Enhancing the sweat resistance of sunscreens.

BACKGROUND: While sunbathing of performing outdoor sport activities, sunscreens are important for protection of uncovered skin against ultraviolet (UV) radiation. However, perspiration negatively affects the performance of a sunscreen film by weakening its substantivity and uniformity through the activation of two mechanisms, namely sunscreen wash-off and sunscreen redistribution. MATERIAL AND METHODS: We used a perspiring skin simulator to investigate the effect of sunscreen formulation on its efficiency upon sweating. Specifically, we modified the sunscreen formulation by incorporating a hydrophobic film former and adding water-absorbing particles. Sunscreen performance before and after perspiration is assessed by in vitro sun protection factor measurements, direct detection of changes in the sunscreen distribution using UV reflectance imaging, and by coherent anti-Stokes Raman scattering (CARS) microscopy for microscopic characterization of the UV filter relocation. RESULTS: The results show that incorporating a hydrophobic film former can decrease sunscreen wash-off due to sweating, while an excessive amount of film former might negatively affect the sunscreen distribution. The addition of water-absorbing particles, on the other hand, had either a negative or positive impact on the sunscreen substantivity, depending on the particle properties. While the addition of large water-absorbing particles appeared to increase sunscreen redistribution, smaller particles that could form a gel-like structure upon contact with water, appeared to change sunscreen wetting and sweat droplet spreading, thereby decreasing sunscreen wash-off and sunscreen redistribution. CONCLUSIONS: We find that using a combination of hydrophobic film formers, which increase water resistance, and small water-absorbing particles, which change the wetting behavior, can make sunscreen formulations more sweat-resistant and less runny.

In vitro skin model for characterization of sunscreen substantivity upon perspiration.

OBJECTIVE: The resistance of sunscreens to the loss of ultraviolet (UV) protection upon perspiration is important for their practical efficacy. However, this topic is largely overlooked in evaluations of sunscreen substantivity due to the relatively few well-established protocols compared to those for water resistance and mechanical wear. METHODS: In an attempt to achieve a better fundamental understanding of sunscreen behaviour in response to sweat exposure, we have developed a perspiring skin simulator, containing a substrate surface that mimics sweating human skin. Using this perspiring skin simulator, we evaluated sunscreen performance upon perspiration by in vitro sun protection factor (SPF) measurements, optical microscopy, ultraviolet (UV) reflectance imaging and coherent anti-Stokes Raman scattering (CARS) microscopy. RESULTS AND CONCLUSION: Results indicated that perspiration reduced sunscreen efficiency through two mechanisms, namely sunscreen wash-off (impairing the film thickness) and sunscreen redistribution (impairing the film uniformity). Further, we investigated how the sweat rate affected these mechanisms and how sunscreen application dose influenced UV protection upon perspiration. As expected, higher sweat rates led to a large loss of UV protection, while a larger application dose led to larger amounts of sunscreen being washed-off and redistributed but also provided higher UV protection before and after sweating.

OBJECTIF: La résistance des écrans solaires à la perte de protection contre les ultraviolets (UV) à cause de la transpiration est importante quant à leur efficacité pratique. Cependant, ce point est généralement négligé dans les évaluations de la substantivité des écrans solaires en raison du nombre relativement faible de protocoles bien établis, en comparaison avec ceux pour la résistance à l'eau et l'usure mécanique. MÉTHODES: Dans le but de parvenir à une meilleure compréhension fondamentale du comportement des écrans solaires en cas d'exposition à la sueur, nous avons développé un simulateur de peau transpirante, dont la surface de substrat imite la transpiration de la peau humaine. À l'aide de ce simulateur, nous avons évalué les performances des écrans solaires lors de la transpiration par des mesures in vitro du facteur de protection solaire (FPS), par microscopie optique, par imagerie de la réflectance ultraviolette (UV) et par microscopie cohérente de diffusion Raman anti-Stokes (coherent anti-Stokes Raman scattering, CARS). RÉSULTATS ET CONCLUSION: Les résultats ont montré que la transpiration réduisait l'efficacité de l'écran solaire en raison de deux mécanismes, à savoir le lavage de l'écran solaire (altération de l'épaisseur du film) et la redistribution de l'écran solaire (altération de l'uniformité du film). De plus, nous avons étudié comment le taux de transpiration affectait ces mécanismes et comment la dose d'application d'écran solaire influençait la protection UV en cas de transpiration. Comme l'on pouvait s'y attendre, des taux de sueur plus élevés ont entraîné une perte importante de protection contre les UV, tandis qu'une dose d'application plus importante a conduit à des quantités plus importantes d'écran solaire lavé et redistribué, mais a également fourni une protection contre les UV plus élevée avant et après la transpiration.

