Percutaneous absorption of sunscreens from liquid crystalline phases

Advancements in sunscreen formulations: integrating polyphenolic nanocarriers and nanotechnology for enhanced UV protection

Sunscreens are essential in protecting the skin from harmful effects of ultraviolet radiation (UVR). These formulations, designed to absorb, block, or scatter UVR, offer vital protection against skin aging, sunburns, and the development of skin cancers like melanomas. However, some sunscreens, especially those containing organic/chemical compounds, can cause allergic reactions. To address this, researchers are extensively investigating formulations that incorporate plant extracts rich in polyphenols, such as flavonoids and carotenoids, which can be considered safer alternatives. Products derived from plants are commonly used in cosmetics to counteract skin aging due to their antioxidant activity that combat harmful free radicals. This review focuses on evaluating the advancements in chemical and natural sunscreens, exploring the integration of polyphenolic nanocarriers within sunscreen formulas, their interaction with UVR, and utilizing nanotechnology to enhance their effectiveness. An attempt has been made to highlight the concerns related to toxicity associated with their use and notable advancements in the regulatory aspects governing their utilization.

Excellent ultraviolet-blocking properties of chiral nematic liquid crystals

We report the evaluation of chiral nematic liquid crystal (CNLC) in blocking ultraviolet (UV). The CNLC was coated on a calcium fluoride substrate to measure the spectral transmittance, which was measured to detect the UV-blocking effect of CNLC. The results show that CNLC could reduce UVB (290-320 nm) by 99.9% and UVA (320-400 nm) by 95.6%. The barrier effect of cake-shaped semi-solidified CNLC microspheres was further investigated, and it was found that cake-shaped semi-solidified CNLC microspheres could reduce UVB by 58.2% and UVA by 34.1%. This is due to the chemical absorption property of CNLC, which has UV-absorbing functional groups such as the benzene rings. And the physical reflection properties of CNLC could periodically reflect a certain wavelength of light. Liquid crystal (LC) is a rich set of soft materials with rod-like structures widely existing in nature, which is harmless to the human body and environment. Therefore, using CNLC's function of blocking UV, a new sunscreen can be developed.

Chemical and Pharmacological Properties of Decoquinate: A Review of Its Pharmaceutical Potential and Future Perspectives

Decoquinate (DQ) is an antimicrobial agent commonly used as a feed additive for birds for human consumption. Its use as an additive is well established, but DQ has the potential for therapy as an antimicrobial drug for veterinary treatment and its optimized derivatives and/or formulations, mainly nanoformulations, have antimicrobial activity against pathogens that infect humans. However, DQ has a high partition coefficient and low solubility in aqueous fluids, and these biopharmaceutical properties have limited its use in humans. In this review, we highlight the antimicrobial activity and pharmacokinetic properties of DQ and highlight the solutions currently under investigation to overcome these drawbacks. A literature search was conducted focusing on the use of decoquinate against various infectious diseases in humans and animals. The search was conducted in several databases, including scientific and patent databases. Pharmaceutical nanotechnology and medicinal chemistry are the tools of choice to achieve human applications, and most of these applications have been able to improve the biopharmaceutical properties and pharmacokinetic profile of DQ. Based on the results presented here, DQ prototypes could be tested in clinical trials for human application in the coming years.

Sunscreens and their usefulness: have we made any progress in the last two decades?

Sunscreens have now been around for decades to mitigate the Sun's damaging ultraviolet (UV) radiation which, although essential for the existence of life, is a recognized prime carcinogen. Accordingly, have suncreams achieved their intended purposes towards protection against sunburns, skin photo-ageing and the like? Most importantly, however, have they provided the expected protection against skin cancers that current sunscreen products claim to do? In the last two decades, there have been tens, if not hundreds of studies on sunscreens with respect to skin protection against UVB (280‒320 nm)-traditionally sunscreens with rather low sun protection factors (SPF) were intended to protect against this type of radiation-and UVA (320‒400 nm) radiation; a distinction between SPF and UVA protection factor (UVA-PF) is made. Many of the studies of the last two decades have focused on protection against the more skin-penetrating UVA radiation. This non-exhaustive article reviews some of the important facets of what is currently known about sunscreens with regard (i) to the physical UV filters titanium dioxide (TiO₂) and zinc oxide (ZnO) and the mostly photo-unstable chemical UVB/UVA filters (e.g., octinoxate (OMC) and avobenzone (AVO), among others), (ii) to novel chemical sunscreen agents, (iii) to means that minimize the breakdown of chemical filters and improve their stability when exposed to UV sunlight, (iv) to SPF factors, and (v) to a short discussion on non-melanoma skin cancers and melanoma. Importantly, throughout the article we allude to the safety aspects of sunscreens and at the end ask the question: do active ingredients in sunscreen products pose a risk to human health, and what else can be done to enhance protection? Significant loss of skin protection from two well-known commercial suncreams when exposed to simulated UV sunlight. Cream I: titanium dioxide, ethylhexyl triazone, avobenzone, and octinoxate; Cream II: octyl salicylate, oxybenzone, avobenzone, and octinoxate.

