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Biomedical subjects

C Migliaresi

Publications and source records attributed to C Migliaresi.

At least 19 recordsLinked to original sources
PubMed2005

The healing of confined critical size cancellous defects in the presence of silk fibroin hydrogel.

In vitro and in vivo behaviour of an injectable silk fibroin (SF) hydrogel was studied through osteoblast cultures and after implantation in critical-size defects of rabbit distal femurs. A commercial synthetic poly(D,L lactide-glycolide) copolymer was used as control material. In vitro biocompatibility was evaluated by measuring LDH release, cell proliferation (WST1), differentiation (ALP, OC), and synthetic activity (collagen I, TGF ss1, IL-6). Bone defect healing rate and quality of the newly formed bone inside the defects were determined in vivo by measuring trabecular bone volume (BV/TV), trabecular thickness (Tb.Th), trabecular number (Tb.N), trabecular separation (Tb.Sp), mineral apposition rate (MAR) and bone formation rate (BFR/B.Pm). In vitro tests indicated that both materials significantly increased cell proliferation in comparison with the negative control. A significant increase in the TGF-beta1 level was found for SF hydrogel in comparison with the control material and negative control. Both materials promoted bone healing when used to fill critical size defects in rabbit femurs. The new-formed bone of the SF hydrogel treated defects showed significantly higher BV/TV, Tb.Th, MAR and BFR/B.Pm and lower Tb.Sp values in comparison with the control gel. At 12 weeks the re-grown bone of the SF hydrogel-treated defects appeared more similar to normal bone than that of the control synthetic polymeric material-treated defects, except for the Tb.N value that differed significantly from that of normal bone (p<0.05). MAR and BFR/B.Pm presented significantly (p<0.05) higher values for SF hydrogel-treated defects in comparison with controls treated with a synthetic polymeric material, confirming that SF hydrogel accelerated remodelling processes.

Animals↗
PubMed2004

Endothelialization of a non-woven silk fibroin net for use in tissue engineering: growth and gene regulation of human endothelial cells.

We have previously shown that a biomaterial consisting of a non-woven fibroin net produced from silk (Bombyx mori) cocoons is an excellent scaffolding material for a wide variety of human cells of different tissue types. Endothelialization must take place for a biomaterial to be successful after implantation. Therefore, primary human endothelial cells and the human endothelial cell lines, HPMEC-ST1.6R and ISO-HAS-1, were examined for adherence and growth patterns on the fibroin nets by confocal laser scanning microscopy after vital staining of the cells and by electron microscopy. Endothelial cells adhered and spread along individual fibers of the nets and did not fill the gaps between individual fibers. Higher attachment and growth coverage was obtained if nets were first coated with gelatin, fibronectin or collagen type I. Proinflammatory markers of endothelial cells on the fibers exhibited a non-activated state and LPS-stimulated cells exhibited activation of these markers. Furthermore, a typical PECAM-1 localization at cell-cell contacts was observed. Scanning electron microscopic examination of fibroin nets after removal of cells did not demonstrate any changes to the fibroin structure. HUVEC and HDMEC on fibroin nets embedded in collagen type I gels formed microvessel-like structures. Thus, silk fibroin nets are a highly endothelial cell-compatible scaffolding material that support the growth, normal and inducible cell functions and angiogenesis potential of human endothelial cells in vitro similar to that observed in vivo.

Animals↗
PubMed2004

Fibroin hydrogels for biomedical applications: preparation, characterization and in vitro cell culture studies.

