Novel extra cellular-like matrices to improve human ovarian grafting

Thawing fertility: a view of ovarian tissue cryopreservation processes and review of ovarian transplant research

Individuals with a disease or treatment that increases their risk of premature gonadal insufficiency may opt to undergo fertility preservation. Those who are postpubertal can often cryopreserve gametes, sperm, or eggs to expand their biologic family using assisted reproductive technologies. Ovarian tissue cryopreservation (OTC) and testicular tissue cryopreservation may be an option for individuals who are unable to use standard fertility preservation techniques. The development of OTC was critical for many patients, including prepubertal children with ovaries that do not yet produce eggs, adolescents who make few good-quality eggs, and adult women with ovaries who cannot undergo ovarian stimulation. The only option to restore fertility and hormone production after OTC is through ovarian tissue transplantation (OTT). Ovarian tissue cryopreservation and OTT have been successful for some patients. Although OTC is no longer considered experimental by the American Society for Reproductive Medicine, the process is far from standardized. Significant research needs to be done, especially at the point of OTT, to improve the success and longevity of ovarian tissue function. This article lists the main steps from surgical procurement of the ovarian tissue to transplantation and restoration of function. Our pediatric hospital program has had to decide which options in procurement, processing, cryopreservation, and warming will be used in our clinical laboratory. The options and limitations within the research and analyses are briefly discussed. Literature focusing on techniques to improve OTT effectiveness and longevity was reviewed. Ovarian tissue transplantation studies that performed xenograft experiments after pretreatment of the tissue graft by a ligand or drug, treatment of the host, or encapsulation of the ovarian tissue were identified. The intended effects of the treatments include increasing vascularization, reducing apoptosis, and directing activation or suppression of primordial follicles. Robust research in this area must continue with rigorous analyses to make strides in improving fertility preservation and restoration options for patients.

Melatonin and ovarian tissue transplantation: Current frontiers in research

The progress achieved in anticancer therapy in recent years has been paralleled by an increase in the survival of women with cancer globally. Nonetheless, the gonadotoxic impact of anticancer drugs has led to ovarian failure in treated women. While there are documented cases of successful ovarian tissue transplants resulting in restored fertility and childbirth, challenges persist, including suboptimal functional recovery and limited graft lifespan. Melatonin, an inert hormone primarily secreted by the mammalian pineal gland, exhibits diverse physiological functions, including antioxidative, anti-inflammatory, anti-apoptotic, and angiogenesis-regulating properties. Consequently, researchers have explored melatonin as a modulator to enhance graft function recovery in ovarian transplantation experiments, yielding promising outcomes. This review examines the relevant literature, consolidating findings that underscore the positive effects of melatonin in safeguarding the morphology and structure of transplanted ovarian tissues, facilitating graft function recovery, and extending lifespan. The amassed evidence supports the consideration of melatonin as a prospective protective agent for human ovarian tissue transplantation in the future.

OUP accepted manuscript

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.

Plant Recombinant Human Collagen Type I Hydrogels for Corneal Regeneration

Purpose

To determine feasibility of plant-derived recombinant human collagen type I (RHCI) for use in corneal regenerative implants

Methods

RHCI was crosslinked with 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide (EDC) and N-hydroxysuccinimide (NHS) to form hydrogels. Application of shear force to liquid crystalline RHCI aligned the collagen fibrils. Both aligned and random hydrogels were evaluated for mechanical and optical properties, as well as in vitro biocompatibility. Further evaluation was performed in vivo by subcutaneous implantation in rats and corneal implantation in Göttingen minipigs.

Results

Spontaneous crosslinking of randomly aligned RHCI (rRHCI) formed robust, transparent hydrogels that were sufficient for implantation. Aligning the RHCI (aRHCI) resulted in thicker collagen fibrils forming an opaque hydrogel with insufficient transverse mechanical strength for surgical manipulation. rRHCI showed minimal inflammation when implanted subcutaneously in rats. The corneal implants in minipigs showed that rRHCI hydrogels promoted regeneration of corneal epithelium, stroma, and nerves; some myofibroblasts were seen in the regenerated neo-corneas.

Conclusion

Plant-derived RHCI was used to fabricate a hydrogel that is transparent, mechanically stable, and biocompatible when grafted as corneal implants in minipigs. Plant-derived collagen is determined to be a safe alternative to allografts, animal collagens, or yeast-derived recombinant human collagen for tissue engineering applications. The main advantage is that unlike donor corneas or yeast-produced collagen, the RHCI supply is potentially unlimited due to the high yields of this production method.

Lay Summary

A severe shortage of human-donor corneas for transplantation has led scientists to develop synthetic alternatives. Here, recombinant human collagen type I made of tobacco plants through genetic engineering was tested for use in making corneal implants. We made strong, transparent hydrogels that were tested by implanting subcutaneously in rats and in the corneas of minipigs. We showed that the plant collagen was biocompatible and was able to stably regenerate the corneas of minipigs comparable to yeast-produced recombinant collagen that we previously tested in clinical trials. The advantage of the plant collagen is that the supply is potentially limitless.

