Development of Artificial Sweat - Experiment

3.0 Literature Review :

3.1 Biosensor

The terminology for biosensor is usually used for equipment or devices used to monitor the metabolic system or element of biomocules. In addition, the particular term used, is referring to a sensor that uses a biological element, such as enzymes, antibodies, DNA, microorganisms or cell. Besides that, based on the IUPAC,it state that biosensor is an integrated equipment that have the capability to give a good analytical data and information in terms of qualitative and quantitative by using the element of biological recognition that interact with the transducer. Figure 1.1 and 1.2 show the schematic diagram.

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3.1.1 Structural Component of Biodetection

The partition in a biosensor that can operate with optimum condition consists of 3 components which are, (a) Bio-recognition elements, where the biomolecules are being placed and integrated which normally known as the immobilization on the surface of sensor, (b) Transducer or Detector devices, where the electrochemical and optical transduction occurs, (c) Processing Signal.

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3.1.2 Immobilization Bioreceptor

In the development of biosensors, the bioreceptors or biomolecules are important in selectively and add with the sensitivity to certain analytes, to ensure that they need to be situated and connected with a transducer in order to achieve the effectiveness of the biosensor in detecting certain analyte. The immobilization bioreceptor’s techniques involves, Adsorption, Microencapsulation, Entrapment, Covalent Attachment and also Cross-Linking.

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3.1.3 Performance of Biosensor

In the development of biosensors, things that should be emphasized is the operated performance of the biosensor in detecting analytes. The biosensor performance covers the aspects of the selectivity, sensitivity, accuracy, solution conditions, the “responds time” ( t_r), the “delay time” (t_d) and also the “lifetimes”.

3.1.4 Application Related to Smart Wearable of Biosensor For Sweat Sensor

There are various types of application in sensors that already applicable in the market, such as Smart Bra, Thick-film textile-based amperometic sensors and biosensors, Global Positioning System, Wireless Hands-free Communication, Smart Shirt and the most important sensor, is Smart Sensor that will be discussed in this research.

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3.2 Sweat

Generally, we know that sweat is excreted by sweat glands while the other term in this review, define the term for human sweat as nonexercise-induced eccrine (thermoregulatory) sweat which is secreted by healthy person and but not focusing on the Apocrine. A person, body region, diet, season, degree of acclimation, activity level ,race ,gender ,and also the sampling techniques can give high possibility affect to the variety in the composition of sweat between an individual. (Buckley and Lewis, 1960; Shirreffs and Maughan, 1997; Patterson et al., 2000, 2002; Hayden et al., 2004; Morgan et al., 2004; Shirreffs and Maughan, 1997; Jacobi et al., 2005; Robinson and Robinson, 1954).

3.2.1 Composition of Sweat :

Human sweat is composed of highly variable amounts of primary electrolytes, ionic constituents, organic acids and carbohydrates, amino acids, nitrogenous substances, and vitamins and miscellaneous constituents (Fig. 1). Sweat is 99.0–99.5% water and 0.5–1.0% solids (half inorganic and half organic), with specific gravity of 1.001– 1.008 (Robinson and Robinson, 1954; Rothman, 1954; Spector, 1956; Geigy, 1970, 1981; Altman and Dittmer, 1974; Agache and Candas, 2004). Nevertheless, this research report only focusing in the electrolyte, organic acids and carbohydrates and also pH.

3.2.1.1 Electrolytes

In general, concentrations of electrolytes in sweat were highly changeable and can assume to be countless. The major constituents of electrolyte were Na and Cl, and the minority amounts were consists of Ca, K, and PO4 (Robinson and Robinson, 1954; Rothman, 1954).In addition, there was reported in a journal that stated, the concentrations of primary electrolytes in the 45 formulations of artificial SSFL which were generally within ranges for human sweat. Unfortunately, median value were not be equivalentl to human sweat.There was lot of formulations lacked of many of the electrolytes present in human sweat (Fig. 1a). In such a case, some are as minimal as a solution of Na and Cl ions (Chiba et al., 1997; Mawn et al., 2005) while there was also occurred among the 45 formulations of artificial SSFL, 7 lacked Na ,8 lacked Cl, 41 lacked Ca, 38 lacked K, 44 lacked Mg, 34 lacked PO4, and all lacked HCO3 (Table 1).

