Biomedical subjects

L Ambrosio

Publications and source records attributed to L Ambrosio.

At least 19 recordsLinked to original sources

PubMed2001

Mechanical strength of tooth fragment reattachment.

The aim of this study was static and fatigue test investigation of the strength of a tooth fragment reattached with adhesives to the tooth body. Central bovine incisor teeth were used, and standardized fragments were obtained by cutting the incisal edge of the selected teeth. All the fragments were reattached using a multistep dentine adhesive system, and the specimens were randomly divided into two groups (A and B). Group B specimens underwent a further dental treatment: a circumferential double chamfer prepared around the external cut interface was filled with light cured composite restorative resin. Static and fatigue bending tests were performed and linear elastic equations were used to analyze and compare the strength of the treated teeth. The results indicated that the static and fatigue bending properties were improved by using reinforcement with composite restorative resin.

Acrylic Resins↗

PubMed2001

Improvement of swelling properties of poly(2-hydroxyethyl methacrylate) hydrogel by means of biomimetic method.

Poly(2-hydroxyethyl methacrylates) (PHEMAs) structurally modified by means of polymer blends and random copolymers are intensively studied in order to improve mechanical properties. It was recently shown that a hydroxyapatite coating, which should improve the bonding of this biomaterial to the bone, can be obtained by means of the biomimetic method. When PHEMA is submitted to the biomimetic method, its swelling ratio is improved. This can be ascribed to the deposition of a silicatic layer, which improves the hydrophilicity, on the surface of the internal pores during the first stage of the method. This appears to be a valuable result for producing modified PHEMAs with improved mechanical properties and good swelling. The experimental results indicate the following: stronger interactions with the water molecules are set up, an induction period is observed that is linked to the rate of the reactions occurring at the surface of the glass and the establishment of a convenient concentration of the silicate ions at the external surface of the polymer, and the diffusion of simulated body fluid into the pores is the limiting stage of the process.

Biocompatible Materials↗

PubMed2001

Biocompatibility and biodegradation of intravitreal hyaluronan implants in rabbits.

To study the biocompatibility and the biodegradation rate in vivo of new intravitreal implants made with three different hyaluronic acid esters: Hyaff7, Hyaff11 and Hyaff11p75 (100% ethyl ester, 100 and 75% benzyl esters, respectively), the plugs were implanted through a sclerotomy at 3.5 mm from the limbus of rabbit eyes. In order to evaluate the in vivo biodegradation the shaft diameter of the plugs was measured by ultrasound biomicroscopy. Slit lamp microscopy, ophthalmoscopy and ERG were performed periodically. The effects of the implants on ocular tissues were also evaluated histologically. All the plugs showed a good biocompatibilitv. Plugs of both the total esters, Hyaff7 and Hyaff11, were found to undergo a slow dissolution process for 60 and 150 days, respectively. The partial benzyl ester, Hyaff11p75, was completely reabsorbed after 15 days. Analysis of variance showed a high correlation between biodegradation rate and the time of resorption (F = 90.5; p < 0.001). The biodegradation rate of each implant is related to the chemical structure of the three types of Hyaff (F = 4.51; p = 0.005). The present data suggest that intravitreal implants based on hyaluronic acid esters represent useful biocompatible and biodegradable devices for a potential drug delivery system in the treatment of posterior segment ocular diseases.

Animals↗

PubMed2001

Morphology and metabolism of hepatocytes cultured in Petri dishes on films and in non-woven fabrics of hyaluronic acid esters.

Polymers of hyaluronic acid (Hyal) esters exhibit good tissue compatibility and are available in various geometrical configurations. These properties can be exploited for the design of innovative bioartificial liver support devices (BALSDs) using primary hepatocytes. In this paper, we report a preliminary investigation of the polymer feasibility of the ethyl and the benzyl Hyal ester in the form of films and non-woven fabrics for the in vitro culture of primary rat hepatocytes. Cell function was evaluated daily in Petri dishes with respect to the rate of ammonia elimination (AER) and urea synthesis (USR). Cells cultured in non-woven fabrics of the ethyl ester of Hyal (HYAFF7nw) exhibited an initial AER about 32% lower and synthesised urea 33% faster than that of cells on collagen films. After a week in culture, cells on collagen films retained only a minor fraction of their initial rates. Cells cultured in non-woven fabrics of HYAFF7nw retained about 62 and 44% of their initial AER and USR, respectively, and exhibited an AER approximately equal to and a USR 3.6 times greater than those of cells adherent to collagen. These results suggest that non-woven fabrics of HYAFF7nw are promising substrata for hepatocyte culture in BALSDs.

Ammonia↗

PubMed2001

Drosophila-raf acts to elaborate dorsoventral pattern in the ectoderm of developing embryos.

