PlasmaBased Processes and Potential Applications to Biomaterials

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Plasma-Based Processes andPotential Applications
to Biomaterials

• Andranik Sarkissian, Ph.D., P.Phys.MBA

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Outline

• Objectives
• Introduction to Fundamental Concepts in Plasma
  Physics
• Various Plasma Sources
• Interaction of Plasma-Materials
• Applications to Surface Engineering
• Examples

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Objectives

• To provide an overview of the basic concepts in
  plasma physics
• To describe how these concepts help us to design
  the necessary tools that find applications in
  Surface Engineering
• To describe how these tools can be used to modify
  the surface properties of materials

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Introduction What is a Plasma

• States of Matter (Ancient View)
• Earth, Water, Wind, Fire
• States of Matter (Modern View)
• Solid, Liquid, Gas, Plasma

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What is a Plasma

• Neutral Atoms or Molecules
• Electrons bonded to the nucleus
• Charged Atoms or Molecules
• Electron(s) detached from nucleus (ionization)
• Requires additional supply of Energy
• Electron attached to a neutral (negative ions)

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Introduction Plasma Production

• Energy Transfer often involves EM field
• Accelerating electrons transfer energy to neutral
  atoms and molecules via collisions
• DC Field (0 Hz)
• AC Field (100 Hz)
• RF Field (13.6MHz, 27 MHz)
• Microwave (300MHz-10 GHz)
• A e -gt A e e A e -gt A e
• A2 e -gt A A e e A2 e -gt A A e e

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Charged Particle Motion in Electric and Magnetic
Fields

• In an electric field E force on particle with
  charge q is F qE
• In a uniform magnetic field B the force on a
  charged particle moving with a velocity V is F
  qVxB

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Motion in Magnetic Fields

• Cyclotron Frequency ?c eB/m
• Gyro radius rg ?c V gt
• rg V / ?c
• 10 eV electron in a 100G field has a gyration
  radius of 1mm.

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Charged Particle Motion in Electric and Magnetic
Fields

• In a crossed Electric and Magnetic field the
  Force on the particle is F q.E VxB
• Drift motion for the charged particles with Vd
  E/B

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Collisions Mean Free Path

• Mean Free Path between Collisions ? 1 /
  (Nst),
• st is total collision cross section st Ssi
• N is the gas particle density

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Collisions

• Collision Frequencies in Plasma
• ? ve.t gt ?k Nsve where ve is the average
  electron speed
• Gas phase Reaction Rate R ne?k
• Maxwellian Energy Distribution
• ve,, ?k , R, can be calculated
• Typical Collision Frequencies
• ?ee 3.10-5 ne /Te3/2 ?ei 1.510-5
  ne /Te3/2

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Mobility

• The changes in drift velocity of a charged
  particle in response to a change in an applied
  electric field is defined as charged particle
  mobility VdµiE
• An important consequence of different mobility
  for electrons and ions in a rapidly changing
  field is the application of RF-BIASING
  scheme

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Collective Behavior

• Plasmas under go collective behavior unlike non
  ionized gases.
• A plasma (composed of charged particles) is
  electrically neutral over a volume a ?D3 where
  Debye Shielding Distance
• ?D Const.(Te / ne)1/2, Const (e0/e2)
• ?D 740.(Te (eV)/ ne)1/2 cm,
• Plasma Frequency ?c ?D / Ve
• In a Chamber d50 cm, at 1 Torr (3.2x 1016
  cm-3), Te 1 eV, ne 1010 cm-3 gt ?D 74 µm
  
• Te 10 eV, ne 103 cm-3 gt ?D 74 cm Can we
  speak of Plasma in this case?

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Plasma Sheath

• Plasma Sheath
• Random Flux of Particles to adjacent wall
  G(1/4)N.v
• Charge separation due to difference in electron
  and ion fluxes gt Electric Field
• The region where E field is established is call
  Plasma Sheath

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Non-equilibrium Plasma

• Energy Gain From Field Wf F. ? eE ?
• Force on a charged particle F q.E eE
• Loss of electron Energy per collision
• ?W(2me/mH)(We - WH) Wf
• (We - WH) 1/2 (me/mH)(eE/Nsel)
• e.g. 1 Torr gas pressure and eE 1eV/cm
• (We - WH) 1000 eV
• Te gt Tigt Tg 10eV gt 0.5eV gt 0.05eV
• Low pressure discharges are not in a
  thermodynamic equilibrium state

