Preparation of Calcium-Loaded Liposomes and Their Use in Calcium Phosphate Formation

Abstract

Liposome encapsulation technology has been used to entrap aqueous calcium salts within dipalmitoylphosphatidylcholine lipid vesicles, which were then used to form calcium phosphate minerals. The calcium encapsulation efficiency was found to depend upon a number of factors that included calcium salt concentration, vesicle size, lipid concentration, and method of vesicle preparation. Removal of unencapsulated calcium by ion exchange resulted in calcium-loaded liposome suspensions with calcium 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, exhibited metastability as a result of the physical separation of calcium (intravesicular) and phosphate (extravesicular) ions. Calcium ion release and mineral formation was activated by a bilayer-to-micelle mesophase transformation induced by the addition of lipid surfactant. Characterization of the mineral product by infrared spectroscopy, X-ray diffraction, and electron microscopy revealed the formation of apatite and brushite mineral under basic and acidic conditions, respectively. The potential use of calcium-loaded liposomes for in situ formation of mineral for medical and dental applications is discussed.

Structural studies of the biomineralized species of calcified pancreatic stones in patients suffering from chronic pancreatitis

“…This is also supported by the presence of weak doublet at 2323 cm À1 that, the metal ion is coordinated to carboxyl group (M-CMO), which cannot be seen in artificially synthesized CaCO 3 crystals [48] and hence the possibility of this band due to CO 2 can be ruled out in the present case. The bands at 957 cm À1 and the other at 1057 cm À1 are due to the r 1 (A 1 ) and r 3 (E) PO 4 3À molecular ion in a complex [34]. The band observed at 957 cm À1 is due to of PO 4 3À .…”

Thermal gelation and tissue adhesion of biomimetic hydrogels

“…This process was repeated a minimum of five times or until NaIO 4 could not be detected in the supernatant, using a standard spectrophotometric method [27]. CaCl 2 -entrapped liposomes (CCVs) used for control experiments were prepared by the reported method [26].…”

Liposomes in tissue engineering and regenerative medicine

“…Phospholipids spontaneously self-assemble into ordered lyotropic liquid-crystalline phases in the presence of water [10]. The formation of these lipid-based structures depends on the phospholipid intrinsic factors, such as the nature and size of the lipid headgroup and the length and degree of unsaturation of the acyl chains, and on the extrinsic factors, such as temperature, pH, concentration and the presence of solutes and other lipids [7,10]. Examples of lipid-based structures are monolayers, lipid bilayers, micelles, liposomes and tubules [7,15].…”