Drug Encapsulation and Aerodynamic Behavior of a Lipid Microtubule Aerosol

Morphological control of poly(ethylene glycol)-block-poly(epsilon-caprolactone) copolymer aggregates in aqueous solution

In aqueous solution, it was found that the amphiphilic copolymer poly(ethylene glycol)-b-poly(caprolactone) (PEG(5000)-b-PCL(4100)) formed different morphologies, including long rod-like, short rod-like, or spherical aggregates, when the copolymer concentration was increased. Nearly identical morphologies were observed with the addition of increasing amounts of PEG(2000)-distearoylphosphoethanolamine (PEG(2000)-DSPE) to the copolymer. The morphologies of the aggregates in solution were confirmed by negative stain transmission electron microscopy (TEM) and cryogenic-TEM (cryo-TEM). The critical micelle concentrations of the PEG(5000)-b-PCL(4100) copolymer, PEG(2000)-DSPE and a mixture of the two materials (PEG(5000)-b-PCL 4100/PEG(2000)-DSPE) were evaluated to determine the thermodynamic stability of the aggregates. Differential scanning calorimetry was performed to gain insight into the degree of mixing of PEG(5000)-b-PCL(4100) and PEG(2000)-DSPE. Overall, combining PEG(5000)-b-PCL(4100) and PEG(2000)-DSPE produced a single population of mixed micelles with rod-like or spherical morphologies depending on the material composition and concentration.

Phospholipid/protein cones

The presence of protein in tubule-forming solutions of the diacetylenic phospholipid 1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine results in the formation of hollow cones rather than the expected hollow cylinders. Differential phase-contrast video microscopy reveals that cones grow from proteinaceous nodules in a fashion similar to cylindrical tubule growth from spherical vesicles. Spatially resolved electron-beam energy-dispersive X-ray fluorescence spectroscopy shows the protein to be associated with the cone wall. Small-angle X-ray scattering shows that, like the protein-free cylinders, the cones are multilamellar with essentially identical interlamellar spacing.

Phosphonate lipid tubules II

We describe a new chiral tubule-forming lipid in which the C-O-P phosphoryl linkage of the archetypal tubule-forming molecule, 1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine, "DC(8,9)PC", is replaced by a C-P linkage. Tubule formation with this phosphonate analogue proceeds under the same mild conditions as with DC(8,9)PC and produces similar yields, but synchrotron small-angle X-ray scattering, atomic force microscopy, and optical microscopy show the new tubules to have diameters 1.94 times as great, to be significantly shorter, and to be thinner-walled. A significant portion of the enantiomerically pure chiral phosphonate precipitate is in the form of stable open helices, and these helices are divided almost evenly between left- and right-handed members.

Formation of high axial ratio microstructures from peptides modified with glutamic acid dialkyl amides

A growing number of amphiphiles are known to form high axial ratio microstructures (HARMs) such as the hollow cylindrical microstructures called lipid tubules. As a prelude to exploring the potential of HARMs formed from lipopeptides in controlled release drug delivery, several microstructure formation conditions were investigated. We report the preparation of several glutamic acid dialkyl amides with varying alkyl chain lengths bearing a verity of peptides (1-4 amino acids) [peptide-Glu-(NHCnH2n+1)2, n=12, 14, 16]. These surfactants have been rapidly and efficiently converted into HARMs in aqueous buffer at physiological pH and ionic strength, or in buffer containing MeOH or EtOH. Helical ribbons and tubular HARMs were produced that were stable for as long as 6 months below the phase transition temperatures of the compounds. To estimate the stability of HARMs in vivo, HARMs formed from (Pro)3-Glu(NHC16H33)2 were incubated with DOPC liposomes or fetal calf serum at 40 degreesC. HARM size and shape did not change significantly, suggesting that such lipopeptide particles can retain their morphology long enough in vivo to be useful as drug delivery vehicles.