Carbon Biomaterials and Hydrogels Flashcards
(25 cards)
What are the natural forms of carbon?
Gas (CO, CO2), Graphite, Diamond
Describe characteristics of graphite.
Anisotropic - directional dependent characteristics Layered in plane Hexagonal covalent bonding (1.42Å) High melting point dry lubricant conductive
Describe characteristics of diamond.
Tetrahedral covalent bonding (1.54Å) Isotropic Extremely high melting point (4000°C) High hardness non-conductive Insoluble
Describe characteristics of fullerene.
AKA Bucky Balls
yet to be produced on a large scale
Folded or rolled graphene (carbon nanotubes)
Describe characteristics of pyrolytic carbon.
Polycrystalline (10nm crystal size)
behaves isotropically
Brittle - bonds in layers are unidirectional
High strength - layers held by C-C bonds
Good wear resistance - self-lubricating
Good fatigue resistance - failure from repeated stress in opposite directions
extremely biocompatible
nonreactive
critical surface tension - 50 dyn/cm upon exposure to blood
absorbs proteins from the blood (no denaturing reaction)
proteins on surface are in dynamic equilibrium
Applications of pyrolytic carbon?
Mechanical heart valves - bi-leaflet, pivot on hinges
Finger joint arthroplasty - due to wear and tear over long periods of time, severe repeated injury, degenerative diseases, not a lot of room
Describe characteristics of hydrogels.
3D network of hydrophilic cross-linked polymers
do not dissolve in water but swell (90% water)
good optical transparency
very similar to soft tissues
Describe properties of hydrogel.
solid and liquid like properties
possess a high degree of biocompatibility
Range of rigidities: Sol>Jelly>Gel>Hydrogel
How can you classify hydrogels?
Water content Porosity Fabrication Biodegradability Preparation Origin
Describe hydrogel swelling.
influenced by type and composition of monomers environmental factors (pH, Temperature, ionic strength) Cross-linking (permeability and mechanical strength)
Describe hydrogel porosity.
affects diffusion of molecules
more porosity, greater diffusion
Describe chemical fabrication.
involves covalent cross linking of polymer chains
thermoset hydrogels - remain solid after setting
volume phase transition
have reliable shape, stability, and memory
Describe physical fabrication.
non-covalently cross-linked hydrogen bonding predominates thermoplastic hydrogels - can go back to liquid sol-gel phase transition limited shape, stability, and memory
Describe biodegradability of hydrogels.
biodegradable and bioinert
Describe copolymer preparation.
at least one of the monomers must by hydrophilic
Describe Semi-Interpenetrating Network (Semi-IPN)
When one polymer is linear and penetrates another cross linked network without any other chemical bonds
often they have rapid kinetic response rates to pH or Temperature due to absence of cross-links
retain pore size characteristics
Describe Interpenetrating Network (IPN)
Results in permanent interlocking of network segments
These end up being dense hydrogels with stiffer and tougher mechanical properties
What are natural hydrogels?
Proteins - Gelatin
Polysaccharides - Chitin, Starch, Alginate, Agarose
Describe gelatin.
prepared by thermal denaturation of collagen
Ala-Gly-Pro-Arg-Gly-Glu-4Hyp-Gly-Pro
What is chitin found?
crab shells
What is alginate derived from?
algae
What is agarose?
derived from seaweed, low melting temperature, thermoplastic
What are synthetic hydrogels?
Polyethleneglycol (PEG) - cross-linked, easy to modify
Acrylamide - bioinert
Pore size depends on concentration of the two components, decreases as acrylamide concentration increases
What are application of hydrogels?
contacts water carriers 3D cell culture synthetic skin - made from collagen or cartilage from shark skins pill capsules implant coatings electrophoresis gels drug delivery
