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Biomaterials > Biomaterials Exam I Review > Flashcards

Biomaterials Exam I Review Flashcards

1
Q

Aufbau Principles

A

The lower energy states before the higher ones. No energy state can be occupied by more than 2 electrons (Pauli exclusion), each need their own spin.

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2
Q

Periods on the Periodic Table

A

Horizontal

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3
Q

Groups on the Periodic Table

A

Vertical

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4
Q

Ionic Bond formation

A

Primary bond. Involves the sharing/transfer of electrons. Occurs with large electronegativity differences.

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5
Q

Ionic bond properties

A

Nondirectional, so they are very brittle, they will shatter rather than deform.

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6
Q

Covalent bond formation

A

Primary bond where both atoms are electronegative and the electrons are shared. Orbitals hybridize.

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7
Q

Sigma bond

A

Part of a covalent bond. Short bond lying on the internuclear axis that allows rotation.

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8
Q

Pi bond

A

Part of a covalent bond. Bond because of orbital overlap, prevents rotation.

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9
Q

Metallic bond formation

A

Electropositive ion cores surrounded by a sea of electrons (negative)

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10
Q

Metallic bond properties

A

Nondirectional, easier to deform. High electrical conductivity because electrons can easily move.

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11
Q

Van de Waals

A

Secondary bond. Arise from dipoles, albeit permanent, polar-induced, or fluctuations

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12
Q

Hydrogen Bond

A

Secondary bond. X~H-Y, where X and Y are F, O, or N. Very important for synthetic polymers and biomolecules.

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13
Q

Single Crystal Materials (Crystalline)

A

Periodic and Repeated arrangement of atoms that is perfect throughout the entire specimen (ex. NaCl)

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14
Q

Polycrystalline Materials

A

Collection of many small crystals or grains, whose size and number play a role in material properties.

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15
Q

Amorphous Materials

A

Lacks a systematic and regular atomic arrangement over large atomic distances

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16
Q

Braggs Law and Diffraction

A

Used constructive and destructive interference to determine the crystallinity of a material. n(gamma)=2dsinØ. When constructive interference: crystalline. Crystalline material has narrow distinct X-ray diffraction peaks compared to amorphous.

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17
Q

Metal Classification

A

Metallic bonding, simple crystal structure, e.g., carbon material

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18
Q

Ceramics Classification

A

Combo of ionic or covalent bonding with a complicated crystal structure or amorphous, e.g., glass

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19
Q

Polymers Classification

A

Primarily Covalent bonding. In thermoplastics secondary bonds hold it together, where in thermosets covalent cross linking holds. e.g., composite materials

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20
Q

Structure-Property Relationship

A

Composition does not equal property. Atomic arrangement can create a different crystal e.g., diamond and graphite

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21
Q

Crystallinity effects on opacity?

A

Polycrystallinity increases opacity

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22
Q

Crystallinity effects on degradation/corrosion?

A

Low crystallinity and more grain boundaries means a faster degradation for ceramics/polymers and low metal corrosion resistance

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23
Q

Ultimate tensile strength (uts)

A

The highest amount of stress a material can withstand.

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24
Q

Fracture stress

A

Point that a brittle material breaks.

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25
Q

Yield Stress

A

The point at which a ductile material’s stress stain graph is no longer linear

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26
Q

Youngs Modulus

A

Stress over strain for the linear part

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27
Q

Ductility strain

A

The point at which the effects are no longer reversible (plastic deformation occurs)

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28
Q

Fatigue

A

Structures fail due to cyclic stresses that are lower than UTS. One of the biggest challenges in biomaterials. Run fatigue tests before insertion for load-bearing materials. If not load bearing, make sure the biomaterial matches the native tissue mechanical properties.

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29
Q

Polymer

A

Substance composed of molecules which have long sequences of one or more atom species or groups of atoms linked by primary (most often covalent) bonds

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30
Q

Thermoplastic Polymers

A

Linear and branches structures. Can be melted with heat and reshaped/molded. Semicrystalline or amorphous.

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31
Q

Thermosets

A

Cross-linked, rigid/rubbery. Intractable and cannot be melted and molded, it will decompose/melt with heat

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32
Q

Homopolymers

A

Polymers from the polymerization of a single monomer with ‘n’ degrees of polymerization

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33
Q

Copolymers

A

Polymers whose molecules have more than one type of repeat unit

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34
Q

Statistical copolymers

A

The sequential distribution of repeat units that obeys statistical laws

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35
Q

Random Copolymer

A

A ‘true random’ with no order whatsoever

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36
Q

Alternating copolymer

A

Specific repeated sequence for more than one type of monomer

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37
Q

Graft copolymer

A

Branches polymers with the branch having a different composition from the main chain

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38
Q

Block copolymer

A

Repeat units that exist in blocks of the same type. Can be manipulated to make channels, etc.

