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82 Cards in this Set
- Front
- Back
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medical device |
a product used for medical purposes in patient diagnosis, therapy, or surgery |
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biomaterial |
a material intended to interface with biological systems to evaluate, treat, augment, or replace any tissue, organ or function - First selected by physicians |
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Medical Device History |
'38: FDA Act -> no misbranding Things were expanded slowly to make sure things were safe, expanded to more products '76: Later, they had to review all devices before the market '90: Must report any issues to FDA More and new regulations controlling followed |
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Body-implant relationships |
Biocompatibility: Implant causes chronic inflammation, thrombosis, carcinogenecity Implant failure: Biodegredation, biofouling, calcification Materials characterize the biological responses |
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Polyurethane Biodegredation Cases |
PUR started to biodegrade Through Stress cracking and metal ion-induced oxidation Due to ether content of PUR |
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Silicone Breast Implants Cases |
Leaking silicone from silicone bag lead to dizzines |
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Metals in Biomaterials & properties & alloying |
non-directional Properties depend on crystal structure Defects can either help or hurt the material Solid solution: maintain normal crystal structure after impurity alloying are solid solutions, increase electrical strength, impart corrosion resistance, or change electrical properties |
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Ceramics in Biomaterials |
non-directional ionic bonds between cations and anions Crystalline or amorpous glasses, very hard but brittle, resistant to degradation |
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Structure of Ceramics |
Magnitude of electrical charge, physical sizes of cation and anion effect the packing and stability (if too small, its unstable) -ion coordination number: number of neighbors: rc/ra ratio -defects must not affect neutrality |
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Polymers in biomaterials |
chain or organic materials, used in biomedical applications, directional covalent bonds - at a certain degree of polmerization, then the polymer starts acting like it should - XLing, conformation chaning by rotation of bonds, configuration changed by breaking bonds |
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Spectroscopy |
measures how compounds absorb different types of energy |
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Chromatography |
physically separate molecules based on chemical characteristics |
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UV-Vis Spectroscopy Details |
-Absorption of UV-VIS radiation causes valence electrons to go to a higher energy state -Based on chemical structures/f-nal groups -absorbs at pi electrons/heteroatoms (non carbon ring members)/non-bonding valence shell elections - good at the whole concentraion |
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UV-Vis Mechanism; chromophore |
1. Source with energy 2. Filter chooses selected wavelength 3. Detector converts energy of signal to electrical signal which is processed 4. signal collected again for another wavelength Can be used to ID samples or groups, requiring chromophore (light absorbing groups) Quantification: Beer-Lambert's Law: A = elC |
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IR Spec |
Molecules absorb at resonant frequencies, depend on dipole moment (IR active) Also uses Beer-Lambert's Law Fingerprint region to specially characterize the molecule |
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NMR |
radiation in the radiofrequency region to excite molecules Magnetic field is needed to observe the nuclear transitions Oriented nuclei are then flipped into a higher energy state when spin is flipped, new B field is created Effective B field is detetected compared to shifts against a standard (TMS), affected by electronegativity of atoms (more deshielded, further away they go) |
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Size Exclusion Chromotography |
Based on size with porous beads, larger molecules that cant fit in pores elute first |
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Gel Permeation Chromotography |
A type of size exclusion chromatography, the sample is injected in the mobile phase, we can determine elution graphs gel filtration is different bc it uses aqueous solvents in mobile and hydrophilic in stationary |
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X-Ray Diffraction |
Measures how X-rays are diffracted from atoms-> Determines structures of crystals can be used for all matierials |
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Structure and Property Relationships |
atoms make subunits-> subunits make bulk -> material then fabricated to make a devices Chemical Structure dictates crystallinity, manufacturing can change it |
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Linear/Planar/Volume Defects in Crystal Structure |
Linear: Causes localized strains in crystal structure Planar: Material surface and grain boundaries -> non-optimal coordination number Volume Defects: 3D regions without long range order, aggregates and voids |
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Linear Dislocations |
Edge: Shift in plane Screw: twist in one point Mixed: consists of both |
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Deformation; slip |
Defects in crystal structure impact properties Slip: plastic deformation by movement of dislocations; more slip planes, more ductile; ceramics less ductile because less slip because electroneutrality. Bond energy is related |
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Planar Defects |
polycrystalline composed of a large number of small, randomly oriented crystals or grains Surface grains are more reactive and higher energy Grain boundaries: also have sub-optimal coordination number |
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Plastic Deformation |
dislocation glide along slip plane Grain boundaries are like speed bumps and stop dislocation movement, so smaller grains increases strength |
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Electron Microscopy |
