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Medical Adhesives and Sealants

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Title: Medical Adhesives and Sealants


1
Medical Adhesives and Sealants
2
Adhesion
Definition The state at which two surfaces are
held together by interfacial forces, which may
consist of all known chemical attractive forces,
as well as mechanical interlocking action or both.
3
Adhesive
  • A substance capable of holding materials together
    in a functional manner by surface attachment
    (performance). A general term that includes
    cement, glue, mucilage and paste.

4
Sealant
  • A material applied to a joint in paste or liquid
    form that hardens or cures in place, forming a
    barrier against gas or liquid entry.

5
Adhesives and Sealants-Biomaterials?
  • Join components of medical devices-Mechanical
    fastening
  • Prevent corrosion
  • Resist fatigue
  • Fill space smooth contours-joining prosthesis
    to bone
  • Wound sealing closure

6
Adhesive Materials can be classified in a number
of ways
  • Natural or synthetic polymer base
  • Thermoplastic or thermosets
  • Physical form (one or multiple component, films,
    etc)
  • Functional type (structural, hot melt, pressure
    sensitive
  • Chemical families (epoxy, silicone, etc.)

7
General Considerations in the Application of
Adhesive Bonding
  • When applied adhesives have to 'wet' the surface
  • They need to be mobile and flow into all the tiny
    nooks and crannies of the substrate
  • If the adhesive does not wet the substrate well,
    poor adhesion is likely to be a result
  • Once good wetting takes place, an adhesive needs
    to become solid and not flow at all. This is
    called setting or curing (polymerization) and,
  • Positional indication (imaging).

8
Adhesive Joint
  • Breaking strength is determined by
  • Mechanical properties of the materials of the
    joint
  • The extent of the interfacial contact (number,
    extent, type and distribution of voids)
  • Presence of internal stresses
  • The joint geometry and,
  • The details of mechanical loading.

9
Adhesives are Polymers
  • Thermoplastics
  • Thermosets
  • Available as solids, liquids and pastes and most
    can be supported by films of various thickness.

10
Adhesives
  • Acrylics
  • Epoxies
  • Polyurethanes
  • Silicones

11
Bonding Mechanisms
  • Mechanical Interlocking
  • Formation of covalent bonds across the interface
  • Electrostatic Attraction-dominant
  • Forces are not significant beyond 0.5
    nm-therefore contact is necessary

12
Surface Treatment
  • No treatment (low cost poor reproducibility)
  • Solvent wiping
  • Vapor degreasing
  • Mechanical abrasion
  • Plasma treatment
  • Etching
  • Chemical deposition-primers, organosilanes

13
Modes of Failure
A uniform stress pattern in an adhesive joint is
seldom produced by the application of external
force.
  • Structural failure
  • Adhesive failure
  • Cohesive failure

14
Urethanes
  • Urethane polymerization-diisocyanate and a diol
    or diamine
  • Two part system- mix, spread and cure
  • Flexible joint and sealing agent.

15
Poly (methyl methacrylate) PMMA
R-Group
Bone Cement
16
Selection of the starting monomers
  • C4-C12-alkyl acrylates supply the initial
    adhesion owing to the low glass transition
    temperature (Tg).

17
Cure Profile of Condensation versus Addition
Polymerization
Addition polymer
Condensation polymer
Degree of Cure -----gt
Time
18
  • Cyanoacrylates
  • In 1959, a variety of cyanoacrylate adhesives
    were developed, some types of which are now used
    for surgical purposes in US, Canada, and Europe.
    These glues polymerize on contact with basic
    substances such as water or blood to form a
    strong bond.
  • The first glue developed was methyl
    cyanoacrylate, which was studied extensively for
    medical applications and was rejected due to its
    potential tissue toxicity such as inflammation or
    local foreign body reactions. Methyl alcohol has
    a short molecular chain which contributes to
    these complications.
  • By changing the type of alcohol in the compound
    to one with a longer molecular chain, the tissue
    toxicity is much reduced. All the medical grade
    tissue adhesives currently available for human
    use contain butyl-esters.

19
  • Cyanoacrylate adhesives were first used on
    wounded soldiers in Vietnam a quick spray over
    the wounds stopped bleeding and bought time until
    conventional surgery could be performed.
  • Midwives found cyanoacrylate glue and medical
    cyanoacrylate glues useful as the tissue
    adhesives. Some even used Super Glue
    successfully in lieu of suture to close the
    perineum.
  • Surgeons have used household cyanoacrylate
    adhesive to apply sutureless pericardial patches
    that stopped bleeding in critically injured
    patients with torn or ruptured myocardium.
    Cyanoacrylates are also used in repairing corneas
    and retinas and as synthetic skin in treating
    severe burns.

