Enhancing Tumor Accumulation and Cellular Uptake of Layered Double Hydroxide Nanoparticles by Coating/Detaching pH-Triggered Charge-Convertible Polymers

Layered Double Hydroxides: Recent Progress and Promising Perspectives Toward Biomedical Applications

Layered double hydroxides (LDHs) have been widely studied for biomedical applications due to their excellent properties, such as good biocompatibility, degradability, interlayer ion exchangeability, high loading capacity, pH-responsive release, and large specific surface area. Furthermore, the flexibility in the structural composition and ease of surface modification of LDHs makes it possible to develop specifically functionalized LDHs to meet the needs of different applications. In this review, the recent advances of LDHs for biomedical applications, which include LDH-based drug delivery systems, LDHs for cancer diagnosis and therapy, tissue engineering, coatings, functional membranes, and biosensors, are comprehensively discussed. From these various biomedical research fields, it can be seen that there is great potential and possibility for the use of LDHs in biomedical applications. However, at the same time, it must be recognized that the actual clinical translation of LDHs is still very limited. Therefore, the current limitations of related research on LDHs are discussed by combining limited examples of actual clinical translation with requirements for clinical translation of biomaterials. Finally, an outlook on future research related to LDHs is provided.

Layered double hydroxides and their tailored hybrids/composites: Progressive trends for delivery of natural/synthetic-drug/cosmetic biomolecules

Layered double hydroxides (LDHs) are well-known and important class of hydrotalcite-type anionic clays (HTs) materials that are cost-effective with additional advantages of facile synthesis, composition, tenability, and reusability. These convincing characteristics are liable for their applications in various fields related to energy, environment, catalysis, biomedical, and biotechnology. HTs/LDHs are generally synthesized from low cost abundantly available chemical precursors through the aqueous synthetic pathways under mild reaction conditions. These materials can be termed green materials based on their non-toxic nature, availability of precursors, facile and low-cost production using aqueous medium conditions with less hazardous effluents. Diverse and fascinating characteristics have been attributed to HTs/LDHs like anion exchange ability, surface basicity, biocompatibility, controlled release of the anion specific area, porosity, easy surface modification, and pH dependent biodegradability. Hence, HTs/LDHs and their modified and/or functionalized nanohybrids/nanocomposites are reported as the potential drug delivery carriers with a capability to stabilize the susceptible bioactive molecules, may enhance the solubility of poorly soluble drugs along with controlled drug/bioactive molecule release and delivery. These clay and bioactive hybrid materials have good biocompatibility, less cytotoxicity, and better site-targeting with improved cellular uptake than that of free parent biomolecules. These lamellar solids of micro/nanostructure are compatible, host-guest materials and able to fabricate with drugs/cosmeceutical/bio- or synthetic polymers without any change in their molecular structure and reactivity along with improvement in their stabilities. Other important features are facile synthesis, basicity, high stability with easy storage, and efficient administration with low bio-toxicity. This study enlightens the applications of HTs/LDHs along with their hybrids/composites in the field of drug/cosmeceutical/gene delivery systems of natural/synthetic biomolecules.

Multifunctional Layered Double Hydroxides for Drug Delivery and Imaging

Two-dimensional nanomaterials, particularly layered double hydroxides (LDHs), have been widely applied in the biomedical field owing to their biocompatibility, biodegradability, controllable drug release/loading ability, and enhanced cellular permeability. Since the first study analyzing intercalative LDHs in 1999, numerous studies have investigated their biomedical applications, including drug delivery and imaging; recent research has focused on the design and development of multifunctional LDHs. This review summarizes the synthetic strategies and in-vivo and in-vitro therapeutic actions and targeting properties of single-function LDH-based nanohybrids and recently reported (from 2019 to 2023) multifunctional systems developed for drug delivery and/or bio-imaging.