Uses wave-like properties of accelerated electrons to form images |
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Scanning Electron Microscopy |
Electrons from focused beam interact to spray electrons everywhere. Elastically (back scattered) or inelastically (from 2ndary electrons). Spray of electrons is collected then projected |
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SEM Instrumentation |
Source Lenses Sample Holder Detector Computer necessity for conductive materials to reduce Sputter deposition from metallic target Coating has to be thin and conformational Visualization for surface topography of biomaterials Need vacuum |
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Polymer Crystallinity |
Lamella forms crystalline portions, forms spherulite: 3D aggregates of lamellae |
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Thermal Transitions |
Tm = Melting Temperature: Atomic movement breaks the ordered structure (semicrystalline -> amorphous) Tc = crystallization temperature, sufficient energy to move into a highly ordered crystalline state Tg = glass transition temperature: temperature below which the material is considered to be a glass (glassy -> rubbery) |
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Differential Scanning Calorimetry |
Compares heat flow between sample and a reference as a function of temperature Tg to Tc to Tm |
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Mechanical Properties and Testing |
Tensile/compression Shear/torsion bending viscoelasticity hardness Testing: Loads are added to sample. Extensometer records instantaneous lengths. Processor sends the info into a stress-strain plot |
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Brittle vs Ductile/ elastic deformation |
Brittle: very little plastic deformation/little necking, ductile: a lot Elastic deformation: changes in atomic spacing and stretching of bonds/ resistance by interatomic bonding forces |
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Deformation in polymers |
elastic deformation: amorphous chains length and relax Plastic: chains lengthen, lamellae folds tilts, blocks of crystalline separate, further orientation |
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Time dependent properties |
Creep: Hold stress constant, strain increases then levels off Strain: Hold strain constant, the stress decreases |
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Stress concentrators |
stress increases at cracks, notches, sharp corners, and pores |
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Fatigue Fracture |
brittle with little plastic deformation. Stress increases the dislocation and creates more imperfections. 1. crack initiates 2. propogates 3. failure occurs rapidly after a certain size can occur in cycle loading tested by repeating cycles of loading; caused by stress flows |
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Stress Shielding |
Bone resorption leads to bone fractures bc the material takes all of the stress |
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Compliance matching |
Restenosis can occur when synthetic graft failure. |
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Biomaterial degradation: Biological Environment |
Body: mild environment with neutral pH and constant temp. ions facilitate corrosion of metals. Inflammatory cells can change local chemistry |
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Biomaterial Degradation: Corrosion of Metals |
lowest free energy state in an oxygenated and hydrated environment is an oxide corrosion: when metal atoms become ionized or become oxygenated effects of corrosion: loss of structural integrity or loss of function |
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Galvanic Corrosion |
Two different metals/alloys in close proximity in an electrolytic environment, denoted by electric potentials |
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Corrosion rates |
potential of anode/cathode/area of electrode/intermediate resistivity |
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Oxygen depletion in corrosion and different types |
areas of oxygen depletion are anodic - bc there is not oxygen (oxygen increases cathodic reactions) crevice, pitting (scratches and holes on the surface), localized corrosion (in a area like a corner), intergranular (in the grains, caused by impurities, have higher energy) |
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stress corrosion |
tensile become anodic, compressive become cathodic. Tensile side starts cracking |
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Fatigue Corrosion |
max stress without failure continuously decreases, corrosion affects it more |
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Corrosion and implants |
stress corrosion is most common, with some intergranular, interface of implants, at screws and plates |
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halting corrosion |
break in electrical connection; depletion of cathodic reactants or species accepting electrons; buildup of anodic productions passivation: occurs when surface oxidation leads to a stable solid that coats the metal surface |
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Biodegredation of ceramics |
passivating layers can form on cermaics, more stable than metals bc of ionic bonds, can be inert, resorbable, or controlled surface reactivity, stress induced/porosity calcium phosphate hydroxyapatite: resorbable ceramics erode under physiological conditions. Based on chemical susceptibility, amount of crystalinity, water available, surface area to volume |
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Biodegredation Terminology |
biodegredation: a biological agent, causes chemical change bioerosion: water insoluble polymer that turns water soluble without regard to mechanism. Physical/chemical bioresorption, bioabsorption: polymerizing or degradation of cellular activity |
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Chemical Degredation and Erosion |
Chemical: Bonds are broken, mediated by water and enzymes Erosion: physical change |
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Degredation mechanisms |
Hydrolysis -> dep on hydrophilicity (polyester, polyanhydrides) oxidation -> surfacedegradationwith chain transfer of radical water (polyether, poly(ethylene carbonate)) enzymatic: surface level bc enzyme cant penetrate |
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Factors that accelerate hydrolysis |
