Layered double hydroxide-based nanocomposite scaffolds in tissue engineering applications

Electrospun polycaprolactone coated with gum tragacanth containing layered double hydroxide/thymol nanohybrid for wound dressing application

Incorporating a nanohybrid containing a natural antibacterial agent into nanofibrous scaffolds can synergistically affect wound healing. In this study, polycaprolactone (PCL) nanofibrous membranes were fabricated via electrospinning. Gum-tragacanth (GT)-containing thymol (Thy)-loaded layered double hydroxide (LDH) nanohybrids were coated on the nanofiber surface, which provided a sustained thymol release. The LDH/Thy nanohybrids were prepared using a co-precipitation method. LDH/Thy was added to the GT solution at different concentrations (0, 0.1, 1, and 10 % w/v, followed by dip-coating onto PCL nanofiber surfaces. The nanofibers were characterized using scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and energy-dispersive X-ray spectroscopy (EDX). These mats were evaluated for their hydrophilicity, in vitro drug release, mechanical and antibacterial properties, cytocompatibility, cell attachment, and in vivo wound healing performance. Results demonstrated that the inclusion of LDH/Thy significantly improved the hydrophilicity. The mechanical study showed that adding LDH (10 %) nanoparticles to PCL/GT nanofibers increased tensile strength from 0.27 to 1.74 MPa, respectively. In addition, the PCL/GT/LDH/Thy nanofibers exhibited superior antibacterial activity against Escherichia coli (Gram-negative), Staphylococcus aureus (Gram-positive), and methicillin-resistant Staphylococcus aureus (MRSA), which correlated with the sustained release of thymol (78 % over 110 h). Moreover, after five days, the nanofibers showed no cytotoxic activity against the L929 mouse fibroblast cell line and provided an appropriate microenvironment for cell attachment. The animal study results revealed that the average wound healing rate of PCL/GT/LDH/Thy nanofibers significantly increased compared to the control group on the 10th day post-treatment (from 80.33 % to 48.5 %, respectively), along with improved wound closure quality. The synergistic effect of PCL/GT/LDH/Thy could provide helpful information and implications for promoting their application in wound dressings.

Colloidal ZnAl-Layered Double Hydroxide Nanomaterials for Effective Prevention of SARS-CoV-2

SARS-CoV-2 is a threat to global public health, which requires the development of safe measures to reduce the spread of this coronavirus. Herein, in this study, we prepared and examined potential antiviral agents based on ZnAl-layered double hydroxide (ZnAl-LDH) materials. ZnAl-LDH-based samples were synthesized via a one-pot low-temperature coprecipitation method, which features an ultrathin structure. The incorporation of trace amounts of Ag induces the formation of ZnO particles on the ZnAl-LDH surface, where both ZnO and Ag enhance UV light absorption. Interestingly, ZnAl-LDH-Ag shows a significantly high anticoronavirus effect upon exposure to the daylight lamp of the operation console and ultraviolet light. Moreover, ZnAl-LDH and ZnAl-LDH-Ag potently blocked the entry of SARS-CoV-2 pseudoparticles to cells. The in vivo biocompatibility experiment has demonstrated that ZnAl-LDH-Ag is a potentially biocompatible and potent anti-SARS-CoV-2 agent for virus prevention. The synergistic interactions between these nanoparticles continuously generate reactive oxygen species (ROS), leading to effective and sustained viral inactivation. This light-sensitive ROS production introduces a photocatalytic inactivation mechanism in antiviral materials. Moreover, unlike conventional antiviral agents that rapidly deplete their active components, the layered structure of this composite enables the controlled long-term release of antiviral radicals, enhancing its durability. ZnAl-LDH-Ag has been expected to be a promising solution for long-lasting antiviral applications.

Layered Double Hydroxides (LDH) as Delivery Vehicles of a Chimeric Protein Carrying Epitopes from the Porcine Reproductive and Respiratory Syndrome Virus

The Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) causes reproductive failure and respiratory symptoms, leading to huge economic losses for the pig farming industry. Although several vaccines against PRRSV are available in the market; they show an overall low efficacy, and several countries have the need for vaccines covering the local, circulating variants. This project aims at developing a new chimeric antigen targeting specific epitopes from PRRSV and evaluating two test adjuvants to formulate a vaccine candidate. The test antigen was called LTB-PRRSV, which was produced recombinantly in Escherichia coli and consisted of the heat labile enterotoxin B subunit from E. coli (LTB) and four epitopes from PRRSV. LTB-PRRSV was rescued as inclusion bodies and methods for its solubilization, IMAC-based purification, and refolding were standardized, leading to mean yields of 18 mg of pure protein per liter culture. Layered double hydroxides (LDH) have been used as vaccine adjuvants given their biocompatibility, low cost, and positive surface charge that allows an efficient adsorption of negatively charged biomolecules. Therefore, LDH were selected as delivery vehicles of LTB-PRRSV. Pure LTB-PRRSV was adsorbed onto LDH by incubation at different LDH:LTB-PRRSV mass ratios (1:0.25, 1:0.5, 1:1, and 1:2) and at pH 9.5. The best adsorption occurred with a 1:2 mass ratio, and in a sucrose-tween solution. The conjugates obtained had a polydispersity index of 0.26, a hydrodynamic diameter of 192 nm, and a final antigen concentration of 64.2 μg/mL. An immunogenicity assessment was performed by injecting mice with LDH:LTB-PRRSV, Alum/LTB-PRRSV, or LTB-PRRSV in a scheme comprising three immunizations at two-week intervals and two dose levels (1 and 5 μg). LTB-PRRSV was capable of inducing strong humoral responses, which lasted for a longer period when LDH was used as the delivery vehicle/adjuvant. The potential of LDH to serve as an attractive carrier for veterinary vaccines is discussed.

Recent progress in lactate oxidase-based drug delivery systems for enhanced cancer therapy

Lactate oxidase (LOX) is a natural enzyme that efficiently consumes lactate. In the presence of oxygen, LOX can catalyse the formation of pyruvate and hydrogen peroxide (H2O2) from lactate. This process led to acidity alleviation, hypoxia, and a further increase in oxidative stress, alleviating the immunosuppressive state of the tumour microenvironment (TME). However, the high cost of LOX preparation and purification, poor stability, and systemic toxicity limited its application in tumour therapy. Therefore, the rational application of drug delivery systems can protect LOX from the organism's environment and maintain its catalytic activity. This paper reviews various LOX-based drug-carrying systems, including inorganic nanocarriers, organic nanocarriers, and inorganic-organic hybrid nanocarriers, as well as other non-nanocarriers, which have been used for tumour therapy in recent years. In addition, this area's challenges and potential for the future are highlighted.

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.

3D Printing Drug-Free Scaffold with Triple-Effect Combination Induced by Copper-Doped Layered Double Hydroxides for the Treatment of Bone Defects

Tissue-engineered poly(l-lactide) (PLLA) scaffolds have been widely used to treat bone defects; however, poor biological activities have always been key challenges for its further application. To address this issue, introducing bioactive drugs or factors is the most commonly used method, but there are often many problems such as high cost, uncontrollable and monotonous drug activity, and poor bioavailability. Here, a drug-free 3D printing PLLA scaffold with a triple-effect combination induced by surface-modified copper-doped layered double hydroxides (Cu-LDHs) is proposed. In the early stage of scaffold implantation, Cu-LDHs exert a photothermal therapy (PTT) effect to generate high temperature to effectively prevent bacterial infection. In the later stage, Cu-LDHs can further have a mild hyperthermia (MHT) effect to stimulate angiogenesis and osteogenic differentiation, demonstrating excellent vascularization and osteogenic activity. More importantly, with the degradation of Cu-LDHs, the released Cu2+ and Mg2+ provide an ion microenvironment effect and further synergize with the MHT effect to stimulate angiogenesis and osteogenic differentiation, thus more effectively promoting the healing of bone tissue. This triple-effect combined scaffold exhibits outstanding antibacterial, osteogenic, and angiogenic activities, as well as the advantages of low cost, convenient procedure, and long-term efficacy, and is expected to provide a promising strategy for clinical repair of bone defects.

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.

In Situ Growth of Mg-Fe Layered Double Hydroxides (LDH) Film on Titanium Dental Implant Substrates for pH Regulation in Oral Environments

Layered double hydroxides (LDHs) consist of two-dimensional, positively charged lamellar structures with the ability to host various anions in the interlayer spaces, which grants them unique properties and tunable characteristics. LDHs, a class of versatile inorganic compounds, have recently emerged as promising candidates for enhancing osseointegration. A suitable alkaline microenvironment is thought to be beneficial for stimulating osteoblasts’ differentiation (responsible for bone matrix formation) while suppressing osteoclast generation (responsible for bone matrix disintegration). LDHs are prone to adjusting their alkalinity and thus offering us the chance to study how pH affects cellular behavior. LDHs can indeed modulate the local pH, inflammatory responses, and oxidative stress levels, factors that profoundly influence the behavior of osteogenic cells and their interactions with the implant surface. Herein, we deposited Mg–Fe LDH films on titanium substrates for dental implants. The modified Ti substrates was more alkaline in comparison to the bare ones, with a pH higher than 8 after hydrolysis in an aqueous environment.

