**Sterilization by Gamma Irradiation**

Kátia Aparecida da Silva Aquino

*Federal University of Pernambuco-Department of Nuclear Energy Brazil* 

#### **1. Introduction**

170 Gamma Radiation

Zimmermann, F.K., Kern, R. & Rosenberger, H. (1975). A yeast strain for simultaneous

mutation. *Mutat. Res*. Vol. 28, No. 3 (June), pp. 381-388.

detection of induced mitotic crossing over, mitotic gene conversion and reverse

Sterilization is defined as any process that effectively kills or eliminates almost all microorganisms like fungi, bacteria, viruses, spore forms. There are many different sterilization methods depending on the purpose of the sterilization and the material that will be sterilized. The choice of the sterilization method alters depending on materials and devices for giving no harm. These sterilization methods are mainly: dry heat sterilization, pressured vapor sterilization, ethylene oxide (EtO) sterilization, formaldehyde sterilization, gas plasma (H2O2 ) sterilization, peracetic acid sterilization, e-beam sterilization and gamma sterilization.

Gamma radiation sterilization and e-beam sterilization are mainly used for the sterilization of pharmaceuticals. Gamma radiation delivers a certain dose that can take time for a period of time from minutes to hours depending on the thickness and the volume of the product. Ebeam irradiation can give the same dose in a few seconds but it can only give it to small products. Depending on their different mechanism of actions, these sterilization methods affect the pharmaceutical formulations in different ways. Thus, the sterilization method chosen must be compatible with the item to be sterilized to avoid damage.

To be effective, gamma or e-beam sterilization requires time, contact and temperature. The effectiveness of any method of sterilization is also dependent upon four other factors like the type of microorganism present. Some microorganisms are very difficult to kill. Others die easily the number of microorganisms present. It is much easier to kill one organism than many the amount and type of organic material that protects the microorganisms. Blood or tissue remaining on poorly cleaned instruments acts as a shield to microorganisms during the sterilization process, the number of cracks and crevices on an instrument that might harbor microorganisms. Microorganisms collect in, and are protected by, scratches, cracks and crevices such as the serrated jaws of tissue forceps.

Finally, here is no single sterilization process for all the pharmaceuticals and medical devices. It is hard to assess a perfect sterilization method because every method has some advantages and disadvantages. For this reason, sterilization process should be selected according to the chemical and physical properties of the product. It is fairly clear that different sterilization processes are used in hospital and in industry applications. While EtO or autoclave sterilization is used in hospitals, gamma radiation or e-beam sterilization is used in industry depending on the necessity of a developed institution. Superiority of radiation sterilization to EtO and other sterilization methods are known by all over the

Sterilization by Gamma Irradiation 173

without use of catalysts. Thus, radiation processing uses highly penetrating gamma radiation from sealed radiation sources travelling at almost the speed of light, to bombard and kill bacteria in products sealed inside their final packaging. In this way the irradiated product remains sterile until the packaging is removed. The energy carried by the gamma radiation is transferred to the product being irradiated by collisions between the radiation and the atoms of the product. In these collisions atoms lose their bound electrons in a process called ionization. It is this process that results in irreparable damage to the life sustaining chemistry of living organisms and the initiation of crosslinking chemistry or

Gamma rays are generally used for the sterilization of gaseous, liquid, solid materials, homogeneous and heterogeneous systems and medical devices, such as syringes, needles, cannulas, etc. Gamma irradiation is a physical means of decontamination, because it kills bacteria by breaking down bacterial DNA, inhibiting bacterial division. Energy of gamma rays passes through hive equipment, disrupting the pathogens that cause contamination. These photon-induced changes at the molecular level cause the death of contaminating organisms or render such organisms incapable of reproduction. The gamma irradiation process does not create residuals or impart radioactivity in the processed hive equipment. Complete penetration can be achieved depending on the thickness of the material. It supplies energy saving and it needs no chemical or heat dependence. Depending on the radiation protection rules, the main radioactive source has to be shielded for the safety of

the operators. Storage of is needed depending on emitting gamma rays continuously

The first aspect to consider when sterilizing with gamma is product tolerance to the radiation. During use of this type of radiation, high-energy photons bombard the product,

main chair scission in polymeric materials.

Fig. 1. Disintegration of 60Co

**3. Gamma sterilization** 

**3.1 General aspects** 

world. These factors facilitate to understand the relatively fast increase of the constitution of irradiation institutions. Thus, this chapter will discuss the use of sterilization by gamma radiation.
