Metals are strong, durable, plastic, and for many other properties have won their place in medicine, in particular, in orthopedics in the manufacture of bone implants and immobilizers and, especially, sets of surgical instruments.
The main restraints for the use of metal alloys in medicine are their susceptibility to corrosion when reacting with living tissues. In this respect, the platinum group metals are ideal (gold, platinum, iridium, osmium, palladium, rhodium), but they cannot be used en masse, for obvious reasons.
Alloyed stainless steels create excellent sets of surgical instruments, but conflict with body tissues, causing complications. The titanium and tantalum metals became a compromise between these substances: durable, almost not subject to corrosion, having a high melting point, biologically neutral - they are perceived by the body as its own tissue. Due to the “shape memory” effect, these metals have become widely used in vascular and neurosurgery for the manufacture of sutures, sets of surgical instruments, reticular vascular stents, endoprostheses in ophthalmology and dentistry. We will understand their properties.
Titanium is a silvery paramagnetic metal, lightweight and twice as strong as iron, with a low coefficient of thermal expansion and electrical conductivity. At temperatures up to 530–560 ° C, the metal surface is covered with a strong, absolutely neutral protective oxide film of TiO2, and the alloy becomes comparable to platinum. Human lymph destroys it at a rate of 0.00003 mm / year. The most popular medicine brands of titanium are technically pure VT1-0, VT1-00, VT1-00sv. Ta, Al, V, Mo, Mg, Cr, Si, Sn, Zr, Au and platinum group metals are used as alloying additives.
In implantology, orthopedics, and surgery, a Ti-6Al-4V alloy is common, whose mechanocompatibility with bones is close to ideal - 5¸20 GPa. Titanium-niobium alloys have a modulus of elasticity up to 40 GPa and below, and their development is relevant, unlike biotoxic aluminum and vanadium, and titanium nickelide has a “shape memory” and is irreplaceable, in particular, in the treatment of vertebral injuries and muscular dystrophy .
Tantalum is a heavy refractory metal of silver-bluish “lead” shade - a structural metal, highly plastic, well processed by any means (stamping, rolling, forging, twisting, cutting). Tantalum is easily processed into thin wire and rolled into sheets, and is also resistant to aggressive media, which is why it is so valuable in the production of sets of surgical instruments. It is resistant to HNO3, H2SO4, HCl, H3PO4, as well as organic acids of any concentration. In this parameter, it is surpassed only by noble metals, but not in all cases. Like the titanium, the body perceives tantalum as its own fabric.
Tantalum is one of the rare metals: its reserves are approximately 0.0002%, so it is not used in its pure form - only as a film on the base metal. The film, by the way, is three to four times harder than pure titanium.
Steel, titanium and other metal alloys with the addition of tantalum are widely in demand in chemical-medical instrument making. In particular, coils, distillers, aerators, X-ray equipment, sets of surgical instruments, sterilizers, complex devices for duplicating the work of vital organs like “artificial heart”, “artificial lung”, “artificial kidney”, etc., are made of them. Titanium heads of devices for ultrasound have the longest service life of all materials, even under the influence of ultrasonic vibrations.
As part of an extensive range of titanium-tantalum sets of surgical instruments, there are hundreds of names of spatulas, clips, expanders, mirrors, clamps, scissors, forceps, scalpels, sterilizers, tubes, bits and tweezers. The characteristics of lightweight titanium instruments are of paramount importance for military field surgery and various expeditions, where every 5-10 grams of excess load is an essential burden. These metals screen radiation of radioactive isotopes, and therefore are actively used in various protective devices and radiological equipment.
About 5% of tantalum produced in the world is consumed for medical needs. Structures are made from tantalum sheets and wires for plastic, cardio, neuro, and osteosurgery for suturing, splicing bone fragments, stenting, and vascular clipping. With tantalum plates and nets, maxillofacial surgeons splint the jaws, sew muscles, tendons and even nerves with a tantalum thread. Tantalum nets are indispensable in ophthalmoprosthetics.
Static electrofields of the alloy can activate desirable bioprocesses in the human body: tantalum pentoxide coatings have high electret properties; therefore, its electret films are widely used in vascular surgery, endoprosthesis and the creation of medical instruments.
Elastic endoprostheses made of titanium wire mesh are common in reconstructive surgery for plastics of soft tissues - they are strong at zero risk of adverse events. But the main plus of titanium is increased strength combined with low weight.
Half a thousand different designs of vascular stents, differing in alloy (compositions of noble metals, as well as titanium alloys VT6S, VT8, VT14, VT23, nitinol), the length, hole pattern and type of coating have been developed.
Currently, more and more advanced technologies of neuro-osteo- and vasoplasty are being developed, however, titanium-tantalum materials used for this purpose continue to hold the palm in front of all the others.
Titanium-tantalum plates cover the defects of the skull and are used in the cosmetic restoration of the face, chest and buttocks. Clips of titanium or tantalum pinch arterial aneurysm. For the manufacture of clips use flat wire made of pure titanium or tantalum, in some cases - from silver. Such products are absolutely bioinert.
Titan, tantalum and their alloys have found widespread medical use in prosthetic dentistry, because the oral cavity is a rather aggressive environment, and even the precious metals in it are subject to corrosion and tearing away. Extruded and solid titanium crowns are very popular, while plasma-sprayed crowns made of titanium nitride TiN are indistinguishable from gold in appearance and properties.
Dental implant - the basis for crowns, as well as bridges and dentures - is a tapered pin with a thread that is screwed directly into the jaw bone. Most often for the manufacture of the screw part of the implant is pure medical titanium with a surface tantalum-niobium coating, contributing to the activation of the process of osseointegration. There are implants of porous tantalum, more flexible than titanium, and without the risk of complications. Tantalum is heavier than titanium, and its porous structure facilitates the implant, moreover, deposition on tantalum is not required.
In the third millennium, medical science and technology are the main driving forces of civilization, and the importance of titanium and tantalum in modern medicine cannot be overestimated. Despite the short history of use, they have become one of the leading materials in use in many medical areas.
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