Calibrated Bioresorbable Microspheres as an Embolic Agent: An Experimental Study in a Rabbit Renal Model.

PURPOSE: To evaluate the time frame of resorption and tissue response of newly developed bioresorbable microspheres (BRMS) and vessel recanalization after renal embolization. MATERIALS AND METHODS: Embolization of lower poles of kidneys of 20 adult rabbits was performed with BRMS (300-500 µm). Two rabbits were sacrificed immediately after embolization (day 0). Three rabbits were sacrificed after follow-up angiography at 3, 7, 10, 14, 21, and 30 days. The pathologic changes in the renal parenchyma, BRMS degradation, and vessel recanalization were evaluated histologically and angiographically. RESULTS: Embolization procedures were successfully performed, and all animals survived without complication. Infarcts were observed in all kidneys that received embolization harvested after day 0. Moderate degradation of BRMS (score = 1.07 ± 0.06) was observed by day 3. Of BRMS, 95% were resorbed before day 10 with scant BRMS materials remaining in the arteries at later time points. Partial vessel recanalization was observed by angiography starting on day 3, whereas new capillary formation was first identified histologically on day 7. Vascular inflammation associated with BRMS consisted of acute, heterophilic infiltrate at earlier time points (day 3 to day 10); this was resolved with the resorption of BRMS. Inflammation and fibrosis within infarcted regions were consistent with progression of infarction. CONCLUSIONS: BRMS were bioresorbable in vivo, and most BRMS were resorbed before day 10 with a mild tissue reaction. Vessel recanalization occurred secondary to the resorption of BRMS.