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My Ph.D. Thesis
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Thermo-responsive Hydrogels for Intravitreal
Injection and Biomolecule Release
Ph.D. Thesis
Department of Chemical and Biological Engineering
Pawel W. Drapala
Advisor: Victor H. Pérez-Luna
1. Background and Significance
Age-Related Macular Degeneration (AMD)
Specific Aims
poly(ethylene glycol) (PEG) hydrogels
2. Thermo-Responsive Hydrogels
poly(N-isopropylacrylamide) (PNIPAAm),
Transition Temperature & Swelling
Volume Phase Transition Temperature (VPTT)
3. Copolymer Synthesis, Characterization and Degradation
Degradable Cross-links
Chain Transfer Agents (CTAs)
Selection of Hydrogel Formulations
Presentation Outline
Background and Significance
Thermo-Responsive Hydrogels
Copolymer Synthesis, Characterization and
Degradation
Release of Therapeutic Proteins
Biocompatibility of Drug Delivery System
Conclusions
4. Release of Therapeutic Proteins
Release of Proteins from Nondegradable Hydrogels
Higuchi Analysis of Diffusive-Controlled Systems
Effect of CTAs on Protein Release
PEGylated & Tethered IgG Release
5. Biocompatibility of Drug Delivery System
Bioactivity & Potential Cytotoxicity of Drug Delivery System
Cytotoxicity of Release Samples
Bioactivity of Release Samples
6. Contributions & Conclusion
Age-Related Macular Degeneration (AMD)
Normal Vision Age-related macular
degeneration
Incidence Rate: ~ 1 in 1,359 (~ 200,000 people in the United States)[1]
Elevated levels of Vascular Endothelial Growth Factor (VEGF)
“Wet” AMD:
• angiogenesis
• vascular leakage
• damage to photoreceptors
• vision loss
Angiogenesis Inhibitors:
• Avastin® & Lucentis®
• Injected into the vitreous every 4 to 6 weeks (half-life: 4.32 days)[2]
• Halt progression of wet AMD
• May lead to complications
[1] Facts About Age-Related Macular Degeneration. National Eye Institute. 2010.
[2] S. J. Bakri, M. R. Snyder, J. M. Reid, J. S. Pulido, and R. J. Singh. Pharmacokinetics of Intravitreal Bevacizumab. Ophthalmology,114(5):855-859, 2007.
Background and Significance
Thermo-Responsive Hydrogels
Copolymer Synthesis, Characterization and
Degradation
Release of Therapeutic Proteins
Biocompatibility of Drug Delivery System
Conclusions
Aim 1. Determine the optimal hydrogel composition for localized drug delivery.
Hydrophobic/Hydrophilic Balance
Kinetics of Phase Change
Aim 2. Increase the duration (extend the therapeutic effect) of protein release from
thermo-responsive hydrogels.
Degradation kinetics of hydrogel crosslinks
Covalent Attachment of Proteins to the Hydrogel
Aim 3. Evaluate potential toxicity of degradation products and bioactivity of the released
angiogenesis inhibitor proteins.
Cytotoxicity of the drug delivery system
Activity of released anti-VEGF agents from the hydrogels
Specific Aims
Central Hypothesis: better treatment of wet AMD can be achieved by
localized and prolonged release of active angiogenesis inhibitor
proteins using thermo-responsive hydrogels by tailoring of hydrogel
structure, degradability, and controlling protein-polymer interactions.
Background and Significance
Thermo-Responsive Hydrogels
Copolymer Synthesis, Characterization and
Degradation
Release of Therapeutic Proteins
Biocompatibility of Drug Delivery System
Conclusions
poly(ethylene glycol) (PEG) hydrogels
APS
PEG-DA PEG Hydrogel
Background and Significance
Thermo-Responsive Hydrogels
Copolymer Synthesis, Characterization and
Degradation
Release of Therapeutic Proteins
Biocompatibility of Drug Delivery System
Conclusions
Hydrogels are hydrophilic 3-D networks of polymer chains High water content preserves protein bioactivity - ideal for protein drug delivery applications
Hydrogels are prevented from dissolving due to chemical or physical cross-links Protects the encapsulated proteins from immune recognition and clearance.
