On-Demand Reversible UV-Triggered Interpenetrating Polymer Network-Based Drug Delivery System Using the Spiropyran-Merocyanine Hydrophobicity Switch

Mucin-Based Dual Cross-Linkable IPN Hydrogel Bioink for 3D Bioprinting and Cartilage Tissue Engineering

The cartilage possesses limited regenerative capacity, necessitating advanced approaches for its repair. This study introduces a bioink designed for cartilage tissue engineering (TE) by incorporating ionically cross-linkable alginate into the photo-cross-linkable MuMA bioink, resulting in a double cross-linked interpenetrating network (IPN) hydrogel. Additionally, hyaluronic acid (HA), a natural component of cartilage and synovial fluid, was added to enhance the scaffold's properties. HA has been demonstrated to improve cartilage lubrication, regulate inflammation, promote cell proliferation, and support extracellular matrix (ECM) deposition and regeneration, making it valuable for cartilage TE. Comprehensive experiments were conducted to assess morphology, swelling, degradation, mechanical and rheological properties, printability, and biocompatibility. Results indicated that the double cross-linked scaffolds comprising MuMA, alginate, and HA exhibited compressive moduli comparable to native cartilage, unlike single cross-linked variants. The double cross-linking also influenced degradation, water uptake, and porosity, contributing to the scaffold durability and stability for chondrocyte support. Biocompatibility tests with C28/I2 cells demonstrated the cell-supportive and chondrogenic potential of the bioink. This study establishes mucin as a versatile material for specialized cartilage tissue engineering applications.

Light-/pH-Regulated Spiropyran Smart-Responsive Hydrophilic Separation Platform for the Identification of Serum Glycopeptides from Hepatocellular Carcinoma Patients

Smart-responsive materials have attracted much attention in the enrichment of post-translational modifications of proteins. In this work, for the first time, we developed a smart enrichment strategy (MNPs-l-DOPA/PEI-SP) based on the change in hydrophilic properties of spiropyran under the regulation of light and pH to realize the controllable enrichment and release of intact glycopeptides. The enrichment mechanism and possible binding mechanism were verified by theoretical calculations. The smart enrichment platform based on MNPs-l-DOPA/PEI-SP was used to screen glycoprotein biomarkers for hepatocellular carcinoma (HCC) to evaluate its cancer diagnostic and monitoring performance. A total of 3,864 intact N-glycopeptides containing 166 N-glycoproteins were successfully identified in serum samples of early-stage HCC patients, while 3,266 intact N-glycopeptides containing 193 glycoproteins were identified in normal control (NC) serum samples. This work not only provides new ideas for the efficient enrichment of intact glycopeptides with smart-responsive material, but also broadens the research possibilities for biomarker discovery in HCC serum liquid biopsies.

Photo-induced time-dependent controllable wettability of dual-responsive multi-functional electrospun MXene/polymer fibers

Switchable wettability potential in smart fibers is of paramount importance in various applications. Light-induced controllable changes in surface wettability have a significant role in this area. Herein, smart waterborne homopolymer, functional copolymer with different polarity and flexibility, and multi-functional terpolymer particles containing a time-dependent dual-responsive acrylated spiropyran, as a polymerizable monomer, were successfully synthesized through eco-friendly single-step emulsifier-free emulsion polymerization. Presence of 10 wt% of butyl acrylate and dimethylaminoethyl methacrylate relative to methylmethacrylate as functional comonomers decreased the Tg of the samples almost 20 ℃ and increased their polarity. The optical properties of the particles were investigated, and the UV-vis and fluorescence spectroscopy results showed that not only polarity and flexibility of the polymer chains may have a positive effect on improving the optical properties, but also the simultaneous presence of functional groups has a synergistic effect. The smart polymer particles with flexibility and polarity features exhibited higher absorption and emission compared to other samples. Inspired by these findings, multi-functional smart polymer fibers were prepared using the electrospinning method. The smart multi-functional electrospun fibers containing few-layer Ti3C2 MXenes were synthesized to improve the fibers' properties and change the surface wettability due to the hydrophilic functional groups of MXene. Field-emission scanning electron microscopy images displayed the successful preparation of few-layer MXenes. Smooth and bead-free fibers with bright red fluorescence emission under UV irradiation were shown using fluorescence microscopy. The study on the surface wettability of fibers revealed that UV and visible light irradiation induced reversible time-dependent changes in the wettability of the smart multi-functional MXene/polymer electrospun fibers from hydrophobic to hydrophilic, reaching a water contact angle of 10° from an initial water contact angle of 100° under UV light and also changing to superhydrophilic state with passing time. Upon visible light exposure, the fibers returned to their original state. Furthermore, the fibers demonstrated a high stability over five alternating cycles of UV and visible light irradiation. This study shows that the fabrication of time-dependent smart fibers, utilizing the flexibility and polarity in the presence of MXenes, significantly improves and controls surface wettability changes. The outstanding dynamically photo-switchable wettability of these fibers may offer exciting opportunities in various applications, especially in the separation of oil from water contaminants.

