Nanotechnology in dentistry: Present and future perspectives on dental nanomaterials

OBJECTIVES

The number of dental nanomaterials has increased significantly over the past years. A variety of commercial dental nanomaterials are available and researched. Nevertheless, how these nanomaterials work, what makes them special and whether they are superior to traditional dental materials is not always clear to dentists and researchers. The objective of this review paper is, therefore, to give an overview of the principles of nanomaterials and basic research and applications of dental nanomaterials.

METHODS

The fundamentals of materials science of nanomaterials as well as their advantages and disadvantages are elaborated. The most important dental nanomaterials are discussed. This is mainly based on a survey of the literature and a review of the most frequently cited scientific papers in the international peer reviewed journal Dental Materials over the past five years. The developments of commercial dental nanomaterials as well as aspects of their clinical use are considered in this review.

RESULTS

Nanomaterials have unique structures and properties that distinguish them from other materials. The journal Dental Materials is the journal with the highest numbers of articles and citations on the subject of dental nanomaterials. The most frequently reported dental nanomaterials are nanocomposites, nanoparticles, antimicrobial nanomaterials and bio-mineralization systems. Hallmarks of dental nanomaterials include a set of unique properties and challenges in the preparation of these materials.

SIGNIFICANCE

By understanding the physical principles of dental nanomaterials, their strengths, limitations and their specific benefits will be better appreciated. Dental nanomaterials have potential for the future but currently do not always exhibit superior properties, for example in clinical situations.

Multimodal Mesoporous Silica Nanocarriers for Dual Stimuli-Responsive Drug Release and Excellent Photothermal Ablation of Cancer Cells

Background

Core-shell types of mesoporous silica nanoparticles (MSNs) with multimodal functionalities were developed for bio-imaging, controlled drug release associated with external pH, and near-infrared radiation (NIR) stimuli, and targeted and effective chemo-photothermal therapeutics.

Materials and Methods

We synthesized and developed a core-shell type of mesoporous silica nanocarriers for fluorescent imaging, stimuli-responsive drug release, magnetic separation, antibody targeting, and chemo-photothermal therapeutics. Also, the biocompatibility, cellular uptake, cytotoxicity, and photothermal therapy on these FS3-based nanocarriers were systematically investigated.

Results

Magnetic mesoporous silica nanoparticles was prepared by coating a Fe₃O₄ core with a mesoporous silica shell, followed by grafting with fluorescent conjugates, so-called FS3. The resulting FM3 was preloaded with therapeutic cisplatin and coated with polydopamine layer, so-called FS3P/C. Eventually, graphene oxide-wrapped FS3P/C (FS3P-G/C) exhibited high sensitivity in the dual stimuli (pH, NIR)-responsive controlled release behavior. On the other hand, Au NPs-coated FS3P/C (FS3P-A/C) exhibited more stable release behavior, irrespective of pH changes, and exhibited much more enhanced release rate under the same NIR irradiation. Notably, FS3P-A/C showed strong NIR absorption, enabling photothermal destruction of HeLa cells by its chemo-photothermal therapeutic effects under NIR irradiation (808 nm, 1.5 W/cm²). The selective uptake of FS3-based nanocarriers was confirmed in cancer cell lines including HeLa (American Type Culture Collection - ATCC) and SHSY5Y (ATCC 2266) by the images obtained from confocal laser scanning microscopy, flow cytometry, and transmission electron microscopy instruments. Cisplatin-free FS3-based nanocarriers revealed good cellular uptake and low cytotoxicity against cancerous HeLa and SH-SY5Y cells, but showed no obvious toxicity to normal HEK293 (ATCC 1573) cell.

Conclusion

Along with the facile synthesis of FS3-based nanocarriers, the integration of all these strategies into one single unit will be a prospective candidate for biomedical applications, especially in chemo-photothermal therapeutics, targeted delivery, and stimuli-responsive controlled drug release against multiple cancer cell types.

