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Metals and Minerals in Medical Implants

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Metals and minerals are vital components of medical devices that allow millions of people to enjoy healthy lifestyles. Devices implanted into the human body can replace, support, or enhance an existing body part. Other devices can diagnose, monitor, or treat clinical conditions, both saving lives and improving people’s quality of life. There are a wide variety of medical devices with different minerals and metals in each one. Here are just a few examples:

 

 

Dental Implants

are permanent fixes placed in the jawbone to provide a stable base for an oral prosthesis such as a crown, bridge, denture, or even a broader facial prosthesis. The commodities listed are preferred due to resistance to corrosion, the unlikelihood of them causing a negative reaction from the body, their ability to be molded into shape to fit the jaw, and their strength.

 

COBALT
Cobalt-chromium-molybdenum alloys are mainly used for denture frameworks.1
Image Source: By James St. John

GOLD
Gold is used in dental prostheses, including inlays, onlays, crowns, bridges, periodontal splints, and post and cores.2 The most common gold alloys are copper, platinum, zinc, or silver, which are used to strengthen the gold.3

IRON
Iron is a major constituent for stainless steel and is one of the most common metals used for dental crowns, dental surgical tools, and instruments.4

NICKEL
Nickel is alloyed with titanium to make nitinol, which is used in dental braces and dental drills.5

SILVER
Silver is alloyed with other metals (tin, zinc, and copper) to make dental fillings.6

TANTALUM
Tantalum can be used to coat carbon foam scaffolds to create a biocompatible replacement for bone implants, including dental implants. It is porous and improves contact between bone structure and dental implant.7
Image Source: By Jurii

TITANIUM
Titanium has mechanical properties quite close to bone, and it allows for osseointegration, a process which allows bone to integrate with the metal.8 

ZIRCONIUM
Zirconium is a major constituent for ceramics used for dental applications.9 Its wear-resistance properties, inertness, and mechanical properties are well-suited for dental crowns.10

 

 

Sensory and Neurological Implants

are implantable devices that communicate with the nervous system to either record electrical nerve activity or to electrically stimulate nerve cells that would improve senses that are not functioning properly. Examples include:

Cochlear Implants are designed to transmit sounds of speech into the brain, allowing the person to hear. 

Retinal Prostheses are fitted with sensors that trigger an electronic pulse. This pulse then stimulates nerves in the retina, which pass signals down the optic nerve to the brain to create an image. 

Electrical Stimulators or Functional Neuromuscular Stimulation are devices that deliver electrical impulses to nerves in the brain, treating disorders as deafness, incontinence, chronic pain, depression, and Parkinson’s disease, among others.

 

GOLD
Gold-based electrodes is used in bioelectronics—as electrical conductors for glucose biosensors, cochlear implants, and in electrodes that enable communication between the brain and various machine formats.11,12

IRIDIUM
Iridium-oxide is used as a coating for gold, copper, and titanium wires for functional electrical stimulation electrodes.13
Image Source: By James St. John 

LITHIUM
Lithium-iodide batteries are suitable for implantable devices due to their long lifespan (reducing the need for repeated surgeries to replace the battery), low-discharging drain, stable voltage characteristics, and reliable performance. The lithium battery chemistry is also convenient for devices that need to be small and lightweight.14

PLATINUM
Platinum is currently one of the best electrode materials and is also used in guidewires, neuromodulation devices and stents, coils, and catheters.15,16

SILVER
Silver is used as a coating agent in implant devices due to its anti-inflammatory and infection suppressant properties.17

TITANIUM
Titanium is also used as an electrode material, as well as a non-toxic exterior for medical implants.18

 

 

Orthopedic Implants

are used to relieve issues with the bones and joints in the body. They can be either permanent joint replacements or temporary implant devices. Permanent orthopedic implants are expected to stay in the body for a long time. They can be implanted into joints like hips, knees, ankles, shoulders, elbows, and wrists. Temporary orthopedic implants, meanwhile, are small devices needed to fix fractured bones and are expected to serve for a short period of time until the bones heal. These include plates, screws, pins, wires, and nails.

