Tunable metallization by assembly of metal nanoparticles in polymer thin films by photo- or electron beam lithography

The technique of patterning of surfaces with metal-rich structures on micro- or nanoscales was developed by assembling metal nanoparticles into a thin film of polymer in a controllable way. Palladium (Pd) nanoparticles were incorporated into a thin film of poly(methyl methacrylate) (PMMA) using palladium (II) bis(acetylacetonato), Pd(acac)(2), as a precursor vaporized in a nitrogen atmosphere. Depending upon its dose, the irradiation of a PMMA film by UV light or an electron beam (EB) enhances its reducing capability against Pd(acac)(2). This dependency on dose can be used to control the formation and assembly of Pd nanoparticles. Using this technique, binary patterns consisting of metal-rich and metal-poor regions in the polymer film can be created simply by irradiating the surface of the polymer through a binary photomask. Besides the creation of binary patterns, it is also possible to create grayscale patterns where the density of Pd nanoparticles can be tuned to provide shades of gray by the use of light with continuously modulated intensity. Because the electron beam also enhances the reducing power of PMMA against Pd(acac)(2), it is thus possible to obtain highly metallized films with nanoscale pattern features. The PMMA film can be selectively removed by oxygen plasma treatment or by pyrolysis. Thus, highly metallized surfaces with binary or grayscale patterns can be obtained by selective removal of the PMMA films. The metallized regions possess relatively high resistivity against CF(4) plasma compared to the bare silicon surface; therefore, the metallized surface patterns can be transferred onto the underlying silicon substrate by CF(4) plasma treatment. Because of the nanosize effect of metal nanoparticles, the thermal treatment at 900 degrees C, which is significantly lower than the melting temperature of the bulk Pd, yields continuous metallic features by binding the assembled nanoparticles.     

Directed assembly of nanoparticles along predictable large-scale patterns using micromolded hydrogels

We present a new technology to organize microparticles and nanoparticles along micropatterns of variable complexity over centimeter-squared surfaces. This technology relies on the fabrication of textured hydrogels, which serve as templates for directed assembly after the deposition of a droplet of colloids on their surfaces. We show that directed assembly occurs spontaneously during water evaporation, and we demonstrate the efficiency of this mechanism for a variety of organic and inorganic nano-objects. The dynamics of this process is also uncovered by light microscopy, showing that the patterns imprinted on the gel determine fluid flow during water evaporation and allow for directed movements toward predictable positions. We finally propose different methods to transfer assembled particles from hydrogels to glass, silicon, or metallic surfaces, and we show that the assembled and transferred particles retain their surface properties for bioassays. Beyond the originality of this spontaneous assembly mechanism, it constitutes an attractive technology for nano-object large-scale integration, which does not require costly environmental control equipment.     

Effects of crosslinker density on the polymer network structure in poly‐N,N‐dimethylacrylamide hydrogels

To investigate the effects of crosslinker density on the properties of hydrogels, compression tests, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and Raman measurements were performed on poly‐N,N‐dimethylacrylamide hydrogels. The results of the compression tests showed that the Young's modulus increases as the crosslinker density increases. To understand the mechanism of the change in the mechanical properties, the structures of the polymer networks and water and the molecular vibrations were analyzed using SEM, DSC, and Raman methods. From the SEM images, it was found that the porosity estimated from the mesh size and cell density increases with increasing crosslinker density. In addition, the DSC and Raman results show that the thickness of the bound water increases as the porosity increases, although the density of the polymer chains in the porous wall remains nearly constant. The increase in the number density of polymer chains can be one of the mechanisms contributing to the increase in the mechanical strength of the hydrogels at lower crosslinker density below 5 mol %, as proposed by previous studies. At higher crosslinker density, however, the number density of polymer chains does not increase with increasing crosslinker density. The present results suggest that the bound water plays an important role in strengthening the hydrogel. The water structure may be one of the dominant factors governing the chemical and physical properties of hydrogels. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 1017–1027     

Controlled synthesis of responsive hydrogel nanostructures via microcontact printing and ATRP