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Various types of Plasma Sources

• DC Discharges
• Without Magnetic Confinement
• Discharge Tubes
• Parallel Plate
• Hollow Cathode

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Various types of Plasma Sources

• With Magnetic Confinement
• Magnetron (variety)
• PIG Discharges

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Various types of Plasma Sources

• RF Discharges
• Capacitively Coupled
• Inductively Coupled

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Various types of Plasma Sources
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Various types of Plasma Sources

• Microwave Discharge
• Remote Plasma
• Microwave Cavity

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Various types of Plasma Sources

• Microwave Discharge
• Electron Cyclotron Resonance (ECR)
• The condition when electron cyclotron frequency,
  ?eeB/me , is the same as the frequency of the
  electric field oscillations is called ECR. The
  result is that electrons gain energy from the
  field constantly.
• The resonance condition for electrons at 2.45 GHz
  corresponds to B 875 Gauss

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Various types of Plasma Sources

• Plasma Torches
• DC
• RF
• Microwave

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How Biomaterials Field Benefits from Plasma
Technology

• The Non-Equilibrium State of Plasma Allows
  Development of New Material Coatings Not
  available by Conventional Means
• Charged particles Can Be Manipulated by External
  Fields in Order to Impart a predermined energy on
  the Material surface thus influencing the film
  Characteristics
• Higher kinetic energy of impinging particles on
  the surface allows reducing the process
  temperature

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Advantages of Plasma Surface Engineering

• Most Medical Prosthesis (as well as many other
  high tech components) require surface properties
  that differ from bulk properties
• Plasma Technology allows us to control the
  material structure on atomic scale (monolayer)

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Disadvantages of Plasma Surface Engineering

• Slow
• Expensive

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Plasma-Based Processes

• Implantation (1)
• Sputtering(2)
• Etching (3)
• Deposition
• Physical (4)
• Chemical (5,6)
• Others
• Arc evaporation
• e-beam

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Ion Implantation (conventional)

• Plasma Created
• Ions extracted from plasma
• Ions accelerated to high energy
• Ions Implanted
• non selective

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Ion Implantation (conventional)

• Plasma Created
• Ions extracted from plasma
• Ions accelerated to high energy
• Ions Mass Separated Magnetically
• Selected Ions Implanted

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Ion Implantation (Plasma-Based)

• Plasma Created
• Object Immersed in Plasma
• Object Biased to Negative Voltage
• Electrons repelled
• Ions accelerated and interact with object

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Applications of Ion Implantation

• Metal parts on heart valves are ion implanted by
  carbon to make them biocompatible
• Radioisotops are implanted in prosthesis for
  localized radiotherapy

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Sputtering

• Ion Beam Assisted
• Plasma-Based Sputtering (immersion)

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Plasma-Based Deposition

• Physical Vapor Deposition
• Sputter Deposition
• e-beam deposition
• Plasma Enhanced Chemical Vapor Deposition
• Deposition by Plasma Spray
• Deposition by Laser Ablation

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Sputter Deposition

• Ion Plating
• Ion Beam Assisted Deposition
• Planar Diode
• DC
• RF
• Triode Discharge

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Sputter-Deposition

• Magnetrons
• DC
• RF

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Applications of Sputter Deposition

• Sputter deposition can be used for coating
  medical implants. It allows insulating films,
  such as calcium phosphate, to be deposited
  uniformly over large areas. The coating is
  relatively dense, adheres well to the substrate,
  and closely resembles that of the object.
  Sputtering can also coat materials that are
  sensitive to heat.
• Example of rf magnetron sputtering deposited thin
  ( 1µm) films of hydroxyapatite onto titanium.

