"Feeling the force" in reproduction: Mechanotransduction in reproductive processes

A Review: Biomechanical Aspects of the Fallopian Tube Relevant to its Function in Fertility

The fallopian tube (FT) plays a crucial role in the reproductive process by providing an ideal biomechanical and biochemical environment for fertilization and early embryo development. Despite its importance, the biomechanical functions of the FT that originate from its morphological aspects, and ultrastructural aspects, as well as the mechanical properties of FT, have not been studied nor used sufficiently, which limits the understanding of fertilization, mechanotrasduction, and mechanobiology during embryo development, as well as the replication of the FT in laboratory settings for infertility treatments. This paper reviews and revives valuable information on human FT reported in medical literature in the past five decades relevant to the biomechanical aspects of FT. In this review, we summarized the current state of knowledge concerning the morphological, ultrastructural aspects, and mechanical properties of the human FT. We also investigate the potential arising from a thorough consideration of the biomechanical functions and exploring often neglected mechanical aspects. Our investigation encompasses both macroscopic measurements (such as length, diameter, and thickness) and microscopic measurements (including the height of epithelial cells, the percentage of ciliated cells, cilia structure, and ciliary beat frequency). Our primary focus has been on healthy women of reproductive age. We have examined various measurement techniques, encompassing conventional metrology, 2D histological data as well as new spatial measurement techniques such as micro-CT.

Facilitation of Ovarian Response by Mechanical Force-Latest Insight on Fertility Improvement in Women with Poor Ovarian Response or Primary Ovarian Insufficiency

The decline in fertility in aging women, especially those with poor ovarian response (POR) or primary ovarian insufficiency (POI), is a major concern for modern IVF centers. Fertility treatments have traditionally relied on gonadotropin- and steroid-hormone-based IVF practices, but these methods have limitations, especially for women with aging ovaries. Researchers have been motivated to explore alternative approaches. Ovarian aging is a complicated process, and the deterioration of oocytes, follicular cells, the extracellular matrix (ECM), and the stromal compartment can all contribute to declining fertility. Adjunct interventions that involve the use of hormones, steroids, and cofactors and gamete engineering are two major research areas aimed to improve fertility in aging women. Additionally, mechanical procedures including the In Vitro Activation (IVA) procedure, which combines pharmacological activators and fragmentation of ovarian strips, and the Whole Ovary Laparoscopic Incision (WOLI) procedure that solely relies on mechanical manipulation in vivo have shown promising results in improving follicle growth and fertility in women with POR and POI. Advances in the use of mechanical procedures have brought exciting opportunities to improve fertility outcomes in aging women with POR or POI. While the lack of a comprehensive understanding of the molecular mechanisms that lead to fertility decline in aging women remains a major challenge for further improvement of mechanical-manipulation-based approaches, recent progress has provided a better view of how these procedures promote folliculogenesis in the fibrotic and avascular aging ovaries. In this review, we first provide a brief overview of the potential mechanisms that contribute to ovarian aging in POI and POR patients, followed by a discussion of measures that aim to improve ovarian folliculogenesis in aging women. At last, we discuss the likely mechanisms that contribute to the outcomes of IVA and WOLI procedures and potential future directions.

Micro-scale probing of the Rat's oviduct detects its viscoelastic property needed for creating a biologically relevant substrate for In-Vitro- Fertilization

Techniques used in assisted reproductive technology such as In-Vitro- Fertilization (IVF) process, often only replicate the biomechanical environment for embryo. Despite its importance, the biomechanics of the Oviduct tissue that is usually called Fallopian Tube in Human, the natural site of fertilization, has not been replicated nor sufficiently studied. This work studies the time-independent and time-dependent biomechanics of the oviduct tissue by realizing a viscoelastic model that accurately fit on the experimental indentation data collected on the mucosal epithelial lining of the oviduct tissue of rats. Nano-scale experiments with varying indentation rates ranging from 0.3 to 8 μms were conducted using atomic force microscopy (AFM) resulting in instantaneous elastic modulus ranging from 0.86 MPa to 6.46 MPa correspondingly. This result showed strong time dependency of the mechanical properties of the oviduct. An improved viscoelastic equation based on the fractional viscoelastic model was proposed. This modified relation successfully captured all the experimental data found at different rates (R2 > 0.8). Using the proposed model, the pure elasticity of the oviduct (i.e., about 317.2 kPa) and the viscoelastic parameters were found.

Mechanobiology of the female reproductive system

BACKGROUND

Mechanobiology in the field of human female reproduction has been extremely challenging technically and ethically.

METHODS

The present review provides the current knowledge on mechanobiology of the female reproductive system. This review focuses on the early phases of reproduction from oocyte development to early embryonic development, with an emphasis on current progress.

MAIN FINDINGS RESULTS

Optimal, well-controlled mechanical cues are required for female reproductive system physiology. Many important questions remain unanswered; whether and how mechanical imbalances among the embryo, decidua, and uterine muscle contractions affect early human embryonic development, whether the biomechanical properties of oocytes/embryos are potential biomarkers for selecting high-quality oocytes/embryos, whether mechanical properties differ between the two major compartments of the ovary (cortex and medulla) in normally ovulating human ovaries, whether durotaxis is involved in several processes in addition to embryonic development. Progress in mechanobiology is dependent on development of technologies that enable precise physical measurements.

