Grafting of CAG peptides and (polyethylene glycol) on unsaturated polyurethane films to promote selective adhesion and migration of urethral epithelial cells

Selective adhesion and migration of urethral epithelial cells (HUCs) over fibroblasts (FIBs) are very important in the reconstruction of the urethral epithelial layer and prevention of ureteral scarring and stenosis. In this study, unsaturated polyurethane (PPFU-CO-SS) films were co-grafted with a cell-resisting poly(ethylene glycol) (PEG) layer and HUC-selective Cys-Ala-Gly (CAG) peptides, whose physicochemical changes were confirmed by X-ray photon spectroscopy, fluorescence spectroscopy and water contact angle measurements. The adhesion and activation of platelets on the PEG/CAG grafted surface were significantly reduced compared to those on the PPFU-CO-SS, resulting in a similar status as that on a PEG-grafted surface. The HUC-selective material could obviously promote the adhesion and migration of HUCs. The ratio of the urethral epithelial cells to fibroblasts on the PEG/CAG grafted surface was nearly 3-fold that on the unmodified PPFU-CO-SS in a co-culture competitive environment. The urethral epithelial cells cultured on the PEG/CAG grafted surface also had the highest migration rate, which was 2.24-fold compared to that on the PPFU-CO-SS control.

Electrospinning: Application and Prospects for Urologic Tissue Engineering

Functional disorders and injuries of urinary bladder, urethra, and ureter may necessitate the application of urologic reconstructive surgeries to recover normal urine passage, prevent progressive damages of these organs and upstream structures, and improve the quality of life of patients. Reconstructive surgeries are generally very invasive procedures that utilize autologous tissues. In addition to imperfect functional outcomes, these procedures are associated with significant complications owing to long-term contact of urine with unspecific tissues, donor site morbidity, and lack of sufficient tissue for vast reconstructions. Thanks to the extensive advancements in tissue engineering strategies, reconstruction of the diseased urologic organs through tissue engineering have provided promising vistas during the last two decades. Several biomaterials and fabrication methods have been utilized for reconstruction of the urinary tract in animal models and human subjects; however, limited success has been reported, which inspires the application of new methods and biomaterials. Electrospinning is the primary method for the production of nanofibers from a broad array of natural and synthetic biomaterials. The biomimetic structure of electrospun scaffolds provides an ECM-like matrix that can modulate cells' function. In addition, electrospinning is a versatile technique for the incorporation of drugs, biomolecules, and living cells into the constructed scaffolds. This method can also be integrated with other fabrication procedures to achieve hybrid smart constructs with improved performance. Herein, we reviewed the application and outcomes of electrospun scaffolds in tissue engineering of bladder, urethra, and ureter. First, we presented the current status of tissue engineering in each organ, then reviewed electrospun scaffolds from the simplest to the most intricate designs, and summarized the outcomes of preclinical (animal) studies in this area.

Developing improved tissue-engineered buccal mucosa grafts for urethral reconstruction

INTRODUCTION

We aimed to compare alternative synthetic scaffolds suitable for future implantation and to examine the use of an inhibitor of lysyl oxidase (beta-amino-propionitrile [β-APN]) to reduce contraction in these implants.

METHODS

Three synthetic scaffolds were compared to natural dermis as substrates for the production of tissue-engineered skin. For natural dermis, Euroskin was used to provide a cell-free cadaveric dermis. Synthetic scaffolds consisted of microfibrous poly-L-lactic acid (PLA), nanofibrous poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), and a micro-/nanofibrous trilayer of PLA-PHBV-PLA. The latter were all electrospun and then all four scaffolds (three synthetic, one natural) were placed in six well plates. A culture well was formed on the scaffold using a 1 cm diameter stainless steel ring and 1.5×105 oral fibroblasts were seeded one side; after two days of culture, the ring was placed on the other side of the scaffolds and 3×105 oral keratinocytes were seeded on to the scaffolds and cultured with keratinocytes uppermost. After a further two days of culture, scaffolds were cut to 1 cm2 and raised to an air-liquid interface on stainless steel grids; some were treated with 200 μg/mL β-APN throughout the culture period (28 days). Contraction in vitro was assessed by serial digital photography of cell-seeded scaffolds and cell-free scaffolds three times a week for 28 days. All cell-seeded scaffolds were assessed for cell metabolic activity, mechanical properties, histology, and morphology by scanning electron microscopy (SEM).

