1
|
Qiao L, Vega DA, Schmid F. Stability and Elasticity of Ultrathin Sphere-Patterned Block Copolymer Films. Macromolecules 2024; 57:4629-4634. [PMID: 38765499 PMCID: PMC11100483 DOI: 10.1021/acs.macromol.4c00460] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2024] [Revised: 04/05/2024] [Accepted: 04/12/2024] [Indexed: 05/22/2024]
Abstract
Sphere-patterned ultrathin block copolymer films are potentially interesting for a variety of applications in nanotechnology. We use self-consistent field theory to investigate the elastic response of sphere monolayer films with respect to in-plane shear, in-plane extension, compression deformations, and bending. The relations between the in-plane elastic moduli are roughly compatible with the expectations for two-dimensional elastic systems with hexagonal symmetry, with one notable exception: The pure shear and the simple shear moduli differ from each other by roughly 20%. Even more importantly, the bending constants are found to be negative, indicating that free-standing block copolymer membranes made of only a sphere monolayer are inherently unstable above the glass transition. Our results are discussed in view of the experimental findings.
Collapse
Affiliation(s)
- Le Qiao
- Institut
für Physik, Johannes Gutenberg-Universität
Mainz, Mainz D55099, Germany
| | - Daniel A. Vega
- Instituto
de Física del Sur (IFISUR), Consejo Nacional de Investigaciones
Científicas y Técnicas (CONICET), Universidad Nacional del Sur, Bahía Blanca 8000, Argentina
| | - Friederike Schmid
- Institut
für Physik, Johannes Gutenberg-Universität
Mainz, Mainz D55099, Germany
| |
Collapse
|
2
|
Spencer RKW, Santos-Pérez I, Rodríguez-Renovales I, Martinez Galvez JM, Shnyrova AV, Müller M. Membrane fission via transmembrane contact. Nat Commun 2024; 15:2793. [PMID: 38555357 PMCID: PMC10981662 DOI: 10.1038/s41467-024-47122-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2023] [Accepted: 03/20/2024] [Indexed: 04/02/2024] Open
Abstract
Division of intracellular organelles often correlates with additional membrane wrapping, e.g., by the endoplasmic reticulum or the outer mitochondrial membrane. Such wrapping plays a vital role in proteome and lipidome organization. However, how an extra membrane impacts the mechanics of the division has not been investigated. Here we combine fluorescence and cryo-electron microscopy experiments with self-consistent field theory to explore the stress-induced instabilities imposed by membrane wrapping in a simple double-membrane tubular system. We find that, at physiologically relevant conditions, the outer membrane facilitates an alternative pathway for the inner-tube fission through the formation of a transient contact (hemi-fusion) between both membranes. A detailed molecular theory of the fission pathways in the double membrane system reveals the topological complexity of the process, resulting both in leaky and leakless intermediates, with energies and topologies predicting physiological events.
Collapse
Affiliation(s)
- Russell K W Spencer
- Institute for Theoretical Physics, Georg-August University, Göttingen, Germany.
| | - Isaac Santos-Pérez
- Electron Microscopy and Crystallography Platform, Center for Cooperative Research in Biosciences (CIC bioGUNE), Derio, Spain
| | - Izaro Rodríguez-Renovales
- BREM Basque Resource for Electron Microscopy, Leioa, Spain
- Instituto Biofisika (CSIC, UPV/EHU), Barrio Sarriena, Leioa, Spain
| | - Juan Manuel Martinez Galvez
- Instituto Biofisika (CSIC, UPV/EHU), Barrio Sarriena, Leioa, Spain
- Department of Biochemistry and Molecular Biology, University of the Basque Country, Leioa, Spain
| | - Anna V Shnyrova
- Instituto Biofisika (CSIC, UPV/EHU), Barrio Sarriena, Leioa, Spain.
- Department of Biochemistry and Molecular Biology, University of the Basque Country, Leioa, Spain.
| | - Marcus Müller
- Institute for Theoretical Physics, Georg-August University, Göttingen, Germany.
| |
Collapse
|
3
|
Wang X, Xu S, Cohen FS, Zhang J, Cai Y. Mimicking effects of cholesterol in lipid bilayer membranes by self-assembled amphiphilic block copolymers. SOFT MATTER 2023; 19:5487-5501. [PMID: 37434554 PMCID: PMC11239197 DOI: 10.1039/d3sm00804e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/13/2023]
Abstract
The effect of cholesterol on biological membranes is important in biochemistry. In this study, a polymer system is used to simulate the consequences of varying cholesterol content in membranes. The system consists of an AB-diblock copolymer, a hydrophilic homopolymer hA, and a hydrophobic rigid homopolymer C, corresponding to phospholipid, water, and cholesterol, respectively. The effect of the C-polymer content on the membrane is studied within the framework of a self-consistent field model. The results show that the liquid-crystal behavior of B and C has a great influence on the chemical potential of cholesterol in bilayer membranes. The effects of the interaction strength between components, characterized by the Flory-Huggins parameters and the Maier-Saupe parameter, were studied. Some consequences of adding a coil headgroup to the C-rod are presented. Results of our model are compared to experimental findings for cholesterol-containing lipid bilayer membranes.
