Stem cell therapy for bladder regeneration: A comprehensive systematic review

Abstract

Tissue engineering has been considered a potential choice for urinary system reconstruction. Here, we aim to a broad spectrum of employed stem cells in bladder regeneration by performing a comprehensive systematic review. In January 2024, we searched Scopus, PubMed, and Embase databases for studies that tried bladder regeneration by tissue engineering using stem cells. We excluded non-English studies, review articles, and manuscripts that met the other exclusion criteria. Among 43 included studies, comparative studies demonstrated the similar or superior potentiality of stem cells to regenerate tissues and improve bladder function compared with autologous cells. Furthermore, data suggest an increased use of bio-synthetic scaffolds and their appropriate bio-compatibility with stem cells. The evidence establishes that adipose-derived and bone marrow-derived mesenchymal stem cells are the most frequently used stem cells. And both are suitable for urothelium and smooth muscle formation along with the capability of bone marrow-derived mesenchymal stem cells for lamina propria formation. Additionally, the competency of smooth muscle-derived progenitor cells, urine-derived stem cells, umbilical mesenchymal SCs for smooth muscle and urothelium regeneration, and the capability of hair follicle stem cells for smooth muscle formation are demonstrated. Also, the superiority of endothelial progenitor cells for neo-vascularization and smooth muscle progenitor cells for neuron formation are demonstrated. In addition to adding growth factors to the culturing media, hypoxic conditions and intra-peritoneal incubation are introduced as promoter conditions that can improve histological and physiological components. Available evidence is limited, although it suggests the precious capability of stem cells for bladder regeneration.

Graphical abstract

Highlights

• •Mesenchymal stem cells are the most frequently used stem cells for bladder regeneration and are suitable for urothelium and smooth muscle formation.
• •BMScs are capable of lamina propria regeneration and vascularization along with collagen formation.
• •Smooth muscle-derived progenitor cells, urine-derived and umbilical mesenchymal stem cells are appropriate for smooth muscle and urothelium regeneration.
• •Endothelial and smooth muscle progenitor cells are superior for neo-vascularization and neuron formation respectively.

1. Introduction

Approximately 13,000 patients require cystectomy due to several conditions, such as bladder cancer, bladder dystrophy, and neurogenic bladder, annually [1,2]. In 1851, the first urinary diversion was performed, followed by the first uretero-intestinal implantation in 1878 (Fig. 1) [3]. However, according to the modified surgical techniques, the most commonly employed technique for restoring bladder storage and voiding capacity is still using a gastrointestinal segment [7]. The mentioned bladder alternatives make cystectomy a surgical dilemma due to several perioperative complications. Urinary collection devices can affect the patient’s mental health and social life. Additionally, despite all advances in surgical methods, ileal neobladder and urinary diversion to the gastrointestinal tract are associated with complications such as uretero-intestinal strictures, urinary tract infections, vitamin deficiency, and metabolic imbalances [8,9].

Fig. 1.

Bladder alternatives, from urinary diversion to bladder regeneration. In 1888, the first ileal neo-bladder was created, and afterward, the stomach and rectum were used for bladder reconstruction [4]. In 1935, the cutaneous ureterostomy was introduced to have the best survival outcomes [5,6]. In 1991, tissue engineering was defined as culturing different cell types and constructing viable grafts for tissue replacement [10]. However, the initial report on bladder regeneration using autologous facia was published about 70 years earlier [11]. Afterward, in the 1960s, non-seeded biomaterials were first employed for bladder regeneration [12,13]. In the late 1990s, bladder acellular matrix and small intestinal submucosa were introduced as novel biomaterials for BR, followed by seeding scaffolds with autologous cells such as urothelial and smooth muscle cells [[14], [15], [16], [17], [18], [19]]. Finally, in 2006, Atala et al. introduced the first regenerated bladder in a human model by seeding cells on the PGLA/collagen scaffold [20, 86].

