Degradation behaviour of self-reinforced 80L/20G PLGA devices in vitro.

In vitro degradation of self-reinforced PLGA 80L/20G material and bioabsorbable stents was studied in artificial urine and phosphate buffer solution (PBS) to define if the media have an effect on the degradation rate in urological applications. After six weeks, the Mv of the samples immersed in PBS was 40% (16.7 kDa) from the initial value and 57% (24.0 kDa) for the samples immersed in artificial urine. The strength loss of samples that were immersed in PBS was slower when compared with samples in artificial urine. The bending strength of samples immersed 15 weeks in artificial urine was 43% (21.7 MPa) of the bending strength of samples immersed in PBS (50.9 MPa), and the shear strength was 13% (artificial urine 3.7 MPa, PBS 28.8 MPa), respectively. The maximum compression force in PBS was slightly over at the initial level after 2 weeks of immersion. It decreased to half (102.2N) of the initial value (204.1N) in 8 weeks, and after 12 weeks it was 25% (50.8 N) of the initial value. The compression force in artificial urine was 35% (66.8 N) of the initial value (193.9 N) after 8 weeks. In 12 weeks it had lowered to 26 N in artificial urine, which was 14% of the initial value. The degradation rate of self-reinforced L-lactic and glycolic acid stents in vitro tests in artificial urine was coinciding with our clinical test. Based on these results, it is possible to make a sufficiently accurate in vitro model for the degradation rate of bioabsorbable polymers for urological applications.

Viscoelastic memory and self-expansion of self-reinforced bioabsorbable stents.

The possibility to decide the speed and rate of expansion of stents is of great clinical importance by reason of the varying requirements for different indications to use stents. Self-reinforced bioabsorbable stents can be made self-expanding owing to the viscoelastic memory of the material. Stents are stable at room temperature and expansion occurs at body temperature. The level at which the expansion stops depends on the material, crystallinity, initial diameter of spira and annealing temperature. The expansion rate can be estimated by logarithmic equation, if material, draw ratio and diameter of stent wire are constant. This is, however, possible only if processing parameters are constant. Based on the present results annealing temperature and expansion time were seen to be directly proportional to the expansion rate of the stent.

Expansion and bioabsorption of the self-reinforced lactic and glycolic acid copolymer prostatic spiral stent.

PURPOSE: Self-reinforced bioabsorbable stents can be made self-expanding due to the viscoelastic memory of the oriented bioabsorbable materials. A new self-expandable self-reinforced copolymer of lactic/glycolic acid, lactic/glycolic molar ratio 80:20 stent was developed to prevent postoperative urinary retention after procedures that induced prostatic edema. In in vitro experiments the expansion rate has been up to 100% during the first few hours at body temperature. We investigated the expansion rate and biodegradation of the self-reinforced lactic and glycolic acid copolymer prostatic spiral stent in vivo in the prostatic urethra. MATERIALS AND METHODS: A total of 39 men, 52 to 84 years old, with lower urinary tract symptoms due to benign prostatic enlargement underwent interstitial laser coagulation of the prostate. A self-reinforced copolymer of lactic/glycolic acid, lactic/glycolic molar ratio 80/20 stent was inserted into the prostatic urethra at the end of the operation. The stent lumen diameter was 4.5 mm. The location and diameter of the lumen and degradation of the stent were studied with transrectal ultrasound at 1, 2, 4 and 6 months postoperatively. At 6 months patients underwent cystoscopy. RESULTS: All except 1 patient voided on postoperative day 1. Mean lumen diameter was 7.4 mm. (range 6.2 to 8.2) at 1 month and 7.2 mm (range 6.2 to 7.5) at 2 months. At 4 months the stent was degraded into small pieces. No pieces of stent were found in the prostatic urethra on ultrasound or cystoscopy at 6 months. However, a portion of the spiral stent was found at the bottom of the bladder in 2 patients. CONCLUSIONS: The speed and expansion rate of the self-reinforced copolymer of lactic/glycolic acid, lactic/glycolic molar ratio 80/20 stent was sufficient to lock the stent in place and ensure voiding in cases of edema induced bladder outlet obstruction. Strength retention greater than 2 months was long enough to avoid later impairments of voiding.

The cytostatic effect of 9-cis-retinoic acid, tretinoin, and isotretinoin on three different human bladder cancer cell lines in vitro.

Retinoids have been shown to have activity in both preclinical and clinical bladder cancer studies but their exact role in its treatment and prevention remains obscure. In this study cytostatic activity of a novel 9-cis-retinoic acid (9-cis-RA) was compared with two other retinoids: tretinoin and isotretinoin, in three different bladder cancer cell lines: RT4 (well differentiated), 5637 (moderately differentiated) and T24 (poorly differentiated). The three retinoids were incubated at concentrations of 0.3, 3 and 30 microg/ml with bladder cancer cells in microtitre plates for 3 and 6 days. The cytostatic effect was estimated by using luminometric measuring of ATP activity of viable cells in suspension. Compared with the older retinoids, tretinoin and isotretinoin, the highest concentration of 9-cis-RA had a cytostatic efficacy in all three bladder cancer cell lines tested. A clear dose response relationship was observed in isotretinoin-treated cultures after 6 days and in all 9-cis-RA-treated cultures. Tretinoin was either ineffective or had a stimulating effect on poorly differentiated tumour cells. To conclude, isotretinoin and 9-cis-RA had a cytostatic effect on human bladder cancer cells in vitro. However, the possibility of stimulating cancer growth at small doses, at least with tretinoin, and toxicity at high doses must be considered when planning clinical trials.