Macromolecular Rapid Communications
Communication
Stimuli-Triggered Growth and Removal of a Bioreducible Nanoshell on Nanoparticles Li-Fen Han, Qian-Bao Chen, Zong-Tao Hu, Jia-Gang Piao, Chun-Yan Hong, Jun-Jie Yan, Ye-Zi You*
A new and easy method of stimuli-triggered growth and removal of a bioreducible nanoshell on nanoparticles is reported. The results show that pH or temperature could induce the aggregation of disulfide-contained branched polymers at the surface of nanoparticles; subsequently, the aggregated polymers could undergo intermolecular disulfide exchange to cross-link the aggregated polymers, forming a bioreducible polymer shell around nanoparticles. When these nanoparticles with a polymer shell are treated with glutathione (GSH) or D,L-dithiothreitol (DTT), the polymer shell could be easily removed from the nanoparticles. The potential application of this method is demonstrated by easily growing and removing a bioreducible shell from liposomes, and improvement of in vivo gene transfection activity of liposomes with a bioreducible PEG shell.
1. Introduction In recent years, there has been intense interest surrounding the fabrication of core–shell nanoparticles that consist of either organic or inorganic cores coated with a polymer shell.[1] These core–shell particles often exhibit properties that are substantially different from those of the templated core, they can be used to prepare nanocapsules for the delivery of drug, gene, and protein, which makes them attractive from both a scientific and a technological viewpoint.[2] Though many methods, including precipitation polymerization,[1a,3] surface-initiated polym erization,[2b,3a,4] and layer-by-layer (LBL) assembly,[1b,5] etc. have been successfully developed for growing a polymeric
L.-F. Han, Q.-B. Chen, J.-G. Piao, Prof. C.-Y. Hong, J.-J. Yan, Y.-Z. You CAS Key Laboratory of Soft Matter Chemistry, Department of Polymer Science and Engineering, University of Science and Technology of China, Hefei 230026, Anhui, P. R. China E-mail: [email protected] Dr Z.-T. Hu Diagnosis and Treatment Center of Tumor, 105th Hospital of PLA, Hefei 230031, Anhui, P. R. China Macromol. Rapid Commun. 2014, 35, 649−654 © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
nanoshell on the surface of nanoparticles, they need pre-modifying the surface, or suffer from very complicated procedures. On the other hand, it is difficult to remove the shell on demand in some cases. It is thus highly desirable to develop a simple and versatile approach to grow a polymer shell onto nanoparticles without premodifying the nanoparticles, and remove the shell on demand. To the best of our knowledge, stimulus-triggered growth and removal of bioreducible nanoshell on nanoparticles has never been realized so far. Here, we report a novel and easy method for reversibly growing a bioreducible nanoshell on nanoparticles without pre-modifying the surface of nanoparticles, in which temperature or pH triggers the growth of a bioreducible nanoshell onto silica nanoparticles, and reducing agent triggers the removal of the bioreducible nanoshell from silica nanoparticles. This method greatly simplifies the process of coating a nanoshell onto nanoparticles, and can be extended to prepare bioreducible nanocapsules. Most important, the nanoshell is cross-linked via disulfide bonds, which are responsive to glutathione (GSH), and so the polymer shell is bioreducible, and this method will have potential application in nanomedicine.
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DOI: 10.1002/marc.201300885
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2. Experiment Section 2.1. Temperature-Induced Growth of Bioreducible Shell on Nanoparticles and GSH-Induced Removal of Bioreducible Shell from Nanoparticles After SiO2 nanoparticles (0.105 g) in deionized water (29 mL) in a flask was ultrasonicated for 30 min, pH of the suspension was adjusted to 9.0, and heated to 50 °C. Subsequently, PEG-based branched copolymer (0.112 g) dissolved in water (8 mL) was added dropwise into the suspension and reacted for 12 h at 50 °C, then PEG-coated silica nanoparticles (SiO2@PEG) were obtained by centrifuging and washing with water. The PEG nanoshell was removed from silica nanoparticles after SiO2@PEG was treated with GSH (10 × 10−3 M) for 10 min.
