Chirila / Harkin Biomaterials and Regenerative Medicine in Ophthalmology

1. Auflage 2009
ISBN: 978-1-84569-743-3
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: 6 - ePub Watermark

E-Book, Englisch, 560 Seiten

Reihe: Woodhead Publishing Series in Biomaterials

With an increasingly aged population, eye diseases are becoming more widespread. Biomaterials have contributed in recent years to numerous medical devices for the restoration of eyesight, improving many patients' quality of life. Consequently, biomaterials and regenerative medicine are becoming increasingly important to the advances of ophthalmology and optometry. Biomaterials and regenerative medicine in ophthalmology reviews the present status and future direction of biomaterials and regenerative medicine in this important field.Part one discusses applications in the anterior segment of the eye with chapters on such topics as advances in intraocular lenses (IOLs), synthetic corneal implants, contact lenses, and tissue engineering of the lens. Part two then reviews applications in the posterior segment of the eye with such chapters on designing hydrogels as vitreous substitutes, retinal repair and regeneration and the development of tissue engineered membranes. Chapters in Part three discuss other pertinent topics such as hydrogel sealants for wound repair in ophthalmic surgery, orbital enucleation implants and polymeric materials for orbital reconstruction.With its distinguished editor and international team of contributors, Biomaterials and regenerative medicine in ophthalmology is a standard reference for scientists and clinicians, as well as all those concerned with this ophthalmology. - Reviews the increasingly important role of biomaterials and regenerative medicine in the advancement of ophthalmology and optometry - Provides an overview of the present status and future direction of biomaterials and regenerative medicine in this important field - Discusses applications in both the anterior and prosterior segments of the eye with chapters on such topics as synthetic corneal implants and retinal repair and regeneration

Professor Traian Chirila is a senior scientist at the Queensland Eye Institute, Australia. Professor Chirila has over thirty years experience in polymer science and biomaterials and is highly respected for his ongoing contribution to the field of ophthalmology.

Autoren/Hrsg.

Chirila, Traian

Harkin, Damien

Leseproben

1

An introduction to ophthalmic biomaterials and their application through tissue engineering and regenerative medicine

T.V. Chirila    Queensland Eye Institute, Australia

Abstract

This chapter presents a brief history of the development of ophthalmic biomaterials. Particularities in the development of ophthalmic biomaterials are discussed and some of their historic priorities within the general field of biomaterials are revealed or emphasized. The chapter then discusses the role and integration of ophthalmic biomaterials in tissue engineering and regenerative medicine applications.

Key words

ophthalmic biomaterials

polymers

tissue engineering

repair

regenerative medicine

1.1 Introduction

The ultimate goal of the research and development of materials (other than drugs) for applications in medicine, which we call biomaterials, has always been to emulate natural materials. Since the natural target for biomaterials, i.e. our body's tissues and organs, is exceedingly complex, it is not surprising that in many instances the laboratory-made materials cannot match in their performance the natural entities they are meant to augment or replace. This is obviously different from the development of materials for industrial applications, which usually perform better than their natural counterparts (if the latter exist), and also evolve relatively fast, unhindered by biological constraints. For too long, an acceptable end-performance in the short term was the main requirement from a biomaterial, with little attention paid to changing its bulk and/or surface properties through the manipulation of composition and/or structure, in order to maximize the clinical outcome. Over the past six decades or so, however, the progress in bringing the properties and functionality of biomaterials close to those of their biological targets has been remarkable. While the above statements are also valid for ophthalmic biomaterials, their development has shown some particular features. The general developments in the field of biomaterials have customarily been gauged through the achievements in the branches of orthopaedic biomaterials and – to a lesser extent – biomaterials for cardiology while the progress of ophthalmic biomaterials has usually been ignored or seldom presented.

There are many definitions of the concept of ‘biomaterials’, all conveying essentially the same message (Ratner et al., 2004). Nevertheless, the term can also be used for ‘biological materials’, and attempts have been made to reconcile such dual meaning (Nerem and Sambanis, 1995). I shall not delve further into terminological aspects except for warning against some unacceptable inconsistencies such as: the use of ‘biopolymer’ instead of ‘biomaterial’; using the term ‘biomaterials’ exclusively for natural biological materials or, worse, to describe specifically biological matter deposited on non-biological substrata; and the more recent use of the qualifier ‘biosynthetic’ to designate a biomaterial resulting from the combination of a biopolymer with a synthetic polymer. In my role as an editor, I devoted much attention to avoiding such ambiguities throughout this book.