A cross-sectional view of an in vivo
calcium-phosphate-coated implant nine weeks after
it was put in place. The pink areas show natural
bone, while the black area is the implant
(magnification x40).
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PECVD

• Plasma Produces Significant Radicals
• Allows deposition at lower temperatures
• Allows deposition of new materials
• All Types of Plasma sources can be used for
  applications to PECVD
• Lower frequency sources gt higher ion energy
• Higher frequency sourcesgt stable discharge

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Other Deposition Techniques

• Cathodic Arc Discharge
• Arc is a self sustained current channel
• Laser Ablation
• Plasma Spray

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Applications of Plasma Spray

• Plasma spray of bioceramics is a mature
  technology
• Plasma-Assisted coatings for reduced friction and
  wear

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Plasma Polymerization

• Plasma polymerization is a procedure, in which
  gaseous monomers, stimulated through a plasma
  condense on substrates, as high cross-linked
  layers.
• Condition for this process is the presence of
  chain-producing atoms, such as carbon, silicium
  or sulfur, in the working gas.
• Monomer molecules in plasma fragment into
  reactive components resulting in cross-linked and
  disordered structures

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Plasma-Material InteractionsPolymers

• Three Ways To Modify Surface of Polymers by
  Plasma (1)
• Treatment of Functional Groups gt Alter Chemical
  Reactivity of the Surface gt Surface properties
  Change but Bulk Remains the same
• Hydrophobicity or Hydrophilicity
• Decrease or Increase Capillary flow
• Cleaning, prior to adhesive bonding,
• catheters, Dialysis Pump Parts, Syringe
  Components, blood bags, etc
• Sterilizing, etc

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Plasma-Material InteractionsPolymers

• Three Ways To Modify Surface of Polymers by
  Plasma (2)
• Plasma Induced Grafting by Interaction of noble
  gas ions (Ar or He) with the Surface gt New Free
  Radical Sites gt Reaction with other monomers gt
  Surfaces with Special Properties
• Low friction film can be grafted to polyethylene
  catheters by exposing them to pure Ar plasma
  initially, and then to CH4, CH4/CF4, or H2/CF4
  plasmas for film deposition.
• Cleaning time / Deposition time (1- 2 min /
  30-60 min)

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Plasma-Material InteractionsPolymers

• Three Ways To Modify Surface of Polymers by
  Plasma (3)
• Plasma Deposition
• In plasma deposition, a thin polymer coating is
  formed at the substrate surface through
  polymerization of the process gas. Depending on
  the selection of the gas and process parameters,
  these thin coatings can be deposited with various
  properties or physical characteristics. Coatings
  produced in this manner through plasma deposition
  exhibit different properties than films derived
  from conventional polymerization, including a
  high degree of cross-linking and extremely strong
  adherence to the substrate.

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Applications of Plasma-Polymer Interactions

• ADHESION PROMOTION
• Many polymers have a low to medium surface
  energyexamples include polypropylene,
  polyethylene and Teflon.
• Difficult to effectively apply adhesives or
  coatings.
• Using oxygen plasma increase hydrophilicity gt
  Improve adhesive bonding
• For example, plasma processing can increase the
  surface energy of polypropylene from 29 to 72
  dynes/cm
• Medical applications include surface preparation
  for adhesive bonding of catheters and balloon
  catheters, dialysis filters, and other
  components, and bonding needles to syringe hubs.

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Applications of Plasma-Polymer Interactions

• HYDROPHILIC PROPERTIES
• A specially developed plasma activation process
  can be used to make a substrate surface
  hydrophilic. This permanently hydrophilic
  character can impart to woven or nonwoven
  textiles the capability to be used as blood
  filters or filtering membranes for various
  applications, including microfiltration
  components for dialysis filter systems.

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Applications of Plasma-Polymer Interactions

• BIOCOMPATIBILITY
• Plasma activation of surfaces to prepare them for
  cell growth or protein bonding is another
  important application.
• Examples of in vitro uses of plasma treatment
  include preparation of petri dishes and
  microtiter plates for laboratory experiments or
  drug-production purposes.
• Examples of in vivo uses includes use of plasma
  to enhance the biocompatibility of implants by
  treating the surface of a device to increase the
  adherence of a hemocompatible coating. Among the
  applications in this domain are vascular grafts,
  lenses, and drug-delivery implants. When
  required, surfaces can also be modified to
  decrease the bonding of proteins.

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Applications of Plasma-Polymer Interactions

• BARRIER COATINGS
• Plasma modification can be used to deposit thin,
  dense barrier coatings that have the effect of
  decreasing the permeability of plastic parts to
  alcohol or other liquids or vapors.
• For example, plasma treatment of high-density
  polyethylene can decrease the material's
  permeability to alcohol by a factor of 10.