Hyaluronic Acid Molecular Weight-Dependent Modulation of Mucin Nanostructure for Potential Mucosal Therapeutic Applications.

This study investigates the effects of different molecular weight hyaluronic acids (HAs) on the mucosal nanostructure using a pig stomach mucin hydrogel as a mucosal barrier model. Microparticles (1.0 µm) and nanoparticles (200 nm) were used as probes, and their movement in mucin was studied by a three-dimensional confocal microscopy-based particle tracking technique and by Nanoparticle Tracking Analysis (NTA) after addition of high-molecular weight (900 kDa) and low-molecular weight (33 kDa) HA. This demonstrated a molecular weight-dependent HA modulation of the mucin nanostructure with a 2.5-fold decrease in the mobility of 200 nm nanoparticles. To further investigate these mechanisms and to verify that the natural viscoelastic properties of mucus are not undesirably altered, rheological measurements were performed on mucin hydrogels with or without HA. This suggested the observed particle mobility restriction was not attributed to alterations of the natural mucin cohesive and viscoelastic properties but, instead, indicates that the added high-molecular weight HA primarily modulates the mucin nanostructure and mesh size. This study, hereby, demonstrates how mucus nanostructure can be modulated by the addition of high-molecular weight HA that offers an opportunity to control mucosal pathogenesis and drug delivery.

Sequence-Controlled Glycopolymers via Step-Growth Polymerization of Precision Glycomacromolecules for Lectin Receptor Clustering.

A versatile approach for the synthesis of sequence-controlled multiblock copolymers, using a combination of solid phase synthesis and step-growth polymerization by photoinduced thiol-ene coupling (TEC) is presented. Following this strategy, a series of sequence-controlled glycopolymers is derived from the polymerization of a hydrophilic spacer macromonomer and different glycomacromonomers bearing between one to five α-d-Mannose (Man) ligands. Through the solid phase assembly of the macromonomers, the number and positioning of spacer and sugar moieties is controlled and translates into the sequence-control of the final polymer. A maximum M̅n of 16 kDa, corresponding to a X̅n of 10, for the applied macromonomers is accessible with optimized polymerization conditions. The binding behavior of the resulting multiblock glycopolymers toward the model lectin Concanavalin A (ConA) is studied via turbidity assays and surface plasmon resonance (SPR) measurements, comparing the ability of precision glycomacromolecules and glycopolymers to bind to and cross-link ConA in dependence of the number of sugar moieties and overall molecular weight. The results show that there is a clear correlation between number of Man ligands and Con A binding and clustering, whereas the length of the glycooligomer- or polymer backbone seems to have no effect.

Neonatal Fc Receptor Binding Tolerance toward the Covalent Conjugation of Payloads to Cysteine 34 of Human Albumin Variants.

The long circulatory half-life of albumin facilitated by the interaction with the cellular recycling neonatal Fc receptor (FcRn) is utilized for drug half-life extension. FcRn engagement effects following covalent attachment of cargo to cysteine 34, however, have not been investigated. Poly(ethylene glycol) polymers were used to study the influence of cargo molecular weight on human FcRn engagement of recombinant wild type (WT) albumin and an albumin variant engineered for increased FcRn binding. Decreased affinity was observed for all conjugates; however, the engineered albumin maintained an affinity above that of unmodified wild type albumin that promotes it as an attractive drug delivery platform.

Tunable CD44-specific cellular retargeting with hyaluronic acid nanoshells.

PURPOSE: In this work we specifically investigate the molecular weight (Mw) dependent combinatorial properties of hyaluronic acid (HA) for exhibiting stealth and targeting properties using different Mw HA nanoshells to tune nanoparticle retargeting to CD44-expressing cancer cells. METHODS: HA of different Mw was covalently grafted onto model polystyrene nanoparticles and advanced surface analysis by X-ray photoelectron spectroscopy performed to quantify and evaluate the effect of the coating procedure. Specific CD44-mediated retargeting was investigated by flow cytometry and confocal microscopy using isogenic D44-deficient and CD44-expressing MCF-7 breast adenocarcinoma cells. RESULTS: Surface analysis demonstrated effective surface coating with 33, 260 and 900 kDa HA resulting in increased colloidal stability and highly negative surface charge due to presentation of up to 4.7% carboxyl groups that indicates an extended and non-constricted HA polymer surface. Reduced non-specific particle interaction in CD44(-) cells was shown for all HA nanoshells but CD44-dependent cellular retargeting and internalization in CD44(+) cells was highly dependent on the coating HA Mw properties. CONCLUSION: The combination of advanced surface characterization and evaluation of particle interactions in isogenic cells with and without CD44 receptor demonstrates direct evidence for the dual capacity of HA for stealth and CD44-mediated retargeting tunable by the HA molecular weight.

