Facile Fabrication of Redox-Responsive Covalent Organic Framework Nanocarriers for Efficiently Loading and Delivering Doxorubicin

Comprehensive Computational Investigation of the Porphyrin-Based COF as a Nanocarrier for Delivering Anti-Cancer Drugs: A Combined MD Simulation and DFT Calculation

As nanomaterials have gained prominence in drug delivery technology, exploring their feasibility through computational methods is beneficial before practical tests. In this study, we aim to evaluate the capability of the porphyrin-based covalent organic framework COF-366 as a nanocarrier for two anticancer drugs, irinotecan (IRI) and doxorubicin (DOX). The optimal binding conformation of the drug molecules on the COF surface was predicted by using molecular docking. Subsequently, molecular dynamic simulation (MD) was performed to assess the adsorption mechanism of drug molecules on the COF in the aqueous environment. The free energy of adsorption for DOX and IRI was estimated to be -20.07 and -23.89 kcal/mol, respectively. The adsorption of both drugs on the COF surface is mainly influenced by the π-π interaction. Furthermore, density functional theory (DFT) calculation, natural bond orbital (NBO), and quantum theory of atoms in molecules (QTAIM) analyses were employed to investigate the structural stability of Drug@COF complexes and gain a detailed understanding of the interaction between them at the molecular level. Based on DFT results, it was found that in addition to π-π interaction, the bis-piperidine-phenylene interaction affects the adsorption of IRI on the COF surface. Moreover, the diffusion behavior of the drug molecule inside the COF pore was simulated using a ten-layer COF. Based on the mean square displacement analysis, the diffusion coefficients of DOX and IRI within the COF pore were calculated to be 108 and 97 um2/s, respectively. This computational study sheds light on how different types of interactions between the drug molecule and COF affect the adsorption and diffusion process. Our findings validated that the porphyrin-based COF-366 can serve as a nanobased platform for delivering DOX and IRI.

Porous Organic Polymer-Based Nanocomposites for Hypoxia Relieving and Enhanced Chemotherapy in Hepatocellular Carcinoma

Uncontrolled proliferation and altered metabolism of cancer cells result in an imbalance of nutrients and oxygen supply, and persuade hypoxia. Hypoxia, in turn, activates the transcription gene HIF-1α, which eventually upregulates the efflux transporter P-gp and induces multidrug resistance (MDR). Thus, hypoxia leads to the development of resistance to conventional therapies. Therefore, the fabrication of a nanoscale porous system enriched with upconversion nanoparticles to target cancer cells, evade hypoxia, and enhance anticancer therapy is the key goal of this article. Herein, upconversion nanoparticles are embedded in a nanoscale porous organic polymer (POP) and further conjugated with a targeting moiety and a catalase molecule. The nanoscale POP embedded in UCNPs is generated at room temperature. The targeting ligand, lactobionic acid, is attached after polymer coating, which effectively targets liver cancer cells. Then, catalase is grafted effectively to produce oxygen. Endogenously generated oxygen alleviates hypoxia in liver cancer cells. The drug- and catalase-loaded composite exhibit greater cytotoxicity in hypoxic liver cells than in normal cells by overcoming hypoxia and downregulating the hypoxia-inducible factors.

Facile Synthesis of a Multifunctional Porous Organic Polymer Nanosonosensitizer (mHM@HMME) for Enhanced Cancer Sonodynamic Therapy

Sonodynamic therapy (SDT), which involves the activation of sonosensitizers to generate cytotoxic reactive oxygen species under ultrasound irradiation, is a promising noninvasive modality for cancer treatment. However, the clinical translational application of SDT is impeded by the lack of efficient sonosensitizers, the inefficient accumulation of sonosensitizers at tumor sites, and the complicated immunosuppressive tumor microenvironment. Herein, we developed a facilely synthesized multifunctional porous organic polymer nanosonosensitizer (mHM@HMME) for enhanced SDT. Specifically, mHM@HMME nanosonosensitizers were prepared by incorporating chemotherapeutic mitoxantrone into the one-step synthesis process of disulfide bond containing porous organic polymers, followed by loading with organic sonosensitizer (HMME) and camouflaging with a cancer cell membrane. Due to the cancer cell membrane camouflage, this multifunctional mHM@HMME nanosonosensitizer showed prolonged blood circulation and tumor targeting aggregation. Under ultrasound irradiation, the mHM@HMME nanosonosensitizer exhibited a satisfactory SDT performance both in vitro and in vivo. Moreover, the potent SDT combined with glutathione-responsive drug release in tumor cells induced robust immunogenic cell death to enhance the antitumor effect of SDT in turn. Overall, this facilely synthesized multifunctional mHM@HMME nanosonosensitizer shows great potential application in enhanced SDT.

