Filteration, Radiation, Ultrasonic sterilization

1. FILTRATION, RADIATION
AND ULTRASONIC
STERILIZATION
PRIYA DIXIT
DEPARTMENT OF BIOTECHNOLOGY
ERA UNIVERSITY, LUCKNOW

2. FILTRATION

3. • Filtration is the preferred method of sterilizing heat sensitive liquid and gases without exposure to denaturing
heat. Rather than destroying contaminating microorganisms, it simply removes them. It is the method of choice
for sterilizing antibiotic solutions, toxic chemicals, radioisotopes, vaccines, and carbohydrates, which are all
heat-sensitive. In the food industry, filtration finds utility in beer making to remove yeast before final bottling.
• Filtration physically removes microbes because it employs membranes whose precisely defined pores are too
small to allow their passage. It is obviously only useful for liquids and gases. Filtration does not effectively
remove viruses from solution because they are typically too small.
• The process of filtration is unique among sterilization techniques in that it removes, rather than destroys, microorg
anisms. Further, it is capable of preventing the passage of both viable and nonviable particles.
• Filters may also be required in industrial applications where they become part of venting systems on fermenters,
centrifuges, autoclaves and freeze-driers. Certain types of filter (membrane filters) also have an important
role in sterility testing, where they can be employed to trap and concentrate contaminating organisms from
solutions under test. These filters are then placed on a solid nutrient medium or in a liquid medium and incubated
to encourage colony growth or turbidity.

4. • The major mechanisms of filtration are sieving, adsorption and trapping within the matrix of the filter
material. Of these, only sieving can be regarded as absolute as it ensures the exclusion of all particles above a define
d size. It is generally accepted that synthetic membrane filters, derived from cellulose esters or other polymeric mat
erials, approximate most closely to sieve filters; while fibrous pads, sintered glass and sintered ceramic
products can be regarded as depth filters relying principally on mechanisms of adsorption and entrapment.
• To sterilize sera, sugars and antibiotic solutions.
• To obtain bacteria free filtrates of clinical samples.
• Purification of water.
• This method is commonly used for sensitive pharmaceuticals and protein solutions in biological research.
• A filter with pore size 0.2 μm will effectively remove bacteria. If viruses must also be removed, a much smaller
pore size around 20 nm is needed. The pore size for filtering bacteria , yeasts, and fungi is in the range of 0.22-
0.45 μm (filtration membranes are most popular for this purpose).
• Prions are not removed by filtration.

5. • To ensure sterility, the filtration system must be tested to ensure that the membranes have not been punctured prior to or
during use.
• To ensure the best results, pharmaceutical sterile filtration is performed in a room with highly filtered air (HEPA
filtration) or in a laminar flow cabinet or "flowbox", a device which produces a laminar stream of HEPA filtered air.
Several Types of Filters:
1. Candle filters
2. Asbestos disc filters
3. Sintered glass filters
4. Membrane filters
5. Air filters
6. Depth Filters
7. Syringe filters
• Sterilize solutions that may be damaged or denatured by high temperatures or chemical agents.

6. 1. Candle filters : Candle filters are simple devices made out of clay and used to filter drinking water in
order to removes turbidity, suspended materials and pathogens. Removal takes place by physical process such as
mechanical trapping and adsorption on the ceramic candles, which have micro-scale pores.
• It adds that while RO and UV filters remove pesticides up to 99%, a candle water filter's efficiency ranges from
53% to 99%. They also remove chlorine and E. coli bacteria up to 99%. ... Reports suggest that the efficiency
of candle filters in removing pesticides ranges from 53% to 99%.
• Candle Filters are also used for thickening to produce a concentrated flowable slurry by partial removal of the
liquid phase as filtrate.

7. 2. Asbestos disc filters: Asbestos-based filters were very widely used in many industries
including the production of cider, fruit juices, wine, in medicineand sewage treatment for the
filtration of very fine materials from liquids and gases. Both chrysotile and amphibole asbestos
fibers were used in fiber and powder form for filtration processes.
• Disposable , single use disc.
• Filter disc is made up of Asbestos.
• High adsorbing capacity.
• Alkalinize filtered Fluid.
3. Sintered glass filters: Fritted glass is finely porous glass through which gas or liquid
may pass. It is made by sintering together glass particles into a solid but porous body. This porous
glass body can be called a frit. Applications in laboratory glassware include use in fritted
glass filter items, scrubbers, or spargers.
In a fritted glass filter, a disc or pane of fritted glass is used to filter out solid particles, precipitate, or
residue from a fluid, similar to a piece of filter paper. The fluid can go through the pores in the
fritted glass, but the frit will often stop a solid from going through. A fritted filter is often part of a
glassware item, so fritted glass funnels and fritted glass crucibles are available

8. 4.Membrane filters: Membrane filters have a known uniform porosity of predetermined size (generally 0.45 µm )
sufficiently small to trap microorganisms. Using the membrane filter technique, sample is passed through the membrane using a
filter funnel and vacuum system. Any organisms in the sample are concentrated on the surface of the membrane.
Membrane filters are the most common type of filters used for liquid sterilization in the microbiology laboratory. Membrane
filters are composed of high tensile strength polymers such as cellulose acetate, cellulose nitrate, or polysulfone. Membrane
filters are prepared as circular membranes of about 150μm thickness and contain millions of microscopic pores of uniform
diameters; the size of which is adjusted based on requirements, during the polymerization process.
Porosities of membrane filters range from 0.1μm to 10μm and the most commonly used membrane filter has the pore size of
0.22μm and 0.45μm.

