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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
Structural Aspects of Biomaterials
Class Structure
CLASS: Tu/Th: 12:30-2pm 203 McLaughlin Hallhttp://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 3-4:30 or by appointment,5134 EH, lpruitt@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
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.
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.
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 recalls2. Premature failure in metal prostheses due to corrosion3. Implant failures due to oxidation and aging of the polymer component4. Stress shielding/ femoral stem design—stresses, bone resorption, evolution
of design and materials 5. Clinical case study (Dr. Mike Ries, Orthopedic Surgery, UCSF, Feb 21)-
surgical procedures, osteolysis6. Evolution of materials (UHMWPE)- the effects of microstructural changes on
fatigue, fracture, wear 7. Spinal Implants (Dr. Andy Kohm, Kyphon). Design/ clinical aspects.
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
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)
Soft Tissue
SOFT TISSUE: Structural Properties, wound healing, stability, biofixation. Design issues.
Case Studies:1. Dow- Corning Breast implant case2. Soft implants: facial, occular
Biomaterials
ClassificationsBiocompatibilityApplications
Biomaterials and implants
• Replace component of living being
• Restore Function
• Harmonious interaction with host
• Biocompatibility
• Long-term structural integrity
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
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.
Evolution of materials in TJR
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.
Polymers in the body
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
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
Implant reactions in the body
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
Bioactivity spectra
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.
Inflammation process
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
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.
Orthopedic Implants
Dental Implants
Cardiovascular devices
LVAS: Pump Drive Unit
Soft Tissue Reconstruction
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
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
Questions?