Sterilization of Implants

Materials Implanted into the body of human or an animal must be sterile to avoid subsequent infection that can lead to serious illness or death.

Repeated use of devices such as surgical instruments (expensive)

Sterilization of Implants

Biomaterials Science: An Introduction to Materials inMedicine; Ratner, B.D.; Hoffman, A.S.; Schoen, F.J.;Lemmons, J.E.; Eds.; 1996, Academic Press: USAISBN: 0-12-582460-2pp. 41 5420

Sterilization of Biomaterials

ت8رو8ن کردن یا استریل کردن: فرایندی است که س;

٬باکتری، قارچمیکروارگانیسمها و عوامل انتقال دهنده آنها از جمله

و ویروس را از سطح اجسام از بین می برد.اسپور باکتری

5 ع4اری از ب4اکتری ی4ا ق4ارچ ی4ا وی4روس اس4تریل ی4ا س4ترون ب4ه مع4نی ک4امال

م4ورد )در غیربیم4اری زا و بیم4اری زا میکروارگانیس4مهای دیگ4ر ی4ا

اشیای بی جان( است.

هدف از استریل کردن جلوگیری از انتقال عفونت است.

Staphylococcus aureus bacteria magnified about 10,000x

 

Escherichia coli Bacteria A cluster of magnified 10,000 times

© 2006 Kaiser Permanente Health Plan, Inc.

Infection Control Definintions

Sterilization Validated process used to render a product free of all forms of viable microorganisms

Disinfection Destruction of pathogenic and other kinds of microorganisms by thermal or chemical means.

Destroys most recognized pathogenic microorganisms, but not necessarily all microbial forms, such as bacterial spores

Categories of Medical Devices

Critical

Enters sterile tissue or vascular system )e.g., surgical instruments, cardiac and urinary catheters, implants(

Semi-Critical

Contacts mucous membranes or non-intact skin )e.g., endoscopes, respiratory therapy and anesthesia equipment, diaphragm rings(

Non-Critical

Contacts intact skin )e.g., bedpans, blood pressure cuffs, crutches(

STERILIZATION METHODS

Considerations:

1. Does this technique damage the materials? )heat resistance & radiation sensitivity(

2. Effect of “over-exposure”?

3. Effect with “under-exposure”? Sterility?

4. Economic consideration

Place in barrier package sterilize package provides barrier to microorganisms until use

STERILIZATION OF IMPLANTS

Sterile: Absence of all living organisms.

Sterility tests of an experimental vascular graft illustrating negative (Sterile, left) and positive (nonsterile, right) results.

Determination of Sterility: 1. “yes” or “no” resultImmerse into liquid culture if not sterile media becomes cloudy due to microbial growth2. Sterilization validation studies - Used to determine “sterility assurance level” SAL

-SAL: Sterility Assurance Level سطح اطمینان استریل بودن

- SAL accepted minimum: probability that an implant will remain non-sterile following exposure to a given sterilization process. The generally accepted minimum SAL for implants is 10 -6 or a probability of no more than one million that the implant will remain nonsterile.

تعری4ف استریلیزاس4یون در پزش4کی ب4ا محی4ط و م4واد غ4ذایی متف4اوت است. میلی4ون ذره موج4ود در بس4ته ۱در علم پزش4کی یع4نی از SALضریب

اس4تریل اگ4ر ح4داکثر ی4ک میکروارگانیس4م زن4ده وج4ود داش4ته باش4د، آن بسته استریل محسوب می گردد.

.در مواد غذایی و محیط این عدد بیشتر است

STERILIZATION OF IMPLANTS

Determination of SAL1. Determine _________________________

- # of viable microorganisms on an implant BEFORE sterilization

- measure on 10-30 samples

- shake/sonicate/wash off microorganisms from implant into sterile fluid determine # with standard techniques

2. Do a _________________________________________________

- determine microbial kill rate of sterilization process

- plot # of microorganisms remaining vs. exposure time to sterilization process

log # microorganisms

Minutes of exposure-6

So, exposure time should be at least, “x minutes”

x

© 2006 Kaiser Permanente Health Plan, Inc.

*Reprinted with permission from: Muscarella LF, “Automatic Flexible Endoscope Reprocessors,” Gastrointestinal Endoscopy Clinic of North America, 2000 April;10(2):245-257

Reprocessing Algorithm*

Reusable?

Discard after initial

use

Thoroughly cleaned?

Heat sensitive?

Pressurized Steam or Dry Heat Sterilization

Low Temp Gas, Plasma or Vapor Sterilization

Long, thin lumens?

Just-In-Time Liquid Sterilant or Cold Liquid Sterilant

NoNo

NoNo

Yes Yes

Yes

Yes Yes

STERILIZATION METHODS

1. Steam Sterilization / Autoclaving

- 1st method used to sterilize implants

- oldest, safest, and most cost effective method ______________________________________________________

- 15-30 min, 15 Psi [after all surfaces reach 121 C]

- Packaging: must allow steam to penetrate- Tyvek )HDPE fibers bonded together(

  Tyvek® brand is produced by DuPont. It is a family of tough durable sheet products of high-density polyethylene fibers. The sheet is formed first by spinning continuous strands of very fine interconnected fibers )seven times finer than human hair(, and then bonding them together with heat and pressure. Here is an image of Tyvek magnified 200 times.

