Photo, pH, and thermo triple-responsive spiropyran-based copolymer nanoparticles for controlled release

Light-Modulated Morphological Transformation of Spiropyran Derivative from Nanosphere to Nanorod

The construction of tunable morphological systems has important implications for understanding the mechanism of molecular self-assembly. In this study, a spiropyran derivative M1 is reported with light-responsive assembly morphology, which can be tuned from nanosphere to nanorod by ultraviolet light irradiation. The absorption spectra show that M1 molecules are transformed from closed-ring (SP) isomers into open-ring (MC) isomers and start to form H-aggregates with increasing irradiation time. Density functional theory calculations indicate that MC-MC isomers possess stronger binding energy than SP-SP isomers. The MC isomers may thus facilitate the dissociation of the SP-SP aggregates and promote the change of self-assembled morphology with the aid of stronger π-π stackings and dipole-dipole interactions. The research gives an effective method for modulating the morphology of assemblies, with great potential for applications in smart materials.

UV-Light-Induced Morphological Transformation of Spiropyran Assemblies from Irregular Sheet-like Structures to Nanospheres

Studies on self-assembling systems with a controllable morphology responding to light stimulation are significant for revealing the process and mechanism of assembly. Here, a molecule of spiropyran derivative (SP) possessing photoresponsive assembly morphology is constructed. SP self-assembles into irregular sheet-like structures whose morphology can be significantly transformed into regular nanospheres under continuous ultraviolet light stimulation. The UV-vis absorption spectra indicate that 56% of SP are isomerized from closed-ring form (SPC) to open-ring form (SPO) with color changes from colorless to magenta. Furthermore, theoretical calculations demonstrate that SPO-SPO aggregates possess stronger van der Waals forces than do SPC-SPC aggregates and tend to form stable intermediates combined with SPO isomers. Therefore, the isomerization of SP from SPC to SPO and the differences in intermolecular interactions are important factors in the morphological transition. Our study provides an efficient strategy to modulate the assembled morphology, which holds great promise to be applied in the field of smart materials.

Photoresponsive Spiropyran and DEGMA-Based Copolymers with Photo-Switchable Glass Transition Temperatures

Herein, novel photoresponsive spiropyran (SP)-based P(DEGMA-co-SpMA) copolymers with variable percentages of SP fractions are synthesized. The SP group present in these polymers exhibited the abilities of reversible photoisomerism. Their photoresponsive, structural, and thermal properties have been investigated and compared using various characterization techniques. These light-responsive copolymers are found to exhibit photoswitchable glass transition temperature (Tg ), high thermal stability (Td > 250°C), instant photochromism as well as fluorescence upon exposure to UV light. It is demonstrated that the Tg of these synthesized polymers increased when irradiated with UV light (λ = 365 nm), as a consequence of the photoisomerization of incorporated SP groups into their merocyanine form. This increase in Tg is attributed to an increase in polarity and a decrease in the overall entropy of the polymeric system when it switches from the ring-closed SP form (less-ordered state) to the ring-opened merocyanine form (more-ordered state). Therefore, such polymers with a unique feature of phototunable glass transition temperatures provide the possibility to be integrated into functional materials for various photoresponsive applications.

NIR light, pH, and redox-triple responsive nanogels for controlled release

Herein we report a novel spiropyran (SP)-based organic-inorganic composite nanogel (NG), which was prepared using upconverting nanoparticles, spiropyran, acrylic acid and N,N'-bis(acryloyl)cystamine (BAC) compounds under emulsion polymerisation. Compared with other polymer nanoparticles, the crosslinked multi-stimulus responsive nanogels can adjust the release rate by altering more of the parameters and this can meet the needs of a complex biological environment to control the release of drugs. Doxorubicin hydrochlorides were used as a simulated drug to test the drug loading performance and controllable drug release performance of the composite NGs. Under near-infrared light (NIR) irradiation, an acidic environment or a reducing agent, the delivery of the loaded drugs was by controlled release over 24 hours. Under mild triple stimulation (NIR light, pH 6, and 4 mM reducing agent), the loaded drug could be released more efficiently. The organic-inorganic composite NGs with highly-efficient and controllable release performance for loaded drugs provide many choices for novel stimulus responsive nanocarriers.

Joining Two Switches in One Nano-Object: Photoacidity and Photoisomerization in Electrostatic Self-Assembly

Multi-switchable supramolecular nano-objects that respond to irradiation of different wavelengths with changes in size and shape have been built from two different water-soluble molecular switches, joined by attachment to the same polyelectrolyte. Accordingly, two wavelength-specific reactions, namely the excited-state proton dissociation of a photoacid and the cis-trans isomerization of an azo dye, are combined in one supramolecular nano-object that is stable in aqueous solution. The concept has potential in the fields of sensors, molecular motors, and transport.