RESULTS

The mean fibre diameters and pore sizes of PLA and PHBV scaffolds were 2.4±0.77, 0.85±0.21 μm (p<0.001), and 10.8±2.3, 4.3±1.1 μm (p<0.001), respectively. Oral fibroblasts and keratinocytes were tightly adhered and grew well on both surfaces of trilayer. The ultimate tensile strength (UTS) and Young's modulus (YM) of PLA samples were significantly lower than Euroskin (p<0.001 and p<0.05, respectively); only the UTS of the trilayer samples was slightly significantly lower (p<0.05). Metabolic activity was significantly increased for cells on all scaffolds, without significant differences between them from Day 0 to Day 28. There were no adverse effects of β-APN on cell viability. With respect to contraction, cells on trilayer and PHBV monolayers did not undergo any significant contraction; however, cells on PLA monolayer and Euroskin contracted 25.3% and 56.4%, respectively, over 28 days. The addition of 200 μg/ml β-APN significantly reduced contraction of Euroskin compared with the control (p<0.01); however, β-APN did not affect PLA contraction during this culture period (p>0.05).

CONCLUSIONS

This study shows that a trilayer micro-nano-3D porous synthetic scaffold is suitable for oral keratinocyte and fibroblast growth with good cell viability and minimal contraction. This material also has good mechanical properties and histological analyses showed its ability to mimic normal human oral mucosal morphology. Furthermore, synthetic trilayer scaffolds have advantages over biological scaffolds - there is no risk of disease transmission or immunological rejection and they appear resistant to contraction. We suggest they present a good alternative to allodermis for future use in urethral reconstruction.

Comparative study of isolation, expansion and characterization of epithelial cells

BACKGROUND AIMS

The human epithelial cells (EPCs) have been identified as the essential element for the regeneration of skin construct for burns, wounds and various tissue engineer-based products.

METHODS

In this study, the isolation, expansion and characterization of EPCs from various sources such as juvenile foreskin (JSK), buccal mucosa (BM), penile skin (PS) and urothelium (UR) in serum-free and xeno-free EpiLife media were evaluated.

RESULTS

The growth kinetics study revealed that EPCs from JSK and BM had notably higher growth rates compared with the others. Overall, the EPCs from all sources retained basic morphological characteristics and the functional characteristics such as Pan Cytokeratin (AE1/AE3). In addition, the cryopreservation stability of EPCs was accessed for post-thaw viability and found to be greater than 80% at 1 year of storage, but demonstrated reduced cell recovery (51%) at the second year in fetal bovine serum-free cryopreservation media.

CONCLUSIONS

Our result suggests that the EPCs from four cell sources can be grown in feeder-free, serum-free and xeno-free systems using commercially available EpiLife medium without losing epithelial cell characteristics even after passage 4. However, its suitability for clinical application must be accessed by preclinical and clinical studies.

Study of clinical practical model of urinary system injury

Background:

In order to improve the clinical treatment level of urinary system injury, it is necessary to build up an animal model of urinary system wound, which is not only analogous to real clinical practice, but also simple and practical.

Methods:

We have developed the third generation of firearm fragment wound generator based on the first and the second producer. The best explosive charge of the blank cartridge was selected by gradient powder loading experiments. The firearm fragment injuries were made to the bulbous urethra of 10 New Zealand male rabbits. One week preoperatively and 2, 4 and 8 weeks postoperatively, all the animals underwent urethroscopy and urethrography. At 2, 4 and 8 weeks postoperatively, two animals were randomly selected and killed, and the urethra was cut off for pathological examination.

Results:

The shooting distance of the third generation of firearm fragment wound generator is 2 cm. The best explosive charge of the blank cartridge is 1 g of nitrocotton. All rabbits survived the procedures and stayed alive until they were killed. Injuries were limited to bulbous urethra and distal urethra. Round damaged areas, 1–1.5 cm in length, on the ventral wall were observed. Ureteroscopy results showed that canal diameter gradually shrank by over 50% in 9 rabbits. The rate of success was 90%. Urethrography result noted that a 1–1.3 cm stricture was formed at the bulbous urethra. Histology results of injured stricture urethra showed that fibrous connective tissue hyperplasia and hyaline degeneration caused further stricture in the canal.

Conclusions:

The third generation of firearm fragment wound generator imitates the bullet firing process and is more accurate and repeatable. The corresponding rabbit model of traumatic complex urethral stricture simulates the real complex clinical conditions. This animal model provides a standardized platform for clinical researches on treating traumatic injuries to the urinary system.