In contrast with the mentioned bladder alternatives, bladder regeneration (BR) tissue engineering does not have a prolonged background; however, according to recent advances in bio-engineering, it has become a hot topic. Fig. 1 provides a historical timeline of advances in bladder alternatives and regeneration. BR using bioengineering requires choosing the appropriate scaffold and the essential use of various types of cells to achieve optimum muscle function and bladder wall integrity with minimum inflammation and fibrosis formation [21]. Several studies demonstrated that the seeded grafts have more appropriate outcomes than non-seeded ones. So, BR via tissue engineering has some cornerstones, including appropriate scaffold identification, suitable cell seeding, and optimal cell nutrition by providing an appropriate blood supply [22].

Scaffolds are divided into two main types: a: natural and biological scaffolds like acellular matrices (small intestinal submucosa (SIS) and bladder acellular matrix (BAM)) and biological materials such as collagen, and b: synthetic polymers [[22], [23], [24]]. Both host autologous cells and stem cells (SCs) are employed for seeding on the mentioned scaffolds. Autologous cells, including fibroblasts, urothelial, and smooth muscle cells, can be obtained from bladder biopsy. However, SCs have several routes of achievement and require isolation. Furthermore, they require stimulation to differentiate into specific cell types. Then, SCs and autologous cells must be cultured with specific growth factors and conditions and seeded on scaffolds [[22], [23], [24]]. After cell seeding, maintaining the graft’s viability is essential, and it can be achieved by maintaining blood supply. Before the vascularization of the regenerated tissue, the blood supply can be sustained by using omentum before organ transplantation. Also, biologic scaffolds, such as SIS, have vascular microenvironments. Furthermore, creating a sustainable resource for cell nutrition is essential. It is only achievable by the neo-vascularization of the regenerated graft and can be improved by using specific cell types and growth factors [[22], [23], [24]].

The mentioned issues are fundamental concepts of tissue regeneration. However, what has evolved from 30 years ago is a rapid replacement of autologous cells by SCs according to their appropriate capability for tissue regeneration and superior proliferation in addition to possible differentiation of autologous cells to malignant ones [25].

Several studies investigated the different types of SC differentiation into the bladder urothelium and smooth muscle cells. Induced pluripotent and multipotent SCs, including bone marrow derived mesenchymal SCs (BMSC), adult SCs such as adipose, urine, or hair follicle SCs (HFSC), and fetal SCs such as amniotic-derived or umbilical cord-derived mesenchymal stromal cells have been examined to transdifferentiate into bladder urothelium [21,25,26]. Furthermore, Adipose derived SCs (ADSCs), BMSCs, HFSCs, and muscle-derived SCs have been employed for bladder smooth muscle regeneration [25]. In addition, endothelial progenitor cells have been examined to optimize regenerated bladder neovascularization [27]. Moreover, the type of scaffolds and subsidiary factors such as induced genes, growth factors, and different culturing conditions such as co-culturing and culturing in hypoxic media may affect the outcomes [25,[27], [28], [29]]. Therefore, the present study investigates the current application of SC therapies for BR by performing a systematic literature review.

2. Methods

2.1. Database search and literature screening

A systematic search was conducted in PubMed, Embase, and Scopus databases on January 2024 for articles on BR by tissue engineering that employed SCs using search terms including stem cell, precursor cell, progenitor cell, tissue engineering, guided tissue regeneration, tissue regeneration, regenerative medicine, urinary bladder, bladder, and urinary conduits in various combinations and synonyms used in the literature which are available in Supplementary Table B.

2.2. Description of intervention and inclusion criteria

All English-language animal studies were retrieved in case of available full text. Reviews, articles that did not involve SCs, only investigated SCs differentiation into different cell types, investigated other than bladder organ regeneration (including ureter and sphincter), and used intravesical injection of SCs without tissue engineering and scaffolds were excluded.

