Cell attachment/detachment behavior on poly(<Emphasis Type="Italic">N</Emphasis>-isopropylacrylamide)-based microgel films: the effect of microgel structure and swelling ratio

Microgels are cross-linked soft particles with a three-dimensional network structure that are swollen in a good solvent. Poly(N-isopropylacrylamide) (pNIPAAm)-based microgels have attracted great attentions for their temperature responsive property, particularly in recent years, pNIPAAm-based microgel films were utilized as a new kind of thermoresponsive surface to tune cell attachment/detachment behavior via temperature stimuli. However, some results are not consistent, for example, different polymerization conditions may bring out different results even for pure pNIPAAm microgel. This work aims to find out which factor plays the critical role for successful cell detachment on the pNIPAAm-based microgel films. The results unraveled that the structure and swelling ratio of the microgel rather than the film thickness plays a key role on the successful cells detachment, unlike linear pNIPAAm films in which the cells’ attach/detach property is only determined by the film thickness. For poly(N-isopropylacrylamide–styrene) microgel film, NIH3T3 cells could only detach when the microgel has a uniform structure and the volume dilatation of the microgel (20/38 °C) is larger than 4.     

Properties and drug release profile of poly(N-isopropylacrylamide) microgels functionalized with maleic anhydride and alginate

This study highlights the advantages of functionalized poly(N-isopropylacrylamide) (PNIPAAm) microgels over pure PNIPAAm microgels in terms of polymer network properties and drug release profiles. PNIPAAm network was modified by addition of maleic anhydride (MA) as a comonomer and by formation of interpenetrating polymer network in the presence of alginate. The functionalized thermosensitive microgels in the size range from 20 to 80 μm and with better performance in comparison with pure PNIPAAm microgels were prepared by inverse suspension polymerization. The impact of MA and alginate on the PNIPAAm microgel structure was evaluated through analysis of microgel size, size distribution, volume phase transition temperature (VPTT), equilibrium swelling ratio as well as morphology of the system. It was shown that the controlled modification of PNIPAAm network could result in microgels of considerably improved swelling capacity with unchanged thermosensitivity and maintained open pore morphology. In addition, drug release behavior of microgels could be markedly altered. Release of procaine hydrochloride from the selected microgels was studied using Franz diffusion cell at temperatures below and above VPTT of the microgels. Temperature-controlled drug release pattern was dependent on the type of functionalization of PNIPAAm network. According to drug loading properties and drug release mechanism, PNIPAAm/MA copolymer microgels demonstrated the optimal performances.     

Temperature-, pH-, and magnetic-field-sensitive hybrid microgels

We demonstrate a simple route for the preparation of novel hybrid particles with multiple sensitivities. Aqueous polymeric microgels are modified by magnetite nanoparticles in the preparation of temperature- and pH-sensitive hybrids with a high magnetic response. Up to 15 wt % of magnetite nanoparticles are loaded into microgels. The influence of the amount of magnetite in the microgel structure on the morphology and colloidal properties is discussed. The presence of the magnetite nanoparticles in the microgel decreases its degree of swelling and shifts the volume phase-transition temperature to higher values. Nanostructured composite films with controlled morphologies can be prepared by water evaporation and deposition of the hybrid microgels on a solid substrate.     

Design of multicomponent microgels by selective deposition of nanomaterials

In the present paper a method for the targeted deposition of different nanomaterials on aqueous microgels is described. In the first stage poly(3,4-ethylenedioxythiophene) (PEDOT) nanorods are introduced into the microgel structure by in situ oxidative polymerization. In the second stage hydrogen tetrachloroaurate is used to transform PEDOT chains to an oxidized state in the microgel structure, leading to the fixation of chloroaurate anions on the surface of the PEDOT nanorods. The reduction of chloroaurate ions induces the formation of gold nanoparticles (AuNPs) predominantly located on the PEDOT surface. Obtained microgel/PEDOT/AuNP hybrid particles with different nanoparticle loadings exhibit superior colloidal stability and temperature sensitivity. The microgel/PEDOT/AuNP hybrid microgels exhibit extraordinary catalytic activity in aqueous media.     

