File Name: biomaterials and tissue engineering in urology .zip
- Bioengineered Tissues for Urogenital Repair in Children
- Tissue Engineering of Urinary Bladder and Urethra: Advances from Bench to Patients
- Clinical Regenerative Medicine in Urology
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Bioengineered Tissues for Urogenital Repair in Children
Tissue engineering is defined as the combination of biomaterials and bioengineering principles together with cell transplantation or directed growth of host cells to develop a biological replacement tissue or organ that can be a substitute for normal tissue both in structure and function.
Despite early promising preclinical studies, clinical translation of tissue engineering in pediatric urology into humans has been unsuccessful both for cell-seeded and acellular scaffolds.
This can be ascribed to various factors, including the use of only non-diseased models that inaccurately describe the structural and functional modifications of diseased tissue. The paper addresses potential future strategies to overcome the limitations experienced in clinical applications so far.
The development of smart scaffolds that release trophic factors in a set and timely manner will probably improve regeneration. Modulation of innate immune response as a major contributor to tissue regeneration outcome is also addressed. It is unlikely that only one of these strategies alone will lead to clinically applicable tissue engineering strategies in pediatric urology.
In the meanwhile, the fundamental new insights into regenerative processes already obtained in the attempts of tissue engineering of the lower urogenital tract remain our greatest gain.
Tissue engineering is defined as the combination of biomaterials and bioengineering principles with cell transplantation or directed growth of host cells to develop a biological replacement tissue or organ that can be a substitute for normal tissue both in structure and function [ 1 ], [ 2 ].
The lack of available autologous tissue, either from loss through injury or disease or from congenital absence, has driven the search for new ways to regenerate tissue. This is especially true in pediatric urology, where either malformations such as posterior urethral valves and bladder exstrophy or urologic comorbidities in patients with spina bifida come with devastating long-term sequelae, in particular renal function loss due to elevated bladder and voiding pressure because of low bladder compliance.
Bladder replacement with enterocystoplasty has been a major advancement in this respect, and is considered the gold standard in low-compliance bladders. It allows protecting the upper urinary tract and achieves social continence in most patients [ 3 ], but is associated with complications such as urinary tract infections UTIs , stone formation, electrolyte imbalances, mucus production, and eventually malignant transformation [ 4 ], [ 5 ], [ 6 ].
Congenital and acquired urethral diseases like hypospadias or epispadias, as well as strictures and fistulas, represent a major challenge both in adult and pediatric urology; patients often need multiple surgeries, and urethral replacement in these cases can be difficult because of limited autologous tissue.
Theoretically, the prospect of tissue engineering therefore yields a promise unmatched by conventional surgical means; however, as we will aim to show in this review, the discrepancy of early pretensions and the clinical results so far have been far from satisfying. As of yet, there is no objective evidence that tissue engineering approaches in urology can achieve equal or superior outcomes compared to traditional therapies [ 7 ], [ 8 ].
However, these failures have led to new insights into mechanisms of regenerative processes, and this raises the hope that more sophisticated strategies will lead to new directions with better results. Tissue engineering in pediatric urology comprises both replacement strategies of the upper urogenital tract — i. As tissue engineering of the kidney is a very distinct topic by itself [ 9 ] and most lessons were learned in the pursuit of bladder replacement and urethral grafting, this review will therefore focus on tissue engineering aspects of the lower urogenital tract.
Tissue engineering requires the use of scaffolds and matrices on which to grow new tissue on. To render them useful, these scaffolds require certain biocompatibility properties: a scaffold should provide an ideal environment for cell migration, proliferation, and differentiation. It should not inhibit cell-cell interaction, while at the same time be able to fully degrade in a timely manner that leads neither to an accumulation of degradation products, which inhibit further regeneration, nor to a too early degradation while regeneration is still incomplete.
Also, an ideal matrix should be immunologically inert without unwanted inflammatory response or graft rejection [ 10 ]. A variety of biomaterials have been described for clinical applications. They can be divided into synthetic and naturally derived extracellular matrices. Synthetic scaffolds contain biodegradable polymers such as polyglycolic acid PGA , polylactide, poly glycolide-co-lactide [ 11 ], poly ethylene glycol [ 12 ], polycapronolactone, etc.
