Good news is now arriving frequently from the tissue engineering community, who really seem to be hitting their stride of late, especially when it comes to muscle. Recreating structured muscle is the simple stuff on a relative scale of difficulty - at least in comparison to lungs and other intricate organs - but this is still a very challenging task. Dumb muscle isn't just dumb muscle: it has to be the right shape, have the right nerve structures, the right distribution of tiny blood vessels, the right layering and fiber types, and so forth. Don't underestimate just how much work was involved in coming to the point at which researchers can announce this latest advance:

Researchers have built the first functional anal sphincters in the laboratory, suggesting a potential future treatment for both fecal and urinary incontinence. Made from muscle and nerve cells, the sphincters developed a blood supply and maintained function when implanted in mice.

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Current options for repair of the internal anal sphincter include grafts of skeletal muscle, injectable silicone material or implantation of mechanical devices, all of which have high complication rates and limited success. To engineer an internal anal sphincter in the laboratory, the researchers used a small biopsy from a human sphincter and isolated smooth muscle cells that were then multiplied in the lab. In a ring-shaped mold, these cells were layered with nerve cells isolated from mice to build the sphincter. The mold was placed in an incubator for nine days, allowing for tissue formation. The entire process took about six weeks.

Numerous laboratory tests of the engineered sphincters, including stimulating the nerve cells, showed normal tissue function, such as the ability to relax and contract. The sphincters were then implanted just under the skin of mice to determine how they would respond in the body. Mice with suppressed immune systems were selected so that there would be no issues with rejection. ... After 25 days of implantation, each sphincter was re-tested and also compared with the animals' native sphincters. The engineered sphincters had developed a blood vessel supply and continued to function like native tissue.

As the news release points out, this is one of the areas where the available prosthetic alternatives are just not that great; engineering a replacement sphincter in machinery is a hard challenge at our present level of technological prowess. So that a research team has constructed a functional biological sphincter is very promising - and this is especially true given that there are dozens of sphincters scattered throughout the body. It is an oft-reused structure, and being able to build any one type of sphincter from a patient's own cells implies that building the others is also a very realistic goal. So all in all, this is an encouraging example of progress in the field.