Lecture 9 Flashcards
An example of a natural hydrogel
ECM
Engineering of hydrogels Important properties to tune
- Viscosity, elasticity, injectability: network architecture and dynamics
- Size of « pores», permeability: architecture and chemical nature (affinities)
- Passive matrix swelling in buffer, serum : network/water interactions
- Active matrix (controlled release) : network/water interactions, permeability
- Self-hydrolysis, degradation : chemistry/biochemistry
Definition of a hydrogel
Network (or micro-network = microgel) swollen by a liquid.
Hydrogel = swollen in aqueous media
Structural components of hydrogel
Cross-link, elastic chain, loop, pendant chains
Gel fraction
«Infinite» networks , i.e. 3D molecules with size of whole flask
Elastically active strands
chain with 2 cross-links at the ends
Cross-link
inter-chain connection that connect more than 3 Infinite clusters
Sol fraction
all clusters of Finite size
Critical gel point
At p = pc= 1/f-1
Gel Point
critical % of connected objects, critical time of cluster divergence
Being above a threshold concentration is also required
Correlation length
typical size of the largest finite cluster in the gel
Common Hydrogels
collagen, gelatins
Collagen properties
A componant of extracellular matrix (ECM) Cross-linkable Adhesion of cells (+ fibronectin) Degradation (collagenase) Fluidification at high T
-Weak gels, Immune response, Contamination
Hyaluronates
Componant of ECM
Cross-linkable (hydrazide ou radicals)
Biodegradable (hyaluronidase).
- Weak gels, purification (elicitationof immune response, toxins)
Fibrine, cross-linked proteins
Formed upon clusterization = rigid (enthalpic gels), Prepared from blood (of the patient), Compatibility/degradability, Compatible with most other proteic factors
- VERY fragile gels, Contamination
Common polysaccharides: Alginates
Non mammal (algae) / low cost, low toxicity, absence of cell adhesion, Cross-linked by cations (Ca2+)
- Degradation upon diffusion of Ca2+, Weak adhesion of cells
synthetic polymers
Low toxicity of PEO and protein/cell repellence, stimuli-responsive
- Usually non degradable, unknown toxicity
In good solvent conditions,
monomer-solvent contacts are energetically favored vs monomer-monomer ones.
In poor solvents,
chains collapse to maximize monomer-monomer contacts
To date, polyelectrolytes display
the sharpest transitions. Any parameter (pH, ionic strength), affect the quality of solvent close to theta temperature.
The swelling of gels dominated by
chain’s motion
How to increase speed of swelling?
micro-porous systems
Cross-links enables one to control « patterns » of cell adhesion and growth but
no penetration in highly crosslinked gels
-Cells cannot move in the gel without ____ (except if macroporous)
breaking the network
Material sensed as elastic ONLY if
strain applied for a duration shorter than life time (frequency > 1/taulife)
