Regulatory challenges for autologous tissue engineered products on their way from bench to bedside in Europe

Comparison of oral morbidity and mid-term efficacy of anterior urethroplasty using an autologous tissue-engineered graft (MukoCell®) versus native oral mucosa graft

OBJECTIVE

Our study aimed to compare surgical success rate (SR) and oral morbidity of augmentation urethroplasty for anterior urethral strictures using autologous tissue-engineered oral mucosa graft (TEOMG) named MukoCell® versus native oral mucosa graft (NOMG).

METHODS

We conducted a single-institution observational study on patients undergoing TEOMG and NOMG urethroplasty for anterior urethral strictures >2 cm in length from January 2016 to July 2020. SR, oral morbidity, and potential risk factors of recurrence were compared between groups were analyzed. A decrease of maximum uroflow rate < 15 mL/s or further instrumentation was considered a failure.

RESULTS

Overall, TEOMG (n = 77) and NOMG (n = 76) groups had comparable SR (68.8% vs. 78.9%, p = 0.155) after a median follow-up of 52 (interquartile range [IQR] 45-60) months for TEOMG and 53.5 (IQR 43-58) months for NOMG. Subgroup analysis revealed comparable SR according to surgical technique, stricture localization, and length. Only following repetitive urethral dilatations, TEOMG achieved lower SR (31.3% vs. 81.3%, p = 0.003). Surgical time was significantly shorter by TEOMG use (median 104 vs. 182 min, p < 0.001). Oral morbidity and the associated "burden" in patients' quality of life were significantly less at 3 weeks following the biopsy required for TEOMG manufacture, compared to NOMG harvesting and totally absent at 6 and 12 months postoperatively.

CONCLUSIONS

The SR of TEOMG urethroplasty appeared to be comparable to NOMG at a mid-term follow-up but taking into account the uneven distribution of stricture site and the surgical techniques used in both groups. Surgical time was significantly shortened, since no intraoperative mucosa harvesting was required, and oral complications were diminished through the preoperative biopsy for MukoCell® manufacture.

Tissue Engineering of the Urethra: From Bench to Bedside

Tissue engineering (TE) is a promising approach for repair/substitution of damaged tissues and organs. Urethral strictures are common and serious health conditions that impair quality of life and may lead to serious organ damage. The search for ideal materials for urethral repair has led to interest of scientists and surgeons in urethral TE. Over the last decades, a significant amount of preclinical studies and considerable progress have been observed. In contrast, urethral TE has made slow progress in clinical practice so far. To address this, we conducted a systematic review of the literature on clinical applications of TE constructs for urethral repair in the last three decades. In summary, the TE approach is promising and effective, but many issues remain that need to be addressed for broader adoption of TE in urethral repair. Better design of trials, better cooperation of research groups and centralization could lead to reduction of costs and slowly proceed to commercialization and routine use of TE products for urethral reconstruction.

A systematic review and meta-analysis of urethral complications and outcomes in transgender men

BACKGROUND

Urologic problems, such as urethral fistulas and strictures, are among the most frequent complications occurring after phalloplasty. Although many studies have reported successful phalloplasty and urethral reconstruction with reliable outcomes in transgender men, no method has become standardized so far. This study aimed to summarize the results of reports on urological complications and outcomes in transgender men with respect to various types of urethral reconstruction.

METHODS

A comprehensive literature search of PubMed, Scopus, and Google Scholar databases was conducted for studies related to phalloplasty in transsexuals. Data on various phallic urethral techniques, urethral complications, and outcomes were collected and analyzed using the random-effects model.

RESULTS

A total of 21 studies (1,566 patients) were included: eight studies (1,061 patients) on "tube-in-tube," nine studies (273 patients) on "prelaminated flap," and six studies (221 patients) on "second flap." Compared with the tube-in-tube technique, the prelaminated flap was associated with a significantly higher urethral stricture/stenosis rate; however, there was no difference between the prelaminated flap and the second flap techniques. For all phalloplasty patients, the pool rate of urethral fistula or stenosis is 48.9%, the rate of the ability to void while standing is 91.5%, occurrence rate of tactile or erogenous sensation is 88%, the prosthesis complication rate is 27.9%, and patient-reported satisfactory outcome rate is 90.5%.

CONCLUSION

Urethral reconstruction with a prelaminated flap was associated with a significantly higher urethral stricture rate and increased need of revision surgery compared with that observed using a skin flap. Overall, most patients were able to void while standing and were satisfied with the outcomes.

