Biomaterials Flashcards
Define prosthetic
an artificial device that replaces a missing body part, which may be lost through trauma, disease, or congenital conditions
Define implant
a medical device placed inside the body to replace/support a missing biological structure
Define Biomaterial
a material intended to interface with biological systems to evaluate, treat, augment, or replace any tissue, organ, or function of the body
Define Biological Material
a material such as bone, skin, or artery produced by a biological system
Define Osseointegration
the formation of a direct interface between an implant and bone without intervening soft tissue
Define Osteoinduction
undifferentiated and pluripotent cells are stimulated to develop into the bone-forming cell lineage
Define Osteoconduction
the process by which bone is directed to conform to a material’s surface
What is the role of osteoblasts and osteocytes?
involved in the formation/mineralization of bone
What is the role of osteoclasts only?
involved in the resorption of bone tissue
Define biocompatible (FDA)
produces no harm to the host
Define biocompatible (Ours)
the ability of a material to perform with an appropriate host response in a specific situation
Define Biomedical material
the broadest category for materials used in or on the surface of the human body
Define thrombogenicity
the tendency of a material to interact with the blood to produce a clot
Define carcinogenicity
A substance that is able to cause cancer usually be damaging the genome or disrupting metabolic processes
Define mutagenicity
the ability to cause genetic damage
Define stress shielding
the interface between bond and an implant with a high modulus begins to deteriorate
Define fatigue failure
micro-defect creates nucleation point that will fracture under repeated loading/unloading
Define aseptic loosening
the failure of the bond between an implant and bone in the absence of infection usually caused by wear debris
Define fretting fatigue
occurs when a foreign body is statically pressed against the surface of the specimen upon which a cyclic stress is being applied
Define tension
pull
Define compression
push
Define shear stress
scissors, slide
Define extensometer
used to measure the change in dimensions of a test sample along the axis of loading
Define proportional limit
highest stress where stress is linearly proportional to strain
Define yield stress
stress which causes the onset of permanent deformation (also called yield strength or elastic limit)
Define ultimate strength
the area under the stress strain curve up to the failure point
Define strain hardening
an increase in stress levels after the yield stress is reached
Define viscoelastic material
show a time-dependent deformation component due to viscous flow within the material
Define Class I Biomedical Device
low to moderate risk to the patient and/or user (elastic bandages, stethoscopes, surgical tools)
Define Class II Biomedical Device
pose a moderate to high risk to the patient and/or user (infusion pumps, surgical drapes, acupuncture needles)
Define Class III Biomedical Device
have a high risk to the patient and/or user (pacemaker, vascular stents, implants)
Define tough
a material that is both strong and ductile (withstand both high stresses and high strains)
Define generation III alloy
Designed to act as temporary structures that can degrade over time allowing native tissue to integrate with the implant and eventually replace it
Ionic bond
a type of chemical bonding that involves the electrostatic attraction between oppositely charged ions
Metallic bond
a type of chemical bonding that arises from the electrostatic attractive force between conduction electrons and positively charged metal ions
Tightly packed cations surrounded by an electron cloud
Allows for good charge transfer that makes metals good conductors of heat and electricity
Covalent bond
a type of chemical bond that involves the sharing of electron pairs between atoms
Sigma bond
the strongest covalent bonds, due to head-on overlapping of orbitals on two different atoms
Pi bond
where two lobes of an orbital on one atom overlap two lobes of an orbital on another atom
Hydrogen bond
a partially electrostatic attraction between a H atom bound to a more electronegative atom such as FON and another similar atom
Properties of polymers (modulus, toughness, plastic deformation)
Low modulus
Higher toughness than ceramics
Large plastic deformation
Composition of polymers
Long molecules built from monomers (ex: DNA/protein)
Crosslinked polymers common in implants → toughen material and make it insoluble
High Density Polyethylene
POLYMER
Plastic liner of hip implant
Can be crosslinked or not
Non-toxic, super insoluble
Poly(ether ether ketone) or PEEK
POLYMER
spinal implants
Poly(methyl methacrylate) or PMMA
POLYMER
bone cement
Poly(hydroxyethyl methacrylate) or pHEMA
POLYMER
soft contact lenses
poly(lactic-co-glycolid acid) or PGLA
POLYMER
polylactic resorbable orthopedics
Properties of ceramics (modulus, toughness, plastic deformation, insulator/conductor)
Hard (high modulus)
Brittle (less tough than polymers) with little plastic deformation
Insulators
Composition of ceramics
Composed of metallic and non-metallic elements, can be crystalline or amorphous
Define glass
CERAMIC
Amorphous solid with slow transition to liquid after glass transition temperature, undefined composition
What is the composition of window glass?
