[The cryopreservation of composite tissues: principle, literature review and preliminary results of our own experiments].

The cryopreservation of cells and human tissues has generated a great interest from the scientific community since 1949 when the cryoprotective activity of glycerol was discovered. For a homogeneous cellular group or a one-layer cellular tissue it is easy to define the optimal technique conditions of its cryopreservation (cryoprotective agents, speed and steps of freezing, speed of warming). It is considered successful when a high recovery of the cellular structures and tissue components after warming is achieved. The cryopreservation of a whole composite tissue is less easy to obtain. Each tissue presents its own parameters and its own reactivity during the cryopreservation process. The challenge consists in, on the one hand, the selection of the ideal cryoprotective agents'combination which can fit the needs of the different tissues and on the other hand, the definition of adequate technical parameters. The aim of this work is to demonstrate the feasability to cryopreserve a composite tissue in order to carry out surgical reconstructive procedures of particular anatomical and functionnal units (metacarpo-phalangeal and proximal interphalangeal joints, flexor system apparatus, extensor system, median nerve, etc.) with complete revitalization of the allograft using vascular microsurgical procedures. To do so, our present work is divided into three different parts. The first chapter deals with the fundamental principles of the cryobiology of biological structures with special interest in the liquid transfer process between the extracellular and intracellular compartments and ice initiation and agregation during the freezing process. The different physical and chemical reactions and their consequences on the biological tissues are described according to the different cryoprotective agents used, should they belong to the extracellular or intracellular cryoprotective groups. The second chapter makes a review of the litterature concerning the results of all experiments made on the cryopreservation of the different tissue structures as skin, vessels, bones, cartilage, periosteum, nerves, cornea, on the one hand, and the different organs as kidneys, liver, heart, trachea, lung, parathyroid glands and ovaries, on the other hand. We are reporting the results of these experiments focusing on the immunomodulation effect of cryopreservation on the antigenic response of biological structures. These experiments were made either on organs or on the cells involved in the immunogenic process. In the third chapter, we are reporting the results of our experiments carried out in the Aquitaine Hand Institute in the field of the cryopreservation of the xenografts of digital segments on the rabbit. These digital segments were cryopreserved, then warmed and revitalized through vascular microsurgical techniques. The preliminary results are very encouraging and pave the way to the allotransplantation of cryopreserved composite organs in our common surgical activity.