Sterilization is a process composed of a series of physical and / or chemical procedures that, through repeatable, standardized and documentable methodologies, are aimed at the complete destruction of any pathogenic microorganism, both in vegetative form and in the form of spores.

These procedures destroy microorganisms, causing the lethal alteration of some of their essential components; in particular, the denaturation of proteins, nucleic acids and the degradation of membrane and cell wall components takes place.

The probability of the presence of viable micro-organisms on the product after the sterilization procedure is indicated by the sterility assurance level, which defines its “completeness”, and if this level is below 10 to minus 6, it means that the probability of finding micro-organisms is less than one in a million and that therefore the material can be considered sterile (technical concept of sterility).


Why is this procedure so important?

Over time, this process has assumed an increasingly important role, especially for patients who undergo invasive diagnostic and/or therapeutic interventions, who are therefore more exposed to hospital infections; in fact, the majority of infections, caused by surgical wounds, are evidently contracted in the operating environment, and this means that the main responsibility for the infection is due to the pollution of medical surgical devices.

The use of sanitary materials that are not properly sterilized or disinfected, or contaminated, can cause infections in three different ways:

– transmission of a pathogenic microorganism from one patient to another;

– transmission of the same pathogenic micro-organism from a healthcare professional to a patient;

– transmission of infection from a patient to a caregiver of care.

Operators, therefore, should know each device, know how to use it and check the material before each use, evaluate the correct functioning, and identify any problems or risks, in order to guarantee not only the safety of the patient but of the entire operating team. Many instructions are indicated in writing in the internal regulations of the department or in the user manual that is provided by the manufacturer.

When is sterilization applied and what are the main steps?

Sterilization takes place on any object that comes into contact with the patient’s skin or mucous membranes; any medical device that is introduced into the body or into the body.

This process consists of a series of phases ranging from decontamination to the use of the device and must be carried out in the correct way, so as not to expose the patient and operators to further risks.

First of all, the product used is immersed in a decontaminating liquid and transported to an area suitable for carrying out the subsequent phases.

Decontamination can be either automatic, using appropriate equipment, or manual, through the use of dedicated containers or tanks.

Then the washing takes place, in a dedicated space (different from the packaging one) manually or automatically, in order to remove the residues of substances used in the production and thusto reduce the microbial concentration. To allow the detachment of organic residues on surfaces that are difficult to reach, a preventive action can be implemented at washing, i.e. treatment in an ultrasonic tank.

Then rinse with demineralized running water and dry (using paper cloths, TNT, canvas with low particle release, …), to prevent the presence of moisture from promoting the growth of microorganisms on the surface of the product or compromising the process.

Finally, after checking the integrity and functionality of the instrument, packaging takes place; that is, the insertion of the device into a supply chain system known as “sterile barrier”, which directs it to the actual sterilization phase, designed to preserve an appropriate sterility until their use.

This sterile barrier system can consist of an envelope, a container, a medical paper, and must of course allow the penetration and contact of the objects concerned, with the sterilizing agents. It must be practical and economical and must minimize the risk of contamination of the contents at the time of opening.

The duration of maintenance of the sterility characteristics of a medical device is determined by the mode of transport, conservation and storage, therefore by the environments and by all the improper handling of the packaging. Therefore, each company carries out an assessment based on its own facilities where the transport and storage of sterilized products takes place and will have to provide all the necessary information.

A lot of information, including sterilization date and expiration, department or service to which it belongs, content, name of the operator, sterilization cycle reference number, sterilizing machine reference, can be found on the adhesive labels that are specially applied on the product packaging.

In addition, through the same labeling, the traceability of the product becomes possible, the DMs are uniquely and unequivocally identified. All the elements considered critical that characterize the process to which the device has been subjected, and the characteristics of the patient on whom it has been used, are highlighted.

Paragraph 4.2 of the UNI EN 556-1 standard says that: “The manufacturer or supplier (of sterile devices) must demonstrate conformity (protocol that provides for a tolerance of a single device that may not be perfectly sterile out of 1 million), providing documentation and records proving that the DMs have been subjected to a validated sterilization process”.

There are several methods of sterilization:

– Steam sterilization – effect of steam under pressure

– Hot air sterilization – effect of dry heat

– Gas sterilization – effect of a gas mixture

– Sterilization by formaldehyde and steam

– Sterilization withpe racetic acid

– Plasma gas sterilization

– Sterilization with rays

The choice of method is determined by the type of material to be sterilized, because the purpose is precisely to obtain absolute asepticity, maintaining the utmost regard for the object in question to be sterilized.

INFRA, for a choice of technical reliability, combined with economic optimization, adopts only two sterilization methods, according to the product category: gamma sterilization and ETO or EO (ethylene oxide) gas sterilization.

If we are talking about products intended for a chemotherapy application, the gamma irradiation procedure is adopted, because it is a closed system product, so there cannot be a crack for the gas to enter the product.

The gamma sterilization process exploits a form of electromagnetic energy characterized by depth of penetration and low dosing rates, i.e. gamma irradiators; These effectively annihilate all the microorganisms present on the product, and on the packaging thanks to a very low temperature and without leaving residues.

The product and packaging then receive a series of radiations, the amount of which depends on the type of product and dosage requirements. In fact, radiation is released according to a precise dosage (dosimetric release), allowing treatments, controls and then immediate release for shipment.

This procedure is generally suitable for: disposable medical products, packaged products, food products, cosmetics, fabric-based devices, implantable medical devices (such as stents, heart valves, orthopedic products), pharmaceutical products and packaging, medical devices in combination that may contain a pharmaceutical or biological product, as well as raw materials.

Range sterilization can rightly be defined as a safe, reliable, easy to validate and above all effective technology because it guarantees sterility and effectiveness in treatment, in accordance with regulatory requirements and product properties; it offers flexibility and versatility, because it effectively sterilizes a wide range of products that differ according to dosage requirements, density and size of the box/package.

Finally,the second sterilization technique that INFRA has decided to adopt on the remaining categories of products, is ETO or EO sterilization, i.e. a process based on the diffusion of ethylene oxide gas, able to sterilize the products by eliminating the presence of any living microorganism. When a molecule of gas, ethylene oxide, reacts with microbial DNA and annihilates it, the desired condition of sterility occurs.

The procedure requires the simultaneous control of four variable but independent parameters: gas concentration, temperature, relative humidity and exposure time.

The effectiveness of ethylene oxide sterilization is determined by the ability of the gas to diffuse freely through a product and a package. In fact, the products to be sterilized are placed in breathable packages, allowing ethylene oxide to penetrate the sterile barrier and reach every surface of the device.

This procedure offers several advantages including: sterilization at low temperatures, which guarantees the integrity of the product; flexibility and versatility, because it efficiently sterilizes a wide range of products that can be distinguished by dosage, density, package size; parametric release, because the products are released after treatment going to reduce the time to market; gsterility and efficacy of treatment, because in compliance with regulatory and product requirements; compatibility with different types of polymers, resins, natural materials, metals (resin-based polymeric products, disposable medical devices, procedure kits, surgical trays, synthetic gowns) and products derived from the drug-device combination, which requires sterilization of the external contact surface ( filled syringes, drug-coated stents).

In conclusion, it is hoped that the dissertation developed has aroused reasons for interest or at least contributes to raising awareness of the importance of sterilization practices and how basic it is for the patient’s condition to scrupulously observe all the indications reported and consolidated by years of clinical practice.