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MAT3430 > Surfaces and Interface > Flashcards

Surfaces and Interface Flashcards

1
Q

What is the foreign body response to biomedical implants?

A

1) surgical implant
2) adsorption of proteins
3) neutrophils and macrophage interrogation
4) secretion of cytokines
5) fibroblasts arrive and synthesis collagen
6) encapsulation of implant

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2
Q

What is the acute response to an implant?

A

resolves quickly, usually less than a week

1) surgical implant
2) adsorption of proteins
3) neutrophils interrogation

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3
Q

What is the chronic response to an implant?

A

1) macrophage interrogation
2) secretion of cytokines
3) fibroblasts arrive and synthesis collagen
4) encapsulation of implant

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4
Q

If there is an anti-adhesive coating on a metal/polymer implant, what is the effect?

A
  • Bacterial repelling proteins

- no reaction with bacterial binding proteins

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5
Q

What is the effect if there is no coating on an implant?

A 
1) no fibroblast adhesion 
dead space
2) inflammation activate myofibroblasts 
= collagen production
= alpha SMA expression
3) thick contractile capsule is produced
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6
Q

What is the effect if there is total coating on an implant?

A

1) excessive cell adhesion
2) attachment activated myofibroblasts
= collagen production
= alpha-SMA expression
3) Contractile capsule formed

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7
Q

What is the effect is there is a patterned coating on an implant?

A

1) balance cell adhesion
2) pattern suppresses myofibroblasts
= low collagen production
= no alpha-SMA expression
2) implant integration - no capsule

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8
Q

What are cohesive forces?

A

forces that hold atoms together

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9
Q

What are the two classifications of inter-atomic bonds?

A

primary

secondary

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10
Q

What does the strength of inter-atomic bonds determine?

A

ability to reform after breakage

determine the physical properties of a material

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11
Q

What are the three types of primary atomic bonds?

A

ionic
covalent
metallic

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12
Q

What is the key difference between primary and secondary bonds?

A

secondary bonds do not share electrons

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13
Q

What are inter atomic secondary bonds?

A

charge variations among molecules or atomic groups induce polar forces that attract the molecule

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14
Q

What are van der waal forces?

A

form basis of dipole attraction
in a symmetrical molecule (inert gas) the electron fields constantly fluctuate
= charge becomes momentarily positive or negative

A fluctuating dipole moment is created(weak)

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15
Q

How does bond distance determined?

A

distance between centre of an atom and that of its neighbour (limited by the diameter of the atom involved) is the limited factor that prevents the atoms/molecules approaching too closely

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16
Q

How can conditions of equilibrium described?

A

in terms of energy rather than the inter-atomic forces

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17
Q

How can energy be defined?

A

as a force integrated over a distance

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18
Q

How does an atom attain its equilibrium position?

A

attractive and repulsive forces
if an atom is moved from its position, either a repulsive or an attractive force is required to move the atom back to it equilibrium position

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19
Q

What is thermal energy?

A

accounted for by the kinetic energy of the atom or molecules at a given temperature

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20
Q

How are temperature and kinetic energy related (with regards to atoms)?

A

high the temperature, the greater the amplitude
= greater the kinetic or internal energy
The atoms in a crystal at temperature above absolute zero are in a constant state of vibration, and the average amplitude is dependent on the temperature

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21
Q

How is the energy change plotted as a function of displacement in either direction?

A

By multiplying the force by the atomic displacement from its equilibrium position

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22
Q

What is the depth of the energy curve determined by?

A

magnitude of the attractive repulsive forces

- shallower curve, less energy is needed to separate the atoms than for deeper curve

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23
Q

What is thermal conductivity related to?

A

interatomic spacing
- only to the extent that the heat is conducted from one atom or molecule to th next as adjacent basic structural units are affected by the kinetic energy of their neighbouring atoms

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24
Q

What are the two important concepts in understanding solid state diffusion?

