Recent advances in antimicrobial surfaces via tunable molecular interactions: Nanoarchitectonics and bioengineering applications

Infections can lead to severe health issues, even death. Surfaces, such as those of biomedical devices, implants, textiles, tables and doorknobs, play a crucial role as carriers for pathogens to migrate, attach and proliferate. Implementing surfaces with antimicrobial properties offers a reliable and long-lasting approach to combat surface transmission of germs, minimize microbial colonization, and reduce infections. In this review, we present recent advancements in antimicrobial surfaces, categorized into four groups based on their action mechanisms: antifouling, bactericidal, antifouling and bactericidal, and dynamic or stimuli-responsive surfaces. The work highlights the fabrication processes and properties of each category, along with discussing their structure-performance relationships. Special attention is given to various anchoring strategies involving tunable molecular interactions. The review also introduces relevant biomedical applications.     

Redox-responsive supramolecular nanoparticles based on amphiphilic sulfonatocalixarene and selenocystamine dihydrochloride

A supramolecular nanoparticle was fabricated based on the aggregation of amphiphilic p-sulfonatocalixarene induced by selenocystamine dihydrochloride (Se-Cys). Owing to the property of Se-Cys, the nanoparticles showed the redox-responsive disassembly behaviors with the addition of H2O2 and GSH     

Poly(N-isopropylacrylamide)-grafted dual stimuli-responsive filter paper for protein separation

Thermal and salt dual stimuli-responsive filter-paper-based membranes were prepared by UV-induced grafting of NIPAM-based polymers on paper surface. The grafting ratio could be controlled by monomer concentration during grafting polymerization. The results from pressure drop measurement of the mobile phase flowed cross the membrane demonstrate that an appropriate grafting ratio would be 8%-10%. Protein adsorption on the membrane through hydrophobic interaction could be promoted by increasing temperature and lyotropic salt concentration. The effect of grafted polymer structure on protein binding performance was studied. Filter paper grafted with NIPAM-based branched copolymer consisting of hydrophobic monomer moieties shows ten times higher protein binding capacity than that of the original filter paper. The separation of plasma proteins using the dual stimuli-responsive membrane was examined to demonstrate feasible application for hydrophobic interaction chromatographic separation of proteins.     

Mechanically Strong Janus Poly(N-isopropylacrylamide)/Graphene Oxide Hydrogels as Thermo-responsive Soft Robots

Simple preparation of stimuli-responsive hydrogels with good mechanical properties and mild stimuliresponsiveness is essential for their applications as smart soft robots.Mechanically strong Janus poly(Nisopropylacrylamide)/graphene oxide (PNIPAM/GO) nanocomposite hydrogels with stimuli-responsive bending behaviors are prepared through a simple one-step method by using molds made of a Teflon plate and a glass plate.Residual oxygen in the air bubbles on the Teflon plate surface affects the polymerization and hence the cross-linking density,leading to the different swelling/deswelling rates of the two sides of the gels.Therefore,the hydrogels exhibit bending/unbending behaviors upon heating/cooling in water.The incorporation of GO nanosheets dramatically enhances the mechanical properties of Janus hydrogels.Meanwhile,the photo-responsive property of the GO nanosheets also imparts the hydrogels with remotecontrollable deformation under IR irradiation.The application of the Janus PNIPAM/GO hydrogels as thermo-responsive grippers is demonstrated.     

Responsive polymers for analytical applications: A review

Stimuli-responsive polymers are capable of translating changes in their local environment to changes in their chemical and/or physical properties. This ability allows stimuli-responsive polymers to be used for a wide range of applications. In this review, we highlight the analytical applications of stimuli-responsive polymers that have been published over the past few years with a focus on their applications in sensing/biosensing and separations. From this review, we hope to make clear that while the history of using stimuli-responsive polymers for analytical applications is rich, there are still a number of directions to explore and exciting advancements to be made in this flourishing field of research.     

Improved functionality and control in the isomerization of a calix[4]arene-capped azobenzene

An improved azobenzene core capped by two calix[4]arene units isomerizes readily between trans and cis configurations via photochemical and/or thermal means. In addition, the presence of acid (particularly HCl) increases the rate of thermal cis→trans conversion. These enhancements to the functional response, control, and understanding of calixarene-capped azobenzene isomerization are important for future application in the dynamic encapsulation of small chemical species.     

