Biologically Inspired Textiles

A Abbott, M Ellison

• Publisher: Woodhead Publishing
• Year: 2008
• Print ISBN: 9781845692476
• eBook ISBN: 9781845695088
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

Biomimetic materials are those inspired from nature and implemented into new fibre and fabric technologies. Biologically inspired textiles explores the current state of the art in this research arena and examines how biomimetics are increasingly applied to new textile technologies.Part one discusses the principles, production and properties of biomimetics. Chapters include recombinant DNA technologies and their application for protein production, spinning of fibres from protein solutions and structure/function relationships in spider silk. The second part of the book provides a review of the application of biomimetics to a range of textile applications, including the design of clothing and self cleaning textiles.Written by a distinguished team of international authors, Biologically inspired textiles is a valuable reference for textile technologists, fibre scientists, textile manufacturers and others in academia. - Discusses the principles, production and properties of biomimetics - Reviews the application of biomimetics to a range of textile disciplines - Chapters explore recombinant DNA technologies, spinning of fibres and structure/function relationships in spider silk

Part I

Biomimetic principles, production and properties

1

Recombinant DNA methods applied to the production of protein-based fibers as biomaterials

F. Teulé; R. Lewis University of Wyoming, USA

W. Marcotte, Jr.; A. Abbott Clemson University, USA

Abstract

The protein compositions of selected high-performance biological materials such as silks, collagen and mussel byssus threads are reviewed. The possible roles of key amino structural motifs present in these fibrous proteins are outlined. Experimental investigation of structure/function relationships in fibrous proteins is discussed. More specifically, the structural characterization of artificial silk proteins, produced through the expression of native silk cDNAs, synthetic silk gene analogs or designer silk genes in different expression systems, is reviewed in detail. Finally, the most popular and most successful unicellular or multicellular expression systems available for the production of such fibrous proteins are described.

Key words

expression of native or synthetic silk gene analogs

structural characterization

recombinant silk proteins

biological materials

expression systems

1.1 Introduction

Biological organisms produce a wealth of natural fibrous polymers that have evolved to achieve highly specialized roles and to allow organism adaptation and survival. Some of the more interesting fibrous materials such as wool, silks, skin, cartilage and tendons are composed of fibrous proteins.

The literature is replete with details on the compositions, structures, mechanical and other physical and chemical properties of many of these protein-based biomaterials. This richness of information, along with scientific progress in the fields of genetic engineering and materials science, make it feasible to realize the production of biomaterials using recombinant DNA technologies.

It is the intent of this review to touch upon much of the rationale and methods for creation of genetically engineered systems for the production of fibrous protein polymers. We will focus on the utilization of spider silk gene mimics as a demonstration of a successful design, implementation and production scheme.

1.2 Biomimetics and protein-based biomaterials

Protein-based materials or protein fibers were thought for a long time to be a unique characteristic of the animal kingdom. However, such fibrous proteins have since been identified in plants. In wheat, a large, highly elastic storage protein called gluten, important in the expansion or rising of wheat-based doughs, was recently characterized as one of the first plant fibrous proteins (Tatham and Shewry, 2000).

The basic components of these natural fibrous materials are structural fibrous proteins. Such proteins are found in hair, tendons, cartilages, skins, arteries, muscles of mammals or in cuticles and silks of many arthropods. The individual proteins that make up these fibers or fibrous materials are of a specific sequence and often share structural amino acid motifs from one type of protein to another. In addition, many of these fibrous proteins have the ability to self-assemble, in an ordered manner, into a supramolecular network. The resulting supramolecular structure is often insoluble and is maintained, depending on its origin, by a combination of intra- and/or inter-molecular cross-linking, hydrophobic interactions, hydrogen bonding and coulombic interactions. Cross-linking is often necessary to hold the ‘structure’ together and can be different in nature depending on the amino acid residues involved. The molecular architecture (sequence and composition) of the individual proteins forming the network and the level and types of cross-links involved determine the mechanical and physical properties of the final fibrous materials, and the sequence in which these fibrous materials are assembled may be equally critical.

