Lecture 9

Question 1

An example of a natural hydrogel

Answer 1

ECM

Question 2

Engineering of hydrogels Important properties to tune

Answer 2

• 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

Question 3

Definition of a hydrogel

Answer 3

Network (or micro-network = microgel) swollen by a liquid.

Hydrogel = swollen in aqueous media

Question 4

Structural components of hydrogel

Answer 4

Cross-link, elastic chain, loop, pendant chains

Question 5

Gel fraction

Answer 5

«Infinite» networks , i.e. 3D molecules with size of whole flask

Question 6

Elastically active strands

Answer 6

chain with 2 cross-links at the ends

Question 7

Cross-link

Answer 7

inter-chain connection that connect more than 3 Infinite clusters

Question 8

Sol fraction

Answer 8

all clusters of Finite size

Question 9

Critical gel point

Answer 9

At p = pc= 1/f-1

Question 10

Gel Point

Answer 10

critical % of connected objects, critical time of cluster divergence
Being above a threshold concentration is also required

Question 11

Correlation length

Answer 11

typical size of the largest finite cluster in the gel

Question 12

Common Hydrogels

Answer 12

collagen, gelatins

Question 13

Collagen properties

Answer 13

A componant of extracellular matrix (ECM)
Cross-linkable
Adhesion of cells (+ fibronectin)
Degradation (collagenase)
Fluidification at high T

-Weak gels, Immune response, Contamination

Question 14

Hyaluronates

Answer 14

Componant of ECM
Cross-linkable (hydrazide ou radicals)
Biodegradable (hyaluronidase).

• Weak gels, purification (elicitationof immune response, toxins)

Question 15

Fibrine, cross-linked proteins

Answer 15

Formed upon clusterization = rigid (enthalpic gels), Prepared from blood (of the patient), Compatibility/degradability, Compatible with most other proteic factors

• VERY fragile gels, Contamination

Question 16

Common polysaccharides: Alginates

Answer 16

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

Question 17

synthetic polymers

Answer 17

Low toxicity of PEO and protein/cell repellence, stimuli-responsive

• Usually non degradable, unknown toxicity

Question 18

In good solvent conditions,

Answer 18

monomer-solvent contacts are energetically favored vs monomer-monomer ones.

Question 19

In poor solvents,

Answer 19

chains collapse to maximize monomer-monomer contacts

Question 20

To date, polyelectrolytes display

Answer 20

the sharpest transitions.
Any parameter (pH, ionic
strength), affect the quality of
solvent close to theta
temperature.

Question 21

The swelling of gels dominated by

Answer 21

chain’s motion

Question 22

How to increase speed of swelling?

Answer 22

micro-porous systems

Question 23

Cross-links enables one to control « patterns » of cell adhesion and growth but

Answer 23

no penetration in highly crosslinked gels

Question 24

-Cells cannot move in the gel without ____ (except if macroporous)

Answer 24

breaking the network

Question 25

Material sensed as elastic ONLY if

Answer 25

strain applied for a duration shorter than life time (frequency > 1/taulife)