Quiz 2 L8 Flashcards
Biomaterial
A biomaterial is a nonviable material used in a medical device, intended to interact with biological systems. -> later definitions, materials can be viable
Biocompatibility
“Biocompatibility” is the ability of a material to perform with an appropriate host response in a specific application.
Wide patient-to-patient variability will be seen including. (Is inclusive design possible?)
* Age
* Sex
* Generalhealthandconcurrentdisease * Physicalmobility
* Lifestyle
Examples appropriate host response biocompatibility
Examples of “appropriate host responses” include resistance to blood clotting, resistance to bacterial colonization, and normal, uncomplicated healing.
Major material variables that could influence the host response
Bulk material composition, micro- (or nano)-structure, morphology
Surface chemical composition, chemical gradients, surface molecular mobility
Crystallinity and crystallography
Elastic constants
Water content, hydrophobic–hydrophilic balance
Surface electrical/electronic properties
Macro-, micro-, nano- porosity
Corrosion parameters, ion release profile, metal ion toxicity (for metallic materials)
Surface topography
Surface energy
Degradation profile, degradation product form and toxicity (for polymeric materials)
Leachables, additives, catalysts, contaminants and their toxicity (for polymeric materials)
Dissolution/degradation profile, degradation product toxicity (for ceramic materials)
Wear debris release profile
Major characteristics of the generic host response to biomaterials
Protein adsorption and desorption characteristics
Tissue/organ specific cell responses (e.g. osteoclasts and osteoblasts for bone, endothelial proliferation)
Generalised cytotoxic effects
Activation of clotting cascade
Delayed hypersensitivity
Neutrophil activation
Platelet adhesion, activation, aggregation
Mutagenic responses, genotoxicity
Macrophage activation, foreign body giant cell production, granulation tissue formation
Complement activation
Reproductive toxicity
Fibroblast behaviour and fibrosis
Antibody production, immune cell responses
Tumour formation
Microvascular changes
Acute hypersensitivity/anaphylaxis
Examples of specific applications biocompatibility
Examples of “specific applications” include a hemodialysis membrane, a urinary catheter, or a hip joint replacement prosthesis.
What are ways to create biomaterials
Industrial material adaptation (use off-the-shelf that’s already available)
Design of passive materials (no active interaction with the body)
Design of bioactive and degradable materials (material for particular signalling response, signalling factors can be released)
Self-assembling materials (micro/nanoscale assembly in situ, control functionality, particulate formation…)
Constructive remodelling materials (materials facilitate appropriate host response)
Describes the types of polymers and chemical bonds that make up hydrogels
Flexible polymer
Semi-flexible polymer
Irreversible bonds
Reversible bonds
Degradable chemistry
Computational modeling and simulations in predicting and analyzing the behavior of biomaterials and cell interactions
Network mechanics
Transport
Spatiotemporal degradation patterns
Cytoskeleton contraction
Integrin-ligand bonds
Mechanical confinement
Growth kinetics
Evolution of construct mechanics
Five basic types of mechanical loading situations
(A) tension
(B) compression
(C) shearing
(D) torsion (E) bending
Modulus of elasticity
Modulus is defined as being the slope of the straight-line portion of a stress (σ) strain (ε) curve.
- When under stress, materials will first exhibit elastic properties: the stress causes them to deform, but the material will return to its previous state after the stress is removed.
- After passing through the elastic region and through
their yield point, materials enter a plastic region, where they exhibit permanent deformation even after the tensile stress is removed.
What do stress strain curves illustrate and for what types of loads
Stress strain curves visually display the material’s deformation in response to a tensile, compressive,
or torsional load.
Can indicate -> elastic region, plastic region, yield point, and ultimate tensile strength.
Yield point stress strain
yield point of a material occurs when the material transitions from elastic behavior - where removing the applied load will return the material to its original shape - to plastic behavior, where deformation is permanent.
Can find yield strength and strain
Do all materials exhibit yield
No
Composites and ceramics both fail at very low strains
without exhibiting yield.
Elastomeric materials do not exhibit a yield point, they just deform until they break.
What are the typical stress strain curves of polymers
A brittle material which will break without yielding, such as a filled plastic material.
A material that exhibits a zero-slope curve, like many thermoplastics.
An elastomeric material which will slowly increase the applied load until failure, such as silicone rubber.
What does modulus tell you
Brittle materials such as metals, plastics, and composites will exhibit a steeper slope and higher modulus value than ductile materials such as rubber.
Tensile testing
- A tensile testing machine performs fundamental and common types of mechanical testing.
- A tensile test applies tensile (pulling) force to a material and measures the specimen’s response to the stress.
- Tensile tests determine how strong a material is and how much it can elongate.
- Tensile tests are typically conducted on electromechanical or universal testing machines
Isotropy
Isotropic materials are materials whose properties remain the same when tested in different directions.
Isotropic materials differ from anisotropic materials, which display varying properties when tested in different directions. less strength when force is applied in the opposite direction (with or against the grain).
3 commonly found polymer conformations and structures Architecture affects physical properties
Linear, branched, network polymer
Compression testing
- Compression testing is one of the most fundamental types of mechanical testing, alongside tensile and flexion tests.
- Compression tests are used to determine a material’s behavior under applied crushing loads.
- Typically conducted by applying compressive pressure to a test specimen (usually of either a cuboid or cylindrical geometry) using plates or specialized fixtures on a universal testing machine.
- During the test, various properties of the material are calculated and plotted as a stress-strain diagram which is used to determine qualities such as elastic limit, proportional limit, yield point, yield strength, and, for some materials, compressive strength
- Compression testing allows manufacturers to assess the integrity and safety of materials, components, and products during several phases of the manufacturing process.
