Physicochemical and biological assessment of silver nanoparticles immobilized Halloysite nanotubes-based resin composite for dental applications

A review of new generation of dental restorative resin composites with antibacterial, remineralizing and self-healing capabilities

Dental restorative resin composites are widely used to repair tooth decay owing to attractive esthetics, adequate mechanical properties and minimally invasive tooth structure preparations. Nevertheless, dental restorative resin composites still face challenges because of their relatively high failure rate and short lifespan caused by secondary caries and bulk fracture. Thus, attempts have been carried out to explore a new generation of dental restorative resin composites with antibacterial, remineralizing, and self-healing capabilities to inhibit bacteria and lengthen the lifetime of the restorations. Such novel restorative composites can inhibit bacterial activity, reduce acid production, promote mineral regeneration and present a renewable advantage to achieve a higher performance, which are inspiring and provide support for further basic and clinical research. In this review, antibacterial dental restorative resin composites are first introduced, followed by remineralizing, self-healing, and multifunctional dental resin composites with two or more of the functions mentioned above. Meanwhile, we explain the mechanism of the corresponding dental restorative resin composites and describe their characteristics. Finally, we conclude and put forward prospects. This review will attract both researchers and clinicians in this field and help to provide innovative ideas to design new restorative resin composites for biomedical applications.

Modification of polymethylmethacrylate bone cement with halloysite clay nanotubes

BACKGROUND

Polymethylmethacrylate (PMMA) bone cement is used in orthopedics and dentistry to get primary fixation to bone but doesn't provide a mechanically and biologically stable bone interface. Therefore, there was a great demand to improve the properties of the PMMA bone cement to reduce its clinical usage limitations and enhance its success rate. Recent studies demonstrated that the addition of halloysite nanotubes (HNTs) to a polymeric-based material can improve its mechanical and thermal characteristics.

OBJECTIVES

The purpose of the study is to assess the compressive strength, flexural strength, maximum temperature, and setting time of traditional PMMA bone cements that have been manually blended with 7 wt% HNT fillers.

METHODS

PMMA powder and monomer liquid were combined to create the control group, the reinforced group was made by mixing the PMMA powder with 7 wt% HNT fillers before liquid mixing. Chemical characterization of the HNT fillers was employed by X-ray fluorescence (XRF). The morphological examination of the cements was done using a scanning electron microscope (SEM). Analytical measurements were made for the compressive strength, flexural strength, maximum temperature, and setting time. Utilizing independent sample t-tests, the data was statistically assessed to compare mean values (p < 0.05).

RESULTS

The findings demonstrated that the novel reinforced PMMA-based bone cement with 7 wt% HNT fillers showed higher mean compressive strength values (93 MPa) and higher flexural strength (72 MPa). and lower maximum temperature values (34.8 °C) than the conventional PMMA bone cement control group, which was (76 MPa), (51 MPa), and (40 °C), respectively (P < 0.05). While there was no significant difference in the setting time between the control and the modified groups.

CONCLUSION

The novel PMMA-based bone cement with the addition of 7 wt% HNTs can effectively be used in orthopedic and dental applications, as they have the potential to enhance the compressive and flexural strength and reduce the maximum temperatures.

Evaluation of the Impact of Irradiance Lamps and Storage Media on Elution of TEGDMA from Dental Composites

OBJECTIVES

 The aim of this study was to evaluate and compare the effect of irradiance light and storage media on the elution of triethylene glycol dimethacrylate (TEGDMA) from conventional Filtek Z350XT 3M ESPE and two bulk-fill composites Shofu Beautifil-Bulk and Filtek Bulk fill flowable 3M ESPE using high-performance liquid chromatography (HPLC).

MATERIALS AND METHODS

 Shofu Beautifil-Bulk, Filtek Bulk fill flowable 3M ESPE, and Filtek Z350XT 3M ESPE were the three types of composites used in this study. Disk shaped samples of 4-mm thickness and 10-mm diameter were fabricated using a stainless steel mold and were polymerized using light emitting diode (LED) and quartz tungsten halogen (QTH) lamps. After polymerization, the samples were immersed in ethanol, artificial saliva with betel quid extract, and distilled water for 1, 7, and 30 days, respectively. The elution of monomer TEGDMA was evaluated using HPLC.

STATISTICAL ANALYSIS

 To evaluate the mean concentration difference, mixed way analysis of variance (ANOVA) was applied. Between different light, materials, and within the time duration, Tukey's post hoc test was used. A p value of 0.05 was considered significant.

RESULTS

 During the first day of storage, a significant amount of monomer TEGDMA elution was seen in all the materials. The highest values observed to be in the disks cured with QTH lamp. However, the highest elution was seen when the disks were immersed in ethanol/water solution. While the most stable medium was distilled water, artificial saliva with betel nut extract also had a significant effect on the elution of TEGDMA. The highest value obtained was of Filtek Bulk fill flowable 3M ESPE after 30 days of immersion in both LED and QTH cured disks.

