Surface Properties of Biomaterials Flashcards
What is surface tension?
excess energy caused by regions or atoms on the surface not bonded; unfilled valence shells
What interactions occur on the surface of the material? (3)
- surface tension
- adsorption
- absorption
- biocompatibility
What is adsorption?
adhesion of molecules to a solid surface
What is absorption?
penetration of molecules into the bulk of another material
What is biocompatibility at the surface of a material?
controlling protein adsorption to the surface
Protein adsorption can cause: (4)
- more proteins to attach
- inflammatory response
- cellular interaction inhibiting proliferation
- biofilm formation
What are 2 properties that impact adsorption?
- surface hydrophobicity
- surface charge
Protein adsorption increases with increased _________________
hydrophobicity
Surface charge occurs by:
dissociation of ionizable surface groups or through adsorption of ions from a solution
Steric hinderance
presence of chemical groups prevents or slows down adsorption
Surface roughness can _______ proteins
trap
Contact Angle analysis determines
the hydrophobicity of the surface
Advancing contact angle measured by
adding water slowly to surface with syringe
Receding contact angle is measured by
removing water from surface with syringe
Contact Angle Hysteresis is measured by
subtracting the advancing by receding values
Contact Angle Hysteresis describes
how the surface tension of the material changes before and after it is exposed to an aqueous environment.
The lowest critical surface tension value means
the most hydrophobic surface
What are the two types of surface treatments? And what do they include?
- chemical - covalent and non-covalent bonding to surface
- biological - covalent and non-covalent bonding to surface
What is Plasma treatment? What surface is to be treated? What happens to the electrodes in the chamber? Do they interact with the cathode surface?
chemical surface treatment & covalent bonding
plasma environment created by applying an electric potential across a gas.
cathode = surface to be treated = negative potential relative to anode
Electrons move around chamber from cathode to anode and collide with molecules to form gaseous ions and radicals = interact with cathode surface and cause reactions
What is Chemical Vapor Deposition (CVD)? What does it cause to happen? What is it used for?
chemical surface treatment & covalent bonding
a mix of gases exposed to a material at a high temperature.
causes decomposition of one or more components of the gas mixture and subsequent deposition.
used for pyrolytic carbon coatings and Tantalum
What is Physical Vapor Deposition (PVD)? What do the ions/atoms do to the surface? What does it increase? What devices is it used for?
chemical surface treatment & covalent bonding
Deposition of atoms generated through physical processes.
- ions or atoms strike surface and condense it to form a thin film
increases water resistance of metal implants
for orthopedics or surgical tools.
What is radiation grafting/photografting? What is it typically used for?
chemical surface treatment & covalent bonding
material is exposed to source of high energy, ionizing radiation, electron beam or UV light which forms the reaction at the surface.
used for hydrogels to bind to hydrophobic substrates
In Self-Assembled Monolayers (SAM) what is amphiphilic? What are the three key regions?
chemical surface treatment & covalent bonding
amphiphilic = hydrophilic (polar) and hydrophobic (non-polar) areas
- attachment group
- long hydrocarbon (alkyl) chain
- functional polar head group
What are Langmuir-Blodgett Films similar to? What is the Langmuir trough used for?
chemical surface treatment & non-covalent bonding
similar to SAMs with hydrophilic head and hydrophobic tail
Langmuir trough used for molecules transferred to the surface of the biomaterial - reaches critical area = function of size and type of hydrophobic tail on molecule.
What happens in Layer-by-layer Coatings?
chemical surface treatment & non-covalent bonding
+ charge substrate put in anionic solution, surface becomes - charge, rinsed, substrate put in cationic solution, adsorption of + charge occurs, surface becomes + charge, rinsed
cycle repeats until coating of desired thickness is reached
What happens with Covalent Biological Coatings? What are the two methods?
attaching biologically active molecules to substrates through covalent bonds.
post-fabrication methods or attachment during synthesis
What happens with Non-Covalent Biological Coatings? What is used to prevent formation of clots? What region is added to the heparin?
involves adsorption of biomolecule into the biomaterial, then cross-linking to improve the coating stability
heparin = complex carbohydrate -> prevents clots
hydrophobic region added = negative charge so no modification of biomolecule = allows for adsorption of heparin to + charged surfaces