Topological Analysis and Structural Determination of 3D Covalent Organic Frameworks

3D covalent organic frameworks (3D COFs) constitute a new type of crystalline materials that consist of a range of porous structures with numerous applications in the fields of adsorption, separation, and catalysis. However, because of the complexity of the three-periodic net structure, it is desirable to develop a thorough structural comprehension, along with a means to precisely determine the actual structure. Indeed, such advancements would considerably contribute to the rational design and application of 3D COFs. In this review, the reported topologies of 3D COFs are introduced and categorized according to the configurations of their building blocks, and a comprehensive overview of diffraction-based structural determination methods is provided. The current challenges and future prospects for these materials will also be discussed.

Strategies for utilizing covalent organic frameworks as host materials for the integration and delivery of bioactives

Covalent organic frameworks (COFs), a new and developing class of porous framework materials, are considered a type of promising carrier for the integration and delivery of bioactives, which have diverse fascinating merits, such as a large specific surface area, designable and specific porosity, stable and orderly framework structure, and various active sites. However, owing to the significant differences among bioactives (including drugs, proteins, nucleic acid, and exosomes), such as size, structure, and physicochemical properties, the interaction between COFs and bioactives also varies. In this review, we firstly summarize three strategies for the construction of single or hybrid COF-based matrices for the delivery of cargos, including encapsulation, covalent binding, and coordination bonding. Besides, their smart response release behaviors are also categorized. Subsequently, the applications of cargo@COF biocomposites in biomedicine are comprehensively summarized, including tumor therapy, central nervous system (CNS) modulation, biomarker analysis, bioimaging, and anti-bacterial therapy. Finally, the challenges and opportunities in this field are briefly discussed.

Covalent Organic Frameworks: Opportunities for Rational Materials Design in Cancer Therapy

Nanomedicines are extensively used in cancer therapy. Covalent organic frameworks (COFs) are crystalline organic porous materials with several benefits for cancer therapy, including porosity, design flexibility, functionalizability, and biocompatibility. This review examines the use of COFs in cancer therapy from the perspective of reticular chemistry and function-oriented materials design. First, the modification sites and functionalization methods of COFs are discussed, followed by their potential as multifunctional nanoplatforms for tumor targeting, imaging, and therapy by integrating functional components. Finally, some challenges in the clinical translation of COFs are presented with the hope of promoting the development of COF-based anticancer nanomedicines and bringing COFs closer to clinical trials.

Covalent-Organic Framework-Based Materials in Theranostic Applications: Insights into Their Advantages and Challenges

Nanomedicine has been essential in bioimaging and cancer therapy in recent years. Nanoscale covalent-organic frameworks (COFs) have been growing as an adequate classification of biomedical nanomaterials with practical application prospects because of their increased porosity, functionality, and biocompatibility. The high sponginess of COFs enables the incorporation of distinct imaging and therapeutic mechanisms with a better loading efficiency. Nevertheless, preliminary biocompatibility limits their possibility for clinical translation. Thus, cutting-edge nanomaterials with high biocompatibility and improved therapeutic efficiency are highly expected to fast-track the clinical translation of nanomedicines. The inherent effects of nanoscale COFs, such as proper size, modular pore geometry and porosity, and specific postsynthetic transformation through simple organic changes, make them particularly appealing for prospective nanomedicines. The organic building blocks of COFs may also be postmodified for particular binding to biomarkers. The exceptional features of COFs cause them to be an encouraging nanocarrier for bioimaging and therapeutic applications. In this review, we have systematically discussed the advances of COFs in the field of theranostics by providing essential features of COFs along with their synthetic methods. Further, the applications of COFs in the field of theranostics (such as drug delivery systems, photothermal, and photodynamic therapy) are discussed in detail with the help of available literature to date. Furthermore, the advantages of COFs over other materials for therapeutics and drug delivery are discussed. Finally, the review concludes with potential future COF applications in the theranostic field.

Recent bio-applications of covalent organic framework-based nanomaterials

Appearing as a new class of functional organic materials, covalent organic frameworks (COFs) have aroused a huge wave of interest in versatile fields ever since they were first proposed in 2005. Thanks to but not limited to their ultralight weights, high surface areas, ordered channels, variable functional groups and well-defined crystal structures, the applications of COF-based biomaterials in the fields of drug loading and delivery, photodynamic therapy, photothermal therapy, bioimaging, etc. are comprehensively summarized and introduced. The existing challenges and future prospects for this emerging but hot research direction are also discussed. It is hoped that this review will serve as a guidance for future research on COFs as multifunctional bioplatforms.

Polymeric nanoparticles (PNPs) for oral delivery of insulin

Successful oral insulin administration can considerably enhance the quality of life (QOL) of diabetes patients who must frequently take insulin injections. Oral insulin administration, on the other hand, is seriously hampered by gastrointestinal enzymes, wide pH range, mucus and mucosal layers, which limit insulin oral bioavailability to ≤ 2%. Therefore, a large number of technological solutions have been proposed to increase the oral bioavailability of insulin, in which polymeric nanoparticles (PNPs) are highly promising for oral insulin delivery. The recently published research articles chosen for this review are based on applications of PNPs with strong future potential in oral insulin delivery, and do not cover all related work. In this review, we will summarize the controlled release mechanisms of oral insulin delivery, latest oral insulin delivery applications of PNPs nanocarrier, challenges and prospect. This review will serve as a guide to the future investigators who wish to engineer and study PNPs as oral insulin delivery systems.