CONCLUSION

 Filtek Bulk fill flowable 3M ESPE shows better properties in relation to the release of monomer TEGDMA as it releases less amount of monomer in the storage media. The release of monomer was highest in ethanol as compared to artificial saliva and distilled water with the passage of time.

Salt-induced Fmoc-tripeptide supramolecular hydrogels: a combined experimental and computational study of the self-assembly

Delving into the mechanism behind the molecular interactions at the atomic level of short-sequence peptides plays a key role in the development of nanomaterials with specific structure-property-function relationships from a bottom-up perspective. Due to their poor water solubility, the self-assembly of Fmoc-bearing peptides is usually induced by dissolution in an organic solvent, followed by a dilution step in water, pH changes, and/or a heating-cooling process. Herein, we report a straightforward methodology for the gelation of Fmoc-FFpY (F: phenylalanine; Y: tyrosine; and p: PO42-), a negatively charged tripeptide, in NaCl solution. The electrostatic interactions between Fmoc-FFpY and Na+ ions give rise to different nanofibrillar hydrogels with rheological properties and nanofiber sizes modulated by the NaCl concentration in pure aqueous media. Initiated by the electrostatic interactions between the peptide phosphate groups and the Na+ ions, the peptide self-assembly is stabilized thanks to hydrogen bonds between the peptide backbones and the π-π stacking of aromatic Fmoc and phenyl units. The hydrogels showed self-healing and thermo-responsive properties for potential biomedical applications. Molecular dynamics simulations from systems devoid of prior training not only confirm the aggregation of peptides at a critical salt concentration and the different interactions involved, but also corroborate the secondary structure of the hydrogels at the microsecond timescale. It is worth highlighting the remarkable achievement of reproducing the morphological behavior of the hydrogels using atomistic simulations. To our knowledge, this study is the first to report such a correspondence.

Enhancing Presurgical Infant Orthopedic Appliances: Characterization, Mechanics, and Biofilm Inhibition of a Novel Chlorhexidine-Halloysite Nanotube-Modified PMMA

Objectives

This in vitro study aimed to develop a novel nanocomposite acrylic resin with inherent antimicrobial properties. This study evaluated its effectiveness against microbial biofilm formation, while also assessing its physical and mechanical properties.

Methods

Polymethylmethacrylate (PMMA) was modified with four different concentrations of chlorhexidine halloysite nanotubes (CHX-HNTs): 1%, 1.5%, 3%, and 4.5 wt.% by weight, along with a control group (0 wt.% CHX-HNTs). The biofilm inhibition ability of the modified CHX-HNTs acrylic against Candida albicans, Staphylococcus aureus, Streptococcus pneumoniae, and Streptococcus agalactiae was assessed using microtiter biofilm test. In addition, ten samples from each group were then tested for flexural strength, surface roughness, and hardness. Statistical analysis was performed using one-way ANOVA and Tukey's test for comparison (P < 0.05).

Results

CHX-HNTs effectively reduced the adhesion of Candida albicans and bacteria to the PMMA in a dose-dependent manner. The higher the concentration of CHX-HNTs, the greater the reduction in microbial adhesion, with the highest concentration (4.5 wt.%) showing the most significant effect with inhibition rates ≥98%. The addition of CHX-HNTs at any tested concentration (1%, 1.5%, 3%, and 4.5 wt.%) did not cause any statistically significant difference in the flexural strength, surface roughness, or hardness of the PMMA compared to the control group.

Conclusions

The novel integration of CHX-HNT fillers shows promising results as an effective biofilm inhibitor on acrylic appliances. This new approach has the potential to successfully control infectious diseases without negatively affecting the mechanical properties of the acrylic resin. Clinical Relevance. The integration of CHX-HNTs into presurgical infant orthopedic appliances should be thoroughly assessed as a promising preventive measure to mitigate microbial infections. This evaluation holds significant potential for controlling infectious diseases among infants with cleft lip and palate, thereby offering a valuable contribution to their overall well-being.

QbD-Assisted Development and Optimization of Doxycycline Hyclate- and Hydroxyapatite-Loaded Nanoparticles for Periodontal Delivery