In the early Drosophila embryo the activity of the EGF-receptor (Egfr) is required to instruct cells to adopt a ventral neuroectodermal fate. Using a gain-of-function mutation we showed that D-raf acts to transmit this and other late-acting embryonic Egfr signals. A novel role for D-raf was also identified in lateral cell development using partial loss-of-function D-raf mutations. Thus, we provide evidence that zygotic D-raf acts to specify cell fates in two distinct pathways that generate dorsoventral pattern within the ectoderm. These functional requirements for D-raf activity occur subsequent to its maternal role in organizing the anterioposterior axis. The consequences of eliminating key D-raf regulatory domains and specific serine residues in the transmission of Egfr and lateral epidermal signals were also addressed here.

Animals↗

PubMed2001

Network formation of low molecular weight hyaluronic acid derivatives.

The oscillatory and steady shear rheological properties of the benzyl esters of hyaluronic acid (HA), partially esterified (Hyaff 11p50), at low molecular weight (150 kDa) were evaluated and compared to the properties of HA at the same molecular weight. At concentrations up to 40 mg cm(-3) both Hyaff 11p50 solutions and HA solutions, behaved as viscous fluids. At higher concentrations, HA ester solutions exhibited an elastic response typical of weak gels, whereas HA exhibited a viscous behaviour. A solid-like response was also observed by lowering the temperature. These results indicate that hyaluronic acid ester solutions can form a weak gel network. The rheological properties of HA derivatives changed significantly compared to HA solutions. The improved elasticity and residence times of these solutions expand the possible applications of hyaluronic acid in the biomedical field.

Dose-Response Relationship, Drug↗

PubMed2000

Polymer-based composite hip prostheses.

A composite hip prosthesis (CHP) made from poly(ether-imide) reinforced with carbon and glass fibres was manufactured and characterized. The main objective of the study was to evaluate the effect of fibre organization on the mechanical properties of the composite femoral implant and compare with the bone. A stacking sequence of drop-off plies of carbon/glass fibres reinforcing poly(ether-imide) (PEI) constitutes a symmetrical and balanced CHP. The hip was manufactured according to the finite element modelling (FEM) design and using the compression moulding and water-jet technologies. The measured stress-strain data according to tensile, flexural and torsional tests showed agreement with the numerical calculation. Young's modulus and the strength in tension are uniform along the stem axis (40 GPa and 600 MPa, respectively) while the elastic modulus in bending varies from 10 to 60 GPa in the tip-head direction. The composite stem showed a linear load-displacement relation up to 4500 N without breaking. Mechanical behaviour of the CHP is compared to that of a canine femur. Comparison with metal prostheses has also been undertaken. CHPs control stress-strain distributions, and hence the mechanical signals to bone, through a material-structure design.

Animals↗

PubMed2000

Synthesis, chemical and rheological characterization of new hyaluronic acid-based hydrogels.

New hyaluronic acid-based hydrogels have been synthesized. The carboxylate groups of hyaluronan were activated in order to bind the amino terminal groups of the di-amine cross-linking reagent. Different hydrogels were obtained according to the different di-amine cross-linking agents (1,3-diaminepropane, 1.6-diaminohexane, PEG500 di-amine. and PEG800 di-amine). The cross-linked polymer (C.L.Hyal) was then sulphated (C.L.HyalS) by a heterogeneous reaction using sulphur trioxide pyridine complex (SO3-Py). The thermo-mechanical properties and swelling degree were evaluated and are discussed in relation to the chemical structure and the hydrophilic character of the gels. The different behaviours of C.L.Hyal and C.L.HyalS indicate the important role of sulphated groups.

Biocompatible Materials↗

PubMed1998

Viscoelastic behavior of composite ligament prostheses.

Despite the compelling need for artificial connective tissue replacements for orthopedic applications, to date, there is no material which can adequately reproduce the mechanical behavior of natural tissue with necessary long-term endurance. In this work, we introduce a novel soft composite material as a more suitable candidate for connective tissue replacement. The material proposed is based on a hydrogel-polymer matrix reinforced with poly(ethylene terephthalate) fibers wound helically to mimic the architecture of the collagen fibers in natural tissue. Macroscopic behaviors such as static stress-strain, stress relaxation, and dynamic frequency responses can be modulated with choice of the components and design of the composite structure. In doing so, the mechanical characteristics of natural ligaments can be qualitatively reproduced and sustained over time.

Composite Resins↗

PubMed1998

Composite hydrogels for implants.