Collapse
Affiliation(s)
- Xiaoyuan Wang
- School of Mathematics and Statistics, Wuhan University, Wuhan 430072, China
| | - Shixin Xu
- Zu Chongzhi Center for Mathematics and Computational Sciences (CMCS), Global Health Research Center (GHRC), Duke Kunshan University, 8 Duke Ave, Kunshan, Jiangsu, China
| | - Fredric S Cohen
- Department of Physiology and Biophysics, Rush University Medical Center, Chicago, Illinois, USA
| | - Jiwei Zhang
- School of Mathematics and Statistics, and Hubei Key Laboratory of Computational Science, Wuhan University, Wuhan 430072, China.
| | - Yongqiang Cai
- School of Mathematical Sciences, Laboratory of Mathematics and Complex Systems, MOE, Beijing Normal University, 100875 Beijing, China.
| |
Collapse
|
4
|
Sun L, Pan F, Li S. Self-Assembly of Lipid Mixtures in Solutions: Structures, Dynamics Processes and Mechanical Properties. MEMBRANES 2022; 12:membranes12080730. [PMID: 35893448 PMCID: PMC9394357 DOI: 10.3390/membranes12080730] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/07/2022] [Revised: 07/19/2022] [Accepted: 07/20/2022] [Indexed: 02/01/2023]
Abstract
The self-assembly of lipid mixtures in aqueous solution was investigated by dissipative particle dynamics simulation. Two types of lipid molecules were modelled, where three mixed structures, i.e., the membrane, perforated membrane and vesicle, were determined in the self-assembly processes. Phase behaviour was investigated by using the phase diagrams based on the tail chain lengths for the two types of lipids. Several parameters, such as chain number and average radius of gyration, were employed to explore the structural formations of the membrane and perforated membrane in the dynamic processes. Interface tension was used to demonstrate the mechanical properties of the membrane and perforated membrane in the equilibrium state and dynamics processes. Results help us to understand the self-assembly mechanism of the biomolecule mixtures, which has a potential application for designing the lipid molecule-based bio-membranes in solutions.
Collapse
Affiliation(s)
| | - Fan Pan
- Correspondence: (F.P.); (S.L.)
| | | |
Collapse
|
5
|
Cai Y. Tilt Modulus of Bilayer Membranes Self-Assembled from Rod-Coil Diblock Copolymers. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2022; 38:5820-5828. [PMID: 35437996 DOI: 10.1021/acs.langmuir.2c00427] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Quantitatively understanding membrane fission and fusion requires a mathematical model taking their underlying elastic degrees of freedom, such as the molecule's tilt, into account. Hamm-Kozlov's model is such a framework that includes a tilt modulus along with the bending modulus and Gaussian modulus. This paper investigates the tilt modulus of liquid-crystalline bilayer membranes by applying self-consistent field theory. Unlike the widely used method in molecular dynamics simulation which extracts the tilt modulus by simulating bilayer buckles with various single modes, we introduce a tilt constrain term in the free energy to stabilize bilayers with various tilt angles. Fitting the energy curve as a function of the tilt angle to Hamm-Kozlov's elastic energy allows us to extract the tilt modulus directly. Based on this novel scheme and focused on the bilayers self-assembled from rod-coil diblock copolymers, we carry out a systematic study of the dependence of the tensionless A-phase bilayer's tilt modulus on the microscopic parameters.
Collapse
Affiliation(s)
- Yongqiang Cai
- School of Mathematical Sciences, Laboratory of Mathematics and Complex Systems, MOE, Beijing Normal University, 100875 Beijing, China
| |
Collapse
|
6
|
Wang X, Li S, Cai Y. Analytical Calculation of the Elastic Moduli of Self-Assembled Liquid-Crystalline Bilayer Membranes. J Phys Chem B 2021; 125:5309-5320. [PMID: 33989496 DOI: 10.1021/acs.jpcb.1c01116] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Liquid-crystalline orders are ubiquitous in membranes and could significantly affect the elastic properties of the self-assembled bilayers. Calculating the free energy of bilayer membranes with different geometries and fitting them to their theoretical expressions allow us to extract the elastic moduli, such as the bending modulus and Gaussian modulus. However, this procedure is time-consuming for liquid-crystalline bilayers. In paper reports a novel method to calculate the elastic moduli of the self-assembled liquid-crystalline bilayers within the self-consistent field theory framework. Based on the asymptotic expansion method, we derive the analytical expression of the elastic moduli, which reduces the computational cost significantly. Numerical simulations illustrate the validity and efficiency of the proposed method.