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39
Q

Step-growth polymerization

A

polymerization in which the chain grows step wise between any two molecular species, can grow on either side of the chain. Occurs through condensation reactions.

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40
Q

Chain-growth polymerization

A

Polymerization in which a polymer chain only grows by the reaction of monomers with a reactive end group on one end of the chain. Started by an indicator and is a fast reaction. Occurs by reaction with a free radical. Common imitators: AIBN (light), and benzoyl peroxide (∆)

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41
Q

Draw the polyester making process

A

nHO-R-OH + nHOOC-R’-COOH -> H(O-R-OCO-R’-CO)OH + (2n-1)H2O

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42
Q

Draw the polyamide making process

A

nNH2-R-NH2 + nHOOC-R’-COOH -> H)NH-R-NH-CO-R’-CO)OH + (2n-1)H2O

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43
Q

Free Radical Polymerization Termination, Combination

A

2 radicals combine together to form a pairing

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44
Q

Free Radical Polymerization Termination, Disproportionation

A

Creates a double bond in the chain, chain length does not grow

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45
Q

Anionic Polymerization

A

Active center has an ionic charge (no termination step), retains end groups, adding monomers will make the chain grow more. Can be used to make block copolymers

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46
Q

Draw polypropylene

A

-[CH2-CH-CH3]-

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47
Q

Draw Polystyrene

A

-[CH2-CH-Benz]-

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48
Q

Polytetrafluroethylene (PTFE), TEFLON

A

-[CF2-CF2]-

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49
Q

Poly(methyl methacrylate) PMMA, Plexiglass

A

-[CH2-C-CH3-COOCH3]-

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50
Q

Mn

A

Number average molar mass. sum(NiMi)/sum(Ni)

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51
Q

Mw

A

Weight-average molar mass. sum(NiMi^2)/sum(NiMi)

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52
Q

PDI

A

Polydispersity Index, Mw/Mn

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53
Q

Xn

A

Number-average degree of polymerization. Mn/Mo

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54
Q

Xw

A

Weight-average degree of polymerization, Mw/Mo

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55
Q

End Group Analysis

A

A way to measure molecular weight. Use titrations to measure n groups, but this only works for very particular molecules

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56
Q

Gel permeation chromatography (GPC)

A

Size exclusion column. Dilute polymers are run through a column of porous beads. The high MW molecules cannot bind and elute first, the lower MW molecules pass elute later

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57
Q

MaChain entanglement, IMF summation, and the time scale of motion (Slower polymer motion)ss Spectroscopy

A

Another way to determine the molecular weight. Samples become charged as they are passed through an electric field, and they go a specific path based on their weight

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58
Q

What makes polymers unique? (3 answers)

A
  1. Chain entanglement
  2. Summation of IMFs
  3. The time scale of motion (slower polymer motion)
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59
Q

Crystal unit cell

A

Smallest part of a lattice that determines the 3D nature of the crystal

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60
Q

Are polymers crystalline?

A

No, either semicrystalline or amorphous

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61
Q

Branches effect on crystallinity?

A

Decreases

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62
Q

Cross-links effect on crystallinity?

A

decreases

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63
Q

Big end groups effect on crystallinity

A

decreases

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64
Q

Effect of an irregular side group on crystallinity?

A

If the side group is small, no effect (ex. F), if big, decrease crystallinity

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65
Q

Isotactic

A

When the end groups face the same way (highly crystalline)

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66
Q

Syndiotactic

A

When the end groups oppose on another on the chain (highly crystalline)

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67
Q

Atactic

A

When the end groups are random on the chain, amorphous (not crystalline)

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67
Q

Increasing polymer IMF, _____ Crystallinity

A

Increase. Polymers are more tightly packed

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68
Q

Polymer Quenching -> ______ Crystallinity

A

Decreases. The quick heat/cool process can make the crystals have many different mechanical properties

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69
Q

Polymer Annealing -> ________ Crystallinity

A

Increases. The long term heat makes the polymer become more ductile and less brittle.

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70
Q

Drawing -> _____ Crystallinity

A

Die forces reduced orientation of amorphous structure, increases crystallinity

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71
Q

Melting transition

A

Primary thermotransition. Enough energy to overcome overall chain motion to overcome secondary bonds. Discontinuous heat graph

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72
Q

Glass transition

A

Amorphous material only. When the molecule has enough energy to cause molecular motion around the polymer backbone. Temperature at which a glassy polymer becomes rubbery, molecular motion of amorphous regions around the backbone

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73
Q

Tg above room temperature

A

Glassy material

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74
Q

Tg below room temperature

A

Rubbery material

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75
Q

Backbone effect on Tg?

