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2018 Volume Issue 8
2018, 0(8): 959-972
doi: 10.11777/j.issn1000-3304.2018.18102
Abstract:
Self-assembly of block copolymers, which are composed of covalently connected incompatible polymer chains, can result in various ordered structures at the nanometer scale. This phenomenon, widely known as the microphase separation of block copolymers, may provide a technological platform for the development of next-generation nanopatterning techniques based on the " top-down” strategy. During the past decade, a unique class of novel amphiphilic macromolecules termed as giant surfactants have been reported, which are constructed from selected building blocks of cluster-like molecules having three-dimensional rigid conformations and nanometer sizes. By combining different " click-type” reactions, a highly efficient and modular synthetic method has been developed to prepare covalent conjugates of these molecular clusters and polymer chains. The resulting giant surfactants can be viewed as structural analogues of common block copolymers, and similarly, they also display interesting self-assembly behaviors both in solutions and in bulk. Herein, recent advances on the study of self-assembly of giant surfactants are summarized, with a particular emphasis on the molecular topology effects that can significantly change their self-assembly behaviors. As revealed by small angle X-ray scattering and transmission electron microscopy techniques, giant surfactants were able to self-assemble in bulk to form a series of highly ordered nanostructures with feature sizes below 10 nm or even 5 nm, with clearly shifted phase boundaries. More importantly, through rational molecular design to tune the molecular topology of giant surfactants, formation of some unusual nanostructures driven by molecular topological variations was achieved. Typical examples include several unconventional spherical phases, such as the Frank-Kasper A15 phase, the Frank-Kasper σ phase, and a quasicrystalline spherical phase, which were observed in multitailed giant surfactants, and a highly asymmetric lamellar phase formed by self-assembly of multiheaded giant surfactants. It is believed that these studies provide not only insights towards understanding the molecular topological effects in macromolecular self-assembly, but also experimental foundation for the development of block copolymer lithography that can afford nanostructures with sub-10-nm feature sizes.
Self-assembly of block copolymers, which are composed of covalently connected incompatible polymer chains, can result in various ordered structures at the nanometer scale. This phenomenon, widely known as the microphase separation of block copolymers, may provide a technological platform for the development of next-generation nanopatterning techniques based on the " top-down” strategy. During the past decade, a unique class of novel amphiphilic macromolecules termed as giant surfactants have been reported, which are constructed from selected building blocks of cluster-like molecules having three-dimensional rigid conformations and nanometer sizes. By combining different " click-type” reactions, a highly efficient and modular synthetic method has been developed to prepare covalent conjugates of these molecular clusters and polymer chains. The resulting giant surfactants can be viewed as structural analogues of common block copolymers, and similarly, they also display interesting self-assembly behaviors both in solutions and in bulk. Herein, recent advances on the study of self-assembly of giant surfactants are summarized, with a particular emphasis on the molecular topology effects that can significantly change their self-assembly behaviors. As revealed by small angle X-ray scattering and transmission electron microscopy techniques, giant surfactants were able to self-assemble in bulk to form a series of highly ordered nanostructures with feature sizes below 10 nm or even 5 nm, with clearly shifted phase boundaries. More importantly, through rational molecular design to tune the molecular topology of giant surfactants, formation of some unusual nanostructures driven by molecular topological variations was achieved. Typical examples include several unconventional spherical phases, such as the Frank-Kasper A15 phase, the Frank-Kasper σ phase, and a quasicrystalline spherical phase, which were observed in multitailed giant surfactants, and a highly asymmetric lamellar phase formed by self-assembly of multiheaded giant surfactants. It is believed that these studies provide not only insights towards understanding the molecular topological effects in macromolecular self-assembly, but also experimental foundation for the development of block copolymer lithography that can afford nanostructures with sub-10-nm feature sizes.
2018, 0(8): 973-986
doi: 10.11777/j.issn1000-3304.2018.18065
Abstract:
Side-chain liquid crystalline polymer (SCLCP) can form columnar liquid crystalline (LC) phases, in addition to the conventional nematic and smectic phase. For the SCLCP containing the discotic mesogenic group attached to the main-chain through a flexible spacer, the columnar phase relies on the assembly of the discotic mesogens. On the other hand, the SCLCP with extended conformation, such as mesogen-jacketed LC polymers and dendronized polymers, can exhibit the columnar phase based on the parallel packing of the cylindrical chains. In this case, " single chain column” is considered to be the building block of the columnar phase in general. Recently, our work on hemiphasmid SCLCP demonstrates that the " multi-chain column” is also important for the columnar phases of SCLCP. Hemiphasmid SCLCP possesses the hemiphasmid side-chain composed of a rod-like mesogen linked with a half-disk end group. It can readily self-organize into columnar phases with a pretty lager lattice parameter (e.g., 5 – 10 nm). It is found that the number of repeating units (Zrep) packed in a column stratum with a thickness of ~ 0.4 nm is surprisingly large. As an example, for the hexagonal columnar phase with the a parameter of ~ 6 nm, the value of Zrep is ~ 10. Squeezing a chain segment with 10 repeating units into the 0.4 nm-thick column stratum is physically unreasonable. The " unusual Zrep” indicates the existence of " multi-chain column” that consists of a bundle of chains (e.g., 4 – 5 chains) laterally associated together. We synthesized a series of hemiphasmid SCLCPs with different chemical structures. Various main-chains have been employed, including polystyrene, poly(methacrylate), polyacetylene, and polynorbornene. The hemiphasmid moieties can invoke different rod-like mesogens, and can be attached to the main-chain directly or via a flexible spacer. For all the samples obtained, we have verified that the " multi-chain column” is applicable. The formation of " multi-chain column” can be understood from the nano-segregation among the main-chain, the rod-like mesogen and the flexible tails. Theoretical analysis indicates that the " multi-chain column” is a structure of thermodynamic equilibrium. The number of chains in the column is dependent on the volume fraction of the rigid component of the SCLCP. We propose that the chains in the column can interlock and intertwine, resulting in the intra-column entanglement. This hypothesis is supported by the study of hemiphasmid side-chain polynorbornene, which illustrates that the intra-column entanglement can endow the polymer with properties of thermoplastic elastomer. Moreover, the polymer can further exhibit excellent multi-shape memory effect at high strain. We anticipate that the further study of the " multi-chain column”, which has been overlooked for years, will deepen our understanding of some fundamental issues of the structure and dynamics of polymers, and will also help to explore the new properties and applications of SCLCPs.