Collapse
Affiliation(s)
- Xiaoyuan Wang
- School of Mathematics and Statistics, Guizhou University, Huaxi District, 550025 Guiyang, China
| | - Sirui Li
- School of Mathematics and Statistics, Guizhou University, Huaxi District, 550025 Guiyang, China.,School of Mathematical Sciences, Zhejiang University, 886 Yuhang Road, Xihu District, 310027 Hangzhou, China
| | - Yongqiang Cai
- School of Mathematical Sciences, Laboratory of Mathematics and Complex Systems, MOE, Beijing Normal University, 100875 Beijing, China
| |
Collapse
|
7
|
Dixit M, Lazaridis T. Free energy of hydrophilic and hydrophobic pores in lipid bilayers by free energy perturbation of a restraint. J Chem Phys 2021; 153:054101. [PMID: 32770888 DOI: 10.1063/5.0016682] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The free energy of pore formation in lipid bilayers has been previously calculated using a variety of reaction coordinates. Here, we use free energy perturbation of a cylindrical lipid exclusion restraint to compute the free energy profile as a function of pore radius in dimyristoylphosphatidylcholine (DMPC) and dioleoylphosphatidylcholine (DOPC) bilayers. Additionally restraining the headgroups to lie on the membrane surface allows us to also calculate the free energy profile of hydrophobic pores, i.e., cylindrical pores lined by acyl chains. For certain pore radii, the free energy of wetting of hydrophobic pores is calculated using the density bias method. It is found that wetting of hydrophobic pores becomes thermodynamically favorable at 5.0 Å for DMPC and 6.5 Å for DOPC, although significant barriers prevent spontaneous wetting of the latter on a nanosecond time scale. The free energy of transformation of hydrophilic pores to hydrophobic ones is also calculated using free energy perturbation of headgroup restraints along the bilayer normal. This quantity, along with wetting and pore growth free energies, provides complete free energy profiles as a function of radius. Pore line tension values for the hydrophilic pores obtained from the slope of the free energy profiles are 37.6 pN for DMPC and 53.7 pN for DOPC. The free energy profiles for the hydrophobic pores are analyzed in terms of elementary interfacial tensions. It is found that a positive three-phase line tension is required to explain the results. The estimated value for this three-phase line tension (51.2 pN) lies within the expected range.
Collapse
Affiliation(s)
- Mayank Dixit
- Department of Chemistry, City College of New York, 160 Convent Ave., New York, New York 10031, USA
| | - Themis Lazaridis
- Department of Chemistry, City College of New York, 160 Convent Ave., New York, New York 10031, USA
| |
Collapse
|
8
|
Yang Y, Bu X, Zhang X. Regulation Mechanism of Bubbling Deformation and Fracture Toughness of the Membrane by Asymmetric Phospholipids: A Model System Study. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2020; 36:10138-10146. [PMID: 32787040 DOI: 10.1021/acs.langmuir.0c01580] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Dynamic regulation of the deformation modulus and fracture toughness of a membrane is critical to organelles and cells for matching their conflicting needs of resilient and fractured behaviors. These properties implement the protection of the function in the normal condition and the fission function in the endocytosis condition of a membrane. Naturally, a membrane contains phospholipids that have different hydrophilic and hydrophobic group length. The diffusion and aggregation of the phospholipids with asymmetry of the hydrophilic-hydrophobic ratio on the membrane play a key role in regulating the mechanical behaviors passively to the external force. In present work, the effects of the asymmetry of phospholipids on the bubbling deformation and fracture toughness of the membrane to external stretching are investigated in a model system. A disk-shaped micelle formed from the blend of symmetric and asymmetric diblock copolymers in a selective solvent is considered as the membrane sheet. Its mechanically responsive behaviors are investigated by self-consistent field theory. By analyzing the evolution of different components during the stretching process, the mechanism of formation of the bubbling structure is revealed. Moreover, the fracture toughness depending on the asymmetry of the phospholipids is determined quantitatively.
Collapse
Affiliation(s)
- Yang Yang
- School of Science, Beijing Jiaotong University, Beijing 100044, PR China
| | - Xiangyu Bu
- School of Science, Beijing Jiaotong University, Beijing 100044, PR China
| | - Xinghua Zhang
- School of Science, Beijing Jiaotong University, Beijing 100044, PR China
| |
Collapse
|
9
|
Cai Y, Li S, Shi AC. Elastic properties of self-assembled bilayer membranes: Analytic expressions via asymptotic expansion. J Chem Phys 2020; 152:244121. [PMID: 32610980 DOI: 10.1063/5.0009734] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
Bilayer membranes self-assembled from amphiphilic molecules are ubiquitous in biological and soft matter systems. The elastic properties of bilayer membranes are essential in determining the shape and structure of bilayers. A novel method to calculate the elastic moduli of the self-assembled bilayers within the framework of the self-consistent field theory is developed based on an asymptotic expansion of the order parameters in terms of the bilayer curvature. In particular, the asymptotic expansion method is used to derive analytic expressions of the elastic moduli, which allows us to design more efficient numerical schemes. The efficiency of the proposed method is illustrated by a model system composed of flexible amphiphilic chains dissolved in hydrophilic polymeric solvents.