All these bio-based polymers display exceptional mechanical properties. More importantly, they are biodegradable and, thus, are attractive as a potential source of exploitable, environmentally-friendly materials. However, engineering new bio-based fibers having desired or customized mechanical properties is extremely challenging. To achieve this goal, the molecular architecture of the molecules composing these fibers, as well as their assembly processes, need to be fully understood in order to control assembly in the manufacturing process. Protein-based fibers are very suitable for bioengineering and remarkable efforts are being made in this field to understand the structure/function relationships of protein polymers. Because of the availability of technologies allowing the manipulation of genes encoding proteins, the prospect of designing and manufacturing new, possibly customized, protein-based polymers seems within reach.

Although there are many diverse types of fiber proteins, we will limit our discussion primarily to silk and collagen proteins for the sake of brevity. However many of the rules that govern the structure/function relationships of these specific fibrous materials or fibers are relevant to others as well (e.g. elastins-, lamprinbased materials).

1.3 Characteristics of some natural protein-based materials

1.3.1 Homopolymers

Silks

Many arthropods such as insects (Lepidoptera), and arachnids (Araneidae) produce silks. These highly insoluble proteinacious fibers share several structural motifs and characteristics. The primary structures of the different silk proteins are usually highly repetitive and comprise combinations of crystalline structures (tightly packed β-pleated sheets with more loosely associated β-sheets) and amorphous regions (α-helices, β-spirals or ‘spacer’ regions) (Xu and Lewis, 1990; Beckwitt and Arcidiacono, 1994; Guerette et al., 1996; Simmons et al., 1996; Hayashi and Lewis, 1998). Although most silk-producing organisms may only produce one type of silk, some arachnids such as Araneidae spiders have a more complex spinning apparatus and are able to produce several types of silks (Peters, 1955; Lucas, 1964). In these spiders, the different silks originate from different silk glands and differ in both amino acid composition and mechanical properties. The wide range of mechanical properties exhibited by these different silks allow for their adapted use in various applications from web construction, prey swathing, safety line or dragline, to cocoon construction (Lewis, 1992).

The cocoon silk of moth larvae such as Bombyx mori (Bombycidae, Lepidoptera) is the main source of silk exploited by textiles industries. B. mori, like all lepidopteran caterpillars, possesses a pair of modified salivary glands (labial glands) that are responsible for silk production. This silk-secreting system is linked to an outlet by which the silk is pulled out as the worm moves its head from left to right following a figure-eight-shaped trajectory (Sehnal and Akai, 1990).

The fibrous core of B. mori cocoon silk is composed of a 350 kDa heavy-chain fibroin (H-fibroin, Bm-Fhc) and a 25 kDa light-chain fibroin (L-fibroin, Bm-Lc) covalently linked by disulfide bonds. These fibroins are also associated with a small glycoprotein of approximately 27 kDa (P25) but there is no evidence of covalent links (Tanaka et al., 1999a; Tanaka et al., 1999b). P25 may play a role in the transport of the two fibroins from the cells to the gland lumen. The heavy-chain fibroin is the fiber protein responsible for silk formation.

B. mori silk fibroins are characterized by a high glycine content. The fibroin primary sequence is highly repetitive and displays a noticeable (GA)_n motif containing glycine and alanine residues interspaced with serine-containing polyhexapeptide repeats GAGAGS and GAGAGX with X = Y or V (Zhou et al., 2000). The short GAGAGS repeat can form crystalline regions in both morphological states of silk studied: silk I and silk II. Silk I or ‘water soluble silk’ is obtained from the desiccated gland content without any mechanical disturbance (storage state of the fibroin) (Lotz and Cesari, 1979). The more stable silk II (β-silk fibroin) is observed in the spun cocoon fiber. Silk I is converted to silk II by mechanical stress or shearing that occurs when the fiber is being pulled out. The crystalline structure of silk II is viewed as extende...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright page
• Contributor contact details
• Woodhead Publishing in Textiles
• Introduction
• Part I: Biomimetic principles, production and properties
• Part II: Biomimetic applications in textiles
• Index