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Hierarchical materials with interconnected pores from capillary suspensions for bone tissue engineering 用于骨组织工程的具有毛细悬浮液互联孔隙的分层材料
Pub Date : 2024-08-08 DOI: arxiv-2408.04337
Souhaila Nider, Femke De Ceulaer, Berfu Göksel, Annabel Braem, Erin Koos
The increasing demand for bone grafts due to the aging population has openednew opportunities for the manufacture of porous ceramics to assist in bonereconstruction. In our study, we investigate a new, promising method tomanufacture hierarchically porous structures in a straightforward, and tuneableway. It consists of combining the novel technology of capillary suspensions,formed by mixing solid particles and two immiscible liquids, one less than 5vol%, with freeze casting. We have successfully achieved alumina and$beta$-TCP materials with both <2 $mu$m and 20-50 $mu$m as the smallest andlargest pore size, respectively. The microstructure exhibits fully open poresand high levels of porosity (> 60%). The capillary suspensions' rheologicalbehaviour indicates that silica nano-suspensions as a secondary fluid creates astronger internal particle network than sucrose for the alumina system.Conversely, the opposite was observed with the $beta$-TCP system. Thesedifferences were attributed to the change in affinity between the secondaryfluids and the solid loading. In our study, both systems have served to deepenthe knowledge about the new area of capillary suspensions and prove their usein hierarchical porous scaffolds for bone tissue engineering.
人口老龄化导致对骨移植的需求不断增加,这为制造多孔陶瓷以帮助骨重建提供了新的机遇。在我们的研究中,我们研究了一种新的、有前途的方法,它能以直接、可调整的方式制造分层多孔结构。它包括将毛细悬浮液的新技术与冷冻铸造技术相结合,毛细悬浮液是由固体颗粒与两种不相溶的液体(其中一种浓度小于 5%)混合形成的。我们已成功制备出氧化铝和β-三氯氧磷材料,两者的含量均为 60%。)毛细悬浮液的流变行为表明,在氧化铝体系中,作为辅助流体的二氧化硅纳米悬浮液比蔗糖能形成更强的内部颗粒网络。这些差异归因于二次流体与固体负载之间亲和力的变化。在我们的研究中,这两种体系都加深了人们对毛细悬浮液这一新领域的认识,并证明了它们在骨组织工程分层多孔支架中的应用。
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引用次数: 0
Analytical model for the motion and interaction of two-dimensional active nematic defects 二维活性向列缺陷运动和相互作用的分析模型
Pub Date : 2024-08-08 DOI: arxiv-2408.04706
Cody D. Schimming, C. J. O. Reichhardt, C. Reichhardt
We develop an approximate, analytical model for the velocity of defects inactive nematics by combining recent results for the velocity of topologicaldefects in nematic liquid crystals with the flow field generated fromindividual defects in active nematics. Importantly, our model takes intoaccount the long-range interactions between defects that result from the flowsthey produce as well as the orientational coupling between defects inherent innematics. We show that the model can analytically predict bound states betweentwo $+1/2$ winding number defects, effective attraction between two $-1/2$defects, and the scaling of a critical unbinding length between $pm 1/2$defects with activity. The model also gives predictions for the trajectories ofdefects, such as the scattering of $+1/2$ defects by $-1/2$ defects at acritical impact parameter that depends on activity. In the presence of circularconfinement, the model predicts a braiding motion for three $+1/2$ defects thatwas recently seen in experiments.
