Silicone Gel Breast Implants

1
Silicone Gel Breast Implants

• Stanley Lee
• Kellen Mazzarella
• Jeremy Thompson
• Emily Trieu
• ME117
• 05/13/03

2
Overview

• Historical Origins
• Structural Analysis
• Manufacturing Protocols
• Regulatory Issues
• State of the Art

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Historical Origins

• 1890 paraffin wax injections
• 1920 fat transplants from abdomen, buttocks
• 1940 Japanese prostitutes use silicone shots
• 1950 polyvinyl sponge implants
• 1961 Cronin Gerow (UT) create first silicone
  implant w/ Dow Corning
• Dow Corning 360 medical grade silicone fill
• Thick silicone elastomer shell
• 1962 Timmie Jean Lindsey receives first silicone
  implant
• 1962-1964 clinical trials
• 1964 Dow Corning publicly markets implants

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Historical Origins

• 1973 2nd generation implants introduced
• Thin shells, thin gel
• 1985 3rd generation implants introduced
• Thick textured shell w/ barrier layer
• Current manufacturers
• INAMED Aesthetics (McGhan)
• Mentor Corporation
• Former manufacturers
• Dow Corning Corporation
• Medical Engineering Corporation
• Bioplasty Inc.
• Baxter Healthcare Corporation
• Porex Technologies
• Surgitek

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Evolution of Implant Design

• 1st Generation Implants
• 1963-1972
• Thick shell wall, viscous gel and Dacron patches
• capsular contracture lead to second generation

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Evolution of Implant Design

• 2nd Generation Implant
• Thin wall and less viscous gel
• Low tear strength
• Capsular contracture

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Evolution of Implant Design

• 3rd Generation Implant
• Stronger, thicker shell, more viscous gel and
  barrier layer
• Other gel implants
• 240 styles of breast implants manufactured

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Manufacturing Requirements

• Preclinical Data
• Materials selected for properties required for
  intended use Chemical Analysis
• Data on the effects of manufacturing process and
  possible reactions to device in an implantable
  state
• Chemical Analysis
• Analysis of the extractable and released
  chemicals
• Filler materials
• Saline-normal physiological sterile saline
• Silicone gel-provide composition of filler
  material, long-term stability data and
  accelerated aging

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Manufacturing Requirements

• Biological Aspects
• Toxicology and Pharmacokinetic studies
• Example-Shell
• Compatibility between filler and shell
• Effects of shell surface texture on surrounding
  tissues
• Integrity points tested for approriate resistance
  to failure
• Test for static rupture, fatigue rupture, static
  impact
• Mechanical Properties
• Cohesivity of Silicone Gel
• Rupture rate of shell
• Abrasion properties of shell

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Silicone Chemistry

• Silicones
• Broad class-thousands synthesized
• Base structure, polydimethylsiloxane
• R1 and R2 can be methyl, vinyl, amin, hydrogen or
  hydroxy groups
• Can fold into ring, where n3 to over 100

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Silicone Chemistry

• Silicone Gel
• Vary viscosity via crosslinking
• Peroxide based crosslinking agent ? platinum
  based
• Dow Silastic II trimethyl end-blocked dimethyl
  and methylvinyl polysiloxane containing trimethyl
  end-blocked dimethylvinyl as a diluent and
  crosslinked with dimethylhydrogen end-blocked
  dimethyl polysiloxane catalyzed with
  chloroplatinic acid and a siloxane polymer
  containing methyl and vinyl groups
• Elastomer Shell
• contains amorphous fumed silica as reinforcing
  agent
• mixed to form uncured silicone elastomer
• Barrier coating-diphenyl silicone copolymer,
  fluorosilicone copolymer

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Gel Structural Analysis

• 10-20 crosslinked silicone
• Silicone oil swells silicone shells
• Lowers shell tensile strength
• Increases bleeding

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Gel Structural Analysis

• Measures Complex Modulus
• GG1iG2
• G1(t0/?0)cos d
• elastic component
• G2(t0/?0)sin d
• viscous component
• t0 amplitude of shear stress
• ?0 amplidtude of shear strain

