Mechanisms of drug release from microspheres and microcapsules.pptx

Mechanisms of drug release from microspheres and microcapsules

1. Mechanisms of drug release from microspheres and microcapsules Presented by: Ishika Choudhary M . Pharma

2. Introduction Microspheres and microcapsules are extensively used in controlled drug delivery systems (CDDS) to regulate drug release, minimize side effects, and enhance bioavailability. These drug carriers protect the drug from degradation and control its release over a specific period . Understanding the mechanisms of drug release is crucial for designing efficient sustained, controlled, or targeted drug delivery systems .

3. Difference Between Microspheres and Microcapsules Feature Microspheres Microcapsules Structure Solid matrix with drug uniformly dispersed within the polymer Core-shell structure with drug encapsulated in a polymeric shell Drug Release Mechanism Diffusion, erosion, swelling Shell rupture, diffusion, enzymatic degradation Example PLGA microspheres, Chitosan microspheres Gelatin microcapsules, Ethyl cellulose-coated microcapsules

4. Mechanisms of Drug Release from Microspheres and Microcapsules 1. Diffusion-Controlled Release Definition: Drug diffuses from the microparticle to the external environment following a concentration gradient . Common in: Non-degradable polymers such as ethyl cellulose, polymethacrylate, and polyvinyl alcohol (PVA) .

5. Types of Diffusion-Controlled Release: (a) Reservoir System (Microcapsules): The drug is enclosed within a polymeric membrane and diffuses through pores or the membrane itself. Rate controlled by membrane permeability and thickness . Example: Ethyl cellulose-coated microcapsules of theophylline .

6. (b) Matrix System (Microspheres): Drug is dispersed within a polymeric matrix and releases as it diffuses out. Rate controlled by polymer porosity, drug loading, and polymer degradation . Example: Chitosan microspheres for insulin delivery .

7. 2. Swelling-Controlled Release Hydrophilic polymers absorb water, swell , and increase pore size, allowing drug diffusion. Occurs in hydrogel-based microspheres and water-soluble polymer systems. Common in polymers like polyvinyl alcohol (PVA), polyacrylates, and gelatin . Example: PVA-based microspheres for peptide and protein drug delivery .

8. 3. Erosion and Degradation-Controlled Release The polymer degrades or erodes , allowing drug release. Common in biodegradable polymers like PLGA (poly(lactic-co-glycolic acid)), PLA (polylactic acid), and polyanhydrides . Types of Polymer Degradation: (a) Bulk Degradation (Hydrolytic Degradation): Water penetrates the polymer, breaking bonds throughout the matrix . Common in PLGA, PLA, and polylactic acid microspheres . Drug release rate is nonlinear . Example: PLGA microspheres for paclitaxel delivery in cancer therapy .

9. (b) Surface Erosion: Polymer degrades layer by layer , maintaining the structure while releasing the drug. Occurs in hydrophobic polymers like polyanhydrides . Example: Polyanhydride microspheres for controlled chemotherapy .

10. 4. Osmotic Pressure-Controlled Release The microcapsule absorbs biological fluids , creating osmotic pressure. The pressure forces the drug out through micro-sized pores . Example: Osmotically controlled microcapsules of nifedipine .

11. 5. Enzyme-Triggered Release Biodegradable polymers degrade due to enzyme activity , leading to drug release. Used in targeted drug delivery systems where specific enzymes control release at the disease site . Example: Gelatin microcapsules degrade in presence of proteolytic enzymes , allowing site-specific release in tumors or inflammation sites .

12. 6. pH-Sensitive Release The drug release is controlled by pH variations in the gastrointestinal tract (GIT) or other tissues. Used in enteric-coated and tumor -targeted drug delivery systems . Example: Eudragit-coated microcapsules release drugs in the intestine (pH 6-7), preventing gastric degradation .

13. 7. Ion-Exchange Controlled Release Used in polyelectrolyte-based microspheres , where ionic interactions regulate drug release . Drug molecules are bound to ion-exchange resins and released in response to changes in ionic strength or pH . Example: Chitosan microspheres for controlled insulin release in diabetic patients .

14. Factors Affecting Drug Release from Microspheres and Microcapsules Factor Impact on Drug Release Polymer Type Hydrophilic polymers release drugs faster than hydrophobic ones. Microparticle Size Smaller microspheres have higher surface area , leading to faster release. Drug Solubility Water-soluble drugs diffuse faster than poorly soluble ones. Polymer Crosslinking High crosslinking density slows drug release. Environmental Conditions pH, temperature, and enzymatic activity affect polymer degradation and drug release.

15. Mathematical Models of Drug Release Several kinetic models describe drug release from microspheres and microcapsules: 1. Zero-Order Kinetics Drug release independent of concentration . Example: Osmotically controlled systems.

16. 2. First-Order Kinetics Drug release is concentration-dependent . Example: Diffusion-based microspheres.

17. Conclusion The mechanisms of drug release from microspheres and microcapsules are essential for designing advanced controlled drug delivery systems . The choice of polymer, formulation method, and release kinetics determines the drug’s therapeutic efficacy. By selecting the appropriate mechanism and mathematical model , pharmaceutical scientists can develop optimized drug delivery systems for sustained and targeted therapy .

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