2.3. Data extraction

After an initial literature search and reviewing for duplications, two independent authors (AF and NC) performed the screening process on the Rayyan.ai website by reviewing all studies' titles and abstracts. In case of any disagreement, the decision to include or exclude the study was made by a third author (MMZ). Afterward, the available full text for manuscripts was reviewed. Data was extracted regarding each study’s first author, country of origin, population, type of SCs, achieving route, scaffold type, and specific culturing conditions. Furthermore, outcome measures were evaluated, including histopathology, bladder physiological function evaluation (such as urodynamics), adverse events, and complications.

3. Results

3.1. Research selection and data synthesis

As shown in Fig. 2, 2405 studies were identified through initial literature searching. After excluding the duplications, 606 studies were screened by their title and abstracts, which resulted in the exclusion of 337 studies. Of the remaining 269, 226 were excluded because 1: did not meet the inclusion criteria, 2: the full text was unavailable, 3: were congress abstract papers, and 4: were non-English papers. Finally, 43 studies were included in the present systematic review. The characteristics of the included studies are summarized in Supplementary Table A.

Fig. 2.

PRISMA flow diagram.

3.2. Geographical distribution and methodological variance

Twenty-two studies were from Asia, 11 from Europe, and ten from America. China is the leading country with 19 included studies. Also, seven studies from Poland, five from the United States, three from Brazil, and two from Korea were identified. Mexico, Spain, Switzerland, Russia, Canada, Malaysia, and Germany are other countries with one included study. Of the 43 studies, 11 were published between 2020 and 2023, and another 32 were published between 2004 and 2019, indicating the novelty of using SCs in BR. Twenty studies used synthetic biomaterials as scaffolds, 18 used BAM, seven used SIS, two used human amniotic membrane, and one used inferior vena cava (IVC) acellular matrix. Hypoxia, co-culturing of SCs with native autologous bladder cells, and increased cells are identified as promoting conditions [27,29,30].

Among all included studies, only three study tried total bladder regeneration in-vivo [39,48.62]. All used BAM as scaffold. In two of them, BAM were seeded with ADSC [39,48], and in another one were seeded with BMSC [62]. Meng L et al. used omentum incubation before new bladder transplantation as enhancing factor and reported no leakage, stricture, or obstruction in the control group [48]. Also, Xiong Y et al. reported hydroureter in all animals with total bladder regeneration [62] (Table 2).

Table 2.

Studies that tried total bladder regeneration in-vivo.

First author	Year/Country	Objective/Methods	Sample size	Scaffold	Stem cell	Route of achieving	Histopathology	Other results
Manzano V [39]	2020/Spain	Comparing BAM alone and seeded BAM with ADSC for BR. Group 1: ADSC-seeded BAM Group 2: Non-seeded BAM	6	BAM	ADSC	Human surplus fat tissue	• Group 1 expressed more urothelial markers significantly compared with 2 (P63). • In group 1, the stratified urothelium was observed, but the phenotype was immature. • Higher density of α- SMA positive cells and well-organized smooth muscle fibers were observed in group 1.	• Quantifying the CD31+ cells did not reveal a significant difference between groups 1 and 2; however, group 1 had more blood vessels.
Meng L [48]	2015 /China	Build tissue-engineered tubular substitutions by seeding ADSC and bladder smooth muscle cells onto two sides of BAM. Group 1: Seeded scaffold Group 2: Non-seeded scaffold	25	BAM	ADSC	Rabbit’s inguinal subcutaneous tissue	• One layer of urothelium and neovascularization was identified after incubation in the omentum in group 1. • After 16 weeks, multilayer uro-epithelium covered the luminal surface. • After 16 weeks of transplantation, scaffolds showed α-SMA smooth muscle cells and appropriate neovascularization.	• Intravenous urography revealed no evidence of leakage, stricture, or obstruction in contrast with the control group.
Xiong Y [62]	2015/China	Bladder regeneration using BMSC and BAM	12	BAM	BMSC	Rabbit’s bone marrow	• After 14 days, about half of BMSC exhibited epithelium-like morphology. • UPK1A was expressed in urothelium cells and induced BMSC cells in contrast with non-induced BMSC. However, the morphology of induced and non-induced BMSCs was similar. • A Matured multilayered epithelium was formed after 4 weeks. • The proliferation of the induced cells was appropriate after seeding on BAM.	• Hydroureter existed in all animals after 4 weeks. • No hydronephrosis or leakage was seen.