Collapse
Affiliation(s)
- Yongqiang Cai
- Department of Mathematics, National University of Singapore, 21 Lower Kent Ridge Road, Singapore 119077, Singapore
| | - Sirui Li
- School of Mathematics and Statistics, Guizhou University, Huaxi District, Guiyang 550025, People's Republic of China
| | - An-Chang Shi
- Department of Physics and Astronomy, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4M1, Canada
| |
Collapse
|
10
|
Liu B, Zhang X, Yan D. The responsive behaviors of bilayer membrane under uniaxial mechanical probe. J Chem Phys 2020; 152:104901. [PMID: 32171195 DOI: 10.1063/5.0001784] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
In experiments, atomic force microscopy technology was used to measure the modulus of the membrane. However, these studies mainly focus on the linear responsive behavior. In the present work, a theoretical study is performed to show the nonlinear responsive behavior, which includes the stretching induced structural transitions. It demonstrates that the structural transition of the bilayer membrane takes place during the stretching process of the mechanical probe. A vertical cylindrical micelle can be obtained by stretching the membrane under deep compression conditions, and the cylindrical micelle can grow continuously along the axial direction. Moreover, under shallow compression conditions, the probe pulls a spherical micelle from the membrane, and then, the membrane returns to flatness. A comprehensive study is performed to show the mechanism of the responsive behaviors of the structural transition during the compression and stretching processes. When the probe acts on the B-rich layer, it is more likely to pull out a regular micelle. However, when the probe acts on the bottom A-rich layer, complex vesicles are more likely to be pulled out from the bilayer membrane. This study provides a comprehensive diagram of the mechanical responsive behavior of the membrane, which would be a guide for an experiment of biomembranes and the design of new self-assembled structures.
Collapse
Affiliation(s)
- Baopi Liu
- Department of Physics, Beijing Normal University, Beijing 100875, China
| | - Xinghua Zhang
- School of Science, Beijing Jiaotong University, Beijing 100044, China
| | - Dadong Yan
- Department of Physics, Beijing Normal University, Beijing 100875, China
| |
Collapse
|
11
|
Han Y, Xu Z, Shi AC, Zhang L. Pathways connecting two opposed bilayers with a fusion pore: a molecularly-informed phase field approach. SOFT MATTER 2020; 16:366-374. [PMID: 31799560 DOI: 10.1039/c9sm01983a] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
A phase field model with two phase fields, representing the concentration and the head-tail separation of amphiphilic molecules, respectively, has been constructed using an extension of the Ohta-Kawasaki model (Macromolecules, 1986, 19, 2621-2632). It is shown that this molecularly-informed phase field model is capable of producing various self-assembled amphiphilic aggregates, such as bilayers, vesicles and micelles. Furthermore, pathways connecting two opposed bilayers with a fusion pore are obtained by using a combination of the phase field model and the string method. Multiple fusion pathways, including a classical pathway and a leaky pathway, have been obtained depending on the initial separation of the two bilayers. The study shed light on the understanding of the membrane fusion pathways and, more importantly, laid a foundation for further investigation of more complex membrane morphologies and transitions.
Collapse
Affiliation(s)
- Yucen Han
- Beijing International Center for Mathematical Research, Peking University, Beijing 100871, China.
| | | | | | | |
Collapse
|
12
|
Cai Y, Zhang P, Shi AC. Elastic properties of liquid-crystalline bilayers self-assembled from semiflexible-flexible diblock copolymers. SOFT MATTER 2019; 15:9215-9223. [PMID: 31642464 DOI: 10.1039/c9sm01844a] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
The mechanical response and shape of self-assembled bilayer membranes depend crucially on their elastic properties. Most of the studies focused on the elastic properties of fluid membranes, despite the ubiquitous presence of membranes with liquid-crystalline order. Here the elastic properties of liquid-crystalline bilayers self-assembled from diblock copolymers composed of a semiflexible block are studied theoretically. Specifically, the self-consistent field theory (SCFT) is applied to a model system composed of semiflexible-flexible diblock copolymers dissolved in flexible homopolymers that act as solvents. The free energy of self-assembled tensionless bilayer membranes in three different geometries, i.e. planar, cylindrical and spherical, is obtained by solving the SCFT equations using a hybrid method, in which the orientation-dependent functions are treated using the spherical harmonics, whereas the position-dependent operators are treated using the compact difference schemes. The bending modulus κM and Gaussian modulus κG of the bilayer are extracted from the free energies. The effects of the molecular parameters of the system, such as the chain rigidity and the orientational interaction, are systematically examined.
Collapse
Affiliation(s)
- Yongqiang Cai
- Department of Mathematics, National University of Singapore, Singapore 119076, Singapore.
| | - Pingwen Zhang
- LMAM, CAPT and School of Mathematical Sciences, Peking University, Beijing 100871, P. R. China.
| | - An-Chang Shi
- Department of Physics and Astronomy, McMaster University, Hamilton L8S 4M1, Ontario, Canada.
