Ceramic coatings on devices such as this drug-eluting stent equip metal materials with ceramic properties.
One area in which ceramic use is expanding is hip-replacement implants. Conventional hip replacements consist of metal-to-plastic components. However, the friction of the components, especially those made from polyethelene, produces debris. In turn, the debris causes inflammation, which reduces the efficacy of the product over time. This results in the need for revision surgery after roughly 15 to 20 years.
Component erosion rarely posed a problem in the past. Because patients requiring hip replacements tended to be elderly, their life spans were not supposed to outlast that of the implant. However, the demand for replacements from both younger patients and older people who continue their active lifestyles into retirement thrust revision surgery to the forefront of hip-replacement concerns.
Ceramic components may quell these concerns. “Studies have shown that ceramic particles produce less cell reaction than poly or metal particles,” says Keith Ferguson, business development manager for Morgan Technical Ceramics (San Mateo, CA; www.morgantechnicalceramics.com). “Loosening of hip joints may be caused by particulates generated in the implanted joint, so ceramic appears to be a favorable choice.”
Morgan Advanced Ceramics produces both Vitox implantable-grade alumina and Zyranox implantable-grade zirconia. According to the company, trials conducted on its HIP Vitox ceramic-on-ceramic hip joints demonstrated a wear rate of as little as 0.032 mm3 per million cycles.
Ceramic-on-ceramic hip replacements may produce less debris than implants having plastic or metal components.
“Ceramic is hard to beat!” says Ferguson. “Ceramic-on-ceramic coupling produces the lowest volume of particulates of any commercial coupling to date.” He also notes that polyetheylene-on-metal, cross-linked polyethylene-on-metal, and metal-on-metal implants may produce 100 to 1000 times more particles than ceramic-on-ceramic implants.
It may be too soon to gauge the effects of time on ceramic-on-ceramic hip replacements. But clinical studies monitored by FDA have indicated that
ceramic hip replacements produce negligible amounts of debris and have the potential to last significantly longer than their predecessors.
Despite the facts, many people remain skeptical of ceramic hip implants, resulting from a 2001 recall of one supplier’s zirconia-based components that experienced fracturing. However, most modern ceramic implants are constructed from alumina, which has demonstrated durability. Since FDA approval of complete ceramic-on-ceramic implants in 2003, there has been little negative backlash.
Currently, ceramic hip replacements are used primarily for younger hip-replacement candidates, or those who lead active lifestyles. Widespread acceptance of ceramic replacements is slow, due to their being relatively new to the market and more expensive than traditional replacements.
Ceramics’ presence in hip replacements is becoming increasingly noticeable, but use of the materials is emerging as a trend in other implants as well.
Regardless of their bioactive properties, ceramics are not always the best choice for an application. Yet nonceramic components and devices can reap the benefits of bioactivity through the use of ceramic coatings. Most commonly used on implants made from metallic alloys, hydroxyapatite coatings facilitate the bonding of bone to implants. The bone-bonding capabilities of hydroxyapatite are often credited with prolonging the life of hip and knee implants.
“We believe in the long-term biocompatibility of ceramics,” says Laurent-Dominique Piveteau, project manager for Debiotech SA (Lausanne, Switzerland; www.debiotech.com). “These are, most of the time, inert materials that have shown excellent behavior when implanted. By using them as thin coatings on a metallic substrate, we combine the best of two worlds: we have the mechanical properties of the metals, but the body is in contact with the stable ceramic.”
Debiotech has licensed a ceramic technology to produce the Debiostent, a drug-eluting stent that features a ceramic coating for biocompatibility. The company also attributes unique drug-absorption properties to the porous ceramic coating, thus establishing the material as suitable for some drug-delivery applications.
The firm plans on applying the coating to other implantable devices in the future. “We will be able to combine short-term drug delivery and long-term stability,” says Piveteau. “After implantation, the devices will locally release drugs over a few days or a few weeks. In the longer run, when the drug isn’t needed any more, we will have an implant that integrates easily into the body.”
Though the rise of ceramics in coatings and hip replacements is perhaps the most noticeable, ceramic use is becoming increasingly prevalent in components for other implantables. Greatbatch Inc. (Clarence, NY; www.greatbatch.com) produces a range of electromagnetic interference (EMI)–filtered hermetic feed-throughs. Feed-throughs are integral pieces in such implantables as pacemakers, cardioverter defibrillators, neurostimulators, and cochlear electronic devices, protecting these life-supporting devices from exposure to EMI. Feed-throughs and other ceramic implantables play vital roles in enabling normal lifestyles for patients with otherwise debilitating problems.
“Ceramics will continue to play a strong roll in implantables. In addition to hips, all other load-bearing joints are good candidates for ceramics, including the spine,” says Ferguson.
Beyond their use for implants, ceramics are impacting the medical device and manufacturing community through their use in various other devices. Piezoelectric ceramics are frequently employed in transducers for computed tomography and ultra-sonic imaging systems. Meanwhile, ceramic bearings for linear motion applications withstand harsh environments and meet stringent manufacturing requirements issued by FDA.
From components to coatings, the employment of ceramics in implantable devices is a growing trend in the industry. Proving that they aren’t just for vases, ceramics are improving the quality of life and extending lives.