Drug delivery using biocompatible covalent organic frameworks (COFs) towards a therapeutic approach

Covalent organic frameworks (COFs) are constructed exclusively with lightweight organic scaffolds, which can have a 2D or 3D architecture. The ease of synthesis, robust skeleton and tunable properties of COFs make them superior candidates among their counterparts for a wide range of uses including biomedical applications. In the biomedical field, drug delivery or photodynamic-photothermal (PDT-PTT) therapy can be individually considered a potential parameter to be investigated. Therefore, this comprehensive review is focused on drug delivery using COFs, highlighting the encapsulation and decapsulation of drugs by COF scaffolds and their delivery in biological media including live cells. Versatile COF scaffolds together with the delivery of several drug molecules are considered. We attempted to incorporate the status of drug encapsulation and decapsulation considering a wide range of recent publications.

Imine-Linked Covalent Organic Frameworks: A Biocompatible and pH-Dependent Carrier for In Vitro Sustained Release of Doxorubicin

Among the novel drug delivery systems (DDSs), covalent organic frameworks (COFs) show promising features in pharmaceutical science. In this paper, an imine-linked COF with hexagonal topology was synthesized using the autoclave condition. Then, the prepared COF (APB-COF) was used as a pH-dependent carrier for in vitro release of doxorubicin (DOX). The intrinsic properties of APB-COF caused reaching an excellent drug encapsulation efficiency. DOX@APB-COF shows an exemplary pH-dependent release in two different pHs. DOX release at pH = 7.4 was 32%, which increased to 54% by changing the pH to the cancer cell pH (pH = 5.4). Moreover, the cytotoxicity of APB-COF and DOX@APB-COF was studied using the standard MTT test against MCF10 (normal breast cell line) and MDAmb231 cells (breast cancer cell line), respectively. It was observed that the APB-COF does not affect cell proliferation, whereas the DOX@APB-COF only limits cancer cell proliferation. Using APB-COF as the drug carrier can pave the way for using COFs in innovative DDSs.

An overview of the synthetic strategies of C3-symmetric polymeric materials containing benzene and triazine cores and their biomedical applications

C3-symmetric star-shaped materials are an emerging category of porous organic polymers with distinctive properties such as permanent porosity, good thermal and chemical stability, high surface area, and appropriate functionalization that promote outstanding potential in various applications. This review is mostly about constructing benzene or s-triazine rings as the center of C3-symmetric molecules and using side-arm reactions to add functions to these molecules. Over and above this, the performance of various polymerization processes has been additionally investigated in detail, including the trimerization of alkynes or aromatic nitriles, polycondensation of monomers with specific functional groups, and cross-coupling building blocks with benzene or triazine cores. Finally, the most recent progress in biomedical applications for C3-symmetric materials based on benzene or s-triazine have been summarized.

Recent advances in covalent organic frameworks (COFs) for wound healing and antimicrobial applications

Covalent organic frameworks (COFs) are crystal-like organic structures such as cartography buildings prepared from appropriately pre-designed construction block precursors. Moreover, after the expansion of the first COF in 2005, numerous researchers have been developing different materials for versatile applications such as sensing/imaging, cancer theranostics, drug delivery, tissue engineering, wound healing, and antimicrobials. COFs have harmonious pore size, enduring porosity, thermal stability, and low density. In addition, a wide variety of functional groups could be implanted during their construction to provide desired constituents, including antibodies and enzymes. The reticular organic frameworks comprising porous hybrid materials connected via a covalent bond have been studied for improving wound healing and dressing applications due to their long-standing antibacterial properties. Several COF-based systems have been planned for controlled drug delivery with wound healing purposes, targeting drugs to efficiently inhibit the growth of pathogenic microorganisms at the wound spot. In addition, COFs can be deployed for combinational therapy using photodynamic and photothermal antibacterial therapy along with drug delivery for healing chronic wounds and bacterial infections. Herein, the most recent advancements pertaining to the applications of COF-based systems against bacterial infections and for wound healing are considered, concentrating on challenges and future guidelines.

Covalent Organic Frameworks: Recent Progress in Biomedical Applications

Covalent organic frameworks (COFs) are a type of crystalline organic porous material with specific features and interesting structures, including porosity, large surface area, and biocompatibility. These features enable COFs to be considered as excellent candidates for applications in various fields. Recently, COFs have been widely demonstrated as promising materials for biomedical applications because of their excellent physicochemical properties and ultrathin structures. In this review, we cover the recent progress of COF materials for applications in photodynamic therapy, gene delivery, photothermal therapy, drug delivery, bioimaging, biosensing, and combined therapies. Moreover, the critical challenges and further perspectives with regards to COFs for future biology-facing applications are also discussed.