Merocyanines: Electronic Structure and Spectroscopy in Solutions, Solid State, and Gas Phase

Merocyanines, owing to their readily tunable electronic structure, are arguably the most versatile functional dyes, with ample opportunities for tailored design via variations of both the donor/acceptor (D/A) end groups and π-conjugated polymethine chain. A plethora of spectral properties, such as strong solvatochromism, high polarizability and hyperpolarizabilities, and sensitizing capacity, motivates extensive studies for their applications in light-converting materials for optoelectronics, nonlinear optics, optical storage, fluorescent probes, etc. Evidently, an understanding of the intrinsic structure-property relationships is a prerequisite for the successful design of functional dyes. For merocyanines, these regularities have been explored for over 70 years, but only in the past three decades have these studies expanded beyond the theory of their color and solvatochromism toward their electronic structure in the ground and excited states. This Review outlines the fundamental principles, essential for comprehension of the variable nature of merocyanines, with the main emphasis on understanding the impact of internal (chemical structure) and external (intermolecular interactions) factors on the electronic symmetry of the D-π-A chromophore. The research on the structure and properties of merocyanines in different media is reviewed in the context of interplay of the three virtual states: nonpolar polyene, ideal polymethine, and zwitterionic polyene.

Fine-tuning of membrane permeability by reversible photoisomerization of aryl-azo derivatives of thymol embedded in lipid nanoparticles

Responsiveness of liposomes to external stimuli, such as light, should allow a precise spatial and temporal control of release of therapeutic agents or ion transmembrane transport. Here, some aryl-azo derivatives of thymol are synthesized and embedded into liposomes from 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine to obtain light-sensitive membranes whose photo-responsiveness, release behaviour, and permeability towards Cl- ions are investigated. The hybrid systems are in-depth characterized by dynamic light scattering, atomic force microscopy and Raman spectroscopy. In liposomal bilayer the selected guests undergo reversible photoinduced isomerization upon irradiation with UV and visible light, alternately. Non-irradiated hybrid liposomes retain entrapped 5(6)-carboxyfluorescein (CF), slowing its spontaneous leakage, whereas UV-irradiation promotes CF release, due to guest trans-to-cis isomerization. Photoisomerization also influences membrane permeability towards Cl- ions. Data processing, according to first-order kinetics, demonstrates that Cl- transmembrane transport is enhanced by switching the guest from trans to cis but restored by back-switching the guest from cis to trans upon illumination with blue light. Finally, the passage of Cl- ions across the bilayer can be fine-tuned by irradiation with light of longer λ and different light-exposure times. Fine-tuning the photo-induced structural response of the liposomal membrane upon isomerization is a promising step towards effective photo-dynamic therapy.

