Formulation, Development and Evaluation of Resveratol Nanostructured Lipid Carrier System Loaded Gel

Natural active ingredients, such as resveratrol, are chemicals derived from plants, microbes, or animals that have been studied for their pharmacological and therapeutic effects, including antibacterial, anti-inflammatory, and antioxidant capabilities.  Because of their potential as efficient therapies for illnesses with fewer side effects and cost-effectiveness when delivered properly, these substances have become more important in modern medicine than the bulk of pharmaceutical medications.  Natural active ingredients have been increasingly popular in skincare products in recent years.  This widespread application is attributed to the skin's therapeutic benefits, which include antibacterial, anti-inflammatory, and wound-healing properties.  These ingredients are commonly used to treat specific skin concerns or disorders, such as inflammation, dryness, ageing, and acne. Despite their numerous benefits, natural chemicals in topical dosage forms remain difficult to deliver through the skin without losing effectiveness.  Poor skin permeability, which prevents penetration into the stratum corneum and outermost layer, is a significant barrier.  Because of this phenomenon, natural substances are unable to reach the deeper layers and achieve maximal efficiency.  Natural compounds may also decay and lose efficacy when exposed to light, heat, and air.  Natural components might be challenging to incorporate into skin care products due to variances in skin permeability, solubility, and other physical properties.  Natural substances may nevertheless cause skin irritation or allergic reactions in certain people, which raises safety concerns when compared to synthetic products. It has been proposed that lipid-based drug delivery systems (LBDDS) that mimic the function of the skin barrier can improve the performance and distribution of natural active ingredients.  LBDDS has been shown to improve skin permeability and protect natural components from degradation, hence increasing stability and bioavailability while reducing toxicity.  Nanostructured lipid carriers are the most popular.  Physically, LBDDS is typically liquid; however, when high-melting lipids are used or adsorbed onto the carrier, it can be solid or semi-solid at room temperature.  Lipid particulates may also be present.

The figure below depicts the morphological models of several LBDDS, including nanostructured lipid carriers.  Nanostructured lipid carriers (NLCs) are drug delivery devices that have a core matrix composed of both liquid and solid lipids.

Furthermore, NLCs are second-generation lipid nanoparticles with excellent drug loading capacity and an unstructured matrix, making them suitable for drug delivery systems.  Because of their unique properties, NLCs have been extensively studied as alternate carriers for the cutaneous delivery of pharmaceuticals, particularly natural active compounds.  Biocompatible chemicals, drug release modification, skin adhesion, film-forming ability with hydration of the superficial skin layers, and increased penetration and permeation into deeper skin layers are among the associated benefits identified.  NLCs, or nanostructured lipid carriers, represent a novel type of drug delivery vehicle. NLC offers several advantages, including biocompatibility, biodegradability, non-immunogenicity, high drug loading capacity, increased stability, controlled drug release, and ease of manufacture with scalability.  These carriers are ideal for drug delivery due to their advantages. Nanogels are attractive delivery methods for transdermal medication delivery.  Transdermal drug delivery devices have several advantages, including improving patient compliance, lowering dosing frequency, eliminating first-pass metabolism, and easily stopping drug action following device removal.  Transdermal administration helps to build up adequate drug concentrations in the target location.  The critical characteristics for producing successful TDDS are high drug loading, biocompatibility, and biodegradability, all of which are present in nanostructured gels. Nanogels are attractive delivery methods for transdermal medication delivery.  Transdermal drug delivery devices have several advantages, including improving patient compliance, lowering dosing frequency, eliminating first-pass metabolism, and easily stopping drug action following device removal.  Transdermal administration helps to build up adequate drug concentrations in the target location.  The critical characteristics for producing successful TDDS are high drug loading, biocompatibility, and biodegradability, all of which are present in nanostructured gels. Topical treatment is a significant usage in dermatological medicine.  The physical chemistry of the skin and the patient's application method dictate how a topical drug is given.  The type of carrier influences the topical's efficacy.  Nanogels may improve the success rate of treating people with skin diseases.

Skin:

Topical medication delivery systems are applied to specific parts of the body's surface.  To treat localised skin problems, they provide drugs locally rather than systemically.  Topical administration has a number of advantages over other techniques of administration.  When topical therapy is applied to the affected area, the primary benefit is that there are seldom systemic side effects [1]. Topical administration prevents first-pass metabolism by spreading the active ingredient through the skin.

