use of silver nanoparticles in medically-related pressure measurements. · 2018. 11. 6. ·...

Department of ORTHOPAEDIC SURGERY

Use of silver nanoparticles in medically-related pressure

measurements.Thomas L. Smith PhD, *Baxter McGuirt BS, Lawrence X. Webb MD, Brian Werner MD, William Wagner PhD, *David Carroll PhD

Wake Forest University School of Medicine, Department of Orthopaedic Surgery*Wake Forest Center for Nanotechnology


Nanotechnology and Orthopaedics

2003 Dr. David Carroll joined the faculty of Wake Forest and began making contacts with many departments within the university

Tuesday morning (0630) meeting with Orthopaedic surgeons, basic scientists, residents and students to discuss research topics related to trauma and inflammation.

Topic of nanopressure measurements came up and the potential applications in medicine were apparent.


Pressure measurementsin Orthopaedics

Is compartment syndrome a big deal??

You bet!

Mary Decker – Olympic distance runner – Shin Splints



Untreated compartment syndrome Necrosis of muscleResectionamputation



Trauma and Compartment Syndrome



Trauma and Compartment Syndrome

InflammationSwellingOcclusionIschemiaTissue loss


Compartment syndrome

Appropriate treatment Relieves pressure Avoids necrosis/amputation

Knowledge of pressure is essential



Pressure measurements are vital

18 ga(1.3 mm)



Pressure measurements are vital Is there a way to make these

measurements with less trauma? More accuracy?


Collaboration betweenWake Forest University Health sciences and Wake Forest University Nanotech…


Why do we need small Pressure Sensors?

The “Plasmon Ruler”

nanoTorr: a novel Pressure Sensor

Calibration and initial data


What we need1) A pressure transducer that is < 1 micron in diameter.2) Signal transmission that is optical to avoid necessity of in vivo

wiring.3) Tissue borne or catheter based4) No hysteresis.5) 2 to 5 mmHg resolution.6) Less than 2% drift of static pressure measures over 24 hours.7) Non saturable8) Throw away transducers / simple to manufacture9) Sterilizable10) Simple to use

a TALL order to be sure…


A ConceptTake a collection of nanoparticles dispersed in a soft polymer matrix. This can be made into a micron sized sphere, or perhaps a coating on a fiber optic.

SSPB∆⋅∆= 0

If the bulk modulus of the polymer is small, then small pressures will push the nanoparticles closer together

Can this be made?

If the nanoparticles interact, and if that interaction is a function of distance between them, and if that interaction results in shifts in some external observable characteristic, then the pressure on the outside of the collection of nanoparticles results in shifts in that characteristic.


Surface Plasmonsexcitations that interact. These interactions are a function of distance. These excitations are responsible for the absorption and color of metal

nanoparticles

23

00cos

2cos

ra

m

mout

θεεεεθφ EE

+−

+−=

30

0 4cos

rmout επε

θφ rpE ⋅+−=

E

Incoming electromagnetic wave _

+

_

+

_

+

_

+

The incoming wave results in an oscillating charged dipole. These oscillations are quantized and known as “plasmons.”


Surface Plasmons

Jensen,Kelly,Lazarides,Schatz, “Electrodynamics of noble metal nanoparticles and nanoparticle clusters.” J. Cluster Sci. Vol. 10, No. 2, 1999

These quantized excitations result in specific features in the absorption spectrum of metallic nanoparticles. The strong resonances are dependent on the particle size and geometry.

The resonance peak of the spectrum is also dependent on the surrounding dielectric medium, and can be affected by additional external electric fields (like other particles).

Different diameters give different absorptions (colors)


Surface Plasmon InteractionsBringing another particle close to the first causes an interaction between the plasmons of the two particles.

This interaction is dependent on the distance between the particles, and results in a change in the absorption characteristics of both particles.

d


Surface Plasmon InteractionsThe interaction of

plasmons causes a shift toward the IR in the absorption spectrum of the nanoparticles.

The closer the nanoparticles come to each other, the larger the shift in the resonance peak of the absorption spectrum.


Simulated and experimental resonance shiftsfor 88nm gold nanoparticles, and the derived plasmon ruler equation:

“On the universal scaling behavior of the distance Decay of plasmon coupling in metal-nanoparticle pairs: A plasmon ruler equation.” Jain, Huang, El-SayedNano Letters 2007: Vol.7 No.7 pp. 2080-2088

Georgia Tech-For given metals we can empirically derive a plasmon ruler equation that relates changes in the plasmon resonance to the interparticle gap/diameter ratio.

