TY - JOUR
T1 - Nanospheres with a smectic hydrophobic core and an amorphous PEG hydrophilic shell
T2 - Structural changes and implications for drug delivery
AU - Murthy, N. Sanjeeva
AU - Zhang, Zheng
AU - Borsadia, Siddharth
AU - Kohn, Joachim
N1 - Publisher Copyright: © 2018 The Royal Society of Chemistry.
PY - 2018
Y1 - 2018
N2 - The structure of nanospheres with a crystalline core and an amorphous diffuse shell was investigated by small-angle neutron scattering (SANS), small-, medium-, and wide-angle X-ray scattering (SAXS, MAXS and WAXS), and differential scanning calorimetry (DSC). Nanospheres, 28 to 35 nm in diameter, were prepared from a triblock copolymer with poly(ethylene glycol) (PEG) hydrophilic end-blocks and oligomers of alternating desaminotyrosyl-tyrosine octyl ester (DTO) and suberic acid (SA) as the central hydrophobic block. In the lyophilized nanospheres, the diffraction patterns show that the PEG shell is ∼10 nm in thickness and crystalline, and the hydrophobic core is ∼10 nm in diameter with a smectic liquid crystalline texture. In aqueous dispersions, the hydrated PEG forms an amorphous shell, but the crystalline phase in the core persists at concentrations down to 1 mg ml-1 as evidenced by the sharp MAXS diffraction peak at a d-spacing of 24.4 Å and a melting endotherm at 40 °C. As the dispersion is diluted (<1 mg ml-1), the core becomes less ordered, and its diameter decreases by 50% even though the overall size of the nanosphere remains essentially unchanged. It is likely that below a critical concentration, intermixing of hydrophobic segments with the PEG segments reduces the size and the crystallinity of the core. At these concentrations, the PEG corona forms a eutectic with water. The mechanisms by which the concentration of the dispersion influences the structure of the nanospheres, and consequently their drug-release characteristics, are discussed.
AB - The structure of nanospheres with a crystalline core and an amorphous diffuse shell was investigated by small-angle neutron scattering (SANS), small-, medium-, and wide-angle X-ray scattering (SAXS, MAXS and WAXS), and differential scanning calorimetry (DSC). Nanospheres, 28 to 35 nm in diameter, were prepared from a triblock copolymer with poly(ethylene glycol) (PEG) hydrophilic end-blocks and oligomers of alternating desaminotyrosyl-tyrosine octyl ester (DTO) and suberic acid (SA) as the central hydrophobic block. In the lyophilized nanospheres, the diffraction patterns show that the PEG shell is ∼10 nm in thickness and crystalline, and the hydrophobic core is ∼10 nm in diameter with a smectic liquid crystalline texture. In aqueous dispersions, the hydrated PEG forms an amorphous shell, but the crystalline phase in the core persists at concentrations down to 1 mg ml-1 as evidenced by the sharp MAXS diffraction peak at a d-spacing of 24.4 Å and a melting endotherm at 40 °C. As the dispersion is diluted (<1 mg ml-1), the core becomes less ordered, and its diameter decreases by 50% even though the overall size of the nanosphere remains essentially unchanged. It is likely that below a critical concentration, intermixing of hydrophobic segments with the PEG segments reduces the size and the crystallinity of the core. At these concentrations, the PEG corona forms a eutectic with water. The mechanisms by which the concentration of the dispersion influences the structure of the nanospheres, and consequently their drug-release characteristics, are discussed.
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U2 - 10.1039/c7sm02472j
DO - 10.1039/c7sm02472j
M3 - Article
C2 - 29372231
SN - 1744-683X
VL - 14
SP - 1327
EP - 1335
JO - Soft matter
JF - Soft matter
IS - 8
ER -