Ethylene vinyl alcohol copolymer, commonly abbreviated as EVOH, is the chemical backbone of a widely used class of liquid embolic agent for brain and spinal vascular procedures. Unlike coils or particles, an EVOH-based liquid embolic agent is delivered as a fluid that solidifies inside the blood vessel itself, allowing it to conform to irregular or branching vascular anatomy. This article explains the underlying chemistry, the injection technique operators use to control its behavior, and how radiopacity is achieved for real-time visualization, using INVAMED's LIBRO as a manufacturer example of this technology class.
How Does an EVOH-Based Liquid Embolic Agent Solidify Inside a Vessel?
EVOH liquid embolics belong to a broader family sometimes referred to informally as onyx-type agents, reflecting the shared underlying chemistry across this device class. The copolymer is dissolved in dimethyl sulfoxide, or DMSO, a solvent that keeps the EVOH in a liquid, injectable state while it remains inside the delivery catheter. Once the mixture exits the catheter tip and contacts blood or another aqueous environment, the DMSO diffuses outward into the surrounding fluid. As the DMSO leaves the mixture, the EVOH copolymer precipitates out of solution, transitioning from a liquid to a soft, coherent solid that takes the shape of the vessel lumen it fills. This precipitation reaction happens progressively from the outside of the injected column inward, which is a defining mechanical property of this agent class.
Why Is Controlled Injection Technique Critical for Liquid Embolic Agents?
Because the precipitation reaction begins at the interface between the embolic agent and blood, operators typically use a slow, controlled injection technique rather than a rapid bolus delivery. A slower injection rate allows the outer surface of the EVOH column to solidify progressively, forming a stable "skin" or shell that helps contain the material as more agent is introduced behind it. This controlled approach gives the interventionalist time to pause, assess the material's progression under fluoroscopic guidance, and adjust the injection as needed before continuing. Rushing the injection can compromise this stepwise solidification process, which is why controlled delivery is a foundational principle of working with EVOH-based agents rather than an optional refinement.
The Role of DMSO Compatibility in Catheter Selection
Because DMSO is an aggressive solvent, it can degrade certain catheter materials if used with incompatible equipment. Neurointerventional teams generally select microcatheters that are specifically rated as DMSO-compatible before beginning an EVOH embolization procedure. This compatibility requirement is a practical consideration that distinguishes liquid embolic procedures from those using aqueous-based agents, and it underscores why procedural planning extends beyond the embolic agent itself to the full delivery system.
Achieving Radiopacity: Why Tantalum Powder Is Added
An EVOH and DMSO mixture alone would be difficult to visualize under fluoroscopy, so manufacturers incorporate a radiopaque component into the formulation. INVAMED's LIBRO, available in 6% and 8% concentrations, contains tantalum powder specifically to provide this radiopacity, according to information published by the manufacturer. Tantalum is a dense metal that appears clearly on fluoroscopic imaging, allowing the treating physician to track the embolic column's progression in real time as it fills the target vasculature. This visualization capability is what allows operators to make injection-pause decisions during the controlled delivery process described above.
Clinical Applications of EVOH Liquid Embolic Agents
EVOH-based liquid embolic agents such as LIBRO are used in the embolization of cerebral arteriovenous malformations and hypervascular tumors, as stated by the manufacturer. In AVM cases, the agent is directed toward the nidus to reduce or eliminate abnormal arteriovenous shunting. In hypervascular tumor cases, embolization is often performed prior to surgical resection to reduce intraoperative blood loss. Devices and materials used across these procedures are described further on INVAMED's neurovascular interventions category page. No specific numeric performance data, such as occlusion rates, is available for LIBRO beyond what the manufacturer has published, and this article does not present any such figures.
Is tantalum powder used for any purpose other than visualization?
Tantalum powder is included in formulations such as LIBRO specifically to provide radiopacity so the embolic column can be seen under fluoroscopy during the procedure, according to the manufacturer. It does not participate in the chemical precipitation reaction between EVOH and DMSO. Its role is confined to enabling real-time imaging visibility.
Device availability and regulatory status vary by country. Please contact INVAMED or your authorized local distributor for current regulatory information applicable to your region.