Gold nanoparticles bound on microgel particles and their application as an enzyme support

Submicron-sized poly(N-isopropyl acrylamide)/polyethyleneimine core-shell microgels were prepared in aqueous media by using tert-butyl hydroperoxide (TBHP) as an initiator, and then the gold nanoparticles (～8?nm) were formed on the surface of the microgels. The amino groups on the polyethyleneimine (PEI) chains act as the binder for the assembly of the gold nanoparticles/microgel complex. In aqueous media the microgels are highly stable with the gold nanoparticles on their extended PEI chains, and this multi-scale nanoparticle complex can be recovered from water and redispersed in water. The nanogold/microgel particles were conjugated with the enzymes horseradish peroxidase (HRP) and urease. It is found that under identical assay conditions the enzyme/nanogold/microgel systems exhibit enhanced biocatalytic activity over free enzymes in solution, especially at lower enzyme concentrations. In addition, compared to free HRP, the HRP/nanogold/microgel systems show higher activity at varied pHs and temperatures, as well as higher storage stability. Thus the novel nanogold/microgel particles can serve as an excellent support for enzymes.     

Ultrastrong Anchoring Yet Barrier‐Free Adsorption of Composite Microgels at Liquid Interfaces

Microgel particles display an interesting duality with properties attributed typically both to polymeric and colloidal systems. When adsorbed at a liquid‐liquid interface, this duality becomes particularly apparent as the various phenomena at play are governed by different aspects of these soft and responsive particles. The introduction of a solid, fluorescently labeled, polystyrene core into the microgels allows direct and accurate visualization without the necessity of potential perturbing sample preparation techniques. By combining in‐situ imaging and tensiometry, we determine that composite microgels at a wide variety of oil‐water interfaces anchor strongly, with adsorption energies of approximately 10⁶ k_BT, typical for particle adsorption, yet accumulate at the interface spontaneously without any energy barrier, which is more typical for polymers. The high adsorption energies allow the particle to spontaneously form very dense crystalline packings at the liquid interface in which the microgels are significantly compressed with respect to their swollen state in bulk solutions. Finally, we demonstrate the unique nature of these particles by producing highly stable and monodisperse microgel‐stabilized droplets using microfluidics.     

分散聚合法制备P（AM—AN）微凝胶及其性能研究

以偶氮二异丁腈（AIBN）为引发剂,N,N’-亚甲基双丙烯酰胺（Bis—A）为交联剂,聚乙烯吡咯烷酮（PVPK-30）为稳定剂,在乙醇／水的混合介质中使亲水性丙烯酰胺（AM）与疏水性丙烯腈（AN）进行分散共聚,制得一系列P（AM—AN）微凝胶,通过扫描电子显微镜（SEM）和差示扫描量热仪（DSC）考察了共聚单体AN的用量对微凝胶形态及其热稳定性的影响,结果表明,随着反应体系中AN用量的增大,所得微凝胶的玻璃化转变温度提高,有利于其在较高温度下使用。     

Functional Microgels: Recent Advances in Their Biomedical Applications

Here, a spotlight is shown on aqueous microgel particles which exhibit a great potential for various biomedical applications such as drug delivery, cell imaging, and tissue engineering. Herein, different synthetic methods to develop microgels with desirable functionality and properties along with degradable strategies to ensure their renal clearance are briefly presented. A special focus is given on the ability of microgels to respond to various stimuli such as temperature, pH, redox potential, magnetic field, light, etc., which helps not only to adjust their physical and chemical properties, and degradability on demand, but also the release of encapsulated bioactive molecules and thus making them suitable for drug delivery. Furthermore, recent developments in using the functional microgels for cell imaging and tissue regeneration are reviewed. The results reviewed here encourage the development of a new class of microgels which are able to intelligently perform in a complex biological environment. Finally, various challenges and possibilities are discussed in order to achieve their successful clinical use in future.     

