Nanogels of carboxymethyl chitosan and lysozyme encapsulated amorphous calcium phosphate to occlude dentinal tubules

Nano-CT characterization of dentinal tubule occlusion in SDF-treated dentin

Dentin hypersensitivity is an oral health concern affecting a large percentage of the world's adult population. Occlusion of the exposed dentinal tubules is among the treatment options available, and silver diammine fluoride (SDF) is an occluding agent used for interrupting or dampening the stimulus of the dental pulp nerves that produce pain. In addition to dentin permeability testing, the evaluation of desensitizing agents occluding dentinal tubules strongly relies on microscopic techniques, such as scanning electron microscopy (SEM). Limitations of SEM are that it provides only surface images that lack detailed information on the depth of penetration and amount of material present within the treated specimen, and it is prone to sample preparation artifacts. Here, we present high-resolution X-ray computed tomography (nano-CT) as a potential method for investigating dentin specimens with occluded tubules. We studied human dentin treated with SDF as an exemplary dentinal occlusion treatment option. We evaluated the silver deposits formed on the dentin surface region near the dentinal tubules and in the tubular regions using cross-section SEM, Energy Dispersive X-ray (EDX) analysis, and nano-CT. The resulting images obtained by SEM and nano-CT had comparable resolutions, and both techniques produced images of the tubules' occlusion. Nano-CT provided three-dimensional images adequate to quantitate tubule size and orientation in space. Moreover, it enabled clear visualization of dentinal tubules in any virtual plane and estimation of the amount and depth of occluding material. Thus, nano-CT has the potential to be a valuable technique for evaluating the occluding effects of virtually any material applied to dentinal tubules, supporting deciding between the best occluding treatment options.

Biomineralization-Inspired Anti-Caries Strategy Based on Multifunctional Nanogels as Mineral Feedstock Carriers

Background

Dentin caries remains a significant public concern, with no clinically viable material that effectively combines remineralization and antimicrobial properties. To address this issue, this study focused on the development of a bio-inspired multifunctional nanogel with both antibacterial and biomineralization properties.

Methods

First, p(NIPAm-co-DMC) (PNPDC) copolymers were synthesized from N-isopropylacrylamide (NIPAm) and 2-methacryloyloxyethyl-trimethyl ammonium chloride (DMC). Subsequently, PNPDC was combined with γ-polyglutamic acid (γ-PGA) through physical cross-linking to form nanogels. These nanogels served as templates for the mineralization of calcium phosphate (Cap), resulting in Cap-loaded PNPDC/PGA nanogels. The nanogels were characterized using various techniques, including TEM, particle tracking analysis, XRD, and FTIR. The release properties of ions were also assessed. In addition, the antibacterial properties of the Cap-loaded PNPDC/PGA nanogels were evaluated using the broth microdilution method and a biofilm formation assay. The remineralization effects were examined on both demineralized dentin and type I collagen in vitro.

Results

PNPDC/PGA nanogels were successfully synthesized and loaded with Cap. The diameter of the Cap-loaded PNPDC/PGA nanogels was measured as 196.5 nm at 25°C and 162.3 nm at 37°C. These Cap-loaded nanogels released Ca2+ and PO43- ions quickly, effectively blocking dental tubules with a depth of 10 μm and promoting the remineralization of demineralized dentin within 7 days. Additionally, they facilitated the heavy intrafibrillar mineralization of type I collagen within 3 days. Moreover, the Cap-loaded nanogels exhibited MIC50 and MIC90 values of 12.5 and 50 mg/mL against Streptococcus mutans, respectively, with an MBC value of 100 mg/mL. At a concentration of 50 mg/mL, the Cap-loaded nanogels also demonstrated potent inhibitory effects on biofilm formation by Streptococcus mutans while maintaining good biocompatibility.

Conclusion

Cap-loaded PNPDC/PGA nanogels are a multifunctional biomimetic system with antibacterial and dentin remineralization effects. This strategy of using antibacterial nanogels as mineral feedstock carriers offered fresh insight into the clinical management of caries.

