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Latest Granulation Techniques and Technologies I

Writer： admin Time：2021-01-15 10:31 Browse：℃


Abstract
Granulation is the enlargement process of powder through agglomeration. It is also an important operation unit of preparation of most tablets and capsules. Its goal is to process fine powder into granules with good fluidity and no powder and then to facilitate tablet compression. However, high requirements on uniformity and physical and chemical properties of granules (including granularity, bulk density, porosity, hardness, moisture, compressibility and so on) generate challenges to granulation techniques and technologies. Granulation can be classified into two types: wet granulation (solution is used) and dry granulation (no solution is used). No matter which kind of granulation is used, the operators should have deep understanding to API’s physical and chemical properties, excipients’ type, granules’ fluidity and release properties, etc.. Current granulation techniques and technologies include spraying and drying granulation, rolling granulation, high shear granulation and fluid bed granulation. Just like other scientific branches, granulation technologies also develops continuously and it is not inevitable for the appearance of innovative technologies.
What is granulation
Generally speaking, the first step of granulation is to mix excipients and API so as to distribute API uniformly in the mixture. The granule size ranges from 0.2mm to 4.0mm in pharmaceutical industry but the main granules size only ranges from 0.2-0.5mm. These intermediate granules will be packed in sachets, compressed into tablets or filled into capsules after being mixed with other excipients.
 
The purpose of granulation
Granulation can increase API uniformity in the final products. After granulation, material density is increased so that the volume of unit material is reduced for more convenient storing and transport and more precise metering. As a result, problems such as dust, toxic drugs and some other harms can be effectively avoided. Besides, the product appearance and properties are bettered. The ideal granule properties are: good roundness (better granule fluidity), narrow size distribution (higher component uniformity), proper porosity (better compressibility) and proper water content and hardness (to avoid tablet breaking and dust flying during tablet pressing).
 The comparison of granulation technology
Granulation is also a process to transform powder and particles. Through granulation, granules with different properties can be produced depending on the size, type and dosage of drugs and excipients, volume of adhesive, granulation time, granulating machine, drying speed (temperature and time) and so on. Granules are mainly formed through solid bridge, chemical reaction, crystallization and colloidal granule deposition, etc.. And the process from powder to granules includes wetting, nucleating, agglomeration or growth, solidification and breaking.

The classification of granulation technology
The mixed powder of drugs and excipients can be directly compressed or produced to granules through agglomeration or granulation. Granulating methods include dry granulation and wet granulation. During dry granulation, material is compressed to blocks mechanically or by roller. On the other hand, during wet granulation, solution (adhesive and solvent) can bring about cohesion between the material. Wet granulation is more widely applied than dry granulation. It consists of several operation steps, including mixing, drying and screening. These steps are complex, time-consuming and space-consuming.
 
While deciding granulating technique, the operator should have deep understanding to drugs’ properties, excipients’ type, target granules’ fluidity and release performance and so on. In the past tens of years, granulating techniques, including rolling granulation, spraying granulation, fluid-bed granulation, low/high shear granulation, squeezing granulation and so on, have been widely adopted. Other granulating techniques are also being developed, improved and perfected as new technologies and techniques are developed and innovated. To make brief introduction, development, advantages and limitations are summarized in the following table.
 
The comparison of granulation technology

Technologies / techniques Description Features Advantage Disadvantages Equipment
Pneumatic dry granulation Dry granulation
Moderate pressure and separated airflow		 High porosity, high compressibility, smell covering, quick release and better release performance High drug loading, suitable for heat- and humidity-sensitive drugs, higher drug stability, less material consumption and waste Repeated granulation, weak separation, poor brittleness Roller compressor and airflow-cyclone separator or vacuum generator
Reverse wet granulation Wet granulation
Water or other solvent as the granulation solution		 Granules are uniformly wetted
Tablets dissolve uniformly		 Wide granule size distribution, high roundness, suitable for drugs of poor water solubility Some large granules, low porosity, disadvantages of other granulation methods High shear granulator
Steam granulation Wet granulation
Steam as the granulation solution		 Good dispersion, uniform distribution, large surface area and good roundness Environment-friendly, sterile and solution-free, no harmful material Partially being over-heated or -wetted, high energy consumption, not suitable for heat-sensitive drugs, not suitable for all adhesives High shear granulator with steam generating and controlling device
Moisture activation dry granulation Wet granulation
1-4% water as the granulating solution and moist absorbent		 Narrow size distribution, good fluidity and compressibility Low energy consumption and no drying for the granules, wide application, continuous operation Not suitable for water-sensitive drugs or high loaded drugs, limited proper absorbent High shear granulator with a spraying device
Thermal adhesion granulation Wet granulation
Small amount of water or solvent as the granulation solution and being heated to 30-130°C		 Good fluidity, low brittleness, and high tensile strength of tablets High drug loading, no drying, no flying dust High energy consumption, not suitable for heat- or humidity-sensitive drugs, not suitable for some adhesives Mixer or similar equipment with a heating device
Melting granulation Wet granulation
Meltable adhesive as granulating solution and being heated to 50-90°C		 Controllable drugs release and better dissolution No water or solution, no drying, low energy consumption, short operation Not proper to heat-sensitive drugs, limited proper adhesive High shear granulator or fluid bed granulator
Frozen granulation Wet granulation
Solution or suspension being sprayed, frozen and dried in vacuum		 Uniform size, good fluidity and high roundness Uniform granule, controllable granule density, less material loss, suitable for drugs which are not sensible to heat Limited proper solvent, only suitable for solution or suspension granulation Spraying frozen and drying granulator
Foam granulation Wet granulation
Foam as the granulation solution		 Uniform distribution of adhesive, preventing granules from excessively wetted and large foam surface area No spraying, small amount of water, short granulation time and suitable for water-sensitive drugs Not suitable for water-sensitive drugs, limited proper adhesive High shear granulator or fluid bed grnulator with foam generator
 
 
 
 

 

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