The current research aims to develop a carrier system for the delivery of a matrix metalloproteinase (MMP) inhibitor along with a bioceramic agent to the periodontal pocket. It is proposed that the present system, if given along with a systemic antibiotic, would be a fruitful approach for periodontitis amelioration. To fulfill the aforementioned objective, a doxycycline hyclate- and hydroxyapatite-adsorbed composite was prepared by a physical adsorption method and successfully loaded inside sodium alginate-chitosan nanoparticles and optimized based on particle size and drug content. Optimized formulation was then subjected to different evaluation parameters like encapsulation efficiency, hydroxyapatite content, ζ potential, surface morphology, in vitro drug release, cell line studies, and stability studies. For the optimized formulation, particle size, polydispersity index (PDI), entrapment efficiency, ζ potential, and drug content were found to be 336.50 nm, 0.23, 41.77%, -13.85 mV, and 14.00%, respectively. The surface morphology of the placebo and adsorbed composite-loaded nanoparticles as observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed the spherical shape and rough surface of the particles. In gingival crevicular fluid (GCF) 7.6, a sustained drug release profile was obtained up to 36 h. In vitro % viability studies performed on murine fibroblast cells (NIH3T3) and human periodontal ligament (hPDL) cell lines confirmed the proliferative nature of the formulation. Also, when subjected to stability studies for 4 weeks, particle size, PDI, and drug content did not vary considerably, thereby ensuring the stable nature of nanoparticles. Henceforth, sodium alginate-chitosan nanoparticles appeared to be a good carrier system for doxycycline hyclate and hydroxyapatite for periodontal therapy. If given along with a system antibiotic, the system will serve as a fruitful tool for infection-mediated periodontal regeneration and healing.

Recent Advances of Halloysite Nanotubes in Biomedical Applications

Halloysite nanotubes (HNTs) have emerged as a highly regarded choice in biomedical research due to their exceptional attributes, including superior loading capacity, customizable surface characteristics, and excellent biocompatibility. HNTs feature tubular structures comprising alumina and silica layers, endowing them with a large surface area and versatile surface chemistries that facilitate selective modifications. Moreover, their substantial pore volume and wide range of pore sizes enable efficient entrapment of diverse functional molecules. This comprehensive review highlights the broad biomedical application spectrum of HNTs, shedding light on their potential as innovative and effective therapeutic agents across various diseases. It emphasizes the necessity of optimizing drug delivery techniques, developing targeted delivery systems, rigorously evaluating biocompatibility and safety through preclinical and clinical investigations, exploring combination therapies, and advancing scientific understanding. With further advancements, HNTs hold the promise to revolutionize the pharmaceutical industry, opening new avenues for the development of transformative treatments.

Fabrication of Flexible Films for Supercapacitors Using Halloysite Nano-Clay Incorporated Poly(lactic acid)

In the past few years, significant research efforts have been directed toward improving the electrochemical capabilities of supercapacitors by advancing electrode materials. The present work signifies the development of poly(lactic acid)/alloysite nano-clay as an electrode material for supercapacitors. Physico-chemical characterizations were analyzed by Fourier transform infrared spectroscopy, wide-angle X-ray diffraction, and a universal testing machine. Cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge-discharge techniques were employed to evaluate electrochemical characteristics. The optimized poly(lactic acid)/halloysite nano-clay film revealed the highest specific capacitance of 205.5 F g-1 at 0.05 A g-1 current density and showed 14.6 Wh kg-1 energy density at 72 W kg-1 power density. Capacitance retention of 98.48% was achieved after 1000 cycles. The microsupercapacitor device presented a specific capacitance of 197.7 mF g-1 at a current density of 0.45 mA g-1 with 10.8 mWh kg-1 energy density at 549 mW kg-1 power density.

Influence of inorganic nanoparticles on dental materials' mechanical properties. A narrative review

Inorganic nanoparticles have been widely incorporated in conventional dental materials to help in improving their properties. The literature has shown that incorporating nanoparticles in dental materials in different specialties could have a positive effect on reinforcing the mechanical properties of those materials; however, there was no consensus on the effectiveness of using nanoparticles in enhancing the mechanical properties of dental materials, due to the variety of the properties of nanoparticles itself and their effect on the mechanical properties. This article attempted to analytically review all the studies that assessed the effect of different types of inorganic nanoparticles on the most commonly used dental materials in dental specialties such as polymethyl methacrylate, glass ionomer cement, resin composite, resin adhesive, orthodontic adhesive, and endodontic sealer. The results had shown that those inorganic nanoparticles demonstrated positive potential in improving those mechanical properties in most of the dental materials studied. That potential was attributed to the ultra-small sizes and unique physical and chemical qualities that those inorganic nanoparticles possess, together with the significant surface area to volume ratio. It was concluded from this comprehensive analysis that while a definitive recommendation cannot be provided due to the variety of nanoparticle types, shapes, and incorporated dental material, the consensus suggests using nanoparticles in low concentrations less than 1% by weight along with a silane coupling agent to minimize agglomeration issues and benefit from their properties.

