Photoluminescent Polymer Nanoparticles Based on Oxazolidine Derivatives for Authentication and Security Marking of Confidential Notes.

Colloidal materials have widely been used to develop innovative anticounterfeiting nanoinks for information encryption. Latex nanoparticles based on methyl methacrylate (MMA) and 2-hydroxyethyl methacrylate (HEMA) bearing hydroxyl functional groups were synthesized via semicontinuous miniemulsion polymerization. The size determination of the nanoparticles and microscopic results showed mostly spherical nanoparticles with a narrow size distribution and a mean size of about 80 nm. Two oxazolidine derivatives were physically doped at the surface of the nanoparticles to prepare photoluminescent polymer nanoparticles. Hydroxyl functional groups at the surface of the nanoparticles led to their hydrogen bonding interactions with the doped luminescent compounds. Optical analysis of the photoluminescent nanoparticles displayed different fluorescence emission and UV-vis absorbance intensities based on the amount of polar groups located at the surface of colloidal nanoparticles. Reducing the particle size to below 100 nm along with increasing the surface area can assist the decrease of the light reflectance and improvement of the latex nanoparticles' efficiency in the anticounterfeiting industry. This preparation methodology can efficiently provide remarkable photoreversible anticounterfeiting nanoinks used in different applications, such as print marking, security encoded tags, labeling, probing, and handwriting.

Encryption and optical authentication of confidential cellulosic papers by ecofriendly multi-color photoluminescent inks.

Photodetection of originality and authentication of security documents such as money, passport, bank note, and national card have been a significant challenge in recent decade. Using of advanced optical systems could remarkably reduce copy and counterfeiting of such national and international documents. Novel ecofriendly multi-color photoluminescent inks were developed for information encryption on cellulosic papers and optical authentication of confidential/original documents by synthesis of water-based latex nanoparticles modified with photoluminescent coumarin (blue emission) and two photochromic spiropyran derivatives (red and orange emissions). Some of the latexes with higher fluorescence emission were formulated to water-based inks, and then loaded to stamps with different marks for printing of quick response code, barcode, finger print, and other marks on cellulosic documents. All of the printed marks display ultra-bright blue, red, and orange fluorescence emissions upon UV irradiation, which have potential applications in encryption, security marking and optical authentication of confidential cellulose substrates.

Rewritable Anticounterfeiting Polymer Inks Based on Functionalized Stimuli-Responsive Latex Particles Containing Spiropyran Photoswitches: Reversible Photopatterning and Security Marking.

Increase of safety in security documents by using anticounterfeiting inks based on fluorochromic and photochromic compounds has attracted a great deal of attention in the recent years. Herein, we developed novel functionalized stimuli-responsive latex particles containing spiropyran (1 wt %) by semicontinuous emulsifier-free emulsion polymerization, which are usable as anticounterfeiting inks for marking on security documents and also photopatterning on cellulosic papers. The size and morphology of the latex particles were characterized by scanning electron microscopy and dynamic light scattering and their functionality was characterized by Fourier-transform infrared spectroscopy. All the stimuli-responsive latexes are composed of spherical particles with different hydroxyl, epoxy, and carboxylic acid functional groups, and the size of the particles varies in the range of 400-900 nm. Additionally, the latex particles undergo a remarkable light-induced size variation (aggregation-disaggregation) upon UV illumination (365 nm), depending on the functional group type, as a result of π-π stacking interactions and also electrostatic attractions between the different particles. The photochromic behavior, kinetics of the SP ⇌ MC isomerization, photoswitchability, and photofatigue-resistant characteristics of the prepared latexes were extensively investigated. The results display that the photochromic behavior and SP ⇌ MC isomerization can significantly be influenced by the polar interactions between the functional groups and MC molecules. As a novel application, the prepared stimuli-responsive latexes were used as anticounterfeiting inks for writing on cellulosic paper and also security marking on several monies, where the written phrase displayed red fluorescence emission and coloration under and after UV illumination (365 nm), respectively. Additionally, the latexes were sprayed on cellulosic papers to prepare stimuli-responsive papers for investigation of their photopatterning ability under UV irradiation and different masking. The presence of functional groups and large particle sizes are the main effective factors for stabilization of the latex particles on cellulosic papers. This is the first report on application of functionalized stimuli-responsive latex particles containing spiropyran as anticounterfeiting inks for security marking and photopatterning on cellulosic papers, directly and without using further additives.