Silk fibroin hydrogels prepared either by treating a 2% (w/v) silk fibroin aqeuous solution at 4 degrees C (thermgel) or by adding 30% (v/v) of glycerol (glygel), were characterized by using Environmental Scanning Electron Microscopy (ESEM), Fourier Transform Infrared Spectroscopy (FT-IR), Differential Scanning Calorimetry (DSC), Thermogravimetrical Analysis (TGA) and molecular weight determination. The preparation procedure affected morphology and molecular weight of hydrogels, with no or negligible differences being displayed by FT-IR and DSC analyses. While thermgel presented a well uniform porous structure, the morphology of glygel appeared to be non-porous and heterogeneous. Glygel presented lower water content and lower degradation temperatures, associated with the presence of glycerol but likely also to less-organized protein structures. Cytoxicity tests with human osteoblast-like cells indicated that both gels were not cytoxic, while cell cultures pointed out a faster cell proliferation on glygel and a higher cell activation and differentiation on thermgel. These gels could be used as scaffolds able to promote in situ bone regeneration.

Animals↗
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↗
PubMed1996

Polymeric membranes for hybrid liver support devices: the effect of membrane surface wettability on hepatocyte viability and functions.

Extracorporeal therapies based on membrane hybrid liver support devices using primary hepatocytes are an interesting approach to the treatment of acute hepatic failure. In such devices, semipermeable polymeric membranes are effectively used as immunoselective barriers between a patient's blood and the xenocytes in order to prevent the immune rejection of the graft. The membranes may act also as the substratum for cell adhesion, thus favouring the viability and functions of anchorage-dependent cells such as the hepatocytes. Membrane cytocompatibility is expected to depend on the surface properties of the polymer, such as its morphology and its physico-chemical properties. In this paper, we report our investigation on the effect of the surface wettability of membranes on hepatocyte viability and functions. Polypropylene microporous membranes were modified to increase their surface wettability and were used as substrata for rat hepatocyte adhesion culture. Isolated hepatocytes were also cultured on collagen as a reference substratum. Hepatocyte viability generally improved as the cells were cultured on more wettable membranes. In agreement with the viability data, the increasing wettability of the membrane surface also improved some metabolic functions.

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↗
PubMed1990

Water sorption and mechanical properties of dental composites.

The physical properties of four commercial dental composites were investigated through differential scanning calorimetry, water sorption and desorption measurements and flexural mechanical properties tests. The differential scanning calorimetry curves of samples as prepared and after different times of ageing in water indicated that the small residual monomer reactivity, present in the as prepared samples, disappeared after immersion in water, which probably acts as a plasticizer and facilitates a further crosslinking reaction of the material and the residual monomer desorption. Consistently, water causes the embrittlement of the material, as detected from the flexural mechanical properties. Water sorption and desorption kinetics were measured at different temperatures, the water diffusion coefficients were calculated and the activation energies of the diffusion process were determined. The SEM analysis of the fracture surfaces and the decrease of the water uptake on the temperature indicated the existence of a good filler/matrix adhesion.

Adsorption↗
PubMed1984

Preparation and strength of poly(ethylene terephthalate) fiber bundles for model synthetic tendons.

Poly(ethylene terephthalate) fibers suited for model synthetic tendons were prepared on a pilot-plant scale by additional drawing (postdrawing) of commercial textile fibers texturized by false twist. The modified fibers have a tensile modulus of 7-9 GPa, a one-minute creep modulus of 5-6 GPa, tensile strength 0.55-0.63 GPa, and strain at break of 16-19%. It is essential for their application in synthetic tendons that plastic deformation was reduced to about 0.5%, which could be completely eliminated by subsequent mechanical conditioning of fibers. Since the strength of model tendons consisting of 20 vol % of fibers and of a hydrogel matrix is primarily determined by the strength of the fibers, some aspects of the theory of strength of fiber bundles are briefly recapitulated. The prediction is compared with earlier experimental results obtained for the synthetic tendons. Such an approach, taking into account the fiber-strength distribution in the bundle, predicts a strength of model tendons lower by 20-40% than does the rule of mixtures.

Polyethylene Terephthalates↗
PubMed1983

[Initial observations on the biocompatibility of a polymer used as a skin dressing].