偶氮苯基型离子液体溶液对空气中湿度的变色响应

Room temperature ionic liquids (ILs) that can exhibit a colorimetric response to moisture in the air are rarely reported in the literature. In this study, an azophenolic IL solution exhibited a spontaneous a colorimetric response, driven by the formation of hydrogen bonding between the [PhN＝NPhO] anion and moisture in the air. This phenomenon was clearly understood using ultraviolet-visible (UV-Vis) absorption spectroscopy, nuclear magnetic resonance (NMR) spectra, experimental data, and theoretical calculations. Specifically, in the UV-Vis absorption spectra, absorption around 455 nm decreased, while the band around 343 nm increased in the IL CHCl₃ solution as time progressed; this was accompanied by a color change from orange to faint yellow. This spontaneous, self-responsive process was further observed using ¹H NMR data. When the IL solution was placed with sufficient time, all the ¹H NMR peaks of the azophenolic anion shifted downfield, but no new signals appeared in the upfield region. The reason for this was easily identified as the stimuli in the air, such as CO₂ and moisture. When pure CO₂ was bubbled through the IL CHCl₃ solution, the solution color changed from its original orange to light orange, but could not change further to faint yellow, which ruled out CO₂ gas as a stimulus. When a small amount of water was gradually added to the IL solution (MeCN solvent), the absorption band around 474 nm decreased, coupled with an increase in the absorption band around 347 nm. This was accompanied by a color change from orange to faint yellow, which was almost identical to the self-responsive process in CHCl₃ and CCl₄. Moreover, two cuvettes of IL CHCl₃ solution were placed under relative humidities of 28% and 100%, respectively; the IL CHCl₃ solution required a much longer time to exhibit a complete color change from orange to faint yellow under a lower relative humidity, demonstrating that moisture is the most likely stimulus triggering the self-responsive color change of the IL solution. As revealed by the Gaussian 09 program at the B3LYP/6-31++G(p, d) level, the distance between the oxygen atom on the azophenolic anion and the hydrogen atom on the H₂O molecule was 0.174 nm, and the corresponding angle was 171.12°. Furthermore, the atomic dipole moment corrected Hirshfeld (ADCH) charge of the oxygen atom on the azophenolic anion was −0.52, and it increased to −0.62 after the azophenolic anion interacted with the H₂O. Reduced density gradient analysis revealed that the spike corresponding to O∙∙∙H―O for the IL-H₂O complex was located at around −0.04 a.u.. All the above data indicate that the presence of hydrogen bonding rendered the IL solution responsive to the moisture stimulus, and this response was accompanied by a color change that was visible to the naked eye. To the best of our knowledge, this is the first demonstration of a colorimetric change in an IL solution in response to moisture. We hope this work can help us to gain insight into some seemingly abnormal phenomena that occur during the research process.     

Recent developments in Pickering emulsions for biomedical applications

Pickering emulsions, stabilised by organic or inorganic particles, offer long-term dispersibility of liquid droplets and resistance to coalescence. The versatility of stabilising particles and their ability to encapsulate and release cargo with high internal payload capacity makes them attractive in a wide variety of applications, ranging from catalysis to the cosmetic and food industry. While these properties make them an equally promising material platform for pharmaceutical and clinical applications, the development of Pickering emulsions for healthcare is still in its infancy. Herein, we summarise and discuss recent progress in the development of Pickering emulsions for biomedical applications, probing their design for passive diffusion-based release as well as stimuli-responsive destabilisation. We further comment on challenges and future directions of this exciting and rapidly expanding area of research.     

“Aggregation-induced emission” of transition metal compounds: Design,mechanistic insights,and applications

In the last decades, compounds with ‘Aggregation-Induced Emission’ (AIE), which are weakly or non-emissive at all in solution but exhibit a strong luminescence in aggregated states, have emerged as an extraordinary breakthrough in the field of luminescent materials, allowing to circumvent ‘Aggregation Caused Quenching’ (ACQ), which in many cases prevents the development of efficient solid-state materials for optoelectronic applications.Since the discovery of AIE, many AIE-active materials have been developed, most of them composed of organic molecules, and thus fluorescent in nature. Although a wide range of applications such as bioimaging, sensing, multi-stimuli responsive materials, and optoelectronic devices have been proposed for this new class of materials, triplet harvesting phosphorescent materials have much longer lifetimes as compared to their singlet harvesting analogues, and for this particular reason, the development of AIE-active phosphorescent materials seems to be a promising strategy from the applications point of view. In this respect, the synthesis of new AIE-active systems including heavy metals that would facilitate the population of low-lying excited triplet states via spin-orbit coupling (SOC), for which the strength increases as the fourth power of atomic number, i.e. Z⁴, is highly desirable. This review covers the design and synthetic strategies used to obtain the AIEgens reported in the literature that contain either d-block metals such as Cu(I), Zn(II), Re(I), Ru(II), Pd(II), Ir(III), Pt(II), Au(I), and Os(IV), describing the mechanisms proposed to explain their AIE. New emerging high-tech applications such as OLEDs, chemical sensors or bioimaging probes proposed for these materials are also discussed in a separate section.