Biomedical subjects

L Fambri

Publications and source records attributed to L Fambri.

9 recordsLinked to original sources

PubMed2002

Finite element analysis of a glass fibre reinforced composite endodontic post.

In this work the mechanical response to external applied loads of a new glass fibre reinforced endodontic post is simulated by finite element (FE) analysis of a bidimensional model. The new post has a cylindrical shape with a smooth conical end in order to adequately fit the root cavity, and to avoid edges that could act as undesired stress concentrators. Mechanical data obtained by three-point bending tests on some prototypes fabricated in the laboratory are presented and used in the FE model. Under various loading conditions, the resulting stress component fields are hence compared with those obtained in the case of two commercial endodontic posts (i.e. a cast metal post and a carbon fibre post) and with the response of a natural tooth. The gold cast post-and-core produces the greatest stress concentration at the post-dentin interface. On the other hand, fibre-reinforced composite posts do present quite high stresses in the cervical region due to their flexibility and also to the presence of a less stiff core material. The glass fibre composite shows the lowest peak stresses inside the root because its stiffness is much similar to dentin. Except for the force concentration at the cervical margin, the glass fibre composite post induces a stress field quite similar to that of the natural tooth.

Acrylic Resins↗

PubMed2002

Poly(D, L-lactide/epsilon-caprolactone)/hydroxyapatite composites as bone filler: an in vivo study in rats.

In this study, a novel composite bone substitute was implanted in animal models (rats) and their in vivo characteristics were examined. A D,L-lactide and E-caprolactone copolymer (Mw: 80,000; Mn:40,000, and PI:2.00) was synthesized by ring-opening polymerization of the respective dimers using stannous octoate as the catalyst. The final ratio of D,L-lactide to epsilon-caprolactone obtained by 1NMR was 60/40. Hydroxyapatite (HA) powder was loaded in the copolymer. The HA/copolymer ratio was 60/40 (w/w). These composites were easily shaped by hand. Animal tests were performed on mature wistar rats (n=30). Defects were created on the proximal, the thickest part of the femur. The bone defects of the first group were filled with polymer/HA composite, the second group filled with only HA and the third group was left empty. Histologic examination of bone tissues showed new bone formation around the yellow-green polymer/HA composite material in the first group of animals whereas no evidence of new bone growth was observed in other groups.

Animals↗

PubMed2001

Poly(epsilon-caprolactone-co-D,L-lactide) /silk fibroin composite materials: preparation and characterization.

Poly(epsilon-caprolactone-co-D,L-lactide) copolymers with 10, 30, and 50% by weight of silk particles (size range: 5-250 microm) derived from Bombyx mori were blended in acetone solution. After evaporation of the solvent, the morphology, thermal behavior, and mechanical properties of the composites were examined. The composites were transparent and the silk fibroin particles were homogeneously distributed within the composite structure. The particles appeared as bright reflected images under the optical microscope, suggesting that they were in a crystalline state. DSC thermograms of the composites revealed that the glass transition of the matrix was at ca. -18 degrees C. Degradation of the silk fibroin occurred beyond 270 degrees C. The decomposition temperatures and degradation rate decreased with increasing silk fibroin content as revealed by TGA analysis. FTIR spectra of the composites showed absorption bands at 1730 and 1088 cm(-1) for the copolymer and at 3273 and 1617 cm(-1) for the silk fibroin. Although the characteristic lines of poly(epsilon-caprolactone-co-D,L-lactide) were independent of filler concentration. the absorption bands of the beta-sheet form of the silk fibroin increased slightly due to the interaction of silk fibroin with the copolymer.

Calorimetry↗

PubMed2000

Poly(D,L-lactide/epsilon-caprolactone)/hydroxyapatite composites.

In this study, elastomeric D,L-lactide and epsilon-caprolactone copolymers with two different molecular weights (Mn: 108.000 and 40.000) were synthesized by ring-opening polymerization of the respective dimers by using stannous octoate as the catalyst, as a potential bone-filling material. The final ratio of D,L-lactide to epsilon-caprolactone obtained by 1NMR was 60/40 (comparing to the initial ratio of 50/50). Both copolymers were amorphous having Tg at around -21 degrees C. Different amounts of hydroxyapatite (HA) powder were loaded within the copolymers. These composites were easily shaped by hand. Mechanical properties of the composites changed with the HA loading and the molecular weight of the copolymer. The percent elongation decreased, while both the Young's modulus and yield point (stress) increased with the HA content. The copolymers were degraded within the Ringer solutions in about 6 weeks. The molecular weight distribution became broader during degradation. Incorporation of HA reduced the degradation rate.

Biodegradation, Environmental↗

PubMed2000

Preparation and properties of poly(L-lactide)/hydroxyapatite composites.

