Biomaterials and Medical Device - Associated Infections

L Barnes, Ian Cooper

• Publisher: Woodhead Publishing
• Year: 2014
• Print ISBN: 9780857095978
• eBook ISBN: 9780857097224
• Topic: Medicine
• Subtopic: Immunology

Despite advances in materials and sterilisation, patients who receive biomaterials of medical device implants are still at risk of developing an infection around the implantation site. This book reviews the fundamentals of biomaterials and medical device related infections and methods and materials for the treatment and prevention of infection. The first part of the book provides readers with an introduction to the topic including analyses of biofilms, diagnosis and treatment of infection, pathology and topography. The second part of the book discusses a range of established and novel technologies and materials which have been designed to prevent infection. - Provides analysis of biofilms and their relevance to implant associated infections. - Assesses technologies for controlling biofilms. - Considers advantages and disadvantages of in vivo infection studies.

Part One

Introduction to biomaterials and medical device-related infections

1

Introduction to biomaterials and medical device-associated infections

I.R. Cooper University of Brighton, Brighton, UK

Abstract

The use of medical devices to alleviate patient suffering is common practice in modern medicine. Such devices can incorporate chemicals to reduce microbial colonisation in an attempt to decrease infection rates. However, the prolonged and unnecessary use of medical devices has been linked to an increase in microbial resistance to antibiotics, and means that the patient might have to undergo a secondary treatment, sometimes requiring surgery to remove an infected implant. This chapter will briefly explore the history of biomedical devices, moving on to discuss the contemporary use of smart materials to deliver site-specific responses to treat conditions. It will describe some of the key advances made in material chemistry, and link these to the prevention of rejection by the host and a reduction in infectious disease, as well as reviewing some of the key pathogenic organisms associated with device infection, and the relative cost linked to device-associated infections.

Keywords

Infection

Device

Biomaterial

Healthcare

Cost

Pathogen

1.1 History of biomaterials

The use of artificial medical devices has increased dramatically over the previous decades. Devices ranging from catheters to artificial hearts, stents and replacement joints are widely used in modern medicine to reduce patient morbidity and increase quality of life. Evidence suggests that biomaterials have been used for many thousands of years in an attempt to ameliorate patient suffering. Early devices include a leather toe (Finch et al., 2012), which was entirely external to the body and used to provide ambulatory stability to the patient after physical trauma. Modern devices include entirely internal structures, such as drug-eluting stents, which are sited in the body through surgical procedures. They are usually made of metal (Merkely et al., 2009), and are used to treat biochemical conditions. Focus has now shifted towards not only making devices clean and sterile at the manufacturing stage, but to make them chemically resistant to colonisation by microbial cells, whilst not evoking an immune response by the human host.

Modern technology has given medical and related scientists access to a wide range of materials able to be used in treatment regimes. These now include plastics, ceramics, metals, and bioactive polymers. As our understanding of the human immune response to the implantation of devices improves, alongside our understanding of microbial pathogenicity cycles, it has become clear that the precise chemical composition of the device is critical for several reasons. Firstly, the ability of the pathogen to adhere and survive on a surface must be minimalised in order to prevent post-operative infections developing. Secondly, the need for the device to prevent human immune responses from developing in order to avoid the device being rejected, must be prioritised. Also, the device must be able to either maintain its properties if it is a permanent implant, or it must be able to biodegrade if it is temporary device, without causing physical harm to the patient as it reduces.

1.1.1 The birth of biomaterials: early materials used

One of the earliest biomedical devices discovered is an artificial toe discovered in Egypt, and currently housed in the British museum. It is made from leather, and appears to have been sewn to another material to facilitate walking by the wearer, dating from the first millennium BC (Reeves, 1999). Another Egyptian biomedical device was the use of wooden splints to treat fractured arm bones (Smith and Dawson, 1924). Both of these early examples of biomaterial are externally applied. This is important to note, as a large proportion of modern devices are now used as implantations, or pushing through the intact skin or mucous membranes, such as catheters. It is also important to note that both of these devices were constructed from naturally occurring materials: leather and wood. As technology has advanced we are now able to employ a wide range of materials, sometimes combined together, to facilitate a more comprehensive approach to treatment. There is evidence that amputation was employed to treat severe injury in Ancient Egypt (Nerlich et al., 2000; Williams, 2010). It is likely that, as today, amputation was considered as an option for the treatment of severe infection as well as injury from physical trauma. This is usually an option of last resort, used only in an attempt to save the patients’ life. However, it is also considered in relation to the use of artificial prostheses, where evidence suggests that this practice is centuries old; analysis indicating that the wearer of the artificial toe lost the original toe due to amputation (Nerlich et al., 2000). This data inextricably links the science of biomaterial prostheses design to medicine in an attempt to ameliorate suffering and improve patients’ lives.

1.1.2 Types of early medical device

Moving in to the modern era, biomedical devices can now be constructed using machines, and can come from a range of materials. Examples include metals, such as stainless steel (Torricelli et al., 2003), ceramics (Ngai et al., 2014), plastic (Lim et al., 2013), and bio-responsive polymers in recent years (Keegan et al., 2007). Depending on the body location, the physical and biological pressures of that location will vary. For example, a prosthetic knee will face greater sheer during walking than a dental implant. However, a dental implant will be subject to both sheer associated with mastication and greater degrees of chemical stress in relation to nutritional intake, as well as microbial metabolism and acid production in response to nutrient availability. A full assessment of the biological and physical needs of each device must be made if successful utilisation and application is to be achieved.

According to broad consensus, a biomaterial is defined as a nonviable material used in a medical device, intended to interact with biological systems (Williams, 1987). Within this scope, biomaterials can be largely divided in to one of three types, or generations of device:

1. bioinert;

2. biologically active and biologically degradable; and

3. location-specific response-inducing materials.

The original devices were usually made of one solid material, an example of which would be the wrought iron false tooth found in a Roman cadaver from approximately the year 200 AD (Crubezy et al., 1998). These first generation devices were designed to allow functionality, with no proper understanding of the biological processes underpinning the structures. That being said, Crubezy et al., did note that the iron tooth implant had achieved a degree of osteointegration, suggesting at least partial success of the implantation procedure (Crubezy et al., 1998). Being constructed of such materials, there was a much reduced chance of unwanted leakage or particle release that has been associated with some of contemporary materials. They were also largely biologically inert, which satisfies the criterion for inducing as little host response to a foreign body as possible. Another example would be polymethylmethacrylate (PMMA), which shows good adhesive property, and an example of these would be to act as cement to solidify prostheses to damaged bones (Charnley, 1960). However, some biochemical problems have been noted post-implantation of PMMA, leading on to further research in to its use.

1.1.3 Problems associated with early biomaterials and the need for further development

The two key problems associated with the...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright page
• List of contributors
• Woodhead Publishing Series in Biomaterials
• Part One: Introduction to biomaterials and medical device-related infections
• Part Two: Technologies and materials for controlling biofilms
• Index