Triggerable Patches for Medical Applications

Medical patches have garnered increasing attention in recent decades for several diagnostic and therapeutic applications. Advancements in material science, manufacturing technologies, and bioengineering have significantly widened their functionalities, rendering them highly versatile platforms for wearable and implantable applications. Of particular interest are triggerable patches designed for drug delivery and tissue regeneration purposes, whose action can be controlled by an external signal. Stimuli-responsive patches are particularly appealing as they may enable a high level of temporal and spatial control over the therapy, allowing high therapeutic precision and the possibility to adjust the treatment according to specific clinical and personal needs. This review aims to provide a comprehensive overview of the existing extensive literature on triggerable patches, emphasizing their potential for diverse applications and highlighting the strengths and weaknesses of different triggering stimuli. Additionally, the current open challenges related to the design and use of efficient triggerable patches, such as tuning their mechanical and adhesive properties, ensuring an acceptable trade-off between smartness and biocompatibility, endowing them with portability and autonomy, accurately controlling their responsiveness to the triggering stimulus and maximizing their therapeutic efficacy, are reviewed.

Recent Development of Photochromic Polymer Systems: Mechanism, Materials, and Applications

Photochromic polymer is defined as a series of materials based on photochromic units in polymer chains, which produces reversible color changes under irradiation with a particular wavelength. Currently, as the research progresses, it shows increasing potential applications in various fields, such as anti-counterfeiting, information storage, super-resolution imaging, and logic gates. However, there is a paucity of published reviews on the topic of photochromic polymers. Herein, this review discusses and summarizes the research progress and prospects of such materials, mainly summarizing the basic mechanisms, classification, and applications of azobenzene, spiropyran, and diarylethene photochromic polymers. Moreover, 3-dimensional (3D) printable photochromic polymers are worthy to be summarized specifically because of its innovative approach for practical application; meanwhile, the developing 3D printing technology has shown increasing potential opportunities for better applications. Finally, the current challenges and future directions of photochromic polymer materials are summarized.

Highly Efficient Photoswitchable Smart Polymeric Nanovehicle for Gene and Anticancer Drug Delivery in Triple-Negative Breast Cancer

Over the past few decades, there has been significant interest in smart drug delivery systems capable of carrying multiple drugs efficiently, particularly for treating genetic diseases such as cancer. Despite the development of various drug delivery systems, a safe and effective method for delivering both anticancer drugs and therapeutic genes for cancer therapy remains elusive. In this study, we describe the synthesis of a photoswitchable smart polymeric vehicle comprising a photoswitchable spiropyran moiety and an amino-acid-based cationic monomer-based block copolymer using reversible addition-fragmentation chain transfer (RAFT) polymerization. This system aims at diagnosing triple-negative breast cancer and subsequently delivering genes and anticancer agents. Triple-negative breast cancer patients have elevated concentrations of Cu2+ ions, making them excellent targets for diagnosis. The polymer can detect Cu2+ ions with a low limit of detection value of 9.06 nM. In vitro studies on doxorubicin drug release demonstrated sustained delivery at acidic pH level similar to the tumor environment. Furthermore, the polymer exhibited excellent blood compatibility even at the concentration as high as 500 μg/mL. Additionally, it displayed a high transfection efficiency of approximately 82 ± 5% in MDA-MB-231 triple-negative breast cancer cells at an N/P ratio of 50:1. It is observed that mitochondrial membrane depolarization and intracellular reactive oxygen species generation are responsible for apoptosis and the higher number of apoptotic cells, which occurred through the arrest of the G2/M phase of the cell cycle were observed. Therefore, the synthesized light-responsive cationic polymer may be an effective system for diagnosis, with an efficient anticancer drug and gene carrier for the treatment of triple-negative breast cancer in the future.