Side-chain liquid crystalline polymer (SCLCP) can form columnar liquid crystalline (LC) phases, in addition to the conventional nematic and smectic phase. For the SCLCP containing the discotic mesogenic group attached to the main-chain through a flexible spacer, the columnar phase relies on the assembly of the discotic mesogens. On the other hand, the SCLCP with extended conformation, such as mesogen-jacketed LC polymers and dendronized polymers, can exhibit the columnar phase based on the parallel packing of the cylindrical chains. In this case, " single chain column” is considered to be the building block of the columnar phase in general. Recently, our work on hemiphasmid SCLCP demonstrates that the " multi-chain column” is also important for the columnar phases of SCLCP. Hemiphasmid SCLCP possesses the hemiphasmid side-chain composed of a rod-like mesogen linked with a half-disk end group. It can readily self-organize into columnar phases with a pretty lager lattice parameter (e.g., 5 – 10 nm). It is found that the number of repeating units (Zrep) packed in a column stratum with a thickness of ~ 0.4 nm is surprisingly large. As an example, for the hexagonal columnar phase with the a parameter of ~ 6 nm, the value of Zrep is ~ 10. Squeezing a chain segment with 10 repeating units into the 0.4 nm-thick column stratum is physically unreasonable. The " unusual Zrep” indicates the existence of " multi-chain column” that consists of a bundle of chains (e.g., 4 – 5 chains) laterally associated together. We synthesized a series of hemiphasmid SCLCPs with different chemical structures. Various main-chains have been employed, including polystyrene, poly(methacrylate), polyacetylene, and polynorbornene. The hemiphasmid moieties can invoke different rod-like mesogens, and can be attached to the main-chain directly or via a flexible spacer. For all the samples obtained, we have verified that the " multi-chain column” is applicable. The formation of " multi-chain column” can be understood from the nano-segregation among the main-chain, the rod-like mesogen and the flexible tails. Theoretical analysis indicates that the " multi-chain column” is a structure of thermodynamic equilibrium. The number of chains in the column is dependent on the volume fraction of the rigid component of the SCLCP. We propose that the chains in the column can interlock and intertwine, resulting in the intra-column entanglement. This hypothesis is supported by the study of hemiphasmid side-chain polynorbornene, which illustrates that the intra-column entanglement can endow the polymer with properties of thermoplastic elastomer. Moreover, the polymer can further exhibit excellent multi-shape memory effect at high strain. We anticipate that the further study of the " multi-chain column”, which has been overlooked for years, will deepen our understanding of some fundamental issues of the structure and dynamics of polymers, and will also help to explore the new properties and applications of SCLCPs.
2018, 0(8): 987-996
doi: 10.11777/j.issn1000-3304.2018.18083
Abstract:
Given the unique properties and functions, such as bioactivity and good biocompatibility, the self-assembly of peptide, specially amphipathic peptide, and their applications have become the research focus in the fields of supermolecular chemistry as well as functional polymeric and biomedical materials. Generally, most of peptide building blocks are prepared from chemical synthesis such as solid phase peptide synthesis, or genetic engineering. Those " bottom up” methods may be suffered by time consuming and cost, which limit the practical application of assembly peptides materials. Degradation of natural proteins such as casein, corn protein and so on, provides us a convenient way to obtain the mixed peptides. However, most of researches about these mixtures are focused on their bio-functions or surfactant property. The usage of them as building blocks of assembly peptide is overlooked. Silk fibroin from Bombyx mori silkworm silk is with highly repetitive sequences, such as GAGAGY and GAGAGS, their different assembly properties and the relevant structures not only play an important role in the forming of animal silks and silk fibroin based materials, but also have crucial effect on their excellent comprehensive performance. According to the selectivity of different enzymes, there are enzymes which work on the Tyr-Gly or Ala-Gly peptide bone, respectively. Therefore, it provides us the opportunity to harvest the silk peptides with special sequence economically via degrading silk fibroin by those enzymes. We introduced in this paper the enzymatic degradation, a " top down” method on obtaining peptide with specific sequences from silk fibroin and investigated their assembly properties. In addition, we summarized the construction of functionalization amphiphilic peptides with one of those silk peptides (GAGAGAGY) as building block as well as their assembly and applications like the forming pH responsive peptide hydrogel, flexible thermochromism materials and unique peptide surfactant. Finally, we prospected the application of top down method on obtaining functional peptide building blocks as well as application of the silk peptide obtained by this way on construction functional peptides.
Given the unique properties and functions, such as bioactivity and good biocompatibility, the self-assembly of peptide, specially amphipathic peptide, and their applications have become the research focus in the fields of supermolecular chemistry as well as functional polymeric and biomedical materials. Generally, most of peptide building blocks are prepared from chemical synthesis such as solid phase peptide synthesis, or genetic engineering. Those " bottom up” methods may be suffered by time consuming and cost, which limit the practical application of assembly peptides materials. Degradation of natural proteins such as casein, corn protein and so on, provides us a convenient way to obtain the mixed peptides. However, most of researches about these mixtures are focused on their bio-functions or surfactant property. The usage of them as building blocks of assembly peptide is overlooked. Silk fibroin from Bombyx mori silkworm silk is with highly repetitive sequences, such as GAGAGY and GAGAGS, their different assembly properties and the relevant structures not only play an important role in the forming of animal silks and silk fibroin based materials, but also have crucial effect on their excellent comprehensive performance. According to the selectivity of different enzymes, there are enzymes which work on the Tyr-Gly or Ala-Gly peptide bone, respectively. Therefore, it provides us the opportunity to harvest the silk peptides with special sequence economically via degrading silk fibroin by those enzymes. We introduced in this paper the enzymatic degradation, a " top down” method on obtaining peptide with specific sequences from silk fibroin and investigated their assembly properties. In addition, we summarized the construction of functionalization amphiphilic peptides with one of those silk peptides (GAGAGAGY) as building block as well as their assembly and applications like the forming pH responsive peptide hydrogel, flexible thermochromism materials and unique peptide surfactant. Finally, we prospected the application of top down method on obtaining functional peptide building blocks as well as application of the silk peptide obtained by this way on construction functional peptides.
2018, 0(8): 997-1015
doi: 10.11777/j.issn1000-3304.2018.18084
Abstract:
Some amphiphilic copolymers in water can undergo a reversible sol-gel transition upon heating. If the transition temperature lies between room temperature and body temperature, the aqueous system can be readily mixed with drugs or cells at room temperature, and the mixture is injectable; the injected formulation is physically gelled at body temperature, and the gelation is free of any chemical crosslinking. This affords an amazing biomaterial type, yet many questions are open in light of fundamental research and potential clinical applications. In particular, block copolymers composed of hydrophilic poly(ethylene glycol) (PEG) and some hydrophobic biodegradable polyesters such as poly(lactide-co-glycolide) (PLGA) are of great clinical potential, yet of very unclear physical crosslinking points. This feature article summarizes the corresponding extensive investigations in the authors’ group led by Ding at Fudan University for a decade. The Ding group has found the significant effects of the end groups of the copolymer, molar mass dispersity ÐM, and other molecular parameters on thermogellability, and revealed the corresponding rules of molecular design, based on their polymer chemistry studies. For instance, with increase in ÐM under either given number average or weight average molecule weight, the sol-gel transition temperature for some block copolymer aqueous systems could shift unidirectionally, which indicates that the effect of molecular weight distribution could not be interpreted simply from addition of the effects of molecular weight or ÐM affords an independent adjustable parameter. The Ding group has shed light on the mechanism of their thermogelling by putting forward the model of percolated micelle network to describe the internal structure of the physical hydrogel, and extended the range of the thermogellable molecular composition of the copolymers to a large extent by establishing a blend strategy, based on their polymer physics studies. The Ding group have also put forward many strategies for the clinical applications of the thermogels using animal models, including prevention of postoperative tissue adhesion, submucosal cushion for endoscopic submucosal dissection, sustained release carriers of antitumor drugs such as camptothecin derivatives, long-acting formulations of polypeptide drugs such as exenatide in treatment of type II diabetes, and tissue engineering of cartilage. The Ding group has also laid a material basis towards potential products of medical devices and drug carriers including the appropriate way of sterilization and improvement of the handling property of the synthesized polymers. The Ding group suggest some perspectives in the end of this feather article.