It bypasses the active ingredient's metabolism before reaching the point of action.  Topical medicines can improve patient compliance since they are easy to use and suitable for self-administration.  Topical therapy avoids the risks and complications associated with intravenous administration by eliminating the need for complex delivery techniques.  Furthermore, the skin contains the majority of the human body's surface area.  It has a fairly broad variety of applications and can deliver more medication to specific locations with greater precision. It has the potential to reduce dose frequency by maintaining a high local drug concentration in the surrounding tissues over time.  Because the medicine does not reach the bloodstream, topical treatment reduces the risk of systemic side effects. However, there are some downsides.  These consist of: 

1. Skin irritation caused by the drug or its excipients. 
2. Certain drugs have minimal skin penetration. 
3. Agents with large particle sizes are not suitable for this method. 
4. the risk of allergic reactions. 
5. Sexual transformation [2]. 

Several semi-solid topical dosage formulations with antibacterial and anti-inflammatory characteristics were developed as part of this study.

The three most important pathways of skin absorption are those for medication penetration via the skin.  [3, 4]

1. Transcellular: The keratin-coated nucleus permits drugs to enter and exit the cell membrane.
2. Secondary, intercellular: In the lipid-rich extracellular space, molecules travel around nucleated cells.
3. Trans appendageal: Sweat glands, hair follicles, and sebaceous glands aid in these transports.

This is a breakthrough in pharmaceutics or cosmeceuticals using a nanostructured lipid carrier system loaded gel.  The formation of gel.

Gels are semi-solid structures composed of a liquid phase trapped within a three-dimensional matrix of polymers.  They are widely used for topical drug administration due to their excellent patient compliance, ease of application, and ability to deliver both hydrophilic and lipophilic medications.  "Gelatin" is the source of the word "gel," and "gel" and "jelly" share a shared origin.  Gelu means "drop" in Latin, whereas gel denotes "freeze" or "freeze." This source demonstrates the essential concept that liquids are solids that retain liquid properties and are elastic but do not flow.  In the late 1800s, scientists attempted to differentiate semisolids based on their phenomenological features rather than their chemical composition, and the name "gel" was first used to describe these materials.  There are currently no analytical methods available for identifying drug compounds.  Gels are tougher than jellies because they have more cross connections, are denser, or are just less liquid.  Gel-forming polymers create materials of varied hardnesses, including sols, slimes, jellies, gels, and hydrogels.

GEL DEVELOPMENT OBJECTIVES-

1. To enhance the stability and solubility of pharmaceutical compounds 
2. To achieve controlled drug release 
3. To boost the bioavailability of medications either locally or systemically 
4. To enhance patient adherence

COMPONENT OF GEL-

1. Gelling agent: The primary component of a gel is a gelling agent, which is a substance that imparts a gel-like texture, functioning to thicken or stabilise mixtures. An example of this is CARBOPOL. 

2. Solvent: A solvent is a substance that dissolves a solute to form a solution; it is typically a liquid. It serves as the medium in which other components are dispersed or dissolved. An example is purified water.

3. Active Pharmaceutical Ingredient (API): An API is the physiologically active component of a pharmaceutical drug that produces the intended effects in the body.  It is the substance that provides the medication's therapeutic action.  For example, RESVERATOL.

4. Penetration enhancers: A penetration enhancer is a chemical that promotes the absorption of active substances through the skin or other biological barriers.  Specifically, DIMETHYL SULPHOXIDE 

5. Preservatives: By inhibiting the growth of microorganisms such as moulds, fungi, and bacteria, preservatives extend shelf life and prevent spoilage.  Examples include PROPYL PARABEN and METHYL PARABEN.

6. pH Adjusters: Using a pH adjuster, you can vary and stabilise the acidity or alkalinity (pH) of your product.  It is required in formulations where stability, safety, and efficacy rely on maintaining a specific pH range.  For example, TRIETANOLAMINE.

APPLICATION-

1. Topical application of antibacterial, anti-inflammatory, and cosmetic compounds
2. System for transdermal medicine delivery.
3. Ophthalmic and dental formulations.

RESVERATROL is the natural active ingredient.