Tissue engineering: recent advances and review of clinical outcome for urethral strictures

PURPOSE OF REVIEW

Urethrotomy remains the first-line therapy in the treatment of a urethral stricture despite data showing no real chance of a cure after repeated urethrotomies. An anastomotic or an augmentation urethroplasty using oral mucosa can be offered to patients following failed urethrotomy. The potential for a tissue engineered solution as an alternative to native tissue has been explored in recent years and is reviewed in this article.

RECENT FINDINGS

More than 80 preclinical studies have investigated a tissue-engineered approach for urethral reconstruction mostly using decellularized natural scaffolds derived from natural extracellular matrix with or without cell seeding. The animal models used in preclinical testing are not representative of disease processes seen with strictures in man. The available clinical studies are based on small noncontrolled series.

SUMMARY

There is a potential role for tissue engineering to provide a material for substitution urethroplasty and work has demonstrated this. Further work will require a rigorous basic science programme and adequate evaluation of the material prior to its introduction into clinical practice. The research with tissue engineering applied to the urethra has not yet been resulted in a widely available material for clinical use that approaches the efficacy seen with the use of autologous grafts.

Treatment of Urethral Stricture Disease in Women: Nonsystematic Review of Surgical Techniques and Intraoperative Considerations

Female urethral strictures are rare, but underdiagnosed pathologies that can cause voiding dysfunction. These strictures are best managed with open reconstruction, as endoscopic treatments have high rates of failure. A flap urethroplasty can be performed with vaginal, labial or bladder tissue. Meanwhile, graft urethroplasties can utilize vaginal, labial, buccal or lingual tissue. It is important to consider the etiology and type of stricture, local vascularity, and prior attempts at repair when selecting the type of repair. Multiple different techniques have been described with theoretical advantages to each one. While some studies have reviewed a few of the reconstructive techniques to treat female urethral strictures, no single study has accounted for each individual technique. In this review, we discuss techniques captured by a number of systematic reviews and other articles. We will herein focus on reviewing and describing each unique technique of reconstruction in the setting of female urethral stricture.

Safety and mid-term surgical results of anterior urethroplasty with the tissue-engineered oral mucosa graft MukoCell® : A single-center experience

OBJECTIVE

To assess the mid-term efficacy and safety of anterior urethroplasty using an autologous tissue-engineered oral mucosa graft (MukoCell^® ).

METHODS

The data of 77 patients with anterior urethral strictures undergoing treatment with MukoCell^® at a tertiary center from June 2016 to May 2019 were analyzed. Patients' characteristics, pre- and postoperative diagnostics, perioperative complications, and follow-up data were obtained. The overall stricture-free survival, outcomes of the different surgical techniques, stricture localizations, stricture length, early complications of the procedure and risk factors of recurrence were assessed.

RESULTS

The median follow-up period was 38 months (interquartile range 31-46). The overall recurrence-free rate of anterior urethroplasty using MukoCell^® was 68.8%, 24 patients (31.2%) developed a recurrence of the stricture. The stricture recurrences were observed at a median of 7 months (interquartile range 3-13) only in patients with at least one previous surgery or repeated dilatations in their medical history. No oral-urethral adverse events related to the use of MukoCell^® were observed, except for a urethrocutaneous fistula (1.3%) requiring reoperation.

CONCLUSIONS

Anterior one-stage urethroplasty using MukoCell^® showed in our hands a mid-term success rate of up to 68.8% without significant adverse events after a median follow-up period of 38 months. This procedure might be an alternative option for long-segment urethral reconstruction.

Regenerative Medicine of Epithelia: Lessons From the Past and Future Goals

This article explores examples of successful and unsuccessful regenerative medicine on human epithelia. To evaluate the applications of the first regenerated tissues, the analysis of the past successes and failures addresses some pending issues and lay the groundwork for developing new therapies. Research should still be encouraged to fill the gap between pathologies, clinical applications and what regenerative medicine can attain with current knowledge.

Mechanical, compositional and morphological characterisation of the human male urethra for the development of a biomimetic tissue engineered urethral scaffold

This study addresses a crucial gap in the literature by characterising the relationship between urethral tissue mechanics, composition and gross structure. We then utilise these data to develop a biomimetic urethral scaffold with physical properties that more accurately mimic the native tissue than existing gold standard scaffolds; small intestinal submucosa (SIS) and urinary bladder matrix (UBM). Nine human urethra samples were mechanically characterised using pressure-diameter and uniaxial extension testing. The composition and gross structure of the tissue was determined using immunohistological staining. A pressure stiffening response is observed during the application of intraluminal pressure. The elastic and viscous tissue responses to extension are free of regional or directional variance. The elastin and collagen content of the tissue correlates significantly with tissue mechanics. Building on these data, a biomimetic urethral scaffold was fabricated from collagen and elastin in a ratio that mimics the composition of the native tissue. The resultant scaffold is comprised of a dense inner layer and a porous outer layer that structurally mimic the submucosa and corpus spongiosum layers of the native tissue, respectively. The porous outer layer facilitated more uniform cell infiltration relative to SIS and UBM when implanted subcutaneously (p < 0.05). The mechanical properties of the biomimetic scaffold better mimic the native tissue compared to SIS and UBM. The tissue characterisation data presented herein paves the way for the development of biomimetic urethral grafts, and the novel scaffold we develop demonstrates positive findings that warrant further in vivo evaluation.

