Regenerative Medicine in the Genitourinary System

Regenerative Medicine in the Genitourinary System gives the reader a comprehensive overview of tissue engineering used to treat genitourinary disorders and infertility, also providing a great learning platform for researchers in different fields such as cell biology, pharmaceutics, clinicians, chemists, material scientists, and more. The book covers the latest innovations on the subject, but also acts as a resource for tissue engineering applications and regenerative medicine. Over the last several decades, tissue engineering has continued to make considerable advancements in therapeutic and clinical strategies that address male/female urological or genitourinary diseases. Although several articles have been published on this topic, there are very few book chapters and no single book currently available dedicated to this topic.

• Provides extensive principles of tissue engineering in urinary and reproductive systems
• Presents excellent examples of tissue engineering and regenerative medicine (translational medicine) to tackle diseases and disorders related to the urinogenital system
• Includes chapters covering erectile disfunction, as well as tissue engineering strategies to treat male and female infertility

• Language: English
• Publisher: Academic Press
• Release date: Apr 19, 2024
• ISBN: 9780443158353

Book preview

Section 1

Introduction

Outline

Chapter 1. Genitourinary tissue engineering: Promises, advances, and challenges

Chapter 1: Genitourinary tissue engineering

Promises, advances, and challenges

Haalah Islam¹, Morvarid Saeinasab¹,², and Farshid Sefat¹,³     ¹Department of Biomedical and Electronics Engineering, School of Engineering, University of Bradford, Bradford, United Kingdom     ²Faculty of Biology, Medicine and Health, University of Manchester, Manchester, United Kingdom     ³Interdisciplinary Research Centre in Polymer Science & Technology (Polymer IRC), University of Bradford, Bradford, United Kingdom

Abstract

The regenerative tissue engineering field has continued to make considerable advancements in therapeutic and clinical strategies that address male/female urological or genitourinary diseases. Regenerative tissue engineering adopts principles from engineering, transplantation, material science, and cell biology fields in an effort to replace and repair damaged organ systems and the tissues that are incorporated in these systems. This is a review that intends to give a comprehensive overview of stem cell use as well as tissue engineering technological devices that are specially used to treat genitourinary diseases. The themes currently used in this tissue engineering field include using adult stem cells and embryonic stem cells that are seeded onto resorbable biocompatible matrices for the implantation procedures as substitute tissue samples which is conducive to the growth of host tissues. Adult stem cells injection therapy for organ rehabilitation is developing rapidly toward restoring organ function and structure. Promising discoveries have shown the emergence of new classes of regenerative medicine and clinical therapies to be applied into genitourinary system tissue engineering.

Keywords

Congenital urethral; Extracellular matrix; Genitourinary system; Tissue engineering

1.1. Introduction

The Genitourinary system is large and is made up of many organs, these have vital roles in fulfilling normal and healthy functions of the human body. Therefore, the problems and treatments for these conditions are wide and vast. Over 400 million people worldwide are affected by urinary tract abnormalities (Davis, Cunnane, O'Brien, et al., 2018). The most prevalent urethral abnormalities, urethral strictures, affect 1 in 1000 males over the age of 65. Congenital urethral birth defects such as hypospadias, impact 1 in every 300 births (Pastorek et al., 2021). Subsequently, in the first 5 years following surgery, 20% of urethra reconstruction issues occur (Wang et al., 2021).

Numerous illnesses can affect urological tissues. Most of these diseases are acquired or congenitally present defects. Patients may need surgical reconstruction to restore the genitourinary tract to its normal state, depending on how severe the aberration is and whether the condition is reoccurring. In the present era, it is still challenging to repair and replace these damaged or aberrant tissues (Caneparo, Sorroza-Martinez, et al., 2021).

When organs are damaged or organ failure has occurred, the available surgical procedures include organ transplantation. Surgical interventions are accompanied by a variety of issues, including disease transmission, rejection, and excessive demand, which outweigh the supply. Hence, the need for transplantable tissues and organs is growing, leading to the development and improvement of procedures in regenerative medicine (Guruswamy Damodaran & Vermette, 2018).

High hopes have been placed in regenerative medicine using tissue engineering technology because of its progress and promise for ground-breaking therapeutic approaches. Functional outcomes are still unsatisfactory because of poor healing, extensive scarring, and recurrent fibrosis. A unique tissue engineering technology-based approach is being gradually researched for better, more fruitful results. The potential to create organ-specific grafts makes tissue engineering the most promising method for enhancing the outcomes of reconstructive urological treatments. In addition, stem cells and growth factors have a unique opportunity to modify the healing environment specifically, which could advance reconstructive urology to the molecular level (Adamowicz et al., 2019; Chua et al., 2020).

