Yingtai: Preparation Process of Freeze-Dried Microspheres
Freeze-dried microspheres (freeze-dried microsphere formulations) are porous microsphere preparations obtained by removing water from a microsphere solution via sublimation using freeze-drying technology. This technique first involves preparing a microsphere suspension containing active ingredients using methods such as emulsification, spray freezing, or microfluidics. The suspension is then subjected to freeze-drying under low-temperature vacuum conditions, where water is directly sublimated from the solid to the gaseous state, ultimately forming porous microspheres with high specific surface area and excellent redispersibility. Freeze-dried microsphere technology effectively enhances the stability of thermosensitive drugs (e.g., proteins, vaccines) and extends shelf life while maintaining uniform particle size and drug-loading performance. It has significant applications in biopharmaceuticals (e.g., long-acting injectables), tissue engineering (e.g., cell scaffolds), and high-end cosmetics, particularly for high-value products requiring room-temperature storage and sensitivity to moisture.
01 Freeze-Dried Microsphere Preparation Process
The preparation of freeze-dried microspheres combines microsphere formation technology with freeze-drying processes, making it suitable for encapsulating active ingredients such as thermosensitive drugs, proteins, and vaccines. The core process can be divided into three stages: microsphere preparation, pre-freezing treatment, and freeze-drying, with the following detailed steps:
01 Microsphere Preparation (Droplet Generation and Solidification)
1. Sample Preparation
- Prepare a 1% sodium alginate and 5% mannitol solution (2.5 g mannitol, 0.5 g sodium alginate, 1 stirring bar, 47 mL water).
2. Pipeline Rinsing
- Set channel and time parameters. For example, with two channels (Channels 4 and 5), set the time amplitude to 100% and 24%. To speed up rinsing, set the microsphere volume to 100 μL, freezing time to 5 s, and injection speed to 100.
- Consume 1 mL of water in the test tube to perform air expulsion until the pipeline is cleared.
3. Liquid Nitrogen Addition
- Add an appropriate amount of liquid nitrogen to the equipment.
4. Droplet Formation
- Set microsphere volume (e.g., 20 μL), freezing time (e.g., 30 s), injection speed (e.g., 25). (For viscous samples, excessively high injection speeds may cause bubbles, affecting droplet formation.)
02 Pre-Freezing Treatment (Freezing of Solidified Microspheres)
- Transfer the microsphere suspension to a tray and rapidly freeze it in liquid nitrogen to form an ice crystal framework. Rapid freezing reduces ice crystal size and increases microsphere porosity.
03 Freeze-Drying (Lyophilizer Processing)
- Primary Drying (Sublimation Phase):
- Evacuate the lyophilizer (≤0.1 mBar) and gradually increase the temperature to -20°C to 0°C to sublimate ice crystals (approx. 24–48 hours).
- Secondary Drying (Desorption Phase):
- Further increase the temperature to 20°C–30°C to remove bound water (approx. 4–12 hours).
- Endpoint Determination:
- The material should appear as a loose, porous powder with residual moisture ≤3% (measurable via a moisture analyzer).
04 Post-Processing and Packaging
- Collection and Sieving:
- Sieve (e.g., 100–200 mesh) to remove agglomerated particles.
- Quality Testing:
- Particle size analysis (laser diffraction), morphology (SEM observation of porous structure).
- Drug loading/encapsulation efficiency (HPLC/UV detection), redispersibility (tested in saline or buffer solution).
02 Application Scenarios
Freeze-dried microsphere technology combines the drug-loading/controlled-release properties of microspheres with the stability advantages of freeze-drying, making it widely applicable in pharmaceuticals, biomaterials, cosmetics, and food industries. Key application scenarios include:
01 Biopharmaceuticals
- Long-acting injectables: e.g., PLGA freeze-dried microspheres for sustained-release drugs (leuprolide, growth hormone), enabling continuous release for weeks to months.
- Vaccine delivery: Protects antigens (e.g., mRNA vaccine microspheres), improving room-temperature stability and addressing cold-chain transportation challenges.
- Protein/peptide drugs: Prevents denaturation of biomacromolecules (e.g., insulin, interferon), maintaining activity post-reconstitution.
- Cancer therapy: Drug-loaded microspheres (e.g., doxorubicin) for localized embolization chemotherapy, with freeze-drying extending shelf life.
02 Regenerative Medicine & Tissue Engineering
- 3D cell culture scaffolds: Freeze-dried alginate/collagen microspheres provide porous structures for stem cell proliferation and differentiation.
- Wound healing: Growth factor-loaded (e.g., EGF) freeze-dried microspheres promote chronic wound repair.
03 High-End Cosmetics
- Active ingredient preservation: Freeze-dried microspheres encapsulate vitamin C, hyaluronic acid, etc., releasing upon hydration to prevent oxidation.
- Targeted skincare: Microspheres enable slow release of whitening agents (e.g., arbutin), reducing skin irritation.
04 Food & Nutraceuticals
- Probiotic protection: Freeze-dried lactic acid bacteria microspheres improve survival rates and shelf life.
- Flavor encapsulation: Microspheres entrap volatile flavors (e.g., lemon essential oil) for controlled release.
05 Diagnostics & Testing
- In vitro detection carriers: Freeze-dried fluorescent microspheres for immunochromatographic test strips (e.g., COVID-19 antigen tests).
- Contrast agents: Porous freeze-dried microspheres loaded with gas enhance ultrasound imaging contrast.