我们通过将向列液晶中拓扑缺陷速度的最新研究成果与活性向列中单个缺陷产生的流场相结合,建立了非活性向列缺陷速度的近似分析模型。重要的是,我们的模型考虑到了缺陷产生的流动所导致的缺陷之间的长程相互作用以及固有向列缺陷之间的取向耦合。我们的研究表明,该模型可以分析预测两个绕组数为 $+1/2$ 的缺陷之间的结合态、两个绕组数为 $-1/2$ 的缺陷之间的有效吸引力,以及绕组数为 $pm 1/2$ 的缺陷之间的临界解结合长度随活性变化的比例。该模型还给出了缺陷轨迹的预测,如在取决于活性的临界冲击参数下,$+1/2$缺陷对$-1/2$缺陷的散射。在存在环形约束的情况下,该模型预测了三个 $+1/2$ 缺陷的编织运动,这也是最近在实验中看到的。
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引用次数: 0
Coarse-grained models for phase separation in DNA-based fluids 基于 DNA 的流体中的粗粒度相分离模型
Pub Date : 2024-08-08 DOI: arxiv-2408.04435
Soumen De Karmakar, Thomas Speck
DNA is now firmly established as a versatile and robust platform forachieving synthetic nanostructures. While the folding of single molecules intocomplex structures is routinely achieved through engineering basepairsequences, much less is known about the emergence of structure on larger scalesin DNA fluids. The fact that polymeric DNA fluids can undergo phase separationinto dense fluid and dilute gas opens avenues to design hierachical andmultifarious assemblies. Here we investigate to which extent the phase behaviorof single-stranded DNA fluids is captured by a minimal model of semiflexiblecharged homopolymers while neglecting specific hybridization interactions. Wefirst characterize the single-polymer behavior and then perform directcoexistence simulations to test the model against experimental data. Weconclude that counterions not only determine the effective range of directelectrostatic interactions but also the effective attractions.
DNA 现已成为实现合成纳米结构的通用而强大的平台。单分子折叠成复杂结构通常是通过碱基配对序列工程实现的,但人们对 DNA 流体中更大规模结构的出现却知之甚少。事实上,聚合 DNA 流体可以在稠密流体和稀薄气体之间发生相分离,这为设计层次丰富的组装体开辟了道路。在这里,我们研究了单链 DNA 流体的相行为在多大程度上可以被忽略特定杂交相互作用的半柔性带电均聚物的最小模型所捕获。我们首先描述了单聚合物的行为特征,然后进行了直接共存模拟,根据实验数据对模型进行了检验。我们得出结论:反离子不仅决定了直接静电相互作用的有效范围,还决定了有效吸引力。
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引用次数: 0
Simplifying FFT-based methods for mechanics with automatic differentiation 通过自动微分简化基于 FFT 的力学方法
Pub Date : 2024-08-07 DOI: arxiv-2408.03804
Mohit Pundir, David S. Kammer
Fast-Fourier Transform (FFT) methods have been widely used in solid mechanicsto address complex homogenization problems. However, current FFT-based methodsface challenges that limit their applicability to intricate material models orcomplex mechanical problems. These challenges include the manual implementationof constitutive laws and the use of computationally expensive and complexalgorithms to couple microscale mechanisms to macroscale material behavior.Here, we incorporate automatic differentiation (AD) within the FFT framework tomitigate these challenges. We demonstrate that AD-enhanced FFT-based methodscan derive stress and tangent stiffness directly from energy densityfunctionals, facilitating the extension of FFT-based methods to more intricatematerial models. Additionally, AD simplifies the calculation of homogenizedtangent stiffness for microstructures with complex architectures andconstitutive properties. This enhancement renders current FFT-based methodsmore modular, enabling them to tackle homogenization in complex multiscalesystems, especially those involving multiphysics processes. Our work willsimplify the numerical implementation of FFT-based methods for complex solidmechanics problems.