9. Uses of membrane filter:
• Sterilization of fluid materials (pharmaceuticals, ophthalmic solutions, antibiotics, and other heat-
sensitive solutions in laboratories and industries.
• Identification and enumeration of microorganisms.
Advantages of Filtration Sterilization:
• Less capital intensive
• Suitable for heat-sensitive liquids (infusions, vaccines, hormones, etc).
• Large volume of liquids can be filtered reasonably fast.
• Limitations of Filtration Sterilization:
• Only liquids and gases can be sterilized by this process.
• Filters are expensive to replace, especially nano-filters.
• Inherent limitations of materials used in filters affect the efficacy of this process i.e, breakage of glass
filters, rupture of the membrane filter and absorption of the filtrate by Sietz filter.
• Clogging may occur.

10. • There are present mainly four types of membrane filter. These filters are classified based on their pore size such as;
1. Microfiltration
2. Ultrafiltration
3. Nanofiltration
4. Reverse osmosis (RO)
Microfiltration
• It separates those particles that have a size range of 0.1 to 10 μm.
• From the approximate molecular weight, it separates those macromolecules which has a molecular weight of less than
100,000 g/mol.
• It is designed to separate sediment, algae, protozoa or large bacteria from the supplied liquid sample.
• In the water treatment plant, it is used to separate pathogens such as the protozoa Cryptosporidium and Giardia lamblia, etc.
• In industries, it is used for the cold sterilization of beverages and pharmaceuticals. It basically eliminates bacteria and other
undesired suspensions from liquids such as juice, wine, and beer in particular.
• It is also used for petroleum refining. It removes particulates from flue gases.

11. Ultrafiltration
• The pore size of an Ultrafiltration membrane ranges from 0.1 μm to 0.01 μm.
• It is designed to eliminate proteins, endotoxins, viruses, and silica.
• Generally, it retains those Suspended solids and solutes which possess a high molecular weight and pass those solutes that
have a low molecular weight such as water.
Nanofiltration
• The pore size of a Nanofiltration membrane ranges from 0.001 μm to 0.01 μm. The pore size of the Nanofiltration membrane
is smaller than microfiltration and ultrafiltration.
• It is designed to separate multivalent ions, synthetic dyes, sugars and specific salts.
• In Oil and Petroleum chemistry, it is used to remove tar components in feed and for the Purification of gas condensates.
Reverse osmosis (RO)
• The pore size of a Reverse osmosis membrane ranges from 0.0001 μm to 0.001 μm. It has the finest separation membrane.
• It can retain all molecules except for water.
• It required osmotic pressure due to the small size of the pores.

12. Method of Membrane Filter:
1.First, collect the sample and dilute it.
2.Select the suitable nutrient medium for isolation and enumeration of different pathogenic microorganisms.
3.Transfer the medium into an absorbent pad containing a Petri plate. Immerse the absorbent pad within a liquid broth.
The saturated absorbent pad will promote microbial growth.
4.Use a sterilized forceps to place the membrane filter over the carbon disk.
5.Sterilize the opening of the sample bottles by flame and pour the sample through the funnel.
6. Draw the sample through the filter turn on the vacuum.
7.After that remove the filter from the funnel by using sterile forceps and placed it over the prepared petri dish.
8.Incubate the Petri plate for an appropriate period of time and at the desired temperature.
9.Perform Quantitative analysis, use a colony counter to count the numbers of colonies on the Petri plate.
10.Perform Qualitative analysis, to identify the isolated colony and for water quality check. Subculture the isolated
colony, stain them, observe under microscope, and perform further biochemical tests to distinguish the distinct type.

13. Advantages of Membrane Filter:
• Absolute sterilization - separates particles based on size
• Used for heat sensitive media
• Removal of multiple particle sizes
• Allows for fairly high throughput
• It provides relevant and reliable results.
Disadvantages of Membrane Filter:
• Each filter has a specific nominal pore size
• Unable to separate microorganisms that have the same size
• May require a high differential pressure
• It provides relevant and reliable results.
5. Air filters: A particulate air filter is a device composed of fibrous, or porous materials which removes
solid Particulates such as dust, pollen, mold, and bacteria from the air. Filters containing an adsorbent or catalyst such
as charcol (carbon) may also remove odours and gaseous pollutants such as volatile organic compounds or ozone.
Air filters are used in applications where air quality is important, notably in building ventilation systems and in engines.