Mesoporous Silica Nanoparticles-Based Nanoplatforms: Basic Construction, Current State, and Emerging Applications in Anticancer Therapeutics

In recent years, researchers are developing novel nanoparticles for diagnostic applications using imaging techniques and for therapeutic purposes through drug delivery techniques. The unique physical and chemical properties of mesoporous silica nanoparticles (MSNs) make it possible to integrate a variety of commonly used therapeutic and imaging agents to construct a multimodal synergistic anticancer drug delivery system. Herein, recent advances in MSNs synthesis for drug delivery and smart response applications are reviewed. First, synthetic strategies for the fabrication of ordered MSNs, hollow MSNs, core-shell structured MSNs, dendritic MSNs, and biodegradable MSNs are outlined. Then, the recent research progress in designing functional MSN materials with various controlled release mechanisms in anticancer therapy is discussed, and new properties are introduced to suggest the latest design requirements as drug delivery materials. The review also highlights significant achievements in bioimaging using MSNs and their multifunctional counterparts as delivery vehicles. Finally, personal views on key directions for future work in this area are presented.

Physically stimulus-responsive nanoparticles for therapy and diagnosis

Nanoparticles offer numerous advantages in various fields of science, particularly in medicine. Over recent years, the use of nanoparticles in disease diagnosis and treatments has increased dramatically by the development of stimuli-responsive nano-systems, which can respond to internal or external stimuli. In the last 10 years, many preclinical studies were performed on physically triggered nano-systems to develop and optimize stable, precise, and selective therapeutic or diagnostic agents. In this regard, the systems must meet the requirements of efficacy, toxicity, pharmacokinetics, and safety before clinical investigation. Several undesired aspects need to be addressed to successfully translate these physical stimuli-responsive nano-systems, as biomaterials, into clinical practice. These have to be commonly taken into account when developing physically triggered systems; thus, also applicable for nano-systems based on nanomaterials. This review focuses on physically triggered nano-systems (PTNSs), with diagnostic or therapeutic and theranostic applications. Several types of physically triggered nano-systems based on polymeric micelles and hydrogels, mesoporous silica, and magnets are reviewed and discussed in various aspects.

The Effect of Topology on Block Copolymer Nanoparticles: Linear versus Star Block Copolymers in Toluene

Linear and star block copolymer (BCP) nanoparticles of (polystyrene-block-poly(4-vinylpyridine))_n (PS-b-P4VP)_n with arm numbers of 1, 2, 3, and 4 were prepared by two methods of polymerization-induced self-assembly (PISA) and general self-assembly of block copolymers in the low-polar organic solvent, toluene. The effect of the arm number on the size and/or morphology of the (PS-b-P4VP)_n nanoassemblies synthesized by the two methods in toluene and on the polymerization kinetics was investigated in detail. Our results show that in toluene, a low-polar solvent, the topology not only affected the morphology of the BCP nanoparticles prepared by PISA, but also influenced the BCP nanoparticles synthesized through general self-assembly.

Synthesis of novel combinatorial drug delivery system (nCDDS) for co-delivery of 5-Fluorouracil and Leucovorin calcium for colon targeting and controlled drug release

Objective: Purpose of the current study was to improve the oral effectiveness of 5-Fluorouracil (5-FU) by developing novel controlled, combinatorial drug delivery system (nCDDS) for co-delivery of 5-FU and Leucovorin (LC) for colon targeting.Significance: on the basis of results obtained, novel controlled, combinatorial drug delivery system (nCDDS) could be an effective strategy for the colon targeting of 5-FU and LC.Methods: Free radical polymerization method was tuned and used to fabricate this nCDDS. The nCDDS is synthesized in two steps, firstly synthesis of 5-fluoruracil/leucovorin calcium loaded nanogels and secondly, pre-synthesized 5-FU & LC loaded nanogels were dispersed in pectin based polymerized matrix hard gel. The nanogels and nCDD gels were characterized for network structure, thermal stability and surface morphology. Swelling and in-vitro release studies were carried out at different pH 1.2 and 7.4 both for naive nanogels and combined matrix gels. In-vivo study of combinatorial gel was performed on rabbits by using HPLC method to estimate plasma drug concentration and pharmacokinetics parameters.Results: Structure and thermal analysis confirmed the formation of stable polymeric network. SEM of nanogels and combinatorial gels showed that the spongy and rough edges particles and uniformly distributed in the combinatorial gel. The prepared nCDDS showed excellent water loving capacity and pH responsiveness. Combinatorial gel showed excellent characteristic for colonic delivery of drugs, which were confirmed by various in-vitro and in-vivo characterization. Acute oral toxicity study of combinatorial gel confirmed the biocompatible and non-toxic characteristics of developed formulation.Conclusion: Conclusively it can be found that nCDDS showed excellent properties regarding drug targeting in a controllable manner as compared to naive PEGylated nanogels.

