Abstract

The aim of Ayurveda is to maintain & promote health of normal individual&cure disease of sick person.Now a days there is increase in demand of herbal products not only for health care but also beauty care product. Gel is one of the beauty care product & also used in industries for many purposes like hair dyes, analgesics, toothpaste. These are semisolids systems, consisting of either suspensions made up of small inorganic particles or large organic molecules interpenetrated by liquid. Here the simple method to prepare the gel and parameters required for its standerdisation will be discussed.

Introduction

A gel (from the lat. Gelu — freezing, cold, ice or gelatus — frozen, immobile) is a solid, jelly-like material that can have properties ranging from soft and weak to hard and tough. Gels are defined as a substantially dilute cross-linked system, which exhibits no flow when in the steady-state. [1] By weight, gels are mostly liquid, yet they behave like solids due to a three-dimensional cross-linked network within the liquid. It is the crosslinking within the fluid that gives a gel its structure (hardness) and contributes to the adhesive stick (tack).[2] In this way gels are a dispersion of molecules of a liquid within a solid in which the solid is the continuous phase and the liquid is the discontinuous phase. Gels consist of a solid three-dimensional network that spans the volume of a liquid medium and ensnares it through surface tension effects. Hydrogel, Xerogel, Organogel and some naturally occurring animal gels are types of the gels. Simple method to prepare the Gel will be described below. Standard parameters to assure the quality of Gel like firmness, relaxation, swelling, adhesiveness, tack, stickiness, cohesiveness, rupture/burst and extensibility etc are required for quality assurance.

Composition of Gel

Gels consist of a solid three-dimensional network that spans the volume of a liquid medium and ensnares it through surface tension effects. This internal network structure may result from physical bonds (physical gels) or chemical bonds (chemical gels), as well as crystallites or other junctions that remain intact within the extending fluid. Virtually any fluid can be used as an extender including water (hydrogels), oil, and air (aerogel). Both by weight and volume, gels are mostly fluid in composition and thus exhibit densities similar to those of their constituent liquids. Edible jelly is a common example of a hydrogel and has approximately the density of water

Types of Gel

(a) Hydrogel

Hydrogel is a network of polymer chains that are hydrophilic, sometimes found as a colloidal gel in which water is the dispersion medium. Hydrogels are highly absorbent (they can contain over 99.9% water) natural or synthetic polymers. Hydrogels also possess a degree of flexibility very similar to natural tissue, due to their significant water content. Common uses for hydrogels include:

• currently used as scaffolds in tissue engineering. When used as scaffolds, hydrogels may contain human cells to repair tissue.
• hydrogel-coated wells have been used for cell culture[3]
• environmentally sensitive hydrogels which are also known as 'Smart Gels' or 'Intelligent Gels'. These hydrogels have the ability to sense changes of pH, temperature, or the concentration of metabolite and release their load as result of such a change.
• as sustained-release drug delivery systems.
• provide absorption, desloughing and debriding of necrotic and fibrotic tissue.
• hydrogels that are responsive to specific molecules, such as glucose or antigens, can be used as biosensors, as well as in DDS.
• used in disposable diapers where they absorb urine, or in sanitary napkins
• contact lenses (silicone hydrogels, polyacrylamides)
• EEG and ECG medical electrodes using hydrogels composed of cross-linked polymers (polyethylene oxide, polyAMPS and polyvinylpyrrolidone)
• water gel explosives
• rectal drug delivery and diagnosis

Common ingredients are e.g. polyvinyl alcohol, sodium polyacrylate, acrylate polymers and copolymers with an abundance of hydrophilic groups.

Natural hydrogel materials are being investigated for tissue engineering; these materials include agarose, methylcellulose, hyaluronan, and other naturally derived polymers.

(b) Organogel

An organogel is a non-crystalline, non-glassy thermoreversible (thermoplastic) solid material composed of a liquid organic phase entrapped in a three-dimensionally cross-linked network. The liquid can be, for example, an organic solvent, mineral oil, or vegetable oil. The solubility and particle dimensions of the structurant are important characteristics for the elastic properties and firmness of the organogel. Often, these systems are based on self-assembly of the structurant molecules.[4][5]. Organogels have potential for use in a number of applications, such as in pharmaceuticals,[6] cosmetics, art conservation,[7] and food.[8]

(c) Xerogel

Xerogel is a solid formed from a gel by drying with unhindered shrinkage. Xerogels usually retain high porosity (15-50%) and enormous surface area (150–900 m2/g), along with very small pore size (1-10 nm). When solvent removal occurs under hypercritical (supercritical) conditions, the network does not shrink and a highly porous, low-density material known as an aerogel is produced. Heat treatment of a xerogel at elevated temperature produces viscous sintering (shrinkage of the xerogel due to a small amount of viscous flow) and effectively transforms the porous gel into a dense glass.

