Dégradation et biodégradation des matériaux biorésorbables
Jean COUDANE
Centre de Recherches sur les Biopolymères Artificiels
UMR CNRS 5473
Faculté de Pharmacie, Montpellier, France
[email protected]
Sophia Antipolis 30 Mars 2006
Plan
Introduction-mécanisme-évaluation
Dégradation hydrolytique
Dégradation enzymatique
1
Poly (α
α-hydroxy acides)
Biomatériaux polymères
de synthèse dégradables
O
PLA/PLGA
(biomédical)
O
n
O
CH
CH3
PCL
(environnemental)
in
tr
od
uc
ti
o
C
n
O
C
CH2
n
O
O
C
(C H 2 ) 5
n
General Degradation Mechanism of PLA-based Devices
1-Penetration of H2O
Surface mechanism
enzymatic
Water uptake :
2-Hydrolysis of polymeric chains
Size-dependent
Core mechanism
Hydrolytic
Massive objects
Decrease of molar masses
formation of low molecular masses compounds
Variation in composition (copolymers)
Modification of surface aspect
Differentiation between surface and core
a-Weight loss
3-Elimination of degradation compounds
b-Acid lactic titration
2
in
tr
od
uc
ti
on
Degradation percentage vs random chain scission
Molar masses
Mn= 72000
Mn= 7200
Mn= 720
Mn/2
1/1000
1/100
1/10
DPn0= 1000 DPn= 500
DPn0=100
DPn= 50
DPn0=10
DPn= 5
SEC-Half degradation
No lag time
Weight loss
Soluble oligomers, Mn<720, DPn<10
At least 1/10
WL-degradation
Lag time
DP=1
Lactic acid formation
LA-degradation
At least 5/10
int
r
od
uc
tio
n
Lag time
Degradation percentage vs depolymerization
Molar masses
10 chain breakings
(1/100)
Mn= 72000
DPn= 1000
Mn≈ 71000
DPn= 990
Mn constant
no significant SEC-degradation
WL-degradation
Weight loss
Immediate weight loss
No lag time
Lactic acid formation
LA-degradation
Immediate lactate formation
No lag time
3
in
u
od
tr
ion
ct
Molar masses
Random Chain Scission
Mn decrease
Depolymerization
Mn constant
No lag time
Weight loss
Immediate weight loss
delayed
weight loss
Good evaluation
of degradation
Lag time
Lactic acid
No lag time
Immediate lactate
formation
Good evaluation
of degradation
No lag time
delayed
lactate
formation
Lag time
Plan
Introduction-mécanismes
Dégradation hydrolytique
Dégradation enzymatique
4
ion e
at iqu
d
t
a
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Dé ydr
h
Li et al 1990
First step of degradation: water uptake
PBS 37°C
plates (2-3 mm)
37.5% LLact
37.5% DLact
25% Gly
water uptake
Distilled water 37°C
PLA37.5GA25
Time (days)
PLA x
30
x= % unités L-lactique
PLA75GA25
75% LLact
0% DLact
25% Gly
water uptake
PLAxGAy y= % unités glycolique
Stereochemistry
Hydrophobicity
crystallinity
Time (weeks) 10
modulus (Gpa)
ion e second step of degradation: hydrolysis of polymeric backbone Li et al 1990
at iqu
d
t
a
gr oly
PBS, 37°C plates (2-3 mm)
Dé ydr
h
PLA37.5GA25
Continuous decrease of
molar masses
10
Time (days)
core
modulus (Gpa)
SEC
surface
PLA75GA25
Time min
Core-surface effect
5
Time (weeks)
5
ion e
at iqu Third step of degradation: weight loss
d
t
a
gr oly
Dé ydr
PBS 37°C
plates (2-3 mm)
h
Weight loss %
Li et al 1990
PLA37.5GA25
Time (days)
lag time
Weight loss %
Delayed loss of
matter
PLA75GA25
Time (weeks)
Random chain scission
ion e
at iqu
d
t
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gr oly
Dé ydr
h
General degradation mechanism of PLA-based devices
Soluble oligomers
Soluble oligomers
Time in weeks
0
15
Water absorption and degradation
without loss of matter
Beginning of the
loss of matter
Central degradation and
formation of an outer membrane
Formation of hollow structure
Weight loss
Role of Polydispersity
Same results in vivo
6
ion e
at iqu
d
t
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gr oly
Dé ydr
h
Dégradation interne- cas du PLA
From massive objects to micro/nanoparticles
7
Influence of size on degradation
Grizzi et al, 1996
From plates to microparticles
Molecular weight
% of initial Mw
water uptake (%)
ion e
at iqu
d
t
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Dé ydr
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plates
films
µspheres
+ others
plates
plates
films
Plates 2-3mm
Beads 0.5-1mm
ion e
at iqu
d
t
a
gr oly
Dé ydr
h
L-lactic acid (mM)
Weight loss (%)
PLA50
plates
beads
µspheres
films
µspheres 125-250 µm
Films ≈ 60µm
Influence of size on degradation
Grizzi et al, 1996
From plates to microparticles
Molecular weights
(SEC)
Differentiation
core-surface
films
plates
microspheres
beads
Degradation time maximum 30 weeks
8
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at iqu
d
t
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Dé ydr
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O
(CH2)4 C
C
H
O
(CH2)4 C
Water uptake (%)
40
30
20
10
0
100
Time (days)
200
Molar Masses
80000
60000
40000
20000
0
100
200
Time (days)
x
40
30
20
10
0
0,00
PCL
4,00
8,00
12,00
16,00
Time (hours)
