Degradable redox-responsive disulfide-based nanogel drug carriers via dithiol oxidation polymerization

Nanogels: Recent Advances in Synthesis and Biomedical Applications

In the context of advanced nanomaterials research, nanogels (NGs) have recently gained broad attention for their versatility and promising biomedical applications. To date, a significant number of NGs have been developed to meet the growing demands in various fields of biomedical research. Summarizing preparation methods, physicochemical and biological properties, and recent applications of NGs may be useful to help explore new directions for their development. This article presents a comprehensive overview of the latest NG synthesis methodologies, highlighting advances in formulation with different types of hydrophilic or amphiphilic polymers. It also underlines recent biomedical applications of NGs in drug delivery and imaging, with a short section dedicated to biosafety considerations of these innovative nanomaterials. In conclusion, this article summarizes recent innovations in NG synthesis and their numerous applications, highlighting their considerable potential in the biomedical field.

Designed to Degrade: Tailoring Polyesters for Circularity

A powerful toolbox is needed to turn the linear plastic economy into circular. Development of materials designed for mechanical recycling, chemical recycling, and/or biodegradation in targeted end-of-life environment are all necessary puzzle pieces in this process. Polyesters, with reversible ester bonds, are already forerunners in plastic circularity: poly(ethylene terephthalate) (PET) is the most recycled plastic material suitable for mechanical and chemical recycling, while common aliphatic polyesters are biodegradable under favorable conditions, such as industrial compost. However, this circular design needs to be further tailored for different end-of-life options to enable chemical recycling under greener conditions and/or rapid enough biodegradation even under less favorable environmental conditions. Here, we discuss molecular design of the polyester chain targeting enhancement of circularity by incorporation of more easily hydrolyzable ester bonds, additional dynamic bonds, or degradation catalyzing functional groups as part of the polyester chain. The utilization of polyester circularity to design replacement materials for current volume plastics is also reviewed as well as embedment of green catalysts, such as enzymes in biodegradable polyester matrices to facilitate the degradation process.

Bioreducible Amphiphilic Hyperbranched Polymer-Drug Conjugate for Intracellular Drug Delivery

This paper reports synthesis of a bioreducible hyperbranched (HB) polymer by A2+B3 approach from commercially available dithiothreitol (DTT) (A2) and an easily accessible trifunctional monomer (B3) containing three reactive pyridyl-disulfide groups. Highly efficient thiol-activated disulfide exchange reaction leads to the formation of the HB polymer (Mw = 21000; Đ = 2.3) with bioreducible disulfide linkages in the backbone and two different functional groups, namely, hydroxyl and pyridyl-disulfide in the core and periphery, respectively, of the HB-polymer. Postpolymerization functionalization of the hydroxyl-groups with camptothecin (CPT), a topoisomerase inhibitor and known anticancer drug, followed by replacing the terminal pyridyl-disulfide groups with oligo-oxyethylene-thiol resulted in easy access to an amphiphilic HB polydisulfide-CPT conjugate (P1) with a very high drug loading content of ∼40%. P1 aggregated in water (above ∼10 μg/mL) producing drug-loaded nanoparticles (Dh ∼ 135 nm), which showed highly efficient glutathione (GSH)-triggered release of the active CPT. Mass spectrometry analysis of the GSH-treated P1 showed the presence of the active CPT drug as well as a cyclic monothiocarbonate product, which underpins the cascade-degradation mechanism involving GSH-triggered cleavage of the labile disulfide linkage, followed by intramolecular nucleophilic attack by the in situ generated thiol to the neighboring carbonate linkage, resulting in release of the active CPT drug. The P1 nanoparticle showed excellent cellular uptake as tested by confocal fluorescence microscopy in HeLa cells by predominantly endocytosis mechanism, resulting in highly efficient cell killing (IC50 ∼ 0.6 μg/mL) as evident from the results of the MTT assay, as well as the apoptosis assay. Comparative studies with an analogous linear polymer-CPT conjugate showed much superior intracellular drug delivery potency of the hyperbranched polymer.