Microemulsion systems: from the design and architecture to the building of a new delivery system for multiple-route drug delivery

Poorly soluble active pharmaceutical ingredients (APIs) create major problems in drug dosage form formulation resulting in significant delays in drug pharmaceutical screening, impairing the drug dosage form production. Aiming to minimize the use of excipients for increasing drug apparent solubility and, as a result, its bioavailability, exploration of innovative approaches is an earnest need. Microemulsion is an alternative drug delivery system that emerged as a valuable tool to achieve safe formulations for insoluble compounds and to improve their biopharmaceutical properties and pharmacokinetics. This review aims to present the state of the art of microemulsion systems, bringing an overview about their origin and how they can be properly produced and thoroughly characterized by different approaches. Furthermore, comments on regulatory issues regarding stability assessment and toxicity evaluation are discussed. The review concludes with a current opinion on microemulsion systems. The overall objective of this work was to describe all the potentialities of microemulsion systems as a drug carrier for therapeutic purposes, highlighting the unique features of this nanotechnological platform. Display Image.

Using ordered mesoporous silica SBA-15 to limit cutaneous penetration and transdermal permeation of organic UV filters

Avobenzone (AVO), oxybenzone (OXY), and octyl methoxycinnamate (OMC), are widely used UV filters. The aim of this study was to investigate the effect of incorporation in mesoporous silica (SBA-15) on their cutaneous deposition and permeation. Stick formulations containing "free" and "incorporated" UV filters (SF1 and SF2, respectively) were prepared and characterized with respect to their physicochemical, thermal, and functional properties. Cutaneous delivery experiments using porcine skin with quantification by UHPLC-MS/MS, demonstrated that skin deposition of AVO and OXY after application of SF2 for 6 and 12 h was significantly lower than that from SF1 at each time-point (Student t-test, p < 0.05): e.g. OXY permeation across the skin was 30-, 12- and 1.5-fold lower after 6, 12 and 24 h, respectively, following application of SF2. Cutaneous biodistribution profiles of AVO and OXY to 800 µm evidenced a significant decrease in the amounts in the viable epidermis and dermis. In contrast, deposition of the more lipophilic OMC was not significantly different (p ˃ 0.05). In vitro photoprotective efficacy results demonstrated that adsorption/entrapment of UV filters enhanced the sun protection factor by 94%. In conclusion, SBA-15, an innovative mesoporous material, increased photoprotection by UV filters while reducing their cutaneous penetration and transdermal permeation.

Nanostructured liquid crystalline formulation as a remarkable new drug delivery system of anti-epileptic drugs for treating children patients

PURPOSE

Development of a new dosage-form of antiepileptic-drugs appropriated for children.

METHODS

Clonazepam (Cl) was formulated as cubosomal-gel (cub-gel) to be used as a patch reservoir through transdermal-route. Cubosomes prepared using glycerol-mono-oleate(GMO)/Pluronic-F127(PF127) mixture. An actual-statistical design was used to investigate the effect of different stabilizing agents (Ethanol and PVA) and surfactant concentration on cubosomes' particle size and entrapping-efficiency. The selected formulae were evaluated by testing particle-morphology, in vitro drug release and stability. Cub-gel was prepared using selected cubosome formulae. The optimal cub-gel subjected to in vitro dissolution, ex-vivo permeation and skin deposition studies followed by studying its pharmacological effect.

RESULTS

Using PVA or Et as stabilizers with PF127 significantly decreases the average cubosomes'PS (352 ±  2.8 and 264 ± 2.16 nm) and increases EE (58.97 ± 4.57% and 54.21 ± 3.89%). Cubosomes increase the initial release rate of Cl to ensure rapid therapeutic effect (37.39% and 46.04% in the first hour) followed by a prolonged release till 4 h. Cub-gel containing PVA showed significantly higher Cl-transdermal permeation when compared to Cl-suspension. Moreover, increases the retention-time (89.57% at 48 h) and skin-deposition up to 6-times. It also reduces the epileptic seizures and alters the behavioral parameters induced by pilocarpine.