| |
Collapse
|
13
|
Xu R, Dehghan A, Shi AC, Zhou J. Elastic property of membranes self-assembled from diblock and triblock copolymers. Chem Phys Lipids 2019; 221:83-92. [PMID: 30926383 DOI: 10.1016/j.chemphyslip.2019.03.015] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2018] [Revised: 03/23/2019] [Accepted: 03/25/2019] [Indexed: 01/31/2023]
Abstract
The elastic property of membranes self-assembled from AB diblock and ABA triblock copolymers, as coarse-grained model of lipids and the bolalipids, are studied using the self-consistent field theory (SCFT). Specifically, solutions of the SCFT equations, corresponding to membranes in different geometries (planar, cylindrical, spherical, and pore) have been obtained for a model system composed of amphiphilic AB diblock copolymers and ABA triblock copolymers dissolved in A homopolymers. The free energy of the membranes with different geometries is then used to extract the bending modulus, Gaussian modulus, and line tension of the membranes. The results reveal that the bending modulus of the triblock membrane is greater than that of the diblock membrane. Furthermore, the Gaussian modulus and line tension of the triblock membrane indicate that the triblock membranes have higher pore formation energy than that of the diblock membranes. The equilibrium bridging and looping fractions of the triblock copolymers are also obtained. Implications of the theoretical results on the elastic properties of biologically equivalent lipid bilayers and the bolalipid membranes are discussed.
Collapse
Affiliation(s)
- Rui Xu
- Department of Physics & Astronomy, McMaster University, 1280 Main Street West, Hamilton, Ontario, L8S 4M1, Canada
| | - Ashkan Dehghan
- Department of Physics & Astronomy, McMaster University, 1280 Main Street West, Hamilton, Ontario, L8S 4M1, Canada
| | - An-Chang Shi
- Department of Physics & Astronomy, McMaster University, 1280 Main Street West, Hamilton, Ontario, L8S 4M1, Canada.
| | - Jiajia Zhou
- Center of Soft Matter Physics and its Applications, Beihang University, Beijing 100191, China; School of Chemistry, Key Laboratory of Bio-Inspired Smart Interfacial Science and Technology of Ministry of Education, Beihang University, Beijing 100191, China; Beijing Advanced Innovation Center for Biomedical Engineering, Beihang University, Beijing 100191, China.
| |
Collapse
|
14
|
Bowman C, Chaplain M, Matzavinos A. Dissipative particle dynamics simulation of critical pore size in a lipid bilayer membrane. ROYAL SOCIETY OPEN SCIENCE 2019; 6:181657. [PMID: 31032022 PMCID: PMC6458407 DOI: 10.1098/rsos.181657] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/30/2018] [Accepted: 01/22/2019] [Indexed: 05/14/2023]
Abstract
We investigate with computer simulations the critical radius of pores in a lipid bilayer membrane. Ilton et al. (Ilton et al. 2016 Phys. Rev. Lett. 117, 257801 (doi:10.1103/PhysRevLett.117.257801)) recently showed that nucleated pores in a homopolymer film can increase or decrease in size, depending on whether they are larger or smaller than a critical size which scales linearly with film thickness. Using dissipative particle dynamics, a particle-based simulation method, we investigate the same scenario for a lipid bilayer membrane whose structure is determined by lipid-water interactions. We simulate a perforated membrane in which holes larger than a critical radius grow, while holes smaller than the critical radius close, as in the experiment of Ilton et al. (Ilton et al. 2016 Phys. Rev. Lett. 117, 257801 (doi:10.1103/PhysRevLett.117.257801)). By altering key system parameters such as the number of particles per lipid and the periodicity, we also describe scenarios in which pores of any initial size can seal or even remain stable, showing a fundamental difference in the behaviour of lipid membranes from polymer films.
Collapse
Affiliation(s)
- Clark Bowman
- Division of Applied Mathematics, Brown University, Providence, RI 02912, USA
| | - Mark Chaplain
- School of Mathematics and Statistics, University of St Andrews, St Andrews KY16 9SS, UK
| | - Anastasios Matzavinos
- Division of Applied Mathematics, Brown University, Providence, RI 02912, USA
- Author for correspondence: Anastasios Matzavinos e-mail:
| |
Collapse
|
15
|
Cai Y, Zhang P, Shi AC. Liquid crystalline bilayers self-assembled from rod-coil diblock copolymers. SOFT MATTER 2017; 13:4607-4615. [PMID: 28604893 DOI: 10.1039/c7sm00354d] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
The structure and phase behaviour of bilayer membranes self-assembled from rod-coil diblock copolymers are studied using the self-consistent field theory, focusing on the occurrence and relative stability of liquid crystalline phases induced by the geometric shape and orientational interaction of the rod-blocks. A variety of liquid crystalline bilayers, corresponding to the smectic phases in bulk systems, are predicted to occur as equilibrium phases of the system. The ordered morphologies and phase behaviour of the system are analyzed. Phase diagrams of the self-assembled bilayers are constructed. The theoretical results provide an understanding of the formation mechanisms of these intricate phases.
