Recent advances in sterilization

Recent Advances in Sterilization
& Disinfectant
Dr R Sathyajith

Recent Advances in Sterilization
• Sterilization, as a specific discipline, has
been with us for approximately 120 years,
since the invention of the steam autoclave
by Charles Chamberland in 1879
• We have seen progressive refinement in
steam sterilizers: from the early, manually
operated equipment to modern
microprocessor-controlled, automatic
machines.
• Although the efficiency, reliability, and
performance monitoring of modern
equipment is continually improving, the
fundamental process remains essentially
the same.

Plasma Sterilization
• Sterilization is defined as any process that
destroys all micro-organisms
• Conventional methods (autoclaving and
ethylene oxide fumigation), though proven
effective, do have their disadvantages
such as long sterilization times, tenuous
operating conditions and lack of versatility.
• Plasma sterilization is fast evolving into a
promising alternative to standard
sterilizing techniques.

• Research on plasma sterilization started
way back in 1960. Since then, extensive
studies are being performed.
• Not future technology! Plasmas are used
today!
• Plasmas are currently employed in many
industries to accomplish both highly
effective, and delicate sterilization.

 First discovered
by Sir William
Crookes, in 1879
But it wasn’t
called “plasma”
until 1928, when
Irving Langmuir
coined the term.

• Plasma is basically ionized gas. When you
apply an electric field to a gas, it gets
ionized into electrons and ions.
• Plasma is usually comprised of UV
photons, ions, electrons and neutrals.
• A plasma is a quasi-neutral collection
capable of collective behavior
• Their combined photolytic, chemical and
electric action efficiently kills most micro-
organisms.

• Electrical Plasma, used in sterilization, can
be classified into two types broadly:
 Volume plasma & Surface plasma.

• Initial literature that worked on establishing
plasma sterilization as a safe, viable
method of sterilization used mostly volume
plasma generated from gases such as He,
N2, O2.
• However recent literature has started
leaning towards using Dielectric Barrier
Discharge (DBD) Plasma, which is surface
plasma.

Volume Plasma
• Plasma is classified as volume plasma
when it is generated by injecting a gas at a
specific flow rate into a chamber fitted with
electrodes and grounded sufficiently.
• When the circuit was closed, the gas
inside the chamber would be subjected to
an electric field and hence ionized,
creating plasma.

Volume Plasma
• Most of the research in plasma
sterilization pertains to volume discharge.
Triphasic behavior was observed in
these experiments.
UV irradiation
Photo-desorption
Chemical etching

Surface Plasma
• Surface plasma is usually when the
electrodes (power & ground) are
embedded into a dielectric and hence
plasma is generated on the surface of the
dielectric itself.
• DBD discharge is generated between two
electrodes with a dielectric barrier in
between them, about a few mm is a
surface plasma.

Methods
• Dielectric Discharge Barrier (DBD)
• Inductively Coupled Plasmas (ICP)
• Atmospheric Pressure Plasma Jet (AAPJ)
• Microwave (MW) Plasmas
• MW plasma most effective
• All methods < 10 min treatment time
(much less than conventional methods!)

• Plasma sterilization operates
synergistically via three mechanisms:
Free radicals interactions
UV/VUV radiative effects
Volatilization

Plasma - Volatilization
• It is able to vaporize microbiological
matter, causing physical destruction of
spores.
• The spores are basically made up of
simple atoms like C, O, N, H etc.
• Charged particles react with cellular
atoms/chemical bonds of microbiological
layer to form gaseous compounds.
• When the organism loses such atoms that
are intrinsic to its survival, it dies

Plasma - UV
• UV/VUV radiation causes
1.Formation of thymine dimers in DNA,
inhibiting bacterial replication.
2.Base damage
3.Strand breaks

Plasma - Mechanism
• Damaged DNA/RNA causes microbial
death by 4 mechanisms:
1.Apoptosis – Nucleus programmed to
shrink and cause cell to commit suicide.
2.Autophagy
3.Necrosis
4.Mitotic Catastrophe – radiation causes
mis-segregation of chromosomes, leading
to Apoptosis

Why Plasma sterilization?
• The process is usually at room
temperature and hence poses no dangers
associated with high temperatures (unlike
autoclaves)
• Doesn’t involve any chemicals and hence
is non-toxic (unlike EtOH)
• Time of treatment is fast and of the order
of 1 min or less.
• Is versatile and can sterilize almost any
material and any shape

Disadvantages of Plasma Sterilization
• Weak penetrating power of the plasma.
Complications arise in:
Presence of organic residue
Packaging material
Complex geometries
Bulk sterilization of many devices
• Solutions: Introduce preferentially
targeting UV/VUV radiation of proper
wavelength

Disadvantages of Plasma Sterilization
• Cannot be used on paper, cellulose or
linen
• Can corrode certain materials
• Inability to process liquids, powders, or
strong absorbers (cellulosics)
• Lumen restrictions

Gas Plasma
• Low-Temperature Hydrogen Peroxide Gas
Plasma (LTHPGP)
• Gas Plasma (vaporized hydrogen
peroxide) is a relatively new option that
can provide low heat sterility cycles with
none of the off-gassing concerns present
with EtO.
• Gas plasma sterilization technology based
of Plasma was patented in 1987, and
marketed in US 1993.