A

1a) all atoms do not possess the same amount of energy (distribution of atoms with energies varying from very low to very high
1b) if the energy of particular atom exceeds the bonding energy, it can move to another position in the lattice

2a) at any temp, there are a finite no. of missing atoms (Vacancies)= open areas through which diffusion can occur
2b) atom change position in pure, single element solid even under equilibrium conditions = self diffusion
2c) diffusion may also occur in the other direction to produce a concentration of atom in solution(supersaturated sugar solution - sugar molcules diffuse toward each other
2d) diffusion rates from a given substance depend mainly on temperature and the chemical potential gradient or conc gradient

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25
What is adhesion?
a molecular or atomic attraction between two coating surfaces gets promoted by interfacial forces or attraction between different molecules or atoms of two different species
26
What are the different ways adhesion may occur?
– Chemical Adhesion – Mechanical Adhesion (structural interlocking) – A combination of both.
27
What is an adhesive?
Substance that promotes adhesion of a substance or material to another
28
What is adhesion bonding?
Process of joining two materials by means of an adhesive agent that solidifies during the bonding process
29
What is cohesion?
force of molecular attraction between molecules or atoms of the same species (molecules of the same kind are attracted)
30
What is mechanical bonding?
strong attachment of one substance to another (not by molecular attraction) - it may involve the penetration of the adhesive into microscopic or sub-microscopic irregularities
31
How is adhesion dependent on surface energy?
For Adhesion to exist, the surfaces must be attracted to one another at their interface
32
Why doesn't surface exist between two gasses?
they lack an interface
33
How does the surface energy of an internal atom differ to a surface atom?
The energy at the surface of a solid is greater than that of it’s interior A bond balance exists around interior atom , while surface atom is free to develop bonds to the molecules at the surface
34
What is wetting?
ability of a liquid to maintain contact with a solid surface, resulting from intermolecular interactions when the two are brought together
35
What is wettability?
The degree of wetting (wettability) is determined by a force balance between adhesive and cohesive forces. Relative interfacial tension between a liquid and a solid substrate that results in a contact angle of less than 90 degree.
36
Which factors influence the ability of an adhesive to wet the surface of the adherent ?
1) cleanliness of the surface 2) thickness of the wetting surface 3) morphology of the surface 4) surface energy of the moducules
37
What is a wetting agent?
a surface active substance that reduces the surface tension of a liquid to promote wetting or adhesion - if the liquid does not wet the surface of the adherent, adhesion between liquid and surface will be negliable or non-existent
38
What is a contact angle?
angle of interection between a liquid and a surface of a solid = measured from the solid surface through the liquid to the liquid vapour tangent line orientating at the terminus of the liquid/solid interfact
39
How is contact angle used as a measure of wettability?
no wetting occur at a contact angle of 180* | complete wetting occurs at an angle of 0*.
40
How do low surface energy materials differ from high surface energy material?
low surface energy materials - do not adhere well to other materials high surface energy materials do adhere well to other surfaces
41
Why would you modify a surface?
improve compatibility with the polymer matrix via specific interactions or chemical reaction between the polymer and silane organo functional group.
42
What are the two types of molecules most commonly used to modify the surface properties of polymers?
1. Polydimethylsiloxane (PDMS) | 2. Fluoromethyl groups
43
What is the structure of PDMS?
Polydimethylsiloxane - inorganic siloxane backbone with pendant methyl groups - principle role of the backbone in the surface activity of silicones is its ability to present the attached organic groups at interfaces - the key property of the backbone is its flexibility and its intrinsic surface activity
44
What provides PDMS with its excellent non-adhesive characteristics?
The low surface energies and low cohesive strength conferred by the methyl group combine
45
What is PDMS used for?
- emerge as molecules with the potential to affect the surface properties of polymers to which they have been blended or co-polymerised - low surface energy enables the siloxanes segments to migrate to the top surface of the polymer interface and provides very hydrophobic surface
46
What are the properties of PDMS?
1) low surface tension 2) high gas permeability 3) biocompatibility 4) low glass transitition temperature 5) low b.p 6) variety of configuration 7) liquid nature of high Molecular weight 8) small temperature variation of physical constants
47
How is PDMS used in polyurethanes?
Producing a silicone rich surface: – Carbinol-terminated, (ethyleneoxide dimethylsiloxane ethyleneoxide ABA block polymer) can be used to modify the surface properties of polyurethanes. – Low molecular weight siloxanes, ranging from 1000 to 3000 can be incorporated in the polymer backbone by direct addition during the polymerization reaction
48