14. • Some buildings, as well as aircraft and other human-made environments (e.g., satellites, and space shuttles) use foam, pleated paper, or
spun fibre glass filter elements. another method, air ionizers, use fibers or elements with a static electric charge, which attract dust particles.
the air intakes of internal combustion engines and air compressors tend to use either Paper, Foam or cotton filters.
• Use in biosafety applications such as biosafety cabinets. Biological safety cabinets contain a filter known as high-efficiency
particulate air (HEPA) filter, which is a type of Air filter.
HEPA Filter:
• HEPA is an acronym for “High Efficiency Particulate Air.
• This type of air filter can remove at least 99.97% of dust, pollen, mold, bacteria and any airborne particles with a size of 0.3
micrometres (μm).
Application Performance
A Industrial, Noncritical 99.97% @ 0.3µm
B Nuclear Containment 99.97% @ 0.3µm
C Laminar Air Flow 99.99% @ 0.3µm
D Ultra- low penetration air(ULPA) 99.9995% @ 0.12µm
E Stopping toxic, nuclear,chemical and biological threats 99.9995% efficiency

15. Construction:
• HEPA filter is constructed of borosilicate microfibres in the form of pleated sheet
• Sheet is pleated to increase the overall filtration surface area.
• The pleats are separated by serrated aluminum baffles or stitched fabric ribbons, which direct airflow
through the filter.
• This combination of pleated sheets and baffles acts as filtration medium.
• It is installed into an outer frame made of fire-rated particle board, aluminum, or stainless steel
• The frame-media junctions are permanently glued or ‘‘pot-sealed’’ to ensure a leak proof
Filtration Mechanisms:
1. Inertial Impaction : particle inertia causes it to leave the flow streamlines and impact on the fiber.
2. Diffusion: The particles traverse the flow stream, they collide with the fiber and are collected.
3. Interception : These mid-sized particles follow the flow stream as it bends through the fiber spaces.
Particles are intercepted or captured when they touch a fiber.

16. LAF (LAMINAR AIR FLOW) /A LAMINAR FLOW
HOOD/CABINET
A Laminar flow hood/cabinet is an enclosed workstation that is used to create a contamination-free work
environment through filters to capture all the particles entering the cabinet.
• These cabinets are designed to protect the work from the environment and are most useful for the aseptic
distribution of specific media and plate pouring.
• Laminar flow cabinets are similar to biosafety cabinets with the only difference being that in laminar flow
cabinets the effluent air is drawn into the face of the user.
• In a biosafety cabinet, both the sample and user are protected while in the laminar flow cabinet, only the sample
is protected and not the user.

17. Components/ Parts of Laminar flow hood
A laminar flow cabinet consists of the following parts:
1. Cabinet
• The cabinet is made up of stainless steel with less or no gaps or joints preventing the collection of spores.
• The cabinet provides insulation to the inner environment created inside the laminar flow and protects it from the outside environment.
• The front of the cabinet is provided with a glass shield which in some laminar cabinets opens entirely or in some has two openings for the user’s hands to enter the cabinet.
2. Working station
• A flat working station is present inside the cabinet for all the processes to be taken place.
• Culture plates, burner and loops are all placed on the working station where the operation takes place.
• The worktop is also made up of stainless steel to prevent rusting.
3. Filter pad/ Pre-filter
• A filter pad is present on the top of the cabinet through which the air passes into the cabinet.
• The filter pad traps dust particles and some microbes from entering the working environment within the cabinet.
4. Fan/ Blower
• A fan is present below the filter pad that sucks in the air and moves it around in the cabinet.
• The fan also allows the movement of air towards the HEPA filter sp that the remaining microbes become trapped while passing through the filter.

18. 5. UV lamp
• Some laminar flow hoods might have a UV germicidal lamp that sterilizes the interior of the cabinet and contents before the operation.
• The UV lamp is to be turned on 15 minutes before the operation to prevent the exposure of UV to the body surface of the user.
6. Fluorescent lamp
• Florescent light is placed inside the cabinet to provide proper light during the operation.
7. HEPA filter
• The High-efficiency particulate air filter is present within the cabinet that makes the environment more sterile for the operation.
• The pre-filtered air passes through the filter which traps fungi, bacteria and other dust particles.
• The filter ensures a sterile condition inside the cabinet, thus reducing the chances of contamination.
Principle/ Working of Laminar flow hood:
• The principle of laminar flow cabinet is based on the laminar flow of air through the cabinet.
• The device works by the use of inwards flow of air through one or more HEPA filters to create a particulate-free environment.
• The air is taken through a filtration system and then exhausted across the work surface as a part of the laminar flow of the air.
• The air first passes through the filter pad or pre-filter that allows a streamline flow of air into the cabinet.
• Next, the blower or fan directs the air towards the HEPA filters.

