Characteristics of Metals for Implantation in Body Piercing
Written by Aidan Jones
When assessing the performance of any material in the human body, it is important to observe all aspects of both biofunctionality and biocompatibility. The medical industry has benefited from a wide range of available materials since the mid 1990s, making it easier to satisfy the mechanical and physical functionality of implantable devices. This means that material selection for medical applications is usually based on considerations of biocompatibility. When considering alloys for implantation, particularly long term, the susceptibility of that material to corrosion and any resulting effects that may have on the surrounding tissue are crucial points in biocompatibility. Corrosion resistance of alloys relies on their passivation by a thin surface layer of oxide.
For medical devices, 316L steel, titanium and Cobalt Chrome are the most commonly used alloys.
In the body piercing industry currently we utilise 316L ASTM F-138 steel and G23 ASTM F-136 titanium, so my comparison will largely be relating to only these two. Of the 3 of these alloys, steel is the least corrosion resistant and in terms of medical devices is only recommended for temporary implants only. Many jewellery companies utilise a variant of the same alloy, 316LVM to improve this. The VM stands for Vacuum Molding. This process is claimed to remove impurities from the steel during the process, thus improving the qualities of the material. This is, however, somewhat of a misnomer as there is no viable method to precisely test and prove these claims. The effectiveness of this process is individual to each piece of jewellery and accurate testing of the process would result in damage or destruction of the jewellery, rendering it unwearable.
Titanium does not corrode in the body, by virtue of the development of a passive oxide film. However, it has been observed that metal ions over time can diffuse through the oxide layer and accumulate in the surrounding tissue.
When metal implants are placed in a human body, they become surrounded by a fibrous layer of tissue proportionate in thickness to the amount and toxicity of these diffused ions and the amount of movement between the implant and the adjacent tissues. Pure and alloyed titanium may elicit a minimal fibrous encapsulation under certain conditions, compared to the development of fibrous layers as much as 2mm thick encountered with the use of steel implants. This fibrous encapsulation containing potentially toxic ion diffusion can lead to further complications depending on the individual’s sensitivity or even allergy to the material, as seen with nickel diffusion. Nickel absorbed into the body can have toxic effects in relatively small doses According to the ADSTR, approximately 10%-20% of the population display sensitivity towards Nickel. While it is true that aluminium can have a toxic effect on the body, this is evident only in incredibly high amounts and usually through absorbing aluminium dust through the lungs. Aluminium can be absorbed orally with no ill effect. Vanadium which is also found the titanium alloy is not toxic in common concentrations. The only notable instance where vanadium becomes toxic is when vanadium pentoxide is released into the air and large amounts of these particles are inhaled.
When considering the biofunctionality of materials for jewellery, tensile strength and weight are critical factors to consider to ensure the health and long term success of a piercing. Titanium alloys like those used in our body jewellery have much higher tensile strength than that of most steel alloys and weigh between 45-60% lighter per volume depending on the alloys compared. Increased tensile strength properties means jewellery maintains structural integrity and function, particularly in styles of construction that utilise tension fittings. Utilising lighter jewellery can assist in minimising the amount of fibrous tissue produced in early stages of wound healing due to minimising weight induced pressure and movement of the jewellery to the surrounding tissues. Minimising fibrous tissue development in the first 4-6 weeks of wound healing is important in mitigating potential long term issues and complications associated with body piercings. Another factor we often face in regards to biofunctionality and piercings is the impact they may have on other procedures, particularly in the case of MRI scanning. Ferromagnetic items like steel body jewellery must be removed prior to an MRI. Implant grade titanium alloys used in surgical implants and body jewellery are paramagnetic, meaning the magnetic fields of an MRI do not affect it.
The presence of metal implants when undergoing diathermy is an important consideration. Titanium implants have a considerably lower electrical and thermal conductivity than those made of steel. Using a judicious approach with Bipolar Diathermy rather than Unipolar Diathermy results in levels of electrical and thermal conductivity through titanium implants that are within tolerable limits to the human body.
When all aspects of purpose are considered for body piercing materials and with the aim of best practice in mind, G23 ASTM F-136 titanium is a superior choice to 316L ASTM F-138 steel. It is lighter, stronger, more corrosion resistant and made of far less toxic materials. All of these factors significantly benefit initial wound healing phases and the long term health of a piercing by virtue of minimising scar tissue encapsulation of the wound site.
Characteristics of metals used in implants. - PubMed - NCBI. [online] Ncbi.nlm.nih.gov. Available at: https://www.ncbi.nlm.nih.gov/m/pubmed/9440845/
Characteristics of metals used in implants.
Gotman I. J Endourol. 1997.
Authors Gotman I1.
Department of Materials Engineering, Technion, Haifa, Israel.
Citation J Endourol. 1997 Dec;11(6):383-9
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