Hypoxia-preconditioned adipose-derived stem cells combined with scaffold promote urethral reconstruction by upregulation of angiogenesis and glycolysis

Rationale

Tissue engineering is a promising alternative for urethral reconstruction, and adipose-derived stem cells (ADSCs) are widely used as seeding cells. Hypoxia preconditioning can significantly enhance the therapeutic effects of ADSCs. The low oxygen tension of postoperative wound healing is inevitable and may facilitate the nutritional function of ADSCs. This study aimed to investigate if hypoxia-preconditioned ADSCs, compared to normoxia-preconditioned ADSCs, combined with scaffold could better promote urethral reconstruction and exploring the underlying mechanism.

Methods

In vitro, paracrine cytokines and secretomes that were secreted by hypoxia- or normoxia-preconditioned ADSCs were added to cultures of human umbilical vein endothelial cells (HUVECs) to measure their functions. In vivo, hypoxia- or normoxia-preconditioned ADSCs were seeded on a porous nanofibrous scaffold for urethral repair on a defect model in rabbits.

Results

The in vitro results showed that hypoxia could enhance the secretion of VEGFA by ADSCs, and hypoxia-preconditioned ADSCs could enhance the viability, proliferation, migration, angiogenesis, and glycolysis of HUVECs (p < 0.05). After silencing VEGFA, angiogenesis and glycolysis were significantly inhibited (p < 0.05). The in vivo results showed that compared to normoxia-preconditioned ADSCs, hypoxia-preconditioned ADSCs combined with scaffolds led to a larger urethral lumen diameter, preserved urethral morphology, and enhanced angiogenesis (p < 0.05).

Conclusions

Hypoxia preconditioning of ADSCs combined with scaffold could better promote urethral reconstruction by upregulating angiogenesis and glycolysis. Hypoxia-preconditioned ADSCs combined with novel scaffold may provide a promising alternative treatment for urethral reconstruction.

Challenges for Cell-Based Medicinal Products From a Pharmaceutical Product Perspective

Advanced therapy medicinal products (ATMPs), such as somatic cell-therapy medicinal products or tissue-engineered products for human use, offer new and potentially curative opportunities to treat yet untreatable diseases or disorders. For cell-therapy medicinal products (CBMPs), multiple stability and quality challenges exist and relate to the cellular composition and unstable nature of these parenteral preparations. It is the aim of this review to discuss open questions and problems associated with the development, manufacturing and testing of CBMPs from a pharmaceutical drug product perspective. This includes safety, storage and handling, particulates, the choice of container closure systems and integrity. Analytical methods commonly used to evaluate the quality of the final CBMP to ensure patient's safety will be discussed. Particulate contamination in final products deserve special attention since CBMPs cannot be sterile filtered. Visible and sub-visible particles may represent environmental contaminations or may form during storage. They may be introduced from processing materials such as single use product contact materials, ancillary materials, or any components such as primary packaging used for the final product. Currently available analytical methods for detecting particulates may not be easily applicable to CBMPs due to their inherent particulate nature and appearance.

Full-thickness tissue engineered oral mucosa for genitourinary reconstruction: A comparison of different collagen-based biodegradable membranes

Tissue engineering is a method of growing importance regarding clinical application in the genitourinary region. One of the key factors in successfully development of an artificially tissue engineered mucosa equivalent (TEOM) is the optimal choice of the scaffold. Collagen scaffolds are regarded as gold standard in dermal tissue reconstruction. Four distinct collagen scaffolds were evaluated for the ability to support the development of an organotypical tissue architecture. TEOMs were established by seeding cocultures of primary oral epithelial cells and fibroblasts on four distinct collagen membranes. Cell viability was assessed by MTT-assay. The 3D architecture and functionality of the tissue engineered oral mucosa equivalents were evaluated by confocal laser-scanning microscopy and immunostaining. Cell viability was reduced on the TissuFoil E® membrane. A multi-stratified epithelial layer was established on all four materials, however the TEOMs on the Bio-Gide® scaffold showed the best fibroblast differentiation, secretion of tenascin and fibroblast migration into the membrane. The TEOMs generated on Bio-Gide® scaffold exhibited the optimal cellular organization into a cellular 3D network. Thus, the Bio-Gide® scaffold is a suitable matrix for engineering of mucosa substitutes in vitro.