The Development of a Novel Sodium Alginate-Based Edible Active Hydrogel Coating and Its Application on Traditional Greek Spreadable Cheese

The necessity of reducing the greenhouse effect by decreasing the carbon dioxide fingerprint directed the food packaging technology to use biobased raw materials. Alginates, which are derived from brown algae species, are one of the most promising biobased biopolymers for the development of edible active coatings capable of protecting food from oxidation/bacterial spoilage. In this study, sodium alginate, which was plasticized with glycerol and mixed with a biobased thymol/natural halloysite nanohybrid, was used to develop novel edible active coatings. Nanocomposite coatings were also developed in this project by mixing pure halloysite with sodium alginate/glycerol matrix and were used as reference material for comparison reasons. Instrumental analysis indicated a higher compatibility of a thymol/halloysite nanohybrid with a sodium alginate/glycerol matrix compared to pure halloysite with a sodium alginate/glycerol matrix. Increased compatibility resulted in improved tensile properties, water/oxygen barrier properties, and total antioxidant activity. These edible active coatings were applied to traditional Greek spread cheese and showed a reduction in the mesophilic microbial population over one log10 unit (cfu/g) compared to uncoated cheese. Moreover, the reduction in the mesophilic microbial population increased with the increase in halloysite and thymol content, indicating such sodium alginate/glycerol/thymol/halloysite hydrogels as promising edible active coatings for dairy products.

Antibacterial and Physicochemical Properties of Orthodontic Resin Cement Containing ZnO-Loaded Halloysite Nanotubes

Demineralized white lesions are a common problem when using orthodontic resin cement, which can be prevented with the addition of antibacterial substances. However, the addition of antibacterial substances such as zinc oxide alone may result in the deterioration of the resin cement's functions. Halloysite nanotubes (HNTs) are known to be biocompatible without adversely affecting the mechanical properties of the material while having the ability to load different substances. The purpose of this study was to prepare orthodontic resin cement containing HNT fillers loaded with ZnO (ZnO/HNTs) and to investigate its mechanical, physical, chemical, and antibacterial properties. A group without filler was used as a control. Three groups containing 5 wt.% of HNTs, ZnO, and ZnO/HNTs were prepared. TEM and EDS measurements were carried out to confirm the morphological structure of the HNTs and the successful loading of ZnO onto the HNTs. The mechanical, physical, chemical, and antibacterial properties of the prepared orthodontic resin cement were considered. The ZnO group had high flexural strength and water absorption but a low depth of cure (p < 0.05). The ZnO/HNTs group showed the highest shear bond strength and film thickness (p < 0.05). In the antibacterial test, the ZnO/HNTs group resulted in a significant decrease in the biofilm's metabolic activity compared to the other groups (p < 0.05). ZnO/HNTs did not affect cell viability. In addition, ZnO was cytotoxic at a concentration of 100% in the extract. The nanocomposite developed in this study exhibited antimicrobial activity against S. mutans while maintaining the mechanical, physical, and chemical properties of orthodontic resin cement. Therefore, it has the potential to be used as an orthodontic resin cement that can prevent DWLs.

Silver Nanoparticles in Dental Applications: A Descriptive Review

Silver nanoparticles have been a recent focus of many researchers in dentistry, and their potential uses and benefits have drawn attention in dentistry and medicine. The fabrication and utilization of nanoscale substances and structures are at the core of the rapidly developing areas of nanotechnology. They are often used in the dental industry because they prevent bacteria from making nanoparticles, oxides, and biofilms. They also stop the metabolism of bacteria. Silver nanoparticles (AgNPs) are a type of zero-dimensional material with different shapes. Dentistry has to keep up with changing patient needs and new technology. Silver nanoparticles (AgNPs) can be used in dentistry for disinfection and preventing infections in the oral cavity. One of the most interesting metallic nanoparticles used in biomedical applications is silver nanoparticles (AgNPs). The dental field has found promising uses for silver nanoparticles (AgNPs) in the elimination of plaque and tartar, as well as the elimination of bacterial and fungal infections in the mouth. The incorporation of AgNPs into dental materials has been shown to significantly enhance patients' oral health, leading to their widespread use. This review focuses on AgNP synthesis, chemical properties, biocompatibility, uses in various dental fields, and biomaterials used in dentistry. With an emphasis on aspects related to the inclusion of silver nanoparticles, this descriptive review paper also intends to address the recent developments of AgNPs in dentistry.

Clindamycin-Loaded Halloysite Nanotubes as the Antibacterial Component of Composite Hydrogel for Bone Repair

A new drug delivery system consisting of clindamycin phosphate entrapped in acid-etched halloysite nanotubes was successfully prepared and characterized. It was then used as an antibacterial component of the multicomponent hydrogel designed as a material for bone regeneration. First, halloysite (HNT) was etched and clindamycin phosphate (CP) was entrapped in both raw and modified nanotubes, resulting in HNT-CP and EHNT-CP systems. They were characterized using SEM, TEM, TGA and FTIR; the entrapment efficiency and release of CP from both systems were also studied. EHNT-CP was then used as an antibacterial component of the two hydrogels composed of alginate, collagen and β-TCP. The hydrogels were prepared using different crosslinking procedures but had the same composition. The morphology, porosity, degradation rate, CP release profile, cytocompatibility, antibacterial activity and ability to induce biomineralization were studied for both materials. The hydrogel obtained by a chemical crosslinking with EDC followed by the physical crosslinking with calcium ions had better properties and was shown to have potential as a bone repair material.

