Enzyme-Induced Kinetic Control of Peptide–Polymer Micelle

Letter Cite This: ACS Macro Lett. 2019, 8, 676−681

pubs.acs.org/macroletters

Enzyme-Induced Kinetic Control of Peptide−Polymer Micelle Morphology Daniel B. Wright,†,‡ Abelardo Ramírez-Hernań dez,¶,▽ Mollie A. Touve,†,‡ Andrea S. Carlini,†,‡ Matthew P. Thompson,†,‡ Joseph P. Patterson,○,‡ Juan J. de Pablo,*,§,⊥ and Nathan C. Gianneschi*,†,‡

Downloaded by BUFFALO STATE at 19:02:21:422 on May 23, 2019 from https://pubs.acs.org/doi/10.1021/acsmacrolett.8b00887.

†

Department of Chemistry, Department of Materials Science and Engineering, and Department of Biomedical Engineering, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States ○ Department of Chemistry, University of California, Irvine (UCI), Irvine, California 92697-2025, United States ‡ Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093, United States § Institute for Molecular Engineering, The University of Chicago, Chicago, Illinois 60637, United States ⊥ Materials Science Division & Institute for Molecular Engineering, Argonne National Laboratory, 9700 South Cass Avenue, Lemont, Illinois 60439, United States ¶ Department of Biomedical Engineering, Chemical Engineering Program and ▽Department of Physics and Astronomy, The University of Texas at San Antonio, San Antonio, Texas 78249, United States S Supporting Information *

ABSTRACT: In this paper, experiment and simulation were combined to provide a view of the molecular rearrangements underlying the equilibrium and nonequilibrium transitions occurring in stimuli-responsive block copolymer amphiphile self-assemblies. Three block copolymer amphiphiles were prepared, each consisting of a hydrophilic peptide brush, responsive to proteolytic enzymes, and containing one of three possible hydrophobic blocks: (1) poly(ethyl acrylate), (2) poly(styrene), or (3) poly(lauryl acrylate). When assembled, they generate three spherical micelles each responsive to the addition of the bacterial protease, thermolysin. We found core-block-dependent phase transitions in response to the hydrophilic block being truncated by the stimulus. In one example, we found an unexpected, well-defined, pathway-dependent spherical micelle to vesicle phase transition induced by enzymatic stimulus.

T

he design of nanostructures formed from block copolymer amphiphiles is usually based on the rationale that thermodynamics govern the formation and that the equilibrium structure is inevitable. Regardless, very often, polymeric nanostructures are trapped in nonequilibrium states, and the equilibrium structures are not reached within the experimental time scales.1−4 These kinetically trapped structures have been effectively exploited to allow access to materials with highly complex morphologies.5−11 This can be achieved where polymer dynamics and intermolecular interactions have been controlled to produce complex structures at a local minimum free energy and rapidly locked in place.9,12 For example, Eisenberg and co-workers observed reversible transitions between micelles and vesicles by controlling solvent conditions, which highlights not only the ability to lock in structures but also the ability to induce nonequilibrium transitions between local minima.13−15 In addition to changing the solution conditions, stimuli can be applied that directly change the structure of the amphiphiles, leading to additional morphology control by the use of responsive triggers that break and make bonds, such as pH, light, or enzymes.16−22 © XXXX American Chemical Society

In this work, we prepared a set of enzyme-responsive micelle-forming block copolymers where we examined response to enzymatic cleavage of the peptide block23−28 as a result of altering the core block in a systematic manner both experimentally and in silico (Figure 1). The development of a corroboration between the two methods will serve as the basis for a high-throughput screening and synthesis of novel responsive nanostructures. We hypothesized that by altering the nature of the core-forming block, a rich range of micellar phases would be accessed in response to enzymatic stimuli, which are limited when high Tg hydrophobic blocks are solely employed.29−31 The amphiphilic diblock copolymers were synthesized by RAFT polymerization with subsequent conjugation with the thermolysin-responsive peptide sequence GPLGLAGGWGERDGS (Figure S1 and Table 1). An excess of peptide was utilized in this postpolymerization coupling, yet the coupling is limited to 80%. We believe this is a maximum Received: November 15, 2018 Accepted: April 30, 2019