In this study, two different viscosity-average molecular weight (eta = 4.0 and 7.8) poly(L-lactide) (PLLA) were synthesized by ring-opening polymerization and the poly(L-lactide)/hydroxyapatite composites (PLLA/HA) were prepared by blending HA particles (size range: 25-45 microm and Ca/P = 1.69) with a content of 10, 30, and 50 wt% in PLLA solution with further evaporation of the solvent. The plain PLLA polymers and PLLA/HA composites were compression-molded and machined to yield 25 x 3 x 2 mm3 specimens. The molar mass of resulting specimens was decreased drastically due to the hydrolytic and thermal degradation of ester bonds. Scanning electron microscopy and thermal gravimetric results indicated that the compositions of HA in PLLA were well dispersed. With increasing HA content, the crystallinity of PLLA/HA composites are slightly increased due to the effect of HA as a nucleating agent. The dynamic mechanical analysis is useful in studying the viscoelastic behaviour of the PLLA/HA composites and no secondary relaxation was observed below the glass-to-rubber transition (60 degrees C). The mechanical properties of the PLLA/HA composites were found to vary with HA content. Increased levels of HA resulted in increased bending modulus and strength.

Absorbable Implants↗

PubMed1997

Experimental evaluation of a resorbable intramedullary plug for cemented total hip replacement.

In order to evaluate degradation kinetics and biocompatibility of a resorbable poly(D,L-lactic acid) (PDLLA) plug for total cemented hip prostheses, an experimental in vitro and in vivo study was carried out. Degradation rate studies were performed in Ringer solution and after in vivo plug implantation in the femoral medullar cavity of rabbits. In vitro biocompatibility was evaluated in murine fibroblast cell cultures. PDLLA plugs showed faster degradation kinetics in vivo than in vitro. Histological evaluations showed that PDLLA completely disappeared in vivo 26 weeks after implantation. Fibrous tissue in the medullar cavity was observed at 13 weeks, but no histological changes were observed after 26 weeks. Also, the in vitro tests showed good biocompatibility of the biomaterial. Our results show the possibility of considering this resorbable plug for clinical situations instead of the traditionally used plugs [polyethylene, poly(methyl methacrylate) or cancellous bone] due to its biocompatibility, degradation properties and simplicity of use.

Animals↗

PubMed1994

Polymerization kinetics, glass transition temperature and creep of acrylic bone cements.

Sulfix-6 and Zimmer LVC 60/30 bone cements were selected and the polymerization kinetics and resulting glass transition temperature Tg; creep behaviour in the dry or water-saturated state; and sorption and diffusion of water were studied. The calculation of conversion was based on a comparison of the residual polymerization heat measured by differential scanning calorimetry and the corresponding theoretical value. The conversion reached 99% after 90 min of quasi-adiabatic polymerization starting at 23 degrees C or after 10 min of isothermal polymerization at 37 degrees C. The Tgs of the cements prepared in the former way were about 82 and 100 degrees C, respectively. Creep rate of the bone cements at 37 degrees C decreased with the time of creeping. Sorbed water enhanced the compliance, but reduced the creep rate for long times so that water sorption during the service time may not have detrimental effects on the creep resistance of the cements. Both types of cements contained about 1% of low molar mass substances extractable by water. Measurements of the sorption kinetics of water showed that the diffusion coefficient is 0.14 x 10(-11) and 0.22 x 10(-11) m2/s and 1 yr sorption achieves 2.11% and 2.89% for Sulfix and Zimmer, respectively.

Adsorption↗

PubMed1994

A study on the in vitro degradation of poly(lactic acid).

The in vitro degradation of samples of L- and D,L-lactic acid polymers, P(L)LA and P(DL)LA respectively, having different molecular weights, morphology and/or geometry, has been studied through the determination of viscometric molecular weight, mass and mechanical properties as function of the immersion time in Ringer solution at 37 degrees C. In particular have been compared the degradation kinetics of P(L)LA, amorphous and crystalline, and of P(L)LA and P(DL)LA having different molecular weight and sample geometry. From the molecular weight versus the degradation time data, a degradation rate has been defined, as the derivative of the function best fitting the data, normalized to the molecular weight of the polymer at each time. The behavior of the degradation rate curves, plotted against the degradation time, has been interpreted and compared with relation to the initial physical and geometrical characteristics of the PLA samples.

Biodegradation, Environmental↗

PubMed1992

Reproducibility of late phase pulmonary response to exercise and its relationship to bronchial hyperreactivity in children with chronic asthma.

To determine the reproducibility of the delayed response to exercise and its effect on bronchial hyperreactivity, we had 26 asthmatic children perform treadmill exercise challenge on two occasions 1 week apart. Both challenges were preceded by 2 control days and 1 histamine challenge day, and were followed by another histamine challenge day. Peak expiratory flow rate (PEFR) was measured hourly for 12 hours on each control day and for 12 hours after each exercise or histamine challenge. During the first week, five patients showed a late reaction (PEFR change > 15%) after exercise, which was present in only two of them the following week. These two patients, however, also showed a spontaneous fall > 15% of PEFR from baseline during the other control study days. A similar pattern was seen in two other patients who had a late response during the second exercise challenge but not during the first. No significant change occurred in histamine PC-20 FEV1 between before and after the exercise challenges. An apparent late asthmatic response after exercise challenge may represent a within-day fluctuation in pulmonary mechanics that develops spontaneously in children with asthma.

Aerosols↗