Biomaterials & Tissue Engineering: Midterm 1

class 1 biomaterials are … invasive and have … internal contact

minimally; no

class 2 biomaterials are … invasive and have a … usage period

more; relatively short

class 3 biomaterials are … invasive, risky, and …

very; implantable

stress = ?

force/area

what is strain?

deformation under stress

strain = ?

L-L0/L0

Young’s modulus = ?

stress/strain

embryonic (pluripotent) stem cells differentiate into…

mesenchymal (multipotent) stem cells

how are induced pluripotent stem cells formed?

somatic cells + reprogramming factors

what are the 3 components of tissue engineering?

cells, scaffold, signals

what creates the crystal structure of metallic bonds?

positively charged metal ions + free electron cloud

body-centered cubic crystalline structure (BCC): … atoms per cube

2

face-centered cubic crystalline structure (FCC): … atoms per cube

4

hexagonal close-packed crystalline structure (HCP): … atoms per cube

6

… crystalline structure(s) is/are ductile, plastic, and workable

body-centered cubic; face-centered cubic

… crystalline structure(s) is/are brittle

hexagonal close-packed

elastic deformations are reversible. stress is…

within the linear region

plastic deformations are irreversible. stress is…

beyond the yield point

metallic bonds can/cannot stretch and return to their original state

can

permanent deformations are due to…

dislocations

slipping dislocations are when…

crystal blocks slip along slip planes

why are body-centered and face-centered cubic crystalline structures ductile, while hexagonal close-packed crystalline structures brittle?

body-centered and face-centered crystalline structures have many slip planes, while hexagonal close packed have few

twinning dislocations occur when…

atomic orientation is reorganized

a passive layer is a … that forms by reaction with …

metal oxide film; oxygen

tribocorrosion occurrs when the … is ruptured, exposing … underneath and allowing it to corrode

passive layer; reactive metal

corrosion is a(n) … reaction requiring a(n) …

electrochemical; electrolyte

melt casting takes … metal, cools it, and … shapes it

molten; mechanically

what are the 4 steps of melt casting?

nucleation, crystal growth, grain formation, interface development

what are vacancies in metals?

gaps in the metal lattice where dislocation and deformation occur

reducing grain size strengthens metal by…

increasing total grain boundary

cold-working/strain hardening strengthens metal by deforming at temperatures … the melting point to …

below; increase dislocation density

solid-solution hardening strengthens metals by adding a(n) … to …

impurity atom; reduce lattice strain

alloys have a … yield point compared to pure metal

higher

in an alloy, the … is more abundant, and the … is less abundant

solvent; solute

to form an alloy by substitution…

atoms (of similar atomic size and crystal structure) are substituted into the metal lattice

when forming an alloy by substitution, the solvent is an element of … valency

lower

to form an interstitial alloy…

smaller atoms (CHBNO) are inserted into lattice holes

316L stainless steel is …% iron and …% chromium

60-65, 17-20

316L stainless steel has … corrosion resistance because…

fair, chromium-oxide layer automatically reforms with oxygen, but oxygen is low inside the body

316L stainless steel is heavy

heavy

titanium-based alloys have a … corrosion resistiance

high

what process forms the titanium-oxide film on titanium alloys?

anodization

titanium-based alloys are heavy/light,

have a low/high modulus,

and are easy/difficult to mill,

meaning they have low/high wear resistance

light, low, easy, low

cobalt-based alloys have a low/high modulus,

low/high wear resistance,

low/high fatigue strength,

low/high corrosion resistance

high, high, high, high

what happens if cobalt-based alloys corrode inside the body?

toxic cobalt and chromium ions will be released, which can cause cancer

what are the 3 methods to improve metal osseointegration?

bioactive coatings, changing topology, increasing porosity

what is an example of a bioactive coating?

hydroxyapatite

what topological features of a metal implant can be changed to improve osseointegration?

roughness (short wavelengths), waviness (longer wavelengths), lay (direction of pattern), flaws (interruption of pattern)

how does porosity improve osseointegration?

permits nutrient exchange and tissue ingrowth

how can increasing porosity to improve osseointegration be detrimental?

reduces the implant’s overall strength and increases corrosion

how is porosity produces?

laser melting

Wolff’s Law: bones adapt to load, so decreasing load will … bone density

decrease

stress-shielding is when bone density… due to…

decreases, no force

what features of a metal implant can be adjusted to minimize stress-shielding?

flexible material, geometry, topology

what metals are bioresorbable?