In the development of a dressing for burn wound covers, a material is required which combines good oxygen permeability, high water content and good biocompatibility with reasonable mechanical properties. One of the most important functions of the cover is to protect the burned surfaces from drying out and to constitute the first defence against microbial invasion. In this study composite sheets crosslinked either in presence of glicerol or diacetin, obtained by reinforcing PHEMA with a tricot PET net have been implanted subacute in rabbits, to test their biocompatibility. The same composites crosslinked in presence of diacetin and grafted on a polybutadene film, have been used as a skin graft on rabbits.

Animals↗
PubMed1983

[Biological and surgical aspects of the use of polymers in experimental surgery. 1: implants on the oculo-extrinsic musculature].

Composite sheets obtained reinforcing PHEMA with a tricot PET net have been implanted in rabbits to test their potential applications for cross-eye surgical correction. The mechanical characterization of the composites has been carried out both in static tension and fatigue. The clinical evaluation was performed on twelve adult New Zealand white Rabbits implanting the sheets on the rectus dorsalis muscle of the eye. The material seems to be highly compatible with the surrounding tissue, mechanical satisfying and clinically helpful in correcting many of the pathological conditions connected with strabismus. The long term behaviour of the implanted prosthesis in still under investigation.

Animals↗
PubMed1983

Mechanical properties of hydrophilic copolymers of 2-hydroxyethyl methacrylate with ethyl acrylate, n-butyl acrylate, and dodecyl methacrylate.

Copolymers were prepared of 2-hydroxyethyl methacrylate, which is strongly hydrophilic, with hydrophobic comonomers having a low glass transition temperature, i.e., ethyl acrylate, n-butyl acrylate, and dodecyl methacrylate. The glass transition temperature, T alpha (1 Hz), of polymers in the dry state (xerogels) was determined by means of dynamic mechanical measurements. The dependence of T alpha on composition in all the three series of copolymers was described in terms of a one-parameter equation. The equilibrium swelling of copolymers in water decreases more steeply than the weight fraction of 2-hydroxyethyl methacrylate. When swollen in water to equilibrium, all copolymers with ethyl acrylate or n-butyl acrylate are in the rubberlike state; their tensile modulus E assumes values in the range 0.17-0.50 MPa. While poly(2-hydroxyethyl methacrylate) has the modulus E = 0.39 MPa, the tensile strength sigma u = 0.32 MPa, and the strain-at-break epsilon u = 1.81, for the weight fraction of the comonomer in the range 0.36 less than or equal to omega 2 less than or equal to 0.56 it is possible to achieve sigma u and epsilon u lying in the respective ranges 0.7-0.9 MPa and 5-7. Copolymers with the dodecyl methacrylate content omega 2 less than 0.2 or omega 2 greater than 0.8 are rubberlike, and at 0.30 less than or equal to omega 2 less than or equal to 0.62 they become leathery; the latter have the modulus E and strength sigma u within the ranges 12-32 and 3-4 MPa, respectively. The stress-strain curves of these copolymers evidence yielding and orientation hardening which have been tentatively explained by the nonhomogeneous composition and structure of the copolymers.

Acrylates↗
PubMed1981

Mechanical properties of model synthetic tendons.

Model synthetic tendons consisting of 20 vol % of texturized poly(ethylene terephthalate) fibers and of the water-swollen poly(2-hydroxyethyl methacrylate) matrix have the tensile modulus E = 1.5 +/- 0.1 GPa, strength and strain-at-break sigma b = 85 +/- 10 MPa and epsilon b = 0.08 +/- 0.02. The force required for breaking tendons with the diameters 2, 3, 4 mm is, respectively, 300, 500, and 960 N. By these properties model synthetic tendons closely imitate the properties of natural tendons. Long-term (100 min) and repeated short-term (30 times 1 min) creep shows that on loading model tendons lose some 10% of their stiffness, but that the whole deformation is reversible. The shape of the compliance vs. time dependence of synthetic tendons closely resembles the dependence determined for the parent fiber. The stiffness and strength of a tendon are given by those of the fiber bundle used; by varying fiber volume fraction, it is possible to adjust the required mechanical properties of tendons.

Animals↗