pH-Responsive size-shrinkable mesoporous silica-based nanocarriers for improving tumor penetration and therapeutic efficacy

Poor tumor penetration is a major obstacle to nanomedicine for achieving effective anticancer therapy. Tumor microenvironment-induced nanomedicine size shrinkage is a promising strategy to overcome the drug penetration barrier across the dense tumor matrix. Herein, we design a size-shrinkable nanocarrier that uses acid as a means of triggering a change in particle size for co-achievement of efficient tumor accumulation followed by deep tumor penetration and rapid clearance from the body. This nanocarrier is constructed from a pH-sensitive lipid layer shell and an ultrasmall amino-functionalized mesoporous silica nanoparticle core capable of loading drugs. After intravenous injection into mice bearing the 4T1 tumor, the nanocarrier with an initial hydrodynamic size of about 33 nm could effectively accumulate at the tumor site through the enhanced permeability and retention effect. Subsequently, in the acidic tumor microenvironment, the lipid layer comprising 9 alkyl-spiropyran (SP-C9) undergoes a volume shrinkage due to the conversion of hydrophobic SP-C9 to amphiphilic 9 alkyl-merocyanine (MC-C9), thus leading to a significant decrease in the entire particle size (hydrodynamic size ∼17 nm) for enhanced intratumoral penetration. Moreover, we find that this size-shrinkable nanocarrier could be rapidly excreted out of the body based on the ICP analysis, significantly reducing biosafety issues. Benefiting from the effective tumor accumulation and penetration of the nanocarrier, the released doxorubicin shows potent antitumor efficacy. This demonstrates the high potential of the designed nanocarrier in solid tumor treatment.

A pH, thermal and light triple-stimuli responsive micellar solution formed by a cationic surfactant and trans-o-hydroxycinnamic acid

Controlling the viscoelastic characteristics of wormlike micelles is of great significance to both basic theory and practical applications. In this article, a novel multi-stimuli responsive wormlike micellar solution was prepared by mixing cationic surfactant 3-hexadecyloxy-2-hydroxypropyltrimethylammonium bromide (R₁₆HTAB) with trans-o-hydroxycinnamic acid (OHCA). Rheological studies, nuclear magnetic resonance (¹H-NMR) spectroscopy, UV-vis spectroscopy, and cryogenic-transmission electron microscopy (cryo-TEM) were utilized to investigate the wormlike micellar system's multi-responsive activity. The results showed that the self-assembled structure and viscoelasticity of the mixed system could be regulated by pH, temperature, and light irradiation. With the increasing trans-OHCA concentration, η₀ of the mixed solution increases first and then decreases and the turning point is presented at 30 mM trans-OHCA, indicating the transformation of spherical micelles to wormlike micelles, and then to short micelles. The microstructure of the mixed systems could be reversibly altered by adjusting the pH between 6.41 and 3.90, which was ascertained by cryogenic-transmission electron microscopy (cryo-TEM). The relationship of temperature and η₀ obeys the Arrhenius law, attributed to the decreasing micellar contour length. η₀ of a 40 mM R₁₆HTAB/15 mM OHCA solution sharply increases after UV irradiation, mainly because the cis-isomer could insert into the micelle more easily, and the transition mechanism was studied by UV-vis and ¹H NMR. The multi-responsive self-assembled system may open a new vista for building multi-functional aggregates to adapt to various environmental changes.