The group of naturally derived scaffolds basically comprises either matrices made from proteins such as collagen [ 13 ] or laminin [ 14 ], or matrices made of chemically or enzymatically decellularized tissues such as porcine small intestine submucosa SIS [ 15 ] or bladder acellular matrix [ 16 ], [ 17 ].
These scaffolds maintain features of their underlying organ or tissue, including an environment that can contain growth factors or a microstructure that facilitates cell-matrix interaction to allow for better cell migration and repopulation. Western blots and enzyme-linked immunosorbent assay procedures showed that SIS extracellular matrix ECM contains as much as 0. As many of the abovementioned constituents are highly conserved proteins, they may function as bioresponse modifiers or promote such responses also in humans.
One drawback of these scaffolds is that they are inextricably linked with a considerable intrinsic variation between grafts of the same source [ 23 ].
This has been studied extensively in porcine SIS. For example, SIS harvested from proximal intestine showed inferior regenerative properties when compared to SIS from distal intestine [ 24 ]. Additionally, age of the source animals may play a pivotal role. Several studies showed that SIS used from older animals showed less muscle regeneration [ 25 ], [ 26 ].
Moreover, the need for sterilization before use in preclinical or clinical studies raises the concern that this can alter or diminish the structural or functional properties in these naturally derived scaffolds [ 27 ], [ 28 ]. Several studies have also evaluated combination of biomaterials by creating bi-layered hybrid scaffolds with the aim of optimizing biomechanical properties or creating an optimized microenvironment for different cellular layers [ 29 ], [ 30 ].
A relatively new type of biomaterial made from silk stands in between these groups. On the one hand, it is derived from a natural source instead of being a synthetic product. On the other hand, it is highly reproducible and comes with little intrinsic variability, similar to synthetic biomaterials. These scaffolds consist of silk fibroin SF , which is one of the two components of natural silk.
Fibroin fibers form the structural core, while the other component sericin acts as the gum-like coating between the fibers. By removing the highly antigenic sericin, SF retains the structural qualities of silk while being largely immunologically inert [ 31 ]. SF contains excellent tensile and elasticity characteristics compared to other biomaterials. SF polymers can be processed in different ways, which allows the creation of numerous matrix configurations, such as three-dimensional porous forms, nanofibers, hydrogels, films, and tubes, depending on the application.
Additionally, SF contains tailorable degradation characteristics dependent on scaffold pore size and fibroin content [ 10 ]. SF, when compared to other naturally derived or synthetic scaffolds, has demonstrated less inflammatory responses and immunogenic activity [ 32 ].
Promising results have been demonstrated in a study of ventral onlay urethroplasty as well. Compared to SIS matrices, SF grafts did not produce relevant inflammatory response and supported wide urethral calibers without strictures 3 months after urethroplasty [ 35 ]. To overcome the limitations of acellular scaffolds and to facilitate faster regeneration, the application of matrices from either group seeded with cells in vitro before implantation has been studied [ 36 ].
The obvious primary source of cells are autologous donor cells that are expanded in vitro , and then combined with the scaffold and implanted into the specific body site, because autologous cells do not inherit the risk of rejection and associated complications [ 37 ], [ 38 ].
For bladder reconstruction, this is performed usually by combining cells of urothelial and bladder smooth muscle origin. To allow cells to survive and multiply on the scaffold, they need specific metabolic and nutritional conditions, which are achieved by in vitro bioreactors [ 39 ]. Interestingly, in a meta-analysis of animal studies, a cellular graft did not lead to advantageous results when compared to acellular grafts [ 40 ]. Other, more sophisticated cell sources, which have recently gained attention in tissue engineering scenarios, like mesenchymal stem cells, will be discussed in a later section of the paper.
Bladder reconstruction has been named one of the major surgical challenges both in adult and pediatric urology [ 41 ]. It is therefore not surprising that the first attempt to augment bladders goes back as far as , when Neuhoff used fascia as a free tissue graft in dogs [ 42 ].
In the s, a plastic mold with a distensible rubber bag was used to create a fibrotic cavity in which the ureters drained after cystectomy, mostly in carcinoma patients [ 43 ].
About 10 years later, a gelatin sponge was the first biodegradable scaffold for bladder replacement used clinically in tuberculosis patients [ 44 ].