Some amphiphilic copolymers in water can undergo a reversible sol-gel transition upon heating. If the transition temperature lies between room temperature and body temperature, the aqueous system can be readily mixed with drugs or cells at room temperature, and the mixture is injectable; the injected formulation is physically gelled at body temperature, and the gelation is free of any chemical crosslinking. This affords an amazing biomaterial type, yet many questions are open in light of fundamental research and potential clinical applications. In particular, block copolymers composed of hydrophilic poly(ethylene glycol) (PEG) and some hydrophobic biodegradable polyesters such as poly(lactide-co-glycolide) (PLGA) are of great clinical potential, yet of very unclear physical crosslinking points. This feature article summarizes the corresponding extensive investigations in the authors’ group led by Ding at Fudan University for a decade. The Ding group has found the significant effects of the end groups of the copolymer, molar mass dispersity ÐM, and other molecular parameters on thermogellability, and revealed the corresponding rules of molecular design, based on their polymer chemistry studies. For instance, with increase in ÐM under either given number average or weight average molecule weight, the sol-gel transition temperature for some block copolymer aqueous systems could shift unidirectionally, which indicates that the effect of molecular weight distribution could not be interpreted simply from addition of the effects of molecular weight or ÐM affords an independent adjustable parameter. The Ding group has shed light on the mechanism of their thermogelling by putting forward the model of percolated micelle network to describe the internal structure of the physical hydrogel, and extended the range of the thermogellable molecular composition of the copolymers to a large extent by establishing a blend strategy, based on their polymer physics studies. The Ding group have also put forward many strategies for the clinical applications of the thermogels using animal models, including prevention of postoperative tissue adhesion, submucosal cushion for endoscopic submucosal dissection, sustained release carriers of antitumor drugs such as camptothecin derivatives, long-acting formulations of polypeptide drugs such as exenatide in treatment of type II diabetes, and tissue engineering of cartilage. The Ding group has also laid a material basis towards potential products of medical devices and drug carriers including the appropriate way of sterilization and improvement of the handling property of the synthesized polymers. The Ding group suggest some perspectives in the end of this feather article.
2018, 0(8): 1016-1032
doi: 10.11777/j.issn1000-3304.2018.18020
Abstract:
Self-assembly from block copolymers is a bottom-up process, a relatively inexpensive and simple approach for the preparation of large-scale nano-patterns. This self-assembly from diblock copolymers is driven by the combination of repulsive and attractive interactions due to the covalent bond linkage. The intrinsic immiscibility or incompatibility among the A or B block segments possesses the repulsive force and then confines into nanoscaled domain through the microphase separation because of the attractive force from the covalent bond linkage of A and B block segments. In general, these diblock copolymers can form different well-defined nanostructures in the bulk state including alternative lamellae, bicontinuous double gyroid, hexagonally packed cylinder, and body-centered cubic (BCC) structures, depending on the relative volume fractions of the block copolymer segments, interaction parameters (χ), and degrees of polymerization (N). However, the preparation of block copolymers with controlled volume fraction would be complicated and time-consuming; thus the diblock copolymers (A-b-B) blending with their homopolymer or low-molecular-weight compound would be an easier method for preparing different self-assembled nanostructures. Therefore, self-assembly nanostructures of block copolymer mixtures through mediated hydrogen bonding interactions have attracted much interest in polymer science because of their potential applications in photonic, electronic and biomedical fields, which could offer the unique possibility to create new functional polymeric materials with tunable and responsive behaviors. In this review article, we describe the self-assembly nanostructure of the block copolymer mixtures including block copolymer/low molecular weight compound, block copolymer/homopolymer, and block copolymer/block copolymer mixtures in bulk and solution states by mediated hydrogen bonding strength. Mediated strength of hydrogen bonding in block copolymer blending with homopolymer or block copolymer could provide order-order phase transition from typical lamellar, double gyroid, cylinder, and BCC spherical structure, even various hierarchical self-assembly structures such as three-phase lamellae, core-shell cylinder, and cylinder in lamellae structures in bulk state. Furthermore, it also possesses the different micellar structures of block copolymer mixtures such as spheres, rods, vesicles, and even large compound micelles in solution state.
Self-assembly from block copolymers is a bottom-up process, a relatively inexpensive and simple approach for the preparation of large-scale nano-patterns. This self-assembly from diblock copolymers is driven by the combination of repulsive and attractive interactions due to the covalent bond linkage. The intrinsic immiscibility or incompatibility among the A or B block segments possesses the repulsive force and then confines into nanoscaled domain through the microphase separation because of the attractive force from the covalent bond linkage of A and B block segments. In general, these diblock copolymers can form different well-defined nanostructures in the bulk state including alternative lamellae, bicontinuous double gyroid, hexagonally packed cylinder, and body-centered cubic (BCC) structures, depending on the relative volume fractions of the block copolymer segments, interaction parameters (χ), and degrees of polymerization (N). However, the preparation of block copolymers with controlled volume fraction would be complicated and time-consuming; thus the diblock copolymers (A-b-B) blending with their homopolymer or low-molecular-weight compound would be an easier method for preparing different self-assembled nanostructures. Therefore, self-assembly nanostructures of block copolymer mixtures through mediated hydrogen bonding interactions have attracted much interest in polymer science because of their potential applications in photonic, electronic and biomedical fields, which could offer the unique possibility to create new functional polymeric materials with tunable and responsive behaviors. In this review article, we describe the self-assembly nanostructure of the block copolymer mixtures including block copolymer/low molecular weight compound, block copolymer/homopolymer, and block copolymer/block copolymer mixtures in bulk and solution states by mediated hydrogen bonding strength. Mediated strength of hydrogen bonding in block copolymer blending with homopolymer or block copolymer could provide order-order phase transition from typical lamellar, double gyroid, cylinder, and BCC spherical structure, even various hierarchical self-assembly structures such as three-phase lamellae, core-shell cylinder, and cylinder in lamellae structures in bulk state. Furthermore, it also possesses the different micellar structures of block copolymer mixtures such as spheres, rods, vesicles, and even large compound micelles in solution state.
2018, 0(8): 1033-1047
doi: 10.11777/j.issn1000-3304.2018.18050
Abstract:
Gold nanostructures with unique optical, electrical and catalytic properties have found widespread use in diverse fields ranging from optics and sensing to nanomedicine and catalysis. There is growing interest in self-assembly of gold nanostructures because their localized surface plasmon resonance undergoes strongly interparticle coupling in close proximity, leading to collective properties that are distinctively different from that of individual building blocks. Considerable progress has been made in tailored synthesis of gold nanostructures and surface-engineering approaches to introduce functional coatings on the nanostructures, giving rise to nanoscale building blocks with defined structural parameters and properties, which make them excellent model systems to study the self-assembly of nanoparticles driven by functiona coatings. Polymers, especially amphiphilic block copolymers, exhibit intrinsic self-assembly in solution and bulk phase. Accumulated evidence has demonstrated that both molecular structures of the polymers and self-assembly conditions have a key impact on the structures formed by self-assembly, producing a wide spectrum of structures such as spherical micelles, cylindrical micelles, lamellae, and vesicles. As such, polymer coatings, which are commonly explored to impart colloidal stability of nanostructures, have emerged as an intriguing class of functional coatings to direct their self-assembly. The ability to tailor the structural details of the polymer coatings such as molecular weight, graft density and amphiphilicity is key to achieve controlled morphology and functionality of the resultant plasmonic assemblies. In this review, we summarize current strategies for constructing well-defined Au nanoparticle building blocks including " one-pot synthesis”, " grafting to”, and " grafting from” strategies. Based on these methods, assemblies of polymer-decorated nanoparticles were designed and formed across multiple dimensions, which brings about potential applications resulting from emerging optical, electronic, and catalytic properties. A protypical example is surface-enhanced Raman scattering (SERS) which is greatly amplified in the interstitial space of the assemblies because of interparticle plasmonic coupling, providing a transduction mechanism for ultrasensitve detection. The ability of dissipating the energy of light irradiate through the combination of photothermal conversion and Mie-scattering makes it possible for the assemblies of Au nanoparticles to serve as imaging probes and therapeutic agents. Representative assemblies of Au nanoparticles, that have shown potentials for sensing and biomedicine, are highlighted in this review. We also emphasize the fundamental and technical challenges for precise control over polymer-guided self-assembly of gold nanoparticles. The combination of simulation and experiment open the avenue to a systematic understanding on the self-assembly of nanoparticles.