Nanocarriers address intracellular barriers for efficient drug delivery, overcoming drug resistance, subcellular targeting and controlled release

The cellular barriers are major bottlenecks for bioactive compounds entering into cells to accomplish their biological functions, which limits their biomedical applications. Nanocarriers have demonstrated high potential and benefits for encapsulating bioactive compounds and efficiently delivering them into target cells by overcoming a cascade of intracellular barriers to achieve desirable therapeutic and diagnostic effects. In this review, we introduce the cellular barriers ahead of drug delivery and nanocarriers, as well as summarize recent advances and strategies of nanocarriers for increasing internalization with cells, promoting intracellular trafficking, overcoming drug resistance, targeting subcellular locations and controlled drug release. Lastly, the future perspectives of nanocarriers for intracellular drug delivery are discussed, which mainly focus on potential challenges and future directions. Our review presents an overview of intracellular drug delivery by nanocarriers, which may encourage the future development of nanocarriers for efficient and precision drug delivery into a wide range of cells and subcellular targets.

A heparin-based nanogel system for redox and pH dual-responsive delivery of cisplatin

Heparin recently has been discovered as a novel anti-cancer agent. The combinations of heparin with other agents was reported not only to reduce the undesired effects of free heparin and increase the cellular uptake of the delivered molecules, but also is the basis for the design and development of multi-stimulation response systems to improve their killing cancer cell efficiency at the target positions. This study aimed to design a redox and pH dual-responsive anticancer system based on heparin for cisplatin (CPT) therapy. Heparin was first cross-linked with Poloxamer 407 chains via disulfide bridges to form a redox-sensitive system Hep-P407. CPT was then encapsulated into the Hep-P407 system via the complex of Platin and carboxyl groups to form the redox/pH-responsive system CPT@Hep-P407. The obtained Hep-P407 systems were proved and characterized using specific techniques including1H-NMR, zeta potential, Dynamic Light Scattering (DLS) and Fourier-transform infrared spectroscopy. The dual-responsive behavior to redox and pH of CPT@Hep-P407 was proved through DLS, zeta andin vitrorelease analysis meanwhile its cytotoxicity was investigated using Resazurin assay. The CPT@Hep-P407 system is expected to be a promising redox/pH-responsive anticancer system based on heparin for CPT therapy.

Internal stimuli-responsive nanocarriers for controlled anti-cancer drug release: a review

Cancer disease is one of the most frequent life-threatening, with a high fatality rate worldwide. However, recent immunotherapy studies in various tumours have yielded unsatisfactory outcomes, with just a few individuals experiencing long-term responses. To overcome these issues, nowadays internal stimuli-responsive nanocarriers have been widely exploited to transport a wide range of active substances, including peptides, genes and medicines. These nanosystems could be chemically adjusted to produce target-based drug release at the target location, minimizing pathological and physiological difficulties while increasing therapeutic efficiency. This review highlights the various types of internal stimuli-responsive nanocarriers and applications in cancer diagnosis. This study can provide inspiration and impetus for exploiting more promising internal stimuli-responsive nanosystems for drug delivery.

Redox-Responsive Drug Delivery Systems: A Chemical Perspective

With the widespread global impact of cancer on humans and the extensive side effects associated with current cancer treatments, a novel, effective, and safe treatment is needed. Redox-responsive drug delivery systems (DDSs) have emerged as a potential cancer treatment with minimal side effects and enhanced site-specific targeted delivery. This paper explores the physiological and biochemical nature of tumors that allow for redox-responsive drug delivery systems and reviews recent advances in the chemical composition and design of such systems. The five main redox-responsive chemical entities that are the focus of this paper are disulfide bonds, diselenide bonds, succinimide-thioether linkages, tetrasulfide bonds, and platin conjugates. Moreover, as disulfide bonds are the most commonly used entities, the review explored disulfide-containing liposomes, polymeric micelles, and nanogels. While various systems have been devised, further research is needed to advance redox-responsive drug delivery systems for cancer treatment clinical applications.