DEAE-Dextran Coated AgNPs: A Highly Blendable Nanofiller Enhances Compressive Strength of Dental Resin Composites

Micro-crack formation and resultant bacterial infiltration are major causes of secondary caries formation in dental resin-based composite restorations. Improving dental resin composites’ mechanical and biological properties using highly bendable nanoparticles (NPs) can resolve this issue. This study aims to develop novel Diethylaminoethyl (DEAE)-Dextran silver nanoparticles (AgNPs) and subsequently modify composite resins with these NPs to enhance their mechanical and antibacterial properties. DEAE-Dextran AgNPs were successfully synthesized using a chemical reduction method that was confirmed with the help of ultraviolet-visible (UV-Vis) spectroscopy, scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), Zeta potential, and energy-dispersive X-ray spectroscopy (EDS). Antibacterial activity of a composite disc with DEAE-Dextran AgNPs was tested against Streptococcus mutans, Enterococcus faecalis, and oral microcosm. The composite discs prepared with DEAE-Dextran AgNPs exhibited excellent antibacterial activity compared with composite resin reinforced by simple AgNPs (p < 0.05). Mechanical properties were significantly enhanced by adding DEAE-Dextran into composite resin (p < 0.05). Moreover, unlike AgNPs, DEAE-Dextran AgNPs were found to be less hemolytic. The results establish strong ground applications for DEAE-Dextran-modified dental composite resins in restorative dental applications.

Preparation of Silica Aerogel/Resin Composites and Their Application in Dental Restorative Materials

As the most advanced aerogel material, silica aerogel has had transformative industrial impacts. However, the use of silica aerogel is currently limited to the field of thermal insulation materials, so it is urgent to expand its application into other fields. In this work, silica aerogel/resin composites were successfully prepared by combining silica aerogel with a resin matrix for dental restoration. The applications of this material in the field of dental restoration, as well as its performance, are discussed in depth. It was demonstrated that, when the ratio of the resin matrix Bis-GMA to TEGDMA was 1:1, and the content of silica aerogel with 50 μm particle size was 12.5%, the composite achieved excellent mechanical properties. The flexural strength of the silica aerogel/resin composite reached 62.9546 MPa, which was more than five times that of the pure resin. Due to the presence of the silica aerogel, the composite also demonstrated outstanding antibacterial capabilities, meeting the demand for antimicrobial properties in dental materials. This work successfully investigated the prospect of using commercially available silica aerogels in dental restorative materials; we provide an easy method for using silica aerogels as dental restorative materials, as well as a reference for their application in the field of biomedical materials.

Natural Nanoclay-Based Silver-Phosphomolybdic Acid Composite with a Dual Antimicrobial Effect

The problem of microbial growth on various surfaces has increased concern in society in the context of antibiotic misuse and the spreading of hospital infections. Thus, the development of new, antibiotic-free antibacterial strategies is required to combat bacteria resistant to usual antibiotic treatments. This work reports a new method for producing an antibiotic-free antibacterial halloysite-based nanocomposite with silver nanoparticles and phosphomolybdic acid as biocides, which can be used as components of smart antimicrobial coatings. The composite was characterized by using energy-dispersive X-ray fluorescence spectroscopy and transmission electron microscopy. The release of phosphomolybdic acid from the nanocomposite was studied by using UV-vis spectroscopy. It was shown that the antibiotic-free nanocomposite consisting of halloysite nanotubes decorated with silver nanoparticles loaded with phosphomolybdic acid and treated with calcium chloride possesses broad antibacterial properties, including the complete growth inhibition of Staphylococcus aureus and Pseudomonas aeruginosa bacteria at a 0.5 g × L^-1 concentration and Acinetobacter baumannii at a 0.25 g × L^-1 concentration.

Therapeutic Applications of Antimicrobial Silver-Based Biomaterials in Dentistry

Microbial infection accounts for many dental diseases and treatment failure. Therefore, the antibacterial properties of dental biomaterials are of great importance to the long-term results of treatment. Silver-based biomaterials (AgBMs) have been widely researched as antimicrobial materials with high efficiency and relatively low toxicity. AgBMs have a broad spectrum of antimicrobial properties, including penetration of microbial cell membranes, damage to genetic material, contact killing, and dysfunction of bacterial proteins and enzymes. In particular, advances in nanotechnology have improved the application value of AgBMs. Hence, in many subspecialties of dentistry, AgBMs have been researched and employed, such as caries arresting or prevention, root canal sterilization, periodontal plaque inhibition, additives in dentures, coating of implants and anti-inflammatory material in oral and maxillofacial surgery. This paper aims to provide an overview of the application approaches of AgBMs in dentistry and present better guidance for oral antimicrobial therapy via the development of AgBMs.