CONCLUSIONS

Cubosomal-gel could be considered an innovative dosage-form for Cl through the transdermal route.

In Vitro Evaluation of Sunscreen Safety: Effects of the Vehicle and Repeated Applications on Skin Permeation from Topical Formulations

The evaluation of UV-filter in vitro percutaneous absorption allows the estimation of the systemic exposure dose (SED) and the margin of safety (MoS) of sunscreen products. As both the vehicle and pattern of application may affect sunscreen safety and efficacy, we evaluated in vitro release and skin permeation of two widely used UV-filters, octylmethoxycinnamate (OMC) and butylmethoxydibenzoylmethane (BMBM) from topical formulations with different features (oil in water (O/W) emulsions with different viscosity, water in oil (W/O) emulsion, oils with different lipophilicity). To mimic in-use conditions, we carried out experiments repeating sunscreen application on the skin surface for three consecutive days. BMBM release from all these vehicles was very low, thus leading to poor skin permeation. The vehicle composition significantly affected OMC release and skin permeation, and slight increases of OMC permeation were observed after repeated applications. From skin permeation data, SED and MoS values of BMBM and OMC were calculated for all the investigated formulations after a single application and repeated applications. While MoS values of BMBM were always well beyond the accepted safety limit, the safety of sunscreen formulations containing OMC may depend on the vehicle composition and the application pattern.

Liquid-crystalline nanoarchitectures for tissue engineering

Hierarchical orders are found throughout all levels of biosystems, from simple biopolymers, subcellular organelles, single cells, and macroscopic tissues to bulky organs. Especially, biological tissues and cells have long been known to exhibit liquid crystal (LC) orders or their structural analogues. Inspired by those native architectures, there has recently been increased interest in research for engineering nanobiomaterials by incorporating LC templates and scaffolds. In this review, we introduce and correlate diverse LC nanoarchitectures with their biological functionalities, in the context of tissue engineering applications. In particular, the tissue-mimicking LC materials with different LC phases and the regenerative potential of hard and soft tissues are summarized. In addition, the multifaceted aspects of LC architectures for developing tissue-engineered products are envisaged. Lastly, a perspective on the opportunities and challenges for applying LC nanoarchitectures in tissue engineering fields is discussed.

Lamellar Liquid Crystal Improves the Skin Retention of 3-O-Ethyl-Ascorbic Acid and Potassium 4-Methoxysalicylate In Vitro and In Vivo for Topical Preparation

The study aimed at increasing the skin retention of 3-O-ethyl-ascorbic acid (EA) and potassium 4-methoxysalicylate (4-MSK) via topical administration for effective skin-whitening. To achieve this goal, EA and 4-MSK were formulated into lamellar liquid crystalline (LLC) cream, and response surface methodology (RSM) was employed to optimize the formulation. Polarized light microscopy (PLM), differential scanning calorimetry (DSC), and rheological experiments were performed to confirm the presence of the LLC structure in the base of cream. In addition, a comparison analysis of the skin retention of the two drugs between the LLC cream and the common o/w (COW) cream was made through in vitro permeation and in vivo drug distribution experiments. As a result, the optimal formulation was defined as 1.2% of EA, 1.48% of 4-MSK, 14.05% of Schercemol™ DISM Ester (DISM) as the oil, 4.0% of Emulium® Delta as the emulsifier, and 3.0% of stearyl alcohol as the co-emulsifier. In comparison with the COW cream, the LLC cream significantly increased the skin retention of EA and 4-MSK both in vitro and in vivo. In conclusion, the LLC carrier serves as a promising choice for topical preparation by enhancing skin retention and providing desirable rheological characteristics.

Relationship between composition and organizational levels of nanostructured systems formed by Oleth 10 and PPG-5-Ceteth-20 for potential drug delivery

In this paper, nanostructured systems were developed, with the aid of ternary phase diagrams, from two surfactants, of differing degrees of lipophilicity (PPG-5-Ceteth-20 and the Oleth 10) and two oil phases (oleic acid and isopropyl myristate). It was observed that there were differences between the four resulting phase diagrams in the physical properties of the systems they represent. Thus, due to the capacity of Oleth 10 (as surfactant) and oleic acid (as the oil phase) to reduce interfacial tension, large regions of translucent systems were seen on the diagrams produced by them. By polarized light microscopy, it was possible to identify the isotropic and anisotropic properties of these systems, which were confirmed by small-angle X-ray scattering (SAXS) analysis. Furthermore, it was found that increasing the proportion of water in the formulations led to more highly organized structures, resulting in narrower and well defined SAXS peaks.