A tissue-specific scaffold for tissue engineering-based ureteral reconstruction

Terminally differentiated somatic cells can rapidly change phenotypes when they are isolated from their native tissue and cultured in vitro. This problem may become a barrier to tissue engineering-based organ reconstruction, which utilizes somatic cells. The present study was designed to validate the feasibility of maintaining the urothelial cell phenotype in a tissue-specific ureteral scaffold. The tissue-specific scaffold was fabricated by blending poly (L-lactic acid) (PLLA) and ureteral extracellular matrix (UECM) using electrostatic spinning technology. PLLA was used to enhance the mechanical properties, and UECM was used to mimic the natural components of the ureter. Primary urothelial cells (UCs), derived from ureteral mucosa, were seeded onto the tissue-specific scaffold to assess cell adhesion, proliferation and phenotypes at designated time points. The results showed that UCs in the tissue-specific scaffold exhibited better proliferation compared to cells in pure PLLA or a PLLA-small intestinal submucosa (PLLA-SIS) scaffold (p<0.05). At different time points, the expression of a UC-specific marker (UroplakinⅢ) in the tissue-specific scaffold was significantly higher than its expression in pure PLLA or a PLLA-SIS scaffold (p<0.05). Therefore, the tissue-specific scaffold appears to be an ideal substrate for promoting UC survival and phenotype maintenance.

Adjunctive maneuvers to treat urethral stricture: a review of the world literature

The development of urethral stricture (US) or bladder neck contracture is a relatively uncommon but well described condition observed primarily in men. Despite familiarity with US disease, management remains challenging for urologists. Risk factors for the development of USs or bladder neck contracture include primary treatment modality, tobacco smoking, coronary artery disease and poorly controlled diabetes mellitus. Numerous treatment options exist for this condition that vary in procedural complexity, including intermittent self catheterization (CIC), serial urethral dilation, endoscopic techniques and open reconstructive repairs. Repetitive procedures for this condition may carry increased failure rates and morbidities. For the treatment of refractory or recalcitrant bladder neck contracture, newer intralesional anti-proliferative, anti-scar agents have been used in combination with transurethral bladder neck incisions to augment outcome and long-term effect. The primary focus of this systematic review of the published literature is to streamline and summarize various and newer therapeutic modalities available to manage patients with US or bladder neck contracture.

Tissue engineering of ureteral grafts by seeding urothelial differentiated hADSCs onto biodegradable ureteral scaffolds

The study is aimed to evaluate the differentiation potential of human adipose-derived stem cells (hADSCs) into urothelial lineage, and to assess possibility of constructing ureteral grafts using the differentiated hADSCs and a novel polylactic acid (PLA)/collagen scaffolds. HADSCs were indirectly cocultured with urothelial cells in a transwell coculture system for urothelial differentiation. After 14 days coculturing, differentiation was evaluated by detecting urothelial lineage markers (cytokeratin-18 and uroplakin 2) in mRNA and protein level. Then the differentiated hADSCs were seeded onto PLA/collagen ureteral scaffolds and cultured in vitro for 1 week. The biocompatibility of the scaffolds was tested by scanning electron microscopy (SEM) and MTT analysis. At last, the cell/scafflod grafts were subcutaneously implanted into 4-week-old female athymic mice for 14 days. The results demonstrated that the hADSCs could be efficiently induced into urothelial lineage by indirect coculture. The differentiated cells seeded onto the PLA/collagen ureteral scaffolds survived up to 7 days and maintained proliferation in vitro, which indicated that the scaffolds displayed good biocompatibility. In vivo study showed that the differentiated cells in the grafts survived, formed multiple layers on the scaffolds and expressed urothelial lineage markers. In conclusion, hADSCs may serve as an alternative cell resource in cell-based tissue engineering for ureteral reconstruction. These cells could be employed to construct a model of ureteral engineering grafts and be effectively applied in vivo, which could be a new strategy on ureteral replacement with applicable potential in clinical research.