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Gel Structural Analysis

• Increased catalyst concentration increases the
  mechanical properties of the gel
• Loaded at strainstrainfailure

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Structural Analysis of the Shell

• Mechanical properties of silicone elastomer
• Minimum thickness (pressure vessel)
• Leak-before-break condition
• Abrasive Wear

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Mechanical Properties of Silicone Elastomer

• 6.2 MPa
• Elongation 600
• K1c 1
• Tear Strength 150 lb/in

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Minimum Shell Thickness

• Spherical pressure vessel
• 6.2 MPa
• P 150 KPa
• r 30mm
• t .35mm

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Leak Before Break Condition

• Ccgtt
• Hole due to injection or suture
• K1c1
• Cc.4mm
• t .35mm
• Leak before break condition is met

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Abrasive Wear

• Initiated By Fold Flaw
• Unfolded implants N 5,000,000 Cycles
• Folded Implants N 250,000 Cycles
• Abrasive debris often described as sand-like
• Actual failure mechanism is combination of
  fatigue stress, torsional stress, and abrasion

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Factor of Safety

• Calculations done with FDA minimum values
• Factor of safety from 1.2-1.4

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FDA Approval Process

• 1963 Dow Corning begins selling implants w/o
  regulation, safety data
• FDA does not have authority over medical devices
  yet
• May 1976 Medical Device Amendments gave FDA
  control over medical devices
• Implants can remain on market, safety data will
  be ask for later
• Jun. 1976 breast implants classified as class II
  device
• Jun. 1988 breast implants reclassfied as class
  III device following reports of complications
• Apr. 1991 FDA requires manufacturer PMAs by July
  9, 1991
• Jan. 1992 FDA recommends voluntary moratorium to
  await safety data
• Implants only allowed for FDA studies, not
  augmentation
• 1999 FDA finalizes the type of safety data
  wanted from companies
• Mar. 2000 approval of Mentor Corporation, McGhan
  Medical Corporation PMAs

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Biocompatibility Studies

• 1992 IEAG Department of Health, UK
• Animal studies show silicones do not affect
  antibody, immune, and resistance to infection
  responses
• No evidence of increased risk of connective
  tissue disease
• 1997 IRG Independent Review Group, UK
• No evidence of abnormal immune response from
  silicone exposure
• No link b/t breast implants and connective tissue
  disease in hosts or their children, need more
  data
• Silicone not toxic or poisonous, likely diseases
  caused by other factors
• 2000 IOM Department of Health and Human
  Services, US
• Lack evidence to establish silicone implants
  cause autoimmune disease
• Local complications such as rupture, pain,
  capsular contracture, disfigurement, infection
  lead to multiple surgeries and are the primary
  safety issue

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Failures Recalls

• 1984 jury finds Maria Sterns autoimmune disease
  to be caused by silicone implants, Dow Corning
  loses case and pays 2 million in damages
• 1991 a jury links Mariann Hopkins connective
  tissue disease to ruptured implants, Dow Corning
  loses case and pays 7.3 million in damages
• 1994 largest class action law suit in history
  against Dow Corning, Medical Engineering
  Corporation, Baxter
• set amounts of damages awarded to women with
  certain medical conditions
• RECALLS
• 1989 polyurethane coated implants shown to
  degrade into cancer causing agents and taken off
  market
• 1999 McGhans Trilucent soy bean filled implants
  taken off market, deterioration of filling may
  cause cancer and affect unborn babies

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On the Horizon

• Return to Old Protocols
• Use textured shell
• Subglandularly
• Cohesive, formed gel
• Place under fat and pectoral fassica
• Now fluid flow
• Maintain shape
• Inamed Corp.

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One the Horizon

• COX-2 Inhibitor Shell
• Help prevent capsular contraction
• Fibrilar encapsulation doesnt adhere to
  surrounding tissue
• Increased myofibroblast concentration
• COX-2 stimulated by proinflamatory cytokines
• TNF-alpha
• IL-1
• Add COX-2 inhibitor to prevent capsular
  contraction

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Questions