Finger on the pulse
Pulsed UV sterilisation is a relatively new technology in the world of aseptic processing but interest is growing as new systems are tailored to specific applications. Dr Alex Wekhof, founder of SteriBeam Systems in Germany outlines some of their applications and benefits
The unique sterilisation properties of intense pulsed ultraviolet (PUV) have been recognised during past 15-20 years through several interesting r&d developments. The particular properties of PUV are summarised in some ground-breaking papers written by this author1-3, 5 and by others, most notably Louis Panico4 presented in various publications which are referenced at the end of this article. As stated in these articles, sterilisation systems using intense pulsed UV light feature the following advantages:
- Sterilisation is achieved in a fraction of a second A few or, in some cases, just one pulse can achieve up to a 6 log reduction for most micro-organisms
- By using the UVB part of spectra, sterilisation action can penetrate most clear packages (which is not possible with standard 254 nm mercury-based lamps)
- The systems offer a high UV output and the full UV spectrum
- An adjustment of flash lamp spectra enables the major output to fit into a specific UV band (UVC: 200-280 nm, UVB: 280-315 nm, or UVA: 315-400 nm)
- They can also offer a low Infrared (IR) or heat part of lamp spectra (above 700 nm)
- The lamps can be instantly turned on or off
- They are environmentally safe (no mercury in lamps)
- They offer deep UV penetration in purification and surface treatment processes.
These benefits mean there is a solid potential for the use of PUV systems in cleanrooms in the pharmaceutical industry. So far, the pharmaceutical manufacturer's main means of sterilisation has been through radiation sources (gamma and e-beams) or hazardous substances such as peroxide, ozone, ethylene oxide, with or without autoclaves, or steam.
At present just a handful of companies are engaged in the production of PUV systems, mostly in the form of PUV modules, which are sold tofull-scale equipment manufacturers who then build them into production lines. The reason for this is the current absence of clear-cut market for such systems, a lack of an established track record of their use and, as yet, low demand for large-scale PUV systems for sterilisation. The current demand is for small units for varying tasks in niche markets.
To combat this situation, SteriBeam has positioned itself as a designer and manufacturer of full, turnkey sterilisation equipment to serve specific tasks in the pharmaceutical market, particularly in the cleanroom segment where aseptic requirements are important. An example of a SteriBeam system is presented in figure 1. Such a systems can be used to perform up to a 6 log sterilisation of all micro-organisms in following applications:
- Sterilising surfaces of syringe tubs in class C rooms before their automatic transfer to aseptic class A rooms
- Sterilising surfaces of various vials before or after their filling
- Sterilising the content of vials, eye drops bottles, before being shipped to the end user
- Sterilising surfaces in cleanrooms without creating associated problems with chemicals, handling, dust, etc
- Sterilising air (in combination with pre-filters)
- Sterilising medical devices, packaging materials or textile items being moved through to cleanrooms by means of pass-through conveyer tunnels
- Sterilising of packaged food to prolong its shelf life by 15% to 40%.
Such a module can be mounted in pass-through conveyer tunnels leading from class C cleanroom to a class A cleanroom, or in air ducts of ventilation systems, or on walls to disinfect the air. The visible light from the lamp can be absorbed by a filter, letting only UV light pass through.
Such a module can be connected to a power-control unit by a cable of up to 3 m long. It can also be mounted over a conveyer carrying food items to reduce the bacterial count and thus increase the shelf life of various foodstuffs. R&d tests with SteriBeam desktop systems have been successfully performed in a some European food centres, and ahowed positive results for fish, some meat products, some fruits and vegetables, and also for some baked products. PUV systems can also be used to sterilise packages and medical instruments2,5.
SteriBeam also offers a 6 log sterilisation PUV tunnel (see figure 2) that has a 360º capability to illuminate all open sides of a product, and also the ability to pass through UV-transparent packaging, such as polypropylene (PP) bags containing saline .
Such a system is designed to serve as a pass-through tunnel to an aseptic class A cleanroom. It complies fully with GMP (aseptic room) specs by having a full HVAC (filtered and temperature-controlled) ventilation system, maintaining the air pressure at a slight increase in each of the three sequential processing sections which are separated by alternating doors. These include: the product sorting and entrance section; the product handling and PUV sterilising section; and the exit section, releasing the sterilised product into the aseptic class A room.
The system is fully robotic, and comes complete with controls and recording systems, including a video-camera and a thin flim transistor ( TFT) display to monitor product passage through the system.
Another such tunnel has been developed for sterilising vials (normal glass, UV glass and various plastic materials, transparent to UV light: LDPP, Nylon, Teflon, PE, etc), with volumes from as low as 20 ml to 100 ml, and productivity rates up to 3,600 vials/hr.
The full processing costs for sterilisation of products with PUV ranges from €0.02/tub to €0.0001/vial. This cost includes depreciation, maintenance and energy costs).
Intense PUV systems can alsobe a very efficient way of supplying sterile air to cleanrooms. Respective PUV modules can be mounted easily in existing heating, ventilation and air conditioning ducts for decontamination of air in hospitals, or on the walls or ceiling in microbiology laboratories, or in any other cleanroom facilities