Biomedical applications of stimuli-responsive "smart" interpenetrating polymer network hydrogels

In recent years, owing to the ongoing advancements in polymer materials, hydrogels have found increasing applications in the biomedical domain, notably in the realm of stimuli-responsive "smart" hydrogels. Nonetheless, conventional single-network stimuli-responsive "smart" hydrogels frequently exhibit deficiencies, including low mechanical strength, limited biocompatibility, and extended response times. In response, researchers have addressed these challenges by introducing a second network to create stimuli-responsive "smart" Interpenetrating Polymer Network (IPN) hydrogels. The mechanical strength of the material can be significantly improved due to the topological entanglement and physical interactions within the interpenetrating structure. Simultaneously, combining different network structures enhances the biocompatibility and stimulus responsiveness of the gel, endowing it with unique properties such as cell adhesion, conductivity, hemostasis/antioxidation, and color-changing capabilities. This article primarily aims to elucidate the stimulus-inducing factors in stimuli-responsive "smart" IPN hydrogels, the impact of the gels on cell behaviors and their biomedical application range. Additionally, we also offer an in-depth exposition of their categorization, mechanisms, performance characteristics, and related aspects. This review furnishes a comprehensive assessment and outlook for the advancement of stimuli-responsive "smart" IPN hydrogels within the biomedical arena. We believe that, as the biomedical field increasingly demands novel materials featuring improved mechanical properties, robust biocompatibility, and heightened stimulus responsiveness, stimuli-responsive "smart" IPN hydrogels will hold substantial promise for wide-ranging applications in this domain.

Stimuli responsiveness of recent biomacromolecular systems (concept to market): A review

Stimuli responsive delivery systems, also known as smart/intelligent drug delivery systems, are specialized delivery vehicles designed to provide spatiotemporal control over drug release at target sites in various diseased conditions, including tumor, inflammation and many others. Recent advances in the design and development of a wide variety of stimuli-responsive (pH, redox, enzyme, temperature) materials have resulted in their widespread use in drug delivery and tissue engineering. The aim of this review is to provide an insight of recent nanoparticulate drug delivery systems including polymeric nanoparticles, dendrimers, lipid-based nanoparticles and the design of new polymer-drug conjugates (PDCs), with a major emphasis on natural along with synthetic commercial polymers used in their construction. Special focus has been placed on stimuli-responsive polymeric materials, their preparation methods, and the design of novel single and multiple stimuli-responsive materials that can provide controlled drug release in response a specific stimulus. These stimuli-sensitive drug nanoparticulate systems have exhibited varying degrees of substitution with enhanced in vitro/in vivo release. However, in an attempt to further increase drug release, new dual and multi-stimuli based natural polymeric nanocarriers have been investigated which respond to a mixture of two or more signals and are awaiting clinical trials. The translation of biopolymeric directed stimuli-sensitive drug delivery systems in clinic demands a thorough knowledge of its mechanism and drug release pattern in order to produce affordable and patient friendly products.

Phototriggered structures: Latest advances in biomedical applications

Non-invasive control of the drug molecules accessibility is a key issue in improving diagnostic and therapeutic procedures. Some studies have explored the spatiotemporal control by light as a peripheral stimulus. Phototriggered drug delivery systems (PTDDSs) have received interest in the past decade among biological researchers due to their capability the control drug release. To this end, a wide range of phototrigger molecular structures participated in the DDSs to serve additional efficiency and a high-conversion release of active fragments under light irradiation. Up to now, several categories of PTDDSs have been extended to upgrade the performance of controlled delivery of therapeutic agents based on well-known phototrigger molecular structures like o-nitrobenzyl, coumarinyl, anthracenyl, quinolinyl, o-hydroxycinnamate and hydroxyphenacyl, where either of one endows an exclusive feature and distinct mechanistic approach. This review conveys the design, photochemical properties and essential mechanism of the most important phototriggered structures for the release of single and dual (similar or different) active molecules that have the ability to quickly reason of the large variety of dynamic biological phenomena for biomedical applications like photo-regulated drug release, synergistic outcomes, real-time monitoring, and biocompatibility potential.