Properties of Gel

Many gels display thixotropy - they become fluid when agitated, but resolidify when resting. In general, gels are apparently solid, jelly-like materials. By replacing the liquid with gas it is possible to prepare aerogels, materials with exceptional properties including very low density, high specific surface areas, and excellent thermal insulation properties.

Naturally Occurring Gels in Animal Kingdom

Some species secrete gels that are effective in parasite control. For example, the long-finned pilot whale secretes an enzymatic gel that rests on the outer surface of this animal and helps prevent other organisms from establishing colonies on the surface of these whales' bodies.[9]

Application of Gel

Many substances can form gels when a suitable thickener or gelling agent is added to their formula. This approach is common in manufacture of wide range of products, from foods to paints and adhesives.

Hydrogels existing naturally in the body include mucus, the vitreous humor of the eye, cartilage, tendons and blood clots. Their viscoelastic nature results in the soft tissue component of the body, disparate from the mineral-based hard tissue of the skeletal system. Researchers are actively developing synthetically derived tissue replacement technologies derived from hydrogels, for both temporary implants (degradable) and permanent implants (non-degradable). A review article on the subject discusses the use of hydrogels for nucleus pulposus replacement, cartilage replacement, and synthetic tissue models. Also gels are used in, Deodorant, Gel Capsules, HairGel, Lipstick, Moisturising Cream, Petroleum Jelly, Shampoo,Soap,Toothpaste,Transdermal delivery system,Wax.

Process Of Making Gel

Material

1. Water 2. Carbopav 3. Sodium Prophyl Paraffin 4. Sodium Methyl Paraffine 5. Tea (Tri Eethanol Arisine)

Method

• Take 240 gm of demineralized water in a Beaker& sprinkle 1gm of carbopav on it. Don’t stir the beaker.
• In Beaker B take 30 gm of water& add SMP&SPP in a ratio 0.05:0.5 gm i.e.1:10 stirr it well.
• Add solution from beaker B in a beaker A and stirr the solution continuously until the gel get forms.
• The Ph of the gel should be in between 6.5 to 7.If Ph is less then add TEA as neutralizer instead of paraffin. If we have to add decoction or extract in gel, minus that much quantity of water from original preparation.

Standard Parameters for Gel

1. Gel concentration
2. Temperature
3. Maturing time
4. Additives
5. pH
6. Viscosity
7. Gel strength-LERA Texture Analyser (TA)[11] Firmness, Relaxation, swelling, adhesiveness, stickness, cohesiveness, rupture/burst.
8. Elasticity-Bloom Test [12].
9. Gel geometry.

By measuring the force: deformation relationship & force required to rupture the gel, enough information can be obtained to classify gels into categories such as brittle, firm, weak, elastic etc. (Mitchell,1976)

Conclusion

Gel are mostly liquids but behave like solids. These are semisolid systems, consisting of either suspensions made up of small inorganic particles or large organic molecules interpenetrated by liquid here. Gels are used widely in beauty care products like soap, shampoo, hair gel, lipstick, under eye gel, also for medicinal purposes like capsule, suppositories, analgesics. Also used in corporate industries. As importance of gel is increasing now a days its standardization is must for quality assurance. All gels exhibit viscoelastic properties and thus a complete rheological description requires the measurement of parameters over several decades of time (Mitchell, 1976). However for quality control purposes generally only a single quantity is determined utilizing a well-established empirical procedure such as the “Bloom test” (British Standard BS 757:1975; AOAC 1986).

The gelling behavior of natural polymers varies with the raw material and the method of extraction, it is therefore essential for both purchasers and manufacturers of all gelling agents to have reliable tests for evaluating “gel strength”.

Rheological measurements are used to complement information relating to the structure of products containing gels as a means of at-line monitoring, an integral part of good process control

Instrumental measures can be used in place of sensorial methods of evaluating the textural characteristics of gels, providing objective measures to subjective characteristics.

References

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3. Tissue Cells Feel and Respond to the Stiffness of Their Substrate
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9. Eileen May Dee, Mark McGinley and C.Michael Hogan. 2010. Long-finned pilot whale. Encyclopedia of Earth. National Council for Science and the Environment. Washington DC. eds. Peter Saundry and Cutler Cleveland
10. Mitchell, J. (1976). Rheology of Gels. Journal of Texture Studies, 7, 313-339.
11. .Munoz, A., Pangborn, R. and Noble, A. (1986). Sensory and Mechanical Attributes of Gel Texture – I Effect of Gelatin Concentration. Journal of Texture Studies, 17, 1-16.
12. Stevens, P., Wijaya, I. and Paterson, J. (1995). Modelling of Physical Properties of Gelatin: Gel Strength. Food Australia, 47 (4), 167-172.