Nanotechnology proposed to improve bone implants

Nanotech advances are leading toward bone implants that are are smart, multifunctional devices that will be capable of improved integration with surrounding bone tissue, and that will resist inflammation, bacterial growth, and the recurrence of bone cancer. From Chemical Technology magazine “Instant insight: Bone repair breakthrough“:

Thomas Webster and colleagues at Brown University, Providence, US, explain why today’s bone implants are so much more than your grandparent’s hip replacement thanks to nanotechnology

Bone fracture is very common among the elderly as bones become more brittle as we age. Active young people also have a high risk of bone fracture through every day life and sporting activities. If a fracture is small, it can be filled with bone cement, such as polymethylmethacrylate. However, if the fracture is large, more durable metal implants, such as titanium and titanium-based alloys, are used. The goal is to not only fill the fracture space with a strong material that can support the body’s weight, but also to promote new bone growth to fully restore the bone’s functions.

In the past, bone implants were made of inert materials, chosen because they didn’t severely influence bodily functions or generate scar tissue, which is a thick, insensitive tissue layer that can form around an implant. But this simple design principle causes implants to loosen from the surrounding bone after around 10 to 15 years. Loosening becomes worse with time and can cause significant pain. As a result, patients often undergo additional surgery (called revision surgery) to remove the loose implant and insert a new one. Revision surgery is clearly undesirable as it is costly, painful and requires therapy all over again for the patient. …

Nanotechnology has taken a bold new step towards improving orthopedic implant devices. Orthopedic nanotechnology is based on understanding cell-implant interactions. Cells do not interact directly with an implant but instead interact through a layer of proteins that absorb almost instantaneously to the implant after insertion. Scientists have improved numerous implant materials, including titanium and titanium alloys, porous polymers, bone cements and hydroxyapatite, by placing nanoscale features on their surfaces. The bulk materials’ properties remain unchanged, maintaining their desirable mechanical properties, but the surface changes enhance the interactions with proteins. This causes bone-forming cells to adhere to the implant and activates them to grow more bone.

Scientists are also creating ‘smarter’ implants that can sense what type of tissue is growing on them, communicate the information to a hand-held device and release drugs on demand to promote tissue growth. These implants are designed to help avoid complications frequently observed after bone implantation, such as infection, inflammation (or scar tissue growth), implant loosening and, in the case of bone cancer, cancer reoccurrence. Scientists have been investigating implants that have inherent mechanisms to protect the body from infection (such as silver and zinc) or inhibit cancer growth (such as selenium).

Significant promise can be drawn from recent advances in biomaterials research, especially where nanotechnology is involved. But discovering the perfect biomaterial that can last the lifetime of a patient is still a challenge.

The authors present their proposals for nanotechnology-enabled bioactive bone implants in the Journal of Materials Chemistry (abstract) (free access full text).

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