Patient-reported outcomes for typical single cheek harvesting vs atypical lingual, labial or bilateral cheeks harvesting: a single-center analysis of more than 800 patients

PURPOSE

The optimal harvesting site for oral grafting in patients with urethral strictures remain controversial, with no study investigating morbidity on large scale. We aimed to compare typical single cheek harvesting vs atypical lingual, labial or bilateral cheeks harvesting in terms of complications and patient-reported outcomes.

METHODS

Within 827 patients treated at our referral center with oral graft urethroplasty, we compared typical vs atypical harvesting techniques. A self-administered, semiquantitative, non-validated questionnaire assessed early (10 days) and late (4 months) postoperative complications and patient-reported outcomes. A semiquantitative score was calculated according to patient responses, and it was used to assess early (6 questions) and late (13 questions) patient dissatisfaction status. Patients were defined early and/or late dissatisfied when they scored ≥ 7 and ≥ 10 at the early or late questionnaires, respectively.

RESULTS

Between 1998 and 2019, our patients predominantly received typical single cheek harvesting (89% vs 11%), with + 1.5% increase rate per year (p < 0.001). Early and late dissatisfied patients were, respectively, 170 (23%) vs 39 (44%) and 59 (8%) vs 16 (18%) in the typical vs atypical groups. Atypical harvesting was associated with higher rates of early (Odds ratio [OR]: 2.34; 95% Confidence interval [CI] 1.44-3.75; p = 0.001) and late (OR: 2.37; 95%CI 1.22-4.42; p = 0.008) postoperative dissatisfaction.

CONCLUSIONS

Typical single cheek harvesting was the preferred surgical option at our center and it was associated with negligible early and late rates of complications and patient's dissatisfaction. Conversely, atypical lingual, labial or bilateral cheeks harvesting was associated with higher complications and frequent patient dissatisfaction.

Current state of urethral tissue engineering

PURPOSE OF REVIEW

Urethrotomy remains the first-line therapy in the treatment of a urethral stricture despite data showing no real chance of a cure after repeated urethroplasties. An anastomotic or an augmentation urethroplasty with oral mucosa should be offered to patients with a failed urethrotomy. The availability of grafts can be a concern for both patients and surgeons. The potential for a tissue-engineered solution has been explored in recent years and is explored in this article.

RECENT FINDINGS

More than 80 preclinical studies have investigated a tissue-engineered approach for urethral reconstruction mostly using decellularized natural scaffolds with or without cell seeding. The animal models used in preclinical testing are not representative of disease processes seen with strictures in man. The available clinical studies were of small sample size and lacked control groups. The choice of biomaterial were mostly acellular matrices derived from natural extracellular matrix. The reported success rates in the pilot clinical studies were highly variable.

SUMMARY

The research with tissue engineering of the urethra has not yet been translated into a clinically available material. This is an area where much more research is needed and we would conclude that it is an area of unmet clinical need where users of tissue-engineered urethra in the future need to carry out a rigorous basic science programme and need to be cautious in drawing conclusions based on initial experience and report on long-term clinical results.

Urothelial or oral mucosa cells for tissue-engineered urethroplasty: A critical revision of the clinical outcome

OBJECTIVE

To report the clinical outcome of urethral reconstruction by cultured urothelial or oral mucosa cells for tissue-engineered urethroplasty.

METHODS

We systematically searched for studies reporting the use of tissue-engineered techniques for hypospadias and urethral stricture repair in humans in PubMed and Embase (OvidSP) through January, 1990 to June, 2018. We excluded studies based on titles that clearly were not related to the subject, studies in which tissue-engineered biomaterial were used only in laboratory or experimental animals, and in the absence of autologous cultured epithelial cells. Studies were also excluded if they were not published in English, had no disease background and adequate follow-up. Finally, we search all relevant abstract presented at two of the main urological meetings in the last 10 years: European Association of Urology (EAU) and American Urological Association (AUA).

RESULTS

A total of six articles, reporting the clinical use of tissue-engineered techniques in humans, were fully reviewed in our review. The epithelial cells were harvested from the urethra (10 patients), the bladder (11 patients) and the mouth (104 patients). The tissue-engineered grafts were used in children for primary hypospadias repair in 16 cases, and in adults for posterior and anterior urethral strictures repair in 109 cases. Tissue-engineered grafts were showed working better in children for primary hypospadias repair than in adults for urethral strictures repair.

