Water is an integral part of collagen's triple helical and higher order structure. Studies of model triple helical peptides have revealed the presence of repetitive intrachain, interchain, and intermolecular water bridges (Bella et al., Structure 1995, 15, 893-906). In addition, an extended cylinder of hydration is thought to be responsible for collagen fiber assembly. Confocal Raman spectroscopy and dynamic vapor sorption (DVS) measurements of human Type I collagen and pigskin dermis were performed to probe relative humidity (RH)-dependent differences in the nature and level of collagen hydration. Raman spectra were also acquired as a function of time for both Type I collagen and pigskin dermis samples upon exchange of a 100% RH H(2) O to deuterium oxide (D(2) O) environment. Alterations in Amide I and III modes were consistent with anticipated changes in hydrogen bonding strength as RH increased and upon H → D exchange. Of note is the identification of a Raman spectral marker (band at 938 cm(-1) ) which appears to be sensitive to alterations in collagen-bound water. Analysis of DVS isotherms provided a quantitative measure of adsorbed and absorbed water vapor consistent with the Raman results. The development of a Raman spectral marker of collagen hydration in intact tissue is relevant to diverse fields of study ranging from the evaluation of therapeutics for wound healing to hydration of aging skin.
Gels made with three different polymers widely used as rheology modifiers in cosmetic formulations (cross-linked poly(acrylic acid), cross-linked poly(maleic acid-alt-methyl vinyl ether) copolymer and cross-linked poly(acrylic acid-co-vinyl pyrrolidone) copolymer) were characterized by rheological and sensory evaluation methods to determine the relationship between sensorial perception and corresponding rheological parameters. Both conventional rheological characterization methods and a more recent method, Fourier Transform Rheology with Large Amplitude Oscillatory Flow data (LAOS), were utilized to characterize the material with and without wall slip. Sensorial analyses were implemented in vivo to evaluate the perceived ease of initial and rub-out spreadability, cushion, pick-up and slipperiness attributes of the gels. Results were statistically analysed by both variance (ANOVA) and principle component analysis (PCA). Sensorial panel testing characteristics discriminated the three materials, and PCA analyses revealed that sensory attributes could be well predicted by rheological methods. Rheological experiments, without wall slip, revealed that gel strength in the linear viscoelastic region (LVR) and yield stress of these materials are similar, but exhibit significantly different wall slip and thixotropy behaviour in the low shear rate region under wall slip conditions. Above the critical shear rate, which corresponds to the yield stress, all tested materials did not slip and behaved as conventional, shear thinning polymeric fluids. In particular, the rheological parameters and sensorial perception of the 1% cross-linked vinyl pyrrolidone/acrylic acid copolymer were significantly affected by wall slip and/or thixotropy-related shear banding phenomena.
Cellulose ethers are naturally derived ingredients that are commonly used in personal care products as rheology modifiers, film formers, stabilizers, and sensorial agents. In this work, we investigated the physicochemical properties of various grades of hydroxyethylcellulose (HEC), hydroxypropylcellulose (HPC), hydroxypropylmethylcellulose (HPMC), methylcellulose (MC), and sodium carboxymethylcellulose (CMC). In addition, we also studied the influence of hydrophobic modification on the structure of HEC by carrying out experiments with cetyl hydroxyethylcellulose (HMHEC). Rheological, friction coefficient, dynamic vapor sorption (DVS), surface tension analysis, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA) data were generated for the cellulose ethers in order to obtain information about their viscosity, lubricity, moisture absorption, solubility in the bulk solution phase, physical properties, and thermal degradation profile, respectively.
Objective The tactile sensation of hair is an important consumer‐perceivable attribute. There are limited instrumental options to measure the haptic properties of hair. In this study, we introduce a novel technique using the acoustic emissions produced when skin comes in contact with dry hair in a stroking motion. Methods Using a free‐field microphone with a frequency response of 8–12,500 Hz, we recorded acoustic emission data of the interaction of skin with hair. Data were captured with Electroacoustics Toolbox software and analysed with Matlab. Acoustic emission profiles were generated allowing us to monitor the acoustic response at distinct frequencies. Results Various experiments were conducted to develop this novel technique as a suitable measure to monitor the surface properties of hair. Increasing the normal force and velocity of the interaction led to an increase in acoustic emissions. We also examined the acoustic profile of hair that underwent chemical treatment. For example, bleached hair produced a much higher magnitude acoustic response than the corresponding virgin hair. On the other hand, hair conditioner systems mitigated the acoustic response. Finally, investigations of textured hair revealed that the three‐dimensional structure of the hair fibre assembly and its ability to return to its original state when perturbed produce the most dominant acoustic response for this type of hair. Conclusion We introduce a cutting‐edge method to reproducibly evaluate the surface properties of hair. Different types of hair geometry produce unique acoustic profiles as do hair types that experience harsh damaging treatments. This is also a very practical and efficient way to evaluate the degree of protection or conditioning of the fibre.
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