Biomedical subjects

M C Tanzi

Publications and source records attributed to M C Tanzi.

At least 19 recordsLinked to original sources

PubMed2007

Skin-derived stem cells transplanted into resorbable guides provide functional nerve regeneration after sciatic nerve resection.

The regeneration in the peripheral nervous system is often incomplete and the treatment of severe lesions with nerve tissue loss is primarily aimed at recreating nerve continuity. Guide tubes of various types, filled with Schwann cells, stem cells, or nerve growth factors are attractive as an alternative therapy to nerve grafts. In this study, we evaluated whether skin-derived stem cells (SDSCs) can improve peripheral nerve regeneration after transplantation into nerve guides. We compared peripheral nerve regeneration in adult rats with sciatic nerve gaps of 16 mm after autologous transplantation of GFP-labeled SDSCs into two different types of guides: a synthetic guide, obtained by dip coating with a L-lactide and trimethylene carbonate (PLA-TMC) copolymer and a collagen-based guide. The sciatic function index and the recovery rates of the compound muscle action potential were significantly higher in the animals that received SDSCs transplantation, in particular, into the collagen guide, compared to the control guides filled only with PBS. For these guides the morphological and immunohistochemical analysis demonstrated an increased number of myelinated axons expressing S100 and Neurofilament 70, suggesting the presence of regenerating nerve fibers along the gap. GFP positive cells were found around regenerating nerve fibers and few of them were positive for the expression of glial markers as S-100 and glial fibrillary acidic protein. RT-PCR analysis confirmed the expression of S100 and myelin basic protein in the animals treated with the collagen guide filled with SDSCs. These data support the hypothesis that SDSCs could represent a tool for future cell therapy applications in peripheral nerve regeneration.

Action Potentials↗

PubMed2006

Bioabsorbable scaffold for in situ bone regeneration.

A non-porous poly-DL-lactide tubular chamber filled by demineralised bone matrix (DBM) and bone marrow stromal cells (BMSC) in combination, was evaluated as a scaffold for guided bone regeneration (GBR) in an experimental model using the rabbit radius. The tubular chamber had an internal diameter of 4.7 mm, a wall thickness of 0.4 mm and a length of 18 mm. Autologous BMSC were obtained, under general anaesthesia from rabbit iliac crest and isolated by centrifugation technique. Allogenic DBM was obtained from cortico-cancellous bone of rabbits. In general anaesthesia, a 10-mm defect was bilaterally created in the radii of 10 rabbits. On the right side (experimental side) the defect was bridged with the chamber filled with both BMSC and DBM. On the left side (control side) the defect was treated by positioning DBM and BMSC between the two stumps. At an experimental time of 4 months histology and histomorphometry demonstrated that the presence of a tubular chamber significantly improved bone regrowth in the defect The mean thickness of newly-formed bone inside the chamber was about 56.7+/-3.74% of the normal radial cortex, in comparison with 46.7+/-10.7% when DBM and BMSC without the chamber were placed in the defect, P<0.05). These results confirmed the effectiveness of the chamber as a container for factors promoting bone regeneration.

Absorbable Implants↗

PubMed2006

Antibacterial activity of zinc modified titanium oxide surface.

Titanium-based implants are successfully used for various biomedical applications. However, in some cases, e.g. in dental implants, failures due to bacterial colonization are reported. Surface modification is a commonly proposed strategy to prevent infections. In this work, titanium oxide, naturally occurring on the surface of titanium, was modified by promoting the formation of a mixed titanium and zinc oxide, on the basis of the idea that zinc oxide on titanium surface may act as the zinc oxide used in pharmaceutical formulation for its lenitive and antibacterial effects. The present work shows that it is possible to form a mixed titanium and zinc oxide on titanium surfaces, as shown by Scanning Electron Microscopy and XPS analysis. To this end titanium was preactivated by UV on crystalline titanium oxide, both in the anatase form or in the co-presence of anatase and rutile. By performing antibacterial assays, we provide evidence of a significant reduction in the viability of five streptococcal oral strains on titanium oxide surfaces modified with zinc. In conclusion, this type of chemical modification of titanium oxide surfaces with zinc might be considered a new way to reduce the risk of bacterial colonization, increasing the lifetime of dental system applications.

