Cellular and Molecular Bioengineering

, Volume 10, Issue 5, pp 387–403 | Cite as

Phase-Separated Liposomes Enhance the Efficiency of Macromolecular Delivery to the Cellular Cytoplasm

  • Zachary I. Imam
  • Laura E. Kenyon
  • Grant Ashby
  • Fatema Nagib
  • Morgan Mendicino
  • Chi Zhao
  • Avinash K. Gadok
  • Jeanne C. StachowiakEmail author



From viruses to organelles, fusion of biological membranes is used by diverse biological systems to deliver macromolecules across membrane barriers. Membrane fusion is also a potentially efficient mechanism for the delivery of macromolecular therapeutics to the cellular cytoplasm. However, a key shortcoming of existing fusogenic liposomal systems is that they are inefficient, requiring a high concentration of fusion-promoting lipids in order to cross cellular membrane barriers.


Toward addressing this limitation, our experiments explore the extent to which membrane fusion can be amplified by using the process of lipid membrane phase separation to concentrate fusion-promoting lipids within distinct regions of the membrane surface.


We used confocal fluorescence microscopy to investigate the integration of fusion-promoting lipids into a ternary lipid membrane system that separated into liquid-ordered and liquid-disordered membrane phases. Additionally, we quantified the impact of membrane phase separation on the efficiency with which liposomes transferred lipids and encapsulated macromolecules to cells, using a combination of confocal fluorescence imaging and flow cytometry.


Here we report that concentrating fusion-promoting lipids within phase-separated lipid domains on the surfaces of liposomes significantly increases the efficiency of liposome fusion with model membranes and cells. In particular, membrane phase separation enhanced the delivery of lipids and model macromolecules to the cytoplasm of tumor cells by at least four-fold in comparison to homogenous liposomes.


Our findings demonstrate that phase separation can enhance membrane fusion by locally concentrating fusion-promoting lipids on the surface of liposomes. This work represents the first application of lipid membrane phase separation in the design of biomaterials-based delivery systems. Additionally, these results lay the ground work for developing fusogenic liposomes that are triggered by physical and molecular cues associated with target cells.


DOTAP Fusion Transmembrane delivery Membrane Biophysics Biomaterials 





1,2 Dioleoyl-sn-glycero-3-phosphocholine


1,2 Dioleoyl–3-trimethylammonium-propane


1,2 Dipalmitoyl-sn-glycerol-3-phosphoethanolamine-N-[Methoxy(Polyethylene glycol)-2000]

Texas Red-DPPE

Texas Red-1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine

Oregon Green-DPPE

Oregon Green-1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine


Molar fraction


Giant unilamellar vesicle


Small unilamellar vesicle

Rhodamine B-dextran

Rhodamine B isothiocyanate-dextran average molecular weight of 10,000


Tetramethylrhodamine isothiocyanate-dextran average molecular weight of 20,000



This work was supported by the National Science Foundation Division of Materials Research (DMR 1352487 to Stachowiak) and also National Institute of General Medical Science (Grant No. GM112065). We thank the BME Community of Undergraduate Research Scholars for Cancer (BME CUReS Cancer) an NSF sponsored Research Experience for Undergraduates (REU) at The University of Texas at Austin for enabling Grant Ashby to work in the Stachowiak Laboratory at UT Austin. We thank the laboratories of Professors Aaron Baker and Janet Zoldan for assistance with lentiviral transfection.


All authors, including Z. I. Imam, L. E Kenyon, G. Ashby, F. Nagib, M. Mendicino, C. Zhao, A. K. Gadok, and J. C. Stachowiak, declare that they have no conflict of interest.


No human studies were carried out by the authors for this article. No animal studies were carried out by the authors for this article.

Supplementary material

12195_2017_489_MOESM1_ESM.docx (2.5 mb)
Supplementary material 1 (DOCX 2517 kb).


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Copyright information

© Biomedical Engineering Society 2017

Authors and Affiliations

  • Zachary I. Imam
    • 1
  • Laura E. Kenyon
    • 1
  • Grant Ashby
    • 1
  • Fatema Nagib
    • 1
  • Morgan Mendicino
    • 1
  • Chi Zhao
    • 1
  • Avinash K. Gadok
    • 1
  • Jeanne C. Stachowiak
    • 1
    Email author
  1. 1.Department of Biomedical EngineeringThe University of Texas at AustinAustinUSA

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