Jancy Ayyaswamy1 & Sujatha Ramasamy2
1 – Scientist-D & 2 -Scientist-B, Technology Information, Forecasting and Assessment Council (TIFAC), New Delhi, India.
An implant is a medical device manufactured to replace a missing biological structure, support a damaged biological structure, or enhance an existing biological structure. The surface of implants that contact the body might be made of a biomedical material such as titanium, silicone or apatite depending on what is the most functional.
Commonly used biomedical implants are fracture care devices, expandable rib cages, finger and toe replacements, spinal fusion cages, maxio facial prostheses intramedullary nails, external fixators. Titanium and its alloys offer excellent metallurgical features which makes them highly suitable for a wide range of applications including biomedical arena. The exceptionally high strength to weight ratio, outstanding corrosion resistance and tissue tolerance combined with Biological compatibility has made Titanium, the most preferred metal in this field world wide.
Titanium offers a number of advantages over 316L Stainless Steel which was a more familiar choice over the past few decades. The lighter weight (the density of the Titanium is 4.5 gm/cc against 7.85 gm/cc of steel) of an implant made of titanium, imparts more comfort to a patient and facilitate easier movement. Titanium is resistant to inter-granular pitting and crevice corrosion to a much higher degree than stainless steel. The modulus of titanium is closer to that of the bone (bone-20 GPa, Ti = 100 GPa, SS = 200 GPa) compared to stainless steel.
As a result, when a titanium implant is fitted on to a bone, both the implant and the bone flex to a more similar degree, resulting in better stress distribution in the surrounding region and consequent lower osteoporosis (weakening of bone due to calcium depletion) over time. The USP of Titanium over other materials is its property of osseo-integration, which means, Titanium implants have the property to naturally bond with human bone and tissue.
The rib cages, rods, plates and pins, made of Titanium, when once inserted into the body can last for more than 20 years. The dental implants and posts of titanium would last even longer.
Titanium has an added advantage to be used in medicinal field which is its non-ferromagnetic property, that enables the patients with titanium implants to be safely examined with MRIs and NMRIs. On the flip side, there is a disadvantage created by metal implants in human body, viz. corrosion. When a metal device is implanted into the human body, it is continually exposed to extracellular tissue fluid. The exposed metal surface of the implant undergoes an electrochemical dissolution of material at a finite rate, due to interactions with the surrounding environment. In the case of the human body, this environment could contain water, complex organic compounds, dissolved oxygen, sodium chloride, bicarbonate, potassium, calcium, magnesium, aminoacids, proteins, saliva, plasma, lymph etc. On inserting the implant in the body, the tissue environment is disturbed, disrupting blood supply to the surrounding tissue and the ionic equilibrium. The initiation of corrosion could be the result of various conditions existing along the implant surface, whether it is the formation of localized electrochemical cells resulting in pitting attack, or the crevice corrosion at the interface between a plate and a locking screw, or any one of the other forms of corrosion. Studies are underway around the world, to mitigate the problem by adopting a series of surface modification techniques, depending on the type of material used.
Thanks to the efforts of health industry, with the advent of newer drugs day by day, the average lifespan of man has increased. As a part of the ageing process, man would start requiring more biomedical implants. Indian Health care industry should now surge ahead and find new applications for this ‘wonder material’ so that such implants are affordable by a common man and also continue research to manage the risks associated with the implants in human body and finally one-day eliminate the risks also.
- TIFAC Completion Report for the Project on ‘Recycling of Titanium Scrap & Titanium Castings’ prepared by Mishra Dhatu Nigam Ltd