Hydroxyapatite(HA), Growth Factors and Nanotechnology are all increasingly familiar words for anyone involved in medical technology. Now researchers at world famous MIT have worked their magic and come up with a thin, layered coating which combines the osteoblast friendly HA with a tuned dose of growth factor in a way which optimises prosthetic implant integration and makes current cemented techniques look decidedly old-school.
According to an MIT news release, every year, more than a million Americans receive an artificial hip or knee prosthesis. Such implants are designed to last many years, but in about 17 percent of patients who receive a total joint replacement, the implant eventually loosens and has to be replaced early, which can cause dangerous complications for elderly patients.
To secure hip and knee prosthetic implants, one option is to use bone cement, a polymer that resembles glass when hardened. In some cases, this cement ends up cracking and the implant detaches from the bone, causing chronic pain and loss of mobility for the patient.
A team of MIT chemical engineers has developed a new coating for implants that could help them better adhere to the patient’s bone, obviating the need for cements and preventing premature failure.
The new coating consists of a very thin film, ranging from 100 nanometers to one micron, composed of layers of materials that help promote rapid bone growth. One of the materials, hydroxyapatite, is a well characterised natural component of bone, made of calcium and phosphate. This material attracts mesenchymal stem cells from the bone marrow and provides an interface for the formation of new bone. The other layer releases a growth factor that stimulates mesenchymal stem cells to transform into bone-producing cells called osteoblasts.
Once the osteoblasts form, they start producing new bone to fill in the spaces surrounding the implant, securing it to the existing bone and eliminating the need for bone cement. Having healthy tissue in that space creates a stronger bond and greatly reduces the risk of bacterial infection around the implant.
Speaking about current implant failure, lead author Nisarg Shah says “Typically, in such a case, the implant is removed and replaced, which causes tremendous secondary tissue loss in the patient that wouldn’t have happened if the implant hadn’t failed. 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.”
“This would allow the implant to last much longer, to its natural lifetime, with lower risk of failure or infection,” says Paula Hammond, the David H. Koch Professor in Engineering at MIT and senior author of a paper on the work appearing in the journal Advanced Materials.
Haven’t we heard this before?
HA coating and use of growth factors is not unknown in prosthesis development. What’s different here however is that the MIT team can control the thickness of its film and the amount of growth factor released by using a method called layer-by-layer assembly, in which the desired components are laid down one layer at a time until the desired thickness and drug composition are achieved.
“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.
Source: MIT News