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Abstract
The objective of the present work was to investigate the effect of chitosan concentration
and lipid type on the characteristics of chitosan-coated liposomes and their interactions
with leuprolide. Liposomes from lipid of high purity and low purity were prepared
and coated by chitosan. Physical properties, drug entrapment efficiency, and stability
upon dilution were respectively compared. Results showed that the particle size increment
of liposomes from low purity lipid was larger than that from high purity lipid, indicating
a thicker coating layer. The high zeta potential of particles from low purity lipid
was thought to play an important role in the resistance to flocculation. As to particles
from high purity lipid, polymer bridging caused flocculation at low polymer concentration
while at high concentration, the adsorbed chitosan molecule led to steric stabilization.
Drug entrapment efficiency decreased as chitosan was added to liposomes, showing the
disturbance of bilayers. Upon dilution, the leakage of leuprolide from low purity
liposomes was larger than that from high purity liposomes. In conclusion, low purity
lipid possessed more negative charge and formed thicker adsorptive layer by stronger
electrostatic attraction with chitosan. The interaction between chitosan and the polar
head groups on the surface of phospholipid bilayers may interfere with leuprolide
entrapped in liposomes and result in the leakage of leuprolide.