Biotextiles as Medical Implants

M W King, B S Gupta, R Guidoin

• Publisher: Woodhead Publishing
• Year: 2013
• ISBN:
  9780857095602
• Topic: Technology & Engineering
• Subtopic: Biomedical Science
• Index: Technology & Engineering

Textiles play a vital role in the manufacture of various medical devices, including the replacement of diseased, injured or non-functioning organs within the body. Biotextiles as medical implants provides an invaluable single source of information on the main types of textile materials and products used for medical implants. The first part of the book focuses on polymers, fibers and textile technologies, and these chapters discuss the manufacture, sterilization, properties and types of biotextiles used for medical applications, including nanofibers, resorbable polymers and shaped biotextiles. The chapters in part two provide a comprehensive discussion of a range of different clinical applications of biotextiles, including surgical sutures, arterial prostheses, stent grafts, percutaneous heart valves and drug delivery systems.This book provides a concise review of the technologies, properties and types of biotextiles used as medical devices. In addition, it addresses the biological dimension of how to design devices for different clinical applications, providing an invaluable reference for biomedical engineers of medical textiles, quality control and risk assessment specialists, as well as managers of regulatory affairs. The subject matter will also be of interest to professionals within the healthcare system including surgeons, nurses, therapists, sourcing and purchasing agents, researchers and students in different disciplines.

• Provides an invaluable single source of information on the main types of textile materials and products used for medical implants
• Addresses the technologies used and discusses the manufacture, properties and types of biotextiles
• Examines applications of biotextiles as medical implants, including drug delivery systems and stent grafts and percutaneous heart valves

Part I

Technologies

1

Manufacture, types and properties of biotextiles for medical applications

B.S. Gupta, North Carolina State University, USA

Abstract:

Textiles are known to have unique properties that lend themselves to use in many different types of technical products, among which perhaps the best known are medical materials. Presented in this chapter are aspects of polymer, fiber and textile science that should serve as useful background knowledge of the materials used in constructing products and whose in vitro and in vivo physical and mechanical performances are discussed in this book.

Key words

polymer

fiber

wet spinning

dry spinning

melt spinning

dry-jet wet spinning

emulsion spinning

gel spinning

heat setting

crimping

false-twist texturing

fiber properties

characteristics of fabrics

1.1 Introduction

Although textiles have been used in medicine since as long ago as 2000 BC, it is only after the advent of synthetic polymers that biomaterial scientists have recognized the unique properties that fibrous polymers possess and the unique potential they present for use in the broad field of medicine. Primarily, this is because polymer-based materials are lightweight, flexible and, on a weight-for-weight basis, exceptionally strong. Since the majority of fibers are manufactured from pre-existing or synthesized polymers, they can also be formed in different cross-sectional shapes and sizes, and oriented and crystallized to different levels that greatly extend their potential applications. One polymer can also be alloyed with another polymer and/or chemically or physically modified to further vary its performance characteristics.

For these reasons there are applications for fibrous polymers in many different types of medical products:

• absorbent materials for blood and other fluids resulting from injury, surgery or incontinence;

• protective gowns, masks and covers for patients, nurses and doctors;

• dressings and bandages for treating and managing wounds;

• fabrics for repair of fractures and rehabilitation of injured tissues;

• many different types of prostheses to serve as substitutes for damaged or failing organs.

Among the latter, some relatively well-known products are surgical sutures, arterial and stent grafts, hernia and prolapsed repair meshes, tendon and ligament prostheses, heart valves, and heart support devices. These are examples of flexible textile-based structures. However, rigid polymers are used as orthopedic implants for repairing or replacing joints and bones. Currently, fibrous materials are also attracting interest for use as moulds or scaffolds for engineering tissues.