676

DOI: 10.1021/acsmacrolett.8b00887 ACS Macro Lett. 2019, 8, 676−681

Letter

ACS Macro Letters

Figure 1. (A) Peptide−polymer amphiphiles (PPAs). EA = ethyl acrylate, LA = lauryl acrylate, St = styrene. (B) In silico model of a PPA. Figure 2. (A) Cryo-TEM images of 4 before peptide cleavage. (B) Cryo-TEM images of 4 after peptide cleavage (red arrows indicate ice). (C) Distribution of hydrodynamic diameter for 4 assembled after peptide cleavage and ideal assembly post cleavage.

given the excess and that this is a steric effect of coupling two larger macromolecules together. We term the resulting polymers peptide−polymer amphiphiles (PPAs). The coronal block remained constant with varying core blocks. Three different core blocks were studied: (1) Poly(ethyl acrylate) with both a low Tg and solvophobicity in water, yielding what was expected to be dynamic micelles.32 (2) Poly(styrene), with both a high Tg and solvophobicity in water, was expected to yield frozen micelles.11,33 (3) Poly(lauryl acrylate), with a low Tg yet conversely high solvophobicity, was predicted to form nonergodic micelles in solution.5 PPAs were assembled by first dissolving in DMF and dialyzing via a solvent switch protocol into aqueous solution, in an effort to produce uniform structures that are formed under thermodynamic control (see SI for experimental details).11,33,34 The solvent switch protocol optimizes the exchange of polymers between nanostructures and thus allows micellization to occur under thermodynamic control when the interfacial energy between the core and solvent is low.35 Thus, the free energy barrier associated with the exchange of polymers between micelles is decreased, allowing for faster relaxation to equilibrium structures.36,37 In these experiments, regardless of the chemical nature of the core polymers, the size distribution of the self-assembled structures displayed low polydispersity, with an average size of 30 nm and spherical morphology, as deduced by dynamic light scattering (DLS) and cryogenic transmission electron microscopy (cryo-TEM) (Table 1 and Figures 2 and 3). Given the large hydrophobic fraction of 1, 2, and 3, the aggregation numbers of these micelles were probably large, hence with comparable diameters to 4, 5, and 6.31,38 The micellar nanoparticles at 100 nM with respect to peptide were then incubated with thermolysin (10

Figure 3. (A) Cryo-TEM images of 5 before peptide cleavage. (B) Cryo-TEM images of 5 after peptide cleavage. (C) Distribution of hydrodynamic diameter for 5: assembled, after peptide cleavage, ideal assembly, and peptide cleavage heated.

nM) at 37 °C to cleave the peptide (recognition sequence labeled in italics, Figure 1A). After 24 h the reaction products were further analyzed by high-performance liquid chromatography (HPLC) (Figure S2), DLS, and cryo-TEM. HPLC

Table 1. Characteristics of the PPA Nanostructures polymer

core blocka

MnSECb

MnNMRc

Đb

mc

nc

xd

peptide assembly Dh (nm)f

post incubation Dh (nm)f

ideal assembly Dh (nm)f

1 2 3 4 5 6

EA LA St EA LA St

7.0 10.2 7.3 32.1 34.5 27.9

5.1 8.0 5.1 25.0 31.9 23.8

1.2 1.3 1.2 1.2 1.4 1.3

3 3 3 20 20 20

19 20 18 20 19 20

0.67 0.67 0.67 0.80 0.75 0.75

30 33 29 28 33 25

35 287 Ppte 23 198 Ppte

33 38 25 30 35 20

a

EA = ethyl acrylate, LA = lauryl acrylate, St = styrene. bFrom SEC based on poly(styrene) standards in DMF. cDetermined by end-group analysis from 1H NMR spectroscopy. dDetermined by HPLC analysis. ePrecipitate. fDetermined by DLS at 0.2 wt %. 677