Photoluminescent Nanoinks with Multilevel Security for Quick Authentication of Encoded Optical Tags by Sunlight: Effective Physicochemical Parameters on Responsivity, Printability, and Brightness

Investigation of developed photoactive security inks and anticounterfeiting technologies in recent years indicates significant challenges for future of this research area, such as increase of security, fast responsivity, and facile authentication. Here, amine-functionalized latex nanoparticles were synthesized by emulsion copolymerization of methyl methacrylate (MMA) and 2-(dimethylamino)ethyl methacrylate (DMAEMA). Size of the latex nanoparticles was increased as a function of poly(dimethylaminoethyl acrylate) (PDMAEMA) contents, and also a decrease of particle size was obtained in response to an increase of temperature from 25 to 70 °C, above the lower critical solution temperature (LCST) of PDMAEMA. Surface physical modification of the functional latex nanoparticle with spiropyran photoswitches led to the development of anticounterfeiting nanoinks that have multilevel security and photochromic/fluorescence properties with a higher intensity and also brightness. The photoluminescent nanoinks were made of spiropyran latex nanoparticles and used for printing of the encoded optical security tags on cellulosic papers and banknotes. The results displayed that an increase of the particle size above 100 nm and an increase of the PDMAEMA contents led to a remarkable decrease of printability, fluorescent emission, brightness, intensity of photochromism, and also resolution of the printed security tags. As a significant advantage of the developed security inks, the printed security tags could be authenticated easily and fast upon sunlight irradiation by means of photochromism. The responsivity of encoded tags from the invisible to visible state is immediate upon sunlight irradiation for some seconds, whose intensity of coloration is appropriate and detectable clearly by naked eyes. The security anticounterfeiting inks based on spiropyran with multilevel security have been reported for the first time for applying in printing of encoded security tags on cellulosic papers, banknotes, and other documents, where the printed marks are detectable on sunlight exposure.

Prevent or Cure-The Unprecedented Need for Self-Reporting Materials

Self-reporting smart materials are highly relevant in modern soft matter materials science, as they allow for the autonomous detection of changes in synthetic polymers, materials, and composites. Despite critical advantages of such materials, for example, prolonged lifetime or prevention of disastrous material failures, they have gained much less attention than self-healing materials. However, as diagnosis is critical for any therapy, it is of the utmost importance to report the existence of system changes and their exact location to prevent them from spreading. Thus, we herein critically review the chemistry of self-reporting soft matter materials systems and highlight how current challenges and limitations may be overcome by successfully transferring self-reporting research concepts from the laboratory to the real world. Especially in the space of diagnostic self-reporting systems, the recent SARS-CoV-2 (COVID-19) pandemic indicates an urgent need for such concepts that may be able to detect the presence of viruses or bacteria on and within materials in a self-reporting fashion.

Rhodamine-Installed Polynorbornenes: Molecular Design, Structure, and Stimuli-Responsive Properties

The synthesis of a number of tailored architectures of rhodamine dye-norbornene conjugate monomers and corresponding homopolymers derived from them is described. The impact of the monomer architecture on the mechanochromic, photochromic, and thermochromic properties of rhodamine-modified polynorbornenes is reported. Color changes were caused by the reversible interconversion between the "open" and "closed" spirolactam form of the covalently attached dye. Monomers were synthesized in two principle architectures that varied on: (1) the number of polymerizable norbornene groups tethered to a bifunctional rhodamine dye; (2) the presence of flexible methylene spacers between the dye and the polymerizable norbornene groups. Introduction of norbornene groups on each of the two hydroxy groups of a bifunctional rhodamine resulted in a cross-linked polymer that exhibited better mechanochromic, photochromic, and thermochromic properties compared to the corresponding polymer without cross-links, derived from the derivatization of bifunctional rhodamine with only one norbornene. The introduction of flexible methylene spacers between the two polymerizable norbornenes and the dye molecule resulted in a polymeric framework with rapidly reversible color-changing properties upon mechanical or photostimulation. The ideal monomer molecular structure, whereby (1) attaching norbornene on both sides of the rhodamine dye and (2) methylene spacers between the dye and norbornenes on both sides afforded the nonpareil polymer structure that was capable of thermoreversible mechanochromic and photochromic features, and irreversible thermochromic features. These new materials may find utility as multi-stimuli-responsive soft materials.

Solid Multiresponsive Materials Based on Nitrospiropyran-Doped Ionogels

The application of molecular switches for the fabrication of multistimuli-responsive chromic materials and devices still remains a challenge because of the restrictions imposed by the supporting solid matrices where these compounds must be incorporated: they often critically affect the chromic response as well as limit the type and nature of external stimuli that can be applied. In this work, we propose the use of ionogels to overcome these constraints, as they provide a soft, fluidic, transparent, thermally stable, and ionic-conductive environment where molecular switches preserve their solution-like properties and can be exposed to a number of different stimuli. By exploiting this strategy, we herein pioneer the preparation of nitrospiropyran-based materials using a single solid platform that exhibit optimal photo-, halo-, thermo-, and electrochromic switching behaviors.