Gas Plasma - Steps
• The Vacuum Phase
The chamber is evacuated, reducing
internal pressure in preparation for the
subsequent reaction.
• The Injection Phase
A measured amount of liquid peroxide is
injected into the chamber, evaporating the
aqueous hydrogen peroxide solution and
dispersing it into the chamber, where it
kills bacteria on any surface it can reach.

Gas Plasma - Steps
• The Diffusion Phase
The hydrogen peroxide vapor permeates
the chamber, exposing all load surfaces to
the Sterilant and rapidly sterilizes devices
and materials without leaving any toxic
residues. At the completion of this phase,
the chamber pressure is reduced and the
plasma discharge is initiated.

Gas Plasma - Steps
• The Plasma Phase
An electromagnetic field is created in
which the hydrogen peroxide vapour
breaks apart, producing a low-temperature
plasma cloud that contains ultraviolet light
and free radicals. Following the reaction,
the activated components lose their high
energy and recombine to form oxygen and
water.

Gas Plasma - Steps
• Phases 1, 2, and 3 are then run a second
time for added efficacy. This built-in
reprocessing assures optimal sterilization
for even the most difficult-to-sterilize
devices.
• The Vent Phase
The chamber is vented to equalize the
pressure enabling the chamber door to be
opened. There is no need for aeration or
cool-down. Devices are ready for
immediate use.

Gas Plasma
• The Sterrad system offers a
short cycle (averaging 75 minutes),
low temperature and humidity,
no aeration requirement,
no chemical residues,
negligible environmental impact, and
wide compatibility with materials.
Its drawback is an inability to process
liquids, powders, or strong absorbers
(e.g., cellulosics).

Gas Plasma
• The Biological indicator used with system
is Bacillus atrophaeus spores and Bacillus
sterothermophilis.
• The newer version of Sterrad, which
employs a new vaporization system that
removes most of the water from hydrogen
peroxide, has a cycle time from 28-38
minutes.

Gas Plasma - Prions
• The effectiveness of low-temperature
STERRAD® technology against the prion
threat confirmed that it is possible to
eliminate these deadly pathogens while
helping to preserve the integrity of medical
devices, including heat sensitive surgical
instruments

Plasma - Current Research
• The fundamental underlying physics in the
process of plasma sterilization is to a large
extent not understood.
• Sporadic research efforts & a lot of
conflicting opinions
 Importance of UV photons over neutrals
 Failure criterion

Plasma - Current Research
• To harness the ability of plasma
sterilization to produce fast, easy, non-
toxic sterilization that can be applied to a
wide variety of materials
• Major challenge
Huge amount of power that goes into
operating these devices (voltages of 12
kV)

Pulsed light sterilization
• Pulsed light is a non-thermal sterilization
method that uses brief intense pulses or
flashes of white light to kill micro-
organisms.
• The basic principle of Pulsed Light
sterilization is to destruct microorganisms
with short intense light flashes generated
by Xenon lamps.

• Energy, needed for product decontamination is
accumulated in a capacitor.
• A high-voltage signal initiates the so called ‘arc
formation’.
• An ‘arc’ is highly ionized gas with strong
currents. Xenon gas is used, because of its
capacity to convert electrical energy into light
energy. This arc starts the flash of intense
luminosity.
• The peak power of one flash is around 1
megawatt.

• The flashes present a continuous
spectrum, rich in UV light that lasts a few
hundred of microseconds.
• The housing of the lamp is made of
quartz, so almost no optical energy is
wasted.
• The flashes are controlled and
concentrated by aluminum reflectors,
specifically designed for each application.

• Each flash produces an enormous amount
of energy. With a lamp energy of 300 J
and a flash time of 0.3 mS that’s 1Mwatt.
Or, 1 kW per square cm of the treated
object.
• The microorganisms absorb all the energy,
mainly that of the further UV domain.

• Pulsed light has a complete destructive effect on
microorganisms, a combination of two
phenomenon :
Sterilizing effect of UV : the DNA in the cells of
microorganisms absorbs the UV rays. This
ruptures the double strands of DNA and
provokes the formation of abnormal single-
strand bonds. This prevents DNA replication.
The microorganism’s protein production and cell
metabolism is blocked: and it dies.
Power of the flash : intense energy delivered in a
very short time increases this lethal effect.