快速傅立叶变换(FFT)方法已广泛应用于固体力学领域,以解决复杂的均质化问题。然而,目前基于 FFT 的方法面临着一些挑战,限制了它们对复杂材料模型或复杂力学问题的适用性。这些挑战包括手工实现构成规律,以及使用计算昂贵的复杂算法将微观机理与宏观材料行为结合起来。我们证明,基于 AD 增强的 FFT 方法可以直接从能量密度函数推导出应力和切线刚度,从而促进基于 FFT 的方法扩展到更复杂的材料模型。此外,AD 简化了具有复杂结构和构造特性的微结构的均质化切线刚度计算。这一改进使当前基于 FFT 的方法更加模块化,使它们能够处理复杂多尺度系统中的均质化问题,特别是那些涉及多物理过程的问题。我们的工作将简化复杂固体力学问题中基于 FFT 方法的数值实现。
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引用次数: 0
Dissociation line and driving force for nucleation of the nitrogen hydrate from computer simulation. II. Effect of multiple occupancy 计算机模拟氮水合物的离解线和成核驱动力。II.多重占据的影响
Pub Date : 2024-08-06 DOI: arxiv-2408.03257
Miguel J. Torrejón, Jesús Algaba, Felipe J. Blas
In this work, we determine the dissociation line of the nitrogen (N$_{2}$)hydrate by computer simulation using the TIP4P/Ice model for water and theTraPPE force field for N$_{2}$. This work is the natural extension of ourprevious paper in which the dissociation temperature of the N$_2$ hydrate hasbeen obtained at $500$, $1000$, and $1500,text{bar}$ [emph{J. Chem. Phys.}textbf{159}, 224707 (2023)] using the solubility method and assuming singleoccupancy. We extend our previous study and determine the dissociationtemperature of the N$_2$ hydrate at different pressures, from $500$ to$4500,text{bar}$, taking into account single and double occupancy of theN$_{2}$ molecules in the hydrate structure. We calculate the solubility ofN$_2$ in the aqueous solution, as a function of temperature, when it is incontact with a N$_{2}$-rich liquid phase and when in contact with the hydratephase with single and double occupancy via planar interfaces. Both curvesintersect at a certain temperature that determines the dissociation temperatureat a given pressure. We observe a negligible effect of the occupancy on thedissociation temperature. Our findings are in very good agreement with theexperimental data taken from the literature. We have also obtained the drivingforce for nucleation of the hydrate as a function of the temperature andoccupancy at several pressures. As in the case of the dissociation line, theeffect of the occupancy on the driving force for nucleation is negligible. Tothe best of our knowledge, this is the first time that the effect of theoccupancy on the driving force for nucleation of a hydrate that exhibits sIIcrystallographic structure is studied from computer simulation.
在这项工作中,我们使用水的 TIP4P/Ice 模型和 N$_{2}$ 的 TraPPE 力场,通过计算机模拟确定了氮(N$_{2}$)水合物的解离线。这项工作是我们上一篇论文的自然延伸,在上一篇论文中,我们使用溶解度方法并假设单占位,得到了 N$_2$ 水合物在 $500$、$1000$ 和 $1500text{bar}$[emph{J. Chem. Phys.}textbf{159}, 224707 (2023)]时的解离温度。我们扩展了之前的研究,考虑到水合物结构中 N$_{2}$ 分子的单占有和双占有,确定了 N$_2$ 水合物在 500 美元到 4500 美元不同压力下的解离温度。当水溶液与富含 N$_{2}$ 的液相接触时,以及当水合物通过平面界面与单双占位的水合物相接触时,我们计算了 N$_2$ 在水溶液中的溶解度与温度的函数关系。两条曲线在某一温度相交,该温度决定了给定压力下的解离温度。我们观察到占位对解离温度的影响微乎其微。我们的发现与文献中的实验数据非常吻合。我们还获得了水合物成核的驱动力,它是若干压力下温度和占位率的函数。与解离线的情况一样,占位对成核驱动力的影响可以忽略不计。据我们所知,这是首次通过计算机模拟研究占位率对呈现 sII 晶体结构的水合物成核驱动力的影响。
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引用次数: 0
Ultimately deformed double-network gels possess positive energetic elasticity 最终变形的双网凝胶具有正能量弹性
Pub Date : 2024-08-05 DOI: arxiv-2408.02523
Chika Imaoka, Tatsunari Masumi, Jian Ping Gong, Tsutomu Indei, Tasuku Nakajima
The elasticity of rubbery polymer networks has been considered to beentropy-driven. On the other hand, studies on single polymer chain mechanicshave revealed that the elasticity of ultimately stretched polymer chains isdominated by the energetic contribution mainly originating from chemical bonddeformation. Here, we experimentally found that the elasticity of thedouble-network gel transits from the entropy-dominated one to the internalenergy-driven one with its uniaxial deformation through the thermodynamicanalysis. Based on this finding, we developed a simple mechanical model thattakes into account the energetic contribution and found that this modelapproximately reproduces the temperature dependence of the stress-strain curveof the double-network gel. This study demonstrates the importance of thechemical perspective in the mechanical analysis of highly deformed rubberypolymer networks.
