Nanocoating Encourages Bone Growth in Hip Replacements

Hip replacement surgery seems commonplace, what with 1 million Americans receiving the procedure each year. Yet while it may seem routine at this point, the truth is that 17 percent of patients experience some kind of problem with the implant requiring an earlier than expected replacement.

Now researchers at MIT have developed a nanomaterial that could avoid the need for a large portion of these replacements. The research, which was initially published in the Wiley journal Advanced Materials, was able to create a nanocoating that would replace the bone cement typically used in these procedures.

The nanocoating uses hydroxyapatite nanoparticles that not only initially secures the implant to the bone, but also encourages faster bone tissue growth. The bone cement currently used, to fix the replacement hip to the femur, can harden to a consistency like glass—and, like glass, sometimes cracks and detaches from the implant, leaving the patient in chronic pain.

“Typically, in such a case, the implant is removed and replaced, which causes tremendous secondary tissue loss in the patient,” says Nisarg Shah in a news release by MIT News. Shah is a graduate student in Paula Hammond’s lab (which we previously wrote about in the context of lithium ion batteries) and one of the author’s of the research. “Our idea is to prevent failure by coating these implants with materials that can induce native bone that is generated within the body. That bone grows into the implant and helps fix it in place.”

The hydroxyapatite nanoparticles are in fact a natural component of bone and attract mesenchymal stem cells from the bone marrow. The material is also made up of thin layers of other materials that encourage the mesenchymal stem cells to become bone producing cells known as osteoblasts. Together this mix of materials stimulates the production of bone tissue that fills in the space around the implant.

“When bone cement is used, dead space is created between the existing bone and implant stem, where there are no blood vessels. If bacteria colonize this space they would keep proliferating, as the immune system is unable to reach and destroy them. Such a coating would be helpful in preventing that from occurring,” Shah says.

This is not the first time attempts have been made to use hydroxyapatite for orthopedic implants. But previously it has always resulted in coatings that are too thick and suffer the same demise of the bone cement, breaking away from the implant.

The MIT team has been able to control the thickness of the material by using layer-by-layer assembly.

“This is a significant advantage because other systems so far have really not been able to control the amount of growth factor that you need. A lot of devices typically must use quantities that may be orders of magnitude more than you need, which can lead to unwanted side effects,” Shah says.

The research is currently still at the point of animal studies, but the results thus far have been very encouraging, according to the researchers.

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