MFAP4-Deficiency Aggravates Age-Induced Changes in Resistance Artery Structure, While Ameliorating Hypertension.

BACKGROUND: Abnormalities of resistance arteries may play essential roles in the pathophysiology of aging and hypertension. Deficiency of the vascular extracellular matrix protein MFAP4 (microfibrillar-associated protein 4) has previously been observed as protective against aberrant arterial remodeling. We hypothesized that MFAP4-deficiency would reduce age- and hypertension-dependent arterial changes in extracellular matrix composition and stiffening. METHODS: Mesenteric arteries were isolated from old (20-23 months) littermate Mfap4+/+ and Mfap4-/- mice, and 2-photon excitation microscopy imaging was used to quantify elastin and collagen volumes and dimensions in the vascular wall. Ten-week-old littermate Mfap4+/+ and Mfap4-/- mice were subjected to 20 days of continuous Ang II (angiotensin II) infusion and hypertension was monitored using invasive blood pressure measurements. Arterial stiffness, responses to vascular constrictors, and myogenic tone were monitored using wire- or pressure-myography. Collagen contents were assessed by Western blotting. RESULTS: MFAP4-deficiency significantly increased collagen volume and elastin fragmentation in aged mesenteric arteries without affecting arterial stiffness. MFAP4-deficient mice exhibited reduced diastolic pressure in Ang II-induced hypertension. There was no significant effect of MFAP4-deficiency on mesenteric artery structural remodeling or myogenic tone, although collagen content in mesenteric arteries was tendentially increased in hypertensive Mfap4+/+ mice relative to Mfap4-/- mice. Increased efficacy of vasoconstrictors (phenylephrine, thromboxane) and reduced stiffness were observed in Ang II-treated Mfap4-/- mouse mesenteric arteries in ex vivo myography recordings. CONCLUSIONS: MFAP4-deficiency reduces the elastin/collagen ratio in the aging resistance artery without affecting arterial stiffness. In contrast, MFAP4-deficiency reduces the stiffness of resistance arteries and ameliorates Ang II-induced hypertension.

Cu Elimination from Cu-Coordinating Macromolecules.

We demonstrate a simple, fast, and efficient process for the elimination of Cu impurities from water-soluble Cu-coordinating macromolecules that are difficult to purify via standard polymer purification techniques. The process is based on the complexation and precipitation of Cu by sodium diethyldithiocarbamate and was investigated for two different compound classes known to coordinate to Cu in aqueous solution. More than 99.9% of the Cu impurity was eliminated, with a remaining level below the detection limit (0.0005 wt %). Further analysis by 1H NMR, MALDI, ATR-IR, and SEC showed no degradation or side reactions of the polymers induced by the treatment. This process thus compliments the growing toolbox of Cu-catalyzed conjugation techniques as a mild, effective, and scalable tool for the removal of Cu from water-soluble and Cu-coordinating polymers.

Extended blood circulation and joint accumulation of a p(HPMA-co-AzMA)-based nanoconjugate in a murine model of rheumatoid arthritis.

BACKGROUND: We recently synthesized a hydrophilic polymer, poly(N-(2-hydroxypropyl)methacrylamide-co-N-(3-azidopropyl)methacrylamide), p(HPMA-co-AzMA), by RAFT polymerization using a novel azide-containing methacrylamide monomer that through a post modification strategy using click chemistry enabled facile preparation of a panel of versatile and well-defined bioconjugates. In this work we screen a panel of different molecular weight (Mw) fluorescently tagged p(HPMA-co-AzMA) in healthy mice, by live bioimaging, to select an extended circulatory half-life material for investigating joint accumulation in a murine collagen antibody-induced arthritis model. FINDINGS: Fluorescence image analysis revealed half-lifes of <20 min, 2.8 h and 6.4 h for p(HPMA-co-AzMA) of 15, 36 and 54 kDa, respectively, with ~10% polymer retained in the blood after 24 h for the highest Mw. p(HPMA-co-AzMA) of 54 kDa showed enhanced accumulation in the joints of the arthritic mouse model with a bioavailability (AUC = 1783% · h) ~12 times higher (P = 0.01) than healthy control (AUC = 148% · h). CONCLUSIONS: p(HPMA-co-AzMA) of 54 kDa exhibited extended circulatory half-life and preferential accumulation in inflamed joints of a murine model of rheumatoid arthritis (RA). This combined with well-defined polymer size and versatility for conjugation of a range of biomolecules promotes p(HPMA-co-AzMA) for potential applications in the delivery of drugs for treatment of RA.