BioEME C117 Structural Aspects of Biomaterials

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Structural Aspects of Biomaterials

BioE/ME C117 Structural Aspects of
Biomaterials Course Overview Professor Lisa A.
Pruitt, Ph.D. Associate Dean of Virtual Learning
and Outreach Education Chancellor's Professor of
Mechanical Engineering and Bioengineering
Adjunct Professor of Orthopaedic Surgery, UCSF
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Class Structure

• CLASS Tu/Th 1230-2pm 203 McLaughlin Hall
• http//www.me.berkeley.edu/ME117
• http//webcast.berkeley.edu
• Discussion Mondays, 203 Mclaughlin. Mechanics
  and design will be taught in discussion.
• You are responsible for all material presented in
  discussion.
• Office Hrs (Prof. Lisa Pruitt)Tuesdays 3-430 or
  by appointment,5134 EH, lpruitt_at_me
• Teaching Assistants Arun Chawan, Jevan
  Furmanski, Shikha Gupta, Sheryl Kane,
• and Cheng Li (office hrs TBA)
• Course components HW (25), EXAMS, April 11/13
  (25), TERM PROJECT (50)
• No late homework excepted. All HW is to be
  prepared professionally (typed). Assignments will
  be marked down for grammatical errors.
• This year our class is webcast. Please use
  microphones when asking questions.
• Reader CopyWorld

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Course Goals

• Assessment of structure and mechanical functions
  of load bearing tissues and their replacements.
• Examination of biocompatibility of biomaterials
  and host response to structural implants.
• Quantitative treatment of biomechanical issues
  and constitutive relationships of tissues and
  their replacements.
• Material selection for load bearing applications
  including orthopedics, dentistry, cardiology and
  reconstructive surgery.
• Mechanical design for longevity of devices
• Understanding of legal and ethical aspects of
  medical devices.

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Course topics

• Overview of medical devices, FDA regulatory
  issues, biocompatibility and sterilization
  technology
• Biomechanical properties isotropy/anisotropy,
  stiffness,
• bending stresses, contact stresses,
  multiaxial loading,
• plasticity, fatigue, fracture, wear,
  corrosion, design issues.
• Orthopedics, Dental, Cardiovascular, and Soft
  Tissue Reconstruction. Case studies.

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Orthopedics

• ORTHOPEDICS TISSUES AND BIOMATERIALS Structure
  and function of
• orthopedic tissues. Bone, cartilage,
  intervertebral discs. Total joint replacements,
• Spinal implants, Fracture Fixation. Mechanisms
  for damage and disease.
• Clinical treatments.
• Case Studies
• 1. Sulzer recall-good manufacturing practice,
  legal and ethical issues associated with device
  recalls
• 2. Premature failure in metal prostheses due to
  corrosion
• 3. Implant failures due to oxidation and aging of
  the polymer component
• 4. Stress shielding/ femoral stem
  designstresses, bone resorption, evolution of
  design and materials
• 5. Clinical case study (Dr. Mike Ries, Orthopedic
  Surgery, UCSF, Feb 21)- surgical procedures,
  osteolysis
• 6. Evolution of materials (UHMWPE)- the effects
  of microstructural changes on fatigue, fracture,
  wear
• 7. Spinal Implants (Dr. Andy Kohm, Kyphon).
  Design/ clinical aspects.

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Dentistry

• DENTAL TISSUES AND BIOMATERIALS
• Structure and function of dental tissues. Dental
  materials/restorative materials
• Progression of disease. Clinical treatments.
• Case Studies
• 1. Fracture in mineralized tissues (Rob Ritchie,
  March 9)
• 2. Implant design/materials

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Cardiology

• CARDIOVASCULAR TISSUES AND BIOMATERIALS
  Structure and function of vascular tissue.
  Etiology of disease. Clinical treatments.
  Vascular devices. Design issues.
• Case Studies
• 1. Heart Valves, materials, design philosophies,
  clinical
• 2. Stents Fatigue and Fracture (Scott Robertson,
  LBL, April 4th)
• 3. Stent design (Dr. Alan Pelton, Nitinol Device
  Company, April 6th)

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Soft Tissue

• SOFT TISSUE Structural Properties, wound
  healing, stability, biofixation. Design issues.
• Case Studies
• 1. Dow- Corning Breast implant case
• 2. Soft implants facial, occular

