Principle, Procedure, Merits, Demerits and Applications of Mechanical Method of Sterilization : Pharmaguideline -->

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Principle, Procedure, Merits, Demerits and Applications of Mechanical Method of Sterilization

Autoclave - Sterilization is accomplished by heating objects under atmospheric pressure with saturated steam at 121°C for 15 minutes.

Mechanical Method of Sterilization

Autoclave - Sterilization is accomplished by heating objects under atmospheric pressure with saturated steam at 121°C for 15 minutes. Cellular protein coagulation destroys microorganisms, and the object is sterile. This device involves applying high-pressure saturated steam to equipment and supplies at various temperatures and times to sterilize them. A portable autoclave and a stationary autoclave are likely to be used. Large-scale sterilization is done with a stationary autoclave.

Hot air oven - Sterilization is achieved through dry heat and an electrical device. The device was invented by Pasteur. In general, it can be operated between 50°C and 300°C by means of a thermostat. Depending on the time and temperature, it requires direct heating.

Microwaves - The frequency of microwaves is 2,450 megahertz (2.4 gigahertz), which is the common frequency for radio waves. In water and other nutrients, these waves are absorbed at atomic level and are then converted directly into motion. Motion then becomes heat.

Mechanical Sterilization Equipment

Air filter - High-efficiency particulate air or also known as High-Efficiency Particulate Absorber (HEPA) is used to capture particulates in the air. As a result, particles 0.3 microns or smaller are trapped 99.97 percent of the time by these filters. HEPA filters circulate air particles in four directions viz.

Filtration through bacteria-proof filters can be used to sterilize thermolabile medicament solutions. A sterilized receiver is used to collect the sterile filtrate after the filters retain the bacteria. It is necessary that all parts that come in contact with the filtrate, as well as the filter, receive, and any connectors, are sterile, in order to obtain a sterile filtrate.

Ceramic filters - Filter candles are also known as these. Porcelain or kieselguhr is used, and there are several pore sizes you can choose from. Filters of this type are usually softer than porcelain ones. They are numbered according to their pore size. Sterilization of a candle is performed by placing it in a sterilization solution and attaching its opening to the vacuum system. The candle is compressed when vacuum is applied. Because the inside and the outside of the candle have different pressures, the solution moves inside. A sterile container is used to collect the filtrate. When the filter is continuously used, it becomes somewhat clogged. A nail brush can be used to scratch the outer surface and water can be passed through in reverse direction to clean this surface. Ceramic filters have the disadvantage that they are prone to absorbing materials from aqueous solutions.

Seitz filters - There are two parts to it. A compressible asbestos sheet is placed on the perforated disc at the lower part. Nuts connect the two parts. One of the parts has a valve for releasing vacuum. Asbestos sheets may also contain cellulose and alkaline earth like magnesium compounds, in addition to asbestos fibers. This asbestos material is meant to be discarded after use. In aqueous solutions of asbestos salts, asbestos pads can yield alkalis and precipitate alkaloids. The fibrous nature of asbestos pads makes them susceptible to shedding fibres into filters and absorbing drugs from solutions. It is therefore a good practice to reject a few milliliters of filtrate and to fix a sintered glass disc in the filtration unit immediately following seitz filtering.

Sintered glass filters - Glass borosilicate is used to make these. Disc molds are filled with finely powdered glass, which has been separated into particles of the right size. A suitable adhesion between the granules is achieved by heating the Moulds. There are different pore sizes of sintered glass filters available and they are numbered accordingly. Discs of suitable shape and size are fused to funnels. Pore sizes 5 and 3 should be selected for bacterial proof filtration. Reduced pressure is used during the filtration process. Insoluble substances are not absorbed by sintered glass filters. This is possible because these filters are made from borosilicate glass, which remains pH-neutral and prevents fibre loss. Once a sintered glass filter has been used, it should be cleaned by passing water in the reverse direction. Passing 1% sodium nitrate with strong sulfuric acid through the filter may remove organic matter.

Sintered metal filters - Sintered glass filters have metallic counterparts. Stainless steel is typically used for these. While they have greater mechanical strength, they are susceptible to attacks from solutions that pass through them.

Four basic steps are involved in sterilization by filtration: -
  • Through one of the bacterial-proof filters described earlier, the solution is filtered.
  • A presterilized container is filled with filtered solution aseptically.
  • Containers must be sealed aseptically.
  • Sterility testing is performed.
Injections sterilized by filtration must undergo sterility tests.


  • Temperature labile drugs such as blood products, insulin, and enzymes can be sterilized using this method.
  • The preparation is sterile and is free of living and dead bacteria.
  • Sterilization and clarification go hand in hand.
  • Using a parenteral solution in an emergency situation is a great way to administer medication quickly.


  • Carelessly handling a unit can lead to leaks.
  • Immediate detection of defects is not possible with media.
  • Only solution-based medicaments are suitable for the process.


In addition to sterilizing parenteral solutions containing thermolabile drugs, the method is effective in sterilizing other products containing protein matter that gets coagulated upon heating, i.e., insulin, blood serum, etc.
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Ankur Choudhary is India's first professional pharmaceutical blogger, author and founder of, a widely-read pharmaceutical blog since 2008. Sign-up for the free email updates for your daily dose of pharmaceutical tips.
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