The phytoalexin resveratol (3,5,4'-trihydroxystilbene) is a polyphenol.  (For example, a chemical that plant tissues produce when they come into contact with a parasite and specifically inhibits the parasite's growth.)  Plants use the enzyme stilbene synthase to produce this stilbenoid, a stilbene derivative.  Resveratrol is a fat-soluble compound that exists in both cis and trans molecular structures.  offering a range of effects, including immunomodulation, neuroprotection, anti-inflammatory, anti-ageing, and anti-cancer.

Neuro-protection: Furthermore, resveratrol improves central nervous system performance while decreasing neuronal damage and apoptosis.  Resveratrol has been shown to enhance memory recovery after fluoride exposure and reduce neurodegeneration in the mouse cerebral cortex.  Additionally, resveratrol therapy improves memory, learning, and cognition in rats suffering from vascular dementia.  According to Corpas and colleagues, resveratrol improves cognition in mice models of Alzheimer's disease and boosts neuroprotection in amyloid and tau disorders. However, human resveratrol treatment produces varied responses.  A meta-analysis of randomized controlled studies suggests that resveratrol may be beneficial or have no meaningful effect on the chosen measures of cognitive performance.  Resveratrol has been shown in studies to have neuroprotective properties against intracerebral hemorrhage, cerebral neurodamage, and central nervous system traumas such as stroke.  Resveratrol also has neuroprotective effects in rat brains injured by cerebral ischemia/reperfusion by reducing the volume of cerebral infarction and increasing the expression of intracellular signalling pathway components such as kinases like JAK2, PI3K, or Akt, as well as anti-apoptotic molecules, while suppressing the expression of pro-apoptotic caspase-3 and Bax.

Anti-cancer properties: Resveratrol may have anti-cancer properties due to its various actions, including antioxidant effects and inhibiting the production of pro-apoptotic proteins and molecules that contribute to tumour growth, according to multiple in vitro and in vivo studies.  Resveratrol is well known to reduce the chance of developing several cancers, including thyroid, breast, colorectal, gastric, pancreatic, and cervical cancer.  According to study, resveratrol preserves healthy cells while eliminating malignant cells.  This can be connected to different cellular targets and resveratrol metabolic pathways in both malignant and healthy cells. This can be connected to different cellular targets and resveratrol metabolic pathways in both malignant and healthy cells.  Furthermore, dosage influences the dual pattern of resveratrol action.  While higher amounts induce cell necrosis or apoptosis regardless of whether the cell is healthy or sick, lower levels stimulate the creation of cell survival proteins.  High dosages of resveratrol damage cellular structure, impede protein and nucleic acid synthesis, and eventually cause cell death.  Monteillier and colleagues found that when mice with developed lung cancer were given 60 mg/kg resveratrol intranasally, tumour multiplicity and volume decreased significantly due to enhanced apoptosis. Furthermore, when compared to untreated controls, resveratrol treatment of gastric cancer cells enhanced pro-apoptotic proteins like Bax while reduced anti-apoptotic proteins like Bcl-2.  Resveratrol treatment at 20 μM inhibits STAT3 signalling and cytokine production in osteosarcoma cells, reducing cell viability, self-renewal, and tumorigenesis.  Resveratrol's anticancer activities are mostly dependent on reducing the production of carcinogenesis-related proteins, such as phospholipid scramblase 1, activating the mitochondrial ROS signalling pathway, and triggering caspase 3 cleavage.  Resveratrol also suppresses the cell cycle by inducing S-phase arrest in gastric cancer cells in a dose-dependent manner. Resveratrol has also been demonstrated to diminish drug resistance in cancer cells and improve the efficacy of anticancer treatments.  In vitro and in vivo study support resveratrol's favourable anticancer effect.

Activities to avoid aging: Antiaging research must focus on longevity, which is also an important measure of antiaging efficacy.  A growing corpus of studies suggests that resveratrol may help people live longer lives.  Autophagy's antiaging and life-extending effects may be linked to its ability to promote the clearance of dysfunctional proteins and damaged cellular organelles including mitochondria and endoplasmic reticulum.  A study found that resveratrol may induce autophagy in human cells in vitro and Caenorhabditis elegans in vivo.  It also increased the lifespan of Caenorhabditis elegans, whereas sirtuin (Sirt)1 knockdown or deletion prevented this effect.  According to the findings, resveratrol promoted longevity via triggering autophagy in a Sirt1-dependent manner.