Light-Induced Aggregation and Disaggregation of Stimuli-Responsive Latex Particles Depending on Spiropyran Concentration: Kinetics of Photochromism and Investigation of Reversible Photopatterning.

Light-controlling the physical and chemical properties of smart polymers by using photochromic compounds has been an interesting research subject. Incorporation of spiropyran (SP) on the surface of particles can induce photoswitchable aggregation/disaggregation to stimuli-responsive colloids. Herein, we developed a novel class of stimuli-responsive latex particles bearing SP with different contents (0, 0.5, 1, 3, and 5 wt %) by semicontinuous emulsifier-free emulsion copolymerization, which is able to change the particle size by light-induced aggregation/disaggregation in response to ultraviolet (UV) irradiation and visible light. The scanning electron microscopy images revealed the spherical morphology of the latex particles, with the size in the range of 400-900 nm. Light-induced aggregation and disaggregation of stimuli-responsive latex particles were investigated by dynamic light scattering and also confirmed by variation of transmittance during UV illumination time using ultraviolet-visible spectroscopy. The range of the light-induced shift in the particle size is about 200-600 nm (depending on the concentration of SP), where the reduction of transmittance upon UV irradiation (and conversely upon visible light) confirms the ability of latex particles for displaying reversible photoswitchable aggregation/disaggregation and also light-controlling the particle size. The kinetics of SP to merocyanine (MC) and MC to SP isomerizations were experimentally investigated and fitted by exponential equations. The photochromic latexes displayed remarkable photoswitchability and photofatigue resistant properties under alternating UV and visible light irradiation cycles. Additionally, these stimuli-responsive latexes displayed potential applications such as anticounterfeiting inks in erasable and rewritable writings on cellulosic papers for increasing safety in security documents.

Nanomedicine and advanced technologies for burns: Preventing infection and facilitating wound healing.

According to the latest report from the World Health Organization, an estimated 265,000 deaths still occur every year as a direct result of burn injuries. A widespread range of these deaths induced by burn wound happens in low- and middle-income countries, where survivors face a lifetime of morbidity. Most of the deaths occur due to infections when a high percentage of the external regions of the body area is affected. Microbial nutrient availability, skin barrier disruption, and vascular supply destruction in burn injuries as well as systemic immunosuppression are important parameters that cause burns to be susceptible to infections. Topical antimicrobials and dressings are generally employed to inhibit burn infections followed by a burn wound therapy, because systemic antibiotics have problems in reaching the infected site, coupled with increasing microbial drug resistance. Nanotechnology has provided a range of molecular designed nanostructures (NS) that can be used in both therapeutic and diagnostic applications in burns. These NSs can be divided into organic and non-organic (such as polymeric nanoparticles (NPs) and silver NPs, respectively), and many have been designed to display multifunctional activity. The present review covers the physiology of skin, burn classification, burn wound pathogenesis, animal models of burn wound infection, and various topical therapeutic approaches designed to combat infection and stimulate healing. These include biological based approaches (e.g. immune-based antimicrobial molecules, therapeutic microorganisms, antimicrobial agents, etc.), antimicrobial photo- and ultrasound-therapy, as well as nanotechnology-based wound healing approaches as a revolutionizing area. Thus, we focus on organic and non-organic NSs designed to deliver growth factors to burned skin, and scaffolds, dressings, etc. for exogenous stem cells to aid skin regeneration. Eventually, recent breakthroughs and technologies with substantial potentials in tissue regeneration and skin wound therapy (that are as the basis of burn wound therapies) are briefly taken into consideration including 3D-printing, cell-imprinted substrates, nano-architectured surfaces, and novel gene-editing tools such as CRISPR-Cas.