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102 Cards in this Set
- Front
- Back
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What is the definition of a biomaterial? |
-non viable material in medical device that interacts with biological systems -used to make a device that replaces a function of a body in a safe, reliable manner -any substance OTHER THAN DRUG that treats, changes or replaces |
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What are biomaterials used for? |
-replace part of the body that has lost function (total hip replacement) -correct abnormalities (spinal rod) -improve function (pacemaker) -assist in healing (suture) |
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What are some metals used as biomaterials? |
-stainless steel -cobalt alloys -titanium alloys *has to be non corrosive |
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What are some ceramics used as biomaterials? |
-aluminum oxide -zirconia -calcium phosphates |
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What are some SYNTHETIC polymers used as biomaterials? |
-silicones -polyethylene -polyvinyl chloride -polyurethanes -polylactides |
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What are some NATURAL polymers used as biomaterials? |
-collagen -gelatin -elastin -silk -polysaccharides |
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What are some biological materials used as biomaterials? |
-modified allogenic and xenogenic tissues |
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What are some composites used as biomaterials? |
-continuous phosphate with discontinuous component |
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What are the material attributes considered for biomedical applications? |
-biocompatibility (non carcinogenic, non toxic, non allergenic) -sterilizability (not destroyed by typical techniques) -physical characteristics (strength, elasticity, durability) -manufacturability (machinable, moldable, extrudable) |
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Is a dialysis machine a biomaterial? |
It consists of biomaterials but is not a biomaterial in itself
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What use is metal as a biomaterial? |
-good strength and generally biocompatible
-used for joint replacements and stints -ductile and tough |
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What use are ceramics as a biomaterial?
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-very hard with good wear resistance
-brittle and hard -inorganic -orthopedic setting |
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What use are polymers as a biomaterial? |
-many applications -polymer can degrade to strengthen a bone -ductile and soft |
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Which material attributes are more straightforward and why? |
-sterilizability -physical characteristics -manufacturability *more straightforward than biocompatibility because we know more about chemistry than biology* |
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Describe biocompatibility. |
-ability of a material to perform with an appropriate host response in a specific function -no general set of criteria since it depends on the materials application -depends on the contact time (1-2 second needle versus 10-15 year hip replacement) |
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Yield strength? |
-stress at which noticeable plastic strain first occurs -noticeable strain often taken to be 0.2% |
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Proportional limit? |
-when the relationship between stress and strain stops being linear -often used as yield strength since it is hard to define |
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Breaking strength? |
-point at which the material fractures -not the ultimate tensile strength unless the material is brittle |
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Ultimate tensile strength? |
-onset of necking -maximum stress that the material can take |
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Ductility? |
-amount of plastic strain required to cause a material to fracture |
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Hardness? |
-how successfully a material resists deformation |
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Resilience? |
-measure of the elastic energy that can be stored in a unit volume of stressed material -area under linear portion of stress strain |
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Toughness? |
-energy required to break a material |
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What does the presence of micro cracks do? |
-causes measured UTS to be smaller than theoretical UTS -because crack propagation occurs -materials with defects fail faster |
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What is fatigue? |
-progressive deterioration of the strength of a material due to loading over time that can cause the material to fail at lower stress levels |
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What is the process of failure? |
1) crack initiation: small crack created at a point of high stress 2) crack propagation: crack increases in length 3) final failure: rapid propagation of crack |
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What is fatigue strength? |
-stress level that causes failure after a given number of cycles |
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What is fatigue life? |
-the number of cycles required to cause fatigue fracture at a specific stress |
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What is viscoelasticity? |
-when the response of a material to imposed stress resembles the behaviour of a solid or liquid, depending on the rate of application of stress -**time dependant |
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What is stress relaxation? |
-the decrease in stress over time for a material under constant strain |
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What is creep? |
-plastic deformation of a sample under constant load over time -increase in strain (elongation) over time due to a constant applied load |
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Surface properties? |
1) surfaces have unique reactivity 2) surface is inevitably different from the bulk 3) mass of material that makes up the surface zone is very small 4) surfaces readily contaminate 5) surface molecules can exhibit considerable motility |
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What does surface energy determine? |
-protein adsorption to materials -blood clotting due to material contact -cellular response to materials |
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What is surface tension? |
-excess energy at interface -causes thermodynamic instability |
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What are hydrogen bonds like in surface chemistry? |
-thermodynamically unfavourable
-they minimize surface tension by adsorption (adhesion to the surface) of other molecules |
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What are some anatomical and physiological barriers to pathogens? |
-intact skin
-ciliary clearance (coughing) -low stomach pH (digestive) -lysozomes in tears and saliva |