DOI: 10.1021/acsmacrolett.8b00887 ACS Macro Lett. 2019, 8, 676−681

Letter

ACS Macro Letters

polymer system remains in a kinetically trapped morphology,42,43 stable in solution far from equilibrium. To test this hypothesis, the metastable vesicle was heated to 110 °C for 72 h and vortexed in an effort to allow it to completely relax. Under these conditions (as for the solvent switch approach), the system did relax to yield the spherical micelle phase (Figure S6). The assembly pathway takes a distinctly different route of reorganization depending on the conditions. The enzyme is able to force the polymers into a kinetically trapped but well-defined morphology. With experimental evidence in hand, we performed coarsegrained simulations to explore the mesoscopic self-organization of these materials. The copolymer is represented by a beadspring model, with molecular architecture as shown in Figure 1. The intra-molecular interactions that act along the chain

analysis verified the cleavage of the peptide for all three micelles had a similar yield (Figure S2). The behavior of the macromolecular aggregates after enzyme incubation was strongly dependent on the nature of the core block. When the core block possesses low Tg and low solvophobicity, that is, core blocks are highly mobile and the core−solvent interfacial energy is low, as is the case for the poly(ethyl acrylate) PPA, the micelles remained unaltered in size and morphology (Figure 2). On the other extreme, the poly(styrene) PPA micelles, with a low internal mobility and high solvophobicity, undergo macroscopic aggregation and precipitate from solution (Figure S5). The intermediate case, with highly mobile core and high solvophobicity, poly(lauryl acrylate) PPA, displays a richer set of behaviors. The material undergoes a nonequilibrium transition from a small spherical micelle to a larger vesicular structure (Figure 3). To elucidate the role of the kinetic pathway in the final self-assembled structure, we also performed a solvent switch protocol on the enzyme-treated block copolymers, which provides a representative, thermodynamically controlled assembly pathway of the cleaved polymers, termed the ideal assemblies (Table 1). Furthermore, controls with deactivated enzyme were also utilized (Figures S3 and S4) with no observed morphology change. It was observed that for the ideal assemblies, the representative thermodynamic structures upon cleavage were all spherical micelles with diameters comparable to the preenzyme-treated assemblies. Consistent with our design rationale was the behavior of the poly(ethyl acrylate) PPA system. It is understood that poly(ethyl acrylate) micelles are dynamic, and therefore the reorganization of the PPAs induced by the enzyme was under thermodynamic control, producing nanostructures that were of the lowest free energy and governed by the packing parameter (equilibrium geometry of the surfactant).37,39 Hence, the postincubation and ideal assembly structures were, within experimental error,40 indistinguishable (Figure 2), yielding spherical micelles with diameters of approximately 30 nm. On the other hand, high solvophobicity leads to different molecular aggregates depending on the assembly pathway. The poly(styrene) systems precipitated out of solution upon cleavage of the peptide in the coronal-forming block. This indicates that the macroscale precipitates formed with enzyme incubation were under kinetic control and were thermodynamically unstable, as the ideal assembly showed that stable spherical micelles are accessed in solution if the polymers were able to rearrange (possible via a solvent switch approach). Yet, because of the high Tg of the core, local reorganization of the polymer chains was inhibited. Therefore, macroscopic precipitation occurs during the first initially unstable phase in an attempt to reduce unfavorable water−core interactions immediately upon cleavage.41 The cleavage of the poly(lauryl acrylate) PPAs showed the formation of vesicles that were stable in solution (Figure 3). Again, the removal of solvent and application of the solvent switch method to these PPAs following enzymatic cleavage yield spherical micelles: the ideal assembly. Therefore, we understand the presence of these vesicles as the result of accessing a kinetically favorable pathway. Upon cleavage of the peptide, unfavorable interactions begin to occur, and the mobile micelle core begins to rearrange locally within the new aggregate.5,6 This local reorganization allows for the nanostructure to relax, with the high solvophobicity inhibiting polymer chain exchange between structures. Therefore, the

