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Biomaterials > Ch 2 - Chemical Structure of Biomaterials > Flashcards

Ch 2 - Chemical Structure of Biomaterials Flashcards

1
Q

Crystalline

A
  • Periodic pattern of atoms (Long-Range Order)

* i.e. metals, ceramics, polymers

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2
Q

Amorphous

A
  • Lacking systemic atomic arrangement (like liquid)

* i.e. ceramics, polymers

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3
Q

Structure of metals

A
  • Non-directional metallic bonding

* Crystal structures (where atoms are located e.g. BCC/FCC, HCP)

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4
Q

Unit cell

A

Config. of atoms that is repeated in all 3 dimensions to form final material

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5
Q

Coordination number (CN)

A

nearest neighbor atoms

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6
Q

Atomic Packing Factor (APF)

A

APF (per unit cell) = V_atoms/V_total
• BCC = 0.68
• FCC/HCP = 0.74

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7
Q

Face-centered cubic (FCC)

A
  • a = 2r*√(2)
  • APF = 0.74
  • CN = 12
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8
Q

Body-centered cubic (BCC)

A
  • a= 4r/√(3)
  • APF = 0.68
  • CN = 8
  • e.g. Ti β-phase = improved \ductility
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9
Q

Hexagonal-close packed (HCP)

A
  • APF = 0.68

* e.g. Titanium α-phase

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10
Q

Ductility

A

Plastic deformation before fracture

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11
Q

Lattice structures

A
  • Cartesian representation
  • Defines unit cell by \lattice parameters e.g. lengths of edges (a,b,c) and angles b/w axes (α, β, γ)
  • \lattice points = vertices of unit cell
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12
Q

Crystal system

A 
Unique combinations of lattice parameters (a,b,c) and (α, β, γ)
• BCC
	1 . Cubic (3 same lengths)
	2. Tetragonal (2 same length)
	3. Orthorhombic (all diff lengths)
	4. Rhombohedral (//)
• HCP
	1 . Hexagonal (2 same length)
	2. Monoclinic (~rhombohedral)
	3. Triclinic (no edges/angles equal)
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13
Q

Miller indices

A

Coordinate system to indicate location of points and orientation of planes (i.e. cubic crystals)

1 . Determine plane intersection of x, y, and z axes 	(if // to axis, "intercept" is ∞)

2. Reciprocal of intercepts
3. Clear fractions (LCD)
4. Record as "(h k l)"
5. Indicate any negative #s w/ bar over integer
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14
Q

Defects

A
  • \point defects i.e. vacancies & self-interstitials

* \impurities i.e. solid solutions (alloys) & liquid solutions

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15
Q

Point defects

A
  • Gen’lly occur b/c of thermodynamics of crystal growth
  • Creation of defects is favorable b/c it ↑ entropy of system (thermodynamically favorable)
  • e.g. \vacancies & \self-interstitials
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16
Q

Vacancy

A

Missing atom (expected at lattice site)

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17
Q

Self-interstitial

A
  • Atom is crowded into interstitial space b/w 2 adjacent atoms
  • Occupying what should be “empty” space
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18
Q

Why form crystalline structures?

A

Balancing thermodynamic need to form bonds (crystal) and creation of defects (↑ entropy, also ↑ \strain)

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19
Q

Lattice strain

A
  • Strains in local lattice struc., caused by both vacancies and interstitials
  • esp. interstit. defects in metals b/c of large atoms v. small space
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20
Q

Solid solution

A

[metals/ceramics]
• Normal crystal structure is maintained + addition of impurity atoms
• e.g. metal alloys (impurity atom improves prop’s of host material)

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21
Q

Weight % composition

A

Weight_elem/W_total

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22
Q

Atom % composition

A

Moles_elem/Moles_total

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23
Q

Liquid solution

A

[metals/ceramics]
• \solute (impurity) mixes in \solvent (host)
• e.g. \interstitial OR \substitutional solutions
* Ceramics: must not affect electroneutrality (solute ion must be similar in size/charge to solvent ion AND simultaneous diffusion for BOTH species)

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24
Q

Interstitial solution

A

[metals/ceramics]
• Impurities fill spaces BETWEEN solvent atoms
• Gen’lly when solute smaller than solvent (↓ lattice strain)

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25
Q

Substitutional solution

A

[metals/ceramics]
• Impurity/solute atoms REPLACE solvent atoms
• Gen’lly favored if \Hume-Rothery rules are satisfied
* Typ. for solute anions b/c too large for interstitial space