Preparation and evaluation of liquid-crystal formulations with skin-permeation-enhancing abilities for entrapped drugs

The usefulness of liquid crystals (LC) in topical formulations for application to skin was evaluated by measuring the in vitro permeation profile of a model compound, calcein, entrapped in a LC formulation, through excised hairless rat skin and a three-dimensional cultured human-skin model; the viability was determined using the MTT assay. Two physically stable LCs were prepared from a mixture of mono-, di-, and tri-esters 1, and monoesters 2, composed of erythritol and phytanylacetic acid. Cryo-transmission electron microscopy (cryo-TEM), electron diffraction patterns, and small-angle X-ray diffraction (SAXS) observations of the LC nanodispersions showed that the structures of the LCs were reverse hexagonal (LC-A) and cubic (LC-B). The skin-permeation properties of calcein were enhanced by entrapping in the LCs as a result of the increase in calcein partition from the LC dispersion solution into the skin; the properties were analyzed using a skin-permeation-time profile. Drug partitioning could also be modified by the LC structure. No skin damage was caused by the LC formulation in these experiments.The present study suggests that LC dispersions are potential additives in topical drug formulations and cosmetic formulations.

Topical delivery of lipophilic drugs from o/w Pickering emulsions

Surfactant-free emulsions stabilized by solid particles (Pickering emulsions) have been evaluated in the terms of skin absorption of lipophilic drugs. The behavior of three formulations: a surfactant-based emulsion, a Pickering emulsion stabilized by silica particles and a solution in triglyceride oil, were compared in order to assess the effect of the surface coating of Pickering emulsions as new dosage forms for topical application. Such comparative investigation was performed in vitro on excised pig skin in Franz diffusion cells with all-trans retinol as model lipophilic drug. Surfactant-based (classical, CE) and Pickering (PE) oil-in-water emulsions containing retinol were prepared with the same chemical composition (except the stabilizing agent: surfactant or silica particles), the same droplet size and the same viscosity. No permeation through the skin sample was observed after 24h exposure because of the high lipophilic character of retinol. Penetration of retinol was 5-fold larger for both CE and PE than for the solution in triglyceride. The distribution of retinol inside the skin layers depended significantly on the emulsions type: the classical emulsion allowed easy diffusion through the stratum corneum, so that large amounts reached the viable epidermis and dermis. Conversely, high storage of retinol inside the stratum corneum was favored by the Pickering emulsion. The retinol content in stratum corneum evaluated by skin stripping, demonstrated the increased retinol accumulation from PE. Therefore Pickering emulsions are new drug penetration vehicles with specific behavior; they are well-suited either for targeting the stratum corneum or aimed at slow release of drug from stratum corneum used as a reservoir to the deeper layers of skin.

Structural changes of biocompatible neutral microemulsions stabilized by mixed surfactant containing soya phosphatidylcholine and their relationship with doxorubicin release

Depending on the composition, the mixture of surfactant, oil and water, may form supramolecular aggregates with different structures which can significantly influence the drug release. In this work several microemulsion (ME) systems containing soya phosphatidylcholine (SPC) and eumulgin HRE40 (EU) as surfactant, cholesterol (O) as oil phase, and ultra-pure water as an aqueous phase were studied. MEs with and without the antitumoral drug doxorubicin (DOX) were prepared. The microstructures of the systems were characterized by photon correlation spectroscopy, rheological behavior, polarized light microscopy, small-angle X-ray scattering (SAXS) and X-ray diffraction (XRD). The results reveal that the diameter of the oil droplets was dependent on the surfactant (S) amount added to formulations. The apparent viscosity was dependent on the O/S ratio. High O/S ratio leads to the crystallization of cholesterol polymorphs phases which restricts the mobility of the DOX molecules into the ME structure. Droplets with short-range spatial correlation were formed from the ME with the low O/S ratio. The increase of the cholesterol fraction in the O/S mixture leads to the formation of ordered structures with lamellar arrangements. These different structural organizations directly influenced the drug release profiles. The in vitro release assay showed that the increase of the O/S ratio in the formulations inhibited the constant rate of DOX release. Since the DOX release ratio was directly dependent on the ratio of O/S following an exponential decay profile, this feature can be used to control the DOX release from the ME formulations.