Redox- and pH-Responsive Water-Soluble Flexible Organic Frameworks Realize Synergistic Tumor Photodynamic and Chemotherapeutic Therapy

Water-soluble 3D polymers with inherent nanoscale pores have been shown to be ideal platforms for the inclusion and delivery of drugs and hold a great promise as biocompatible materials for diagnostic and therapeutic purposes. Herein, a low cytotoxic water-soluble flexible organic framework FOF-S6 with a hydrodynamic diameter of about 127.5 nm is synthesized through the formation of a hydrazone bond from a semirigid tetraaldehyde and a flexible biacylhydrazines which contains a disulfide bond (1:2). FOF-S6 has the ability to dissociate and release inclusion complexes in response to weakly acidic media and glutathione (GSH) overexpressed in tumor cells. More importantly, a facile strategy is developed to contain and deliver aggregation-induced emission photosensitizers (AIE PS, TBD-DQA-540) and chemotherapeutic drugs (Doxorubicin hydrochloride, DOX). DOX-PS@FOF-S6 is synthesized by a one-pot method, which can realize efficient photo-chemotherapy under the guidance of fluorescence imaging, thereby improving the multidrug resistance of tumor cells and the instability of photosensitizers, so as to improve the tumor treatment efficacy.

Covalent Organic Frameworks as Nanocarriers for Improved Delivery of Chemotherapeutic Agents

Cancer has become one of the main causes of death worldwide. Chemotherapy as one of the main therapy modalities is very unsatisfactory. The various nanocarriers have brought new opportunities for effective tumor treatment. However, most of the current nanocarriers still suffer from low efficiency and confront significant challenges in overcoming multiple biological barriers. Compared with conventional nanocarriers, covalent organic frameworks (COFs) with unique and attractive features exhibited great potential to serve as a promising platform for anticancer drug delivery. In this review, we first summarize the strategies and challenges of nanocarriers for cancer chemotherapy and then highlight the recent advances in COF-based nanocarriers for improved delivery of chemotherapeutic agents. Finally, the challenges remaining for COF-based nanocarriers for clinical applications are outlined.

Self-Sacrificially Degradable Pseudo-Semiconducting Polymer Nanoparticles that Integrate NIR-II Fluorescence Bioimaging, Photodynamic Immunotherapy, and Photo-Activated Chemotherapy

Semiconducting polymers (SP) hold great promise for cancer phototherapy due to their excellent optical properties; however, their clinical application is still hampered by their poor biodegradability. Herein, a self-sacrificially biodegradable pseudo-semiconducting polymer (PSP) for NIR-II fluorescence bioimaging, photodynamic immunotherapy, and photoactivated chemotherapy (PACT) is reported. The PSP can further co-assemble with an amphiphilic polyester with pendant doxorubicin (DOX) in its side chains via reactive oxygen species (ROS)-responsive thioketal linkages (PE^DOX ), which are denoted as NP@PE^DOX /PSP. The NP@PE^DOX /PSP can accumulate at tumor sites and generate ROS for photodynamic immunotherapy as well as near-infrared-II fluorescence (NIR-II) for bioimaging upon irradition at 808 nm. The ROS could break up thioketal linkages in PE^DOX , resulting in rapid doxorubicin (DOX) release for PACT. Finally, both PE^DOX and PSP are degraded sacrificially by intracellular glutathione (GSH), resulting in the dissociation of NP@PE^DOX /PSP. This work highlights the application of self-sacrificially degradable PSP for NIR-II fluorescence bioimaging, photodynamic immunotherapy, and PACT in cancer therapy.

Porous organic polymers for drug delivery: hierarchical pore structures, variable morphologies, and biological properties

Porous organic polymers have received considerable attention in recent years because of their applicability as biomaterials. In particular, their hierarchical pore structures, variable morphologies, and tunable biological properties make them suitable as drug-delivery systems. In this review, the synthetic and post forming/control methods including templated methods, template-free methods, mechanical methods, electrospun methods, and 3D printing methods for controlling the hierarchical structures and morphologies of porous organic polymers are discussed, and the different methods affecting their specific surface areas, hierarchical structures, and unique morphologies are highlighted in detail. In addition, we discuss their applications in drug encapsulation and the development of stimuli (pH, heat, light, and dual-stimuli)-responsive materials, focusing on their use for targeted drug release and as therapeutic agents. Finally, we present an outlook concerning the research directions and applications of porous polymer-based drug delivery systems.

Recent Progress in External-Stimulus-Responsive 2D Covalent Organic Frameworks

Recently, smart 2D covalent organic frameworks (COFs), combining the advantages of both inherent structure features and functional building blocks, have been demonstrated to show reversible changes in conformation, color, and luminescence in response to external stimuli. This review provides a summary on the recent progress of 2D COFs that are responsive to external stimuli such as metal ions, gas molecules, pH values, temperature, electricity, light, etc. Moreover, the responsive mechanisms and design strategies, along with the applications of these stimulus-responsive 2D COFs in chemical sensors and photoelectronic devices are also discussed. It is believed that this review would provide some guidelines for designing novel single-/multistimulus-responsive 2D COFs with controllable responsive behaviors for advanced photoelectronic applications.