k

(

2

)

backbones are given by βuintra = 22 rij − l0 , where the distance between two bonded particles is rij, the equilibrium bond length is l0, and β = 1/kBT. To describe the intermolecular interactions, we have used the standard DPD model.44−48 Thus, the inter-molecular interactions are represented by soft potentials which allow for large time and length scales to be simulated, explicitly, the effective intermolecular force that a bead i feels due to the interaction with a bead j, is given by Fij = FijC + FijD + FijR . This total force has a conservative, dissipative, and random pairwise contribution. These are central forces and the corresponding rij 2

( ) (r ̂ ·v ),

magnitudes are: FijC = aij 1 − rij/r0 , FijD = −γ 1− r

(

FijR

(

)

0

ij ij

)

= σ 1 − rij/r0 ξij , for rij < r0 and are zero otherwise. and The vector vij = vi − vj is the relative velocity between the two interacting particles, γ and σ represent the strength of dissipation and fluctuation, respectively. To ensure local momentum conservation, the random force has the symmetry property ξij = ξji, also γ and σ are related via the fluctuation−dissipation theorem by σ2 = 2γkBT. Note that r0 sets the length scale in the simulations and the parameters aij quantify the repulsion between segments, representing the exclude volume interactions and the chemical incompatibility between unlike monomers. Following previous works on the modeling of polymersomes,51,49 the simulation parameters were chosen as follows: k2 = 40kBT, l0 = 0.85r0, σ = 3, and the reduced number density is fixed to ρ = 3. The intermolecular interaction parameters between the same chemical species were aij = 25, and the solvophobicity parameter was controlled by aTS (which took values 35 and 200, representing low and high solvophobicity). The intermolecular interactions between the coronal block and solvent was chosen as aHS = 26 (good solvent condition). The time step used to integrate the

equations of motion is Δt = 0.001τ, where τ = r02m /kBT . All simulations were performed using HOOMD-Blue.50−53 Images and movies were created by using VMD.54 To mimic the enzymatic reaction in the simulations, we used the following protocol. First, the PPAs were equilibrated under the solvent switch protocol. After equilibration, the branched peptide chains, attached to the polymer backbone, are deleted, and the system is followed during relaxation. To represent the experimental systems, we have varied the solvophobicity of the polymer tail. In all cases, spherical micelles are formed by the PPAs when equilibrated, as observed experimentally (Figure 4). When the solvophobicity is low (EA side chains), the 678

DOI: 10.1021/acsmacrolett.8b00887 ACS Macro Lett. 2019, 8, 676−681

Letter

ACS Macro Letters

initially surprising. Moreover, the ability to form models that can accurately predict block copolymer morphology switches, specifically ones far from equilibrium and unpredicted by conventional methods, will ultimately improve the fields’ capabilities to develop new solutions within a desired application.

simulation results show that after peptide cleavage, the micelles remain spherical (see Figure 4).

■

ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsmacrolett.8b00887. Synthesis of the PPAs and further characterization of polymers and particles, cryo-TEM, and DLS of particles (PDF) Movie of morphological evolution of polymer micelles after enzyme treatment for the lauryl acrylate core block (MPG)

Figure 4. Morphological transitions induced by the enzyme in silico. (The red schematic is to highlight aggregation formation.)

■

When the solvophobicity is large, the morphological evolution becomes more interesting (LA side chains, Figure 4). Here, we observe the fusion of spherical micelles to produce larger aggregates with hydrophobic cores. This process occurs relatively fast, with their diffusion and collision rates slowing as they increase in size. In this later stage, the time scales for collision are dominated by the free diffusion of the larger micelles. As more micelles collide, they display strong interface fluctuations, until eventually a small pocket of solvent is engulfed, creating a vesicle (see sequence of frames in Figure 5 and associated Movie S1).

