It will be interesting to watch the accelerating development of biological versus non-biological replacements for damaged tissue over the next few decades. Both are improving at a fair pace, and there is a sizable area of overlap between the two sides of the field. If a nonbiological alternative gets the job done, then why not use it in place of engineered tissue? At the moment, new patient-matched engineered tissue would be a better long term alternative, considering the various challenges that result from introducing long-term implants into the body, but in near all cases that is not yet an option. Twenty years from now, however, many forms of replacement will have competing tissue engineered and wholly artificial alternatives available in the market, and the trade-offs will be more subtle.
The liquid strength of cartilage, which is about 80 percent water, withstands some of the toughest forces on our bodies. Synthetic materials couldn't match it until "Kevlartilage" was developed. Many people with joint injuries would benefit from a good replacement for cartilage, such as the 850,000 patients in the U.S. who undergo surgeries removing or replacing cartilage in the knee. While other varieties of synthetic cartilage are already undergoing clinical trials, these materials fall into two camps that choose between cartilage attributes, unable to achieve that unlikely combination of strength and water content.
The other synthetic materials that mimic the physical properties of cartilage don't contain enough water to transport the nutrients that cells need to thrive. Meanwhile, hydrogels - which incorporate water into a network of long, flexible molecules - can be designed with enough water to support the growth of the chondrocytes cells that build up natural cartilage. Yet those hydrogels aren't especially strong. They tear under strains a fraction of what cartilage can handle.
The new Kevlar-based hydrogel recreates the magic of cartilage by combining a network of tough nanofibers from Kevlar with a material commonly used in hydrogel cartilage replacements, called polyvinyl alcohol, or PVA. In natural cartilage, the network of proteins and other biomolecules gets its strength by resisting the flow of water among its chambers. The pressure from the water reconfigures the network, enabling it to deform without breaking. Water is released in the process, and the network recovers by absorbing water later. This mechanism enables high impact joints, such as knees, to stand up to punishing forces. Running repeatedly pounds the cartilage between the bones, forcing water out and making the cartilage more pliable as a result. Then, when the runner rests, the cartilage absorbs water so that it provides strong resistance to compression again.
The synthetic cartilage boasts the same mechanism, releasing water under stress and later recovering by absorbing water like a sponge. The nanofibers build the framework of the material, while the PVA traps water inside the network when the material is exposed to stretching or compression. Even versions of the material that were 92 percent water were comparable in strength to cartilage, with the 70-percent version achieving the resilience of rubber. As the nanofibers and PVA don't harm adjacent cells, researchers anticipate that this synthetic cartilage may be a suitable implant for some situations, such as the deeper parts of the knee.
Link: http://ns.umich.edu/...-the-real-thing
View the full article at FightAging