A

Flexible backbone low Tg. Rigid backbone has a high Tg (double, triple bonds)

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76
Q

Pendent groups effect on Tg?

A

Increased steric hinderance -> less flexible -> lower Tg

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77
Q

IMF effect on Tg?

A

Higher IMFs, higher Tg

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78
Q

Crosslinking effect on Tg?

A

Increase cross linking, increase IMFs, increase Tg

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79
Q

Plasticizer effect on Tg?

A

Plasticizer is a small molecule that can be added during the polymer process, missile and fills in volume within the chain, lowers Tg

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80
Q

True or False: glass transition temp is always lower than melting transition temp

A

True! Tg=(0.5-0.8)Tm

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81
Q

The longer the side chain, the ____ the Tg

A

Lower, because it is now acting as items that take up a lot of space, plasticizers can fit in

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82
Q

Differential Scanning Calorimetry (DSC)

A

Can measure the thermal transition. Sample on a heater with a reference pan, measures ex/endo heat flow.

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83
Q

Fiber polymer examples:

A

KelvarTM/Nylon. Linear and brittle, no curve in stress/strain graph

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84
Q

Glass polymer examples:

A

polystryene (PS), PMMA, linear with a quick breaking point (compared to fiber polymers)

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85
Q

Semi-crystalline polymer examples

A

polyethylene, polypropylene. Ester-> plastic materials with strain hardening effects

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86
Q

Elastomer polymer examples

A

Polyisoprene, polybutadiene, no linearity, plastic deformationSt

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87
Q

stress hardening effect

A

Increasing deformation increases stress, polymers can sometimes rearrange and lower these stress levels as they deform

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88
Q

Ductile-brittle Transition

A

Make rubbery go to brittle by increasing the strain rate of decreased temperature quickly.

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89
Q

Creep

A

Viscoelastic behavior. Time dependent extension under load. Apply a fixed load and measure the elongation.

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90
Q

Stress Relaxation

A

Viscoelastic behavior. A time dependent decrease in stress at a fixed strain. Polymer chains move around to relieve the stress

91
Q

Degradation

A

The chemical process that results in the cleavage of covalent bonds in the backbone/crosslinks

92
Q

Erosion

A

physical change in size, shape, or mass as a result of degradation or dissolution

93
Q

Erosion can be driven by 3 chemical process, name them:

A
  1. Cleavage of crosslinks between water soluble polymer chains
  2. Transformation or cleavage of hydrophobic side chain X that leads to addition of polar group Y
  3. Cleavage of the backbone
94
Q

What is bulk erosion?

A

The rate of water penetration into the solid device is greater than the rate the polymer is made water soluble. The polymer is eroding from both the inside and the outside. Changes mechanical properties.

95
Q

What is surface erosion?

A

Polymer is degraded by actions at the surface of the molecule rather than within. No changes to the mechanical properties.

96
Q

Oxidative Degradation (bad)

A

The polymer chain is attached by reactive species (ROSs) or cytokines/chemokines. Polymers that are meant to be permanent can now degrade readily

97
Q

Enzymatic Degradation (ugly)

A

Major degradation mechanism for natural polymers, but is pretty selective. Not predictable, because the level of enzymes vary from time to time etc. They perform surface erosion.

98
Q

Hydrolytic Degradation

A

Host induced and pH/enzyme catalyzed. “Good” degradation. Polyanhydrides erode faster than polyesters, which erode faster than polyamides. The more polar, the quicker degradation.

99
Q

Crystallinity Increases, Hydrolytic Erosion _______?

A

Decreases

100
Q

Above Tg, Hydrolytic Erosion _____?

A

Increases. (faster erosion when rubbery bc the molecules have more room to move, known as the ‘free volume theory’

101
Q

Higher the MW, Hydrolytic Erosion _____?

A

Decreases, more mass to penetrate

102
Q

The more the surface area, Hydrolytic Erosion _____?

A

Increases, more access to penetrate into the material

103
Q

Increased mechanical stress, Hydrolytic Erosion _____?

A

Increases, can invade microcracks

104
Q

Advantages of degradable biomaterials

A

Permanent implants can cause chronic inflammation and stress shielding (bad!)
Can be gradually absorbed by the body
Adjustable degradation rate

105
Q

How to store degradable biomaterials?

