Renato Toffanin

Articular cartilage repair in rabbits by using suspensions of allogenic chondrocytes in alginate

The feasibility of allogenic implants of chondrocytes in alginate gels was tested for the reconstruction in vivo of artificially full-thickness-damaged articular rabbit cartilage. The suspensions of chondrocytes in alginate were gelled by the addition of calcium chloride solution directly into the defects giving in situ a construct perfectly inserted and adherent to the subchondral bone and to the walls of intact cartilage. The tissue repair was controlled at 1, 2, 4 and 6 months after the implant by NMR microscopy, synchrotron radiation induced X-ray emission to map the sulfur of glycosaminoglycans and by histochemistry. Practically a complete repair of the defect was observed 4-6 months from the implant of the chondrocytes with the recovery of a normal tissue structure. Controls in which Ca-alginate alone was implanted developed only a fibrous cartilage.

Structural investigations of cross-linked hyaluronan

Structural properties of several cross-linked hyaluronan derivatives, obtained by scanning electron microscopy, monodimensional NMR microscopy and small angle X-ray scattering of synchrotron radiation, are presented and compared with those observed for non-modified hyaluronic acid, used as a reference material. The experimental results, obtained in different media, showed a consistent picture of the synthesized matrices. In particular, the presence of zones of denser polymeric material observed by electron microscopy resulted in a higher transversal relaxation rate of the bulk water protons as well as in a decrease of the diffusion coefficient obtained by NMR microscopy. Moreover, the presence of polymer junction zones gave rise to the appearance of a well-defined correlation peak in the pattern of intensity of the scattered X-radiation.

Collagen fibrils are differently organized in weight-bearing and not-weight-bearing regions of pig articular cartilage.

The magnetic resonance (MR) appearance of the weight-bearing (loaded) and not-weight-bearing (unloaded) regions in T(2)-weighted images of pig articular cartilage is different. On the hypothesis that this difference may be ascribed, at least in part, to a different collagen fibre organization in the two regions, this organization was studied using biochemical, histological, and X-ray diffraction methods. While the mean concentrations of collagen and of its cross-links were the same in the two regions, a regular small angle X-ray diffraction pattern was observed only for the habitually loaded tissue. It was also seen by light microscopy that the four typical functional zones were well displayed in the loaded cartilage whereas they were not clearly depicted in the unloaded tissue. Collagen presented a high concentration of fibrils forming an intricate and dense meshwork at the surface of both loaded and unloaded cartilage. A second zone of high collagen concentration was present at the upper layer of the deep zone of loaded cartilage. By contrast, this lamina of highly concentrated fibrils was lacking in unloaded cartilage and collagen fibrils appear thinner. Our study proves that the organization of collagen fibres is different for the loaded and unloaded regions of articular cartilage. It also suggests that this different organization may influence the MR appearance of the tissue. J. Exp. Zool. 287:346-352, 2000.

NOVEL BIOMATERIALS BASED ON CROSS-LINKED HYALURONAN: STRUCTURAL INVESTIGATIONS

ABSTRACT Structural properties of several cross-linked hyaluronan derivatives, obtained by electron microscopy, monodimensional NMR microscopy and low angle X-ray scattering by synchrotron radiation, are presented and compared with those observed for non-modified hyaluronic acid used as reference material. The experimental results, obtained in different media by the different techniques, showed a consistent picture of the synthesized matrices. In particular, the presence of zones of more dense polymeric material observed by electron microscopy resulted in a higher transversal relaxation rate of the bulk water protons as well as in a decrease of the diffusion coefficient obtained by NMR microscopy. Moreover the presence of polymer junction zones gave rise to the appearance of an additional correlation peak in the pattern of the intensity of the scattered X-radiation.

Short-TE projection reconstruction MR microscopy in the evaluation of articular cartilage thickness

Abstract. The aim of this study was to assess the potential of projection-reconstruction (PR) MR microscopy in the accurate measurement of cartilage thickness. Short-TE PR microimages were acquired at 7.05 T on bone-cartilage cylindrical plugs excised from four regions of two disarticulated femoral heads (i. e. superior, inferior, posterior and anterior), using an NMR instrument equipped with a microimaging accessory. The PR microimages were then correlated with conventional spin-echo (SE) microimages and with histology. On PR microimages, acquired with an echo time of 3.2 ms, the cartilage signal was increased, allowing an accurate delineation of the cartilage from the tidemark/cortical bone region. As a consequence, by the PR method a more precise measurement of cartilage thickness compared with that performed by the conventional SE approach was feasible. An excellent correlation between PR microimages and histology was also obtained (r = 0.90). By the proposed method it is possible to accurately determine the cartilage thickness better than with the conventional SE sequences.

Magnetic resonance microscopy of osteoporotic bone

Magnetic resonance microscopy (MRM) may be very useful in the ex vivo study of osteoporosis as non destructive technique able to provide three dimensional information of the bone architecture. However, the trabecular width appears larger in conventional MR images, as the susceptibility effect at the bone-marrow interface causes signal dephasing. Such an effect can be minimized if the echo-time (TE) or voxel size are reduced. The purpose of our research was the development of new MRM techniques that have a potential role in the characterization of trabecular bone architecture. In this study we describe the use of short-TE projection reconstruction MRM for the study of normal and osteoporotic bone explants. This method promises to be more accurate than conventional MRM in the analysis of trabecular bone. In vivo projection reconstruction MR imaging could be applied to evaluate bone architecture and bone quality evolution after space flight exposure.

Short-TE projection reconstruction NMR microscopy of trabecular bone

The aim of this study was to assess the potential of projection reconstruction (PR) NMR microscopy in the quantitative evaluation of trabecular bone architecture. Short-TE PR spin-echo microimages were acquired at 7.05 T on normal bone explants. The main structural parameters such as bone volume fraction (BVF), trabecular thickness (Tb.Th.) and trabecular separation (Tb.Sp.) were obtained from the 3D microimages using the method of directed secants. Quantitative structural data were then compared with those derived from conventional spin-echo microimages. Our study indicates that projection reconstruction NMR microscopy promises to be more accurate than the conventional FTI method in the analysis of trabecular bone.