Anti-Bacterial Agents↗

PubMed2005

Microspheres leaching for scaffold porosity control.

Scaffold morphology plays a key role in the development of tissue engineering constructs. The control of pore size, shape and interconnection is needed to achieve adequate nutrient transport and cell ingrowth. Several techniques are available for scaffold manufacturing, but none allows easy control of morphology and is, at the same time, applicable to a wide variety of materials. To investigate the possibility of processing a wide range polymers by solvent casting/particulate leaching with accurate control of scaffold morphology, three different porogens (gelatin microspheres, paraffin microspheres and sodium chloride crystals) were used to fabricate scaffolds from commonly employed biodegradable polymers. The outcome of processing was evaluated in terms of scaffold morphology and structure/properties relationships. Highly porous scaffolds were obtained with all porogens and well defined spherical pores resulted from microspheres leaching. Furthermore, scaffolds with spherical pores showed better mechanical performance and lower flow resistance. Cytocompatibility tests performed showed no evidence of processing residuals released from the scaffolds. Solvent casting/microspheres leaching, particularly gelatin microspheres leaching, can be used to process a large number of polymers and enables to tailor scaffold pore size, shape and interconnection, thus providing a powerful tool for material selection and optimization of scaffold morphology.

Microscopy, Electron, Scanning↗

PubMed2003

Design, synthesis and properties of polyurethane hydrogels for tissue engineering.

Due to their similarity to natural soft tissues, water-swellable polymeric materials (hydrogels) are, in principle, ideal candidates for scaffolds/matrices in tissue engineering. Polyurethanes (PU), hydrophilic but water-insoluble, can be obtained by the incorporation of hydrophilic soft segments, e.g. poly(ethylene oxide) (PEO). These materials possess the favorable characteristics of the family of PUs as well as the ability to mimic soft tissues. In this work, new crosslinked PU-hydrogels were prepared in a one-step bulk polymerization process using an aliphatic diisocyanate, PEO, a low molecular weight diol, and a tri-functional crosslinking agent. A porous structure was also obtained by air-incorporation under mechanical stirring at a controlled high speed during the polymerization. Structural characteristics of the compact (PU-HyC) and the porous (PU-HyP) material were investigated. Molecular weight between cross-links, M(c), and crosslinking density, rho(x), were typical of a low crosslinking degree. A homogeneous distribution of non-interconnecting pores (phi100 microm) was observed in PU-HyP. Both materials showed a high water adsorption. The swelling behavior and weight loss in water was affected by porosity. For their mechanical behavior in the swollen state, the novel PU hydrogels can be considered for biomedical applications where good mechanical properties are required (i.e. 3D scaffold for tissue engineering).

Journal Article↗

PubMed2000

Enhanced wear performance of highly crosslinked UHMWPE for artificial joints.

It is well known that osteolysis induced by polyethylene wear debris is the main cause of long-term failure of hip and knee prostheses. We developed a treatment of medical-grade ultra-high molecular-weight polyethylene (UHMWPE) in order to improve its tribologic properties and reduce its wear. Medical-grade UHMWPE was irradiated with a 200 kGy dose of radiation, thermally stabilized at a temperature close to the melting point, and then sterilized with ethylene oxide. The irradiation treatment was performed to crosslink the UHMWPE. The thermal stabilization treatment, contributing to the reaction between the free radicals generated by the irradiation process, was chosen to enhance crosslinking and to prevent oxidation and the shortening of chains. The non-invasive sterilization process with ethylene oxide was chosen to prevent the re-formation of free radicals. The wear performance of this material was compared to UHMWPE, untreated or treated with different sterilization techniques, using gamma and beta irradiation. Insoluble crosslinked constituents were measured with an extraction method. Wear was evaluated using a flat-on-ring wear test machine. While small differences were found among the different sterilization processes, 200 kGy-irradiated UHMWPE followed by thermal treatment and sterilization with ethylene oxide had the least wear and the greatest amount of crosslinking.

