GELS STRUCTURE
LIQUID PHASE
CROSSLINKS
POLYMERIC CHAINS
MATRICES ARE COHERENT SYSTEMS
MADE UP BY A
POLYMERIC NETWORK TRAPPING A CONTINUOUS LIQUID
PHASE. THEY SHOW
MECHANICAL PROPERTIES IN
BETWEEN THOSE OF SOLIDS AND LIQUIDS
20 mm
0.2 mm
Schneider et al. J. American Chemical Society, 2002.
(a) Laser scanning confocal microscopy. Green regions are fluorescently
stained self-assembled peptide, and black regions are water-filled pores and
channels.
(b) CryoTEM. Dark structures are selfassembled peptide scaffold, while lighter
gray areas are composed of vitrified water.
PHYSICAL CROSSLINKS (weak)
ENTANGLEMENTS
(TOPOLOGICAL
CONSTRAINS)
CONNECTING
DISORDERED
ZONES
Van der Walls,
dipole-dipole,
hydrogen bonding,
Coulombic
hydrophobic interactions
ORDERED
ZONES
POLYSACCARIDES (GLUCANS, XANTHAN)
PHYSICAL CROSSLINKS (strong)
Ca++ Ca++ Ca++ Ca++ Ca++ Ca++
EGGS BOX STRUCTURE
Ca
+
Ca2++
O
INTERACTION BETWEEN
THE BIVALENT ION AND
GULURONIC UNIT
O
OH
OH
HO
O
O
OH
O
OH
O
O
ALGINATES
OH
CHEMICAL CROSSLINKS (strong: covalent bond)
SCLEROGLUCAN
CROSSLINKED WITH
BORAX
T. Coviello et al., Int. J. Biol. Macromolecules, 32 (2003) 83
POROUS GELS: Cellulose – Acrylic Acid
Acrylic acid
mass fraction
Cellulose
mass fraction
Crosslinking
irradiation
intensity
Surface picture (406035) (ESEM)
Cross-section picture (406035) (ESEM)
Surface picture (208035) (ESEM)
Cross-section picture (208035) (ESEM)
GEL SUPERPOROSI
a) Monomer dilution
e) Oxidant
a) Monomer dilution
b) Neutralization
f) Reductant
b) Neutralization
c) Crosslinker
g) Bicarbonate
c) Crosslinker
f) Reductant
d) Foaming aid
g) Bicarbonate
d) Foaming aid
and stabilizer
SPH
e) Oxidant
thermal initiator
SAP
Figure 6.2. Schematic representation of steps involved in the production of Super porous
hydrogels (SPH) and Super absorbent polymers (SPA) (with permission from ref.[46]).
POROSITA’
FARMACO
2*RD
RP
CATENE
POLIMERICHE
RD/RP
0.01
MEZZO POROSO
Il moto del farmaco
avviene nel fluido di
rilascio che riempe i
canali le cui pareti
sono costituite dal
polimero
ZONA 0.1
MEZZO CONTINUO
INTERMEDIA
Il moto del farmaco
avviene tra le maglie
del reticolo polimerico
contenenti anche le
molecole del fluido di
rilascio
DIFFUSIONE
R=0
DRUG
R = Rp
De = Dw *e/t
TORTUOSITA’
Lc/Rp
POROSITA’ Vv/VT
IMPRINTED GELS
MOLECULAR IMPRINTING
I
I
I
COMPLEX
FORMATION
I
I
I
CROSSLINKING
I = initiator
= template
= functional
monomers
= crosslinking
monomers
WASHING
IMPRINTED POLYMERIC GELS: CHARACTERISTICS
Binding affinity:
a measure of how well the template molecule is attracted to
the binding site
Selectivity :
the ability to differentiate between the template and other
molecules
Binding capacity :
the maximum amount of template bound per mass or
volume of polymer
BINDING AFFINITY
M   T  MT 
kf
Macromolecular
sites concentration
kr
Template
concentration
Rf  k f M T 
Forward reaction (binding)
Rr  kr MT 
Backward reaction (un-binding)
kf

1
MT 
Ka 


Association
k r K d M T 
constant
SELECTIVITY
a = Ka1/Ka2
1≤a≤8
EXAMPLE : SWELLING CONTROL
A
A
A
A
A
A
P
= PROTEIN
A
A
A
= DRUG
A =ANALYTE
NETWORK SWELLING:
DRUG CAN BE RELEASED
EXAMPLE 2: TARGETED DELIVERY
TISSUES OR CELLULAR LINING
HYDROGEL
R
DRUG
IMPRINTED
FILM
R
CELLULAR
RECEPTOR
BIBLIOGRAFIA
1)
Lapasin R, Pricl S, Rheology of Industrial Polysaccharides; Theory and
Applications, Chapman and Hall, London, 1995.
2)
Coviello T, Grassi M, Rambone G, Santucci E, a Carafa M , Murtas E, Riccieri F M,
Franco Alhaique F. Novel hydrogel system from scleroglucan: synthesis and
characterization J. Contr. Rel. 60, 367–378, 1999.
3)
A. Kydonieus (Ed.), Treatise on Controlled Drug Delivery, Marcel Dekker, New York,
1992, pp. 54-55.
4)
Colombo, P. 1993. Swelling-controlled release in hydrogel matrices for oral route.
Adv. Drug. Dev. Rev., 11, 37 – 57
5)
Grassi M, Colombo I, Lapasin R. Drug release from an ensemble of swellable
crosslinked polymer particles. J. Contr. Rel. 68, 97-113, 2000.