2.2. Temperature-Induced Growth of a Second Bioreducible Shell on Nanoparticles After SiO2 nanoparticles (0.125 g) in phosphate buffered saline (PBS, 27 mL) in a flask was ultrasonicated for 30 min, pH of the suspension was ≈8.0, and then the suspension was heated to 50 °C. Subsequently, PEG-based branched copolymer (0.105 g) dissolved in PBS (8 mL) was added dropwise into the suspension within 12 h at 45 °C, and PEG-coated silica nanoparticles (SiO2@ PEG) were obtained. Then, branched poly(amido amine) (HPAA-1, 0.095 g) prepared via Micheal addition of N,N’-Cystaminebisacrylamide (CBA) and N,N’-dimethyldipropylenetriamine (DMDPTA), in PBS (8 mL) was added dropwise in PEG@SiO2 suspension within 12 h at 45 °C, and a second shell grew on silica nanoparticles.
3. Results and Discussion To grow a nanoshell on nanoparticles, disulfide-contained branched polymer (PEG-based branched polymer) was prepared via reversible addition–fragmentation chain transfer (RAFT) polymerization of 2-(2-methoxyethoxy) ethyl methacrylate (MEO2MA) and oligo(ethylene glycol) methacrylate (OEGMA) using N,N’-cystaminebisacrylamide (CBA) as branching unit.[6] On one hand, the obtained PEG-based branched polymer is temperature-responsive, and its lower critical solution temperature (LCST) is 45 °C (Figure S3, Supporting Information).[7,8] On the other hand, this polymer can self-crosslink via the intermolecular disulfide-exchange in aggregated state when heating is applied.[6d,7] Temperature-triggered growth of nanoshell onto nanoparticle is shown in Figure 1A. First, the silica nanoparticles were dispersed in water at 50 °C, then PEG-based branched polymers in water were added into the silicadispersed system slowly. In the water of 50 °C, PEG-based branched polymers are poor soluble, and they shrink and collapse together into small nanoparticles due to that they liberate the absorbed water molecules at high
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temperatures.[8] The formed polymer nanoparticles are not stable in water, and they absorb onto the surface of silica nanoparticles. These absorbed PEG aggregations are very soft, and they can pack close enough on the surface of silica nanoparticles to undergo inter-nanoparticle disulfide-exchange at 50 °C,[9] cross-linking the absorbed nanoparticles to form a PEG-based nanoshell (13 nm) around silica nanoparticles (Figure 1B). The size of the nanoparticles increased from 196 to 229 nm after growing a PEG-based nanoshell based on dynamic light scattering (DLS) results (Figure S9, Supporting Information), indicating that PEG-based nanoshell has grown on the surface of silica nanoparticles. Moreover, this shell can be easily removed by treating these nanoparticles with glutathione (GSH) or D,L-dithiothreitol (DTT), it is clear that there is no nanoshell on the surface of silica nanoparticles after being treated with GSH (Figure 1B). DLS result shows that the size of nanoparticles with a PEG nanoshell decreased from 229 to 201 nm after being treated with GSH, indicating that GSH can remove the nanoshell from nanoparticles (see Figure S9, Supporting Information). Furthermore, the silica template is dissolved away to leave a hollow capsule (see Figure 1C) via HF treating the core-shell nanoparticles. The formed nanocapsules are cross-linked by disulfides, and hence the nanocapsules are bioreducible, and they can degrade in the presence of DTT, which is verified by the significant decrease in the size of nanocapsules after being treated with 10 × 10−3 M DTT (Figure S11 and S12, Supporting Information). This method can also be used to further grow a second nanoshell onto nanoparticles. In order to address this, we prepared temperature-responsive branched poly(amido amine) (HPAA-1) via Michael addition of DMDPTA with CBA. HPAA-1 has a LCST to be 37 °C (Figure S5, Supporting Information), and disulfide bonds in the backbone. It can also self-crosslink via intermolecular disulfide-exchange in aggregated state.[6d,7a] After we dispersed silica nanoparticles in PBS buffer at 45 °C, PEG-based branched polymers in water was first added into silica-dispersed system slowly, and a bioreducible PEG shell with thickness of 15 nm was linked onto the nanoparticles (silica@ PEG) (Figure 2). Subsequently, HPAA-1 in water was added into the above dispersed system of silica@PEG slowly. At 45 °C, HPAA-1 become poor soluble, and they shrink and collapse together into small nanoparticles. These formed nanoparticles are not stable in aqueous solution, and absorbed onto the surface of silica@PEG. Simultaneously, these absorbed nanoparticles underwent inter-nanoparticle disulfide-exchanges, cross-linking the absorbed HPAA-1 to form a second bioreducible shell around nanoparticles of silica@PEG (Figure 2). It is clear that there are two layered shells on the surface of silica nanoparticles in the TEM images. The peak at 1650 cm−1 for amido unit appeared in the FT-IR spectrum of the formed
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Figure 1. A) The schematic procedure for stimulus-induced growth and removal of a bioreducible shell on silica nanoparticles and the formation of bioreducible nanocapsules. B) TEM images of silica nanoparticles (a), silica nanoparticles with a bioreducible PEG shell (b), and silica nanoparticles with a bioreducible PEG shell after treated with GSH (c). C) TEM images of silica nanoparticles (a), silica nanoparticles with a bioreducible PEG-based shell (b), and the nanocapsules via HF etching the core (c).
