cordifolia (Giloy) are widely used in the preparation of herbal medicines and formulations in the traditional Indian health care system called Ayurveda. These were analyzed for 4 minor (K, Ca, Cl, Mg) and 13 traces (As, Ce, Co, Cr, Cu, Fe, Hg, La, Mn, Na, Se, V, and Zn) including toxic elements by instrumental neutron activation analysis (INAA). Samples in powder form along with reference materials (NIST SRM 1547 and INCT MPH-2) as comparators were irradiated for 1 min/6 h in Dhruva/CIRUS reactors at BARC, Mumbai. Gamma activity was measured by high-resolution gamma-ray spectrometry. In general, K, Ca, Fe, Mn, and Zn contents are very high in all the samples but Santalum album, widely used as a perfume, is more enriched in K, Ca, Cr, Zn, and Se. The concentration of Ca is always high as a major constituent (> 10 mg/g) in all the stem/bark of plant species. A strong inverse correlation (R2 = 0.9999) was observed between Fe and Zn in all three samples and that may be useful in drug manufacturing.
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