Novel Indoline Spiropyrans Based on Human Hormones β-Estradiol and Estrone: Synthesis, Structure, Chromogenic and Cytotoxic Properties

The introduction of a switchable function into the structure of a bioactive compound can endow it with unique capabilities for regulating biological activity under the influence of various types of external stimuli, which makes such hybrid compounds promising objects for photopharmacology, targeted drug delivery and bio-imaging. This work is devoted to the synthesis and study of new spirocyclic derivatives of important human hormones-β-estradiol and estrone-possessing a wide range of biological activities. The obtained hybrid compounds represent an indoline spiropyrans family, a widely known class of organic photochromic compounds. The structure of the compounds was confirmed by ¹H and ¹³C NMR, IR, HRMS and single-crystal X-ray analysis. The intermolecular interactions in the crystals of spiropyran (3) were defined by Hirshfeld surfaces and 2D fingerprint plots, which were successfully acquired from CrystalExplorer (v21.5). All target hybrids demonstrated pronounced activity in the visible region of the spectrum. The mechanisms of thermal isomerization processes of spiropyrans and their protonated merocyanine forms were studied by DFT methods, which revealed the energetic advantage of the protonation process with the formation of a β-cisoid CCCH conformer at the first stage and its further isomerization to more stable β-transoid forms. The proposed mechanism of acidochromic transformation was confirmed by the additional NMR study data that allowed for the detecting of the intermediate CCCH isomer. The study of the short-term cytotoxicity of new spirocyclic derivatives of estrogens and their 2-formyl-precursors was performed on the HeLa cell model. The precursors and spiropyrans differed in toxicity, suggesting their variable applicability in novel anti-cancer technologies.

A comprehensive review on the COVID-19 vaccine and drug delivery applications of interpenetrating polymer networks

An interpenetrating polymer network (IPNs) is a concoction of two or more polymers (natural, synthetic, and/or a combination of both) in which at least one polymer is synthesized or crosslinked in the intimate presence of the other. These three-dimensional networked systems have gained prominence in a series of biomedical applications, especially in the last two decades. The last decades witnessed a surge in the meaningful applications of interpenetrating polymer networks, especially in drug delivery as simple IPN systems advanced and resulted in the formation of highly efficient microspheres, nanoparticles, nanogels, and hydrogels, intelligent enough to sense and respond to changes in external stimuli such as temperature, pH, and ionic strength. The structure of the polymers, crosslinking agents, crosslinking density, and polymerization method play an integral role in determining the properties and application of IPNs in drug delivery. This review article is a modest effort to highlight the importance and applications of different types of interpenetrating polymer networks for the sustained, site-specific drug delivery of various therapeutic formulations, as witnessed in scientific research literature over the past 22 years (2000-2022). A special section of the manuscript is devoted to studying the efficacy of network polymers in vaccine delivery and highlighting the future scope (if any) of incorporating the IPN system in COVID-related vaccine/drug delivery. Four key focus areas in this review article [1, 2].

Multi-responsive on-demand drug delivery PMMA-co-PDEAEMA platform based on CO2, electric potential, and pH switchable nanofibrous membranes

This study investigated the release characteristics of curcumin (CUR)-loaded switchable poly(methyl methacrylate)-co-poly(N,N-diethylaminoethyl methacrylate) (PMMA-co-PDEAEMA) membranes following the application of various stimuli, as well as the platform's applicability in wound dressing and tissue engineering applications. The free-radical polymerization method was used to synthesize the PMMA-co-PDEAEMA copolymer. The drug-loaded nanofibrous membrane with electric potential (EP)-, CO₂-, and pH-responsive properties was developed by the electrospinning of PMMA-co-PDEAEMA and CUR. The resulted structure was characterized by a scanning electron microscope (SEM) coupled with X-ray energy dispersive spectroscopy and wide-angle X-ray scattering measurements. The release characteristics of the CUR-loaded wound covering were analyzed in various simulated environments at varying voltages, alternated CO₂/N₂ gas bubbling, and at two different pH values; the results demonstrated high drug release controllability. Loaded CUR displayed high stability and better solubility compared with free CUR. The CUR-loaded tissue also exhibited high antibacterial activity against Escherichia coli and staphylococcus aureus bacteria. In addition, the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay depicted high biocompatibility of up to 95% in the CUR-loaded membrane. This platform could be a promising candidate for usage in tissue engineering and medical applications such as targeted drug delivery, biodetection, reversible cell capture-and-release systems, and biosensors.