From these models we can see that the plasmon resonance as the gap shrinks are nearly negligible until the gap is roughly half the diameter of the nanoparticles.


The GaTech work before was for two particles. We have studied this numerically for small collections to see if the concept extends. It does…

Gold: n = 0.467 +2.415i, at λ = 532 nm, d=2.4r

Gold: n = 0.467 +2.415i, at λ = 532 nm, d=4r


Particles in the nanospheres are held apart by surfactants around them


The surface plasmon of silver nanoparticles can easily be tuned through varying the growth method. This allows us to tune the plasmon to windows in the near-IR where human tissue is transparent.

The Optical Signatures of different diameter particles are strikingly different. UV-Vis absorptionspectra are shown here.

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1.0485nm

422n

m

376n

m35

0nm

Nanodisks

Abso

rban

ce (a

.u.)

Wavelength (nm)

350 400 450 500 550 600 650 700 750 800 850 9000.0

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rban

ce (a

.u.)

Wavelength (nm)

(a) Ag Seeds (b) 2.0ml (c) 1.0ml (d) 0.5ml (e) 0.25ml (f) 0.125ml (g) 0.06ml


NANODISK FORMATION AND TRANSFORMATION

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300 400 500 600 700 800

Abs

orba

nce

Wavelength (nm)

before aging5 min

10 min30 min

1 h4 h11 h22 h

57 h

Agingat 40oC

0 min5 min

4 h 57 h


40oC4 hours 57 hours


TEM OF TRIANGLES AND DISKS

Silver nanodisks

Truncated triangular nanoplates


Pressure Sensor Design By controlling nanoparticle concentration inside

a compressible polymer matrix we can create a matrix of interacting particles.

Applying pressure to this nanocomposite material will then cause the whole material to compress, causing a change in the interparticle distance which will yield a measurable change in the absorption spectrum.


Pressure Sensor Design Desirable polymers for a pressure sensor have

a low bulk modulus and are biologically compatible to enable use of these in diagnostic technologies.

In the following we use poly(dimethylsiloxane) (PDMS) as our polymer matrix. It features a small bulk modulus (300 MPa), has been FDA approved for use in the body, and is non-solvent in aqueous environments.


Resonance Shifts in Pressure Sensors

Absorption Spectra Shift with Applied Pressure of PDMS Loaded with Silver Nanoparticles

0.3

0.35

0.4

0.45

0.5

0.55

0.6

0.65

381 431 481 531 581 631 681

Wavelength (nm)

% A

bsor

ptio

n

Uncompressed Absorption SpectraCompressed Absorption Spectra

Our initial tests with compressing a sample manually between two plates show an increase in absorption with applied pressure, as well as a slight shift in peak wavelength.


Resonance Shifts in Pressure Sensors

Our compression tests are the first to confirm a shift in the absorption spectrum peak with an increase in pressure.

However the applied pressures are large (~1200 mm Hg) compared to the clinically relevant pressures of compartment syndrome and V.A.C.


An Alternative Method for Detecting Plasmon Interactions

Modelling of the nanoparticle pairs shows that in addition to the plasmon resonance shift these materials should show a change in their absorption spectrum shape, especially on the high wavelength side of the resonance peak.


An Alternative Method for Detecting Plasmon Interactions

This change in the shape of the absorption spectrum occurs as some of the nanoparticle pairs experience a shift in their absorption resonance toward the IR.

As more of the particle population shifts toward the IR the shape of the absorption spectrum can begin to change before the average spectrum of the whole material shows detectable changes.


PDMS Compression Test (August 17, 2007)

0.5

0.55

0.6

0.65

0.7

0.75

0.8

350 400 450 500 550 600 650

Wavelength (nm)

Abs

orpt

ion

(%)

UncompressedCompressed

Slope = 35

Slope = 42

Analysis of our compression tests shows that while the overall resonance shift is small, the shape of the curve changes substantially (shown here by comparing the slope on the high-wavelength side of the absorption peak). This can result in a tenfold increase in pressure sensitivity.


The change in absorption spectrum shape can be seen over steps of 30 mm Hg. This is a greater pressure resolution than expected from plasmon resonance shifts, and places us in the clinically relevant range.

Absorption vs. Wavelength 0.8ml

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0.25

0.3

0.35

0.4

0.45

0.5

400 450 500 550 600 650 700 750 800

Wavelength (nm)

Tran

smis

sion

(AU

)

10mm Hg40mm Hg70mm Hg100mm Hg


Our experiments show nearly a 1% change in the absorption with only 100mm Hg of applied pressure with repeatable, reliable results.