20
Methyl 2- cyanopropanoate
R-Group
Methyl ?-cyanoacrylate monomer polymerizes in the
presence of trace amounts of almost any
electron-donor compound (the initiator) by
anionic vinyl polymerization, examples include
water, alcohols, amines, carboxylate ions, and
electron rich olefins.
21
  • Medical grade products currently available
    contain either butyl, isobutyl or octyl esters.
    They are bacteriostatic and painless to apply,
    break down harmlessly in tissue by hydrolysis and
    are essentially inert once dry.
  • Butyl products are rigid when dry, but provide a
    strong bond octyl products are more flexible
    when dry, but produce a weaker bond.
  • Histoacryl Blue (n-butyl cyanoacrylate) has been
    used extensively for a variety of surgical
    applications including middle ear surgery, bone
    and cartilage grafts, repair of cerebrospinal
    fluid leaks, and skin closure -- adhesives appear
    are basically safe.
  • DMSO (dimethyl sulfoxide) or acetone serve as
    removers.

22
The Market
  • The global medical and surgical sealant market is
    542 million (2001) and growing rapidly (19
    annually), driven particularly in the U.S.
  • Adhesives and sealants are a critical component
    of medical devices.
  • Seven and a half million people receive medical
    device implants annually.
  • As medical devices become smaller and more
    complex, greater demands are being made on the
    materials and components used in them.
  • Medical devices are being exported from the U.S.
    to foreign countries at an increasing rate.
  • Devices intended for the growing markets of South
    America and the Pacific Rim must be engineered to
    be cheaper and more rugged than in the US.

23
Considerations
  • One mitigating factor when it comes to the
    advancement of new technologies in the adhesives
    market is the speed with which the adhesive can
    be applied on the production line and how long it
    takes before the finished product can be placed
    on the market.
  • This is an area where UV-curable adhesives have
    made the strongest technological advances of any
    of the newer technologies currently on the market.

24
Light Cure Systems
  • Designed for high speed cure on demand medical
    product assembly.
  • Solvent free
  • Wide range of viscosities designed for automated
    dispensing

25
Light Cure Adhesives
  • consist essentially of low or medium molecular
    weight resins (called oligomers), monofunctional
    or multifunctional monomers, photoinitiators
    and/or photosensitisers
  • wavelengths of 365-250nm.
  • typically 5-15 seconds at 80-100 mW/cm2 is
    sufficient for curing adhesive
  • visible light curing materials (e.g. resins used
    in dental restoration or for bonding and sealing
    photo-optic devices) can be cured with blue light
    (wavelength 470nm).

26
Typical Applications
  • Bonding latex balloon onto PVC lumen in
    catheters.
  • Bonding high pressure latex balloons onto
    urethane lumens in high pressure catheters.
  • Bonding balloon to multi-lumen tubes in
    angioplasty, thermo dilution, foley and high
    pressure catheters.
  • Bond needle to tubing in winged infusion sets.

27
Flexible Adhesive Applications
  • Bonding/sealing tracheal tubes made of silicone
    rubber.
  • Bonding/sealing extruded silicone parts,
    colostomy, ileostomy, urostomy bags and
    appliances.
  • Bonding/sealing the balloon to the tracheal tube.
  • Bonding/sealing the cuff and tube assemblies in
    endotracheal, tracheotomy, gastrostomy devices,
    foley catheters and other fabricated silicone
    parts.
  • Sealing of inflators.

28
Pressure-Sensitive Adhesives
  • Arcylics on PET
  • Labels-many medical devices require a label that
    can be printed after the adhesive has been
    applied and/or can be written on after
    application to the device.
  • Adhesive tapes for attaching equipment drapes in
    sterile environment applications.
  • Lidding-effective protective barrier against
    contamination for storage or shipping
  • EKG electrode bonding

29
Surgical Drapes
30
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31
Benefits of Adhesives
  • Joins dissimilar materials
  • Even stress distribution
  • Fills large gaps
  • Seals and bonds
  • Easily automated
  • Aesthetically acceptable

32
Limitations of Adhesives
  • Requires cure
  • Requires fixture time
  • Can be messy
  • Requires chemicals in plant
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