Wearable patch delivery system for artificial pancreas health diagnostic-therapeutic application: A review

The advanced stimuli-responsive approaches for on-demand drug delivery systems have received tremendous attention as they have great potential to be integrated with sensing and multi-functional electronics on a flexible and stretchable single platform (all-in-one concept) in order to develop skin-integration with close-loop sensation for personalized diagnostic and therapeutic application. The wearable patch pumps have evolved from reservoir-based to matrix patch and drug-in-adhesive (single-layer or multi-layer) type. In this review, we presented the basic requirements of an artificial pancreas, surveyed the design and technologies used in commercial patch pumps available on the market and provided general information about the latest wearable patch pump. We summarized the various advanced delivery strategies with their mechanisms that have been developed to date and representative examples. Mechanical, electrical, light, thermal, acoustic and glucose-responsive approaches on patch form have been successfully utilized in the controllable transdermal drug delivery manner. We highlighted key challenges associated with wearable transdermal delivery systems, their research direction and future development trends.

Multiswitchable photoacid-hydroxyflavylium-polyelectrolyte nano-assemblies

Light- and pH-responsive nano-assemblies with switchable size and structure are formed by the association of a photoacid, anthocyanidin, and a linear polyelectrolyte in aqueous solution. Specifically, anionic disulfonated naphthol derivatives, neutral hydroxyflavylium, and cationic poly(allylamine) are used as building blocks for the ternary electrostatic self-assembly, forming well-defined supramolecular assemblies with tunable sizes of 50 to 500 nm. Due to the network of possible chemical reactions for the anthocyanidin and the excited-state dissociation of the photoacid upon irradiation, different ways to alter the ternary system through external triggering are accessible. The structure and trigger effects can be controlled through the component ratios of the samples. Dynamic and static light scattering (DLS, SLS) and ζ-potential measurements were applied to study the size and the stability of the particles, and information on the molecular structure was gained by UV-vis spectroscopy. Isothermal titration calorimetry (ITC) provided information on the thermodynamics and interaction forces in the supramolecular assembly formation.

Photoluminescent and Chromic Nanomaterials for Anticounterfeiting Technologies: Recent Advances and Future Challenges

Counterfeiting and inverse engineering of security and confidential documents, such as banknotes, passports, national cards, certificates, and valuable products, has significantly been increased, which is a major challenge for governments, companies, and customers. From recent global reports published in 2017, the counterfeiting market was evaluated to be $107.26 billion in 2016 and forecasted to reach $206.57 billion by 2021 at a compound annual growth rate of 14.0%. Development of anticounterfeiting and authentication technologies with multilevel securities is a powerful solution to overcome this challenge. Stimuli-chromic (photochromic, hydrochromic, and thermochromic) and photoluminescent (fluorescent and phosphorescent) compounds are the most significant and applicable materials for development of complex anticounterfeiting inks with a high-security level and fast authentication. Highly efficient anticounterfeiting and authentication technologies have been developed to reach high security and efficiency. Applicable materials for anticounterfeiting applications are generally based on photochromic and photoluminescent compounds, for which hydrochromic and thermochromic materials have extensively been used in recent decades. A wide range of materials, such as organic and inorganic metal complexes, polymer nanoparticles, quantum dots, polymer dots, carbon dots, upconverting nanoparticles, and supramolecular structures, could display all of these phenomena depending on their physical and chemical characteristics. The polymeric anticounterfeiting inks have recently received significant attention because of their high stability for printing on confidential documents. In addition, the printing technologies including hand-writing, stamping, inkjet printing, screen printing, and anticounterfeiting labels are discussed for introduction of the most efficient methods for application of different anticounterfeiting inks. This review would help scientists to design and develop the most applicable encryption, authentication, and anticounterfeiting technologies with high security, fast detection, and potential applications in security marking and information encryption on various substrates.

Dual Photo- and pH-Responsive Spirooxazine-Functionalized Dextran Nanoparticles

A dual photo- and pH-responsive spirooxazine-functionalized polymer was synthesized by functionalization of dextran with a spirooxazine derivative (SO-COOH). The functionalized dextran derivatives can form nanoparticles in aqueous medium. Under UV light irradiation, the spirooxazine-functionalized dextran (Dex-SO) nanoparticles isomerize to zwitterionic merocyanine-functionalized dextran (Dex-MC), which leads to aggregation. However, the process is reversible upon irradiation with visible light. Under acidic conditions, the hydrophobic spirooxazine is protonated, and the nanoparticles aggregate or swell at pH values of 5 or 3, respectively. The encapsulation of the hydrophobic fluorescent dye Nile Red as model drug allowed us to gain more information about the structural changes under stimulation of UV light and acid treatment.

