Polymeric Hydrogel Nanocapsules: A Thermo and pH Dual-responsive Carrier for Sustained Drug Release
Corresponding Author: Chunpeng Wang
Nano-Micro Letters,
Vol. 6 No. 3 (2014), Article Number: 200-208
Abstract
Hydrogel capsules show attractive prospects in drug delivery recently because of high drug loading and sustained release behavior. In this study we reported a simple and convenient route to fabricate poly (acrylic acid)-poly (N-isopropylacrylamide) (PAA-PNIPAm) hydrogel capsules by using hydroxypropylcellulose-poly (acrylic acid) (HPC-PAA) complexes as the templates. The capsules showed a high drug loading (∼280% to the weight of capsules) for Doxorubicin hydrochloride. The release of drug from the capsules was responsive to the temperature and pH of the surroundings, showing a low-rate but sustained release behavior favorable for low-toxic and long-term therapy. Together with the convenient preparation, high drug loading, dual responsivity as well as the sustained release feature, it is implied that this polymeric hydrogel capsule might be a promising candidate for new drug carriers.
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- K. Kataoka, A. Harada and Y. Nagasaki, “Block copolymer micelles for drug delivery: design, characterization and biological significance”, Adv. Drug Del. Rev. 47(1), 113–131 (2001). http://dx.doi.org/10.1016/S0169-409X(00)00124-1
- N. Kolishetti, S. Dhar, P. M. Valencia, L. Q. Lin, R. Karnik, S. J. Lippard, R. Langer and O. C. Farokhzad, “Engineering of self-assembled nanoparticle platform for precisely controlled combination drug therapy”, Proc. Natl. Acad. Sci. 107(42), 17939–17944 (2010). http://dx.doi.org/10.1073/pnas.1011368107
- Y. Chen, X. Zheng, X. Wang, C. Wang, Y. Ding and X. Jiang, “Near-Infrared emitting gold clusterpoly (acrylic acid) hybrid nanogels”, ACS Macro Lett. 3(1), 74–76 (2014). http://dx.doi.org/10.1021/mz4005748
- R. C. Nagarwal, S. Kant, P. Singh, P. Maiti and J. Pandit, “Polymeric nanoparticulate system: a potential approach for ocular drug delivery”, J. ControlledRelease 136(1), 2–13 (2009). http://dx.doi.org/10.1016/j.jconrel.2008.12.018
- J. Panyam and V. Labhasetwar, “Biodegradable nanoparticles for drug and gene delivery to cells and tissue”, Adv. Drug Del. Rev. 55(3), 329–347 (2003). http://dx.doi.org/10.1016/S0169-409X(02)00228-4
- T. R. Hoare and D. S. Kohane, “Hydrogels in drug delivery: progress and challenges”, Polymer 49(8), 1993–2007 (2008). http://dx.doi.org/10.1016/j.polymer.2008.01.027
- J. Kost and R. Langer, “Responsive polymeric delivery systems”, Adv. Drug Del. Rev. 46(1-3), 125–148 (2001). http://dx.doi.org/10.1016/S0169-409X(00)00136-8
- J. Della Rocca, D. Liu and W. Lin, “Nanoscale metal-organic frameworks for biomedical imaging and drug delivery”, Acc. Chem. Res. 44(10), 957–968 (2011). http://dx.doi.org/10.1021/ar200028a
- Y. Chen, P. A. Wilbon, J. Zhou, M. Nagarkatti, C. Wang, F. Chu and C. Tang, “Multifunctional selffluorescent polymer nanogels for label-free imaging and drug delivery”, Chem. Commun. 49(3), 297–299 (2013). http://dx.doi.org/10.1039/C2CC37386F
- J. Wang, K. Yao, C. Wang, C. Tang and X. Jiang, “Synthesis and drug delivery of novel amphiphilic block copolymers containing hydrophobic dehydroabietic moiety”, J. Mater. Chem. B 1(17), 2324–2332 (2013). http://dx.doi.org/10.1039/C3TB20100G
- G. Stoychev, N. Puretskiy and L. Ionov, “Selffolding all-polymer thermoresponsive microcapsules”, Soft Matter 7(7), 3277–3279 (2011). http://dx.doi.org/10.1039/C1SM05109A
- S. Sivakumar, V. Bansal, C. Cortez, S. F. Chong, A. N. Zelikin and F. Caruso, “Degradable, surfactant-free, monodisperse polymer-encapsulated emulsions as anticancer drug carriers”, Adv. Mater. 21(18), 1820–1824 (2009). http://dx.doi.org/10.1002/adma.200802475.