BAM = BMSC = Bone marrow-derived mesenchymal stem cell/ADSC = Adipose-derived stem cell/BMSC = Bone marrow-derived mesenchymal stem cell.

3.3. Stem cell utilization overview

ADSC (24) [[30], [31], [32], [33], [34], [35], [36], [37], [38], [39], [40], [41], [42], [43], [44], [45], [46], [47], [48], [49], [50], [51], [52], [53]], BMSCs (13) [21,35,43,[54], [55], [56], [57], [58], [59], [60], [61], [62], [63]], HFSCs (2) [64,65], endothelial progenitor cells (3) [27,49,66], embryonic germ cell-derived SCs (1) [29], (1), skeletal muscle-derived SCs (1) [50], urine-derived SCs (1) [67], umbilical mesenchymal SCs (1) [68], and smooth muscle-derived progenitor cells (1) [69] were employed SCs in included studies.

In 24 studies involving ADSC, SCs were obtained from animal adipose tissue in 17 studies and from human adipose tissue in seven studies [[30], [31], [32], [33], [34], [35], [36], [37], [38], [39], [40], [41], [42], [43],[45], [46], [47], [48], [49], [50],52,53,70]. BMSCs were obtained from animal and human bone marrow in 12 and 1 studies, respectively [21,35,43,[54], [55], [56], [57], [58], [59], [60], [61], [62], [63]]. Additional sources were animal peripheral blood (2) [66,69], animal skin (2) [64,65], human urine (1) [67], human newborn umbilical cord (1) [68], human embryonic germ cells (1) [29], and animal skeletal muscle tissue (1) [50]. The route of achieving, employed scaffolds, advantages, disadvantages, adverse events, and associated complications based on each type of SCs are available in Table 1.

Table 1.

Data synthesis based on stem cell type.

