Formation of Asymmetric and Symmetric Hybrid Membranes of Lipids and Triblock Copolymers.

Hsiang-Chi Tsai,Yu-Jane Sheng,Yan-Ling Yang,Heng-Kwong Tsao

doi:10.3390/polym12030639

Hsiang-Chi Tsai, Yu-Jane Sheng + Show 2 more

Open Access

https://doi.org/10.3390/polym12030639

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Journal: Polymers	Publication Date: Mar 11, 2020
Citations: 15	License type: CC BY 4.0

Affiliation: National Taiwan University, National Central University

Abstract

Hybrid membranes formed by co-assembly of AxByAx (hydrophilic-hydrophobic-hydrophilic) triblock copolymers into lipid bilayers are investigated by dissipative particle dynamics. Homogeneous hybrid membranes are developed as lipids and polymers are fully compatible. The polymer conformations can be simply classified into bridge- and loop-structures in the membranes. It is interesting to find that the long-time fraction of loop-conformation () of copolymers in the membrane depends significantly on the hydrophilic block length (x). As x is small, an equilibrium always results irrespective of the initial conformation distribution and its value depends on the hydrophobic block length (y). For large x, tends to be time-invariant because polymers are kinetically trapped in their initial structures. Our findings reveal that only symmetric hybrid membranes are formed for small x, while membranes with stable asymmetric leaflets can be constructed with large x. The effects of block lengths on the polymer conformations, such as transverse and lateral spans ( and ) of bridge- and loop-conformations, are discussed as well.

Highlights

Amphiphilic molecules such as lipid and block copolymers possess both hydrophilic and hydrophobic moieties
Results and Discussion and the hybrid lipid/copolymer membrane are constructed by forming a lipid membrane first and incorporating triblock copolymers into the membrane with different conformations
The influences of the lengths of the hydrophilic A-blocks on the steady-state/equilibrium structures of hybrid membranes were explored

Summary

Introduction

Amphiphilic molecules such as lipid and block copolymers possess both hydrophilic and hydrophobic moieties. It is known that Ax By Ax triblock copolymers can exhibit two possible conformations, U- (loop) or I- (bridge) shape, in the polymer membrane [32,33,34,35,36]. Since the Ax By Ax triblock copolymers can exhibit two possible conformations, loop or bridge, the formations of asymmetric lipid/triblock hybrid membranes are inherently more complicated than their lipid/diblock counterparts [29,30,31]. The lipid/triblock hybrid membrane is called symmetric as the fractions of the loop-shape copolymers in the upper and lower leaflets are the same, and is designated asymmetric otherwise. A dissipative particle dynamics (DPD) method was employed to study both symmetric and asymmetric hybrid membranes They can be created initially by evenly or unevenly distributing triblock copolymers into the two leaflets of lipid membranes. The dependence of the equilibrium fraction of loop conformation on the hydrophobic block length (y) was studied as well

Model and Simulation Method

Results and Discussion

Formation of Stable Asymmetric Membranes by Long Hydrophilic A-Block

Evolution toward Symmetric Membrane with Short Hydrophilic A-Block

By A3 with φp tails

Thickness

Conclusions