PEG hydrogels: nontoxic, non-immunogenic, anti-fouling
Can be polymerized under mild conditions via free radical polymerization:
poly(N-isopropylacrylamide)
(PNIPAAm)
NIPAAm
PEG-DA
PNIPAAm-co-PEG Hydrogel
Background and Significance
Thermo-Responsive Hydrogels
Copolymer Synthesis, Characterization and
Degradation
Release of Therapeutic Proteins
Biocompatibility of Drug Delivery System
Conclusions
∆ Time ∆ Temp.
Intravitreal
Injection
Tem perature (oC )
30 32 34 36 38 40
No
rm
aliz
ed
Ab
so
rb
an
ce
0.0
0.2
0.4
0.6
0.8
1.0
0 m M
4 m M
8 m M
12 m M
16 m M
C ross-linker:
T e m p e ra tu re (o C )
2 0 2 2 2 4 2 6 2 8 3 0 3 2 3 4 3 6 3 8 4 0
Sw
ell
ing
Ra
tio
0
1 0
2 0
3 0
4 0
5 0
6 0
7 0
8 m M P E G -D A
1 2 m M P E G -D A
1 6 m M P E G -D A
Transition Temperature & Swelling
𝑄𝑆𝑤𝑒𝑙𝑙𝑖𝑛𝑔 =𝑊𝑆𝑤𝑜𝑙𝑙𝑒𝑛 −𝑊𝐷𝑟𝑦
𝑊𝐷𝑟𝑦
Background and Significance
Thermo-Responsive Hydrogels
Copolymer Synthesis, Characterization and
Degradation
Release of Therapeutic Proteins
Biocompatibility of Drug Delivery System
Conclusions
Swollen
Hydrophilic
State (7°C)
Collapsed
Hydrophobic State
(37°C)
Volume Phase Transition Temperature
(VPTT)
• The VPTT can be readily manipulated by Hydrophobic/Hydrophilic monomer ratios[3]
PEG elevates VPTT
Poly(L-lactic acid) (PLLA) decreases the VPTT
[3] H. G. Schild. Poly (N-Isopropylacrylamide) - Experiment, Theory and Application. Progress in Polymer Science, 17(2):163-249, 1992.
[PEG-DA]* VPTT
0 mM 32.4 °C (± 0.3)
4 mM 33.4 °C (± 0.1)
8 mM 34.7 °C (± 0.4)
12 mM 35.3 °C (± 0.3)
16 mM 35.8 °C (± 0.1)
[cross-linker] PEG♯ PEG-b-PLLA
0.5 mM 32.1 °C (± 0.7) 29.8 °C (± 0.7)
1 mM 32.5 °C (± 0.9) 31.6 °C (± 0.7)
2 mM 33.2 °C (± 0.6) 32.0 °C (± 0.6)
3 mM 33.9 °C (± 0.9) 32.9 °C (± 0.7)
* PEG MW = 575 Da ♯ PEG MW = 3400 Da
Background and Significance
Thermo-Responsive Hydrogels
Copolymer Synthesis, Characterization and
Degradation
Release of Therapeutic Proteins
Biocompatibility of Drug Delivery System
Conclusions
Degradable Cross-links: poly(L-lactic acid)
Acry-PLLA-b-PEG-b-PLLA-Acry
Lactic Acid PEG
PLLA-b-PEG rate of ester hydrolysis in-vivo[4,5]:
hydrophobicity
steric effects
cross-linking density
length of the PLLA oligomer
autocatalysis
size/charge of the encapsulated biomolecules
[4] Darrell Irvine. Molecular Principles of Biomaterials. MIT OpenCourseWare, 2006.
[5] J. L. West and J. A. Hubbell. Photopolymerized hydrogel materials for drug delivery applications. Reactive Polymers, 25(2-3):139-147, 1995.