A

Avoid moisture and pack in air-tight aluminum foil, low air temp. Do not autoclave/irradiate, but ethylene oxide (gassing) is okay

106
Q

Draw PGA

A

poly(glycolic acid), H-[-O-CH2-C=O-]n-OH

107
Q

polyglycolic acid

A

Simplest aliphatic polyester. Highly crystalline, high Tm/low solubility. Rapid mechanical deterioration upon degradation. Used in bone pins, bone screws

108
Q

Draw PLA

A

Poly(lactic acid), H-[-O-CH-CH3-C=O-C]n-OH

109
Q

polylactic acid

A

Chiral molecule, can be D-PLA or L-PLA. PLLA is most often used because it’s the most natural in the body. Semi-crystalline PDLA and PLLA, amorphous DLPLA

110
Q

PLGA

A

Copolymer of LA and GA. PLLA is more hydrophobic, reduces breakdown of PGA. No linear relationship between the glycolic acid and lactic acid ratio and the mechanical and degradation properties of the copolymers.

111
Q

About polyanhydrides

A

Most reactive and hydrolytic ally unstable polymers used in biomaterials. Fast degradation with high biocompatibility. Used in drug delivery.

112
Q

What is a hydrogel?

A

Materials composed of hydrophilic, cross-linked polymer chains. Highly water-swollen. Can synthesize dry and put in water, or synthesize in aqueous then swell with water

113
Q

Crosslinks

A

Covalent bonds, H-Bonds, strong VdWs

114
Q

Ionic hydrogel

A

When a polyanion is exposed to a multivalent cation, they bind and crosslink, making an inotropic hydrogel (ex. alginate). Or when a polycation and a polycation bind, making polyelectrolyte complex (PEC) hydrogel

115
Q

Swelling behavior

A

The thermodynamic compatibility between the water and polymer chains.

116
Q

Hydrogel advantages

A

Closely mimic mechanical properties of soft tissues, and may be polymerized into any geometry. Can make a cell-responsive hydrogel.

117
Q

Smart Hydrogels

A

Environmentally responsive and slow change in swelling due to changes in pH, temperature, ionic strength, nature of swelling ages, electric/magnetic stimuli. This is a reversible process. (ex. pH increase makes an acid lose its H+ ion, becomes more hydrophilic)

118
Q

Body-centered cubic (BCC)

A

When there is a crystal repeat every corner of a cube and the middle.

119
Q

Face-centered cubic (FCC)

A

When there is a crystal repeat every corner of a cube, nothing in the center of the cube.

120
Q

Metal Vacancy defect

A

Lack of one of the positive ions, highly reactive in this area.

121
Q

Metal interstitial defect

A

An additional positive ion on top of the positive ions there already, higher energy here.

122
Q

Substitutional atom

A

Can fit another atom where a vacancy defect once was

123
Q

Impurity atom

A

Atom added on top of the positive ion core, can create alloys, which have superior mechanical strength/corrosion resistance, etc.

124
Q

Line Defects - Edge dislocation

A

Occurs when an extra plane or layer of atoms extends part way into the crystal, which causes atoms in that region of the crystal to be compressed, but in the region where the extra plane does not extend they are spread apart.

125
Q

Line defects - Screw dislocation

A

A rotational defect, shifts like a spiral staircase.

126
Q

Metal deformation

A

Applying a shear stress breaks down a bone. This can go ahead and create a new bond behind where the bond was broken, pushing the material. This repeats. Occurs more easier on plans with higher atomic density. Only a small stress is needed, as one row of bonds is broken at a time.

127
Q

Elastic vs Plastic deformation

A

Elastic: all lattice bends, no bonds broken, and is reversible
Plastic: only one part of the lattice (where the force is applied) moves, break one row of bonds, and is not reversible

128
Q

Grain boundaries

A

Atoms at grain boundaries are in a higher state of energy than those in the center/ So the total interfacial energy in materials with large grains is lower than those with less grains as there are less boundary areas

129
Q

Solid Solution strengthening

A

Adding point defects (alloying), makes metal stronger and prevents dislocation

130
Q

Strain hardening

A

Adding line defects (cold working), think blacksmith

131
Q

Grain Size Strengthening

A

Add planar defects, thermal processing

132
Q

Corrosion

A

The unwanted chemical reaction of a metal with its environment, results in its degradation to oxides, hydroxides, and other compounds. Occurs through coupling of oxidation and reduction

133
Q

Anode

A

Metal is oxidized, losing electrons

134
Q

Cathode

A

Metal is reduced, gains electrons

135
Q

Half cell potential

A

The electrical potential at equilibrium, characteristic of a metal measured against hydrogen reference.

