Biomaterials and Tissue Engineering in Urology

John Denstedt,A Atala

• Éditeur: Woodhead Publishing
• Année: 2009
• ISBN:
  9781845696375
• Sujet: Technology & Engineering
• Sous-sujet: Materials Science

Urology is the branch of medicine dealing with disorders or diseases of the male genitor-urinary tract and the female urinary tract. This important book summarises the wealth of recent research on the use of biomaterials and tissue engineering to treat urological disorders.Part one reviews the fundamentals with chapters on such topics as biofilms and encrustation formation. Part two then discusses recent advances in biomaterials and design of urological devices such as metal ureteral stents, self-lubricating catheter materials and penile implants. Chapters in Part three address urological tissue engineering with coverage of themes such as artificial and natural biomaterials, nano-technology and placental stem cells for tissue engineering the regeneration of urological tissue and organs.With its eminent editors and international team of contributors, Biomaterials and tissue engineering in urology is an invaluable resource to researchers of urological biomaterials, devices and regenerative medicine in both industry and academia, as well as an important reference for medical practitioners.

• Provides a comprehensive review of biomaterials and tissue engineering in urology
• Explores the fundamentals of urology, focusing on biofilms and encrustation and formation
• Discusses recent advances in biomaterials and the design of urological devices, catheters and stents

Part I

Fundamentals

Outline

Chapter 1: Introduction to biofilms in urology

Chapter 2: In vivo models for ureteral stents

Chapter 3: Models for the assessment of biofilm and encrustation formation on urological materials

1

Introduction to biofilms in urology

P. CADIEUX and G. WIGNALL, University of Western Ontario, Canada

R. CARRIVEAU, University of Windsor, Canada

Abstract

Despite significant resources and several decades of research aimed at their prevention and treatment, biofilm-associated infections continue to be the major cause of urological device failure. Numerous strategies have been targeted towards improving device design, biomaterial composition, surface characteristics and drug elution, but have been largely thwarted by microorganisms and their arsenal of attachment, host evasion, antimicrobial resistance and dissemination strategies. This is not entirely surprising considering that natural biofilm formation has been occurring for billions of years and remains a significant element of microbe survival and evolution. Thus, the fact that biofilms develop on and in the biomaterials and tissues of humans is largely an extension of this natural tendency and underscores why they are so difficult to combat. Biofilm structure and composition intrinsically offer a protective environment for microorganisms, shielding them from the shear stress of urine flow, attack by the host immune system and antimicrobials. Furthermore, many biofilm organisms go into a metabolically quiescent state that renders them more tolerant to antibiotics and host immune factors able to penetrate the biofilm matrix. Finally, most organisms causing biofilm-associated urinary tract infections originate from the host’s own oral cavity, skin, gastrointestinal and urogenital tracts and therefore have already adapted to many host defense mechanisms. Ultimately, while biofilms continue to hold the upper hand with respect to recurrent infections and urinary tract biomaterial use, significant progress has been made in understanding these dynamic microbial communities and novel approaches offer promise for biofilm prevention and removal. These include novel device designs, antimicrobials, anti-adhesive coatings, biodegradable polymers and biofilm-disrupting compounds and therapies.

