Over the past decades, radiation processing has gained traction for preservation of a host of things ranging from everyday use food products to artefacts for prolonged usage by saving them from the vagaries of nature and possibilities of physical harm.
Sterilisation, polymer cross-linking (tapes, tubes, cables, etc), tyre belt vulcanisation, and the irradiation of certain food items for hygienisation, are well-established technologies where ionising radiation has made deep inroads. Either gamma radiation from isotopic sources or high energy electrons from accelerators are being applied in these processes.
One important field where the use of ionising radiation is making some path-breaking impact is the preservation of medical products, including medicines and other equipment used both for treating and testing patients. A big challenge for medical applications is the need to keep the products sterile — free from harmful contaminants such as fungi, bacteria, viruses, and spore forms. Radiation treatment methodologies are well-established for sterilisation of medical products as well as for tissue grafts.
Commercial radiation sterilisation has now been used for more than 50 years. During this period, the market for disposable medical products has undergone enormous growth, and with it the use of ionising radiation as a method of sterilisation. About 40-50 per cent disposable medical products in the developed world are radiation sterilised.
It is worth mentioning here how exactly ionising radiation works. Ionising radiation has high energy which is enough to break the molecular bonds and ionise atoms. As a result, materials exposed to this radiation undergo modification in their physical, chemical and biological properties.
The International Atomic Energy Agency (IAEA), which is committed to the cause of promoting peaceful use of nuclear technology, has invested both time and energy to study or promote the study of various ways through which radiation technology can be used in the preservation of medical products.
Two ways that have gained popularity in the field of medical sciences for the purpose include, fumigation and gamma processing.
Fumigation
Fumigation involves the use of gases, which are poisonous for living creatures, for sterilisation of medical products. Ethylene oxide ((CH2)2O) and methyl bromide (CH3Br) are the gases most frequently used for these purposes. Research and monitoring of results under controlled conditions has, however, found that the effectiveness of fumigation by gas diffusion is hard to predict, even when most important treatment parameters (gas concentration, temperature and contact time) are accurately controlled.
Moreover, when poisonous gases are used, there are concerns relating to safety and protection of the environment. (CH2)2O, which has proved to be very dangerous because it is carcinogenic, extremely flammable and explosive, must today be used in approved equipment including a detoxification compartment. It has also been demonstrated that ethylene oxide may be emitted over time from the fumigated products and subsequently contaminate the indoor air.
CH3Br, like many other halogen derivatives that deteriorate the ozone layer, is already prohibited in many countries. 2-phenylphenol is used in ethanol solution and may cause serious skin irritation. Paradichlorobenzene is a mild fumigant that seems to be effective as a fungicide; however, it is hazardous if inhaled.
Gamma processing
The gamma processing or gamma sterilisation process uses Cobalt-60 radiation to kill microorganisms on a variety of different products. Cobalt-60 does not occur in nature; it is artificially produced in a reactor. Processing with gamma irradiation yields quick turnaround time, easily penetrating packaging and product, and is ideal for many types of materials.
The objects to be sterilised are put on a conveyor, which transports them to the vicinity of a strong gamma radiation source such as Cobalt-60. After stopping in the radiation field so the object receives the required dosage, the conveyor moves on and exposes the next object. Instead of the stop-and-go action, the conveyor could move continuously at a speed that ensures the proper dosage (continuous processing). The ionising radiation causes excitations and ionizations.
Gamma processing has several advantages over other treatment methods. The process can be applied on products of any shape because gamma rays are powerful and can penetrate right through any package and products
Since the process is cold, heat sensitive plastic medical devices and pharmaceutical products can safely be sterilised, thus not harming their configuration through resultant chemical reactions
The process offers a flexibility in packaging as the products can be packed individually in sealed bags and sterilised in the fully packed form. Since sterilisation is effected after final packaging, products sterility is retained indefinitely provided the package is undamaged.
This is a continuous, fully automated process with a single parameter to be controlled – the exposure time. One doesn’t have to wait as the treated product can be used immediately after the process is completed.
There are clear guidelines on which products can be sterilised. Products that can be sterilised using this method are covered under Drugs and Cosmetic Act Rules, 1945, and cleared by Food and Drug Administration, Maharashtra.
With IAEA support, several gamma and electron beam irradiation facilities have been built in developing countries, and some new technologies have been developed and transferred to member states over the past couple of years.
Sterilisation of single-use medical devices
The need for safe and sterile products is more important today than ever. Gamma sterilisation is a simple, proven process that’s safe, reliable, and highly effective at treating single-use medical devices.
Sterilisation of tissue-based devices
Tissue-based devices basically come from human donors. While it is currently not equired by regulatory standards, tissue banks are choosing to terminally sterilise such devices with gamma so as to increase patient safety. This is a classic case of value addition by gamma sterilisation.
Sterilisation of combination devices
A combination device is basically a product that involves a medical device and/or a drug and/or a biologic — combining any two of these product categories, and sometimes even all three.
Sterilisation can affect drug properties and material properties, so sterilisation by gamma irradiation is applied to ensure that the combination device’s sterility and functionality are maintained.
Sterilisation of pharmaceuticals
Due to the high demand for terminally sterilised products in the pharmaceutical industry, gamma has proven itself to be an effective method. Some of the advantages of gamma over other modalities include high penetration power.
Over the years, the manufacturers and suppliers of gamma irradiators have put significant efforts into responding to the growing needs of the industry. The main elements which have been the focus of continuous attention include cost effectiveness of the radiation process, dose uniformity in product, turnaround time and operational reliability.
