Biomedical subjects

Adriana Bigi

Publications and source records attributed to Adriana Bigi.

5 recordsLinked to original sources

PubMed2007

Effects of freezing on the biomechanical and structural properties of human posterior tibial tendons.

This work analyzes the effects of storage by fresh-freezing at -80 degrees C on the histological, structural and biomechanical properties of the human posterior tibial tendon (PTT), used for ACL reconstruction. Twenty-two PTTs were harvested from eleven donors. For each donor one tendon was frozen at -80 degrees C and thawed in physiological solution at 37 degrees C, and the other was tested without freezing (control). Transmission electron microscopy (TEM), differential scanning calorimetry (DSC) and biomechanical analysis were performed. We found the following mean changes in frozen-thawed tendons compared to controls: TEM showed an increase in the mean diameter of collagen fibrils and in fibril non-occupation mean ratio, while the mean number of fibrils decreased; DSC showed a decrease in mean denaturation temperature and denaturation enthalpy. Biomechanical analysis showed a decrease in ultimate load and ultimate stress, an increase in stiffness and a decrease in ultimate strain of tendons. In conclusion fresh-freezing brings about significant changes in the biomechanical and structural properties of the human PTT. A high variability exists in the biophysical properties of tendons among individuals and in the effects of storage on tendons. Therefore, when choosing an allograft tendon, particular care is needed to choose a biomechanically suitable graft.

Adult↗

PubMed2006

Nanocomposites of hydroxyapatite with aspartic acid and glutamic acid and their interaction with osteoblast-like cells.

The direct synthesis of hydroxyapatite (HA)-aspartic acid (ASP) and HA-glutamic acid (GLU) nanocrystals was carried out in presence of different amounts of the amino acids in solution. ASP and GLU incorporation into HA crystals reduces the coherent length of the perfect crystalline domains along the long dimension (002) and, even more, along the cross section (310) of the apatite crystals, suggesting a specific interaction of the amino acids with the HA structure. FTIR analysis indicates that the carboxylic groups of the acidic amino acids interact with the calcium ions of HA. The relative amount of ASP incorporation into HA nanocrystals is greater than that of GLU, suggesting a greater affinity of ASP for HA. Osteoblast-like, MG63, cells cultured on the composite nanocrystals display good proliferation and increased values of ALP activity, collagen type I, TGF-betaI and osteocalcin production, indicating that the presence of the acidic amino acids enhances osteoblast activation and extra-cellular matrix mineralization processes.

Aspartic Acid↗

PubMed2006

The effect of hydroxyapatite nanocrystals on microvascular endothelial cell viability and functions.

To favor bone reconstitution with biomaterials endothelial cells should maintain proper functions to drive angiogenesis. To this aim nanocrystals of hydroxyapatite (HA) have been synthesized and characterized on endothelial cells. Microvascular endothelial cells have been exposed to stoichiometric HA nanocrystals. Cell morphology and organization of cytoskeletal proteins have been monitored by SEM analysis and immunofluorescence. Biochemical markers of physiological and pathological responses of endothelial cells, endothelial constitutive nitric oxide synthase, and cycloxygenase-2 (ecNOS and COX-2, respectively) have been measured by immunofluorescence. Crystallized HA sustained endothelial survival without any cytotoxic effect. At the observation with SEM, endothelial cell morphology was maintained in the presence of HA. The localization and organization of beta-actin documented the formation of stress fibers, indicating an activation of endothelial cells induced by HA nanocrystals. Immunohistochemistry for biochemical key signaling pathways in endothelium demonstrated that nanocrystals of HA maintained the expression of ecNOS and did not increase COX-2 expression. In conclusion, the present findings indicate that HA nanocrystals exhibit high biocompatibility for microvascular endothelium. In the presence of HA nanocrystals endothelial cells maintain biochemical markers of healthy endothelium. They do not acquire a proinflammatory or thrombogenic phenotype, but express markers of functioning endothelium that might contribute to angiogenesis.

Actins↗

PubMed2005

Nanocrystalline hydroxyapatite coatings on titanium: a new fast biomimetic method.

We obtained a fast biomimetic deposition of hydroxyapatite (HA) coatings on Ti6Al4V substrates using a slightly supersaturated Ca/P solution, with an ionic composition simpler than that of simulated body fluid (SBF). At variance with other fast deposition methods, which produce amorphous calcium phosphate coatings, the new proposed composition allows one to obtain nanocrystalline HA. Soaking in supersaturated Ca/P solution results in the deposition of a uniform coating in a few hours, whereas SBF, or even 1.5SBF, requires 14 days to deposit a homogeneous coating on the same substrates. The coating consists of HA globular aggregates, which exhibit a finer lamellar structure than those deposited from SBF. The extent of deposition increases on increasing the immersion time. Transmission electron microscope (TEM) images recorded on the material detached from the coating show that the deposition is constituted of thin nanocrystals. Electron diffraction (ED) patterns recorded from most of the crystals exhibit the presence of rings, which can be indexed as reflections characteristic of HA. Furthermore, several HA single-crystal spot ED images were obtained from individual crystals.

Alloys↗

PubMed2003

Structural differences between "dark" and "bright" isolated human osteonic lamellae.

This investigation presents new insights into the structure of human secondary lamellae. Lamellar specimens that appear dark and bright on alternate osteon transverse sections under circularly polarizing light were isolated using a new technique, and examined by polarizing light microscopy, synchrotron X-ray diffraction, and confocal microscopy. A distribution of unidirectional collagen bundles and of two overlapping oblique bundles appears on circularly polarizing light microscopy images in relation to the angle between the specimen and the crossed Nicols' planes. The unidirectional collagen bundles observed at 45 degrees run parallel to the osteon axis in the dark lamellar specimens and perpendicular to it in the bright ones. Small and wide-angle micro-focus X-ray diffraction indicates that the dark lamellae are structurally quite homogeneous, with collagen fibers and apatite crystals preferentially oriented parallel to the osteon axis. Bright lamellar specimens exhibit different orientation patterns with the dominant ones bidirectional at +/-45 degrees with respect to the osteon axis. Accordingly, confocal microscopy evidences the presence of longitudinal bundles in dark lamellar specimens and oblique bundles in the bright ones. Radial bundles are evidenced in both lamellar types. The alternate osteon structure is described by a rather continuous multidirectional pattern, in which dark and bright lamellae display different mechanical and possibly biological functions.

Adult↗