Biocompatible Materials↗

PubMed2000

Novel poly(urethane-aminoamides): an in vitro study of the interaction with heparin.

In order to obtain heparin-binding polyurethanes, tertiary amino-groups have been introduced in the polymer backbone by attributing a key-role to the chain extender, i.e. substituting butanediol, commonly used in polyurethane synthesis, with a tailor-made diamino-diamide-diol. In this work a poly(ether-urethane-aminoamide) (PEU/PIME/al) was obtained with poly(oxytetramethylene) glycol 2000, 1,6-hexamethylene-diisocyanate and the new chain extender, in the molar ratio 1:2:1. The heparin binding capacity of PEU/PIME/al was evaluated with 125I labelled heparin, using for comparison the analogous polymer obtained with a diamide-diol (i.e. the poly(ether-urethane-amide) PEU/PIBLO/al), and two commercially available biomedical polyurethanes (Pellethane 2363 and Corethane). pH and ionic strength dependence of the heparin uptake were investigated by treating all the polyurethanes with solutions of 125I heparin into buffers from pH 4 to 9 or NaCl molarity from 0.0 to 1.0. The stability of the interaction with bound heparin was investigated by sequential washing treatments (PBS, 1 N NaOH, 2% SDS solution), then analysing the residual radioactivity on the materials. Results indicated that the heparin binding of PEU/PIME/al is significantly higher and more stable than that of the other polyurethanes, with a time-dependent kinetic. The interaction with heparin appears to be prevalently ionic, with the contribution of other electrostatic and hydrophobic interactions. Activated partial thromboplastin time (APTT), performed on human plasma with polyurethane-coated, heparinized test tubes, indicated that bound heparin maintains its biological activity after the adsorption.

Animals↗

PubMed2000

In vitro stability of polyether and polycarbonate urethanes.

The in vitro structural stability of poly-ether-urethanes (PEUs) and poly-carbonate-urethanes (PCUs) was examined under strong acidic (HNO3) or alkaline (NaClO) oxidative conditions and in presence of a constant strain state. Polyurethane (PU) samples were represented by sheets solvent-cast from commercial pellets or by tubular specimens cut from commercial catheters. The specimens were strained at 100% uniaxial elongation over appropriate extension devices and completely immersed into the oxidative solutions at 50 degrees C for 7-14 days. The changes induced by the oxidative treatments were then evaluated by molecular weight analysis, tensile mechanical tests, and scanning electron microscopy. In the experiments with solvent-cast samples, the PEU Pellethane was degraded more in the alkaline oxidative conditions and mainly in the absence of an applied uniaxial stress. All the tested PCUs were, on the contrary, more affected by the acidic oxidative agent. All the PCUs proved to have overall better stability than the PEU. The susceptibility to oxidation was also dependent on the shape and bulk/surface organisation acquired by the same polymer during its processing. When the oxidative test was applied to catheters made of a PEU and a PCU, the results confirmed the better stability of poly-carbonate-urethanes.

Biocompatible Materials↗

PubMed1999

Synergistic effects of oxidative environments and mechanical stress on in vitro stability of polyetherurethanes and polycarbonateurethanes.