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.

Optimization of methacrylated gelatin /layered double hydroxides nanocomposite cell-laden hydrogel bioinks with high printability for 3D extrusion bioprinting

Layered double hydroxides (LDHs) offer unique source of inspiration for design of bone mimetic biomaterials due to their superior mechanical properties, drug delivery capability and regulation cellular behaviors, particularly by divalent metal cations in their structure. Three-dimensional (3D) bioprinting of LDHs holds great promise as a novel strategy thanks to highly tunable physiochemical properties and shear-thinning ability of LDHs, which allow shape fidelity after deposition. Herein, we introduce a straightforward strategy for extrusion bioprinting of cell laden nanocomposite hydrogel bioink of gelatin methacryloyl (GelMA) biopolymer and LDHs nanoparticles. First, we synthesized LDHs by co-precipitation process and systematically examined the effect of LDHs addition on printing parameters such as printing pressure, extrusion rate, printing speed, and finally bioink printability in creating grid-like constructs. The developed hydrogel bioinks provided precise control over extrudability, extrusion uniformity, and structural integrity after deposition. Based on the printability and rheological analysis, the printability could be altered by controlling the concentration of LDHs, and printability was found to be ideal with the addition of 3 wt % LDHs. The addition of LDHs resulted in remarkably enhanced compressive strength from 652 kPa (G-LDH0) to 1168 kPa (G-LDH3). It was shown that the printed nanocomposite hydrogel scaffolds were able to support encapsulated osteoblast survival, spreading, and proliferation in the absence of any osteoinductive factors taking advantage of LDHs. In addition, cells encapsulated in G-LDH3 had a larger cell spreading area and higher cell aspect ratio than those encapsulated in G-LDH0. Altogether, the results demonstrated that the developed GelMA/LDHs nanocomposite hydrogel bioink revealed a high potential for extrusion bioprinting with high structural fidelity to fabricate implantable 3D hydrogel constructs for repair of bone defects.

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.

Surface modification of two-dimensional layered double hydroxide nanoparticles with biopolymers for biomedical applications

Layered double hydroxides (LDHs) are appealing nanomaterials for (bio)medical applications and their potential is threefold. One can gain advantage of the structure of LDH frame (i.e., layered morphology), anion exchanging property towards drugs with acidic character and tendency for facile surface modification with biopolymers. This review focuses on the third aspect, as it is necessary to evaluate the advantages of polymer adsorption on LDH surfaces. Beside the short discussion on fundamental and structural features of LDHs, LDH-biopolymer interactions will be classified in terms of the effect on the colloidal stability of the dispersions. Thereafter, an overview on the biocompatibility and biomedical applications of LDH-biopolymer composite materials will be given. Finally, the advances made in the field will be summarized and future research directions will be suggested.

Drug-Containing Layered Double Hydroxide/Alginate Dispersions for Tissue Engineering

Alginate (Alg) is increasingly studied as a constitutive material of scaffolds for tissue engineering because of its easy gelation and biocompatibility, and the incorporation of drugs into its formulation allows for its functionality to be extended. However, Alg presents a low cell adhesion and proliferation capacity, and the incorporation of drugs may further reduce its biocompatibility. Layered double hydroxides (LDH) are promising fillers for Alg-based biomaterials, as they increase cell adhesion and interaction and provide drug storage and controlled release. In this work, LDH containing ibuprofen or naproxen were synthesized by coprecipitation at a constant pH and their properties upon their incorporation in Alg dispersions (LDH-Drug/Alg) were explored. Drug release profiles in simulated body fluid and the proliferation of pre-osteoblastic MC3T3-E1 cells by LDH-Drug/Alg dispersions were then evaluated, leading to results that confirm their potential as biomaterials for tissue engineering. They showed a controlled release with diffusive control, modulated by the in-situ formation of an Alg hydrogel in the presence of Ca2+ ions. Additionally, LDH-Drug/Alg dispersions mitigated the cytotoxic effects of the pure drugs, especially in the case of markedly cytotoxic drugs such as naproxen.

