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History of Biomaterials

1.1. Introduction

The aim of this chapter is to give an outline of the long, progressive and amazing history of biomaterials.

To begin the chapter entitled "History of biomaterials" it is necessary to give a first simple definition of the term "biomaterials":

"Biomaterials are materials intending to supply all or part of a deficient organ".

This quite restricted definition - which will be improved throughout this book - gives an idea and an overview of the goals, needs and even potential applications of biomaterials. We will discover that even through the use of biomaterials dates from a very long time ago, the notion of biomaterials science emerged in the 1960s due to the agreement of a few of open-minded scientists wishing to build this new domain of science. Then, the word "biomaterials" started to be used at the same time as the birth of learned societies in this domain: European and American researchers worked a lot to build the American and European Societies for Biomaterials. This will be developed later.

1.2. The evolution of biomaterials: several generations

Today, we can briefly differentiate four generations of biomaterials:

Even if these four generations of biomaterials have been identified, the duration of each one is very variable. The last 20 years have led to so much progress in the disciplines involved in biomaterials science that it is very difficult to schedule the duration of the last generation, as well as imagining what the next one will be.

The use of biomaterials for therapeutic purposes such as the repairing of wounded organs began a very long time ago. It was at first strictly linked to the accessibility of people to "materials", their knowledge of the materials' properties as well as the methods and processes they used to transform and develop them. As it is difficult to date the beginning of the uses of biomaterials, this chapter will intend to describe what we know about the first materials used with the aim of repairing an organs or a part of an organ. We will also discover the unlimited imagination of human beings as well as the diversity of materials they used as "biomaterials" to prevent a deficiency and/or to repair unhealthy or wounded tissues or organs.

To date, the use of biomaterials seems to have started from antiquity and probably since the origins of human beings. The evidence of their use as implants or prostheses were mainly discovered during the two last centuries on human skeletons or skulls during the excavations of sites which were attributed to different civilizations of antiquity: Egyptian, Roman, Greek and Etruscan. It is worthy to note that the literature is prolix about the "probable" uses of biomaterials for dental applications by the antique civilizations and even the following ones. This is probably due to the fact that since antiquity, the proof of its use for dental applications were the most numerous and/or variously encountered: wire to link teeth together, teeth implants, filling materials, etc. In contrast, despite the full of imagery vision of the replacement of injured or amputated limbs by wooden pieces, it is quite difficult to find very ancient examples of other medical applications and real uses of biomaterials such as in ophthalmology, vascular surgery, orthopaedic surgery, etc. Such examples would probably have taken place a long time after antiquity. The question which arises is: did these materials really exist as biomaterials - therapeutic purposes to replace missing teeth or limbs of living men or were they only used to improve the esthetical aspect of remains and of graves? The response to the last question is of importance to certify the exact beginning of the use of biomaterials for organ repairing.

Only historians can date the beginning of the existence of "biomaterials" and bring the proof of its literal use, that is material to mitigate a deficiency of all or part of a hurt or wounded organ. As a matter of fact, recently questioned historians said that they had never heard about the use of biomaterials in antiquity. Despite this interrogation something in the history of biomaterials sounds very strange. Whereas in the first civilizations human beings had yet to imagine their uses and found the necessity of their use in aiding deficiencies of some of their organs or parts of organs, today the term "biomaterials" is neither correctly or currently used except for the "specialists of the domain" although everybody in his/her life will have to face its use and to understand how it works. Therefore, the existence of biomaterials is very ancient while the science of biomaterials appeared very recently.

From the outset, human beings resorted to biomaterials to improve their conditions of health. It is very difficult to make a clear and precise classification of the uses of biomaterials because much is missing and it is clear that most of the work still has to be achieved. The aid of the historian community would be helpful to enlist, to propose and to validate a classification for: a time schedule; application of the device; choice of the material. A proposed "easy classification" is made here, looking for different materials, which were used by human beings in various applications; then this classification will mix applications and materials. The aim is to show that applied research in the biomaterials field started with the existence of men and was the fruit of their imagination and of their intelligence.

1.3. Was gold the first "biomaterial"?

Was gold the first "biomaterial"? The response to the question is not so simple. The use of materials for dental repair could have started in antiquity when men used diverse natural organic and/or inorganic materials such as bones, animal teeth or even wood to replace missing teeth.

Based on the literature, one of the "first biomaterials" could have been a hybrid material made of an animal tooth linked to the patient's teeth by a gold wire. This "first" dental prosthesis had been attributed to the Etruscan civilization and could be dated around 2,600 years ago. It was used to replace the upper incisors with a cow tooth fixed to the neighboring teeth by a gold wire.

The use of gold is not surprising since, gold being a noble metal, it exhibits a relative chemical inertness and an excellent resistance to chemical attacks because it is not sensitive to oxidation. This explains its prolonged use in dental applications and the fact that this metal is still considered as a "gold standard" in dentistry. The "chemical" properties added to its ductility and malleability easily explained the importance of its use in many medical applications.

The way gold material was used for dental repairing seemed to be very different between the occidental and the oriental societies [SCH 98]. The differences reported by Bardinet in his history of dental prosthesis [BAR 90] were shown on skeletons and found to be technical in nature. Then, despite these different techniques carried out, Bardinet concluded and assumed that the unique and common aim of using gold was to consolidate teeth anchorage: gold is one of the first "biomaterials" used in former civilizations.

Due to these reported observations, studies and conclusions, until the 18th century, dental prostheses consisted of human teeth (extracted from patients) bound by golden wire ligatures. It is necessary to wait to the end of the 19th century for the appearance of gold teeth prostheses elaborated by imprint and casting techniques [VAN 85]. The dentist Aguilhon de Sarran from the "French Society of Stomatology" proposed this application of gold in 1903: having taken a tooth imprint, he melted gold and poured it into the mould to obtain an inlay in gold. Some years later, Solbrig developed this technique; today the gold inlay remains the oldest effective closing technique. This active and fruitful period in terms of innovation in dental repair was followed by the development of the dental crown technique; for its many advantages and lack of weaknesses, gold-based alloys were commonly used. Today, and mostly for aesthetic reasons, the metallic parts (gold or other metallic materials) are masked by using ceramic materials since their esthetical appearance imitates natural teeth well.

Therefore, to conclude on gold, this metal appears to be one of the first and principal materials used in by ancient civilizations and, incredibly, it is still used today.

Despite gold being used in dental repair, the examples are numerous and varied on the use of other materials than gold for...