GELS STRUCTURE

GELS STRUCTURE

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

CROSSLINKS POLYMERIC CHAINS

LIQUID PHASE

(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.

20 m 0.2 m

Schneider et al. J. American Chemical Society, 2002.

PHYSICAL CROSSLINKS (weak)

ENTANGLEMENTS (TOPOLOGICAL CONSTRAINS)

ORDERED ZONES

CONNECTING DISORDERED

ZONES

Van der Walls, dipole-dipole,

hydrogen bonding, Coulombic

hydrophobic interactions

POLYSACCARIDES (GLUCANS, XANTHAN)

PHYSICAL CROSSLINKS (strong)

Ca++ Ca++Ca++ Ca++ Ca++Ca++

EGGS BOX STRUCTURE

OO O

OH

OH

OHOH

OH

O

O OH

O

OCa 2+Ca++

INTERACTION BETWEEN THE BIVALENT ION AND

GULURONIC UNIT

ALGINATES

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

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]).

a) Monomer dilution

c) Crosslinker

b) Neutralization

d) Foaming aid and stabilizer

e) Oxidant

f) Reductant

g) Bicarbonate

SPH

a) Monomer dilution

c) Crosslinker

b) Neutralization

d) Foaming aid

e) Oxidant thermal initiator

f) Reductant

g) Bicarbonate

SAP

POROSITA’

RD/RP0.01 0.1ZONA

INTERMEDIAMEZZO POROSO

CATENE POLIMERICHE

FARMACO

Il moto del farmaco avviene nel fluido di rilascio che riempe i canali le cui pareti sono costituite dal polimero

MEZZO CONTINUO

2*RD RP

Il moto del farmaco avviene tra le maglie del reticolo polimerico contenenti anche le molecole del fluido di rilascio

DIFFUSIONE

R = 0

R = Rp

DRUG

De = Dw */TORTUOSITA’

Lc/Rp

POROSITA’ Vv/VT

IMPRINTED GELSMOLECULAR IMPRINTINGMOLECULAR IMPRINTING

I

I

I

I

I

I

I = initiator= template

= functional monomers

= crosslinking

monomers

COMPLEX FORMATION

CROSSLINKING

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

MTTMk

k

f

rMacromolecular sites concentration

Template concentration

TMkR ff Forward reaction (binding)

MTkR rr Backward reaction (un-binding)

TMMT

Kkk

K dr

fa

1Association

constant

SELECTIVITY

= Ka1/Ka2

1 ≤ ≤ 8

APA A P

AA

PA

A PA

A

A

A

AA

A

A

A

A

NETWORK SWELLING:DRUG CAN BE RELEASED

EXAMPLE : SWELLING CONTROL

PA

A

PA

APA A

PA

A

= DRUGA =ANALYTE

P = PROTEIN

IMPRINTED FILM

DRUG

HYDROGEL

EXAMPLE 2: TARGETED DELIVERY

R CELLULAR RECEPTOR

TISSUES OR CELLULAR LINING

R

BIBLIOGRAFIA1) 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.