Development of a three-point cantilever bending technique to study the mechanical properties of hair styling ingredients.

BACKGROUND: The mechanical properties of hair treated with styling ingredients is an important aspect to determine if products will be efficacious when used by the consumer. Measurement techniques have been proposed in earlier work; however, these are mostly aimed at hairspray systems and not the myriad of styling products available to the modern-day consumer. AIM: In this article, experimental and data analysis guidelines are proposed for the evaluation of styling ingredients using a three-point cantilever bending technique. Most of the experiments were carried out on polysaccharide-based ingredients-guar hydroxypropyltrimonium chloride (Guar HPTC) and cassia hydroxypropyltrimonium chloride (Cassia HPTC)-to establish basic characterization concepts of the polymer-fiber assemblies. METHODS: A three-point cantilever bending technique was developed using a texture analyzer housed in a temperature and humidity-controlled chamber. Scanning electron microscopy (SEM) studies were conducted to monitor the fracture mechanics of polymer-fiber assemblies. RESULTS: Fundamental studies were carried out to determine the effect of concentration, molecular weight (MW), and chemistry of the polysaccharides on the calculated indices, which characterize the stiffness, flexibility, elasticity, and plasticity of the treated hair. Experiments were conducted in a controlled temperature and humidity environment, which allowed us to monitor the behavior of the polymer-treated hair from 40-90% RH. Studies were also conducted on polymer blends and conventional styling polymers to provide guidance of the performance of naturally-derived polymers to their synthetic counterparts. CONCLUSIONS: A detailed description is provided for a user-friendly, quick method to measure the mechanical properties of styling ingredients on hair. We provide guidelines for three-point cantilever bending tests of straight hair tresses treated with conventional and naturally-derived styling polymers. Indices were developed to characterize the force-distance curves and were designated as E1, F1, position of F1, post-fracture gradient, toughness, E10/E1, and F10/F1. These indices provide an overall characterization of the stiffness, flexibility, elasticity, and plasticity of polymer-treated hair.

Hydrophobically Modified Isosorbide Dimethacrylates as a Bisphenol-A (BPA)-Free Dental Filling Material.

A series of bio-based hydrophobically modified isosorbide dimethacrylates, with para-, meta-, and ortho- benzoate aromatic spacers (ISBGBMA), are synthesized, characterized, and evaluated as potential dental restorative resins. The new monomers, isosorbide 2,5-bis(4-glyceryloxybenzoate) dimethacrylate (ISB4GBMA), isosorbide 2,5-bis(3-glyceryloxybenzoate) dimethacrylate (ISB3GBMA), and isosorbide 2,5-bis(2-glyceryloxybenzoate) dimethacrylate (ISB2GBMA), are mixed with triethylene glycol dimethacrylate (TEGDMA) and photopolymerized. The resulting polymers are evaluated for the degree of monomeric conversion, polymerization shrinkage, water sorption, glass transition temperature, and flexural strength. Isosorbide glycerolate dimethacrylate (ISDGMA) is synthesized, and Bisphenol A glycerolate dimethacrylate (BisGMA) is prepared, and both are evaluated as a reference. Poly(ISBGBMA/TEGDMA) series shows lower water sorption (39-44 µg/mm3) over Poly(ISDGMA/TEGDMA) (73 µg/mm3) but higher than Poly(BisGMA/TEGDMA) (26 µg/mm3). Flexural strength is higher for Poly(ISBGBMA/TEGDMA) series (37-45 MPa) over Poly(ISDGMA/TEGDMA) (10 MPa) and less than Poly(BisGMA/TEGDMA) (53 MPa) after immersion in phosphate-buffered saline (DPBS) for 24 h. Poly(ISB2GBMA/TEGDMA) has the highest glass transition temperature at 85 °C, and its monomeric mixture has the lowest viscosity at 0.62 Pa·s, among the (ISBGBMA/TEGDMA) polymers and monomer mixtures. Collectively, this data suggests that the ortho ISBGBMA monomer is a potential bio-based, BPA-free replacement for BisGMA, and could be the focus for future study.

Influence of various environmental parameters on sweat gland activity.

The choice of environmental conditions when conducting antiperspirant studies greatly affects the quantity of sweat output. Our initial goal in this work was to develop an in-house procedure to test the efficacy of antiperspirant products using replica techniques in combination with image analysis. To ameliorate the skin replica method, we conducted rheological studies using dynamic mechanical analysis of the replica formulation. In terms of sweat output quantification, our preliminary results revealed a considerable amount of variation using the replica technique, leading us to conduct more fundamental studies of the factors that influence sweating behavior and how to best design the experimental strategy. In accordance with the FDA's protocol for antiperspirant testing, we carried out gravimetric analyses of axillae sweating under a variety of environmental conditions including temperature and humidity control. Subjects were first acclimatized in an environmentally controlled room for 30 min, and then placed in a sauna for an additional 30 or 45 min, depending on which test we administered. In Test 1 (30 min total in the sauna), the first 10 min in the sauna was another equilibration period, followed by a 20 min sweat production stage. We monitored axillae sweating during the last 20 min in the sauna by gravimetric analysis. At time (t) = 30 min in the sauna, skin replicas were taken and later analyzed using imaging and image analysis techniques. Test 1 was carried out on over 25 subjects, both male and female, from various racial backgrounds. In Test 2, subjects spent 45 min in the sauna after the initial 30-min period in the environmental room. During the 45 min, we obtained gravimetric readings of absorbent pads placed in the axillae. We conducted studies at various temperature and relative humidity settings. We also studied the influence of several external parameters on sudoriferous activity. Test 2 was a range-finding experiment on two subjects to determine the optimized environmental conditions for the hot room procedure. In addition to the replica and gravimetric techniques, we also measured flux density to determine the onset of firing of sweat glands to ensure that our environmental preconditioning step (30 min in the environmental room) brought subjects to the point that their sweat glands were activated. Although flux density measurements are usually carried out to determine transepidermal water loss (TEWL), we found that they can be equally useful for monitoring the onset of sweat production. Thermal infrared imaging experiments were also carried out allowing us to generate full-body images of subjects containing anatomical thermal distribution data with high accuracy. Overall, we conclude that our in-house hot room procedure offers much potential as an effective and cost-efficient screening tool for narrowing copious antiperspirant formulations to a select few for expensive clinical evaluation.