1.2. Regenerative medicine

Regenerative medicine is the process in which the body employs its own mechanisms with assistance from foreign biological material to reproduce cells and reconstruct tissues and organs (NIH, 2022).

For damaged tissues to be permanently repaired there are certain conditions that must be satisfied. The developed cells must be sufficient to fill the gap in the damaged tissue, they must be able to differentiate into the desired phenotypes, have the appropriate 3D scaffold structure and produce an extracellular matrix (ECM). The engineered cells must be structurally and mechanically biocompatible with the native cell and have a low risk of rejection and minimal associated biological risks.

The ECM of a cell depends on the native tissue type. In addition to cell adhesion proteins like fibronectin and laminin and structural proteins such as collagen and elastin, ECMs also contain proteoglycans, which are protein-polysaccharide complexes where sugars are linked to core proteins; these are commonly glycosaminoglycans (GAGS).

1.3. Principles of tissue engineering

The goal of tissue engineering is to restore physiological function and fulfill the biochemical purpose. The developments in prostheses, reconstructive surgery, transplantation, cell biology, biochemistry, molecular biology, and genetics are all strongly related to tissue engineering. Tissue engineering concepts can be used in a wide variety of applications in order to restore many organs and functions of the human body as demonstrated in Fig. 1.1.

To provide innovative methods and treatments for tissue and organ regeneration, the interdisciplinary area of tissue engineering incorporates components from biology, material science, medicine, and engineering. It describes the use of scaffolds or synthetic material-derived building blocks made of cells for tissue repair. Scaffolds are materials that have been designed to result in favorable biological interaction. They provide a biochemical and physical environment that is similar to that of natural tissue in addition to acting as a support for cells (Pastorek et al., 2021).

Tissue engineering primarily uses three components: cells, biomaterials, and growth factors (GFs).

1.3.1. Source of cells

Cells are the living part of the tissue, they are responsible for the production of the ECM, cytokines, and proteins; they provide cells with their function and repair properties of the tissue.

• Allograft

An allograft is when tissue is taken from a genetically unrelated donor and used on a patient.

• Xenograft

Xenografts are cells taken from another species and used on a patient; this could be from rabbits, mice, cows, and pigs.

• Isograft

In an isograft, the tissue is taken from a genetically identical donor and used on the patient. Using a twin donor is highly successful due to its low rejection rate.

1.3.1.1. Stem cells

To restore biological functions, several genitourinary tract problems can be treated or replaced. Growing tissue shortages pose a threat to current therapeutic strategies. Therefore, the utilization of stem cells shows promise (Caneparo, Sorroza-Martinez, et al., 2021). Given that they mimic crucial host-derived biological processes like mitosis, proliferation, differentiation, and death, stem cells could be a useful alternative (Davis, Cunnane, Mulvihill, et al., 2018).

Figure 1.1  Overview of tissue engineering. Source: Created by Biorender.

Due to their stability and capacity for self-renewal, stem cells are helpful in reconstructive urology. Excellent urological regenerating capabilities can be seen in mesenchymal stem cells (MSCs), embryonic stem cells (ESCs), and adult stem cells (ASCs). Numerous stem cell therapies have been used to repair damaged lower urinary tract components. In vitro and in vivo pre-clinical investigations have produced promising outcomes (Davis, Cunnane, Mulvihill, et al., 2018). Adipose-derived stromal stem cells are potential substitutes for the treatments for genitourinary diseases now provided to patients because of their accessibility, high yield when harvested, anti-fibrotic, immunomodulatory, and proangiogenic capabilities (Caneparo, Sorroza-Martinez, et al., 2021; Davis, Cunnane, Mulvihill, et al., 2018).

1.3.2. Biomaterials

Biomaterials come in the form of scaffolds. They provide structural support, and are a framework which allows cell adhesion, and promotes cell proliferation. Scaffolds must be biocompatible and biodegradable into non-toxic components. Biomaterials can be metal polymers or from a natural source.

Bioscaffolding is a biocompatible scaffold that contains and delivers biologics, which are cells, genes, and proteins. If the bioscaffold interacts with the host cells it indicates successful reconstruction or regeneration. Successful bioscaffolding stimulates the cell's native ECM's protein synthesis.

