Spatial Distribution of PEO-PPO-PEO Block copolymer and PEO Homopolymer in Lipid Bilayers

Published

April 7, 2020

Author(s)

Mihee Kim, Frank Heinrich, Greg Haugstad, Guichuan Yu, Guangcui Yuan, Sushil K. Satija, Wenjia Zhang, Hannah S. Seo, Joseph M. Metzger, Samira M. Azarin, Timothy P Lodge, Benjamin J. Hackel, Frank S. Bates

Abstract

Maintaining the integrity of cell membranes is indispensable for cellular viability. Poloxamer 188 (P188), a poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymer with a number average molecular weight of 8,400 g/mol and containing 80% by mass PEO, protects cell membranes from various external injuries, and has the potential to be used as a therapeutic agent in additional applications. The membrane protection mechanism associated with P188 is intimately connected with how this block copolymer interacts with the lipid bilayer, the main component of a cell membrane. Here, we report the distribution of P188 in a model lipid bilayer comprising 1-palmitoyl-2-oleoyl-glycero-3-phosphocholine (POPC) using neutron reflectivity (NR) and atomic force microscopy (AFM). We also investigated the association of a PEO homopolymer (8400 g/mol) that does not protect living cell membranes. These experiments were conducted following incubation of a 4.5 mM polymer solution in a buffer with supported POPC bilayer membranes followed by washing with the aqueous medium. Contrary to previous reports, both P188 and PEO penetrate into the inner portion of the lipid bilayer as revealed by NR, with approximately 30 % by volume occupancy across the membrane without loss of bilayer structural integrity. These results indicate that PEO is the chemical moiety that principally drives P188 binding to bilayer membranes. No defects or phase-separated domains were observed in either P188- or PEO-incubated lipid bilayers when examined by AFM, indicating that polymer chains mingle homogeneously with lipid molecules in the bilayer. Remarkably, the breakthrough force required for penetration of the AFM tip through the bilayer membrane is unaffected by the presence of the large amount of P188 and PEO.

Citation

Langmuir

Volume

36

Issue

13

Pub Type

Journals

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Keywords

Cell membrane protection | Poloxamer 188 (P188) | PEO-PPO-PEO block copolymers | PEO homopolymer | Supported lipid bilayer | Neutron reflectivity | Atomic force microscopy

Citation

Kim, M. , Heinrich, F. , Haugstad, G. , Yu, G. , Yuan, G. , Satija, S. , Zhang, W. , Seo, H. , Metzger, J. , Azarin, S. , Lodge, T. , Hackel, B. and Bates, F. (2020), Spatial Distribution of PEO-PPO-PEO Block copolymer and PEO Homopolymer in Lipid Bilayers, Langmuir, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=928696 (Accessed December 12, 2024)