Medical Plastic Data Service Magazine



Our 30th Year of Publication
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Cover Story

Sterilization Technologies For Medical Plastic Products And Devices


All materials used in medical devices, including the plastics used in them, are essential to be capable of being sterilized without loss of performance.


Sterilization can be defined as the removal or destruction of all living organisms, including resistant forms such as bacterial or fungal spores. Bacterial spores are most resistant to destruction, and if the sterilization is effective in eliminating them then it can generally be assumed that all other pathogenic and nonpathogenic organisms have been destroyed. It is important to reduce or eliminate the bioburden of certain medical devices and the materials used in their manufacture before end use.


Bio-burden is the concentration or the number of microorganisms like pyrogens, viruses, molds, and fungi present in or on a material. Pyrogens are substances that can cause a fever. There are various tests that can detect the number and kinds of micro-organisms including pyrogens and remnants of bacteria. A product may be sterile but it still may contain pyrogens. Use of high temperatures or radiation will typically kill pyrogens. It is important to realize that production in a ‘‘clean room’’ does not make a device sterile; it simply reduces the initial bioburden and concentration of foreign particles in or on the material to make sterilization more effective. Cleanliness does not mean sterile.


A comparative analysis for various sterilizations methods is given in the following table :


Comparison of Common Sterilization Methods

Sterilization Characteristic Steam Dry heat Ethylene oxide (EtO) Gamma radiation Electron beam (e-beam)
Process type Batch Batch Batch Batch Continuous
Post-sterilization testing for Sterility Assurance Level (SAL) Parametric release; biological indicators Parametric release; biological indicators Parametric release; biological indicators Dosimetric release Dosimetric release
Post-sterilization treatment Need to dry the product None Need to aerate product to remove residues None None
Penetration Requires vapor permeable packaging. Surface penetration Good penetration Requires gas-permeable packaging; high pressure, temperatures for improved penetration Excellent penetration Near complete penetration, need dosimeters; low penetration in high- density materials
Safety Almost no safety concerns Almost no safety concerns Considered a mutagen/ carcinogen; need to remove residual absorbed EtO Minimal concern; environmentally safe; non-toxic (need protection from radiation) Almost no safety Concerns
Reliability Excellent Good Good Excellent Excellent
Turnaround time Slow Slow Slow Fast Fast
Process Parameter Controls Temperature, pressure, vacuum, relative humidity, time Temperature, pressure, vacuum, time Temperature, pressure, vacuum, relative humidity, gas conc., time Time Time
Material constraints Heat resistant and hydrolysis resistant materials only Heat-resistant materials only Polymers that do not absorb or degrade with EtO Radiation stable polymers; complex parts and kits not effectively sterilized e-Beam stable polymers; low- density materials only
Relative cost Inexpensive Relatively inexpensive High capital investment High capital investment High capital investment
Advantages Simple process, widely used, excellent for reusable devices, excellent for heat- stable liquids Relatively simple process Well characterized, good for kits, combination products, parametric release Simple, fast, excellent penetration, dose uniformity Simple, fast, less material degradation
Disadvantages Comparatively high temperatures, generally not appropriate for single-use devices and large lots High temperatures, limited use Relatively complex process; some limits to penetration; need to remove EtO residuals Limited applicability to kits and complex designs/ products; no drug/ combination products; material degradation Limited penetration, poor on high-density products, dosimetric release is not very uniform, affected by part configuration


Sterilization procedure includes always some disadvantages due to the simple fact that there is a certain amount of energy necessary to destroy living germs, even those, which are specialized on harsh living conditions. On the other hand, a sterilization procedure should be as fast and reliable as possible and has no impact on plastic materials as well. The various sterilization technologies in use by industry includes:



• Steam sterilization
• Dry Heat Sterilization
• Ethylene Oxide ( EtO ) Steriization
• Gamma Radiation Sterilization
• Electron-beam sterilization



A vast majority of plastic medical devices, which are applied sterile, are sterilized by γ-radiation or ethylene-oxide, especially almost all single-use devices. γ-radiation may be preferred due to its faster and less restrictive sterilization procedure regarding the actual geometry and shape of the device, however, it may cause more aging damage to the chemical structure of the plastics.


The following table gives overview on radiation stability of various Plastics.


Radiation Stability of Various Plastics

Polymer Comment
Polyolefins Polyethylene can cross-link. Polypropylene is especially susceptible to degradation and discoloration. Stabilized polypropylene and polypropylene copolymer grades are good
PVC Susceptible to degradation and color change. Tint- based, stabilizers are incorporated into PVC to prevent discoloration and degradation
Acrylics Must be stabilized to prevent degradation and color change
Polycarbonates Must be stabilized to prevent degradation and color change
Polyurethanes Some discoloration that reverses over time
Acetals Typically not used for gamma sterilization
Polyamides Polyamides containing aromatic rings are good Polyamides 10, 12, 6/10, and 6/12 are good
Polyester Aromatic polyesters are radiation stable
High-temperature thermoplastics PEK, PEEK, PEI, Polysulfones – Good
Fluoropolymers Teflon embrittles when exposed to gamma radiation. Teflon and FEP must be stabilized. All other fluoropolymers are stable to gamma radiation
Elastomers Generally stable to gamma and e-beam radiation
Thermosets Thermosets typically are radiation stable


References :
01 - “Emerging Trends in Medical Plastic Engineering and Manufacturing” By : Markus Schonberger and Marc Hoffstetter
02 - “Plastics In Medical Devices” By : Vinny R Sastri


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