Layered double hydroxide-based nanomaterials for biomedical applications

Against the backdrop of increased public health awareness, inorganic nanomaterials have been widely explored as promising nanoagents for various kinds of biomedical applications. Layered double hydroxides (LDHs), with versatile physicochemical advantages including excellent biocompatibility, pH-sensitive biodegradability, highly tunable chemical composition and structure, and ease of composite formation with other materials, have shown great promise in biomedical applications. In this review, we comprehensively summarize the recent advances in LDH-based nanomaterials for biomedical applications. Firstly, the material categories and advantages of LDH-based nanomaterials are discussed. The preparation and surface modification of LDH-based nanomaterials, including pristine LDHs, LDH-based nanocomposites and LDH-derived nanomaterials, are then described. Thereafter, we systematically describe the great potential of LDHs in biomedical applications including drug/gene delivery, bioimaging diagnosis, cancer therapy, biosensing, tissue engineering, and anti-bacteria. Finally, on the basis of the current state of the art, we conclude with insights on the remaining challenges and future prospects in this rapidly emerging field.

Topology dependent modification of layered double hydroxide for therapeutic and diagnostic platform

Layered double hydroxide is a family of two-dimensional materials with wide range of compositions. Recently, its ability to accommodate various chemical species and biocompatibility have been attracted in the biomedical applications to develop drug delivery system and nanodiagnostics. In this review, we categorized biomedical approaches of layered double hydroxide with respect to the three topologies of, namely, interlayer space, outer surface with particle edge, and the lattice points. There have been extensive researches on the intercalation of drug or tracing to make use of interlayer space of layered double hydroxide for drug stabilization, sustained release, cellular delivery and etc. Outer surface or edge has been utilized to immobilization of large therapeutic moieties and to attach tracing moiety. Lattice points consisting of various metal species could be utilized for the specific metal species like paramagnetic elements or radioisotopes. Based on these topologies in layered double hydroxide, both the synthetic routes and the achieved functionalities in terms of biomedical application will be discussed.

Interference of layered double hydroxide nanoparticles with pathways for biomedical applications

Recent decades have witnessed a surge of explorations into the application of multifarious materials, especially biomedical applications. Among them, layered double hydroxides (LDHs) have been widely developed as typical inorganic layer materials to achieve remarkable advancements. Multiple physicochemical properties endow LDHs with excellent merits in biomedical applications. Moreover, LDH nanoplatforms could serve as "molecular switches", which are capable of the controlled release of payloads under specific physiological pH conditions but are stable during circulation in the bloodstream. In addition, LDHs themselves are composed of several specific cations and possess favorable biological effects or regulatory roles in various cellular functions. These advantages have caused LDHs to become increasingly of interest in the area of nanomedicine. Recent efforts have been devoted to revealing the potential factors that interfere with the biological pathways of LDH-based nanoparticles, such as their applications in shaping the functions of immune cells and in determining the fate of stem cells and tumor treatments, which are comprehensively described herein. In addition, several intracellular signaling pathways interfering with by LDHs in the above applications were also systematically expatiated. Finally, the future development and challenges of LDH-based nanomedicine are discussed in the context of the ultimate goal of practical clinical application.

Two-Dimensional Ultra-Thin Nanosheets with Extraordinarily High Drug Loading and Long Blood Circulation for Cancer Therapy

Nanoparticle drug delivery is largely restricted by the low drug loading capacity of nanoparticle carriers. To address this critical challenge and maximize the potential of nanoparticle drug delivery, a 2D ultra-thin layered double hydroxide (LDH) nanosheet with exceptionally high drug loading, excellent colloidal stability, and prolonged blood circulation for cancer treatment is constructed. The nanosheet is synthesized via a biocompatible polymer-assisted bottom-up method and exhibits an ultra-thin 2D sheet-like structure that enables a considerable amount of cargo anchoring sites available for drug loading, leading to an extraordinary 734% (doxorubicin/nanoparticle mass ratio) drug loading capacity. Doxorubicin delivered by the nanosheet remains stable on the nanosheet carrier under the physiological pH condition, while showing sustained release in the tumor microenvironment and the intracellular environment, thus demonstrating on-demand drug release as a result of pH-responsive biodegradation of nanosheets. Using in vitro and in vivo 4T1 breast cancer models, the nanosheet-based ultra-high drug-loading system demonstrates even enhanced therapeutic performance compared to the multilayered LDH-based high drug-loading system, in terms of increased cellular uptake efficiency, prolonged blood circulation, superior therapeutic effect, and reduced systemic toxicity.

