Hair is an appendage of the epidermis formed by three main structures: the medulla, the cortex and the cuticle. It is composed mainly of keratin and a mixture of lipids located between both the cortex and cuticle, and the cuticles themselves. Hair lipids have a similar function to the lipid barrier of skin; i.e., to maintain the integrity of the hair fiber.1
The hair exposome is the sum of multiple exposure factors affecting an individual’s hair throughout his or her life. These factors may include exposure to high temperatures due to hair dryers, flat irons, etc.; or to aggressive chemistries with high pH levels, such as hair bleaches or dyes. Together with environmental assaults from sunlight and pollution, these factors damage the hair’s fibers.2
Such damage appears in the form of keratin degradation,3 loss of lipids, the oxidation of pigments, etc., and translates as a loss in the mechanical properties, hydration, color and brightness of hair, along with split ends and brittleness.4 While some commercial hair formulas help to mitigate these effects, their benefits are generally limited due to a low capacity to cover and penetrate the hair fiber.
In the present study, a novel delivery system based on bicelles was explored for hair after initially being developed for skin. As previously reported,5 bicelles are lipid discoidal nanostructures ~15-25 nm in size. They comprise long and short alkyl chain phospholipids dispersed in an aqueous solution. The bicelles are further encapsulated in liposomesa in order to stabilize them. The result is a dual system of spherical vesicles, ~200-500 nm in diameter, containing the bicelles—which, in turn, can contain
According to previous work,5 this combination of lipid composition, small size and morphological versatility demonstrate high applicability to skin care. Bicelles are capable of passing through the intracellular spaces of the stratum corneum and, thanks to their nanostructure and composition, serve as good topical carriers.5
To transfer this skin-relevant system to hair, the external vesicles were redesigned to electrostatically adhere to the hair cuticle and surround the hair fiber. This would then allow the internal bicelle disks to penetrate hair and deliver their payload—in the present study, ingredients for heatb and pollution protectionc (see Figure 1). Further, the lipid contents of the system reinforce hair’s lipid structure, helping to prevent the weakening of cuticles and protect the cortex.
The studies described herein were conducted to evaluate the capacity of this dual system to protect hair and repair damage from daily assaults caused by heat styling, bleaching, pollution and solar radiation. To evaluate effects, samples of virgin, bleached and dyed hair, 20-25 cm in length, were treated (or not) with a base serum (0.1 g of serum/g of hair) comprising: water, glycerine, hydroxyethylcellulose, carboxymethylcellulose and citric acid, with or without the dual system, then exposed these scenarios. Changes in hair characteristics were determined by various analytical techniques, described below.
Hair Adherence and Wash-off Resistance
The capacity of the delivery system to adhere to hair fibers and resist wash-off was evaluated first. A comparative study was carried out based on three-dimensional (3D) reconstructions of hair images taken at different depths using confocal microscopy.
Virgin hair samples were incubated for 5 hr with three different variations of the described serum containing fluorescent traces: a) a control leave-on serum; b) a leave-on serum containing 1% liposomes; and c) a leave-on serum containing 1% of the dual delivery system.
After incubation, the hair samples were washed with neutral shampoo for 2 min, rinsed with water for 1 min, dried, then analyzed. The fluorescent tracers utilized were lipophilic rhodamine and hydrophilic sodium fluorescein, which provided visual evidence of the serum’s degree of hair adherence, coverage and wash-off resistance. Figure 2 shows images of the three hair samples studied; green represents sodium fluorescein and red, rhodamine.
As shown in Figure 2a, a patchy distribution of fluorescent molecules was observed on the surface of the hair fiber after treatment with the leave-on control serum. This indicates low adherence and high wash-off. In Figure 2b, higher fluorescence was observed, although large empty spaces are still visible, indicating imperfect coverage by the liposomes and their partial removal by washing. In contrast, the hair sample treated with the dual delivery system (Figure 2c) showed total coverage of the fiber, also indicating resistance to wash-off.
Heat protection: Heat exposure can severely damage hair, causing cuticles to open and, subsequently, lose hydration. This loss in water content indicates hair damage and has many implications, such as the degradation of mechanical properties; previous research confirms the critical role moisture plays in hair’s physical and cosmetic properties.6 As an example, tensile properties are related to the moisture level within the hair fiber, so diminution of the water content in hair fibers can result in the deterioration of hair elasticity and strength.7
Thus, to evaluate the protective and repair effects of the dual systemb, hair samples were analyzed by scanning electron microscopy (SEM) and thermal gravimetric analysis (TGA) before and after treatment (or not) with the test serums and ironing. Prior to treatment, all samples were washed with a neutral shampoo for 2 min, rinsed with water for 1 min and blown dry. Exposure to heat consisted of ironing the hair tresses at 200°C for 5 sec, 3×.
The dual system of spherical vesicles containing bicelles loaded with actives showed previous efficacy in skin care. Here, it was redesigned electrostatically for hair.
Untreated hair: Figure 3a and Figure 3b show images of the virgin hair samples before and after heat treatment with the iron. As expected, Figure 3a shows no damage. However, after ironing, damage to the cuticles is clearly visible. The TGA results also showed that after ironing, the water content of hair decreased from 10.52% to 6.04% (see Figure 4a, orange bar).
Treated hair: Hair pretreated with the control leave-on serum (0.1 g of serum/g of hair) was not protected against the effects of ironing. As shown in Figure 3c, hair fiber cuticles were damaged similarly to the untreated, ironed hair shown in Figure 3b. The TGA result also was similar to that of untreated hair after ironing (see Figure 4a, green bar). However, the hair sample pretreated with the same leave-on serum containing 1% of the dual systemb maintained the integrity of the cuticles (see Figure 3d); TGA results corroborated that hair did not lose hydration (see Figure 4a, purple bar).
The results indicated that, compared with untreated hair, the dual system protected against thermal aggression, minimizing cuticle damage and the loss of hydration.
Damage repair: The ability of the dual systemb to repair hair after thermal damage incurred also was examined. To this end, virgin hair samples were ironed and posttreated (or not, as the control) with the test serum containing 1% of the dual system (0.1 g of serum/g of hair) for five days, once per day. Figure 3e and Figure 3f show the hair samples after one and five applications of the leave-on serum. Results showed hair cuticle integrity was recovered during the five-day treatment.
TGA results concurred with the SEM results (see Figure 4b), indicating an increase in water content: from 6.04% after ironing, to 9.52% after one application and reaching a complete 10.54% recovery, compared with the previous virgin hair reading of 10.52%, after five applications. The authors concluded the heat protection and repair benefits of the system are likely related to its ability to adhere to and completely envelop the hair fiber, preventing direct contact with damaging heat. Further, since the ingredient has the capacity to penetrate the hair fiber, it reinforces hair’s lipid content, which helps it to recover and maintain integrity after thermal assault.
Hydration recovery: Next, the ability of the dual system to recover hair hydration lost to bleaching was assessed. Water content was quantified in five different scenarios: virgin hair, bleached hair, bleached hair treated with the placebo serum, and bleached hair treated either one or 10 times with the serum containing the dual system at 1%. Quantification was made by means of TGA.
The bleaching procedure consisted of incubating hair samples in a bleach solution (9% H2O2, pH 9) for 2 hr and 30 min in a shaking water bath at 40°C, followed by rinsing with water for 1 min. This procedure was repeated twice, then samples were washed with neutral shampoo for 2 min and rinsed with water for 1 min.
Bleached hair samples were separated into two groups: one for the placebo serum and another for the test serum. Measurements were carried out the next day. As shown in Figure 5, the water content in virgin hair was ~11% (dark blue bar), whereas the bleaching procedure reduced it to 10.6% (pink bar; p = 0.0833).
Treatment with the placebo serum provided a slight increase in hydration in bleached hair, to 10.75% (green bar; p = 0.0833). On the other hand, a single treatment with the serum containing the dual system fully recovered hair’s initial hydration levels to 11.25% (purple bar; p = 0.0495). After 10 daily applications of the active serum, hydration increased even more, to ~11.5% (light blue bar; p = 0.0495), slightly surpassing the value in virgin hair.
The authors propose that this recovery in hair hydration after bleaching is likely associated with the system’s ability to restore hair’s lipid structure, to keep the cuticles closed and thus favor water retention.
Recovering elasticity and strength: The mechanical properties of hair also are negatively affected by bleaching. To explore the capacity of the dual system to recover hair’s physical properties, measurements of 10 fibers from two hair sample scenarios were taken. A dynamometer was used to determine the elasticity and 50% break stress level of each group. Hair fibers were then bleached and treated (or not) for five days with the leave-on serum incorporating the active at 1% were compared.
As shown in Figure 6, after a five-day treatment with the 1% dual-system serum, hair’s elasticity increased by 19% and break stress increased by 21%, compared with untreated hair. The cortex is the structure responsible for the mechanical properties of hair and its integrity is reflected in elasticity and resistance to breakage. Treatment with the dual system appeared to reinforce damaged hair fibers and improve the recovery of its mechanical properties.
Pollution and UV Exposure
Exposure to fumes, heavy metal particulates and UV rays also negatively affect hair structure, leading to loss of shine, movement/balance and hydration, along with changes in color.1, 8 An additional assay was thus designed to test the ability of the dual system to protect against the effects of pollution and UV exposure. For these tests, carotenes were incorporatedc into the bicelles for delivery into hair as they are rich in antioxidants and can counteract oxidizing processes caused by air pollution and UV exposure. Further, the electrostatic charges of the external vesicles in the system repel particulate matter and prevent it from adhering to hair. To study the shielding effect of this system against pollution, two models were used: urban pollution and exhaust fumes.
The carotene system reduced color loss caused by UV exposure and washing, thanks to its antioxidative properties.
Urban pollution: Hair tresses treated once with the leave-on serum containing 1% of the carotene systemc or a placebo and were exposed to urban pollution in Barcelona. In preparation, tresses were washed with neutral shampoo for 2 min, rinsed with water for 1 min and divided into two groups for the placebo and carotene system treatments. After treatment with 0.1 g of product/g of hair, the samples were placed on a terrace in a flat located in the Eixample neighborhood in Barcelona, where they remained for one week. Heavy metal content in the samples was subsequently measured by mass spectroscopy.
As shown in Figure 7, hair treated with the leave-on serum incorporating the carotene system showed less heavy metal content than in the placebo hair sample—from 27.4% to 96.9% less. These results indicated the carotene system repelled heavy metal particulates from adhering to hair.
Exhaust fumes: Next, hair tresses were prepared and treated with placebo or carotene serum as described above, but this time, samples were exposed directly to the exhaust fumes emitted by a motorcycle for 10 min each day, for a total of 10 days. Following exposure, the heavy metal content was again measured by mass spectroscopy. Figure 8 revealed similar results. Hair treated with the carotene system showed less heavy metal content than hair treated with the placebo—from 33.4-85.5% less. This indicated the carotene system was effective even under the extreme condition of direct exposure to fumes.
UV exposure: The degradation of hair protein is one of the primary types of damage caused by UV radiation. Tryptophan plays an important role in the internal structure of hair, and quantifying its levels can thus indicate the general state of hair proteins. This test evaluated the ability of the carotene systemc to protect tryptophan in hair from photo-degradation.
For this purpose, tryptophan levels were quantified in three hair sample groups:
a) Hair treated with the leave-on serum (placebo) for five days;
b) Hair treated with the leave-on serum incorporating 1% of the carotene system for five days; and
c) Hair treated with the leave-on serum incorporating 5% of the carotene system for five days.
All samples were prepared as described previously, then analyzed by spectrofluorometry for tryptophan baseline levels. Hair samples were then exposed for 67 hr to UV radiation (500 W/ m2) using a lampd, after which tryptophan levels were again measured by spectrofluorometry.
Figure 9 shows the results of tryptophan degradation after UV exposure. The placebo-treated hair showed 35% degradation, whereas the hair treated with the carotene system at 1% and 5% showed 30% (p = 0.0189) and 5% (p = 0.0038) degradation, respectively. These results indicate the carotene system protected the tryptophan in hair samples. Further, this protection was progressive, depending on the concentration used. The authors attribute this protection to the ability of the system to effectively cover hair and supply lipids and antioxidant molecules to its internal structures.
Color loss: To evaluate the capacity of the carotene systemc to prevent color loss in dyed hair exposed to UV and washing, two scenarios were tested:
a) Hair samples (bleached + dyed) treated with the placebo serum (control); and
b) Hair samples (bleached + dyed) treated with the same serum incorporating the carotene system at 1%.
The samples were exposed to artificial light (450 J/cm2)d, equivalent to 4 hr of sun exposure in June in Barcelona. After exposure, samples were washed with neutral shampoo for 2 min and rinsed with water for 1 min. The hair was then divided into two groups: one treated with the placebo serum and the other, the same serum incorporating the carotene system at 1%. The same cycle of light exposure and washing was then repeated daily for a total of 10 days; the quantification of color in the samples was evaluated by spectrofluorometry after one, five and 10 cycles. Results are shown in Figure 10.
Exposure to fumes, heavy metal particulates and UV rays degrades hair shine, movement, hydration and color.
The carotene system reduced color loss caused by UV exposure and washing. After one cycle of UV exposure/washing/rinsing/treatment/washing/rinsing/treatment, color loss was reduced by 21.7% in the samples treated with 1% carotene system. After five cycles, color loss was reduced by 14.8%, and, at the end of 10 cycles, color loss was reduced by 16.6%. This demonstrated the ability the carotene system’s antioxidant properties to protect the dye pigments from oxidation and reduce overall color loss in hair.
Discussion and Conclusions
Exposure to substances in the environment and beauty routines that include hair drying, bleaching and straightening causes damage to hair fibers. These aggressions have become important concerns of hair exposome, and directly influence beauty and wellness.
To prevent hair damage, one strategy is to use a protective product on daily basis. However, most commercial products focus on providing substances such as oils or polymers to make hair shine; or peptides and other molecules to recover the keratin structure.
Although these strategies are valid and may be effective, they often produce short-term results for different reasons. One relates to the vehicle in which they are provided; if it cannot completely cover hair, the unprotected portions will continue to be damaged. Another reason is the lack of effective hair penetration. If nourishing substances only reach the hair surface, its internal pigments and structures impacting mechanical properties will hardly be affected.
Finally, most treatments focus on reinforcing hair protein content. However, the hair’s lipid structure, responsible for smooth, closed cuticles and the integrity of hair fibers, is often ignored.
The unique structure of the described dual systema offers a new approach for hair protection and treatment. It is highly efficient in covering the external parts of hair due to its outer charged vesicle. In addition, it can effectively penetrate hair thanks to the internal bicelles, which can deliver different molecules inside the hair shaft to treat different conditions. Finally, the lipid composition of the system reinforces hair’s lipid structure.
In the described studies, the authors have demonstrated the capacity of two forms of the system. The firstb protects fibers against thermal damage and recovers hydration and mechanical properties after bleaching procedures. The secondc protects against the adherence to hair of heavy metals and pollution, prevents the degradation of tryptophan by UV radiation and reduced color loss in dyed hair caused by UV exposure and daily washing.
Taken together, this solution offers a promising tool for the integral treatment of hair. Further research will analyze and reveal its full potential as a new platform for advanced hair care.
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