Surfaces that are spatially functionalized with intelligent hydrogels, especially at the micro‐ and nanoscale, are of high interest in the diagnostic and therapeutic fields. Conventional methods of the semiconductor industry have been successfully employed for the patterning of hydrogels for various applications, but methods for fabricating precise 3 D patterns of hydrogels at the micro‐ and nanoscale over material surfaces remain limited. Herein, microcontact printing (µCP) followed by atom transfer radical polymerization (ATRP) was applied as a platform to synthesize temperature responsive poly(N‐isopropylacrylamide) hydrogels with varied network structures (e.g. different molecular weight crosslinkers) over gold surfaces. The XY control of the hydrogels was achieved using µCP, and the Z (thickness) control was achieved using ATRP. The controlled growth and the responsive behavior of hydrogels to temperature stimuli were characterized using Fourier transform infrared (FTIR) spectroscopy and atomic force microscopy (AFM). The results demonstrate that this platform allows for the controlled growth of hydrogel nanostructures using the controlled ATRP mechanism. It is also shown that the molecular weight of the crosslinker affects the rate of hydrogel growth. These PNIPAAm‐based crosslinked hydrogel patterns were also demonstrated to have a temperature‐dependent swelling response. Using this technique, it is possible to synthesize responsive hydrogel patterns over various surfaces for potential applications in the biomedical field. Copyright © 2009 John Wiley & Sons, Ltd.     

Spherical phospholipid polymer hydrogels for cell encapsulation prepared with a flow-focusing microfluidic channel device

To prepare spherical polymer hydrogels, we used a flow-focusing microfluidic channel device for mixing aqueous solutions of two water-soluble polymers. Continuous encapsulation of cells in the hydrogels was also examined. The polymers were bioinspired 2-methacryloyloxyethyl phosphorylcholine polymer bearing phenyl boronic acid groups (PMBV) and poly(vinyl alcohol) (PVA), which spontaneously form a hydrogel in aqueous medium via specific molecular complexation upon mixing, even when they were in cell culture medium. The microfluidic device was prepared with polydimethylsiloxan, and the surface of the channel was treated with fluoroalkyl compound to prevent sticking of the polymers on the surface. The microfluidic channel process could control the diameter of the spherical hydrogels in the range of 30-90 μm and generated highly monodispersed diameter spherical hydrogels. We found that the polymer distribution in the hydrogel was influenced by the PVA concentration and that the hydrogel could be dissociated by the addition of d-sorbitol to the suspension. The single cells could be encapsulated and remain viable in the hydrogels. The localized distribution of polymers in the hydrogel may provide an environment for modulating cell function. It is concluded that the spontaneous hydrogel formation between PMBV and PVA in the flow-focusing microfluidic channel device is applicable for continuous preparation of a spherical hydrogel-encapsulating living cell.     

Evaluation of Nonionic Block Polymer Surfactants in Maize Root Proteome Extraction within Water�COrganic Solvent Phases

In the present work, six nonionic block copolymer surfactants consisting of poly(ethylene glycol) (PEG), polyethylene (PE), and poly(propylene glycol) (PPG) were exploited to extract total proteins from maize (Zea mays L.) roots within a water?Corganic solvent system. After the treatment, proteins were partitioned into aqueous phase, interphase, and organic phase. The total yield was increased by up to 30% after adding PE-PEG block polymer surfactant compared with control. Two-dimensional electrophoresis (2-DE) was further used to evaluate proteins in water phase and interphase; the results revealed that the spot numbers and density were all improved, and well-focused electrophoretic patterns were achieved with higher density and without excess Joule heating problem after adding nonionic block polymer surfactants. Among the six investigated block polymers, PE-PEG extracted the largest amount of proteins.     