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What are the innate immunity defences? |
Cellular -macrophages -neutrophils -mast cells -natural killer cells -dendritic cells Humoral -complement -antimicrobial peptides |
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What are the adaptive immunity defences? |
Cellular -T and B cells Humoral -antibodies |
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Which host defences are used in wound healing? |
Intact Skin Cellular Innate Immunity -macrophages -neutrophils -mast cells -natural killer cells -dendritic cells Humoral Innate Immunity -complement -antimicrobial peptides |
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What are the phases of wound healing? |
1) hemostasis 2) inflammation 3) tissue formation 4) remodeling |
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Describe hemostasis? |
-stops blood loss from damaged blood vessels by sealing damaged area until tissue is repaired 1) vasoconstriction (blood vessels contract) 2) platelet plug formation (temporarily blocks leak) 3) fibrin clot formation (blood clotting) |
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Signs of inflammation? |
-swelling -pain -redness -heat |
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Steps of inflammation? |
1) tissue damage triggers increase in blood flow and capillary permeability 2) permeable capillaries allow influx of fluid and cells 3) phagocytes migrate to site of inflammation 4) phagocytes and antibacterial exudate destroy bacteria |
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Steps of leukocyte extravasation? |
1) selectin-mucin interaction mediate rolling 2) chemokines/chemoattractants induce change in integrins 3) integrins adhere firmly to ICAMs |
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Steps in extravasation? |
1) selectin-mucin interactions mediate rolling 2) chemokins/chemoreactants induce change in integrins 3) integrins adhere firmly to ICAMs |
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Steps in complement cascade? |
1) formation of a terminal complement complex 2) release of complement fragments that bind to pathogen surface and facilitate phagocytosis 3) release of complement fragments that enhance inflammatory response |
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Main events in FBR (Foreign Body Reaction)? |
1) protein adsorption 2) provisional matrix formation (fibrin clot) 3) complement activation 4) macrophage adhesion and activation 5) foreign body giant cell formation 6) fibrous capsule formation |
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Blood-implant interactions? |
1) proteins in the serum adsorb to surface of material 2) provisional fibrin matrix is formed on and around the biomaterial 3) complement system activated by surface contact |
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Bonding in metals? |
-electrons are mobile in a pool around cations -this causes the high electrical conductivity of metals |
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Grain boundaries? |
-reduce conductivity -increase corrosion |
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Describe the 4 main methods of metal product manufacturing? |
1) machining: metal is cut 2) metal casting: melted and poured (can cause shrinkage larger grain sizes) 3) forming: rolling to compress, extruding, or hammering 4) sintering: powdered metal with pressure applied, reduces porosity |
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Pros and cons of stainless steel as a biomaterial? |
Pros
-low cost -good short term corrosion and fatigue resistance -easily machined Cons -corroded in long term -high modulus -potentially allergenic |
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Pros and cons of Co-based metals as biomaterials? |
Pros -long-term corrosion resistance -super fatigue and wear resistant -biocompatible Cons -difficult to machine -more expensive -high modulus -potentially allergenic |
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Pros and cons of titanium as biomaterial? |
Pros -light -very corrosion resistant -excellent biocompatibility -low Young's modulus Cons -lower shear strength -low wear resistance -expensive |
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What are some design considerations for metal biomaterials? |
-typically want to match material properties of tissue with mechanical properties of metal -consider how it may fail in vivo (corrosion, wear, fatigue) -need to consider cost |
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What is stress shielding? |
Reduction in bone density as a result of the removal of stress on a bone due to an implant. A material with low Young's modulus will prevent this. |
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Explain the steps of corrosion? |
metal atoms (anode) dissolve and M+ leaves the surface and enters the solution -surface become negative -makes it harder for other ions to leave and equilibrium is reached equilibrium must become upset -cathodic reaction must occur to consume e- in the body, excess e- consumed by dissolved O2 -occurs at microscopic cathode on the surface |
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Explain galvanic corrosion? |
-two metals in contact with each other with physiological solution as salt barrier -more anodic materials undergo dissolution at an accelerated pace -more cathodic materials act as e- sink |
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Explain crevice corrosion? |
1) initially anodic and cathodic reaction is occurring 2) O2 in crevice is depleted, only metal oxidation can occur in the crevice 3) buildup of M+ causes influx of Cl- creating MCl 4) chlorine dissociated with H2O into MOH + H+ + Cl- 5) H+ lowers pH and accelerates corrosion |
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Explain pitting corrosion? |
-occurs in pits on surface -small area for anodic reactions -large area for cathodic -accelerates corrosion and makes pits larger -dangerous b/c difficult to detect |
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Explain inter granular corrosion? |
-occurs along grain boundaries -similar to crevice corrosion -accelerates corrosion |
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Explain fretting corrosion? |
-metals in contact with each other -movement causes pits to form -try to reduce the amount of parts in a system |
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Explain stress corrosion? |
-cracks formed from stress -pitting corrosion causes cracks to propagate and failure occurs early |
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How do you improve corrosion resistance? |
1) Passivate the surface (treat with acid) 2) Choose more corrosion resistant material (Titanium) 3) Proper handling of implant (avoid scratches) 4) Avoid combinations of metals in close proximity |
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Interfacial wear? |
occurs when bearing surfaces come into contact with no lubrication |
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Fatigue wear? |
progressive failure due to application of cyclical stresses |
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What is the impact of wear particles? |