 

 

Autoclavable Medical Packaging: Tyvek ®

STERILIZATION METHODS

Kills microorganisms by destroying metabolic and structural components essential to their replication.

Advantages:- Efficient, fast, simple- No toxic residues

Disadvantages- High temperature & pressure limit the range of

implant & packaging compatibility )polymers & adhesives melting & softening(

- If Tg < 121 C, will deform- If hydrophilic, will adsorb water- If biodegradable, will decompose )polyesters,

polyamides, polyanhydrides(

1. Steam Sterilization / Autoclaving

Application of Steam autoclave :

surgical instruments. not well suited for heat sensitive materials and instruments.

•Many surgical instruments are not designed to withstand prolonged heat and moisture of the steam sterilization process. •This leads to alternative sterilization categories: chemical sterilization and radiation sterilization, which allow heat andmoisture sensitive materials to be sterilized.

3. Ethylene Oxide )EtO( 1950

STERILIZATION METHODS3. Ethylene Oxide )EtO(

- Ethylene oxide: effective low temperature, boils at 11 C, Temperatures reached 50-60°C-Kills microorganisms including spores. by alkylating proteins and DNA-must have direct contact with microorganisms-Nearly half of all medical devices are sterilized by EtO

1. Place on EtO-permeable packaging )Tyvek(2. Into EtO sterilization chamber3. Pull vacuum )remove air(4. Inject EtO gas: [EtO] = 600-1200 mg/L, T = 30 - 50C, time = 2-48 h5. Remove vacuum6. Air or nitrogen washes – flush out EtO residues

FDA: 5-250 ppm

EtO Applications:Heat or moisture sensitive items. Compatible with wide a range of implant and packaging materials )suture, intraocular lens, ligaments, tendons, heart valve, vascular grafts(

Advantages of EtO gasEffective, high penetration, compatible

Disadvantages of EtO gas•Longer than steam sterilization, typically, 16-24 hours for a complete cycle. •Extremely reactive and flammable, risk of chemical accident that could harm hospital workers and patients.•Can leave toxic residues on sterilized items )aeration( •Possesses several physical and health hazards to personnel and patients that merit special attention )contact with eyes and inhalation should be avoided & <1ppm- 8h working day (.•Impact of CFC on earth’s ozone layer lead ETO/ Freon to pure EtO

2.Radiation• 60Co gamma rays• Utilizes ionizing radiation involves gamma rays from Co 60 isotope

source or machine- generated accelerated electrons.• If sufficient radiation dose is delivered to all surfaces of the implant,

the implant can be rendered sterile.• Non use state: source lowered into a deep (20-25 ft) water filled pool

Common Radiation SterilizationA. Gamma, Beta Sterilization

The product exposed to radiation for 10 to 20 hours, depending on the strength of the source. The highest temperatures reached in 30-40°C. A dose of 2.5 megarad is generally selected for many items.

Ionizing radiation produces ions by knocking electrons out of atoms. These electrons are knocked out violently, and strike an adjacent atom and either attach themselves to it, or dislodge an electron from the second atom. The result is ionic energy that becomes converted to thermal and chemical energy. This energy kills microorganisms by disruption of the DNA molecule, therefore preventing cellular division and propagation of biologic life.

Applications of Co radiation

Widely used for medical products (sutures, drapes, metallic bone implants, knee & hip prostheses, syringes, neurosurgery devices).Wide range of materials are compatible with radiation sterilization, polyethylene, polyesters, polystyrene, polysulfones, polycarbonate. But fluoropolymer, PTFE is not compatible!

Advantages:•Simple, rapid, effective, readily controlled (dosimetry)•Large & small material product cost effective•Non toxicDisadvantages:•High capital costs•Continual decay of the isotope results longer processing times & periodic need for additional isotope

Other High Temperature / Pressure SterilizationA. Dry HeatProcess at 160-170°C for a minimum of 2 hours.Limited applications.

Applications:Anhydrous oils, petroleum products, and bulk powders that steam and ethylene oxide gas cannot penetrate.

Low Temperature methodsA. Sterrad - Low Temperature Hydrogen Peroxide Plasma•Low temperature )45-50°C(, non-toxic, but fairly expensive•Fill the gap between autoclave: high temperature steam sterilization )safest, fastest and least expensive( and EtO gas sterilization, which leaves toxic residuals •Quickly sterilize most medical instruments and materials without leaving any toxic residues(.

Process:hydrogen peroxide is activated to create a reactive plasma or vapor.Operating cycle times range from 45-70 minutes, depending on size of system.Hydrogen peroxide is a known antimicrobial agent that is capable of inactivating resistant bacterial spores.