Dual antisense oligonucleotide targeting miR-21/miR-155 synergize photodynamic therapy to treat triple-negative breast cancer and inhibit metastasis

Triple negative breast cancer (TNBC) is a greatly aggressive subtype of breast cancer with high recurrence and mortality rates. Chemotherapy as a primary treatment for cancer is limited due to toxic side effects and drug resistance. Therefore, low toxicity and more effective breast cancer therapeutic approaches are greatly desired. In this study, a strategy which using ZIF-90 nanoparticles co-deliver Ce6-anti-miR-21 and Ce6-anti-miR-155 into the tumor cells was developed. Due to the pH responsive drug release of ZIF-90, antisense oligonucleotides (anti-miRNAs) and photosensitizers are able to be efficiently released inside tumor microenvironment. The nano delivery system captures overexpressed oncogenic miRNAs while the photosensitizer Ce6 generates ROS under light irradiation to effectively induce the apoptosis of tumor cell. This combinatorial effect was verified by results showing that the purposed therapic method could effectively inhibit tumor cell proliferation and metastasis. The concept of antisense oligonucleotide combined with photodynamic therapy has great potential in cancer treatment or adjuvant therapy.

Characteristic Synthesis of a Covalent Organic Framework and Its Application in Multifunctional Tumor Therapy

For decades, covalent organic frameworks (COFs) have attracted wide biomedical interest due to their unique properties including ease of synthesis, porosity, and adjustable biocompatibility. Versatile COFs can easily encapsulate various therapeutic drugs due to their extremely high payload and porosity. COFs with abundant functional groups can be surface-modified to achieve active targeting and enhance biocompatibility. In this paper, the latest developments of COFs in the biomedical field are summarized. First, the classification and synthesis of COFs are discussed. Cancer diagnosis and treatment based on COFs are studied, and the advantages and limitations of each method are discussed. Second, the specific preparation methods to obtain specific therapeutic properties are summarized. Finally, based on the combination and modification of COFs with various components, this review system summarizes different combination therapies. In addition, the main challenges faced in COF research and prospects for applying COFs to cancer diagnosis and treatment are evaluated. This review provides enlightening insights into the interdisciplinary research on COFs and applications in biomedicine, which highlight the great expectations for their further clinical transformation.

2D and 3D Covalent Organic Frameworks: Cutting-Edge Applications in Biomedical Sciences

Covalent organic frameworks (COFs) are crystalline porous organic structures with two- or three-dimensional (2D or 3D) features and composed of building blocks being connected via covalent bonds. The manifold applications of COFs in optoelectronic devices, energy conversion and storage, adsorption, separation, sensing, organocatalysis, photocatalysis, electrocatalytic reactions, and biomedicine are increasing because of their notable intrinsic features such as large surface area, porosity, designable structure, low density, crystallinity, biocompatibility, and high chemical stability. These properties have rendered 2D and 3D COF-based materials as desirable entities for drug delivery, gene delivery, photothermal therapy, photodynamic therapy, combination therapy, biosensing, bioimaging, and anticancer activities. Herein, different reactions and methods for the synthesis of 2D and 3D COFs are reviewed with special emphasis on the construction and state-of-the-art progress pertaining to the biomedical applications of 2D and 3D COFs of varying shapes, sizes, and structures. Specifically, stimuli-responsive COFs-based systems and targeted drug delivery approaches are summarized.

Emerging porous organic polymers for biomedical applications

This review summarizes and discusses the recent progress in porous organic polymers for diverse biomedical applications such as drug delivery, biomacromolecule immobilization, phototherapy, biosensing, bioimaging, and antibacterial applications.

Post-synthetic modifications in porous organic polymers for biomedical and related applications

Porous organic polymers (POPs) are prepared by crosslinked polymerization of multidimensional rigid aromatic building blocks. Generally, POPs can be classified into crystalline covalent organic frameworks (COFs) and other poorly crystalline or amorphous porous polymers. Due to their remarkable intrinsic properties, such as high porosity, stability, tunability, and presence of numerous building blocks, several new POPs are being developed for application across various scientific fields. The essential sensitive functional groups needed for specific applications are not sustained under harsh POP preparation conditions. The recently developed post-synthetic modification (PSM) strategies for POPs have enabled their advanced applications that are otherwise restricted. Owing to the advanced PSM strategies POPs have experienced a blossoming resurgence with diverse functions, particularly in biomedical applications, such as bioimaging tools, drugs, enzymes, gene or protein delivery systems, phototherapy, and cancer therapy. This tutorial review focuses on the recently developed PSM strategies for POPs, especially for biomedical applications, and their future perspectives as promising bioapplicable materials.

