Biomedical subjects

F Guitian

Publications and source records attributed to F Guitian.

6 recordsLinked to original sources

PubMed2003

Mechanism of bone-like formation on a bioactive implant in vivo.

The physical and chemical nature of the remodelled interface between the porous A3 glass-ceramic, composed of (wt%): SiO(2) = 54.5; CaO = 15.0; Na(2)O = 12.0; MgO = 8.5; P(2)O(5) = 6.0 K(2)O = 4.0, and the surrounding bone was studied after implantation into rat tibias. The interfaces which developed new bone layer in direct contact with the implants were examined by analytical scanning and transmission electron microscopy after implantation for 6, 8 and 12 weeks. Degradation processes of the implants also encouraged osseous tissue ingrowths into the pores of the material, changing drastically the macro- and microstructure of the implants. The ionic exchange initiated at the implant interface with the physiological environment was essential in the integration process of the implant, through a dissolution-precipitation-transformation mechanism. The interfaces developed non-toxic biological and chemical activities and remained reactive over the 12-week implantation period. These findings were significant as indicative of morphological and chemical integration of the A3 glass-ceramic into the structure of living bone tissue. A3 glass-ceramic could be suitable for the repair or replacement of living bone.

Animals↗

PubMed2002

Water absorption characteristics of dental composites incorporating hydroxyapatite filler.

Water uptake characteristics of BisGMA-based composites incorporating untreated and surface-treated hydroxyapatite (HA) with a silane coupling agent have been investigated. The water absorption and desorption behaviour of these composites obeyed the classical diffusion theory. The diffusion coefficients of the composites during first absorption were very similar to that for the base resin, suggesting that the water uptake process occur mainly in the resin matrix. The incorporation of HA reduced the water uptake of the base resin and lower uptake was found for those formulated with surface-treated HA. It was also observed that the equilibrium uptake decreased with increasing filler loading. However, the filled specimens had a higher water absorption than which would be expected on the basis of the resin content. This increase in the water uptake was largely due to the presence of porosity and filler particle aggregates in the microstructure of composites, although the adsorption of some water onto the filler surface has not been ruled out. The experimental composites showed higher solubilities than that obtained for the base resin.

Absorption↗

PubMed2001

Transmission electron microscopy of the interface between bone and pseudowollastonite implant.

This paper reports on the structural morphology of the interface in vivo between implants composed of bioactive synthetic pseudowollastonite ceramic and bone in rat tibias. Thin sections of the interfaces were examined after 6 and 8 weeks of implantation period in a high resolution transmission electron microscope up to the lattice plane resolution level. The interfaces developed normal biological and chemical activities and remained reactive over the 8-week period. The regions showing direct bone tissue bonding to the implant contained nanocrystals of hydroxyapatite-like phase growing epitaxially across the interface in the [002] direction. The nanocrystals were also identified in the bone tissue formed in the interfacial area. The reactivity of the implant caused in the first instance formation of an amorphous woven type of bone, which transformed into a crystalline lamellar type containing collagen fibres. The Ca/P ratio of the interfacial region was found to be between 1.67 in the mature bone tissue formed about 5 microm from the interface, and 2.06 in the regions right at the interface.

Animals↗

PubMed2000

Morphological and structural study of pseudowollastonite implants in bone.

In vitro experiments show that pseudowollastonite (alpha-CaSiO3) is a highly bioactive material that forms a hydroxyapatite surface layer on exposure to simulated body fluid and also to human parotid saliva. This finding is very significant, as it indicates that the pseudowollastonite can be physically and chemically integrated into the structure of living bone tissue, and therefore could be suitable for repair or replacement of living bone. The physical and chemical nature of the remodelled interface between the pseudowollastonite implants and the surrounding bone has been studied after in vivo implantation of 20 pseudowollastonite cylinders into rat tibias. The interfaces formed after 3, 6, 8 and 12 weeks of implantation were examined histologically using an optical microscope and also by analytical scanning electron microscopy. SEM and X-ray elemental analysis showed that the new bone was growing in direct contact with the implants. Other examinations found that the bone was fully mineralized. The ionic exchange taking place at the implant interface with the body fluids was essential in the process of the implant integration through a dissolution-precipitation-transformation mechanism. The study found the interface biologically and chemically active over the 12-week implantation period. The rate of new bone formation decreased after the first 3 weeks and reached constant value over the following 9 weeks. The osteoblastic cells migrated towards the interface and colonized the surface at the contact areas with the cortical regions and also bone marrow.

Animals↗

PubMed1999

Bioactivity of pseudowollastonite in human saliva.

OBJECTIVES: Pseudowollastonite (CaO.SiO2) was found to be bioactive in a simulated body fluid environment. In the present study, 'in vitro' bioactivity of pseudowollastonite was further assessed in human parotid saliva. The main objective was to compare behaviour of the material in a natural medium of high protein content (human parotid saliva) with its behaviour in an acellular protein-free solution (simulated body fluid). METHODS: Samples of polycrystalline pseudowollastonite were immersed for one month in human parotid saliva at 37 degrees C. Changes in ionic concentrations in the human parotid saliva and the pH right at the interface of pseudowollastonite/human parotid saliva were determined. The products of the interfacial reactions were studied by thin-film X-ray diffraction, scanning and transmission electron microscopy. RESULTS: The results confirmed formation of a hydroxyapatite-like layer on the surface of the material, and also suggested that the mechanism of hydroxyapatite-like layer formation in saliva was similar to that showed in simulated body fluid. CONCLUSIONS: The hydroxyapatite-like layer formed at the interface was found to be compact, continuous and composed of many small crystallites with ultrastructure similar to that of natural cortical bone and dentine. The study also concluded that the high pH conditions (10.32) existing right at the pseudowollastonite/human parotid saliva interface promoted hydroxyapatite-like precipitation. At this stage of the study, similarities of the material behaviour in saliva and acellular simulated body fluid suggest that the pseudowollastonite could be of interest in specific periodontal applications for bone restorative purposes.

Body Temperature↗

PubMed1996

Morphological studies of pseudowollastonite for biomedical application.

Pseudowollastonite ceramic (psW) composed of CaO.SiO2 was found to be bioactive in a simulated body fluid environment. The chemical reaction initiated at the material surface resulted in hydroxyapatite (HA) formation. These bone-bonding properties are essential for securing the necessary physico-chemical integration of the material with living bone. Materials behaving in this way can be considered for potential biomedical application as bone tissue substitute for a natural bone repair or replacement as implant. A mechanism of hydroxyapatite formation on pseudowollastonite ceramics surface was investigated during exposure to a stimulated body fluid (SBF) for a period of 3 weeks. Morphology and structure of the surface product and its original substrate was examined by thin-film X-ray diffraction, scanning electron microscopy and high-resolution transmission electron microscopy. HA crystals were found to form on an amorphous silica intermediate layer. (100) lattice planes of HA were resolved and identified. Concentration of ions in the SBF and pH of the SBF were monitored throughout the exposure. Additional pH measurements were made at the interface of psW with SBF. The HA formation occurred when there was a sudden increase of pH from 7.25 to 10.5 at the interface of psW with SBF as a result of ionic exchange between 2H+ and Ca2+ within the psW network. This ionic exchange transformed the psW crystals into an amorphous silica phase. The appropriate pH and the ion concentrations were essential for partial dissolution of the amorphous silica phase and subsequent precipitation of a Ca-P rich phase which then transformed to HA.

Biocompatible Materials↗