19. • The HEPA filters then trap the bacteria, fungi and other particulate materials so that the air moving out of it is particulate-free air.
• Some of the effluent air then passes through perforation present at the bottom rear end of the cabinet, but most of it passes over the working
bench while coming out of the cabinet towards the face of the operator.
• The laminar flow hood is enclosed on the sides, and constant positive air pressure is maintained to prevent the intrusion of contaminated
external air into the cabinet.
Procedure for running the laminar flow cabinet
The procedure to be followed while operating a laminar flow cabinet is given below:
1. Before running the laminar flow cabinet, the cabinet should be checked to ensure that nothing susceptible to UV rays is present inside the
cabinet.
2. The glass shield of the hood is then closed, and the UV light is switched on. The UV light should be kept on for about 15 minutes to ensure
the surface sterilization of the working bench.
3. The UV light is then switched off, and a time period of around 10 minutes is spared before the airflow is switched on.
4. About 5 minutes before the operation begins, the airflow is switched on.
5. The glass shield is then opened, and the fluorescent light is also switched on during the operation.
6. To ensure more protection, the working bench of the cabinet can be sterilized with other disinfectants like 70% alcohol.
7. Once the work is completed, the airflow and florescent lamp both are closed and the glass shield is also closed.

20. Types of laminar flow cabinet
Depending on the direction of movement of air, laminar flow cabinets are divided into two types:
1. Vertical laminar flow cabinet
• In the vertical flow cabinets, the air moves from the top of the cabinet directly towards the bottom of the cabinet.
• A vertical airflow working bench does not require as much depth and floor space as a horizontal airflow hood which makes it
more manageable and decreases the chances of airflow obstruction or movement of contaminated air downstream.
• The vertical laminar flow cabinet is also considered safer as it doesn’t blow the air directly towards the person carrying out
the experiments.
2. Horizontal laminar flow cabinet
• In the horizontal laminar flow cabinets, the surrounding air comes from behind the working bench, which is then projected by
the blower towards the HEPA filters.
• The filtered air is then exhausted in a horizontal direction to the workplace environment.
• One advantage of this cabinet is that airflow parallel to the workplace cleanses the environment with a constant velocity.
• The elluent air directly hits the operator, which might reduce the security level of this type of laminar flow cabinets.

22. Uses of Laminar flow hood
The following are some common uses of a laminar flow cabinet in the laboratory:
1. Laminar flow cabinets are used in laboratories for contamination sensitive processes like plant tissue culture.
2. Other laboratories processes like media plate preparation and culture of organisms can be performed inside the cabinet.
3. Operations of particle sensitive electronic devices are performed inside the cabinet.
4. In the pharmaceutical industries, drug preparation techniques are also performed inside the cabinet to ensure a particulate-free environment during the
operations.
5. Laminar flow cabinets can be made tailor-made for some specialized works and can also be used for general lab techniques in the microbiological as
well as the industrial sectors.
Precautions
While operating the laminar airflow, the following things should be considered:
1. The laminar flow cabinet should be sterilized with the UV light before and after the operation.
2. The UV light and airflow should not be used at the same time.
3. No operations should be carried out when the UV light is switched on.
4. The operator should be dressed in lab coats and long gloves.
5. The working bench, glass shield, and other components present inside the cabinet should be sterilized before and after the completion of work.

23. Depth Filters
• A depth filter is a fibrous sheet or mat made from a random array of overlapping paper or borosilicate (glass) fibers. The depth
filter traps particles in the network of fibers in the structure.
• Depth filters are the variety of filters that use a porous filteration medium to retain particles throughout the medium, rather
than just on the surface of the medium. These filters are commonly used when the fluid to be filtered contains a high load of
particles because, relative to other types of filters, they can retain a large mass of particles before becoming clogged.
• Depth filtration typified by multiple porous layers with depth are used to capture the solid contaminants from the liquid phase.
• Depth filters pose the added advantage that they are able to attain a high quantity of particles without compromising the
separation efficiency.
Uses
1. Filter sterilization of air in industrial processes.
2. Forced air heating and cooling systems used in houses contains simple depth filter to trap dust, spores, and allergens.

24. 6. Syringe filters
• A syringe filter (sometimes called a wheel filter if it has a wheel-like shape) is a single-use filter cartridge. It is attached to the
end of a syringe for use. Syringe filters may have Luer lock fittings, though not universally so. The use of a needle is optional;
where desired it may be fitted to the end of the syringe filter.
• A syringe filter generally consists of a plastic housing with a membrane that serves as a filter. The fluid to be purified may be
cleaned by drawing it up the syringe through the filter, or by forcing the unfiltered fluid through the filter.
• The syringe filter body may be made of such materials as polypropylene and nylon. The filter membrane may be
of PTFE, nylon, or other treated products for specific purposes. Most manufacturers publish compatibility wallcharts advising
users of compatibility between their products and organic solvents or corrosive liquids (e.g. trifluoroacetic acid)

25. Application
• Syringe filters may be used to remove particles from a sample, prior to analysis by HPLC or
other techniques involving expensive instruments. Particles easily damage an HPLC due to the
narrow bore and high pressures within. Syringe filters are quite suitable for Schlenk line work,
which makes extensive use of needles and syringes (see cannula transfer). Being relatively
affordable, they may be used for general purpose filtration, especially of smaller volumes
where losses by soaking up filter paper are significant.
• Syringe filters are also available for the filtration of gases, and for the removal of bacteria from
a sample.