橡胶聚合物网络的弹性一直被认为是由熵驱动的。另一方面,对单聚合物链力学的研究表明,最终拉伸聚合物链的弹性主要由化学键变形产生的能量贡献所主导。在此,我们通过热力学分析实验发现,双网络凝胶在单轴变形时,其弹性从熵主导型转变为内能驱动型。基于这一发现,我们建立了一个考虑到能量贡献的简单力学模型,并发现该模型近似再现了双网凝胶应力-应变曲线的温度依赖性。这项研究证明了从化学角度分析高度变形的橡胶聚合物网络的重要性。
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引用次数: 0
Role of softness on transition temperatures for pNIPAM microgels 软度对 pNIPAM 微凝胶过渡温度的影响
Pub Date : 2024-08-05 DOI: arxiv-2408.02490
Syamjith KS, Shubhasmita Rout, Alan R Jacob
Poly(N-isopropylacrylamide) (pNIPAM) microgels are renowned for theirthermoresponsive behavior, exhibiting a distinct volume phase transition (VPT)upon temperature changes. This study investigates the influence of microgelsoftness, controlled by varying the crosslinking density during synthesis viafree radical polymerization (FRP), on the difference between the volume phasetransition temperature (VPTT) and the electrokinetic transition temperature(ETT). These transition temperatures mark the points at which the microgel sizeand surface charge, respectively, undergo significant alterations in responseto temperature. Here, we investigate this phenomenon, employing dynamic lightscattering (DLS) and electrophoretic light scattering (ELS) measurements tocharacterize the size and electrophoretic mobility response of pNIPAM microgelswith different crosslinking densities as a function of temperature. Byanalyzing the observed trends in the difference between the transitiontemperatures, we aim to develop a hypothesis that provides a deeper physicalunderstanding of the microgel structure and its relationship to transitiontemperatures. This investigation thus sheds light on the intricate interplaybetween microgel structure and its thermoresponsive behavior, offering insightsfor the design and optimization of pNIPAM microgels for future applications.