CONCLUSION

One hundred and twenty-five patients received tissue-engineered urethroplasty using cultured epithelial cells for primary hypospadias or urethral strictures repair. The studies demonstrate a high degree of heterogeneity respect to epithelial cells (from urethra, bladder, and mouth), type of scaffold, etiology, site of urethral stricture, number of patients, follow-up and outcomes.

Preclinical study for treatment of hypospadias by advanced therapy medicinal products

PURPOSE

This paper explores the feasibility of a new therapy for the treatment of hypospadias patients. Hypospadias is a very common congenital malformation of male genitals, with very high rate of recurrences after surgery. The field of regenerative medicine, which offers innovative solutions for many pathologies, still does not offer reliable solution for this pathology. Here, we propose quality, safety, and clinical feasibility assessment for an oral mucosa advanced therapy medicinal product (ATMP) grown on a biocompatible scaffold for a clinical study on urethral reconstruction of hypospadias patients.

METHODS

Urethral and oral mucosal epithelia from donor biopsies were cultivated between two fibrin layers, under clinical-grade conditions for cell and tissue characterization and comparison, aimed at tissue engineering. In addition, single-clone analyses were performed to analyze gene expression profiles of the two epithelia by microarray technology.

RESULTS

Oral mucosa appeared suitable for urethral reconstruction. The resulting ATMP was proven to maintain stem cells and regenerative potency. The preclinical safety studies were performed on human tissues to assess abnormalities and tumorigenicity, and confirmed the safety of the ATMP. Finally, the patient selection and the clinical protocol for the upcoming clinical trial were defined.

CONCLUSIONS

Against this backdrop, in this paper, we are proposing a new reproducible and reliable ATMP for the treatment of hypospadias.

Tissue engineering of the urethra: where are we in 2019?

Purpose

The purpose of this review is to assess the potential role of tissue engineering for urethral reconstruction. It is well- recognised that urethrotomy remains the first-line therapy in the treatment of urethral stricture. Following on from the randomised study which recommended no difference between urethrotomy and urethral dilation, Steenkamp et al. reported long-term success rates of only 20%. Patients with longer strictures, penile or distal urethral strictures, and extensive periurethral spongiofibrosis typically do not respond well to repeated incisions. This report reviews the potential role of tissue engineering as applied to augmentation urethroplasty, which is the treatment of choice following failed urethrotomy.

Methods

A review of the literature was carried out. The principal emphasis was on tissue engineering as applied to augmentation urethroplasty, but an introductory section reviews the use of urethrotomy and the background to contemporary practise with augmentation urethroplasty using oral mucosa.

Results

It is evident that a cellular matrix which requires the ingrowth of cells is unlikely to be successful except for very short strictures. Other approaches such as injection of stem cells have not been adequately trialled in humans to date. Tissue-engineered substitute for autologous oral mucosa has been used and the results relating to this are reviewed.

Conclusions

Tissue engineering of autologous tissue for urethroplasty is expensive. It is unnecessary for the majority of cases, but could be potentially useful for very lengthy strictures, for instance, relating to lichen sclerosis. Whilst tissue-engineered oral mucosa has been successfully used, a great deal more work would be necessary to develop an appropriate matrix. Another study has looked at a larger series using an alternative tissue-engineered substitute, but the results have been very disappointing. At present, it has to be concluded that there is no effective and validated tissue engineering solution for the management of urethral stricture disease.

3D Bioprinting in Skeletal Muscle Tissue Engineering

Skeletal muscle tissue engineering (SMTE) aims at repairing defective skeletal muscles. Until now, numerous developments are made in SMTE; however, it is still challenging to recapitulate the complexity of muscles with current methods of fabrication. Here, after a brief description of the anatomy of skeletal muscle and a short state-of-the-art on developments made in SMTE with "conventional methods," the use of 3D bioprinting as a new tool for SMTE is in focus. The current bioprinting methods are discussed, and an overview of the bioink formulations and properties used in 3D bioprinting is provided. Finally, different advances made in SMTE by 3D bioprinting are highlighted, and future needs and a short perspective are provided.

Development of a visible light, cross-linked GelMA hydrogel containing decellularized human amniotic particles as a soft tissue replacement for oral mucosa repair