Autologous urothelial cells transplantation onto a prefabricated capsular stent for tissue engineered ureteral reconstruction

In this study, we have fabricated an artificial ureter by transplantation of in vitro-expanded urothelial cells onto an in vivo-prefabricated capsular stent using tissue engineering methods. Spiral poly (L-lactic acid) (PLLA) stents were transplanted into the subcutaneous of Wistar rats for a period of 1, 2 or 3 weeks to induce the formation of connective tissue capsules on their surfaces. The capsular PLLA stents were then decellularized and further recellularized with bladder epithelial cells to fabricate artificial ureters. The results showed that the entrapped cells in all capsules remained continuously proliferation and lined up in continuous layers. In addition, the urothelial cells on the capsular stents with an embedding period of 2 or 3 weeks showed higher proliferative viability compared with the cells on the stents with an embedding time of 1 week (P < 0.05). The results of the study indicated that the prefabricated capsular stents could serve as alternative cell carriers for tissue engineered ureters, especially with embedding time from 2 to 3 weeks.

New ureteral scaffold constructed with composite poly(L-lactic acid)-collagen and urothelial cells by new centrifugal seeding system

A tissue-engineered ureteral scaffold was constructed with composited poly L-lactic acid (PLLA)-collagen endoluminal stent and uroepithelial cells (UECs) using a new seeding system. The electrospun PLLA-collagen nanofibrous mesh was seeded efficiently with human ureteral epithelial cells using a modified centrifugal seeding device. The cellular nanofibrous mesh was then wound around a spiral endoluminal stent to form a cellular composited PLLA-collagen ureteral scaffold. The cellular ureteral scaffold was subcutaneously implanted into nude mice. Cell attachment, distribution, and viability in vitro were investigated along with the cell fate in vivo. (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay showed that scaffolds seeded with centrifugal method had higher cellular activity than scaffolds seeded with static method (p < 0.05), and the metabolic activity per cell had no significant differences between the two methods (p > 0.05). Histologic analysis showed that the entrapped UECs remained in the scaffolds after 2 wk of implantation. The results of the study indicated that the composited PLLA-collagen endoluminal stent could serve as alternative cell carrier for tissue engineering ureter. In addition, the new modified centrifugal seeding system allowed rapid homogeneous distribution of cells onto the nanofibrous mesh, which will be useful to ureteral reconstruction.

Transdifferentiation of human adipose-derived stem cells into urothelial cells: potential for urinary tract tissue engineering

Autologous urothelial cells (UCs) provide a cell source for urinary tissue engineering because they can be used safely due to their lack of immunogenicity. However, these cells cannot be harvested under the following circumstances: malignancy, infection and organ loss, etc. Human adipose-derived stem cells (HADSCs) possess the traits of high differentiation potential and ease of isolation, representing a promising resource for tissue engineering and regenerative medicine. Nevertheless, HADSCs have been poorly investigated in urology and the optimal approaches to induce HADSCs into urothelium are still under investigation. In this study, we hypothesized that the change of microenvironment by a conditioned medium was essential for the transdifferentiation of HADSCs into UCs. We then used a conditioned medium derived from urothelium to alternate the microenvironment of HADSCs. After 14 days of culture in a conditioned medium, about 25-50% HADSCs changed their morphology into polygonal epithelium-like shapes. In addition, these cells expressed up-regulating of urothelial lineage-specific markers (uroplakin 2and cytokeratin-18) and down-regulating of mesenchymal marker (vimentin) in RNA and protein level, respectively, which confirmed that HADSCs were induced into urothelial lineage cells. We also measured the growth factors in the conditioned medium in order to analyze the molecular mechanisms regulating transdifferentiation. We observed that the expression levels of PDGF-BB and VEGF were significantly higher than those of the control group after 14 days induction, suggesting they were abundantly secreted into the medium during the culturing period. In conclusion, HADSCs showed in vitro the upregulation of markers for differentiation towards urothelial cells by culturing in an urothelial-conditioned medium, which provides an alternative cell source for potential use in urinary tract tissue engineering.

Ureteral stents: new ideas, new designs

Ureteral stents represent a minimally invasive alternative to preserve urinary drainage whenever ureteral patency is deteriorated or is under a significant risk to be occluded due to extrinsic or intrinsic etiologies. The ideal stent that would combine perfect long-term efficacy with no stent-related morbidity is still lacking and stent usage is associated with several adverse effects that limit its value as a tool for long-term urinary drainage. Several new ideas on stent design, composition material and stent coating currently under evaluation, foreseen to eliminate the aforementioned drawbacks of ureteral stent usage. In this article we review the currently applied novel ideas and new designs of ureteral stents. Moreover, we evaluate potential future prospects of ureteral stent development adopted mostly by the pioneering cardiovascular stent industry, focusing, however, on the differences between ureteral and endothelial tissue.

