Formulation, Optimization And Characterization Of Anhydrous Polyherbal Face Wash Tablets: A Sustainable Unit-Dose Approach

The word “cosmeceutical” describes products with bioactive substances meant to improve skin health, bridging the gap between medications and cosmetics¹. Due to growing consumer knowledge of the possible long-term dermatological problems connected with synthetic chemicals, the worldwide cosmetics industry has seen a substantial transition towards “Green Cosmetics” in recent years². The main purpose of face wash formulations is to remove makeup, dead skin cells, excess sebum and environmental contaminants from the stratum corneum of the face without totally removing the skin’s natural moisture barrier³. Conventional synthetic surfactants, especially sodium lauryl sulphate (SLS), are known to disturb the skin’s natural acid layer and result in transepidermal water loss (TEWL), which causes persistent dryness, irritation and redness⁴. Because of their wide pharmacological spectrum and excellent safety profile, polyherbal compositions that make usage of the synergistic effects of numerous plant extracts are being given priority^{5, 6}.

Conventional face wash formulas are mostly liquid or semi-solid solutions that include up to 90% water⁷. To stop microbiological growth, strong artificial preservatives such parabens must be added due to the high-water content⁸. An important development in sustainable pharmacy is anhydrous (waterless) technology. These formulations naturally inhibit microbial development and lessen the need for preservatives by eliminating aqueous phase^{7, 9}. Additionally, eliminating water weight greatly lowers the carbon footprint related to international logistics and transportation¹⁰. Because they are water-activated and travel-friendly, dry powder face washes provide a first step toward waterless cosmetics, but they are still prone to spills, moisture absorption during storage and incorrect consumer dispensing⁷.

The unit-dose compressed tablet technique is a crucial technological advancement to get around these restrictions¹¹. By ensuring that the customer uses a precise, preset amount of the formulation for a single application, unit dosage administration via tablets prevents product waste¹². Tablets enable extremely sustainable, eco-friendly, biodegradable packaging options, in contrast to liquid washes packaged in plastic collapsable tubes¹³. Tablets are also highly portable and ideal for travel, as they are spill-proof and exempt from international airport liquid volume restrictions¹⁴.

In the end, these anhydrous polyherbal tablets reduce the possibility of redness and skin irritation brought on by harsh synthetic cleansers¹⁵. In order to provide a stable, environmentally responsible and skin-friendly cleaning option, the current work focuses on the formulation, optimisation, and characterisation of an anhydrous polyherbal face wash tablet.

MATERIALS AND METHODS: 

Materials:

Gathering of plant materials

Neem (Azadirachta indica) leaves, Tulsi (Ocimum tenuiflorum) leaves, Palash (Butea monosperma) flowers and Orange (Citrus sinensis) peels were among the necessary herbal ingredients that were gathered from nearby plants, marketplaces and botanical gardens.

Herbal powders preparation

The gathered plant materials were thoroughly cleansed to get rid of contaminants and dirt¹⁶. Following that, the materials were shade-dried for a few days so as to preserve the active ingredients¹⁷. Following full drying, the materials were ground into a coarse powder using a mechanical grinder¹⁸. To create a fine powder, each powder was separately sieved through sieve number 80 and kept in airtight containers for later use¹⁹.

Gathering of excipients

Reetha (Sapindus mukorossi) powder, Acacia (Acacia senegal) gum, Corn (Zea mays) starch, Potato (Solanum tuberosum) starch, Rice (Oryza sativa) powder, Sandalwood (Santalum album) powder and Menthol (Mentha arvensis) powder were all obtained from reliable sources. After being individually sieved via sieve number 80, each powder was kept in airtight containers¹⁹.

Figure 1. Process flow of preparing herbal powders from fresh ingredients via shade drying

Methods:

Formulation of anhydrous polyherbal face wash tablets (direct compression method)

1. Firstly, the required quantity of neem leaves, tulsi leaves, palash flowers and orange peels powders were taken and triturated in a mortar in order to get a homogeneous mixture^{18, 20}.
2. To this mixture, reetha powder and rice powder were added and mixed thoroughly to enhance cleansing and exfoliating properties^{21, 22}.
3. Further, corn starch was added as a diluent and disintegrant to the above mixture²³.
4. Acacia gum was incorporated as a natural binder and mixed uniformly²⁴.
5. Sandalwood powder was added to provide fragrance and skin toning effect²⁵.
6. Potato starch was added as a lubricant to improve flow properties²⁶.
7. Menthol powder was added at the final stage to impart a cooling sensation²⁷.
8. The entire mixture was blended thoroughly to get a homogeneous powder blend²⁰.
9. The prepared mixture was run through a sieve no. 60 to ensure uniform mixing and flow¹⁹.
10. The final powder blend was compressed into tablets using a tablet compression machine (direct compression method was employed)²⁸.
11. The compressed tablets were dedusted to remove excess powder²⁸.
12. The prepared tablets were collected and stored in an air-tight container for further use²⁹.