increased reactivity of labile bond access of water to polymer chains hydrophobicity decreases time, crystallinity decreases it too bc water can travel through amorphous regions |
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Macrophage-Mediated Biodegredation |
Phagocytosis, engulfment, extracellular degradation |
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Implant Surface |
Monocyte Adhesion -> macrophage differentiation -> fusion of macrophages -> FBGC Formation |
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Cell Mediated Biodegradation |
cells with the enzymes and etc bio degrade |
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Biodegradable polymers |
Biomolcules from biochem basically |
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Polymer Oxidation |
Reactive oxygen species initiate, propagate, termination |
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modulation of biodegradation |
cell adhesion/function cell-mediating additives surface modification drugs Polymer stability polymer chemistry additives |
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Biodegredation in-vivo vs in vitro |
in vivo: chemical and physical normal stuff in vitro: oxygen radicals, acids, hydrolytic enzymes, high concentrations of agent to accelerate degredation, complare with in vivo biodegradation |
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Foreign Body Response to implant |
protein adsorption macrophage attack frustrated phagocytosis collagenous encapsulation |
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Characterizing Polymer Degradation |
Morphological changes mass loss thermal behavior changes (DSC) Molecular weight (GPC) Change in chemistry (IR) (NMR) |
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Biodegration hypothesis |
hypothesize degradation mechanisms: chemical changes, physical damage. Surface vs bulk degradation selection of degradation test media: depends on environment in body (pH and cell differences( |
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Chemical Degradation and erosion |
over time, as MW decreases, strength stays the same at first then decreases, then mass decreases the bonds break first, which eventually decreases strength, which eventually decreases mass some parts decrease more than others |
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Biostable vs Resorbable Devices |
Biostable: ID failure mechanisms due to degradation, hope for long term stability Resorbable Devices: ID degradation rate and understand how that will be affected over time |
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Accelerated Testing |
Understand and make it similar to in vitro models Treat polymers with high concentrations of agent to accelerate degradation in vivo biodegradation to compare with |
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Characterizing the Degradation of Acceleration |
Morphological Changes: swelling, deformation, bubbling, disappearance Mass loss DSC MW changes through SEC/GPC Changes in chemistry (IR/NMR)\ MW changes, then strength is impacted, then mass is impacted |
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Hydrogel Swelling |
Swelling means degradation with chain scission. If there less crosslink density, then there is more swelling |
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PEG analysis of accelerted testing |
PEGDA has ester ends that are susceptible to hydrolysis, PEGDAA is resistant with amide ends, making it more stable. However, the ether backbone contributes to oxidative degradation. |
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Göpferich Theory of Polymer Erosion |
If polymer is not soluble, and hydrolysis is the only mechanism of degradation, then the two rates dominate erosion behavior. Tdiff: rate into matrix Tc: Rate of chain cleavage Bulk Deg: Tdiff>Tc Surface Erosion: Tc>Tdiff |
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Bulk vs Surface Degradation |
Surface Erosion: Poly(ortho)esters and polyanhydrides, mass is faster than water intake Bulk Degradation: PLA, PGA, PLGA, PCL; degradation takes place throughout the whole sample, water intake is faster than degredation |
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Hydrolytic Rate of Biodegradation |
Chamical stability of groups Catalysts Morphology Hydrophobicity SA-> volume, Initial MW and polydispersity can be used for drug delivery |
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Enzyme-Labile polymers |
naturally occuring polymers affected by enzymes. Controlled by enzyme concentration, affinity to substrate, SA to Volume Ratio, MW/Polydispersity |
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Resorbable Ceramics |
Calcium Phosphate, erode and dissolute using physiological conditions Rate dependent on solubility Preferentially at grain boundaries Microstructure, can increase the resorbability |
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Affects of Resorbable Ceramics |
Chemical susceptability/crystallinity/water/SA to V ratio |
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Composite Materials |
Improve bulk or surface properties of biomaterials by including a polymer into the mix. |
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Naturally vs Synthetic Polymers |
Natural is polymers (carbs/proteins), Synthetic is created polymers Natural: integrate into the body better; harder to harvest though & foreign body reaction Synthetic: mass produced; cannot directly aid healing |
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Surface Properties of Biomaterials |
Proteins adsorb to surface, how much and what they do is a property hydrophobicity surface roughness and topography chemical composition dictates |
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Physical properties |
Things such as crystallinity, thermal transitions, melting point -> affects water uptake chemical composition dictates |
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Addition vs Condensation Polymerization |
Radical is addition, condensation removes a water and adds it on |
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Copolymers/graft |
Multiple mers, alternating-> flips block -> in bulks graft -> side chains are different mers |
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Bulk Polymerization vs solution polymerization |
Bulk: monomer and initiator are there and mixed. high purity/ lots of heat dissipation solution polymerization does it in a organic solvent that is thermoconductive suspension polymerization; mix in an insoluble plate emulsion polymerization: use of surfactant gseous/solid/plasma: done in those phases |