- B. Städler, A. D. Price, R. Chandrawati, L. Hosta-Rigau, A. N. Zelikin and F. Caruso, “Polymer hydrogel capsules: en route toward synthetic cellular systems”, Nanoscale 1, 68–73 (2009). http://dx.doi.org/10.1039/B9NR00143C
- G. K. Such, A. P. Johnston and F. Caruso, “Engineered hydrogen-bonded polymer multilayers: from assembly to biomedical applications”, Chem. Soc. Rev. 40(1), 19–29 (2011). http://dx.doi.org/10.1039/C0CS00001A
- A. G. Skirtach, A. M. Yashchenok and H. Möhwald, “Encapsulation, release and applications of LbL polyelectrolyte multilayer capsules”, Chem. Commun. 47(48), 12736–12746 (2011). http://dx.doi.org/10.1039/C1CC13453A
- L. Loretta, P. Rivera-Gil, A. Z. Abbasi, M. Ochs, C. Ganas, I. Zins, C. Sönnichsen and W. J. Parak, “LbL multilayer capsules: recent progress and future outlook for their use in life sciences”, Nanoscale 2(4), 458–467 (2010). http://dx.doi.org/10.1039/B9NR00341J
- G. Ibarz, L. Dähne, E. Donath and H. Moehwald, “Smart micro-and nanocontainers for storage, transport, and release”, Adv. Mater. 13(17), 1324–1327 (2001). http://dx.doi.org/10.1002/1521-4095(200109)13:17
- G. B. Sukhorukov, A. A. Antipov, A. Voigt, E. Donath and H. Möhwald, “pH-Controlled macromolecule encapsulation in and release from polyelectrolyte multilayer nanocapsules”, Macromol. Rapid Commun. 22(1), 44–46 (2001). http://dx.doi.org/10.1002/1521–3927
- A. A. Antipov, G. B. Sukhorukov and H. Möhwald, “Influence of the ionic strength on the polyelectrolyte multilayers’ permeability”, Langmuir 19(6), 2444–2448 (2003). http://dx.doi.org/10.1021/la026101n
- R. Chandrawati, B. Städler, A. Postma, L. A. Connal, S.-F. Chong, A. N. Zelikin and F. Caruso, “Cholesterol-mediated anchoring of enzyme-loaded liposomes within disulfide-stabilized polymer carrier capsules”, Biomaterials 30(30), 5988–5998 (2009). http://dx.doi.org/10.1016/j.biomaterials.2009.07.040
- Y. Yan, A. P. Johnston, S. J. Dodds, M. M. Kamphuis, C. Ferguson, R. G. Parton, E. C. Nice, J. K. Heath and F. Caruso, “Uptake and intracellular fate of disulfide-bonded polymer hydrogel capsules for doxorubicin delivery to colorectal cancer cells”, ACS Nano 4(5), 2928–2936 (2010). http://dx.doi.org/10.1021/nn100173h
- S. F. Chong, R. Chandrawati, B. Städler, J. Park, J. Cho, Y. Wang, Z. Jia, V. Bulmus, T. P. Davis and A. N. Zelikin, “Stabilization of polymerhydrogel capsules via thioldisulfide exchange”, Small 5(22), 2601–2610 (2009). http://dx.doi.org/10.1002/smll.200900906
- M. Motornov, H. Royter, R. Lupitskyy, Y. Roiter and S. Minko, “Stimuli-esponsive hydrogel hollow capsules by material efficient and robust crosslinking-precipitation synthesis revisited”, Langmuir 27(24), 15305–15311 (2011). http://dx.doi.org/10.1021/la204286a
- B. Städler, A. D. Price and A. N. Zelikin, “A critical look at multilayered polymer capsules in biomedicine: drug carriers, artificial organelles, and cell mimics”, Adv. Funct. Mater. 21(1), 14–28 (2011). http://dx.doi.org/10.1002/adfm.201001676
- S. De Koker, L. J. De Cock, P. Rivera-Gil, W. J. Parak, R. Auzély Velty, C. Vervaet, J. P. Remon, J. Grooten and B. G. De Geest, “Polymeric multilayer capsules delivering biotherapeutics”, Adv. Drug Del. Rev. 63(9), 748–761 (2011). http://dx.doi.org/10.1016/j.addr.2011.03.014