Advances of functional nanomaterials for magnetic resonance imaging and biomedical engineering applications

Functional nanomaterials have been widely used in biomedical fields due to their good biocompatibility, excellent physicochemical properties, easy surface modification, and easy regulation of size and morphology. Functional nanomaterials for magnetic resonance imaging (MRI) can target specific sites in vivo and more easily detect disease-related specific biomarkers at the molecular and cellular levels than traditional contrast agents, achieving a broad application prospect in MRI. This review focuses on the basic principles of MRI, the classification, synthesis and surface modification methods of contrast agents, and their clinical applications to provide guidance for designing novel contrast agents and optimizing the contrast effect. Furthermore, the latest biomedical advances of functional nanomaterials in medical diagnosis and disease detection, disease treatment, the combination of diagnosis and treatment (theranostics), multi-model imaging and nanozyme are also summarized and discussed. Finally, the bright application prospects of functional nanomaterials in biomedicine are emphasized and the urgent need to achieve significant breakthroughs in the industrial transformation and the clinical translation is proposed. This article is categorized under: Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Diagnostic Tools > Diagnostic Nanodevices Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease.

Development and Evaluation of pH-Responsive Pluronic F 127 Co-Poly- (Acrylic Acid) Biodegradable Nanogels for Topical Delivery of Terbinafine HCL

Research aimed to develop and evaluate biodegradable, pH-responsive chemically cross-linked Pluronic F127 co-poly- (acrylic acid) nanogels for dermal delivery of Terbinafine HCL (TBH) to increase its permeability and as a new approach to treat skin fungal infections. TBH-loaded nanogels were successfully synthesized from acrylic acid (AA) and Pluronic F127 by free-radical copolymerization technique using N,N′-methylene bisacrylamide (MBA) as crosslinker and ammonium persulphate (APS) as initiator. Prepared nanogels exhibited 93.51% drug entrapment efficiency (DEE), 45 nm particle size, pH-dependent swelling and release behavior. Nanogels were characterized using different physicochemical techniques. The ex-vivo skin retention studies through rat skin showed about 42.34% drug retention from nanogels while 1% Lamisil cream (marketed product) showed about 26.56% drug retention. Moreover, skin irritation studies showed that nanogels were not irritating. Nanogels showed improved in-vitro antifungal activity against Candida albicans compared to commercial product. In-vivo studies on rats infected with Candida albicans confirmed superiority of nanogels over 1% Lamisil for eradication of fungal infection. This confirms that TBH loaded in Pluronic F127 co-poly-(acrylic acid) nanogels provided greater targetibility and cure rates of poorly soluble TBH in animal model and hence nanogels could be a potential carrier for effective topical delivery of TBH for skin fungal infection treatment.

Synthesis, characterisation and evaluation of hyperbranched N-(2-hydroxypropyl) methacrylamides for transport and delivery in pancreatic cell lines in vitro and in vivo

Hyperbranched polymers have many promising features for drug delivery, owing to their ease of synthesis, multiple functional group content, and potential for high drug loading with retention of solubility. Here we prepared hyperbranched N-(2-hydroxypropyl)methacrylamide (HPMA) polymers with a range of molar masses and particle sizes, and with attached dyes, radiolabel or the anticancer drug gemcitabine. Reversible addition-fragmentation chain transfer (RAFT) polymerisation enabled the synthesis of pHPMA polymers and a gemcitabine-comonomer functionalised pHPMA polymer pro-drug, with diameters of the polymer particles ranging from 7-40 nm. The non-drug loaded polymers were well-tolerated in cancer cell lines and macrophages, and were rapidly internalised in 2D cell culture and transported efficiently to the centre of dense pancreatic cancer 3D spheroids. The gemcitabine-loaded polymer pro-drug was found to be toxic both to 2D cultures of MIA PaCa-2 cells and also in reducing the volume of MIA PaCa-2 spheroids. The non-drug loaded polymers caused no short-term adverse effects in healthy mice following systemic injection, and derivatives of these polymers labelled with ⁸⁹Zr-were tracked for their distribution in the organs of healthy and MIA PaCa-2 xenograft bearing Balb/c nude mice. Tumour accumulation, although variable across the samples, was highest in individual animals for the pHPMA polymer of ∼20 nm size, and accordingly a gemcitabine pHPMA polymer pro-drug of ∼18 nm diameter was evaluated for efficacy in the tumour-bearing animals. The efficacy of the pHPMA polymer pro-drug was very similar to that of free gemcitabine in terms of tumour growth retardation, and although there was a survival benefit after 70 days for the polymer pro-drug, there was no difference at day 80. These data suggest that while polymer pro-drugs of this type can be effective, better tumour targeting and enhanced in situ release remain as key obstacles to clinical translation even for relatively simple polymers such as pHPMA.

