Intrinsically radiopaque iodine-containing polyvinyl alcohol as a liquid embolic agent: evaluation in experimental wide-necked aneurysms

Liquid Embolic Agents for Endovascular Embolization: A Review

Endovascular embolization (EE) has been used for the treatment of blood vessel abnormalities, including aneurysms, AVMs, tumors, etc. The aim of this process is to occlude the affected vessel using biocompatible embolic agents. Two types of embolic agents, solid and liquid, are used for endovascular embolization. Liquid embolic agents are usually injectable and delivered into the vascular malformation sites using a catheter guided by X-ray imaging (i.e., angiography). After injection, the liquid embolic agent transforms into a solid implant in situ based on a variety of mechanisms, including polymerization, precipitation, and cross-linking, through ionic or thermal process. Until now, several polymers have been designed successfully for the development of liquid embolic agents. Both natural and synthetic polymers have been used for this purpose. In this review, we discuss embolization procedures with liquid embolic agents in different clinical applications, as well as in pre-clinical research studies.

Recent progress in liquid embolic agents

Vascular embolization is a non-surgical procedure used to treat diseases or morbid conditions related to blood vessels, such as bleeding, arteriovenous malformation, aneurysm, and hypervascular tumors, through the intentional occlusion of blood vessels. Among various types of embolic agents that have been applied, liquid embolic agents are gaining an increasing amount of attention owing to their advantages in distal infiltration into regions where solid embolic agents cannot reach, enabling more extensive embolization. Meanwhile, recent advances in biomaterials and technologies have also contributed to the development of novel liquid embolic agents that can resolve the challenges faced while using the existing embolic materials. In this review, we briefly summarize the clinically used embolic agents and their applications, and then present selected research results that overcome the limitations of the embolic agents in use. Through this review, we suggest the required properties of liquid embolic agents that ensure efficacy, which can replace the existing agents, providing directions for the future development in this field.

Biodegradable poly(lactide-co-glycolide) microspheres encapsulating hydrophobic contrast agents for transarterial chemoembolization

Transarterial chemoembolization (TACE) is a therapeutic approach to address hepatocellular carcinoma by obstructing the blood supply to the tumor using embolic agents and improving the local delivery of anticancer agents. Size-calibrated polymeric microspheres (MSs) termed drug-eluting beads (DEBs) are the most prevalent solid embolic materials; however, their limitations include insufficient X-ray visibility or biodegradability. In this study, size-controlled polymeric MSs with inherent radiopacity and biodegradability were created, and their embolic effect was assessed. Poly(lactide-co-glycolide) MSs (PLGA MSs) incorporating a hydrophobic X-ray contrast agent and an anticancer drug were produced by the w/o/w emulsion process. Their sizes were exactly calibrated to 71.40 ± 32.18 and 142.66 ± 59.92 μm in diameter, respectively, which were confirmed to have sizes similar to the clinically available DEBs. The iodine content of PLGA MSs was calculated as 144 mgI/g, and the loading quantity of the drug was 1.33%. Manufactured PLGA MSs were gradually degraded for 10 weeks and consistently released the anticancer drug. Following the PLGA MSs injection into the renal artery of New Zealand white rabbit test subjects, their deliverability to the targeted vessel through the microcatheter was confirmed. Injected PLGA MSs were clearly imaged through the real-time X-ray device without blending any contrast agents. The embolic effect of the PLGA MSs was ultimately established by the atrophy of an embolized kidney after 8 weeks. Consequently, the designed PLGA MS is anticipated to be an encouraging prospect to address hepatocellular carcinoma.

Restorative treatment strategies for patients with cleidocranial dysplasia

OBJECTIVE

To develop a suitable treatment strategy for patients with cleidocranial dysplasia (CCD) who miss the optimal early treatment stage.

MATERIALS AND METHODS

This study enrolled 15 patients with CCD who had all missed the optimal treatment stage and were diagnosed with CCD through clinical examinations and genetic tests. Based on the chief complaints and requirements of the patients, three different therapeutic schedules were devised for these patients. Schedules I (periodontal and endodontic treatments) and II (periodontal, endodontic and prosthodontic treatments) were used for patients with low requirements, whereas Schedule III (multidisciplinary strategy, including periodontal, endodontic, surgical, orthodontic and prosthodontic treatments) was used for patients with high requirements.

RESULTS

Schedules I, II and III were used in five, seven and three patients, respectively. Schedule III treatments produced the best outcomes in terms of occlusion and esthetics.

CONCLUSIONS

Schedule III based on a comprehensive multidisciplinary therapy is an ideal restorative therapeutic strategy and can achieve good outcomes for patients with CCD who missed the optimal treatment stage.