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Biomaterials

• Classifications
• Biocompatibility
• Applications

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Biomaterials and implants

• Replace component of living being
• Restore Function
• Harmonious interaction with host
• Biocompatibility
• Long-term structural integrity

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Structural biological materials

• Hard Tissues Bone, enamel, dentin
• Soft Tissues Cartilage, tendon, ligament,
  vitreous humor,vasculature,skin, organs
• Fluids Blood, synovial fluid
• Problems when used as an implant material
  Infection, resorption, inflammation, rejection

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Synthetic Biomaterial Classes

• METALS Co-Cr alloys, Stainless steels, Gold,
  Titanium alloys, Vitallium, Nitinol (shape memory
  alloys).
• Uses orthopedics, fracture fixation,dental and
  facial reconstruction, stents.
• CERAMICS Alumina, Zirconia, Calcium Phosphate,
  Pyrolitic Carbon.
• Uses orthopedics, heart valves, dental
  reconstruction.
• COATINGS Bioglasses, Hydroxyapatite,
  Diamond-like carbon, polymers.
• Uses orthopedics, contact lenses, catheters,
  in-growth.

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Evolution of materials in TJR
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Biomaterial Classes cont.

• POLYMERS Silicones, Gore-tex (ePTFE),
  polyurethanes, polyethylenes(LDPE,HDPE,UHMWPE,),
  Delrin, polysulfone, polymethylmethacrylate.
• Uses orthopedics, artificial
  tendons,catheters, vascular grafts, facial and
  soft tissue reconstruction.
• HYDROGELS Cellulose, Acrylic co-polymers.
• Uses drug delivery, vitreous implants,wound
  healing.
• RESORBABLES Polyglycolic Acid, Polylactic acid,
  polyesters.
  Uses sutures,drug
  delivery, in-growth, tissue engineering.

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Polymers in the body
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Implant Factors

• Bulk properties chemical composition, structure,
  purity and presence of leachables.
• Surface properties smoothness, COF, geometry,
  hydrophilicity, and surface charge
• Mechanical properties match properties of
  component being replaced, such as elastic
  modulus. Stability and fixation.
• Long-term structural integrity design for
  fatigue and fracture loading, wear, creep,
  plastic deformation, and stress corrosion cracking

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Host Factors

• Species (simulated tests in smaller species do
  not always capture response in humans)
• Age and health status
• Immunological/metabolic status
• Choice of surgeon

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Implant reactions in the body
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Biocompatibility

• Arises from differences between living and
  non-living materials
• Bioimplants trigger inflammation or foreign body
  response
• New biomaterials must be tested prior to
  implantation according to FDA regulation
• WWII Validated biocompatibility of several
  materials including PMMA

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Bioactivity spectra
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Foreign Body Response

• Rapid dilation of capillaries, increased
  permeability of endothelial cell linings and cell
  reactions
• Macrophages release degradative enzymes
  (lysozymes) that attempt to digest the foreign
  material
• Macrophages multiply (Mitosis) and serve as
  progenitor to the giant cell
• Undigestable frustrated phagocytosis. Size scale
  is important.

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Inflammation process
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Response to inflammation

• Decreased tissue mass and formation of new
  tissue through granulation
• Collagen and other molecules are synthesized
• Formation of scar tissue
• Remodeling process differs for various tissues

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Applications of Biomaterials

• Orthopedics artificial hips,knees, shoulders,
  wrists intervertebral discs fracture fixation
  bone grafts.
• Cardiovascular heart valves, PTCA balloons,
  pacemakers, catheters, grafts, stents.
• Dental enamels, fillings,prosthetics,
  orthodontics.
• Soft tissue wound healing, reconstructive and
  augmentation, occular.
• Surgical staples, sutures, scalpels.

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Orthopedic Implants
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Dental Implants
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Cardiovascular devices
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LVAS Pump Drive Unit
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Soft Tissue Reconstruction
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Challenges

• Biofixation and stability of an implant
• Long-term wear and debris generation
• In-vivo degradation through complex
  bio-chemi-mechanical actions
• Inert materials do not elicit pro-active
  responses in the body
• Solutions are often temporary for tissue
  replacement

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Current Trends

• Interdisciplinary approach merge engineering,
  biology, and materials science
• Engineer new biological and hybrid materials
• Develop smart or pro-active materials which
  can assist in tissue regeneration or treatment

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Questions?