Light responsive hydrogels for controlled drug delivery

Light is an easy acquired, effective and non-invasive external stimulus with great flexibility and focusability. Thus, light responsive hydrogels are of particular interests to researchers in developing accurate and controlled drug delivery systems. Light responsive hydrogels are obtained by incorporating photosensitive moieties into their polymeric structures. Drug release can be realized through three major mechanisms: photoisomerization, photochemical reaction and photothermal reaction. Recent advances in material science have resulted in great development of photosensitizers, such as rare metal nanostructures and black phosphorus nanoparticles, in order to respond to a variety of light sources. Hydrogels incorporated with photosensitizers are crucial for clinical applications, and the use of ultraviolet and near-infrared light as well as up-conversion nanoparticles has greatly increased the therapeutic effects. Existing light responsive drug delivery systems have been utilized in delivering drugs, proteins and genes for chemotherapy, immunotherapy, photodynamic therapy, gene therapy, wound healing and other applications. Principles associated with site-specific targeting, metabolism, and toxicity are used to optimize efficacy and safety, and to improve patient compliance and convenience. In view of the importance of this field, we review current development, challenges and future perspectives of light responsive hydrogels for controlled drug delivery.

Soft nano and microstructures for the photomodulation of cellular signaling and behavior

Photoresponsive soft materials are everywhere in the nature, from human's retina tissues to plants, and have been the inspiration for engineers in the development of modern biomedical materials. Light as an external stimulus is particularly attractive because it is relatively cheap, noninvasive to superficial biological tissues, can be delivered contactless and offers high spatiotemporal control. In the biomedical field, soft materials that respond to long wavelength or that incorporate a photon upconversion mechanism are desired to overcome the limited UV-visible light penetration into biological tissues. Upon light exposure, photosensitive soft materials respond through mechanisms of isomerization, crosslinking or cleavage, hyperthermia, photoreactions, electrical current generation, among others. In this review, we discuss the most recent applications of photosensitive soft materials in the modulation of cellular behavior, for tissue engineering and regenerative medicine, in drug delivery and for phototherapies.

Log P Determines Licorice Flavonoids Release Behaviors and Classification from CARBOMER Cross-Linked Hydrogel

The dynamic drug release mechanisms from Carbomer 940 (CP) hydrogels have not been systematically explored elsewhere. This study aimed to investigate the quantitative structure−activity relationship of licorice flavonoids (LFs) compounds on their drug release from CP hydrogels based on LFs-CP interactions and drug solubility in the release medium. Ten LFs-CP hydrogels were formulated, and their in vitro release study was conducted. The intermolecular forces of LFs-CP systems were characterized by FTIR, molecular docking and molecular dynamic simulation. Ten LFs compounds were classified into I (high-release capability) LFs and II (low-release capability) LFs according to the different negative correlations between drug release percent at 48 h and intermolecular forces of drugs-CP, respectively. Moreover, high-release LFs possessed significantly lower log P and higher drug solubility in the release medium than low-release LFs. All I LFs release behaviors best followed the first-order equation, while II LFs release characteristics best fitted the zero-order equation except for isoliquiritigenin. Log P mainly affect the hydrogel relaxation process for I drugs release and the drug diffusion process for II drugs release. Higher log P values for LFs resulted in higher intermolecular strength for I drugs-CP systems and lower drug solubility in the release medium for II drugs, which hindered drug release. Hydrophobic association forces in drug-CP hydrogel played a more and more dominant role in hindering I LFs release with increasing release time. On the other hand, lower drug solubility in the release medium restricted II LFs release, and the dominant role of drug solubility in the release medium increased in 24 h followed by a significant decline after 36 h. Collectively, log P of LFs served as a bridge to determine LFs compound release behaviors and classification from CP hydrogels, which provided guidelines for reasonable design of LFs hydrogels in pharmaceutical topical formulations.

