The effect of amphotericin B on the viability of cryopreserved human skin

International heart valve bank survey: a review of processing practices and activity outcomes

A survey of 24 international heart valve banks was conducted to acquire information on heart valve processing techniques used and outcomes achieved. The objective was to provide an overview of heart valve banking activities for tissue bankers, tissue banking associations, and regulatory bodies worldwide. Despite similarities found for basic manufacturing processes, distinct differences in procedural details were also identified. The similarities included (1) use of sterile culture media for procedures, (2) antibiotic decontamination, (3) use of dimethyl sulfoxide (DMSO) as a cryoprotectant, (4) controlled rate freezing for cryopreservation, and (5) storage at ultralow temperatures of below −135°C. Differences in procedures included (1) type of sterile media used, (2) antibiotics combination, (3) temperature and duration used for bioburden reduction, (4) concentration of DMSO used for cryopreservation, and (5) storage duration for released allografts. For most banks, the primary reasons why allografts failed to meet release criteria were positive microbiological culture and abnormal morphology. On average, 85% of allografts meeting release criteria were implanted, with valve size and type being the main reasons why released allografts were not used clinically. The wide variation in percentage of allografts meeting release requirements, despite undergoing validated manufacturing procedures, justifies the need for regular review of important outcomes as cited in this paper, in order to encourage comparison and improvements in the HVBs' processes.

The cryopreservation of composite tissues: Principles and recent advancement on cryopreservation of different type of tissues

Cryopreservation of human cells and tissue has generated great interest in the scientific community since 1949, when the cryoprotective activity of glycerol was discovered. Nowadays, it is possible to reach the optimal conditions for the cryopreservation of a homogeneous cell population or a one cell-layer tissue with the preservation of a high pourcentage of the initial cells. Success is attained when there is a high recovery rate of cell structures and tissue components after thawing. It is more delicate to obtain cryopreservation of composite tissues and much more a whole organ. The present work deals with fundamental principles of the cryobiology of biological structures, with special attention to the transfer of liquids between intra and extracellular compartments and the initiation of the formation and aggregation of ice during freezing. The consequences of various physical and chemical reactions on biological tissue are described for different cryoprotective agents. Finally, we report a review of results on cyropreservation of various tissues, on the one hand, and various organs, on the other. We also report immunomodulation of antigenic responses to cryopreserved cells and organs.

La cryopréservation de tissus composites: principe, revue de la littérature et expérience de l'équipe bordelaise

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.

Development and characterization of tissue-engineered aortic valves

Tissue-engineered aortic valves, known as recellularized heart valves, were developed by seeding human neonatal fibroblasts onto decellularized, porcine aortic valves. Recellularized heart valves were cultured up to 8 weeks in a novel bioreactor that imposed dynamic pulsatile fluid flow to expose the dermal fibroblasts to mechanical forces. Our data showed that, under static or dynamic flow conditions, dermal fibroblasts attached to and migrated into the decellularized, porcine valve scaffolding. The human cells remained viable as indicated by MTT viability staining. Gradual colonization of the decellularized porcine scaffolding by the human dermal fibroblasts was shown histologically by hematoxylin & eosin staining, immunocytochemically using a monoclonal antibody directed against prolyl-4-hydroxylase (an intracellular enzyme expressed by human fibroblasts synthesizing collagen), and quantitative digital image analyses. Thymidine and proline radiolabeled analog studies at 1, 2 and 4 weeks of individual leaflets cultured statically demonstrated that the human fibroblasts were mitotic and synthesized human extracellular matrix proteins, thereby supplementing the existing porcine matrix. The overall approach results in a heart valve populated with viable human cells. In the development of valves that perform in a similar manner as natural biological structures, this approach may present some unique benefits over current medical therapies.