Photopolymerization of poly(ethylene glycol) diacrylate on eosin-functionalized surfaces

We describe a new method that allows photopolymerization of hydrogels to occur on surfaces functionalized with eosin. In this work, glass and silicon surfaces were derivatized with eosin and photopolymerization was carried out using visible light (514 nm). This mild condition may have advantages over methods that use ultraviolet (UV) light (e.g., for encapsulation of cells and proteins, in drug screening, or in biosensing applications). The hydrogel formed on the modified surface is remarkably stable for an extended period of time. The resultant hydrogel was hydrated for more than 18 months without suffering delamination from the substrate surface. This strongly suggests covalent attachment of the hydrogel to the surface. Contact angle titration measurements and X-ray photoelectron spectroscopy analysis of eosin surfaces before and after irradiation in the presence of triethanolamine suggest that the eosin radical is responsible for the covalent attachment of the gel onto the substrate surface. This method allows for 2-D patterning of hydrogels, which is demonstrated here using the microcontact printing technique. However, noncontact photolithography could be used to form similar patterns by directing light through a mask. This method can be easily implemented to form arrays of fluorophores and proteins in situ.     

Hybrid Monte Carlo self-consistent field approach to model a thin layer of a polyelectrolyte gel near an adsorbing surface

The use of thin layers of a surface bound (polyelectrolyte) hydrogels for measuring the concentration of metal ions from electrolyte solutions is our motivation for modeling such hydrogels. The gels are composed of polymeric species with conformational degrees of freedom on the nanometer scale. The polymer conformations are affected by the presence of cross-links in the gel on a five to ten times larger length scale, and the repulsive interactions generated by the charges along the chains. Here we present a hybrid computational Monte Carlo Self-consistent field (MC-SCF) approach to model such hydrogels. The SCF formalism is used to evaluate the conformational properties of the chains, implementing a freely jointed chain model, in between featureless cross-links. The Monte Carlo simulation method is used to sample the (restricted) translational degrees of freedom of the cross-links in the gel. We consider the case that the polymers in the gel have an affinity for surface positioned at the edge of the simulation volume. The polymer density decays as a power-law from the surface to the gel-density with an exponent close to -4/3. The gel features relatively large density fluctuations which is natural for a gel with a low density (φ ≈ 0.035), a low degree of cross-linking (average of three chainparts per cross-link), and relatively large chains (N = 50) in between the cross-links. Some parts of the gel can break loose from the gel and sample the adjoining volume. Representative snapshots exemplify large density fluctuations, which explain the large pore size distribution observed in experimental counterparts.     

Immobilized streptavidin gradients as bioconjugation platforms

Surface density gradients of streptavidin (SAV) were created on solid surfaces and demonstrated functionality as a bioconjugation platform. The surface density of immobilized streptavidin steadily increased in one dimension from 0 to 235 ng cm(-2) over a distance of 10 mm. The density of coupled protein was controlled by its immobilization onto a polymer surface bearing a gradient of aldehyde group density, onto which SAV was covalently linked using spontaneous imine bond formation between surface aldehyde functional groups and primary amine groups on the protein. As a control, human serum albumin was immobilized in the same manner. The gradient density of aldehyde groups was created using a method of simultaneous plasma copolymerization of ethanol and propionaldehyde. Control over the surface density of aldehyde groups was achieved by manipulating the flow rates of these vapors while moving a mask across substrates during plasma discharge. Immobilized SAV was able to bind biotinylated probes, indicating that the protein retained its functionality after being immobilized. This plasma polymerization technique conveniently allows virtually any substrate to be equipped with tunable protein gradients and provides a widely applicable method for bioconjugation to study effects arising from controllable surface densities of proteins.     

Stimuli‐Responsive Biomolecule‐Based Hydrogels and Their Applications

This Review presents polysaccharides, oligosaccharides, nucleic acids, peptides, and proteins as functional stimuli‐responsive polymer scaffolds that yield hydrogels with controlled stiffness. Different physical or chemical triggers can be used to structurally reconfigure the crosslinking units and control the stiffness of the hydrogels. The integration of stimuli‐responsive supramolecular complexes and stimuli‐responsive biomolecular units as crosslinkers leads to hybrid hydrogels undergoing reversible triggered transitions across different stiffness states. Different applications of stimuli‐responsive biomolecule‐based hydrogels are discussed. The assembly of stimuli‐responsive biomolecule‐based hydrogel films on surfaces and their applications are discussed. The coating of drug‐loaded nanoparticles with stimuli‐responsive hydrogels for controlled drug release is also presented.     