Mg, Zn, Fe

metal degradation is similar to…

corrosion

what features can be adjusted to tune metal degradation?

surface topology, material, surface coating

bioceramics are chemically organic/inorganic, meaning they are not…

inorganic, 1 C covalently bound to HON

bioceramics typically have … and … elements

metallic; nonmetallic

what is crystallinity?

degree of structural order

a true ceramic is …, meaning it has periodic arrangement

crystalline

polycrystals like … have … in a(n) … phase

bioglass and glass-ceramics; smaller crystals; amorphous

amorphous structures lack …

long-range order

fracture toughness is the energy required to …

elastically deform, inelastically deform, then fracture

strength is a measure of how much …

force can be supported

ductility is a measure of how much …

energy can be absorbed

fracture toughness is the area under the…

stress-strain curve

Kic fracture toughness is the resistance to…

propagation of flaws under stress

Kic fracture toughness = ?

stress * sqrt(crack length)

a brittle material has low/high toughness

low

a ductile material has low/high toughness

high

toughening mechanisms

how does densification/consolidation affect a bioceramic material?

removes porosity from powder compact

what happens when a bioceramic is sintered?

heated below melting point, reducing surface energy and reducing curvature

list the polymorphs (crystal structures) of zirconia from biggest to smallest volume.

monoclinic, tetragonal, cubic

what are the 3 most common bioinert ceramic materials?

alumina, zirconia, zirconia-toughened alumina

how does adding Yttria stabilize zirconia?

enables a metastable tetragonal phase; under stress, martensite transformation from tetragonal to monoclinic polymorph increases volume and blocks crack propagation

bioactive ceramics are calcium phosphates, such as…

hydroxyapatite, tricalcium phosphate (TCP)

what are three examples of bioresorbable ceramics?

calcium phosphate, calcium carbonate, and calcium sulfate

how can the degradation rate of a bioresorbable ceramic be increased?

decrease the calcium ratio

other than the calcium content, what other factors affect the degradation rate of a biodegradable ceramic?

surface area, particle size, chemical and biological conditions

bioglass is/is not a true ceramic because it is…

is not; amorphous

bioactivity index IB is a measure of…

bioactivity

t0.5bb is the time it takes for…

½ of the bioglass interface to bind

IB = ?

100/t0.5bb

bioglasses in this IB range only bind to hard tissue

0-8

bioglasses in this IB range bind to hard and soft tissue

>8

glass transition temp (Tg) is the temperature at which…

porosity reduces, material can be compressed to become denser and stronger

crystallization onset temp (Tc) is the temperature at which…

crystallization begins, reducing bioactivity

the narrow bioceramics sintering window lies between…

glass transition temperature and crystallization onset temperature

in the process of bioglass degradation, bioglass exchanges … with …, which increases …

This breaks … bonds and forms …, or …

Then … precipitate from solution, forming …

Ca+ and Na+; body fluid; pH; Si-O-Si; Si-OH, silica gel; Ca2+ and PO43-, biocompatible material

carbon nanomaterials are … with human blood and have good … and …

compatible; chemical stability and friction properties

0D carbon nanomaterials

fullerene, graphene quantum dot

1D carbon nanomaterial

carbon nanotube

2D carbon nanomaterial

graphene

what are the two ways that carbon nanomaterials can be produced?

bottom-up; top-down

what elements are biopolymers typically made of?

C and H, sometimes O, Cl, F, N, Si, P, S

most biopolymers have a carbon backbone, but some may have … backbones

silicon or phosphorus

what determines the physical and chemical properties of polymers?

pendant groups

what are the 3 polymerization mechanisms?

chain growth, step growth, condensation polymerization