The biomaterial used as the scaffold matrix must be dynamic, while still allowing for cell growth, and therefore must be permeable. The permeability of the scaffold must be in line with that of the native tissue in order for the proper functioning of the organ can continue, where the permeability of the scaffold is not appropriate problems occur. In the case of the bladder, fibrosis results from competition between renewing cells from the native tissue and urine seeping through the pores of the scaffold or biomaterial (Chua et al., 2020).

1.3.2.1. Extracellular matrix

ECM scaffolds are processed mechanically, chemically, and enzymatically to produce tissue that preserves the essential structural components. The goal of properly made ECMs is to offer a biologically active tissue or organ substitute that may successfully integrate into the host tissue and replace the functionality of the damaged tissue. The ECM scaffold should be biocompatible to reduce inflammatory and rejection reactions (Davis, Cunnane, O'Brien, et al., 2018). The decellularized organ-specific ECM scaffolds can either be used as bioinks for 3D bioprinting applications to produce organs, or they can be repopulated and recellularized with the appropriate cells and growth factors. Decellularized ECMs are also used to create hydrogels or to enhance the biological characteristics of synthetic materials (Hassanpour et al., 2018).

To repair a damaged urinary tract segment ECMs are often obtained from swine organs and are decellularized to produce a biocompatible and biodegradable biomaterial. An integrated tissue-engineered ECM should maintain or restore the urinary tract structure or replace normal functionality (Davis, Cunnane, O'Brien, et al., 2018). Another area of research is a bioengineered ovary. Research suggests when a decellularized ovarian ECM is used as a native scaffold, it can offer an excellent 3D microstructure for regenerative efforts in order to support cell activity (Hassanpour et al., 2018).

1.3.2.2. Scaffolds

A suitable scaffold should have a 3D structure, be non-toxic, and be biodegradable. The scaffold can also be thought of as a cell transport system that promotes cell motility, division, and proliferation (Wang et al., 2020).

There are several types of scaffolds some include hydrogels, woven silk, nano fibers, microfibers, decellularized organs, and composites.

The organic polymer collagen makes up a significant portion of the ECM. It is an excellent substrate for cell attachment and proliferation because it has ligands that act as surface binding sites. When collagen is cross-linked with acetic acid or used in conjunction with other synthetic polymers, its low Youngs Modulus (E) can be raised. It is possible to create a porous collagen scaffold using freeze-drying procedures.

Water-soluble polymer chains are cross-linked to form insoluble networks, forming hydrogels. Hydrogels mimic soft tissue's high-water content, they are used to regenerate soft tissue.

Although synthetic polymers can be processed using a variety of methods to produce scaffolds, they lack binding sites and must have adhesive proteins applied to their surface in order to function effectively. The degradation products of the synthetic polymer could be cytotoxic and result in an inflammatory response even if the polymer itself is not.

1.3.3. Fabrication

• Foaming

Hydrogels can be foamed by bubbling CO2; a cell culture strainer is used to act as a filter and control pore size.

• Electrospinning

Through a network of connected micron-scale fibers, a high-voltage electric field is applied to spin fibers. Through a small nozzle, fibers made from a polymer solution are extruded.

• Rapid prototyping

Complex geometries are created using computer control. To build up successive layers and form a sold scaffold shape. Stereolithography, 3D printing, and selective laser sintering are utilized in rapid prototyping.

• 3D bio-printing

3D bioprinting techniques include thermal inkjet, micro-extrusion, and laser assistance.

• Thermal inkjet printers use electrical heating of the printhead to create air-pressure pulses that drive droplets from the nozzle, whereas acoustic printers use pulses produced by piezoelectric or ultrasound pressure.

• Micro-extrusion printers use pneumatic or mechanical dispensing apparatus to extrude continuous beads of material or cells.

• By focusing lasers on substrate absorption, laser-assisted printers create pressures that push materials containing cells onto a collection substrate.

• Freeze-drying

Freeze-drying of collagen scaffold gives a porous scaffold. Directional cooling can be used to create elongated pores, used for nerve regeneration.

• Decellularization

When all cellular components have been eliminated from a tissue or organ, the remaining structural characteristics of the ECM act as a scaffold.

1.3.4. Structure and material properties

The structural properties of a scaffold are determined by native tissue force and deformation, or stress and strain characteristics. The behavior of the material under various loading conditions, such as tension, compression, torsion, or bending, will differ, as will the associated modulus of elasticity or stiffness; this must be tested to determine the scaffold's suitability.