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26
Q

Hume-Rothery rules

A
  • Diff. in size of atomic radii < 15% (min. lattice strain)
  • EN are similar (same/bond lengths/strengths)
  • Valence charges are similar (same bond lengths/strengths)
  • Crystal structures are identical (only if large ~50% solute) → otherwise forms 2 interpenetrating crystals (complex)
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27
Q

Structure of ceramics

A

• Crystal structure (composed of ions, rather than atoms)
* Must be electrically neutral
• Optimal stability when cations have max # anions (and vice versa)

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28
Q

AX crystals

A
  • Cation (A) and anion (X) have EQUAL charge

* Must have equal # of both to be stable ceramic

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29
Q

[A]_m*[X]_p crystals

A

• Cation (A) and anion (X) have DIFFERENT charges

* # m, p must balance charges to maintain electroneutrality

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30
Q

[A]_m[B]_n[X]p crystals

A
  • 2 cations (A,B) and 1 anion (X)

* e.g. ZSCAP and FECAP ceramics

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31
Q

Carbon-based materials e.g. graphite

A
  • Sometimes classified as ceramic (loose defin.)
  • Crystalline structure, but no standard unit cell
  • Ability to adsorb gases e.g. CV devices
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32
Q

Schottky defect

A

[ceramics]
• Vacancies of BOTH cation and anion (must balance ratio to maintain electroneutrality)
• Created based on same thermo. principles for ceramics as in metals (↑ entropy)

33
Q

Frenkel defect

A

[ceramics]
• Vacancy/interstitial pair is created to maintain electroneutrality
• Typ. only w/ cations b/c anions are too large for interstitial spaces (→ lattice strain)

34
Q

Macromolecules

A
  • Scale: xE5-xE6 g/mol
  • e.g. polymeric mat’ls
  • Typ. CH covalent bonds = main constituent
35
Q

Mer

A

\repeat unit (fixed # of atoms) of polymers

36
Q

Monomer

A

1 mer

37
Q

Oligomer

A

2-10 mers

38
Q

Polymer

A

“many” mers

39
Q

Saturated

A

∀ carbon in the mer has 4 other atoms

40
Q

Unsaturated

A
  • <=3 atoms per carbon, allows for double bonds

* May affect X-talinity and crosslinking

41
Q

Bifunctional

A

\repeat units can bond w/ mers on BOTH ends (most polymers)

42
Q

Trifunctional

A

\repeat units can bond w/ THREE (3) other mers → polymer network

43
Q

Degree of polymerization

A

“n” = # repeat units in polymer

44
Q

Number-average molecular weight

A

[ M_n = (ΣNM)/(ΣN) ]

• N = # chains of single MW
• M = avg. molec weight for chosen MW range
* Treats all polymer chains equally

45
Q

Weight-average molecular weight

A

[ M_w = (ΣNM^2)/(ΣNM) ]

  • Weight larger chains as larger contribution to final value
46
Q

Polydispersity Index (PI)

A

[ PI = M_w/M_n ]

  • Min. value = 1 (all polymers have same MW = \monodispersed; ideal for predicting prop’s)
  • Shows MW distrib. (PI ↑ as MW broadens)
47
Q

Conformation

A
  • ROTATION of single (σ) bonds
    • Impaired by bulky side groups
    • Frozen by rigid C==C (double bonds)
48
Q

Configuration (tacticity)

A
  • BREAKING/REFORMING primary bonds

• \isotactic, \syndiotactic and \atactic config.’s

49
Q

Isotactic configuration

A

R groups on same side of chain

50
Q

Syndiotactic configuration

A

R groups on alternate sides of chain

51
Q

Atactic configuration

A

R groups randomly distributed

52
Q

Special case: repeat unit contains C==C bond

A
  • \cis = constituents on same side

* \trans = constituents on opposite sides

53
Q

Linear polymers

A

\repeat units joined end-to-end

54
Q

Branched polymers

A

Synthesis conditions produce side reactions, which produce chains that branch off main polymer chain

55
Q

Crosslinked polymers

A

• (“ladder”) adjacent chains joined at certain points via covalent bonds → 3D polymer network
• May be induced during synthesis or afterwards via nonreversible chemical rxn
• ↑ MW of polymer chains as they are bonded together
* ↓ X-talinity when crosslinked (b/c need movement)

56
Q

Polymerization

A
  • Synthesis of polymers through repeated chemical rxns, which join individual mer units into a chain
  • \addition & \condensation
57
Q

