Biomaterials Exam 1 (ch 1-3)

Biomaterial

a material intended to interface with biological systems to evaluate, treat, augment, or replace any tissue, organ, or function of the human body.

Biomaterials science

the study of biomaterials and their interactions with the biological environment

1st generation of biomaterials were designed to be

inert

2nd generation of biomaterials were designed to be

bioactive\integration\interaction

3rd generation of biomaterials were designed to be

fully interactive/healing

what makes a implantable device successful (6)

1. Clinical issues:

   1. biocompatibility

   2. patient factors (health, anatomy, weight, physical activity)

2. Structural requirements

   1. stress strain- material properties

3. Implant design

   1. fits good w body

4. Material selection

5. Processing

   1. machining/sterilization

6. Regulatory issues

   1. FDA approval

FDA approval process (3)

1. biocompatibility analysis

2. simulated loading conditions

3. clinical trials

Def of biocompatibility

ability of a material to perform its designed function with respect to a medical therapy without eliciting any undesirable local or systemic effects in the recipient

biological responses of implants (6)

1. inflammation

2. immune system activation

3. localized blood clotting

4. infection

5. tumor formation

6. implant calcification

list important factors of biocompatibility and suitability (5)

1. type of material

2. shape of implant

3. material degradation characteristics

4. surface chemical properties

5. chemical and mechanical properties

biological response (most basic level to decide implant success)

the protein and cellular responses to the material determine the overall success of the implant

what are the four things that help classify a biomaterial

1. property

2. clinical application

3. structure

4. synthetic vs. natural

List the 3 types of biomaterials based on structure

1. metals

2. polymers

3. ceramics

metals/alloys advantages vs. disadvantages

Advantages

• strength

• conductive

• machining

Disadvantages

• not flexible

• corrosive

• toxins

• expensive

ceramics advantages vs. disadvantages

Advantages

• bone compatibility

• porous

Disadvantages

• fragile

• brittle

• hard to machine

polymers advantages vs. disadvantages

Advantages

• flexible

• ductile

• versatile

• custom design

• easy to machine

Disadvantages

• lack of strength

• degradation

composites advantages vs. disadvantages

Advantages

• many properties

Disadvantages

• manufacturing process

• has weaknesses

• can separate

crystaline

atoms are arranged in a periodic pattern resulting in long-range order

amorphous

lacks systematic atomic arrangement and can be considered to possess a molecular structure much more like that of a liquid

metals are what chemical structure

crystalline

crystal structures are described based on their

unit cell- the configuration of atoms in a small section of the crystal that is repeated in a 3D to form the material

crystal structure are compared based on their _____ and ______

coordination number- each atom in a crystal has a coordinate number equal to the number of nearest neighbor atoms

atomic packing factor- based on the atomic hard sphere model, depicting each atom as a sphere requiring a fixed volume

FCC structure

• atoms are located at each of the corners as well as the center of each face

• coordination number- 12

• APF- 0.74

BCC structure

• atoms at all 8 corners and a single atom at the center of the cube

• coordination number- 8

• APF- 0.68

which is denser FCC or BCC

FCC

point defects

involves only one or two atoms in a crystal

common types of point defects

1. vacancy- found at a lattice site where an atom would normally be present but is missing

2. self-interstitial- occurs when an atom from the crystal is crowded into the interstitial space between 2 adjacent atoms

Impurities

can be an artifact of material processing or can be added deliberately to alter the final properties of a material

solid solution

formed if the normal crystal structure is maintained upon addition of the impurity atoms

example: metal alloy

liquid solution

host material is the solvent while the impurity is the solute

types of liquid solutions

1. interstitial solutions- fill spaces between solvent atoms

2. substitutional solution- tales the place of the solvent atoms

concentration of an alloy can be described as the

weight percent composition

ceramic structures of thought to be composed of ____ rather than atoms

ions

ceramic crystal structure is affected by two parameters

1. magnitude of electrical charge on constituent ion'

2. physical size of ions

an ions coordination number refers to the number of

nearest neighbors with opposite charges

certain ratios will _____ between cations and anions producing______

not allow close contact, unstable structures

the ____ cations and anions are, the more stable

closer

point defects- ceramic structure

individual point defects do not occur instead groups of defects are formed:

miss an anion → also miss a cation (equal charge)

types of ceramic structure point defects

1. Schottky- vacancies in both cations and anions in the correct ratio to maintain neutrality

2. Frenkel- a vacancy pair is created to maintain electroneutrality

both Schottky and Fenkel defects can act as

stress concentrators

If rc~ra, which defect is more likely to occur

Schottky

what bond is the main constituent in polymers?

hydrogen-carbon bonds

mer

smallest building block (polymer)

equivalent to unit cell in metals

unsaturated

2 of carbons in repeat unit are bonded with double bonds

bifunctional

may bond with other mers on both ends

trifunctional

three active bonds that can bond with other mers

degree of polymerization

number of repeat units in a polymer usually indicated by the letter n in the chemical equation

the smallest possible value for polydispersity index (PI)

1

increases as the molecular weight distribution broadens

what plays a major role in the mechanical properties of polymers?

mer configuration

conformation

used to describe the part of the structure of a molecule that can be changed by rotation around a single bond

cant bend

bulky side groups and carbon double bonds prevent from rotation

configuration

the part of the structure of a molecule that cannot be changed except by the breaking down and reforming of primary bonds

cant change order

List 3 common types of configuration

1. isotactic- same side of chain

2. syndiotactic- alternate positions on either side of the chain

3. atactic- random

What structures can polymers resemble

1. linear- repeat units joined in an end to end fashion

2. branched- chains that branch off the main polymer chain

3. crosslinked polymers- adjacent chains are joined at certain points via covalent bonds, forming a 3D polymer network