Dual-stimuli-responsive porous polymer enzyme reactor for tuning enzymolysis efficiency

A strategy for preparing a dual-stimuli-responsive porous polymer membrane enzyme reactor (D-PPMER) is described, consisting of poly (styrene-maleic anhydride-N-isopropylacrylamide-acrylate-3',3'-dimethyl-6-nitro-spiro[2H-1-benzopyran-2,2'-indoline]-1'-esterspiropyran ester) [P(S-M-N-SP)] and D-amino acid oxidase. Tunable control via "on/off" 365 nm UV light irradiation and temperature variation was used to change the membrane surface configuration and adjust the enzymolysis efficiency of the D-PPMER. A chiral capillary electrophoresis technique was developed for evaluation of the enzymatic efficiency of D-PPMER with a Zn(II)-dipeptide complex as the chiral selector and D,L-serine as the substrate. Interestingly, the enzymatic kinetic reaction rate of D-PPMER under UV irradiation at 36 °C (9.2 × 10^-2 mM·min^-1) was 3.2-fold greater than that of the free enzyme (2.9 × 10^-2 mM·min^-1). This was because upon UV irradiation at high temperature, the P(SP) and P(N) moieties altered from a "stretched" to a "curled" state to encapsulate the enzyme in smaller cavities. The confinement effect of the cavities further improved the enzymatic efficiency of the D-PPMER. This protocol highlights the outstanding potential of smart polymers, enables tunable control over the kinetic rates of stimuli-responsive enzyme reactors, and establishes a platform for adjusting enzymolysis efficiency using two different stimuli.

Polymeric Micro/Nanocarriers and Motors for Cargo Transport and Phototriggered Delivery

Smart polymer-based micro/nanoassemblies have emerged as a promising alternative for transporting and delivering a myriad of cargo. Cargo encapsulation into (or linked to) polymeric micro/nanocarrier (PC) strategies may help to conserve cargo activity and functionality when interacting with its surroundings in its journey to the target. PCs for cargo phototriggering allow for excellent spatiotemporal control via irradiation as an external stimulus, thus regulating the delivery kinetics of cargo and potentially increasing its therapeutic effect. Micromotors based on PCs offer an accelerated cargo-medium interaction for biomedical, environmental, and many other applications. This review collects the recent achievements in PC development based on nanomicelles, nanospheres, and nanopolymersomes, among others, with enhanced properties to increase cargo protection and cargo release efficiency triggered by ultraviolet (UV) and near-infrared (NIR) irradiation, including light-stimulated polymeric micromotors for propulsion, cargo transport, biosensing, and photo-thermal therapy. We emphasize the challenges of positioning PCs as drug delivery systems, as well as the outstanding opportunities of light-stimulated polymeric micromotors for practical applications.

Photosensitive drug delivery systems for cancer therapy: Mechanisms and applications

Over the past three decades, various photosensitive nanoparticles have been developed as potential therapies in human health, ranging from photodynamic therapy technologies that have already reached clinical use, to drug delivery systems that are still in the preclinical stages. Many of these systems are designed to achieve a high spatial and temporal on-demand drug release via phototriggerable mechanisms. This review examines the current clinical and experimental applications in cancer treatment of photosensitive drug release systems, including nanocarriers such as liposomes, micelles, polymeric nanoparticles, and hydrogels. We will focus on the three main physicochemical mechanisms of imparting photosensitivity to a delivery system: i) photochemical reactions (oxidation, cleavage, and polymerization), ii) photoisomerization, iii) and photothermal reactions. Photosensitive nanoparticles have a multitude of different applications including controlled drug release, resulting from physical/conformational changes in the delivery systems in response to light of specific wavelengths. Most of the recent research in these delivery systems has primarily focused on improving the efficacy and safety of cancer treatments such as photodynamic and photothermal therapy. Combinations of multiple treatment modalities using photosensitive nanoparticulate delivery systems have also garnered great interest in combating multi-drug resistant cancers due to their synergistic effects. Finally, the challenges and future potential of photosensitive drug delivery systems in biomedical applications is outlined.

