Gelatin and PLG-based Scaffolds Differentially Support Follicle Integrity and Oocyte Growth in a 3D printed Scaffold

For many children facing life-threatening cancers, the very treatments that save their lives can steal their future fertility. Chemotherapy and radiation often damage the ovaries, the organs that produce eggs and essential hormones. In adults, doctors can sometimes freeze and store ovarian tissue for later use, but this approach is dangerous for children. Their ovaries contain immature eggs that cannot be frozen individually, and re-implanting their own tissue carries a risk of re-introducing cancer cells if the disease had spread there. To solve this, scientists are working on a different kind of solution: a bioprosthetic ovary. This is an artificial organ built from a scaffold, a tiny, porous structure designed to hold isolated egg sacs, called follicles, and help them grow and mature outside the body until they are ready for use. The goal is to replace the damaged tissue with this engineered support system, allowing the body to produce hormones and eventually release healthy eggs.

The challenge lies in finding the right material to build this scaffold. The follicle is a delicate, three-dimensional structure that must be held securely while also being allowed to expand as it grows. It needs to interact with surrounding support cells and receive nutrients, much like a plant needs the right soil to take root and bloom. Researchers have previously used a material called gelatin, which is derived from collagen, because it mimics the natural environment of the body and helps cells stick to it. More recently, they have also looked at a synthetic, ultra-porous material called ultra-fluffy poly(lactic-co-glycolic acid), or UF-PLG. This material is incredibly light and can absorb many times its own weight in liquid, offering a different kind of structure. The question was whether one of these materials was clearly superior, or if they offered different strengths that might need to be combined.

A team of researchers set out to compare these materials directly. They used a 3D printer to create tiny scaffolds from three different substances: pure gelatin, pure UF-PLG, and a hybrid version where the UF-PLG was coated with gelatin. They printed these scaffolds with a specific geometric pattern, consisting of five layers of struts arranged at a sixty-degree angle to one another, creating corners that could physically cradle the spherical follicles. They then took secondary follicles, which are small egg sacs about the size of a grain of sand, from the ovaries of young mice. Each follicle was placed onto one of the three types of scaffolds and left to grow in a nutrient-rich liquid for two, four, or six days. The scientists then examined the follicles under powerful microscopes to see how well they stayed attached, whether they kept their shape, and how much the egg inside grew.

The results revealed a clear split in performance. The scaffolds made of pure gelatin were excellent at keeping the follicles safe and secure. Almost all of the follicles placed on these scaffolds stayed attached, and they maintained their structural integrity, meaning the protective layers around the egg did not break. The gelatin also encouraged the surrounding support cells to migrate onto the scaffold and wrap around the follicle, creating a strong, integrated unit. In contrast, the follicles on the pure UF-PLG scaffolds fared poorly. Most of them fell off the structure entirely, and those that stayed often ruptured, losing their protective shell. The hybrid scaffolds, which combined the two materials, showed a middle ground for attachment but offered a surprising advantage for growth.

While the gelatin scaffolds were the best at holding the follicles in place, they were not the best at helping the egg inside grow to full size. The researchers measured the diameter of the eggs to see if they reached a size that indicates they are ready to be fertilized, a benchmark known as developmental competence. In mice, an egg needs to reach a diameter of roughly 70 to 72 micrometers to be considered competent. The eggs on the gelatin scaffolds grew, but they remained smaller than this target. However, the eggs on the hybrid UF-PLG-gel scaffolds grew larger than the benchmark, reaching an average diameter of 75.6 micrometers. This suggests that while the gelatin was better at keeping the follicle from falling apart, the hybrid material provided an environment that allowed the egg to expand more freely.

The researchers also tested whether making the scaffolds stiffer would change the outcome. They increased the amount of chemical crosslinking, which acts like a glue to harden the material, and found that this did make the gelatin scaffolds significantly stiffer. However, this change in stiffness did not dramatically alter how well the follicles attached or how much the eggs grew. The differences between the materials themselves were far more important than the differences in how hard they were. This finding suggests that the chemical nature of the material, rather than just its physical hardness, is the primary driver of how the follicle behaves.

These findings point to a new way of thinking about building artificial organs. For a long time, scientists hoped to find a single material that could do everything perfectly: hold the tissue securely and help it grow to maturity. This study suggests that such a "one-size-fits-all" material may not exist. Instead, the needs of a follicle for stability are different from its needs for growth. The gelatin provided the stability needed to keep the structure intact, while the UF-PLG component seemed to offer the space or signals necessary for the egg to reach its full potential. This implies that the most effective bioprosthetic ovaries of the future may need to be built with multiple materials, carefully arranged to provide a secure home for the follicle while simultaneously offering a permissive environment for the egg to mature. By understanding that different stages of development require different physical environments, scientists can move closer to creating a reliable solution for restoring fertility to those who have lost it to cancer.