Abstract
We designed a novel lyophilization method using controlled rate slow freezing (CSF) with lyoprotective agent (LPA) to achieve intact lipid nanovesicles after lyophilization. During the freezing step, LPA prevented water supercooling, and the freezing rate was controlled by CSF. Regulating the freezing rate by various liquid media was a crucial determinant of membrane disruption, and isopropanol (freezing rate of 0.933 °C/min) was the optimal medium for the CSF system. Lyophilized lipid nanovesicle using both CSF and LPA retained 92.9% of the core material and had uniform size distributions (Z-average diameter = 133.4 nm, polydispersity index = 0.144), similar to intact vesicles (120.7 nm and 0.159, respectively), after rehydration. Only lyophilized lipid nanovesicle using both CSF and LPA showed no changes in membrane fluidity and polarity. This lyophilization method can be applied to improve storage stability of lipid nanocarriers encapsulating drugs while retaining their original activity.
Highlights
We designed a novel lyophilization method using controlled rate slow freezing (CSF) with lyoprotective agent (LPA) to achieve intact lipid nanovesicles after lyophilization
Attempts to improve the integrity of lipid bilayer membranes by incorporating a lyoprotective agent (LPA) in the lipid nanovesicle solution to support a frozen matrix have been unsuccessful in terms of maintaining intact nanovesicle size distributions and morphology
The freezing rate, the velocity to pass through the critical zone of ice crystal formation (− 5 to 0 °C), determines the ice crystal size and distribution
Summary
We designed a novel lyophilization method using controlled rate slow freezing (CSF) with lyoprotective agent (LPA) to achieve intact lipid nanovesicles after lyophilization. Lyophilized lipid nanovesicle using both CSF and LPA showed no changes in membrane fluidity and polarity This lyophilization method can be applied to improve storage stability of lipid nanocarriers encapsulating drugs while retaining their original activity. Attempts to improve the integrity of lipid bilayer membranes by incorporating a lyoprotective agent (LPA) in the lipid nanovesicle solution to support a frozen matrix have been unsuccessful in terms of maintaining intact nanovesicle size distributions and morphology. These results suggest that the use of LPA alone is insufficient to retain the integrity of membranes during lyophilization. Precise control of the freezing rate is necessary to diminish disruption of lipid bilayer membranes by ice crystal formation
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