Background and Significance
Thermo-Responsive Hydrogels
Copolymer Synthesis, Characterization and
Degradation
Release of Therapeutic Proteins
Biocompatibility of Drug Delivery System
Conclusions
∆ Temp. ∆ Time
“Biodegradable”: material initially in solid or gel-phase, subsequently reduced to soluble fragments that are metabolized or excreted under physiological conditions (i.e. saline environment, pH = 7.4, 37 °C)
Degradation Profiles
Time (days)
0 5 10 15 20
Sw
ellin
g R
ati
o
20
40
60
80
100
120
PNIPAAm-co-PEG-b-PLLA (degradable)
PNIPAAm-co-PEG (nondegradable)
Room Temperature (24 oC)
Tim e (days)
0 5 10 15 20
Sw
ellin
g R
ati
o
0
5
10
15
20
25
30PNIPAAm -co -PEG-b-PLLA (degradable)
PNIPAAm -co -PEG (nondegradable)
Physiological Tem perature (37 oC )
• Swelling Ratios (below and above the VPTT) as function of incubation time for:
Nondegradable hydrogels cross-linked with Acry-PEG-Acry (PEG-DA)
Degradable hydrogels cross-linked with Acry-PLLA-b-PEG-b-PLLA-Acry
Molar concentrations: Cross-linker = 1 mM
PNIPAAm = 350 mM
Background and Significance
Thermo-Responsive Hydrogels
Copolymer Synthesis, Characterization and
Degradation
Release of Therapeutic Proteins
Biocompatibility of Drug Delivery System
Conclusions
𝑄𝑆𝑤𝑒𝑙𝑙𝑖𝑛𝑔 =𝑊𝑆𝑤𝑜𝑙𝑙𝑒𝑛 −𝑊𝐷𝑟𝑦
𝑊𝐷𝑟𝑦
Chain Transfer Agents (CTAs)
PNIPAAm cannot exceed 32 kDa and PEG can not exceed 50 kDa for clearance by the renal system[6,7]
Lower the MW of growing PNIPAAm polymer chains using Glutathione CTA:
CTA-Initiated Growing Polymer Radical
Terminated Polymer Growing PNIPAAm Radical
[4] N. Bertrand, J. G. Fleischer, K. M. Wasan, and J. C. Leroux. Pharmacokinetics and biodistribution of N-isopropylacrylamide copolymers for the design of pH-
sensitive liposomes. Biomaterials, 30(13):2598-2605, 2009.
[5] T. Yamaoka, Y. Tabata, and Y. Ikada. Distribution and tissue uptake of poly(ethylene glycol) with different molecular-weights after intravenous administration
to mice. Journal of Pharmaceutical Sciences, 83(4):601-606, 1994.
Background and Significance
Thermo-Responsive Hydrogels
Copolymer Synthesis, Characterization and
Degradation
Release of Therapeutic Proteins
Biocompatibility of Drug Delivery System
Conclusions
P ∙ +XR → R ∙ +XP
CTA Reaction
Glutathione
0 mg/mL 1 mg/mL 2 mg/mL 3 mg/mL 4 mg/mL1 mM2 mM3 mM4 mM5 mM6 mM7 mM
YesYesYes YesNo Yes YesNo No Yes YesNo No No YesNo No No No Yes
Glutathione Concentration (Chain Transfer Agent)
Acry-PLLA-b-PEG-b-PLLA-Acry
Molarity (Cross-linker)
Selection of Hydrogel Formulations
Does the polymerization
produce a hydrogel?
Is the produced hydrogel injectable
via 30-gauge needle?
