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.
2
Q
Periods on the Periodic Table
A
Horizontal
3
Q
Groups on the Periodic Table
A
Vertical
4
Q
Ionic Bond formation
A
Primary bond. Involves the sharing/transfer of electrons. Occurs with large electronegativity differences.
5
Q
Ionic bond properties
A
Nondirectional, so they are very brittle, they will shatter rather than deform.
6
Q
Covalent bond formation
A
Primary bond where both atoms are electronegative and the electrons are shared. Orbitals hybridize.
7
Q
Sigma bond
A
Part of a covalent bond. Short bond lying on the internuclear axis that allows rotation.
8
Q
Pi bond
A
Part of a covalent bond. Bond because of orbital overlap, prevents rotation.
9
Q
Metallic bond formation
A
Electropositive ion cores surrounded by a sea of electrons (negative)
10
Q
Metallic bond properties
A
Nondirectional, easier to deform. High electrical conductivity because electrons can easily move.
11
Q
Van de Waals
A
Secondary bond. Arise from dipoles, albeit permanent, polar-induced, or fluctuations
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.
13
Q
Single Crystal Materials (Crystalline)
A
Periodic and Repeated arrangement of atoms that is perfect throughout the entire specimen (ex. NaCl)
14
Q
Polycrystalline Materials
A
Collection of many small crystals or grains, whose size and number play a role in material properties.
15
Q
Amorphous Materials
A
Lacks a systematic and regular atomic arrangement over large atomic distances
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.
17
Q
Metal Classification
A
Metallic bonding, simple crystal structure, e.g., carbon material
18
Q
Ceramics Classification
A
Combo of ionic or covalent bonding with a complicated crystal structure or amorphous, e.g., glass
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
20
Q
Structure-Property Relationship
A
Composition does not equal property. Atomic arrangement can create a different crystal e.g., diamond and graphite
21
Q
Crystallinity effects on opacity?
A
Polycrystallinity increases opacity
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
23
Q
Ultimate tensile strength (uts)
A
The highest amount of stress a material can withstand.
24
Q
Fracture stress
A
Point that a brittle material breaks.
25
Yield Stress
The point at which a ductile material's stress stain graph is no longer linear
26
Youngs Modulus
Stress over strain for the linear part
27
Ductility strain
The point at which the effects are no longer reversible (plastic deformation occurs)
28
Fatigue
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.
29
Polymer
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
30
Thermoplastic Polymers
Linear and branches structures. Can be melted with heat and reshaped/molded. Semicrystalline or amorphous.
31
Thermosets
Cross-linked, rigid/rubbery. Intractable and cannot be melted and molded, it will decompose/melt with heat
32
Homopolymers
Polymers from the polymerization of a single monomer with 'n' degrees of polymerization
33
Copolymers
Polymers whose molecules have more than one type of repeat unit
34
Statistical copolymers
The sequential distribution of repeat units that obeys statistical laws
35
Random Copolymer
A 'true random' with no order whatsoever
36
Alternating copolymer
Specific repeated sequence for more than one type of monomer
37
Graft copolymer
Branches polymers with the branch having a different composition from the main chain
38
Block copolymer
Repeat units that exist in blocks of the same type. Can be manipulated to make channels, etc.
39
Step-growth polymerization
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.
40
Chain-growth polymerization
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 (∆)
41
Draw the polyester making process
nHO-R-OH + nHOOC-R'-COOH -> H(O-R-OCO-R'-CO)OH + (2n-1)H2O
42
Draw the polyamide making process
nNH2-R-NH2 + nHOOC-R'-COOH -> H)NH-R-NH-CO-R'-CO)OH + (2n-1)H2O
43
Free Radical Polymerization Termination, Combination
2 radicals combine together to form a pairing
44
Free Radical Polymerization Termination, Disproportionation
Creates a double bond in the chain, chain length does not grow
45
Anionic Polymerization
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
46
Draw polypropylene
-[CH2-CH-CH3]-
47
Draw Polystyrene
-[CH2-CH-Benz]-
48
Polytetrafluroethylene (PTFE), TEFLON
-[CF2-CF2]-
49
Poly(methyl methacrylate) PMMA, Plexiglass
-[CH2-C-CH3-COOCH3]-
50
Mn
Number average molar mass. sum(NiMi)/sum(Ni)
51
Mw
Weight-average molar mass. sum(NiMi^2)/sum(NiMi)
52
PDI
Polydispersity Index, Mw/Mn
53
Xn
Number-average degree of polymerization. Mn/Mo
54
Xw
Weight-average degree of polymerization, Mw/Mo
55
End Group Analysis
A way to measure molecular weight. Use titrations to measure n groups, but this only works for very particular molecules
56
Gel permeation chromatography (GPC)
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
57
MaChain entanglement, IMF summation, and the time scale of motion (Slower polymer motion)ss Spectroscopy
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
58
What makes polymers unique? (3 answers)
1. Chain entanglement
2. Summation of IMFs
3. The time scale of motion (slower polymer motion)
59
Crystal unit cell
Smallest part of a lattice that determines the 3D nature of the crystal
60
Are polymers crystalline?
