Water-soluble polyvinyl alcohol microspheres for temporary embolization: development and in vivo characteristics in a pig kidney model

Characterization of Calibrated Gelatin Sponge Particles in a Rabbit Renal Embolization Model

PURPOSE

To evaluate the level of artery occlusion, degradation periods, tissue response and vessel recanalization of calibrated gelatin sponge particles after segmental renal artery embolization.

MATERIALS AND METHODS

Superselective embolization of 14 adult rabbits was performed with calibrated gelatin sponge particles (150-350 μm). Two rabbits were killed immediately after the procedure (day 0). One pair of rabbits was killed on each of the following days: 1, 3, 7, 14, 28 and 56. One rabbit from each pair underwent CT angiography before embolization and killing. The pathologic changes of the embolized renal parenchyma and embolic characteristics of calibrated gelatin sponge particles were evaluated histologically and angiographically.

RESULTS

Calibrated gelatin sponge particles were distally located in interlobular artery with a dense packing on day 0. The level of occlusion paralleled the size of the particles. Partial degradation of the particles was observed on day 3, and complete degradation was observed on day 14. Vessel recanalization was observed through both CTA and histological analysis starting on day 3. Vascular inflammation responding to gelatin sponge particles was mild and subsided with the degradation of the particles. On day 28 and day 56, attenuation of embolized vessels occurred due to marked intimal proliferation, and vascular occlusion developed.

CONCLUSIONS

Gelatin sponge particles of 150-350 μm produced dense and distal embolization, and were resorbed before day 14 with a mild tissue reaction. Vessel recanalization occurred secondary to the resorption of gelatin sponge particles, but permanent vascular occlusion developed due to marked intimal hyperplasia after day 28.

Embolic effects of Bletilla striata microspheres in renal artery and transplanted VX2 liver tumor model in rabbits

OBJECTIVES

To evaluate the characteristics of Bletilla striata microspheres (BSMs) and its effects as an embolic agent in a rabbit model.

METHODS

BSMs were prepared with an emulsification-cool condensation-chemical cross-linking method. The characteristics of BSMs in vitro were observed. Embolization experiments were performed in renal artery of rabbit and in a rabbit liver VX2 carcinoma model. Seventy-two New Zealand rabbits were divided into 2 groups, and the right renal artery was embolized with BSMs (200 μm in diameter) in the experimental group and with polyvinyl alcohol (PVA) of the same size in the control group. The pathological findings were examined with hematoxylin-eosin and Masson stainings. Liver and renal functions were tested before and after embolization. VX2 tumor was transplanted in 15 New Zealand rabbits, which were randomly divided into 3 groups (n=5). Group A were treated with saline, group B with a mixture of doxorubicin and lipiodol, and group C with hepatic arterial infusion of BSMs (200 μm in diameter). Tumor growth rate was evaluated by magnetic resonance imaging scan. Apoptosis-related factors (bax, bcl-2) and tumor vascular endothelial cell growth factor (VEGF) were evaluated through immunohistochemical staining.

RESULTS

The characteristics of BSMs in vitro were in full compliance with the requirements for use in interventional procedures. In the renal artery embolization experiment, after BSMs intervention, it was more difficult to form collateral circulation than that with PVAs, and the kidney manifested atrophy and calcification. There were no significant difference of liver and renal functions in rabbits between groups. In the liver VX2 carcinoma embolization experiment, compared with group A, the growth rate of VX2 liver tumor and Bcl-2 levels was reduced, while apoptosis index, Bax, and VEGF were increased in group B (P<0.05). There were no significant difference between groups B and C (P>0.05).

CONCLUSIONS

The characteristics of BSMs in vitro and in vivo meet the requirements for its use as an embolic agent in interventional approaches.

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.

Preparation and evaluation of biocompatible long-term radiopaque microspheres based on polyvinyl alcohol and lipiodol for embolization

The aim of this work was to develop long-term radiopaque microspheres (LRMs) by entrapping lipiodol in biocompatible polyvinyl alcohol with multiple emulsions chemical crosslinking method. The high content of lipiodol (0.366 g/mL) was hardly released from LRMs in vitro and the radiopacity could maintain at least 3 months after subcutaneous injection in mice without weakening. A series of tests was performed to evaluate the feasibility of LRMs for embolization. LRMs were proved to be smooth, spherical, and well dispersed with diameter range of 100–1200 μm. Young's modulus of LRMs was 55.39 ± 9.10 kPa and LRMs could be easily delivered through catheter without aggregating or clogging. No toxicity of LRMs was found to mouse L929 fibroblasts cells and only moderate inflammatory in surrounding tissue of mice was found after subcutaneous injection of LRMs. After LRMs were embolized in renal artery of a rabbit, the distribution and radiopacity of LRMs in vivo were easily detectable by X-ray fluoroscopy and computed tomography (CT) imaging, respectively. More accurate distribution of LRMs in embolized kidney and vessels could be detected by high-revolution visualization of micro-CT ex vivo. In conclusion, the LRMs were proved to be biocompatible and provide long-term radiopacity with good physical and mechanical properties for embolization.