The in vitro structural stability of polyetherurethanes (PEUs) and polycarbonateurethanes (PCUs and PCUUs) was examined under strong oxidative conditions (0.5N HNO3, pH 0.3; and NaClO, 4% Cl2 available, pH approximately 13) and in the presence of a constant strain state. Solvent-cast dog-bone shaped specimens were strained at 100% uniaxial elongation over extension devices and completely immersed in the oxidative solutions at 50 degrees C for 15 days. Unstrained polyurethane (PU) samples were treated in the same way for comparison. The modification of the PU molecular structure was determined by DSC, GPC, ATR-FTIR, static contact angle, and surface roughness analyses. The incubation in nitric acid and sodium hypochlorite brought about a greater degradation of samples tested under the applied strain with the exception of PEU treated with nitric acid. PEU was the most affected material, showing bulk deterioration in NaClO and significant modifications in nitric acid, with the appearance of new IR bands, which were assigned to oxidation products. A higher phase separation between soft and hard domains occurred in PCUs upon incubation in nitric acid, the treatment with NaClO gave rise to new bands in the IR spectra, denoting the presence of oxidation products at the surface. The surface roughness greatly increased in strained PCUs with SEM evidence of deep cracks and holes or ragged and stretched fractures perpendicular to the direction of stress. PCUU underwent complex chemical modifications with a marked decrease of N-H and urea IR absorptions and showed a lower degradation than PEU and PCUs under mechanical constraint. From these results, sodium hypochlorite appears to be able to create an ESC-like degradation for PUs that are resistant to other aggressive chemical environments.

Microscopy, Electron, Scanning↗

PubMed1999

Polyurethane-maleamides for cardiovascular applications: synthesis and properties.

Several polyurethane-maleamides (PUMAs) containing polyether or polycarbonate soft segments, and aromatic or aliphatic hard segments were synthesized by solution or bulk polymerization, using maleic acid (MA) or a mixture of MA and butanediol as chain extenders. Using this process, activated double bonds are introduced into the polymer chains and the base polyurethanes may undergo further modification via specific grafting, thus improving their tissue compatibility. PUMAs chemicophysical properties were evaluated by gel permeation chromatography (GPC), intrinsic viscosity analyses, differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FT-IR) and tensile mechanical tests. Polycarbonate diol (PCU)-based PUMAs showed higher molecular weights than polyether diol (PEU)-based ones. The use of butanediol in mixture with maleic acid led to an increase of molecular weights. FT-IR confirmed the presence of the bands related to the amide groups and to the conjugated double bond, yet more evident for the polymer obtained in solution. The higher crystallinity shown by this polymer was also indicative of a better phase separation. All the PCU-PUMAs exhibited similar tensile properties with a higher stiffness than PEU-PUMAs. Among the PEU-PUMAs, the highest tensile properties were shown by the polymer obtained in solution, and by the one derived from a mixture of maleic acid and butanediol.

Journal Article↗

PubMed1997

Chemical stability of polyether urethanes versus polycarbonate urethanes.

The relative chemical stability of two commercially available polyurethanes-Pellethane, currently used in biomedical devices, and Corethane, considered as a potential biomaterial-was investigated following aging protocols in hydrolytic and oxidative conditions (HOC, water, hydrogen peroxide, and nitric acid) and in physiological media (PHM, phosphate buffer, lipid dispersion, and bile from human donors). The chemical modifications induced on these polymers were characterized using differential scanning calorimetry (DSC), gel permeation chromatography (GPC), and Fourier transform infrared spectroscopy (FTIR). With the exception of nitric acid, all of the aging media promoted a mild hydrolytic reaction leading to a slight molecular weight loss in both polymers. When aged in water and hydrogen peroxide, Pellethane experienced structural modifications through microdomain phase separation along with an increase of the order within the soft-hard segment domains. The incubation of Pellethane in nitric acid also resulted in an important decrease of the melting temperature of its hard segments with chain scission mechanisms. Moreover, incubation in PHM led to an increase of the order within shorter hard-segment domains. FTIR data revealed the presence of aliphatic amide molecules used as additives on the Pellethane's surface. The incubation of Corethane under the same conditions promoted an almost uniform molecular reorganization through a phase separation between the hard and soft segments as well as an increase of the short-range order within the hard-segment domains. Incubation of this polymer in nitric acid also resulted in a chain scission process that was less pronounced than that measured for the Pellethane samples. Finally, lipid adsorption occurred on the Corethane sample incubated in bile for 120 days. Overall data indicate that polycarbonate urethane presents a greater chemical stability than does polyetherurethane.

Calorimetry, Differential Scanning↗

PubMed1995

Polyurethane-coated, self-expandable biliary stent: an experimental study.

