Metals, Ceramics, Glasses, and Glass-Ceramics Flashcards
1
Q
Common Alloys..
A
- classified by American Society for Testing and Materials (ASTM)
- Ti alloys, Co-Cr alloys, Stainless Steel
2
Q
Titanium Alloys
A
- Commercially pure Ti with some oxygen, aluminum, and vanadium
- Two most common: CP (commercially pure) and extra-low interstitial (ELI)
- in ELI, aluminum is alpha phase stabilizer, while vanadium is a beta phase stabilizer
- addition of O, C, and N interstitially in both alloys strengthens the metal, making deformation more difficult (impeding dislocation motion)
- superior corrosion resistance, bioinert (minimal fibrous capsule), less stress shielding due to similar elastic modulus to bone
3
Q
Nitinol
A
- equally nickel and titanium alloy with shape memory properties
- two different temp-dependent crystal structures (martensite in low temp, austenite in high temp), in different phases the material has different properties
- nickel is allergenic at high concentrations, can use titanium oxide layer as a barrier
4
Q
Stainless Steel
A
- Iron and carbon alloy with impurities
- chromium, nickel, Mo, some N, Mg, P, and C added
- 316L is widely implanted (0.03% max carbon, prevents chromium carbide formation which would reduce oxide layer and decrease corrosion resistance)
- properties are customizable through processing like coldworking or annealing
- all have face centered cubic structure that is non-magnetic
- adding in larger atoms in alloys leads to distortions in crystal structure (grain boundary irregularities), but smaller atoms in interstitial spaces prevents dislocations
5
Q
Cobalt-Chromium alloys
A
- F75 alloy is popular (mostly Co, less Cr)
- very corrosion resistant
- add tungsten or molybdenum, since they’re larger atoms can impede dislocation motion
- Co absorb stress in phase transformation, leading to excellent wear resistance
- hard to fabricate to shape (in alpha phase can form large grain sizes)
6
Q
Type 1 Bioceramics
A
- dense, nonporous, almost inert (no biological bonding at tissue interface)
- morphological fixation
- implanted via compression loading (movement can wear particles and lead to formation of fibrous capsule)
- ex: alumina (biocompatible, fine grain size, high wear resistance, strength/hardness, can cause stress shielding in older patients)
7
Q
Type 2 Bioceramics
A
- nearly inert, microporous, rely on ingrowth of tissues into the pores on the surface or throughout the implant
- biological fixation
- pore size must exceed 100 microns for proper ingrowth of tissue
- used for non-loading (porosity reduces the mechanical strength)
- interconnects pores or coats porous metals (derived from hydroxyapatite, or converted from coral or animal bone)
8
Q
Type 3 Bioceramics
A
- elicit a biological response at the interface, forming interfacial bond between the tissue and material
- bioactive fixation (‘binds’ to bone, sometimes soft tissue)
- examples: non-porous hydroxyapatite and composites, bioactive glasses and glass-ceramics
9
Q
Types 3A-3D Bioceramics
A
- vary in concentrations of silicon, sodium, calcium, and phosphorous pentoxides that results in varying binding properties
- A: ‘bioactive bone boundary’, forms a bond with bone
- B: silicate glasses, act like type 2
- C: resorbable glasses that disappear within 10-30 days
- D: non-practical glasses, too weak for implantation
- collagenous soft tissues can bind to bioactive silicate glasses in specific tiny region (see triangle graph)
10
Q
Type 3A Surface Reaction stages
A
- Stage 1: exchange of alkali ions from implant and hydronium ions from solution
- Stage 2: silica structure breaks down, dissolves at interface
- Stage 3: re-polymerization of SiO2 rich layers on inactive glass surfaces
- Stage 4: amorphous film of calcium phosphate precipitates on the silica-rich layer, followed by crystallization to form carbonated-HA crystals (HCA, Stage 5)
- ALSO: released silica and calcium ions stimulate bone cells to produce more (osteogenic)
- HA materials can be integrated directly into endogenous (natural) HA through bone resorption
- Stages must be completed rapidly to properly repair bones, prevents foreign body response (if too fast or slow, might fall into wrong region)
11
Q
Type 4 Bioceramics
A
- resorbable, designed to degrade over time and be replaced by bone
- main crystalline component of bone is calcium-deficient carbonate hydroxyapatite
- HA and tricalcium phosphate (ceramics) used as fillers, coatings, and cements (helps inspire fusion of mineralized bone)
- TCP degrades faster, but HA is more osteoconductive
- challenge to meet proper strength and performance requirements while material degrades, and match resorption rates to ingrowth of natural host tissue
- various ways of biodegradation
12
Q
Alumina
A
- inert bioceramic, extracted from bauxite and cryolite ores
- dissolved in sodium hydroxide, then precipitated via adding salt
- finally, uses calcination to form alumina
- inert, resistant to corrosion, elicits minimal FBR, stable, but very brittle (great hardness and scratch resistance, low coefficient of friction, but not ductile)
- alloyed with zirconia and chromium oxide (other materials too) to extend implant life
13
Q
Zirconia
A
- inert bioceramic
- extracted from baddeleyite (zirconium oxide mineral)
- volume changes occur in structural transformations upon cooling when in its pure oxide form (leads to cracking)
- add yttria or magnesia to stabilize either structure
- when cracks form in these composites, compressive stress forms to resist the crack front (increased toughness)
14
Q
Hydroxyapatite
A
- formed/taken from hydroxylapatite, which mimics mineralized bone
- bone apatite is deficient in hydroxide (hexagonal crystal structure with lattice vacancies that can be filled)
- calcium substitution by lead, sodium, etc. destabilizes structure and increases the solubility (can also enhance bone growth culture)
- widely used as synthetic bone graft substitutes, designed to be osteoinductive (more so osteoconductive)
- prepared through sintering, heating while pressing
- make a compromise between mechanical strength and osteoconductivity
15
Q
Carbon Biomaterials
A
- inherently biocompatible, with diversity in structure and properties
- graphite (soft, anisotropic layered in-plane covalent bons, interplane van der Waals interactions) is lubricating
- diamond (hardest material known, tetrahedral symmetry in three dimensions)
- spectrum from amorphous to perfect crystalline graphite
- diverse uses: conjugation of bioactive or fluorescent molecules, like drug delivery, phototherapy and imaging, biosensors, antimicrobial therapy, blood compatible coatings
