1
Q
What is a biological composite?
A
A material made by living organisms that combines inorganic minerals (like hydroxyapatite or calcium carbonate) with organic polymers (like collagen or chitin) to achieve superior mechanical properties.
2
Q
What are polymorphs
A
different crystalline structures of the same chemical substance
- ex: aragonite and calcite are both polymorphs of calcium carbonate
3
Q
Compare Brushite vs. Hydroxyaptite (HA)
A
- both are calcium phosphate polymorphs
- HA is thermodynamically stable and is the principal mineral in bone and teeth
- brushite is kinetically favorable (forms more easily) but is less stable: it can act as a precursor to HA during mineralization
4
Q
What is a hierarchical structure
A
A structure that is organized into distinct, repeating patterns across multiple length scales, from the nanoscale to the macro-scale. This allows materials like bone to achieve a combination of strength and toughness
5
Q
What is organic templating in biomineralization?
A
The process where pre-formed organic matrices (like collagen) act as a scaffold or blueprint to guide the nucleation, growth, morphology, and assembly of inorganic minerals
6
Q
What is interfacial inorganic deposition?
A
A biomineralization pathway that uses organized organic boundaries, like vesicles, to control mineral nucleation and growth
- these boundaries create a confined space where ion concentration, pH, and nucleation can be precisely regulated
7
Q
What is the difference between heterogeneous and homogeneous nucleation
A
- homogeneous nucleation occurs spontaneously within a solution
- heterogeneous nucleation occurs on a pre-existing surface (like an impurity, organic template, or vesicle membrane)
- heterogeneous nucleation is easier because the surface lowers the energy barrier required for a stable crystal nucleus to form
8
Q
Differentiate between intra fibrillar and extra fibrillar mineralization
A
- intrafibrillar mineralization is the formation of oriented hydroxyapatite crystals within the gap regions of collagen fibrils, guided by the collagen template
- extrafibrillar mineralization occurs in the space outside of the collagen fibrils and is typically less organized
9
Q
What is the core function of a Ventricular Assist Device (VAD)
A
To act as a mechanical pump that helps a weakened heart (usually the left ventricle) pump blood to the body
10
Q
what is the core function of Extracorporeal membrane oxygenation (ECMO)
A
- to act as an artificial lung
- takes blood out of the body, performs gas exchange (adds O2 and removes CO2) in an oxygenator, and returns the blood to the body
11
Q
What material is a VAD pump housing typically made from and why
A
- titanium alloy (Ti-6Al-4V)
- lightweight, high strength, corrosion resistance, and excellent biocompatibility
12
Q
what material is a VAD outflow graft (vascular conduit) typically made from and why
A
- polyester (PET)
- is woven/knitted to be porous, which promotes natural tissue ingrowth from the aorta, creating a durable leak-proof seal
13
Q
what are the two primary, dangerous complications for any blood-contacting device?
A
- thrombosis: formation of blood clots
- hemolysis: mechanical breakdown/rupture of red blood cells
14
Q
How do advanced VADs (like Maglev pumps) mitigate hemolysis
A
- by using magnetic levitation, the impeller “floats” with no mechanical contact or bearings
- this reduces friction and shear stress on the blood cells
15
Q
how are blood-contacting surfaces (VADs, ECMO) treated to prevent thrombosis
A
they are given anticoagulant or hemocompatible coatings
ex: heparin, phosphorylcholine, or zwitterionic polymers (which prevent protein adhesion)
16
Q
what to consider when choosing materials for a VAD?
A
- housing materials should be high strength, corrosion resistant, and biocompatible
- driveline should be flexible
- vascular graft should promote tissue integration and prevent leakage
- blood contacting surfaces should minimize protein adsorption and thrombosis
17
Q
what is the key advantage of polymers over metallic and ceramic biomaterials
A
polymers can integrate with both hard tissues (like bone) and soft tissues (like muscle, skin, or the eye)
their mechanical properties are highly tunable
18
Q
What is “PEGylation”
A
a process where PEG (polyethylene glycol) is attached to a drug or drug carrier
- the PEG acts as a stealth cloak, hiding it from the immune system to increase its circulation time in the body
19
Q
how does a drug-eluting depot like “lupron depot
work
A
the drug encapsulated in microspheres made of a biodegradable polymer like PLGA
The polymer slowly degrades in the body via hydrolysis, providing a long-acting, sustained release of the drug over weeks or months
20
Q
give examples of two synthetic polymers used as biomaterials
A
any two of polyethylene (PE), polyester (PLGA, PLA, PET), silicone (PDMS), polyurethane (PU), PMMA, PEEK, PEG
21
Q
give examples of two natural polymers used as biomateraisl
A
any two of:
- polysaccharides: chitosan, alginate, ceelulose
- proteins: collagen, elastin, fibroin (Silk)
22
Q
what is a common application of PMMA (polymethylmethacrylate)
A
intraocular lenses (IOLs), also bone cement
23
Q
what is a common application of UHMWPE (ultra-high-molecular-weight polyethylene)
A
the joint liner (bearing surface) in a total hip or knee replacement
24
Q
what are common applications of PLGA (Polylactic-cp-glycolic acid)?