0 mg/mL 1 mg/mL 2 mg/mL 3 mg/mL 4 mg/mL1 mM2 mM3 mM4 mM5 mM6 mM7 mM
Yes No No No NoYes No No No NoYes Yes No No NoYes Yes Yes No NoYes Yes Yes Yes NoYes Yes Yes Yes NoYes Yes Yes Yes Yes
Glutathione Concentration (Chain Transfer Agent)
Acry-PLLA-b-PEG-b-PLLA-Acry
Molarity (Cross-linker)
Background and Significance
Thermo-Responsive Hydrogels
Copolymer Synthesis, Characterization and
Degradation
Release of Therapeutic Proteins
Biocompatibility of Drug Delivery System
Conclusions
Selection of Hydrogel Formulations
Does the injectable hydrogel fully degrade within 30 days at 37 °C?
swollen hydrophilic state collapsed hydrophobic state partially degraded
collapsed state
∆ Temp. ∆ Time
0 mg/mL 1 mg/mL 2 mg/mL 3 mg/mL 4 mg/mL1 mM2 mM3 mM4 mM5 mM6 mM7 mM
NoNoNo Yes
No Yes YesNo Yes
NoNo
Glutathione Concentration (Chain Transfer Agent)
Acry-PLLA-b-PEG-b-PLLA-Acry
Molarity (Cross-linker)
Background and Significance
Thermo-Responsive Hydrogels
Copolymer Synthesis, Characterization and
Degradation
Release of Therapeutic Proteins
Biocompatibility of Drug Delivery System
Conclusions
Selection of Hydrogel Formulations
Does the injectable hydrogel fully degrade within 30 days at 37 °C?
swollen hydrophilic state collapsed hydrophobic state partially degraded
collapsed state
∆ Temp. ∆ Time
0 mg/mL 1 mg/mL 2 mg/mL 3 mg/mL 4 mg/mL1 mM2 mM3 mM4 mM5 mM6 mM7 mM
NoNoNo Yes
No Yes YesNo Yes
NoNo
Glutathione Concentration (Chain Transfer Agent)
Acry-PLLA-b-PEG-b-PLLA-Acry
Molarity (Cross-linker)
Background and Significance
Thermo-Responsive Hydrogels
Copolymer Synthesis, Characterization and
Degradation
Release of Therapeutic Proteins
Biocompatibility of Drug Delivery System
Conclusions
Degradable Hydrogels
Time (days)0 2 4 6 8 10 12 14
Sw
elli
ng R
atio
0
20
40
60
Nondegradable Hydrogels (control)
Time (days)0 2 4 6 8 10 12 14
Sw
elli
ng R
atio
0
20
40
60
No Glutathione
0.5 mg/mL Glutathione
1.0 mg/mL Glutathione
Degradation Profiles
Swelling Ratios (with and without Glutathione CTA) as function of incubation time:
Nondegradable hydrogels at 37 °C cross-linked with: Acry-PEG-Acry (PEG-DA)
Degradable hydrogels at 37 °C cross-linked with: Acry-PLLA-b-PEG-b-PLLA-Acry
CTA
[mg/mL] Qt=0
VPTT
[°C]
3 mM PEG cross-links
0 20.4 33.3
0.5 31.0 34.4
1.0 32.5 36.2
3 mM PLLA-b-PEG-b-
PLLA cross-links
0 23.9 32.9
0.5 34.7 34.1
1.0 37.4 35.0
Background and Significance
Thermo-Responsive Hydrogels
Copolymer Synthesis, Characterization and
Degradation
Release of Therapeutic Proteins
Biocompatibility of Drug Delivery System
Conclusions
Release of Proteins from
Nondegradable Hydrogels
T im e (days)
0 10 20 30 40
IgG
Re
lea
se
d o
f E
nc
ap
su
late
d (
%)
0
20
40
60
80
100
IgG Release from PNIPAAm-co-PEG hydrogels
∆ Time
Background and Significance
Thermo-Responsive Hydrogels
Copolymer Synthesis, Characterization and
Degradation
Release of Therapeutic Proteins
Biocompatibility of Drug Delivery System
Conclusions
Modes of Mass Transport:
Diffusion – due to concentration gradients
Convection – due to dehydration
Kinetics – due to hydrolytic degradation
24 °C 24 °C
24 °C 37 °C
∆ Time
∆ Temp.
