Publications by authors named "Yingshan Ma"

2 Publications

  • Page 1 of 1

Phytoglycogen Nanoparticles: Nature-Derived Superlubricants.

ACS Nano 2021 05 7;15(5):8953-8964. Epub 2021 May 7.

Department of Chemistry, University of Toronto, Toronto, Ontario, Canada, M5S 3H6.

Phytoglycogen nanoparticles (PhG NPs), a single-molecule highly branched polysaccharide, exhibit excellent water retention, due to the abundance of close-packed hydroxyl groups forming hydrogen bonds with water. Here we report lubrication properties of close-packed adsorbed monolayers of PhG NPs acting as boundary lubricants. Using direct surface force measurements, we show that the hydrated nature of the NP layer results in its striking lubrication performance, with two distinct confinement-controlled friction coefficients. In the weak- to moderate-confinement regime, when the NP layer is compressed down to 8% of its original thickness under a normal pressure of up to 2.4 MPa, the NPs lubricate the surface with a friction coefficient of 10. In the strong-confinement regime, with 6.5% of the original layer thickness under a normal pressure of up to 8.1 MPa, the friction coefficient was 10. Analysis of the water content and energy dissipation in the confined NP film reveals that the lubrication is governed by synergistic contributions of unbound and bound water molecules, with the former contributing to lubrication properties in the weak- to moderate-confinement regime and the latter being responsible for the lubrication in the strong-confinement regime. These results unravel mechanistic insights that are essential for the design of lubricating systems based on strongly hydrated NPs.
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http://dx.doi.org/10.1021/acsnano.1c01755DOI Listing
May 2021

Impact of phase separation morphology on release mechanism of amorphous solid dispersions.

Eur J Pharm Sci 2019 Aug 12;136:104955. Epub 2019 Jun 12.

Department of Pharmaceutical Sciences, Leslie Dan Faculty of Pharmacy, University of Toronto, Toronto, Ontario M5S 3M2, Canada. Electronic address:

Amorphous solid dispersions (ASDs) can phase separate in the gel phase during dissolution, lowering the chemical potential and thus the driving force for drug release. The purpose of this study is to explore the connection between amorphous phase separation in the hydrated ASD and its resulting release rate. Poorly soluble model compounds - indomethacin (IND) and ritonavir (RTV) - were formulated as ASDs using PVP as carrier. Rotating disk dissolution studies with varying drug loading levels of IND-PVP and RTV-PVP showed that the drug release was fastest at an intermediate drug loading level. This was in part due to faster erosion of the ASD at lower drug loading levels. More interestingly, at low drug loading levels, PVP and the drug co-eroded, while at high drug loading levels, PVP was released preferentially. In the case of RTV-PVP, the loading level corresponding to this transition was correlated with the change in phase separation morphology as probed by confocal fluorescence imaging studies. At low drug loading levels, the hydrophobic domains were discrete domains while at high drug loading levels, hydrophobic domains were continuous. Our results suggest that at low drug loadings, release is mediated by erosion of the polymer along with embedded drug rich droplets, whereas at high drug loadings, formation of a drug-rich domain continuous morphology leads to preferential release of the polymer-rich domains. The transition from hydrophobic discrete to hydrophobic continuous morphology occurs at the percolation threshold. We discuss the two mechanisms of phase separation and its impact on the drug release from ASDs in the context of the ternary phase diagram.
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http://dx.doi.org/10.1016/j.ejps.2019.104955DOI Listing
August 2019