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (N.C.G.). *E-mail: [email protected] (J.P.P.). ORCID

Joseph P. Patterson: 0000-0002-1975-1854 Juan J. de Pablo: 0000-0002-3526-516X Nathan C. Gianneschi: 0000-0001-9945-5475 Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS N.C.G. and J.J.P. acknowledge support of this collaborative project from the Army Research Office (MURI: W911NF-151-0568). We acknowledge the use of the UCSD Cryo-Electron Microscopy Facility, which was supported by NIH grants to Dr. Timothy S. Baker and a gift from the Agouron Institute to UCSD. We gratefully acknowledge the computing resources provided on Bebop, a high-performance computing cluster operated by the Laboratory Computing Resource Center at Argonne National Laboratory.

Figure 5. Morphological evolution of polymer micelles after enzyme treatment for the lauryl acrylate core block.

Simulations of the ideal assembly conditions (truncated peptide block, equilibrated by the solvent switch method) produced spherical micelles, in agreement with experiments. Both experiment and simulation support the conclusion that a nonequilibrium transition occurs when the polymer architecture is altered by the enzymes and the resulting structure is highly pathway-dependent. We note that the simulation was not able to model “frozen” cores (i.e., styrene) because the intermolecular interactions are soft and the crossing of polymer segments is unavoidable unless unreasonably low temperatures or exceptionally high densities are employed. To capture the associated physics, Lennard-Jones-type intermolecular interactions would be more appropriate, requiring computational capability beyond the scope of this study. In this work, our aim was to prepare diblock copolymers that differed in micellar core behavior in response to changes in response to stimuli at the hydrophilic corona. Our findings show that for PPAs studied, depending on the pathway (and core block identity), either stimuli-induced kinetically trapped morphologies were accessed or equilibrated structures were accessed. This fundamental study, combining experiment and simulation, provides an understanding of morphology control of the studied block copolymer assemblies in solution in response to stimuli, even in the case where outcomes are

■

REFERENCES

(1) Hadgiivanova, R.; Diamant, H.; Andelman, D. Kinetics of Surfactant Micellization: A Free Energy Approach. J. Phys. Chem. B 2011, 115 (22), 7268−7280. (2) Nicolai, T.; Colombani, O.; Chassenieux, C. Dynamic polymeric micelles versus frozen nanoparticles formed by block copolymers. Soft Matter 2010, 6 (14), 3111−3118. (3) Denkova, A. G.; Mendes, E.; Coppens, M.-O. Non-equilibrium dynamics of block copolymer micelles in solution: recent insights and open questions. Soft Matter 2010, 6 (11), 2351−2357. (4) Meli, L.; Lodge, T. P. Equilibrium vs Metastability: HighTemperature Annealing of Spherical Block Copolymer Micelles in an Ionic Liquid. Macromolecules 2009, 42 (3), 580−583. (5) Jain, S.; Bates, F. S. Consequences of Nonergodicity in Aqueous Binary PEO−PB Micellar Dispersions. Macromolecules 2004, 37 (4), 1511−1523. (6) Jain, S.; Bates, F. S. On the Origins of Morphological Complexity in Block Copolymer Surfactants. Science 2003, 300 (5618), 460−464. (7) Mai, Y.; Eisenberg, A. Self-assembly of block copolymers. Chem. Soc. Rev. 2012, 41 (18), 5969−5985. (8) Walther, A.; Goldmann, A. S.; Yelamanchili, R. S.; Drechsler, M.; Schmalz, H.; Eisenberg, A.; Müller, A. H. E. Multiple Morphologies, 679