A pH-responsive dissociable mesoporous silica-based nanoplatform enabling efficient dual-drug co-delivery and rapid clearance for cancer therapy

The balance between tumor accumulation and renal clearance has severely limited the efficacy of mesoporous silica-based drug nanocarriers in cancer therapy. Herein, a pH-responsive dissociable mesoporous silica-based nanoplatform with efficient dual-drug co-delivery, tumor accumulation and rapid clearance for cancer therapy is achieved by adjusting the wetting of the mesoporous silica surface. At pH 7.4, the synthesized spiropyran- and fluorinated silane-modified ultrasmall mesoporous silica nanoparticles (SP-FS-USMSN) self-assemble to form larger nanoclusters (denoted as SP-FS-USMSN cluster) via hydrophobic interactions, which can effectively co-deliver anticancer drugs, doxorubicin hydrochloride (Dox) and curcumin (Cur), based on the mesopores within SP-FS-USMSN and the voids among the stacked SP-FS-USMSN. At pH 4.5-5.5, the conformational conversion of spiropyran from a "closed" state to an "open" state causes the wetting of the SP-FS-USMSN surface, leading to the dissociation of the SP-FS-USMSN cluster for drug release and renal clearance. The in vitro and in vivo studies demonstrate that the Cur and Dox co-loaded SP-FS-USMSN cluster (Cur-Dox/SP-FS-USMSN cluster) possesses great combined cytotoxicity, and can accumulate into tumor tissue by its large size-favored EPR effect and potently suppress tumor growth in HepG2-xenografted mice. This research demonstrates that the SP-FS-USMSN cluster may be a promising drug delivery system for cancer therapy and lays the foundation for practical mesoporous silica-based nanomedicine designs in the future.

Cell adhesion control by photoinduced LCST shift of PNIPAAm-based brush scaffolds

Cell adhesion was markedly regulated on spiropyran-containing PNIPAAm-based brush scaffolds by photoinduced LCST shift across a standard culture temperature.

Gated Mesoporous Silica Nanocarriers for Hypoxia-Responsive Cargo Release

Mesoporous silica nanocarriers (MSNs) are appealing in terms of their large cavity surface area and high loading capacity, but they have been suffering from premature cargo release. Herein, we report a gated smart MSN that is sensitive to low oxygen concentration (i.e., hypoxia) via taking advantage of the superior electron-accepting ability of the azobenzene moiety. The azobenzene polymer was employed as the responsive gate-keeper that was deposited on the MSN surface, followed by coating with amphiphilic Pluronic F68 for steric stabilization. The obtained nanocarriers were less than 200 nm. The in vitro polymer degradation was spectrophotometrically witnessed via the employment of a reducing agent, namely, sodium dithionite, with a strong electron-donating ability. The hypoxia-responsive cargo release from the gated MSN was quantitatively demonstrated in breast cancer cells (MCF-7) using the fluorescence resonance energy transfer (FRET) technique where coumarin 6 and rhodamine B was selected as the FRET donor and acceptor, respectively. The FRET ratio was used as the index and decreased linearly over time under hypoxia, whereas it almost remained steady under normoxia. In addition, a model photosensitizer, namely, chlorin e6, was also loaded in the gated MSN whose toxicity under hypoxia was verified. This study developed a hypoxia-responsive MSN with the azobenzene polymer as the removable gate-keeper, which would expand the application of MSNs in pharmaceutical and biomedical areas since the low oxygen concentration is a unique trigger in many pathological conditions.

Programming Stimuli-Responsive Behavior into Biomaterials

Stimuli-responsive materials undergo triggered changes when presented with specific environmental cues. These dynamic systems can leverage biological signals found locally within the body as well as exogenous cues administered with spatiotemporal control, providing powerful opportunities in next-generation diagnostics and personalized medicine. Here, we review the synthetic and strategic advances used to impart diverse responsiveness to a wide variety of biomaterials. Categorizing systems on the basis of material type, number of inputs, and response mechanism, we examine past and ongoing efforts toward endowing biomaterials with customizable sensitivity. We draw an analogy to computer science, whereby a stimuli-responsive biomaterial transduces a set of inputs into a functional output as governed by a user-specified logical operator. We discuss Boolean and non-Boolean operations, as well as the various chemical and physical modes of signal transduction. Finally, we examine current limitations and promising directions in the ongoing development of programmable stimuli-responsive biomaterials.