聚(N-异丙基丙烯酰胺)(pNIPAM)微凝胶因其更高的粘弹性而闻名,在温度变化时会出现明显的体积相变(VPT)。本研究探讨了微凝胶软度对体积相变温度(VPTT)和电动转变温度(ETT)之间差异的影响,微凝胶软度是在通过自由基聚合(FRP)合成过程中通过改变交联密度来控制的。这些转变温度分别标志着微凝胶尺寸和表面电荷随温度发生显著变化的点。在此,我们采用动态光散射(DLS)和电泳光散射(ELS)测量方法来研究这一现象,以描述不同交联密度的 pNIPAM 微凝胶的尺寸和电泳迁移率随温度变化的响应。通过分析观察到的过渡温度差异趋势,我们提出了一个假设,旨在加深对微凝胶结构及其与过渡温度关系的物理理解。因此,这项研究揭示了微凝胶结构与其热致伸缩行为之间错综复杂的相互作用,为未来应用中 pNIPAM 微凝胶的设计和优化提供了启示。
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引用次数: 0
Minimal actuation and control of a soft hydrogel swimmer from flutter instability 从扑腾不稳定性中实现对软水凝胶游泳器的最小驱动和控制
Pub Date : 2024-08-05 DOI: arxiv-2408.02560
Ariel Surya Boiardi, Giovanni Noselli
Micro-organisms propel themselves in viscous environments by the periodic,nonreciprocal beating of slender appendages known as flagella. Active materialshave been widely exploited to mimic this form of locomotion. However, therealization of such coordinated beating in biomimetic flagella requires complexactuation modulated in space and time. We prove through experiments onpolyelectrolyte hydrogel samples that directed undulatory locomotion of a softrobotic swimmer can be achieved by untethered actuation from a uniform andstatic electric field. A minimal mathematical model is sufficient to reproduce,and thus explain, the observed behavior. The periodic beating of the swimminghydrogel robot emerges from flutter instability thanks to the interplay betweenits active and passive reconfigurations in the viscous environment.Interestingly, the flutter-driven soft robot exhibits a form of electrotaxiswhereby its swimming trajectory can be controlled by simply reorienting theelectric field. Our findings trace the route for the embodiment of mechanicalintelligence in soft robotic systems by the exploitation of flutter instabilityto achieve complex functional responses to simple stimuli. While theexperimental study is conducted on millimeter-scale hydrogel swimmers, thedesign principle we introduce requires simple geometry and is hence amenablefor miniaturization via micro-fabrication techniques. We believe it may also betransferred to a wider class of soft active materials.
微生物通过被称为鞭毛的细长附肢的周期性、非互惠性跳动,在粘性环境中推动自身前进。活性材料已被广泛用于模拟这种运动形式。然而,要在仿生鞭毛中实现这种协调跳动,需要在空间和时间上进行复合调节。我们通过在聚电解质水凝胶样品上的实验证明,软机器人游动器的定向起伏运动可以通过来自均匀静态电场的无约束驱动来实现。一个最基本的数学模型就足以再现并解释观察到的行为。由于在粘性环境中主动和被动重构之间的相互作用,水凝胶游泳机器人的周期性跳动从扑腾不稳定性中产生。有趣的是,扑腾驱动的软机器人表现出一种电游动,只需调整电场方向就能控制其游泳轨迹。我们的发现为在软机器人系统中体现机械智能指明了方向,即利用扑动不稳定性实现对简单刺激的复杂功能响应。虽然实验研究是在毫米级的水凝胶游泳器上进行的,但我们介绍的设计原理只需要简单的几何形状,因此可以通过微加工技术实现微型化。我们相信,它还可以应用于更广泛的软活性材料。
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引用次数: 0
MetaParticles: Computationally engineered nanomaterials with tunable and responsive properties 元粒子:具有可调节和响应特性的计算工程纳米材料
Pub Date : 2024-08-05 DOI: arxiv-2408.02564
Massimiliano Paesani, Ioana M. Ilie
In simulations, particles are traditionally treated as rigid platforms withvariable sizes, shapes and interaction parameters. While this representation isapplicable for rigid core platforms, particles consisting of soft platforms(e.g. micelles, polymers, elastomers, lipids) inevitably deform uponapplication of external stress. We introduce a generic model for flexibleparticles which we call MetaParticles (MP). These particles have tunableproperties, can respond to applied tension and can deform. A metaparticle isrepresented as a collection of Lennard-Jones beads interconnected byspring-like potentials. We model a series of metaparticles of variable sizesand symmetries, which we subject to external stress followed by relaxation uponstress release. The positions and the orientations of the individual beads arepropagated by Brownian dynamics. The simulations show that the mechanicalproperties of the metaparticles vary with size, bead arrangement and area ofapplied stress, and share an elastomer-like response to applied stress.Furthermore, metaparticles deform following different mechanisms, i.e., smallMPs change shape in one step, while larger ones follow a multi-step deformationpathway, with internal rearrangements of the beads. This model is the firststep towards the development and understanding of particles with adaptableproperties with biomedical applications and in the design of bioinspiredmetamaterials.