Physiological
Temperature (37 °C)
Room Temperature (24 °C)
Higuchi Analysis of
Diffusive-Controlled Systems
𝜕𝐶
𝜕𝑡= 𝛻 ∙ 𝐷𝑔𝛻𝐶
𝑀𝑡𝑀∞= 1 −
8
2𝑛 + 1 2𝜋2∙ exp− 2𝑛 + 1 2𝜋2𝐷𝑔
𝛿2𝑡
∞
𝑛=0
𝑀𝑡𝑀∞≅ 4𝐷𝑔𝑡
𝜋𝛿2
12
T im e (days)
0 1 2 3 4 5
BS
A R
ele
as
ed
of
En
ca
ps
ula
ted
(%
)
0
20
40
60
80
100
Body Tem perature (37 oC)
Room Tem perature (23 oC)
BSA Release from PNIPAAm-co-PEG hydrogels y = 27.868x + 4.8453
R² = 0.9851
0
10
20
30
40
50
60
0 0.5 1 1.5 2
Mt/M
∞
tn
T = 24°C
y = 62.536x - 15.542 R² = 0.8923
0
10
20
30
40
50
60
70
0 0.5 1 1.5M
t/M
∞
tn
T = 37°C
Background and Significance
Thermo-Responsive Hydrogels
Copolymer Synthesis, Characterization and
Degradation
Release of Therapeutic Proteins
Biocompatibility of Drug Delivery System
Conclusions
Effect of CTAs on Protein Release
Time (days)0 2 4 6 8 10 12 14
Re
lea
se
d o
f E
nca
psu
late
d (
%)
0
20
40
60
80
100
No CTA
0.5 mg/mL CTA
1.0 mg/mL CTA
Time (days)0 2 4 6 8 10 12 14
Re
lea
se
d o
f E
nca
psu
late
d (
%)
0
20
40
60
80
100
Nondegradable Hydrogels
cross-linked with
Acry-PEG-Acry
Degradable Hydrogels
cross-linked with
Acry-PLLA-b-PEG-b-PLLA-Acry
Background and Significance
Thermo-Responsive Hydrogels
Copolymer Synthesis, Characterization and
Degradation
Release of Therapeutic Proteins
Biocompatibility of Drug Delivery System
Conclusions
Burst Release in initial deswelling phase: accounts for over 70% of total released protein.
PEGylated & Tethered IgG Release
∆ Temp. ∆ Time
Swollen Hydrophilic State Collapsed Hydrophobic
State
Partially Degraded
Collapsed State
PEGylation
Immunoglobulin G (IgG) Acry-PEG-SVA
PEGylated
IgG
Hydrogel Synthesis (with PEGylated IgG)
PEGylated IgG Release
Background and Significance
Thermo-Responsive Hydrogels
Copolymer Synthesis, Characterization and
Degradation
Release of Therapeutic Proteins
Biocompatibility of Drug Delivery System
Conclusions
SDS-PAGE Analysis of IgG PEGylation
Background and Significance
Thermo-Responsive Hydrogels
Copolymer Synthesis, Characterization and
Degradation
Release of Therapeutic Proteins
Biocompatibility of Drug Delivery System
Conclusions
Lane 1:
molecular weight marker
Lane 2:
No PEGylation control IgG
Lane 3:
IgG PEGylated at 1 to 5 molar ratio of IgG to Acry-PEG-SVA
Lane 4:
IgG PEGylated at 1 to 15 molar ratio of IgG to Acry-PEG-SVA
Release (at 37 °C) of IgG with varying
degree of PEGylation
Time (days)0 2 4 6 8 10
Rele
ased o
f E
ncapsula
ted (
%)
0
20
40
60
80
100
Time (days)0 2 4 6 8 10
Rele
ased o
f E
ncapsula
ted (
%)
0
20
40
60
80
100
No PEGylation
1:5 IgG to Acry-PEG-SVA Molar Ratio
1:15 IgG to Acry-PEG-SVA Molar Ratio
Nondegradable Hydrogels
cross-linked with
Acry-PEG-Acry
Degradable Hydrogels
cross-linked with
Acry-PLLA-b-PEG-b-PLLA-Acry
Background and Significance
Thermo-Responsive Hydrogels
Copolymer Synthesis, Characterization and
Degradation
Release of Therapeutic Proteins
Biocompatibility of Drug Delivery System
Conclusions
VEGF
Receptor binding domain
Binding to VEGFR-2Migration
ProliferationNeovascularization
Bioactivity & Potential Cytotoxicity
