Washat Roxanne Ware

NIST Center for Neutron Research

Fayetteville State University 

1
 Introduction

 Building the Network 

 Characteristics of the Network 

 Data: Dynamic Light Scattering , Rheology, Small Angle Neutron Scattering 

 Building the Vesicle

 Lipid Extrusion 

 Cryogenic Electron Microscopy Images 

 Next Steps and Why This Is Important 

 What’s left? 

2
*https://biologydictionary.net/cytoskeleton/

• Cell membrane is made up of a 

lipid bilayer and is soft and has 

viscoelastic properties. 

• Question: How do the extracellular 

matrix and cytoskeletal network 

affect the dynamics of this bilayer? 

3

Cell Membrane
*https://biologydictionary.net/cytoskeleton/

DMPC/DMPG

Polyethylene 

Glycol

Water

4
 Introduction

 Building the Network 

 Characteristics of the Network 

 Data: Dynamic Light Scattering , Rheology, Small Angle Neutron Scattering 

 Building the Vesicle

 Lipid Extrusion 

 Cryogenic Electron Microscopy Images 

 Next Steps and Why This Is Important 

 What’s left? 

5
 Created a network that mimics the cytoskeletal 

network and extracellular matrix with polyethylene 

glycol. 

 Why polymer? 

 Viscoelastic Properties 

 Cheap and abundant 

 Knowledge about their properties 

*https://slideplayer.com/slide/10581332/

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*used 100,000 MW 

and 35,000 MW 

PEG to create 9 

different wt%. 

• C*-point at which polymer coils/chains begin to overlap in solution

• Important because we are trying to recreate a matrix that mimics ECM/cytoskeletal network 

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10-2 10-1 100 101 102 103 104 105 106

0.0

0.2

0.4

0.6

0.8

1.0

 0.1% 

2.5%

Coef

Time (μs)

35K PEG @ 40C

8

• Key Findings: Higher concentrations 

have a steeper curve->shifted to the 

left->meaning smaller particles that 

are moving rapidly. 
0

12345

2x10-7

3x10-7

4x10-7

5x10-7

6x10-7

7x10-7

8x10-7

100K

35K

D(C) (cm2s-1)

C (wt%)

Diffusion @ 40C

9

• DLS can tell you about the size of particles 

in solution and their diffusivity in solution

• Key Findings: Positive slope so we know 

water is a good solvent for PEG; slopes 

start to converge between 2.5 wt% and 5 

wt%.

• Important: DLS couldn’t pick up good 

readings after 5 wt%. 
0.0001

0.001

0.01

0.1

1

0.01 0.1 1 10 100 1000

viscosity (Pa.s)

shear rate (1/s)

10%

7.50%

5%

2.50%

1%

0.25%

0.75%

0%

• Test: Does increasing 

concentration increase viscosity? 

• Key Findings: Viscosity increases 

with concentration, with a more 

dramatic increase between 2.5 and 

5 wt%, which could suggest that 

something is happening to our 

polymer coils in solution. 

• Polymers in solution are Newtonian 

fluids. 

10

Literature Value of D2O

Concentrations 100K PEG
y = 2.5658E-03x1.2097E+00

R2 = 9.8312E-01

y = 7.0070E-05x3.7331E+00

R2 = 9.9672E-01

1.00E-03

1.00E-02

1.00E-01

1.00E+00

0.10 1.00 10.00 100.00

Relative Viscosity

C* 

Viscosity vs C*

Molecular Weight 

(kg/mol)

Experimental C* 

(weight %)

100 3.21

Key Findings: Power law for low concentration and 

high concentration have different slopes. The point 

at which they overlap is our c*. Experimental c* is 

approx. 3.21 wt%. 

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At which concentration do we begin to see 

overlap in our PEG solutions? 
 Correlation Length 

12

nm
• Nanoscale Structures

• Neutrons are shot through a beam 

onto sample, where they scatter at 

different Q’s (scattering angles). 

• Structure, size, etc. 

• Length of instrument is 30m. 

SMALL ANGLE NEUTRON 

SCATTERING (SANS)

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14

6789

0.1

23456

I(q)

456

789

0.01

23456789

0.1

2345

q (Å

-1

)

 0.1% 

 Fit

• Data fit to model to determine 

correlation length. 

• Key Findings: Model fit data over 

entire q range. 
Key Findings: • We found that 

correlation length is 

inversely proportional 

to concentration. • Higher 

concentrations 

have smaller 

correlation lengths

• Higher molecular 

weights have 

smaller correlation 

lengths.

• Important: SANS 

measures entire length 

of coil in wt. % ‘s lower 

than 2.5.

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Low Conc. High Conc.
 Introduction

 Building the Network 

 Characteristics of the Network 

 Data: Dynamic Light Scattering , Rheology, Small Angle Neutron Scattering 

 Building the Vesicle

 Lipid Extrusion 

 Cryogenic Electron Microscopy Images 

 Next Steps 

 What’s left? 

 Why This Is Important 

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Hydrophilic 

head 

Hydrophobic 

tail 

DMPC/DMPG

PEG

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18

• Mixed DMPC/DMPG 

charged lipid to form lipid 

bilayer 

• Extruded in solution 

through 400 nm, 200 nm, 

and 100 nm filter 

• Multilamellar->Unilamellar

https://biopharma.co.uk/blog/2016/11/16/why-you-should-choseextrusion-for-your-liposomal-enhancement/

Before 

Extrusion: 

Cloudy Solution 

After Extrusion: 

Clear Solution 
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~100 nm
 Introduction

 Building the Network 

 Characteristics of the Network 

 Data: Dynamic Light Scattering , Rheology, Small Angle Neutron Scattering 

 Building the Vesicle

 Lipid Extrusion 

 Cryogenic Electron Microscopy Images 

 Next Steps and Why This Is Important 

 What’s left? 

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 Next steps include using Neutron Spin Echo Spectroscopy to study the structure 

dynamics of the liposome vesicles in polymer solution. 

https://en.wikipedia.org/wiki/Liposome

Correlation Length

Bending Modulus

Lipid Bilayer

Lipid Bilayer

Polymer in Solution 

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 Drug delivery technology

 Stem Cell Research

 Gene Therapy 

 Cancer Therapy 

 Increasing knowledge about the membrane 

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Acknowledgements

Dr. Antonio Faraone, NIST 

Dr. Elizabeth Kelley, NIST 

Dr. Michihiro Nagao, NIST

Prof. Erkan Senses, Koc University

Dr. Tom Cleveland, NIST and IBBR

Dr. Joseph Dura and Dr. Jullie

Bourchers, NCNR SURF 

Coordinators 

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Questions and Answers?

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