Applications:Heat sensitive medical equipment such as endoscopic equipment.

B. Steris System 1 Sterile Processing SystemMore common, low temperature )50-56°C(, 30 minutes.uses the Steris 20 Sterilant Concentrate that combines peracetic acid (chemical biocidal agent(, and a proprietary anti-corrosion formulation to kill microorganisms at low temperature.

Peracetic acid is an oxidant and disinfecting agent for liquid immersion.Reacts with most cellular components to destroy cells.

Application:Only immersible instruments can be used with this method, and only a few instruments can be sterilized at one time. No packaging required.

C. Cidex OPA Solution – Alternative to GlutaraldehydeHigh Level Disinfectant )HLD( for reprocessing heat sensitive medical devices.

Provides high-level disinfection in 12 minutes at room temperature )20C( and is particularly active against mycobacteria, including glutaraldehyde-resistant strains of M. chelonae.

Advantages•Broad materials compatibility of glutaraldehyde )but does not contain glutaraldehyde(• requires no activation•minimal odor The Cidex OPA Solution is replacing Cidex and Cidex Plus due to their toxicity concerns.Applications: Surgical cameras )endoscopes(,Cleaning and drying before immersion, rinsing with sterile water prior to use.

Other Chemical SterilizationA. Glutaraldehyde (Cidex Plus and Cidex)Two of the brand names for Glutaraldehyde )disinfectant in the medical industry). provide sterilization after 10 hours of use

• Cidex Plus Solution is a disinfectant that is used to disinfect medical instruments.It is a 3.4% alkaline glutaraldehyde solution, which has tuberculocidal and high leveldisinfection capabilities. It achieves high-level disinfection in 20 minutes at25°C and has up to a 28-day reuse life.

• Cidex Activated Dialdehyde Solution is used to disinfect medical instruments andendoscopes. This solution can also be used in an automated reprocessor. )Anautomated reprocessor is the machine used to disinfect endoscopic and medicaldevices with a high level disinfectant solution.( It is a 2.4% alkaline glutaraldehyde solution, which has tuberculocidal and high-level disinfection capabilities. It achieves high-level disinfection in 45 minutes at 25°C and has up to a 14-day reuse life.

Both have been used as a cold liquid high-level disinfectant for heat sensitive equipment.

B. VHP MD SeriesHydrogen peroxide in vaporized form for sterilizationSterrad system uses vaporized hydrogen peroxide to initiate the sterilization, and then plasma )created by RF energy( to complete the sterilization process.VHP is injected into the chamber via a series of pulses to sterilize packaged medical and diagnostic devices. The cycle time is 2 hours and the operating temperature ranges from 30-40°C.

Note: This system is large capital equipment that uses hydrogen peroxide as thesterilant and it can sterilize multiple pieces of equipment at one time. On the other hand, the Steris System 1 is a portable tabletop system that uses peracetic acid as the sterilant and it is used to sterilize equipment right before use.

The VHP system is relatively new )out on market for a year( and has yet to becommonly used in medical sterilization applications. Like the Sterrad system, it isintended to fill the gap between steam sterilization and EtO gas sterilization.

C. Chlorine DioxideChemical liquid sterilization process. The best operating temperature is 25-30°C, while using low concentrations ofClO2. The process requires 6 hours of contact time to achieve sterilization. A processor converts a compound of dilute chlorine gas with sodium chlorite to form ClO2 gas and this gas is then exposed to the equipment in a sterilizing chamber.

Note: This alternative may corrode some materials and must be generated onsite.Prehumidification of the ClO2 is also required.

D. Ozone New in USAOzone sterilizes by oxidationDestroys organic and inorganic matters.

The cycle time may be up to 60 minutes depending on the size of the chamber or load of items to be sterilized.

Corrosive, able to damage moisture sensitive equipment.

It penetrates membrane of cells causing them to explode.

Other Radiation SterilizationA. E-Beam RadiationHigh dose of electrons in a narrow beam Limited penetrating power, less than gamma radiation. a 10MeV Ebeam will penetrate about 5 cm of a unit-density material.

No need to water filled pool (Unlike gamma)

Application:The radiation can change the properties of some materials like plastics and have adverse affects on glues or adhesives.

B. X-Ray SterilizationBased on obtaining X-rays through conversion of electron beams. Same penetrating properties as the rays produced by Cobalt-60.Faster, more flexible, and more environmentally friendly.

X-rays offer excellent product penetration in sterilization, thoroughly treating the surface and interior of a product.

Traditional methodsDry heat is rare because of extreme temperature>140 C.Implants are occasionally sterilized in hospitals by immersion in an aqueous glutaraldehyde solution.Only in special circumstances, where the implant is sensitive to heat and aeration time after EtO is not acceptable.SAL requires meticulous attention to detail & long immersion times.

New technologies

Gaseous chlorine dioxideLow temperature gas plasmaGaseous ozone alternatives to EtOVapor-phase hydrogen peroxide

Machine generated X-rays advantage of nonisotopic source & peneterating power similar to gamma rays

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