26. Irradiation

27. • Commercial radiation sterilization has existed since the late 1950s and has grown tremendously in popularity over the last 60 years.
Radiation sterilization relies on ionizing radiation, primarily gamma, X-ray or electron radiation, to deactivate microorganisms such as
bacteria, fungi, viruses and spores.
• Due to numerous advantages over heat or chemical based sterilization techniques, this method is particularly attractive in medicine
and healthcare-related fields. For example, radiation sterilization is readily applied during tissue allograft preparation, pharmaceutical
packaging and medical device manufacturing.
• Radiation can be lethal to biological organisms by inducing genetic damage and chemical changes in key biological macromolecules.
During sterilization treatment, the sample of interest is bombarded with high energy electrons or high energy electromagnetic
radiation, which leads to the formation of extremely unstable free radicals, molecular ions and secondary electrons.
• These radiation products then react with nearby molecules to fracture and alter chemical bonds. DNA in particular is highly sensitive
to the damaging effects of radiation and will break, depolymerize, mutate and alter structure upon exposure to ionizing radiation.
Incomplete repair of DNA damage ultimately leads to loss of genetic information and cell death. Thus, radiation can kill harmful
microorganisms and be used as a sterilization technique.
• The sensitivity of a given biological organism to radiation is given by the decimal reduction dose (D10 value), the dose of radiation
which leads to a 10-fold reduction in microorganism population. In order to be effective, sterilization treatment must be dosed to
account for the D10 values of microorganisms present, the initial level of bioburden, and the diversity of the bioburden in the sample.

28. Radiation used for sterilization is of two types
1. Ionizing radiation, e.g., X-rays, gamma rays, and high speed electrons .
2. Non-ionizing radiation, e.g. ultraviolet light, and infrared light.
These forms of radiation can be used to kill or inactivate microorganisms.
Ionizing radiation
X-Ray Radiation
Electron beam accelerators will also generate X-rays for sterilization. X-rays are produced when high energy electrons from the
accelerator interact with high atomic number nuclei, such as atoms of tungsten or tantalum. In a process known as Bremsstrahlung, the
deceleration of the electron when passing the nucleus results in the release of X-rays. Electron energies of 5-7 MeV are commercially
used; the energies of the resultant X-rays lie along a spectrum ranging from zero to the energy of the electron beam.
In practice, X-rays used for sterilization can be more penetrating than either gamma-rays or electron beams. They are largely directional
since generated X-rays propagate in the same direction as the incident electron. Thus, a concerted stream of X-rays is sent towards the
product of interest and multiple rows of products can be sterilized simultaneously. Of radiation sterilization techniques, X-ray
sterilization can achieve the highest dose uniformity ratio (DUR), the ratio between maximum and minimum dose required for
sterilization. DUR measures the range of doses delivered to the product and is important to optimize for irradiation sensitive materials in
order to minimize degradation.

29. Gamma Radiation
• Gamma radiations are high-energy radiations emitted from certain radioisotopes such as Caesium-137 (137Cs) and Cobalt-60
(60Co), both relatively inexpensive bioproducts of nuclear fission. Gamma rays are similar to x-rays but are of shorter
wavelength and higher energy. They are capable of great penetration into the matter, and they are lethal to all life, including
microorganisms. Gamma rays are attractive for use in commercial sterilization of materials of considerable thickness or
volume, eg., packaged food or medical devices.
• Gamma radiation sterilization is the most popular form of radiation sterilization. Co-60 and, to a lesser extent, Cs-137 serve as
radiation sources and undergo decomposition to release high energy gamma rays. The produced electromagnetic radiation is
highly penetrating and can kill contaminating microorganisms. Both radioisotopes are viable sources of radiation due to their
highly stability (with half-lives >5 years) and gamma emission properties. However, Co-60 tends to be favored because it can
be easily manufactured from natural metal, is not fissile or flammable and is less soluble in water.
• Radioactive Co is formed inside a nuclear reactor by neutron bombardment of the abundant, non-radioactive Co-59 isotope.
Co-60 atoms then decay to nonradioactive Ni-60 atoms by emitting one electron and two gamma rays at energies of 1.17 MeV
and 1.33 MeV. Gamma rays are released in an isotropic fashion and are not high enough in energy to induce radioactivity in
other materials. In general, production requirements for Co-60 makes gamma sterilization at individual hospital sites
unattractive but it is feasible through large scale commercial manufacturing. Gamma based radiation sterilization has been
deemed safe and effective by a number of government and public health agencies including the US Center for Disease Control
and Prevention, the Food and Agriculture Organization, the United Nations and the World Health Organization.

30. Electron Beam Radiation (E-Beam Radiation)
• Sterilization can alternatively be accomplished using electron beam irradiation. High energy electrons capable of
inducing biological damage are generated by electron beam accelerators. In most cases, electron energies of ~10
MeV are used, but the exact energies can be tuned to optimize penetration depth and limit breakdown of the
irradiated material.
• Gamma irradiation and e-beam irradiation differ in sample penetration depth, exposure time required for
effective sterilization and product compatibility. Because the penetration ability of electrons is lower than that of
gamma rays, e-beam sterilization is limited in application to lower density or smaller products. However, e-beam
sterilization can use higher dosages and shorter treatment times (seconds vs. min/hours) as compared to gamma
radiation sterilization, allowing for higher throughput and reducing negative effects on treated products. In terms
of cost, e-beam sterilization is equivalent to or less expensive than gamma sterilization.