Tumor microenvironment-responsive S-NSs-TPZ-ICG intelligent nanoplatforms for synergistically enhanced tumor multimodal therapy

Nanosheet carriers loaded with drugs and phototherapeutics are used for effective cancer therapy, but the process remains challenging. Here, we prepared sulfur nanosheets (S-NSs) and then loaded tirapazamine (TPZ) and indocyanine green (ICG) with a loading efficiency of 6.3% and 94%, respectively. The obtained S-NSs-TPZ-ICG exhibits near-infrared (NIR) fluorescence, high ¹O₂ generation and photothermal conversion capabilities, good biocompatibility, and tumor microenvironment responsiveness. In vivo and in vitro experiments reveal that S-NSs-TPZ-ICG can be selectively decomposed under acidic and H₂O₂ conditions to release TPZ and ICG, and significantly inhibit tumor growth under laser irradiation without obvious toxic side effects.

Ruthenium photosensitizer anchored gold nanorods for synergistic photodynamic and photothermal therapy

Ruthenium polypyridyl complexes have been widely used as bioprobes and photosensitizers. However, several disadvantages including slow cellular uptake, nonspecific binding with biomolecules and toxicity limit their applications. In this study, a nanocarrier of human serum albumin coated gold nanorods was developed to deliver a ruthenium photosensitizer for PDT/PTT combination therapy. The HSA coating endowed the nanodrug with high biocompatibility and stability under physiological conditions. Ru-GNR-HSANPs generate ¹O₂ and hydroxyl radicals to kill cancer cells under blue light irradiation, and exhibit excellent photothermal anticancer effects under 808 nm light irradiation. Significant synergistic anticancer effects were achieved by combined PDT/PTT therapy. Importantly, Ru-GNR-HSANPs can have the synergistic PDT/PTT functions with no need of drug release from the carrier.

Nanotechnology in combating biofilm: A smart and promising therapeutic strategy

Since the birth of civilization, people have recognized that infectious microbes cause serious and often fatal diseases in humans. One of the most dangerous characteristics of microorganisms is their propensity to form biofilms. It is linked to the development of long-lasting infections and more severe illness. An obstacle to eliminating such intricate structures is their resistance to the drugs now utilized in clinical practice (biofilms). Finding new compounds with anti-biofilm effect is, thus, essential. Infections caused by bacterial biofilms are something that nanotechnology has lately shown promise in treating. More and more studies are being conducted to determine whether nanoparticles (NPs) are useful in the fight against bacterial infections. While there have been a small number of clinical trials, there have been several in vitro outcomes examining the effects of antimicrobial NPs. Nanotechnology provides secure delivery platforms for targeted treatments to combat the wide range of microbial infections caused by biofilms. The increase in pharmaceuticals' bioactive potential is one of the many ways in which nanotechnology has been applied to drug delivery. The current research details the utilization of several nanoparticles in the targeted medication delivery strategy for managing microbial biofilms, including metal and metal oxide nanoparticles, liposomes, micro-, and nanoemulsions, solid lipid nanoparticles, and polymeric nanoparticles. Our understanding of how these nanosystems aid in the fight against biofilms has been expanded through their use.

New tricks of old drugs: Repurposing non-chemo drugs and dietary phytochemicals as adjuvants in anti-tumor therapies

Combination therapy has long been applied to enhance therapeutic effect and deal with the occurrence of multi-drug resistance in cancer treatment. However, the overlapping toxicity of multiple anticancer drugs to healthy tissues and increasing financial burden on patients emerged as major concerns. As promising alternatives to chemo agents, repurposed non-chemo drugs and dietary phytochemicals have been investigated as adjuvants to conventional anti-tumor therapeutics, offering a safe and economic strategy for combination therapy. In this review, we aim to highlight the advances in research about combination therapy using conventional therapeutics and repurposed drugs or phytochemicals for an enhanced anti-tumor efficacy, along with the mechanisms involved in the synergism. Beyond these, we outlined the potential challenges and solutions for clinical translation of the proposed combination therapy, providing a safe and affordable strategy to improve the reach of cancer therapy to low income regions with such new tricks of old drugs.