Gold nanostructures with unique optical, electrical and catalytic properties have found widespread use in diverse fields ranging from optics and sensing to nanomedicine and catalysis. There is growing interest in self-assembly of gold nanostructures because their localized surface plasmon resonance undergoes strongly interparticle coupling in close proximity, leading to collective properties that are distinctively different from that of individual building blocks. Considerable progress has been made in tailored synthesis of gold nanostructures and surface-engineering approaches to introduce functional coatings on the nanostructures, giving rise to nanoscale building blocks with defined structural parameters and properties, which make them excellent model systems to study the self-assembly of nanoparticles driven by functiona coatings. Polymers, especially amphiphilic block copolymers, exhibit intrinsic self-assembly in solution and bulk phase. Accumulated evidence has demonstrated that both molecular structures of the polymers and self-assembly conditions have a key impact on the structures formed by self-assembly, producing a wide spectrum of structures such as spherical micelles, cylindrical micelles, lamellae, and vesicles. As such, polymer coatings, which are commonly explored to impart colloidal stability of nanostructures, have emerged as an intriguing class of functional coatings to direct their self-assembly. The ability to tailor the structural details of the polymer coatings such as molecular weight, graft density and amphiphilicity is key to achieve controlled morphology and functionality of the resultant plasmonic assemblies. In this review, we summarize current strategies for constructing well-defined Au nanoparticle building blocks including " one-pot synthesis”, " grafting to”, and " grafting from” strategies. Based on these methods, assemblies of polymer-decorated nanoparticles were designed and formed across multiple dimensions, which brings about potential applications resulting from emerging optical, electronic, and catalytic properties. A protypical example is surface-enhanced Raman scattering (SERS) which is greatly amplified in the interstitial space of the assemblies because of interparticle plasmonic coupling, providing a transduction mechanism for ultrasensitve detection. The ability of dissipating the energy of light irradiate through the combination of photothermal conversion and Mie-scattering makes it possible for the assemblies of Au nanoparticles to serve as imaging probes and therapeutic agents. Representative assemblies of Au nanoparticles, that have shown potentials for sensing and biomedicine, are highlighted in this review. We also emphasize the fundamental and technical challenges for precise control over polymer-guided self-assembly of gold nanoparticles. The combination of simulation and experiment open the avenue to a systematic understanding on the self-assembly of nanoparticles.
2018, 0(8): 1048-1065
doi: 10.11777/j.issn1000-3304.2018.18064
Abstract:
At the end of the last century, Professor Jiang Ming et al. succeeded in fabricating regular nanostructures through localizing interactions in the systems of polymer complexes. Through continuous expansion and deepening of this principle and method, a new strategy of macromolecular self-assembly was established. This review summarizes recent developments and applications of non-covalently connected micelles (NCCMs), including: Introducing of new driving forces such as supramolecular interactions to drive the formation of NCCMs, providing the resultant NCCMs with new features and functions; Applying the principle to the self-assembly of biological macromolecules, thereby developing an entirely green route to self-assembly of macromolecules; Also, through localizing covalent crosslinking reaction of one block of a diblock copolymer, we realized micellization of the block copolymer in its common solvent induced by the crosslinking reaction, resulting in highly efficient fabrication of core-stabilized micelles as well as a new pathway for controlling the kinetics of polymer micellization, the structures and the properties of the polymeric micelles.
At the end of the last century, Professor Jiang Ming et al. succeeded in fabricating regular nanostructures through localizing interactions in the systems of polymer complexes. Through continuous expansion and deepening of this principle and method, a new strategy of macromolecular self-assembly was established. This review summarizes recent developments and applications of non-covalently connected micelles (NCCMs), including: Introducing of new driving forces such as supramolecular interactions to drive the formation of NCCMs, providing the resultant NCCMs with new features and functions; Applying the principle to the self-assembly of biological macromolecules, thereby developing an entirely green route to self-assembly of macromolecules; Also, through localizing covalent crosslinking reaction of one block of a diblock copolymer, we realized micellization of the block copolymer in its common solvent induced by the crosslinking reaction, resulting in highly efficient fabrication of core-stabilized micelles as well as a new pathway for controlling the kinetics of polymer micellization, the structures and the properties of the polymeric micelles.
2018, 0(8): 1066-1072
doi: 10.11777/j.issn1000-3304.2018.17233
Abstract:
An amine group capped Fe3O4 nanoparticle (NP) (~ 10 nm) is derived after ligand exchange with a silane against the oleic acid capped Fe3O4 NP. Via the termination between the cationic end of a living polymer chain with the amine group onto the NP surface, polymer chains are covalently grafted onto the NP surface, forming the polymer/Fe3O4 composite NP. The number of the grafted living polymer chains is determined by the molecular weight of the polymer chains. When a sufficiently long polymer chain with hydrodynamic size larger than the NP diameter is used, the arisen steric repulsion enables only one polymer chain to graft onto the NP surface. The obtained composite NP displays a parachute structure due to the distribution of the grafting polymer chain on one side of the modified Fe3O4 NP surface. When a short polymer chain is used, many chains can graft onto the NP surface to form a core/shell like structure. For example, the single poly(4-vinylbenzyl chloride) chain grafted an amine group capped Fe3O4 composite Janus NP is amphiphilic, which can serve as a functional solid emulsifier that can easily emulsify water/toluene to obtain a stabilized emulsion. In analogy of a molecular surfactant, a self-assembled monolayer from the composite NPs is achieved by crosslinking the composite NPs at a water/oil interface. The Fe3O4 composite Janus NPs can be manipulated with a magnet. Accordingly, the stabilized emulsion droplets emulsified by the composite Janus NPs can be driven with a magnet. This report provides a simple method to massively synthesize Janus NPs at a high solid content. In addition, a huge family of functional Janus NPs will be derived after selective growth of functional species from either poly(4-vinylbenzyl chloride) or (and) the amine group capped side of the parent composite NP.