Electrospun Nanofibrous Scaffolds of Polycaprolactone/Gelatin Reinforced with Layered Double Hydroxide Nanoclay for Nerve Tissue Engineering Applications

Nerve tissue engineering (NTE) is an effective approach for repairing damaged nerve tissue. In this regard, nanoparticle-incorporated electrospun scaffolds have aroused a great deal of interest in NTE applications. In this study, layered double hydroxide (LDH)-incorporated polycaprolactone (PCL)/gelatin (Gel) nanofibrous scaffolds were fabricated by an electrospinning technique. The physicochemical, mechanical, and biological properties of the scaffolds were examined. Also, the phase identification, morphology, and elemental composition were studied using X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy, respectively. The results revealed that the inclusion of LDH nanoparticles into the PCL/Gel scaffold has improved its mechanical strength and elongation at the break, while the degradation rate was enhanced in comparison with the pure PCL/Gel mat. The LDH-enriched electrospun PCL/Gel scaffolds exhibited a considerable impact on cell attachment and proliferation. The gene expression results showed that the neuron-specific (γγ) enolase (NSE) gene expression was significantly decreased in the scaffolds containing 1 and 10 wt % LDH compared to the scaffold without LDH, whereas in the scaffold with 0.1 wt % LDH, a slight increase in expression was observed. It can be deduced that electrospun PCL/Gel scaffolds containing LDH with optimum concentration can be a promising candidate for nerve tissue engineering applications.

The effect of LDHs nanoparticles on the cellular behavior of stem cell-laden 3D-bioprinted scaffold

Three-dimensional (3D)-bioprinting as an emerging approach for tissue engineering possesses the promise to create highly mimicked organs or tissues by using computer-aided design. For biomedical applications in tissue engineering in our previous work, we developed an optimized nanocomposite bioink based on methylacrylated gelatin (GelMA), methylacrylated chitosan (ChitMA), and double-layered hydroxide (LDHs) nanoparticles by using 3D-bioprinting technology. Herein, we used the previous formulation to fabricate human bone marrow mesenchymal stem cells (hBMMSCs)-laden nanocomposite bioinks. The effect of LDHs nanoparticles on the cellular behaviors of the encapsulated-hBMMSCs in the scaffolds was evaluated for the first time. Live/Dead, PrestoBlue, and DAPI/Actin analysis were carried out to assess the cell viability, proliferation rate, and cellular morphology of encapsulated hBMMSCs within the scaffolds. In addition, osteogenic differentiation studies were performed culturing the scaffolds for up to 21 days. Results show that LDHs nanoparticles in the GelMA/ChitMA scaffold formulation increased the viability of hBMMSCs, did not cause any adverse effect on the proliferation rate, cell morphology of the hBMMSCs, and increased the Runx2 protein expression of the encapsulated-hBMMSCs in the scaffolds. This study progresses the LDHs containing nanocomposite bioink for cell printing applications in tissue engineering.

Conventional and Recent Trends of Scaffolds Fabrication: A Superior Mode for Tissue Engineering

Tissue regeneration is an auto-healing mechanism, initiating immediately following tissue damage to restore normal tissue structure and function. This falls in line with survival instinct being the most dominant instinct for any living organism. Nevertheless, the process is slow and not feasible in all tissues, which led to the emergence of tissue engineering (TE). TE aims at replacing damaged tissues with new ones. To do so, either new tissue is being cultured in vitro and then implanted, or stimulants are implanted into the target site to enhance endogenous tissue formation. Whichever approach is used, a matrix is used to support tissue growth, known as ‘scaffold’. In this review, an overall look at scaffolds fabrication is discussed, starting with design considerations and different biomaterials used. Following, highlights of conventional and advanced fabrication techniques are attentively presented. The future of scaffolds in TE is ever promising, with the likes of nanotechnology being investigated for scaffold integration. The constant evolvement of organoids and biofluidics with the eventual inclusion of organ-on-a-chip in TE has shown a promising prospect of what the technology might lead to. Perhaps the closest technology to market is 4D scaffolds following the successful implementation of 4D printing in other fields.

Conventional and Recent Trends of Scaffolds Fabrication: A Superior Mode for Tissue Engineering

Tissue regeneration is an auto-healing mechanism, initiating immediately following tissue damage to restore normal tissue structure and function. This falls in line with survival instinct being the most dominant instinct for any living organism. Nevertheless, the process is slow and not feasible in all tissues, which led to the emergence of tissue engineering (TE). TE aims at replacing damaged tissues with new ones. To do so, either new tissue is being cultured in vitro and then implanted, or stimulants are implanted into the target site to enhance endogenous tissue formation. Whichever approach is used, a matrix is used to support tissue growth, known as 'scaffold'. In this review, an overall look at scaffolds fabrication is discussed, starting with design considerations and different biomaterials used. Following, highlights of conventional and advanced fabrication techniques are attentively presented. The future of scaffolds in TE is ever promising, with the likes of nanotechnology being investigated for scaffold integration. The constant evolvement of organoids and biofluidics with the eventual inclusion of organ-on-a-chip in TE has shown a promising prospect of what the technology might lead to. Perhaps the closest technology to market is 4D scaffolds following the successful implementation of 4D printing in other fields.