Production of an optimized tissue-engineered pig connective tissue for the reconstruction of the urinary tract

Nonurological autologous tissues are used for urethral reconstruction to correct urinary tract disorders but are still leading to complications. Other substitutes have been studied on small animal models without great success. For preclinical tests, we selected the porcine model for its similarity to the human urinary tract. Up to now, porcine skin fibroblasts were not able to synthesize enough extracellular matrix under standard conditions to sustain the formation of an adequate tissue for transplantation purposes. Therefore, our goal was to optimize the harvesting site and culture conditions to obtain a thick and easy to handle porcine fibroblast tissue. The oral mucosa was found to be the ideal harvesting site, and a culture temperature of 39°C enabled the formation of a good porcine fibroblast sheet. We successfully superimpose three fibroblast sheets that merged into a thick and resistant tissue where physiological extracellular matrix was produced. Mechanical resistance evaluation by uniaxial traction on the three-layer fibroblast constructs also demonstrated its suitable properties. The production of this porcine connective tissue offers an interesting option in the field of urological tissue engineering. Autologous experiments on a larger animal model are now possible and accessible, allowing the performance of long-term in vivo studies.

Introduction to biodegradable polylactic acid ureteral stent application for treatment of ureteral war injury

OBJECTIVE

• To study the operability and effectiveness of a biodegradable ureteral stent for clinical treatment of ureteral war injury using a canine model.

MATERIALS AND METHODS

• A device was designed and employed to generate firearm fragment wounds in unilateral ureters (on randomly chosen sides) of nine beagles (Group A). The wounded ureters were then debrided and sutured. • Intravenous pyelography (IVP) and radioactive renography were performed 40, 80 and 120 days postoperatively. In Group B, firearm fragment wounds were made to the bilateral ureters in nine beagles. A polylactic acid stent was placed unilaterally (on a randomly chosen side) whereas the ureter on the other side was debrided and sutured without stenting. • Both IVP and radioactive renography were performed 40, 80 and 120 days postoperatively. The operability and effectiveness of the biodegradable ureteral stent were studied thereafter.

RESULTS

• In Group A, hydronephrosis and hydroureter occurred and worsened postoperatively on the wounded sides in all nine beagles. The ratio of the renal partial concentration indices (RPCI) between the kidneys (unwounded side : wounded side) increased. • The ratio of the kidney washout half-time between the kidneys (unwounded side : wounded side) decreased. In Group B, neither hydronephrosis nor hydroureter was found postoperatively in the stented ureters but both occurred in the unstented ureters in all nine beagles. • The ratio of RPCI between kidneys (stented side : unstented side) increased whereas the kidney washout half-time ratio between the stented and unstented sides decreased. Differences were significant.

CONCLUSION

• In Group A, the new canine model for firearm fragment wounds was tested and proved to be operable and effective. In Group B, hydronephrosis and hydroureter were effectively prevented in ureters by biodegradable stent placement compared with the non-stented ureters where hydronephrosis and hydroureter occurred. The renal concentration capacity was effectively protected and the half-time of kidney washout was shortened.

Human urine-derived stem cells seeded in a modified 3D porous small intestinal submucosa scaffold for urethral tissue engineering

The goal of this study was to determine whether urothelial cells (UC) and smooth muscle cells (SMC) derived from the differentiation of urine-derived stem cells (USC) could be used to form engineered urethral tissue when seeded on a modified 3-D porous small intestinal submucosa (SIS) scaffold. Cells were obtained from 12 voided urine samples from 4 healthy individuals. USC were isolated, characterized and induced to differentiate into UC and SMC. Fresh SIS derived from pigs was decellularized with 5% peracetic acid (PAA). Differentiated UC and SMC derived from USC were seeded onto SIS scaffolds with highly porous microstructure in a layered co-culture fashion and cultured under dynamic conditions for one week. The seeded cells formed multiple uniform layers on the SIS and penetrated deeper into the porous matrix during dynamic culture. USC that were induced to differentiate also expressed UC markers (Uroplakin-III and AE1/AE3) or SMC markers (α-SM actin, desmin, and myosin) after implantation into athymic mice for one month, and the resulting tissues were similar to those formed when UC and SMC derived from native ureter were used. In conclusion, UC and SMC derived from USC could be maintained on 3-D porous SIS scaffold. The dynamic culture system promoted 3-D cell-matrix ingrowth and development of a multilayer mucosal structure similar to that of native urinary tract tissue. USC may serve as an alternative cell source in cell-based tissue engineering for urethral reconstruction or other urological tissue repair.