Advances in the Novel Nanotechnology for the Targeted Tumor Therapy by the Transdermal Drug Delivery

Despite modern medicine advances greatly, cancer remains a serious challenge to world health for which effective methods of treatment have hardly been developed yet. However, throughout the recent years, the rapid-developing nanotechnology has provided a new outlook of cancer therapy by transdermal drug delivery. By disrupting the stratum corneum, drugs are delivered through the skin and navigated to the tumor site by drug delivery systems such as nanogels, microneedles, etc. The superiorities include the improvement of drug pharmacokinetics as well as reduced side effects. This paper reviews the reported novel development of transdermal drug delivery systems for targeted cancer therapy. Advanced techniques for penetrating the skin will be discussed as well.

Reversible Protein Capture and Release by Redox-Responsive Hydrogel in Microfluidics

Stimuli-responsive hydrogels have a wide range of potential applications in microfluidics, which has drawn great attention. Double cross-linked hydrogels are very well suited for this application as they offer both stability and the required responsive behavior. Here, we report the integration of poly(N-isopropylacrylamide) (PNiPAAm) hydrogel with a permanent cross-linker (N,N'-methylenebisacrylamide, BIS) and a redox responsive reversible cross-linker (N,N'-bis(acryloyl)cystamine, BAC) into a microfluidic device through photopolymerization. Cleavage and re-formation of disulfide bonds introduced by BAC changed the cross-linking densities of the hydrogel dots, making them swell or shrink. Rheological measurements allowed for selecting hydrogels that withstand long-term shear forces present in microfluidic devices under continuous flow. Once implemented, the thiol-disulfide exchange allowed the hydrogel dots to successfully capture and release the protein bovine serum albumin (BSA). BSA was labeled with rhodamine B and functionalized with 2-(2-pyridyldithio)-ethylamine (PDA) to introduce disulfide bonds. The reversible capture and release of the protein reached an efficiency of 83.6% in release rate and could be repeated over 3 cycles within the microfluidic device. These results demonstrate that our redox-responsive hydrogel dots enable the dynamic capture and release of various different functionalized (macro)molecules (e.g., proteins and drugs) and have a great potential to be integrated into a lab-on-a-chip device for detection and/or delivery.

Comprehensive review on ultrasound-responsive theranostic nanomaterials: mechanisms, structures and medical applications

The field of theranostics has been rapidly growing in recent years and nanotechnology has played a major role in this growth. Nanomaterials can be constructed to respond to a variety of different stimuli which can be internal (enzyme activity, redox potential, pH changes, temperature changes) or external (light, heat, magnetic fields, ultrasound). Theranostic nanomaterials can respond by producing an imaging signal and/or a therapeutic effect, which frequently involves cell death. Since ultrasound (US) is already well established as a clinical imaging modality, it is attractive to combine it with rationally designed nanoparticles for theranostics. The mechanisms of US interactions include cavitation microbubbles (MBs), acoustic droplet vaporization, acoustic radiation force, localized thermal effects, reactive oxygen species generation, sonoluminescence, and sonoporation. These effects can result in the release of encapsulated drugs or genes at the site of interest as well as cell death and considerable image enhancement. The present review discusses US-responsive theranostic nanomaterials under the following categories: MBs, micelles, liposomes (conventional and echogenic), niosomes, nanoemulsions, polymeric nanoparticles, chitosan nanocapsules, dendrimers, hydrogels, nanogels, gold nanoparticles, titania nanostructures, carbon nanostructures, mesoporous silica nanoparticles, fuel-free nano/micromotors.