在模拟中,颗粒传统上被视为具有可变尺寸、形状和相互作用参数的刚性平台。虽然这种表示方法适用于刚性核心平台,但由软平台(如胶束、聚合物、弹性体、脂质)组成的粒子在受到外部应力时不可避免地会发生变形。我们为柔性粒子引入了一个通用模型,称之为元粒子(MP)。这些粒子具有可调整的特性,可以对施加的张力做出反应,并且可以变形。元粒子被表示为由类似于弹簧的电势相互连接的伦纳德-琼斯珠的集合。我们对一系列大小和对称性各异的元粒子进行建模,使其受到外部应力的作用,然后在应力释放时发生松弛。各个珠子的位置和方向通过布朗动力学传播。模拟结果表明,元粒子的机械特性随尺寸、珠子排列和受力面积的变化而变化,并且对外加应力具有类似弹性体的响应。此外,元粒子的变形机制各不相同,即小的元粒子只需一步就能改变形状,而大的元粒子则要经过多步变形,珠子内部要重新排列。该模型是开发和了解具有生物医学应用和生物启发元材料设计的可适应特性的微粒的第一步。
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引用次数: 0
Three-phase equilibria of hydrates from computer simulation. I. Finite-size effects in the methane hydrate 计算机模拟的水合物三相平衡。I. 甲烷水合物中的有限尺寸效应
Pub Date : 2024-08-04 DOI: arxiv-2408.02098
S. Blazquez, J. Algaba, J. M. Míguez, C. Vega, F. J. Blas, M. M. Conde
Clathrate hydrates are vital in energy research and environmentalapplications. Understanding their stability is crucial for harnessing theirpotential. In this work, we employ direct coexistence simulations to studyfinite-size effects in the determination of the three-phase equilibriumtemperature ($T_3$) for methane hydrates. Two popular water models, TIP4P/Iceand TIP4P/2005, are employed, exploring various system sizes by varying thenumber of molecules in the hydrate, liquid, and gas phases. The results revealthat finite-size effects play a crucial role in determining $T_3$. The studyincludes nine configurations with varying system sizes, demonstrating thatsmaller systems, particularly those leading to stoichiometric conditions andbubble formation, may yield inaccurate $T_3$ values. The emergence of methanebubbles within the liquid phase, observed in smaller configurations,significantly influences the behavior of the system and can lead to erroneoustemperature estimations. Our findings reveal finite size effects on thecalculation of the $T_3$ by direct coexistence simulations and clarify thesystem size convergence for both models, shedding light on discrepancies foundin the literature. The results contribute to a deeper understanding of thephase equilibrium of gas hydrates and offer valuable information for futureresearch in this field.
克拉水合物在能源研究和环境应用中至关重要。了解它们的稳定性对于利用它们的潜力至关重要。在这项工作中,我们采用直接共存模拟来研究确定甲烷水合物三相平衡温度($T_3$)时的无限大效应。我们采用了两种常用的水模型 TIP4P/Ice 和 TIP4P/2005,通过改变水合物、液相和气相中的分子数量来探索各种系统大小。研究结果表明,有限尺寸效应在确定 $T_3$ 时起着至关重要的作用。该研究包括九种不同系统尺寸的配置,表明较小的系统,特别是那些导致化学计量条件和气泡形成的系统,可能会产生不准确的 $T_3$ 值。在较小配置中观察到的液相中甲烷气泡的出现极大地影响了系统的行为,并可能导致错误的系统温度估计。我们的研究结果揭示了有限尺寸对通过直接共存模拟计算 $T_3$ 的影响,并澄清了两种模型的系统尺寸收敛性,揭示了文献中发现的差异。这些结果有助于加深对天然气水合物相平衡的理解,并为该领域的未来研究提供了宝贵信息。
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引用次数: 0
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arXiv - PHYS - Soft Condensed Matter
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