Stem cell	Rout of achievement	Scaffolds	Advantages and specific conditions	Adverse events, disadvantages, and complications
ADSC	-Animal adipose tissue -Human adipose tissue	-Extracellular matrix hydrogel -IVC decellularized matrix -BAM -SIS -Adipose tissue extract and PLCL multilayer -Heparin–polycaprolactone/BAM -Bilayer silk-Fibroin skeleton and BAM hydrogel -Lipid-Nanosphere-small MyoD activating RNA/BAM -Compressed collagen hydrogels -Multilayered PLCL -PLCL/chitosan -GO/6 ARM-PEG-amine/PCL -BAM/alginate di-aldehyde-gelatin hydrogel-silk mesh -Matrigel and BAM 3D -PLCL nanofibrous membrane -Polyglycolic-acid scaffold -Polylactic-co-glycolic acid coated with collagen or fibrin	-Appropriate urothelium, myofibroblast and collagen type 2 formation. -High capability to express SMC markers like α-SMA. -Improved bladder elasticity when co-cultured with fibroblasts. -Improved vascularization when co-cultured with SMCs. -Improve muscle and neuron regeneration with intraperitoneal incubation. -Improved bladder capacity, angiogenesis and SMC formation. -When adding VEGF solution, connective tissue and urothelium smooth muscle formation and vascularization are improved.	-Stone formation. -Graft penetration when seeding on BAM. -Urinary leakage when seeding on PLCL/chitosan scaffold. -Increased mortality rate when seeding on PLC scaffold compared with SIS. -Abnormal permeability.
BMSC	-Animal bone marrow -Human bone marrow	-Poly (1,8-octa methylene-citrate-co-octanol) -SIS -ATE and PLCL multilayer scaffold -BAM -PLGA/collagen compound scaffold -PLCL and amniotic membrane bio-composite -Poly-l-lactide/silk fibroin scaffold -Human amniotic membrane -Elastomeric (1,8-octane diol-co-citrate) based thin films -Poly-l-Lactic acid (PLLA)	-Closer protein homogeneity to the native bladder. -Appropriate capability for bladder muscle, urothelium, and lamina propria regeneration. -Enhanced the muscle-to-collagen fiber ratio. -UP1a (urothelial marker) expression. -Increased UPK1A expression in induced BMSC compared with non-induced. -Higher IL-4, TGF-b1, and IFN-c expression compared with the non-seeded group. -Improved bladder capacity and shape when seeding on PLGA/collagen compound scaffold compared with SIS. -Compared with SIS, improved urothelium and smooth muscle formation when seeding on PLGA/collagen compound scaffold. -Improved cell proliferation in 3D dynamic culture condition. -Bladder extracellular matrix improved SMC markers expression.	-Bladder’s hyperactivity with irregular storages. -Absence of bladder contractility. -Urothelium hyperplasia. -Hydroureter. -Bladder stone. -Retarded cell proliferation when adding Myogenic growth factor.
EPC	-Animal adipose tissue -Animal peripheral blood	-BAM -SIS -Matrigel synthetic graft	-Improved vascularization and angiogenesis. -More proliferation compared with ADSCs. -Improved bladder capacity either in hypoxic or normoxic condition. -Improved bladder compliance under hypoxic conditions. -Improved blood vessels, SMC, urothelium and nerve formation under hypoxic conditions. -Increased VEGF and bFGF under hypoxic condition.	-Absence of α-SMA expression. -Lower VEGF expression compared with ADSCs.
HFSC	-Animal skin and subcutaneous tissue.	-BAM	-Appropriate bio-compatibility with BAM. -The high relative growth rate on BAM. -Appropriate smooth muscle regeneration.	-Similar hair structures formation after long term follow-up.
Embryonic germ cell-derived stem cell	-Human embryonic germ cells	-SIS	-Improved growth rate in co-culturing with SMC and urothelial cells. -According to a well-organized bladder pattern, co-culturing with SMCs is superior to urothelial cells.	-Matrix penetration when co-cultured with urothelial cells.
Umbilical cord-derived mesenchymal stem cell	-Human’s newborn umbilical cords	-BAM	-Capability of urothelium and SMC formation. -Well-organized transitional epithelium. -Make the regenerated bladder prone to neovascularization.
Smooth muscle-derived progenitor cell	-Animal’s peripheral blood	-BAM	-Improved both bladder capacity and compliance. -Capability of smooth muscle formation, neovascularization, neuron regeneration, and urothelial formation. -Stronger contractile strength than the non-seeded group. -Improved migration and viability of SMC.	-Graft calcification. -Urinary leakage (however, lower than control group).
Skeletal muscle-derived stem cell	-Animal’s skeletal muscle	-Polyglycolic-acid scaffold	-Reduced fibrosis formation.
Urine-derived stem cell	-Human urine	-Heparin-immobilized bFGF modified scaffold.	-Urothelial and SMC markers expression. -Improved bladder shape and volume. -Appropriate urothelium, muscle bundles, and submucosa formation. -Reduced T CD8+ accumulation.

Footnotes: ADSC = adipose-derived stem cell; PLCL = poly (l-lactide)/poly (ε-caprolactone); IVC = inferior vena cava; BAM = bladder acellular matrix; SIS = small intestinal submucosa; SMC = smooth muscle cell; BMSC = bone marrow-derived stem cell; EPC = endothelial progenitor cell; HFSC = hair follicle-derived stem cell; VEGF = vascular endothelial growth factor; bFGF = basic fibroblast growth factor.

3.4. Functional and histopathological evaluations

Twenty-four studies conducted functional assessments of the regenerated bladder using urodynamic studies, electromyography, simple cystometry, and cystography [21,27,30,32,[34], [35], [36], [37], [38],40,41,46,47,[51], [52], [53],56,60,61,63,64,67,69,70]. All except one study included histopathological evaluations [58]. Parameters such as bladder size, compliance, elasticity, contractility, and rupture tolerance were scrutinized in studies examining the functionality of the regenerated bladder.