Table 1. Composition of anhydrous polyherbal face wash tablet formulation

Characterization of polyherbal formulations:

Pre-compression characterization of powder blend

a) Angle of repose

The maximum angle formed between the surface of a pile of powder and the horizontal plane is known as the angle of repose. It is employed to assess the powder blend’s flow characteristics. By allowing the powder to pass through a funnel that is fixed at a specific height to create a conical heap, the Funnel technique determines the angle of repose. The angle of repose can be calculated using the formula below after measuring the heap’s height (h) and radius (r): 

θ = tan?¹ (h/r)

where, θ = Angle of repose; h = Height of powder cone; r = Radius of powder cone. Better flow characteristics are indicated by a lower angle of repose^{9, 20}.

Table 2. Powder flow characteristics according to angle of repose

b) Bulk density

The ratio of the weight of powder to its bulk volume prior to tapping is known as bulk density. It is crucial for figuring out tablet compression characteristics and gives information about the packing qualities of powder particles.

After precisely weighing the powder mixture, it is poured into a graduated cylinder. The powder’s initial volume is recorded. To calculate the bulk density, use the following formula:

Bulk density = Weight of powder / Bulk volume

Depending on the type of powder, bulk density values can vary, although they typically fall between 0.3– 0.8 g/cm³ or g/ml^{9, 20}.

c) Tapped density 

The proportion of weight of powder to the volume occupied upon tapping is referred to as tapped density. It offers details on compressibility and powder packing. 

A graduated cylinder is filled with a specified amount of powder, then it is manually tapped 50 times. The following formula is used to determine the tapped density:

Tapped density = Weight of powder / Tapped volume

Because tapping causes powder particles to settle closer together, tapped density is always higher than bulk density^{9, 20}.

d) Carr’s index (Compressibility index)

Powder blends compressibility and flowability are assessed using carr’s index. The bulk density and tapped density numbers are employed to compute it. The formula that follows is utilised to determine the carr’s index: 

Carr’s Index = (Tapped density − Bulk density) / Tapped density ×100

Lower values indicate better compressibility and flow characteristics²⁰.

Table 3. Carr’s index and associated powder blend flow characteristics

e) Hausner’s ratio

Powder flow characteristics are determined using hausner’s ratio. The ratio of tapped density to bulk density is used to calculate it²⁰.

Hausner Ratio = Tapped density / Bulk density

Table 4. Hausner’s ratio and associated powder blend flow characteristics

f) Loss on drying (LOD)

An essential evaluation metric for figuring out how much moisture and volatile matter present in the powder blend is LOD. Because too much moisture can impact the stability, flow characteristics, compressibility, and hardness of tablets, it is especially crucial for anhydrous formulations. Additionally, a high moisture level may shorten the formulation’s shelf life by encouraging microbial development.

This process involves precisely weighing a predetermined amount of powder blend and drying it at 105 °C in a Hot air oven until the weight remains constant. The amount of moisture in the sample is indicated by the weight loss during drying. The formula that follows is utilised to determine the percentage LOD:

%LOD = (Initial weight − Final weight) / Initial weight ×100

The LOD value should typically be kept below 5% for stable anhydrous tablet formulations so as to ensure the formulation’s quality and stability⁹.

                         (a)                                     (b)                                        (c)                                   (d)                        

Figure 2. Pre-compression characterization of powder blend: (a) Angle of repose determination (b) Bulk density measurement (c) Tapped density measurement (d) Sample preparation for loss on drying (LOD)

Post-compression characterization of polyherbal face wash tablets

a) Physical appearance

The physical attributes of the created tablets, including colour, shape, surface texture and odour are assessed visually. To guarantee high quality and user acceptability, tablets should be devoid of chips, fractures and surface irregularities³⁰.

b) pH Determination

To make sure the formulation is suitable for the skin, pH level of the tablet solution is measured. Using a digital pH meter, one may determine the pH after the tablet is dissolved in distilled water in order to make a 1% aqueous solution. The pH value of skin care products should be between 5.5-6.5 to be able to prevent skin irritation³¹.

c) Weight variation test

Tablet weight homogeneity is guaranteed using the weight variation test. An analytical balance is used to weigh each of the twenty randomly chosen tablets. After calculating the average weight, the weights of each tablet are compared to the average weight. The formula that follows is utilised to determine the percentage deviation:

%Deviation = (Individual weight − Average weight) / Average weight ×100

Tablets must adhere to weight variation limits based on their average weight in accordance with pharmacopeial standards (USP/IP). The permissible variance is ±5% for tablets weighing 250 mg or more⁹.

