The fabrication, via a two steps approach, of a novel bicontinuous Double Network (BCDN) material is reported. We first use a bicontinuous emulsion as template to obtain a poly(butyl acrylate) (PBA) ...and poly(acrylic acid) (PAA) bicontinuous amphiphilic material. The material is then swollen with the precursor of a second hydrophilic polymer (PNIPAM, poly(N-isopropylacrylamide)). After polymerization of these precursors, the two responsive polymers, PNIPAM and PAA, form a double-network within a bicontinuous templated material, i.e. a bicontinuous double network (BCDN) material. The advantages of using such unique and complex double network architecture are manifold. PBA increases the mechanical properties of the hydrogel all together with the hydrophilic double network that also decouples the pH and temperature responsiveness. Among different possible applications, we tested this responsive hydrogels for its biomedical application. It can be used as pH and temperature sensitive devices for on-demand drug delivery. In addition, the release of a drug confined in the amphiphilic bicontinuous structure follows different kinetics profiles, depending on pH and temperature. This last result indicates that it is possible to control and regulate the release of an encapsulated drug according to the fluctuations of physiological conditions.
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•Fabrication of a novel bicontinuous Double Network (BCDN) material is reported.•Bicontinuous emulsion as template to obtain bicontinuous amphiphilic material•Two responsive polymers form a double-network within bicontinuous templated material.•pH and temperature sensitive devices for on-demand drug delivery•Release of a drug confined in the amphiphilic BCDN
Self-seeding is a process unique to polymer crystals, which consist of regions of different chain packing order and different crystallinity. Here we report the synergistic self-seeding behaviour of ...pairs of core-crystalline block copolymer (BCP) micelle fragments and show how this strategy can be employed to control the morphology of these BCP comicelles. Each micelle fragment has a critical dissolution temperature (
), and unimers of each BCP have a characteristic epitaxial growth rate. The
value affects the dissolution sequence of the fragments upon heating, while the unimer growth rate affects the growth sequence upon cooling. By carefully choosing micelle fragments having different
values as well as growth rates, we could prepare patchy comicelles and block comicelles with uniform and controllable length. This synergistic self-seeding strategy is a simple yet effective route to control both length and morphology of core-crystalline comicelles.
Do it yourself: When short fragments (ca. 50 nm) of rodlike PI‐PFS block copolymer micelles in decane are heated above a characteristic temperature (60 °C) and then cooled to room temperature, a ...smaller number of longer micelles with a narrow length distribution are obtained. This process resembles self‐seeding of polymer crystals, involving selective dissolution of the fragments of the lowest degree of crystallinity with the surviving submicroscopic seeds acting as nuclei for the growth of micelles upon cooling.
The self-assembly of block copolymers in solution leads to micellar structures with various morphologies. One way to modify the morphology of these micelles is to blend the block copolymer with a ...homopolymer corresponding to the core-forming block. Although the self-assembly of blends of amorphous homopolymers and block polymers has been extensively studied, there are few examples of solution self-assembly of blends of a core-crystalline block copolymer with a semicrystalline homopolymer. Here we describe a systematic study of the assembly in decane of blends of a polyferrocenylsilane-block-polyisoprene sample (PFS48-b-PI264) with two different PFS homopolymer samples (PFS50 and PFS20). We examine the structures formed as a function of blend composition and compare them to the structures formed from the individual components. PFS48-b-PI264 itself forms long cylindrical micelles, while the two homopolymer samples form stacks of lamellar crystals. Self-assembly of block copolymer mixtures leads to structures with an elongated planar core and fiber-like protrusions from the ends. The details of the structure vary in an interesting and systematic way as the ratio of homopolymer/block copolymer is increased, with important differences seen for the PFS50 and PFS20 homopolymer samples. This study demonstrates that cocrystallization plays a crucial role in determining the structures formed from these mixtures.
Living crystallization-driven self-assembly in solution has proven to be an excellent method to prepare core-crystalline micelles with an exquisite control over their size and morphology. While ...numerous studies have been performed to test their assembly in various media for potential applications, their stability under different stimuli remains yet to be established. In the present study, we performed light scattering and transmission electron microscopy experiments to investigate the effect of concentration on the self-seeding of core-crystalline one-dimensional (1D) seed crystallites with a long corona forming block. As previously reported, the seed crystallites dissolve much easier at low concentrations than at relatively high concentrations. We also observe that for all concentrations, the micelle width broadens during annealing. To explain these results, we developed a model based on a scaling approach. We show that the growth of ribbon-like core-crystalline micelles depends on the distance between the corona chains grafted on the micelle core, the thickness of the core, and, more surprisingly, on the number of chains constituting the core. This scaling approach also allowed us to explain how the interactions between the corona-forming block and the solvent influence the behavior of the seed crystallites at different annealing temperatures and concentrations. This model should thus prove very useful to understand and predict the effect of different media and stimuli on the size, morphology, and stability of core-crystalline micelles.
