Advances in surface design and biomedical applications of magnetic nanoparticles.

Despite significant efforts by scientists in the development of advanced nanotechnology materials for smart diagnosis devices and drug delivery systems, the success of clinical trials remains largely elusive. In order to address this biomedical challenge, magnetic nanoparticles (MNPs) have gained attention as a promising candidate due to their theranostic properties, which allow the simultaneous treatment and diagnosis of a disease. Moreover, MNPs have advantageous characteristics such as a larger surface area, high surface-to-volume ratio, enhanced mobility, mass transference and, more notably, easy manipulation under external magnetic fields. Besides, certain magnetic particle types based on the magnetite (Fe3O4) phase have already been FDA-approved, demonstrating biocompatible and low toxicity. Typically, surface modification and/or functional group conjugation are required to prevent oxidation and particle aggregation. A wide range of inorganic and organic molecules have been utilized to coat the surface of MNPs, including surfactants, antibodies, synthetic and natural polymers, silica, metals, and various other substances. Furthermore, various strategies have been developed for the synthesis and surface functionalization of MNPs to enhance their colloidal stability, biocompatibility, good response to an external magnetic field, etc. Both uncoated MNPs and those coated with inorganic and organic compounds exhibit versatility, making them suitable for a range of applications such as drug delivery systems (DDS), magnetic hyperthermia, fluorescent biological labels, biodetection and magnetic resonance imaging (MRI). Thus, this review provides an update of recently published MNPs works, providing a current discussion regarding their strategies of synthesis and surface modifications, biomedical applications, and perspectives.

Radiopacity and mechanical properties of dental adhesives with strontium hydroxyapatite nanofillers.

OBJECTIVES: Dental resins filled with hydroxyapatite (HAp) nanoparticles have significantly revolutionized restorative dentistry offering advantages such as remineralization potential and increase of polymerization. However, these materials have limited radiopacity hindering the diagnosis of secondary caries. The present study investigated the development of a new radiopaque dental adhesive by incorporating novel pure strontium hydroxyapatite nanoparticles [Sr10(PO4)6(OH)2, SrHAp] synthesized by a simple hydrothermal method. METHODS: Strontium phosphates were prepared using co-precipitation (SrHAp0h) and hydrothermal treatment for 2 and 5h (SrHAp2h and SrHAp5h). The crystallinity, crystallite size, textural and morphology features of the nanoparticles were characterized by XRD, FT-IR, micro-Raman and TEM. Strontium hydroxyapatite (SrHAp) or calcium hydroxyapatite (HAp) nanoparticles were then incorporated (10 wt%) into an adhesive resin of a commercial three-step etch-and-rinse adhesive to evaluate the radiopacity of disk-shaped specimens, degree of conversion (DC) assessed by FT-IR and mechanical properties by three-point bending test. The unfilled adhesive was used as negative control. RESULTS: While SrHAp0h and SrHAp2h resulted a phase mixing, the pure and highly crystalline phase of strontium hydroxyapatite free of calcium was obtained with 5h hydrothermal treatment (SrHAp5h). The TEM images revealed nanorods morphology for SrHAp5h. SrHAps incorporated into adhesive showed higher radiopacity, no alteration on DC despite slightly reducing the mechanical properties. SIGNIFICANCE: Although the mechanical properties are slightly impaired, incorporation of SrHAp nanoparticles offers potential method to improve radiopacity of restorative dental resins, easing the tracking of actual remineralization effects and enabling diagnosis of recurrent caries.

Ultrafast sonochemistry-based approach to coat TiO2 commercial particles for sunscreen formulation.