- T. Chen, B. Du and Z. Fan, “Facile fabrication of polymer nanocapsules with cross-linked qrganicinorganic hybrid walls”, Langmuir 28(30), 11225–11231 (2012). http://dx.doi.org/10.1021/la301872q
- M. Motornov, Y. Roiter, I. Tokarev and S. Minko, “Stimuli-responsive nanoparticles, nanogels and capsules for integrated multifunctional intelligent systems”, Prog. in Polym. Sci. 35(1-2), 174–211 (2010). http://dx.doi.org/10.1016/j.progpolymsci.2009.10.004
- Y. Zhao, H. C. Shum, L. L. Adams, B. Sun, C. Holtze, Z. Gu and D. A. Weitz, “Enhanced encapsulation of actives in self-sealing microcapsules by precipitation in capsule shells”, Langmuir 27(23), 13988–13991 (2011). http://dx.doi.org/10.1021/la2034774
- N. Elsner, V. Kozlovskaya, S. A. Sukhishvili and A. Fery, “pH-Triggered softening of crosslinked hydrogenbonded capsules”, Soft Matter 2(11), 966–972 (2006). http://dx.doi.org/10.1039/B608317J
- V. Kozlovskaya and S. A. Sukhishvili, “Amphoteric hydrogel capsules: multiple encapsulation and release routes”, Macromolecules 39(18), 6191–6199 (2006). http://dx.doi.org/10.1021/ma0613640
- V. Kozlovskaya, E. Kharlampieva, M. L. Mansfield and S. A. Sukhishvili, “Poly (methacrylic acid) hydrogel films and capsules: response to pH and ionic strength, and encapsulation of macromolecules”, Chem. Mater. 18(2), 328–336 (2006). http://dx.doi.org/10.1021/cm0517364
- Y. Chen, X. Zheng, H. Qian, Z. Mao, D. Ding and X. Jiang, “Hollow core-porous shell structure poly (acrylic acid) nanogels with a superhigh capacity of drug loading”, ACS Appl. Mater. Inter. 2(12), 3532–3538 (2010). http://dx.doi.org/10.1021/am100709d
- Y. Chen, D. Ding, Z. Mao, Y. He, Y. Hu, W. Wu and X. Jiang, “Synthesis of hydroxypropylcellulose-poly (acrylic acid) particles with semi-interpenetrating polymer network structure”, Biomacromolecules 9(10), 2609–2614 (2008). http://dx.doi.org/10.1021/bm800484e
- Y. Chen, J. Nan, C. Wang and F. Chu, “Hollow poly (N-isopropylacrylamide)-co-poly (acrylic acid) microgels with high loading capacity for drugs”, J. Appl. Polym. Sci. 124(6), 4678–4685 (2012). http://dx.doi.org/10.1002/app.35515
- X. Lu, Z. Hu and J. Schwartz, “Phase transition behavior of hydroxypropylcellulose under interpolymer complexation with poly (acrylic acid)”, Macromolecules 35(24), 9164–9168 (2002). http://dx.doi.org/10.1021/ma0208842
- H. Gao, W. Yang, K. Min, L. Zha, C. Wang and S. Fu, “Thermosensitive poly (N-isopropylacrylamide) nanocapsules with controlled permeability”, Polymer 46(4), 1087–1093 (2005). http://dx.doi.org/10.1016/j.polymer.2004.11.078
- K. S. Soppimath, T. M. Aminabhavi, A. R. Kulkarni and W. E. Rudzinski, “Biodegradable polymeric nanoparticles as drug delivery devices”, J. Controlled Release 70(1-2), 1–20 (2001). http://dx.doi.org/10.1016/S0168-3659(00)00339-4
- G. Li, S. Song, L. Guo and S. Ma, “Self-assembly of thermo-and pH-responsive poly (acrylic acid)-b-poly (N-isopropylacrylamide) micelles for drug delivery”, J. Polym. Sci., Part A: Polym. Chem. 46(15), 5028–5035 (2008). http://dx.doi.org/10.1002/pola.22831
- W. Tong, W. Dong, C. Gao and H. Möhwald, “Chargecontrolled permeability of polyelectrolyte microcapsules”, J. Phys. Chem. B 109(27), 13159–13165 (2005). http://dx.doi.org/10.1021/jp0511092