Experimental study of temperature-sensitive chitosan/β-glycerophosphate embolic material in embolizing the basicranial rete mirabile in swines

The aim of the present study was to evaluate the feasibility of the non-adhesive temperature-sensitive liquid embolic material, chitosan/β-glycerophosphate (C/GP), in embolizing the basicranial rete mirabile (REM) in a swine model of cerebral arteriovenous malformation (cAVM). A total of 24 domestic swines were used as the experimental animals, among which 12 pigs underwent direct embolization of one side of the REM, while the other 12 pigs underwent embolization of the bilateral REM following anastomosis of the carotid artery and jugular vein. A super-selective microcatheter was introduced into the REM during the embolization procedure, and the C/GP hydrogel was injected until an image of the REM disappeared in the angiography examination. Further angiography examinations were performed after 2 and 6 weeks, and histological examination of the REM was performed after 6 weeks. Of the 24 domestic swines, 23 cases underwent successful thrombosis. Convulsions occurred in one case and that pig died during the embolization procedure. Following embolization, the angiography observations revealed that the embolized REM was no longer able to be developed, and adhesion of the microcatheter tip with the embolic agent did not occur. In addition, no apparent revascularization was observed in the angiography examinations performed at weeks 2 and 6. Therefore, the current preliminary study indicated that use of the non-adhesive temperature-sensitive embolic material was feasible for the embolization of cAVM; thus, C/GP may be used as an ideal embolic material for the treatment of cAVM.

Assessment of EmboGel--a selectively dissolvable radiopaque hydrogel for embolic applications

PURPOSE

To evaluate the embolic properties of an alginate-based embolic biomaterial (EmboGel) and its solvent (EmboClear) in treatment of aneurysms.

MATERIALS AND METHODS

EmboGel is a mixture of iohexol and alginate that polymerizes into a hydrocoil when delivered through a coaxial catheter with a distal mixing tip, exposing alginate to a calcium chloride solution. In contrast to previously reported embolic agents, EmboGel can be selectively dissolved by EmboClear, a mixture of the enzyme alginate lyase and ethylenediaminetetraacetic acid (EDTA). The embolic and contrast properties of EmboGel were assessed in in vitro models of saccular aneurysm and an aortic aneurysm endoleak. The dissolvability of EmboGel with EmboClear was assessed further after endovascular delivery in the New Zealand white rabbit in the native aortoiliofemoral territory, a created saccular aneurysm, and the native carotid arteries.

RESULTS

EmboGel effectively filled aneurysm cavities in the case of stent excluded saccular and fusiform aneurysms. EmboGel was readily dissolved by EmboClear in vitro and after in vivo embolization. When the distal abdominal aorta and pelvic arteries were occluded with EmboGel, within 1 minute of EmboClear infusion, patency of the aorta and most of the pelvic circulation was regained as noted by angiography. Embolization in the subclavian artery and numerous distal branches was rapidly dissolved by EmboClear. Finally, the carotid artery occluded with EmboGel regained patency after administration of EmboClear.

CONCLUSIONS

EmboGel is a dissolvable alginate-based biomaterial that can be used for numerous embolic applications. EmboGel can be selectively dissolved with EmboClear, a solution of alginate lyase and EDTA.

Volume changes of experimental carotid sidewall aneurysms due to embolization with liquid embolic agents: a multidetector CT angiography study

Iodine-containing polyvinyl alcohol polymer (I-PVAL) is a novel precipitating liquid embolic that allows for artifact-free evaluation of CT angiography (CTA). As accurate aneurysm volumetry can be performed with multidetector CTA, we determined volumes of experimental aneurysms before, immediately after, and 4 weeks after embolization of 14 porcine experimental carotid sidewall aneurysms with this liquid embolic. An automated three-dimensional software measurement tool was used for volumetric analysis of volume-rendering CTA data. Furthermore, intra-aneurysmal pressure changes during liquid embolization were measured in four silicone aneurysms and potential polymer volume changes within 4 weeks were assessed in vitro. Liquid embolic injection was performed during temporary balloon occlusion of the aneurysm neck, resulting in a mean occlusion rate of 98.3%. Aneurysms enlarged significantly during embolization by 61.1 +/- 28.9%, whereas a significant shrinkage of 5.6 +/- 2.7% was observed within the follow-up period. Histologic analysis revealed an inflammatory foreign body reaction with partial polymer degradation. In silicone aneurysm models, intra-aneurysmal pressure remained unchanged during liquid embolic injection, whereas balloon inflation resulted in a mean pressure increase of 31.2 +/- 0.7%. No polymer shrinkage was observed in vitro. The aneurysm enlargement noted was presumably due to pressure elevation after balloon inflation, which resulted in dilatation of the weak venous wall of the newly constructed aneurysm--another shortcoming of this experimental aneurysm model. The volume decrease after 4 weeks expressed partial polymer degradation.