nanoparticles, and the size of the nanoparticles increased to 257 nm after being coated with a second nanoshell (see Figures 2C and S10, Supporting Information), indicating that a second nanoshell has been grown onto the nanoparticles. Besides temperature, pH also can be used as a stimulus to induce the growth of nanoshell onto nanoparticles. pH-responsive disulfide-contained branched poly(amido amine) (HPAA-2) was prepared via Michael addition of 1-(2-aminoethyl) piperazine (AEPZ) with CBA (Figure S7, Supporting Information). On one hand, HPAA-2 is pHresponsive, but not temperature-responsive. One the
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other hand, it can self-cross-link at high temperatures (Figure S8, Supporting Information). After the silica nanoparticles were dispersed in PBS buffer with pH of 9.0, pH-responsive HPAA-2 in water was added into silica-dispersed system. HPAA-2s become poor soluble at pH of 9.0, and they shrink and collapse together into small nanoparticles at pH of 9.0. These formed polymer nanoparticles are not stable and absorb onto the surface of silica nanoparticle. Simultaneously, these absorbed nanoparticles undergo inter-nanoparticle disulfide exchanges, cross-linking the absorbed nanoparticles to form a bioreducible shell (≈10 nm) around silica
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Figure 2. A) The schematic procedure for stimulus-induced growth of a second bioreducible shell on nanoparticles. B) TEM images of silica nanoparticles (1), silica nanoparticles with a bioreducible PEG-based shell (2), and silica nanoparticles with a bioreducible PEG shell and a branched poly(amido amine) nanoshell (HPAA-1) (3). C) The sizes the silica nanoparticles with a bioreducible nanoshell (a) and the silica nanoparticles with a bioreducible PEG-based nanoshell and a second HPAA-1 nanoshell (b).
nanoparticles (Figure 3). It should be noted that all the procedure was carried out at 45 °C, this temperature can facilitate the inter-nanoparticles crosslinking, and the small polymer nanoparticles absorbed on the surface can not be cross-linked at temperatures below 30 °C. Furthermore, there is no nanoshell formation on the surface if the experiment was carried out under pH of 7.0 at 45 °C due to there is no polymer aggregations formed at pH of
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Figure 3. A) TEM images of silica nanoparticles. B) TEM images of silica nanoparticles with a poly(amido amine) (HPAA-2) shell.