Collapse
Affiliation(s)
- Yongqiang Cai
- School of Mathematical Sciences, Peking University, Beijing 100871, P. R. China.
| | - Pingwen Zhang
- LMAM, CAPT and School of Mathematical Sciences, Peking University, Beijing 100871, P. R. China.
| | - An-Chang Shi
- Department of Physics and Astronomy, McMaster University, Hamilton, Ontario L8S 4M1, Canada.
| |
Collapse
|
16
|
Qiang X, Wang X, Ji Y, Li S, He L. Liquid-crystal self-assembly of lipid membranes on solutions: A dissipative particle dynamic simulation study. POLYMER 2017. [DOI: 10.1016/j.polymer.2017.03.021] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
|
17
|
Huang C, Quinn D, Sadovsky Y, Suresh S, Hsia KJ. Formation and size distribution of self-assembled vesicles. Proc Natl Acad Sci U S A 2017; 114:2910-2915. [PMID: 28265065 PMCID: PMC5358381 DOI: 10.1073/pnas.1702065114] [Citation(s) in RCA: 92] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
When detergents and phospholipid membranes are dispersed in aqueous solutions, they tend to self-assemble into vesicles of various shapes and sizes by virtue of their hydrophobic and hydrophilic segments. A clearer understanding of such vesiculation processes holds promise for better elucidation of human physiology and disease, and paves the way to improved diagnostics, drug development, and drug delivery. Here we present a detailed analysis of the energetics and thermodynamics of vesiculation by recourse to nonlinear elasticity, taking into account large deformation that may arise during the vesiculation process. The effects of membrane size, spontaneous curvature, and membrane stiffness on vesiculation and vesicle size distribution were investigated, and the critical size for vesicle formation was determined and found to compare favorably with available experimental evidence. Our analysis also showed that the critical membrane size for spontaneous vesiculation was correlated with membrane thickness, and further illustrated how the combined effects of membrane thickness and physical properties influenced the size, shape, and distribution of vesicles. These findings shed light on the formation of physiological extracellular vesicles, such as exosomes. The findings also suggest pathways for manipulating the size, shape, distribution, and physical properties of synthetic vesicles, with potential applications in vesicle physiology, the pathobiology of cancer and other diseases, diagnostics using in vivo liquid biopsy, and drug delivery methods.
Collapse
Affiliation(s)
- Changjin Huang
- Department of Biomedical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213
| | - David Quinn
- Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213
| | - Yoel Sadovsky
- Magee-Womens Research Institute, University of Pittsburgh, Pittsburgh, PA 15213
- Department of Obstetrics, Gynecology, and Reproductive Sciences, University of Pittsburgh, Pittsburgh, PA 15213
- Department of Microbiology and Molecular Genetics, University of Pittsburgh, Pittsburgh, PA 15219
| | - Subra Suresh
- Department of Biomedical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213;
- Department of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, PA 15213
- Department of Computational Biology, Carnegie Mellon University, Pittsburgh, PA 15213
- School of Medicine, University of Pittsburgh, Pittsburgh, PA 15261
| | - K Jimmy Hsia
- Department of Biomedical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213;
- Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213
| |
Collapse
|
18
|
Ilton M, DiMaria C, Dalnoki-Veress K. Direct Measurement of the Critical Pore Size in a Model Membrane. PHYSICAL REVIEW LETTERS 2016; 117:257801. [PMID: 28036217 DOI: 10.1103/physrevlett.117.257801] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/17/2015] [Indexed: 05/27/2023]
Abstract
We study pore nucleation in a model membrane system, a freestanding polymer film. Nucleated pores smaller than a critical size close, while pores larger than the critical size grow. Holes of varying size were purposefully prepared in liquid polymer films, and their evolution in time was monitored using optical and atomic force microscopy to extract a critical radius. The critical radius scales linearly with film thickness for a homopolymer film. The results agree with a simple model which takes into account the energy cost due to surface area at the edge of the pore. The energy cost at the edge of the pore is experimentally varied by using a lamellar-forming diblock copolymer membrane. The underlying molecular architecture causes increased frustration at the pore edge resulting in an enhanced cost of pore formation.
Collapse
Affiliation(s)
- Mark Ilton
- Department of Physics & Astronomy, McMaster University, Hamilton, Ontario L8S 4M1, Canada
| | - Christian DiMaria
- Department of Physics & Astronomy, McMaster University, Hamilton, Ontario L8S 4M1, Canada
| | - Kari Dalnoki-Veress
- Department of Physics & Astronomy, McMaster University, Hamilton, Ontario L8S 4M1, Canada
- Laboratoire de Physico-Chimie Théorique, UMR CNRS Gulliver 7083, ESPCI ParisTech, PSL Research University, 75005 Paris, France
| |
Collapse
|
19
|
Schmid F. Physical mechanisms of micro- and nanodomain formation in multicomponent lipid membranes. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2016; 1859:509-528. [PMID: 27823927 DOI: 10.1016/j.bbamem.2016.10.021] [Citation(s) in RCA: 71] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/26/2016] [Revised: 10/19/2016] [Accepted: 10/27/2016] [Indexed: 12/17/2022]
Abstract
This article summarizes a variety of physical mechanisms proposed in the literature, which can generate micro- and nanodomains in multicomponent lipid bilayers and biomembranes. It mainly focusses on lipid-driven mechanisms that do not involve direct protein-protein interactions. Specifically, it considers (i) equilibrium mechanisms based on lipid-lipid phase separation such as critical cluster formation close to critical points, and multiple domain formation in curved geometries, (ii) equilibrium mechanisms that stabilize two-dimensional microemulsions, such as the effect of linactants and the effect of curvature-composition coupling in bilayers and monolayers, and (iii) non-equilibrium mechanisms induced by the interaction of a biomembrane with the cellular environment, such as membrane recycling and the pinning effects of the cytoplasm. Theoretical predictions are discussed together with simulations and experiments. The presentation is guided by the theory of phase transitions and critical phenomena, and the appendix summarizes the mathematical background in a concise way within the framework of the Ginzburg-Landau theory. This article is part of a Special Issue entitled: Lipid order/lipid defects and lipid-control of protein activity edited by Dirk Schneider.