of Drug Delivery System
Background and Significance
Thermo-Responsive Hydrogels
Copolymer Synthesis, Characterization and
Degradation
Release of Therapeutic Proteins
Biocompatibility of Drug Delivery System
Conclusions
Avastin® and Lucentis ® inhibit the binding of VEGF to its receptor VEGFR-2
Abrogate VEGF-induced neovascularization[7]
Extract Sample 1
Extract Sample 2
Extract Sample 3
Extract Sample 4
Extract Sample 5
Bulk Avastin®
Bulk Lucentis®
PBS (control)
PEGylated Avastin®
PEGylated Lucentis®
Released Control
Released Avastin®
Released Lucentis®
Released PEGylated Avastin®
Released PEGylated Lucentis®PEGylation
Encapsulation Release
Sampling Schedule
Schematic Model of VEGF Pathway Inhibition
[7] A. Klettner and J. Roider. Comparison of bevacizumab, ranibizumab, and pegaptanib in vitro: Efficiency and possible additional pathways. Investigative
Ophthalmology & Visual Science, 49(10):4523-4527, 2008.
VEGF
Receptor binding domain
Avastin®/Lucentis®
Binding to VEGFR-2Migration
ProliferationNeovascularization
Bioactivity & Potential Cytotoxicity
of Drug Delivery System
Background and Significance
Thermo-Responsive Hydrogels
Copolymer Synthesis, Characterization and
Degradation
Release of Therapeutic Proteins
Biocompatibility of Drug Delivery System
Conclusions
Avastin® and Lucentis ® inhibit the binding of VEGF to its receptor VEGFR-2
Abrogate VEGF-induced neovascularization[7]
Extract Sample 1
Extract Sample 2
Extract Sample 3
Extract Sample 4
Extract Sample 5
Bulk Avastin®
Bulk Lucentis®
PBS (control)
PEGylated Avastin®
PEGylated Lucentis®
Released Control
Released Avastin®
Released Lucentis®
Released PEGylated Avastin®
Released PEGylated Lucentis®PEGylation
Encapsulation Release
Sampling Schedule
Schematic Model of VEGF Pathway Inhibition
[7] A. Klettner and J. Roider. Comparison of bevacizumab, ranibizumab, and pegaptanib in vitro: Efficiency and possible additional pathways. Investigative
Ophthalmology & Visual Science, 49(10):4523-4527, 2008.
Cytotoxicity of post-polymerization
buffer extracts
Unreacted acrylamide monomers[6] and TEMED[7] are toxic
Removed from hydrogels by extraction through gentle agitation in PBS
5 Extractions, 20 minutes each, buffer 20x hydrogel volume
Background and Significance
Thermo-Responsive Hydrogels
Copolymer Synthesis, Characterization and
Degradation
Release of Therapeutic Proteins
Biocompatibility of Drug Delivery System
Conclusions
MTS Cytotoxicity of Buffer Extracts
Buffer Extraction Step
1st 2nd 3rd 4th 5th Control
No
rma
lize
d A
bso
rba
nce
0.0
0.2
0.4
0.6
0.8
1.0
1.2
Protein Lost in Each Extraction Step
Buffer Extraction Step
1st 2nd 3rd 4th 5th Total
IgG
Pro
tein
Lo
ss (
%)
0
5
10
15
20
25
30
No Glutathione
0.5 mg/mL Glutathione
1.0 mg/mL Glutathione
[6] A. S. Wadajkar, B. Koppolu, M. Rahimi, and K. T. Nguyen. Cytotoxic evaluation of N-isopropylacrylamide monomers and temperature sensitive poly(N-
isopropylacrylamide) nanoparticles. Journal of Nanoparticle Research, 11(6):1375-1382, 2009.
