What is Micelle?
Micelles are colloidal aggregates formed by the self-assembly of amphiphilic molecules (surfactants) in a solvent above a critical concentration, known as the critical micelle concentration (CMC). They consist of a hydrophobic core and a hydrophilic outer shell, with the hydrophobic tails oriented inwards and the hydrophilic heads outwards in polar solvents like water, or vice versa in non-polar solvents (inverse micelles)
Properties of Micelle
- Amphiphilic Nature: Micelles are formed by molecules with both hydrophilic and hydrophobic regions. The hydrophobic tails aggregate in the micelle core, while the hydrophilic heads form the outer shell, allowing solubilization of hydrophobic compounds in the core and interaction with the aqueous environment.
- Nanoscale Size and Morphology: Micelles typically range from 5 to 100 nm in size, with various shapes like spherical, cylindrical, or worm-like. Their small size and high surface area-to-volume ratio make them suitable for applications like drug delivery, catalysis, and nanoreactors.
- Thermodynamic Stability: Micelles are thermodynamically stable above the CMC, with a dynamic equilibrium between monomers and micellar aggregates. This stability allows them to encapsulate and solubilize hydrophobic molecules, making them useful as delivery vehicles.
- Stimuli-Responsiveness: Micelles can be designed to respond to external stimuli like pH, temperature, or ionic strength, enabling controlled release of encapsulated molecules or triggering structural changes for specific applications.
Formation Mechanism of Micelle
Before reaching the CMC, surfactant molecules arrange themselves at the solvent-air interface. Above the CMC, they spontaneously self-assemble into micelles, driven by the hydrophobic effect and minimization of free energy. The formation is an entropy-driven process, where the hydrophobic tails are shielded from the solvent, increasing the overall disorder and entropy of the system.
Applications of Micelle
- Drug Delivery: Micelles can solubilize and encapsulate hydrophobic drugs in their core, improving bioavailability and targeted delivery.
- Detergents and Cleaning Agents: Micelles can solubilize and remove dirt and oil stains due to their amphiphilic nature.
- Cosmetics and Personal Care Products: Micelles are used as emulsifiers, solubilizers, and delivery systems for active ingredients.
- Environmental Remediation: Micelles can solubilize and facilitate the removal of hydrophobic pollutants from soil and water.
- Nanomaterials Synthesis: Micelles can act as templates or reactors for the synthesis of nanoparticles with controlled size and shape.
- Sensing and Diagnostics: Micelles can encapsulate fluorescent probes or quenchers, enabling their use in sensing and diagnostic applications.
Application Cases
| Product/Project | Technical Outcomes | Application Scenarios |
|---|---|---|
| Micellar Drug Delivery Systems | Micelles can solubilise and encapsulate hydrophobic drugs, improving their bioavailability and reducing side effects. They can also target specific tissues or cells, enhancing therapeutic efficacy. | Targeted delivery of anticancer drugs, gene therapy, and imaging agents for improved diagnosis and treatment. |
| Micellar Enzyme Immobilisation | Micelles can solubilise and stabilise enzymes, enhancing their activity and stability in non-aqueous environments. Immobilised enzymes can be easily recovered and reused, reducing costs. | Biocatalysis in organic solvents for synthesis of fine chemicals, pharmaceuticals, and biofuels. |
| Micellar Extraction and Separation | Micelles can selectively extract and separate organic compounds from aqueous solutions, offering an environmentally friendly alternative to traditional solvent extraction methods. | Wastewater treatment, removal of pollutants, and recovery of valuable compounds from industrial effluents. |
| Micellar Enhanced Oil Recovery | Surfactant micelles can reduce the interfacial tension between oil and water, mobilising trapped oil and improving oil recovery from reservoirs. | Enhanced oil recovery from mature oil fields, increasing the economic viability of marginal reservoirs. |
| Micellar Nanoreactors | Micelles can act as nanoscale reactors, confining and controlling chemical reactions within their core, enabling the synthesis of nanoparticles and other nanomaterials with precise control over size and shape. | Synthesis of quantum dots, metal nanoparticles, and other nanomaterials for applications in electronics, catalysis, and biomedical imaging. |
Latest innovations of Micelle
Self-Micellizing Fatty Acid Compositions
- Compositions containing omega-3 fatty acids (triglycerides, esters, or free fatty acids) and surface-active agents that form micelles in aqueous media. The micelle formation enhances the bioavailability of omega-3 fatty acids, making it independent of food effects.
- The compositions can be formulated as free-flowing powders by drying the aqueous solutions with solid carriers like silicon dioxide or maltodextrin. This allows for convenient dosage forms like tablets or capsules.
Micelle-Forming Excipients
- Polysorbates (e.g., 15-31% w/w) and poloxamers (e.g., 0.5-5% w/w poloxamer 237) are used as surface-active agents to induce micelle formation. The specific combination and ratios optimize micelle properties.
- Phospholipids (1-10% w/w) can be included to further stabilize the micelles.
Micelle Formulation Techniques
- Prepare micelle formulations by mixing the drug/fatty acid, surfactants, water, and excipients, then dry to obtain a free-flowing powder.
- Reachers can add unsaturated fatty acid esters (1-20% w/w) and polyols (0-50% w/w) to modulate drug solubilization and micelle properties.
Technical Challenges
| Optimising Micelle Stability | Developing strategies to enhance the stability and robustness of micelle formulations, ensuring consistent performance and prolonged shelf-life. |
| Controlled Release Mechanisms | Exploring mechanisms for controlled and sustained release of active ingredients from micelle carriers to achieve desired pharmacokinetic profiles. |
| Micelle-Drug Interactions | Investigating the interactions between micelle components and drug molecules to optimise drug loading, solubilisation, and release kinetics. |
| Scalable Manufacturing Processes | Developing scalable and cost-effective manufacturing processes for micelle-based formulations to enable commercial viability. |
| Micelle Characterisation Techniques | Advancing analytical techniques for comprehensive characterisation of micelle size, shape, charge, and stability under various conditions. |
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