How is surface modification achieved though tri-fluoromethyl groups?
functionalised additive can be introduced within a linear polymer chain containing many tri-fluoromethyl groups. • By using this additive, a polymer film with different fluorination levels in the surface layer and the bulk polymer can be made
49
Which environments are polyolefins widely used?
hygiene, medical, absorbents, wipes, filters or battery separators
50
Which property limits the use of polyolefins?
polyolefins are hydrophobic | = limits their use in applications where wett ability is required
51
How can plasma treatment be used for surface modification?
* Surface graft polymerization involves the attachment of synthetic monomers to the peroxide groups established by the plasma treatment. * The attached monomers then polymerize on the surface of the membrane, forming a hydrophilic polymer layer
52
What is plasma treatment?
• Involves using plasma (a low pressure gas containing electron, photons, ions, and other charged particles) in the presence of oxygen to form peroxides on the surface of the membrane. • The peroxides then decompose to form oxygen-containing radical groups such as hydroxyls, carbonyls, or carboxyls. Plasma treatment may also be used to pretreat the membranes for a subsequent technique known as surface graft polymerization. Surface
53
What is chemical oxidation?
* It involves the use of oxidants such as chromic acid, nitric acid, and potassium permanganate to oxidize the membrane surface introducing oxygen-containing groups onto the surface of the membrane. * Redox initiators, such as ferric chloride can also oxidize the surface to create active sites where surface graft polymerization can occur
54
What is radiation induces graft polymerisation?
* Ultraviolet and ionization radiation are used to form active sites on the surface of the membrane. * Monomers can then be grafted to these active sites. * Subsequent polymerization of the monomer may then occur, forming a hydrophilic or hydrophobic layer
55
What is hydrophilization?
• Organic chemical reactions utilising specific functional groups which are attached by ionic or polar bonds to membrane surface groups, such as benzene rings, double bonds, and halides.
56
What is the key advantage of hydrophilization?
specific functional groups are bonded to the surface of the membrane, giving the membrane surface the characteristics specified by the specific functional groups.
57
Why is low surface energy silicone particularly troublesome in surface contamination?
Low surface energy silicones are commonly present in the lab and natural environment and their contamination is particularly troublesome and is found on many surfaces because few materials have surface energies lower than silicone compounds
58
Why do metals and inorganics re-contaminate quickly?
For high surface energies, such as metals and inorganics, the driving force for reducing the interfacial energy is extremely high – A “clean” metal surface will re-contaminate with a monolayer of organic material in a vacuum environment at 10-6 Torr in approximately 1 sec. – In atmospheric pressure contamination of mono or multi-layers will occur instantly
59
Why is contamination of polymers significantly lower than metals or inorganics?
polymers have significantly lower surface energies | therefor the driving force to reduce interfacial energy is lower and consequently is slow (natural and lab environment)
60
When would a glass be regarded as glasslike?
having one monolayer of hydrocarbon at its surface
61
What is molecular orientation explain in terms of?
thermodynamic terms | as mechanism for reducing the interfacial energy
62
How and why can the volume fraction of the material with the boundary layer be controlled>
by modifying the bulk properties of the material | - the composition changes continuously across the inter-phasial boundary.
63
What are the techniques for surface characterisation?
1) Thermodynamic Analysis 2) Surface Electrical properties 3) Surface chemistry analysis 4) spatially resolved surface chemistry analysis 5) Surface Topogaphy 6) Surface Crystallinity and Atomic Organisation
64
What are the types of thermodynamic analysis that are used for surface characterisation?
- contact angle analysis (surface energies) | - BET (surface area)
65
What are the types of Surface Electrical properties that are used for surface characterisation?
- zeta potential - faraday cup - surface potential difference analyser - rest potential - vibrating electrode
66
What are the types of surface chemistry analysis that are used for surface characterisation?
– ESCA (Electron Spectroscopy for Chemical Analysis) – AES (Auger Electron Spectroscopy – SIMS (Secondary Ion Mass Spectroscopy) – ISS (Ion Scattering Spectroscopy) – ELS (Electron Loss Spectroscopy) – ATR–IR (Attenuated Total Reflectance Infrared Analysis)
67
What are the types of Spatially Resolved Surface Chemistry Analysis that are used for surface characterisation?
– SAM (Scanning Auger Microprobe) | – EDXA (Energy Dispersive x-ray analysis
68
What are the types of Surface Topography that are used for surface characterisation?
– LM (Light Microscopy) – SEM (Scanning Electron Microscopy)
69
What are the types of Surface Crystallinity and Atomic Organisation that are used for surface characterisation?
– LEED (Low Energy Electron Diffraction) – SEXAFS (Surface Extended X-ray Absorption Fine Structure) – FEM (Field Ion Microscopy)
70
What is the degree os biocompatibility of a material a function of?