An amine group capped Fe3O4 nanoparticle (NP) (~ 10 nm) is derived after ligand exchange with a silane against the oleic acid capped Fe3O4 NP. Via the termination between the cationic end of a living polymer chain with the amine group onto the NP surface, polymer chains are covalently grafted onto the NP surface, forming the polymer/Fe3O4 composite NP. The number of the grafted living polymer chains is determined by the molecular weight of the polymer chains. When a sufficiently long polymer chain with hydrodynamic size larger than the NP diameter is used, the arisen steric repulsion enables only one polymer chain to graft onto the NP surface. The obtained composite NP displays a parachute structure due to the distribution of the grafting polymer chain on one side of the modified Fe3O4 NP surface. When a short polymer chain is used, many chains can graft onto the NP surface to form a core/shell like structure. For example, the single poly(4-vinylbenzyl chloride) chain grafted an amine group capped Fe3O4 composite Janus NP is amphiphilic, which can serve as a functional solid emulsifier that can easily emulsify water/toluene to obtain a stabilized emulsion. In analogy of a molecular surfactant, a self-assembled monolayer from the composite NPs is achieved by crosslinking the composite NPs at a water/oil interface. The Fe3O4 composite Janus NPs can be manipulated with a magnet. Accordingly, the stabilized emulsion droplets emulsified by the composite Janus NPs can be driven with a magnet. This report provides a simple method to massively synthesize Janus NPs at a high solid content. In addition, a huge family of functional Janus NPs will be derived after selective growth of functional species from either poly(4-vinylbenzyl chloride) or (and) the amine group capped side of the parent composite NP.
2018, 0(8): 1073-1080
doi: 10.11777/j.issn1000-3304.2018.17319
Abstract:
Multifunctional magnetic nano-carriers, with high saturation magnetization, high drug-loading and rapid response for external magnetic field, have been widely applied in biomedical fields, such as bioimaging, targeting therapy, diagnostics and so on. In this study, a new efficient way for superficial modification of magnetic composite microspheres based on strong interaction between gold nanoparticles and thiol compounds was explored. Using the distilled-precipitation polymerization technique, we firstly constructed magnetic composite microspheres, (MSP@P(MAA-Cy), with acid-dissolvable magnetic supraparticles (MSP) as the core and a redox-degradable poly(methylacrylic acid-co-N,N-bis(acryloyl)cystamine) (P(MAA-Cy) as the shell, gold nanoparticles (AuNP) with the size of 10 − 30 nm were then deposited onto the surface of the MSP@P(MAA-Cy) microspheres. Through control of the reaction parameters in the distilled-precipitation polymerization, uniform polymer shell with the thickness of 30 − 40 nm was obtained. In addition, the amount and the size of the AuNP particle on the surface of MSP@P(MAA-Cy) microspheres could be adjusted by manipulating the ratio of the raw materials and reaction parameters. With an increase in the feeding amount of gold precursor, i.e. the feeding molar ratio of HAuCl4 to sodium citrate dihydrate (keep constant in all recipes) changed from 1:20 to 1:5, the particle size of the AuNP increased. Meanwhile, prolonging reaction time also could increase the density and particle szie of the AuNP. Due to the strong interaction between the thiol-modified fluorescent ligands and gold nanoparticles on the surface of MSP@P(MAA-Cy)-AuNP, single or dual fluorescent ligands (FA-PEG-SH and Rho-PEG-SH) could be easily assembled onto the surface of the magnetic polymer composite microspheres by one-step reaction, and the amount of the fluorescent ligands regulated by a convenient and fast way, which should give a new stratagy for onsite-assembly of functional ligands on the surface of magnetic composite microspheres without any post-treatment for personalized targeting cancer therapy.
Multifunctional magnetic nano-carriers, with high saturation magnetization, high drug-loading and rapid response for external magnetic field, have been widely applied in biomedical fields, such as bioimaging, targeting therapy, diagnostics and so on. In this study, a new efficient way for superficial modification of magnetic composite microspheres based on strong interaction between gold nanoparticles and thiol compounds was explored. Using the distilled-precipitation polymerization technique, we firstly constructed magnetic composite microspheres, (MSP@P(MAA-Cy), with acid-dissolvable magnetic supraparticles (MSP) as the core and a redox-degradable poly(methylacrylic acid-co-N,N-bis(acryloyl)cystamine) (P(MAA-Cy) as the shell, gold nanoparticles (AuNP) with the size of 10 − 30 nm were then deposited onto the surface of the MSP@P(MAA-Cy) microspheres. Through control of the reaction parameters in the distilled-precipitation polymerization, uniform polymer shell with the thickness of 30 − 40 nm was obtained. In addition, the amount and the size of the AuNP particle on the surface of MSP@P(MAA-Cy) microspheres could be adjusted by manipulating the ratio of the raw materials and reaction parameters. With an increase in the feeding amount of gold precursor, i.e. the feeding molar ratio of HAuCl4 to sodium citrate dihydrate (keep constant in all recipes) changed from 1:20 to 1:5, the particle size of the AuNP increased. Meanwhile, prolonging reaction time also could increase the density and particle szie of the AuNP. Due to the strong interaction between the thiol-modified fluorescent ligands and gold nanoparticles on the surface of MSP@P(MAA-Cy)-AuNP, single or dual fluorescent ligands (FA-PEG-SH and Rho-PEG-SH) could be easily assembled onto the surface of the magnetic polymer composite microspheres by one-step reaction, and the amount of the fluorescent ligands regulated by a convenient and fast way, which should give a new stratagy for onsite-assembly of functional ligands on the surface of magnetic composite microspheres without any post-treatment for personalized targeting cancer therapy.
2018, 0(8): 1081-1088
doi: 10.11777/j.issn1000-3304.2018.18009
Abstract:
Amphiphilic macromolecular brushes with pH-responsiveness and reduction responsiveness were synthesized by reversible addition-fragmentation chain transfer polymerization and atom transfer radical polymerization. The side chains of the brush polymers were covalently connected to the backbones through redox-responsive disulfide bonds. The structure, molecular weight and molecular weight distribution of the brush polymers were characterized by 1H-NMR and gel permeation chromatography. At pH = 10.0, the amphiphilic brush polymers self-assembled into multi-component micelles with POEGMA shells and PtBMA/PDMAEMA cores. In the cores, the two hydrophobic blocks segregated into distinct domains due to their incompatibility, and the hydrophilic POEGMA blocks formed the coronae to stabilize the structures. The PtBMA chains with larger volume percentage formed the continuous phases, while the PDMAEMA chains with smaller volume percentage formed the discontinuous phases. At pH = 4.0, protonated PDMAEMA chains were highly stretched and formed the coronae of the micelles. Excessive reductant was added into the micellar solution to reduce the disulfide bonds between PDMAEMA side chains and the backbones, and mesoporous polymeric micelles with thiol groups inside the pores were obtained. 1H-NMR results of multi-component micelles, before and after treatment with the reductant, indicated that the PDMAEMA side chains were removed completely. Transmission electron microscopy (TEM) and dynamic light scattering were used to characterize the morphology and the size of the micelles. Based on TEM results, the average size of the pores in the micelles was about 2 nm, which was consistent with the average size of the PDMAEMA discontinuous phases. After the cleavage of the disulfide bonds and the removal of PDMAEMA chains from the micelles, thiol groups were produced on the walls of the pores. The thiol groups can be used as reducing agent and stabilizer in the in situ synthesis of gold nanoparticles. By thiol-bromine reactions, mesoporous micelles with polythiophene derivatives inside the pores were synthesized. The micelles showed high sensitivity and excellent selectivity for Hg2+.