高密度自由醛基聚合物粉体材料的制备与应用

在酸性条件和剧烈搅拌下, 将质量分数为2.0%的聚乙烯醇水溶液缓慢滴加到过量25%(质量分数)的戊二醛水溶液中, 得到的产物不是凝胶, 而是粒度在50～150 nm之间的刚性粉末. 该粉末体相和表面依然保留着高密度的自由醛基. 理论计算得出粉末中整体醛基的量大于5.5 mmol/g, 而实验测得表面醛基的量大于1.6 mmol/g. 将醛基粉体材料进一步和氨基化合物反应, 其官能团分别转化为—NH2, —SH和—NH—NH2. 这类新型的大分子化合物普遍具有三维的亲水性表面、足够数量且灵活的功能性官能团和低的荧光背景, 是制备3D生物芯片的优良材料. 其中, 醛基和酰肼基粉末对肝素具有良好的固定效果, 固定的肝素分子依然具有较高的抗凝血活性.     

Patterned surfaces via self-assembly

The self-assembly of block copolymers, homopolymers and surfactants on surfaces often leads to well-defined patterns with topologically or chemically distinct regions. Important recent developments in controlling the nature of the pattern include methods to produce patterns via passive adsorption of a solid substrate; coupling of substrate topology and polymer phase separation in order to effect control over pattern formation; and methods to `tune' the surface potential of the substrate to eventually control pattern formation. The use of the polymer-patterned surface as a nanolithography mask has also been demonstrated in two very interesting systems. © 1999 Elsevier Science Ltd.     

Molecular Imprinting of Cyclodextrin Supramolecular Hydrogels Improves Drug Loading and Delivery

Cyclodextrin‐based controlled delivery materials have previously been developed for controlled release of different therapeutic drugs. In this study, a supramolecular hydrogel made from cyclodextrin‐based macromonomers is subjected to molecular imprinting to investigate the impact on release kinetics and drug loading, when compared with non‐imprinted, or alternately imprinted hydrogels. Mild synthesis conditions are used to molecularly imprint three antibiotics—novobiocin, rifampicin, and vancomycin—and to test two different hydrogel chemistries. The release profile and drug loading of the molecularly imprinted hydrogels are characterized using ultraviolet spectroscopy over a period of 35 days and compared to non‐imprinted, and alternately imprinted hydrogels. While only modest differences are observed in the release rate of the antibiotics tested, a substantial difference is observed in the total drug‐loading amount possible for hydrogels releasing drugs which has been templated by those drugs. Hydrogels releasing drugs which are templated by other drugs do not show improved release or loading. Analysis by FTIR does not show substantial incorporation of drug into the polymer. Lastly, bioactivity assays confirmed long‐term stability and release of incorporated antibiotics.     

Strong and tough hydrogels crosslinked by multi-functional polymer colloids

Tough polymer hydrogels have great potential applications in soft actuators, artificial muscles, tissue engineering, and so forth. To improve the strength and toughness of hydrogels, numerous strategies have been developed to integrate efficient energy dissipation mechanisms into the hydrophilic networks. Among them, the use of macro-crosslinkers to replace conventional chemical ones has become promising to develop tough hydrogels. Polymer colloids—including nano-/microparticles, nano-/microgels, hydrophobic associates, and block copolymer assemblies—have been employed in literature as multi-functional macro-crosslinkers that link polymer chains through covalent bonds or noncovalent interactions. The dislocation, deformation, desociation, and rupture of polymer colloids upon loadings are the major mechanisms to dissipate energy. This article provides a comprehensive account of most recent progresses on tough hydrogels crosslinked by polymer colloids, and explores the toughening mechanisms. It aims to inspire novel designs of tough hydrogels with multi-functionalities. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 1336–1350     

Polyvinyl alcohol hydrogels I. Microscopic structure by freeze-etching and critical point drying techniques

