The sterilization process and the modifications induced in ... Thesis Tessar… · – The sterilization is realized by hydrogen peroxide (58%) in vapour phase (45 min) and plasma

Master in BiomaterialsInteruniversity Research Centre

on Materials for Biomedical Engineering

The sterilization process and the modifications induced in biomaterials

Master Thesis

Candidate: Tutor:dr. Francesco Tessarolo prof. Maria Cristina TanziUniversity of Trento Polytechnic of Milan

July, 13 2005, CIRMIB School, Ischia (Na)

Presentation outline

• Definition of Biomaterial, Medical Device, Sterility

• Description of the most diffused sterilization technique

• A practical example to:– Select the most suitable sterilization technique for a specific device– Assess the sterilization effects on device materials– Evaluate the sterilization alteration and estimate the device life-cycle – Summary the possible modification induced by sterilization

• Overview on innovative experimental techniques

• Some considerations on sterilization future developementsF. Tessarolo: “ The sterilization processes and the modifications induced on biomaterials” July, 13 2005, CIRMIB School, Ischia (Na)

Biomaterial:

a natural or synthetic material that is used or is suitable for use

in contact or for introduction into living tissue especially as part of a medical device.

F. Tessarolo: “ The sterilization processes and the modifications induced on biomaterials” July, 13 2005, CIRMIB School, Ischia (Na)

Medical device (Directive 93/42/EEC)

• EU: Any instrument, apparatus, appliance, material or other article, whether used alone or in combination, including the software necessary for its proper application, intended by the manufacturer to be used for human beings for the purpose of:

– Diagnosis, prevention, monitoring, treatment or alleviation of disease;– Diagnosis, prevention, monitoring, treatment, alleviation of or compensation for an injury or

handicap;– Investigation, replacement or modification of the anatomy or of a physiological process;– Control of conception:– And which does not achieve its principal intended action in or on the human body by

pharmacological, immunological or metabolic means, but which may be assisted in its faction by such means.

• US: A medical device is an “instrument, apparatus, implement, machine, implant, in vitro reagent, or other similar or related article, including any component, part or accessory, which is:

– recognized in the official National Formulary, or the United State Pharmacopoeia, or any supplement to them,– intended for use in the diagnosis of disease or other conditions, or in the cure, mitigation, treatment, or prevention of disease, in man or

other animals, or– intended to affect the structure or any function of the body of man or other animals, and which does not achieve its primary intended

purposes through chemical action within or on the body of man or other animals and which is not dependent upon being metabolized for the achievement of any of its principal intended purpose.”


Risk Based Classification of MDs

• High risk - Class III:• Invasive surgical devices which operate in contact with the heart, the central circulatory

system or the central nervous system• Drug releasing devices• Devices produced including animal tissues

• Moderate risk - Class IIb• Devices which release or exchange ionizing radiation within the body

• Moderate risk - Class IIa• Invasive surgical devices not included in class III• Devices which release or exchange energy within the body in a different form from

class IIb,

• Low risk - Class I• All other devices.

This classification account for the global risk associated to the device including: infection risk, malfunctioning risk, electrical risk, personnel risk, etc.


Spaulding classification: infective risk (1972)

Low level disinfectionIn contact with healthy skinLow

High level disinfection or sterilization

In contact with intact mucous membranesPrior to use in immuno compromised patients

Intermediate

SterilizationIn close contact with a break in the skin or mucous membraneFor introduction into sterile body areas

High

RecommendationApplication Risk

[ US Medical Device Agency, Guidance 1996]

Devices infective risk is the major issue in risk managementand nosocomial infection control


Sterility and Sterilization

Sterility is:• (Theoretic definition) the abssence of any viable organism

including bacteria, mycobacteria, spores, and virus.• (Statistic definition) the probability 10-6 of recovering a viable

organism on a sterilized device (UNI-EN 556)

Sterilization is:• (Operative definition) the capability to reduce the bioburden

(CFU count) by a factor ≥106

Note: no requirements for prions or endotoxins

≤


Sterilization techniques

Obsolete or underverification/development

• Steam-formaldehyde moisture• Plazlyte®

• Experimental techniques

Actually available• Dry heat• Steam• Ethylene oxide• Ionising radiation (gamma, beta, e-beam, x-ray)• Sterrad ®

• UV irradiation• Glutaraldehyde• Ultra-filtration• Aseptic manufacturing


Steam

• Active principle– Microorganisms inactivation and destruction is realized by coagulation and denaturation

processes on enzymes and microbial proteins.

