Evaluation of an experimental periodontal ligament for dental implants.

To improve the devices used in dental implantology, a new experimental supporting element has been developed. The device, made of titanium, poly(methylmethacrylate) and Dacron tissue, has been tested for the osteointegrability of its outer Dacron coat by implants in mandibular bone of rabbits. The Dacron filamentous tissue became incorporated by the bone at 3 month post-implantation. This might provide a reliable mechanical anchorage of the device and a barrier against epithelial proliferation and microbial contamination. Preliminary results relating to in vitro evaluation of the poly(methyl methacrylate)-Dacron fixation strength predict favourable mechanical behaviour at this interface and in the complete implanted device.

Implant effects on polyurethane and silicone cardiac pacing leads in humans: insulation measurements and SEM observations.

Recently, polyurethane cardiac pacing leads have been under discussion because of some failures, probably due to modification of surface insulating properties. In order to verify the reliability of polyurethane versus silicone rubber as coating material, the authors, starting from previous clinical research, have carried out a study of electrical insulation related to implant time. At the same time the outer and inner lead surfaces have been submitted to scanning electron microscope (SEM) analysis. The results show, for the polyurethane leads, a significant increase in the leakage or currents in explanted samples, and a significant degradation (cracking) of the outer surfaces.

Analysis of the mechanical properties of in vitro reconstructed epidermis: preliminary results.

Human epidermis can be reconstructed in vitro and is currently used in autografts for the treatment of severe, extensive burns and pigmentation disorders. However, there are neither international standards nor a common nomenclature for engineered tissues. The paper discusses the results of a preliminary study on human cultured epidermis to assess its mechanical tensile strength, and to eventually establish mechanical evaluation criteria that will enable test and comparison of the behaviour of different engineered tissue products. To perform uniaxial tension tests a traditional testing machine was adapted, and dedicated sample holding frame and grips designed.

A 5-year analysis of organ donors and recipients in Italy.

This article describes the improvement of organ donation and transplantation in Italy during 1995-1999. In 1999, the mean number of donors per million population reached 13.7 in Italy. In addition, an analysis regarding major characteristics of donors and recipients is presented, focusing particularly on donor characteristics that have changed in the past 5 years. Despite the encouraging results, further efforts are required to reach the European mean, which still remains higher than the Italian national mean. In particular, an increase of organ donation and procurement in regions with a poor activity in this field is crucial. A 1999 law on donation and transplantation should help in solving problems that continue to affect part of the nation, especially preparing the healthcare staff dedicated to organ retrieval to promote organ procurement.

[Statistical bases and models for the selection of kidney transplant recipients]. / Basi statistiche e modelli per la scelta del ricevente del trapianto renale.

The thesis of this study is that the use of discrete simulations is the most appropriate instrument to support the definition of a kidney allocation procedure. We first furnished a general description of what it means to run a simulation to solve the problems related to the study of the statistical characteristics of any population. In the second part of the paper we mathematically formalized the subject of our study: the statistical properties of waiting lists, allocation algorithm and transplants. The third part reported the results of several simulations we have done with the aim to show the potential of these methods at assessing the most appropriate adjustments for the optimization of any allocation scheme.

[Waiting lists for transplantation in Italy]. / Le liste di attesa trapianto in Italia.

To plan health services it is essential to gauge the needs. In transplant field in Italy, the first suitable data for waiting lists were collected in 1998. The data collected by Istituto Superiore di Sanità gave us a shot of patients field in waiting list at that time. We here analyse more significant data about heart, liver and kidney waiting lists. The situation is very different among north, centre and south of Italy: in South, where transplant activity is low, we found rare transplant centres, and most of patients prefer north centres. In kidney waiting list we found 1100 patients living in southern regions but registered in the waiting list of a different region. These data can help in planning development lines in Italy.

[The national program of pediatric transplantation]. / Il programma nazionale di trapianto pediatrico.

The national programme for paediatric transplants currently implemented at the Istituto Superiore di Sanità is one of the first results of the efforts devoted to the definition of an efficient co-ordination policy of the transplantation activity in Italy. Since 1997 the programme has allowed all transplant centres throughout Italy to share unified waiting lists for kidney, heart, lung and liver, which gives paediatric patients a much better possibility than with local waiting lists. We present the regulations, criteria and operative solutions adopted to make the programme work, and the analysis of the data collected in these three years. The analysis gives statistical information on the composition and evolution of waiting lists and transplants done, which may be useful in the continuous process of revision and improvement of the criteria for recipient selection.

Organ transplantation in Italy: analysis of donors and recipients.

The Istituto Superiore di Sanità (The Italian National Institute of Health) has been collecting information regarding organ donation and transplantation in Italy. Herein we describe organ procurement and transplant activity in Italy in the years 1992 1997 and show some of the characteristics regarding both donors and transplanted patients who received kidneys, hearts, livers and lungs. Although transplantation in Italy has been very difficult because of shortage of organ donors, national rates have been improving year after year. The present situation should ameliorate further to enable Italy to reach the same level of other advanced European countries.

Analysis of organ donation in Italy.

In 1995 the Italian Institute of Health began assembling information regarding organ donors, recipients, and transplants. Data on more than 3000 transplants were collected and recorded to date. In addition to characteristics of donors and donating hospitals, this article describes donation activity and organ procurement in Italy from 1992 to 1996. Despite the encouraging results, the donation situation in Italy remains a challenge due to the nonhomogeneous distribution of organ donation throughout the country. It is hoped that an increase in the rate of organ donation and procurement in some regions will enable Italy to reach the European mean.