Early effective treatment of oral mucosal defects is the key to ensuring defect healing and functional recovery. The application of human amniotic membrane (HAM) in promoting wound healing has been shown to be safe and effective. However, amniotic membrane is thin, easy to tear and difficult to handle. Combined with the natural forces at play in the oral cavity, this has restricted the clinical applications of HAM for healing of mucosal defects. Methacrylated gelatin (GelMA) has good mechanical strength and adhesion, and can be used as a bionic repair film to attach to the damaged surface of oral mucosa, but GelMA lacks bioactive substances and cannot promote the rapid repair of oral mucosal defects. The aim of this study was to design a type of composite GelMA hydrogel mixed with decellularized human amniotic particles (dHAP) as an oral mucosa substitute, to promote regeneration of defective mucosa by stimulating rapid angiogenesis. The composite substitute GelMA–dHAP was easy to synthesize and store, and easy to operate for repair of oral mucosal defects. We show the angiogenic potential of GelMA–dHAP on chick chorioallontoic membrane and the curative effect of GelMA–dHAP as a treatment in the rabbit oral mucosa defect model. In conclusion, this study confirms the effectiveness of GelMA–dHAP as an ideal soft tissue substitute for the repair of oral mucosal defects, overcoming the shortcomings of using HAM or GelMA alone.

Early effective treatment of oral mucosal defects is the key to ensuring defect healing and functional recovery.

Genetically engineered human muscle transplant enhances murine host neovascularization and myogenesis

Engineered tissues are a promising tool for addressing the growing need for tissues and organs in surgical reconstructions. Prevascularization of implanted tissues is expected to enhance survival prospects post transplantation and minimize deficiencies and/or hypoxia deeper in the tissue. Here, we fabricate a three-dimensional, prevascularized engineered muscle containing human myoblasts, genetically modified endothelial cells secreting angiopoietin 1 (ANGPT1) and genetically modified smooth muscle cells secreting vascular endothelial growth factor (VEGF). The genetically engineered human muscle shows enhanced host neovascularization and myogenesis following transplantation into a mouse host, compared to the non-secreting control. The vascular, genetically modified cells have been cleared for clinical trials and can be used to construct autologous vascularized tissues. Therefore, the described genetically engineered vascularized muscle has the potential to be fully translated to the clinical setting to overcome autologous tissue shortage and to accelerate host neovascularization and integration of engineered grafts following transplantation.

Luba Perry et al. report transplantation of engineered prevascularized human muscle into mice to repair an abdominal muscle defect. They show that genetically engineering smooth muscle cells to secrete VEGF and endothelial cells to secrete ANGPT1 significantly improves host neovascularization and myogenesis.

Fiber density of collagen grafts impacts rabbit urethral regeneration

There is a need for efficient and “off-the-shelf” grafts in urethral reconstructive surgery. Currently available surgical techniques require harvesting of grafts from autologous sites, with increased risk of surgical complications and added patient discomfort. Therefore, a cost-effective and cell-free graft with adequate regenerative potential has a great chance to be translated into clinical practice. Tubular cell-free collagen grafts were prepared by varying the collagen density and fiber distribution, thereby creating a polarized low fiber density collagen graft (LD-graft). A uniform, high fiber density collagen graft (HD-graft) was engineered as a control. These two grafts were implanted to bridge a 2 cm long iatrogenic urethral defect in a rabbit model. Histology revealed that rabbits implanted with the LD-graft had a better smooth muscle regeneration compared to the HD-graft. The overall functional outcome assessed by contrast voiding cystourethrography showed patency of the urethra in 90% for the LD-graft and in 66.6% for the HD-graft. Functional regeneration of the rabbit implanted with the LD-graft could further be demonstrated by successful mating, resulting in healthy offspring. In conclusion, cell-free low-density polarized collagen grafts show better urethral regeneration than high-density collagen grafts.

Anterior Urethroplasty Using a New Tissue Engineered Oral Mucosa Graft: Surgical Techniques and Outcomes

PURPOSE

We investigated whether tissue engineered material may be adopted using standard techniques for anterior urethroplasty.

MATERIALS AND METHODS

We performed a retrospective multicenter study in patients with recurrent strictures, excluding those with failed hypospadias, lichen sclerosus, traumatic and posterior strictures. A 0.5 cm² oral mucosa biopsy was taken from the patient cheek and sent to the laboratory to manufacture the graft. After 3 weeks the tissue engineered oral mucosal MukoCell® graft was sent to the hospital for urethroplasty. Four techniques were used, including ventral onlay, dorsal onlay, dorsal inlay and a combined technique. Cystourethrography was performed 1 month postoperatively. Patients underwent clinical evaluation, uroflowmetry and post-void residual urine measurement every 6 months. When the patient showed obstructive symptoms, defined as maximum urine flow less than 12 ml per second, the urethrography was repeated. Patients who underwent further treatment for recurrent stricture were classified as having treatment failure.

RESULTS

Of the 38 patients with a median age of 57 years who were included in study the strictures were penile in 3 (7.9%), bulbar in 29 (76.3%) and penobulbar in 6 (15.8%). Median stricture length was 5 cm and median followup was 55 months. Treatment succeeded in 32 of the 38 patients (84.2%) and failed in 15.8%. Success was achieved in 85.7% of ventral onlay, 83.3% of dorsal onlay, 80% of dorsal inlay and 100% of combined technique cases. No local or systemic adverse reactions due to the engineered material were noted.