A Two-Step Baromechanical Cycle for Repeated Activation and Deactivation of Mechanophores

Mechanophores that are embedded in a polymer backbone respond to the application of mechanical stretching forces by geometric changes such as bond rupture. Typically, these structural changes are irreversible, which limits the applicability of functional materials incorporating mechanophores. Using computational methods, we, here, present a general method of restoring a force-activated mechanophore to its deactivated form by using hydrostatic pressure. We use the spiropyran-merocyanine (SP-MC) interconversion to show that repeated activation of the SP mechanophore and deactivation of MC can be achieved by alternating mechanical stretching and hydrostatic compression, respectively. In the baromechanical cycle, MC acts as a "barophore" that responds to hydrostatic pressure by bond formation. The activation and deactivation of SP/MC are understood in terms of strain and electronic effects. Beneficially, this two-step baromechanical cycle can be observed in real time by using UV/vis spectroscopy. Our calculations pave the way for improving the applicability and reusability of force-responsive materials.

Photoregulated Morphological Transformation of Spiropyran Derivatives Achieving the Tunability of Interfacial Hydrophilicity

Regulation of self-assembly morphology is an effective strategy to obtain advanced functional materials with expected properties. However, achieving remarkable morphological transformation by light irradiation is still a challenge. Herein, three simple spiropyran derivatives (SP1, SP2, and SP3) are constructed, achieving different degrees of morphological transformation from nanospheres to hollow tadpole-like structures (SP3), tubular structures (SP2), and microsheets (SP1) after ultraviolet light irradiation. Interestingly, the hollow tadpole-like structures (SP3) can further extend to Y-shaped or T-shaped tubular morphology. In the process, SP1, SP2, and SP3 can be isomerized from a closed-ring form (hydrophobicity) to an open-ring form (hydrophilicity) in different degrees, interacting differently with methanol solvent molecules. The formation of hollow structures or microsheets along with the isomerization of spiropyran derivatives contributes to the adjustment of the hydrophilicity of the interface. Therefore, SP1, SP2, and SP3 with photoregulated morphological transformation show promising applications in tunable interface materials.

Spiropyran-Based Drug Delivery Systems

Nanocarriers are rapidly growing in popularity in the field of drug delivery. The ability of nanocarriers to encapsulate and distribute poorly soluble drugs while minimising their undesired effects is significantly advantageous over traditional drug delivery. Nanocarriers can also be decorated with imaging moieties and targeting agents, further incrementing their functionality. Of recent interest as potential nanocarriers are spiropyrans; a family of photochromic molecular switches. Due to their multi-responsiveness to endo- and exogenous stimuli, and their intrinsic biocompatibility, they have been utilised in various drug delivery systems (DDSs) to date. In this review, we provide an overview of the developments in spiropyran-based DDSs. The benefits and drawbacks of utilising spiropyrans in drug delivery are assessed and an outline of spiropyran-based drug delivery systems is presented.

Molecular-Gated Drug Delivery Systems Using Light-Triggered Hydrophobic-to-Hydrophilic Switches

A photoresponsive molecular-gated drug delivery system (DDS) based on silicone-hydrogel (poly(HEMA-co-PEGMEA)) interpenetrating polymer networks (IPNs) functionalized with carboxylated spiropyran (SPCOOH) was designed and demonstrated as an on-demand DDS. The triggered-release mechanism relies on controlling the wetting behavior of the surface by light, exploiting different hydrophobicities between the "closed" and "open" isomers of spiropyran as a photoswitchable molecular gate on the surface of IPN (SP-photogated IPN). Light-triggered release of doxycycline (DOX) as a model drug indicated that the spiropyran (SP) molecules provide a hydrophobic layer around the drug carrier and have a good gate-closing efficiency for IPNs with 20-30% hydrogel content. Upon UV light irradiation, SP converts into an open hydrophilic merocyanine state, which triggers the release of DOX. These results were compared with a previously developed SP-bulk modified IPN using the same hydrogel as a control, proving the efficiency of the gated IPN system. The covalent attachment of SPCOOH to the alcohol groups of the hydrogel and the structural change caused by UV light was indicated with FTIR analysis. XPS results also confirm the presence of SP by indicating the atomic percentage of nitrogen with respect to the hydrogel content.