Mineralization promotion and protection effect of carboxymethyl chitosan biomodification in biomimetic mineralization

Biomimetic mineralization emphasizes reversing the process of dental caries through bio-inspired strategies, in which mineralization promotion and collagen protection are equally important. In this study, carboxymethyl chitosan (CMC) was deemed as an analog of glycosaminoglycan for biomimetic modification of collagen, both of the mineralization facilitation and collagen protection effect were evaluated. Experiments were carried out simultaneously on two-dimensional monolayer reconstituted collagen model, three-dimensional reconstituted collagen model and demineralized dentin model. In three models, CMC was successfully cross-linked onto collagen utilizing biocompatible 1-Ethyl-3(3-dimethylaminopropyl) carbodiimide hydrochloride and N-hydroxy sulfosuccinimide sodium salt to achieve biomodification. Results showed that CMC biomodification increased collagen's hydrophilicity, calcium absorption capacity and thermal degradation resistance. In demineralized dentin model, the activity of endogenous matrix metalloproteinases was significantly inhibited by CMC biomodification. Furthermore, CMC biomodification significantly improved cross-linking and intrafibrillar mineralization of collagen, especially in the two-dimensional monolayer reconstituted collagen model. This study provided a biomimetic mineralization strategy with comprehensive consideration of collagen protection, and enriched the application of chitosan-based materials in dentistry.

Insights into electrospun pullulan-carboxymethyl chitosan/PEO core-shell nanofibers loaded with nanogels for food antibacterial packaging

Nisin, a natural substance from Lactococcus lactis, displays a promising antibacterial ability against the gram-positive bacteria. However, it is susceptible to the external environment, i.e. temperature, pH, and food composition. In this study, a dual stabilization method, coaxial electrospinning, was applied to protect nisin in food packaging materials and the effect of nisin concentration on the properties of the nanofibers was investigated. The core-shell nanofibers with pullulan as a core layer and carboxymethyl chitosan (CMCS)/polyethylene oxide (PEO) as shell layer were prepared, and then the prepared CMCS-nisin nanogels (CNNGs) using a self-assembly method were loaded into the core layer of the nanofibers as antibacterial agents. The result revealed that the smooth surface can be observed on the nanofibers by microstructure characterization. The CNNGs-loaded nanofibers exhibited enhanced thermal stability and mechanical strength, as well as excellent antibacterial activity. Importantly, the as-formed nanofibers were applied to preserve bass fish and found that the shelf life of bass fish packed by CNNGSs with nisin at a concentration of 8 mg/mL was effectively extended from 9 days to 15 days. Taken together, the CNNGs can be well stabilized with the core-shell nanofibers, thus exerting significantly improved antimicrobial stability and bioactivity. This special structure exerts a great potential for application as food packaging materials to preserve aquatic products.

Evaluation of structural integrity effect on adhesion strength of root dentin with a multi-functional irrigation strategy

OBJECTIVES

To evaluate effects of a novel auxiliary irrigation strategy, proanthocyanidin (PA) + carboxymethyl chitosan/amorphous calcium phosphate (CMC/ACP) nanocomplexes, on maintaining the organic-inorganic structural integrity and hence optimizing the adhesion strength of root dentin.

MATERIALS AND METHODS

Dentin specimens (n = 150) were prepared and subjected to the classical irrigating strategy with or without PA and CMC/ACP. The ultrastructure and biomechanical behaviour of dentin were characterized by scanning electron microscopy and atomic force microscope, respectively. Forty single root-canal premolars were employed for push-out bond strength testing. Besides, the antibacterial effects against Enterococcus faecalis were evaluated with confocal laser scanning microscopy. Statistical differences were verified with one-way ANOVA and Tukey's post-tests.

RESULTS

The organic-inorganic structural integrity of root dentin was repaired with the synergetic use of PA and CMC/ACP. Correspondingly, the bond stability between the root canal wall and the AH-Plus sealer was significantly reinforced (P < 0.05). Meanwhile, the tissue biomechanical properties and antibacterial behaviour were enhanced compared to that of control group (P < 0.05).