DOI: 10.1021/acsmacrolett.8b00887 ACS Macro Lett. 2019, 8, 676−681

Letter

ACS Macro Letters

Biomedical Applications. J. Am. Chem. Soc. 2015, 137 (6), 2140− 2154. (29) Barnhill, S. A.; Bell, N. C.; Patterson, J. P.; Olds, D. P.; Gianneschi, N. C. Phase Diagrams of Polynorbornene Amphiphilic Block Copolymers in Solution. Macromolecules 2015, 48 (4), 1152− 1161. (30) Nguyen, M. M.; Carlini, A. S.; Chien, M.-P.; Sonnenberg, S.; Luo, C.; Braden, R. L.; Osborn, K. G.; Li, Y.; Gianneschi, N. C.; Christman, K. L. Enzyme-Responsive Nanoparticles for Targeted Accumulation and Prolonged Retention in Heart Tissue after Myocardial Infarction. Adv. Mater. 2015, 27 (37), 5547−5552. (31) Wright, D. B.; Patterson, J. P.; Pitto-Barry, A.; Cotanda, P.; Chassenieux, C.; Colombani, O.; O’Reilly, R. K. Tuning the aggregation behavior of pH-responsive micelles by copolymerization. Polym. Chem. 2015, 6, 2761. (32) Piogé, S.; Fontaine, L.; Gaillard, C.; Nicol, E.; Pascual, S. SelfAssembling Properties of Well-Defined Poly(ethylene oxide)-bpoly(ethyl acrylate) Diblock Copolymers. Macromolecules 2009, 42 (12), 4262−4272. (33) Stejskal, J.; Hlavatá, D.; Sikora, A.; Konňaḱ , Č .; Pleštil, J.; Kratochvíl, P. Equilibrium and non-equilibrium copolymer micelles: polystyrene-block-poly (ethylene-co-propylene) in decane and in diisopropylether. Polymer 1992, 33 (17), 3675−3685. (34) Wright, D. B.; Patterson, J. P.; Gianneschi, N. C.; Chassenieux, C.; Colombani, O.; O’Reilly, R. K. Blending block copolymer micelles in solution; obstacles of blending. Polym. Chem. 2016, 7, 1577. (35) Meli, L.; Santiago, J. M.; Lodge, T. P. Path-Dependent Morphology and Relaxation Kinetics of Highly Amphiphilic Diblock Copolymer Micelles in Ionic Liquids. Macromolecules 2010, 43 (4), 2018−2027. (36) Halperin, A. On Micellar Exchange: The Role of the Insertion Penalty. Macromolecules 2011, 44 (13), 5072−5074. (37) Halperin, A.; Alexander, S. Polymeric micelles: their relaxation kinetics. Macromolecules 1989, 22 (5), 2403−2412. (38) Wright, D. B.; Patterson, J. P.; Pitto-Barry, A.; Lu, A.; Kirby, N.; Gianneschi, N. C.; Chassenieux, C.; Colombani, O.; O’Reilly, R. K. The Copolymer Blending Method: A New Approach for Targeted Assembly of Micellar Nanoparticles. Macromolecules 2015, 48, 6516. (39) Nose, T.; Iyama, K. Micellization and relaxation kinetics of diblock copolymers in dilute solution based on A−W theory: I. Description of a model for core−corona type micelles. Comput. Theor. Polym. Sci. 2000, 10 (3−4), 249−257. (40) Patterson, J. P.; Robin, M. P.; Chassenieux, C.; Colombani, O.; O’Reilly, R. K. The analysis of solution self-assembled polymeric nanomaterials. Chem. Soc. Rev. 2014, 43 (8), 2412−2425. (41) Bendejacq, D. D.; Ponsinet, V. Double-Polyelectrolyte, LikeCharged Amphiphilic Diblock Copolymers: Swollen Structures and pH- and Salt-Dependent Lyotropic Behavior. J. Phys. Chem. B 2008, 112 (27), 7996−8009. (42) Kelley, E. G.; Murphy, R. P.; Seppala, J. E.; Smart, T. P.; Hann, S. D.; Sullivan, M. O.; Epps, T. H. Size evolution of highly amphiphilic macromolecular solution assemblies via a distinct bimodal pathway. Nat. Commun. 2014, DOI: 10.1038/ncomms4599. (43) Hurter, P. N.; Scheutjens, J. M. H. M.; Hatton, T. A. Molecular modeling of micelle formation and solubilization in block copolymer micelles. 1. A self-consistent mean-field lattice theory. Macromolecules 1993, 26 (21), 5592−5601. (44) Hurter, P. N.; Scheutjens, J. M. H. M.; Hatton, T. A. Molecular modeling of micelle formation and solubilization in block copolymer micelles. 1. A self-consistent mean-field lattice theory. Macromolecules 1993, 26, 5592−5601. (45) Espanol, P.; Warren, P. Statistical mechanics of dissipative particle dynamics. Europhys. Lett. 1995, 30, 191. (46) Groot, R. D.; Warren, P. B. Dissipative particle dynamics: Bridging the gap between atomistic and mesoscopic simulation. J. Chem. Phys. 1997, 107, 4423−4435. (47) Groot, R. D.; Madden, T. J. Dynamic simulation of diblock copolymer microphase separation. J. Chem. Phys. 1998, 108, 8713− 8724.