3.2.1.2 Organic acids and carbohydrates

The summary in Fig. 1c was shown the measurement of the concentrations of organic acids and carbohydrates which was reported in human sweat. (Mickelsen and Keys, 1943; Robinson and Robinson, 1954; Rothman, 1954; Kuno, 1956; Spector, 1956; Elze and Oelsner, 1957b; Reed, 1969; Geigy, 1970, 1981; Altman and Dittmer, 1974; Kaiser et al., 1974; Stu¨ttgen and Schaefer, 1974; Goldsmith, 1999; Guyton and Hall, 2000; Agache and Candas, 2004).However, Lactic acid was plentiful of these constituents and its’ average constitutes was 0.28% of sweat (Spector, 1956; Altman and Dittmer, 1974). Besides that, by reffering to the published Journal of SSFL, acidity of SSFL was due to the high concentrations of both lactic acid and pyruvic acid (Agache and Candas, 2004). The concentrations of organic acids and carbohydrates in 45 artificial SSFL formulations are also summarized in Fig. 1c. The concentration of lactic acid and glucose in artificial SSFL formulations were generally within ranges

outlined for human SSFL.

3.2.1.3 pH

The measurement of pH values for whole body are summarized in Table 2 (median = 5.3). Values of whole body sweat in Table 2, are from a very acidic pH 2.1 (Haudrechy et al., 1997) to an alkaline pH 8.2 (Altman and Dittmer, 1974). There was might be a variety of sweat pH during a period of sweating, either it become less acidic or more acidic (Robinson and Robinson, 1954) and by body region (Collins, 1957). In order to analyze the effects of alkaline sweat, an investigation had been done by using the pH greater than 7. (Jordinson, 1941; Collins, 1957; Brown et al., 1982; Emmett et al., 1988, 1994; Wainman et al., 1994; Schimper and Bechtold, 2005.Due to the various in sweat pH, many investigators have studied dissolution of a test article over a range of pH values (Gallay and Tapp, 1941; Collins, 1957; Brown et al., 1982; Hemingway and Molokhia, 1987).

3.2.2 Physiology of sweat

There are two main types of sweat gland, apocrine and eccrine. Apocrine glands are the largest and they produce a viscous sweat containing lipids, cholesterol and steroids [12,13]. Eccrine glands operate almost the whole body and its amount between 2 and 4 million glands in adult skin. Thermoregulation is regulated by the eccrine sweat glands that helps in maintaining a constant body temperature, and hypothalamus become the centre in controlling the physiological sweat with normal rate of secretion ranging from 0.5 to 1mL/min.

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The characteristics of sweat is a clear hypotonic, and odourless fluid which consists of sodium, chloride, urea, lactate, organic and non-organic compounds [16]. The acidic nature of the excreted sweat is due to transportation and reabsorbing processes, which are relied on the physiological conditions that occur in the duct [17]. For instance, Patterson et al. has proven that the increased blood and sweat pH through the ingestion of sodium bicarbonate is caused by the induction of metabolic alkalosis. However, it is thought and assumed, this is because of the reduced sweat acidification in the reabsorbtive duct of the sweat glands. Furthermore, the relationship of sweat pH to sweat rate [9,15] and even for relationship of pH and sodium (Na+) levels in isolated sweat glands shown that they are directly proportional to each other.

It is known that induce active sweating in human beings will give affect to the heat, mental stimuli, muscular exercise and carbon dioxide [20,21] as the sweating is continued to occur as long as the stimulation lasts and subsides quickly after it ends..

3.2.3 Sweat collection and analysis

The characteristics of sweat sampling and the special samples it requires deserve discussion separated from analysis that can be either different or similar to that in other biofluids.

Nowadays, the purposes of sweat analysis are used even in optimizing the performance of athletes by studying the effects of dehydration but in the diagnosis of disease, detection of drug abuse, a method for testing deodorants .In addition, there are a lot of availability of different methods for the purposes of sweat collection and testing. However, the original method to test the components of sweat after exercise was revealed by using the whole bodywash down technique. Hence, all fluids lost during the aerobics are being stored for analysis [18].The following method was, sweat collection devices consisted of an occlusive bandage formed by one-to-three layers of filter paper, gauze or towel [5]. However, this kind of patch was time-consuming to apply, uncomfortably large, prone to detachment and yielded a small volume of sweat for analysis. In addition, it was found to alter the steady-state pH of the skin, the types of bacteria that colonize the skin and the transport characteristics of the skin, producing skin irritation [6].

To overcome these difficulties, non-occlusive sweat collection devices were developed, consisting of an adhesive layer on a thin transparent film of surgical dressing to which a absorbent pad and the overall being attached to the arm radial region. The transparent film just allow oxygen, water and carbon dioxide to pass through the patch, leaving healthy the underneath skin and prevents from the penetration of the non-volatile substances from the environment [5] .During wearing of the patch, sweat saturates the pad and slowly concentrates it, sweat components are retained, while water evaporates from the patch, thus misleading results of chloride concentration. Hence, its design does not allow to quantatize the concentrations of analytes in sweat, since the whole volume of secreted sweat is unknown.

