303
profiles ΔT 1/2,m/s (°C) (see Note 12) of both the main transition
(m) and the pretransition (s) of the lipid] (Fig. 1), by using the
respective software of the DSC instrumentation (see Note 13).
9. Correlate the obtained calorimetric data with the guest moleculelipid interactions (for example the effect on the mobility of the
polar groups or the acyl chains of the lipids), the potential perturbation of the guest molecule in the membrane or not, and
the resultant cooperativity of the whole system. Use this information to get details of the thermal effects of the drug molecules in the lipid bilayers. These thermal effects may also be
related to its release profile and its ADME (absorption, distribution, metabolism, and excretion) properties (see Note 14).
4 Notes
1. The thin-film hydration method is a technique capable of producing self-assembled liposomal nanostructures by lipids having a high phase transition temperature [11].
2. In the cases of hydrophilic and amphiphilic guest molecules,
such as dendrimers or amphiphilic block copolymers, dissolve
the lipid-molecule mixture in chloroform/methanol (9:1 v/v)
[11], while in the cases of molecules with higher grade of
hydrophobicity dissolve them in chloroform only [4, 5, 17].
3. Examples of usually used water solvents are the HPLC-grade
water and the phosphate buffer saline (PBS). The choice of
each solvent as a hydration medium depends on the preferred
pH value and/or the ionic strength. The DSC measurement of
the same sample can be repeated in different hydration/dispersion media in order to evaluate the effect of the above mentioned parameters on the thermotropic behavior. For example,
Kyrili et al. [20] used both PBS with pH = 7.4 and citrate buffer with pH = 4.0 as hydration media, in order to investigate
the effect of the environmental pH on the thermotropic behavior of hydrogenated soy phosphatidylcholine (HSPC) bilayers
with incorporated pH-responsive block copolymer.
4. The protocol of the sample preparation is found to strictly affect
the obtained thermograms. More analytically, depending on the
different preparation protocol, vehicles with different sizes can
be acquired, which may alter the thermodynamic parameters.
For example, Chiu et al. [21] described that SUVs can produce
a lower resolution peak than MLVs, accompanied with a reduction in cooperativity due to the smaller radius of SUVs over
MLVs, resulting in a less ordered orientation, which increases
the free motion of the hydrocarbon chains. This decrease in
cooperativity, reflected by a slightly broader endothermic peak,
DSC on Liposomes and Bilayers Incorporating Drugs and Biomaterials
profiles ΔT 1/2,m/s (°C) (see Note 12) of both the main transition
(m) and the pretransition (s) of the lipid] (Fig. 1), by using the
respective software of the DSC instrumentation (see Note 13).
9. Correlate the obtained calorimetric data with the guest moleculelipid interactions (for example the effect on the mobility of the
polar groups or the acyl chains of the lipids), the potential perturbation of the guest molecule in the membrane or not, and
the resultant cooperativity of the whole system. Use this information to get details of the thermal effects of the drug molecules in the lipid bilayers. These thermal effects may also be
related to its release profile and its ADME (absorption, distribution, metabolism, and excretion) properties (see Note 14).
4 Notes
1. The thin-film hydration method is a technique capable of producing self-assembled liposomal nanostructures by lipids having a high phase transition temperature [11].
2. In the cases of hydrophilic and amphiphilic guest molecules,
such as dendrimers or amphiphilic block copolymers, dissolve
the lipid-molecule mixture in chloroform/methanol (9:1 v/v)
[11], while in the cases of molecules with higher grade of
hydrophobicity dissolve them in chloroform only [4, 5, 17].
3. Examples of usually used water solvents are the HPLC-grade
water and the phosphate buffer saline (PBS). The choice of
each solvent as a hydration medium depends on the preferred
pH value and/or the ionic strength. The DSC measurement of
the same sample can be repeated in different hydration/dispersion media in order to evaluate the effect of the above mentioned parameters on the thermotropic behavior. For example,
Kyrili et al. [20] used both PBS with pH = 7.4 and citrate buffer with pH = 4.0 as hydration media, in order to investigate
the effect of the environmental pH on the thermotropic behavior of hydrogenated soy phosphatidylcholine (HSPC) bilayers
with incorporated pH-responsive block copolymer.
4. The protocol of the sample preparation is found to strictly affect
the obtained thermograms. More analytically, depending on the
different preparation protocol, vehicles with different sizes can
be acquired, which may alter the thermodynamic parameters.
For example, Chiu et al. [21] described that SUVs can produce
a lower resolution peak than MLVs, accompanied with a reduction in cooperativity due to the smaller radius of SUVs over
MLVs, resulting in a less ordered orientation, which increases
the free motion of the hydrocarbon chains. This decrease in
cooperativity, reflected by a slightly broader endothermic peak,
DSC on Liposomes and Bilayers Incorporating Drugs and Biomaterials