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From the 1970s onwards ceramics have been extremely popular in the manufacture of medical devices. Today, advanced ceramics, also called technical ceramics, are becoming increasingly important in the medical industry. This is because these materials are of several different kinds, and have in many cases been developed with very specialized properties, whether heat resistance, mechanical strength, or electrical insulation.
Globally, the market for technical ceramics was USD 62.05 billion in 2016 and this will rise as developing countries make use of biomedical technology, especially in India and China. Such applications include implants, such as femoral heads, brachytherapy seeds for implantable radiation treatment in cancer, implanted sensors.
What are the Characteristics of Implantables?
Bioceramics account for more than 2 percent of such applications such as implants, kidney dialysis devices, pacemakers, and respirators.
Artificial joints must be strong, stable and biocompatible. High fatigue strength and load-bearing capacity, as well as resistance to wear, are essential. These implants must survive within the body for more than 20 years, while they face extreme conditions, such as corrosive salty body fluids, with varying degrees of load in multiple axes and cyclical mechanical loading.
Other essential properties for biomedical applications are non-toxicity, stability, and non-carcinogenicity. These make up what is termed the material’s biocompatibility. Both in vivo and in vitro tests are used to test biocompatibility.
Why are Ceramics so Highly Preferred to Metals and Plastics?
For one thing, advanced ceramics are extraordinary materials. They are mechanically strong, resistant to heat, and compatible with the environment inside the human body without corrosion, in contrast to most metals and polymers.
Moreover, they can resist a combination of extreme conditions for a long duration.
At the same time, they are lighter than most metals suitable for such use.
These materials are dielectric and act as excellent insulators of electrical current. Very detailed miniature circuits can be patterned on them with ease.
Ceramics are inert, which accounts for their resistance to chemical attack.
They have excellent compressive strength and high resistance to wear.
Their manufacture is relatively inexpensive, as a repetitive production process is used to produce a large number of parts. The raw materials are abundant and cheap.
Ceramic powder is pressed into the required dimensions and shapes, reducing the number of secondary production processes. Machining can be done at this stage to increase the geometric or dimensional accuracy to within micron range.
The chief obstacle to more widespread use of ceramics is setting up a process to produce such components instead of plastics or metals. This may prove a relatively new field for most manufacturers of medical devices.
However, another development which has encouraged the shift to ceramics use is the increasing availability of customization and the emergence of newer materials for ceramic parts. Newer customized components are being created for technical applications, often combining a mix of properties. These ensure that great sophistication, high performance, and optimal accuracy, compared to the relatively crude and imprecise performance obtained with more conventional materials.
Most manufacturers expect to be able to supply custom parts for medical devices rather than one-size-fits-all parts in the future, using technical ceramics. This extends from part design all the way down to materials with specific properties required for a particular device. The great advantage of having such novel materials developed by the supplier for each OEM is that they have already passed risk analysis, biocompatibility, mechanical and electrical testing at the original supplier plant. Independent testing by each customer can, therefore, be avoided.
Technical ceramics are of four types: silicate ceramics, oxide ceramics, non-oxide ceramics, and piezoceramics.
Composite materials comprise such zirconia-alumina hybrids as zirconia-toughened alumina (ZTA) and alumina-toughened zirconia (ATZ). Such combinations allow modulation of their properties to enhance the hardness of zirconia and the flexural strength of alumina.
With designs being tweaked to suit individual customers, the material of choice has shifted from traditional ceramics such as alumina (aluminum oxide) to bioceramics like yttria-stabilized polycrystalline tetragonal zirconia (YTZP). This material boasts excellent mechanical strength, with high intrinsic and flexural strength, compared to alumina. Their unique microstructure sets them apart from other ceramics.
What are Bioceramics?
Bioceramics have emerged as important options for joint repair and replacement because they are biocompatible and encourage osteointegration. Some classes, termed bioactive ceramics, bond with bone and even with soft tissue within living organisms. Others are bioresorbable, allowing full integration into the metabolic processes of the organism.
These materials are very similar in structure to the bone matrix, are biocompatible and can be made to specification. Unlike metal implants, which tend to corrode, or metal-covered-by-ceramic hybrids, which degrade over a longer period, ceramic/ceramic composites have important advantages which are making them the preferred choice in this field.
Bioglass and glass-ceramics belong to the bioactive category. Calcium phosphate ceramics are bioresorbable. These are used for orthopedic, maxillofacial surgery, dental implants. They are resistant to abrasion, strong and inert, with low rejection rates and good delayed tissue growth into the pores of the implant.
Carbon-based ceramics are also promising in their compatibility with blood and tissue. Osteointegration is a highly desirable outcome of using such ceramics, especially with glass ceramics and ceramic/ceramic composites, that lack tissue toxicity and have good shaping capabilities.
What are Electroceramics?
Electroceramics is a newer branch of technical ceramics. Some important electroceramics classes include piezoelectric ceramics like lead zirconate titanate (PZT). This material is inert in itself but can convert mechanical energy to electrical or vice versa. This makes it highly suitable for a wide array of medical implants like motors, actuators, sensors, ultrasonic generators, and precision metering valves.
Precision is a hallmark of piezoceramic applications compared to metal components. For instance, when highly toxic drugs need to be infused over a long duration under precise monitoring, the electroceramic provides precise sensing.
Other applications that employ piezoelectric materials require specific electrical characteristics, which may be met by a modification of PZT. This allows the production of thin small components that can be used in sensors built into various devices to monitor bodily processes in situ.
Single crystal piezoelectric materials are also available, able to send and receive sound waves, which makes it suitable for many medical ultrasonic applications. These novel piezoelectric materials enhance the acoustic characteristics but preserve the complex structure of the transducer and acoustic matching methods.
Still, newer categories include the multilayer ceramics and piezocomposites, which have good electrical and mechanical properties.
Sources and Further Reading