Froeze-etching (FE) and critical point drying (CPD) techniques were employed to prepare samples for investigating surface and bulk structures of polyvinyl alcohol (PVA) hydrogels by scanning electron microscopy. The hydrogels were obtained by freezing homogeneous solutions containing PVA polymer in either water or an aqueous solution of dimethyl sulfoxide (DMSO). An oriented porous structure was observed in the PVA hydrogel prepared without DMSO. The structure on the surface was found to be more porous than in the bulk for PVA hydrogels prepared from aqueous DMSO solutions. For given compositions of the hydrogels, samples prepared by FE technique showed a highly porous fibrillar structure on the surface, while those prepared by CPD technique showed a collapsed fibrillar structure with much less porosity. This marked difference indicates a collapse of the surface structure caused by the CPD technique. The CPD technique also led to significant reduction in porosity and loss of fibrillar structure in the bulk. Volume shrinkage of hydrogels caused by dehydration in ethanol may be responsible for the surface collapse as well as alteration of bulk structure. The FE technique reveals a more native structure of hydrogels than the commonly used CPD technique. However, it suffers from disadvantages such as charging and structural damage at high magnifications.     

不同交联剂对甲基丙烯酸-β-羟乙酯/E-51双甲基丙烯酸酯聚合物水凝胶性能的影响

以水溶性单体甲基丙烯酸-β-羟乙酯(HEMA)与大分子交联剂E-51双甲基丙烯酸酯(E-51-DMA)(质量比HEMA/E-51-DMA=90/10)为主要原料,分别引入了5种小分子交联剂:N,N′-亚甲基双丙烯酰胺(MBA)、二乙烯基苯(DVB)、双甲基丙烯酸乙二醇酯(EDMA)、1,1,1-三(丙烯酰氧甲基)丙烷(TAP)和2,2,2-三(丙烯酰氧甲基)乙醇(TAE),采用本体聚合方法合成了5个系列的聚合物水凝胶.研究了小分子交联剂的类型及用量对水凝胶溶胀性能、杨氏模量以及有效交联密度ve和聚合物-水相互作用参数χ的影响,并比较了不同交联剂的交联效率.结果表明,随着小分子交联剂用量的增大,水凝胶平衡含水量EWC逐渐降低,聚合物体积分数2逐渐增大,反映聚合物网络结构的有效交联密度ve以及热力学参数聚合物-水相互作用参数χ值也随之增大.通过理论交联密度和有效交联密度的线性拟合,得到所选用的5种小分子交联剂在E-51-DMA10/HEMA90水凝胶体系中的交联效率,其顺序为DVB>EDMA>TAE>MBA≈TAP.     

Physics of engineered protein hydrogels

Artificially engineered proteins and synthetic polypeptides have attracted widespread interest as building blocks for polymer hydrogels. The biophysical properties of the proteins, such as molecular recognition abilities, folded chain structures, and sequence-dependent thermodynamic behavior, enable advances in functional, responsive, and tunable gels. This review discusses the design of polymer hydrogels that incorporate protein domains, highlighting new challenges in polymer physics that are presented by this emerging class of materials. Five types of engineered protein hydrogels are discussed: (a) physically associating protein polymer gels, (b) amorphous artificially engineered protein networks, (c) engineered proteins with crystalline domains, (d) stretchable protein tertiary structures in gels, and (e) protein gels with biological recognition properties. The physics of the protein component and the physical properties of the resulting hydrogels are summarized, illustrating how advances in understanding these systems are leading to exciting novel biofunctional hydrogels. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Macromolecular Diffusion in Self-Assembling Biodegradable Thermosensitive Hydrogels