Nanoscale porous organic polymers for drug delivery and advanced cancer theranostics

Finding a personalized nano theranostics solution, a nanomedicine for cancer diagnosis and therapy, is among the top challenges of current medicinal science. Porous organic polymers (POPs) are permanent porous organic materials prepared by linking relatively rigid multidimensional organic building blocks. POP nanoparticles have a remarkable advantage for cancer theranostics owing to their specific physicochemical characteristics such as high surface area, convincing pore size engineering, stimuli-responsive degradability, negligible toxicity, open covalent post-synthesis modification possibilities etc. POPs have crystalline and non-crystalline characteristics; crystalline POPs are popularly known as covalent organic frameworks (COFs), and have shown potential application across research areas in science. The early research and development on theranostics applications of nanoscale POPs has shown tremendous future potential for clinical translation. This tutorial review highlights the recently developed promising applications of nPOPs in drug loading, targeted delivery, endogenous and exogenous stimuli-responsive release, cancer imaging and combination therapy, regardless of their crystalline and poorly crystalline properties. The review will provide a platform for the future development and clinical translation of nPOPs by solving fundamental challenges of cancer nanomedicines in drug loading efficiency, size-optimization, biocompatibility, dispersibility and cell uptake ability.

Nanoscale covalent organic frameworks: from controlled synthesis to cancer therapy

Covalent organic frameworks (COFs), as a new type of crystalline porous materials, mainly consist of light-weight elements (H, B, C, N and O) linked by dynamic covalent bonds to form periodical structures of two or three dimensions. As an attribute of their low density, large surface area, and excellent adjustable pore size, COFs show great potential in many fields including energy storage and separation, catalysis, sensing, and biomedicine. However, compared with metal organic frameworks (MOFs), the relatively large size and irregular morphology of COFs affect their biocompatibility and bioavailability in vivo, thus impeding their further biomedical applications. This Review focuses on the controlled design strategies of nanoscale COFs (NCOFs), unique properties of NCOFs for biomedical applications, and recent progress in NCOFs for cancer therapy. In addition, current challenges for the biomedical use of NCOFs and perspectives for further improvements are presented.

Recent Progress in Nanoscale Covalent Organic Frameworks for Cancer Diagnosis and Therapy

Covalent organic frameworks (COFs) as a type of porous and crystalline covalent organic polymer are built up from covalently linked and periodically arranged organic molecules. Their precise assembly, well-defined coordination network, and tunable porosity endow COFs with diverse characteristics such as low density, high crystallinity, porous structure, and large specific-surface area, as well as versatile functions and active sites that can be tuned at molecular and atomic level. These unique properties make them excellent candidate materials for biomedical applications, such as drug delivery, diagnostic imaging, and disease therapy. To realize these functions, the components, dimensions, and guest molecule loading into COFs have a great influence on their performance in various applications. In this review, we first introduce the influence of dimensions, building blocks, and synthetic conditions on the chemical stability, pore structure, and chemical interaction with guest molecules of COFs. Next, the applications of COFs in cancer diagnosis and therapy are summarized. Finally, some challenges for COFs in cancer therapy are noted and the problems to be solved in the future are proposed.

Strategies and applications of covalent organic frameworks as promising nanoplatforms in cancer therapy

Cancer nanomedicine is the best option to face the limits of conventional chemotherapy and phototherapy methods, and thus the intensive quest for new nanomaterials to improve therapeutic efficacy and safety is still underway. Owing to their low density, well-defined structures, large surface area, finely tunable pore size, and metal ion free features, covalent organic frameworks (COFs) have been extensively studied in many research fields. The recent great interest in nanoscale COFs to improve the properties of bulk COFs has led to broadening of their applicability in the biomedical field, such as nanocarriers with an outstanding loading capacity and efficient delivery of therapeutic agents, smart theranostic nanoplatforms with excellent stability, high ROS generation, light-to-heat conversion capabilities, and different response and diagnostic characteristics. The COFs and related nanoplatforms with a wide variety of designability and functionalization have opened up a new avenue for exciting opportunities in cancer therapy. Herein we review the state-of-the-art technical and scientific developments in this emerging field, focusing on the overall progress addressed so far in building versatile COF-based nanoplatforms to enhance chemotherapy, photodynamic/photothermal therapy, and combination. Future perspectives for achieving the synergistic effect of cancer elimination and clinical translation are further discussed to motivate future contributions and explore new possibilities.

Recent advances in covalent organic frameworks for cancer diagnosis and therapy

In recent years, the number of patients diagnosed with cancer has been soaring. Therefore, the design, development, and implementation of new approaches for the diagnosis and therapy of different types of cancers have attracted an increasing amount of attention. To date, different methods have been used for cancer diagnosis and therapy with main drawbacks in terms of severe side effects, e.g., damage to healthy cells, development of drug resistance and tumor recurrence. Therefore, there is an urgent need for the introduction and application of innovative methods. Covalent organic frameworks (COFs) are versatile materials with excellent properties in terms of biocompatibility, porous and crystalline structure, and easy functionalization. The porous structure and organic monomers in COFs allow them to load different therapeutic drugs and/or functional species efficiently. These promising properties make COFs ideal candidates for medical application, especially in cancer diagnosis and therapy. To date, many studies have focused on the design and synthesis of novel COFs while their application as diagnostic and therapeutic materials remains less understood. In this review, different synthesis and functionalization approaches of COFs were summarized. In particular, cancer diagnosis and therapy based on COFs were investigated and the advantages and limitations of each method were discussed. Most importantly, the mechanism for cancer therapy of COFs and fundamental challenges and perspectives for the application of COFs in cancer theranostics were assessed.