Table 5. USP/IP weight variation limits for tablets

d) Hardness 

The mechanical strength of tablets and their capacity to tolerate handling during packing and transit are indicated by tablet hardness. A Monsanto, Pfizer hardness tester or other such device utilized for measure hardness. Hardness ranges from 3-6 kg/cm² for the majority of tablets to guarantee sufficient strength without compromising disintegration⁹.    

e) Thickness

Tablet thickness is assessed to guarantee consistency in tablet size. It is measured in millimetres (mm) using a Micrometre screw gauge or Vernier calliper. A consistent thickness guarantees that tablets are packaged and look good⁹.

f) Friability test 

The resistance of tablets to abrasion during handling and transit is assessed using friability. Roche friabilator are utilised for conduct the test. Weighing and rotating a sample of tablets at 25 rpm for 4 min. (100 revolutions). The following formula is applied in order to determine the percentage friability:

%Friability = (Initial weight − Final weight) / Initial weight ×100

Less than 1% weight loss is the permissible limit for friability⁹.

g) In-vitro disintegration time

The disintegration test measures how long it takes for tablets to disintegrate into smaller particles in an aqueous medium. A USP disintegration apparatus with distilled water kept at 37°C is used to conduct the test. The quick disintegration of cleansing tablets, like face wash tablets, within 20 to 60 seconds is deemed beneficial^{20, 30}.

h) In-vitro dispersion time

The time needed for the tablet to fully disperse in water was assessed using the dispersion time. The trial was carried out in a petri plate using 6ml of distilled water. The time it took for the tablet to fully disperse into tiny particles were recorded in seconds after it was carefully positioned in the center of the petri dish³¹.

i) Foamability

Foam ability is a crucial factor in face wash compositions, Because foam aids in the cleansing process. The cylinder shake method determines the foaming ability. 10ml of water are utilised for dissolve one tablet and the blend is then agitated in a measuring cylinder. Foaming ability is ascertained by calculating the height of foam generated. Better cleaning results are indicated by higher foam heights^{30, 32}.

j) Spreadability

The ease whereby the formulation spreads across the skin’s surface is often known as spreadability. A specific weight is applied while a tiny quantity of the formulation is placed between two glass plates. The time needed for the formulation to spread is noted and spreadability is determined using the following formula:

S = m × l / t

Where: S = Spreadability; m = Weight applied on the upper slide; l = Length of glass slide; t = Time taken for spreading

Good spreadability guarantees that the product is applied uniformly to the skin³².

k) Washability

The ease with which a product can be washed from the skin with water is determined by its washability. After applying the mixture to the skin, water is used to rinse it off. A decent face wash tablet should be easy to remove and leave no residue³⁰.

l) Skin irritation test

The formulation’s safety is assessed by a skin irritation test. After applying a tiny bit of the tablet solution to the skin, it is checked for redness, irritation, swelling or itching after 1-2 hours. There should be no indications of irritation in a safe formulation^{30, 32}.

m) Stability studies 

Studies of stability are carried out to determine the physical and chemical stability and shelf-life of the prepared tablets under different storage conditions. For a predetermined amount of time (often one to three months), the tablets are kept in sealed containers at room temperature and accelerated conditions (40°C ±2°C and 75% ±5% RH). Physical appearance, pH, hardness and disintegration time are among the criteria that are regularly assessed during the study period. If a formulation’s performance and physical characteristics do not significantly change, it is deemed stable³³.

Figure 3. Post-compression characterization of polyherbal face wash tablets: (a) Physical appearance of formulated tablets (b) pH determination of formulation using calibrated digital pH meter (c) Determination of mechanical breaking force using Monsanto tablet hardness tester (d) Dimensional thickness measurement using Vernier caliper (e) Evaluation of mechanical  integrity and percentage friability using Roche friabilator (f) In-vitro disintegration time test progress monitoring the structural breakdown of the tablets (g) In-vitro dispersion time and visual behaviour characterization of  the tablet in an aqueous medium (h) Evaluation of foam volume via graduated cylinder method (i) Visual assessment of lather consistency and foam texture on hands (j) Determination of  spreadability characteristics using glass slide apparatus (k) Washability and residue clearance assessment under running water (l) Stability evaluation of formulated tablets post 1-3 months storage interval

RESULTS AND DISCUSSION: 

Table 6. Pre-compression characterization of powder blend

Table 7. Post-compression characterization of polyherbal face wash tablets