A
bioresorbable (absorbable) sutures and drug delivery depots
25
what are common applications of silicone elastomer (PDMS)
breast implants and contact lenses
26
what are common applications of PET (polyethylene terephthatate)
vascular grafts
27
what are common applications of PEEK (polyether ether ketone)?
spinal cages (for spinal fusion)
- its a strong, rigid, metal-replacement polymer
28
why are polymers a good mechanical match for soft tissues
they have a low young's moduli (low stiffness) and high deformability, similar to natural tissues like skin, fat, and muscle
- metals/ceramics are a thousand times stiffer
29
compare the stability of a C-C backbone polymers (like PE, PTFE) vs C-O/C-N backbone polymers (like polyesters, polyamides)
- C-C: strong, non-polar bonds. chemically inert and durable (non-biodegradable)
- C-O/C-N: weaker, polar bonds. prone to hydrolysis (breakdown by water). biodegradable
30
what is a thermoplastic?
a polymer that softens/metls when heated and can be reshaped. it is recyclable
ex: PE, PP, PET
31
what is a thermoset
a polymer that is crosslinked into a rigid network
it does not melt when heated (it just burns)
it is non-recyclable but has better thermal stability
ex: crosslinked silicone
32
are polymers with C-C backbones (like PE) mechanically brittle
no not brittle (common misconception)
- they are mechanically tough (UHMWPE is extremely durable) and chemically inert
33
what is the difference between a monomer and a repeat unit in condensation polymerization
the repeat unit has fewer atoms than the monomer because a small molecule (like H2O) is lost during the condensation reaction (lactic acid monomer vs PLA repeat unit)
34
what is degree of polymerization (DP)
the number of repeat units (n) in a single polymer chain
$DP = M_n / M_0
35
what is the difference between addition and condensation polymerization
- addition: monomers add directly (C-C bonds) backbone is all carbon, not atoms lost
- condensation: monomers join by eliminating a small molecule like H2O. backbone contains heteroatoms (like C-O or C-N)
36
what is a polydisperse sample
a realistic polymer sample that contains a broad distribution (a range) of different chain lengths
37
what is the Number-Average Molecular Weight (Mn)
the total mass of the sample divided by the total number of chains (simple mean)
38
what is the weight-average molecular weight (Mw)
an average weighted by the mass of the chains. longer, heavier chains contribute more to this average
39
which is larger, Mn or Mw?
for any polydisperse sample, Mw is always greater than Mn (they are only equal if PDI=1)
40
what is the polydispersity index (PDI) and what does it measure
- PDI=Mw/Mn
- it measures the breadth of the molecular weight distribution. a PDI of 1 is perfectly uniform (Monodisperse)
41
how does branching affect the properties of polyethylene
- less branching (HDPE): chains pack tightly-> high crystallinity and density -> strong and rigid
- more branching (LDPE): chains are tangled -> low crystallinity and density -> soft and flexible
42
what is the clinical importance of the glomerular filtration cutoff (5-6nm)
polymers larger than this cutoff are not filtered by the kidneys and can circulate in the blood for much longer. small polymers are cleared quickly
43
what is the enhanced permeability and retention (EPR) effect
tumor blood vessels are "leaky". large polymers or nanoparticles (50-200nm) can leak out of these vessels and get trapped in the tumor, allowing for targeted drug delivery
44
what is the difference between contour length (L) and end-to-end distance (R)
L: the maximum possible length of the chain if it were stretched perfectly straight
R: the actual average distance between ends of the tangled polymer coil as it tumbles in solution. R is more realistic measure of size and much smaller
45
what is the key assumption and scaling law for the freely jointed chain (FJC) model
- assumption: fixed bond length l. but free bond angles
- scaling law: size R scales with the square root of the number of bonds (n)
46
what is kuhn length (b)
a measure of chain stiffness
it groups a number of real bonds into one "effective" segment. a stiffer polymer (like DNA) has a larger kuhn length
47
describe a good solvent
the polymer likes the solvent
polymer-solvent interactions are strong. the chain EXPANDS (swells) R - N^3/5
48
describe a poor solvent
the polymer hates the solvent
polymer-polymer interactions are strong. the chain COLLAPSES into a globule R-N^1/3
49
describe a theta solvent
polymer-solvent and polymer-polymer interactions are perfectly balanced. The chain acts an "ideal" FRC. the bulk/melt state is a theta solvent R-N^1/2
50
what is the radius of Gyration Rg
the root-mean-square distance of all monomers from the chain's center of mass
its more general measure of size than R, especially for branched polymers
51
when modeling flexible polymer chains (like PEG or PE) what is the bond angle and why
- 110 degrees
- this is the standard angle for sp^3 hybridized atoms, which form the zigzag backbone of these polymers
52
what are disadvantes of polymers as biomaterials
- they easily absorb water and biomolecules and may leach harmful compounds
- they often lack thermal stability, making high-temp sterilization challenging
53
is this a monomer, repeating unit or polymer?
