Definition of Microspheres:

Microspheres are spherical or near-spherical entities composed of a drug dissolved or dispersed within a matrix framework made of polymeric materials.  

Their size varies depending on the intended application. 

Preparation of drug eluting microspheres:

First prepare blank microspheres. 

Then select an appropriate solvent system capable of both dissolving the drug and permeating into the blank microspheres. 

Immerse the blank microspheres in the drug solution to obtain the drug eluting microspheres. 

Drug release:

Diffusion through capsule walls or skeletal structures

Factors affecting release rate:

The smaller the particle size is, the faster the release occurs. 

General Information on Polyembo® Drug Eluting Embolization Microspheres 

● Blue microspheres are chemically synthesized with polyvinyl alcohol (PVA) as the primary component by a patented process. 

● Packaged in pre-filled syringes and stored in 0.9% sodium chloride solution in a wet microsphere format. 

● Non-degradable and non-absorbable within the body, providing permanent and long-lasting embolization. 

● Moist heat sterilization, for single-use only

Sphere 

► Sphere=Complete obstruction of the lumen 

- Smooth surface, perfectly spherical microspheres, not easily aggregated 

- Like the vascular lumen, it is circular in shape, fits well to the vessel wall without displacement. 

-High vascular compliance facilitates “superselective” targeted interventional therapy, enabling more precise embolization of tumor-supplying target vessels. 

Compressibility and elasticity 

►High compressibility=dense embolization 

-Excellent variable elasticity with up to 50% compressibility,  rapidly regaining its original shape upon leaving the catheter, providing dense and secure embolization. 

-Easily pass through microcatheters without blockage -Enable the use of microcatheters smaller than the microsphere diameter  

Selection of Particle Size 

● The diameter of hepatic capillaries typically ranges from 7 to 9 μm, that of hepatic sinusoids ranges from 7 to 12 μm, and the diameter of precapillary terminal arterioles is generally <50 μm. The hepatic artery anterior to the hepatic sinusoids enters the portal venous system via four pathways: the portal vein nourishing vessels, the cholangio-vascular plexus, functional hepatic artery-portal vein anastomoses, and direct hepatic artery-portal vein connections. Intrahepatic vessels feature microcirculatory connections with distinct structural characteristics, with these communicating branches typically measuring less than 50 μm in diameter. 

► Embolization of hepatic sinusoids smaller than 20 μm will cause localized hepatic infarction; 

► The diameter of arteriovenous anastomotic branches typically ranges from 10 to 30 μm, and their embolization may lead to hepatic necrosis. 

► Embolization of hepatic arteries <200 μm typically involves functional terminal arteries, which do not form collateral circulation within the liver post-embolization. In contrast, embolization of larger hepatic arteries initially causes ischemia in hepatocytes surrounding the portal sinusoidal areas. Only when the peripheral arterial blood supply to an entire hepatic lobule is completely blocked can necrosis of the entire lobule occur.  

● Particle size selection 

►70-150 μm: Tumor with insufficient blood supply 

►300~500 μm: Hepatic cancer with rich or moderately rich blood supply; tumors with a diameter <3 cm (alternatively, 100–300 μm may be used) 

►500~710 μm: Lesions with particularly rich blood supply; suitable for tumors >5 cm (first use 100–300 μm, then 300–500 μm). 

►710 μm and above: Large vessels with substantial blood supply  

Selection of Particle Size 

Partially loadable chemotherapy drugs and recommended dosages for polyvinyl alcohol embolization microspheres 

Note: The drug eluting microspheres used in the above data have a size range of 300–500 μm.