State-of-the-art advancement of surface functionalized layered double hydroxides for cell-specific targeting of therapeutics

Over the years, layered double hydroxides (LDHs) hold a specific position in biomedicine due to their tunable chemical composition and appropriate structural properties. However, LDHs lack adequate sensitivity for active targeting because of less active surface area and low mechanical strength in physiological conditions. The exploitation of eco-friendly materials, such as chitosan (CS), for surface engineering of LDHs, whose payloads are transferred only under certain conditions, can help develop stimuli-responsive materials owing to high biosafety and unique mechanical strength. We aim to render a well-oriented scenario toward the latest achievements of a bottom-up technology relying on the surface functionalization of LDHs to fabricate functional formulations with promoted bio-functionality and high encapsulation efficiency for various bioactives. Many efforts have been devoted to critical aspects of LDHs, including systemic biosafety and the suitability for developing multicomponent systems via integration with therapeutic modalities, which are thoroughly discussed herein. In addition, a comprehensive discussion was provided for the recent progress in the emergence of CS-coated LDHs. Finally, the challenges and future perspectives in the fabrication of efficient CS-LDHs in biomedicine are considered, with a special focus on cancer treatment.

Biomaterials Based on Organic Polymers and Layered Double Hydroxides Nanocomposites: Drug Delivery and Tissue Engineering

The development of biomaterials has a substantial role in pharmaceutical and medical strategies for the enhancement of life quality. This review work focused on versatile biomaterials based on nanocomposites comprising organic polymers and a class of layered inorganic nanoparticles, aiming for drug delivery (oral, transdermal, and ocular delivery) and tissue engineering (skin and bone therapies). Layered double hydroxides (LDHs) are 2D nanomaterials that can intercalate anionic bioactive species between the layers. The layers can hold metal cations that confer intrinsic biological activity to LDHs as well as biocompatibility. The intercalation of bioactive species between the layers allows the formation of drug delivery systems with elevated loading capacity and modified release profiles promoted by ion exchange and/or solubilization. The capacity of tissue integration, antigenicity, and stimulation of collagen formation, among other beneficial characteristics of LDH, have been observed by in vivo assays. The association between the properties of biocompatible polymers and LDH-drug nanohybrids produces multifunctional nanocomposites compatible with living matter. Such nanocomposites are stimuli-responsive, show appropriate mechanical properties, and can be prepared by creative methods that allow a fine-tuning of drug release. They are processed in the end form of films, beads, gels, monoliths etc., to reach orientated therapeutic applications. Several studies attest to the higher performance of polymer/LDH-drug nanocomposite compared to the LDH-drug hybrid or the free drug.

Nanoformulation of Paclitaxel: Exploring the Cyclodextrin / PLGA Nano Delivery Carrier to Slow Down Paclitaxel Release, Enhance Accumulation in Vivo

Background: Improving the aggregation and penetration in tumor sites increases the anti-tumor efficacy of nanomedicine. In the current study, we designed cyclodextrin modified PLGA nanoparticles loaded with paclitaxel to elevate the accumulation and prolong circulation of chemotherapy drugs in vivo. Methods: The PLGA nanoparticles loaded with paclitaxel (PTX PLGA NPs) and cyclodextrin (CD) modified PLGA nanoparticles loaded with paclitaxel (PTX PLGA/CD NPs) were prepared using the emulsification solvent evaporation method. The nanoparticles were characterized by particle size, zeta potential, encapsulation efficiency, infrared spectroscopy analysis and X-Ray diffraction (XRD). Then, drug release of the nanoparticles was evaluated via reverse dialysis method in vitro. Finally, the in vivo distribution fate and pharmacokinetic characteristics of the nanoparticles were assessed in mice and rats. Results: The average particle size, zeta potential, and encapsulation efficiency of PTX PLGA NPs were (163.57±2.07) nm, - (20.53±2.79) mV and (60.44±6.80)%. The average particle size, zeta potential, and encapsulation efficiency of PTX PLGA/CD NPs were (148.57±1.66) nm, - (11.42±0.84) mV and (85.70±2.06)%. In vitro release studies showed that PTX PLGA/CD NPs were released more slowly compared to PTX PLGA NPs under normal blood pH conditions, while PTX PLGA/CD NPs were released more completely under tumor site pH conditions. The modified PLGA nanocarrier (PLGA/CD NPs) increased drug residence time and accumulation than the plain PLGA nanocarrier (PLGA NPs) in vivo distribution. In addition, the elimination half-life, area under the drug-time curve, and maximum blood concentration of the nanoparticle group were higher than those of Taxol^®, especially the PTX PLGA/CD NPs group, which was significantly different from Taxol^® and plain nanoparticle groups (p<0.001). Conclusions: The 2-HP-β-CD modified PLGA nanoparticles prolonged circulation time and accumulation of the chemotherapy drug paclitaxel in vivo.