- A. A. Antipov, G. B. Sukhorukov, S. Leporatti, I. L. Radtchenko, E. Donath and H. Möhwald, “Polyelectrolyte multilayer capsule permeability control”, Colloids Surf. Physicochem. Eng. Aspects 198–200, 535–541 (2002). http://dx.doi.org/10.1016/S0927-7757(01)00956-6
- G. R. Martin and R. K. Jain, “Noninvasive measurement of interstitial pH profiles in normal and neoplastic tissue using fluorescence ratio imaging microscopy”, Cancer Res. 54, 5670–5674 (1994). http://cancerres.aacrjournals.org/content/54/21/5670.full.pdf+html
- R. Savic, L. Luo, A. Eisenberg and D. Maysinger, Micellar Nanocontainers “Distribute to defined cytoplasmic organelles”, Science 300(5619), 615–618 (2003). http://dx.doi.org/10.1126/science.1078192
References
K. Kataoka, A. Harada and Y. Nagasaki, “Block copolymer micelles for drug delivery: design, characterization and biological significance”, Adv. Drug Del. Rev. 47(1), 113–131 (2001). http://dx.doi.org/10.1016/S0169-409X(00)00124-1
N. Kolishetti, S. Dhar, P. M. Valencia, L. Q. Lin, R. Karnik, S. J. Lippard, R. Langer and O. C. Farokhzad, “Engineering of self-assembled nanoparticle platform for precisely controlled combination drug therapy”, Proc. Natl. Acad. Sci. 107(42), 17939–17944 (2010). http://dx.doi.org/10.1073/pnas.1011368107
Y. Chen, X. Zheng, X. Wang, C. Wang, Y. Ding and X. Jiang, “Near-Infrared emitting gold clusterpoly (acrylic acid) hybrid nanogels”, ACS Macro Lett. 3(1), 74–76 (2014). http://dx.doi.org/10.1021/mz4005748
R. C. Nagarwal, S. Kant, P. Singh, P. Maiti and J. Pandit, “Polymeric nanoparticulate system: a potential approach for ocular drug delivery”, J. ControlledRelease 136(1), 2–13 (2009). http://dx.doi.org/10.1016/j.jconrel.2008.12.018
J. Panyam and V. Labhasetwar, “Biodegradable nanoparticles for drug and gene delivery to cells and tissue”, Adv. Drug Del. Rev. 55(3), 329–347 (2003). http://dx.doi.org/10.1016/S0169-409X(02)00228-4
T. R. Hoare and D. S. Kohane, “Hydrogels in drug delivery: progress and challenges”, Polymer 49(8), 1993–2007 (2008). http://dx.doi.org/10.1016/j.polymer.2008.01.027
J. Kost and R. Langer, “Responsive polymeric delivery systems”, Adv. Drug Del. Rev. 46(1-3), 125–148 (2001). http://dx.doi.org/10.1016/S0169-409X(00)00136-8
J. Della Rocca, D. Liu and W. Lin, “Nanoscale metal-organic frameworks for biomedical imaging and drug delivery”, Acc. Chem. Res. 44(10), 957–968 (2011). http://dx.doi.org/10.1021/ar200028a
Y. Chen, P. A. Wilbon, J. Zhou, M. Nagarkatti, C. Wang, F. Chu and C. Tang, “Multifunctional selffluorescent polymer nanogels for label-free imaging and drug delivery”, Chem. Commun. 49(3), 297–299 (2013). http://dx.doi.org/10.1039/C2CC37386F
J. Wang, K. Yao, C. Wang, C. Tang and X. Jiang, “Synthesis and drug delivery of novel amphiphilic block copolymers containing hydrophobic dehydroabietic moiety”, J. Mater. Chem. B 1(17), 2324–2332 (2013). http://dx.doi.org/10.1039/C3TB20100G
G. Stoychev, N. Puretskiy and L. Ionov, “Selffolding all-polymer thermoresponsive microcapsules”, Soft Matter 7(7), 3277–3279 (2011). http://dx.doi.org/10.1039/C1SM05109A
S. Sivakumar, V. Bansal, C. Cortez, S. F. Chong, A. N. Zelikin and F. Caruso, “Degradable, surfactant-free, monodisperse polymer-encapsulated emulsions as anticancer drug carriers”, Adv. Mater. 21(18), 1820–1824 (2009). http://dx.doi.org/10.1002/adma.200802475.
