Scale-Dependent Miscibility of Polylactide and Polyhydroxybutyrate: Molecular Dynamics Simulations

Glova, Artyom D.; Falkovich, Stanislav G.; Dmitrienko, Daniil I.; Lyulin, Sergey V.; Larin, Sergey V.; Nazarychev, Victor M.; Karttunen, Mikko

doi:10.1021/acs.macromol.7b01640

Cited by 57 publications

(94 citation statements)

References 96 publications

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“…After equilibration, single polymer samples and binary mixtures (PLGA and PEG together) were simulated at 500 K for 300 ns and 1 μs, respectively, to allow for proper equilibration. 24 Note that 500 K is well above the glass transition temperature for PLGA and PEG. Final configurations at 500 K were annealed down to 300 K at a rate of 10 K ns –1 and simulated for further 300 ns.…”

Section: Methodsmentioning

confidence: 98%

Predicting the Miscibility and Rigidity of Poly(lactic-co-glycolic acid)/Polyethylene Glycol Blends via Molecular Dynamics Simulations

et al. 2020

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The addition of polyethylene glycol (PEG) chains to poly(lactic- co -glycolic acid) (PLGA) matrices is extensively used to modulate the biodegradation, drug loading and release, mechanical properties, and chemical stability of the original system. Multiple parameters, including the molecular weight, relative concentration, polarity, and solubility, affect the physicochemical properties of the polymer blend. Here, molecular dynamics simulations with the united-atom 2016H66 force field are used to model the behavior of PLGA and PEG chains and thus predict the overall physicochemical features of the resulting blend. First, the model accuracy is validated against fundamental properties of pure PLGA and PEG samples. In agreement with previous experimental and theoretical observations, the PLGA solubility results to be higher in acetonitrile than in water, with Flory parameters ν ACN = 0.63 ± 0.01 and ν W = 0.21 ± 0.02, and the Young’s modulus of PLGA and PEG equal to Y = 2.0 ± 0.43 and 0.32 ± 0.34 GPa, respectively. Next, four PEG/PLGA blending regimes are identified by varying the relative concentrations and molecular weights of the individual polymers. The computational results demonstrate that at low PEG concentrations (<8% w/w), homogeneous blends are generated for both low and high PEG molecular weights. In contrast, at comparable PEG and PLGA concentrations (∼50% w/w), short PEG chains are only partially miscible whereas long PEG chains segregate within the PLGA matrix. This behavior has been confirmed experimentally via differential scanning calorimetry and is in agreement with previous observations. Finally, the computed Young’s modulus of PLGA/PEG blends is observed to decrease with the PEG content returning the lowest values for the partial and fully segregated regimens ( Y ≈ 1.3 GPa). This work proposes a computational scheme for predicting the physicochemical properties of PLGA/PEG blends paving the way toward the rational design of polymer mixtures for biomedical applications.

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Section: Methodsmentioning

confidence: 98%

Predicting the Miscibility and Rigidity of Poly(lactic-co-glycolic acid)/Polyethylene Glycol Blends via Molecular Dynamics Simulations

et al. 2020

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“…In addition to the consideration of environmental issues and resource shortages, it is important to choose an applicable polymer as the matrix of the composites. As a biodegradable and environment-friendly bioplastic [10,11], polylactic acid (PLA) can be produced by corns and other food crops [12,13,14] and has been widely used as matrixes for Fused Deposition Modeling (FDM) technology recently [15,16]. However, the brittleness and high cost of PLA limits its application [17].…”

Section: Introductionmentioning

confidence: 99%

Electrical and Thermal Conductivity of Polylactic Acid (PLA)-Based Biocomposites by Incorporation of Nano-Graphite Fabricated with Fused Deposition Modeling

Guo

Ren

et al. 2019

Polymers

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The aim of the study was to improve the electrical and thermal conductivity of the polylactic acid/wood flour/thermoplastic polyurethane composites by Fused Deposition Modeling (FDM). The results showed that, when the addition amount of nano-graphite reached 25 pbw, the volume resistivity of the composites decreased to 108 Ω·m, which was a significant reduction, indicating that the conductive network was already formed. It also had good thermal conductivity, mechanical properties, and thermal stability. The adding of the redox graphene (rGO) combined with graphite into the composites, compared to the tannic acid-functionalized graphite or the multi-walled carbon nanotubes, can be an effective method to improve the performance of the biocomposites, because the resistivity reduced by one order magnitude and the thermal conductivity increased by 25.71%. Models printed by FDM illustrated that the composite filaments have a certain flexibility and can be printed onto paper or flexible baseplates.