Compartmentalized Jet Polymerization as a High‐Resolution Process to Continuously Produce Anisometric Microgel Rods with Adjustable Size and Stiffness

In the past decade, anisometric rod‐shaped microgels have attracted growing interest in the materials‐design and tissue‐engineering communities. Rod‐shaped microgels exhibit outstanding potential as versatile building blocks for 3D hydrogels, where they introduce macroscopic anisometry, porosity, or functionality for structural guidance in biomaterials. Various fabrication methods have been established to produce such shape‐controlled elements. However, continuous high‐throughput production of rod‐shaped microgels with simultaneous control over stiffness, size, and aspect ratio still presents a major challenge. A novel microfluidic setup is presented for the continuous production of rod‐shaped microgels from microfluidic plug flow and jets. This system overcomes the current limitations of established production methods for rod‐shaped microgels. Here, an on‐chip gelation setup enables fabrication of soft microgel rods with high aspect ratios, tunable stiffness, and diameters significantly smaller than the channel diameter. This is realized by exposing jets of a microgel precursor to a high intensity light source, operated at specific pulse sequences and frequencies to induce ultra‐fast photopolymerization, while a change in flow rates or pulse duration enables variation of the aspect ratio. The microgels can assemble into 3D structures and function as support for cell culture and tissue engineering.     

纳米纤维素凝胶微粒及其在Pickering泡沫中的应用

目的研究氧化纳米纤维素/乳酸链球菌素(TONCC/nisin)凝胶粒子的性质及其在环保抗菌泡沫中的应用。方法利用TONCC的表面羧基基团与nisin的表面阳离子的吸附耦合作用,制备TONCC/nisin水凝胶和微凝胶,以微凝胶作为稳定粒子,环氧大豆油丙烯酸酯(AESO)为油相,制备TONCC/nisin/AESO Pickering乳液,对水凝胶、微凝胶、乳液的稳定性进行研究;通过热固化乳液得到环保抗菌的泡沫材料,并对泡沫材料的结构和抗菌效果进行表征。结果水凝胶的结构随着在水中浸泡时长的增加而发生变化,宏观表现为坍塌变形,nisin逐渐析出,微凝胶随着静置时间的延长其粒径变化不大;以微凝胶作为界面稳定剂的AESO乳液的热稳定性较好,在90℃下加热30 min乳液液滴并未发生聚并现象,该乳液固化后形成的多孔泡沫材料对李斯特菌的抑制作用明显,当泡沫中nisin含量为2μg/g时,其抑菌率为43%。结论TONCC和nisin形成的微凝胶粒子在水中稳定性较好,可以用于乳化AESO制备Pickering泡沫,同时赋予泡沫多孔性和抗菌性,在制备环保抗菌泡沫方面有很大的应用潜力。     

A micromechanical model to predict the flow of soft particle glasses

Soft particle glasses form a broad family of materials made of deformable particles, as diverse as microgels, emulsion droplets, star polymers, block copolymer micelles and proteins, which are jammed at volume fractions where they are in contact and interact via soft elastic repulsions. Despite a great variety of particle elasticity, soft glasses have many generic features in common. They behave like weak elastic solids at rest but flow very much like liquids above the yield stress. This unique feature is exploited to process high-performance coatings, solid inks, ceramic pastes, textured food and personal care products. Much of the understanding of these materials at volume fractions relevant in applications is empirical, and a theory connecting macroscopic flow behaviour to microstructure and particle properties remains a formidable challenge. Here we propose a micromechanical three-dimensional model that quantitatively predicts the nonlinear rheology of soft particle glasses. The shear stress and the normal stress differences depend on both the dynamic pair distribution function and the solvent-mediated EHD interactions among the deformed particles. The predictions, which have no adjustable parameters, are successfully validated with experiments on concentrated emulsions and polyelectrolyte microgel pastes, highlighting the universality of the flow properties of soft glasses. These results provide a framework for designing new soft additives with a desired rheological response.     