Most of the studies evaluated bladder function via urodynamic studies. The maximum bladder capacity that triggered the first urine leakage episode is considered bladder maximum capacity. The bladder volume is calculated by perfusion time multiplied by perfusion rate, and bladder compliance is calculated by volume increase divided by pressure change [35]. Several studies used retrograde cystography using contrast infusion and X-ray imaging [36,37]. Furthermore, some studies used computed tomography (CT) urography [41]. Moreover, electromyography (EMG) was another method for evaluating bladder function. In this method, the bladder filling is monitored by placing electrodes in the bladder wall [61].

4. Discussion

4.1. Key findings

SCs are similar or superior to regenerate bladder tissues and improve physiological function compared with autologous native bladder cells [30,54]. Furthermore, data suggest the appropriate bio-compatibility of SCs with both traditional (BAM and SIS) and bio-synthetic scaffolds [53,63,65]. The evidence establishes that ADSC and BMSC are the most frequently used SCs and are suitable for urothelium and smooth muscle formation [33,35]. Also, BMSCs have appropriate potentiality of lamina propria regeneration and vascularization along with collagen formation [56,61]. Additionally, the competency of smooth muscle-derived progenitor cells, urine-derived SCs, umbilical mesenchymal SCs for smooth muscle and urothelium regeneration, and the capability of HFSCs for smooth muscle formation are demonstrated [64,65,68,70,71].

Data reveals the superiority of endothelial progenitor cells for neo-vascularization and smooth muscle progenitor cells for neuron formation [49,66,69]. In addition to adding growth factors to the culturing media, hypoxic conditions and intra-peritoneal incubation are introduced as promoter conditions that can improve histological and physiological components [27,47]. Bladder calculi, graft penetration, urinary leakage, abnormal permeability, lack of contractility, smooth muscle and hyperactivity are identified complications; however, the exact association between type of SCs and complications is still unclear according to the several involving factors [21,36,51,70]. Furthermore, forming hair follicle-like structures in the regenerated bladder is one of the particular adverse events in the case of using HFSCs [64].

4.2. Adipose-derived stem cell

ADSCs are adult SCs with mesodermal origin [72]. According to their easy accessibility, high quantity, less doubling time than other adult SCs, and more autocrine and growth factors production, including vascular endothelial growth factor (VEGF) and insulin-like growth factor 1, they seem to be appropriate SCs to be employed in regenerative medicine [44,73,74]. However, this ability to produce growth factors has disadvantages, such as stimulating malignant tumor growth and making them prone to metastasis [75].

Evidence shows that ADSCs are commonly employed SCs in BR. They are extracted from both animal and human adipose tissues. IVC acellularized matrix, SIS, BAM, and synthetic matrixes such as PLCL multilayered, Matrigel 3D, Polyglycolic-Acid scaffold, alginate di-aldehyde-gelatin hydrogel-silk mesh, and Compressed collagen hydrogels scaffold were used scaffold with ADSCs and have good bio-compatibility [30,[33], [34], [35], [36],[38], [39], [40],48,53,70,76]. Based on our findings, ADSC is appropriate for urothelium regeneration. The results of the included studies indicate controversial issues regarding collagen formation by ADSC. However, better collagen formation was found compared with the non-seeded group on the IVC scaffold [33]. ADSCs can express smooth muscle markers like α-SMA, even similar to skeletal muscle-derived SCs [50].

Xiao D et al. demonstrated that using ADSC can increase threshold pressure; however, Hou X et al. demonstrated no significant change in maximum pressure in the case of ADSCs employment [36,46]. Some studies examined ADSC’s co-culturing with other cells. Smolar J et al. demonstrated that co-culturing with smooth muscle cells can improve vascularization [30]. Studies also reported improved bladder elasticity when ADSCs were co-cultured with fibroblasts; this condition can reduce the regenerated bladder’s rapture tolerance [51]. Zhe Z et al. investigated intraperitoneal incubation on ADSCs, revealing that this condition can improve muscle and neuron regeneration; however, it does not significantly affect neovascularization [47].