A Japanese group in the s even experimented with thin resin-covered paper as bladder augment in tuberculous contracted bladder, creating fibrous pseudo-bladders [ 45 ]. Needless to say, these earliest trials in tissue-engineered bladder augmentation were prone to complications such as bladder shrinkage, and have rightfully faded into obscurity. Many other materials, both synthetic and organic such as pericardium, dura, and placenta , have since been used without promising results.
In the s, after initial reports of successful preclinical studies with acellular [ 46 ] and cell-seeded [ 47 ], [ 48 ] scaffolds, first studies of clinical translation were performed in patients with end-stage low-compliance bladders [ 49 ].
In the study by Atala et al. The cells were obtained by bladder biopsy and grown ex vivo onto the scaffold. The results of the study were regarded encouraging; however, detailed analysis shows that, overall, there was only a very moderate increase of compliance and absolute bladder capacity, translating into even less age-related bladder capacity. Three patients were operated on with an additional omentum wrap on the scaffold.
These patients showed the best results in the study, which might be attributed to better angiogenesis or, even simpler, increased tightness during regeneration, therefore leading to less leakage and inflammatory response. Consequently, a prospective phase II study with the same cell-seeded scaffold with autologous bladder smooth muscle and urothelial cells by Joseph et al.
No significant increase in functional parameters of the bladder were documented, and adverse events, like small-bowel obstruction or even bladder rupture, were reported in all patients during to month follow-ups. Similar experiences were noted in studies with acellular SIS grafts.
Initial preclinical reports showed encouraging results in healthy rabbits [ 51 ], dogs [ 52 ], [ 53 ], and pigs [ 41 ], [ 54 ]; however, translation into use in human patients showed disappointing outcomes. In one series of five bladder exstrophy patients presenting with poor bladder capacity and compliance after complete exstrophy repair and bladder augmentation using a SIS scaffold, bladder capacity and compliance failed to increase significantly while histology showed poor muscle components [ 55 ].
In a similar study from our department with six patients suffering from low-compliance bladder mainly because of bladder exstrophy and spina bifida, similar results were obtained.
After augmentation with SIS, bladder compliance and capacity failed to increase substantially in long-term outcome mean follow-up 24 months [ 56 ]. Bladder compliance postoperatively ranged from 0. Histological examinations showed a complete conversion of SIS, but irregular urothelial lining and bladder wall containing relatively thick connective tissue in four patients and regular urothelium in only two patients.
Furthermore, three patients experienced major complications: two experienced bladder stones and one a bladder rupture. Of note, Von Brunn cell nests, which are distinctive of pathologic bladder wall in exstrophy bladders [ 57 ], were noted in the augment — clear evidence that pathologic tissue regenerates differently and passes pathological features onto regenerative sites.
A third study by Zhang and Liao showed somewhat more promising results [ 58 ]. Bladder augmentation with a large SIS patch was performed in eight patients with neurogenic bladder six with meningomyelocele, two after spinal trauma.
They reported a significant increase in mean bladder capacity from However, it must be taken into account that the relatively short follow-up time prevented the authors from capturing any long-term bladder shrinkage. Additionally, only in three of the patients were bladder biopsies taken postoperatively, which showed incomplete urothelial lining and suboptimal bladder wall formation with little muscle and excessive connective tissue.
Most patients in these unsuccessful clinical studies suffered from spina bifida, and while it is clear that even full regeneration of the bladder cannot restore the full function in the bladder, especially voluntary voiding due to the primary condition, the failure to achieve a stable increase of storage capacity is disappointing and forbids further clinical use of these approaches.
The surgery of large urethral defects as in hypospadias or epispadias often requires substitute tissue such as foreskin [ 59 ] which is often missing, especially in repeat surgery or buccal mucosa [ 60 ] because of the lack of suitable on-site tissue.
To overcome this limitation, attempts to utilize acellular as well as cell-seeded matrices haven been performed. For acellular grafts, regeneration was shown to be unsuccessful for larger defects due to contraction and, therefore, stenosis of the neourethra. Epithelial ingrowth could only be noted in areas not exceeding 0. Several preclinical studies showed somewhat better results in the use of foreskin- or oral mucosa-sourced cell-seeded scaffolds [ 62 ], [ 63 ].