RES has anti-atherosclerotic properties: Atherosclerosis predominantly affects the intimal layer of the arterial artery wall.  Its distinguishing features include extracellular lipid deposition, local smooth muscle cell migration and proliferation, and chronic inflammation.  Clinical events such as coronary artery disease, peripheral arterial disease, and stroke are triggered by luminal constriction and/or thrombus formation [11].  Improving the lipid profile may be important because lipids, particularly low density lipoproteins (LDLs), are involved in the atherosclerotic process.  According to certain preclinical studies, RES may modify this profile, specifically by increasing HDL cholesterol while decreasing plasma triglyceride and LDL cholesterol levels [12]. According to Cho et al. [13], RES may increase the hypocholesterolemic impact of pravastatin by inhibiting 3-hydroxy-3-methyl-glutaryl-CoA reductase (HMG-CoA reductase), an enzyme that interferes with the early stages of cholesterol synthesis.  Furthermore, RES may increase the expression of LDL receptors (LDL-R) in hepatocytes in vitro [14], lowering blood LDL cholesterol levels even further.  Furthermore, RES's antioxidant properties resulted in a boost in numerous endogenous antioxidant systems [16], a reduction in LDL oxidation (a process directly linked to atherogenesis [15], and anti-inflammatory effects [17].  The reduction of smooth muscle cell migration influences RES' antiatherogenic actions [18].

These qualities all show how RES influences important aspects in the atherosclerotic process.  As a result, several potential targets for the beneficial effects of RES in CVDs have been discovered.  In particular, RES inhibits TNF production while activating SIRT-1 (a class III histone deacetylase), eNOS, Nrf2, and the antioxidant response element (ARE).  Thus, the global effect of RES reduces endothelial apoptosis, activation, and vascular inflammation while increasing endothelial function [19].  RES has been proven to work in the early phases of the atherogenic process.  In example, by preventing the activation of the NF-B pathway, RES has been found to lower the expression of adhesion molecules (vascular cell adhesion molecule-1, or VCAM-1, and intercellular adhesion molecule-1, ICAM-1) [20]  RES may limit the formation of foam cells by inhibiting the expression of NADPH oxidase 1 and the creation of monocyte chemotactic protein-1 (MCP-1) in macrophages exposed to LPS [21].  RES may affect inflammation by modulating the expression of miRNAs with pro-inflammatory (miR-155) or anti-inflammatory (miR-663) effects [22].  In terms of anti-inflammatory properties, RES has also been shown to activate Nrf2 and inhibit the production of proinflammatory cytokines in cardiomyocytes, which helps to mitigate endotoxin-induced myocardial damage in mice and may be a means of preventing sepsis-induced cardiomyopathy [23].

Another effect of RES is the inhibition of vascular smooth muscle cell migration and proliferation, which may contribute to its anti-atherogenic characteristics [18,24].  However, a meta-analysis of seven clinical trials [25] discovered that the research either had no effect on the lipid profile or produced positive outcomes.  For example, patients with type 2 diabetes who received 250-1000 mg RES/day observed a reduction in LDL cholesterol [26].  Similarly, RES therapy lowered plasma triglyceride levels in healthy adult smokers (500 mg/day) [28] and healthy obese men (150 mg/day) [27]. RES (350 mg/day of RES-enriched grape extract containing 8 mg RES) reduced oxidized LDL by 20% and LDL cholesterol by 4.5% in those at high CV risk who were taking statins for primary prevention [29].  However, the anti-atherosclerotic effect of RES must be proved in large clinical trials and should not be limited to an effect on serum lipid profile.  RES' antihypertensive effects  Hypertension is a major risk factor for cardiovascular diseases [30].  RES has been proven to have antihypertensive effects in several animal models of hypertension after being given 10-320 mg/kg body weight/day for 14-10 weeks, depending on the study [31]. Notably, in animal models of hypertension and insulin resistance, relatively low dosages of RES (5-10 mg/kg/day) significantly decreased blood pressure [32], suggesting that RES may function better in people with diabetes or metabolic syndrome.  RES was administered before hypertension occurred in a few studies. 

Resveratrol's topical administration is limited due to its low solubility, instability, and low skin permeability.  The resveratrol nanostructured lipid carrier system loaded gel is designed to overcome this.  Small and large molecules are dispersed in aqueous liquid carriers to form a semi-solid preparation known as gel.  Gels are semi-solid systems in which colloidal particles in a liquid media form physical or covalent bonds.

