In a new study, researchers use 3-D printing to make a porous ovary scaffold and seed it with immature egg-producing cells. They show that infertile mice implanted with the engineered ovary are able to ovulate, mate, and give birth to and nurse healthy pups in the normal way. The study is the first to achieve such a result with the help of 3-D printing, and it shows how using the technology to fine-tune the pore architecture of the scaffold is key to success.
The research, published in Nature Communications, is the work of a team that includes members from the Northwestern University Feinberg School of Medicine in Chicago and Northwestern's McCormick School of Engineering in Evanston, both in Illinois.
The researchers undertook the study because they want to find a way to help patients of all ages who undergo treatments (such as for cancer) that impair their ovary function. Young patients who lose ovary function often need hormone replacement therapy to trigger puberty.
In their study paper, the authors note that current approaches - including in vitro fertilization (IVF) and ovarian transplants - do not provide "long-term solutions and leave pediatric patients with metastatic disease without options."
There have been various attempts to engineer ovaries using a range of biomaterials combined with follicles - the spherical pockets inside ovaries that contain immature egg cells and produce hormones - but these have had limited success.
The authors explain that one of the challenges to tissue engineering a replacement ovary - which they term a "bioprosthetic" ovary - is ensuring that the follicles survive in the artificial environment.
Follicles need to be held just right in 3-D
To survive, the follicles need to be held in a particular way in the 3-D environment. They need to stay in place in order to reach maturity, maintain contact with other cells, and produce hormones. If they move too freely and spread, this will not happen.
Mouse studies using bioprosthetic ovaries made from hydrogel scaffolds have succeeded in producing live births. So, this was the starting point for the new study.
Recent advances in 3-D printing - also known as additive manufacturing - are
This so-called 3-D bioprinting has already been used to tissue engineer new skin, bone, heart tissue, cartilage, and other body parts.
The researchers found that 3-D bioprinting offered them a way to vary the pore architecture of the scaffold and use this to control the extent to which the follicles are held in place in 3-D.
They showed that the more interaction there was with the scaffolding, the less the follicles spread and the higher were their chances of survival.
When the researchers transplanted the bioprosthetic ovaries into surgically sterilized mice, the mice ovulated, mated successfully, and gave birth to healthy litters. They were even able to breast-feed their pups.
First successful printing of self-supporting gelatin scaffold
The team used gelatin as the "ink" to print the scaffold. This material is safe for use in humans and is rigid enough for use in surgery, as well as porous enough to allow cells to interact with surrounding tissue.
Senior researcher Ramille Shah, assistant professor of surgery at Feinberg and of materials science and engineering at McCormick, explains that most hydrogels are too weak to produce a 3-D structure. They are mainly made of water and collapse.
"But we found a gelatin temperature that allows it to be self-supporting, not collapse, and lead to building multiple layers," she adds. "No one else has been able to print gelatin with such well-defined and self-supported geometry."
The open architecture of the scaffold did more than just give the follicles the right 3-D support for maturing egg cells and ovulation. It also allowed blood vessels to develop inside the implant so that released hormones could enter the bloodstream and trigger lactation in the female mice, as evidenced by the fact they were able to breast-feed their pups.
The study brings closer the day when bioengineered implants can be used instead of transplanted donor tissue to restore ovary function in humans. Its main contribution is to show the potential for 3-D printing to be part of that journey.
"This is the first study that demonstrates that scaffold architecture makes a difference in follicle survival. We wouldn't be able to do that if we didn't use a 3-D printer platform."
Prof. Ramille Shah