Sterilisation of Biomaterials and Medical Devices

Sophie Lerouge, Anne Simmons

• Publisher: Woodhead Publishing
• Year: 2012
• Print ISBN: 9781845699321
• eBook ISBN: 9780857096265
• Topic: Medicine
• Subtopic: Biotechnology in Medicine

The effective sterilisation of any material or device to be implanted in or used in close contact with the human body is essential for the elimination of harmful agents such as bacteria. Sterilisation of biomaterials and medical devices reviews established and commonly used technologies alongside new and emerging processes.Following an introduction to the key concepts and challenges involved in sterilisation, the sterilisation of biomaterials and medical devices using steam and dry heat, ionising radiation and ethylene oxide is reviewed. A range of non-traditional sterilisation techniques, such as hydrogen peroxide gas plasma, ozone and steam formaldehyde, is then discussed together with research in sterilisation and decontamination of surfaces by plasma discharges. Sterilisation techniques for polymers, drug-device products and tissue allografts are then reviewed, together with antimicrobial coatings for 'self-sterilisation' and the challenge presented by prions and endotoxins in the sterilisation of reusable medical devices. The book concludes with a discussion of future trends in the sterilisation of biomaterials and medical devices.With its distinguished editors and expert team of international contributors, Sterilisation of biomaterials and medical devices is an essential reference for all materials scientists, engineers and researchers within the medical devices industry. It also provides a thorough overview for academics and clinicians working in this area.- Reviews established and commonly used technologies alongside new and emerging processes- Introduces and reviews the key concepts and challenges involved in sterilisation- Discusses future trends in the sterilisation of biomaterials and medical devices

1

Introduction to sterilization: definitions and challenges

S. Lerouge, École de technologie supérieure, Canada

Abstract:

Sterilization is an important step in manufacturing medical devices, as well as in the reprocessing of reusable ones in healthcare centers. This chapter will present the main definitions related to sterilization and the classification of sterilization technologies into industrial/clinical and into traditional/non-traditional methods. The main challenges related to sterilization will also be discussed, such as prion and endotoxin deactivation, the growing use of small and delicate materials, as well as new economic and ecological constraints related to the reduction of costs and the protection of the population/environment, respectively. Finally, a brief overview of the book content will be presented.

Key words

definitions

challenges

security assurance level

disinfection

classification of sterilization techniques

validation and monitoring

prions

1.1 Introduction

Sterilization is an important step of manufacturing of implants or medical devices (MDs) to prevent the spread of infection. It is also a major step when reusing MDs in clinical centers. Failures in adequate sterilization result in significant institutional costs related to patient nosocomial infections and mortality/morbidity concerns. In developed countries, from 5% to 10% of patients admitted to acute care hospitals acquire an infection which was not present or incubating on admission. This rate exceeds 25% in developing countries (Wenzel et al., 2008). Thanks to much progress in the methods for device sterilization, most nosocomial infections nowadays are not related to this issue but rather to direct contact, ventilation, water and autologous infection along urinary catheters (called hospital wacquired urinary tract infections, accounting for about 40% of the total number of all nosocomial infections). However, it is important to consider sterilization issues and requirements at the earliest stages of development of any new MD, to ensure that the final product can be sterilized effectively and safely, with the most cost-effective and environment-friendly procedures. This book aims to help industrial and healthcare workers to choose a sterilization method and better understand regulations and hazards related to the sterilization of MDs.

In the present chapter, the main concepts of sterilization will be defined. We will differentiate between sterilization and disinfection, between industrial and clinical sterilization, as well as between sterilization efficiency and safety, which are two of the most important aspects to consider when choosing a biomaterial, designing the device and choosing the packaging and sterilization technique. This book will focus on medical devices. Methods to reduce microorganisms in food, water or air in healthcare settings will not be discussed. We will present the main challenges facing sterilization and briefly discuss the criteria of an ideal sterilization technique. Finally, a brief overview of the various sterilization technologies available will be given. These will be further detailed in the next chapters.

1.2 Definitions of sterilization in the context of biomaterials

The main concepts of sterilization to be discussed in this section are sterilization efficiency, the difference between real sterilization and disinfection as well as between industrial and clinical sterilization.

1.2.1 Sterilization efficiency

Sterilization efficiency is defined as the ability to remove or destroy all forms of microbial life, including viruses, bacteria and fungi, under vegetative forms or spores (Crow, 1993). Since absolute sterility cannot be verified, the statistical definition of sterility is used in practice, by using the security assurance level (SAL), defined as ‘the probability of a single viable micro organism occurring in or on a product after sterilization’. The worldwide accepted definition of sterility of medical devices is defined as the chance of finding a viable organism in or on a medical device to be at most 1 in 1 000000 or an SAL of at most 10^–6 (Block, 2000). However, in the case of sterile devices intended only for contact with intact skin, the American Food and Drug Administration (FDA) recommends a SAL of 10^–3. Except for the rare instances when sterilization can take place where the sterile products are to be used, MD must be packaged to preserve their sterility during storage, handling and transport. The majority of sterile MDs are terminally sterilized – that is, they are sterilized already packaged. In principle, sterilization should mean the destruction of all forms of pathogens. However, as we will see at the end of this chapter, prions and endotoxins are not completely removed or inactivated by the current sterilization methods and still represent a challenge.

