CERAMICS, CELLS AND TISSUES. BIOCERAMIC COATINGS FOR GUIDED BONE GROWTH

Prefazione - Indice

Prefazione

Before starting the publication of meeting-seminar proceedings we would like to express our appreciation for such a wide partecipation at this third meeting of technicians, researchers, physicians and surgeons who spare no effort in collaborating to obtain in a hard sector, such as this of biomedical field, remarkable results, The difficulties which arise in this field come mainly for its interdiscipliuary character, with different points of view, different semantics and different sensibilities, However the results obtained assume a high social interest. A hearthfelt thanks to our President, who believes in our enterprise and who, wherever we go, supports with great involvements our studies which, today, are reported in the most prestigious and specialized journals of the sector.
This third meeting-seminar on "Ceramics, Cells and Tissues" tackles the problem of ceramic coatings as guidance for bone tissues. Many european countries are represented here also thanks to the opportunity offered by the "Skeletal Implant" committe which gave its consent to our initiative by holding its session in Faenza in coincidence with this meeting-seminar.
We hope this meeting can prove very useful to all the comunity who works in this field, through a targeted debate between the medical applied and the materials science fields. So we shall be able, when we get back to our work, to compare various working methods and models aimed to solve problerns of such high social relevance.

Many kinds of surgical interventions are intended for a definitive stabilization of the implanted prosthesis. Generally these implants are mode with metallic or inert ceramic materials due to their suitable mechanical performances. Unfortunately these materials aro not able to offer good performances in giving rise to a reliable and stable joining with tissues, including among these bone tissue. Therefore a production of devices intended for a definitive stabilization need the presence of a substance able to render the surface of the device bioactive and bioconductive for the tissue to be regenerated. Bioceramic coating are one of the most reliable solutions to get it. The coating with active bioceramics of devices constituted with inert materials is very important to obtain bone growth and its joining to the device.
Definitively, in the 3rd «Ceramics, Cells and Tissues» meeting-seminar the "Bioceramic Coatings for Guided Bone Growth" will be the principal protagonist. From the numerous and very interesting scientific papers (53), some main guideliues are going to arise for the studies in the future of the biomaterials, specifically bioceramics:

• Reaction at the interface;


• Influence on tissues, particularly in the long term;


• Biotolerability of implants: in vitro and in vivo;


• Biostability of implants;


• Chronic adverse effects;


• Bioadaptability of implants;


• Materials in contact with blood;


• Some important chemical and physical characteristics;


• Biocompatibility of implants;


• Biofunctionality of implants;

and in particular:

• Biochemical interactions;


• Ions transport and analysis of the surfaces;


• Compactness and remodelling;


• Mechanical stroogth;


• Wear;


• Degradation.

The most important factor (and to be studied with care) involved in the use of a biomaterial is the series of reactions its presence exerts at the interface material/tissue which has influence and interactive mutual effects between tissue(s) and material, particularly in the long term. Traditionally it was thought that an inert material was the most suitable for a prosthesis to avoid phenomena of tissue reactions; on the contrary the most advanced biophysical studies consider today the extreme relevance of the bioactive ceramics, but it is necessary to promote research on the biochemical mechanism used by tissues to adapt foreign objects to their needs.
We must know better the interface processes between material and tissue, verifying how the different chemical compositions may be correlated with the biological reactivity of the surrounding tissue.
The control of numerous and difficult parameters, the variables involved, the need for an interdisciplinary approach, the differences between the materials placed in contact with living tissues (whose universal laws are only partially known though we are improving our knowledge), all these factors make us anxious about the behaviour of coatings which surgeons have so confidentally applied to metal supports in the past too years.
Surgeons have in fact immediatcly believed that the biochemicai bonding established with bone tissue would guarantee not only protection against any toxic action from a support (particularly if based on metal alloy) as a result of wear, corrosion, or release of ions, but also a biological bonding for stable anchoring in the long terrn.
We unfortunately still do not have at our disposal decisive positive result publication that may justify the initial optimism and many of the experimentals carried out today are not so encouraging. The reason is that there has seldom been an involvment of all the competent fields of study to obtain a good prosthesis coated with bioactive ceramics. In fact there is decisive not only of a correct knowledge of the material and of its behaviour in contact with tissues, but also of the detailed biomechanical principles specific to the prosthesis and its covering (in terms of loads and unloads as well as of prosthetic biofunctionality in time) in compliance with norms (many still"in embrio"), benefitting both prosthesis users and those manufacturers interested in innovatively transfering a prototype from the laboratory into mass production to give surgeons a highly technological but reasonably priced implantable in patients for the longer possible time. However, if we examine the literature of the last 3 years in relation to interfaces (not only at a micrometric but also at a macrometric level) with tissue, generally in the presence of (sometime negligible) microphases, we must note that the perforrnated coatings (those already commercially available produced by plasma spraying) do not always give rise to clinically acceptable results unless they are carried out by scientifically studied tested techniques according to the instructions of medical scientists, and bioengineers dealing with the most sophisticated techniques of biomechanical engineering and implant engineering. All the partecipants in this meeting-seminar must therefore responsably try to answer the following question in order to find the best solution (in terrns of coating of a support) in the most professional way: "what happened - and what is happening - to all the coated implants commercialized over the last ten years?». According to the most optimistic hypotheses, the implants are destined to loose their coating in the long term, and the support (we hope based on titanium) will therefore eventually come in contact with bone (Smith, 1993). What we believe is absolutely necessary, in future, in order to better guarantee a product is without doubt to endeavour towards the creation of universal and well-defined normatives.



A. Ravaglioli and A. Krajewski

IRTEC-CNR, Faenza (Italy)


Faenza, May 2, 1996