Liquid Metal Nanocores Initiated Construction of Smart DNA-Polymer Microgels with Programmable and Regulable Functions and Near-Infrared Light-Driven Locomotion

Due to their sequence-directed functions and excellent biocompatibility, smart DNA microgels have attracted considerable research interest, and the combination of DNA microgels with functional nanostructures can further expand their applications in biosensing and biomedicine. Gallium-based liquid metals (LMs) exhibiting both fluidic and metallic properties hold great promise for the development of smart soft materials; in particular, LM particles upon sonication can mediate radical-initiated polymerization reactions, thus allowing the combination of LMs and polymeric matrix to construct “soft–soft” materials. Herein, by forming active surfaces under sonication, LM nanoparticles (LM NPs) initiated localized radical polymerization reactions allow the combination of functional DNA units and different polymeric backbones to yield multifunctional core/shell microgels. The localized polymerization reaction allows fine control of the microgel compositions, and smart DNA microgels with tunable catalytic activities can be constructed. Moreover, due to the excellent photothermal effect of LM NPs, the resulting temperature gradient between microgels and surrounding solution upon NIR light irradiation can drive the oriented locomotion of the microgels, and remote control of the activity of these smart microgels can be achieved. These microgels may hold promise for various applications, such as the development of in vivo and in vitro biosensing and drug delivery systems.     

反相微乳液聚合法制备聚(丙烯酰胺-co-丙烯酸)pH敏感微凝胶及其性能

以丙烯酰胺(AM)和丙烯酸(AA)单体的水溶液为分散相,失水山梨醇单油酸脂(Span80)/聚氧乙烯失水山梨醇脂肪酸脂(Tween80)/异辛烷为分散介质,分别以N,N′-亚甲基双丙烯酰胺(MBA)、过硫酸铵/亚硫酸氢钠((NH4)2S2O8/NaHSO3)为交联剂和氧化还原引发剂,在30℃进行反相微乳液聚合制备了一系列不同单体摩尔百分数的P(AM-co-AA)微凝胶.通过傅立叶红外光谱、浊度法、透射电镜(TEM)和动态光散射(DLS)等测试手段分别对微凝胶特征官能团的存在、pH敏感性、微观形态、粒径大小及粒径分布等进行表征分析.结果表明,共聚物中存在AM和AA结构单元;样品的TEM照片显示在原料中AA的摩尔百分数为60%时,P(AM-co-AA)微凝胶粒子的数均粒径为90 nm左右,呈现非规则球形;DLS结果表明,P(AM-co-AA)微凝胶与PAM微凝胶相比具有较宽的粒径分布,且随原料中AA摩尔百分数增加,粒径分布逐渐变宽;P(AM-co-AA)微凝胶具有良好的pH敏感性,敏感pH值与AA的解离常数有关,通过调节pH值可以迅速控制自身体积的溶胀与收缩.     

Affinity switching for lysozyme and dual-responsive microgels by stopped-flow technique: Kinetic control and activity evaluation

The use of proteins as therapeutics in nanomedicine is an emerging research field and has developed rapidly.However,proteins are always vulnerable to renal excretion or digestion by the proteolytic system in vivo,which limits their usage to a large extent.Although biocompatible polymers have been covalently linked to proteins to protect them from recognition by the immune system and prolong their circulation time,the biological activity of them is sometimes decreased.To fill this gap,physical isolation,wrapping,or encapsulation techniques are employed.Up to now,various mature examples were reported,but the whole time scales for guest molecules loading and releasing,especially the initial rapid loading process,were rarely mentioned.Herein,a series of dual-responsive poly(N-isopropylacrylamide-co-methacrylic acid)(P(NIPAM-co-MAA)) microgels were synthesized and employed to investigate the kinetics of in situ complexation and release of lysozyme under external stimuli modulation upon a stopped-flow apparatus,which was suitable for rapid dynamic monitoring.Close inspection of the adsorption kinetics during the early stages( 50 s) revealed that the initial microgel collapse occurred within ~1 s,with more rapid transitions being observed when higher lysozyme concentrations were targeted.All the dynamic traces could be well fitted with a double exponential function,suggesting a fast(τ1) and a slow(τ2) relaxation time,respectively.Then,the kinetics of releasing bound lysozyme from microgels was carried on by utilizing the p H-responsive property,and the evaluation of the activity of released lysozyme was synchronously measured in a Micrococcus lysodeikticus(M.lysodeikticus) cell suspension.The corresponding relaxation time(τ) was also calculated by fitting the recorded dynamic traces.We speculate that this work can provide basic dynamics data and theoretical basis for microgels based nanocarriers to be used for protein delivery,controlled release,and possible chemical separation.     

High mechanical strength hydrogels preparation using hydrophilic reactive microgels as crosslinking agents

HRM (hydrophilic reactive microgels) hydrogels based on acrylamide and 2-acrylamido-2-methylpropane sulfonic acid were prepared using HRM as a new crosslinking agent. HRM containing double bonds (C=C) were obtained by chemically modifying hydrophilic microgels (HM) of acrylamide with 2-acrylamido-2-methylpropane sulfonic acid. The resulting HRM hydrogels had high compression strength, elasticity, and elongation under high water content. The excellent mechanical performance is a main result of the unique microstructure of the hydrogels that are crosslinked by HRM instead of the conventional crosslinking agents such as N,N′–methylenebisacrylamide.     