136
Q

The more positive the standard electrode potential, the ______ the metal

A

Less likely it is to erode (less reactive), and less likely to be oxidized

137
Q

Galvanic Corrosion

A

Two different metals with electrical contact. More negative potential metal gives up electrons which travel to the less negative metal, the more neg. one corrodes

138
Q

Pitting Corrosion

A

Starts from surface imperfection, the pit acts as an anode

139
Q

Fretting Corrosion

A

Rubbing one part on another, disrupting the passivating later, which stores the electrolyte/cases fatigue

140
Q

Crevice Corrosion

A

The region of device with poor mass transport, chemical environment is different in the crevice from the surrounding.

141
Q

Stress corrosion cracking

A

The stressed region can degrade due to mechanical energy, fatigue stress corrosion can occur with repeated stress.

142
Q

Stainless steel

A

Most common medical implant type is 316L (L=low carbon).

143
Q

Add Cr to stainless steel

A

Forms an adherent surface oxide and increases corrosive resistance.

144
Q

Carbon in stainless steel

A

High carbon content can form carbide and precipitate at grain boundaries, depleting Cr. Low carbon% -> higher corrosion resistance

145
Q

Cr vs Ni in stainless steel

A

Cr stabilizes the BCC phase, which is weaker than the FCC phase. Ni stabilizes the austenitic (FCC) phase

146
Q

Annealing effect on stainless steel

A

Increases grain size, lower strength and more ductile (less grain boundaries, can’t glide as while -> easier deformation)

147
Q

Cold working effect on stainless steel

A

Greater strength/hardness and less ductile

148
Q

Cobalt Alloys

A

Uses Cr oxide to lower corrosion resistance. High fatigue and UTS yields. Used in dentistry, joints, knee/hip joints.

148
Q

Titanium and Ti-based alloys

A

C, O, and N strengthen the material through solid solution strengthening mechanism. Higher O% yields higher strength and lower ductility. TiO2 is an oxide formed on the surface, corrosion resistant. Very inert, no toxic degradation product.

148
Q

Stress Shielding

A

The high strength of metal makes the joint rely on it more, decreasing the force on the actual tissue and this can decrease bone density, which can cause many complications.

149
Q

Mg Metal

A

Used in many biological processes (safe), safe byproducts and undergoes complete degradation, with similar mechanical properties to cortical bone.

150
Q

Ceramics, glasses, and glass-ceramics

A

Inorganic, nonmetallic solids prepared from powered materials and fabricated through heat application. Difficult to shear, low ductility, high compressive strength, low tensile strength. Low thermal and electrical conductivity. High Tm, high hardness.

Examples: aluminia, sapphire, ruby,

151
Q

Ceramic Dislocation Slip

A

Must occur over 2 atomic positions due to the electroneutrality requirement, less likely to occur, so it has more brittle fractures.

152
Q

What can cause ceramic resorption/degradation?

A

physiochemical dissolution, material solubility, local pH, chemical stacks at grain boundaries, biological factors (e.g., phagocytosis)

153
Q

Calcium Phosphate

A

the mineral phase of bone and teeth. Solubility and hydrolysis decrease with INCREASED Ca/P ratio

154
Q

Hydroxyapatite (HA)

A

Hard tissues that contain a lot of carbonate and HA. Its defects and impurities can be characterized by X-ray diffraction (crystalline) and FTIR (chemical groups)

155
Q

FT-IR

A

Fourier Transition Infrared Spectrum. Measures the vibrations of a chemical bond, each bond has a specific frequency. Infrared spectrometer sheds IR beam onto the sample and measures the radiation at various wavelengths that are transmitted or reflected by the sample. Use an FT to turn the raw data into spectrum..

156
Q

CaP (ceramics) degrades quicker as chemical susceptibility to dissolution ____?

A

Increases

157
Q

CaP (ceramics) degrades quicker as surface area ______?

A

Increases

158
Q

CaP (ceramics) degrades quicker as crystallinity _________?

A

decreases

159
Q

CaP (ceramics) degrades quicker as crystal perfection _____?

A

decreases

160
Q

CaP (ceramics) degrades quicker as grain size ________?

A

decreases

161
Q

CaP (ceramics) degrades quicker as F- substitution _______?

A

decreases

162
Q

Clinical Application of CaP

A

Bioactive and osteoconductive. When dense can be used for unloaded implants. When porous can be granules for filling bone defects, as a coating it can reinforce

163
Q

Bioactive glass and glass-ceramics

A

Surface forms a biologically active carbonated HA layer that bonds with the tissue. The interfacial strength > the bulk strength of both implant and tissue. Highly reactive surface in aqueous medium (1. SiO2, 2. high Na2O and CaO, 3. high CaO/P2O5 ratio)

164
Q

The more SiO2 in the glass ceramic

A

Silicate glass, nearly inert

165
Q

Dense, nonporous, nearly inert. Attachment type to host tissue?

