Ch 1 - Materials for Biomedical Applications Flashcards
Biomaterial
- Material intended to interface w/ biological systems to evaluate, treat, augment or replace any tissue, organ or function of the body
- e.g. not a splinter b/c it’s unintentional
Biomaterials science
- Study of biomaterials and their interactions w/ the biological envir.
- Includes subjects related to materials science (e.g. mech prop’s) and biology (e.g. immunology, toxicology and wound healing)
Biocompatibility
Ability of a material to perform w/ an appropriate host response in a specific application
effects of hosts on materials
- Chem. degrad. rate
- Mech. prop’s
- Phys. prop’s (e.g. swelling in hydrogels)
- Implant calcification (e.g. build-up around heart valves → brittle)
effects of materials on hosts
- Toxicity/chem. rxns
- Approp. size/weight
- Rejection by immune sys. (inflammatory response)
- Heating/cooling prop’s
- Safe failure mode
- Blood clotting
- Carcinogenicity
- Sterility/infection
EX: hip implant
• Contains all 3 major biomaterials: metals, ceramics and polymers
• Components:
1 . Stem: goes into femur (metal)
2. Head: ball attaches to stem (ceramic coating?)
3. Acetabular cup: goes into hip socket (polymeric)
Biological response: Inflammation
- Localized blood clotting, infection, implant calcification)
- Depends on shape/size of implant (scale), location in body, and chem/mech prop’s
Macro > 500 um Micro 1-200 um Nano < 200 nm
Biological response: Proteins/Cellular
Determines overall success of implant (time to failure)
in vitro
in glass
in vivo
in living system
FDA approval
• Biocompatibility testing dictated by ASTM Int’l and ISO
• Approval is NOT for materials (for all uses), it’s for use in the context of devices/drugs
• Steps:
1 . In vitro
2. In vivo w/ healthy animals
3. In vivo w/ diseased animals (if applicable)
4. Controlled clinical trials
Metals
- Inorganic materials w/ non-directional metallic bonds and highly mobile electrons (conductive)
- Strong, ductile (formable)
- Apps: orthopedic replacements (load-bearing)
Ceramics
- Inorganic materials w/ non-directional ionic bonds (encourages integration w/ surrounding tissue) b/w electron-donating and electron-accepting elements
- Very hard and more resistant to degradation than metals, yet quite brittle b/c of ionic bonds
- Apps: orthopedic implants or dental materials (for small loads)
Polymers
- Organic materials w/ long chains held together by directional covalent bonds, esp. those derived from natural sources (e.g. proteins)
- i.e. \elastomers, \hydrogels and \composites
Elastomers
- Can sustain large deformation at low stresses and return to initial form upon release of stress
- i.e. cardiovascular applications
Hydrogels
- Swell in water and retain signif. fraction of water w/o completely dissolving
- i.e. soft tissue applications
Composite
- Composed of +2 chemically distinct components (typ. one is a \polymer)
- Often to optimize \bulk or \surface mech prop’s
Naturally-derived polymers
- Derived from sources within the body
- Typically similar chem compos. to tissue they replace (better integration or remodeling)
- e.g. \collagen and \fibrin proteins (cartilage and orthopedic apps)
- e.g. \chitosan and \alginate (wound dressings)
Synthetically-derived polymers
- Easily mass-produced and sterilized
- Tailored prop’s for specific apps
- Typ. do not interact w/ tissues directly (cannot direct cell/tissue response)
Processing biomaterials
Can affect \bulk and \surface prop’s to produce complex changes
Degradative properties
- Depends on shape/size of implant (scale), location in body, and chem/phys/mech prop’s
- e.g. inflammation: may be designed or undesired
Surface properties
- Determine protein adsorption (attachment)
- e.g. \hydrophobicity (water-fearing moieties, chem prop)
- e.g. surface roughness (trap biological constituents, phys prop)
Material dogma
\surface prop’s → protein attachment → cell/tissue response
Bulk properties
- Most important parameter b/c of long-term impact
• Mech prop’s e.g. strength & stiffness
• Phys prop’s e.g. \crystallinity & \thermal transitions
Anisotropy
- Mech prop’s differ based on direction of loading
* e.g. bones in leg
Crystallinity
Alters water uptake, which can impact degradation and interaction w/ surrounding cells & proteins
Thermal transitions
e. g. melting point
* * Must be stable at body temp.
Chemical composition
- Typ. a result of the type of bonds in mat’l
* Dictates \bulk properties e.g. \hydrophobicity
Quantitative characterization techniques
- \spectroscopy = absorption of energy
* \chromatography = physical separation of molec’s based on chem char’s (e.g. charge or size)
Atomic number
“Z” = # protons
Atomic mass
Measured in \atomic mass units (amu = mass/mole)
Mole
6.02 E23 molec (per mole) = Avogadro’s #
Convert amu/molec to g/mol
1 amu/molec = 1 g/mol
Quantum mechanics (electron movement)
- \Bohr model - electrons orbit nucleus in \orbitals (discrete energy states)
- \Wave-mechanical model - orbitals indic. the probability that an electron will occupy a certain space around nucleus (\electron clouds = probability functions)
Quantum numbers
- Dictate size, shape and orientation of electron probability functions
- Divides electron shells (Bohr energy states) into subshells (s, p, d, f)
Pauli exclusion principle
Each state can hold up to 2 electrons (w/ opposite spin) → predict electron config. of an atom
Aufbau principle
Sequentially adding electrons to energy states (lower to higher)
Hund’s rule
In subshells w/ mult. energy states (e.g. 3p subshells), each subshell must first be filled w/ 1 electron
Closed-shell configuration
- Completely filled orbitals
* Stable, do not participate in most chem rxns
Open-shell configuration
Partially filled orbitals
Valence electrons
- Occupy outermost shell
* Can be shared/exchanged in \open-shell config.
Periodic table
- Organizes elem by incr. atomic #
* Based on # valence electrons
Electropositive, EP[+]
(L) give up electrons to become [+] ions
Electronegative, EN[-]
(R) accept electrons to become [-] ions
Primary bonds
- Sharing/transfer of \valence electrons
- \ionic, \covalent, \metallic bonds
- F_tot(r) = F_attr(r) + F_repuls(r) where r0 = bond length (distance at equilibrium)
Ionic bond
- Transfer of valence electrons
* ΔEN b/w cation & anion
Covalent bond
Sharing valence electrons (typ. polymers)
σ bonds
First bond formed along internuclear axis of 2 atoms (only 1 ∀ pair)
π bonds
- Additional (double/triple) bonds
* Not as strong, but can affect rigidity
Molecular orbitals
Describes energy absorption and excited states of ENTIRE molec (not singular atom)
Bonding molecular orbitals
- Wave functions describing electrons of atomic orbitals from 2 atoms overlap in REINFORCING way
- ↑ probability of finding e- along internuclear axis (attr to nuclei) ∴ highly stable
Antibonding molecular orbitals
- Wave functions overlap in DESTRUCTIVE way and cancel each other in region b/w nuclei
- Greatest e- density found on OPPOSITE sides of nuclei ∴ less stable
Metallic bond
- EP[+] elements
- e- donated to entire structure, “sea of e-“
- Delocalized \valence electrons → high electrical conductivity
- NON-directional electron sharing
Secondary bonds
- \VDW
- \dipoles
- \polar molec’s
- \H bonds
Van der Waals
Attraction b/w atoms w/o electron sharing/transfer
Dipoles
Molec’s w/ portions slightly positively & negatively charged
Polar molec’s
Permanent dipoles (strongest 2 ° bond)
Hydrogen bond
Interactions b/w H,+ and O,2-