Fabrication of a multi-level drug release platform with liposomes, chitooligosaccharides, phospholipids and injectable chitosan hydrogel to enhance anti-tumor effectiveness

Some anti-cancer drugs have poor solubility and availability, and are easily eliminated by rapid metabolism in vivo. To fix the drugs at the administration site and delay their release, a release platform with multi-level and multi-function was designed. The results showed that the curcumin (Cur) loaded liposomes (Cur@Lip) were coated sequentially with positive Chitooligosaccharides (Cur@Lip-Cos) and negative phospholipids (Cur@Lip-Cos-PC), to enhance water solubility, encapsulation efficiency, and delayed the release of the Cur, stability and cell intake of the liposomes, and the bioactivity of the system. The Cur@Lip-Cos could significantly enhance the inhibitory effect of MCF-7, better than the Cur@Lip-Cos-PC. The Lips were then fixed in an injectable thiolated chitosan hydrogel for local immobilization and sustained release which can effectively delay the release of Cur to inhibit MCF-7 growth. In summary, the innovative and biomimetic liposomal hydrogels are expected to provide more ideas for the design of drug carriers.

Nanogels as a Versatile Drug Delivery System for Brain Cancer

Chemotherapy and radiation remain as mainstays in the treatment of a variety of cancers globally, yet some therapies exhibit limited specificity and result in harsh side effects in patients. Brain tissue differs from other tissue due to restrictions from the blood-brain barrier, thus systemic treatment options are limited. The focus of this review is on nanogels as local and systemic drug delivery systems in the treatment of brain cancer. Nanogels are a unique local or systemic drug delivery system that is tailorable and consists of a three-dimensional polymeric network formed via physical or chemical assembly. For example, thermosensitive nanogels show promise in their ability to incorporate therapeutic agents in nano-structured matrices, be applied in the forms of sprays or sols to the area from which a tumor has been removed, form adhesive gels to fill the cavity and deliver treatment locally. Their usage does come with complications, such as handling, storage, chemical stability, and degradation. Despite these limitations, the current ongoing development of nanogels allows patient-centered treatment that can be considered as a promising tool for the management of brain cancer.

Synthesis of Nanogels: Current Trends and Future Outlook

Nanogels represent an innovative platform for tunable drug release and targeted therapy in several biomedical applications, ranging from cancer to neurological disorders. The design of these nanocarriers is a pivotal topic investigated by the researchers over the years, with the aim to optimize the procedures and provide advanced nanomaterials. Chemical reactions, physical interactions and the developments of engineered devices are the three main areas explored to overcome the shortcomings of the traditional nanofabrication approaches. This review proposes a focus on the current techniques used in nanogel design, highlighting the upgrades in physico-chemical methodologies, microfluidics and 3D printing. Polymers and biomolecules can be combined to produce ad hoc nanonetworks according to the final curative aims, preserving the criteria of biocompatibility and biodegradability. Controlled polymerization, interfacial reactions, sol-gel transition, manipulation of the fluids at the nanoscale, lab-on-a-chip technology and 3D printing are the leading strategies to lean on in the next future and offer new solutions to the critical healthcare scenarios.

pH-Sensitive nanogels for drug delivery in cancer therapy

Compared to normal tissue, solid tumors exhibit a lower pH value. Such pH gradient can be used to design pH-sensitive nanogels for selective drug delivery. The acid-sensitive elements in the nanogel cause it to swell/degrade rapidly, followed by rapid drug release.