B. Städler, A. D. Price, R. Chandrawati, L. Hosta-Rigau, A. N. Zelikin and F. Caruso, “Polymer hydrogel capsules: en route toward synthetic cellular systems”, Nanoscale 1, 68–73 (2009). http://dx.doi.org/10.1039/B9NR00143C
G. K. Such, A. P. Johnston and F. Caruso, “Engineered hydrogen-bonded polymer multilayers: from assembly to biomedical applications”, Chem. Soc. Rev. 40(1), 19–29 (2011). http://dx.doi.org/10.1039/C0CS00001A
A. G. Skirtach, A. M. Yashchenok and H. Möhwald, “Encapsulation, release and applications of LbL polyelectrolyte multilayer capsules”, Chem. Commun. 47(48), 12736–12746 (2011). http://dx.doi.org/10.1039/C1CC13453A
L. Loretta, P. Rivera-Gil, A. Z. Abbasi, M. Ochs, C. Ganas, I. Zins, C. Sönnichsen and W. J. Parak, “LbL multilayer capsules: recent progress and future outlook for their use in life sciences”, Nanoscale 2(4), 458–467 (2010). http://dx.doi.org/10.1039/B9NR00341J
G. Ibarz, L. Dähne, E. Donath and H. Moehwald, “Smart micro-and nanocontainers for storage, transport, and release”, Adv. Mater. 13(17), 1324–1327 (2001). http://dx.doi.org/10.1002/1521-4095(200109)13:17
G. B. Sukhorukov, A. A. Antipov, A. Voigt, E. Donath and H. Möhwald, “pH-Controlled macromolecule encapsulation in and release from polyelectrolyte multilayer nanocapsules”, Macromol. Rapid Commun. 22(1), 44–46 (2001). http://dx.doi.org/10.1002/1521–3927
A. A. Antipov, G. B. Sukhorukov and H. Möhwald, “Influence of the ionic strength on the polyelectrolyte multilayers’ permeability”, Langmuir 19(6), 2444–2448 (2003). http://dx.doi.org/10.1021/la026101n
R. Chandrawati, B. Städler, A. Postma, L. A. Connal, S.-F. Chong, A. N. Zelikin and F. Caruso, “Cholesterol-mediated anchoring of enzyme-loaded liposomes within disulfide-stabilized polymer carrier capsules”, Biomaterials 30(30), 5988–5998 (2009). http://dx.doi.org/10.1016/j.biomaterials.2009.07.040
Y. Yan, A. P. Johnston, S. J. Dodds, M. M. Kamphuis, C. Ferguson, R. G. Parton, E. C. Nice, J. K. Heath and F. Caruso, “Uptake and intracellular fate of disulfide-bonded polymer hydrogel capsules for doxorubicin delivery to colorectal cancer cells”, ACS Nano 4(5), 2928–2936 (2010). http://dx.doi.org/10.1021/nn100173h
S. F. Chong, R. Chandrawati, B. Städler, J. Park, J. Cho, Y. Wang, Z. Jia, V. Bulmus, T. P. Davis and A. N. Zelikin, “Stabilization of polymerhydrogel capsules via thioldisulfide exchange”, Small 5(22), 2601–2610 (2009). http://dx.doi.org/10.1002/smll.200900906
M. Motornov, H. Royter, R. Lupitskyy, Y. Roiter and S. Minko, “Stimuli-esponsive hydrogel hollow capsules by material efficient and robust crosslinking-precipitation synthesis revisited”, Langmuir 27(24), 15305–15311 (2011). http://dx.doi.org/10.1021/la204286a
B. Städler, A. D. Price and A. N. Zelikin, “A critical look at multilayered polymer capsules in biomedicine: drug carriers, artificial organelles, and cell mimics”, Adv. Funct. Mater. 21(1), 14–28 (2011). http://dx.doi.org/10.1002/adfm.201001676
S. De Koker, L. J. De Cock, P. Rivera-Gil, W. J. Parak, R. Auzély Velty, C. Vervaet, J. P. Remon, J. Grooten and B. G. De Geest, “Polymeric multilayer capsules delivering biotherapeutics”, Adv. Drug Del. Rev. 63(9), 748–761 (2011). http://dx.doi.org/10.1016/j.addr.2011.03.014
T. Chen, B. Du and Z. Fan, “Facile fabrication of polymer nanocapsules with cross-linked qrganicinorganic hybrid walls”, Langmuir 28(30), 11225–11231 (2012). http://dx.doi.org/10.1021/la301872q
M. Motornov, Y. Roiter, I. Tokarev and S. Minko, “Stimuli-responsive nanoparticles, nanogels and capsules for integrated multifunctional intelligent systems”, Prog. in Polym. Sci. 35(1-2), 174–211 (2010). http://dx.doi.org/10.1016/j.progpolymsci.2009.10.004