CONCLUSION

More studies are needed to understand the roles of forces and changes in the mechanical properties of female reproductive system physiology. Recent and future technological advancements in mechanobiology research will help us understand the role of mechanical forces in female reproductive system disorders/diseases.

How Mechanical Forces Change the Human Endometrium during the Menstrual Cycle in Preparation for Embryo Implantation

The human endometrium is characterized by exceptional plasticity, as evidenced by rapid growth and differentiation during the menstrual cycle and fast tissue remodeling during early pregnancy. Past work has rarely addressed the role of cellular mechanics in these processes. It is becoming increasingly clear that sensing and responding to mechanical forces are as significant for cell behavior as biochemical signaling. Here, we provide an overview of experimental evidence and concepts that illustrate how mechanical forces influence endometrial cell behavior during the hormone-driven menstrual cycle and prepare the endometrium for embryo implantation. Given the fundamental species differences during implantation, we restrict the review to the human situation. Novel technologies and devices such as 3D multifrequency magnetic resonance elastography, atomic force microscopy, organ-on-a-chip microfluidic systems, stem-cell-derived organoid formation, and complex 3D co-culture systems have propelled the understanding how endometrial receptivity and blastocyst implantation are regulated in the human uterus. Accumulating evidence has shown that junctional adhesion, cytoskeletal rearrangement, and extracellular matrix stiffness affect the local force balance that regulates endometrial differentiation and blastocyst invasion. A focus of this review is on the hormonal regulation of endometrial epithelial cell mechanics. We discuss potential implications for embryo implantation.

Forces Involved with Labor and Delivery-A Biomechanical Perspective

Childbirth is a primarily biomechanical process of physiology, and one that engineers have recently begun to address in a broader fashion. Computational models are being developed to address the biomechanical effects of parturition on both maternal and fetal tissues. Experimental research is being conducted to understand how maternal tissues adapt to intrauterine forces near the onset of labor. All of this research requires an understanding of the forces that are developed through maternal efforts-both uterine contractions and semi-voluntary pushing-and that can be applied by the clinician to assist with the delivery. This work reviews the current state of knowledge regarding forces of labor and delivery, with a focus on macro-level biomechanics.

Engineering of Hydrogel Materials with Perfusable Microchannels for Building Vascularized Tissues

Vascular systems are responsible for various physiological and pathological processes related to all organs in vivo, and the survival of engineered tissues for enough nutrient supply in vitro. Thus, biomimetic vascularization is highly needed for constructing both a biomimetic organ model and a reliable engineered tissue. However, many challenges remain in constructing vascularized tissues, requiring the combination of suitable biomaterials and engineering techniques. In this review, the advantages of hydrogels on building engineered vascularized tissues are discussed and recent engineering techniques for building perfusable microchannels in hydrogels are summarized, including micromolding, 3D printing, and microfluidic spinning. Furthermore, the applications of these perfusable hydrogels in manufacturing organ-on-a-chip devices and transplantable engineered tissues are highlighted. Finally, current challenges in recapitulating the complexity of native vascular systems are discussed and future development of vascularized tissues is prospected.

Evidence of biomechanical and collagen heterogeneity in uterine fibroids

Objective

Uterine fibroids (leiomyomas) are common benign tumors of the myometrium but their molecular pathobiology remains elusive. These stiff and often large tumors contain abundant extracellular matrix (ECM), including large amounts of collagen, and can lead to significant morbidities. After observing structural multiformities of uterine fibroids, we aimed to explore this heterogeneity by focusing on collagen and tissue stiffness.

Methods

For 19 fibroids, ranging in size from 3 to 11 centimeters, from eight women we documented gross appearance and evaluated collagen content by Masson trichrome staining. Collagen types were determined in additional samples by serial extraction and gel electrophoresis. Biomechanical stiffness was evaluated by rheometry.

Results

Fibroid slices displayed different gross morphology and some fibroids had characteristics of two or more patterns: classical whorled (n = 8); nodular (n = 9); interweaving trabecular (n = 9); other (n = 1). All examined fibroids contained at least 37% collagen. Tested samples included type I, III, and V collagen of different proportions. Fibroid stiffness was not correlated with the overall collagen content (correlation coefficient 0.22). Neither stiffness nor collagen content was correlated with fibroid size. Stiffness among fibroids ranged from 3028 to 14180 Pa (CV 36.7%; p<0.001, one-way ANOVA). Stiffness within individual fibroids was also not uniform and variability ranged from CV 1.6 to 42.9%.

Conclusions

The observed heterogeneity in structure, collagen content, and stiffness highlights that fibroid regions differ in architectural status. These differences might be associated with variations in local pressure, biomechanical signaling, and altered growth. We conclude the design of all fibroid studies should account for such heterogeneity because samples from different regions have different characteristics. Our understanding of fibroid pathophysiology will greatly increase through the investigation of the complexity of the chemical and biochemical signaling in fibroid development, the correlation of collagen content and mechanical properties in uterine fibroids, and the mechanical forces involved in fibroid development as affected by the various components of the ECM.