TECHNIQUES FOR NLC PREPRATION-

The literature describes a variety of approaches for constructing NLCs.  These consist of: -

1) HIGH PRESSURE HOMOGENISATION - Definition of high pressure homogenization.  A lipid mixture is forced through a small aperture at extremely high pressure (typically 100-1500 bar) in a mechanical process known as high-pressure homogenization (HPH), resulting in nanostructured lipid carriers (NLCs).  Extreme shear and cavitation convert lipid droplets into nanoscale particles, resulting in a stable and constant dispersion.

The two basic HPH approaches for NLC creation are as follows:

1. Hot High Pressure Homogenization:

The medication dissolves or disperses in the lipid phase, causing lipids to melt above their melting point.

A hot aqueous surfactant solution is used to emulsify the lipid phase, the pre-emulsion is homogenized under high pressure, and the completed product is chilled to form solid lipid nanoparticles.

2. Cold, high-pressure homogenization: -

1. The drug is dissolved in melted lipids, which are then immediately cooled and solidified.
2. The solid drug-lipid mixture is ground into small particles.
3. To disperse these particles, use a cold aqueous surfactant solution.
4. Homogenization occurs at or below room temperature.

Benefits:

1. Produces small particles, often less than 200 nm.
2. Improves the effectiveness of medicine encapsulation.
3. Improves bioavailability and physical stability.
4. Adaptable to large-scale manufacturing.

1. High-Pressure Homogenization (HPH) reduces lipid droplets to nanoscale particles through mechanical stress, often between 400 and 1500 bar. This plays a role in NLC formation.

• This results in uniform, small particle sizes (typically less than 100 nm), which enhances stability and bioavailability.

2. Increased Encapsulation Efficiency (EE): Because smaller particles have a larger surface area, they interact more efficiently with lipids and active substances.

• • Studies using HPH for red palm oil NLCs reveal EE values of up to 99.9%.

3. HPH-produced NLCs are thermally and storage stable, preventing the breakdown of delicate chemicals such as carotenoids and surfactants.

4. Formulation Versatility: HPH is compatible with a variety of lipid combinations (such as Precirol ATO 5 and olive oil) and surfactants (such as Tween 80), allowing it to be prepared for oral, topical, and intranasal delivery.

5. Ability to scale

• • HPH is ideal for food and pharmaceutical applications since it can be generated in huge quantities. Increased stability.

2. MICROEMULSION-

Definition

A microemulsion is a clear or translucent, isotropic, thermodynamically stable mixture of water, oil, surfactant, and frequently a co-surfactant.  Droplets are ideal for pharmaceutical delivery and solubilization since their sizes typically range between 10 and 100 nm.

NLC formulation using microemulsion:  This requires producing NLCs with a microemulsion as a precursor or template.  To make NLCs, a microemulsion is often generated first, followed by processes like as high-pressure homogenization or ultrasonication.

Working Mechanism: Microemulsion formation.  A microemulsion is formed by combining the water phase, surfactants, co-surfactants, and oil phase (lipids).

Surfactants make it possible to create nanoparticles by decreasing interfacial tension.

Conversion into NLC: -  Cooling or treating the microemulsion hardens the lipid phase, resulting in nanostructured lipid carriers.

As a result, solid-liquid lipid nanoparticles are disseminated evenly.

Drug Encapsulation:

1. Hydrophilic drugs exist in the aqueous phase, while lipophilic pharmaceuticals are soluble in the lipid phase.
2. The small droplet size and large surface area promote drug absorption and bioavailability.
3. NLCs' solid lipid matrix allows for controlled and extended drug release.
4. They increase stability and protect delicate drugs from degeneration.

Benefits include:

1. Enhanced drug solubility and bioavailability.
2. Suitable for both hydrophilic and lipophilic medicines.
3. Profiles for regulated and prolonged release
4. Longer shelf life and improved stability
5. Scalability and easy setup

3. PROBE SONICATION -

"Probe sonication" is the method of agitating and disturbing particles in a liquid medium using high-frequency ultrasonic waves, typically above 20 kHz, provided by a metal probe known as a sonotrode.  Cell lysis, DNA shearing, and nanoparticle dispersion are all processes that use it extensively in biological, chemical, and medicinal applications.