CONCLUSIONS

Our findings show that a tissue engineered oral mucosa graft can be implanted using the same techniques suggested for anterior urethroplasty and native oral mucosa, and guaranteeing a similar success rate.

Results of Use of Tissue-Engineered Autologous Oral Mucosa Graft for Urethral Reconstruction: A Multicenter, Prospective, Observational Trial

BACKGROUND

Harvest of oral mucosa for urethroplasty due to urethral stricture is associated with donor-site-morbidity. We assessed functionality and safety of an authorized tissue-engineered oral mucosa graft (TEOMG) under routine practice in stricture recurrences of any etiology, location, length and severity (real-world data).

METHODS

99 patients from eight centers with heterogenous urethroplasty experience levels were included in this prospective, non-interventional observational study. Primary and secondary outcomes were success rate (SR) and safety at 12 and 24months.

FINDINGS

All but one patient had ≥1, 77.1% (64 of 83)≥2 and 31.3% (26 of 83)≥4 previous surgical treatments. Pre- and postoperative mean±SD peak flow rate (Qmax) were 8.3±4.7mL/s (n=57) and 25.4±14.7mL/s (n=51). SR was 67.3% (95% CI 57.6-77.0) at 12 and 58.2% (95% CI 47.7-68.7) at 24months (conservative Kaplan Meier assessment). SR ranged between 85.7% and 0% in case of high and low surgical experience. Simple proportions of 12-month and 24-month SR for evaluable patients in all centers were 70.8% (46 of 65) and 76.9% (30 of 39). Except for one patient, no oral adverse event was reported.

INTERPRETATIONS

TEOMG is safe and efficient in urethroplasty.

Tissue engineered extracellular matrices (ECMs) in urology: Evolution and future directions

Autologous gastrointestinal tissue has remained the gold-standard reconstructive biomaterial in urology for >100 years. Mucus-secreting epithelium is associated with lifelong metabolic and neuromechanical complications when implanted into the urinary tract. Therefore, the availability of biocompatible tissue-engineered biomaterials such as extracellular matrix (ECM) scaffolds may provide an attractive alternative for urologists. ECMs are decellularised, biodegradable membranes that have shown promise for repairing defective urinary tract segments in vitro and in vivo by inducing a host-derived tissue remodelling response after implantation. In urology, porcine small intestinal submucosa (SIS) and porcine urinary bladder matrix (UBM) are commonly selected as ECMs for tissue regeneration. Both ECMs support ingrowth of native tissue and differentiation of multi-layered urothelial and smooth muscle cells layers while providing mechanical support in vivo. In their native acellular state, ECM scaffolds can repair small urinary tract defects. Larger urinary tract segments can be repaired when ECMs are manipulated by seeding them with various cell types prior to in vivo implantation. In the present review, we evaluate and summarise the clinical potential of tissue engineered ECMs in reconstructive urology with emphasis on their long-term outcomes in urological clinical trials.

Translational Challenges in Cardiovascular Tissue Engineering

Valvular heart disease and congenital heart defects represent a major cause of death around the globe. Although current therapy strategies have rapidly evolved over the decades and are nowadays safe, effective, and applicable to many affected patients, the currently used artificial prostheses are still suboptimal. They do not promote regeneration, physiological remodeling, or growth (particularly important aspects for children) as their native counterparts. This results in the continuous degeneration and subsequent failure of these prostheses which is often associated with an increased morbidity and mortality as well as the need for multiple re-interventions. To overcome this problem, the concept of tissue engineering (TE) has been repeatedly suggested as a potential technology to enable native-like cardiovascular replacements with regenerative and growth capacities, suitable for young adults and children. However, despite promising data from pre-clinical and first clinical pilot trials, the translation and clinical relevance of such TE technologies is still very limited. The reasons that currently limit broad clinical adoption are multifaceted and comprise of scientific, clinical, logistical, technical, and regulatory challenges which need to be overcome. The aim of this review is to provide an overview about the translational problems and challenges in current TE approaches. It further suggests directions and potential solutions on how these issues may be efficiently addressed in the future to accelerate clinical translation. In addition, a particular focus is put on the current regulatory guidelines and the associated challenges for these promising TE technologies.

[Tissue engineering: a multidisciplinary approach]

The prostheses have been around for thousands of years. Initially, it was substitute materials to replace members (leg, foot, hand) or for surgery (suture). The materials used have evolved, but they had never been created for medical applications. Recently, other strategies have emerged to construct or repair tissues. They are based on the use of biological components such as proteins or cells and provide a biological dimension to the term "biomaterial" and they often involve engineering. We illustrate the tissue engineering approaches using the examples of muscle and vessel regeneration strategies in the frame of restorative medicine.

