Bioengineering trends in female reproduction: a systematic review

Abstract

Background: To provide the optimal milieu for implantation and fetal development, the female reproductive system must orchestrate uterine dynamics with the appropriate hormones produced by the ovaries. Mature oocytes may be fertilized in the fallopian tubes, and the resulting zygote is transported toward the uterus, where it can implant and continue developing. The cervix acts as a physical barrier to protect the fetus throughout pregnancy, and the vagina acts as a birth canal (involving uterine and cervix mechanisms) and facilitates copulation. Fertility can be compromised by pathologies that affect any of these organs or processes, and therefore, being able to accurately model them or restore their function is of paramount importance in applied and translational research. However, innate differences in human and animal model reproductive tracts, and the static nature of 2D cell/tissue culture techniques, necessitate continued research and development of dynamic and more complex in vitro platforms, ex vivo approaches and in vivo therapies to study and support reproductive biology. To meet this need, bioengineering is propelling the research on female reproduction into a new dimension through a wide range of potential applications and preclinical models, and the burgeoning number and variety of studies makes for a rapidly changing state of the field.

Objective and rationale: This review aims to summarize the mounting evidence on bioengineering strategies, platforms and therapies currently available and under development in the context of female reproductive medicine, in order to further understand female reproductive biology and provide new options for fertility restoration. Specifically, techniques used in, or for, the uterus (endometrium and myometrium), ovary, fallopian tubes, cervix and vagina will be discussed.

Search methods: A systematic search of full-text articles available in PubMed and Embase databases was conducted to identify relevant studies published between January 2000 and September 2021. The search terms included: bioengineering, reproduction, artificial, biomaterial, microfluidic, bioprinting, organoid, hydrogel, scaffold, uterus, endometrium, ovary, fallopian tubes, oviduct, cervix, vagina, endometriosis, adenomyosis, uterine fibroids, chlamydia, Asherman's syndrome, intrauterine adhesions, uterine polyps, polycystic ovary syndrome and primary ovarian insufficiency. Additional studies were identified by manually searching the references of the selected articles and of complementary reviews. Eligibility criteria included original, rigorous and accessible peer-reviewed work, published in English, on female reproductive bioengineering techniques in preclinical (in vitro/in vivo/ex vivo) and/or clinical testing phases.

Outcomes: Out of the 10 390 records identified, 312 studies were included for systematic review. Owing to inconsistencies in the study measurements and designs, the findings were assessed qualitatively rather than by meta-analysis. Hydrogels and scaffolds were commonly applied in various bioengineering-related studies of the female reproductive tract. Emerging technologies, such as organoids and bioprinting, offered personalized diagnoses and alternative treatment options, respectively. Promising microfluidic systems combining various bioengineering approaches have also shown translational value.

Wider implications: The complexity of the molecular, endocrine and tissue-level interactions regulating female reproduction present challenges for bioengineering approaches to replace female reproductive organs. However, interdisciplinary work is providing valuable insight into the physicochemical properties necessary for reproductive biological processes to occur. Defining the landscape of reproductive bioengineering technologies currently available and under development for women can provide alternative models for toxicology/drug testing, ex vivo fertility options, clinical therapies and a basis for future organ regeneration studies.

Keywords: bioengineering; cervix; endometrium; fallopian tubes; female reproduction; fertility restoration; myometrium; ovary; uterus; vagina.

Figure 1.

Key milestones during the 20th century forging the development of the bioengineering field. (A) Evidence. (A1) Advances such as the first bone marrow transplant between twins (1) (Thomas et al., 1959), the control of attachment and detachment of cultured cells (2) (Yamada et al., 1990) and the use of cell sheets (3) (Pellegrini et al., 1997) laid the groundwork for scaffold free-approaches. Concomitantly, in 1960, the reconstitution of a complete organ from single-cell suspensions (4) (Weiss and Taylor, 1960) opened an avenue to the present organoids. The in vitro self-organization of retina (5) (Stefannelli et al., 1961) and the 3D organization of breast (6) (Li et al., 1987) and alveolar (7) (Shannon et al., 1987) epithelial cells after culture with Matrigel moved this path further along. (A2) Some works from the 1980s reported the combination of hydrogels with different biological products such as pancreatic islets (8) (Lim and Sun, 1980), E2 (9) (Embrey et al., 1980) and epithelial cells (10) (Yannas et al., 1989), introducing these promising biomaterials for regenerative medicine. In parallel, obtaining ECM from renal glomeruli (11) (Hjelle et al., 1979), from liver connective tissue (12) (Rojkind et al., 1980), and a decade later, an intact acellular matrix from intestinal submucosa (13) (Badylak et al., 1995) and bladder (14) (Chen et al., 1999) provided the beginnings of the dECM scaffold approaches. (A3) The beginnings of co-culture systems are captured in two main works in which embryos were cultured together with trophoblastic vesicles (15) (Camous et al., 1984) and ampullary cells (16) (Bongso et al., 1989). Research that formed the basis of microfluidic systems was reported in the nineties; some examples are the emergence of on-chip capillary electrophoresis (17) (Harrison et al., 1993) and elastomeric microchannel networks for cell culture (18) (Folch and Toner, 1998). Works from the end of the century paved the way for bioprinting: creation of a tissue-engineered ear (19) (Cao et al., 1997), use of 3D printed substrates for cell adhesion (20) (Park et al., 1998) and introduction of soft lithography (21) (Xia and Whitesides, 1998). (B) Applications. The establishment of a capillary system for sperm samples (22) (Ulstein, 1972) and the culture of human ovarian epithelial organoids (23) (Kruk and Auersperg, 1992) were the beginnings of the development of in vitro screening platforms. The next generation in vitro platforms are based on studies like those from 1986 and 1988, which established endometrial epithelial cells were co-cultured with an ECM from glandular structures (24, 25) (Kirk and Alvarez, 1986; Rinehart et al., 1988) and a similar system also containing endometrial stromal cells (26) (Bentin-Ley et al., 1994). Finally, the development of the ESTES technique for dog ovarian transplantation (27) (Estes, 1909) in the early 20th century provided an excellent basis for a later dog uterus replantation (28) (Eraslan et al., 1966), a rabbit fallopian tube and ovary autograft transplantation (29) (Winston and Browne, 1974) and a primate ovarian transplantation (30) (Scott et al., 1981). BM, bone marrow; E2, estradiol; ECM, extracellular matrix; dECM, decellularized extracellular matrix.

Figure 2.

PRISMA flow diagram. Exact terms used for each of the database searches are detailed in Supplementary Table SI. Template adapted from Page et al. (2021). Created with BioRender.com.

Figure 3.

Organ-level overview of the bioengineering studies carried out between January 2000 and September 2021 and included in this systematic review. The studies involved the uterus, ovaries, fallopian tubes and cervix/vagina. The numbers reflect the number of studies included in Table I and Supplementary Table SIV. Created with BioRender.com.