LOS ANGELES — Dr. Tracy Grikscheit held a length of intestine in her gloved hands, examining it inch by inch as if she were checking a bicycle tube for leaks.


The intestine was still attached, at one end, to Mark Barfknecht, a 1-year-old whose pink cheeks belied the reason he was lying on an operating table at Children’s Hospital Los Angeles. Born three months premature, Mark had developed a disorder that affects up to 10 percent of babies who weigh about 3 pounds or less at birth, causing some of their intestinal tissue to die. Mark’s case was so severe that most of his intestines had been removed.


Now Dr. Grikscheit, a surgeon, was trying to determine how much of the rest she could save.


Dr. Grikscheit is renowned for her skill in treating infants like Mark, whose only way to survive may be as what she calls a “short gut kid” — left with too little intestine to absorb food normally and forced to get nutrition through a needle into the bloodstream.


But devoted as she is to saving children in the operating room, Dr. Grikscheit is equally determined to find a better solution than the intravenous feeding, possibly for life, that such patients face. Much of her time is spent in her laboratory across the street, at the hospital’s Saban Research Institute, where she is working with her research team to find a way to make replacement intestines for infants like Mark, using the body itself to nourish and push the engineered tissue to grow.


Dr. Grikscheit’s work is at the forefront of efforts in laboratories around the world to build replacement organs and tissues. Although the long-sought goal of creating complex organs like hearts and livers to ease transplant shortages remains a long way off, researchers are having success making simpler structures like bladders and windpipes, thanks to advances in understanding stem cells — basic cells that can be transformed into other types within the body — and to the development of innovative techniques.


So far Dr. Grikscheit has concentrated on growing rat, mouse and pig intestinal tissue in laboratory animals. But she has recently had success in growing human intestinal tissue, using donor cells, and is beginning to study how to develop the technique for human patients. There are many hurdles, and human testing is still years away, but she has a surgeon’s confidence that the technique will work.


“We have a huge problem that if we solve it, it will change the future for a lot of children,” she said.


In her lab, her team is currently working with mice. They first remove good intestine from the animals, cut it up and treat it with enzymes and other compounds to form clusters of mixed cells, including stem cells that are found in the absorptive lining of the intestine and others that make up the tougher connective tissue.


The clusters are then placed on a piece of porous biodegradable plastic, about the size and shape of the eraser on a pencil. The plastic serves as a scaffold, supporting the cells and orienting them, which has the effect of making the lining grow inward while the connective tissue grows on the outside.


This kind of seeding of scaffolds with cells is a common approach in the field of regenerative medicine, also known as tissue engineering. But in most cases, the goal is to swap the bad organ — a windpipe, for example — with the engineered replacement, where it can grow into its permanent position in the body.


Dr. Grikscheit has had success in the lab with a different method, using another part of the body to nourish the replacement as it grows.


She and her team sew the bundle of cells into the mouse’s omentum, a membranous fold inside the abdomen. There, the bundle is surrounded by blood vessels that supply nutrients, helping it to grow. The plastic eventually dissolves as the bundle grows into a hollow ball of tissue. A few weeks later, Dr. Grikscheit and her researchers remove the ball from the omentum — for study, to better understand how the regenerative growth occurs. The tissue has all the components of intestines, including the lining, muscles, nerves and blood vessels.


In earlier studies in rats, Dr. Grikscheit went a step further, splicing the tissue into the digestive tract of animals that had had much of their intestines removed. Rats with the engineered intestine recovered more quickly than those without it.


By combining this kind of lab work with her surgical practice, Dr. Grikscheit is doing what she has always thought surgeons should do. “You move medicine ahead,” she said.