Mediating bone regeneration by means of drug eluting implants: From passive to smart strategies

In addition to excellent biocompatibility and mechanical performance, the new generation of bone and craniofacial implants are expected to proactively contribute to the regeneration process and dynamically interact with the host tissue. To this end, integration and sustained delivery of therapeutic agents has become a rapidly expanding area. The incorporated active molecules can offer supplementary features including promoting oteoconduction and angiogenesis, impeding bacterial infection and modulating host body reaction. Major limitations of the current practices consist of low drug stability overtime, poor control of release profile and kinetics as well as complexity of finding clinically appropriate drug dosage. In consideration of the multifaceted cascade of bone regeneration process, this research is moving towards dual/multiple drug delivery, where precise control on simultaneous or sequential delivery, considering the possible synergetic interaction of the incorporated bioactive factors is of utmost importance. Herein, recent advancements in fabrication of synthetic load bearing implants equipped with various drug delivery systems are reviewed. Smart drug delivery solutions, newly developed to provide higher tempo-spatial control on the delivery of the pharmaceutical agents for targeted and stimuli responsive delivery are highlighted. The future trend of implants with bone drug delivery mechanisms and the most common challenges hindering commercialization and the bench to bedside progress of the developed technologies are covered.

Transforming healthcare through regenerative medicine

Regenerative medicine therapies, underpinned by the core principles of rejuvenation, regeneration and replacement, are shifting the paradigm in healthcare from symptomatic treatment in the 20th century to curative treatment in the 21st century. By addressing the reasons behind the rapid expansion of regenerative medicine research and presenting an overview of current clinical trials, we explore the potential of regenerative medicine to reshape modern healthcare.

Delivering Nucleic-Acid Based Nanomedicines on Biomaterial Scaffolds for Orthopedic Tissue Repair: Challenges, Progress and Future Perspectives

As well as acting to fill defects and allow for cell infiltration and proliferation in regenerative medicine, biomaterial scaffolds can also act as carriers for therapeutics, further enhancing their efficacy. Drug and protein delivery on scaffolds have shown potential, however, supraphysiological quantities of therapeutic are often released at the defect site, causing off-target side effects and cytotoxicity. Gene therapy involves the introduction of foreign genes into a cell in order to exert an effect; either replacing a missing gene or modulating expression of a protein. State of the art gene therapy also encompasses manipulation of the transcriptome by harnessing RNA interference (RNAi) therapy. The delivery of nucleic acid nanomedicines on biomaterial scaffolds - gene-activated scaffolds -has shown potential for use in a variety of tissue engineering applications, but as of yet, have not reached clinical use. The current state of the art in terms of biomaterial scaffolds and delivery vector materials for gene therapy is reviewed, and the limitations of current procedures discussed. Future directions in the clinical translation of gene-activated scaffolds are also considered, with a particular focus on bone and cartilage tissue regeneration.

History and evolution of the use of oral mucosa for urethral reconstruction

We report here the history and evolution of the use of oral mucosa in reconstructive urethral surgery since it was first used for urethroplasty in 1894. Since that time, many authors have contributed to develop, improve and popularize the use of oral mucosa as a substitute material. Paediatric urologists should be considered pioneers on the use of oral mucosa as they used it to repair primary and failed hypospadias. The use of oral mucosa to repair penile and bulbar urethral strictures was described, for the first time, in 1993. Important evolutions in the technique for harvesting oral mucosa from the cheek were reported in 1996. Today, oral mucosa is considered the gold standard material for any type of anterior urethroplasty in a one- or two-stage repair due to its biological and structural characteristics that make it a highly versatile that is adaptable to any environment required by the reconstructive urethral surgery. As the future approaches, tissue engineering techniques will provide patients with new materials originating from the oral epithelial mucosal cells, which are cultured and expanded into a scaffold. However, the path to reach this ambitious objective is still long and many difficulties must be overcome along the way.

Clinical Experience with Urethral Reconstruction Using Tissue-engineered Oral Mucosa: A Quiet Revolution

Finalising the use of tissue-engineered materials for urethral reconstruction still represents a difficult challenge. We must not deceive patients into thinking that this "quiet revolution" in urethral reconstruction will be available soon for all urethral conditions (congenital or acquired, simple vs complex) requiring surgery. This research and its clinical application require a prospective, multicentre, randomised, double-blind, and placebo-controlled/comparative phase 3 study for a large series of patients, and we are still far from this step.