31. Uses of Ionizing Radiations
• The major method in use for radiation sterilization is gamma irradiation. Gamma radiation is used in the sterilization of;
• Disposables such as plastic syringes, infusion sets, catgut sutures, catheters, gloves, and adhesive dressings before use.
• Bone, tissue grafts, antibiotics, and hormones.
• Irradiation of food (permitted in some countries).
Advantages of Ionizing Radiations
1. High penetrating power: products can be processed in their fully sealed, final packaging thus limiting the risk of
contamination following sterilization.
2. Rapidity of action: saves and efforts.
3. Temperature is not raised: compatible with temperature-sensitive materials, such as pharmaceuticals and biological samples.
4. Flexibility: can sterilize products of any phase (gaseous, liquid, or solid materials), density, size, or thickness.

32. Disadvantages
• Capital costs are high and specialized facilities are often needed e.g. for gamma irradiation
• Use of gamma radiation requires handling and disposal of radioactive material.
• Not compatible with all materials and can cause breakdown of the packaging material and/or product. For example, Common
plastics such as polyvinyl chloride (PVC), acetal, and polytetrafluoroethylene (PTFE) are sensitive to gamma radiation.
Non-ionizing radiation
Non-ionizing radiation uses longer wavelength and lower energy. As a result, non-ionizing radiation loses the ability to penetrate
substances, and can only be used for sterilizing surfaces. The most common form of non-ionizing radiation is ultraviolet light,
which is used in a variety of manners throughout industry.
Non-ionizing radiations are quite lethal but do not penetrate glass, dirt, films, water; hence their use is restricted for disinfection
of clean surfaces in operation theaters, laminar flow hoods as well as water treatment. The recommended dose is 250-300 nm
wavelength, given for 30 minutes.

33. Infra-Red Radiation
• Infra-red rays are low energy type electromagnetic rays, having wavelengths longer than those of visible light. They kill
microorganisms by oxidation of molecules as a result of heat generated. Infra-red rays are used for the rapid mass sterilization of
syringes and catheters.
Infrared Mechanism
• Infrared rays that lie in the waveband range of 0.8–15£ 10¡6 can be easily generated. With the help of an absorbent surface they
are changed into sensible heat, producing high levels of increasing temperature the energy attack on the surface which is
changeable into heat depends on the same geometric conditions as those used for UV lights. So, infrared radiation is the best to
be applied to an even and smooth surface with vertical radiations. Infrared rays have been used to fix the internal phase of
aluminum lids with a plastic coating on the external surface. Since the temperature increase can cause the plastic to soften, the
maximum exposure time and temperature are limited. N.B. infrared rays can’t be used if there is an increase in temperature of
the packaging substances because of infrared application and this leads to softening of the plastics.
Example of Infrared Sterilization Process:
• Infrared rays cause sterilization by heat generation. Substances that need to be sterilized are placed in a moving conveyer belt
and passed through a tunnel which is previously heated using infrared rays to reach a temperature of 180 degrees. The
substances are exposed to that high temperature for a fixed time 7.5 minutes. The substances become sterile included glassware
and metallic instruments. It is basically used in central sterile supply department. It needs special tools, thus is not applied in
diagnostic laboratory.

34. INFRA-RED OVEN

35. Example of Infrared Sterilization Process:
• Infrared rays cause sterilization by heat generation. Substances that need to be sterilized are placed in a moving conveyer
belt and passed through a tunnel which is previously heated using infrared rays to reach a temperature of 180 degrees. The
substances are exposed to that high temperature for a fixed time 7.5 minutes. The substances become sterile included
glassware and metallic instruments. It is basically used in central sterile supply department. It needs special tools, thus is not
applied in diagnostic laboratory.
Short wave IR lamp Medium wave IR lamp Long wave IR lamp
Max. Emission at wavelengths > 0.8
μm/< 2 μm.
Operating temperature 1,400 °C to 3,000
°C.
Application technology characteristics:
Short heating and cooling periods
Max. Emission at wavelengths >2 μm/<4
μm.
Operating temperature 700 °C to 1,000
°C.
Application technology characteristics:
Short heating and cooling periods, high
radiation efficiency.
Max. Emission at wavelengths > 3.5 μm.
Operating temperature 300 °C to 700 °C.
Application technology characteristics:
High mechanical strength, relatively long
heating and cooling period.

36. Uses of IR Radiation
• IR systems normally need low maintenance like changing filters or emitters.
• IR emitters with a high transfer of energy enable surfaces to be heated more rapidly to overcome conduction
losses.
• IR emitters can be used to heat components in a vacuum chamber.
• IR heat is clean, no combustion products and no need to recirculate air.
• IR Infrared systems are custom designed to suit substrate being processed.
Ultraviolet Light (UV) Sterilization
• Sunlight is partly composed of UV light but most shorter wavelengths of light are filtered out by the ozone
layer. There are three types of UV radiation; UVA, UVB, and UVC, classified according to their wavelength.
Short-wavelength UVC is the most damaging type of UV radiation.
Mechanisms of UV Sterilization
• Many cellular materials including nucleic-acids absorb ultraviolet light. It causes bonding of two adjacent
pyrimidines i.e., the formation of pyrimidine dimer, resulting in the inhibition of DNA replication. This leads
to mutation and death of exposed organisms.