Advances and perspectives in carrier-free nanodrugs for cancer chemo-monotherapy and combination therapy

Nanocarrier-based drug delivery systems hold impressive promise for biomedical application because of their excellent water dispersibility, prolonged blood circulation time, increased drug accumulation in tumors, and potential in combination therapeutics. However, most nanocarriers suffer from low drug-loading efficiency, poor therapeutic effectiveness, potential systematic toxicity, and unstable metabolism. As an alternative, carrier-free nanodrugs, completely formulated with one or more drugs, have attracted increasing attention in cancer therapy due to their advantage of improved pharmacodynamics/pharmacokinetics, reduced toxicity, and high drug-loading. In recent years, carrier-free nanodrugs have contributed to progress in a variety of therapeutic modalities. In this review, different common strategies for carrier-free nanodrugs preparation are first summarized, mainly including nanoprecipitation, template-assisted nanoprecipitation, thin-film hydration, spray-drying technique, supercritical fluid (SCF) technique, and wet media milling. Then we describe the recently reported carrier-free nanodrugs for cancer chemo-monotherapy or combination therapy. The advantages of anti-cancer drugs combined with other chemotherapeutic, photosensitizers, photothermal, immunotherapeutic or gene drugs have been demonstrated. Finally, a future perspective is introduced to highlight the existing challenges and possible solutions toward clinical application of currently developed carrier-free nanodrugs, which may be instructive to the design of effective carrier-free regimens in the future.

Layered double hydroxide nanostructures and nanocomposites for biomedical applications

Layered double hydroxide (LDH) nanostructures and related nanocomposites have attracted significant interest in biomedical applications including cancer therapy, bioimaging and antibacterial treatment. These materials hold great advantages including low cost and facile preparation, convenient drug loading, high drug incorporation capacity, good biocompatibility, efficient intracellular uptake and endosome/lysosome escape, and natural biodegradability in an acidic environment. In this review, we summarize the development of three types of LDH nanostructures including pristine LDH, surface modified LDH, and LDH nanocomposites for a range of biomedical applications. The advantages and disadvantages of LDH nanostructures and insights into the future development are also discussed.

Chlorins e6 loaded silica nanoparticles coated with gastric cancer cell membrane for tumor specific photodynamic therapy of gastric cancer

Background: Photodynamic therapy (PDT) is widely recognized as a promising way to cure cancer. However, the limited tumor homing property of currently available drug delivery systems (DDSs) is the bottleneck for the delivery of photodynamic agents. Purpose: In our study, we decorated silica nanoparticles (SLN) with cell membrane (CM) derived from SGC7901 cells to construct carrier (CM/SLN) which was able to to specifically target the homogenous SGC7901 cells. Materials and methods: Furthermore, the decent drug loading capability of CM/SLN was adopted to load photodynamic agent chlorins e6 (Ce6) to finally construct aDDS suitable for tumor-targeted PDT of gastric cancer. Results: The experimental results suggested that CM/SLN/Ce6 was nano-sized particles with good dispersion and stability in physiological conditions. Moreover, due to the modification of CM,CM/SLN/Ce6 could specifically target the homogenous SGC7901 cells both in vitro and in vivo. Most importantly, further in vivo results demonstrated that the CM/SLN/Ce6 showed a better anticancer outcome compared to SLN/Ce6. Conclusion: CM/SLN/Ce6 might be a promising platform for effective tumor targeted PDT of gastric cancer.

Synthesis of photo-excited Chlorin e6 conjugated silica nanoparticles for enhanced anti-bacterial efficiency to overcome methicillin-resistant Staphylococcus aureus

Nano photodynamic therapy to overcome multidrug resistant bacteria.