Long-acting mucoadhesive thermogels for improving topical treatments of dry eye disease

Dry eye disease (DED) is the most common ocular disorder that causes persistent discomfort and blurry vision in patients. Despite pharmacotherapy strategies, the current topical administration of eye drops remains a great challenge owing to their low bioavailability and short residence time. Herein, we demonstrate an effective topical treatment of DED via rational design of a long-acting and mucoadhesive drug delivery system. Specifically, the drug carrier is a chemically ternary material system consisting of gelatin that serves as an enzyme-mediated degradable matrix, poly(N-isopropylacrylamide) as a thermo-responsive regulator, and lectin Helix pomatia agglutinin as a mucus-binding component. The long-acting drug release performance is exploited via initiator effects during the synthesis of the thermo-responsive polymer, while the mucoadhesive feature is inherited from the mucus-binding material. In a rabbit model of DED, a pharmacotherapy based on one-time topical administration of epigallocatechin gallate-loaded carrier onto the cul-de-sac could effectively repair the defective corneal epithelium via mitigating cellular inflammation, oxidative stress, and cell apoptosis for a sustained period over 14 days. These findings on the initiator and synergy effects in the development of the advanced ophthalmic formulation show great promise for efficient management of complex ocular diseases by a simple topical administration route.

Advancing the stimuli response of polymer-based drug delivery systems for ocular disease treatment

Recent exploitations of stimuli-responsive polymers as ophthalmic drug delivery systems for the treatment of eye diseases are summarized and discussed.

Atomistic insights into the adsorption and stimuli-responsive behavior of poly(N-isopropylacrylamide)-graphene hybrid systems

Non-covalent functionalization of graphene materials with responsive polymers is a promising approach for synthesizing new, hybrid composites with improved dispersibility and functional properties. However, the interplay between various components of the hybrid systems, their structural configurations, and stimuli-responsive behavior are not yet well understood at the atomic level. Here, we investigate the temperature-responsive behavior of physisorbed poly(N-isopropylacrylamide) (PNIPAM) on to graphene (G) and graphene oxide (GO) sheets in aqueous solution using large scale molecular dynamics simulations. It was observed that PNIPAM can be spontaneously anchored to the surfaces of both G and GO at 290 K with a macromolecular coil shape. However, the configuration of PNIPAM on G is markedly different in comparison with that on GO, leading to its distinct thermoresponsive behavior. Specifically, the adsorption on G gives rise to an increase in the temperature of the coil-to-globule transition when compared to the native polymer, the origin of which can be interpreted in terms of the interactions and the solvation behavior. The results obtained here are of significance to the design and manipulation of graphene-based stimuli-responsive hybrid systems with optimal functional properties.

Targeted and controlled drug delivery by multifunctional mesoporous silica nanoparticles with internal fluorescent conjugates and external polydopamine and graphene oxide layers

This study demonstrated the targeted delivery and controlled release of cisplatin drug molecules from doubly decorated mesoporous silica nanoparticles (MSNs), which were internally grafted with fluorescent conjugates and externally coated with polydopamine (PDA) and graphene oxide (GO) layers. The brush-like internal conjugates conferred fluorescent functionality and high capacity of cisplatin loading into MSNs, as well as contributing to a sustained release of the cisplatin through a porous channel with the assistance of external PDA layer. A consolidated double-layer formed by electrostatic interactions between the GO nanosheet and the PDA layer induced more controlled release kinetics which was well predicted by Higuchi model. In addition, Our MSNs exhibited stimuli (pH, NIR irradiation)-responsive controlled release as a potential chemo-photothermal agent against cancer cells. In a cell test, multifunctional MSNs showed a low toxicity itself, but gave a high cytotoxicity against human epithelial neuroblastoma cells (SH-SY5Y) after loading cisplatin. Notably, GO-wrapped MSNs exhibited very effective drug delivery because GO wrapping enhanced their dispensability in aqueous solution, photothermal heating effect, and efficient endocytosis into cells. Furthermore, monoclonal antibody (anti-human epidermal growth factor receptor)-conjugated MSNs showed a higher specificity, which resulted in more enhanced anticancer effects in vitro. The current study demonstrated a reliable synthesis of multifunctional MSNs, endowed with fluorescent imaging, stimuli-responsive controlled release, higher specificity, and efficient cytotoxicity toward cancer cells.