37. Uses of UV Sterilization
UV lights are useful for disinfecting surfaces, air, and water that do not absorb the UV rays. Certain types of UV lights can kill
the flu (influenza) virus. Ultraviolet radiation is used for disinfecting enclosed areas such as bacterial laboratory, nurseries,
inoculation hood, laminar flow, and operation theaters. For example, laboratory biological cabinets all come equipped with a
“germicidal” UV light to decontaminate the surface after use.
Effects of UV light in SARS-CoV-2 (COVID-19)
UV radiation kills viruses by chemically modifying their genetic material, DNA, and RNA. The most effective wavelength for
inactivation, 260 nm, falls in the UVC range. Though we do not have much research regarding the effect of UVC in SARS-
CoV-2, concentrated form of UVC is now on the front line in the fight against COVID-19. UVC light is being used to sterilize
buses, UVC-emitting robots to sterilize hospital floors and even banks are using UV light to disinfect money.
Disadvantages
Damages skin and eyes: Conventional UV light can penetrate and damage skin and also cause cataracts.

38. Advantages & Disadvantages Irradiation
Advantages:
No degradation of media during sterilization, thus it can be used for thermally labile media.
Leaves no chemical residue.
Administration of precise dosage and uniform dosage distribution.
Immediate availability of the media after sterilization.
Disadvantages:
This method is a more costly alternative to heat sterilization
Requires highly specialized equipment

39. ULTRASONIC CLEANING

40. • Ultrasonic cleaning is a process that uses ultrasound (usually from 20–40 kHz) to agitate a fluid. The ultrasound can be used
with just water, but use of a solvent appropriate for the object to be cleaned and the type of soiling present enhances the effect.
• Ultrasonic Cleaning is the use of sound waves through water to create microscopic implosions, removing contamination from
surfaces, nooks and crannies. The imploding bubbles act like microscopic scrubbing brushes throughout the cleaning tank and
remove dirt from all over the item, far more effectively than most other methods.
• Cleaning normally lasts between three and six minutes, but can also exceed 20 minutes, depending on which object has to be
cleaned.
• The surface mechanisms of ultrasonic cleaning are well understood, with many works dedicated to this science since the first
commercial ultrasonic cleaning equipment appeared in the 1950s, and came into use as relatively inexpensive home
appliances in about 1970. Ultrasonic cleaning has been used industrially for decades, particularly to clean small intricate parts,
and to accelerate surface treatment processes.
• Ultrasonic cleaners are used to clean many different types of objects, including jewelry, scientific samples, lenses and other
optical parts, watches, dental and surgical instruments, tools, coins, fountain pens, golf clubs, fishing reels, window
blinds, firearm components, car fuel injectors, musical instruments, gramophone records, industrial machine parts and
electronic equipment. They are used in many jewelry workshops, watchmakers' establishments, electronic repair workshops
and scientific labs.

41. • Water or solvents can be used, depending on the type of contamination and the workpiece. Contaminants can include dust, dirt, oil,
pigments, rust, grease, algae, fungus, bacteria, lime scale, polishing compounds, flux agents, fingerprints, soot wax and mold release agents,
biological soil like blood, and so on.
• Ultrasonic cleaning systems are widely used in many industries, including medical device, automotive, aerospace, dental, electronics,
jewelry and weapons. Ideal items for ultrasonic cleaning include medical and surgical instruments, carburetors, firearms, window blinds,
industrial machine parts and electronic equipment.
• Ultrasonic cleaning uses cavitation bubbles induced by high frequency pressure (sound) waves to agitate a liquid. The agitation produces
high forces on contaminants adhering to substrates like metals, plastics, glass, rubber, and ceramics. This action also penetrates blind holes,
cracks, and recesses. The intention is to thoroughly remove all traces of contamination tightly adhering or embedded onto solid surfaces.
Principle:
• In an ultrasonic cleaner, the object to be cleaned is placed in a chamber containing a suitable solution (in an aqueous or organic solvent,
depending on the application). In aqueous cleaners, surfactants (e.g., laundry detergent) are often added to permit dissolution of non-polar
compounds such as oils and greases. An ultrasound generating transducer built into the chamber, or lowered into the fluid, produces
ultrasonic waves in the fluid by changing size in concert with an electrical signal oscillating at ultrasonic frequency. This creates
compression waves in the liquid of the tank which 'tear' the liquid apart, leaving behind many millions of microscopic 'voids'/'partial
vacuum bubbles' (cavitation). These bubbles collapse with enormous energy; temperatures and pressures on the order of 5,000 K and 135
MPa are achieved; however, they are so small that they do no more than clean and remove surface dirt and contaminants. The higher the
frequency, the smaller the nodes between the cavitation points, which allows for cleaning of more intricate detail.