CERAMIC
Mostly silicon-oxygen linkages (70% SiO2) with (14%) sodium oxide and (9%) calcium oxide (soda/lime) (form basic hydroxides in water)
What is the code for bioactive glass?
45S5
What is the composition of bioactive glass?
CREAMIC
Composed of (25%) calcium oxide, (25%) sodium oxide, (6%) phosphorus pentoxide, and (45%) silicon dioxide (compounds naturally present in bone)
What if bioactive glass has too much silica, sodium oxide, or phosphorous pentoxide?
bioinert like window glass
unstable
prevent glass formation or causes crystals
Example of bioactive glass uses and why it was a good replacement
CERAMIC
Used in ear implants to avoid the formation of scar tissue (metal/polymer) that moved the implants out of position, leading to damaging vibrations
Define bioactive bonding
Direct bond to bone, release ok ions
Describe the melt process of making glass
Heat raw materials together → yields dense solid materials with low porosity
Alumina/Zirconia
-used in and properties
ceramic acetabular cups of hip implants
hard with good compression strength
What does hydroxyapatite contain at minimum?
CERAMIC
Contains (at minimum) calcium, hydroxyl groups, and ortho phosphate (Ca to Phos of 1.67)
What happens if you switch the OH- from HA to F or Cl?
Can switch OH- with F- (more hydrophobic) or Cl- (hydrophilic)
What happens if you switch the phosphate from HA to carbonate or silicate?
Can switch phosphate with carbonate or silicate to match bone more closely
A layer of HA forms on top of bioactive glass. Why?
Surface layer forms on bioglass due to the reaction between calcium (bioglass) and soluble phosphates
Porous forms of HA used in…
Porous forms used in cancellous bones, orthopedic surgeries, and dental surgeries
Micropores in HA would…
allow cells that remodel, resorb, and form bonds → increases rate of dissolution
Formation of HA through solid state reactions
can prepare HA, but require high temps and are lengthy and require careful stoichiometric control, yield highly crystalline HA
Formation of HA through sintering
heat above 900*C for several hours, increases mechanical properties, similar tensile strength to bone, fracture toughness much lower than bone
Formation of HA through wet chemical processes
smaller crystals, more homogenous products, make more like bone, low temp
beta tricalcium phosphate
components, uses, properties, solubility
Bioresorbable
Ratio of Ca to PO4 → has low Ca
Denser are less resorbable
Many calcium salts are not soluble (calcium chloride and nitrate will dissolve)
Properties of metals (modulus, tough, plastic deformation, atoms, oxidation)
High modulus / Very tough
Can undergo plastic deformation
Tightly packed atoms with sea of electrons
Usually 0 oxidation
Oxide layer formation in metals
can react with water and oxygen to form oxide layers (may protect the metal underneath)
Can be sloughed off to release metal ions → Fretting fatigue and other wear
Production of metals
Wrought or forged alloys have superior mechanical properties compared to cast ones
Special Stainless Steel (name, composition, additives, generation)
GENERATION 1
Iron with higher Cr/Ni for protective oxide layer
Carbide layer reacts with Cr to use it up and cause oxidation → only short term implants
Oxygen can reform oxide layer if damage occurs, but O2 levels are low in body
Molybdenum for chloride resistance
Oxidation levels of Cr
Cr has three oxidation states: 0, +3, and +6 (dangerous)
CoCrMo (generation, uses, properties, additives) (crystal structure in separate question)
GENERATION 1
Femoral stem of hip implant, knee implants, load bearing
Strong/high modulus, heat/corrosion resistant, expensive, Co/Cr toxic, stress shielding, bend > fracture
Can add tungsten to co-cr alloys, but it reduces corrosion resistance
CoCrMo two crystal structures