• The pulsed UV light causes formation of
Pyrimidine dimers in DNA, resulting in
genetic damage to cells and their ultimate
destruction. Types of damage induced by
pulsed UV light are:
 Photolysis
 Loss of colony-forming ability
 Inability to support phage growth (enzyme
inactivation)
 Destruction of nucleic acid.

Pulsed light sterilization - CLARANOR
1. Electronics bay: powered by the main
current it generates the electrical pulses.
The integrated cooling system regulates
the temperature of the water in the lamp
circuit.
2. Optical cavity: here the light is generated,
powered by the electronic bay. It has flash
lamps associated to the reflector that
focusses the light towards the surface that
needs to be treated.

Pulsed light sterilization - Benefits
• The most important reasons for considering
pulsed UV light systems for sterilization are:
Total DNA destruction
Safety - No mercury, VOC
Inline production
Temperature integrity
Process effectiveness
Process speed - 1-3 pulses 6log reduction
Process flexibility
Free of toxic substances
Worker-friendly (safe and easy to use)
Minimum space requirements

• Pulse light sterilization technology has a
promising application potential in areas
requiring a high level of sterilization
without residual problems and without
heat application and contact.

Hydroclave
• Newer regulations (Environmental and
Medical Waste Regulations) require a
non-incineration technology, which is easy
and safe to operate & has no harmful
emissions & also sterilizes at low cost.
• Hydroclave offers a remarkably simple,
affordable, patented, proven
medical/Infectious waste treatment
process which achieves the highest waste
sterility, at an incredibly low treatment
cost.

Why Hydroclave?
• Performance
Guaranteed high level of sterilization,
including wet waste, metals, liquids and
sharps.
Automatic operation, and not dependent on
operator skill for sterility.
No infectious or harmful emissions.
Mechanical destruction of the waste, and
safe for land-fill.

Why Hydroclave?
• Economic
Low operating cost with low energy
consumption.
Low maintenance costs.
No costly bags, filters or chemicals in the
process.
Very large weight and volume reduction of
the waste.

• Medical Waste is
deposited in the
Hydroclave vessel.
• The Hydroclave can
process:
 Bagged waste, in
ordinary bags
 Sharps containers
 Liquid containers
 Cardboard
containers
 Metal objects
The Hydroclave Process – Stage one

The Hydroclave Process – Stage two
1. Powerful rotators
mix the waste and
breaks it into
small pieces.
2. Steam fills the
double wall
(jacket) of the
vessel and heats
the vessel interior.
3. The liquids in the
waste turn to
steam.
4. After 20 minutes
the waste and
liquids are sterile.
The waste
fragmentation and
sterilization

The Hydroclave Process – Stage three
1. The vent is opened, and
the vessel de-
pressurizes.
2. Steam heat and mixing
continue until all the
liquids are evaporated
and the waste is dry.
Vessel venting and
dehydration

A. The unloading door is
opened.
B. The mixer now rotates in
the opposite direction,
so angled blades on the
mixer can push the
waste out the unloading
door.
C. The dry, sterile waste
can be fine-shredded
further or dropped in a
waste disposal bin.
The Hydroclave Process – Stage four
Unloading the Waste
- The waste is now
ready for safe
disposal!

 Dry waste, regardless of its
original water content.
 Low odor, due to the dryness.
 Volume reduction to 85%
 Weight reduction to 70%
 Accepted as harmless waste
 Sterility of 6log10 achieved
 sterility under any waste load
conditions – even high liquid
load.
The Hydroclave Result

Hydroclave of Needles & Sharps
• The Hydroclave achieves a high degree of
sterility due to a vigorous mixing and
fragmenting of the waste inside the hot vessel:
– it breaks apart the sharps container …
– sets free the sharps into the vessel …
– where they are thoroughly exposed to the
required temperature and pressure.
• It is IMPOSSIBLE for a needle or sharp to be
shielded from the temperature as there are no
“cold spots”, assuring total sterility.

Hydroclave of Needles & Sharps
• If for any reason temperature and pressure
parameters are not met, the Hydroclave
automatically resets and initiates a repeat
sterilization cycle.
• How does the Hydroclave achieve the high
sterility?
By a vigorous mixing and fragmenting of the
waste inside the hot vessel.
• How does the Hydroclave make the waste very
dry?
By applying dry heat from the jacket to the
waste, instead of injecting hot, wet steam into
the waste.