Hydrogel formation triggered by a change in temperature is an attractive mechanism for in situ gelling biomaterials for pharmaceutical applications such as the delivery of therapeutic proteins. In this study, hydrogels were prepared from ABA triblock polymers having thermosensitive poly(N-(2-hydroxypropyl) methacrylamide lactate) flanking A-blocks and hydrophilic poly(ethylene glycol) B-blocks. Polymers with fixed length A blocks (~22 kDA) but differing PEG-midblock lengths (2, 4 and 10 kDa) were synthesized and dissolved in water with dilute fluorescein isothiocyanate (FITC)-labeled dextrans (70 and 500 kDA). Hydrogels encapsulating the dextrans were formed by raising the temperature. Fluorescence recovery after photobleaching (FRAP) studies showed that diffusion coefficients and mobile fractions of the dextran dyes decreased upon elevating temperatures above 25 °C. Confocal laser scanning microscopy and cryo-SEM demonstrated that hydrogel structure depended on PEG block length. Phase separation into polymer-rich and water-rich domains occurred to a larger extent for polymers with small PEG blocks compared to polymers with a larger PEG block. By changing the PEG block length and thereby the hydrogel structure, mobility of FITC-dextran could be tailored. At physiological pH the hydrogels degraded over time by ester hydrolysis, resulting in increased mobility of the encapsulated dye. Since diffusion can be controlled according to polymer design and concentration, plus temperature, these biocompatible hydrogels are attractive as potential in situ gelling biodegradable materials for macromolecular drug delivery.     

Synthetic Hydrogels with Covalently Incorporated Saccharides Studied for Biomedical Applications – 15 Year Overview

Glycosylated materials have attracted special attention in biomedical field because of the unique properties of the individual carbohydrates in recognition mechanisms in many biological events. Sugar residues decorating a polymer surface can be regarded as multivalent ligands for interaction with various glycoproteins. This phenomenon provides the basis for several biomedical applications; of these, ligand-based targeted therapy is the most frequently cited. Materials functionalized with individual carbohydrates can be used for the selective binding of lectin proteins. Carbohydrate–lectin interactions underpin the development of diverse biosensor devices and bioassays aimed at pathogen detection. Because of the high content of hydroxyl groups and the consequent high hydrophilicity, saccharide-based monomers are perfect candidates for incorporation into hydrogels. Such functionalization allows synthetic materials to acquire unique properties and enhance their performance. This review covers developments over the past 15 years in the field of the synthesis of chemically crosslinked nano-, micro- and bulk hydrogels with covalently incorporated mono-, di- or trisaccharides. A brief view on the potential biomedical applications of these unique hydrogels is provided with particular emphasis on carriers for delivery of bioactive molecules, bioactivated materials for cell culture and tissue engineering as well as capture systems for pathogenic microorganisms.     

PVA-PAMPS-PAA三元互穿网络型水凝胶的合成及其性能研究

以2-丙烯酰胺基-2-甲基丙磺酸(AMPS)、丙烯酸(AA)以及聚乙烯醇(PVA)为原料,制备了PVA-PAMPS-PAA三元互穿网络型(T-IPN)水凝胶.红外分析表明,PVA与PAA以及PAMPS之间形成了较强的氢键,使得PVA分子上的C—O伸缩震动吸收峰移向了低波数处.X射线衍射以及电镜分析表明,当PVA用量较低时,PVA能均匀的穿插于凝胶网络中,形成完善的互穿网络结构,当PVA用量过高时,部分的PVA结晶而使得凝胶出现相分离.研究了该三元互穿网络型水凝胶的溶胀性能,结果表明,该水凝胶的平衡溶胀比在200至340之间,并且随着AA以及AMPS用量的增加,凝胶的溶胀速率以及平衡溶胀比均升高.该三元互穿网络型水凝胶在酸性溶液中和在碱性溶液中表现出截然不同的消溶胀性能;并且随着溶液pH的升高,凝胶在pH=9.0附近出现体积突变,表现出pH敏感性.通过研究T-IPN水凝胶的抗压缩性能发现,利用线型高分子、柔性高分子网络以及刚性高分子网络制备的三元互穿网络型水凝胶能在高溶胀比下保持较高的强度.溶胀比为180的T-IPN水凝胶,其最大抗压缩强度可达12.1 MPa.进一步研究发现,凝胶的组成以及溶胀比均对凝胶的抗压缩强度和压缩应变均存在较大的影响.