First biocatalytic synthesis of piperidine derivatives via an immobilized lipase-catalyzed multicomponent reaction

A robust and reusable biocatalyst was constructed via immobilization of lipase onto magnetic halloysite nanotubes for the synthesis of piperidine derivatives.

Therapeutic Applications of Halloysite

In recent years, nanomaterials have attracted significant research interest for applications in biomedicine. Many kinds of engineered nanomaterials, such as lipid nanoparticles, polymeric nanoparticles, porous nanomaterials, silica, and clay nanoparticles, have been investigated for use in drug delivery systems, regenerative medicine, and scaffolds for tissue engineering. Some of the most attractive nanoparticles for biomedical applications are nanoclays. According to their mineralogical composition, approximately 30 different nanoclays exist, and the more commonly used clays are bentonite, halloysite, kaolinite, laponite, and montmorillonite. For millennia, clay minerals have been extensively investigated for use in antidiarrhea solutions, anti-inflammatory agents, blood purification, reducing infections, and healing of stomach ulcers. This widespread use is due to their high porosity, surface properties, large surface area, excellent biocompatibility, the potential for sustained drug release, thermal and chemical stability. We begin this review by discussing the major nanoclay types and their application in biomedicine, focusing on current research areas for halloysite in biomedicine. Finally, recent trends and future directions in HNT research for biomedical application are explored.

Intrinsically radiopaque biomaterial assortments: a short review on the physical principles, X-ray imageability, and state-of-the-art developments

X-ray attenuation ability, otherwise known as radiopacity of a material, could be indisputably tagged as the central and decisive parameter that produces contrast in an X-ray image. Radiopaque biomaterials are vital in the healthcare sector that helps clinicians to track them unambiguously during pre and post interventional radiological procedures. Medical imaging is one of the most powerful resources in the diagnostic sector that aids improved treatment outcomes for patients. Intrinsically radiopaque biomaterials enable themselves for visual targeting/positioning as well as to monitor their fate and further provide the radiologists with critical insights about the surgical site. Moreover, the emergence of advanced real-time imaging modalities is a boon to the contemporary healthcare systems that allow to perform minimally invasive surgical procedures and thereby reduce the healthcare costs and minimize patient trauma. X-ray based imaging is one such technologically upgraded diagnostic tool with many variants like digital X-ray, computed tomography, digital subtraction angiography, and fluoroscopy. In light of these facts, this review is aimed to briefly consolidate the physical principles of X-ray attenuation by a radiopaque material, measurement of radiopacity, classification of radiopaque biomaterials, and their recent advanced applications.

Silver, copper and copper oxide nanoparticles in the fight against human viruses: progress and perspectives

The rapid development of nanomedicine has created a high demand for silver, copper and copper oxide nanoparticles. Due to their high reactivity and potent antimicrobial activity, silver and copper-based nanomaterials have been playing an important role in the search for new alternatives for the treatment of several issues of concern, such as pathologies caused by bacteria and viruses. Viral diseases are a significant and constant threat to public health. The most recent example is the pandemic caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). In this context, the object of the present review is to highlight recent progress in the biomedical uses of these metal nanoparticles for the treatment and prevention of human viral infections. We discuss the antiviral activity of AgNPs and Cu-based NPs, including their actions against SARS-CoV-2. We also discuss the toxicity, biodistribution and excretion of AgNPs and CuNPs, along with their uses in medical devices or on inert surfaces to avoid viral dissemination by fomites. The challenges and limitations of the biomedical use of these nanoparticles are presented.

Recent Progress in Antimicrobial Strategies for Resin-Based Restoratives

Repairing tooth defects with dental resin composites is currently the most commonly used method due to their tooth-colored esthetics and photocuring properties. However, the higher than desirable failure rate and moderate service life are the biggest challenges the composites currently face. Secondary caries is one of the most common reasons leading to repair failure. Therefore, many attempts have been carried out on the development of a new generation of antimicrobial and therapeutic dental polymer composite materials to inhibit dental caries and prolong the lifespan of restorations. These new antimicrobial materials can inhibit the formation of biofilms, reduce acid production from bacteria and the occurrence of secondary caries. These results are encouraging and open the doors to future clinical studies on the therapeutic value of antimicrobial dental resin-based restoratives. However, antimicrobial resins still face challenges such as biocompatibility, drug resistance and uncontrolled release of antimicrobial agents. In the future, we should focus on the development of more efficient, durable and smart antimicrobial dental resins. This article focuses on the most recent 5 years of research, reviews the current antimicrobial strategies of composite resins, and introduces representative antimicrobial agents and their antimicrobial mechanisms.