Collapse
Affiliation(s)
- Friederike Schmid
- Institute of Physics, Johannes Gutenberg University, 55099 Mainz, Germany
| |
Collapse
|
20
|
Smirnova YG, Müller M. Calculation of membrane bending rigidity using field-theoretic umbrella sampling. J Chem Phys 2016; 143:243155. [PMID: 26723640 DOI: 10.1063/1.4938383] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The free-energy change of membrane shape transformations can be small, e.g., as in the case of membrane bending. Therefore, the calculation of the free-energy difference between different membrane morphologies is a challenge. Here, we discuss a computational method - field-theoretic umbrella sampling - to compute the local chemical potential of a non-equilibrium configuration and illustrate how one can apply it to study free-energy changes of membrane transformations using simulations. Specifically, the chemical potential profile of the bent membrane and the bending rigidity of membrane are calculated for a soft, coarse-grained amphiphile model and the MARTINI model of a dioleoylphosphatidylcholine (DOPC) membrane.
Collapse
Affiliation(s)
- Y G Smirnova
- Institute for Theoretical Physics, Georg-August-Universität, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
| | - M Müller
- Institute for Theoretical Physics, Georg-August-Universität, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
| |
Collapse
|
21
|
Ahmadpoor F, Sharma P. Thermal fluctuations of vesicles and nonlinear curvature elasticity--implications for size-dependent renormalized bending rigidity and vesicle size distribution. SOFT MATTER 2016; 12:2523-36. [PMID: 26739194 DOI: 10.1039/c5sm02769a] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Both closed and open biological membranes noticeably undulate at physiological temperatures. These thermal fluctuations influence a broad range of biophysical phenomena, ranging from self-assembly to adhesion. In particular, the experimentally measured thermal fluctuation spectra also provide a facile route to the assessment of mechanical and certain other physical properties of biological membranes. The theoretical assessment of thermal fluctuations, be it for closed vesicles or the simpler case of flat open lipid bilayers, is predicated upon assuming that the elastic curvature energy is a quadratic functional of the curvature tensor. However, a qualitatively correct description of several phenomena such as binding-unbinding transition, vesicle-to-bicelle transition, appearance of hats and saddles among others, appears to require consideration of constitutively nonlinear elasticity that includes fourth order curvature contributions rather than just quadratic. In particular, such nonlinear considerations are relevant in the context of large-curvature or small-sized vesicles. In this work we discuss the statistical mechanics of closed membranes (vesicles) incorporating both constitutive and geometrical nonlinearities. We derive results for the renormalized bending rigidity of small vesicles and show that significant stiffening may occur for sub-20 nm vesicle sizes. Our closed-form results may also be used to determine nonlinear curvature elasticity properties from either experimentally measured fluctuation spectra or microscopic calculations such as molecular dynamics. Finally, in the context of our results on thermal fluctuations of vesicles and nonlinear curvature elasticity, we reexamine the problem of determining the size distribution of vesicles and obtain results that reconcile well with experimental observations. However, our results are somewhat paradoxical. Specifically, the molecular dynamics predictions for the thermo-mechanical behavior of small vesicles of prior studies appear to be inconsistent with the nonlinear elastic properties that we estimate by fitting to the experimentally determined vesicle size-distribution trends and data.
Collapse
Affiliation(s)
- Fatemeh Ahmadpoor
- Department of Mechanical Engineering, University of Houston, Houston, Texas 77204, USA.
| | | |
Collapse
|
22
|
Hoiles W, Krishnamurthy V, Cranfield CG, Cornell B. An engineered membrane to measure electroporation: effect of tethers and bioelectronic interface. Biophys J 2015; 107:1339-51. [PMID: 25229142 DOI: 10.1016/j.bpj.2014.07.056] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2014] [Revised: 06/27/2014] [Accepted: 07/30/2014] [Indexed: 01/19/2023] Open
Abstract
This article reports on the construction and predictive models for a platform comprised of an engineered tethered membrane. The platform provides a controllable and physiologically relevant environment for the study of the electroporation process. The mixed self-assembled membrane is formed via a rapid solvent exchange technique. The membrane is tethered to the gold electrode and includes an ionic reservoir separating the membrane and gold surface. Above the membrane, there is an electrolyte solution, and a gold counterelectrode. A voltage is applied between the gold electrodes and the current measured. The current is dependent on the energy required to form aqueous pores and the conductance of each pore. A two-level predictive model, consisting of a macroscopic and a continuum model, is developed to relate the pore dynamics to the measured current. The macroscopic model consists of an equivalent circuit model of the tethered membrane, and asymptotic approximations to the Smoluchowski-Einstein equation of electroporation that is dependent on the pore conductance and the energy required to form aqueous pores. The continuum model is a generalized Poisson-Nernst-Planck (GPNP) system where an activity coefficient to account for steric effects of ions is added to the standard PNP system. The GPNP is used to evaluate the conductance of aqueous pores, and the electrical energy required to form the pores. As an outcome of the setup of the device and the two-level model, biologically important variables can be estimated from experimental measurements. To validate the accuracy of the two-level model, the predicted current is compared with experimentally measured current for different tethering densities.