RATIONALE AND OBJECTIVES: We describe a self-expanding metallic biliary Gianturco-Rösch stent coated with polymeric material. The coating was designed to prevent the growth of neoplastic and reactive tissue within the biliary ducts. METHODS: The stents were coated with a solvent-casting technique, which consists of dissolving polyurethane (polyether urethane or polycarbonate urethane) pellets in a solvent (dimethylacetamide), dipping the stent in the solution, and completely evaporating the solvent. In vitro mechanical characterization of the stent was performed to determine the adhesion of the coating to the metallic cage, the best introducer caliber for implantation of the device, and the relationship between the stent's diameter and radial stress. RESULTS: Reports in the literature on the biostability of polycarbonate urethane compared with polyether urethane prompted us to use the former material to coat the stents. The solvent technique gives a smooth internal surface of the stent wall, leaving in relief the coated structure of the stent on the external surface. The functional tests demonstrated that the coating did not compromise the original characteristics of the stent in terms of self-expandability, axial flexibility, and increased radial rigidity of the device. CONCLUSION: Functional tests verified coating stability and device handling, which are the first steps toward in vivo experimentation.

Bile Ducts↗

PubMed1993

Comparative biological tests on segmented polyurethanes for cardio-vascular applications.

In order to select a candidate segmented polyurethane (SPU) elastomer for the preparation of cardio-vascular prostheses, a series of biological tests (namely haemolysis, aPTT and PT coagulation tests, cytotoxicity, human endothelial cells seeding) was carried out on five commercially available biomedical polyurethanes. The tests were performed on solvent cast samples, from THF (Cardiothane 51, Pellethane 2363 80A, Estane 5714 F1, and Estane 58810), or DMAC (Biomer). All the materials were sterilized by gamma-irradiation before being tested. From the results obtained all the polyurethanes used in this study were shown to be devoid of toxicity towards blood (as proved by haemolysis and coagulation time tests) or blood cells (as proved by cytotoxicity and cell adhesion assays). A clear difference among the tested copolymers didn't stand out under our test conditions, although Cardiothane, possibly due to its physico-chemical characteristics, was less effective in promoting endothelial cell adhesion.

Animals↗

PubMed1993

[Biodegradation of dacron vascular prostheses. Physico-chemical, histological, morphometric and ultrastructural study].

The paper deals with study of long-term stability as far as concerns Dacron vascular prostheses in woven and knitted double velour. Among our vascular prostheses case-reports, we evaluated three of them explanted after 11, 12, 20 years; all of the prostheses were patent. Chemical-physical, histopathological and ultrastructural analysis have been carried on in order to evaluate in vivo ageing of the examined prostheses. The results all indicate strong alterations of the original properties related to double velour of knitted prostheses and weak alterations of woven one.

Aged↗

PubMed1992

Grafting reactions and heparin adsorption of poly(amidoamine)-grafted poly(urethane amide)s.

Differently terminated poly(amidoamine) (PAA) oligomers were grafted on the surface of poly(ether urethane amide)s (PEUAm), with fumaric or maleic acid moieties. The grafting reaction was Michael-type addition of amino groups to activated double bonds in the PEUAm backbone. PAAs having primary amino, or secondary amino end-groups were directly grafted on the surface of PEUAm sheets. For vinyl-terminated chains an alpha, omega amino-polyether spacer was introduced initially, following the same addition mechanism. Ungrafted and grafted materials were characterized, besides other analytical techniques, by ATR FT-IR spectroscopy. The heparin adsorption on PEAUm films was analysed after its elution from heparinized samples, quantified by coagulation tests (aPTT), and related to the presence of the PAAs chains grafted on to the surface. Results indicate that PAA-grafted PEUAm elastomeric biomaterials, display enhanced heparin adsorption abilities.

Adsorption↗

PubMed1992

Genotoxicity of N-acryloyl-N'-phenylpiperazine, a redox activator for acrylic resin polymerization.