O2-Supplying Nanozymes Alleviate Hypoxia and Deplete Lactate to Eliminate Tumors and Activate Antitumor Immunity

Direct hypoxia alleviation and lactate depletion in the tumor microenvironment (TME) are promising for effective cancer therapy but still very challenging. To address this challenge, the current research directly reshapes the TME for inhibiting tumor growth and activating the antitumor immunity using a drug-free nanozyme. Herein, the acid-sensitive nanozymes were constructed based on peroxidized layered double hydroxide nanoparticles for O₂ self-supply and self-boosted lactate depletion. The coloading of partially cross-linked catalase and lactate oxidase enabled the acid-sensitive nanozymes to promote three reactions, that is, (1) H₂O₂ generation from MgO₂ hydrolysis (30% at pH 7.4 vs 63% at pH 6.0 in 8 h); (2) O₂ generation from H₂O₂ (12% at pH 7.4 vs 21% at pH 6.0 in 2 h); and (3) lactate depletion by in situ generated O₂ (50% under hypoxia vs 75% under normoxia in 24 h in vitro) in parallel or tandem. These promoted reactions together efficiently induced colon cancer cell apoptosis under the hypoxic conditions, significantly inhibited tumor growth (>95%), and suppressed distant tumor growth upon seven administrations in every 3 days and moreover transformed the immunosuppressive tumor into "hot" one in the colon tumor-bearing mouse model. This is the first example for a nanozyme that supplies sufficient O₂ for hypoxia relief and lactate depletion, thus providing a new insight into drug-free nanomaterial-mediated TME-targeted cancer therapy.

Multifunctional green synthesized Cu-Al layered double hydroxide (LDH) nanoparticles: anti-cancer and antibacterial activities

Doxorubicin (DOX) is a potent anti-cancer agent and there have been attempts in developing nanostructures for its delivery to tumor cells. The nanoparticles promote cytotoxicity of DOX against tumor cells and in turn, they reduce adverse impacts on normal cells. The safety profile of nanostructures is an important topic and recently, the green synthesis of nanoparticles has obtained much attention for the preparation of biocompatible carriers. In the present study, we prepared layered double hydroxide (LDH) nanostructures for doxorubicin (DOX) delivery. The Cu–Al LDH nanoparticles were synthesized by combining Cu(NO₃)₂·3H₂O and Al(NO₃)₃·9H₂O, and then, autoclave at 110. The green modification of LDH nanoparticles with Plantago ovata (PO) was performed and finally, DOX was loaded onto nanostructures. The FTIR, XRD, and FESEM were employed for the characterization of LDH nanoparticles, confirming their proper synthesis. The drug release study revealed the pH-sensitive release of DOX (highest release at pH 5.5) and prolonged DOX release due to PO modification. Furthermore, MTT assay revealed improved biocompatibility of Cu–Al LDH nanostructures upon PO modification and showed controlled and low cytotoxicity towards a wide range of cell lines. The CLSM demonstrated cellular uptake of nanoparticles, both in the HEK-293 and MCF-7 cell lines; however, the results were showed promising cellular internalizations to the HEK-293 rather than MCF-7 cells. The in vivo experiment highlighted the normal histopathological structure of kidneys and no side effects of nanoparticles, further confirming their safety profile and potential as promising nano-scale delivery systems. Finally, antibacterial test revealed toxicity of PO-modified Cu–Al LDH nanoparticles against Gram-positive and -negative bacteria.