Tuneable catalytic properties of hybrid microgels containing gold nanoparticles

A novel type of submicrometer-sized hybrid microgels containing gold nano-particles (AuNPs) has been tested as catalyst in reduction of 4-nitrophenol in aqueous medium. The influence of microgel concentration, gold content, as well as temperature of reaction medium on kinetics of 4-nitrophenol reduction process has been investigated. The pseudo-first-order kinetics was used to evaluate the catalytic reaction rate. It has been demonstrated that reaction rate of 4-nitrophenol reduction can be accelerated if the concentration of microgel in the reaction system or amount of gold nanoparticles loaded into microgels increases. Increase of reaction temperature resulted in rapid increase of reduction rate. Compared to pure gold nano-particles hybrid microgels at similar conditions reduce the activation energy of reduction process by a factor of 2. This indicates that localization of AuNPs within microgel template prevents their aggregation and therefore high catalytic activity can be preserved independently from reaction conditions. Additionally, polymeric template provides suitable environment for better mass transfer in present system that improves the catalyst efficiency.     

超临界二氧化碳中N-异丙基丙烯酰胺与二乙二醇二甲基丙烯酸酯的交联聚合

采用超临界二氧化碳（scCO2）沉淀聚合法,在不添加高分子表面活性剂及共溶剂的前提下,以AIBN为引发剂,二乙二醇二甲基丙烯酸酯为交联剂,成功制备了交联的聚（N-异丙基丙烯酰胺）温度敏感型微凝胶;通过扫描电镜（SEM）、差示扫描量热分析（DSC）等方法对聚合物的微观形貌进行了表征,测定了微凝胶的相转变温度,同时也考察了...     

The influence of the degree of heterogeneity on the elastic properties of random sphere packings

The macroscopic mechanical properties of colloidal particle gels strongly depend on the local arrangement of the powder particles. Experiments have shown that more heterogeneous microstructures exhibit up to one order of magnitude higher elastic properties than their more homogeneous counterparts at equal volume fraction. In this paper, packings of spherical particles are used as model structures to computationally investigate the elastic properties of coagulated particle gels as a function of their degree of heterogeneity. The discrete element model comprises a linear elastic contact law, particle bonding and damping. The simulation parameters were calibrated using a homogeneous and a heterogeneous microstructure originating from earlier Brownian dynamics simulations. A systematic study of the elastic properties as a function of the degree of heterogeneity was performed using two sets of microstructures obtained from Brownian dynamics simulation and from the void expansion method. Both sets cover a broad and to a large extent overlapping range of degrees of heterogeneity. The simulations have shown that the elastic properties as a function of the degree of heterogeneity are independent of the structure generation algorithm and that the relation between the shear modulus and the degree of heterogeneity can be well described by a power law. This suggests the presence of a critical degree of heterogeneity and, therefore, a phase transition between a phase with finite and one with zero elastic properties.     

Fibrillized peptide microgels for cell encapsulation and 3D cell culture

One of the advantages of materials produced by self-assembly is that in principle they can be formed in any given container to produce materials of predetermined shapes and sizes. Here, we developed a method for triggering peptide self-assembly within the aqueous phase of water-in-oil emulsions to produce spherical microgels composed of fibrillized peptides. Size control over the microgels was achieved by specification of blade type, speed, and additional shear steps in the emulsion process. Microgels constructed in this way could then be embedded within other self-assembled peptide matrices by mixing pre-formed microgels with un-assembled peptides and inducing gelation of the entire composite, offering a route towards multi-peptide materials with micron-scale domains of different peptide formulations. The gels themselves were cytocompatible, as was the microgel fabrication procedure, enabling the encapsulation of NIH 3T3 fibroblasts and C3H10T-1/2 mouse pluripotent stem cells with good viability.     