No, either semicrystalline or amorphous
61
Branches effect on crystallinity?
Decreases
62
Cross-links effect on crystallinity?
decreases
63
Big end groups effect on crystallinity
decreases
64
Effect of an irregular side group on crystallinity?
If the side group is small, no effect (ex. F), if big, decrease crystallinity
65
Isotactic
When the end groups face the same way (highly crystalline)
66
Syndiotactic
When the end groups oppose on another on the chain (highly crystalline)
67
Atactic
When the end groups are random on the chain, amorphous (not crystalline)
67
Increasing polymer IMF, _____ Crystallinity
Increase. Polymers are more tightly packed
68
Polymer Quenching -> ______ Crystallinity
Decreases. The quick heat/cool process can make the crystals have many different mechanical properties
69
Polymer Annealing -> ________ Crystallinity
Increases. The long term heat makes the polymer become more ductile and less brittle.
70
Drawing -> _____ Crystallinity
Die forces reduced orientation of amorphous structure, increases crystallinity
71
Melting transition
Primary thermotransition. Enough energy to overcome overall chain motion to overcome secondary bonds. Discontinuous heat graph
72
Glass transition
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
73
Tg above room temperature
Glassy material
74
Tg below room temperature
Rubbery material
75
Backbone effect on Tg?
Flexible backbone low Tg. Rigid backbone has a high Tg (double, triple bonds)
76
Pendent groups effect on Tg?
Increased steric hinderance -> less flexible -> lower Tg
77
IMF effect on Tg?
Higher IMFs, higher Tg
78
Crosslinking effect on Tg?
Increase cross linking, increase IMFs, increase Tg
79
Plasticizer effect on Tg?
Plasticizer is a small molecule that can be added during the polymer process, missile and fills in volume within the chain, lowers Tg
80
True or False: glass transition temp is always lower than melting transition temp
True! Tg=(0.5-0.8)Tm
81
The longer the side chain, the ____ the Tg
Lower, because it is now acting as items that take up a lot of space, plasticizers can fit in
82
Differential Scanning Calorimetry (DSC)
Can measure the thermal transition. Sample on a heater with a reference pan, measures ex/endo heat flow.
83
Fiber polymer examples:
KelvarTM/Nylon. Linear and brittle, no curve in stress/strain graph
84
Glass polymer examples:
polystryene (PS), PMMA, linear with a quick breaking point (compared to fiber polymers)
85
Semi-crystalline polymer examples
polyethylene, polypropylene. Ester-> plastic materials with strain hardening effects
86
Elastomer polymer examples
Polyisoprene, polybutadiene, no linearity, plastic deformationSt
87
stress hardening effect
Increasing deformation increases stress, polymers can sometimes rearrange and lower these stress levels as they deform
88
Ductile-brittle Transition
Make rubbery go to brittle by increasing the strain rate of decreased temperature quickly.
89
Creep
Viscoelastic behavior. Time dependent extension under load. Apply a fixed load and measure the elongation.
90
Stress Relaxation
Viscoelastic behavior. A time dependent decrease in stress at a fixed strain. Polymer chains move around to relieve the stress
91
Degradation
The chemical process that results in the cleavage of covalent bonds in the backbone/crosslinks
92
Erosion
physical change in size, shape, or mass as a result of degradation or dissolution
93
Erosion can be driven by 3 chemical process, name them:
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
What is bulk erosion?
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
What is surface erosion?
Polymer is degraded by actions at the surface of the molecule rather than within. No changes to the mechanical properties.
96
Oxidative Degradation (bad)
The polymer chain is attached by reactive species (ROSs) or cytokines/chemokines. Polymers that are meant to be permanent can now degrade readily
97
Enzymatic Degradation (ugly)
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
Hydrolytic Degradation
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
Crystallinity Increases, Hydrolytic Erosion _______?
Decreases
100
Above Tg, Hydrolytic Erosion _____?
Increases. (faster erosion when rubbery bc the molecules have more room to move, known as the 'free volume theory'
101
Higher the MW, Hydrolytic Erosion _____?
Decreases, more mass to penetrate
102
The more the surface area, Hydrolytic Erosion _____?
Increases, more access to penetrate into the material
103
Increased mechanical stress, Hydrolytic Erosion _____?
Increases, can invade microcracks
104
Advantages of degradable biomaterials
Permanent implants can cause chronic inflammation and stress shielding (bad!)
Can be gradually absorbed by the body
Adjustable degradation rate
105
How to store degradable biomaterials?