[7] C. G. Williams, A. N. Malik, T. K. Kim, P. N. Manson, and J. H. Elissee. Variable cytocompatibility of six cell lines with photoinitiators used for polymerizing
hydrogels and cell encapsulation. Biomaterials, 26(11):1211-1218, 2005.
Cytotoxicity of Release Samples
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
PBS Avastin Lucentis Blank Avastin Lucentis Avastin Lucentis
Absorb
ance
Stock Solution Released Released +
PEGylated
MTS cytotoxicity of hydrogel degradation products
Samples consisted of degraded PNIPAAm-co-PEG-b-PLLA hydrogels used for encapsulation and release of Avastin® or Lucentis®.
No statistical significance was detected compared to PBS control
Background and Significance
Thermo-Responsive Hydrogels
Copolymer Synthesis, Characterization and
Degradation
Release of Therapeutic Proteins
Biocompatibility of Drug Delivery System
Conclusions
0
0.02
0.04
0.06
0.08
0.1
0.12
FBS PBS VEGF Avastin Lucentis Blank Avastin Lucentis Avastin Lucentis
Absorb
ance
Bioactivity of Release Samples
Stock Solution Released Released +
PEGylated
BrdU assay results of HUVEC proliferation.
FBS is the positive control and PBS is the negative control. All other samples were cultured in the presence of VEGF.
Thermo-responsive PNIPAAm-co-PEG-b-PLLA hydrogels were used for encapsulation and release of Avastin® or Lucentis®.
Standard deviation bars, *p < 0.001 vs. VEGF, **p < 0.05 vs. VEGF
* *
* *
**
Background and Significance
Thermo-Responsive Hydrogels
Copolymer Synthesis, Characterization and
Degradation
Release of Therapeutic Proteins
Biocompatibility of Drug Delivery System
Conclusions
Contributions & Conclusion
Background and Significance
Thermo-Responsive Hydrogels
Copolymer Synthesis, Characterization and
Degradation
Release of Therapeutic Proteins
Biocompatibility of Drug Delivery System
Conclusions
1. Optimized the precursor formulation so that the hydrogels are both injectable and hydrolytically degradable.
2. Established that the cross-linker molar concentration should fall in the range of 1 to 4 mM in order for the thermo-responsive hydrogels to exhibit a sharp coil-to-globule phase transition ca. 33 °C.
3. Reduced undesirable burst release in the initial swelling phase by tethering of biomolecules through PEGylation and subsequent attachment to the polymer chains.
4. Demonstrated that the hydrogel degradation products were nontoxic under in-vitro cell culture conditions.
5. Confirmed that angiogenesis inhibitors released from PNIPAAm-co-PEG-b-PLLA hydrogels were stable and bioactive.
Conclusion: localized and prolonged release (~2 weeks) of active
angiogenesis inhibitor proteins can be achieved using thermo-responsive
hydrogels by tailoring of hydrogel structure, degradability, and controlling
protein-polymer interactions.
Acknowledgements
Advisors
Victor H. Pérez-Luna
Eric M. Brey
Jennifer J. Kang-Mieler
Graduate Students
Yu-Chieh Chiu (cross-linker synthesis) and Bin Jiang (cell culture)
Undergrad Students
Diana Gutierrez and Alexa L. Beaver
Funding
The Lincy Foundation, The Macula Foundation, Veteran’s Administration
Background and Significance
Thermo-Responsive Hydrogels
Copolymer Synthesis, Characterization and
Degradation
Release of Therapeutic Proteins
Biocompatibility of Drug Delivery System
Conclusions
Recommended