Applications of Silver Nanoparticles in Dentistry: Advances and Technological Innovation

Silver nanoparticles (AgNPs) have been successfully applied in several areas due to their significant antimicrobial activity against several microorganisms. In dentistry, AgNP can be applied in disinfection, prophylaxis, and prevention of infections in the oral cavity. In this work, the use of silver nanoparticles in dentistry and associated technological innovations was analyzed. The scientific literature was searched using PubMed and Scopus databases with descriptors related to the use of silver nanoparticles in dentistry, resulting in 90 open-access articles. The search for patents was restricted to the A61K code (International Patent Classification), using the same descriptors, resulting in 206 patents. The results found were ordered by dental specialties and demonstrated the incorporation of AgNPs in different areas of dentistry. In this context, the search for patents reaffirmed the growth of this technology and the dominance of the USA pharmaceutical industry over AgNPs product development. It could be concluded that nanotechnology is a promising area in dentistry with several applications.

Transformation of Biowaste for Medical Applications: Incorporation of Biologically Derived Silver Nanoparticles as Antimicrobial Coating

Nanobiotechnology has undoubtedly influenced major breakthroughs in medical sciences. Application of nanosized materials has made it possible for researchers to investigate a broad spectrum of treatments for diseases with minimally invasive procedures. Silver nanoparticles (AgNPs) have been a subject of investigation for numerous applications in agriculture, water treatment, biosensors, textiles, and the food industry as well as in the medical field, mainly due to their antimicrobial properties and nanoparticle nature. In general, AgNPs are known for their superior physical, chemical, and biological properties. The properties of AgNPs differ based on their methods of synthesis and to date, the biological method has been preferred because it is rapid, nontoxic, and can produce well-defined size and morphology under optimized conditions. Nevertheless, the common issue concerning biological or biobased production is its sustainability. Researchers have employed various strategies in addressing this shortcoming, such as recently testing agricultural biowastes such as fruit peels for the synthesis of AgNPs. The use of biowastes is definitely cost-effective and eco-friendly; moreover, it has been reported that the reduction process is simple and rapid with reasonably high yield. This review aims to address the developments in using fruit- and vegetable-based biowastes for biologically producing AgNPs to be applied as antimicrobial coatings in biomedical applications.

Physical and Mechanical Properties of Resins Blends Containing a Monomethacrylate with Low-polymerization Shrinkage

Objectives  The aim of this study was to evaluate the Knoop hardness (KH), cross-link density (CLD), water sorption (WS), water solubility (WSB), and volumetric shrinkage (VS) of experimental resins blends containing a monomethacrylate with low-polymerization shrinkage.

Materials and Methods  A blend of bisphenol glycidyl methacrylate (BisGMA) as base monomer was formulated with (Bis-GMA)/triethyleneglycol dimethacrylate (TEGDMA), Bis-GMA/isobornyl methacrylate (IBOMA), or Bis-GMA/TEGDMA/IBOMA in different concentrations (40, 50, or 60 wt%). The camphorquinone (CQ)/2-(dimethylamino) ethyl methacrylate (DMAEMA) was used as the photoinitiator system. The KH and CLD were measured at the top surface using an indenter. For WS and WSB, the volume of the samples was calculated in mm ³ . The samples were transferred to desiccators until a constant mass was obtained (m1) and were subsequently immersed in distilled water until no alteration in mass was detected (m2). The samples were reconditioned to constant mass in desiccators (m3). WS and WSB were determined using the equations m2 − m3/V and m1 − m3/V, respectively. VS results were calculated with the density parameters before and after curing.

Statistical Analysis  Data were submitted to ANOVA and Tukey’s test (α = 0.05).

Results  The resins containing IBOMA showed lower VS results. TEGDMA 40% and TEGDMA/IBOMA 20/20 wt% showed higher KH values. The IBOMA groups showed lower CLD, while TEGDMA groups had higher values of CLD. The BisGMA/TEGDMA resin presented the highest values of WS, and for WSB, all groups showed no significant differences among themselves.

Conclusion  The monomethacrylate with low-polymerization shrinkage IBOMA used alone or in combination with TEGDMA may decrease VS, WS, and CLD values.

Emerging nanomaterials for dental treatments

The emergence of nanomaterials for dental treatments is encouraged by the nanotopography of the tooth structure, together with the promising benefits of nanomedicine. The use of nanoparticles in dentistry, also termed as 'nanodentistry', has manifested in applications for remineralisation, antimicrobial activity, local anaesthesia, anti-inflammation, osteoconductivity and stem cell differentiation. Besides the applications on dental tissues, nanoparticles have been used to enhance the mechanical properties of dental composites, improving their bonding and anchorage and reducing friction. The small particle size allows for enhanced permeation into deeper lesions, and reduction in porosities of dental composites for higher mechanical strength. The large surface area to volume ratio allows for enhanced bioactivity such as bonding and integration, and more intense action towards microorganisms. Controlled release of encapsulated bioactive molecules such as drugs and growth factors enables them to be delivered more precisely, with site-targeted delivery for localised treatments. These properties have benefitted across multiple fields within dentistry, including periodontology and endodontics and reengineering of dental prosthetics and braces. This review summarises the current literature on the emerging field of nanomaterials for dental treatments.