Photo-triggered polymer nanomedicines: From molecular mechanisms to therapeutic applications

The use of nanotechnology to improve treatment efficacy and reduce side effects is central to nanomedicine. In this context, stimuli-responsive drug delivery systems (DDS) such as chemical/physical gels or nanoparticles such as polymersomes, micelles or nanogels are particularly promising and are the focus of this review. Several stimuli have been considered but light as an exogenous trigger presents many advantages that are pertinent for clinical applications such as high spatial and temporal control and low cost. Underlying mechanisms required for the release of therapeutic agents in vitro and in vivo range from the molecular scale, namely photoisomerization, hydrophobicity photoswitching, photocleavage or heat generation via nanoheaters, through to the macromolecular scale. As well as these approaches, DDS destabilization, DDS permeation pore unblocking and formation are discussed.

The light-controlling of temperature-responsivity in stimuli-responsive polymers

Light-controlling of phase separation in temperature-responsive polymer solutions by using light-responsive materials for reversible controlling physical and chemical properties of the media with an out-of-system stimulus with tunable intensity.

Rewritable Anticounterfeiting Polymer Inks Based on Functionalized Stimuli-Responsive Latex Particles Containing Spiropyran Photoswitches: Reversible Photopatterning and Security Marking

Increase of safety in security documents by using anticounterfeiting inks based on fluorochromic and photochromic compounds has attracted a great deal of attention in the recent years. Herein, we developed novel functionalized stimuli-responsive latex particles containing spiropyran (1 wt %) by semicontinuous emulsifier-free emulsion polymerization, which are usable as anticounterfeiting inks for marking on security documents and also photopatterning on cellulosic papers. The size and morphology of the latex particles were characterized by scanning electron microscopy and dynamic light scattering and their functionality was characterized by Fourier-transform infrared spectroscopy. All the stimuli-responsive latexes are composed of spherical particles with different hydroxyl, epoxy, and carboxylic acid functional groups, and the size of the particles varies in the range of 400-900 nm. Additionally, the latex particles undergo a remarkable light-induced size variation (aggregation-disaggregation) upon UV illumination (365 nm), depending on the functional group type, as a result of π-π stacking interactions and also electrostatic attractions between the different particles. The photochromic behavior, kinetics of the SP ⇌ MC isomerization, photoswitchability, and photofatigue-resistant characteristics of the prepared latexes were extensively investigated. The results display that the photochromic behavior and SP ⇌ MC isomerization can significantly be influenced by the polar interactions between the functional groups and MC molecules. As a novel application, the prepared stimuli-responsive latexes were used as anticounterfeiting inks for writing on cellulosic paper and also security marking on several monies, where the written phrase displayed red fluorescence emission and coloration under and after UV illumination (365 nm), respectively. Additionally, the latexes were sprayed on cellulosic papers to prepare stimuli-responsive papers for investigation of their photopatterning ability under UV irradiation and different masking. The presence of functional groups and large particle sizes are the main effective factors for stabilization of the latex particles on cellulosic papers. This is the first report on application of functionalized stimuli-responsive latex particles containing spiropyran as anticounterfeiting inks for security marking and photopatterning on cellulosic papers, directly and without using further additives.

Smart composite hydrogel with pH-, ionic strength- and temperature-induced actuation

A facile and versatile photo-patterning method to fabricate "smart" hydrogels with defined lateral and vertical inhomogeneity of hydrogel composition and dimensions has been developed via generating programmable composite hydrogels and bilayer hydrogels based on thermal and ionic strength-responsive poly(N-isopropylacrylamide) and pH-sensitive poly(acrylic acid) hydrogels. These hydrogels are capable of responding to triple-stimuli and inducing reversible "on" and "off" states upon external stimulation due to abrupt volume changes of the responsive hydrogel networks. Moreover, the composite and bilayer hydrogels show a reversible and repeatable direction-controllable bending behavior upon variation of temperature, ionic strength and pH, which is the result of the structural inhomogeneity and the modulation of the hydrogel solvation state in response to these changes. Importantly, different bending behaviors can be structurally programmed by controlling the patterned components, which undergo different swelling or shrinkage and further generate asymmetric internal stresses within the composite hydrogels in a specific manner. Additionally, such asymmetric internal stresses drive the shape deformations of the composite hydrogels, which are promising for potential applications in soft robots and actuators.