1.2.2 Sterilization versus disinfection

It is important to distinguish sterilization from disinfection, which does not ensure the same security level and does not necessarily inactivate all forms of microorganisms – bacterial spores, for instance. Low, intermediate and high levels of disinfection can be obtained depending on the efficacy of the sterilant, duration of the process and ability to prevent deposition of new pathogens on the product after processing. Methods where samples are not wrapped to keep the sterility post-procedure should also rather be called high-level disinfection.

The choice between sterilization and disinfection must be made according to the risk of spreading infection. The classification originally proposed by Earle H. Spaulding in 1957 has been retained, refined and is still used to determine which devices should be sterilized and which disinfected. Sterilization is required for all critical medical devices – that is, those intended to be used in contact with sterile tissues – and recommended for ‘semi-critical devices’ – for example, those intended to be in contact with mucous tissues or nonintact skin. A high level of disinfection can still be acceptable for these (Spaulding, 1972; McDonnell and Burke, 2011). This category includes respiratory therapy and anesthesia equipment, some endoscopes, laryngoscope blades, esophageal manometry probes, etc. Flexible endoscopes are particularly challenging due to their fragility and their long and narrow lumens; they do not easily withstand sterilization techniques. Moreover, they are difficult to clean.

Laparoscopes and arthroscopes entering sterile tissue ideally should be sterilized between patients. The American Dental Association also recommends surgical instruments that penetrate soft tissue or bone (e.g. extraction forceps, scalpel blades, bone chisels, periodontal scalers and surgical burs) to be classified as critical devices and be sterilized after each use. Proper cleaning and high-level disinfection is, however, currently performed rather than real sterilization.

Sterilization should also not be confused with cleaning, which is defined as the removal of foreign material (soil, dust and organic debris). Thorough cleaning of devices is an important step before high-level disinfection and sterilization, especially in healthcare centers, since it has been demonstrated that it is more difficult to sterilize devices where microorganisms hide behind proteineous or grassy matter. Cleaning becomes a challenge when cavities and long lumens are present, such as in surgical tools for minimally invasive surgical procedures (Alfa and Nemes, 2004). Chemicals, minerals and water can also limit the efficiency of sterilization or induce damage on the MDs, thus rinsing with distilled or demineralized water, followed by complete drying of the instrument, is generally required, as will be discussed in chapters related to the sterilization techniques.

Cleaning is also important in industrial settings where it decreases the bioburden (living organisms) before sterilization, but also to eliminate contaminants originating from manufacturing processes, such as cutting or polishing fluids and particles, mold release agents, polymer processing aids, airborne contamination, etc. These can negatively impact on device bio-compatibility and further processing such as coating adhesion or bonding between two surfaces, corrosion resistance, etc. Finally, the term decontamination refers to the action of reducing the number of microorganisms from objects so they are safe to handle, use or discard.

1.2.3 Industrial versus clinical sterilization

Sterilization is the last step in manufacturing biomedical devices intended for use in contact with sterile tissues, severely damaged skin or mucous and sometimes with intact skin (newborns, etc.).

Industrial sterilization can take place either in-house or as contract sterilization. In-house sterilizers produce goods requiring sterilization and sterilize them as part of their production process. Contract sterilizers are companies that specialize in offering sterilization services to clients, but generally do not produce any of the goods being sterilized. The trend towards the use of contract sterilizers continued throughout the 1990s, as more and more companies focused on their core business and contracted out other services that they needed. Radiation sterilization (described in Chapter 3), in particular, is a technique limited to industrial sterilization and typically used on a contract basis, since this technology requires costly and high-risk radioactive sources.

Clinical sterilization takes place at healthcare centers and faces somewhat different challenges. Indeed, many devices are reusable and must sustain several cycles of cleaning and sterilization in clinical settings. They are then contaminated by a larger amount and variety of pathogens than those present at the end of the manufacturing process. Moreover, presence of biological tissues, blood or soils may prevent the efficiency of the process. In particular, bacteria within biofilms (found on numerous medical devices (e.g. contact lenses, pacemakers, hemodialysis systems, urinary catheters, central venous catheters, endoscopes) have been shown to be up to 1000 times more resistant to antimicrobials than are the same bacteria in suspension (Vickery et al., 2004). Finally, safety issues and duration of the sterilization cycle in clinical settings have more impact than in industrial sterilization. Therefore, as we w...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Contributor contact details
• Woodhead Publishing Series in Biomaterials
• Chapter 1: Introduction to sterilization: definitions and challenges
• Chapter 2: Steam and dry heat sterilization of biomaterials and medical devices
• Chapter 3: Sterilisation of healthcare products by ionising radiation: principles and standards
• Chapter 4: Ethylene oxide (EO) sterilization of healthcare products
• Chapter 5: Non-traditional sterilization techniques for biomaterials and medical devices
• Chapter 6: Sterilization and decontamination of surfaces by plasma discharges
• Chapter 7: Sterilisation techniques for polymers
• Chapter 8: Sterilisation of healthcare products by ionising radiation: sterilisation of drug-device products and tissue allografts
• Chapter 9: Antimicrobial coatings for ‘self-sterilisation’
• Chapter 10: Prions and endotoxins: reprocessing strategies for reusable medical devices
• Chapter 11: Future trends for the sterilisation of biomaterials and medical devices
• Index