Biosynthetic Polymers for Medical Applications

Laura Poole-Warren, Penny Martens, Rylie Green

• Publisher: Woodhead Publishing
• Year: 2015
• ISBN:
  9781782421139
• Topic: Technik & Maschinenbau
• Subtopic: Biomedizinwissenschaft

Biosynthetic Polymers for Medical Applications provides the latest information on biopolymers, the polymers that have been produced from living organisms and are biodegradable in nature. These advanced materials are becoming increasingly important for medical applications due to their favorable properties, such as degradability and biocompatibility.

This important book provides readers with a thorough review of the fundamentals of biosynthetic polymers and their applications. Part One covers the fundamentals of biosynthetic polymers for medical applications, while Part Two explores biosynthetic polymer coatings and surface modification. Subsequent sections discuss biosynthetic polymers for tissue engineering applications and how to conduct polymers for medical applications.

• Comprehensively covers all major medical applications of biosynthetic polymers
• Provides an overview of non-degradable and biodegradable biosynthetic polymers and their medical uses
• Presents a specific focus on coatings and surface modifications, biosynthetic hydrogels, particulate systems for gene and drug delivery, and conjugated conducting polymers

Part One

Introduction and fundamentals

Outline

1. Introduction to biomedical polymers and biocompatibility

2. Nondegradable synthetic polymers for medical devices and implants

3. Biodegradable and bioerodible polymers for medical applications

1

Introduction to biomedical polymers and biocompatibility

L.A. Poole-Warren, and A.J. Patton Graduate School of Biomedical Engineering, University of New South Wales, Sydney, NSW, Australia

Abstract

Significant advances in the field of polymer science over the past century have resulted in synthetic polymers becoming the basis for many new approaches to medical therapies and in particular development of new medical devices. While natural polymers have long been used in medicine and surgery, their application in medical devices has experienced a renaissance with advances in understanding of polymer synthesis and processing. In this chapter, natural polymers are discussed in detail, with a focus on proteins and polysaccharides. The major advantages and disadvantages in relation to use of natural polymers are considered with an emphasis on the key factors impacting their biological performance in tissue contacting devices. Approaches to developing hybrid materials that combine the advantages of both natural and synthetic polymers are becoming increasingly topical and hold much promise for the future of medical devices that can integrate with and drive regeneration of tissues.

Keywords

Biocompatibility; Hybrid biosynthetic polymers; Natural polymers; Synthetic polymers

1.1. Introduction

The key feature of polymers that allows them to be so effectively applied to medical devices is their versatility in terms of the plethora of structures, properties and functions exhibited. Unlike metals and ceramics, polymers can be fabricated in forms that range from soft gels to flexible fibres and porous forms to hard, non-porous bulk materials. Polymers can be classified broadly into those that are biologically derived, or natural polymers, and those that are manufactured or synthetic. Both of these two broad classes of polymers are widely used in biomedical device applications.

Where natural polymers are as old as life itself, synthetic polymers or plastics are man-made materials that have a history of less than 100 years. Over that relatively short period, synthetic polymers have become ubiquitous in commodity products today. Synthesised via covalent linking of multiple small chemical structures called ‘mers’ to form long-chain molecules or polymers, these materials have an extraordinary range of physical properties that allow them to be utilised in almost any application.

Chapter 2 outlines the non-degradable, synthetic materials that are typically used for biomedical applications. Advancements over the past decade are covered with a specific focus on poly(olefins), poly(urethanes), poly(carbonates), poly(siloxanes), poly(amides), poly(ethers) and poly(sulphones). A brief introduction to the chemistry, physical properties, biocompatibility and biostability of seven major classes of synthetic polymers is given. The term ‘non-degradable’ is used to imply that the polymers are resistant to degradation by hydrolytic and other mechanisms operating in biological environments.

Chapter 3 covers degradable polymers commonly used in biomedical applications with a focus on synthetic materials. Degradable polymers are classified into two key groups. The first is biodegradable polymers, which break down under physiological conditions. Biodegradation is a biologically based process that leads to degradation. Biological processes encompass human enzymes, microbial enzymes and even hydrolysis. Degradation refers to bond cleavage and includes hydrolysis of ester bonds or ultraviolet-promoted cleavage of C–C bonds. Typically, biodegradable polymers would include hydrolytically and/or enzymatically susceptible bonds such as polyesters, polyanhydrides, polycarbonates, polyamides and polyurethanes. The second group, bioerodible polymers, in which the chemistry of the polymer is not fundamentally changed during degradation, rather, the physical state changes from a solid structure to a solubilized polymer. ‘Bioresorbable’ is a synonym of bioerodible and the implication is that the polymer is resorbed, or adsorbed, into the surrounding tissue.

Based on excerpts from Chapters 2 and 3.

In this chapter, the natural polymers will be described followed by consideration of the benefits and limitations of both synthetic and natural polymers relating to their application in medical devices. Finally, the critical factors that impact on biocompatibility of both polymer classes will be evaluated. Combining polymers from the two classes to form biosynthetic materials has been proposed to overcome some of the limitations that each type presents for medical device development and this concept forms the basis of this book.

1.2. Natural or biological polymers

All living organisms are made up of proteins, carbohydrates, lipids and nucleic acids, the four key macromolecular building blocks of life. These molecules comprise the natural polymers that have evolved over the ages into the most elegant molecules known to man. To be exploited as materials for biomedical devices, natural polymers are either sourced from tissues derived from living organisms or are synthesised and processed using in vitro techniques via cell culture, recombinant approaches or using cell-free synthetic systems (reviewed in Refs [1,2]).

Biological polymers are capable of supporting complex higher order biological functions and are able to be synthesised by organisms in situ. It is this group of complex, functional polymers that inspire the quest of biomaterials researchers to produce materials capable of repairing, replacing or the ultimate, regenerating tissues and organs in humans. Table 1.1 outlines the four main types of natural polymers and their characteristics and functions.

Looking to the past it is clear that humans have always modified available biological materials as ready resources for producing tools, clothing, medicines, food and shelter. The use of animal hides for clothing, building shelters and constructing watercraft are examples of how these versatile biological polymers have been manipulated for thousands of years to produce useful items. Although lipids, such as autologous fat, and deoxyribose nucleic acids (DNA) have been explored for surgical and pharmaceutical applications, there are limited examples of commercialisation of medical devices based on these polymers. The focus herein will be on protein and carbohydrate polymers, the primary constituents of extracellular matrix (ECM), which are the most commonly applied in biomedical devices.

Table 1.1

Four main types of natural polymers and their characteristics and functions

Polymer	Sources	Characteristics/functions	Device/medical applications
Proteins	Animal tissue such as from bovine, porcine and ovine sources Tissue used...

Table of contents

• Cover image
• Title page
• Table of Contents
• Related titles
• Copyright
• List of contributors
• Woodhead Publishing Series in Biomaterials
• Part One. Introduction and fundamentals
• Part Two. Coatings and surface modifications
• Part Three. Biosynthetic hydrogels
• Part Four. Conjugated conducting polymers
• Index