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Stimuli-Triggered Growth and Removal of a Bioreducible Nanoshell on Nanoparticles
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7.0 (see Figure S14, Supporting Information). Hence, pH can be used a stimulus to induce the growth of a bioreducible shell on nanoparticles. Glutathione is present in extracellular milieu with several micromolar concentration, and disulfide bond is stable in extracellular milieu; however, the glutathione concentration in intracellular environments is 50–1000 times higher than that in extracellular milieu, and disulfide bond can be easily cleaved in intracellular environments.[9] Therefore, disulfidecrosslinked shell on liposomes can keep their structure stable in the extracytoplasmic environment, while inducing break of the disulfidecrosslinked shell after their movement into the cytoplasmic compartment. Liposme can act a vector of DNA,[10] but it is not stable in extracellular milieu. Here, we can grow a bioreducible PEG shell on liposomes via using above method. The bioreducible shell around liposome will make liposome stable in extracytoplasmic environment while the shell can degrade after its movement into the cytoplasmic compartFigure 4. A) In vitro gene transfection activities of polyplexes and polyplexes with a ment, inducing the efficient release bioreducible cross-linked shell in the presence of 10% serum. B) In vivo gene transfection activities of liposome and liposome with a bioreducible cross-linked shell. of payloads, and hence in vivo, the liposomes with a bioreducible crosslinked PEG shell will have a remarkable improvement Supporting Information of gene transfection activity. Therefore, temperature is Supporting Information is available from the Wiley Online used to trigger the growth of bioreducible cross-linked Library or from the author. PEG shell on liposomes, GSH, or DTT can remove the cross-linked PEG shell from liposome (Figure S15, SupAcknowledgements: Financial support from National Natural porting Information). The results show that liposome Science Foundation of China (51033005, 21074121, 21090354 and with a PEG shell has higher transfection activity than 21374107) and the Program for New Century Excellent Talents in those without a cross-linked PEG shell in vitro and in Universities (NCET-08–0520) is gratefully acknowledged. vivo (Figure 4). Received: December 1, 2013; Revised: December 26, 2013; Published online: February 4, 2014; DOI: 10.1002/marc.201300885
4. Conclusions Stimulus-triggered growth of a polymer shell on nanoparticles is reported based on stimulus-induced self-assembly and self-cross-linking of disulfide-contained branched polymers; furthermore, the template is dissolved away to leave a bioreducible nanocapsule. This method provides an easy and versatile method to grow a biocompatible shell on nanoparticles without pre-modifying the surface of nanoparticles, which will have many potential applications in biomedicine.
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Keywords: bioreducible nanoshell; branched polymer; nanoparticle; pH-responsive; temperature-responsive
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Communication
Stimuli-Triggered Growth and Removal of a Bioreducible Nanoshell on Nanoparticles Li-Fen Han, Qian-Bao Chen, Zong-Tao Hu, Jia-Gang Piao, Chun-Yan Hong, Jun-Jie Yan, Ye-Zi You*
A new and easy method of stimuli-triggered growth and removal of a bioreducible nanoshell on nanoparticles is reported. The results show that pH or temperature could induce the aggregation of disulfide-contained branched polymers at the surface of nanoparticles; subsequently, the aggregated polymers could undergo intermolecular disulfide exchange to cross-link the aggregated polymers, forming a bioreducible polymer shell around nanoparticles. When these nanoparticles with a polymer shell are treated with glutathione (GSH) or D,L-dithiothreitol (DTT), the polymer shell could be easily removed from the nanoparticles. The potential application of this method is demonstrated by easily growing and removing a bioreducible shell from liposomes, and improvement of in vivo gene transfection activity of liposomes with a bioreducible PEG shell.
1. Introduction In recent years, there has been intense interest surrounding the fabrication of core–shell nanoparticles that consist of either organic or inorganic cores coated with a polymer shell.[1] These core–shell particles often exhibit properties that are substantially different from those of the templated core, they can be used to prepare nanocapsules for the delivery of drug, gene, and protein, which makes them attractive from both a scientific and a technological viewpoint.[2] Though many methods, including precipitation polymerization,[1a,3] surface-initiated polym erization,[2b,3a,4] and layer-by-layer (LBL) assembly,[1b,5] etc. have been successfully developed for growing a polymeric
L.-F. Han, Q.-B. Chen, J.-G. Piao, Prof. C.-Y. Hong, J.-J. Yan, Y.-Z. You CAS Key Laboratory of Soft Matter Chemistry, Department of Polymer Science and Engineering, University of Science and Technology of China, Hefei 230026, Anhui, P. R. China E-mail: [email protected] Dr Z.-T. Hu Diagnosis and Treatment Center of Tumor, 105th Hospital of PLA, Hefei 230031, Anhui, P. R. China Macromol. Rapid Commun. 2014, 35, 649−654 © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
nanoshell on the surface of nanoparticles, they need pre-modifying the surface, or suffer from very complicated procedures. On the other hand, it is difficult to remove the shell on demand in some cases. It is thus highly desirable to develop a simple and versatile approach to grow a polymer shell onto nanoparticles without premodifying the nanoparticles, and remove the shell on demand. To the best of our knowledge, stimulus-triggered growth and removal of bioreducible nanoshell on nanoparticles has never been realized so far. Here, we report a novel and easy method for reversibly growing a bioreducible nanoshell on nanoparticles without pre-modifying the surface of nanoparticles, in which temperature or pH triggers the growth of a bioreducible nanoshell onto silica nanoparticles, and reducing agent triggers the removal of the bioreducible nanoshell from silica nanoparticles. This method greatly simplifies the process of coating a nanoshell onto nanoparticles, and can be extended to prepare bioreducible nanocapsules. Most important, the nanoshell is cross-linked via disulfide bonds, which are responsive to glutathione (GSH), and so the polymer shell is bioreducible, and this method will have potential application in nanomedicine.