A

Bone growth into surface irregularities by cementing device into the tissue/press fitting into a defect (morphological fixation); movement -> increase thickness of interfacial layer

166
Q

Porous, inert. Attachment type to host tissue?

A

Ingrowth occurs that mechanically attaches the bone to the material (biological fixation). Needs a small pore size for tissue to be viable.

167
Q

Dense, non-porous, surface-reactive. Attachment type to host tissue?

A

Elicit a biological response at the interface, formulation of chemical bonding with the bone (bioactive fixation).

168
Q

Dense, resorbable. Attachment type to host tissue?

A

Slowly is replaced by bone

169
Q

Carbon materials

A

Crystalline (diamond, graphite, fullerene). Quasicrystalline (glassy carbon, inert electrodes)

170
Q

Composite

A

Consisting of 2 or more chemically distinct parts in the macro-scale, with distinct interfaces separating them. Fiber/particulate particles usually consist of one or more discontinuous phases (stronger) embedded in a continuous phase (matrix). Bone and tendons are composites

171
Q

Surface Importance

A

It is the first contact with a biological system, and has different properties than the bulk. Easily contaminated. Surface structure is often mobile/

172
Q

Surface anatomy

A

Hydrocarbon -> polar organic molecules -> absorbed water -> metal oxide -> bulk implant?

173
Q

Wettability

A

Hydrophobicity and hydrophilicity. Hydrophobic surfaces have low surface energy, water beads at the surface (PE, PTFE)
Hydrophilic surfaces have higher surface energy, with water wetting the surface
Surface structure can be mobile, hydrophilic domains may rearrange to face surface in aqueous environments (e.g., contact lenses)

174
Q

Contact Angle

A

Describes the shape of a liquid drop resting on a solid surface (measures gettability of a surface). The HIGHER the contact angle, the LOWER the surface energy/tension. The more hydrophobic the surface, the higher the contact angle. (ex. skin, PE, PP, and PTFE have high contact angles, where PE/PP and PET-PEG have low contact angles)

175
Q

Characteristic IR Absorption bands

A

Absorption bands are assigned to functional groups. The wavenumber is more frequently ones (1/wavelength). Shifts in the frequency of absorption bands and changes in band intensities indicate chemical structure changes or changes in sample environment. Gives a bulk view

176
Q

ATR-FTIR

A

Attenuated Total Reflectance-FTIR provides specific surface information, only goes in 1-5µm, inexpensive and quick but not very surface sensitive and needs a flat surface to have good contact with the internal reflective element (IRE)

177
Q

X-ray Photoelectron Spectroscopy

A

Also known as electron spectroscopy for chemical analysis (ESCA). Extremely surface selective and sensitive. Based on the photoelectric effect, the interaction of the X-rays with atoms causes emission of the inner shell electron and kinetic energy of e- can be measured. Then the binding energy can be collected.

binding energy of electron to atom = X-ray energy - kinetic energy of emitted electron

178
Q

ESCA/XPS

A

X-ray is shown onto a surface (several micron penetration), excited photoelectrons jump from the surface and can be measured. Needs to be within a vacuum. Extremely surface sensitive, b/c though it can deeply penetrate into the sample, the emitted electrons will lose their energy and never emerge back to the surface, Å level.

179
Q

ESCA/XPS Advantages/Disadvantages

A

Advantages: Near surface (~8nm), with high information content. Good depth profile with low damage potential/preparation needed.

Disadvantages: expensive, needs a vacuum, not good for a complex surface

180
Q

Secondary Mass Spectrometry (SIMS)

A

Based on the generation of secondary ions due to the bombardment of a solid surface by incident beams of accelerated ions (primary ions, usually argon/xenon). The mass and charge the secondary ions can be measured using a time-of flight mass analyzer.

181
Q

Dynamic SIMS

A

Used for obtaining compositional info as a function of the depth below the surface. High ion doses, fast surface erosion. Only can detect atomic fragments and the deeper the beam the more artifacts/higher SNR

182
Q

Static SIMS

A

Used for sub-monolayer elemental analysis. Low ion dose, adjusted so less than one monolater of surface atoms are sputtered. Can look at large fragments

183
Q

SIMS Advantages/Disadvantages

A

Advantages: Most surface sensitive, (15Å or smaller). Useful with isotopes, can achieve high spatial resolution by focusing the primary ion beam.

