Use of silver nanoparticles in medically-related pressure measurements.

Transcription

1 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

2 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.

3 Pressure measurements in Orthopaedics Is compartment syndrome a big deal?? You bet! Mary Decker Olympic distance runner Shin Splints

4 Pressure measurements in Orthopaedics Untreated compartment syndrome Necrosis of muscle Resection amputation

5 Pressure measurements in Orthopaedics Trauma and Compartment Syndrome

6 Pressure measurements in Orthopaedics Trauma and Compartment Syndrome Inflammation Swelling Occlusion Ischemia Tissue loss

7 Compartment syndrome Appropriate treatment Relieves pressure Avoids necrosis/amputation Knowledge of pressure is essential

8 Compartment syndrome Pressure measurements are vital 18 ga (1.3 mm)

9 Compartment syndrome Pressure measurements are vital Is there a way to make these measurements with less trauma? More accuracy?

10 Collaboration between Wake Forest University Health sciences and Wake Forest University Nanotech

11 Why do we need small Pressure Sensors? The Plasmon Ruler nanotorr: a novel Pressure Sensor Calibration and initial data

12 What we need 1) 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 based 4) No hysteresis. 5) 2 to 5 mmhg resolution. 6) Less than 2% drift of static pressure measures over 24 hours. 7) Non saturable 8) Throw away transducers / simple to manufacture 9) Sterilizable 10) Simple to use a TALL order to be sure

13 Take 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. A Concept 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. If the bulk modulus of the polymer is small, then small pressures will push the nanoparticles closer together B S P S = 0 Can this be made?

14 Surface Plasmons excitations that interact. These interactions are a function of distance. These excitations are responsible for the absorption and color of metal nanoparticles Incoming electromagnetic wave E φ φ out out = E 0 _ p r cosθ + 4πε ε ε ε m = E0 cosθ + E0a ε + 2ε m 0 3 r 3 m cosθ 2 r The incoming wave results in an oscillating charged dipole. These oscillations are quantized and known as plasmons.

15 Surface Plasmons Different diameters give different absorptions (colors) 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). Jensen,Kelly,Lazarides,Schatz, Electrodynamics of noble metal nanoparticles and nanoparticle clusters. J. Cluster Sci. Vol. 10, No. 2, 1999

16 Surface Plasmon Interactions Bringing another particle close to the first causes an interaction between the plasmons of the two particles. d This interaction is dependent on the distance between the particles, and results in a change in the absorption characteristics of both particles.

17 Surface Plasmon Interactions The 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.

18 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. Simulated and experimental resonance shifts for 88nm gold nanoparticles, and the derived plasmon ruler equation: On the universal scaling behavior of the distance Decay of plasmon coupling in metalnanoparticle pairs: A plasmon ruler equation. Jain, Huang, El-Sayed Nano Letters 2007: Vol.7 No.7 pp

19 Gold: n = i, at λ = 532 nm, d=4r 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 = i, at λ = 532 nm, d=2.4r

20 Particles in the nanospheres are held apart by surfactants around them

21 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. Absorbance (a.u.) (a) (b) (c) (f) (g) (d) (e) (a) Ag Seeds (b) 2.0ml (c) 1.0ml (d) 0.5ml (e) 0.25ml (f) 0.125ml (g) 0.06ml Absorbance (a.u.) nm 350nm 422nm 485nm Nanodisks Wavelength (nm) Wavelength (nm) The Optical Signatures of different diameter particles are strikingly different. spectra are shown here. UV-Vis absorption

22 NANODISK FORMATION AND TRANSFORMATION 5 min Absorbance h 57 h 11 h 4 h 1 h 30 min 10 min 5 min before aging 0 min Wavelength (nm) Aging 4 h at 40 o C 57 h

23 4 hours 57 hours 40 o C

24 TEM OF TRIANGLES AND DISKS Truncated triangular nanoplates Silver nanodisks

25 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.

26 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.

27 Resonance Shifts in Pressure Sensors % Absorption Absorption Spectra Shift with Applied Pressure of PDMS Loaded with Silver Nanoparticles Wavelength (nm) Uncompressed Absorption Spectra Compressed 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.

28 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.

29 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.

30 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.

31 PDMS Compression Test (August 17, 2007) Slope = Absorption (%) 0.65 Slope = 42 Uncompressed Compressed Wavelength (nm) 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.

32 Absorption vs. Wavelength 0.8ml Transmission (AU) mm Hg 40mm Hg 70mm Hg 100mm Hg Wavelength (nm) 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.

33 Pressure Sensor Results Percent Change in Absorption vs. Nanoparticle Concentration Our experiments show nearly a 1% change in the absorption with only 100mm Hg of applied pressure with repeatable, reliable results. Percent Change in Absorption Particle Volume (AU) % Change We have also observed a saturation point in the absorption spectrum change, after which adding more particles to the nanocomposite diminishes the pressure sensitivity.

34 Nanopressure 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.

35 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.

36 SEM images of our nanocomposites also show large-scale clumping of nanoparticles. Figures: SEM micrographs of a a large region of the pressure sensor (top) and a single clump of nanoparticles (bottom) 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.

37 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.

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

39 Pressure Sensor Applications We have also developed means of encapsulating nanoparticles in microspheres of sodium alginate. Figure: An 80 μm sodium alginate microsphere loaded with nanoparticles. The size of these spheres can be controlled by varying the extrusion parameters. Building micron-sized pressure sensors using this method could lead to an injectable pressure sensor providing real-time, in vivo measurement.

40 Extending to lower pressures

41 Head to Head Ag 0 Ag 0 Ag 0 Ag 0 Ag 0 Ag 0 Ag 0 Ag 0 Ag 0 Ag 0 Ag 0 Ag 0 Ag 0 Ag 0 Ag 0 Ag 0 Ag 0 Ag 0 Ag 0 Ag 0 Ag 0 Ag 0 Ag 0 Ag 0 Ag 0 Ag 0 Ag 0 Ag 0 Ag 0 Ag 0 Ag 0 Ag 0 Ag 0 Ag 0 Ag 0 Ag 0 Ag 0 Ag 0 Ag 0 Ag 0 Ag 0 Ag 0 3 ~ 3.6 nm 3 ~ 3.6 nm

42 Length of C 16 chain is ~ 1.8 nm. 3.0 ~ 3.6 nm Double chain layer structures

43 Side by side

44 Shoulder by shoulder

45

46 Extending to lower pressures Sensor Optical Response vs Gauge Pressure Optical Signal Shift 1.40% 1.20% 1.00% 0.80% 0.60% 0.40% 0.20% 0.00% Pressure (mm Hg)

47 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.

48 Applications 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 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. Acute Compartment Sydrome is a lifethreatening 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

49 Further Thanks to: Nicole Levy-Polyachenko PhD. Bill Wagner PhD. Louis Argenta MD. Mike Morykwas PhD. The Wound Center of Wake Forest University The 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

50 Thank You!