CONCLUSIONS

The synergistic utilization of PA and CMC/ACP can preserve the structural integrity of root dentin, contributing to optimizing the sealing effects of root canal. Moreover, the novel irrigation strategy demonstrated a favourable antimicrobial activity.

CLINICAL RELEVANCE

The combination of PA and CMC/ACP can serve as a promising auxiliary irrigation strategy to optimize the outcomes of chemical preparation, enhance the sealing effects of root canal and hence improve the success rate of treatment.

Effects of immunoglobulin Y-loaded amorphous calcium phosphate on dentinal tubules occlusion and antibacterial activity

Aim: This study aimed to evaluate the effects of immunoglobulin Y (IgY)-loaded amorphous calcium phosphate (ACP) (IgY@ACP) on dentinal tubule occlusion and antibacterial activity.

Methodology: IgY@ACP was synthesized based on a biomimetic mineralization strategy. The structure was examined by transmission electron microscopy and Fourier transform infrared spectroscopy. The IgY release property was assessed in vitro. The cell biocompatibility of IgY@ACP was evaluated by CCK-8. The dentin disks were prepared using healthy human molars, and their dentinal tubules were exposed to EDTA. Subsequently, they were randomly selected and treated with or without IgY@ACP for 7 days. The tubule occlusion morphologies and newly formed layers were observed by scanning electron microscopy (SEM) and x-ray diffraction, respectively. To evaluate the acid resistance and abrasion resistance of IgY@ACP, dentin disks that were treated for 1 day were immersed in acid solution or subjected to a toothbrush. The antibacterial effects against Streptococcus mutans (S. mutans) were evaluated by colony-forming unit (CFU) counting, adhesion property assessment, and crystal violet and live/dead bacterial staining. Finally, the occlusion effect was evaluated in rat incisors in vivo. One-way analysis of variance (ANOVA) was performed for statistical analysis. The level of significance was set at 0.05.

Results: IgY@ACP presented an amorphous phase with a nanosize (60–80 nm) and sustained release of protein within 48 h. The CCK-8 results showed that IgY@ACP had good biocompatibility. After treatment with IgY@ACP for 1 day, the majority of dentinal tubules were occluded by a 0.3-μm-thick mineralized layer. Seven days later, all dentinal tubules were occluded by mineralization with a thickness of 1.4 μm and a depth of 16 μm. The newly mineralized layer showed hydroxyapatite-like diffraction peaks. In addition, IgY@ACP had good acid and abrasion resistance. After treatment with IgY@ACP, the CFU counting and adhesion rate of S. mutans were significantly reduced, the crystal violet staining was lighter, and the S. mutans staining revealed more dead cells. Most importantly, IgY@ACP had a certain occluding property in rat incisors in vivo.

Conclusion: IgY@ACP can effectively occlude dentinal tubules with acid-resistant stability and has prominent anti-S. mutans effects, rendering it a potentially suitable desensitization material in the clinic.

Silk Sericin Enrichment through Electrodeposition and Carbonous Materials for the Removal of Methylene Blue from Aqueous Solution

The recycling and reuse of biomass waste for the preparation of carbon-based adsorbents is a sustainable development strategy that has a positive environmental impact. It is well known that a large amount of silk sericin (SS) is dissolved in the wastewater from the silk industry. Utilizing the SS instead of discharging it into the environment without further treatment would reduce environmental and ecological problems. However, effective enrichment of the SS from the aqueous solution is a challenge. Here, with the help of carboxymethyl chitosan (CMCS), which can form a gel structure under low voltage, an SS/CMCS hydrogel with SS as the major component was prepared via electrodeposition at a 3 V direct-current (DC) voltage for five minutes. Following a carbonization process, an SS-based adsorbent with good performance for the removal of methylene blue (MB) from an aqueous solution was prepared. Our results reveal that the SS/CMCS hydrogel maintains a porous architecture before and after carbonization. Such structure provides abundant adsorption sites facilitating the adsorption of MB molecules, with a maximum adsorptive capacity of 231.79 mg/g. In addition, it suggests that the adsorption is an exothermic process, has a good fit with the Langmuir model, and follows the intra-particle diffusion model. The presented work provides an economical and feasible path for the treatment of wastewater from dyeing and printing.