Electrospun Fibrous Membrane Containing a Cyclodextrin Covalent Organic Framework with Antibacterial Properties for Accelerating Wound Healing

Skin wounds are usually accompanied by bacterial infections and inflammations, leading to delayed wound healing, which remain a great challenge in clinical treatment. Therefore, it is of great significance to develop wound dressings that inhibit bacterial infections to accelerate wound healing. Herein, we reported the fabrication of inclusion complex (a β-cyclodextrin covalent organic framework loaded with enrofloxacin and flunixin meglumine)-incorporated electrospun thermoplastic polyurethane fibers (named ENR-FM-COF-TPU) via electrospinning. The obtained ENR-FM-COF-TPU fibrous membrane exhibited excellent physicochemical and biological properties such as uniform and stable morphology, proper hydrophobicity, good water uptake capacity, and admirable biocompatibility, which showed perfect behavior as a wound dressing. In addition, the ENR-FM-COF-TPU membrane achieved a sustained drug release of enrofloxacin and flunixin meglumine and displayed powerful antibacterial activity against Staphylococcus aureus and Escherichia coli with 99% inhibitory efficiency for 50 h. More importantly, the wound healing therapy effect was investigated using a full-thickness skin defect model of mice. It suggested that the ENR-FM-COF-TPU membrane could significantly accelerate and enhance wound healing through downregulating inflammatory cytokines (IL-1β and TNF-α) and increasing the expression of growth factors (VEGF and EGF). Due to its excellent properties, the ENR-FM-COF-TPU membrane may have promising potential in wound healing applications.

Polymeric Drug Delivery System Based on Pluronics for Cancer Treatment

Pluronic polymers (pluronics) are a unique class of synthetic triblock copolymers containing hydrophobic polypropylene oxide (PPO) and hydrophilic polyethylene oxide (PEO) arranged in the PEO-PPO-PEO manner. Due to their excellent biocompatibility and amphiphilic properties, pluronics are an ideal and promising biological material, which is widely used in drug delivery, disease diagnosis, and treatment, among other applications. Through self-assembly or in combination with other materials, pluronics can form nano carriers with different morphologies, representing a kind of multifunctional pharmaceutical excipients. In recent years, the utilization of pluronic-based multi-functional drug carriers in tumor treatment has become widespread, and various responsive drug carriers are designed according to the characteristics of the tumor microenvironment, resulting in major progress in tumor therapy. This review introduces the specific role of pluronic-based polymer drug delivery systems in tumor therapy, focusing on their physical and chemical properties as well as the design aspects of pluronic polymers. Finally, using newer literature reports, this review provides insights into the future potential and challenges posed by different pluronic-based polymer drug delivery systems in tumor therapy.

In vivo oral insulin delivery via covalent organic frameworks

With diabetes being the 7th leading cause of death worldwide, overcoming issues limiting the oral administration of insulin is of global significance. The development of imine-linked-covalent organic framework (nCOF) nanoparticles for oral insulin delivery to overcome these delivery barriers is herein reported. A gastro-resistant nCOF was prepared from layered nanosheets with insulin loaded between the nanosheet layers. The insulin-loaded nCOF exhibited insulin protection in digestive fluids in vitro as well as glucose-responsive release, and this hyperglycemia-induced release was confirmed in vivo in diabetic rats without noticeable toxic effects. This is strong evidence that nCOF-based oral insulin delivery systems could replace traditional subcutaneous injections easing insulin therapy.

Smart Nanomaterials for Biomedical Applications-A Review

Recent advances in nanotechnology have forced the obtaining of new materials with multiple functionalities. Due to their reduced dimensions, nanomaterials exhibit outstanding physio-chemical functionalities: increased absorption and reactivity, higher surface area, molar extinction coefficients, tunable plasmonic properties, quantum effects, and magnetic and photo properties. However, in the biomedical field, it is still difficult to use tools made of nanomaterials for better therapeutics due to their limitations (including non-biocompatible, poor photostabilities, low targeting capacity, rapid renal clearance, side effects on other organs, insufficient cellular uptake, and small blood retention), so other types with controlled abilities must be developed, called "smart" nanomaterials. In this context, the modern scientific community developed a kind of nanomaterial which undergoes large reversible changes in its physical, chemical, or biological properties as a consequence of small environmental variations. This systematic mini-review is intended to provide an overview of the newest research on nanosized materials responding to various stimuli, including their up-to-date application in the biomedical field.