Hydrophilic composite structures are designed to mimic the transport and mechanical properties of natural soft tissue such as tendons, ligaments and intervertebral discs. Mechanical and viscoelastic behaviour of a soft composite material based on a hydrogel matrix reinforced with bundles of polyethylene therephthalate (PET) fibres is analysed. The typical J-shaped stress-strain behaviour, displayed by natural tendons and ligaments, is reproduced. The mechanical characteristics, such as the extent of the 'toe-in region' and the elastic modulus in the linear region, can be controlled by varying the winding angle of the fibres and the matrix composition. Dynamic mechanical analysis showed the dual behaviour of the composite systems due to the progressive contribution of the PET fibres. Different poly(2-hydroxyethylmethacrylate)/polycaprolactone (PHEMA/PCL) semi-interpenetrating polymer networks (IPNs) hydrogel composite systems reinforced with PET fibres have been investigated for potential use as intervertebral disc prostheses. Compression properties have been evaluated by static and dynamic tests. Uniaxial compression tests on the swollen samples showed an increase of the modulus and maximum stress with increasing content of PCL and PET fibres. Creep behaviour is also dependent on the hydrogel composition. The composite PHEMA/PCL hydrogels showed compression properties similar to those expressed by canine intervertebral discs in different spinal locations.

Animals↗

PubMed1997

The differential effects of poly(2-hydroxyethyl methacrylate) and poly(2-hydroxyethyl methacrylate)/poly(caprolactone) polymers on cell proliferation and collagen synthesis by human lung fibroblasts.

Because of its chemical versatility and demonstrated biocompatibility, poly(2-hydroxyethyl methacrylate) (pHEMA) has been widely used as a polymer for biomedical applications. Since this hydrophilic material shows a poor interface with cells, blendings with other polymers were done to improve cytocompatibility. In our polymer, the presence of hydrophobic dominions on the material surface, due to the interpenetrating polymerization of pHEMA with poly(caprolactone) (PCL), seems to ameliorate the cytocompatibility in terms of cell adhesion and metabolism. For our experiments, we used IMR-90 human fibroblasts, as these cells strongly regulate DNA, RNA, and protein synthesis as anchorage-dependent variables. Cell attachment on a pHEMA/PCL interpenetrating polymer network was optimal, suggesting a strong adhesion between the cells and the polymer surface. Cell adhesion was weaker on pHEMA, as a significant fraction of the fibroblasts revealed a lack of spreading, with most cells remaining spherical. Moreover, only fibroblasts seeded on pHEMA significantly decreased mRNA synthesis; collagen production and cell shapes ranged from fully flat and proliferating, to minimally spread and nonproliferating. Finally, DNA synthesis, as a measure of cell proliferation, was markedly inhibited in cells cultured on pHEMA but not on pHEMA/PCL. In conclusion, our results suggest that control of cell growth and metabolism by biomedical polymers is based on physicochemical mechanism(s) in which the hydrophilicity/hydrophobicity ratio of the material surfaces may play an important role.

Base Sequence↗

PubMed1997

Characterization of maternal and zygotic D-raf proteins: dominant negative effects on Torso signal transduction.

The maternal D-raf serine/threonine kinase acts downstream of Torso (Tor) for specification of cell fates at the embryonic termini. D-raf activity is also required in other signal transduction pathways and consistent with its pleiotropic role, we find accumulation of a 90-kD D-raf protein throughout embryonic development. We also characterize the accumulation of maternal D-raf proteins in 0-2-hr embryos derived from females with germ cells lacking D-raf activity. Accumulation of a 90-kD or truncated mutant D-raf protein is observed for some of these embryos, while others lack the maternal D-raf protein. Then to determine whether rescue of the Tor pathway is influenced by pools of nonfunctional maternal D raf. wild-type D-raf mRNA was injected into embryos that inherit maternal stores of inactive 90-kD of truncated D-raf protein. For embryos lacking the maternal D-raf protein, a high level of terminal rescue is obtained. In contrast, rescue is reduced or not observed for embryos that accumulate mutant maternal D-raf proteins. These findings suggest that mutant forms of D-raf may deplete the embryo of a positive activator and/or form inactive protein complexes that affect rescue of the Tor pathway.

Animals↗

PubMed1997

Comparison between in vitro and in vivo UHMW-PE degradation.

There is an increasing interest in orthopedics for clinical problems associated with wear and failure of ultra-high-molecular-weight (UHMW) polyethylene devices. Wear not only affects the implant performance but, more importantly, produces the release of particulate debris in the surrounding tissues and fluids. The debris in turn cause a deleterious biological response that can include an inflammatory reaction with subsequent loosening of the implant components. Surface wear is certainly promoted from the oxidation process that can occur during the prosthesis life. However, the oxidation mechanism involved during the implantation period has not been described yet for the UHMW-polyethylene devices. Here, the comparison of FT-IR spectra of a retrieved acetabular cup (9 years in a human body) and thin UHMW-PE films treated respectively with: H2O2, KO2/THF, and Fe[II]/H2O2 solutions indicates the effect of the high reactive hydroxyl radicals as the most important cause of in vivo polymer degradation.