Biomimetic mineralisation systems for in situ enamel restoration inspired by amelogenesis

Caries and dental erosion are common oral diseases. Traditional treatments involve the mechanical removal of decay and filling but these methods are not suitable for cases involving large-scale enamel erosion, such as hypoplasia. To develop a noninvasive treatment, promoting remineralisation in the early stage of caries is of considerable clinical significance. Therefore, biomimetic mineralisation is an ideal approach for restoring enamel. Biomimetic mineralisation forms a new mineral layer that is tightly attached to the surface of the enamel. This review details the state-of-art achievements on the application of amelogenin and non-amelogenin, amorphous calcium phosphate, ions flow and other techniques in the biomimetic mineralisation of enamel. The ultimate goal of this review was to shed light on the requirements for enamel biomineralisation. Hence, herein, we summarise two strategies of biological minimisation systems for in situ enamel restoration inspired by amelogenesis that have been developed in recent years and compare their advantages and disadvantages.

The dual anti-caries effect of carboxymethyl chitosan nanogel loaded with chimeric lysin ClyR and amorphous calcium phosphate

In this study, we evaluated the anti-biofilm and anti-demineralization abilities of a novel material, CMC-ClyR-ACP nanogel, designed by loading the chimeric lysin ClyR and amorphous calcium phosphate (ACP) into a nanocarrier material carboxymethyl chitosan (CMC), in a demineralization model. Dynamic light scattering, transmission electron microscopy, and Fourier transmission infrared spectroscopy showed that CMC-ClyR-ACP nanogel was synthesized successfully. Enamel samples prepared from premolars were divided into five groups according to their treatments with: (i) double distilled water ddH₂ O, (ii) CMC-ACP, (iii) CMC-ClyR-ACP, (iv) ClyR, or (v) 0.12% chlorhexidine. Streptococcus mutans was allowed to form biofilms on the teeth for two days before treatment procedures were carried out from day 3 to day 6. The relative biofilm viability analyzed by Cell Counting Kit-8 showed that it was significantly lower (at 55.7%) for CMC-ClyR-ACP than seen for ddH₂ O (89.9%), which was consistent with result of confocal laser scanning microscopy. The percentage surface hardness loss of CMC-ClyR-ACP (29.2%) was significantly lower than that of CMC-ACP (51.0%) and ClyR (58.7%) alone, and there was no significant difference between CMC-ClyR-ACP and chlorhexidine (26.9%), which was confirmed by scanning electron microscopy. Therefore, CMC-ClyR-ACP nanogel may be an effective strategy for the control of enamel demineralization.

Building an aprismatic enamel-like layer on a demineralized enamel surface by using carboxymethyl chitosan and lysozyme-encapsulated amorphous calcium phosphate nanogels

OBJECTIVES

The purpose of this study was to prepare carboxymethyl chitosan (CMC) and lysozyme nanogels that could encapsulate amorphous calcium phosphate (ACP) for achieving its controlled delivery, thus forming an aprismatic enamel-like layer on the demineralized enamel surface.

METHODS

CMC/LYZ-ACP nanogels were developed, and the controlled delivery of ACP from the nanogels was induced by the presence of NaCl. The nanogel morphologies at various NaCl concentrations was measured by transmission electron microscopy (TEM). The particle sizes and zeta potentials (ζ-potential) of the samples were determined using a combined dynamic light scattering/particle electrophoresis instrument. Comparing the remineralization effect of the CMC/LYZ-ACP nanogels on the demineralized enamel surface with that of a fluoride treatment, the remineralization effect was examined by nanoindentation tests, X-ray diffraction (XRD), confocal laser scanning microscopy (CLSM), and scanning electron microscopy (SEM).

