Ceramic Implant Material Would Allow Ultrasound Brain Surgery

Over the past several decades, bioceramics have helped improve the quality of life for millions of people. These specially designed materials, which include polycrystalline aluminum oxide, HA (a calcium phosphate mineral that is also the major component of bones in vertebrates), partially stabilized zirconium oxide, bioactive glass or glass-ceramics, and polyethylene-HA composites, have been successfully used for the repair, reconstruction and replacement of diseased or damaged parts of the body, especially bone.

Researchers from the University of California, Riverside recently developed a ceramic skull implant that could make it easier to tackle diseases such as cancer and Parkinson’s with pioneering ultrasound treatment.

Ultrasound—sound waves that operate at a higher frequency than those audible to humans—can be used to treat a variety of brain disorders, including Alzheimer’s and Parkinson’s diseases. Ultrasound can also be used to kill cancer cells, dissolve blood clots during stroke, and open the blood-brain barrier to enhance drug delivery.

But while ultrasound brain surgery offers enormous potential for treating neurological diseases and cancers, getting sound waves through the skull and into the brain poses considerable challenges. The cranium is between 2 and 8 mm thick, and because it's relatively dense, most sound waves are reflected or absorbed before they reach the brain.

“When you're generating sound waves and trying to penetrate sound waves through structures, these sound waves can be dispersed through a process called attenuation,” Andrew Feeney, a research fellow at Warwick University’s Centre for Industrial Ultrasonics, tells Amit Katwala. “Bone has quite a high attenuation factor, which means that it disperses sound waves in a particular way compared to the media surrounding it.”

But the bioceramic implant developed by the UCR researchers overcomes that challenge by allowing doctors to deliver ultrasound treatments on demand, and on a recurring basis.

The transparent ceramic material, which would replace a portion of the cranium, is a new variation of the ceramic material Yttria Stabilized Zirconia (YSZ). The material is non-porous, which would allow non-focalized, low-intensity ultrasound waves to pass through it and into the brain.

Ceramic materials show significant promise because they are biocompatible, extremely hard, and shatter resistant, making them ideal for implants. The team previously developed a YSZ cranial implant material for laser-based therapies, which is already in preclinical trials.

According to Guillermo Aguilar, professor and chair of mechanical engineering in UCR’s Bourns College of Engineering, the materials are already being used in dental crowns and hip replacements. His team is working to extend their application to the diagnosis and treatment of a wide variety of brain pathologies and neurological disorders.

“Developing an optically and radio-frequency transparent cranial implant was already an exciting accomplishment, and we continue to work to make this implant a reality. Now, proving that ultrasound could be transmitted through the implant could expand its therapeutic capabilities even further.”

Javier E. Garay, professor of mechanical and aerospace engineering at the University of California, San Diego’s Jacobs School of Engineering, led the project with researchers from Centro de Investigación y de Estudios Avanzados (CINVESTAV) del Instituto Politécnico Nacional (IPN), in México City.

Garay says the team's findings could extend the application of zirconia, a material sometimes called the “steel of ceramics” because of its versatility.

“It is important to appreciate that the zirconia we developed works well for this application because we engineered it to have low porosity," Garay says. "Porosity, a common defect in ceramics produced by traditional methods, significantly deteriorates ultrasound transmission as we show in this paper."

The current material could be used to deliver both ultrasound and laser-based treatments.

The research was published in the journal Advanced Healthcare Materials.