Advanced bioengineering of male germ stem cells to preserve fertility

Abstract

In modern life, several factors such as genetics, exposure to toxins, and aging have resulted in significant levels of male infertility, estimated to be approximately 18% worldwide. In response, substantial progress has been made to improve in vitro fertilization treatments (e.g. microsurgical testicular sperm extraction (m-TESE), intra-cytoplasmic sperm injection (ICSI), and round spermatid injection (ROSI)). Mimicking the structure of testicular natural extracellular matrices (ECM) outside of the body is one clear route toward complete in vitro spermatogenesis and male fertility preservation. Here, a new wave of technological innovations is underway applying regenerative medicine strategies to cell-tissue culture on natural or synthetic scaffolds supplemented with bioactive factors. The emergence of advanced bioengineered systems suggests new hope for male fertility preservation through development of functional male germ cells. To date, few studies aimed at in vitro spermatogenesis have resulted in relevant numbers of mature gametes. However, a substantial body of knowledge on conditions that are required to maintain and mature male germ cells in vitro is now in place. This review focuses on advanced bioengineering methods such as microfluidic systems, bio-fabricated scaffolds, and 3D organ culture applied to the germline for fertility preservation through in vitro spermatogenesis.

Biomaterials for Testicular Bioengineering: How far have we come and where do we have to go?

“…Male reproductive tissues are under daily endocrine stimulation, with the rise and fall of testosterone, present a complex microarchitecture that changes due to intense hormonal flow ( 175 ). Aiming to mimetize these elements and testicular ECM, several biotechnological tools have been used to reconstruct testicular tissue and carry out the process of spermatogenesis in vitro ( 173 ) ( Figure 3 ).…”

“…Providing a transitory tissue-mimicking environment for cell proliferation and differentiation to occur, hydrogels have high structural similarity to ECM, being used to encapsulate cells and tissues within reproductive bioengineering. Its composition is mostly water (90%), allowing the diffusion of nutrients, providing physical support for the cells ( 173 ). Recently, several studied applied hydrogels in testicular tissue and in cell culture focusing on the differentiation of spermatogonial stem cells into haploid spermatozoa ( 258 ).…”

“…Several testicular cell culture systems have been studied to mimetize the testicular microenvironment and restore fertility. An emerging field is reproductive tissue engineering (RTE), which is based on the same principles applied for vital organs as the heart, lungs, kidneys, liver, and skin (171)(172)(173). However, RTE must, in addition to reestablishing tissue integrity, generate a suitable microenvironment for the development of germ cells (174).…”

Recent Developments in In Vitro Spermatogenesis and Future Directions

“…A bioreactor is a device that supports the growth of cells and tissues in a biologically active environment by maintaining optimal temperature, pH, oxygen, and nutrient conditional for the cell growth while removing waste. The topic of utilizing microfluidic systems, scaffolds, and bioreactors used in in vitro spermatogenesis has been reviewed elsewhere [75]. In 2022, a group generated human 3D organoids in mini-spin bioreactors from hPSCs [76].…”

Emerging Bioactive Agent Delivery-Based Regenerative Therapies for Lower Genitourinary Tissues

“…Dysfunction in the male reproductive system is the main cause of male infertility, which heavily affects male reproductive health [131][132][133][134]. Fortunately, regenerative therapy offers an opportunity for these patients to recover and even become biological fathers.…”