RESULTS

CMC/LYZ-ACP nanogels were negatively charged spherical structures with a particle size of approximately 300 nm. At high concentrations of NaCl (0.15 M), ACP was dissociated from the disassembled nanogels and transformed into hydroxyapatite (HAP). Groups treated with the CMC/LYZ-ACP nanogels showed the regeneration of an aprismatic enamel-like layer on an acid-etched enamel surface, which provided increased mechanical properties (P < 0.05) and a high impermeability (P < 0.01) compared to those of the fluoride-treated group.

CONCLUSIONS

This research provides a new idea for the stable and controllable delivery of ACP from CMC/LYZ-ACP nanogels, which can form an aprismatic enamel-like layer in situ on the surface of demineralized enamel. In regard to further clinical development, this material and method may be promising for treating early enamel caries.

Acidic Monetite Complex Paste with Bleaching Property for In-depth Occlusion of Dentinal Tubules

Background

Dentin hypersensitivity (DH) is a common dental clinical condition presented with a short and sharp pain in response to physical and chemical stimuli. Currently no treatment regimen demonstrates long-lasting efficacy in treating DH, and unesthetic yellow tooth color is a concern to many patients with DH.

Aim

To develop a bi-functional material which can occlude dentinal tubules in-depth and remineralize dentin for long-lasting protection of the dentin–pulp complex from stimuli and bleach the tooth at the same time.

Methods

A mixture containing CaO, H₃PO₄, polyethylene glycol and H₂O₂ at a specific ratio was mechanically ground using a planetary ball. The mineralizing complex paste was characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Dentin was exposed to the synthesized paste for 8 h and 24 h in vitro. The mineralizing property was evaluated using SEM and microhardness tests. Red tea-stained tooth slices were exposed to the synthesized paste for 8 h and 24 h in vitro. The bleaching effect was characterized by a spectrophotometer.

Results

The complex paste had very a fine texture, was injectable, and had a gel-like property with 2.6 (mass/volume) % H₂O₂ concentration. The X-ray diffraction pattern showed that the inorganic phase was mainly monetite (CaHPO₄). The mineralizing complex paste induced the growth of inorganic crystals on the dentin surface and in-depth occlusion of dentin tubules by up to 80 μm. The regenerated crystals were integrated into the dentin tissue on the dentin surface and the wall of dentinal tubules with a microhardness of up to 126 MPa (versus 137 Mpa for dentin). The paste also bleached the stained dental slices.

Conclusion

The mineralizing complex paste is a promising innovative material for efficient DH management by remineralizing dentin and in-depth occlusion of dentin tubules, as well as tooth bleaching.

Chitosan Derivatives in Macromolecular Co-assembly Nanogels with Potential for Biomedical Applications

Maleoyl-chitosan/poly(aspartic acid) nanogels were developed and characterized in order to assess its suitability for biomedical applications. Thus, the physicochemical properties were investigated and correlated with the composition of the new structures. Dynamic light scattering measurements, correlated with transmission electron microscopy images, demonstrated that nanogels size distribution was narrow with average diameter between 186 and 246 nm, and presented positive zeta potential values. The sensitivity of nanogels at pH and temperature was also evaluated. Nanogels loaded with amoxicillin showed a controlled release profile dependent on nanogel content. The formulations loaded with amoxicillin had antibacterial properties, and the cytotoxicity tests indicated good in vivo biocompatibility. In conclusion, the new synthesized polyelectrolyte nanogels, which can provide a stable environment for the encapsulated drugs, can be used as a multifunctional platform for administration of antimicrobial agents from the spectrum of antibiotics that have a very poor biodistribution.

Therapeutic Management of Demineralized Dentin Surfaces Using a Mineralizing Adhesive To Seal and Mineralize Dentin, Dentinal Tubules, and Odontoblast Processes