The scaffold must have sufficient mechanical integrity for handling in surgery, cell differentiation and proliferation. The degradation must degrade at a controlled rate in order for the tissue to become fully termed, via cell deposition of native ECM; the scaffold must be completely reabsorbed at a controlled rate. The chemical makeup of the scaffold will allow for the provision and binding of ligands that affect cell activity as well as the synchronization of the degradation rate with the rate of cell formation. The scaffold must be rigid, have a good elastic and stiffness modulus, and be strong enough mechanically to sustain wear.

1.3.5. Requirements of scaffold design

For cell migration, nutrition transport, and the movement of regulatory elements, scaffolds need a large number of pores. The density of binding sites available for cell attachment determines the top boundary of the pore size, while cell size determines the lower boundary. The geometry of the pore must be compatible with the morphology of the native cells.

1.3.6. Growth factors

GFs, which play a crucial role in tissue regeneration, are biomechanical signals that instruct cells on how to operate via protein or mechanical stimulation. GF treatment for tissue regeneration is constrained by the requirement for large numbers. As a result, high volumes become necessary, which are expensive and increase the risk of side effects. Therefore, new methods are being developed to deliver bioactive chemicals locally and precisely. The required dose of GFs could be decreased as a result of these scaffolds' ability to keep the biomolecules at the fracture site in vivo. These GFs then work to draw endogenous stem cells from nearby tissues and drive their development into the porous scaffold's tissue (De Witte et al., 2018).

Several scaffold-based techniques have been investigated in order to meet the requirements for GF delivery. The utilization of covalent or non-covalent protein binding to the scaffold, micro- or nanoparticles as protein reservoirs or physical protein trapping within the scaffold are all possible GF delivery techniques (De Witte et al., 2018). Table 1.1 shows research that has been conducted for tissue engineering and regenerative medicine of the genitourinary system, and any growth factors that have been used.

1.3.7. Decellularization

Decellularized tissues and organs can serve as scaffolds on which transplanted cells can be placed later. These tissues and organs are devoid of cells and genetic material but retain the detailed structure of the ECM. They are able to mimic the physiological conditions that exist naturally (Guruswamy Damodaran & Vermette, 2018).

Organ and tissue decellularization can result in the creation of bioscaffolds made of naturally occurring matrices that are comparable to native tissue or organs in terms of composition, microstructure, and biomechanical properties while retaining the majority of the signaling cues required for organ development, repair, and physiological regeneration. For different tissues and organs, numerous decellularization techniques have been devised in an effort to strike a compromise between cell loss and ECM maintenance. This is brought on by the pro-inflammatory reactions brought on by the retention of cellular debris from insufficient decellularization. On the other side, a thorough and severe decellularization procedure will denature proteins and bleach growth hormones (Simões et al., 2017). Some decellularization techniques involve the removal of all genetic, protein and cellular components only leaving behind the structural components of the ECM, this is then recellularized using the appropriate cells and GFs.

1.4. Genitourinary system anatomy and physiology

The genitourinary system includes organs from the urinary and reproductive systems, it is a complex system that is composed of the kidney, bladder, urethra, ureter, renal, reproductive organs, and genital structures.

The main aim of the urinary system is the filtration of the blood, which creates the waste product of urine. The organs that compose this system are kidneys, renal pelvis, ureters, bladder, and urethra. The renal and urinary systems aid in the body's elimination of urea, a toxic waste liquid, and maintain a balance of potassium, sodium, and water. When foods high in protein, such as meat and poultry, are digested by the body, urea is formed. Urea is transported by the bloodstream to the kidneys, where it is eliminated in the form of urine in combination with water and other waste products (Medicine, 2022).

1.4.1. Urinary structure and function

The human body consists of two kidneys and two ureters, these organs have a range of medical challenges. The function of the kidneys is to remove waste products from the body and in turn balance fluid levels within the body, they are also responsible for the production of red blood cells and to regulate blood pressure via hormones. The ureter carries the urine from the kidneys to the bladder. The bladder is the organ responsible for storing urine in the body until it is excreted. The bladder of a healthy individual is able to expand to store urine and contract for the release of the waste product. The urethra is connected to the bladder and is the external organ of the urinary system that empties the bladder. The bladder is located in the lower abdomen, whereas the kidneys are positioned below the ribs in the middle of the back (Medicine, 2022).

1.4.2. Genital structure and function

The genital structure of the human body consists of both the internal and external reproductive organs. The differences between male and female reproductive organs results in their own unique problems and require medical treatments that are suited to them.