PCLCOOH1
100000
0
Phosphate buffer (pH 7.4), 37°C,
plates of polymers ( Ø = 1cm, t= 2mm)
Substitution ratio = 11%
C
H
1-x
Weight loss (%)
Water uptake (%)
COOH
O
H O
O
0
Gimenez et al, 2000
Chemical modification of PCL
25
20
15
10
5
0
300
PCLCOOH1 Mw
PCL Mw
0
50
100
150
Time (days)
200
PCLCOOH1
PCL
ion e
at iqu
d
t
a
gr oly
Dé ydr
h
Surface Aspect (ESEM)
PCL t98
Magnification: x 150
PCLCOOH1 t98
9
ion e
at iqu
d
t
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Dé ydr
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COOH
O
H O
O
(CH2)4 C
O
C
O
H
(CH2)4 C
x
PCLCOOH11 : 30% in 12h
PCL : 0.7% in 28 weeks
1-Apparent water uptake : (mf-mi0)/mi0
2-Molecular Weights
x=11%
C
H
1-x
PCLCOOH11 : after 24 weeks Mn / 2.5 , Mw / 7 PI PCL : after 28 weeks Mn / 1.1 and Mw / 1.3
3-Weight loss
PCLCOOH11 : 22% in 24 weeks
PCL : 1.6% in 28 weeks
Preferential Degradation of acidic units :
PCLCOOH11: After 24 weeks : 3.5% COOH groups on the chain
ion e
at iqu
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Cas des copolymères
Li et al, 2005
PLA et PGA : dégradation essentiellement hydrolytique
PCL peu de dégradation hydrolytique
H O
Copolymères statistiques PCL-PGA
O
(CH2)4 C
O
1-x
C
H
C
x
Prise d’eau (%)
Perte de masse (%)
H
H O
C
Temps (semaines)
Temps (semaines)
Cop1 à cop7:
taux de PCL
10
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at iqu
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Dé ydr
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Cas des copolymères
Copolymères blocs PEG2000-PLA30000
Stefani et al, 2006
100
LA/EO
90
Effet cœur/surface
80
P50
70
P60
60
P61
50
P67
40
P61UF
30
hydrosoluble
20
10
0
0
10
20
30
40
50
60
70
80
90
Préparation « anionique »
PLA
PEG
90
LA/EO
Après purification
80
70
PSn50
60
PSn50P
50
PSn50UF
40
PSn500
PSn500P
30
PSn500UF
20
10
0
0
20
40
60
80
100
120
Préparation «octanoate d’étain»
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Conclusions on degradation of PLA-based polymers
Degradation rate can be modulated according to some parameters:
Structural parameters
Stereoisomery of PLAX
X > 92 semi-crystalline : slow degradation rate
X≈ 50 amorphous : higher degradation rate
Copolymers
GA : increase hydrophylicity
higher degradation rate
PEO (blocs): variation of
proportions
Size parameters
Massive objects : differentiation core surface
Micro and nanospheres : no differentiation core-surface
Degradation rate function of S/V ratio.
Other parameters
Molecular masses, Polydispersity
Reaction medium : pH, Temperature, presence of enzyme
Purity of polymers
PLA, PLAGA :
days to months
11
Plan
Introduction
Dégradation hydrolytique
Dégradation enzymatique
ion
at ique
degradation medium: enzymes Landry et al 1996
d
t
a
gr m a
PLA50 nanoparticles
Dé nzy
e
100 nm, Albumin coating
pH = 1.2, Pepsin
pH = 7.5, Pancreatic lipase (Mn = 38000)
80
80
500
Incubation time (min)
Weight loss %
Percentage of PLA
converted in lactate
Percentage of PLA
converted in lactate
80
500
Incubation time (min)
12
ion
at ique
d
t
a
gr m a
Dé nzy
e
degradation medium: enzymes Landry et al 1996
PLA50 nanoparticles
105
106
Molar Mass (log scale)
No variation in PLA50 Molar Masses
Surface erosion
ion
at iqueTritiated PCL : Determination of biodegradation kinetics Ponsart et al, 2001
d
t
a
gr m a
Dé nzy
T O
H O
e
x <<1%
O (CH2)4 C C
O (CH2)4 C C
H
x
H
1-x
% of initial radioactivity
Environmental Conditions: PCL film, activated sludge, aqueous medium, 37°C
100
biomass
80
40
60
30
40
20
10
20
0
0
1
2
3
4
5
0
0
10
20
30
40
50
60
70
Time (days)
After 72 days : 75-85% of the initial radioactivity were found in the incubation
medium under the form of tritiated water and the rest on the form of biomass
13
ion
at ique
d
t
a
gr m a
Dé nzy
e
PCL Methylation: influence de la structure sur la
biodegradation
CH3
O
H O
O
O
(CH2)4 C
C
H
Dégradation hydrolytique
O
(CH2)4 C
(x=15%)
C
H
1-x
x
PCLCH3 ≈ PCL
(pH 7.4, 37°C)
Pas de variation significative
(pas de dégradation)
Biodégradation
weight loss (%)
(pH 7.4, 37°C,
pseudomonas cepacia lipase)
[Ponsart et al., 2003]
Diminution de la vitesse de
biodégradation
PCLCH3 < PCL
60
40
20
0
0,00
1,00
2,00
3,00
4,00
5,00
time (days)
conclusions
Paramètres structuraux
Stéréoisomérie, cristallinité, hydrophilie
Masses molaires, polymolécularité
Copolyméres : variation de la composition, variation de la vitesse de dégradation
Taille des objets
Objets massifs: differentiation coeur-surface
Micro and nanospheres : pas de differentiation coeur-surface
Vitesse de dégradation fonction du rapport S/V.
Autres paramètres
Milieu réactionnel: pH, Temperature,
presence of enzyme
14
remerciements
S. Li, H. Garreau, I. Grizzi
S. Ponsart, S. Gimenez, A. des Rieux
15