IN-VITRO RESULTS WITH SPECIAL PLASTICS FOR BIODEGRADABLE ENDOURETERALSTENTS

Internal ureteral stents are widely used in urologic practice for temp orary urinary diversion, but all double-J catheters to date exhibit th e same disadvantage; that is, they have to be removed endoscopically, necessitating further intervention. We tested different materials (des ignated G100X-15xLB and G100X-20xLB) to develop a biodegradable (biodi ssolvable) endoureteral stent that can be held in place without functi onal loss yet could be dissolved by changing the environment. The prin ciple of the biochemical background is based on the physiological mili eu of the urine, The plastics tested are stable in acidic and dissolve in alkaline conditions. In a first step, specimens of two polymers we re placed in artificial urine of different pH over a period of 60 days and monitored for integrity (solution trial). In a second step, artif icial urine was set in motion (744 mL/24 hours) an infusion pump (Volu med mu VP 5000; Fresenius AG, Bad Homburg vdH, Germany) through an inf usion set in which a 30-cm piece of the materials to test had been pla ced (ureter model). Below the inserted specimen, the lumen of the infu sion tube was minimized to make obstruction by fragments more possible , In the solution trial, all specimens remained stable under physiolog ic conditions (pH 5.2) over a period of at least 30 days. The specimen s dissolved completely when the pH was adjusted to an alkaline one (pH 7.9), In the ureter model, with pH values of 7.9, all specimens were decomposed after 20 hours, and no occlusion of the model occurred. Usi ng acidic artificial urine, the specimens remained stable with a smoot h consistent surface. The dissolution was not a standard chemical one; the materials broke into microscopically small pieces, with fragments of G100X-20xLB being smaller than those of G100X-15xLB. Our first in vitro results show that the tested materials are suitable for further development of biodissolvable endoureteral stents, dissolution of whic h can be steered by changing the urinary pH.