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Snapshots of Life: Inside a Bone Remodeling Project

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Osteoclast cells

Caption: Osteoclast cells (red) carve a path through a knee joint (purple and white), enabling a blood vessel to supply the cells (yellow) needed to build new bone.
Credit: Paul R. Odgren, University of Massachusetts Medical School

Bones are one of our body’s never-ending remodeling projects. Specialized cells, called osteoclasts, are constantly attaching to old bone and breaking it down, using acids to dissolve the calcium. In the wake of this demolition, bone-building cells, called osteoblasts, move in and deposit new minerals to patch and remodel the bone, maintaining its strength and durability.

Normally, these two types of cells strike a delicate balance between bone destruction and formation. But if this balance goes awry, it can lead to trouble. With osteoporosis, for example, bone removal exceeds formation, yielding progressively weaker bones that are prone to fracture.

Promoting the Long Term Marriage of Bone and Implant

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Photo of lumpy red material entering an object that is silver with brown stripes.

Caption: Here we see the host bone (red and blue) growing in a cavity of the implant (brown and sliver). A new coating on the implant encourages this stable bond.
Credit: The Hammond Research Group, David H. Koch Institute of Integrative Cancer Research at MIT

Hip, knee, and shoulder joints get worn over time, or damaged by disease or injury. They often require replacement because they cause pain and inhibit movement. Orthopedic surgeons perform more than 1 million joint replacements each year. The worn bone is replaced with plastic or metal implants and cemented in place. The surgery can provide immense relief and restore mobility. But sometimes these implants don’t integrate well with the bone, and ultimately they break free. Replacement surgeries are costly, increase the risk of infection, and are a major challenge for the patient to endure. But recently an NIH-funded team of chemical engineers at MIT developed a special coating for implants that promotes a stronger connection to new bone.

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