Disadvantages: Expensive and hard to interpret

184
Q

Scanning electron microscopy (SEM)

A

Focus/raster a high energy electron beam onto a specimen. Detect the emitted low energy secondary electrons. Reconstruct the secondary electron intensity on a phosphor screen. In conductive materials, energy dispersive X-ray EDX analysis can be used for bulk elemental analysis (few µm deep). For nonconductive materials, they are coated with metal/carbon (grounded) to minimize the accumulation of negative charges, contaminates the surface chemistry info. Good for rough surface and texture evaluation.

185
Q

Atomic Force Microscope (AFM)

A

Measures topography with a force probe. Laser beam reflection offers a convenient and sensitive method of measuring cantilever deflection. Sample is placed on a piezotube, and a laser diode is beamed onto it, moving the cantilever, whose movement is detected and recorded. Can measure the surface at an atomic level.

Can be used with both conductive and non-conductive surfaces, so it can be used under water, in air, or in a vacuum. Atomic level resolution, but not feasible for organic or biological samples. Tip shape (sharpness) limits resolution.

186
Q

Tight junctions

A

Hold cells together, maintain polarity, and prevent transport through space between cells. Uses actin microfilaments to maintain.

187
Q

Desmosomes

A

Homotypic association of cadherins. Linked to intermediate filaments to help resist shear force

188
Q

Gap junctions

A

Big, ion channels used for cell-cell communications, integrins

189
Q

Cadherins

A

Cell-cell contact in desmosomes, homophilic

190
Q

Selectins

A

Cell-cell binding via heterophillic binding to carbonhydrates (e.g., Carbohydrates on Mucins)

191
Q

Cell adhesion molecules (CAMs)

A

Cell-cell binding, homophilic or heterophilic. Many are a part of the immunoglobulin superfamily

192
Q

Proteoglycan receptors

A

Receptors made out of more sugar than protein

193
Q

Integrin

A

Mediate cell-cell and cell-ECM interactions. CAM-integrins are important to signaling cell migration at the beginning of the inflammatory response. The Integrin-ECM interaction: ligand binds to ECM -> signal transduction -> intracellular events that change cell fate.

194
Q

The ECM

A

Insoluble non-cellular material between cells throughout the body. Provides support, tensile strength, substrates for cell adhesion and cell migration, and regulates cell differentiation and metabolic function. Composed of GAGs and fibrosis proteins (structural and adhesive)

195
Q

Glycosaminoglycans

A

Typically hyaluronic acid, keratan sulfate. Proteoglycan is several GAGs covalently acted to one protein core. Highly negative, hydrophilic. Interacts and retains growth factors, stabilizes collagen

196
Q

Collagen

A

ECM structural protein. Triple helix with 3 polypeptide chains. High mechanical and tensile strength

197
Q

Elastin

A

ECM structural protein. Intrinsic crosslinks between fibers allow the stretching and relaxation of the molecule (less plastic deformation and less brittle)

198
Q

Fibronectin

A

ECM adhesion protein. Integrin can bind to the RGD domain

199
Q

Laminin

A

ECM adhesion protein. Key component of basement membranes.

200
Q

What affects cell adhesion to synaptic surfaces? (4 parts)

A
  1. Protein adsorption precedes cellular adhesion
  2. surface free energy/wettability
  3. Surface charge (negative cell, use positive charges to encourage attachment)
  4. Surface topography (different for individual cell needs)
201
Q

How to promote cell adhesion?

A

Immobilize cell adhesion proteins/binding sequence.
Create topographic features
Growth factor immobilization/release

202
Q

How to prevent undesired cell adhesion

A

Create non-fouling surface to prevent protein adsorption and inhibit non-specific cell/surface interactions
Create repellent topography features
Release inhibitory factors (anti-inflammatory or antibiotic)

203
Q

Cell culture

A

Process by which cells are grown under controlled conditions (media, pH, glucose, growth factors, incubation, humidity, CO2 levels, etc).

Primary cells harvested from live organism, isolated and seeded in culture media. Explant culture: collect cells that growth out of the explant in growth media.

