Bioinert Ceramics 1 Flashcards
What are ceramics and glasses?
Solids composed of inorganic non metallic substances
What is the structure of ceramics?
Mostly polycrystalline in regular array - most are variants of FCC and HCP
Microstructure of individual crystals separated by boundary layers with glassy phase, phase boundaries, and open or closed pores
What is the morphology of glasses?
Amorphous and high viscosity, behave like solids
Short range order of atomic arrangement
No microstructure features, don’t undergo crystallization
Ex: tetrahedral silicate glass (SiO2)
Which has higher specific volume at below Tm: amorphous or crystalline structure?
Amorphous
What is the structure of glass-ceramics?
Polycrystalline materials with fine ceramic crystallites in amorphous glassy matrix
Produced by controlled crystallization of glasses (heat treatments)
< 1 micrometer
What are the general properties of ceramic materials?
Brittle - ionic and covalent bonds resist plastic deformation
High modulus and hardness
Difficult to process without flaws
Biological properties can be varied based on chemistry
What kinds of flaws in ceramic materials can cause stress concentrations?
Process induced ex: inclusion or pores
Design induced ex: sharp corners or holes
Service induced ex: pH, wear
Examples of bioceramics
Alumina Bioactive glass Glass-Ceramics Hydroxyapatite (Ha) Tricalcium phosphate
First four used in coating for chemical bonding
Last one used for temporary bone fillers
What are examples of bioinert oxide ceramics? What are they used for? How do they compare?
Single oxides of alumina and zirconia
Used in density for implants, and orthopaedic surgery
Alumina more chemically stable than zirconia, but latter has better mech properties
Advantage of oxide ceramics
Superior degradation resistance and mech properties
Superior wear resistance
Alumina applications
Hip ball and cup (femoral head THR)
Knee joint
Dental implants
Zirconia Applications
Hip ball (femoral head THR) Dental implants
Types of tissue interactions in bioinert ceramics
dense (i.e. morphological) and porous (i.e. biological)
Dense tissue ceramic biomaterial interactions
Non-porous inert materials
Attach to tissue through morphological fixation
Stable interface is crucial, otherwise implant will loosen and fail
Porous tissue ceramic biomaterial interactions
Biological fixation:
With pores > 100 micrometers
bone ingrowth occurs, anchoring bone to material
Good mechanical stability, but lower mech stress and brittleness in implant
General manufacturing steps of oxide ceramics
- Starting material in form of fine powder
- Green body formed (has shape of final component but lower strength)
- Sintering to increase strength and density. Usually Hot isostatic pressing is used
- Grinding and surface polishing
What is the main source of alumina? What is the structure of alumina at 1200C?
Main source is bauxite and corundum
HCP alumina formed about 1200 celsius
Used in high purity with small amount of MgO to help sintering
Average grain size of 4 micrometer to exhibit wear resistance due to low surface roughness
Which compound is added to help sintering of alumina? What is the average grain size?
Alumina used in high purity with small amount of MgO to help sintering
Average grain size of 4 micrometer to exhibit wear resistance due to low surface roughness
What material is used as the femoral head in THR? What properties must this material have?
Alumina has been used for 40 years
Must have high degree of sphericity due to load bearing and wearing surfaces
Long term friction of alumina joint decreases wear properties over time
Rank the wear rates of different acetabular cup and femoral head combinations?
- Metal/Metal (Co-Cr) 0.0003 mm/year
- Ceramic/Ceramic (alumina-alumina) 0.003 mm/year
- Ceramic/Polymer (alumina-UHMWPE) 0.008 mm/year
- Metal/Polymer 0.07-0.19 mm/year