Mimicking the Hierarchical Organization of Natural Collagen: Toward the Development of Ideal Scaffolding Material for Tissue Regeneration

Biological materials found in living organisms, many of which are proteins, feature a complex hierarchical organization. Type I collagen, a fibrous structural protein ubiquitous in the mammalian body, provides a striking example of such a hierarchical material, with peculiar architectural features ranging from the amino acid sequence at the nanoscale (primary structure) up to the assembly of fibrils (quaternary structure) and fibers, with lengths of the order of microns. Collagen plays a dominant role in maintaining the biological and structural integrity of various tissues and organs, such as bone, skin, tendons, blood vessels, and cartilage. Thus, "artificial" collagen-based fibrous assemblies, endowed with appropriate structural properties, represent ideal substrates for the development of devices for tissue engineering applications. In recent years, with the ultimate goal of developing three-dimensional scaffolds with optimal bioactivity able to promote both regeneration and functional recovery of a damaged tissue, numerous studies focused on the capability to finely modulate the scaffold architecture at the microscale and the nanoscale in order to closely mimic the hierarchical features of the extracellular matrix and, in particular, the natural patterning of collagen. All of these studies clearly show that the accurate characterization of the collagen structure at the submolecular and supramolecular levels is pivotal to the understanding of the relationships between the nanostructural/microstructural properties of the fabricated scaffold and its macroscopic performance. Several studies also demonstrate that the selected processing, including any crosslinking and/or sterilization treatments, can strongly affect the architecture of collagen at various length scales. The aim of this review is to highlight the most recent findings on the development of collagen-based scaffolds with optimized properties for tissue engineering. The optimization of the scaffolds is particularly related to the modulation of the collagen architecture, which, in turn, impacts on the achieved bioactivity.

Use of Simvastatin, Fibrin Clots, and Their Combination to Improve Human Ovarian Tissue Grafting for Fertility Restoration After Anti-Cancer Therapy

Anticancer treatments, particularly chemotherapy, induce ovarian damage and loss of ovarian follicles. There are limited options for fertility restoration, one of which is pre-chemotherapy cryopreservation of ovarian tissue. Transplantation of frozen-thawed human ovarian tissue from cancer survivors has resulted in live-births. There is extensive follicular loss immediately after grafting, probably due to too slow graft revascularization. To avoid this problem, it is important to develop methods to improve ovarian tissue neovascularization. The study's purpose was to investigate if treatment of murine hosts with simvastatin or/and embedding human ovarian tissue within fibrin clots can improve human ovarian tissue grafting (simvastatin and fibrin clots promote vascularization). There was a significantly higher number of follicles in group A (ungrafted control) than in group B (untreated tissue). Group C (simvastatin-treated hosts) had the highest levels of follicle atresia. Group C had significantly more proliferating follicles (Ki67-stained) than groups B and E (simvastatin-treated hosts and tissue embedded within fibrin clots), group D (tissue embedded within fibrin clots) had significantly more proliferating follicles (Ki67-stained) than group B. On immunofluorescence study, only groups D and E showed vascular structures that expressed both human and murine markers (mouse-specific platelet endothelial cell adhesion molecule, PECAM, and human-specific von Willebrand factor, vWF). Peripheral human vWF expression was significantly higher in group E than group B. Diffuse human vWF expression was significantly higher in groups A and E than groups B and C. When grafts were not embedded in fibrin, there was a significant loss of human vWF expression compared to groups A and E. This protocol may be tested to improve ovarian implantation in cancer survivors.

Three Decades of Research on Recombinant Collagens: Reinventing the Wheel or Developing New Biomedical Products?

Collagens provide the building blocks for diverse tissues and organs. Furthermore, these proteins act as signaling molecules that control cell behavior during organ development, growth, and repair. Their long half-life, mechanical strength, ability to assemble into fibrils and networks, biocompatibility, and abundance from readily available discarded animal tissues make collagens an attractive material in biomedicine, drug and food industries, and cosmetic products. About three decades ago, pioneering experiments led to recombinant human collagens' expression, thereby initiating studies on the potential use of these proteins as substitutes for the animal-derived collagens. Since then, scientists have utilized various systems to produce native-like recombinant collagens and their fragments. They also tested these collagens as materials to repair tissues, deliver drugs, and serve as therapeutics. Although many tests demonstrated that recombinant collagens perform as well as their native counterparts, the recombinant collagen technology has not yet been adopted by the biomedical, pharmaceutical, or food industry. This paper highlights recent technologies to produce and utilize recombinant collagens, and it contemplates their prospects and limitations.