Two crystal structures → barrier of motion for deformation
Face centered cubic and Hexagonal close packed
Nitinol (composition, uses)
Alloys of 49% Ni and 51% Ti can form stents to be inserted at RT but expand at body temperature
Titanium (generation, properties- special, toxicity, oxide, use, modulus, $)
GENERATION 2
can osseointegrate, nontoxic, stable oxide layer, load bearing, closest modulus to bone, less expensive
Titanium osseointegrate (what/how/use)
Osseointegrate - direct bonds with bone, prevents loosening/vibrations
Not good for temporary
Titanate with O- + Ca from blood + PO4 → bone-apatite (osteocytes remodel)
Describe the alpha grade of titanium and what can be added to stabilize it
𝞪 - commercially pure titanium, low strength
Aluminum, gallium, tin stabilizes
Describe the beta grade of titanium and what can be added to stabilize it
𝜷 - lower modulus, enhanced ductility, low wear resistance
Molybdenum, tantalum, vanadium, niobium, tungsten, chromium, iron, cobalt, nickel, copper, or manganese stabilize
Describe the alpha/beta grade of titanium
𝞪-𝜷 - high tensile/fatigue strength, low ductility, cannot biodegrade
Use of alpha, beta, and alpha/beta alloys of titanium?
alpha and beta → not used in structural, coatings
alpha/beta → structural implants such as femoral stems of hip implants and knee implants
How are the grades of titanium determined?
Based on O2 content (small differences) and can also be classified based on crystal structure
Generation of magnesium alloys and why
Gen 3 → Biodegrade and resorb over time
Two general drawbacks of magnesium
generate hydrogen gas
low solubility with additives
Describe the hydrogen gas production of magnesium and what can modify it
0 oxidation (metal), forms Mg(OH)2 and H2 gas → M(OH)2 will produce MgCl2 (very soluble)
Rate can be controlled with different elements (Ca, Zn)
Adding zinc reduces the rate of hydrogen gas production
What additives can be added to magnesium alloys? What effects can they have?
Low solubility with additives
Such as those that increase corrosion resistance (Mn, Cu, Al, Ca, Zr, Gd)
Amorphous magnesium glass can be created that improves corrosion, hydrogen production, strength, and elasticity, but have lower ductility (more like glass)
Shapes for tensile or compression testing, correlation between
Test tensile strength with dogbone, test compression with cylinder/rectangle
Ceramics are good at compression but bad at tensile (does not correlate)
Hooke’s Law
strain is proportional to stress as long as it is below elastic limit (yield stress)
Revert to original dimension when unloaded
Poisson’s ratio
the ratio of transverse contraction strain to longitudinal extension strain
Volume remains steady, which causes transverse deformation that increases length and decreases diameter
Two shear testing equations
Shear stress = force * cross sectional area II to applied force
Shear stress = shear modulus * shear strain
Two types of bending testing
Bending testing → Three (strength) or four point (material properties)
…….. introduced aseptic techniques in the 1860s
Lister introduced aseptic techniques in the 1860s
……. invented bioactive glass at the University of Florida
Larry L Hench invented bioactive glass at the University of Florida
Three ear bones
The malleus, incus, and stapes are the three ear bones
……….. was the first to do hip replacements, made of ………….
Sir John Chamley was the first to do hip replacements, his were made of stainless steel
Two major types of joints
Static (skull, wrists, teeth)
Mobile (hips, knees, ankles, shoulders, elbows)
Two types of mobile joints
Congruent
Ball-shaped head fits closely into a cup-like socket
Incongruent
Consist of two incongruent hard surfaces that create highly concentrated (heterogeneous) stresses usually compensated by thick cartilage and synovial fluid