Reversibly Softening and Stiffening Organogels Using a Wavelength-Controlled Disulfide-Diselenide Exchange

Wavelength-dependent light-responsive seleno-sulfide dynamic covalent bonds were used to prepare organogels with reversible changes in stiffness. The disulfide cross-link organogels prepared from norbornene-terminated poly(ethylene glycol) (PEG-diNB) and poly(2-hydroxypropyl methacrylate-stat-mercaptoethyl acrylate) (PEG-diNB-poly(HPMA-stat-MEMA)) polymers underwent exchange reactions with 5,5'-diselenide-bis(2-aminobenzoic acid) upon irradiation with UV light. Following irradiation with visible light, the seleno-sulfide bonds were cleaved, reforming disulfide cross-links and the 5,5'-diselenide-bis(2-aminobenzoic acid). Reduction in G' with disulfide-diselenide exchange was consistent with that observed following a thiol-disulfide exchange reaction. Recovery of G' upon disulfide bond formation was 85-95% of the initial value in the as-prepared gel over five cycles of bond cleaving and reformation. This initial study shows the potential of the wavelength-controlled disulfide-diselenide chemistry to develop light-responsive reversible organogels. These organogels have the potential to be used in functional materials such as polymeric actuators or biomimetic soft robotics.

Covalent Post-Assembly Modification: A Synthetic Multipurpose Tool in Supramolecular Chemistry

The use of covalent post-assembly modification (PAM) in supramolecular chemistry has grown significantly in recent years, to the point where PAM is now a versatile synthesis tool for tuning, modulating, and expanding the functionality of self-assembled complexes and materials. PAM underpins supramolecular template-synthesis strategies, enables modular derivatization of supramolecular assemblies, permits the covalent 'locking' of unstable structures, and can trigger controlled structural transformations between different assembled morphologies. This Review discusses key examples of PAM spanning a range of material classes, including discrete supramolecular complexes, self-assembled soft nanostructures and hierarchically ordered polymeric and framework materials. As such, we hope to highlight how PAM has continued to evolve as a creative and functional addition to the synthetic chemist's toolbox for constructing bespoke self-assembled complexes and materials.

Recent Advances in Nanocarrier-Assisted Therapeutics Delivery Systems

Nanotechnologies have attracted increasing attention in their application in medicine, especially in the development of new drug delivery systems. With the help of nano-sized carriers, drugs can reach specific diseased areas, prolonging therapeutic efficacy while decreasing undesired side-effects. In addition, recent nanotechnological advances, such as surface stabilization and stimuli-responsive functionalization have also significantly improved the targeting capacity and therapeutic efficacy of the nanocarrier assisted drug delivery system. In this review, we evaluate recent advances in the development of different nanocarriers and their applications in therapeutics delivery.

An in vitro approach to unveil the structural alterations in d-ribose induced glycated fibrinogen

Plasma proteins persistently bear non-enzymatic post-translational modifications (NEPTM) that proceeds with nucleophilic addition between free amino groups of proteins, and carbonyl group of reducing sugars. Glycation, a prevalent NEPTM rush by the high availability of reducing sugars results in the generation of advanced glycation end products (AGEs). Plasma proteins are more vulnerable to glycation because of the presence of multiple glycation sites and are widely studied. However, fibrinogen glycation is less studied. Therefore, it was designed as an in vitro study to elucidate d-ribose mediated glycative damage suffered by fibrinogen protein at secondary and tertiary structure level. The glycation induced structural alterations were analyzed by UV-vis, fluorescence, circular dichroism, scanning electron microcopy and Fourier transform infrared spectroscopy. Glycation induced protein aggregation and fibrils formation was confirmed by thioflavin T and congo red assay. Moreover, molecular docking study was performed to further validate physicochemical characterization. Structural alterations, increased ketoamines, protein carbonyls and HMF contents were reported in d-ribose glycated fibrinogen against their native analogues. The results validate structural perturbations, increased glycoxidative stress and AGEs formation, which might influence normal function of fibrinogen especially blood coagulation cascade. Thus, we can conclude that under diabetes induced hyperglycemic state in physiological systems, d-ribose induced fibrinogen glycation might play a crucial role in the onset of micro- and macro-vascular complications, thereby worsen the diabetes associated secondary disorders. Moreover, this in vitro study might pave a path to choose fibrinogen as a future biomarker for the early detection of diabetes mediated vascular complications.Communicated by Ramaswamy H. Sarma.

