The Effect of pH on the Degradation of Biodegradable Poly(L-Lactide-Co-Glycolide) 80/20 Urethral Stent Material In Vitro Hanne Juuti, M.Sc., 1 Andres Kotsar, M.D., Ph.D., 2 Joonas Mikkonen, M.Sc., 1 Taina Isotalo, M.D., Ph.D., 3 Martti Talja, M.D., Ph.D., 3 Teuvo L.J. Tammela, M.D., Ph.D., 2 Pertti To ¨ rma ¨la ¨ , Prof. Acad., 1 and Minna Kelloma ¨ ki, Dr. Tech., Prof. 1 Abstract Purpose: To investigate in vitro whether pH ranging between 6 and 9 has an effect on the degradation of stent fibers made of poly(l-lactide-co-glycolide) (PLGA) 80/20. Materials and Methods: The fibers were divided into three groups and immersed in sodium phosphate-buffered saline (Na-PBS) solution with three different pH values: 6, 7.4, and 9. The mechanical and thermal properties were studied, and scanning electron microscopy (SEM) images were taken at specific time points of hydrolysis. Results: The tensile testing showed that the strength of the fibers decreased through hydrolysis and was lost at 8 weeks in all groups. The T m and T g of the PLGA fibers did not indicate any significant differences between the different groups. In SEM images taken at 4 weeks, there were no significant differences between the fibers immersed in Na-PBS solutions of different pH values. However, at 8 weeks the surface of the fiber immersed in saline with a pH of 6 seemed coarser than that of those immersed in neutral (pH 7.4) or alkaline (pH 9) Na-PBS. Conclusion: The studied pH values did not influence the degradation behavior of the PLGA 80/20 fibers. Therefore, rabbits can be used as model animals for human biodegradable urological devices even though the pH of their urine is different. Introduction T he degradation of bioabsorbable poly(a-hydroxyacid)s has been widely studied by several research groups. It is known that the degradation rate is affected by the polymer itself due to such factors as the chemical composition, crys- tallinity, hydrofobicity, molecular weight, and the geometry of the polymer implant. In addition, additives in the polymer and the environment such as pH, ion concentrations, and temperature, have an influence on the degradation rate. 1,2 Studies investigating the degradation of poly(a-hydroxyacid)s in phosphate buffers of different pH values have found that the hydrolysis rates are similar. Studying the polymers in several other buffers has revealed that the degradation rate increases in strongly alkaline conditions and at higher ionic strengths. 2,3 Hurrel and Cameron 2 explained this phenome- non for poly(a-hydroxyacid)s as follows: The rate at which the degradation proceeds through a polymer depends on the rate at which acidic degradation products diffuse out, creating space for water in the structure. If the solution is made more alkaline or more concentrated, the degradation products are mainly neutralized, driving the hydrolysis reaction forward. Further, the solubility of the neutralized acids increases. These effects appear to dominate over autocatalysis caused by degradation products. A braided bioabsorbable stent for urological applications has been previously developed by our research group to avoid the problems caused by biostable stents. 4–8 The degra- dation of bioabsorbable stents has been previously studied in sodium phosphate-buffered saline (Na-PBS) with a pH of 7.4. 9,10 Animal testing of the stents has been carried out in the anterior urethra of New Zealand white rabbits 11 ; the pH of rabbit urine has been shown to be alkaline, normally ranging from 7.6 to 8.8, 12 but it can be strongly affected by the nutri- tion of the rabbits. On a low-alkali diet, the average pH of rabbit urine can decrease to 6.26 due to a dramatic reduction in the soluble bicarbonate excreted daily. In contrast, a high- alkali diet does not raise the pH of rabbit urine that remains below 9 as it does with a normal diet as well. 13 As the pH of the human urine is between 4.5 and 7.8, but commonly 1 Department of Biomedical Engineering, Tampere University of Technology, Tampere, Finland. 2 Department of Urology, Tampere University Hospital, Tampere, Finland. 3 Department of Surgery, Pa ¨ ija ¨ t-Ha ¨ me Central Hospital, Lahti, Finland. JOURNAL OF ENDOUROLOGY Volume 26, Number 6, June 2012 ª Mary Ann Liebert, Inc. Pp. 701–705 DOI: 10.1089/end.2011.0199 701