The development of active ingredients with strong hair care effects has become a hot topic due to the increasing demand for hair dressing, perming and styling, as well as the susceptibility of environmental stress to cause hair damage, which often leads to problems such as dryness, frizz, reduced compliance, damaged hair texture and easy breakage.
The tensile properties of hair strands are related to the moisture and hydrogen bonds in the hair strands, so the introduction of sodium hyaluronate, which has strong moisturizing properties and the ability to form hydrogen bonds, as an active substance for hair strengthening, has certain research value. In this paper, the effects of five different molecular weights and structures of sodium hyaluronate on hair stretching and anti-frizz properties were systematically studied. The mechanism of action of sodium hyaluronate efficacy was further studied.
1. The structure and mechanical properties of hair
1. The structure of the hair
Hair fibers are structurally divided into three main parts. The surface is made up of a thin layer of cuticle cells that envelop and protect the fibers from environmental damage, called the hair epidermis, which make up about 10% of the fiber mass, and these cells are stacked longitudinally and around to form a sheath with exposed edges called cuticles, pointing distal or at the tip of the hair strand.
It has been suggested that cell stacking near the cuticle is important to control water inflow and outflow and maintain normal fiber function and durability. The internal cortex is composed of primary fibers, small protofilaments, intermediate filaments, large interfibril matrix and macrofibrils, and its keratin determines the mechanical properties of the fibers, and the fur cortex is the main part of the hair.
The third part is the hair medulla, which is located near the center of the cortex, and compared to the rest of the hair, it has a higher lipid content and a lower binding strength of disulfide bonds.
- Structure of keratin in hair
Protein is the main component of hair fibers, accounting for 98% of the total fiber mass. Among them, keratin and its related proteins account for 85% of the total protein content of fiber. The cortex is the main site of keratinization, which hardens the hair shaft through the presence of cortical cells rich in keratin filaments.
Hair contains two types of keratin fibers: type I, which consists of acidic amino acid residues, and type II, which contains basic amino acid residues. When type I and type II fibers are arranged in a spiral pattern, dimers are formed, and the dimers are wound together in antiparallel directions to form tetramers, which are parallel to the long axis of the hair shaft and embedded in the amorphous matrix of persulfurin.
The keratin chain is composed of α-keratin in a α-helical conformation, and is wound by ionic forces, hydrogen bonds, van der Waals interactions, and disulfide bonds. Weak hydrogen bonds ensure the connection between the keratin polypeptide chains. These weaker bonds can be easily broken by water, allowing the curls to temporarily straighten. Disulfide bonds are derived from thiocystine-containing bonds, which form strong cross-links between adjacent chains.
- Stretching properties of hair
Hair fibers exhibit a composite structure at the microscopic scale, which consists of a regularly arranged fibril and amorphous matrix, similar to traditional reinforced composites. The fibers and substrate determine the mechanical properties of the hair.
Fibrils are reported to represent crystalline phases in the structure of the hair, which are surrounded by an amorphous matrix phase. Inside the fibers, peptide macromolecules dominate in α-helical conformation, and another study showed that about 40% of the molecules are in a β-folded state.
Intermolecular and intramolecular interactions, such as hydrogen, salt, and disulfide bonds (cross-linking), strengthen the hair fibers and affect hair laxity. The matrix composition consists of connected amorphous beads interspersed with disulfide-rich microfibrils. This composite structural structure of the hair fiber gives it unique stretching properties.
- Hair damage factors and mechanisms
Nowadays, there is a growing demand for hairdressing, with more frequent hair washing, dyeing and styling, as well as environmental stressors that can cause hair damage, which often leads to dryness, frizziness, loss of suppleness, damage to hair and breakage.
The destructive nature of perms is well known. It involves the breaking and reorganization of disulfide bonds within the hair. In addition, the perm process transforms the hydrophobic hair surface into a more hydrophilic one. Therefore, in the interaction with the shampoo, this will exacerbate the lipid loss of the stratum corneum.
Keratin and disulfide bonds are closely related to the stretching properties of hair, so perms can easily affect the stretching properties of hair. Hair is also susceptible to photodamage, with outdoor ultraviolet (UVB) and UVA radiation attacking hair proteins, while visible radiation has no significant effect.
2. The state of water in the hair and its relationship to performance
1. The state of occurrence of water in the hair
It is important to study the effect of water on hair performance because it alters the multiple properties of human keratin fibers, such as hair and nails, and is one of the most obvious external factors affecting the mechanical behavior of hair. Water has an effect on hair swelling, tensile strength, friction, and other properties.
Water that is related to the structure of keratin is defined as bound water, and water that is not directly related to the structure of keratin is free water. This model takes into account the decrease in the binding energy of water molecules already associated with the structure of keratin as the water content increases. Perming, straightening or relaxing, and bleaching during the hair coloring process are the main causes of hair damage.
This type of treatment of the hair usually alters the fibrous structure. The resulting damage adversely affects the absorbency of the hair at ambient humidity and leads to increased swelling or fluid retention when wet, which in turn affects the hair's moisture absorption.
- Effect and mechanism of water occurrence state on hydrogen bonding in hair
The cohesion of α-keratin is provided by different chemical bonds like disulfide bonds, salt bonds, and hydrogen bonds. Disulfide bonds are formed by two sulfur atoms of two adjacent α-keratins and have extremely strong bond energy. They play a pivotal role in styling hair and can be difficult to break by stretching or bending.