Nanoparticle Surface Functionalization: How to Improve Biocompatibility and Cellular Internalization

The use of nanoparticles (NP) in diagnosis and treatment of many human diseases, including cancer, is of increasing interest. However, cytotoxic effects of NPs on cells and the uptake efficiency significantly limit their use in clinical practice. The physico-chemical properties of NPs including surface composition, superficial charge, size and shape are considered the key factors that affect the biocompatibility and uptake efficiency of these nanoplatforms. Thanks to the possibility of modifying physico-chemical properties of NPs, it is possible to improve their biocompatibility and uptake efficiency through the functionalization of the NP surface. In this review, we summarize some of the most recent studies in which NP surface modification enhances biocompatibility and uptake. Furthermore, the most used techniques used to assess biocompatibility and uptake are also reported.

Biocompatibility, mechanical, and bonding properties of a dental adhesive modified with antibacterial monomer and cross-linker

OBJECTIVES

This study investigated the antibacterial, cytotoxicity, and mechanical properties of a dental adhesive modified with quaternary ammonium monomer ((2-acryloyloxyethyl)dimethyldodecylammonium bromide) and cross-linker (bis(2-acryloyloxyethyl)methyldodecylammonium bromide).

MATERIALS AND METHODS

Monomer (M), cross-linker (C), or a combination of these (M + C) were incorporated into adhesive Adper Single Bond Plus (SB) in 5, 10, or 25% (as wt%). A colony-forming unit and MTT assays were used to evaluate antibacterial properties against Streptococcus mutans and cell viability. Resin-dentin beams (0.9 ± 0.1 mm²) were evaluated for micro-tensile bond strength (μTBS) after 24 h, 6 months, and 3 years. Hourglass specimens were evaluated for ultimate tensile strength (UTS) after 24 h, 1 week, and 6 months. Micro-hardness measurements after softening in ethanol were taken as an indirect assessment of the polymer cross-linking density. Kruskal-Wallis, one-way ANOVA, two-way ANOVA, and Student's t test were used for analysis of the antibacterial, cytotoxicity, μTBS, UTS, and hardness data, all with a significance level of p < 0.05.

RESULTS

10%M and 25%M demonstrated a significant reduction in S. mutans relative to SB (p < 0.001). No differences in cytotoxicity were detected for any of the groups. After 6 months, no changes in μTBS were shown for any of the groups. After 3 years, all groups evidenced a significant decrease in μTBS (p < 0.05) except 5%M, 5%C, and 5%M + 5%C. All groups demonstrated either stable or significantly increased UTS after 6 months. Except for the cross-linker groups, a significant decrease in micro-hardness was shown for all groups after softening in ethanol (p < 0.05).

CONCLUSIONS

A 5-10% of monomer may render the resin antibacterial without a compromise to its mechanical and bonding properties.

CLINICAL RELEVANCE

Biomodification of a resin adhesive with an antibacterial monomer and cross-linker may help improve the life span of adhesive restorations.

Development of Chlorhexidine Loaded Halloysite Nanotube Based Experimental Resin Composite with Enhanced Physico-Mechanical and Biological Properties for Dental Applications

Objective: The objective of this study was to explore the effect of Chlorhexidine-loaded Halloysite nanotubes (HNT/CHX) fillers (diverse mass fractions from 1 to 10 wt.%) on physicochemical, morphological and biological properties of newly developed experimental dental resin composite, in order to compare with the properties of composites composed of conventional glass fillers. Methods: The dental resin composites were prepared by incorporating various proportions of HNT/CHX. Six different groups of specimens: control group and five groups composed of varied mass fractions of HNT/CHX (e.g., 1.0, 2.5, 5.0, 7.5 and 10 wt.%) as fillers in each group were fabricated. Mechanical properties of the composites were monitored, using UTM. The degree of conversion of dental resin composites and their depth of cure were also evaluated. Antimicrobial properties of dental composites were studied in vitro by applying agar diffusion test on strain Streptococcus mutans and cytotoxicity were studied using NIH-3T3 cell line. Results: The incorporation of varied mass fractions (1.0 to 5.0 wt.%) of HNT/CHX in dental resins composites enhanced mechanical properties considerably with significant antibacterial activity. The slight decrease in curing depth and degree of conversion values of composites indicates its durability. No cytotoxicity was noticed on NIH-3T3 cell lines. Significance: Consistent distribution of HNT/CHX as a filler into dental composites could substantially improve not only mechanical properties but also biological properties of dental composites.