Surface Modification Flashcards
What is the rationale for surface modification of biomaterials
Purpose:
- to modify blood compatibility
- to influence cell adhesion and growth
- to control protein absorption
- to improve lubricity
- to improve wear resistance and corrosion resistance
- to modify electrical characteristics
Give two advantages of self assembled monolayers
- -fills all surface sites
* -displaces contaminants (primary bonding lowers the surface energy)
Explain briefly the Langmuir-blodgett deposition process
this method possesses films that have polar regions(end) and a nonpolar region.
The hydrophillic head group is attracted to water while the tail is hydrophobic.
This allows for a film of a carboxylic acid to spread on water, with molecules standing on there heads.
multiple layers can than be added by the incorporation of hydrophilicity and hydrophobicity of the heads and tails
layers are bult where hydrophobic tails are attracted to hydrophobic tails, and hydrophillic heads are attracted to hydrophillic heads
Schematically describe the photolithography process using (a) positive resist and (b) negative
resist
For positive resists, the resist is exposed with UV light wherever the underlying material is to be removed. In these resists, exposure to the UV light changes the chemical structure of the resist so that it becomes more soluble in the developer. The exposed resist is then washed away by the developer solution, leaving windows of the bare underlying material. In other words, “whatever shows, goes.”
Negative resists behave in just the opposite manner. Exposure to the UV light causes the negative resist to become polymerized, and more difficult to dissolve. Therefore, the negative resist remains on the surface wherever it is exposed, and the developer solution removes only the unexposed portions.
State the difference between nonspecific and specific chemical reactions
non specific- leave a distribution of different functional groups at the surface
specific- change only one functional group on the surface with high yield and few side reactions
Describe the micro contact printing process
creates a “stamp” that is inked with the desired biomaterial and printed on the substrate. This method employs many of the techniques used in making integrated circuits
Elaborate giving example two representative categories of surface modification
chemical or physical modification= this involves physically altering the atoms, compounds, or molecules on the existing surface (treatment, etching, chemical modification)
overcoatings= this involves overcoating the existing surface with a material having a different composition (coating, grafting, thin film deposition)
. Distinguish between chemical and physical adsorption on the surface
chemical absorption- a chemical bond (ionic or covalent), involving substantial rearrangement of electron density, is formed between the adsorbate and substrate. the nature of this bond may lie anywhere between the extremes of virtually complete ionic or complete covalent character
physical adsorption- the only bonding is by weak van der waal- type of forces. there is no significant redistribution of electron density in either the molecule or a the substrate surface
Define the term “immobilization”
**immobilization can be seen chemically immobilized biomolecules were they are attached by a spacer group (an arm, leash, or tether) this limits its range of travel
Differentiate between self-assembled monolayer and the Langmuir-blodgett deposition process
***self assembled monolayer- spontaneously form as highly ordered structures (two-dimensional crystals) on specific surfaces) there are van der waals interactions of the alkky chains (crystalization). This is usually just one layer that self assembles on the substrate.
langmuir-blodgett deposition process- uses films that are highly ordered organic (polymeric) layers athat contain a polar region (end) and a non polar region…. additional monolayers can be added where hydrophillic head is attracted to the seond layer of a hydrophillic head and the hydrophobic tails are attracted to the other hydrophobic tails. (draw photo). Note this process can have one or more monolayers unlike SAM that usually only has one.
- Describe three strategies for surface modification of biomaterials
self assembled monolayers= surface-coating films that spontaneously form as highly ordered structures (two dimensional crystals) on specific surfaces. The properties of the surface are largely controlled by the functional head group of the molecules comprising the film
electrodeposition=In the electroplating process the substrate is placed in a liquid solution (electrolyte). When an electrical potential is applied between a conducting area on the substrate and a counter electrode (usually platinum) in the liquid, a chemical redox process takes place resulting in the formation of a layer of material on the substrate and usually some gas generation at the counter electrode.
creating surface textures/patterns
- Describe the surface modification carried out through the electrodeposition process
In the electroplating process the substrate is placed in a liquid solution (electrolyte). When an electrical potential is applied between a conducting area on the substrate and a counter electrode (usually platinum) in the liquid, a chemical redox process takes place resulting in the formation of a layer of material on the substrate and usually some gas generation at the counter electrode.
Microcontact printing (right) creates a “stamp” that is inked with the desired biomaterial and printed on the substrate. This method employs many of the techniques used in making integrated circuits
- What is the role of control release strategies in a tissue engineering design process?
- Controlled release: release of bioactive molecule from bound state to freely diffusible state whereupon it can exert its biological activity.
- Provide signals to cells in the vicinity of scaffolds and matrix to behave in desired manner.
- Goal to present a biological active factor to the tissue at a concentration that is optimal