Hydroclave vs Autoclave
• Hydroclave
• Low operating cost by
recycling steam.
• No special bags required
• Treats wet or liquid loads
easily
• Strong weight reduction
• Strong volume reduction
• Consistent high sterility
•Autoclave
• Higher operating cost, no
steam recycling
• High temp/ bags req’d
• Cannot treat wet or liquid
loads
• Weight increase
• No volume reduction
• Spotty sterility

Tata Memorial Hospital 1999-2001
This unit ran 2,200 cycles, has treated 88,000 Kg of
medical waste, and never failed a sterility test on
any cycle.
Downtime was less than 1%, and maintenance cost
minimal

Washer - Disinfector
• Washer disinfectors have a double function
 First a thorough cleaning process using water ,
detergents & enzymes followed by
 Heat disinfection where the water temperature
is elevated almost to boiling point.
• Another key feature of washer-disinfectors is
the extremely high flow of water, in terms of
both volume and pressure
 The massive flow of water spraying all items in
the washer-disinfection process results in very
effective physical (mechanical) cleaning.

Washer – Disinfector Warning
• Not intended or recommend that
Washer/Disinfector be used for the
terminal disinfection or sterilization of any
regulated medical device.
• Washers/ Disinfectors are intended only to
perform an initial step in the processing of
soiled, reusable medical devices.
• If medical devices will be contacting blood
or compromised tissues, such devices
must be terminally processed.

• Washer/Disinfector is intended for use in
the cleaning and disinfecting of reusable
utensils, trays, glassware, bedpans and
urinals.
• It can also be used for rubber and plastic
goods, simple hard-surfaced rigid surgical
instruments, such as forceps and clamps,
and other similar and related articles
found in healthcare facilities.

• Different default cycle modes
• Customizable modes also available
• Three injection pumps are provided with a
standard washer/disinfector.
One enzyme pump,
One detergent pump
One lubricant pump (for Thermal Rinse
phase)

• Each preprogrammed cycle is equipped
with
Pre-Wash
Enzyme Wash
Rinse
Thermal Rinse phases

• Pre-Wash
Cold water enters the sump from the
building supply.
Once the sump fills, pre-wash water is
recirculated and sprayed over the load for
two minutes (factory-setting).
On completion of the phase, water is sent
to the drain.
Recirculation time is adjustable from 15
seconds to15 minutes

• Pulsed Enzyme
Hot tap water enters sump from the building
supply, where a selected amount of enzyme
detergent is added automatically.
The load is sprayed with enzyme solution for 4.0
seconds, then allowed to soak on instruments
for 26 seconds. Spray/soak pattern is repeated
for the selected time interval (4.0 to 15 minutes).
On completion of the phase, the solution is sent
to drain, and the load is rinsed with hot water.

• Wash
Hot tap water enters the sump from the building
supply, where a selected amount of detergent is
added automatically.
Detergent solution is heated and maintained at a
temperature ranging from 140 to 180F (60 to
82C)
Once set temperature is reached, solution is
recirculated and sprayed over the load for the
selected time interval (2.0 to 15 minutes).
On completion of the phase, the solution is sent
to the drain.

• Neutralizer & Rinse
Water enters & may be heated and
maintained at a 110 to 180F (43 to 82C)
for 15 seconds.
Once the sump fills, rinse water is
recirculated and sprayed over the load for
the selected time interval (15 seconds to
15 minutes).
On completion of the phase, water is sent
to the drain.

• HEPA-Filtered Drying
Hot air is recirculated over the load for 6 to
60 minutes at low temperature
(180F/82C), or 6 to 30 minutes at high
temperature (240F /116C).
During the Drying phase, a small quantity
of air is exhausted which is replaced by
HEPA-filtered fresh air.

Newer Disinfectants
• Persistent antimicrobial-drug coating that
can be applied to inanimate and animate
objects containing silver (Surfacine)
• A high-level disinfectant with reduced
exposure time (ortho-phthalaldehyde)
• An antimicrobial drug that can be applied
to animate and inanimate objects
(superoxidized water)
• New sterilization methods – a chemical
sterilization process for endoscopes that
integrates cleaning (Endoclens)

Newer Disinfectants
• Solutions of chlorine dioxide are also
commercially available as liquid sterilants
—under trade names such as Tristel and
Medicide
• Gaseous chlorine dioxide system is
currently being used in several medical
applications, including the sterilization of
contact lenses and the secondary
sterilization of overwrapped foil suture
packages

Recent Research
• Psoralens and UVA (PUVA)
An interesting example of the
development of sterilization techniques for
specific applications is the recently
reported use of ultraviolet light in
combination with psoralens to purge blood
plasma and platelets of pathogenic
organisms.

Recent Research
• Ozone - Its use as a sterilant, however,
has been limited because of its instability,
which precludes storing it ready for use,
and because of the difficulty of generating
pure ozone. The Cyclops Co. has
introduced a machine for sterilizing
endoscopes that pumps humidified ozone
through the unit.

THANK YOU
“Sunlight Is the Best
Disinfectant”

Recent advances in sterilization

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