What does a billionaire-genius-scientist/superhero from a fictional marvel universe have to do with a real life project with serious beneficial scope to real world people? Well it’s not the character of Tony Stark we speaking of, while all due respect to his character for saving half the fictional universe from the mad titan Thanos. But here the reference is towards his suit, especially the Mark III exoskeleton made by Tony Stark as shown in the movie Iron Man (2008). In the movie Tony Stark initially conceptualises the idea of a metallic exoskeleton, Mark I to escape the terrorist group 'Ten Rings' and later improves the model to Mark II when he is safely back in his mansion in Malibu, California. But the structural failure of the Mark II model by freezing out upon reaching the upper atmosphere, forces him to rethink the material system to make his iron suit out of. The solution comes in the form of a Titanium-Gold alloy inspired from a 'Seraphim Tactical satellite' to maintain the fuselage integrity while maintaining the power to weight ratio. Later towards the end, Tony confirms once again that his suit is made up of Gold-Titanium alloy but will stick with the title iron man because the term is "kind of evocative, the imagery, anyway". And according to ironman.fandom.com/wiki , every armour since Mark III has used gold titanium as its shell metal, which gives armour its super hardness and the bio-compatibility to perform extraordinary feats together with the character of Tony Stark
Tony Stark was not far away from reality when he says that Titanium has excellent power to weight ratio, though according E. Svanidze et al (2016) the term should be high strength to weight ratio. Other properties of Titanium which makes it an ideal choice for biological implants are its ability to form a very stable and inert oxide layer, low ion formation levels in aqueous environments, formability and machinability. Further, Ti is one among a few materials capable of osseointegration : which is the ability to provide a contact between bone and implant without the need for a soft connective layer between the two (Yang.Y, et al 2006). High hardness value makes Titanium a popular choice to fabricate bone, dental and cardiovascular implants.
Body parts requiring implants are generally the ones which undergo repetitive cyclic motion for a prolonged number of years for example hip and knee joints. The implants put in these positions face the same repetitive cyclic motion, subjecting these implants to wear and tear of the surface and releasing flakes or ions into biological system. Commercially pure (CP) Ti is not strong enough for a number of medical applications, which require higher strength. The hardness value of Ti can be improved by alloying the pure Ti with additional elements like Cu, Ag, Nb, Zr, Al, V etc. and numerous works have been carried out on these. But it is equally important not to compromise on biocompatibility of the end material system while trying to increase its hardness. The most commonly used alloy composition for fabrication of medical implants is Ti-6Al-4V ELI (Extremely Low Interstitial) grade (Mohammed.M.T, 2017). However, recently it has been shown that Al and V ions released into biological systems are responsible for numerous neurological disorders and toxicity in human tissue like Alzheimer disease and osteomalacia (Gepreel and Niinomi, 2013). Because of either mechanical or chemical failure, most of the biological implants fail within a decade of their replacement surgery and then need to be followed up by revision surgery, which is a painful and expensive procedure.
In 2016, Emilia Morosan and Eteri Svanidze, published an article which suggest a 3-4 times improvement in hardness of Titanium by alloying it with Gold at higher temperature. Gold is another material which is known to possess excellent bio-compatible properties. But the results published by E. Svanidze et al, 2016, were from their experiments on bulk samples prepared by arc melting the Titanium and Gold in stoichiometric ratios. Gold is an expensive metal and using it as the main substituent is bound to increase the cost of implants, thereby making it inaccessible to a major portion of patients requiring these implants. This project proposes depositing a thin film of beta Ti3Au on the commonly used implants to impart higher hardness and bio-compatibility, thereby prolonging the life of these implants without driving the cost higher. The results published by Karimi A. et al 2018, on thin film Ti-Au system for jewellery industry are indicative of improved hardness of Ti by addition of Au. To the best of the knowledge this would be first time a dedicated research is performed on thin film format of beta Ti3-Au system to access its suitability to fabricate biological implants. Though this research will not perform the similar wonders as Tony Stark's exoskeleton suit (not yet!!), if found suitable, this material will alleviate pain and burden caused by revision surgery of biological implants by prolonging their life cycle. Till then it’s good to know that Marvel cinema does use realistic assumptions in their fictional universe.
Keep checking the blog to learn more about various biocompatible materials used in medical implants and their interesting properties….
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