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Knee Joint

One thing baby boomers have in common is the need for joint replacements. The number of hip and knee replacements in the U.S. is approaching one million per year. Over the years ahead, projections indicate there may not be enough surgeons to handle the rapidly growing demand. In many cases, the need for the replacement comes from overuse, injury, or osteoarthritis that led to destruction of cartilage, the flexible connective tissue in hip, shoulder, and knee joints. The common phrase uttered by those facing the joint replacement is “I am down to bone on bone”. All this may change with the development of artificial cartilage.

According to the Journal of Advanced Functional Materials, researchers at Duke University found a way to create artificial replacement tissue that mimics both the strength and suppleness of native cartilage. Native cartilage is smooth and “cushiony”, yet strong and load-bearing. The idea of artificial cartilage is not new, but being able to match the features of the real thing has proven extremely challenging. The concept of artificial cartilage begins with a “scaffold” made from a three-dimensional fabric. Engineered cartilage can be made with a patient’s own adult stem cells, cartilage cells taken from a patient’s knee or, as researchers in Switzerland recently showed, by growing and manipulating cells removed from the nasal septum and implanted in cartilage defects in the knee. The stem cells are injected into the scaffold and then grow into articular cartilage tissue. The fabric is constructed from minuscule woven fibers, with each of the scaffold’s seven layers being about the thickness of a human hair. All of this is now changing and advancing with the advent of 3-D printing.

The toughest challenge has been to develop a material to fill the spaces in between the stem cells — not too hard, not too soft. Xuanhe Zhao, assistant professor of mechanical engineering and materials science at Duke developed the idea of a water-based polymer gel (hydrogel), and collaborated with a team from Harvard University to develop the advanced material. Zhao said It’s extremely tough, flexible and formable, yet highly lubricating. It has all the mechanical properties of native cartilage and can withstand wear and tear without fracturing.”

Case Western Reserve University has received a grant to open a new center designed to develop evaluation technology and set standards for testing and improving engineered cartilage that could one day replace a variety of prosthetic devices. Researchers from across the United States, Europe, and Asia who have committed to both contribute to and use the center met at Case Western Reserve in May. They discussed current technologies and areas to improve. Their first target is knee cartilage.

Creating a large piece of cartilage and implanting it into a knee or hip has not been successful so far, but the new laboratory hopes to find techniques to make it possible.  Comprehensive assessment of engineered cartilage is complex. Experts will come from multiple fields including molecular and cell biology; biomedical, chemical, mechanical and electrical engineering, advanced imaging, and computer modeling.

Hopefully, the new material will be available in the not too distant future. Engineering used to be about designing and building bridges and other large structures. Today, electrical, mechanical, and bio engineers are working with physicians to bring nano-sized structures to our bodies.