Salt bridges or ionic bonds are non-covalent interactions, which are made up of negatively charged and positively charged amino acid interactions. Their interaction is relatively weak compared to disulfide bonds, but their interaction contributes significantly to the stability of the overall structure of the hair strand.
Ionic bonds are susceptible to changes in pH and water content. Water can cause ionic bonds to break and hair to swell. Hydrogen bonds are created between the oxygen atom and the hydrogen atom from the -CO and -NH groups. These bonds are mainly located between the same α-keratin helix. Hydrogen bonds are heavily influenced by water, which can penetrate between the polypeptide chains to break the hydrogen bonds and disturb the rigidity of the molecules.
3. Frizz of hair and its relationship with moisture
The presence or absence of frizz is an important criterion for judging the health of hair, and one manifestation of frizz is the protrusion of small fibers erected at the parting line and through the length of the hair from the main body of the hair. Cuticle shedding and split ends mean that the hair is not in an aligned position and can be described as "frizz".
Another manifestation is hair irregularity, that is, not all the fibers are arranged in a controlled curl, but each fiber has its own shape, which increases the total volume of the hair strands. Frizz is often associated with the weather, especially high humidity and high temperatures. The cause of moisture frizz is the diffusion of water vapor within the hair.
Hair at high humidity can absorb 15-20% of its own weight compared to completely dry hair, and the absorption rate is increased at higher temperatures. During the drying process, water is first removed between the fibers and then from the inside of each fiber.
The potential and application status of sodium hyaluronate in hair care
- Hair care potential of sodium hyaluronate
Sodium hyaluronate belongs to glycosaminoglycan compounds and is a member of the polysaccharide family. The sodium hyaluronate molecule consists of alternating units of N-acetyl-D-glucosamine and glucuronic acid. Its molecular weight is very high, reaching millions. It is a component of connective tissue, epithelial tissue, and neural tissue, and is an important component of the extracellular matrix (ECM).
Sodium hyaluronate does not covalently bind to proteins, but is widely distributed in connective tissues. Chemically, hyaluronic acid is a hydrophilic macromolecule with -COOH and -OH functional groups. Its high solubility in water allows it to form highly viscous solutions, a property that allows it to exhibit unique viscoelastic properties.
Sodium hyaluronate can also be involved in reactions or cross-linking to adjust its chemical properties and water solubility resistance. The amount of water captured is about 1000 times its weight. Solutions and gels of sodium hyaluronate are commonly used as dermal fillers. After injection, it restores skin volume and minimizes the appearance of wrinkles, and is also a very effective and safe ingredient in cosmetic formulations.
However, it is important to note that despite the emergence of cosmetics or personal care products with HA as the main ingredient, the vast majority of products such as body lotions, creams, lipsticks, serums, etc., are aimed at the skin, and very few products act on the hair, and even fewer products have toughening or anti-frizz claims on this basis.
Sodium hyaluronate not only has water absorption properties, but also has multiple carboxyl groups and strong hydrogen bond formation ability, which proves that it may have strong hair repair potential, which is also the research basis and significance of this work.
2. Delivery and application of sodium hyaluronate
Sodium hyaluronate is an extremely important medical and cosmetic raw material, its properties are closely related to its molecular weight, but some macromolecular or medium molecular substances are difficult to penetrate the skin to its area of action, or have certain requirements for its release rate and time, and it is a water-soluble substance, so the sustained release, encapsulation and osmosis of HA is an extremely important research direction.
The skin permeability of HA is related to the spatial peptide concentration and pH. The optimal spatial peptide concentration was 5mg/mL and the optimal pH value was 4.0. The permeability of hyaluronic acid in pig and human skin was verified in in vitro transdermal experiments, and the permeability in the skin of hairless mice was also confirmed in vivo.
In addition, skin barrier disruption was assessed by skin dehydration and histological studies. LFU exposure time is related to drug penetration and skin perturbation. As the duration of exposure increases, skin perturbation increases. They found that 1 min of exposure best facilitated HA penetration without damaging the epidermis.
However, the above wrapping methods have the problem of high cost, and how to promote the penetration of HA and reduce its cost is also a very worthy direction of study.
IV. Conclusion
In this paper, sodium hyaluronate was used as the main research object to explore the strengthening effect and regularity of sodium hyaluronate of different molecular weights on hair strands, and its anti-frizz performance and anti-breakage effect in another dimension were studied.
On this basis, the source of its toughening effect mechanism was further explored, and then a sodium hyaluronate multi-emulsion system was prepared and its specific application effect was evaluated from multiple perspectives.
- Low molecular weight (42K & 4K) sodium hyaluronate has the effect of improving the strength of damaged hair, anti-frizz, and reducing hair combing and friction coefficient. And the two can achieve a toughening effect by affecting the different characteristics of the hair strands, and can obtain stronger efficacy after compounding, and also have good efficacy in actual products.
- The effect of anti-pollution and reducing the combing function and friction coefficient of hair can be understood to come from the film-forming properties of sodium hyaluronate. Therefore, taking the tensile strength of hair as the main research object, through the calculation of elastic modulus, Fourier total reflection infrared and urea experiments, it was proved that sodium hyaluronate can form hydrogen bonds when it enters the hair strands, and the elastic modulus of the hair strands can be increased by increasing the hydrogen bond density, thereby affecting the tensile properties of the hair.
- The specific efficacy and application feasibility of sodium hyaluronate multi-emulsion were explored from three aspects: transdermal effect, hair toughening effect and hair leachate concentration. Based on the above results, this sodium hyaluronate multiple emulsion has a good application prospect.
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