Amphiphilic macromolecular brushes with pH-responsiveness and reduction responsiveness were synthesized by reversible addition-fragmentation chain transfer polymerization and atom transfer radical polymerization. The side chains of the brush polymers were covalently connected to the backbones through redox-responsive disulfide bonds. The structure, molecular weight and molecular weight distribution of the brush polymers were characterized by 1H-NMR and gel permeation chromatography. At pH = 10.0, the amphiphilic brush polymers self-assembled into multi-component micelles with POEGMA shells and PtBMA/PDMAEMA cores. In the cores, the two hydrophobic blocks segregated into distinct domains due to their incompatibility, and the hydrophilic POEGMA blocks formed the coronae to stabilize the structures. The PtBMA chains with larger volume percentage formed the continuous phases, while the PDMAEMA chains with smaller volume percentage formed the discontinuous phases. At pH = 4.0, protonated PDMAEMA chains were highly stretched and formed the coronae of the micelles. Excessive reductant was added into the micellar solution to reduce the disulfide bonds between PDMAEMA side chains and the backbones, and mesoporous polymeric micelles with thiol groups inside the pores were obtained. 1H-NMR results of multi-component micelles, before and after treatment with the reductant, indicated that the PDMAEMA side chains were removed completely. Transmission electron microscopy (TEM) and dynamic light scattering were used to characterize the morphology and the size of the micelles. Based on TEM results, the average size of the pores in the micelles was about 2 nm, which was consistent with the average size of the PDMAEMA discontinuous phases. After the cleavage of the disulfide bonds and the removal of PDMAEMA chains from the micelles, thiol groups were produced on the walls of the pores. The thiol groups can be used as reducing agent and stabilizer in the in situ synthesis of gold nanoparticles. By thiol-bromine reactions, mesoporous micelles with polythiophene derivatives inside the pores were synthesized. The micelles showed high sensitivity and excellent selectivity for Hg2+.
2018, 0(8): 1089-1096
doi: 10.11777/j.issn1000-3304.2018.18035
Abstract:
Unlike the crude study conducted at the beginning of nanomedicine, researchers have devoted more efforts to developing nanosystems with elaborated structures and multifunctions owing to the fact that the tumor microenvironment is complicated. However, it is still a great challenge to prepare these nanoplatforms for drug delivery. In this study, multifunctional prodrug nanocarriers were fabricated by the modularized host-guest self-assembly between cholesterol and β-cyclodextrin. The targeted ligand lactobionic acid (LBA), fluorescent probe fluoresceine isothiocyanate (FITC), and chemtherapeutic drug doxorubicin (DOX) were integrated into the multifunctional supramolecualr drug nanocarriers. The host-guest interaction between Chol-PEG and β-CD-hydrazone-DOX was confirmed by 2D 1H NOESY spectrum. The modularized functional building blocks could self-assemble into micelles with a diameter of 20 nm. The supramolecular nanocarriers showed pH-sensitive drug release behavior. The release of DOX can be greatly accelerated in acidic endo/lysosomal pH. The internalization of the supramolecular drug nanocarriers by HepG2 cells was studied by fluorescence microscopy and flow cytometry. The nanocarriers can be well taken up by cancer cells. Due to the targeting ability of LBA, the internalization of the nanocarriers can be greatly inhibited if the cells are pre-treated by free LBA. At the same time, the fluorescence of FITC can be clearly observed intracellularly, which can be used to track the sub-cellular location of the drug nanocarriers. Finally, the cytotoxicity of the drug nanocarriers was investigaed by MTT assay. With the HepG2 cells pre-treated with free LBA, the cytotoxicity of the drug nanocarriers was significantly reduced, most probably owing to the unsatisfactory cell uptake. The concentration-dependent cytotoxicity toward HepG2 cells was also observed. Therefore, the integration of target ligand and imaging ligand have endowed the nanocarriers with targeted theranostic property. More importantly, since the modularized host-guest self-assembly is dynamically tunable, the percentage of functional ligands could be easily optimized to achieve a better outcome. Such multifunctional prodrug nanocarriers fabricated by modularized host-guest self-assembly may have great potential in drug delivery.
Unlike the crude study conducted at the beginning of nanomedicine, researchers have devoted more efforts to developing nanosystems with elaborated structures and multifunctions owing to the fact that the tumor microenvironment is complicated. However, it is still a great challenge to prepare these nanoplatforms for drug delivery. In this study, multifunctional prodrug nanocarriers were fabricated by the modularized host-guest self-assembly between cholesterol and β-cyclodextrin. The targeted ligand lactobionic acid (LBA), fluorescent probe fluoresceine isothiocyanate (FITC), and chemtherapeutic drug doxorubicin (DOX) were integrated into the multifunctional supramolecualr drug nanocarriers. The host-guest interaction between Chol-PEG and β-CD-hydrazone-DOX was confirmed by 2D 1H NOESY spectrum. The modularized functional building blocks could self-assemble into micelles with a diameter of 20 nm. The supramolecular nanocarriers showed pH-sensitive drug release behavior. The release of DOX can be greatly accelerated in acidic endo/lysosomal pH. The internalization of the supramolecular drug nanocarriers by HepG2 cells was studied by fluorescence microscopy and flow cytometry. The nanocarriers can be well taken up by cancer cells. Due to the targeting ability of LBA, the internalization of the nanocarriers can be greatly inhibited if the cells are pre-treated by free LBA. At the same time, the fluorescence of FITC can be clearly observed intracellularly, which can be used to track the sub-cellular location of the drug nanocarriers. Finally, the cytotoxicity of the drug nanocarriers was investigaed by MTT assay. With the HepG2 cells pre-treated with free LBA, the cytotoxicity of the drug nanocarriers was significantly reduced, most probably owing to the unsatisfactory cell uptake. The concentration-dependent cytotoxicity toward HepG2 cells was also observed. Therefore, the integration of target ligand and imaging ligand have endowed the nanocarriers with targeted theranostic property. More importantly, since the modularized host-guest self-assembly is dynamically tunable, the percentage of functional ligands could be easily optimized to achieve a better outcome. Such multifunctional prodrug nanocarriers fabricated by modularized host-guest self-assembly may have great potential in drug delivery.
2018, 0(8): 1097-1106
doi: 10.11777/j.issn1000-3304.2018.18041
Abstract:
β-cyclodextrin-ferrocene host-guest inclusion complex has been widely used to construct various functional supramolecular hydrogels, but all these reported hydrogels are often very weak and/or brittle. In this work, β-cyclodextrin (β-CD) based linear copolymer (polyβ-CD) was synthesized and used as the macromolecular host, hydrophilic and flexible spacer modified ferrocene (Fc) monomer acted as the guest. The polymerizable Fc monomer was preloaded on polyβ-CD to form a novel type of ‘macromolecular supramolecular cross-linker’ (MSCL) owing to the inclusion complexation between β-CD and Fc. For the first time, stretchable, stab-resistant and adhesive supramolecular hydrogels were prepared via simple free-radical copolymerization of MSCL and acrylamide. Tensile-testing results showed that the obtained supramolecular hydrogel can be stretched up to more than 30 times of its original length without breaking. The gel can also be stabbed by sharp tips of scissors or pencil without fracture, indicating excellent stab resistance property. At the same time, the hydrogel also exhibited strong adhesion to the surfaces of human hand, hydrophilic glass or hydrophobic porcine skin. We attribute these distinguished behaviors to the successful use of polyβ-CD and the introduction of flexible hydrophilic spacer to the Fc monomer. Firstly, polyβ-CD acted as a macromolecular supramolecular imprint to form pre-organized Fc-polyβ-CD complexes, and thus resulted in relatively local high density of pendent Fc groups in the polymeric network. This is different from most of the reported host-guest interaction based supramolecular hydrogels, where the host and guest groups are randomly attached in the polymeric network. Secondly, after copolymerization, polyβ-CD was homogeneously immersed in the network by noncovalent interaction but not covalently conjugated in the network, which would greatly limit its mobility. Finally, the introduction of hydrophilic spacer on Fc not only can yield water soluble Fc-polyβ-CD macromolecular supramolecular complex, but also provide the released free Fc groups with more flexibility. Altogether, the local high density of both the guest and host groups in the network combined with their relatively high flexibility provided the present supramolecular hydrogels with excellent mechanical properties.