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DOI: 10.1002/marc.201300885
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L.-F. Han et al.
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2. Experiment Section 2.1. Temperature-Induced Growth of Bioreducible Shell on Nanoparticles and GSH-Induced Removal of Bioreducible Shell from Nanoparticles After SiO2 nanoparticles (0.105 g) in deionized water (29 mL) in a flask was ultrasonicated for 30 min, pH of the suspension was adjusted to 9.0, and heated to 50 °C. Subsequently, PEG-based branched copolymer (0.112 g) dissolved in water (8 mL) was added dropwise into the suspension and reacted for 12 h at 50 °C, then PEG-coated silica nanoparticles (SiO2@PEG) were obtained by centrifuging and washing with water. The PEG nanoshell was removed from silica nanoparticles after SiO2@PEG was treated with GSH (10 × 10−3 M) for 10 min.
2.2. Temperature-Induced Growth of a Second Bioreducible Shell on Nanoparticles After SiO2 nanoparticles (0.125 g) in phosphate buffered saline (PBS, 27 mL) in a flask was ultrasonicated for 30 min, pH of the suspension was ≈8.0, and then the suspension was heated to 50 °C. Subsequently, PEG-based branched copolymer (0.105 g) dissolved in PBS (8 mL) was added dropwise into the suspension within 12 h at 45 °C, and PEG-coated silica nanoparticles (SiO2@ PEG) were obtained. Then, branched poly(amido amine) (HPAA-1, 0.095 g) prepared via Micheal addition of N,N’-Cystaminebisacrylamide (CBA) and N,N’-dimethyldipropylenetriamine (DMDPTA), in PBS (8 mL) was added dropwise in PEG@SiO2 suspension within 12 h at 45 °C, and a second shell grew on silica nanoparticles.
3. Results and Discussion To grow a nanoshell on nanoparticles, disulfide-contained branched polymer (PEG-based branched polymer) was prepared via reversible addition–fragmentation chain transfer (RAFT) polymerization of 2-(2-methoxyethoxy) ethyl methacrylate (MEO2MA) and oligo(ethylene glycol) methacrylate (OEGMA) using N,N’-cystaminebisacrylamide (CBA) as branching unit.[6] On one hand, the obtained PEG-based branched polymer is temperature-responsive, and its lower critical solution temperature (LCST) is 45 °C (Figure S3, Supporting Information).[7,8] On the other hand, this polymer can self-crosslink via the intermolecular disulfide-exchange in aggregated state when heating is applied.[6d,7] Temperature-triggered growth of nanoshell onto nanoparticle is shown in Figure 1A. First, the silica nanoparticles were dispersed in water at 50 °C, then PEG-based branched polymers in water were added into the silicadispersed system slowly. In the water of 50 °C, PEG-based branched polymers are poor soluble, and they shrink and collapse together into small nanoparticles due to that they liberate the absorbed water molecules at high