Several different polymers, natural as well as synthetic, are used for making fibers to serve this important industry. Fibers can be both bio-absorbable and nonabsorbable and of different hydrolytic stabilities. Textile structures employed in making medical products include braided, knitted, woven and nonwoven fabrics. This chapter provides an overview of textile materials used in medicine in general. It is not restricted to the materials used primarily in implants, but discusses all materials that have found some application in medicine. An understanding of the characteristics of the available raw materials and the assembly structures that can be formed from them can be useful not only for optimizing the performance of current products but also for engineering new products. In essence, this chapter covers aspects of polymer, fiber and textile science that should serve as useful background knowledge of the materials used in constructing products and whose in vitro and in vivo physical and mechanical performance is discussed in the other chapters of the book. The information provided is introductory; however, a list of suggested works is included after the references, which cover the selected topics in much greater detail.

1.2 Fiber structure

The first biofiber to be produced was rayon, which was manufactured from an existing cellulose polymer available in the form of wood. Accordingly, the fiber is termed regenerated because the cellulose chains already existed in wood. A modified cellulose fiber, cellulose acetate, also regenerated, followed, which was produced by changing the chemical nature of the cellulose so that about two of the three existing pendant groups (OH) were replaced with another group (CH₃COO). The vast majority of known manmade and commercially successful fibers are, however, built from small chemical compounds based on petroleum, by first synthesizing chains and then extruding the resulting polymer into fiber.¹

Innovative structures covering different cross-sectional shapes, including hollow, and different sizes, including microdenier or micrometer, or even smaller than this in diameter, could be developed in manufactured fibers. By co-polymerizing, the chemistries of two different monomer compounds could be combined to form a polymer chain with new properties. Likewise, two different polymers could be co-extruded through the same orifice to form an alloy or a bicomponent fiber. These are, therefore, truly synthetic fibers, which cover a broad range of sizes and shapes and a very wide range of mechanical and physical properties.

The building block of a fiber is polymer, which consists of long chain molecules, made up of monomer units linked end to end by covalent bonds. A chain may contain from about a hundred to several thousand of these units, which determine the chain length and its molecular weight. Usually, the greater the molecular weight the greater the thermal stability and the strength. Different polymers have repeat units that differ in chemical constitution, size, shape and functionality; these determine a polymer’s chemical properties and potential physical and mechanical properties. The latter two also depend greatly on chain length, configuration, orientation and packing.

The natural polymers mentioned above are synthesized and grown into fibers by nature. Cotton, wool and silk are some examples. Wood is produced similarly, but not being in a form suitable for use as a textile fiber, it must be chemically modified to produce an appropriate solution, which can then be extruded into a fiber. Rayon and cellulose acetate are examples of this process.¹ Synthetic materials, on the other hand, must be first polymerized into chains, by linking small molecules together end to end, and then extruded into fibers. Chains are built by either a condensation or an addition process.² Nylon and polyester are examples of polymers synthesized by condensation, whereas polyethylene, polypropylene, acrylic and polytetrafluoroethylene (Teflon®) are some examples of polymers prepared by the addition process.

1.3 Formation of synthetic fibers

Many polymers have been produced by the plastics industry, but only a few can be converted into useful fibers. This is because the fiber-forming polymers must be linear, have simple or polar side groups, be meltable or dissolvable in acceptable solvents, and be orientable. The polymers that meet the criteria are extruded into fibers using one of the available methods of spinning. After synthesizing, the polymers are often in the form of powder or chips. These are either reacted with suitable chemicals or melted to cause chains to disentangle and flow freely. The fluid, that is, the solution or the melt, is then extruded into fine streams by forcing the polymer through one to thousands of holes of the required diameter in a spinneret. The streams then solidify to yield a fiber. The three principal methods conventionally used to extrude fibers are wet spinning, dry spinning and melt spinning. Some polymers are unique and require special methods for extruding them into fibers, three of which are dry-jet wet spinning, emulsion spinning and gel spinning. Br...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Contributor contact details
• Woodhead Publishing Series in Textiles
• Preface
• Introduction
• Part I: Technologies
• Part II: Applications
• Index