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The biological response to implanted biomaterials and devices is controlled by their surface chemist

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Surface rearrangement must be prevented or inhibited ... immobilize bioactive agents or coatings with hydroxylated or amine rich surfaces ... – PowerPoint PPT presentation

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Title: The biological response to implanted biomaterials and devices is controlled by their surface chemist


1
Surface modification
  • The biological response to (implanted)
    biomaterials and devices is controlled by their
    surface chemistry and structure.
  • Surface modification allows to influence the
    bio-interaction while retaining the key physical
    properties.
  • Surface modification possible using
  • - Biological methods
  • Mechanical methods
  • Physicochemical methods

2
Surface modification
  • Overview of surface modification possibilities
  • Figure 1, page 202
  • General principles for surface modification
  • Thin interface layer
  • Sufficient delamination resistance
  • Surface rearrangement must be prevented or
    inhibited
  • Simple, scalable and consisting of a limited
    number of steps

3
Surface modification
  • Chemical surface reactions
  • Nonspecific chemical treatment results in a
    distribution of functional/reactive groups on the
    surface
  • Oxidative acid treatment of surface
  • Specific functional group exchange
  • Alkylation, silanization

4
Surface modification
  • Radiation grafting (nonspecific)
  • Three major grafting methods each with a
    different source
  • Ionizing radiation
  • UV radiation
  • High energy electron beams
  • Ionizing radiation used to break chemical bonds
    in material surface to generate free radicals or
    reactive species

5
Surface modification
  • Radiation grafting (nonspecific)
  • Reactive surface exposed to coating material
    which
  • reacts with surface species (free radical
    polymerization!) to create grafted surface layer
  • Grafted surface layers are thick (gt1 mm)
  • Chemical bonding results in sufficient adhesion

6
Surface modification
  • Plasma deposition and/or treatment (nonspecific)
  • What are plasmas?
  • Low-pressure plasmas are partially ionized gases
    and vapors, with substantial proportion of the
    constituent particles (molecules, molecular
    fragments, ions, free radicals) being in exited
    states. These components are able to react with
    each other and with surfaces.

7
Surface modification
  • Plasma deposition and/or treatment (nonspecific)
  • Characteristics of plasmas
  • Plasmas can be ignited and supported with
    electromagnetic fields. They typically emit in a
    wide spectrum, including optical range and UV.
    Their glow depends on the gas composition and
    pressure.
  • The low pressure (10-2 to 10 mbar) plasmas used
    for surface modification are mostly generated
    using a radio frequency glow discharge (RFGD).

8
Surface modification
9
Surface modification
10
Surface modification
  • Plasma treatment (nonspecific)

11
Surface modification
  • Plasma deposition and/or treatment (nonspecific)
  • The ions, molecules and atoms in electronically
    excited states, UV and light emissions and high
    kinetic energy particles activate and/or etch
    surfaces, induce polymerization of organic
    substances in the gas phase and/or on surfaces
    and lead to film building on the substrate
    surface.

12
Surface modification
  • Plasma deposition and/or treatment (nonspecific)
  • The plasmachemical reactions pathways and
    products differ from "conventional" chemistry.
  • Plasmas can induce chemical reactions with gases
    and surfaces which are inert under normal
    conditions.

13
Surface modification
  • Plasma deposition and/or treatment (nonspecific)

14
Surface modification
  • Advantages of plasma processes
  • Shape and size not very important (treatment of
    complex geometric shapes possible)
  • Coatings/surfaces are uniform and free of
    pinholes and voids.
  • Coatings/surfaces are sterile
  • Metals, polymers, semiconductors and ceramics may
    be treated
  • Excellent film adhesion
  • Unique chemical processes occur
  • Straightforward processing with mature technology

15
Surface modification
  • Disadvantages of plasma processes
  • Poorly defined chemistry
  • Scrambling of starting compound occurs
  • Coatings often not well defined
  • Expensive equipment
  • Contamination of ionizing gas/atmosphere can be
    problematic
  • Conclusion plasma processes are useful to
    create functional biomaterials. However, in many
    cases alternative methods are essential.

16
Surface modification
  • Specific chemical reactions to modify surfaces

17
Surface modification
  • Silanization (specific)
  • Si-O covalent bonds used to link or immobilize
    bioactive agents or coatings with hydroxylated or
    amine rich surfaces
  • Useful with silicon, silicones, ceramics (Al2O3),
    glasses and surface oxides of metals/alloys
  • Silane-hydroxyl bond subject to hydrolysis

18
Surface modification
  • Example
  • 1) H2CCH-Si-(OC2H5)3 3 H2O
  • H2CCH-Si-(OH)3 3 C2H5OH
  • 2) H2CCH-Si-(OH)3 HO
  • OH
  • H2CCH-Si-O H2O
  • OH

Surface of biomaterial
19
Surface modification
  • Ion beam implantation
  • Embedding of accelerated ions (at high energy) in
    surface zone of material
  • Mostly metals/alloys modified with C, N, B, Ir to
    increase hardness, wear resistance and corrosion
    resistance

20
Surface modification
  • Langmuir-Blodgett (LB) film deposition
  • Molecules with polar (head) and nonpolar
    (tail) regions (surfactants) are coated on a
    surface to develop well ordered multilayers

21
Surface modification
  • Self-assembled monolayers
  • Spontaneously formed highly ordered films
  • Involve exothermic absorption reactions and van
    der Waals forces
  • Ordered crystalline packing are obtained
  • More stable than LB

22
Surface modification
  • Other options
  • Surface modifying additives
  • Conversion coatings
  • Parylene coating
  • Laser methods
  • Patterning
  • Etc.
  • More examples of biomedical applications ? ZSO

23
Sources of Pictures and Text
http//www.abe.msstate.edu/classes/abe4523_6523/su
rfacemod.pdf http//www.igb.fhg.de/WWW/GF/GrenzflM
em/Grenzflaechen/en/PlasmaImpact.en.html http//jo
urnals.tubitak.gov.tr/chem/issues/kim-00-24-3/kim-
24-3-9-9907-11.pdf http//www.unige.ch/gap-b/proje
t/fatima/haemo/haemo.html http//
www.erc.arizona.edu http//www.novascan.com http/
/www.abo.fi/fak/mnf/fysik/mole/LB.htm
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