Topic 2 Flashcards
(46 cards)
What are nano- and microfabrication technologies?
used to create scaffolds with controlled surface topography
- study cell material interaction and cell biomechanics
- investigate cellular processes, such as adhesion, migration and differentiation
- enhance cell-material interaction without changing chemical composition
What is photolithography?
light is used to generate structures on plantar surfaces. Resolution depends on the wavelength of the light used.
Process of photolithography
- Substrate preparation:
The substrate is prepared and cleaned to ensure a suitable surface for the photoresist. - Photoresist application:
A thin layer of photoresist is applied to the substrate, typically using a spinning technique to create a uniform coating. - Mask alignment and exposure:
The mask is aligned with the photoresist-coated substrate, and light is shone through the mask, exposing the photoresist in specific areas according to the pattern on the mask. - Development:
The exposed photoresist is developed, meaning that the exposed portions are selectively removed or altered based on the type of photoresist used (positive or negative). - Etching or deposition:
The patterned photoresist acts as a mask for subsequent processes, such as etching away unwanted material or depositing a new material in the desired pattern. - Photoresist removal:
Finally, the remaining photoresist is removed, leaving behind the patterned substrate.
Why is titanium used for photolithography
with a top coat of caalcium phosphate, promote bone cell growth
Why micro patterning?
helps to enhance biocompatibility and control cell morphology
What is thermal nano-printing lithography (NIL)?
mechanical embossing technique for large area patterns with resolution of 5-10nm.
Process of thermal nano-printing lithography
solid polymer between a hard stamp and substrate
temp raises to about Tg making the polymer now viscous and the stamp ad substrate compress it (keep temperature and pressure stable)
Temp is lower again so now a solid polymer with the compress new shape
Basic process steps for NIL
1 - begin heating
2 - begin embossing
3 - begin cooling
4 - remoulding at elevated T
5 - demolding at ambient
What is soft lithography?
use of elastomeric materials. method for generating atterns onto a surface with nanometric resolution.
includes replica moulding, micro contact printing, microtranfer moulding etc
What is the most common type of silicon?
polydimethylsiloxane
- two methyl side groups for each silicon atom
Properties of polydimethylsiloxane
- low youngs modulus
- glass transition temp.= 120
- optically transparent for wavelengths from the near UV to the near IR (300-800nm)
- chemically inert
- biocompatible
- stable at temperatures required for biological processes (37-95)
Process of Replica Moulding
1 - fabrication of the intial pattern by photolithhography
2 - mixing of PDMS base with curing agent (10:1)
3 - pouring the PDMS liquid solution in the master surface
4 - thermal curing of PDMS (typically 80 for 30 minutes)
5 - PDMS replica peeling off
What is the collapse of PDMS microstructures?
collapse caused by adhesion force to the ground
if groups are too close or pillars too high
When won’t PDMS collapse?
- the height of the posts is lower than hc (critical height)
- the spacing between the posts is higher than wc (critical spacing)
What is particulate leaching?
a leaching agent (porogen) such as polymer microspheres, salt crystals, sugar crystals, is mixed with a polymeric solution
the dispersion is moulded in the desired shape. After the solvent evaporation, pores are created by treating the material with porogen-soluble solvent.
Advantages of particulate leaching
- the pore size can be controlled by size and amount of particulate particles used
- the pore density can be controlled by changing the concentration of leaching agent
- simple and low cost
- the porosity of scaffolds obtained from this method is reported to be around 50-90%
Limitations of particulate leaching
- the pore shape of the scaffold produced cannot be controlled
- non compatible with polymers that are soluble in the solvent of the porogen
What is freeze-drying?
(or lyophilisation) is a drying process in which the solvent and/r the suspension medium is crytallised at low temperatures and thereafter sublimed from the solid state directly into the vapour state
- can prepare 3D porous scaffolds with porosity beyond 90% and a pore disameter range of 20-400um
Process of freeze drying
1 - the polymer solution is poured into the mould
2 - the temperature of the mould is decreased to solidify the whole system (below freezing point -20, -80)
3 - the frozen product is dried under vaccum resulting in the sublimation of solvent crystals
Advantages of freeze drying
- high porosity
- pore interconnectivity
- control of pore size
- compatible with bioactive materials
Limitations of feeeze drying
- irregularity in pore sizes
- use of cytotoxic solvents
- time consuming process
- high energy consumption
What is electrospinning?
the process of using electrostatic forces to form polymer fibres known as electrospinning
What are the 3 phases of electrospinning?
1 - jet initiation
2 - bending instability
3 - solidification of fibres
Process of electrospinning
1 - stress induced on the charged solution by the electric field and formation of the taylor cone
2 - at high potentials, the electric force overcomes the surface tension and a thin jet emerges at the tip of the cone
3 - chaotic motion of the filament due to electrically driven bending instability, stretching of the jet and solvent evaporation
4 - collection of non woven fibres on the collector