Optimized buffered polymerizations to produce N-vinylcaprolactam-based microgels

Temperature-sensitive N-vinylcaprolactam (VCL)-based microgel particles were synthesized by emulsion polymerization in a batch reactor. To avoid the hydrolysis of VCL, optimized buffered reactions were carried out by using VCL as main monomer, N,N′-methylenebisacrylamide (BA) as cross-linker and a sugar-based comonomer (3-O-methacryloyl-1,2:5,6-di-O-isopropylidene-α-d-glucofuranose, 3-MDG). The amounts of initiator, cross-linker, surfactant, comonomer, and reaction temperature were the reaction variables. The effects of these variables on the kinetic features of the different polymerizations were analyzed. The colloidal characterization of the microgel particles consists of the analysis of the evolution of the average hydrodynamic diameters as a function of the temperature of the medium. The results showed that in all cases BA reacted faster than VCL. All final microgel particles showed swelling-de-swelling behavior by changing the temperature of the medium in which they are dispersed. Initially formed microgel particles were not temperature-sensitive being necessary up to about 30% of VCL conversion for the onset of the swelling-de-swelling behavior. The final colloidal characteristics of these new microgels can be tuned by modulating the reaction variables.     

Synergistic depression of volume phase transition temperature in copolymer microgels

Microgels consisting of poly-N,N-diethylacrylamide (PDEAAM) and copolymer microgels consisting of N,N-diethylacrylamide-co-N-isopropylacrylamide (PDEAAM-co-PNIPAM) have been synthesized via free radical polymerizations. The volume phase transition of the microgels in aqueous solution was investigated by means of dynamic light scattering. All samples revealed a volume phase transition upon heating and the size change was fully reversible. An unusual dependence of transition temperature on the composition of the copolymer microgels was observed and samples were obtained with a transition temperature that was lower than that of both corresponding homopolymer particles. This synergistic behavior could be caused by strong hydrogen bonding between the mono- and the disubstituted acrylamide repeating units at nearly equimolar composition of the microgel.     

The volume transition in thermosensitive core–shell latex particles containing charged groups

An investigation of the volume transition in thermosensitive core–shell particles by dynamic light scattering (DLS) is presented. The core of the particles consists of polystyrene (diameter 118 nm), whereas the thermosensitive shell is composed of a network of poly (N-isopropylacrylamide) containing 2 mol% acrylic acid counits. The hydrodynamic radius of these particles as determined by DLS decreases in a continuous manner when raising the temperature. It is shown that the volume transition in the core–shell microgels remains continuous for a wide range of ionic strengths and pH values. This behavior is opposite to that of macrogels of the same chemical composition, which undergo a discontinuous volume transition. The present investigation therefore demonstrates that affixing the network to solid colloidal particles profoundly alters the volume transition of thermosensitive networks. The reason is that shrinking can take place only along the radial direction of the particles. The solid core thus exerts a strong spatial constraint onto the network, which leads to the observed behavior. Received: 29 March 1999 Accepted in revised form: 16 July 1999     

铅离子敏感N-异丙基丙烯酰胺共聚物微凝胶的制备

采用对N-异丙基丙烯酰胺-丙烯酸共聚微凝胶进行改性的方法合成了含苯并18-冠-6功能基团的PNIPAM微凝胶.红外和核磁光谱等手段证明苯并18-冠-6基团被引入到微凝胶中.改性后的微凝胶仍具有很好的温敏性,但是相转变温度由改性前的30℃提高到42℃,并且溶胀度也大大增加.在不控制离子强度的条件下微凝胶的粒径随Na+浓度增加而减小,但是随Pb2+浓度增加微凝胶粒径先减后增.在控制离子强度不变的条件下Na+浓度对微凝胶的粒径影响很小,但是随Pb2+浓度增加微凝胶粒径明显增大,显示较强的铅离子敏感性。     

Introduction of Quantum Dots into PNIPAM microspheres by precipitation polymerization above LCST

Amphiphilic polymers having different polymerizable functional groups were synthesised and investigated as coatings for semiconductor nanoparticles (Quantum Dots, QDs). QDs coated with hydrophobic ligands were successfully transferred into water using these polymers and the assemblies were co-polymerized with N-isopropylacrylamide (NIPAM) by a precipitation polymerization method. In the resulting hybrid microspheres, QDs were uniformly distributed within the PNIPAM matrix. The influence of different polymerizable groups and counter ions of the amphiphilic polymer on the copolymerization process were investigated.     

Effect of chemical composition on properties of pH-responsive poly(acrylamide-co-acrylic acid) microgels prepared by inverse microemulsion polymerization

In this research, a series of pH-responsive microgels based on acrylamide (AM), acrylic acid (AA) as the main monomers, and N,N′-methylenebisacrylamide as a divinyl cross-linking agent, have been prepared by inverse microemulsion polymerization. The effect of chemical composition of poly(acrylamide-co-acrylic acid) (P(AM-co-AA)) on hydrodynamic diameters, morphology, swelling ratios and pH-responsive behaviour and thermal properties of microgels were discussed. With an increase of the mole percentages of AA in the feed ratio, the microgels have higher swelling ratios. The TEM photographs show that the spherical morphology of the microgels are regular relatively. Comparing with PAM microgels, number-average diameters of P(AM-co-AA) microgels were larger because of the presence of AA chain segment in the polymer chain. Turbidities of microgels determined through UV–vis spectrophotometer indicate that the microgels exhibit favourable pH-responsive behaviour, and responsive pH value is related to the dissociation constant of AA. Moreover, thermal stable properties of microgels were confirmed by differential scanning calorimeter. It was observed that an increase in the mole percentages of AA in the feed ratio provided lower glass transition temperature and thermal decomposition temperature of pH-responsive microgels.