Y. Zhao, H. C. Shum, L. L. Adams, B. Sun, C. Holtze, Z. Gu and D. A. Weitz, “Enhanced encapsulation of actives in self-sealing microcapsules by precipitation in capsule shells”, Langmuir 27(23), 13988–13991 (2011). http://dx.doi.org/10.1021/la2034774
N. Elsner, V. Kozlovskaya, S. A. Sukhishvili and A. Fery, “pH-Triggered softening of crosslinked hydrogenbonded capsules”, Soft Matter 2(11), 966–972 (2006). http://dx.doi.org/10.1039/B608317J
V. Kozlovskaya and S. A. Sukhishvili, “Amphoteric hydrogel capsules: multiple encapsulation and release routes”, Macromolecules 39(18), 6191–6199 (2006). http://dx.doi.org/10.1021/ma0613640
V. Kozlovskaya, E. Kharlampieva, M. L. Mansfield and S. A. Sukhishvili, “Poly (methacrylic acid) hydrogel films and capsules: response to pH and ionic strength, and encapsulation of macromolecules”, Chem. Mater. 18(2), 328–336 (2006). http://dx.doi.org/10.1021/cm0517364
Y. Chen, X. Zheng, H. Qian, Z. Mao, D. Ding and X. Jiang, “Hollow core-porous shell structure poly (acrylic acid) nanogels with a superhigh capacity of drug loading”, ACS Appl. Mater. Inter. 2(12), 3532–3538 (2010). http://dx.doi.org/10.1021/am100709d
Y. Chen, D. Ding, Z. Mao, Y. He, Y. Hu, W. Wu and X. Jiang, “Synthesis of hydroxypropylcellulose-poly (acrylic acid) particles with semi-interpenetrating polymer network structure”, Biomacromolecules 9(10), 2609–2614 (2008). http://dx.doi.org/10.1021/bm800484e
Y. Chen, J. Nan, C. Wang and F. Chu, “Hollow poly (N-isopropylacrylamide)-co-poly (acrylic acid) microgels with high loading capacity for drugs”, J. Appl. Polym. Sci. 124(6), 4678–4685 (2012). http://dx.doi.org/10.1002/app.35515
X. Lu, Z. Hu and J. Schwartz, “Phase transition behavior of hydroxypropylcellulose under interpolymer complexation with poly (acrylic acid)”, Macromolecules 35(24), 9164–9168 (2002). http://dx.doi.org/10.1021/ma0208842
H. Gao, W. Yang, K. Min, L. Zha, C. Wang and S. Fu, “Thermosensitive poly (N-isopropylacrylamide) nanocapsules with controlled permeability”, Polymer 46(4), 1087–1093 (2005). http://dx.doi.org/10.1016/j.polymer.2004.11.078
K. S. Soppimath, T. M. Aminabhavi, A. R. Kulkarni and W. E. Rudzinski, “Biodegradable polymeric nanoparticles as drug delivery devices”, J. Controlled Release 70(1-2), 1–20 (2001). http://dx.doi.org/10.1016/S0168-3659(00)00339-4
G. Li, S. Song, L. Guo and S. Ma, “Self-assembly of thermo-and pH-responsive poly (acrylic acid)-b-poly (N-isopropylacrylamide) micelles for drug delivery”, J. Polym. Sci., Part A: Polym. Chem. 46(15), 5028–5035 (2008). http://dx.doi.org/10.1002/pola.22831
W. Tong, W. Dong, C. Gao and H. Möhwald, “Chargecontrolled permeability of polyelectrolyte microcapsules”, J. Phys. Chem. B 109(27), 13159–13165 (2005). http://dx.doi.org/10.1021/jp0511092
A. A. Antipov, G. B. Sukhorukov, S. Leporatti, I. L. Radtchenko, E. Donath and H. Möhwald, “Polyelectrolyte multilayer capsule permeability control”, Colloids Surf. Physicochem. Eng. Aspects 198–200, 535–541 (2002). http://dx.doi.org/10.1016/S0927-7757(01)00956-6
G. R. Martin and R. K. Jain, “Noninvasive measurement of interstitial pH profiles in normal and neoplastic tissue using fluorescence ratio imaging microscopy”, Cancer Res. 54, 5670–5674 (1994). http://cancerres.aacrjournals.org/content/54/21/5670.full.pdf+html
R. Savic, L. Luo, A. Eisenberg and D. Maysinger, Micellar Nanocontainers “Distribute to defined cytoplasmic organelles”, Science 300(5619), 615–618 (2003). http://dx.doi.org/10.1126/science.1078192