not only the characteristics and properties of the materials and implanted devices but also the conditions of the host organism and of the surgical technique
71
Why is it important to know the wettability of the material to be implanted?
to determine whether or not it should promote the epitaxial cells growth in the body
72
Why is the wet-ability a very important property of surfaces?
can be defined as the ability to wet uniformly and in a stable manner form a liquid substance
73
What is structure?
term used to describe materials at the atomic level in terms of the arrangement of atoms in space
74
What is morphology?
a macroscopic property of materials that represents the form of shape of a surface
75
What is FTIR?
Fourier transform infrared spectroscopy = application of the IR technique in which the collected data -> mathematically transformed with a background spectrum collected with no sample in the excitation beam
76
What is IR?
Infrared spectroscopy - studies the molecular vibration spectrum of a sample by passing infrared radiation through it and measuring the amount of absorption at each frequency
77
What is the difference between IR and FTIR?
speed | FTIR being faster by a least two orders of magnitide
78
What is Raman Spectroscopy?
Raman spectroscopy depends on a change in the induced dipole moment or polarization to produce Raman scattering • When a beam of photons strikes a molecule the photons are scattered elastically (Rayleigh scattering) and inelastically (Raman scattering) generating Stoke's and anti-Stokes lines
79
What is Raman spectroscopy used for?
* Because Raman spectroscopy is a scattering process, samples of any size or shape can be examined. * Very small amounts of material can be studied down to microscopic levels - 10 microns. * Fibre optics can be used for remote sensing. * Aqueous samples can be studied. * The region from 80-500 cm-1 can be studied with no changes on the same instrument
80
What is the time-of-flight secondary ion mass spectrometry?
TOF-SIMS = surface analytical technique that uses an ion beam to remove small numbers of atoms from the outermost atomic layer of a surface
81
How does TOF-SIMS work?
1) A short pulse of primary ions strikes the surface and the secondary ions produces in the sputtering process ae extracted from the sample surface and into a time-of-flight mass spectrometer 2) The secondary ions ae dispersed in time according to their velocities (propotional to their mass/charge ratio m/z) 3) discrete packets of ions of differing mass are detected as a function of time at the end of the flight tube
82
What mass of ions is TOF-SIMS capable of detecting?
over a large mass range of 0 - 10000 atomic mass units at a mass resolution of 10000
83
What are the advantages of TOF-SIMS?
1) The technique has ultra-high sensitivity to surface layers (one atomic thickness), and detection of atomic concentrations as low as 10 ppm. 2) Molecular fragmentation patterns are characteristic of the molecular or crystalline structure of the surface and its reaction products. 3) Distribution of organics and inorganics can be measured on a surface with a sub-micron lateral distribution. 4) Surface layers of insulating materials, including minerals, polymers, organic, and biological materials, can be analysed readily. 5) The technique has a capacity to carry out ultrashallow depth profiling to measure the near surface composition of electronic materials, reacted minerals, and corrosion films. High sensitivity mass spectra can be reconstructed for any location.
84
What is TOF-SIMS able to image?
image the chemical composition of single monolayer films
85
What is TOF-SIMS able to determine?
the composition and number of phases with the ability to detect high molecular weight ions
86
What is the scanning electron microscopy?
= Supplies visual images of materials surfaces. • Micrographs in the magnification range of 10X to 200,000X can be obtained. • Samples can also be viewed using backscattered electrons for image production to show limited elemental distribution data. • The SEM does not suffer from the light microscope problems of light reflecting off at odd angles and being lost from view.
87
What are the advantages to SEM?
High resolution images of surface topography, with excellent depth of field are produced using a highly-focused, scanning (primary) electron beam.
88
What is the atomic-force microscopy (AFM) or scanning force microscopy (SFM)?
veryhigh-resolution type of scanning probe microscopy (SPM), with demonstrated resolution on the order of fractions of a nanometer, more than 1000 times better than the optical diffraction limit
89
What are the key highlights of using AFM/SFM?
* Multiple modes for imaging surface * Topography and heterogeneity * Force curve measurements * Nano-indentation of polymers
90
How does the atomic force microscopy (AFM) work?
AFM, which can be operated in air or water, uses a fine tip to measure surface morphology and properties through an interaction between the tip and surface. Almost all materials can be measured without specific sample preparations. • Topographic images with a height resolution of ~0.1 nm and lateral resolution down to nanometers. • Friction force images to distinguish different materials, phases, and chemical properties • Adhesion forces on surfaces which can be a measure of surface energy (especially useful in revealing surface modifications). Atomic

MAT3430 (12 decks)

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