Biodegradable Urethral Stents
Tammela TL, Talja M.
BJU Int. 2003;92:843–850.
Over the past decade, the development and deployment of a biodegradable urethral stent has gradually gained academic acceptance. The polymers of hydroxyl acids have good biocompatibility properties, and it is possible to make stents with different expansion rates and degradation times. For certain urologic conditions, there is an intrinsic advantage to the use of a bioabsorption device, because it eliminates the need for a second operation for stent removal. In this article, Tammela and Talja review the current state of biodegradable urethral stents and consider future possibilities.
Intraprostatic placement of spiral stents has been confirmed to prevent urinary retention due to edema in the prostate after minimally invasive therapy for benign prostatic hyperplasia (BPH). Biodegradable urethral stents also allow voiding in men with acute retention due to BPH while the size of the prostate is being reduced by 5-α-reductase inhibitor therapy.
In the prostatic urethra, the stents are not covered by the epithelium and are not bioabsorbed but rather biodegraded into fragments that are washed out with urine. However, in strictures of the anterior urethra, biodegradable stents, when inserted immediately after optical urethrotomy, are mostly covered by epithelium. These stents are bioabsorbed (except in cases in which the stent suddenly collapses at the time of the bioabsorption and the fragments of the stent perforate through the mucosa into the lumen, where they may partly obstruct the urethral lumen).
Although the results of the use of bioabsorbable spiral stents for the treatment of recurrent stricture are encouraging, there are still too many failures. An important reason for this appears to be the excessive urethral scarring and periurethral fibrosis present in patients with chronic recurrent urethral strictures. A bioabsorbable spiral stent cannot prevent the scar from shrinking. It is possible that better patient selection may improve results.
Although the biodegradable stent offers a new and convenient option to avoid an indwelling catheter in procedures that cause edema and postoperative urinary retention, costs may be a limiting factor. In addition, irritative symptoms are common to all patients with permanent or temporary urethral stents.
To minimize the effects of degradation and sudden collapse in the terminal phase of bioabsorption, new configurations of bioabsorbable urethral stents should be developed and compared with the other permanent stents available. Recently, the design properties of urethral stents in particular have been the subject of keen investigation. The newest design of biodegradable urethral stents is the helical mesh stent, and preliminary experimental and clinical data will soon be available. Because a bioabsorbable stent cannot prevent the recurrence of urethral stricture after urethrotomy, in the most difficult cases, it would be necessary to develop bioactive biodegradable stents that could modulate the formation of the scar tissue.
Controlled studies are needed to compare bioabsorbable stents with other forms of therapy for the treatment of urethral strictures. Studies to discover the ideal materials, shape, size, and coating materials are needed. Nevertheless, the use of biomaterials in general urologic care is likely and will provide new therapeutic methods to urologists in the near future.