42. • Transducers are usually piezoelectric (e.g. made with lead zirconate titanate (PZT), barium titanate, etc.), but are sometimes magnetostrictive.
The often harsh chemicals used as cleaners in many industries are not needed, or used in much lower concentrations, with ultrasonic
agitation. Ultrasonics are used for industrial cleaning, and also used in many medical and dental techniques and industrial processes.
Cleaning solution
• Ultrasonic activity (cavitation) helps the solution to do its job; plain water would not normally be effective. The cleaning solution contains
ingredients designed to make ultrasonic cleaning more effective. For example, reduction of surface tension increases cavitation levels, so the
solution contains a good wetting agent (surfactant). Aqueous cleaning solutions contain detergents, wetting agents and other components.
Solutions are mostly used warm, at about 50–65 °C (122–149 °F), however, in medical applications it is generally accepted that cleaning
should be at temperatures below 45 °C (113 °F) to prevent protein coagulation.
• Water-based solutions are more limited in their ability to remove contaminants by chemical action alone than solvent solutions; e.g. for
delicate parts covered with thick grease.
• Some machines (which are not unduly large) are integrated with vapour degreasing machines using hydrocarbon cleaning fluids: Three tanks
are used in a cascade. The lower tank containing dirty fluid is heated causing the fluid to evaporate. At the top of the machine there is a
refrigeration coil. Fluid condenses on the coil and falls into the upper tank. The upper tank eventually overflows and clean fluid runs into the
work tank where the cleaning takes place.

43. How do ultrasonic cleaning machines work?
An ultrasonic cleaning machine includes the following basic components:
• Tank – The ultrasonic tank holds the fluid and the items to be cleaned.
• Ultrasonic generator – The ultrasonic generator transforms AC electrical energy to an ultrasonic frequency.
• Ultrasonic transducer – The transducer converts the ultrasonic electrical signal to mechanical energy.
What is an ultrasonic generator?
• The electronic ultrasonic generator is a power supply. It transforms AC electrical energy from a power source such as a wall
outlet, to electrical energy appropriate for energizing a transducer at an ultrasonic frequency. In other words, the ultrasonic
generator sends high-voltage electrical pulses to the transducer.
• While the ultrasonic frequency of 40 kHz is by far the most commonly used frequency for ultrasonic cleaning, some
applications do require a lower or higher frequency for best results.

44. What is an ultrasonic transducer?
• The ultrasonic transducer is the key component in an ultrasonic cleaning system. The ultrasonic transducer is a device that
generates sound above the range of human hearing, typically starting at 20 kHz, also known as ultrasonic vibrations.
• An ultrasonic transducer consists of an active element, a backing and a radiating plate. Most ultrasonic cleaners use
piezoelectric crystals as the active element. The piezoelectric crystal converts electrical energy to ultrasonic energy through
the piezoelectric effect, in which the crystals change size and shape when they receive electrical energy.
• The backing of an ultrasonic transducer is a thick material that absorbs the energy that radiates from the back of the
piezoelectric crystal.
• The radiating plate in an ultrasonic transducer works as a diaphragm that converts the ultrasonic energy to mechanical
(pressure) waves in the fluid. Thus when the piezoelectric crystal receives pulses of electrical energy, the radiating plate
responds with ultrasonic vibrations in the cleaning solution.

45. Ultrasonic cleaning equipment:
Benchtop ultrasonic cleaning tank
• Ultrasonic cleaning equipment is available in a variety of shapes, sizes and configurations, from
small tabletop ultrasonic cleaning tanks to industrial cleaning systems with tank capacities of
hundreds of gallons.
• For the simplest applications, a tabletop or benchtop ultrasonic cleaning tank may be sufficient,
with rinsing done in a sink or separate container
Multi-tank Benchtop Ultrasonic Cleaning System – 3.5 Gallon Wash – Rinse –
Rinse – Dry
Most industrial applications use a multi-tank approach to ultrasonic cleaning that includes a
series of tanks for washing, rinsing and drying. Multi-tank ultrasonic cleaning systems are
available in several form factors, including benchtop and console (also known as wet bench).

46. Free-standing Automated Ultrasonic Cleaning System – Wash – Rinse – Dry
• For even greater efficiency, many industrial ultrasonic cleaning systems add automation. Automation permits the user to wash,
rinse and dry with a single press of a button, like a dishwasher, rather than manually moving baskets of parts from one tank to
the next.

47. Uses:
• Most hard, non-absorbent materials (metals, plastics, etc.) not chemically attacked by the cleaning fluid are suitable for
ultrasonic cleaning. Ideal materials for ultrasonic cleaning include small electronic parts, cables, rods, wires and detailed items,
as well as objects made of glass, plastic, aluminium or ceramic.
• Ultrasonic cleaning does not sterilize the objects being cleaned, because spores and viruses will remain on the objects after
cleaning. In medical applications, sterilization normally follows ultrasonic cleaning as a separate step.
• Industrial ultrasonic cleaners are used in the automotive, sporting, printing, marine, medical, pharmaceutical, electroplating,
disk drive components, engineering and weapons industries.
• Ultrasonic cleaning is used to remove contamination from industrial process equipment such as pipes and heat exchangers.