monomer
54
is this a monomer, repeating unit or polymer?
repeating unit
55
is this a monomer, repeating unit or polymer?
polymer
56
is this a monomer, repeating unit or polymer?
polymer
57
is this a monomer, repeating unit or polymer?
repeating unit
58
is this a monomer, repeating unit or polymer?
monomer
59
from this monomer, what is the resulting polymer/method
the double bond opens up to a single bond
60
from this monomer, what is the resulting polymer/method
- the two double bonds rearrange
- the two outer carbons open up to link to other monomers, and a double bond forms in the middle
61
from this monomer, what is the resulting polymer/method
the COOH of one monomer reacts with the OH of another monomer
- the OH from acid and H from alcohol group leave to form an H2O
62
monomer to polymer method
- if it had C=C bond: use addition
- if it has groups like OH and COOH: use condensation
63
how do i calculate the theoretical yield (mass) for a condensation reaction (like forming a polymer or disaccharide)?
1. write full balanced reaction: 2Monomer -> 1 dimer + 1 H2O
2. Find molar masses of all (ex: H20 is 18g/mol)
3. create a mass ratio: 2(mass monomer) -> 1(mass dimer) +1(mass H2O)
4. equal them out
64
what is the best way to describe the actual size of the polymer coil as it tumbles in a solution
- the root-mean-square end-to-end distance R-n^1/2
65
what are the Freely joint chain model assumptions (FJC)
- fixed bond length
- free bond angle (random and uncorrelated)
- no intramolecular and intermolecular forces
R=(n^1/2)l
66
What are the freely rotating chain model assumptions (FRC)
- fixed bond length
- fixed bond angle
- no intermolecular forces but intramolecular forces between sequential bond vectors are present
R^2=nl^2(c_inf)
67
what is the correction factor
- a characteristic ratio that considers the effect of all intramolecular interactions on bond conformational freedom
- measure of chain stiffness: higher the C_inf, the stiffer the chain
C_inf = (1+cos(theta))/(1-cos(theta))
always greater than 1
68
biological organic-inorganic composite examples
hydroxyapatite base: bone +teeth
silica based:
diatom frustules + sea sponge spicules
calcium carbonate based:
nacre/mother-of-pearl + sea urchin spines + egg shell
69
synthesis conditions of biological composites
mild conditions: ambient temp (0-40C), ambient pressure (1atm), and in an aqueous (water) solution
70
key structural and formation principles of biological composites
1. hierarchical structures: organized across multiple length scales (nano- to macro-) (russian nesting dolls of structure)
2. organic templating: self-assembly guided by an organic matrix (collagen - lego baseplate) to control mineral growth
71
what roles do organic molecules play in biomineralization
- they form secondary bonds with inorganic elements
- they regulate nucleation, growth, and morphology of inorganic crystals
72
common elements that are involed with biomineralization
C, H, O, N, Ca, P
73
true statements about self-assembly in biomineralization
- molecular recognition motids are often employed at the interface through electrostatic interactions or hydrogen bonds
- pre-formed organic molecules control nucleation occurs first, then controls crystal growth with structure and morphology as well as influencing molecular-scale organization an d hierarchial structures
74
calcite description
the stable polymorph of CaCO3 (calcium carbonate) at ambient conditions
75
aragonite description
metastable CaCO3 form, dominant in seashells
76
brishite description
metastable calcium phosphate, forms under acidic/low pH + low temp conditions
- tends to dissolve or transform into HA under physiological conditions
- precursor to hydroxyapatite during bone and tooth mineralization
77
hydroxyaptite description
thermodynamically stable calcium phosphate at physciological pH, =60% of bone
- its crystallization is kinetically unfavorable
78
austenite description
high-temp phase of NiTi (nitinol) or steel, with cubic structure
79
martensite description
transformation products of NiTi or steel at low temp, often stronger or harder