During the last two centuries, a large variety of biomaterials have been reported including metals, minerals, ceramics, wood, biopolymers and synthetic polymers. Most materials to be placed in the eye must be transparent, and this prerequisite is indeed unique to the ophthalmic biomaterials. Consequently, the focus of this book will be synthetic polymers, biopolymers (as such or modified), and combinations of the two, as the other materials are not normally transparent. Although no longer in use today, glass and quartz were the biomaterials of choice for ophthalmic applications before polymers became available, for instance in artificial corneas (Chirila et al., 1998; Chirila and Hicks, 1999; Chirila et al., 2005) and contact lenses (Feinbloom, 1932; Dallos, 1936; Heitz, 1984; Barr and Bailey, 1991). Opaque materials, such as ceramics, may still have minor uses in the eye, but only at locations outside the vision pathway.

1.2 Development of ophthalmic biomaterials: a brief history

In discussing here the evolution of ophthalmic biomaterials I will avoid the rather disconcerting trend of regarding, and even formally citing, biblical stories and anecdotal sources involving saints or other mythical characters, as scientific literature allegedly documenting some sort of respectable antiquity of the disciplines of biomaterials and tissue engineering. With all due respect to anyone's personal beliefs, these sources clearly do not constitute scientific evidence.

The eye is an organ of great complexity, yet it is more accessible to medical observation and surgical manipulation than most of our organs. This probably explains why the eye was the organ in which the first transplantation of donor tissue was successfully performed in humans (Zirm, 1906). Rather inexplicably, Zirm's transplantation of a donor cornea is still not recognized as being the first organ transplantation from a human donor to a human recipient. This accolade is usually reserved for the kidney transplantation reported much later (Murray et al., 1955), even though the latter was performed in identical twins, while the former involved non-related human subjects. However, prior to the episode of corneal transplantation, the eye was also the organ where foreign materials were implanted for the first time with the purpose of fulfilling, in today's terms, a role as biomaterials. In 1862, Onofrio Abbate, an Italian ophthalmologist practising in Cairo (Hirschberg, 1991), presented his experiments with an artificial cornea at the Periodical International Congress of Ophthalmology in Paris. This report was published in the following year in the congress proceedings, a publication that is virtually impossible to obtain nowadays. Fortunately, details of Abbate's work are available in one of the early reviews on artificial cornea (Forster, 1923). His keratoprosthesis was made from a glass disk encased within a skirt of two successive rings, the first made of gutta-percha and the second of casein. Both are natural polymers: gutta-percha is the trans-isomer of natural rubber isolated from trees of the genera Palaquium and Payena (Malaya), and casein is a mixture of phosphoproteins precipitated from milk or cheese. The concept of this device illustrates Abbate’s remarkable anticipation of the need for a skirt made from a material different from that used in the central zone (in this case, glass), in order to promote biointegration. His choice of the skirt materials was, however, not the most appropriate, as casein is brittle and gutta-percha becomes so on exposure to air and light. The device was maintained in animal corneas for no longer than one week. At the end of the same century, Lang implanted spheres fabricated from an artificial material (celluloid) as replacements for the enucleated eye globes (Lang, 1887). Strictly speaking, the socket implant is a cosmetic prosthesis. Soon afterwards, however, the first attempt ever to use a man-made material as a functional prosthesis took place in Germany, when – unaware of Lang's work – Dimmer made an artificial cornea (or keratoprosthesis) from celluloid and implanted it in four human patients (Dimmer, 1889; Dimmer, 1891). Celluloid, the first commercial plastic developed in the world, is a blend of nitrocellulose (a modified biopolymer), camphor, and certain stabilizing agents, therefore not actually a fully synthetic polymer. Regardless, this material was not a fortunate choice, as Dimmer's keratoprostheses were rejected within a few months.

The use of fully synthetic polymers as implantable ophthalmic biomaterials eventually occurred about half a century later, starting with poly(vinyl alcohol) gels inserted as socket implants (Thiel, 1939; Beyer, 1941), followed by the first artificial corneas made of poly(methyl methacrylate) (PMMA) (Wünsche, 1947; Franceschetti, 1949; Kuwahara, 1950; Györffy, 1951), a landmark not exempted from some controversy regarding priority (Chirila and Crawford, 1996), and culminating with the much better known and undisputed development of Ridley's PMMA intraocular lens (IOL) (Ridley, 1951; Ridley, 1952a; Ridley, 1952b). A few years later, poly(1-vinyl-2-pyrrolidinone) became the first synthetic polymer to be implanted in the vitreous cavity as a vitreous substitute (Scuderi, 1954; Hayano and Yoshino, 1959). In parallel developments, synthetic polymers also aroused the interest of the contact lens manufacturers. Feinbloom was the first to use glass (central part) in combination with commercially available synthetic polymers (peripheral part) in scleral contact lenses, and PMMA was among the polymers he proposed (Feinbloom, 1937; Feinbloom, 1940). It is not known with certainty who introduced the first scleral contact lenses made entirely from PMMA, as the unfolding of the subsequent events becomes blurred, an unfortunate result of the fact that the contact lens was perceived from the very beginning as a fast-profit-generating device. As a consequence, the research and development activities were generally carried out in the laboratories of the manufacturers, and the field became...