1. Probe sonication reduces lipid droplet particles to the nanoscale.
2. For even distribution, homogenize the lipid mixture.
3. Improve the encapsulated drug's stability and bioavailability.

The primary mechanism is cavitation, which involves the formation and dissolution of tiny bubbles in liquids caused by ultrasonic vibrations.

1. • The probe generates ultrasonic vibrations by switching between high and low pressure zones.
1. Pressure changes cause cavitation bubbles to form in the liquid.
2. The bubbles rupture, releasing high-energy shockwaves.
3. This energy breaks up lipid clumps and disperses particles, resulting in stable NLCs with uniform size distribution.

Important controllable parameters include amplitude, which determines the strength of ultrasonic energy.

• • Pulse duration helps to control heat accumulation.
  • Sonication duration: Longer durations result in finer particles but increase the danger of degradation.
  • Temperature control: To prevent overheating, samples are regularly stored on ice.

4. SOLVENT DIFFUSION-

Definition and Technique:  This low-energy emulsification approach generates NLCs by allowing a water-miscible organic solvent containing lipids to seep into an aqueous phase, resulting in the formation of spontaneous nanoparticles.  Encapsulating lipophilic drugs in lipid-based nanocarriers is highly beneficial.

Working Principle:

The process consists of two phases: controlled diffusion and mixing.

1. Preparing for the Organic Phase

1. The medicine, as well as solid and liquid lipids, is dissolved in water-soluble organic solvents such as acetone or ethanol.
2. To ensure complete disintegration, this phase is typically heated.

2. Aqueous Phase Preparation:

1. Add stabilisers or surfactants (e.g., Poloxamer or Tween 80) to water.
2. Additionally, heated to the organic phase's temperature.

3. Diffusion and Nanoparticle Formation:

1. The aqueous phase is gradually agitated while the organic phase is added.
2. As the solvent moves through the water, the lipids precipitate and self-assemble into nanoparticles.
3. Surfactants prevent aggregation and stabilise the produced NLCs.

4. Solvent Removal:

1. Evaporation or dialysis removes the organic solvent, leaving behind a stable NLC dispersion. One of the primary advantages is the elimination of high-energy inputs such as sonication or homogenization.
2. Bioactives and delicate drugs are kept under mild conditions.
3. Reproducible and scalable for industrial applications.

Crucial Elements

• • Solvent type and ratio: Must be lipid-compatible and water-miscible.
  • Lipid content influences drug loading and particle size.
  • Temperature and stirring rate: Impact on diffusion rates.
  • Surfactant kind and concentration: Essential for preventing particle aggregation.

5. SOLVENT EMULSIFICATION

Evaporation is a popular method for producing nanostructured lipid carriers (NLCs), especially when working with lipophilic pharmaceuticals and thermosensitive compounds.  It creates stable lipid nanoparticles by combining solvent removal and emulsification.

Definition: Emulsification and Evaporation Method for Solvents

This method involves dissolving lipids and drugs in a water-immiscible organic solvent to form an oil-in-water (O/W) emulsion with an aqueous surfactant solution.  The solvent is then evaporated, precipitating and producing NLCs.

Working Principle: The procedure involves three main steps:

1. Organic Phase Preparation: A volatile, water-insoluble organic solvent (e.g., dichloromethane or chloroform) dissolves both liquid and solid lipids, including the drug.  To ensure complete disintegration, this stage is heated.
2. Emulsification: The organic phase is emulsified into an aqueous phase containing surfactants via high-shear homogenization or mechanical stirring. As a result, lipid droplets are spread throughout the water, forming a fine oil-in-water emulsion.
3. Solvent Evaporation: The lipids precipitate and form nanoparticles as a result of evaporation under low pressure or stirring to remove the organic solvent. Surfactants prevent newly formed NLCs from aggregating and stabilise them.

 Important characteristics:

1. Combines nicely with hydrophobic medicines.
2. Offers high encapsulation efficiency and controlled particle size.
3. Because it avoids high temperatures, it is ideal for heat-sensitive chemicals.
4. One of the most critical requirements is that the solvent be both volatile and insoluble in water.
5. Emulsification energy affects stability and droplet size.
6. Evaporation rate regulates particle size and production.
7. Surfactant concentration influences dispersion and stability.