β-cyclodextrin-ferrocene host-guest inclusion complex has been widely used to construct various functional supramolecular hydrogels, but all these reported hydrogels are often very weak and/or brittle. In this work, β-cyclodextrin (β-CD) based linear copolymer (polyβ-CD) was synthesized and used as the macromolecular host, hydrophilic and flexible spacer modified ferrocene (Fc) monomer acted as the guest. The polymerizable Fc monomer was preloaded on polyβ-CD to form a novel type of ‘macromolecular supramolecular cross-linker’ (MSCL) owing to the inclusion complexation between β-CD and Fc. For the first time, stretchable, stab-resistant and adhesive supramolecular hydrogels were prepared via simple free-radical copolymerization of MSCL and acrylamide. Tensile-testing results showed that the obtained supramolecular hydrogel can be stretched up to more than 30 times of its original length without breaking. The gel can also be stabbed by sharp tips of scissors or pencil without fracture, indicating excellent stab resistance property. At the same time, the hydrogel also exhibited strong adhesion to the surfaces of human hand, hydrophilic glass or hydrophobic porcine skin. We attribute these distinguished behaviors to the successful use of polyβ-CD and the introduction of flexible hydrophilic spacer to the Fc monomer. Firstly, polyβ-CD acted as a macromolecular supramolecular imprint to form pre-organized Fc-polyβ-CD complexes, and thus resulted in relatively local high density of pendent Fc groups in the polymeric network. This is different from most of the reported host-guest interaction based supramolecular hydrogels, where the host and guest groups are randomly attached in the polymeric network. Secondly, after copolymerization, polyβ-CD was homogeneously immersed in the network by noncovalent interaction but not covalently conjugated in the network, which would greatly limit its mobility. Finally, the introduction of hydrophilic spacer on Fc not only can yield water soluble Fc-polyβ-CD macromolecular supramolecular complex, but also provide the released free Fc groups with more flexibility. Altogether, the local high density of both the guest and host groups in the network combined with their relatively high flexibility provided the present supramolecular hydrogels with excellent mechanical properties.
2018, 0(8): 1107-1115
doi: 10.11777/j.issn1000-3304.2018.18053
Abstract:
The Haake rotational rheometer was employed to disentangle the polylactide melt by well-controlled oscillatory shear stress with sinusoidal strain and to monitor the melt viscosity in real time. Fisrtly, a PLA sample was disentangled with different strains at various frequency ranges, and the results indicated that the PLA melt represented the lowest melt viscosity which was four orders of magnitude lower than that of the PLA without any treatment when the strain was 50% with the frequency at 3.5 Hz. Then, the molecular weights of all these PLA were measured by gel permeation chromatography (GPC) and almost no change was detected after the oscillatory shear. Taken into account the results of the melt viscosity and the molecular weight measurement, it was reasonable that the significant reduction of PLA melt viscosity was attributed to the effective disentanglement of PLA chains, rather than their degradation. Furthermore, the effect of oscillatory shear on glass transition, crystallization and melting behavior was also studied. It was found that the effective disentanglement of PLA chains was achieved by oscillatory shearing, leading to a lower glass transition temperature and a cold-crystallization temperature together with largely improved crystallinity of PLA. Simultaneously, when compared to the PLA melt without any treatment, the isothermal crystallization of PLA at 120 °C with the lowest melt viscosity also demonstrated that the oscillatory shear could disentangle the PLA melt and thus accelerated the crystallization of PLA. More importantly, the influence of annealing time (1 − 30 min) and temperature (180 − 200 °C) was investigated as well. The semi-crystallization time at 120 °C of disentangled PLA constantly increased with the increasing annealing time and temperature, which got gradually closer to that of PLA without any treatment. These results demonstrated that the disentanglement could be maintained at relatively low temperature and re-entangled rapidly at relatively high temperature. In summary, the Haake rotational rheometer, the common test instrument for the rheological properties of polymer melt, can be employed for the investigation of the disentanglement of polymer melt, which is not merely a simple and effective method to disentangle the polymer melt, but also a well-controlled and real-time monitoring approach for systematically investigating the disentanglement of polymer melt.
The Haake rotational rheometer was employed to disentangle the polylactide melt by well-controlled oscillatory shear stress with sinusoidal strain and to monitor the melt viscosity in real time. Fisrtly, a PLA sample was disentangled with different strains at various frequency ranges, and the results indicated that the PLA melt represented the lowest melt viscosity which was four orders of magnitude lower than that of the PLA without any treatment when the strain was 50% with the frequency at 3.5 Hz. Then, the molecular weights of all these PLA were measured by gel permeation chromatography (GPC) and almost no change was detected after the oscillatory shear. Taken into account the results of the melt viscosity and the molecular weight measurement, it was reasonable that the significant reduction of PLA melt viscosity was attributed to the effective disentanglement of PLA chains, rather than their degradation. Furthermore, the effect of oscillatory shear on glass transition, crystallization and melting behavior was also studied. It was found that the effective disentanglement of PLA chains was achieved by oscillatory shearing, leading to a lower glass transition temperature and a cold-crystallization temperature together with largely improved crystallinity of PLA. Simultaneously, when compared to the PLA melt without any treatment, the isothermal crystallization of PLA at 120 °C with the lowest melt viscosity also demonstrated that the oscillatory shear could disentangle the PLA melt and thus accelerated the crystallization of PLA. More importantly, the influence of annealing time (1 − 30 min) and temperature (180 − 200 °C) was investigated as well. The semi-crystallization time at 120 °C of disentangled PLA constantly increased with the increasing annealing time and temperature, which got gradually closer to that of PLA without any treatment. These results demonstrated that the disentanglement could be maintained at relatively low temperature and re-entangled rapidly at relatively high temperature. In summary, the Haake rotational rheometer, the common test instrument for the rheological properties of polymer melt, can be employed for the investigation of the disentanglement of polymer melt, which is not merely a simple and effective method to disentangle the polymer melt, but also a well-controlled and real-time monitoring approach for systematically investigating the disentanglement of polymer melt.
2018, 0(8): 1116-1126
doi: 10.11777/j.issn1000-3304.2018.18058
Abstract:
Monte Carlo simulation was employed to investigate the self-assembly behaviors of asymmetric diblock copolymers under spherical shell confinements with different shell thicknesses and selectivity. The asymmetric diblock copolymer that can form hexagonally packed cylinders in bulk state was selected. The simulation results show that, when the cylinder-forming diblock copolymers are confined in spherical shells, the minority blocks can also form cylinder phases. It is found that the orientation of the cylinders highly depends on the shell thickness and selectivity. The formation of the cylinders, that are perpendicular to the shell surfaces and can penetrate the shell from inner to outer surfaces, is a prerequisite to obtain mesoporous polymer capsules. The formation conditions of such cylinders were elucidated in this study. In the neutral spherical shell, the simulation results indicate that the formation of the cylinders that penetrate the shell depends on the structural frustration parameter (i.e., the ratio of the shell thickness D to the equilibrium spacing between the cylinders in bulk, L0). When D is incomparable to L0, the cylinders that penetrate the shell are oberved, otherwise, the cylinders that penetrate the shell disappear. It is interesting to find that the weak repulsions between the shell boundaries and the minority blocks are favorable for the minority blocks to form branched cylinders. The branched cylinders penetrate the shell from inner to outer surfaces and form multiple channels in the shell, which benefits to fabricate polymer capsules with multiple release channels. And the formation of such branched cylinders does not depend on the structural frustration parameter D/L0. On the other hand, in the case of spherical shell with a thin thickness, the minority blocks always form well-defined cylinders that penetrate the shell, no matter whether the repulsions between the shell boundaries and the minority blocks exist. Via investigating the orientation of the polymer chains in each shell, the influence of the shell thicknesses and the repulsions between the shell boundaries and the minority blocks on the orientation of cylinders formed by the minority blocks is further elucidated.