Wear Particles -engulfed by macrophages, results in cell death -promotes bone resorption by osteoclasts Aseptic Loosening -periprosthetic bone loss -fibrous tissue invades bone-implant interface |
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Applications of bioceramics? |
-orthopedic load-bearing coatings -dental implants -bone graft substitutes -bone cements |
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What type of structure is a ceramic? |
-polycrystalline |
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How do nearly inert bioceramics attach to bone? |
-attach by bone growth into surface irregularities by cementing device into tissue or press fitting into a defect |
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How do porous inert bioceramics attach to bone? |
-bone growth occurs that mechanically attaches bone to the material (biological fixation) |
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How do bioactive bioceramics attach to bone? |
attach directly by chemical bonding with the bone (bioactive fixation) |
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How do resorb able ceramics attach to bone? |
designed to be slowly replaced by bone |
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What are the pros of Alumina? |
-scratch resistant -low friction coefficient -very low wear -corrosion resistant |
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What are the cons of Alumina? |
-minimal bone ingrowth -non-adherent fibrous membrane can form (loosening) -interfacial failure and loss of implant can occur |
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What are the applications of Alumina? |
-hip and knee replacements -porous coating for femoral stems -porous bone spacers -dental crowns and bridges |
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What causes degradation of calcium phosphate? |
-physiological dissolution (environment pH) -physical disintegration -biological factors (phagocytosis) |
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What are the uses of calcium phosphate? |
-repair material for bone damaged by trauma or disease -repair and fusion of vertebrae -repair of maxillofacial and dental defects -coating for metal implants |
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What are some factors that affect the dissolution of calcium phosphate? |
1) surface area of implant 2) % crystallinity 3) grain size 4) ionic substitution |
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What is a glass ceramic? |
-inorganic melt cooled to solid without crystallization -an amorphous solid -polycrystalline solid prepared by controlled crystallization of glass |
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Bioactivity in glass ceramics? |
-capable of direct chemical bonding with the host tissue -stimulatory effects on bone-building cells -depends on the amount of SiO2, CaO, and Na2O -cannot be used for loading bearing applications -ideal as bone cement filler |
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What are the factors that determine physical properties of polymers? |
1) molecular architecture 2) molecular weight 3) chemical composition |
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Characteristics and uses of PMMA? |
Characteristics -hydrophobic -hard -rigid -biostable Uses -bone cement -intraocular lenses -contact lenses |
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Characteristics and uses of PE? |
Characteristics -low density cannot withstand sterilization temperatures -high density has good toughness and wear resistance Uses -tubing for drains and catheters -prothetic joints |
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Characteristics and uses of PVC? |
Characteristics -plasticized to make flexible -used for short term applications since plasticizers can cause leaching Uses -tubing -blood storage bags |
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Describe the amorphous glassy state of polymers? |
-stiff, hard, brittle -random coil structure -no melting point |
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Describe the semi-crystalline glassy state of polymers? |
-hard, brittle -crystal formation when cooled -exhibit a melting point |
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Describe the rubbery state of polymers? |
-soft, flexible, extensible -amorphous -above Tg or Tm (if exists) |
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What are cross links? |
-connections between polymer chains -covalent (permeant) -H-bonding (transient) -entanglements (transient) |
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What does cross linking do? |
-increases molecular weight -swell in solvents -elastomers and hydrogels |
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What is the diffusion of small molecular weight polymers useful for? |
-purification of gases by membrane separation -dialysis -packaging -controlled drug delivery -polymer degradation |
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What is diffusion flux in polymers dependant on? |
-solubility of component in polymer -diffusivity of component in polymer |
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What ever happened with that poppet style heart valve? |
-in a small % of patients the poppet jammed or escaped -recovered poppets were yellow, smelled, and had strut grooves |
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Describe the process of bulk erosion? |
1) water penetrates through diffusion 2) hydrolytic cleavage of polymer backbone 3) material begins to fragment 4) elimination of degradation products by body -if water penetration is faster |
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Describe surface erosion? |
-device gets thinner with time -mass loss constant -strength of material retained (just thinner) -if hydrolysis is faster |
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What is the microenvironment characterized by? |
-cellularity -cellular communication -metabolic factors -local geometry |
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What is cellularity? |
-the degree, quality, or condition of cells within a matrix |
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How do cells communicate? |
-secretion of soluble signals -cell-cell contact -adhesive membrane receptors -gap junctions -cell-ECM interactions -specialized receptors |
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What are the tissue engineering scaffold materials?
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-synthetic polymers (foams) -natural polymers (fibres, hydrogels) -ceramic (porous structures) -de-cellurized tissue and cell-derived matrix (skin, ligaments) |
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What are the types of cell cultures? |
-monolayer (adherent cells) -suspension (non-adherent cells) -three-dimensional (scaffolds) |
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What types of cells are used in tissue engineering? |
-primary cells (harvested from patient) -passaged cells (expansion from primary cells) -stem cells (undifferentiated cells) |
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Two lineages of stem cells? |
mesenchymal, hematopoietic |