Key words

biofilm

antibiotics

urinary tract infection

ureteral stent

urethral catheter

uropathogen

conditioning film

antibiotic resistance

1.1 Introduction

Biofilm-related infections remain the major cause of urological device failure despite millions of dollars and several decades of research targeted at their prevention and eradication. The plethora of strategies aimed at improving device design, biomaterial composition, surface characteristics and drug delivery have been generally thwarted by microbes and their abundance of attachment, host evasion, antimicrobial resistance, survival and dissemination strategies. It is important to acknowledge that the formation of biofilms by microorganisms in nature has been going on for billions of years and remains a major part of their current survival and evolution on the planet. Thus, the fact that biofilms develop on and in the tissues and biomaterials of humans is simply an extension of this natural tendency and largely explains why they are so difficult for us to combat. Furthermore, the majority of organisms that cause biofilm-related urinary tract infections originate from our own skin, oral cavity and gastrointestinal tract, and thus have already adapted to many of our defenses. In this chapter, we will first discuss biofilms at their most basic level including why and how they form. It is essential to understand the purpose, formation and structure of both natural and medical biofilms if we are to tackle the clinical problems associated with them and attempt to prevent and eradicate them from patients. Biofilms in medicine in general will follow and then transition into our focus of biofilms in urology and their clinical relevance. We will discuss the basic hydrodynamics of the upper and lower urinary tract along with how biofilms affect, and are affected by, urinary flow. Prosthetic versus non-prosthetic infections will be described as well as the ability of biofilms to resist antimicrobials, host urinary tract defenses and the immune system. The development and implications of chronic infections will be commented on and the effects that biofilms and biofilm-related encrustation have on them. This will lead into current treatment and prevention strategies including novel biomaterial surfaces and design, coatings, antimicrobial strategies and the promising field of biofilm-disrupting agents. We argue that although microbial biofilms continue to hold the upper hand in terms of recurrent infections and the use of biomaterials within the urinary tract, significant progress has been made in understanding these microbial communities and new strategies offer promise in the field.

1.2 What are biofilms and why do they form?

A biofilm can be defined as a community of microorganisms (bacterial, fungal, algal) attached to the interface of a liquid and a surface, and enveloped within a matrix of exopolysaccharides and other biological constituents (Costerton, 2007a; Jass et al., 2003). In the simplest terms, a biofilm is merely a mechanism used by microorganisms to remain in a favorable environment and promote their survival and reproduction within that environment. Thus, on a very basic level, a urinary biofilm on a ureteral stent is no different than those of the thermophilic bacterium Thermus aquaticus at a deep sea hydrothermal vent or Serratia marcescens on your shower wall (Langsrud et al., 2003; Stramer and Starzyk, 1978). In general, if a micro-organism comes in contact with a surface and successfully attaches to it, and the right growth conditions exist (temperature, nutrients, pH, osmolarity, etc.), it will adhere more securely and begin multiplying and forming a biofilm. In addition, biofilms provide a degree of protection for a microbial population. Although microorganisms can survive and multiply very efficiently as single cells within a liquid milieu (such as uropathogens in urine), they are completely exposed to any detrimental environmental conditions that might arise (i.e. increased temperature, host factors, antibiotics) and may be swept away from a favorable environment via shear forces within the surrounding fluid (such as during micturition). Thus, if a single-celled (planktonic) population is exposed to a sudden lethal change in temperature or high concentration of a toxic compound, all cells in the population may be killed. The structure and makeup of a biofilm protects many cells within the population by physically shielding them from the surrounding environment and inducing changes in gene expression that result in metabolic dormancy and/or increased resistance to many inhibitory substances (Donlan, 2003; Fujiwara et al., 1998). Although biofilms are far more complex in reality than described here, it is obvious that their formation improves microorganism population survival, growth and reproduction through multiple mechanisms. It is therefore not surprising that biofilms are relatively ubiquitous throughout every natural environment on the planet, ’from tropical leaves to desert bolders’ (Costerton, 2007a), or more relevant here, from the vaginal epithelia to urinary tract devices. Clearly, biofilms are the greatest challenge faced by medicine and industry in terms of treating wounds, using biomaterials and designing compounds for the prevention and treatment of infection.

1.3 Biofilm formation and structure

At a macroscopic level, most biofilms appear fairly simple in structure, as uncomplicated clusters, chains and/or layers of organisms haphazardly attached to a surface and intermixed with extracellular slime. Based upon this view, one might consider biofilm development simply as the repeated process of single organisms from the surrounding fluid adhering themselves t...

Table des matières

• Cover image
• Title page
• Table of Contents
• Related titles
• Copyright
• Contributor contact details
• Dedication
• Preface
• Part I: Fundamentals
• Part II: Materials and design of urological devices
• Part III: Urological tissue engineering
• Index