Avoid moisture and pack in air-tight aluminum foil, low air temp. Do not autoclave/irradiate, but ethylene oxide (gassing) is okay
106
Draw PGA
poly(glycolic acid), H-[-O-CH2-C=O-]n-OH
107
polyglycolic acid
Simplest aliphatic polyester. Highly crystalline, high Tm/low solubility. Rapid mechanical deterioration upon degradation. Used in bone pins, bone screws
108
Draw PLA
Poly(lactic acid), H-[-O-CH-CH3-C=O-C]n-OH
109
polylactic acid
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
PLGA
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
About polyanhydrides
Most reactive and hydrolytic ally unstable polymers used in biomaterials. Fast degradation with high biocompatibility. Used in drug delivery.
112
What is a hydrogel?
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
Crosslinks
Covalent bonds, H-Bonds, strong VdWs
114
Ionic hydrogel
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
Swelling behavior
The thermodynamic compatibility between the water and polymer chains.
116
Hydrogel advantages
Closely mimic mechanical properties of soft tissues, and may be polymerized into any geometry. Can make a cell-responsive hydrogel.
117
Smart Hydrogels
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
Body-centered cubic (BCC)
When there is a crystal repeat every corner of a cube and the middle.
119
Face-centered cubic (FCC)
When there is a crystal repeat every corner of a cube, nothing in the center of the cube.
120
Metal Vacancy defect
Lack of one of the positive ions, highly reactive in this area.
121
Metal interstitial defect
An additional positive ion on top of the positive ions there already, higher energy here.
122
Substitutional atom
Can fit another atom where a vacancy defect once was
123
Impurity atom
Atom added on top of the positive ion core, can create alloys, which have superior mechanical strength/corrosion resistance, etc.
124
Line Defects - Edge dislocation
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
Line defects - Screw dislocation
A rotational defect, shifts like a spiral staircase.
126
Metal deformation
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
Elastic vs Plastic deformation
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
Grain boundaries
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
Solid Solution strengthening
Adding point defects (alloying), makes metal stronger and prevents dislocation
130
Strain hardening
Adding line defects (cold working), think blacksmith
131
Grain Size Strengthening
Add planar defects, thermal processing
132
Corrosion
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
Anode
Metal is oxidized, losing electrons
134
Cathode
Metal is reduced, gains electrons
135
Half cell potential
The electrical potential at equilibrium, characteristic of a metal measured against hydrogen reference.
136
The more positive the standard electrode potential, the ______ the metal
Less likely it is to erode (less reactive), and less likely to be oxidized
137
Galvanic Corrosion
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
Pitting Corrosion
Starts from surface imperfection, the pit acts as an anode
139
Fretting Corrosion
Rubbing one part on another, disrupting the passivating later, which stores the electrolyte/cases fatigue
140
Crevice Corrosion
The region of device with poor mass transport, chemical environment is different in the crevice from the surrounding.
141
Stress corrosion cracking
The stressed region can degrade due to mechanical energy, fatigue stress corrosion can occur with repeated stress.
142
Stainless steel
Most common medical implant type is 316L (L=low carbon).
143
Add Cr to stainless steel
Forms an adherent surface oxide and increases corrosive resistance.
144
Carbon in stainless steel
High carbon content can form carbide and precipitate at grain boundaries, depleting Cr. Low carbon% -> higher corrosion resistance
145
Cr vs Ni in stainless steel
Cr stabilizes the BCC phase, which is weaker than the FCC phase. Ni stabilizes the austenitic (FCC) phase
146
Annealing effect on stainless steel
Increases grain size, lower strength and more ductile (less grain boundaries, can't glide as while -> easier deformation)
147
Cold working effect on stainless steel
Greater strength/hardness and less ductile
148
Cobalt Alloys
Uses Cr oxide to lower corrosion resistance. High fatigue and UTS yields. Used in dentistry, joints, knee/hip joints.
148
Titanium and Ti-based alloys
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
Stress Shielding
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
Mg Metal
Used in many biological processes (safe), safe byproducts and undergoes complete degradation, with similar mechanical properties to cortical bone.
150
Ceramics, glasses, and glass-ceramics
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
Ceramic Dislocation Slip
Must occur over 2 atomic positions due to the electroneutrality requirement, less likely to occur, so it has more brittle fractures.
152
What can cause ceramic resorption/degradation?
physiochemical dissolution, material solubility, local pH, chemical stacks at grain boundaries, biological factors (e.g., phagocytosis)
153
Calcium Phosphate
the mineral phase of bone and teeth. Solubility and hydrolysis decrease with INCREASED Ca/P ratio
154
Hydroxyapatite (HA)
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
FT-IR
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
CaP (ceramics) degrades quicker as chemical susceptibility to dissolution ____?
Increases
157
CaP (ceramics) degrades quicker as surface area ______?
