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In this eighth newsletter, I would like to share with you three very interesting recent papers. The first one is the result of an inspiring meeting of lithiasis experts that summarises the latest advances in this area of knowledge. This paper, sponsored by U-merge, covers all aspects of lithiasis and in the section on stents, discusses the latest advances related to these medical devices and future lines of research. 

Secondly, I would like to highlight a paper related to the treatment of ureteral strictures after kidney transplantation, which recurrence after endourological treatment and the proposal of this group is the use of metallic stents (Allium), with very encouraging results as a salvage therapy. This type of stents have a very innovative system for their removal, which makes them very attractive and with a very long stenting time.

Finally, I have selected a paper on the role of ureteral stent material and coating to prevent ureteral stent side effects. An interesting systematic review and meta-analysis, with a series of conclusions of huge clinical application and confirming previous scientific evidence that soft biomaterial stents are more suitable to improve patients' quality of life.

3'

I would like to start with a recently published paper in which I have participated, specifically in the section on stents (Urinary stents technology & bioresorbable stents). This paper is a consensus document among experts in stone disease. With respect to ureteral stents, as we have mentioned in previous newsletters, innovation is focusing on three fundamental pillars that seek to improve stents and reduce their adverse effects on patients. As is well known, these adverse effects can affect up to 80% of patients. The development of new biomaterials, new coatings and new designs are part of the different strategies we are working on for these improvements. 

The main focus is on developing coatings to inhibit the adhesion of biofilms, and that these are the matrix that favours asymptomatic bacteriuria, UTIs and stent encrustation. The most advanced developments in this area are related to antimicrobial peptides with bactericidal capacity. In this regard, it is important to emphasize, as we have been doing, that while waiting for progress to be made on new biomaterials and coatings, the other means we have to reduce encrustation is to modify the environment in which the stent is placed. In other words, we can modify the urinary pH and use crystallization inhibitors, which at urinary level complicate the precipitation of salts and the corresponding incrustation of the stent, with scientific evidence already published. This is currently a great alternative strategy while awaiting technological advances in biomaterials and coatings in this area of knowledge.

On the other hand, this paper also discusses the great advances in translational research, working both on the development of biodegradable stents and drug-eluting ureteral stents. With respect to the former, advances in recent years have managed to overcome the main weaknesses that referred to the control of the biomechanical properties of the stent throughout its progressive degradation; the control of the size of the fragments so as not to be obstructive at the ureteral level and good results have also been achieved in the control of the rate of degradation. This allows us to affirm that we are getting closer to its future clinical application.

Finally, in the paper we discuss the other line of research that represents a major innovation and that is the development of drug-eluting ureteral stents, mainly to inhibit the formation of ureteral strictures after endourological treatment. But also for cavitary instillation of chemotherapy in the adjuvant treatment of upper tract urothelial carcinoma. The aim is to take advantage of the scaffold function of the stent to make a local release of drugs that may be useful for adequate healing or for oncological control. As described in the manuscript, advances in the future of stents allow us to say that "the glass is half full and getting fuller"

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I would like to share with you a very recent paper that takes a different approach to the treatment of ureteral strictures related to renal transplantation. The use of metallic stents is infrequent in this field, as it is always considered as rescue or salvage for malignant strictures, with short life expectancy, although lately its use in benign strictures after failure of endourological treatment is proving to be very promising. The aim of the manuscript is to assess the safety and effectiveness of endoscopic treatments with Allium® metal ureteral stent for ureteral strictures after kidney transplantation (KT). As is well known, data from the 2018-Cochrane database, the incidence of strictures after KT is approximately 1.8%. The authors propose in patients in whom previous treatments have failed (JJ stent placement and/or balloon dilatation; previous unsuccessful vesico-ureteric reimplantation), the placement of an Allium stent with balloon dilatation prior to metallic stenting.

It is a prospective clinical study with 68 patients recruited, a stricture length of 2.0 cm and a final follow-up at 1 year after surgery. The results are surprising for this type of patient, with an overall success rate of 90%, a significant improvement in eGRF and a significant decrease in urea nitrogen. With only 10% stent migration, and 7.4% UTI among patients. Compared to previous series, which describe a success rate of 64.3% in this type of patients, the results are very favourable for this type of metallic stent. Therefore, this proposal of endurological salvage for patients with KT-related ureteral strictures who have already undergone previous treatments seems to be an “alternative solution”, also reducing the frequency of stent replacement. Only remember that Allium® stents have an easy and safe placement and removal which are retrieved by unraveling them into a thread-like strip, and they show a period of up to 3 years indwelling time.

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An interesting systematic review and meta-analysis that firstly evaluates the effect of the biomaterial used to fabricate double J ureteral stents in reducing side effects. As well as determining whether certain stent coatings play a role in decreasing ureteral stent-related problems, mainly associated with infection and encrustation.

The manuscript includes a total of 2249 patients. The main findings of this review revealed that “firm ureteral stents” significantly increased the risk of infection, haematuria and lower body pain. Softer DJ stents would lower the risk of UTI significantly; however, these results should be further investigated since it has high heterogeneity. Softer DJ stents also played a key role in reducing haematuria and the risk of lower urinary tract symptoms’. Unfortunately, soft DJ stents have not impact in reducing encrustation.

About coated ureteral stents, mainly Triclosan-eluted and silver nanoparticles with very antimicrobial properties, the results of the systematic review show that despite positive results in vitro, these do not transfer to patients. Triclosan it's not effective to reduce encrustation. Coated stents have not shown the ability to reduce the occurrence of UTI.

The conclusions of this interesting paper, which are applicable to patients, are that soft stents reduce ureteral stent-related symptoms such as haematuria and lower body pain. Coating materials, such as silver nanoparticles or triclosan, are not effective in reducing the risk of infection or encrustation.