N-Acryloyl-N'-phenylpiperazine is a promoter of redox reactions synthesized recently, and proposed as an activator for the polymerization of acrylic resins for biomedical use. The chemical was analyzed for different genotoxicity endpoints, to obtain both information on its possible mutagenic/carcinogenic potential and a model analysis of a tertiary arylamine, which belongs to a class of chemicals commonly used as polymerization accelerators in the biomaterial field. The genotoxicity endpoints considered were: gene mutation in the Salmonella test; structural and numerical chromosome alterations in Chinese hamster V79 cells, evaluated by the micronucleus test together with an immunofluorescent staining specific for kinetochore proteins; in vitro and in vivo DNA damage, evaluated in V79 cells and in mouse liver by the alkaline DNA elution technique. On the whole, the results indicate that N-acryloyl-N'-phenylpiperazine is to be regarded not so much as a DNA-damaging agent, but as a genomic mutagen. Indeed, it was not mutagenic in Salmonella (though its toxicity did not allow testing concentrations over 70 micrograms/plate), and it was weakly positive in inducing chromosomal fragmentation in vitro (one positive, not dose-related, result out of five different doses tested) and in vivo DNA damage (increases in DNA elution rate never doubling control values). The chemical was, however, clearly positive (with dose-dependent effects up to about 25 times the control value) in causing numerical chromosome alterations, at the maximal non-toxic doses.

Acrylic Resins↗

PubMed1991

Comparative physical tests on segmented polyurethanes for cardiovascular applications.

In order to select a candidate segmented polyurethane (SPU) elastomer for cardiovascular prostheses, a series of physical tests was carried out on five commercially available biomedical polyurethanes. The tests were performed on uniformly thick sheets (0.2-0.3 mm), obtained by solvent casting from THF (Cardiothane 51, Pellethane 2363 80A, Estane 5714 F1, and Estane 58810) or DMAC (Biomer). Tensile mechanical tests at 23 and 37 degrees C showed for all the copolymers typical stress/strain behaviour of elastomeric materials, with small individual differences. Hydrolytic stability was investigated at 85, 60, and 37 degrees C, at increasing times of exposure (96-168 h), in water or alkaline buffer (pH = 10). As indicated by gel permeation chromatography, in almost all cases a degradation of the molecular weight (particularly the M w) was noticed after the hydrolytic tests, but tensile, thermal (by DSC) and dynamic mechanical properties were substantially not affected. SEM was also performed on the materials, before and after the hydrolytic tests. Changes in the morphology of the materials (related to degradation effects) was observed only in the case of Biomer, as shown also by the thermomechanical analyses. After this first series of physical tests, a clear choice of a particular SPU among the five investigated was not found.

Blood Vessel Prosthesis↗

PubMed1991

Physical characterization of acrylic bone cement cured with new accelerator systems.

In the attempt to substitute dimethyl-p-toluidine (DMPT), a toxic tertiary aryl-amine accelerator, into the formulation of acrylic cements, less toxic accelerator systems are developed. These systems consist of benzoyl peroxide (BPO) and unsaturated tertiary-aryl-amines, such as acryloyl- (ANP) and methacryloyl-(MNP) N-phenylpiperazine, which can be chemically incorporated in the polymerizing resin or, at least, result in less leaching from cured materials. In this work compressive mechanical properties and ageing tests for colour stability of acrylic cement cured with BPO and ANP or MNP have been considered. For compressive tests, cylindrical specimens were cured with BPO and equivalent molecular amounts of DMPT, ANP and MNP. Compressive yield stress (sigma y), strain at yield (epsilon y, %) and elastic modulus (E) gave very similar results for samples cured with DMPT and ANP, and slightly lower results for samples cured with MNP. In colour stability tests, the samples (disks of 1.5 cm diameter) were exposed to UV light at different irradiation times (up to 42 h). The evaluation of the colour change was performed with a digital analyser for images, and observed under scanning electron microscopy. From the obtained results, ANP appeared to be the best candidate as accelerator in the preparation of biomedical acrylic resins and composites.

Acrylic Resins↗