Versatile Nanoplatforms with enhanced Photodynamic Therapy: Designs and Applications

As an emerging antitumor strategy, photodynamic therapy (PDT) has attracted intensive attention for the treatment of various malignant tumors owing to its noninvasive nature and high spatial selectivity in recent years. However, the therapeutic effect is unsatisfactory on some occasions due to the presence of some unfavorable factors including nonspecific accumulation of PS towards malignant tissues, the lack of endogenous oxygen in tumors, as well as the limited light penetration depth, further hampering practical application. To circumvent these limitations and improve real utilization efficiency, various enhanced strategies have been developed and explored during the past years. In this review, we give an overview of the state-of-the-art advances progress on versatile nanoplatforms for enhanced PDT considering the enhancement from targeting or responsive, chemical and physical effect. Specifically, these effects mainly include organelle-targeting function, tumor microenvironment responsive release photosensitizers (PS), self-sufficient O2 (affinity oxygen and generating oxygen), photocatalytic water splitting, X-rays light stimulate, surface plasmon resonance enhancement, and the improvement by resonance energy transfer. When utilizing these strategies to improve the therapeutic effect, the advantages and limitations are addressed. Finally, the challenges and prospective will be discussed and demonstrated for the future development of advanced PDT with enhanced efficacy.

Exogenous vitamin C triggered structural changes of redox-activated dual core-crosslinked biodegradable nanogels for boosting the antitumor efficiency

Premature leakage of drugs during blood circulation and slow drug release at the tumor site are two major challenges that nanocarriers have to overcome to achieve successful cancer therapy. Herein, a dual core-crosslinked, redox-sensitive polymeric nanogel (sDL) was constructed by the self-assembly of two star-shaped amphiphilic copolymers (4sP(EG-b-LLA)-N₃, 4sP(EG-b-DLA)-N₃) in the presence of a redox-sensitive crosslinker (d-ss-Bu), where hydrophilic polyethylene glycol (PEG) was used as the shell and the functional hydrophobic poly(l-lactide) (PLLA) and poly(d-lactide) (PDLA) were used as the dual crosslinked core via stereocomplex formation and chemical interactions. The dual core-crosslinked structure of the nanogels allowed for almost 2-fold enhanced doxorubicin (DOX)-loading capacity, favorable structural stability to restrict the premature leakage of therapeutic drug and smaller particle size to accelerate the internalization efficiency compared to non-crosslinked nanocarriers. Furthermore, exogenous vitamin C (Vc) can trigger the breakage of redox-sensitive bonds to accelerate drug release from nanogels for improved in vitro antitumor efficacy. Notably, in vivo near-infrared imaging showed that the highly stable DOX-loaded sDL efficiently aggregated at the tumor site. Sequential administration of DOX-loaded sDL and Vc exhibited the highest tumor inhibition effect without associated systemic toxicity compared to the corresponding single injection of Vc or DOX-loaded sDL control groups for in vivo studies, indicating that exogenous administration of Vc can synergistically impact the release of DOX from sDL. Therefore, the developed nanogels proved to be promising smart carriers for achieving precise tunable-stability in response to relevant environments and the combination of Vc to activate reduction-sensitive drug delivery is a promising approach to maximize the therapeutic efficacy.

Synthesis of poly(disulfide)s with narrow molecular weight distributions via lactone ring-opening polymerization

We report the first example of controlled polymerization of poly(disulfide)s with narrow molecular weight distributions. 1,4,5-oxadithiepan-2-one (OTP), a disulfide-containing 7-membered ring lactone, was polymerized by using the diphenylphosphate (DPP) catalyzed lactone ring-opening polymerization method. The polymerization proceeded in a living manner, and the resulting polymers displayed very narrow polydispersity index (PDI) values below 1.1 and excellent backbone degradability responding to reducing conditions and UV irradiation.

We report the first example of controlled polymerization of poly(disulfide)s with narrow molecular weight distributions.