The fabrication of three-dimensional (3D) objects by polymer self-assembly in solution is extremely challenging. Here, multi-tori mesostructures were obtained from the crystallization-driven ...self-assembly of a coil-crystalline block copolymer (BCP) in mixed solvents. The formation of these structures follows a multistep process. First, the BCP self-assembles into amorphous micrometer-large vesicles. Then, the BCP confined in these mesosized vesicles crystallizes. This second step leads to the formation of objects with shapes ranging from closed 3D multi-tori spherical shells to 2D toroid mesh monolayers, depending on the solvent mixture composition. This approach demonstrates how topological constraints induced by the specific interactions between coil-crystalline BCP and solvents can be used to prepare mesostructures of complex morphologies.
Amphiphilic crystalline-coil diblock copolymers polyferrocenyldimethylsilane-block-poly(N-isopropylacrylamide) of two different block ratios (PFS56-b-PNIPAM190 and PFS26-b-PNIPAM520) were ...synthesized by a copper-catalyzed azide–alkyne coupling reaction. They exhibited pronounced differences in self-assembly in alcohol solvents. While PFS56-b-PNIPAM190 formed mixtures of spherical and rod-like micelles in ethanol and 2-propanol, PFS26-b-PNIPAM520 formed long fibers of uniform width in these solvents. We used a seeded growth protocol to grow rod-like PFS26-b-PNIPAM520 micelles of uniform lengths. There were two surprising features of this experiment: First, micelle growth was unusually slow and required a long aging time (40 days) for them to reach their final length. Second, the micelles were characterized by a low number of polymer chains per unit length as determined by multiangle light scattering. This result suggests a loose packing of PFS chains in the micelle core. In an attempt to prepare thermoresponsive nanofibrillar hydrogels from these micelles, we explored approaches to transfer them from 2-propanol to water. These attempts were accompanied by extensive fragmentation of the micelles. We believe the fragility of these micelles is related to the loosely packed nature of the PFS chains in the micelle core. Fragmentation may also be affected by the cononsolvency effect of 2-propanol-water mixtures on the PNIPAM corona of the micelles. We could show, however, that the micelle fragments in water retained their anticipated thermoresponsive behavior.
Multistep crystallization-driven self-assembly has great potential to enable the construction of sophisticated hybrid mesostructures. During the assembly procedure, each step modifies the properties ...of the overall structure. Here, we demonstrate the flexibility and efficiency of this approach by preparing polymer–carbon nanotube (CNT) hybrid mesostructures. We started by growing polyferrocenyldimethylsilane (PFS) homopolymer crystals onto multiwalled CNTs. This first step facilitated the redispersion of the coated CNTs in both polar (2-propanol) and nonpolar (decane) solvents. In the second step of hybrid construction, a unimer solution of a PFS block copolymer was added into the PFS-CNT solution. The PFS coating on the CNT initiated the growth of elongated micelles, resulting in structures that resembled hairy caterpillars. PFS-b-P2VP (P2VP = poly-2-vinylpyridine) micelles were grown from the surface of PFS-CNT hybrids in 2-propanol, and PFS-b-PI (PI = polyisoprene) micelles were grown from these hybrids in decane. These micelles, by transmission electron microscopy were seen to have an unusual wavy kinked structure, very different from the uniform smooth structures normally formed by both block copolymers. For hybrids with PFS-b-PI micelles, cross-linking of the micelle coronas locked the whole structure in place and allowed us to use the partial oxidation of PFS components to grow metal nanoparticles in the core of these micelles. We finally investigated the influence of the corona-forming block used to grow the micelles on the wettability of films made from these mesostructures. Films formed with CNT hybrids grafted with PFS-b-PI micelles were superhydrophobic (contact angle, 152°). In contrast, the surface of the films was much more hydrophilic (contact angle, 54°) when they were prepared from CNT hybrids grafted with PFS-b-P2VP micelles.
The ability to trigger a destabilization of the membrane integrity of liposomes bound to environmentally sensitive hydrophobically modified core−shell hydrogel beads is demonstrated. Hydrogel beads ...with a core composed of poly(N-isopropylacrylamide) lightly cross-linked with bisacrylamide (BA) (pNIPAM) and a shell composed of NIPAM highly cross-linked with BA and containing varying amounts of acrylic acid (AA) p(NIPAM-co-AA) undergo a volume phase transition (VPT) at ≈32 °C, as determined from 1H magic angle spinning (MAS) NMR, regardless of the AA content of the shell. When the shell was hydrophobically modified with either decylamine or tetradecylamine, binding of extruded large unilamellar vesicles (eLUVs) composed of 1-palmitoyl-2-oleoylphosphatidylcholine (POPC) was quantitative, as determined via fluorescence spectroscopy. Fluorescence microscopy showed that such bound eLUVs did not fuse. Hydrogel-bound eLUV membrane permeability was assessed using 31P MAS NMR in the presence of the chemical shift agent praseodymium and demonstrated that only at lower degrees of hydrophobic modification of the core−shell hydrogels was eLUV membrane barrier integrity maintained when T < VPT. At a low degree of hydrophobic modification, cycling the temperature above the VPT even for short periods caused the eLUV membranes to become leaky. Hence, eLUV membrane permeability was coupled to the hydrogel VPT, a situation that would be useful in applications requiring triggered release of liposomal contents.
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