• Pros– High biocidal efficiency against the most resistant spores.– Short time cycle (fast sterilization can be obtained in 3 minutes at 134°C and 2,1 bar).– Absence of toxic residuals on material (except from material by-products induced by

thermodegradation).– High penetration efficiency into narrow device districts.

• Cons– High temperature required for the whole cycle (>121°C).– High humidity (100%) and pressure (>1.1 bar) might induce softening, hydrolysis,

degradation in thermosensitive materials.– Water contaminations may alter surface properties by deposition of new compounds.


Ethylene oxide

• Active principle– Bactericidal, sporicidal and virucidal effects results from the alkylation of sulphydrilic, amino,

carboxylic, phenolic and hydroxylic groups in the nucleic acids.

• Pros– The main advantage is represented by low temperature treatment (as low as 50°C).– High compatibility with a broad materials range. – High penetration on polymeric materials.

• Cons– Sterilization cycle length (> 2 hours except aeration that could require 12 hour in forced

detoxification protocols or up to 14 days if spontaneous).The actual minimal level of detection in treated device is 25 ppm ETO;

– Potential toxicity for patients and personnel (ETO is highly toxic, mutagenic and suspected carcinogenic).

– The high cost of the technology.


Gamma radiation

• Active principle– First phase: photon material interaction. One or more electrons are energized by momentum

transfer. Not the entire energy is transferred to electron buy there is also the production of x rays (Bremsstrahlung).

– Second phase include the transfer of energy from the energized electrons to materials atoms by orbital electrons excitation, ionisation, bond breakage, creation of free radicals. Microorganisms are inactivated mainly by DNA chain cleavage.

• Pros– Low temperature treatment.– High penetration into materials and packaging.– Possibility to easy sterilize difficult and complicated materials geometries.– Possibility to treat a large amount of devices in a short time and safely.– Absence of toxic residuals after sterilization.

• Cons– Huge capital investments. – Radiation induced modification on polymers (embrittlement, discolouration, stiffening,

softening, increase or decrease in melt temperature and decreases in molecular weight). Chain cleavage and crosslinking are the two mechanisms involved.


Sterrad®patented by Advanced Sterilization Products, a division of Johnson & Johnson Medical Inc.

• Active principle– The sterilization is realized by hydrogen peroxide (58%) in vapour phase (45 min) and

plasma phase (15 min) obtained by RF excitation (13.45 MHz, 300W).– Chemical disinfection by nucleation of the H2O2 vapour on surface heterogeneity oxidation in

the first phase realize the main bactericidal effect. The H2O2 is an effective anti microbic that act as precursor in free radicals production.

– The ionisation obtained during the plasma phase is mainly validated in its role of residues detoxifying process without sporicidal effects.

• Pros– Low temperature cycle (<50°C).– Short cycle without the need for aeration or materials detoxification (H2O).– Low risk for exposition to sterilizing agent.

• Cons– Sterilization cycle is ineffective in presence of non negligible level of bioburden and organic

matter. Low level of blood serum invalidate the sterilization efficiency, therefore a deep device cleaning is mandatory.

– FDA approval not obtained for long (>31 cm) and narrow lumens (<6mm).– Sterilization of absorbing materials, nylon, polyester, cotton woven, cellulose, copper, zinc

and brass, is not allowed.


Selection of the optimal technique

• None of the actually available technique is suitable for all biomaterials.

• Any sterilization technique induce modifications in biomaterials

• The elective sterilization process has to be chosen by considering:– Material properties– Device ending purpose– Pre sterilization bioburden and contamination level– Possible toxic compound release– etc…


Which sterilization process?

How to select the elective sterilization technique

for a specific material/device?


A challenging example:

• To restore the original properties (sterility first) of a used device marked as sigle use.

• Reprocessor = Manufacturer

• It is mandatory to obtain the sterility of the reprocessed device and to guarantee, at the same time,– safeness, – material characteristics – performance equivalent to the new one.


Operative flow chart

Step 3Material testing Functionality testing •Biological tests

Step 2Regeneration protocol definitionDisinfection and sterilization

Outcomes:

Regeneration protocol Assessment of sterilization

Step 1Device and Materials investigationfor critical components individuation

optimisation induced modifications

Optimal Sterilization technique identification


Step 1: characterization of new devicesPercutaneous catheters for cardiac electrophysiology and ablation (EP)

Devices Clinical use


Step 1: characterization of new devices

• Polymeric shaft:

4000 3500 3000 2500 2000 1500 100020

30

40

50

60

70

80

90

Etere

C-Cbenzene

C=O

CH2

N-H

Tran

smitt

ance

Wavelength (cm-1)

ATR-FTIR Metronic RF Conductr

ATR-FTIR:

EDS: Presence of barium sulphate

ESEM: Morphological and topographycal identification of the salt dispersion


Step 1: characterization of new devices

• Ablation and recording electrodes:

COM:

EDS: Presence of pure platinum

ESEM:Micro and nano morphology

characterization

AFM: Identification of surface residuals and contamination


Step 2: definition of disinfection and sterilization protocols

•Decontamination–10’ 0,1% NaDCC solution

•Cleaning–Enzymatic detergent, 0,5% in tap water

•Sterrad 100S® sterilization– 54’ short sterilization cycle


Step 3: sterilization induced modifications Surface topography

-2 0 2 4 6 8 10 12 14 16100

200

300

400

500

600

700

800

900

10-1

0 m

Number of reprocessing cycles

RMS Rough exponential fit

Exponential fit :

Y=C+D[1 - exp(-x/t)]

C= 290 ± 60 ÅD= 630 ± 180 Åt= 7 ± 4 cycles

Micro-roughnessincreasing:

New 1 cycle 4 cycles8 cycles

Nano-roughness increasing:

New1 cycle 4 cycles

8 cycles


Step 3: sterilization induced modifications Surface chemistry

Hydrolytic stabilitydecreasing:

200 250 300 350 400-0 ,2

0 ,0

0 ,2

0 ,4

0 ,6

0 ,8

1 ,0

1 ,2

1 ,4

1 ,6

1 ,8

2 ,0

208 nm

new 1 cyc le 4 cyc les 8 cyc les non s terile

Abs

orba

nce

W ave leng th (nm )

Hydrolitic stability and nano-roughness

comparison

0 2 4 6 8-100

0

100

200

300

400

500

600

700

800

900

10-1

0 m


RMS Rough Average Rough

0 2 4 6 80,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

1,8

2,0

2,2

Absorbance at 208 nm

Abso

rban

ce



Step 3: sterilization induced modifications Bacteria interaction

Methods: Testing sterility efficiency up to 6 cycle of reprocessing on devices:

x1

I Sterilization after clinical use

TEST

x5

II, III, IV,V, VI

Sterilizations after simulated use

TEST


Step 3: sterilization induced modifications Bacteria interaction

Results:

Sterility is assured up to 4 cycles of reprocessing and sterilization. Further sterilization cycles might compromise material properties

and favour bacterial persistence


Step 3: sterilization induced modifications Functionality testing

Tissue equivalent phantom for

simulated use

0 2 0 0 4 0 0 6 0 0 8 0 0

0

2 0 0 0 0

4 0 0 0 0

6 0 0 0 0

8 0 0 0 0

1 0 0 0 0 0

(AU

)

T im e (s e c )

A re a N o n L in e a r F it M o d e l t 2 /3

Power delivery quantification and

termistor calibration control

Heating fingerprint characterization


Sterilization can modify:

• Chemical physical characteristics of treated materials

• Thermo-mechanical material properties

• Interaction between biomaterials and biological environment– Biocompatibility– Bioactivity– Cellular spreading and growth– Bacterial adhesion– Toxicity


Innovative and experimental sterilization techniques

• Plasma process for sterilization (MW, RF)

• Supercritical and high pressure CO2

• High voltage pulsed electric field

• Ozone

• Plasma-UV combination treatments


Plasma sterilization

• Plasma: the fourth state of the matter composed by free electrons, ions, excited neutrals and reactive radicals

• Plasma can be produced in vacuum chambers by RF or MW exitation of selected gases (O2, N2, SO2, SF6, NO2, H2O, H2O2, CO2, halogens, air, aldehydes)



• The bactericidal action is realized by chemical and physical etching of exposed surfaces and by UV irradiation.

[Chau TT, et al. Biomaterials 1996, 17:1273]


Plasma sterilization• Process parameters:

[Lerouge S, et al.Plasmas and Polymers 2000, 5:31–46]




• But plasmas are widely used for surface modification, conditioning, radicalisation, coating.

• Often these processes are used for optimising surface properties of biomaterial (enhance cell adhesion, modify surface topography, etc)…


The future

• Develop and use novel sterilization techniques (eg. plasmas) not only as extra treatment after the whole manufacturing process (which alter and/or degrade material properties and sometimes bring to failure of the device) but:

• Implement the sterilization protocol as an integral part of the manufacturing process, taking advantage of the sterilization induced modification as positive and expected improvement for realizing the ready to use medical device.


Documents

The sterilization process and the modifications induced in ... Thesis Tessar… · – The sterilization is realized by hydrogen peroxide (58%) in vapour phase (45 min) and plasma