Fabrication of Thermoresponsive Polymer-Functionalized Cellulose Sponges: Flexible Porous Materials for Stimuli-Responsive Catalytic Systems

In this present work, a thermoresponsive and recyclable catalytic system was prepared by grafting poly( N-isopropylacrylamide)- co-poly(glycidyl methacrylate) (PNIPAM- co-PGM) to a cellulose sponge, which was reinforced by polydopamine (PDA) and (3-aminopropyl)triethoxysilane (APTMS). Au nanoparticles (Au NPs) were loaded via in situ reduction of HAuCl₄ with PDA. Fourier transform infrared, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, and thermogravimetric analysis results revealed that the Au NPs (<10 nm) were homogenously dispersed on the surface of the sponge. Catalytic experiments with sponges prepared without PNIPAM- co-PGM demonstrated an increased reaction rate when the temperature of the reaction medium was elevated. However, in the presence of PNIPAM-i co-PGM in the sponges, the reaction rate was decreased when the reaction temperature was higher than the lower critical solution temperature of the polymer. The sponge could be conveniently separated from the reactions and reused up to 22 cycles.

A New Route to Fabricate Multifunctional and Multistage Composite Nanoparticle

The focus of nanoparticle research is on exploring its application in all kinds of field. Among these, multifunctional nanoparticle attracts increasing interest due to its fittest property and adjustable property. Herein, a multifunctional and multistage nanoparticle considering the advantage of both nanogel and pH-responsive property has been designed and synthesized in the research. The composite nanoparticle was obtained by in situ processing and polymerization technique using acetylated β-cyclodextrin and gelatin as materials. Gelatin was first encapsulated into Ac-β-CD nanoparticle in order to investigate optimal fabrication conditions of W/O/W technique. The results showed that the nanoparticle had monodisperse characteristic and coarse spherical morphology, which was influenced by factors such as PVA concentration and water/oil ratio. In further step, two-phase composite nanoparticle could be obtained by combined W/O/W technique and in situ polymerization using optimal preparative parameters of W/O/W technique. Two-phase structure could be confirmed by TEM images and DLS results. Fabrication temperature had no effect on the diameters of composite nanoparticle, but influenced the encapsulated efficiency of nanogel. Finally, composite nanoparticle showed quick pH response property at mild acid medium and no obvious cytotoxicity.

A photo-switchable and thermal-enhanced fluorescent hydrogel prepared from N-isopropylacrylamide with water-soluble spiropyran derivative

Herein, a photo-switchable and thermal-enhanced fluorescent hydrogel has been fabricated from N-isopropylacrylamide (NIPAAm) with a mixture of water-soluble acryloyl-α-cyclodextrin/acryloyl-α-cyclodextrin-spiropyran (acryloyl-α-CD/ acryloyl-α-CD-SP) as cross-linkers. The physical properties, photochromic properties, and fluorescent behavior of the hydrogel were characterized. The fluorescence emission of the hydrogel can be reversibly switched 'on/off' by UV/visible light irradiation, and meanwhile the fluorescence intensity can be enhanced by increasing the temperature above the volume phase transition temperature (VPTT) of the hydrogel. The hydrogel also shows spatiotemporal fluorescent behavior, excellent cytocompatibility, and fatigue resistance in photochromic and photo-switchable fluorescent behaviors.

Electrolyte and pH-sensitive amphiphilic alginate: synthesis, self-assembly and controlled release of acetamiprid

In this study, a pH-responsive amphiphilic alginate (Ugi-Alg) was synthesized via Ugi reaction without using a catalyst. The structure of Ugi-Alg was confirmed by FT-IR and ¹H NMR spectroscopy. Amphiphilic alginate can form micelles in an aqueous medium due to it's amphiphilic nature.. The impacts of Na⁺ concentration and pH on the micelle size were characterized by dynamic light scattering (DLS) and transmission electron microscopy (TEM). The dynamic light scattering observations showed that micelle size increases with the decrease in Na⁺ concentration in aqueous solution. However, the micelle size decreases first and then increases as the pH value decreases from 5.3 to 2.0. Transmission electron microscopy confirmed that the mean size of micelles is 30–200 nm. In addition, a model hydrophobic pesticide (acetamiprid) was loaded in the micelles. The encapsulation efficiency and release behavior of micelles were studied, which could be controlled by Na⁺ concentration and pH. The results indicated that encapsulation efficiency of acetamiprid increases from 55% to 96% due to the increase in Na⁺ concentration from 0.01 M to 0.3 M. Moreover, with the decrease in pH from 5.3 to 2.0, encapsulation efficiency increases from 55% to 80%. Furthermore, the data of acetamiprid release kinetics could be well-fitted by the Weibull model.

Schematic of Ugi-Alg aggregation in aqueous solution of different NaCl concentrations and pH values.