We have also observed a saturation point in the absorption spectrum change, after which adding more particles to the nanocomposite diminishes the pressure sensitivity.

Percent Change in Absorption vs. Nanoparticle Concentration

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Particle Volume (AU)

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% Change

Pressure Sensor Results


Our experiments show a larger pressure sensitivity by measuring the absorption spectrum shape (slope) than can be seen by looking at the plasmon resonance shift.

This increased pressure sensitivity occurs in samples that have been prepared with less mixing, which we believe leads to this increased sensitivity through greater particle aggregation.

Nanopressure


Confocal images of our nanocomposites show an inhomogenous dispersion of nanoparticles, with many regions of nanoparticles clumped close together.

Figure: Confocal image of a pressure sensor illuminated at 488nm. Significant aggregation has occurred, but the particles have remained independently excitable near the original plasmon resonance.


SEM images of our nanocomposites also show large-scale clumping of nanoparticles.

Within these clumps we see that the nanoparticles are in clumps with intervening layers of PDMS polymer. This intervening layer of polymer serves to keep the particles separated by a few nanometers.

Figures: SEM micrographs of a a large region of the pressure sensor (top) and a single clump of nanoparticles (bottom)


As noted earlier, the smaller the interparticle gap, the larger the plasmon resonance shift given some change in this gap.

Thus the clumping of nanoparticles in our pressure sensors may be leading to increased pressure sensitivity, approaching clinically relevant pressures.


Pressure Sensor Applications For measurement, the pressure sensitive material can be placed on the end of fiber optic, then placed in the body compartment to measure the pressure.

Fiber optic pressure sensors could be made on even the smallest fibers, making the measurement of pressure a much less invasive diagnostic technique.

Figure: A 600 μm fiber optic coated with pressure sensitive material. These can be used to measure interstitial pressure or put into blood vessels to measure arterial pressures.


Pressure Sensor ApplicationsWe have also developed means of encapsulating nanoparticles in microspheres of sodium alginate.

Building micron-sized pressure sensors using this method could lead to an injectable pressure sensor providing real-time, in vivo measurement.

Figure: An 80 μm sodium alginate microsphere loaded with nanoparticles. The size of these spheres can be controlled by varying the extrusion parameters.


Extending to lower pressures


Ag0

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3 ~ 3.6 nm3 ~ 3.6 nm

Headto

Head


3.0 ~ 3.6 nm

Length of C16chain is ~ 1.8 nm.

Double chain layer

structures


Side by side


Shoulder by shoulder


Sensor Optical Response vs Gauge Pressure

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0 5 10 15 20 25 30 35 40 45 50

Pressure (mm Hg)

Op

tica

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ift

Extending to lower pressures


Conclusion

We have constructed pressure sensors based upon silver nanoparticles and simple polymer matrices.

These pressure sensors have demonstrated the sensitivity on the level necessary for clinical relevance.

Our sensors can easily be extended to catheter and injectable architectures for diagnosis.


Applications

Acute Compartment Sydrome is a life-threatening condition in which the interstitial tissue pressure of a body compartment becomes elevated, restricting blood flow. Diagnosis of this condition involves insertion of a large 18-gauge (1.3 mm) needle into the affected compartment to determine the internal pressure. Injectable nanosensors would be less invasive and more accurate than current techniques.

Ischemic necrosis of small and large intestine in young children can be generally diagnosed using catheter based pressure sensors

In biomechanical paradigms of metastasis, mechanical alterations of ECM and its cellular components are linked with the activation of integrins. This promotes mitogenic signaling through Erk as well as cell contractility through Rho. The study and monitoring of these processes requires micron resolution of pressures at the ECM-Cell interface.

Pressure monitoring is crucial for the success of wound treatment using Vacuum Assisted Therapies (VAC). Real time feedback is difficult to achieve using common manometer techniques


Further Thanks to:

Nicole Levy-Polyachenko PhD.Bill Wagner PhD.

Louis Argenta MD.Mike Morykwas PhD.

The Wound Center of Wake Forest UniversityThe Department of Orthopaedics Wake Forest University Baptist Medical Center

The School of Biomedical Engineering at Wake Forest University

This program was funded through:The Center for Nanotechnology and Molecular Materials


Thank You!

use of silver nanoparticles in medically-related pressure measurements. · 2018. 11. 6. ·...

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