VAD Biomer blood sacs: mechanical tests and ultrastructural observations.

Ventricular Assist Devices (VADs) are a support to the heart function and are used as bridge to transplantation for a brief period in patients awaiting a donor heart. They consist of two sacs with two artificial valves that allow blood flow, the whole connected to a specific electronic equipment. This study examines the performance of a segmented-polyurethane elastomer, namely Biomer, that has been extensively used to manufacture pneumatically actuated VAD blood sacs. Specimens obtained from three VAD blood sacs explanted from three human patients and specimens from one unimplanted blood sac were investigated for mechanical performance of the material and for the changes it undergoes as a result of mechanical stress and interaction with the surrounding biological environment. The application of tensile strength at break yielded no relevant differences between unimplanted and explanted specimens. Biomer exhibited a high elongation at break for both groups, with somewhat lower values for explanted specimens. SEM observations carried out on the inner surface--in contact with blood--of unstressed explanted specimens showed no thrombotic deposits, calcifications, microbial contamination or structural changes. The complementary broken surfaces of stressed specimens showed a distinctive fracture pattern.

Mechanical performance of dental amalgam--composite interfaces.

Composite veneering of amalgam is the most aesthetical solution to extensive direct tooth restoration and is applied with success in specific clinical situations. An in-vitro technique has been used to evaluate the mechanical performance of one amalgam bonded to four different composites. The amalgam-composite interfaces were subjected to tensile stress and shear stress at break tests, using dumb-bell and sandwich specimens in a PC-controlled electronic dynamometer equipped with innovative grips. Mean values were higher for tensile stress than for shear stress. Further studies and clinical experimentation will be necessary to explore the question of long-term reliability.

Biomechanical evaluation of cell-loaded and cell-free hydroxyapatite implants for the reconstruction of segmental bone defects.

Porous hydroxyapatite (HA) scaffoldings are currently used in tissue engineering for bone reconstruction. When this osteoconductive biomaterial is combined with osteoprogenitor cells, it acquires osteoinductive features which accelerate and improve bone formation in vivo. The aim of our study was to assess the mechanical properties of HA-bone complexes undergoing indentation tests, and relate stiffness to composition and structure as examined by micro X-ray. To this purpose, 35-mm tibia diaphyseal resections were performed in sheep. Gaps were filled using porous HA cylinders. Implants were loaded with autologous bone marrow stromal cells (BMSC); cell-free cylinders were used as control. After 8 weeks, bone tissue was found within the internal macropores of cell-loaded HA carriers, and in control implants, bone formation was mostly limited to the outer surface. As assessed by indentation testing the stiffness values of bone-HA composites were halfway between those of HA scaffoldings and tibia bone. Cell-loaded implants were stiffer than cell-free ones. In a cell-loaded implant we also analyzed the variation of stiffness along the main axis of the tibia.

Immunogold localisation of P-glycoprotein in supported lipid bilayers by transmission electron microscopy and atomic force microscopy.

In this study, purified P-glycoprotein molecules, a membrane drug pump responsible for the multidrug resistance phenomenon, were incorporated in model membranes deposited onto solid supports, according to the method described by Puu and Gustafson (1997). The insertion of proteins into planar supported model membranes is of interest, as the films are fundamental in biosensor applications and for the investigation of how proteins conform and aggregate in a lipid environment. In our investigation, two model membranes were prepared by transferring liposomes containing P-glycoprotein to different hydrophobic supports: (a) thin amorphous carbon films; (b) Langmuir-Blodgett lipid monolayers on mica. After the labelling of P-glycoprotein with two well-characterised monoclonal antibodies, MM4.17 and MRK-16, samples (a) were observed by transmission electron microscopy (TEM) and samples (b) by atomic force microscopy (AFM). The comparative analysis performed by TEM and AFM allowed us to demonstrate the successful insertion of P-glycoprotein in the model membranes and their stability under different environmental conditions (vacuum, air and water). P-glycoprotein appeared to maintain, after purification and insertion in lipid bilayers, a good part of its conformational features as shown by the P-glycoprotein segments bearing the specific monoclonal antibody epitopes.

Autologous bone marrow stromal cells loaded onto porous hydroxyapatite ceramic accelerate bone repair in critical-size defects of sheep long bones.

The ability of marrow-derived osteoprogenitor cells to promote repair of critical-size tibial gaps upon autologous transplantation on a hydroxyapatite ceramic (HAC) carrier was tested in a sheep model. Conditions for in vitro expansion of sheep bone marrow stromal cells (BMSC) were established and the osteogenic potential of the expanded cells was validated. Ectopic implantation of sheep BMSC in immunocompromised mice led to extensive bone formation. When used to repair tibial gaps in sheep, cell-loaded implants (n = 2) conducted a far more extensive bone formation than did cell-free HAC cylinders (n = 2) over a 2-month period. In cell-loaded implants, bone formation was found to occur both within the internal macropore space and around the HAC cylinder while in control cell-free implants, bone formation was limited mostly to the outer surface and was not observed in most of the inner pores. As tested in an indentation assay, the stiffness of the complex HAC-bone material was found to be higher in cell-loaded implants compared to controls. Our pilot study on a limited number of large-sized animals suggests that the use of autologous BMSC in conjunction with HAC-based carriers results in faster bone repair compared to HAC alone. Potentially this combination could be used clinically in the treatment of extensive long bone defects.