Stimuli-responsive nanocarriers for drug delivery, tumor imaging, therapy and theranostics

In recent years, much progress has been motivated in stimuli-responsive nanocarriers, which could response to the intrinsic physicochemical and pathological factors in diseased regions to increase the specificity of drug delivery. Currently, numerous nanocarriers have been engineered with physicochemical changes in responding to external stimuli, such as ultrasound, thermal, light and magnetic field, as well as internal stimuli, including pH, redox potential, hypoxia and enzyme, etc. Nanocarriers could respond to stimuli in tumor microenvironments or inside cancer cells for on-demanded drug delivery and accumulation, controlled drug release, activation of bioactive compounds, probes and targeting ligands, as well as size, charge and conformation conversion, etc., leading to sensing and signaling, overcoming multidrug resistance, accurate diagnosis and precision therapy. This review has summarized the general strategies of developing stimuli-responsive nanocarriers and recent advances, presented their applications in drug delivery, tumor imaging, therapy and theranostics, illustrated the progress of clinical translation and made prospects.

Multi-responsive, self-healing and adhesive PVA based hydrogels induced by the ultrafast complexation of Fe3+ ions

Herein, a PVA (polyvinyl alcohol)-based multi-responsive hydrogel was prepared by introducing the dynamic and reversible supramolecular complexation between polyvinyl alcohol acetoacetate (PVAA) and Fe3+ ions within 20 s at room temperature. PVAA-Fe hydrogels could be achieved by the simple mixing process of a PVAA aqueous solution with FeCl3 aqueous solution. The soluble PVAA was synthesized by the reaction of PVA with tert-butyl acetoacetate (t-BAA) via transesterification in dimethyl sulfoxide (DMSO). The chemical structure of PVAA was systematically characterized by FT-IR and 1H NMR spectroscopy. The resulting hydrogel showed excellent self-healing behavior without other external stimuli. It was also demonstrated that the PVAA-Fe hydrogel exhibited multi-responsive properties, such as responsiveness to pH, redox, light irradiation and temperature. In addition, the presence of Fe3+ ions and Cl- ions in the gel imparted the PVAA-Fe hydrogel with favorable conductivity. Therefore, the strategy for the facile preparation of the hydrogel in this work could provide a benign and versatile method for achieving multi-functional soft materials for various applications such as smart devices, logic gates, and sensors.

Photothermal-modulated reversible volume transition of wireless hydrogels embedded with redox-responsive carbon dots

The reversible volume transition of redox-responsive hydrogels by near-infrared (NIR) irradiation has recently attracted significant attention as a novel therapy matrix for tracking and treating cancer via stimuli-responsive fluorescence on/off with controllable volume transition via a wireless sensing system. Herein, a NIR-induced redox-sensitive hydrogel was synthesized by blending a hydrogel with IR825-loaded carbon dots (CD) to achieve enhanced mobility of nanoparticles inside a gel network, and reversible volume phase transitions remotely controlled by a smartphone application via the induction of different redox environments. The presence of CD-IR825 in the thermosensitive poly(N-isopropylacrylamide) hydrogel network imparted fluorescence, electronic and photothermal properties to the hydrogels, which resulted in volume shrinkage behavior of the hydrogel upon exposure to NIR laser irradiation due to the redox-sensitive CDs. Under the NIR on/off cycles, the photothermal temperature, fluorescence, and porous structure were reversed after turning off the NIR laser. The hydrogel responsiveness under GSH and NIR light was studied using a wireless device based on the changes in the resistance graph on a smartphone application, generating a fast and simple method for the investigation of hydrogel properties. The in vitro cell viabilities of the MDA-MB cancer cells incubated with the composite hydrogel in the presence of external GSH exhibited a higher photothermal temperature, and the cancer cells were effectively killed after the NIR irradiation. Therefore, the NIR-induced redox-responsive nanocomposite hydrogel prepared herein has potential for use in cancer treatment and will enable the study of nanoparticle motion in hydrogel networks under multiple stimuli via a wireless device using a faster and more convenient method.