A computational study on the interactions between a layered imine-based COF structure and selected anticancer drugs

The covalent organic frameworks (COFs) are important materials in drug delivery. Herein, the interactions between an imine-based COF with selected commercially available anticancer drugs are studied. Molecular dynamics (MD) simulation studies were used. The studies were carried out in four different temperatures to find out the impact of the temperature on the binding free energies between the drugs and COF structure. It was found that the effect of temperature on binding free energy is ignorable. Between the hydrogen bonding, electrostatic, and van der Waals interactions, the last one is the most important one to keep the drug and COF next to each other. Also, the van der Waals interaction is keeping the layers of COF next to each other to create cavities. The cavities can be loaded with different drugs and the system can be used in drug delivery systems. Based on the obtained results, the drugs that are more lipophilic prefer to adhere more strongly to the COF in comparison with hydrophilic drugs.

Recent advances in the redox-responsive drug delivery nanoplatforms: A chemical structure and physical property perspective

Poor water solubility, off-target toxicity, and small therapeutic window are among major obstacles for the development of drug products. Redox-responsive drug delivery nanoplatforms not only overcome the delivery and pharmacokinetic pitfalls observed in conventional drug delivery, but also leverage the site-specific delivery properties. Cleavable diselenide and disulfide bonds in the presence of elevated reactive oxygen species (ROS) and glutathione concentration are among widely used stimuli-responsive bonds to design nanocarriers. This review covers a wide range of redox-responsive chemical structures and their properties for designing nanoparticles aiming controlled loading, delivery, and release of hydrophobic anticancer drugs at tumor site.

Covalent Organic Framework Embedded with Magnetic Nanoparticles for MRI and Chemo-Thermotherapy

Nanoscale imine-linked covalent organic frameworks (nCOFs) were first loaded with the anticancer drug Doxorubicin (Dox), coated with magnetic iron oxide nanoparticles (γ-Fe₂O₃ NPs), and stabilized with a shell of poly(l-lysine) cationic polymer (PLL) for simultaneous synergistic thermo-chemotherapy treatment and MRI imaging. The pH responsivity of the resulting nanoagents (γ-SD/PLL) allowed the release of the drug selectively within the acidic microenvironment of late endosomes and lysosomes of cancer cells (pH 5.4) and not in physiological conditions (pH 7.4). γ-SD/PLL could efficiently generate high heat (48 °C) upon exposure to an alternating magnetic field due to the nCOF porous structure that facilitates the heat conduction, making γ-SD/PLL excellent heat mediators in an aqueous solution. The drug-loaded magnetic nCOF composites were cytotoxic due to the synergistic toxicity of Dox and the effects of hyperthermia in vitro on glioblastoma U251-MG cells and in vivo on zebrafish embryos, but they were not significantly toxic to noncancerous cells (HEK293). To the best of our knowledge, this is the first report of multimodal MRI probe and chemo-thermotherapeutic magnetic nCOF composites.

Nanoscale covalent organic frameworks as theranostic platforms for oncotherapy: synthesis, functionalization, and applications

Cancer nanomedicine is one of the most promising domains that has emerged in the continuing search for cancer diagnosis and treatment. The rapid development of nanomaterials and nanotechnology provide a vast array of materials for use in cancer nanomedicine. Among the various nanomaterials, covalent organic frameworks (COFs) are becoming an attractive class of upstarts owing to their high crystallinity, structural regularity, inherent porosity, extensive functionality, design flexibility, and good biocompatibility. In this comprehensive review, recent developments and key achievements of COFs are provided, including their structural design, synthesis methods, nanocrystallization, and functionalization strategies. Subsequently, a systematic overview of the potential oncotherapy applications achieved till date in the fast-growing field of COFs is provided with the aim to inspire further contributions and developments to this nascent but promising field. Finally, development opportunities, critical challenges, and some personal perspectives for COF-based cancer therapeutics are presented.

pH and Redox Dual-Sensitive Covalent Organic Framework Nanocarriers to Resolve the Dilemma Between Extracellular Drug Loading and Intracellular Drug Release

Cancer poses a serious threat to human health. To enhance the efficacy of tumor chemotherapy, it is urgent to develop novel and effective nanocarriers with the ability to efficiently load and deliver anticancer drugs. Covalent organic frameworks (COF)-based nanocarriers (CONs) have exhibited great potential for drug loading due to their porous structure and high surface area. However, the function of tumor intracellular-triggered drug release has barely been integrated. Herein we first synthesized a kind of hydrazide and disulfide bonds containing building block (4,4'-Dihydrazide diphenyl disulfide, DHDS), which was used to develop a PEGylated pH and redox dual-sensitive CONs (denoted HY/SS-CONs) for efficiently loading and delivering doxorubicin (DOX). The obtained HY/SS-CONs can achieve a very high loading content of DOX and very low premature leakage at physiological condition. However, under tumor intracellular microenvironment, HY/SS-CONs with acid-cleavable hydrazone bonds, and GSH-exchangeable disulfide bonds will undergo rapid disintegration, and efficiently release DOX to kill tumor cells. The COFs-based dual-sensitive nanocarriers provide a promising solution to the dilemma of extracellular drug loading and tumor intracellular drug release.