Module 1 Flashcards
Biomaterial
A nonviable material used in a medical device, intended to interact with biological systems
Bioinert
Materials that do not initiate an immunological response when implanted
Bioactive
Materials that induce a specific or desired biological response
Regenerative
Materials that stimulate a response targeted toward regenerating diseased tissue (tissue engineering)
Biocompatibility
Ability of a material to perform with an appropriate host response in a specific application
- Resistance to blood clotting
- Resistance to bacterial colonization
- Normal healing
Issues affecting biomaterials
Toxicity, wear
Classes of Biomaterials
Polymers, metals, ceramics, composites
Types of Polymers
Silicones, polyurethanes, hydrogeis
Types of Metals
Stainless steel, titanium alloy, cobalt chromium alloy
Types of Ceramics
hydroxyapatite, tricalcium phosphate, silica
Bulk properties
- Determines the toughness, strength and stiffness of a material
- Directly influence dynamic interactions with biological systems
Structure of Atoms
Electron, proton, neutron
Electron (e-)
lightest of the 3, negatively charged, and responsible for conductivity
- Charge = 1.602 x 10^-19 coulombs
- Mass = 9.1 x 10^-31 kg
Proton (p)
Mass 2000x e-, positively charged, and dictate atomic number or element
- Charge = 1.602 x 10^-19 coulombs
- Mass = 1.6 7 x 10^-27 kg
Neutron (n)
Mass similar to p, no charge, no chemical behavior, responsible for isotopes
Theory of Electronegativity
- Ranks the relative strength of each element to attract electrons to complete outer shell
- Electronegativity increases L to R in periodic table (1.0 for Li, 4.0 for F)
Ionic Bonding
- Electron donor atom (metal; cation)
- Electron acceptor atom (non-metal; anion)
- Larger the difference in electronegativity, the stronger the bond
- Cation is surrounded by as many anions as possible
- Form highly ordered crystal structures
- No discrete molecules exist
- Electrons no longer serve as charge carries
Ionic Solids
- Poor electrical conductors
- Relatively unreactive
- Have high melting points
- soluble in water
Covalent Bonding
- Elements bordering metal/non-metals have 4 valence electrons
- Have equal tendency to donate or accept e-
- Instead, share valence e- to form covalent bond
- C atom with 4 covalent bonds has stable outer shell
- Extremely strong bond
- Poor electrical conductors
Metallic Bonding
- Metal atoms do not bond by either ionic or covalent bonding
- Materials are very strong and have high melting points
- A positive core of metal atoms exist
- Delocalized valence e- circulate around ions
- Alloys have very low difference in electronegativity
- Strength increases as ion core becomes more tightly packed
Non-localized bonds
- Permits plastic deformation
- Accounts for electrical and thermal conductivity
- Chemical reactivity
Weak Bonding
- Van der Waals bonds do not rely on gaining/sharing e-
- Polarization
- H-bonding special case involving H atoms
Polarization
Separation of positive and negative charges within molecules, oppositely charged parts attract
Materials used in biomedical & biotech industry
Metals, ceramics, polymers (synthetic & biological)
Alloys
Mixtures of metals
Metals
Materials with metallic bonds
Ceramics
- Inorganic compounds with mixture of ionic and covalent bonding
- Structures not as closely packed as metals
- Packing limited by charge and size
- Inorganic glasses
Inorganic glasses
- Crystal structure forms after melting and cooling
- Orderly structure not maintained
- Amorphous state
Polymers
- Constituent atoms are C
- Covalent bonding forms linear, chainlike structure
- Two e- used in chain, two e- free
- Thermoplastic or thermosetting
Thermoplastic Polymers
- Basic chains are straight, no branching
- Can be melted and remelted without change in structure
- Neighboring chains held together by H bonding or van der Waals forces
- Weak bonding means weak solid
- Lower strength and melting point than thermoset polymers
Thermosetting Polymers
- Has branches and side chains
- Covalent bonds between branches form = cross linking
- Crosslinked polymers have 3 D network
- Do not melt uniformly when reheated
Hooke’s Law
Solid material will extend in the direction of traction in an amount proportional to load when subjected to force
Stiffness
- Ability of material to resist deformation
- E & G are used to characterize stiffness of material
Elastic Strain
Increasing inter-atomic distances (stretching the bonds)
Isotropic Materials
- Material whose properties are same in all directions (longitudinal, transverse)
- Metals, alloys, and ceramics have E & G values that are highly reproducible
Anisotropic
- Polymers and tissue samples
- Stronger in longitudinal than transverse direction
Elastic deformation
when load is removed the material returns to original dimension
Plastic deformation
material does NOT return to original dimensions
- Large scale displacement of atoms without complete rupture (irreversible)
- Strains produced are much greater than in elastic deformation
Ultimate Tensile Strength
The maximum stress that a sample can support. This happens in portions of the stress strain curve beyond the elastic limit
Brittle Materials
Exhibit little or no plasticity before fracture
Ductile
Large amount of plasticity under tension
Malleable
Large amount of plasticity under compression
Toughness
- Total area under the curve
- The ability to store both elastic and plastic energy
Resilience
- Area under the linear portion of the curve
- The ability to store only elastic energy
Elastic Response
Instantaneous elongation is stress applied
Creep
Continuous, time-dependent extension
Stress Relaxation
Continuous drop in load at a constant extension
Fatigue
Occurs when loads are applied and removed for a large number of cycles
Fatigue Strength (Endurance)
Stress which provides low probability of failure after 10^6 to 10^8 cycles (endurance limit)
Hydrophilic
Surface on which water spreads
- more biocompatible
Hydrophobic
Surface on which water beads
Surface energy
The balance of cohesive force and adhesive force
Cohesive force
the force of liquid molecules attracted to each other
Adhesive force
The force of the liquid drop attracted to the surface