Need to do media change (replenish nutrients), passaging (prevent too high of density (which stops cell division), and transfection (introduce foreign DNA)

204
Q

Cell line

A

A group of animal cells derived from a primary culture at the time of first subculture, considered an established cell line when it shows potential fro indefinite subculture in vitro. Can get from cell banks -> thaw and plate

205
Q

Non-covalent suface coating

A

Physical adsorption (not a chemical reaction, cover the surface with densely packed molecules/polymers). Physical vapor deposition, or layer-by-layer (LbL) deposition (can use to make a uniform lipid layer)

206
Q

Original surface modifications can be done through:

A

ion beam etching, plasma etching, chemical reactions (specific or non-specific), mechanical roughening/polishing, and texturization

207
Q

Covalent attachment surface modification

A

Radiation (gamma) or photo (UV) or electron beam grafting
Plasma (gas discharge), (RF, corona, MW, acoustic)
Gas-phase dispersion (eg. chemical vapor deposition)
Silanization
SAM
Biomolecule immobilization

208
Q

What is Plasma?

A

Plasmas are atomically and molecularly dissociated gaseous environments with charge (positive ions, negative ions, free radicals, electrons, atoms, molecules, and photons). Can be produced by RF/microwave/acoustic energy/corona discharge

209
Q

Corona discharge

A

The application of high voltage to an electrode with a sharp tip

210
Q

Plasma deposition

A

Competition between deposition and physical etching (ablation)

First, the gaseous environment and UV emission creases free radical on the substrate that can react and polymerize with molecules from the gas phase.

Reactive molecules within the has phase can then combine to form higher-molecular-weight units that may settle/precipitate onto the surface

211
Q

RFGD Plasma Deposition

A

Gas (single gas or a mixture) is inlet into a vacuum chamber. The samples are placed between two capacitors. RF power is pulses through the reactor and the deposition can occur.

212
Q

biomedical applications of plasma

A

plasma treatment (etching): cleaning, sterilization, and cross-linking surface molecules (increases stability)

213
Q

Plasma etching and sketching

A

Barrier films can be a proactive/electrically-insulating coating, inhibits leachable release and reduces the adsorption of materials from the environment. It provides real active sites for grafting/polymerization/immobilization biomolecules. Can modify the cell and protein reactions

214
Q

TCPS

A

Polystyrene that is surface modified using corona discharges or gas-plasma to produce high energy oxygen ions that graft onto the chains. This makes the polystyrene surface hydrophilic and negatively charged

215
Q

Silanization

A

Hydroxylated surface (silicon, glass, aluminum, metal oxide). Simplicity/stability due to a covalently cross linked structure. The silane hydroxyl linkage is subject to base hydrolysis

216
Q

Self-Assembled Monolayers (SAM)

A

surface films that spontaneously form highly ordered structure on substrates. Chemical absorption and van den waals interactions between alkyl chains 9<# of CH2 for assembly<24. Functional heads point one way for surface interactions and attachment groups have strong interactions with a substrate

217
Q

Multilayer polyelectrolyte adsorption

A

Polyelectrolyte adsorbs on surfaces with opposite charge (eg. positive on HA). Once there is a thin layer, it repeals any more from joining in (thickness/uniformity control). This can repeat multiple times to build a polyelectrolyte complex (PEC) that is complex and ulilateral, LbL deposition

218
Q

Principles of Surface Modification

A

It should be the minimum thickness needed for uniformity, durability, and functionality but no thicker

Should be resistant to delimitation and cracking
-Chemical bonding
-Intermixing components of substrate and surface film at the interfacial zone
-Apply a compatibilizing layer at the interface
-Incorporate appropriate functional groups for strong IMF adhesions

Surface rearrangement cannot occur (Cross-linking to block the ability for the surface structure to move)

219
Q

Biomolecule surface immobilization

A

Used in biosensors. Biocompatibility: ligands/growth factors for cell adhesion. Inhibitory factors to prevent improper adhesion.

220
Q

Methods of biomolecule surface immobilization

A

Physical adsorption (VdWs, electrostatic, affinity complexes), or covalent attachments (hydrogels, solid surfaces, and soluble polymer conjugates)

221
Q

Biotin

A

Vitamin B7/H. The binding of biotin to streptavidin is one of the strongest non-covalent interactions known. Resistant to many things.

222
Q

How to perform covalent immobilization?

A

Start with surface functional groups (-OH, -NH2, -COOH, -SH, -CH=CH2, etc).

A surface that lacks these groups are modified

Spacer groups. These provide steric freedom, thus greater specific bioactivity. ex. PEG

223
Q

Bioorthogonal chemistry/Click chemistry

A

Give cells a sugar with an azide (‘handle’).
Modified sugar incorporated into glycans on cell surface
Add fluorescent green molecule via click chemistry (azide and alkyne combination to make a triazole).
The fluorescent protein can now be used to track cell movements

224
Q

How do we know if we have completed successful immobilization?

A

Sufficient density, immobilized molecules retrain their activity, and they are stable over whatever the application period should be

Biomaterials (2 decks)

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