Collapse
Affiliation(s)
- William Hoiles
- Department of Electrical and Computer Engineering, University of British Columbia, Vancouver, British Columbia, Canada
| | - Vikram Krishnamurthy
- Department of Electrical and Computer Engineering, University of British Columbia, Vancouver, British Columbia, Canada.
| | - Charles G Cranfield
- School of Medical and Molecular Biosciences, University of Technology Sydney, Broadway, New South Wales, Australia; Victor Chang Cardiac Research Institute, Darlinghurst, New South Wales, Australia
| | - Bruce Cornell
- Surgical Diagnostics, Roseville, New South Wales, Australia
| |
Collapse
|
23
|
Dehghan A, Pastor KA, Shi AC. Line tension of multicomponent bilayer membranes. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2015; 91:022713. [PMID: 25768537 DOI: 10.1103/physreve.91.022713] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/26/2014] [Indexed: 06/04/2023]
Abstract
The line tension or edge energy of bilayer membranes self-assembled from binary amphiphilic molecules is studied using self-consistent-field theory (SCFT). Specifically, solutions of the SCFT equations corresponding to an infinite membrane with a circular pore, or an open membrane, are obtained for a coarse-grained model in which the amphiphilic species and hydrophilic solvents are represented by ABandED diblock copolymers and C homopolymers, respectively. The edge energy of the membrane is extracted from the free energy of the open membranes. Results for membranes composed of mixtures of symmetric and cone- or inverse cone-shaped amphiphilic molecules with neutral and/or repulsive interactions are obtained and analyzed. It is observed that an increase in the concentration of the cone-shaped species leads to a decrease of the line tension. In contrast, adding inverse cone-shaped copolymers results in an increase of the line tension. Furthermore, the density profile of the copolymers reveals that the line tension is regulated by the distribution of the amphiphiles at the bilayer edge.
Collapse
Affiliation(s)
- Ashkan Dehghan
- Department of Physics and Astronomy, McMaster University, Hamilton, Ontario, Canada L8S 4M1
| | - Kyle A Pastor
- Department of Physics and Astronomy, McMaster University, Hamilton, Ontario, Canada L8S 4M1
| | - An-Chang Shi
- Department of Physics and Astronomy, McMaster University, Hamilton, Ontario, Canada L8S 4M1
| |
Collapse
|
24
|
Deserno M. Fluid lipid membranes: From differential geometry to curvature stresses. Chem Phys Lipids 2015; 185:11-45. [DOI: 10.1016/j.chemphyslip.2014.05.001] [Citation(s) in RCA: 137] [Impact Index Per Article: 15.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2014] [Revised: 04/21/2014] [Accepted: 05/06/2014] [Indexed: 10/25/2022]
|
25
|
Li D, Liang K, Gruhn T. Mean Field Theory of Diblock Copolymer on Curved Manifolds. ACTA ACUST UNITED AC 2014. [DOI: 10.1002/masy.201400040] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Daming Li
- Department of Mathematics; Shanghai Jiao Tong University; Shanghai 200240 China
| | - Kewei Liang
- Department of Mathematics; Zhejiang University; Hangzhou 310027 China
| | - Thomas Gruhn
- Materials and Process Simulation (MPS); University of Bayreuth; Postfach 10 12 51 D-95440 Bayreuth Germany
| |
Collapse
|
26
|
Li J, Zhang H, Qiu F, Shi AC. Emergence and stability of intermediate open vesicles in disk-to-vesicle transitions. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2013; 88:012719. [PMID: 23944502 DOI: 10.1103/physreve.88.012719] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/22/2012] [Indexed: 06/02/2023]
Abstract
The transition between two basic structures, a disk and an enclosed vesicle, of a finite membrane is studied by examining the minimum energy path (MEP) connecting these two states. The MEP is constructed using the string method applied to continuum elastic membrane models. The results reveal that, besides the commonly observed disk and vesicle, open vesicles (bowl-shaped vesicles or vesicles with a pore) can become stable or metastable shapes. The emergence, stability, and probability distribution of these open vesicles are analyzed. It is demonstrated that open vesicles can be stabilized by higher-order elastic energies. The estimated probability distribution of the different structures is in good agreement with available experiments.
Collapse
Affiliation(s)
- Jianfeng Li
- The State Key Laboratory of Molecular Engineering of Polymers, Department of Macromolecular Science, Fudan University, Shanghai 200433, China.
| | | | | | | |
Collapse
|
27
|
Computational Studies of Biomembrane Systems: Theoretical Considerations, Simulation Models, and Applications. FROM SINGLE MOLECULES TO NANOSCOPICALLY STRUCTURED MATERIALS 2013. [DOI: 10.1007/12_2013_258] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
|