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temperatures.[8] The formed polymer nanoparticles are not stable in water, and they absorb onto the surface of silica nanoparticles. These absorbed PEG aggregations are very soft, and they can pack close enough on the surface of silica nanoparticles to undergo inter-nanoparticle disulfide-exchange at 50 °C,[9] cross-linking the absorbed nanoparticles to form a PEG-based nanoshell (13 nm) around silica nanoparticles (Figure 1B). The size of the nanoparticles increased from 196 to 229 nm after growing a PEG-based nanoshell based on dynamic light scattering (DLS) results (Figure S9, Supporting Information), indicating that PEG-based nanoshell has grown on the surface of silica nanoparticles. Moreover, this shell can be easily removed by treating these nanoparticles with glutathione (GSH) or D,L-dithiothreitol (DTT), it is clear that there is no nanoshell on the surface of silica nanoparticles after being treated with GSH (Figure 1B). DLS result shows that the size of nanoparticles with a PEG nanoshell decreased from 229 to 201 nm after being treated with GSH, indicating that GSH can remove the nanoshell from nanoparticles (see Figure S9, Supporting Information). Furthermore, the silica template is dissolved away to leave a hollow capsule (see Figure 1C) via HF treating the core-shell nanoparticles. The formed nanocapsules are cross-linked by disulfides, and hence the nanocapsules are bioreducible, and they can degrade in the presence of DTT, which is verified by the significant decrease in the size of nanocapsules after being treated with 10 × 10−3 M DTT (Figure S11 and S12, Supporting Information). This method can also be used to further grow a second nanoshell onto nanoparticles. In order to address this, we prepared temperature-responsive branched poly(amido amine) (HPAA-1) via Michael addition of DMDPTA with CBA. HPAA-1 has a LCST to be 37 °C (Figure S5, Supporting Information), and disulfide bonds in the backbone. It can also self-crosslink via intermolecular disulfide-exchange in aggregated state.[6d,7a] After we dispersed silica nanoparticles in PBS buffer at 45 °C, PEG-based branched polymers in water was first added into silica-dispersed system slowly, and a bioreducible PEG shell with thickness of 15 nm was linked onto the nanoparticles (silica@ PEG) (Figure 2). Subsequently, HPAA-1 in water was added into the above dispersed system of silica@PEG slowly. At 45 °C, HPAA-1 become poor soluble, and they shrink and collapse together into small nanoparticles. These formed nanoparticles are not stable in aqueous solution, and absorbed onto the surface of silica@PEG. Simultaneously, these absorbed nanoparticles underwent inter-nanoparticle disulfide-exchanges, cross-linking the absorbed HPAA-1 to form a second bioreducible shell around nanoparticles of silica@PEG (Figure 2). It is clear that there are two layered shells on the surface of silica nanoparticles in the TEM images. The peak at 1650 cm−1 for amido unit appeared in the FT-IR spectrum of the formed
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Stimuli-Triggered Growth and Removal of a Bioreducible Nanoshell on Nanoparticles
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Figure 1. A) The schematic procedure for stimulus-induced growth and removal of a bioreducible shell on silica nanoparticles and the formation of bioreducible nanocapsules. B) TEM images of silica nanoparticles (a), silica nanoparticles with a bioreducible PEG shell (b), and silica nanoparticles with a bioreducible PEG shell after treated with GSH (c). C) TEM images of silica nanoparticles (a), silica nanoparticles with a bioreducible PEG-based shell (b), and the nanocapsules via HF etching the core (c).