Biocompatible Materials↗

PubMed1996

The activity of D-raf in torso signal transduction is altered by serine substitution, N-terminal deletion, and membrane targeting.

The Raf family of serine/threonine kinases are essential components in many receptor tyrosine kinase-mediated signal transduction pathways. Here, we analyze the function of D-raf in the Torso (Tor) pathway required to specify cellular fates at the embryonic poles. Using mutant embryos lacking endogenous D-raf protein, we show that D-raf's serine/threonine kinase activity is essential for its role in Tor signal transduction and that human Raf-1 will substitute for D-raf in this pathway. After Tor activation, D-raf becomes hyperphosphorylated. We identified two putative serine phosphorylation sites (S388 and S743) in SF9 cells and demonstrate that S743 or its phosphorylation is essential for D-raf function in embryos. Alanine substitution at S388, N-terminal truncation, or targeted membrane association permits transmission of the Torso signal by D-raf, but these D-raf molecules differ in their rescuing potential and relative biological activity. Membrane-targeted D-raftor4021 showed the highest level of activity, followed by alanine-substituted D-rafS388A and N-terminal-truncated D-raf delta 445. Since the activity profiles for these altered forms of D-raf are distinct, these findings indicate that each structural modification differentially affects the regulation and/or propagation of the Tor signal by these mutant D-raf proteins.

Alanine↗

PubMed1996

Synthesis and characterization of a new interpenetrated poly(2-hydroxyethylmethacrylate)-gelatin composite polymer.

Poly(2-hydroxyethylmethacrylate) [poly(HEMA)] is a widely used biomaterial which does not allow cell adhesion and growth on its surface, limiting its use in biomedical applications in which cell cohesion is detrimental. We have prepared a poly(HEMA)-gelatin composite hydrogel using a sequential interpenetrating polymer network technique. The properties of this material were compared with poly(HEMA) freeze-dried sponges in terms of morphology, mechanical properties and biocompatibility. Moreover, in vivo biocompatibility experiments highlighted the occurrence of cellular interactions on the surface of the poly(HEMA)-gelatin interpenetrating polymer network, which are usually absent when unmodified poly(HEMA) hydrogels are implanted in the same host organism. These tests also showed a progressive gelatin degradation from the surface to the bulk of the poly(HEMA)-gelatin specimens during short-term (7 d) implantation. Finally, in vitro tests confirmed an improved ability of this composite to scaffold for the cells.

3T3 Cells↗

PubMed1995

Imaging and manipulating chromosomes with the atomic force microscope.

Polytene chromosomes from the salivary gland cells of Drosophila melanogaster were examined by atomic force microscopy. The atomic force microscope (AFM) was capable of resolving chromosomal features down to the limits of the tip sharpness, about 500 A for pyramidal-shaped tips. Resolution was increased to 300 A by using electron beam deposited (EBD) tips with high aspect ratios. This significantly exceeds the resolution obtainable with conventional optical microscopes, but at the cost of compromising the structural integrity of the sample. A reasonable compromise was achieved by using oxide-sharpened tips. In this case high resolution was obtained without sample degradation, but when desired these tips were also capable of sample disintegration with increased scanning force and rate. Thus, oxide-sharpened tips were used to precisely dissect defined chromosomal regions to illustrate their potential use in genetic mapping efforts. This study illustrates the utility of the AFM in the characterization and manipulation of chromosomes and chromosomal DNA.

Animals↗

PubMed1995

Mechanical behaviour of composite artificial tendons and ligaments.

The mechanical behaviour of a soft composite material based on a hydrogel polymer matrix reinforced with bundles of poly(ethylene terephthalate) (PET) fibres is analysed. The composite reproduces the typical J-shaped stress-strain curves displayed by natural tendons and ligaments. The lamination composite theory was used to investigate the role of the fibres and the matrix properties, as well as the role of the winding angle and the volumetric fraction of fibres, on the mechanical response of this system. The results suggested that large variations in the mechanical behaviour can be obtained by changing the winding angle of the fibres in the composite which determines the extent of the 'toe' region and the sensitivity of the system to the rigidity of the fibres.

Animals↗

PubMed1995

Combining optical and atomic force microscopy for life sciences research.

The atomic force microscope (AFM), a three-dimensional imaging tool that can measure structures from the atomic level to micron scale, has been combined with an inverted optical microscope capable of confocal imaging. The robust design of this microscope, termed the BioScope, enables the operator to use fluorescent markers on a wide variety of biological specimens to determine internal structure to 200 nm resolution and determine surface morphology of the same sample to 20 nm resolution while imaging under physiological conditions. In this report we demonstrate the capabilities of the BioScope by examining living Xenopus retinal glial (XR1) cells, Drosophila polytene chromosomes and colloidal gold-labeled plasmid DNA.

Animals↗