Increases
158
CaP (ceramics) degrades quicker as crystallinity _________?
decreases
159
CaP (ceramics) degrades quicker as crystal perfection _____?
decreases
160
CaP (ceramics) degrades quicker as grain size ________?
decreases
161
CaP (ceramics) degrades quicker as F- substitution _______?
decreases
162
Clinical Application of CaP
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
Bioactive glass and glass-ceramics
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
The more SiO2 in the glass ceramic
Silicate glass, nearly inert
165
Dense, nonporous, nearly inert. Attachment type to host tissue?
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
Porous, inert. Attachment type to host tissue?
Ingrowth occurs that mechanically attaches the bone to the material (biological fixation). Needs a small pore size for tissue to be viable.
167
Dense, non-porous, surface-reactive. Attachment type to host tissue?
Elicit a biological response at the interface, formulation of chemical bonding with the bone (bioactive fixation).
168
Dense, resorbable. Attachment type to host tissue?
Slowly is replaced by bone
169
Carbon materials
Crystalline (diamond, graphite, fullerene). Quasicrystalline (glassy carbon, inert electrodes)
170
Composite
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
Surface Importance
It is the first contact with a biological system, and has different properties than the bulk. Easily contaminated. Surface structure is often mobile/
172
Surface anatomy
Hydrocarbon -> polar organic molecules -> absorbed water -> metal oxide -> bulk implant?
173
Wettability
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
Contact Angle
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
Characteristic IR Absorption bands
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
ATR-FTIR
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
X-ray Photoelectron Spectroscopy
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
ESCA/XPS
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
ESCA/XPS Advantages/Disadvantages
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
Secondary Mass Spectrometry (SIMS)
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
Dynamic SIMS
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
Static SIMS
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
SIMS Advantages/Disadvantages
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
Scanning electron microscopy (SEM)
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
Atomic Force Microscope (AFM)
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
Tight junctions
Hold cells together, maintain polarity, and prevent transport through space between cells. Uses actin microfilaments to maintain.
187
Desmosomes
Homotypic association of cadherins. Linked to intermediate filaments to help resist shear force
188
Gap junctions
Big, ion channels used for cell-cell communications, integrins
189
Cadherins
Cell-cell contact in desmosomes, homophilic
190
Selectins
Cell-cell binding via heterophillic binding to carbonhydrates (e.g., Carbohydrates on Mucins)
191
Cell adhesion molecules (CAMs)
Cell-cell binding, homophilic or heterophilic. Many are a part of the immunoglobulin superfamily
192
Proteoglycan receptors
Receptors made out of more sugar than protein
193
Integrin
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
The ECM
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
Glycosaminoglycans
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
Collagen
ECM structural protein. Triple helix with 3 polypeptide chains. High mechanical and tensile strength
197
Elastin
ECM structural protein. Intrinsic crosslinks between fibers allow the stretching and relaxation of the molecule (less plastic deformation and less brittle)
198
Fibronectin
ECM adhesion protein. Integrin can bind to the RGD domain
199
Laminin
ECM adhesion protein. Key component of basement membranes.
200
What affects cell adhesion to synaptic surfaces? (4 parts)
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
How to promote cell adhesion?
Immobilize cell adhesion proteins/binding sequence.
Create topographic features
Growth factor immobilization/release
202
How to prevent undesired cell adhesion
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
Cell culture
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
Cell line
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
Non-covalent suface coating
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
Original surface modifications can be done through:
ion beam etching, plasma etching, chemical reactions (specific or non-specific), mechanical roughening/polishing, and texturization
207
Covalent attachment surface modification
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
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What is Plasma?
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
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Corona discharge
The application of high voltage to an electrode with a sharp tip
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Plasma deposition
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
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RFGD Plasma Deposition
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.
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biomedical applications of plasma
plasma treatment (etching): cleaning, sterilization, and cross-linking surface molecules (increases stability)
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Plasma etching and sketching
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
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TCPS
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
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Silanization
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
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Self-Assembled Monolayers (SAM)
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
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Multilayer polyelectrolyte adsorption
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
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Principles of Surface Modification
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)
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Biomolecule surface immobilization
Used in biosensors. Biocompatibility: ligands/growth factors for cell adhesion. Inhibitory factors to prevent improper adhesion.
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Methods of biomolecule surface immobilization
Physical adsorption (VdWs, electrostatic, affinity complexes), or covalent attachments (hydrogels, solid surfaces, and soluble polymer conjugates)
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Biotin
Vitamin B7/H. The binding of biotin to streptavidin is one of the strongest non-covalent interactions known. Resistant to many things.
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How to perform covalent immobilization?
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
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Bioorthogonal chemistry/Click chemistry
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
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How do we know if we have completed successful immobilization?
Sufficient density, immobilized molecules retrain their activity, and they are stable over whatever the application period should be