A reversed-phase ion-interaction chromatographic method for in-vitro estimation of the percutaneous absorption of water-soluble UV filters

An analytical method based on ion-interaction chromatography with UV detection for simultaneous in-vitro estimation of the percutaneous absorption of the most used water-soluble UV filters in sunscreen cosmetics is proposed. These UV filters were phenylbenzimidazole sulfonic acid, disodium phenyl dibenzimidazole tetrasulfonate, benzophenone-4, and terephthalylidene dicamphor sulfonic acid. The methodology is based on applying the sunscreen containing the target UV filters to human epidermis in a diffusion cell. Analytes are determined in the receptor solution. To ensure skin integrity, screening of the cells was carried out by analytical determination of a marker. Analytical variables such as percentage ethanol, concentration of ion-pairing agent, pH of the mobile phase, and temperature were studied in order to achieve high resolution of the chromatographic peaks in the lowest possible time of analysis. The conditions selected consisted of a mobile phase composed of 35:65 (v/v) ethanol-ammonium acetate buffer solution (pH 4, containing 50 mmol L(-1) tetra-n-butylammonium bromide). The chromatographic determination was carried out with the analytical column at 50 degrees C. UV detection was carried out at the maximum absorption wavelength for each analyte. The limit of detection (3s(y/x)/b) ranged from 16 to 65 ng mL(-1), depending on the analyte.

Relationship between structural features and in vitro release of doxorubicin from biocompatible anionic microemulsion

In this work structural features of anionic microemulsions, containing the pharmaceutical biocompatible components soya phosphatidylcholine (SPC), eumulgin HRE 40 (EU) and sodium oleate (SO) as surfactant, cholesterol (CHO) as oil phase and aqueous buffer were studied. Microemulsions were formulated with and without the antitumor drug doxorubicin (DOX). The various microstructures characterized in the pseudo-ternary phase diagram were analyzed by polarized light microscopy, small-angle X-ray scattering (SAXS) and X-ray diffraction (XRD) as well as by their ability to incorporate and release DOX. The experimental results demonstrated a correlation between the composition, the structural features and drug delivery. It was found that at higher cholesterol contents, the crystallization of CHO polymorph phases changed the mobility of DOX molecules. Droplets were formed with short-range spatial correlation from a microemulsion (ME) with a low surfactant:oil ratio. More ordered structures with lamellar arrangements formed by the increasing of the CHO proportions in the formulation may be due to CHO crystallization. The in vitro release of DOX showed that the presence of a high content of crystalline CHO prolongs the release of DOX from ME. The retention of DOX in the internal oil phase of the ME may modulate the drug release for a prolonged time. These results clearly demonstrate the potential of ME as a drug-delivery system.

Fluorescence of sunscreens adsorbed to dielectric nanospheres: parallels to optical behavior on hacat cells and skin

Sunscreens applied to the skin are retained primarily in the stratum corneum, where they adsorb and act as a barrier preventing UV penetration to deeper layers. Photophysical properties of sunscreens have traditionally been studied either in solvents, which are very different from skin, or in skin or complex artificial skin systems, which are difficult to handle. The purpose of this study was to determine whether polystyrene nanospheres could serve as an improvement over solvents for evaluation of the photophysical properties of sunscreens without the presence of autofluorescence from and interactions with specific skin biomolecules. We used HaCat cells and excised skin for this comparative study with nanospheres. Fluorescence spectral properties of common hydrophobic sunscreens octyl salicylate, padimate O (2-ethylhexyl-4-dimethylaminobenzoate) and octyl methoxycinnamate adsorbed to 220 nm polystyrene spheres are similar to those of sunscreens adsorbed to HaCat cells and excised skin. Specifically, similarity in the emission peaks and their approximate positions, excitation peak positions and a measurable reduction in scattering upon sunscreen addition suggest that polystyrene nanospheres constitute a useful system to evaluate the photophysical properties of topical sunscreens and may serve as a model system for high-throughput evaluation of potential sunscreens. An unexpected result of this comparative study was the observation of an increase in a specific skin component emission caused by addition of padimate O.

