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?