Marine natural pigments as potential sources for therapeutic applications

In recent years, marine natural pigments have emerged as a powerful alternative in the various fields of food, cosmetic, and pharmaceutical industries because of their excellent biocompatibility, bioavailability, safety, and stability. Marine organisms are recognized as a rich source of natural pigments such as chlorophylls, carotenoids, and phycobiliproteins. Numerous studies have shown that marine natural pigments have considerable medicinal potential and promising applications in human health. In this review, we summarize the marine natural pigments as potential sources for therapeutic applications, including: antioxidant, anticancer, antiangiogenic, anti-obesity, anti-inflammatory activities, drug delivery, photothermal therapy (PTT), photodynamic therapy (PDT), photoacoustic imaging (PAI), and wound healing. Marine natural pigments will offer a better platform for future theranostic applications.

A Novel Type of Aqueous Dispersible Ultrathin-Layered Double Hydroxide Nanosheets for in Vivo Bioimaging and Drug Delivery

Layered double hydroxide (LDH) nanoparticles have been widely used for various biomedical applications. However, because of the difficulty of surface functionalization of LDH nanoparticles, the systemic administration of these nanomaterials for in vivo therapy remains a bottleneck. In this work, we develop a novel type of aqueous dispersible two-dimensional ultrathin LDH nanosheets with a size of about 50 nm and a thickness of about 1.4 to 4 nm. We are able to covalently attach positively charged rhodamine B fluorescent molecules to the nanosheets, and the nanohybrid retains strong fluorescence in liquid and even dry powder form. Therefore, it is available for bioimaging. Beyond this, it is convenient to modify the nanosheets with neutral poly(ethylene glycol) (PEG), so the nanohybrid is suitable for drug delivery through systemic administration. Indeed, in the test of using these nanostructures for delivery of a negatively charged anticancer drug, methotrexate (MTX), in a mouse model, dramatically improved therapeutic efficacy is achieved, indicated by the effective inhibition of tumor growth. Furthermore, our systematic in vivo safety investigation including measuring body weight, determining biodistribution in major organs, hematology analysis, blood biochemical assay, and hematoxylin and eosin stain demonstrates that the new material is biocompatible. Overall, this work represents a major development in the path of modifying functional LDH nanomaterials for clinical applications.

MnAl Layered Double Hydroxide Nanoparticles as a Dual-Functional Platform for Magnetic Resonance Imaging and siRNA Delivery

Multifunctional nanoparticles for cancer theranosis have been widely explored for effective cancer detection and therapy. In this work, dually functionalised manganese-based layered double hydroxide nanoparticles (Mn-LDH) were examined as an effective anticancer drug/gene delivery system and for T₁ -weighted magnetic resonance imaging (MRI) in brain cancer theranostics. Such Mn-LDH have been shown to accommodate dsDNA/siRNAs and efficiently deliver them to Neuro-2a cells (N2a). Mn-LDH have also shown high biocompatibility with low cytotoxicity. Importantly, the cell-death siRNA (CD-siRNA) delivered with Mn-LDH more efficiently kills brain cancer cells than the free CD-siRNA. Moreover, Mn-LDH can act as excellent contrast agents for MRI, with an r₁ value of 4.47 mm^-1  s^-1 , which is even higher than that of commercial contrast agents based on Gd complexes (r₁ =3.4 mm^-1  s^-1 ). Altogether, the high delivery efficacy and MRI contrast capability make dual-functional Mn-LDH potential bimodal agents for simultaneous cancer diagnosis and therapy.

Luminescent CaTiO3:Yb,Er nanofibers co-conjugated with Rose Bengal and gold nanorods for potential synergistic photodynamic/photothermal therapy

CaTiO₃:Yb,Er nanofibers, co-conjugated with Rose Bengal and gold nanorods, enable a synergistic photodynamic/photothermal phenomenon for superior cancer cell killing effect.

Photophysics of chlorin e6: from one- and two-photon absorption to fluorescence and phosphorescence

Linear and non-linear optical properties of a known photosensitizer producing singlet oxygen, chlorin e6, have been studied, including dynamics effects.