Polymer concentration, relative molecular mass size and composition all affect the properties of microspheres. Polymer concentration affects the deposition rate during sphere-forming. The higher the concentration, the slower the deposition rate, the larger the particle size of the microspheres, the looser the structure, and the faster the drug release.
The drug properties significantly affect the stability of the microsphere polymer crosslinking, and the drug content affects the microsphere size, specific surface area and gap ratio. For the microspheres prepared by O/W process, the drug with large water solubility can easily diffuse into the aqueous phase, and the encapsulation rate and drug loading capacity are lower than those of fat-soluble drugs.
The solubility of organic solvents in the continuous phase is the key to the particle size, encapsulation rate and drug loading capacity of microspheres.
The solvent volatilization method often uses polyethylene (PVA), gelatin, hydroxypropyl methylcellulose (HPMC), and tween as emulsifiers. The type, concentration and emulsification time of the emulsifier are closely related to the size of the emulsion droplets formed, which directly affects the quality of the microspheres.
- Aqueous phase composition
The addition of buffers, salts or other additives to the aqueous phase can change the solubility of drug and organic solvents in the aqueous phase, thus increasing the drug loading and encapsulation rate, and the sudden release effect is reduced.
The yield and encapsulation rate of microspheres made by reduced pressure evaporation are higher than those made by atmospheric pressure evaporation.
- Droplet dispersion methods
The methods of droplet dispersion include mechanical stirring, ultrasound, electric potential dispersion, etc. The stirring speed can affect the particle size and encapsulation rate of microspheres.