nanoparticles, and the size of the nanoparticles increased to 257 nm after being coated with a second nanoshell (see Figures 2C and S10, Supporting Information), indicating that a second nanoshell has been grown onto the nanoparticles. Besides temperature, pH also can be used as a stimulus to induce the growth of nanoshell onto nanoparticles. pH-responsive disulfide-contained branched poly(amido amine) (HPAA-2) was prepared via Michael addition of 1-(2-aminoethyl) piperazine (AEPZ) with CBA (Figure S7, Supporting Information). On one hand, HPAA-2 is pHresponsive, but not temperature-responsive. One the
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other hand, it can self-cross-link at high temperatures (Figure S8, Supporting Information). After the silica nanoparticles were dispersed in PBS buffer with pH of 9.0, pH-responsive HPAA-2 in water was added into silica-dispersed system. HPAA-2s become poor soluble at pH of 9.0, and they shrink and collapse together into small nanoparticles at pH of 9.0. These formed polymer nanoparticles are not stable and absorb onto the surface of silica nanoparticle. Simultaneously, these absorbed nanoparticles undergo inter-nanoparticle disulfide exchanges, cross-linking the absorbed nanoparticles to form a bioreducible shell (≈10 nm) around silica
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Figure 2. A) The schematic procedure for stimulus-induced growth of a second bioreducible shell on nanoparticles. B) TEM images of silica nanoparticles (1), silica nanoparticles with a bioreducible PEG-based shell (2), and silica nanoparticles with a bioreducible PEG shell and a branched poly(amido amine) nanoshell (HPAA-1) (3). C) The sizes the silica nanoparticles with a bioreducible nanoshell (a) and the silica nanoparticles with a bioreducible PEG-based nanoshell and a second HPAA-1 nanoshell (b).
nanoparticles (Figure 3). It should be noted that all the procedure was carried out at 45 °C, this temperature can facilitate the inter-nanoparticles crosslinking, and the small polymer nanoparticles absorbed on the surface can not be cross-linked at temperatures below 30 °C. Furthermore, there is no nanoshell formation on the surface if the experiment was carried out under pH of 7.0 at 45 °C due to there is no polymer aggregations formed at pH of
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Figure 3. A) TEM images of silica nanoparticles. B) TEM images of silica nanoparticles with a poly(amido amine) (HPAA-2) shell.
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Stimuli-Triggered Growth and Removal of a Bioreducible Nanoshell on Nanoparticles
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7.0 (see Figure S14, Supporting Information). Hence, pH can be used a stimulus to induce the growth of a bioreducible shell on nanoparticles. Glutathione is present in extracellular milieu with several micromolar concentration, and disulfide bond is stable in extracellular milieu; however, the glutathione concentration in intracellular environments is 50–1000 times higher than that in extracellular milieu, and disulfide bond can be easily cleaved in intracellular environments.[9] Therefore, disulfidecrosslinked shell on liposomes can keep their structure stable in the extracytoplasmic environment, while inducing break of the disulfidecrosslinked shell after their movement into the cytoplasmic compartment. Liposme can act a vector of DNA,[10] but it is not stable in extracellular milieu. Here, we can grow a bioreducible PEG shell on liposomes via using above method. The bioreducible shell around liposome will make liposome stable in extracytoplasmic environment while the shell can degrade after its movement into the cytoplasmic compartFigure 4. A) In vitro gene transfection activities of polyplexes and polyplexes with a ment, inducing the efficient release bioreducible cross-linked shell in the presence of 10% serum. B) In vivo gene transfection activities of liposome and liposome with a bioreducible cross-linked shell. of payloads, and hence in vivo, the liposomes with a bioreducible crosslinked PEG shell will have a remarkable improvement Supporting Information of gene transfection activity. Therefore, temperature is Supporting Information is available from the Wiley Online used to trigger the growth of bioreducible cross-linked Library or from the author. PEG shell on liposomes, GSH, or DTT can remove the cross-linked PEG shell from liposome (Figure S15, SupAcknowledgements: Financial support from National Natural porting Information). The results show that liposome Science Foundation of China (51033005, 21074121, 21090354 and with a PEG shell has higher transfection activity than 21374107) and the Program for New Century Excellent Talents in those without a cross-linked PEG shell in vitro and in Universities (NCET-08–0520) is gratefully acknowledged. vivo (Figure 4). Received: December 1, 2013; Revised: December 26, 2013; Published online: February 4, 2014; DOI: 10.1002/marc.201300885
4. Conclusions Stimulus-triggered growth of a polymer shell on nanoparticles is reported based on stimulus-induced self-assembly and self-cross-linking of disulfide-contained branched polymers; furthermore, the template is dissolved away to leave a bioreducible nanocapsule. This method provides an easy and versatile method to grow a biocompatible shell on nanoparticles without pre-modifying the surface of nanoparticles, which will have many potential applications in biomedicine.
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Keywords: bioreducible nanoshell; branched polymer; nanoparticle; pH-responsive; temperature-responsive
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