However, there is a commercial devices for sweat sampling are usually linked to subsequent determination of a given analyte by a dedicated instrument into which the sampler is inserted, as is the case with sweat collection for diagnosis of CF [10]. A recent, no validated sampler for a given application that circumvents sweat-volume related problems and fulfills the present trend to microdevices is a microstrip impregnated with a dye pH indicator [11].

A key aspect of sweat sampling is its noninvasive character, crucial in dealing with people such as hemophiliacs, blood sampling of whom is an either difficult or dangerous task. Sweat sampling can avoids risk of infections to patients who need daily analysis, rather than compared with urine, sweat sample preparation is less complex. Therefore, the use of sweat for commonly frequent analysis practices such as drug control in athletesis preferable. In short, sweat as clinical sample is almost free from impurities or interferents and sample preparation is simple and fast step is quite enough. The main limitations of sweat as clinical sample are the difficulty to produce enough sweat for analysis, sample evaporation, lack of appropriate sampling devices, need for a trained staff, and errors in the results owing to the presence of pilocarpine. In dealing with quantitative measurements, the main drawback is normalization of the sampled volume.

Later on, the method has been discovered within the framework to produce results with a high coefficient of variation, which has lead to the development of sweat collection patches or capsules [22]. For instance, a disposable sweat collector developed by Brisson et al. that consisted of capsule created inside a flexible adhesive membrane pasted onto the skin [23]. After that, these collected samples are then stored at low temperatures for later analysis in a laboratory.

Now, the pH of sweat can only be determined when the subject has already finished exercise and does not give any changes in the results which might occur between the beginning and end of an exercise session. Therefore, it can be validate that a real-time, wearable method of gathering and analysing sweat is preferable and in demand.

Generally, this paper explains about the Development of Smart Patch with On-line Sweat Analysis .Besides that, artificial sweat has been chosen as it is an easily accessible fluid sample. The expected applications of this system for the personal health and sports performance and training.

3.2.3.1 Sweat analysis

Sweating is naturally increased by nervousness, exercise, stress and nausea, and decreased by cold. Sweat excretion is also affected by other factors, such as ambient temperature, relative humidity, body location, hormonal imbalances, overactive thyroid gland and the sympathetic nervous system, and certain foods and medications

A potential, general personal use of sweat is the recently developed smartphone application for in situ colorimetric detection, in prepared microchips, of pH changes in sweat correlated with chloride concentration and sweat rate which, during physical exercise, can indicate to users the proper time for hydratation [11].

3.2.3 Artificial Sweat :

3.2.3.1 Historical of Artificial Sweat :

The term artificial sweat is used throughout this review and encompasses historically used terms such as ‘‘artificial sweat,’’ ‘‘acidic artificial sweat,’’ ‘‘artificial perspiration,’’ ‘‘synthetic perspiration,’’ ‘‘synthetic sweat,’’ ‘‘sweat simulant,’’ and ‘‘simulated sweat.’’.

3.2.3.2 Benefits of a comprehensive artificial sweat

Historical formulations of artificial sweat do not appear to have been characterized and often lacked many constituents present in human sweat. However, only four artificial formulations included more than one amino acid. No vitamins were included in any previous formulation of artificial sweat. Among all historical formulations, one of the most chemically comprehensive recipes was developed by Boman et al. (1983) but contains only select electrolytes, ionic constituents, organic acids, and amino acids. The novel formulation presented herein contains the known human sweat constituents at physiologically relevant levels which provides for a more accurate representation of human than previous artificial sweat models.

Our novel artificial sweat formulation with composition that matches human is a chemically complex solvent. Preparation of this artificial sweat requires time and costs not associated with simpler formulations containing only the main constituents of sweat. However, caution must be used when excluding constituents.

3.2.3.3 Comparison to human sweat

During formulation, we first balanced all ionic constituents and electrolytes except sodium and chloride. Additionally, concentrations of many human sweat constituents vary widely due to factors such as age, diet, season, degree of acclimation, and gender, making it difficult to design an artificial sweat solution that is universally valid. The artificial sweat formulation described in this paper is chemically more comprehensive than any of the 45 previously identified artificial sweat formulations and contains constituents that are nearly all present in concentrations that match median values in human sweat. However, in our review (Stefaniak and Harvey, 2006), we provided estimates of human sweat constituent concentration ranges, pH, and temperature variability that could be used to guide investigations of the relative importance of sweat factors on interactions with materials.

In summary, our artificial sweat, represents a novel comprehensive artificial sweat at median constituent concentrations which equivalent to humans. (Stefaniak et al., in press),