Pb. Messersmith et al., PREPARATION OF CALCIUM-LOADED LIPOSOMES AND THEIR USE IN CALCIUM-PHOSPHATE FORMATION, Chemistry of materials, 10(1), 1998, pp. 109-116
Liposome encapsulation technology has been used to entrap aqueous calc
ium salts within dipalmitoylphosphatidylcholine lipid vesicles, which
were then used to form calcium phosphate minerals. The calcium encapsu
lation efficiency was found to depend upon a number of factors that in
cluded calcium salt concentration, vesicle size, lipid concentration,
and method of vesicle preparation. Removal of unencapsulated calcium b
y ion exchange resulted in calcium-loaded liposome suspensions with ca
lcium concentration as high as 85 mM. Addition of inorganic phosphate
to the calcium-loaded liposomes resulted in liposome suspensions that,
although highly supersaturated with respect to calcium phosphates, ex
hibited metastability as a result of the physical separation of calciu
m (intravesicular) and phosphate (extravesicular) ions. Calcium ion re
lease and mineral formation was activated by a bilayer-to-micelle meso
phase transformation induced by the addition of lipid surfactant. Char
acterization of the mineral product by infrared spectroscopy, X-ray di
ffraction, and electron microscopy revealed the formation of apatite a
nd brushite mineral under basic and acidic conditions, respectively. T
he potential use of calcium-loaded liposomes for in situ formation of
mineral for medical and dental applications is discussed.