4. network- have tri or multifunctional mer units that can bond monomers or other polymers into more complicated formations

polymerization

occurs through repeated chemical reactions that join individual mer units into a longer chain

types of polymerization

1. addition

2. condensation

3. genetic

addition polymerization

product contains same chemical structure as the original mer unit

steps:

1. initiation- activation of monomer through a rxn with either a radical species or anionic or cationic species

2. propagation- monomers continue to sucessfully join the polymer chain and increase its molecular weight

3. termination- free radical (PI>1) or anionic or cationic termination (PI~1)

condensation polymerization

involves more than one monomer species and no radical inhibitor is required

occurs through elimination of one molecule (usually h2o)

products do not have some chemical formular as either mer

PI>1

Longer process

chains of various lengths

Genetic engineering polymerization

the expression within a host organism of a genetic vector that encodes the protein polymer of interest

copolymers

2 or more repeat unit types

types of copolymers

1. random- no pattern

2. alternating

3. block-each type of repeated unit is clustered in regions of blocks alongside the chain

4. graft- homopolymer chains are attached to a main homopolymer chain containing a different repeat unit

which type of copolymer is more likely to form a crystal

block or alternating

methods of polymerization

1. bulk- only monomer and monomer-soluble initiator are present in the reaction

   1. high yield and purity

   2. difficulty with heat dissipation

2. Solution- reaction in water or an appropriate solvent with high thermal conductivity

   1. no heat dissipation

   2. monomer and inhibitor must be soluble in solvent

   3. smaller yield

3. Suspension- monomer and initiators that are not soluble in water are added under stirring to a reactor full of water

   1. formation of monomer droplets

   2. high heat transfer

4. emulsion- the addition under stirring of a hydrophobic monomer, a water soluble initiator, and a surfactant to a reactor containing water

   1. cant see droplets

5. gaseous- gas phase

6. solid-state- monomer in their crystalline state are polymerized through exposure to heat or irradiation

7. Plasma- in a plasma environment

   1. highly uniform

Bulk Polymerization

solution polymerization

suspension polymerization

what affects polymers ability to form a crystal

1. polymers tacticity

2. degree of branching

what are the most important characteristics of crystals

1. the amount of dislocations

2. the type of dislocations

What is a type of edge dislocation that occurs when an extra portion of a plane of atoms terminates in a crystal

edge dislocations

for edge dislocations (linear) what are two important characteristics

magnitude and direction of atomic displacement

The burgers vector is ____ to the dislocation line in an edge dislocation

perpendicular

a linear defect that are caused by shear forces on part of the material that caused the displacement of a portion of the crystal

screw dislocation

The burgers vector is ____ to the dislocation line in a screw dislocation

parallel

dislocation cannot end in a _____ on a crystal, but instead on which a dislocation may move contains both the burger vector and the dislocation line

defect-free region

plastic deformation, caused by dislocations, occurs by

movement of dislocations

in crystals what is plastic deformation referred to as

slip

increased slip system causes more brittle or ductile properties in a crystal

ductile

does a metal object or ceramic object have more slip systems

metal object

atoms not bonded to the max number of neighbors that posses higher energy (surface free energy) than most in the crystal

external surface

the interface between randomly oriented grains is called a ___ and has high chemical reactivity

grain boundary

small angle grain boundaries (grains on either side of the boundary) include two types

1. tilt boundary- aligned edge dislocations

2. twist boundary- aligned screw dislocations

high angle grain boundaries are a more severe misalignment and the ____ the misorientation, the ____ the energy of the boundary

greater, higher

what special type of grain boundary only occurs when there is a mirror image of atomic placement across the boundary

twin boundary

what 3D defect occurs when long-range order of crystal is lost

volume defects/voids

voids are important to biomaterials because they create ___ that can alter to biological response of the material

pores

porogens can be either ___ or ___

solids or gases

percent crystallinity is highly dependent on the chemical structure of the mer. Anything that prevents chain alignment or discourages secondary bonding between chains will ___ the polymer crystallinity

reduce

What factors influence percent crystallinity (4)

1. mer side groups

2. chain branching

3. tacicity

4. regulatory of mer placement in copolymers

Do you expect branch polymer to have more or less crystallinity than one linear polymer?

less due to the branching

the basic unit of crystalline structure is the ____ which is larger than the polymeric crystal’s unit cell and contains a large number of polymer chains folded back on themselves.

lamella

spherulites are the 3D version of

lamella

characteristic thermal transition for crystalline materials is the

melting point

Amorphous ceramics have no distinct ___. As the temp decreases the material becomes more viscous until it is a ____. Above the temp, the material can be handled as a ____

Tm, solid, liquid

for a polymer if the Tm and Tg increases, so does the

molecular weight

in a polymer what is one of the major determinates of Tg

chain flexibility

the ability to crystalize above the Tg temp is known as

crystalline temp Tc

a polymer can be ____ by raising the temp of the sample to a Tc

annealed

a group of characterization techniques that involve the measurement of the physical properties of a material as a function of temp

thermal analysis

power compensated DC

used to keep thermal or mechanical conditions stable

heat flux dsc

measures thermal transitions by detecting the difference in heat flow between a sample and a reference as heat passes through a conductive plate.

endothermic

require energy to proceed and is positive