STATEMENT OF SIGNIFICANCE

The current study demonstrated the reliable synthesis of multifunctional mesoporous silica nanoparticles (MSNs) with internal fluorescent conjugates and external polydopamine and graphene oxide (GO) layers. The combination of internal conjugates and external coating layers produced an effective pore closure effect, leading to controlled and sustained release of small drug molecules. Notably, GO wrapping improved the dispensability and cellular uptake of the MSNs, as well as enhanced drug-controlled release. Our multifunctional MSNs revealed very efficient drug delivery effects against human epithelial neuroblastoma cells by demonstrating several strengths: i) fluorescent imaging, ii) sustained and controlled release of small drug molecules, iii) efficient cellular uptake, cytotoxicity and specificity, and v) stimuli (pH, NIR irradiation)-responsive controlled release as a potential chemo-photothermal agent.

Highly Controlled Diffusion Drug Release from Ureasil-Poly(ethylene oxide)-Na+-Montmorillonite Hybrid Hydrogel Nanocomposites

In this work, we report the effects of incorporation of variable amounts (1-20 wt %) of sodium montmorillonite (MMT) into a siloxane-poly(ethylene oxide) hybrid hydrogel prepared by the sol-gel route. The aim was to control the nanostructural features of the nanocomposite, improve the release profile of the sodium diclofenac (SDCF) drug, and optimize the swelling behavior of the hydrophilic matrix. The nanoscopic characteristics of the siloxane-cross-linked poly(ethylene oxide) network, the semicrystallinity of the hybrid, and the intercalated or exfoliated structure of the clay were investigated by X-ray diffraction, small-angle X-ray scattering, and differential scanning calorimetry. The correlation between the nanoscopic features of nanocomposites containing different amounts of MMT and the swelling behavior revealed the key role of exfoliated silicate in controlling the water uptake by means of a flow barrier effect. The release of the drug from the nanocomposite displayed a stepped pattern kinetically controlled by the diffusion of SDCF molecules through the mass transport barrier created by the exfoliated silicate. The sustained SDCF release provided by the hybrid hydrogel nanocomposite could be useful for the prolonged treatment of painful conditions, such as arthritis, sprains and strains, gout, migraine, and pain after surgical procedures.

Amphiphilic prodrug-decorated graphene oxide as a multi-functional drug delivery system for efficient cancer therapy

Graphene oxide (GO) has shown great potential in drug delivery. However, the aqueous stability, non-specific drug release and slow release rate are major problems of the GO-based drug delivery system. Herein, we for the first time integrate the dispersant, stabilizing agent and active targeting carrier into a novel drug delivery system based on GO/PP-SS-DOX nanohybrids. The redox-sensitive PP-SS-DOX prodrug was obtained by conjugating mPEG-PLGA (PP) with doxorubicin (DOX) via disulfide bond. PEG-FA provided active targeting property for the constructed drug delivery system, GO/PP-SS-DOX/PEG-FA. In this demonstrated system, PP-SS-DOX markedly increases the stability in physiological solutions of GO and guarantees the DOX release in the reductive environment (cancerous cells). And PEG-FA helps target to cancerous tissues and induces FR-mediated endocytosis. In vitro drug release exhibited the obvious reductive sensitivity and the cumulative release amount was up to 90%, while 40% in previous reports within 72 h. The in vitro cytotoxicity of targeting nanohybrids was significantly cytotoxic than that of non-targeting nanohybrids. In vivo results displayed that the as-prepared targeting nanohybrids showed efficacious antitumor effect while it had nearly no systemic adverse toxicity on B16 tumor-bearing mice. Therefore, the in vitro and in vivo results indicate that our constructed GO/PP-SS-DOX/PEG-FA drug delivery system is a promising carrier in cancer therapy.