TiO2 is a common inorganic filter used in sunscreens due to its photoprotective effect on the skin against UV radiation. However, the use of this kind of material in cosmetics is limited by its inherent photocatalytic activity. It is known that coating on TiO2 surface can improve some features. Although, many of the methodologies used for this purpose are still laborious and time-consuming. Thus, this work reports a novel, easy, cheap and fast strategy to coat TiO2 particles by using a sonochemistry approach, aiming to decrease photocatalytic activity and to enhance colloidal stability. For this proposal, SiO2, Al2O3, ZrO2 and sodium polyacrylate (PAANa) were used to tune the surface of commercial TiO2 particles and they were applied in a sunscreen formulation. The samples were characterized by XRPD, FT-IR, DLS, EDS, SEM and TEM. The photocatalytic activity and UV-shielding ability were also evaluated. The sunscreen formulations were prepared and characterized by zeta potential, DLS, and Sun Protection Factor (SPF). FT-IR, EDS, and charge surface of the particles confirmed the success of the sonochemistry coating. Additionally, TiO2@Al2O3, TiO2@SiO2 and TiO2@PAANa show a lower photocatalytic activity than original TiO2 with similar UV-shielding ability. The sunscreens produced with the coated TiO2 have similar SPF to the one with commercial TiO2. Specifically, the sunscreen with TiO2@PAANa shows an increase in colloidal stability. Herein, the incorporation of the sonochemical-coated TiO2 particles in sunscreen formulations may produce sunscreens with better aesthetic appearance and a greater health security due to its lower free radicals production.

Fast ultrasound assisted synthesis of chitosan-based magnetite nanocomposites as a modified electrode sensor.

Chitosan-based magnetite nanocomposites were synthesized using a versatile ultrasound assisted in situ method involving one quick step. This synthetic route approach results in the formation of spheroidal nanoparticles (Fe3O4) with average diameter between 10 and 24nm, which were found to be superparamagnetic with saturation magnetization (Ms) ranges from 32-57emug(-1), depending on the concentration. The incorporation of Fe3O4 into chitosan matrix was also confirmed by FTIR and TG techniques. This hybrid nanocomposite has the potential application as electrochemical sensors, since the electrochemical signal was excepitionally stable. In addition, the in situ strategy proposed in this work allowed us to synthesize the nanocomposite system in a short time, around 2min of time-consuming, showing great potential to replace convencional methods. Herein, the procedure will permit a further diversity of applications into nanocomposite materials engineering.

Novel hydroxyapatite nanorods improve anti-caries efficacy of enamel infiltrants.

OBJECTIVES: Enamel resin infiltrants are biomaterials able to treat enamel caries at early stages. Nevertheless, they cannot prevent further demineralization of mineral-depleted enamel. Therefore, the aim of this work was to synthesize and incorporate specific hydroxyapatite nanoparticles (HAps) into the resin infiltrant to overcome this issue. METHODS: HAps were prepared using a hydrothermal method (0h, 2h and 5h). The crystallinity, crystallite size and morphology of the nanoparticles were characterized through XRD, FT-IR and TEM. HAps were then incorporated (10wt%) into a light-curing co-monomer resin blend (control) to create different resin-based enamel infiltrants (HAp-0h, HAp-2h and HAp-5h), whose degree of conversion (DC) was assessed by FT-IR. Enamel caries lesions were first artificially created in extracted human molars and infiltrated using the tested resin infiltrants. Specimens were submitted to pH-cycling to simulate recurrent caries. Knoop microhardness of resin-infiltrated underlying and surrounding enamel was analyzed before and after pH challenge. RESULTS: Whilst HAp-0h resulted amorphous, HAp-2h and HAp-5h presented nanorod morphology and higher crystallinity. Resin infiltration doped with HAp-2h and HAp-5h caused higher enamel resistance against demineralization compared to control HAp-free and HAp-0h infiltration. The inclusion of more crystalline HAp nanorods (HAp-2h and HAp-5h) increased significantly (p<0.05) the DC. SIGNIFICANCE: Incorporation of more crystalline HAp nanorods into enamel resin infiltrants may be a feasible method to improve the overall performance in the prevention of recurrent demineralization (e.g. caries lesion) in resin-infiltrated enamel.