In vitro and in vivo percutaneous absorption of topical dosage forms: case studies

This article evaluated the influence of vehicle compositions on topical drug availability. In vitro drug release and in vivo experiments were performed in case of the hydrophilic ketamine hydrochloride and the lipophilic piroxicam. Ketamine hydrochloride is a NMDA receptor antagonist that has been useful for anesthesia and analgesia. The study of transdermal ketamine delivery is a novelty, because nobody has investigated the hypnotic effects of ketamine after this administration route. In vitro measurements gave a good basis for screening among the developed products. The physiological changes after ketamine administration showed, that there were significant differences among the parameters tested (breathing rate, duration of sleep) from the developed products (hydrogel, lyotropic liquid crystal and o/w cream) compared to the reference product (Carbopol gel). The in vivo feedback for piroxicam was the measurement of the anti-inflammatory activity by edema inhibition percentage. Significant differences were measured in case of the developed systems compared to the reference.

Optical spectroscopy of hydrophobic sunscreen molecules adsorbed to dielectric nanospheres

Fluorescence and absorption spectra of hydrophobic sunscreens, weakly fluorescent octyl methoxycinnamate, moderately fluorescent octyl salicylate and highly fluorescent 2-ethylhexyl-4-(dimethylamino)benzoate (padimate O) adsorbed to dielectric microspheres in aqueous suspension, have been compared with spectra in organic solution. The fluorescence of adsorbed salicylate and padimate is enhanced compared with fluorescence in methanol: about a factor of 6 and 30 in terms of fluorescence yield per molecule of salicylate and padimate, respectively. Cinnamate, which has a low fluorescence yield, does not show a comparable fluorescence enhancement. The fluorescence amplification is independent of sphere diameter from 30 to 1500 nm, at least for salicylate. The enhancement, as well as the location of absorption spectral peaks, is consistent with a low-dielectric constant environment of the molecules, in spite of the presumed location near the interface between polystyrene (epsilon = 2.4-3.8) and water (epsilon = 78). The adsorbed state of these sunscreens represents a proposed improved in vitro model for the environment of sunscreens in vivo, as well as a general model for chromophores in heterogeneous environments.

Influence of encapsulation on the in vitro percutaneous absorption of octyl methoxycinnamate

The purpose of this study was to evaluate the in vitro transdermal permeation and skin accumulation of one ultraviolet (UV) absorber-octyl methoxycinnamate (OMC)-through pig skin and to determine the quantity of OMC in the skin surface and different pig skin layers (stratum corneum, viable epidermis, dermis, and receptor fluid). Four cases have been considered: the application of oil-in-water (O/W) and water-in-oil (W/O) emulsions containing the same filter free and encapsulated in nanocapsules (NC). The influence of the carrier on the percutaneous penetration was studied. Data showed that UV absorber exhibited increases in skin accumulation when is formulated in emulsions in free form. Skin accumulation of OMC-free in the emulsions was significantly (P < 0.05) greater than that of OMC-encapsulated for all formulations investigated. OMC-free skin accumulation ranged from 127.8 +/- 22.8 microg/cm(2) (O/W emulsion) to 172.1 +/- 12.9 microg/cm(2) (W/O emulsion). OMC-encapsulated skin accumulation ranged from 50.3 +/- 13.1 microg/cm(2) to 43.0 +/- 6.5 microg/cm(2) at NC-O/W and NC-W/O, respectively. No significant differences were found in the transdermal permeation of cinnamate for any of the formulations tested. The results of this study demonstrate that the inclusion of OMC-encapsulated in sunscreen formulations decreases the skin accumulation of the cinnamate since the in vitro release mechanism of OMC-nanocapsules is governed by hydrophobicity and crystallinity of the polymer and by the high lipophilicity of the drug. The crystallinity of the polymer have the ability of reflecting and scattering UV radiation on their own thus leading to photoprotection without the need for molecular sunscreens.

Towards a quantification of disorder in materials: distinguishing equilibrium and glassy sphere packings

This paper examines the prospects for quantifying disorder in simple molecular or colloidal systems. As a central element in this task, scalar measures for describing both translational and bond-orientational order are introduced. These measures are subsequently used to characterize the structures that result from a series of molecular-dynamics simulations of the hard-sphere system. The simulation results can be illustrated by a two-parameter ordering phase diagram, which indicates the relative placement of the equilibrium phases in order-parameter space. Moreover, the diagram serves as a useful tool for understanding the effect of history on disorder in nonequilibrium structures. Our investigation provides fresh insights into the types of ordering that can occur in equilibrium and glassy systems, including quantitative evidence that, at least in the case of hard spheres, contradicts the notion that glasses are simply solids with the "frozen in" structure of an equilibrium liquid. Furthermore, examination of the order exhibited by the glassy structures suggests, to our knowledge, a new perspective on the old problem of random close packing.