Glioblastoma cells cultured in 3D with the Bio-Assembler. Credit: Nano3D Biosciences

Being able to grow more realistic liver, heart, and other tissues in the lab could provide a new lease on life for patients waiting on the transplant list--and lead to more realistic systems for testing drugs. But tissue engineers have found that mimicking these complex, three-dimensional structures in the lab is difficult. Part of what's holding them up are flat, two-dimensional tissue culture systems that grow cells in an environment very different from that inside the body.

Now researchers at Rice University and the MD Anderson Cancer Center in Houston have developed a simple way to make cells form 3-D structures. They developed a gel made up of a polymer, iron oxide nanoparticles, and engineered viruses called phage. When cells are added to this mixture, the phage cause them to absorb the magnetic particles. The Houston group showed that they could use a weak magnet to hold magnetized brain cancer cells in a 3-D suspension. Gene-expression studies showed that these suspended cells behave more naturally than a control group grown on a conventional flat surface: the cancer cells were producing a mix of proteins very similar to what they produce in the body. These results are described in Nature Nanotechnology this week.

The magnetizing gel has been licensed to a startup company, Nano3D Bioscience, which will run tests to compare the technology other methods for making 3-D tissues.

In a unique feat of tissue engineering, scientists from Wake Forest University Baptist Medical Center have created penile erectile tissue and implanted it into male rabbits, allowing the animals to, well, go at it like rabbits.

Researchers implanted scaffolds seeded with cells from rabbit penile tissue. One month later, organized tissue with blood vessels began to grow. Tests showed that the new tissue functioned like a normal penis, with normal blood flow and drainage of the veins. The rabbits even fathered offspring. The research was published today in the Proceedings of the National Academy of Sciences.

"Further studies are required, of course, but our results are encouraging and suggest that the technology has considerable potential for patients who need penile reconstruction," said Anthony Atala, M.D., director of Wake Forest's Institute for Regenerative Medicine, in a statement. "Our hope is that patients with congenital abnormalities, penile cancer, traumatic injury and some cases of erectile dysfunction will benefit from this technology in the future."

During an erection, sponge-like tissue called copora cavernosa fills with blood. This tissue can be damaged by disease, injury, or lack of use, such as after prostate surgery. But according to a press release from Wake Forest, fixing these structures has been a challenge because of "the tissue's unique structure and complex function." Also, "there is no replacement for this tissue that allows for normal sexual function. Various surgeries have been attempted, often multi-stage procedures that can involve a silicone penile prosthesis, but natural erectile function is generally not restored."

Atala's team has previously engineered replacement bladders, which have been implanted in close to 30 people to date. The researchers used similar engineering techniques in the new research. According to the release:

The scientists first harvested smooth muscle cells and endothelial cells, the same type of cells that line blood vessels, from the animals' erectile tissue. These cells were multiplied in the laboratory. Using a two-step process, the cells were injected into a three-dimensional scaffold that provided support while the cells developed. As early as one month after implanting the scaffold in the animal's penis, organized tissue with vessel structures began to form.

The cells were injected into scaffolds on two separate days, enabling them to hold almost six times as many smooth muscle cells as in the previous studies - which the scientists believe was a key to success. During an erection, it is the relaxation of smooth muscle tissue that allows an influx of blood into the penis. The relaxation is triggered by the release of nitric oxide from endothelial cells.