添加AlN对机械合金化Zr65Al7.5CU17.5Ni10非晶态合金热稳定性的影响

以成分为Zr65Al7.5Cu17.5Ni10的元素的粉末混合物及AIN颗粒为起始材料,经机械合金化形成非晶态合金为基体的复合材料,AIN添加量为5％－30％（体积分数,下同）,利用X射线衍射（XRD）,透射电子 显微镜（TEM）和差示扫描量热计（DSC）分析了含AIN复合材料的结构特性,玻璃转变与晶化行为,TEM观察表明,AIN第二相粒子弥散分布在晶Zr基合金基体上,粒子尺寸为20－200nm,仍为初始的晶体结构,与未添加AIN的Zr基非晶态合金相比,含5％－10％AIN的复合材料仍表现出较宽的过冷液态温度区域,玻璃转变温度（Tg)和晶化激活能（Ex)没有显著变化,但晶化起始温度（Tx)向高温移动大约10K,导致过冷液态温度区域的扩宽,AIN含量增至30％,明显的玻璃转变消失,Tx升高的20K。     

A "paint-on" protocol for the facile assembly of uniform microgel coatings for color tunable etalon fabrication

Robust, uniform, monolithic microgel thin films can be created by actively spreading a concentrated solution of microgels onto a Au surface at 30 °C. The method is easy, fast, and seemingly universal: it can be used to coat a variety of Au coated surfaces with microgels containing different chemical functionalities. No control of the deposition conditions, other than temperature and microgel concentration, is required. We show that this technique consistently produces monolithic microgel films on Au-coated surfaces, and it has been extended to coat Si substrates. After deposition of a thin Au overlayer onto the deposited microgel layer, the materials are colored, as evidenced by multiple peaks in their reflectance spectra. The assemblies deposited using the described "paint-on" technique show increased spectral and visual purity over the entire surface area as compared to colored materials made by a previously used passive drying process.     

聚乙二醇基复合相变材料的制备与热性能研究

利用聚乙二醇(PEG)为相变材料、以羟丙基甲基纤维素为分子骨架,采用4,4-二苯基甲烷二异氰酸酯作为交联剂,用化学接枝法成功合成了一种新型复合相变材料。采用红外光谱、差示扫描量热仪、热重仪、扫描电镜和X射线衍射仪对该复合相变材料的化学结构、相变性能、热稳定性、微观形貌和晶体结构等性能进行了表征。结果表明:该复合相变材料的相变过程表现为固-固相变的性质,其相变温度在309~323.2K范围内,相变焓值在89.8~106.8J/g之间。可见,通过化学接枝法得到的复合相变材料具有较好的相变行为,且克服了聚乙二醇在相变过程中的泄露问题。     

Dynamics of interacting Brownian particles in concentrated colloidal suspensions

We are concerned with dynamic properties of interacting Brownian particles in concentrated colloidal suspensions. An effective diffusion coefficient measured by the modulated in phase low-coherence dynamic light scattering technique is investigated as a function of the volume fraction. The experimental results are compared with the numerical ones calculated under both the Cohen-de Schepper approximation for hydrodynamic interaction and the Percus-Yevick approximations for structural effect. It is confirmed that the Brownian motion of particles in the range of volume fraction from 0.01 to 0.2 is mainly dominated by the hydrodynamic interaction rather than the structural effect, which can be described well by the Cohen-de Schepper approximation.     

短切碳纤维导电复合材料渗流和PTC行为的唯象分析

为研究短切碳纤维含量和温度对导电复合材料渗流行为的影响,通过Landau相变理论导出了复合材料电导率与填料体积分数及温度的方程,并用该方程分析了短切碳纤维/乙烯基酯树脂复合材料的渗流和PTC行为。结果表明:复合材料的渗流阈值随温度升高而增加,PTC温度随碳纤维含量增加而上升。当温度由24.6℃上升到108.4℃时,其渗流阈值的理论值由1.06%增加到1.60%;当碳纤维体积分数由3.1%增加到4.6%时,其PTC温度的理论值由120℃上升到170℃。复合材料渗流阈值和PTC温度理论值与实验值符合得很好。