4.3. Bone marrow-derived mesenchymal stem cell

Mesenchymal SCs are highly infrequent in the bone marrow’s cell population. They account for less than 0.01 % of nuclear cells in the bone marrow, so identifying these cells is a dilemma. BMSCs can differentiate to particular cell types by external stimulation factors, including cytokine, chemokine, and growth factors; however, their adhesion to the extracellular matrix is crucial for differentiation [77,78].

Among the included studies, 13 employed BMSCs for BR. Data suggests SIS, BAM, human amniotic membrane, and biomaterials are employed scaffolds [21,35,43,[54], [55], [56], [57], [58], [59], [60], [61], [62], [63]]. Some studies demonstrated that BMSCs have advantages for BR, including closer protein homogeneity to the native bladder and the appropriate capability of these cells for bladder muscle, urothelium and lamina propria regeneration [56,58,61]. However, Wu Q et al. revealed no significant difference in urothelium formation between BMSCs and urothelial cells [54]. Also, BMSCs can improve the muscle-to-collagen fiber ratio. Moreover, BMSCs are superior to the bladder’s native autologous smooth muscle cells for muscle fiber regeneration [59,60].

There are controversial results about the bladder’s activity. Some studies indicated appropriate activity, although, in some studies, the regenerated bladders with BMSC had hyperactivity with irregular storages (about 12 % of regenerated bladders) [21,61]. In addition, Wang J et al. showed that using adipose tissue extract can improve bladder compliance, urothelium and muscle fiber formation, and neovascularization in the case of using BMSCs [35].

4.4. Endothelial progenitor cell

Progenitor cells have less capability to differentiate into different cell types than SCs and have higher levels of transdifferentiating to a specific type of cells. Endothelial progenitor cells can be extracted from peripheral blood and differentiate into mature endothelial cells by graft functionalization. Oligopeptide ligands for integrin adhesion on these cell’s surface, growth factors (VEGF or fibroblast growth factor-2), and antibodies against particular molecules on endothelial progenitor cells such as CD 31 and CD 133 can be used for graft functionalization [72].

Based on the present studies' data, endothelial progenitor cells are obtained from adipose tissue and peripheral blood [27,49,79,80]. BAM, SIS, and Matrigel synthetic grafts are scaffolds for tissue regeneration by these cells [49]. Data suggest hypoxic conditions can amplify the regenerated bladder’s compliance compared to normoxic conditions when using endothelial progenitor cells. Also, this promoter factor can increase blood vessels, smooth muscle cells, and nerve formation in the regenerated bladder [27]. Schultheiss et al. assessed thrombosis formation in the case of using endothelial progenitor cells and reported no evidence of thrombosis [66].

4.5. Hair follicle-derived stem cell

During hair germ formation in the fetal hood, Sox9 expression specifies HFSCs from others. Both embryonic and adult HFSCs express Sox-9, although adult SCs have less proliferation capability. Despite this reduction in proliferation ability, adult HFSCs can differentiate into several cell types, including melanocytes, keratinocytes, smooth muscle cells, and neurons [65,81]. Among all included studies, only two studies examined HFSCs for BR, and both used BAM as the scaffold [64,65]. According to low toxicity, high growth rate, and stagnate phase of about 7–8 days, HFSCs have good bio-compatibility with BAM [65]. Using HFSCs results improved smooth muscle regeneration; however, using these cells does not significantly affect the regenerated bladder’s capacity. Also, after a long-term follow-up, similar hair structures can be formed in the case of HFSC employment [64].

4.6. Embryonic Germ Cell and umbilical cord-derived mesenchymal stem cell

The main difference between embryonic germ cells and others is their ability to differentiate into any tissue except the placenta [72]. Embryonic germ cells can be extracted from the inner cell mass of embryos before implantation. The lower risk of teratoma development from embryonic germ cells compared with induced pluripotent SCs makes them an appropriate option for regenerative medicine. However, some disadvantages exist, such as karyotype abnormality and genome instability during expansion [82].

