Application of titanium alloy in biomedical field

Titanium and titanium alloys are widely used in various biomedical treatment scenarios, including joint and bone replacement, craniofacial and dental implants, surgical instruments, healthcare products, or external and internal prostheses. The usage of titanium alloy in the entire human medical device and the specifications of titanium alloy used in medical devices are shown in Figure 1.

Titanium is widely used in the entire human musculoskeletal structure. The most common biomedical applications of titanium are hip and knee replacement, followed by shoulder and elbow implants. Titanium is also commonly used in the field of spine, including spinal correction components, spinal fixation devices, spinal fusion devices, and in recent years, intervertebral disc replacement. The rib cage made of titanium for children can expand the implant as the body grows, allowing young patients to grow together with the ribs.

 

Finger and toe implants, as well as tibial nails used to reinforce lower leg fractures, are also made of titanium. Nowadays, fixation and reconstruction devices are often used to support fractured bones, such as titanium bone plates, nets, needles, screws, and rods. In order to extend the lifespan of implants for young patients, some applications utilize rough bioactive surfaces to limit absorption and stimulate bone integration.

The application of titanium in neurosurgery and cranioplasty includes skull plates, mesh structures, and acrylic acid. The biocompatibility of titanium helps with faster recovery and reduces the chance of infection. Maxillofacial prostheses made of titanium alloys with appropriate levels of biocompatibility, strength, and osseointegration can stabilize soft tissue prostheses. The application of maxillofacial prostheses after maxillofacial surgery may often be necessary to restore the patient's aesthetic appearance, ability to eat or speak, and replace any missing facial features due to illness or accident injuries. Figure 2 provides a brief description of the design and manufacturing process of a patient specific mandibular prosthesis implant for addressing clinical application related deficiencies in the maxillofacial region.

Titanium alloy is used as a dental implant in dental restoration practice, serving as an artificial tooth root and providing a solid foundation from a single tooth to a complete dental arch. Titanium tooth roots include biocompatible anchors that are implanted into the jawbone through surgery. Once the bone integration period occurs, the natural tooth loses its ability to support the artificial crown. During this period, the bones will grow into titanium implants and surround them to form a strong structural support. Afterwards, use adhesive or screw fastening methods to connect the upper tooth structure components as tooth substitutes to the implant. Orthodontics made of titanium alloy are lighter, stronger, and more biocompatible than steel. In this regard, pure titanium, Ti-6Al-4V, and Ti-6Al-7Nb are the main titanium alloys used in surgical and dental applications. Figure 3 lists the mechanical properties of various titanium alloys used in dental applications.

 

The casting process is crucial for the dental application of titanium, with a focus on low elongation and high strength. Hydrogenation treatment and dehydrogenation treatment are effective techniques for increasing elongation without compromising the strength of cast titanium alloys. These include thermochemical treatment through post heat treatment (such as crushing structures or treatment with beta and alpha beta solutions). Titanium alloys have a higher melting point and are more reactive than other dental alloys, such as Ag and Au based alloys, which are the preferred choice for precision dental castings.

Due to its inherent characteristics such as corrosion resistance, light weight, and toughness, titanium alloys are widely used in the manufacture of temporary or long-term external devices and fixed devices, including prosthetics and orthopedic calipers.

Titanium alloy nails are used to fix false ears and eyes, while pure titanium mesh implants are used to fix orbital fractures. The auditory applications of titanium include bone conduction hearing aids fixed with titanium devices and connected to the middle ear.

 

The carrier structure for replacing heart valves, coronary angioplasty catheters, defibrillators, endovascular stents, pacemaker boxes, and vascular access ports are also made of titanium alloy. The infusion pump uses titanium nickel shape memory alloy, which bends when an electric current is applied, creating heating and cooling cycles that change the shape of the cavity. Urethral stricture can be treated with a titanium urethral stent.

Due to its antibacterial, corrosion-resistant, radiation resistant, durable, and lightweight properties, various surgical instruments such as dental drills, forceps, and laser electrodes typically contain titanium. Titanium is lightweight, reducing the fatigue experienced by surgeons during prolonged use of instruments. For microsurgery procedures such as ophthalmic surgery, titanium surgical instruments are typically anodized to create the necessary non reflective surface for such surgeries. The non-magnetic nature of titanium reduces the possibility of electromagnetic damage or interference to small sensitive implants during surgery. The durability of titanium surgical instruments enables them to withstand repeated sterilization cycles without compromising their corrosion resistance, strength, edge quality, and surface quality.

The application of titanium alloys in healthcare products is constantly expanding. Due to its excellent biocompatibility, low weight, and high strength characteristics, these applications include external prosthetics and wheelchairs, especially those used for sports purposes. The widely used titanium alloys in this regard are TFCA (Ti-4.0Fe-6.7Cr-3.0Al) and TFC (Ti-4.2Fe-6.9Cr), as their costs are lower than pure titanium, as the recovery of titanium containing iron (Fe) or low-cost chromium iron (FeCr) can be used for this purpose.

Even if healthcare products are not implanted in patients, biocompatibility issues such as allergic reactions still need to be addressed, especially for elderly individuals with weaker immune systems who are more inclined to use these healthcare devices. A study involving pure titanium, Ti-6Al-4V, TFC, and TFCA showed that TFC and TFCA had higher cell viability in each group. Therefore, TFC and TFCA may be more widely applied in other types of healthcare products.