Sugary coating could help implants bond with weakened bone
It can be tricky enough getting titanium implants to bond with the surrounding bone, but when the patient has osteoporosis, things get even harder. An experimental coating may help, though, by first boosting and then blocking inflammation.
Osteoporosis results in low bone density, meaning that there's simply less bone tissue to grow into (and integrate with) the surface of an attached titanium implant, such as an artificial hip. As a result, the implant may come loose and fail over time.
Working with colleagues from the National Dental Centre Singapore, scientists from China's University of Macau and Nanjing University set about addressing that problem, by creating the new coating. Chemically bonded to the surface of a titanium implant, it's made up of a modified glycan (a string of linked sugars) along with a bisphosphonate osteoporosis-treatment drug.
When a coated implant is first attached to osteoporotic bone, the glycan prompts the body's nearby macrophage immune cells to initiate inflammation. In the process of doing so, they activate bone cells in the area to grow, so the bone essentially heals itself onto the titanium. If that inflammation were to continue unchecked, though, it would actually set back the healing process.
Fortunately, once the new bone cells have become functional, they naturally secrete an enzyme called alkaline phosphatase. It cleaves the glycan and bisphosphonate from the implant's surface, freeing up the latter of the two to kill the same macrophages that previously activated the bone cells. With those immune cells now gone, the inflammation ceases, but the newly grown bone remains.
In tests performed on rats, the coating reportedly enhanced bone-implant integration by 88.4 percent.
"Interestingly, these macrophages to be killed in the latter part of this healing process are exactly the guys who have made the major contribution to release pro-bone forming cytokines in the earlier stage," says the University of Macau's Prof. Chunming Wang. "So, we described this design as a 'bridge-burning' strategy."
A paper on the research was recently published in the journal Advanced Functional Materials.