Layered Double Hydroxide Modified with Deoxycholic and Hyaluronic Acids for Efficient Oral Insulin Absorption

Introduction

This study aimed to construct a layered double hydroxide (LDH) nanoparticle delivery system that was modified by deoxycholic acid (DCA) and hyaluronic acid (HA) to increase the bioavailability of oral insulin.

Methods

LDH-DCA-HA was synthesized by the hybridization of DCA and HA with LDH. Subsequently, insulin was loaded onto LDH-DCA-HA, resulting in the formation of INS@LDH-DCA-HA. The in vivo and in vitro mechanisms of insulin release, as well as the efficiency of insulin absorption, were analyzed before and after DCA-HA modification.

Results

MTT assay showed that there was satisfactory biocompatibility between LDH-DCA-HA and Caco-2 cells at a concentration below 1000 μg/mL. Flow cytometry analysis revealed that Caco-2 cells absorbed INS@LDH-DCA-HA more readily than insulin. Measurement of transepithelial electrical resistance indicated that INS@LDH-DCA-HA induced the reversible opening of tight cell junctions, thereby facilitating its absorption. This was confirmed via laser confocal microscopy analysis, revealing that a large amount of zonula occludens-1 tight junction (TJ) protein was utilized for the paracellular pathway of nanoparticles. We also measured the blood glucose levels of type I diabetic mice and found that oral INS@LDH-DCA-HA exerted a steady hypoglycemic effect lasting 12 h, with a small range of postprandial blood glucose fluctuation. Immunofluorescence analysis showed that the strong penetration ability of INS@LDH-DCA-HA allowed insulin to enter epithelial cells more readily than free insulin. Finally, immunohistochemical analysis of anti-SLC10A1 protein confirmed that the cholic acid transporter receptor protein played a key role in the functioning of INS@LDH-DCA-HA.

Conclusion

LDH nanoparticles modified by DCA and HA improved the absorption efficiency of insulin by opening the TJs of cells and interacting with the cholic acid transporter receptor protein.

Hierarchical Two-Dimensional Layered Double Hydroxide Coated Polydopamine Nanocarriers for Combined Chemodynamic and Photothermal Tumor Therapy

The combination of chemodynamic therapy (CDT) and photothermal therapy (PTT) has proven to be successful in combating the challenges associated with cancer therapy. A combination of these therapies can maximize the benefits of each therapeutic modality through endogenous reduction-oxidation (redox) reaction and external laser power induction. In the current work, we have designed a copper-aluminum layered double hydroxide (CuAl-LDH) loaded doxorubicin (DOX) by a co-precipitation method; the surface was coated with polydopamine (PDA). The synthesized CuAl-LDH@DOX@PDA nanocarrier (NC) served as a Fenton-like catalyst with photothermal properties. It is well known that metal ion incorporated NCs can induce intracellular depletion of reduced glutathione (GSH) levels along with the reduction of Cu2+ to Cu+. The Cu+ ions in turn react with DOX leading to the generation of intracellular hydrogen peroxide (H2O2) molecules to produce the highly toxic hydroxyl radicals (•OH) through a Fenton-like reaction. The enhanced absorption of CuAl@DOX@PDA at 810 nm, greatly improved the photothermal efficiency in comparison with bare CuAl-LDH and CuAl-LDH@DOX. In vitro studies revealed the tremendous CDT/PTT efficacy of CuAl@DOX@PDA in suppressing A549 cancer cells. Furthermore, reactive oxygen species (ROS) assays and intracellular levels of various ROS cascade biomolecules support our findings in the efficient destruction of cancer cells through synergistic CDT/PTT therapy.