Lakshmanan Y et al. examined the embryonic germ cells seeding on the SIS scaffold. They investigated the effect of these cells co-culturing with the bladder’s urothelial and smooth muscle cells and showed that co-culturing could improve the growth rate; however, co-culturing with smooth muscle cells is superior to urothelial cells according to a well-organized bladder pattern. Also, co-culturing with urothelial cells resulted in matrix penetration [29].

Obtaining embryonic germ cells has been an ethical concern. Recent studies investigated extracting mesenchymal SCs from the umbilical cord, which can be achieved from Wharton’s jelly, cord lining, and perivascular portion [83]. Yuan H et al. employed human umbilical cord mesenchymal SCs seeding on BAM for BR. Their study demonstrated the transdifferentiating ability of human umbilical cord mesenchymal SCs to the urothelium and smooth muscle cells. Also, they showed that these SCs can form well-organized transitional epithelium and make the regenerated bladder prone to neovascularization [68].

4.7. Smooth muscle-derived progenitor cells and skeletal muscle-derived stem cells

Zhoe L et al. used peripheral blood to achieve smooth muscle progenitor cells seeding on BAM for BR, and they demonstrated that smooth muscle progenitor cells can improve both bladder capacity and compliance. Also, smooth muscle formation, neovascularization, and neuron regeneration were investigated, indicating that these aspects improved along with proper urothelium formation [69]. Zambon J et al. tried BR by seeding skeletal muscle-derived SCs on Polyglycolic-Acid scaffold revealing good bio-compatibility and fibrosis reduction compared with non-seeded scaffold [50].

4.8. Urine-derived stem cell

According to the easy and noninvasive accessibility of urine-derived SCs, they seem to be an appropriate cell source for employment in tissue regeneration. Also, they can differentiate into several cell types, including genitourinary, skeletal muscle, and skin cells, because of similar characteristics of urine-derived and mesenchymal SCs [71,84]. Also, their paracrine effect on vascularization and neuron formation makes them a suitable choice for employment in BR [71,85]. Urine-derived SCs can be obtained from voided urine or the upper urinary tract. However, they should not be obtained from patients with bladder cancers due to the possibility of existing malignant cells [84]. A limited number of studies have employed urine-derived SCs in BR. Data suggests enhanced bladder physiological function, including capacity and compliance, along with appropriate urothelium, muscle bundles, and submucosa formation [67].

5. Conclusion

The present study investigated the current state of using different types of SCs in BR by conducting a systematic review. Results demonstrated that SCs have good biocompatibility with both traditional and bio-synthetic scaffolds. According to more experience with BAM and SIS, it is predictable that they are more frequently used. However, comparative studies revealed the superiority of bio-synthetic scaffolds in several specific components. As summarized in Table 1 and Fig. 3, data suggests the competency of ADSCs, BMSC, smooth muscle-derived progenitor cells, urine-derived SCs, and umbilical mesenchymal SCs for smooth muscle and urothelium regeneration and the capability of HFSCs for smooth muscle formation. In addition, the BR outcomes can be improved by employing strengthening factors such as co-culturing SCs, using hypoxic precondition, intraperitoneal incubation, and using particular growth factors and gene expression.

Fig. 3.

Optimal stem cells for bladder’s tissue regeneration [86].

Despite all the mentioned advances in BR, enterocystoplasty is still a gold standard for creating bladder alternatives in the cystectomy population. Future studies should evaluate the role of novel types of SCs, synthetic bio scaffolds advantages, and strengthening factors to achieve better tissue integrity, improved bladder contractility and elasticity, and optimum blood supply.

Author contributions

Conceptualization: [AF and MMZ]; Literature search and data extraction: [AF, NC, and MMZ]; Drafting of the manuscript: [AF], and Critical revision of the manuscript: [MMZ, HB, and SJ].

Funding

The authors did not receive any funding to conduct the present study.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Appendix A. Supplementary data

The following are the Supplementary data to this article: