International Journal of Trichology

ORIGINAL ARTICLE
Year
: 2022  |  Volume : 14  |  Issue : 4  |  Page : 128--134

A method to measure oil penetration into hair and correlation to tensile strength


Priyanka Sureka1, Tanu Agrawal1, Suman Majumder1, Ritambhara Kr2,  
1 R&D, Bajaj Consumer Care Ltd, Mumbai, Maharashtra, India
2 Department of Business and Operations, MS Clinical Research, Bengaluru, Karnataka, India

Correspondence Address:
Tanu Agrawal
Bajaj Consumer Care Ltd R&D, Vinmar House, A-41, MIDC Road, No - 2, MIDC, Andheri (E), Mumbai - 400 093, Maharashtra
India

Abstract

Aim: The aim of this study is to identify a new method to measure oil penetration into hair, compare penetration ability of two types of oil: Type 3 hair oil and coconut oil into the hair shaft and explore its correlation to a physical property of hair, tensile strength. Materials and Methods: The study utilizes the measurements of two parameters, thickness, and cohesive force to define penetration of oil. The hypothesis was that an increase in hair fiber thickness along with reduction in cohesive force would indicate higher penetration of oil into the hair strand. The tensile strength of hair was then determined by measuring the behavior of treated hair strands while an axial stretching load was applied. Results: In experiment of hair thickness measurement, there was a significant increase in the hair fiber thickness post oil application in both the test oils as compared to baseline (untreated control). However, this increase was higher in hair swatches treated with Type 3 hair oil. For cohesive force measurement, significantly lower force was required for hair swatches treated with Type 3 hair oil when compared to coconut oil. For tensile strength, both test oils exhibited increase versus baseline but increase in tensile strength was significantly more with type 3 hair oil when compared to coconut oil. Conclusions: The present study shows that conjoint assessment of hair thickness and cohesive force post oil application can be a suitable method to indicate the extent of oil penetration into the hair. Overall, the study indicated the positive influence of oil penetration on hair strength.



How to cite this article:
Sureka P, Agrawal T, Majumder S, Kr R. A method to measure oil penetration into hair and correlation to tensile strength.Int J Trichol 2022;14:128-134


How to cite this URL:
Sureka P, Agrawal T, Majumder S, Kr R. A method to measure oil penetration into hair and correlation to tensile strength. Int J Trichol [serial online] 2022 [cited 2022 Dec 9 ];14:128-134
Available from: https://www.ijtrichology.com/text.asp?2022/14/4/128/351239


Full Text



 Introduction



Hair is an integrated system in terms of its structure and its chemical and physical behavior[1] [Figure 1]. The tensile behavior of human hair is determined largely by the cortex which lends mechanical properties such as tensile strength and elasticity to the hair fiber.[2] Physical integrity of the hair to combing and grooming forces is more determined by the nonkeratin components of the cuticle and the cell membrane complex (CMC). The CMC binds the cells together and along with other nonkeratin components, forms a major pathway for diffusion of a substance into the hair fibers. Theoretically, two pathways exist for diffusion into human hair-transcellular diffusion and intercellular diffusion. The transcellular route involves diffusion across cuticle cells through both high and low cross-linked proteins. On the other hand, intercellular diffusion involves penetration between cuticle cells through the endocuticle and the CMC protein structures and is the preferred route for large molecules.[1]{Figure 1}

The practice of oiling scalp hair is very prevalent in India. This consumer habit is not merely to enhance beauty, it is more of a traditional ritual which is passed down the generations. Hair oil forms an integral part of the traditional hair care regime in Indian sub-continent and Middle East countries. It is perceived to provide benefits of nourishment, strengthening of hair, faster and better hair growth, and reducing the problem of hair-fall. These benefits are studied through various in vitro and in vivo methods in accordance with the mode of action and anticipated endpoints associated with these oils.

In this study, our aim was to investigate the correlation of the penetration of hair oils into the hair fiber and improvement in the strength of hair. Tensile strength of the hair can be measured by suitable equipment intended for measuring strength properties or elasticity of hair fiber due to tension force or load.[2] For penetration, studies have been done in the past to measure penetration of vegetable oils and mineral oil into human hair shaft through various methods but links to consumer perceptible benefits are not adequate. An exhaustive study was been done to measure penetrability of oils in human hair using secondary ion mass spectrometry in combination with time-of-flight mass spectrometer. This study showed that coconut oil penetrates the hair shaft while mineral oil is unable to penetrate. This study also indicated that the swelling of hair is limited by the presence of oil and since coconut oil was able to penetrate the hair fiber it may provide better protection from damage by hygral fatigue.[3],[4] In another study, a different method was employed to assess penetration of different oil blends in hair using laser scanning confocal microscopy. The study evaluated thin cross sections of human hair treated with oils to comprehend their penetration capability and pattern, which demonstrated that mineral oil has better penetration through the hair shaft than the studied vegetable oils.[5]

The current study was attempted to not only understand the penetration ability of two types of oil into the human hair shaft through a new method but also to correlate this penetration to a physical property of hair, tensile strength. The penetration was assessed by dual measurements of hair fiber thickness and cohesive force. The hypothesis behind this study was that an increase in hair fiber thickness along with consequent reduction in cohesive force would indicate higher penetration of oil into the hair strand. The tensile strength of hair was then determined by measuring the break force of the treated hair strands while an axial stretching load was applied.

 Materials and Methods



Materials

All experiments were done on standard Indian black hair fibers/tresses. Indian black hair fibers/tresses were procured from International Hair Importers and Products, Inc USA. The hair tresses that were used, weighed approximately 3 g, measured 8” in length, 1” wide with flex swatch and had approximately 2600–2800 strands per hair tress. Six of such tresses were used for each product cell to ensure statistical validity. Test product 1 was coconut hair oil and test product 2 was a mix of mineral oil 77%, vegetable oil 21% and 2% excipients (antioxidants, color, and perfume). Mixture of mineral oil and vegetable oil is classified as type 3 hair oil as per IS 7123:2019.[6] Henceforth, in this study test product 2 will be referred to as type 3 hair oil. Washing of hair strands was done with 10% sodium lauryl sulfate solution under running tap water.

Methods

Hair sample preparation

Prior to product application, baseline hair fiber thickness assessment was performed. 0.15 g of test product per g of hair was applied and allowed to rest for 60 min. The hair swatches were washed and were dried completely. This cycle of product application, washing and drying was then repeated for 11 times for thickness and cohesive force measurements and for 12 times for tensile strength measurements.

For thickness and cohesive force measurement, at 12th cycle, 0.20 g of product per g of hair was applied. The swatches were allowed to rest at the room temperature for 20 min. Thickness measurement was then done post acclimatization and was followed by the cohesive force measurement. The relative humidity of the experiment room was maintained at 40%–60%.

Instrumental assessments

Thickness

The hypothesis behind using this technique is that the penetration of oil in the hair fiber would result in its swelling which in turn would increase the hair fiber thickness. Hair fiber thickness was measured through microscopic imaging and diameter analysis technique using Dinolite Digital microscope AM4113/AD4113 SERIES [Figure 2] on Caselite Nova Software version 2.0.{Figure 2}

Dinolite is an advanced tool for hair diagnostics, which provides a thickness measurement with its 1.3-megapixel microscopic digital camera. The microscope has an in-built variable magnification which enables to take images from ×10 magnification to ×200 magnification. Using this camera, multiple images of the hair fibers were taken across the length of the swatch for which the hair swatches were placed on the flat surface maintaining the fixed length from root to top. The camera head was placed on the middle section of the hair swatch. All visible hair fibers in each image were measured for its diameter, only fibers having good focus, clear edges and without overlapping were taken into consideration. On an average, about ten hair fibers per image were measured [Figure 3]. Similarly, five images per swatch were recorded.{Figure 3}

Cohesion test

Upon oil application, liquid bridges are formed between hair fibers and results in an adhesion between hair fiber and oil. The presence of oil films on the surface of fibers leads to capillary adhesion between the fibers. This depends on the thickness of the oil film and on the amount of oil applied. Penetration of oil into the fiber reduces the film thickness which affects the capillary adhesion[7] [Figure 4] and [Figure 5].{Figure 4}{Figure 5}

One of the published ways for evaluating this inter-fiber adhesion is a multipoint contact method which measures an average of the adhesive interactions between a single fiber and its neighbors in a hair assembly. The parameter measured is a “withdrawal” or pull-out force from a hair bundle with a defined packing density.[8] The capillary adhesion force measured on a single fiber due to its contact with other fibers in the assembly is sensitive to the amount of oil on the fiber surface. Therefore, it is possible to determine which oils are more readily diffused into the hair fiber, thereby leaving thinner films of oil on the surface.[7]

In the scenario of similar oil to hair ratio, more is the absorption of oil, lesser is the availability of oil between hair fibers. The thinner the oil film between two hair fibers, lesser force is required to pull out an individual hair fiber from a bundle of hair fibers. In this study, we have used 10 N force gauge from Chatillon, AMETEK, USA [Figure 6].{Figure 6}

Tensile strength assessment

Mechanical strength of the hair can be measured by suitable equipment intended for measuring strength properties or elasticity of hair fiber due to tension force or load. Hair fibers have elastic and plastic property. Plastic property of the hair fiber is measurable when a force is applied; the hair fiber extends in part, due to the applied force and effect, it stretches to about 2% of its original length. After the elastic phase, hair begins the plastic phase when the hair stretches quickly, approximately 25% to 30% in length, with a moderate increase in load. On applying force, the fibers stretch proportionally to the load until rupture occurs. Hair strands are fixed on a support, oriented from root to tip; the device applies a pull force to disrupt the fibers. The break-force is registered by software.[2]

The method involved using Chatillon Motorized Force Tester. Fifteen hair fibers or more were cut from each swatch to perform tensile test. The hair fiber was attached in root to tip alignment and was pulled at a fixed speed [Figure 7]. The force at which the hair breaks was recorded and analyzed. Higher the break force, higher the tensile strength of the hair.{Figure 7}

Correlogram

A correlogram is a graph of a correlation matrix and has been used to represent the correlation between different sets of variables. It is a useful tool that allows to highlight the most correlated variables in a data table. In this matrix, correlation coefficients are colored according to the value. A correlation matrix can be also reordered according to the degree of association between variables.

In this article, the positive correlations are in blue and negative correlations are in red. The extent and size of the circle represents the extent of correlation. The data can further be inferred in terms of percent value. Correlation index of 1 = 100%.

A correlation could be positive, meaning both variables move in the same direction, or negative, meaning that while one variable's value increases, the other's value decreases. Correlation can also be neutral or zero, meaning that the variables are unrelated.

Positive correlation: both variables change in the same directionNeutral correlation: No relationship in the change of the variablesNegative correlation: variables change in opposite directions.

Data analysis

After completion of the study, the instrumental data were exported into an Excel, and then, the data validation was performed. After the completion of data validation, the data were locked for the analysis. In analysis, a 2-tailed t-test at significance level of 5% (P < 0.05) was used to determine the significance difference. The results are presented as Mean ± SD Significant values are highlighted in yellow color for easy representation.

Since the objective is to establish a relationship between a pair of test methods, a statistical tool called the correlation matrix was employed to analyze the correlation among the three assessment data sets.

The statistical analysis was performed using R software-Version 3.4.0.

 Results and Discussion



Hair thickness measurement

It was found that there was a significant increase in the hair fiber thickness post oil application in both the test oils when compared to baseline indicating penetration of oil into the fiber. However, hair swatches treated with type 3 hair oil were observed to have significantly higher change in hair fiber thickness as compared to coconut oil indicating higher penetration efficacy [Table 1] and [Figure 8].{Table 1}{Figure 8}

Cohesive force measurement

The results showed that significantly lower force was required for hair swatches treated with Type 3 hair oil when compared to coconut oil [Table 2] and [Figure 9].{Table 2}{Figure 9}

There was a significant increase in hair fiber thickness post oil application for both the test oils and between the test oils and baseline. In addition to this, there was a significant decrease in cohesive force required for Type 3 hair oil when compared to coconut oil, thereby indicating better absorption of type 3 hair oil.

Tensile strength assessment

For each hair swatch multiple readings (n = 15) were taken. Mean value assessment was performed using t-test, where each value was considered independently [Table 3] and [Figure 10]. There was a significant increase in hair tensile strength post oil application for both the oils and between the oils and baseline (untreated control). However, increase in tensile strength was significantly better with type 3 hair oil when compared to coconut oil.{Table 3}{Figure 10}

Correlogram

To evaluate the dependence or correlation of the three test methods, the entire data set including both coconut oil and Type 3 hair oil was analyzed using the correlation matrix and plot [Table 4] and [Figure 11].{Table 4}{Figure 11}

It was noted that tensile test and thickness measurement show positive correlation (represented with blue color). The correlation was strong at an index of 0.86. Further, the cohesive force shows negative correlation (seen with red color) with both tensile and thickness data. The correlation was 0.60 and 0.70 with tensile and thickness data, respectively. This correlation analysis confirms that increase in hair thickness is directly proportional to the increase in tensile strength. The correlation analysis also shows an inversely proportional relationship between cohesive force and tensile strength. This was further confirmed with an inversely proportional data noted between cohesive force and hair thickness. Overall, the study indicated the positive influence of oil penetration on hair strength.

 Conclusions



The objective of this study is to standardize a new method for determining the penetration of oil and other topical products into hair. The sensitivity of the test method was determined by comparing the penetration abilities of two different types of oil: Type 3 hair oil consisting of 77% light liquid paraffin 21% vegetable oil, and 2% excipients (antioxidants, color, and perfume), and coconut oil into the hair shaft and explore its correlation to a physical property of hair, tensile strength.

The results of this correlation analysis demonstrate that the increase in hair thickness is directly proportional to the increase in tensile strength of the hair. The correlation analysis also reveals an inverse proportionality between cohesive force and tensile strength. This was further supported by an inversely proportional relation between cohesive force and hair thickness. Overall, the findings of the study suggested that oil penetration had a beneficial effect on hair strength.

The studies reported in this article show that conjoint assessment of hair thickness and cohesive force post oil application can be a suitable method to indicate the extent of oil penetration into the hair. This method can serve as a quick preliminary assessment or screening tool for product developers to compare the penetration of different oils. This method can contribute in faster prototyping for hair oils and other topical products. Furthermore, it can be used for efficacy tests for products that claim better penetration or higher tensile strength. This method is simple and does not require specific skillset like sample preparation techniques (hair fixation required in microscopy). Therefore, it can be a comparatively easy and less time-consuming method. For further investigation, other advanced assessment tools such as transmission electron microscopy/scanning electron microscopy or similar microscopic techniques with fluorescent tagging may put more insight into the findings.

Acknowledgments

The authors acknowledge the support of Ilegar S and Humsagar S, MS Clinical Research, Bangalore for technical support in conducting the study.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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