Dentin hypersensitivity is attributable to the exposed dentin and its patent tubules. We proposed the therapeutic management of demineralized dentin surfaces using a mineralizing adhesive to seal and remineralize dentin, dentinal tubules, and odontoblast processes. An experimental self-etch adhesive and a mineralizing adhesive consisting of the self-etch adhesive and 20 wt % poly-aspartic acid-stabilized amorphous calcium phosphate (PAsp-ACP) nanoparticles were prepared and characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), and scanning electron microscopy. After 60 acid-etched midcoronal dentin disks were treated with distilled water (control), a desensitizing agent (Gluma), the experimental self-etch adhesive, and the mineralizing adhesive, dentin permeability was measured and mineralization was evaluated by Raman, FTIR, XRD, TEM, and selected-area electron diffraction, irrespective of abrasive and acidic challenges. In vitro cytotoxicity of the adhesive and the mineralizing adhesive was assessed by Cell Counting Kit-8. The mineralizing adhesive possessed excellent biocompatibility. We proposed a hybrid mineralization layer composed of the light-cured mineralizing adhesive and the mineralized dentin surfaces, as well as interiorly mineralized resin tags and odontoblast processes inside of the dentinal tubules. This hybrid mineralization not only reduced dentin permeability but also resisted abrasive and acidic attacks.

Remineralization, Regeneration, and Repair of Natural Tooth Structure: Influences on the Future of Restorative Dentistry Practice

Currently, the principal strategy for the treatment of carious defects involves cavity preparations followed by the restoration of natural tooth structure with a synthetic material of inferior biomechanical and esthetic qualities and with questionable long-term clinical reliability of the interfacial bonds. Consequently, prevention and minimally invasive dentistry are considered basic approaches for the preservation of sound tooth structure. Moreover, conventional periodontal therapies do not always ensure predictable outcomes or completely restore the integrity of the periodontal ligament complex that has been lost due to periodontitis. Much effort and comprehensive research have been undertaken to mimic the natural development and biomineralization of teeth to regenerate and repair natural hard dental tissues and restore the integrity of the periodontium. Regeneration of the dentin-pulp tissue has faced several challenges, starting with the basic concerns of clinical applicability. Recent technologies and multidisciplinary approaches in tissue engineering and nanotechnology, as well as the use of modern strategies for stem cell recruitment, synthesis of effective biodegradable scaffolds, molecular signaling, gene therapy, and 3D bioprinting, have resulted in impressive outcomes that may revolutionize the practice of restorative dentistry. This Review covers the current approaches and technologies for remineralization, regeneration, and repair of natural tooth structure.

The importance of being amorphous: calcium and magnesium phosphates in the human body

This article focuses on the relevance of amorphous calcium (and magnesium) phosphates in living organisms. Although crystalline calcium phosphate (CaP)-based materials are known to constitute the major inorganic constituents of human hard tissues, amorphous CaP-based structures, often in combination with magnesium, are frequently employed by Nature to build up components of our body and guarantee their proper functioning. After a brief description of amorphous calcium phosphate (ACP) formation mechanism and structure, this paper is focused on the stabilization strategies that can be used to enhance the lifetime of the poorly stable amorphous phase. The various locations of our body in which ACP (pure or in combination with Mg²⁺) can be found (i.e. bone, enamel, small intestine, calciprotein particles and casein micelles) are highlighted, showing how the amorphous nature of ACP is often of paramount importance for the achievement of a specific physiological function. The last section is devoted to ACP-based biomaterials, focusing on how these materials differ from their crystalline counterparts in terms of biological response.

Carbohydrate-based nanomaterials for biomedical applications

Carbohydrates are abundant biomolecules, with a strong tendency to form supramolecular networks. A host of carbohydrate-based nanomaterials have been exploited for biomedical applications. These structures are based on simple mono- or disaccharides, as well as on complex, polymeric systems. Chemical modifications serve to tune the shapes and properties of these materials. In particular, carbohydrate-based nanoparticles and nanogels were used for drug delivery, imaging, and tissue engineering applications. Due to the reversible nature of the assembly, often based on a combination of hydrogen bonding and hydrophobic interactions, carbohydrate-based materials are valuable substrates for the creations of responsive systems. Herein, we review the current research on carbohydrate-based nanomaterials, with a particular focus on carbohydrate assembly. We will discuss how these systems are formed and how their properties are tuned. Particular emphasis will be placed on the use of carbohydrates for biomedical applications. This article is categorized under: Nanotechnology Approaches to Biology > Nanoscale Systems in Biology.