Useful Properties:

1
Silicone Elastomers (crosslinked PDMS)

• Useful Properties
• Bioinert
• Oxidative resistance
• Oxygen permeability
• Soft/flexible (Tg PDMS -127 C)
• Lightly crosslinked ? elastomers

Transdermal drug delivery
2
Augmentation cosmetic Reconstructive follow
mastectomy (breast cancer)
In 2006 in USA 329,000 (augmentation) and
57,000 (reconstruction)
A 1998 federal law says any insurer that covers
mastectomy must cover reconstruction.
3
Silicone Breast Implants
1962 First woman receives silicone breast
implants PU or silicone shell silicone liquid
filler
1984-1991 137 individual lawsuits filed against
Dow Corning
1992 U.S. FDA announced silicone breast
implants ban only available in clinical studies
1993 12,359 individual lawsuits filed against
Dow Corning
1994 Mayo Clinics study published in the New
England Journal of Medicine no increased
risk of connective-tissue disease and other
disorders
1994 19,092 individual lawsuits filed against
Dow Corning
1995 The American College of Rheumatology
issues statement evidence is compelling
that implants did not cause systemic disease
1995 Dow Corning files for Chapter 11 bankruptcy
1997 The American Academy of Neurology
existing research shows no link between
silicone breast implants and neurological
disorders
1999 The Institute of Medicine silicone breast
implants do not cause any major diseases
2001 FDA approved clinical trial of new
cohesive silicone breast implants (Mentor,
McGhan)
2004 FDA defers decision to lift silicone
breast implant ban
2006 FDA lifts 14-year silicone breast implant
ban (18 years of age or older)
http//www.usatoday.com/news/health/2006-11-17-sil
icone_x.htm
4
COHESIVE SILICONE BREAST IMPLANTS

• Shell silicone elastomer (lightly crosslinked
  PDMS)
• Filler silicone gel
• - cohesive because it is very lightly
  crosslinked moves as a whole
• Advantages
• Wont leak if shell breaks
• Holds shape

Cohesive Saline
5
POLYMERS IN OPHTHALMICS

• Intraocular Lens replace opaque crystalline
  lens (cataract) of the eye

Inflexible IOL Tg 105 ?C Rigid Larger
incision needed
Foldable IOL Tg (PDMS) -125 ?C Flexible
PDMS PMMA
Silicone Acrylates
PMMA
6
POLYMERS IN OPHTHALMICS
2. Soft Contact Lenses placed on cornea to
correct vision
Hydrogels

• Poly(hydroxyethylmethacrylate) (PHEMA)
• HEMA monomer EGDMA crosslinker
• 40 wt is water
• insufficient O2 permeability
• Silicone-Acrylates
• PDMS HEMA
• 20-30 wt water
• silicone improves O2 permeability

7
STERILIZATION OF IMPLANTS
Sterile Determination of Sterility 1.
yes or no result Immerse into liquid culture
? if not sterile ? media becomes cloudy due to
microbial growth 2. Sterilization validation
studies - Used to determine sterility
assurance level SAL - SAL - SAL
accepted minimum _________________________
probability that an implant will
remain non-sterile.
8
STERILIZATION OF IMPLANTS

• Determination of SAL
• 1. Determine _________________________
• - of viable microorganisms on an implant
  BEFORE sterilization
• - measure on 10-30 samples
• - shake/sonicate/wash off microorganisms from
  implant ? into sterile fluid ? determine with
  standard techniques
• Do a _____________________________________________
  ____
• - determine microbial kill rate of sterilization
  process
• - plot of microorganisms remaining vs.
  exposure time to sterilization process

So, exposure time should be at least, x minutes
log microorganisms
-6
Minutes of exposure
x
9
STERILIZATION METHODS

• Considerations
• Does this technique damage the materials?
• Effect of over-exposure?
• Effect with under-exposure? Sterility?
• Place in barrier package ? sterilize ? package
  provides barrier to microorganisms until use

10
STERILIZATION METHODS

• Steam Sterilization / Autoclaving
• 1st method used to sterilize implants
• __________________________________________________
  _________
• 15-30 min after all surfaces reach 121 ?C
• Packaging must allow steam to penetrate
• - Tyvek (HDPE fibers bonded together)

11
Autoclavable Medical Packaging Tyvek
  Tyvek brand is produced by DuPont. It is a
family of tough durable sheet products of
high-density polyethylene fibers. The sheet is
formed first by spinning continuous strands of
very fine interconnected fibers (seven times
finer than human hair), and then bonding them
together with heat and pressure. Here is an image
of Tyvek magnified 200 times.    
12
STERILIZATION METHODS

• Steam Sterilization / Autoclaving

• Advantages
• __________________________________________________
  ____________
• Efficient, fast, simple
• No toxic residues
• Disadvantages
• __________________________________________________
  ____________
• If Tg lt 121 ?C, will deform
• If hydrophilic, will adsorb water
• If biodegradable, will decompose (polyesters,
  polyamides, polyanhydrides)
• PVC ? PVOH

• Radiation
• 60Co gamma rays
• Crosslinks UHMWPE (in vacuum) for improved wear
  resistance
• Leads to oxidative degradation of UHMWPE if done
  in air
• Advantages _____________________________________
  _____________
• Disadvantages __________________________________
  ______________
• ____________________________________________
  ____

13
STERILIZATION METHODS
3. Ethylene Oxide (EtO)

• - Ethylene oxide boils at 11 ?C
• Kills microorganisms by alkylating proteins and
  DNA
• Nearly half of all medical devices are sterilized
  by EtO

• Place on EtO-permeable packaging (Tyvek)
• Into EtO sterilization chamber
• Pull vacuum (remove air)
• Inject EtO gas EtO 600-1200 mg/L, T 30 -
  50?C, time 2-48 h
• Remove vacuum
• Air or nitrogen washes flush out EtO residues

Disadvantage ____________________________________
___
14
HOST RESPONSE TO AN IMPLANT
Here, the implant a sensor

• The reaction of a living system to the presence
  of a material
• Sometimes called the foreign body response or
  biofouling
• A protection mechanism
• Extent of response indicates level of
  biocompatibility

15
HOST RESPONSE TO AN IMPLANT - stages
16
HOST RESPONSE TO AN IMPLANT - stages

• Injury
• exudation occurs right after injury ? blood
  blood proteins escape from vasculature and go to
  injury/implant
• 2. Inflammation reaction of vascularized
  living tissue to injury
• Acute (days weeks) Neutrophils (a type of
  leukocyte or wbc)
• Chronic Monocytes (a type of wbc, phagocyte)
  which differentiate into macrophages (a type of
  wbc, phagocyte) upon leaving vasculature
• New blood vessels (neovascularization) and
  connective tissue form
• 3. Granulation Tissue
• - Highly vascularized tissue that replaces
  initial fibrin clot pink granular
• Neovascularization
• Macrophages and also fibroblasts (makes collagen)
  and FBCs (fused macrophages) show up
• 4. Foreign Body Reaction
• Consists of granulation tissue components, FBCs
• 5. Fibrosis and Fibrous Encapsulation
• -The final walling off of implant (isolates
  implant from local environment)
• - More dense than granulation tissue (fibroblasts
  have built it up)