1.4.2.1. Female genitalia

The internal structure of female genitalia includes the vagina, cervix, uterus, ovaries, and fallopian tubes. The external structures consist of the labia majora, labia minora, clitoris, hymen, and vaginal opening (Clinic, 2022a).

There are many uses for the female reproductive system. Along with permitting sexual activity, it also promotes sexual reproduction. The egg gamete is created in the ovaries. These eggs are then transferred to your fallopian tube during ovulation, where sperm fertilization could occur. The fertilized egg is subsequently placed inside the uterus, where the lining thickens as a result of the normal hormone production associated with menstruation. The fertilized egg grows there after implanting into the denser uterine lining. If egg implantation has not taken place, the uterine lining will deteriorate during menstruation. Sex hormones are also produced by the female reproductive system to maintain a regular menstrual cycle. The number of eggs that a woman will have for the duration of her life is determined during fetal development, with each menstrual cycle the number of eggs declines which results in decreased fertility in women as they age (Clinic, 2022a).

1.4.2.2. Male genitalia

The male genitalia is also made up of internal and external components. The internal organs include the vas deferens, prostate and urethra; the penis, scrotum and testicles are the external organs. Similar to the female reproductive system the male reproductive system is responsible for sexual function, additionally it is also responsible for urination (Clinic, 2022b).

The majority of the male reproductive system is external to the pelvic or abdominal cavity. The urinary portion male reproductive system is responsible for removing waste products from the body via urination. The reproductive function is carried out by producing, storing, and transporting the sperm gamete and semen, this is done by producing the male sex hormones in order to carry out this function (Clinic, 2022b).

1.5. Genitourinary conditions

1.5.1. Affecting the ureter

• Megaureter

Megaureter is an abnormality that can affect the ureters. The affected ureter is enlarged and is dysfunctional. A megaureter often measures more than 7 mm, while a normal ureter is ∼4 mm (Nakamura et al., 2020).

• Neurogenic bladder

In individuals with neurogenic bladder leading to spina bifida, lower urinary tract dysfunction and hypertrophy of the bladder wall with a loss of the viscoelastic characteristics due to extracellular matrix components infiltration are common findings (Hwang et al., 2023).

• Urinary tract infections

A bacterial infection of the urinary tract that affects predominantly women (Pereira et al., 2020).

1.5.2. Diseases that lead to damage or loss of function of the kidneys

• Hemolytic-uremic syndrome

Acute renal failure, microangiopathic hemolytic anemia, and sometimes severe thrombocytopenia characterize the uncommon but devastating consequence of bacterial and viral infections (Birlutiu & Birlutiu, 2018).

• Polycystic kidney disease

Polycystic kidney disease is a main factor in end-stage renal disease, which calls for long-term dialysis or kidney transplantation (Mohamed et al., 2022).

1.5.3. Conditions that specifically affect females

• Urinary incontinence

Over 200 million people worldwide experience urinary incontinence, and it is becoming more prevalent as the population ages. The condition affects more women due to muscle, tissue, and nerve damage during birth, it can also be because of obesity.

• Premature ovarian failure

Premature ovarian failure, which causes infertility in women, is on the rise as a result of a number of reasons, most notably the widespread use of chemotherapy. Premature ovarian failure has a variety of causes, including autoimmune, iatrogenic, hereditary, and idiopathic (He et al., 2018).

• Cervical

Women who suffer from ovarian dysfunction face a variety of medical and psychosocial difficulties, including infertility issues and symptoms similar to menopause. Ovarian hormones not only affect the reproductive system but also the breast, blood arteries, and bones (Hassanpour et al., 2018).

1.5.4. Conditions that specifically affect males

• Hypospadias

A condition where abnormalities in the urinary meatus lead to an abnormal urethral development; there is no urethral opening. The condition affects ∼1 in 300 new-born boys (Abbas et al., 2018; Casarin et al., 2022).

• Urethral strictures

The majority of urethral strictures in adults happen as a result of scarring, which replaces the corpus spongiosum's vascular tissue and results in ischemic spongiofibrosis. Scar tissue replaces the injured urethra, decreasing its lumen and eventually causing lower urinary tract blockage (Pastorek et al., 2021).

• Testicular torsion

When the tissues around the testicle, commonly known as the testis, are not securely attached, it is known as testicular torsion. The testes may then twist around the spermatic cord as a result of this. When this occurs, the testicle's blood supply is cut off (Care,