6. SOLVENT INJECTION/ DISPLACEMENT-

Solvent injection (also known as solvent displacement) is a simple and effective approach for producing nanostructured lipid carriers (NLCs), making it ideal for lipophilic drug delivery.  It is based on a solvent's spontaneous diffusion into water, which results in nanoparticles.

Definition:  Techniques for Solvent Injection and Displacement.

Using this approach, an organic solvent containing lipids is introduced into an aqueous phase and agitated.  Lipids precipitate and self-assemble into NLCs, which are stabilised by surfactants due to the solvent's rapid diffusion into water.

Lipid precipitation and solvent diffusion drive the process.

1. Organic Phase Preparation: Medication and lipids are dissolved in water-soluble organic solvents like acetone or ethanol. Heated to ensure a complete breakdown.
2. Injection into Aqueous Phase: The organic phase is rapidly absorbed into a surfactant-containing aqueous solution.  Stirring causes the solvent to mix and diffuse into the water immediately.
3. Surfactants prevent NLCs from aggregating and stabilise them.
4. Solvent Removal: When the organic solvent is removed using dialysis or evaporation, a stable NLC dispersion remains.

 The key benefits include:

1. A simple and flexible procedure.
2. High-energy devices such as homogenisers and sonicators are unnecessary.
3. Because of the gentle processing conditions, it is excellent for heat-sensitive pharmaceuticals.
4. Formation of Nanoparticles: As the solvent diffuses, lipids precipitate, forming nanoparticles.

Critical Parameters:

1. Injection rate affects homogeneity and particle size.
2. Solvent type: Must be lipid-compatible and water-miscible.
3. Lipid content influences drug loading and stability.
4. The choice of surfactant influences shelf life and dispersion quality.

7. PHASE INVERSION

It is a low-energy emulsification process that produces nanostructured lipid carriers (NLCs).  It operates by adjusting the content or temperature of the emulsion to vary its kind.  It is especially useful for producing stable nanoparticles with minimal mechanical effort.

Definition: Method of Phase Inversion

Phase inversion is the process by which an emulsion transitions from oil-in-water (O/W) to water-in-oil (W/O) or vice versa due to changes in composition (for example, surfactant concentrations) or temperature.  This inversion results in the spontaneous formation of fine lipid nanoparticles.

Working Principle:

Phase inversion takes two major forms:

1. The PIT Method, also called temperature-induced phase inversion:

1. Uses nonionic surfactants, whose solubility fluctuates with temperature.
2. Surfactants like O/W emulsions at low temperatures.
3. Surfactant prefers W/O emulsions at high temperatures.
4. At a specific phase inversion temperature (PIT), the solution becomes exceedingly unstable, resulting in small droplets that solidify as NLCs once cooled.

2. Phase Inversion.  Induced by composition:

1. 1. Attained by gradually integrating water into a mixture of lipids and surfactants.
   2. As the water content increases, the system transitions from W/O to O/W.
   3. Surfactants prevent the spontaneous production of nanodroplets during inversion.

One of the primary advantages is that there is no need for sonication or high shear. Suitable for drugs that are sensitive to heat.  Creates stable and consistent nanoparticles.

Critical Parameters:

1. Surfactant type and concentration: These factors influence inversion behaviour.
2. Temperature management is critical to the PIT approach.
3. The water-to-oil ratio influences the stability and size of droplets.
4. Cooling rate: This affects the characteristics of the final particle.

CREATING GEL USING SUBSTITUTES-

1. 1. Active Ingredient (API) (Provides Therapeutic Action): Clindamycin, Diclofenac, and Resveratrol
   2. Gelling Agent (creates the structure of the gel base): sodium alginate, HPMC, and Carbopol 934.
   3. Solvent (dissolves excipients and drugs): Purified water, propylene glycol, and ethanol.
   4. Neutraliser (makes gel by altering pH): A mixture of sodium hydroxide and triethanolamine (TEA).
   5. Humectant (provides a smooth texture while retaining moisture)  Glycerin with Sorbitol
   6. Preservatives (which prevent microbes from growing): Propylparaben and Methylparaben
   7. Penetration Enhancer (increases medication penetration into skin): isopropyl myristate, dimethyl sulfoxide (DMSO),
   8. Colours and fragrances (optional)  Improves acceptability: essential oils and menthol