80
what is interfacial inorganic deposition
a biomineralization pathway that uses two-phase systems (like oil-water boundaries, micelles, or vesicles)
the organized organic boundaries provide control and guide mineral nucleation
- provides spatial control over inorganic morphology
81
natural example of interfacial inorganic deposition
- the formation of silica microskeletons in organisms like diatoms and radiolarians
- this process is controlled within a membrane-bound vesicle called the silica deposition vesicle (SDV)
82
calculating supersaturaton (S)
1. calc Ion Activity Product (IAP) = [IonA]^a[IonB]^b
2. calculate supersaturation S=IAP/Ksp (Ksp - solubility product)
3. S<1: undersaturated (dissolution), S=1: Saturated (equilibrium), S>1: Supersaturated (nucleation favored)
83
what is epitaxial crystal growth?
- a biomineralization pathway where mineral growth occurs on an organic template and is directed by it
- the primary mechanism is LATTICE MATCHING between the ordered organic template and the inorganic crystal, which controls the crystal's orientation
- directional (z-axis)
84
describe the free energy curves for homogeneous nucleation
- G_surface: unfavorable (positive), scales with r^2, energy cost of creating a new surface
- G_bulk: favorable (negatives), scales with -r^3, energy released from forming bonds
- G_nucleation: the total energy (middle hump curve)
85
homogeneous vs heterogeneous nucleation barrier (graphs)
- heterogeneous nucleation occurs on a foreign surface (like an organic template)
- this lowers the surface energy (y*), which in turn lowers the critical energy barrier (G*)
- graphically G_nucleation hump is much lower
86
what is the critical radius r*
r* is the minimum size a nucleus must reach to be stable
- if rr*: volume energy dominates, nucleus is stable and will spontaneously grow
87
Critical Radius formula
r* = -2(surf energy)(volume)/(G_form)
G_form: bulk free energy change
- organic templates lower the surface energy, which results in a smaller r* and a lower G*
88
role of prenucleation cluster (pAsp)
1. act as functional matrix (polyaspartic acid, pAsp)
2. prevent random, uncontrolled nucleation in body fluids
3. guide mineral ions (Ca) into the confined gap regions of collagen fibrils to begin mineralization
89
why is intrafibrillar mineralization critical for bone mechanical properties
- it ensures that apatite crystals align with collagen fibrils, improving strength and toughness
- the gap regions between collagen fibers dictate the mineral shape by confining the growth within a two-dimenstional space (40nm*2nm)
90
what role do prenucleation clusters (pAsp-Ca complexes) play in bone mineralization
- they bind Ca and prevent uncontrolled nucleation in body fluids
- they guide Ca2+ into collagen gap regions (<2nm distance) for confined growth
91
According to "role of confined collagen geometry in decreasing nucleation energy barriers to intraffibrillar mineralization", why does confinement in collagen gap regions lower the nucleation energy barrier
confinement (collagen gap regions) acts as a form of HETEROGENEOUS NUCLEATION
- by confining the nucleus the REACTIVE SURFACE AREA exposed to the solution is reduced
-this decreases the surface energy penality (G_surf) which in turn LOWERS THE TOTAL ENERGY BARRIER (G*) for nucleation
92
based on classical nucleation theory (CNT), how does the nucleation rate (J) depends on supersaturation for intrafibrillar mineralization
ln(j) =(proportional) 1/S
93
the study "role of confined collagen" used simulated body fluid (SBF) and polyaspartic acid (pAsp) as a model for non-collagenous proteins. what are the potential limitations of this approach when extrapolating to real bone mineralization in vivo?
- SBF lacks many ions/proteins found in real extracellular fluid
- polyaspartic acid (pAsp) may not capture the multifunctionality of natural NCPs
- the model ignores dynamic biological regulation (enzymes, cell signaling)
94
difference between laboratory synthesis of inorganic ceramics and biological synthesis of biominerals?
