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

• Main Authors: Hsiang-Chi Tsai, Yan-Ling Yang, Yu-Jane Sheng, Heng-Kwong Tsao
• Format: Article
• Language: English
• Published: MDPI AG 2020-03-01
• Series: Polymers
• Subjects: lipid/triblock hybrid membrane; bridge- and loop-shape; symmetric or asymmetric membrane; dissipative particle dynamics
• Online Access: https://www.mdpi.com/2073-4360/12/3/639

Hybrid membranes formed by co-assembly of A_xB_yA_x (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 (<inline-formula> <math display="inline"> <semantics> <mrow> <msub> <mi>f</mi> <mi>L</mi> </msub> </mrow> </semantics> </math> </inline-formula>) of copolymers in the membrane depends significantly on the hydrophilic block length (x). As x is small, an equilibrium <inline-formula> <math display="inline"> <semantics> <mrow> <msubsup> <mi>f</mi> <mi>L</mi> <mo>*</mo> </msubsup> </mrow> </semantics> </math> </inline-formula> always results irrespective of the initial conformation distribution and its value depends on the hydrophobic block length (y). For large x, <inline-formula> <math display="inline"> <semantics> <mrow> <msub> <mi>f</mi> <mi>L</mi> </msub> </mrow> </semantics> </math> </inline-formula> 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 (<inline-formula> <math display="inline"> <semantics> <mrow> <msup> <mi>d</mi> <mo>&#10178;</mo> </msup> </mrow> </semantics> </math> </inline-formula> and <inline-formula> <math display="inline"> <semantics> <mrow> <msup> <mi>d</mi> <mrow> <mo>‖</mo> </mrow> </msup> </mrow> </semantics> </math> </inline-formula>) of bridge- and loop-conformations, are discussed as well.