Phase Transitions, and Cross-Linking of Crew-Cut Aggregates of Polybutadiene-block-poly(2-vinylpyridine) Diblock Copolymers. Macromolecules 2008, 41 (9), 3254−3260. (9) Shen, H.; Eisenberg, A. Morphological Phase Diagram for a Ternary System of Block Copolymer PS310-b-PAA52/Dioxane/H2O. J. Phys. Chem. B 1999, 103 (44), 9473−9487. (10) Chen, L.; Shen, H.; Eisenberg, A. Kinetics and Mechanism of the Rod-to-Vesicle Transition of Block Copolymer Aggregates in Dilute Solution. J. Phys. Chem. B 1999, 103 (44), 9488−9497. (11) Shen, H.; Zhang, L.; Eisenberg, A. Thermodynamics of CrewCut Micelle Formation of Polystyrene-b-Poly(acrylic acid) Diblock Copolymers in DMF/H2O Mixtures. J. Phys. Chem. B 1997, 101 (24), 4697−4708. (12) Hayward, R. C.; Pochan, D. J. Tailored Assemblies of Block Copolymers in Solution: It Is All about the Process. Macromolecules 2010, 43 (8), 3577−3584. (13) Zhang, L.; Eisenberg, A. Thermodynamic vs Kinetic Aspects in the Formation and Morphological Transitions of Crew-Cut Aggregates Produced by Self-Assembly of Polystyrene-b-poly(acrylic acid) Block Copolymers in Dilute Solution. Macromolecules 1999, 32 (7), 2239−2249. (14) Qi, W.; Ghoroghchian, P. P.; Li, G.; Hammer, D. A.; Therien, M. J. Aqueous self-assembly of poly(ethylene oxide)-block-poly(?caprolactone) (PEO-b-PCL) copolymers: disparate diblock copolymer compositions give rise to nano- and meso-scale bilayered vesicles. Nanoscale 2013, 5 (22), 10908−10915. (15) Cai, S.; Vijayan, K.; Cheng, D.; Lima, E. M.; Discher, D. E. Micelles of Different MorphologiesAdvantages of Worm-like Filomicelles of PEO-PCL in Paclitaxel Delivery. Pharm. Res. 2007, 24 (11), 2099−2109. (16) Che, H.; van Hest, J. C. M. Stimuli-responsive polymersomes and nanoreactors. J. Mater. Chem. B 2016, 4 (27), 4632−4647. (17) Grubbs, R. B.; Sun, Z. Shape-changing polymer assemblies. Chem. Soc. Rev. 2013, 42 (17), 7436−7445. (18) Zhuang, J.; Gordon, M. R.; Ventura, J.; Li, L.; Thayumanavan, S. Multi-stimuli responsive macromolecules and their assemblies. Chem. Soc. Rev. 2013, 42 (17), 7421−7435. (19) Mura, S.; Nicolas, J.; Couvreur, P. Stimuli-responsive nanocarriers for drug delivery. Nat. Mater. 2013, 12 (11), 991−1003. (20) Nelson, A. Stimuli-responsive polymers: Engineering interactions. Nat. Mater. 2008, 7 (7), 523−525. (21) Molla, M. R.; Prasad, P.; Thayumanavan, S. Protein-Induced Supramolecular Disassembly of Amphiphilic Polypeptide Nanoassemblies. J. Am. Chem. Soc. 2015, 137 (23), 7286−7289. (22) Bacinello, D.; Garanger, E.; Taton, D.; Tam, K. C.; Lecommandoux, S. Enzyme-Degradable Self-Assembled Nanostructures from Polymer−Peptide Hybrids. Biomacromolecules 2014, 15 (5), 1882−1888. (23) Ku, T.-H.; Chien, M.-P.; Thompson, M. P.; Sinkovits, R. S.; Olson, N. H.; Baker, T. S.; Gianneschi, N. C. Controlling and Switching the Morphology of Micellar Nanoparticles with Enzymes. J. Am. Chem. Soc. 2011, 133 (22), 8392−8395. (24) Hahn, M. E.; Gianneschi, N. C. Enzyme-directed assembly and manipulation of organic nanomaterials. Chem. Commun. 2011, 47 (43), 11814−11821. (25) Randolph, L. M.; Chien, M.-P.; Gianneschi, N. C. Biological stimuli and biomolecules in the assembly and manipulation of nanoscale polymeric particles. Chem. Sci. 2012, 3 (5), 1363−1380. (26) Chien, M.-P.; Thompson, M. P.; Lin, E. C.; Gianneschi, N. C. Fluorogenic enzyme-responsive micellar nanoparticles. Chem. Sci. 2012, 3 (9), 2690−2694. (27) Chien, M.-P.; Carlini, A. S.; Hu, D.; Barback, C. V.; Rush, A. M.; Hall, D. J.; Orr, G.; Gianneschi, N. C. Enzyme-Directed Assembly of Nanoparticles in Tumors Monitored by in Vivo Whole Animal Imaging and ex Vivo Super-Resolution Fluorescence Imaging. J. Am. Chem. Soc. 2013, 135 (50), 18710−18713. (28) Blum, A. P.; Kammeyer, J. K.; Rush, A. M.; Callmann, C. E.; Hahn, M. E.; Gianneschi, N. C. Stimuli-Responsive Nanomaterials for 680