 

ALUMINUM
Aluminum is used as a major alloying element with titanium for orthopedic applications. The ceramics used in orthopedic implants also contain aluminum oxide and calcium phosphates.19,20

CHROMIUM
Chromium is used in cobalt-chromium-molybdenum alloys. It is known for imparting corrosion resistance to the alloy.21

COBALT
Cobalt alloys for surgical applications are mainly related to orthopedic prostheses for the knee, shoulder, and hip, as well as fracture-fixing devices.22
Image Source: James St. John

IRON
Iron is a major constituent of stainless-steel alloys, and it is used in fracture-fixing plates and bone screws.23

MAGNESIUM
Magnesium and its alloys are used to fabricate degradable metal implants, such as bone screws and plates. It is often alloyed with aluminum and zinc to control its degradation rates.24

MOLYBDENITE
Molybdenum is alloyed with chromium and cobalt to impart hardness and make the alloy highly wear-resistant. It is also added to stainless steel to improve its corrosion resistance.25

NICKEL
Nickel is added to stainless steel to improve its pitting corrosion resistance when used in orthopedic devices. Nickel-titanium alloys are used in spinal fixation, compression screws, plates, and limb-lengthening devices.26

TITANIUM
Titanium is commonly alloyed with other metals to improve certain properties, most commonly aluminum and vanadium, and has the ability to physically bond with bone.27

ZIRCONIUM
Zirconium and its oxides are hard, resistant to wear, and biocompatible. They are a major constituent for ceramics and have been used in joint replacement.28

 

 

Cardiovascular Implants

are used in cases where the heart, its valves, and the rest of the circulatory systems are in disorder. These include artificial hearts, artificial heart valves, cardiac pacemakers, implantable cardioverter-defibrillators, and coronary stents.

 

CHROMIUM
Chromium and its alloys are used in heart valves.29

COBALT
Cobalt and its alloys are used in defibrillators and are designed to send small electrical impulses to the lower chambers of the heart to help them beat in more synchronized patterns and reduce patient symptoms. Cobalt-chromium or stainless steel is used in catheters and stents.30,31

GOLD
Due to its good electrical conductivity, gold is often used to interface between different electrical connections on electronics circuit boards in implantable pacemakers and defibrillators.32

IRON
Stainless steel, which includes iron, is commonly used in guidewires, catheters, and endovascular grafts due to its excellent mechanical properties.33

LITHIUM
Lithium-iodide batteries are suitable for implantable pacemakers due to their long lifespan (reducing the need for repeated surgeries to replace the battery), low-discharging drain, stable voltage characteristics, and reliable performance. The lithium battery chemistry is also convenient for devices that need to be small and lightweight.34

MAGNESIUM
Magnesium and its alloys are used to fabricate degradable metallic stents. It is often alloyed with aluminum and rare-earth elements to control its rate of degradation.35

NICKEL
Nickel-titanium alloys (nitinol) are well-suited for cardiac implantable devices.36,37,38

PLATINUM
Platinum is known for its corrosion resistance and is often used as lead tips for pacemakers and defibrillators. It is also used as radiomarkers on stents, catheters, and guidewires, which improve visibility during cardiovascular procedures, such as balloon angioplasty or stenting.39,40,41

TANTALUM
Tantalum, due to its radio-opacity, is used as a radiomarker on stents and endovascular grafts.42,43,44
Image Source: By Jurii  

TITANIUM
Titanium and its alloys are used in pacemaker encapsulation.45,46

 

The USGS delivers unbiased science and information to increase understanding of ore formation, undiscovered mineral resource potential, mineral production, mineral consumption, and how minerals interact with the environment. The USGS supports data collection and research on a wide variety of non-fuel mineral resources that are important to the Nation’s economic and national security. The agency’s mission is to provide reliable scientific information to describe and understand the Earth; minimize loss of life and property from natural disasters; manage water, biological, energy, and mineral resources; and enhance and protect our quality of life.

www.usgs.gov/minerals

 

Citations:

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