Fu et al. Six months after urethral replacement in contrast to unseeded grafts, persistent epithelium was noted in the cell-seeded group. Analogue results were obtained by the same group using keratinocytes from oral mucosa as a cell source [ 64 ]. Studies of a similar design using cells from oral punch biopsy and combining them with muscle-derived cells on a collagen matrix [ 63 ] or autologous corporal smooth muscle cells SMCs combined with lingual keratinocytes seeded on acellular porcine corpus spongiosum matrices [ 65 ] showed stable regeneration and patent urethras as well.
While these results are promising, two limitations must be taken into account. First, all these studies were performed in healthy animals and results are very limited in terms of follow-up — the longest follow-up was only 6 months. It is therefore not surprising that the limited data on early clinical translation has been disappointing as well.
Bhargava et al. Only one study by Raya-Rivera et al.
Tissue Engineering of Urinary Bladder and Urethra: Advances from Bench to Patients
Part 1 Fundamentals: Introduction to biofilms in urology: In vivo models for ureteral stents; Models for the assessment of biofilm and encrustation formation on urological materials. Part 2 Materials and design of urological devices: Ureteral stents: Design and materials; Metal stents in the upper urinary tract; Coated ureteral stents; Proteus mirabilis biofilm formation and catheter design; Self-lubricating catheter materials; Temporary urethral stents; Penile implants. Part 3 Urological tissue engineering: Artificial biomaterials for urological tissue engineering; Natural biomaterials for urological tissue engineering; Nanotechnology and urological tissue engineering; Assessing the performance of tissue-engineered urological implants; Regenerative pharmacology and bladder regeneration; Autologous cell sources for urological applications; Embryonic stem cells, nuclear transfer, and parthenogenesis-derived stem cells for urological reconstruction; Amniotic fluid and placental stem cells as a source for urological regenerative medicine; The use of adipose progenitor cells in urology; Regenerative medicine of the urinary sphincter via an endoscopic approach; Regenerative medicine of the urinary sphincter via direct injection; Regenerative medicine for the urethra; Penile reconstruction; Tissue engineering in reproductive medicine; Regenerative medicine of the kidney; Stem cells and kidney regeneration; Techniques for engineering bladder tissue. Urology is the branch of medicine dealing with disorders or diseases of the male genitor-urinary tract and the female urinary tract. This important book summarises the wealth of recent research on the use of biomaterials and tissue engineering to treat urological disorders. Part one reviews the fundamentals with chapters on such topics as biofilms and encrustation formation. Part two then discusses recent advances in biomaterials and design of urological devices such as metal ureteral stents, self-lubricating catheter materials and penile implants.
Currently, tissue-engineered biomaterials are developing rapidly in regenerative urology with many important clinical milestones achieved.
Clinical Regenerative Medicine in Urology
Language: English French. Tissue engineering encompasses a multidisciplinary approach geared toward the development of biological substitutes designed to restore and maintain normal function in diseased or injured tissues. This article reviews the basic technology that is used to generate implantable tissue-engineered grafts in vitro that will exhibit characteristics in vivo consistent with the physiology and function of the equivalent healthy tissue. We also examine the current trends in tissue engineering designed to tailor scaffold construction, promote angiogenesis and identify an optimal seeded cell source. Finally, we describe several currently applied therapeutic modalities that use a tissue-engineered construct.
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.
Положение оказалось куда серьезнее, чем предполагала Сьюзан. Самое шокирующее обстоятельство заключалось в том, что Танкадо дал ситуации зайти слишком. Он должен был знать, что случится, если АНБ не получит кольцо, - и все же в последние секунды жизни отдал его кому-то. Он не хотел, чтобы оно попало в АНБ. Но чего еще можно было ждать от Танкадо - что он сохранит кольцо для них, будучи уверенным в том, что они-то его и убили. И все же Сьюзан не могла поверить, что Танкадо допустил бы. Ведь он был пацифистом и не стремился к разрушению.
Сразу же? - усомнилась Сьюзан. - Каким образом. Даже если Цифровая крепость станет общедоступной, большинство пользователей из соображений удобства будут продолжать пользоваться старыми программами. Зачем им переходить на Цифровую крепость. Стратмор улыбнулся: - Это. Мы организуем утечку секретной информации. И весь мир сразу же узнает о ТРАНСТЕКСТЕ.
- Вы его убили.
Вопрос насколько. уступил место другому - с какой целью?. У Хейла не было мотивов для вторжения в ее компьютер.