Addition polymerization

A

• “chain reaction” - bifunctional monomers required; product contains same chemical structure as mer unit
1 . \initiation - initiator species activates monomer (radical or ionic species)
2. \propagation - monomers successively join polymer; active site con’t transfer to new monomer
3. \termination - destruction of active site via rxn (of 2 propag. chains, free radical or ionic solvent)

58
Q

Free radical polymerization

A

[addition polymerization]
1 . \initiation: free radical activates monomer
2. \propagation: monomers join polymer chain
3. \termination: free radical reacts w/ active carbon

59
Q

Ionic polymerization

A

[addition polymerization] * Gen’lly less polydisperse
1 . \initiation: cat/an-ionic species activates monomer
2. \propagation: monomers join polymer chain
3. \termination: charged active site reacts w/ solvent/water or side reactions

60
Q

Condensation polymerization

A
  • “step reaction” involving mult. monomer species
  • Occurs thru elim. of one molec. (typ. water) ∴ product does not have same chem. formula as either mer
  • Need long reaction times and near depletion of monomer → high MW
  • PI values similar to addition polym.
61
Q

Polymer synthesis via genetic engineering

A
  • Potential for greater control over polymer weight distrib./geom.
  • Expression of gene within host (protein polymer of interest, PPOI) → isolated → introduced into host
62
Q

Copolymers

A
  • Mult. repeat unit types
  • Formed by addition polym. or condensation polym., using a blend of monomer types as reactant species
  • \random, \alternating, or \block
63
Q

Homopoolymers

A

1 type of repeat unit

64
Q

Random copolymers

A

2 mer units distrib. along chain w/o specif. pattern

65
Q

Alternating copolymers

A

2 mer units alternate

66
Q

Block copolymers

A

Each type of repeat unit is clustered (blocks)

67
Q

Graft copolymer

A

Homopolymer chains attached as side chains to main homopolymer chain of different repeat unit

68
Q

Polymeric crystal structures

A

• More complex unit cells and contain more atoms
• Depends on tactility and degree of branching (e.g. more branching/bulky side groups reduces X-talinity of polymeric material)
∴ most polymers are semicrystalline

69
Q

Polymeric point defects

A
  • Vacancies = spaces b/w chain ends
  • Impurities may be intentional e.g. copolymers
  • Less impact in polymers (than metals/ceramics)
70
Q

Spectroscopy

A
  • Excitation of electrons (absorption of energy)

* Measures how compounds differ in % absorp.

71
Q

Chromatography

A

• Physical separation of molec’s based on chem char
• e.g. MW or charge
* Does not indic chem composition of mat’l

72
Q

Mass spectrometry

A

• Determines atomic/molec mass of species in mat’l
1 . \ionization chamber (high energy particles)
2. \mass analyzer: Magnetic fieldm
3. Deflection based on mass (lighter = more deflection, only want target mass to hit \detector)
• Can control magnetic field to direct ions of specif. mass to detector
• Computer plot: relative intensity/absorption v. mass
* Highest molec ion ≈ MW of entire molec (all else = fragments of molec)
** App: chem compos of polymers and relative strength/stability of bonds

73
Q

Size-exclusion chromatography (SEC)

A
  • Column w/ beads w/ pores inside
  • Small particles can enter the pores, whereas large particles will float around the pores
  • Larger species elute first b/c they cannot be trapped; smaller particles = longer (\retention time)
  • Pores in beads allow mobile phase to pass thru
  • i.e. either gravity feed (large columns) or pump (small columns) → circulates \mobile phase
74
Q

Stationary phase

A

= column + polymer beads (or small porous silica)

75
Q

Mobile phase

A

= liquid solvent + dissolved sample

76
Q

Retention time

A

• Time retained in porous structure, before elution

* Anything larger than pores cannot enter ∴ only smaller analyte can penetrate network

77
Q

Gel filtration chromatography (GFC)

A

(polar) aqueous solvents + hydrophilic stationary beads

78
Q

Gel permeation chromatography (GPC)

A

(nonpolar) organic solvents + hydrophobic stationary phase

79
Q

High performance liquid chromatography (HPLC) SEC instrumentation

A

1 . Pump (circulation of mobile phase)

  1. Injector (of sample into mobile phase)
  2. Column (separates molec’s based on retention time)
  3. Detector/spectrophotometer (converts amount of analyte in mobile phase to electrical signal)
  4. Processor/computer (converts electrical signal to graph)
  • Must match column w/ expected MW (start w/ broad range of beads, then more distinct beads)
    • App: used to determ. MW of polymers (compared w/ \reference mat’ls to produce \standards of MW v. elution time)

Biomaterials (6 decks)

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