Monte Carlo simulation was employed to investigate the self-assembly behaviors of asymmetric diblock copolymers under spherical shell confinements with different shell thicknesses and selectivity. The asymmetric diblock copolymer that can form hexagonally packed cylinders in bulk state was selected. The simulation results show that, when the cylinder-forming diblock copolymers are confined in spherical shells, the minority blocks can also form cylinder phases. It is found that the orientation of the cylinders highly depends on the shell thickness and selectivity. The formation of the cylinders, that are perpendicular to the shell surfaces and can penetrate the shell from inner to outer surfaces, is a prerequisite to obtain mesoporous polymer capsules. The formation conditions of such cylinders were elucidated in this study. In the neutral spherical shell, the simulation results indicate that the formation of the cylinders that penetrate the shell depends on the structural frustration parameter (i.e., the ratio of the shell thickness D to the equilibrium spacing between the cylinders in bulk, L0). When D is incomparable to L0, the cylinders that penetrate the shell are oberved, otherwise, the cylinders that penetrate the shell disappear. It is interesting to find that the weak repulsions between the shell boundaries and the minority blocks are favorable for the minority blocks to form branched cylinders. The branched cylinders penetrate the shell from inner to outer surfaces and form multiple channels in the shell, which benefits to fabricate polymer capsules with multiple release channels. And the formation of such branched cylinders does not depend on the structural frustration parameter D/L0. On the other hand, in the case of spherical shell with a thin thickness, the minority blocks always form well-defined cylinders that penetrate the shell, no matter whether the repulsions between the shell boundaries and the minority blocks exist. Via investigating the orientation of the polymer chains in each shell, the influence of the shell thicknesses and the repulsions between the shell boundaries and the minority blocks on the orientation of cylinders formed by the minority blocks is further elucidated.
2018, 0(8): 1127-1140
doi: 10.11777/j.issn1000-3304.2018.18079
Abstract:
The trypsin-responsive near-infrared fluorescent/magnetic resonance dual-imaging composite nanospheres, which consist of PAA-decorated Fe3O4 magnetic nanoparticles (MNPs) that serve as the magnetic resonance imaging (MRI) agents and Cy5.5-modified poly-L-lysine (Cy5.5-PLL) as the trypsin-responsive substrate and fluorescent carrier, were successfully fabricated via self-assembly method. The MNPs present negatively charge due to the carboxyl groups from PAA on their surface and the Cy5.5-PLL present positively charge due to the amino groups in PLL chains. The construction of the composite nanospheres was initially performed via the self-assembly driven by the electrostatic interactions between the above mentioned oppositely charged precursors. Subsequently, glutaraldehyde (GA) was introduced to partially crosslink the amino groups in PLL and stabilize the nanospheres. The fluorescent and magnetic characterization of the two precursors of the composite nanospheres, Cy5.5-PLL and MNPs, indicated that Cy5.5-PLL chains showed obvious fluorescent signal and the MNPs displayed the superparamagnetism property. However, the notable fluorescent signal from Cy5.5-PLL in native soluble state was self-quenched thanks to the short distance among the Cy5.5 fluorescent molecules after the construction of the nanospheres. Additionally, the structure of the as-prepared self-assembled nanospheres was stable, resulting from the almost unchanged results of the hydrodynamic size and fluorescence intensity of nanospheres in different buffer solutions. Nevertheless, because of the sensitivity of PLL chains to trypsin, the nanospheres were selectively disintegrated into fragmented segments under the hydrolysis by trypsin, leading to 18-fold amplification of fluorescent intensity in comparison with the self-assembled nanospheres in quenched state. Moreover, the magnetic resonance imaging enhancement was also related to the disintegration of the nanospheres. As expected, the trypsin-positive cells incubated with nanospheres exhibited remarkable fluorescent imaging due to the disintegration of the nanospheres into debris, whereas this disintegration did not take place for the trypsin-negative cells. In vivo fluorescent images of the composite nanospheres in normal nude mice further verified the trypsin-triggered fluorescent imaging. Cytotoxicity study demonstrated that the composite nanospheres presented low toxicity to several cell lines, and exhibited remarkable near-infrared fluorescent/magnetic resonance imaging capabilities, which were sensitive to the presence of trypsin and thus provided excellent opportunity to serve as dual-imaging agents.
The trypsin-responsive near-infrared fluorescent/magnetic resonance dual-imaging composite nanospheres, which consist of PAA-decorated Fe3O4 magnetic nanoparticles (MNPs) that serve as the magnetic resonance imaging (MRI) agents and Cy5.5-modified poly-L-lysine (Cy5.5-PLL) as the trypsin-responsive substrate and fluorescent carrier, were successfully fabricated via self-assembly method. The MNPs present negatively charge due to the carboxyl groups from PAA on their surface and the Cy5.5-PLL present positively charge due to the amino groups in PLL chains. The construction of the composite nanospheres was initially performed via the self-assembly driven by the electrostatic interactions between the above mentioned oppositely charged precursors. Subsequently, glutaraldehyde (GA) was introduced to partially crosslink the amino groups in PLL and stabilize the nanospheres. The fluorescent and magnetic characterization of the two precursors of the composite nanospheres, Cy5.5-PLL and MNPs, indicated that Cy5.5-PLL chains showed obvious fluorescent signal and the MNPs displayed the superparamagnetism property. However, the notable fluorescent signal from Cy5.5-PLL in native soluble state was self-quenched thanks to the short distance among the Cy5.5 fluorescent molecules after the construction of the nanospheres. Additionally, the structure of the as-prepared self-assembled nanospheres was stable, resulting from the almost unchanged results of the hydrodynamic size and fluorescence intensity of nanospheres in different buffer solutions. Nevertheless, because of the sensitivity of PLL chains to trypsin, the nanospheres were selectively disintegrated into fragmented segments under the hydrolysis by trypsin, leading to 18-fold amplification of fluorescent intensity in comparison with the self-assembled nanospheres in quenched state. Moreover, the magnetic resonance imaging enhancement was also related to the disintegration of the nanospheres. As expected, the trypsin-positive cells incubated with nanospheres exhibited remarkable fluorescent imaging due to the disintegration of the nanospheres into debris, whereas this disintegration did not take place for the trypsin-negative cells. In vivo fluorescent images of the composite nanospheres in normal nude mice further verified the trypsin-triggered fluorescent imaging. Cytotoxicity study demonstrated that the composite nanospheres presented low toxicity to several cell lines, and exhibited remarkable near-infrared fluorescent/magnetic resonance imaging capabilities, which were sensitive to the presence of trypsin and thus provided excellent opportunity to serve as dual-imaging agents.
