Issue 8, 2018

Nanospheres with a smectic hydrophobic core and an amorphous PEG hydrophilic shell: structural changes and implications for drug delivery

Abstract

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.

Graphical abstract: Nanospheres with a smectic hydrophobic core and an amorphous PEG hydrophilic shell: structural changes and implications for drug delivery

Supplementary files

Article information

Article type
Paper
Submitted
15 Dec 2017
Accepted
10 Jan 2018
First published
12 Jan 2018

Soft Matter, 2018,14, 1327-1335

Nanospheres with a smectic hydrophobic core and an amorphous PEG hydrophilic shell: structural changes and implications for drug delivery

N. S. Murthy, Z. Zhang, S. Borsadia and J. Kohn, Soft Matter, 2018, 14, 1327 DOI: 10.1039/C7SM02472J

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