Three-dimensional in vitro follicle growth: overview of culture models, biomaterials, design parameters and future directions

Abstract

In vitro ovarian follicle culture is a new frontier in assisted reproductive technology with tremendous potential, especially for fertility preservation. Folliculogenesis within the ovary is a complex process requiring interaction between somatic cell components and the oocyte. Conventional two-dimensional culture on tissue culture substrata impedes spherical growth and preservation of the spatial arrangements between oocyte and surrounding granulosa cells. Granulosa cell attachment and migration can leave the oocyte naked and unable to complete the maturation process. Recognition of the importance of spatial arrangements between cells has spurred research in to three-dimensional culture system. Such systems may be vital when dealing with human primordial follicles that may require as long as three months in culture. In the present work we review pertinent aspects of in vitro follicle maturation, with an emphasis on tissue-engineering solutions for maintaining the follicular unit during the culture interval. We focus primarily on presenting the various 3-dimensional culture systems that have been applied for in vitro maturation of follicle:oocyte complexes. We also try to present an overview of outcomes with various biomaterials and animal models and also the limitations of the existing systems.

Figure 1

A comparison of follicular growth in a 2-D vs 3-D culture system. With 2-D growth granulosa cell migration away from the oocyte is evident with time in culture, leaving the oocyte vulnerable for premature extrusion. Pre-antral follicles embedded in hydrogel maintain their 3-D architecture. Granulosa cell expansion occurs in all directions resulting in less stress on gap junctions.