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“…This system was compared with the one where the grafting density σ = 1.76 nm −2 and the graft length N = 30 in order to examine difference in the structure between the two grafted layers at a fixed product of Nσ. According to our previous estimate of the characteristic ratio [22], the Kuhn segment length A for the lactide chains is equal to approximately 1.6 nm. The contour length L of the grafts under consideration could be calculated as L = aN, where a = 0.38 nm was the contour length of the monomer in the graft.…”

Section: Model and Simulation Methodsmentioning

confidence: 90%

“…The PLAFF3 force field [24], specifically developed for lactide chains on the In contrast to our previous studies, for the present work, the GAFF force field [23] was employed to describe the bonded and non-bonded interactions in the simulated composites [18][19][20][21]. The use of this force field for the simulations of lactide chains was validated in reference [22] on the basis of calculations for the chain's flexibility and the glass transition temperature for the corresponding bulk system. The present study, however, was devoted to composites filled with surface modified cellulose nanocrystals.…”

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confidence: 99%

“…After the compression, the obtained systems were simulated for 1 µs at a temperature of 600 K and at a pressure of 1 bar normal to the CNC surface. The choice of the simulation temperature of 600 K stemmed from the need to study the grafted layer immersed in the melt, as well as the need to accelerate the equilibration [22,28]. It is worth mentioning that the mean-square end-to-end distance H end-to-end of the examined grafts reached a constant value during the first 0.3 µs of the simulations; see Figure S1 in Supplementary Material (SM).…”

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confidence: 99%

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Grafting-Induced Structural Ordering of Lactide Chains

et al. 2019

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The structure of a grafted layer of lactide chains in the "dry brush" regime immersed in a melt of chemically similar polymer was examined while varying graft lengths. To this end, microsecond atomistic molecular dynamics simulations were performed. Almost no influence of graft length on the fraction of the grafted chains backfolded to the grafting surface was found. However, a structural ordering was unexpectedly observed in the system when the length of the grafted lactide chains was close to approximately 10 Kuhn segments. This ordering of the grafts is characterized by the formation of helical fragments whose structure is in good agreement with the experimental data for the α crystal of the lactide chains. Both the backfolding and the structural ordering may be viewed as the initial stage of the crystallization of the layer of grafted lactide chains. In contrast to the known behavior for conventional polymer brushes in the "dry brush" regime, the structure of the grafted lactide chains can be either amorphous or ordered, depending on the graft length N and the grafting density σ when their product Nσ is fixed.of the grafts into populations of backfolded and stretched chains was most pronounced at this σ in 96 comparison with the other grafting densities [19,20]. Having fixed σ, the length of the grafted chains 97 N was varied. Six lengths of the grafted chains, N = 13, 17, 22, 30, 40 and 50, were examined. Snapshots 98 of the systems in the case of N = 13 and 50 are presented in Figure 1. Additionally, a grafted layer in 99 the "dry brush" regime with the grafting density σ = 0.88 nm −2 and the graft length N = 60 was 100 simulated. This system was compared with the one where the grafting density σ = 1.76 nm −2 and the 101 graft length N = 30 in order to examine difference in the structure between the two grafted layers at 102 a fixed product of Nσ. According to our previous estimate of the characteristic ratio [22], the Kuhn 103 segment length A for the lactide chains is equal to approximately 1.6 nm. The contour length L of the 104 grafts under consideration could be calculated as  L aN , where a = 0.38 nm was the contour length 105 of the monomer in the graft. These calculations gave contour lengths L in the range 5-19 nm for the 106 considered length of the grafts at σ = 1.76 nm −2 . Thus, the number of Kuhn segments in the grafts at 107 this σ varied from approximately 3 to 12 units, lying in different orders of magnitude. For the grafts 108 where σ = 0.88 nm −2 , the contour length and the number of Kuhn segments were equal to about 23 nm 109 and 14 units, respectively. The chosen graft lengths were limited by the computational demands 110 required to perform simulations of the corresponding composites. To the best of our knowledge, the 111 considered grafts were among the longest ever studied by using atomistic molecular dynamics 112 simulations. In the present study, the total number of atoms in the system with the grafted layer at 113 σ = 1.76 nm −2 and N = 13 was about 53,000, while the composite c...

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Scale-Dependent Miscibility of Polylactide and Polyhydroxybutyrate: Molecular Dynamics Simulations

Cited by 57 publications

References 96 publications

Predicting the Miscibility and Rigidity of Poly(lactic-co-glycolic acid)/Polyethylene Glycol Blends via Molecular Dynamics Simulations

Predicting the Miscibility and Rigidity of Poly(lactic-co-glycolic acid)/Polyethylene Glycol Blends via Molecular Dynamics Simulations

Electrical and Thermal Conductivity of Polylactic Acid (PLA)-Based Biocomposites by Incorporation of Nano-Graphite Fabricated with Fused Deposition Modeling

Grafting-Induced Structural Ordering of Lactide Chains

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