DOI: 10.1021/acsmacrolett.8b00887 ACS Macro Lett. 2019, 8, 676−681

Letter

ACS Macro Letters (48) Groot, R. D.; Madden, T. J.; Tildesley, D. J. On the role of hydrodynamic interactions in block copolymer mi-crophase separation. J. Chem. Phys. 1999, 110, 9739−9749. (49) Ortiz, V.; Nielsen, S. O.; Discher, D. E.; Klein, M. L.; Lipowsky, R.; Shillcock, J. Dissipative particle dynamics simulations of polymersomes. J. Phys. Chem. B 2005, 109, 17708−17714. (50) Shillcock, J. C.; Lipowsky, R. Tension-induced fusion of bilayer membranes and vesicles. Nat. Mater. 2005, 4, 225. (51) Phillips, C. L.; Anderson, J. A.; Glotzer, S. C. Pseudo-random number generation for Brownian Dynamics and Dissipative Particle Dynamics simulations on GPU devices. J. Comput. Phys. 2011, 230, 7191−7201. (52) Anderson, J. A.; Lorenz, C. D.; Travesset, A. General purpose molecular dynamics simulations fully implemented on graphics processing units. J. Comput. Phys. 2008, 227, 5342−5359. (53) Glaser, J.; Nguyen, T. D.; Anderson, J. A.; Lui, P.; Spiga, F.; Millan, J. A.; Morse, D. C.; Glotzer, S. C. Strong scaling of generalpurpose molecular dynamics simulations on GPUs. Comput. Phys. Commun. 2015, 192, 97−107. (54) Humphrey, W.; Dalke, A.; Schulten, K. VMD: visual molecular dynamics. J. Mol. Graphics 1996, 14, 33−38.

681

DOI: 10.1021/acsmacrolett.8b00887 ACS Macro Lett. 2019, 8, 676−681