- laboratory synthesis requires extreme heat and low/high pressure, while biological synthesis occurs at ambient temp and pressure
95
why does bone exhibit both strength and toughness, while pure hydrozyapatite is brittle?
- bone has hierarchical structures across multiple scales
- crack deflection and energy dissicpation in bone occur across different structural levels
- bone achieves mechanical resilience by combining stiff HA with soft organic collagen
96
why do biological systems achieve reproducible mineral structures under mild conditions?
- mineral nucleation and growth are guided by organic templates
97
interfacial or epitaxial?
interfacial
98
interfacial or epitaxial?
epitaxial
99
interfacial or epitaxial?
interfacial
100
what are common challenges and solutions for blood-contacting biomaterials in VAD and ECMO?
- thrombosis (stationary blood clot) and embolus (traveling blood clot) formation -> anticoagulant or hemocompatible coatings
- protein adsorption and platelet adhesion -> hydrophilic or zwitterionic coatings
- hemolysis (mechanical breakdown of red blood cells) due to shear stress ->smoother flow paths or magnetic levitation
101
why are polymeric biomaterials closer in mechanics to soft tissues
- polymers generally have lower modulus and higher deformability than metals or ceramics
102
why are polyesters and polyamides less chemically stable
- their C-O and C-N bonds are prone to hydrolysis
103
thermoplastics and thermoset polymeric biomaterials
- thermoplastics can be remelted and reshaped
- thermosets and crosslinked hydrogels are not recyclable but show higher thermal stability
104
what is the driving force for mixing
-a negative Gibbs free energy for mixing G_m<0
- this is a battle between enthalpy Hm and entropy Sm, defines by the equation Gm=Hm-TSm
105
in a regular solution where "like prefers like", what are the signs of Hm and Sm
- Sm>0 (entropy favors mixing because it increases disorder)
- Hm>0 (enthalpy opposes mixing because energy is required to break favorable "like-like"
106
what does "like prefer like" imply about interaction energies w?
- self interactions (wAA, wBB) are stronger (more negative) than cross interactions (wAB)
- because w values are negative, this is written as wAB > 1/2(wAA+wBB)
107
how does increasing temp affect the Gm of mixing
- mixing becomes more favorable
- the -TSm term becomes more negative and starts to 'win' against the unfavorable Hm term, making Gm more negative
108
why are polymers (large N) so much harder to dissolve than small molecules
- the entropy of mixing is smaller
- a long connected chain (N) has far fewer possible arrangements than N individual small molecules
- this means the main driving force for mixing significantly weaker
109
what is the flory-huggins equation for Gm
The 1/N in the entropy term shows why the entrpy gain is so small for large polymers
110
On a Gm vs composition plot, what does a single, concave-up U shape mean
- the system is completely miscible (1-phase)
- occurs at high temps (or low X) when entropy term wins
111
on a Gm vs composition plot, what does a hump with two minima mean
- the system is immiscible and will phase-separate into two coexisting phases (defined by the two minima)
- this occurs at low temps (or high X) when the enthalpy term wins
112
What is UCST
- upper critical solution temp
- the system is phase-separated when cold and becomes mixed when heated above the Tc
- this is normal behavior (jello)
113
what is LCST
- lower critical solution temp
- system is mixed when cold, and phase separate when heated above the Tc
- this is weird behavior (PNIPAM)
114
what is the state of PNIPAM in water at a temp below its LCST
- it is hydrophilic, forming extended soluble coils
- mixed, clear solution
- the polymers amide groups form favorable H-bonds with water
115
what happens to PNIPAM in water when heated above its LCST
- it becomes hydrophobic
- thermal motion breaks the H-bonds, and the chains collapse into compact globules to hide from the water
- this causes phase separation and cloudy solution
116
what is LLPS in a cell
- Liquid Liquid Phase Separation
- formation of dynamic, MEMBRANELESS ORGANELLES (biocondensates)
- these are reversible, phase-separated droplets of specific proteins and RNA
117
what is the function of biological LLPS
- to provide the spatiotemporal control
- it can concentrate specific molecules (like enzymes) to speed up reactions, or sequester molecules (like transcription factors) to turn off processes
118
what is the pathological side of LLPS
- when normal, liquid condensates "age" and undergo an irreversible phase transition into solid-like aggregates (fibrils or amyloid)
- this is linked to diseases like ALS and Alzheimers
MSE 425
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