- Materials that exhibit high tensile strength tend to (but do not always!) exhibit low compressive strength and tends vice versa.
Relative molecular mass
Ratio of the average mass per formula unit of a substance to 1/12 of the mass of an atom of nuclide 12C.
Molar mass
- Mass divided by amount of substance.
- Molar mass is usually expressed in g/mol or kg/mol units.
- The g/mol unit is recommended in polymer science, since then the numerical values of the molar mass and the relative molecular mass of a substance are equal.
Molar mass average Mk
Any average of the molar mass for a non- uniform polymer. k subscript specifies the type of average.
An infinite number of molar-mass averages can in principle be defined, but only a few types of averages are directly accessible experimentally.
The most important averages are defined by simple moments of the distribution functions and are obtained by methods applied to systems in thermodynamic equilibrium, such as osmometry, light scattering and sedimentation equilibrium.
Hydrodynamic methods, as a rule, yield more complex molar-mass averages.
- Any molar-mass average can be defined in terms of mass fractions or mole fractions.
- These definitions are most closely related to the experimental determination of molar-mass averages.
Number average molecular mass
- The number average molecular mass is the ordinary arithmetic mean or average of the molecular masses of the individual macromolecules.
Viscosity and shear viscocity
Viscosity is a property of the material which represents the resistance to continuous deformation or flow.
Fluids are typically described in terms of shear viscosity, defined as the ratio between shear stress and shear rate.
Unlike elasticity, the stress is related to the rate of deformation and not to the deformation.
In a fluid, if an external stress is exerted, deformation occurs and the material flows indefinitely until the stress is removed.
What affects viscosity/types of visco
- A Newtonian fluid (e.g. water) is characterized by constant viscosity for any shear rate.
- Most polymer solutions and melts are non-Newtonian fluids, whose viscosity decreases as the shear rate increases (shear thinning behavior).
- Temperature conditions affect significantly the level of viscosity.
Degree of polymerisation
Number of monomeric units in a macromolecule or an oligomer molecule, a block, or a chain.
SEC
size-exclusion chromatography (SEC)
* Separation technique in which separation mainly according to the hydrodynamic volume of the molecules or particles takes place in a porous non-adsorbing material with pores of approximately the same size as the effective dimensions in solution of the molecules to be separated.
- GPC – SEC in which the porous non-adsorbing material is a gel.
Hysteresis
Hysteresis explicitly requires that the loading portion of the stress strain curve must be higher than the unloading curve.
From a stress-strain curve we can see the hysteresis as the area between the loading and unloading curve
Short-range vs long-range intramolecular interactions
Short-range
* Steric or other interaction involving atoms or groups or both situated nearby in sequence along a polymer chain.
* The interacting atoms or groups are typically separated by fewer than ten consecutive bonds in a chain.
Long-range
* Interaction between segments, widely separated in sequence along a polymer chain, that occasionally approach one another during molecular flexing.
* This type of interaction is closely related to the excluded volume of a segment, the latter quantity reflecting interactions involving segments and solvent molecules.
Viscoelasticity
Property of a material which is viscous but which also exhibits certain elastic properties such as the ability to store energy of deformation, and in which the application of a stress gives rise to a strain (or vice versa) that approaches its equilibrium value over a significant time interval.
Viscoelasticity incorporates aspects of both fluid behavior (viscous) and solid behavior (elastic)
Elastic materials store 100% of the energy due to deformation
Viscoelastic materials do not store 100% of the energy under deformation but lose or dissipate some of this energy.
Types of semiflexible materials
isotropic -> strain stiffening
Anisotropic -> stress strain curve depends on the way youre pulling
What is the simplest analog for a linear elastic material
spring :)
Do elastic materials exhibit energy dissipation for loading unloading? Why?
elastic materials do not exhibit energy dissipation or hysteresis as their loading and unloading curve is the same. Indeed, the fact that all energy due to deformation is stored is a characteristic of elastic materials.
Furthermore, under fixed stress elastic materials will reach a fixed strain and stay at that level.
Creep
Creep is in similar to the inverse of stress relaxation
gradual, time-dependent deformation of a material under a constant load or stress over time
A general characteristic of viscoelastic materials is to undergo increased deformation under a constant stress, until an asymptotic level of strain is reached
Shear thinning
Shear thinning is a non-Newtonian behavior where a fluid’s viscosity decreases with increasing shear rate, making it flow more easily under applied stress.
Yield stress
Stress required for a material to flow
Hydrogels
Water-swollen molecular networks
Chemistry controls physical properties (x-link density, network formation, etc) in a large biologically relevant range scale.
Semiflexible materials vs other types of molecular networks
Biopolymer-derived hydrogels can be classified as semiflexible polymers that assemble into fibers to produce fibrous hydrogels with a strain-stiffening response, similar to that of the natural ECM
Purely synthetic, semisynthetic, or nonfibrous forming biopolymers on the other hand, are flexible polymers that are structurally further from the biological ECM.
- Semiflexible polymers, however, can be modified with covalent cross-linking moieties that reduce their ability to form fibers and creates a structure that more closely resembles a flexible polymer network.
- An advantage of synthetic and semisynthetic polymers is that they are more controllable and easily functionalized.
Biomolecular transport for cell communication.
def and types
The exchange of information between cells and their environment happens through three principal transport mechanisms: (a) passive diffusion, (b) convection, and (c) binding-mediated diffusion.
Stress relaxation
Stress relaxation refers to the
behavior of stress reaching a peak and then decreasing or relaxing over time under a fixed level of strain
what model captures viscoelastic solid behaviour
Voigt model creep
