1,721,014 research outputs found
A new hydroxyapatite-based biocomposite for bone replacement
No full textSince the 1970s, various types of ceramic, glass and glass–ceramic materials have been proposed and used to
replace damaged bone in many clinical applications. Among them, hydroxyapatite (HA) has been successfully
employed thanks to its excellent biocompatibility. On the other hand, the bioactivity of HA and its reactivity
with bone can be improved through the addition of proper amounts of bioactive glasses, thus obtaining
HA-based composites. Unfortunately, high temperature treatments (1200 °C ÷ 1300 °C) are usually required
in order to sinter these systems, causing the bioactive glass to crystallize into a glass–ceramic and hence
inhibiting the bioactivity of the resulting composite. In the present study novel HA-based composites are re-
alized and discussed. The samples can be sintered at a relatively low temperature (800 °C), thanks to the em-
ployment of a new glass (BG_Ca) with a reduced tendency to crystallize compared to the widely used 45S5
Bioglass®. The rich glassy phase, which can be preserved during the thermal treatment, has excellent effects
in terms of in vitro bioactivity; moreover, compared to composites based on 45S5 Bioglass® having the same
HA/glass proportions, the samples based on BG_Ca displayed an earlier response in terms of cell proliferation
End-Functionalised 1-Vinyl-2-Pyrrolidone Oligomers Bearing Lactate Functions at One End.
No full text1-Vinyl-2-pyrrolidinone (VP) oligomers bearing a lactate group at one end (PVP-L) were obtained by chain-transfer controlled radical polymerisation carried out in the presence of ethyl L-lactate as chain-transfer agent (CTA). Their number-average molecular weights were in the range 1500-4000 with molecular weight distributions ranging from 1.4 to 1.8. The chain transfer constant, CT, of the ethyl L-lactate/VP system was determined by monitoring the variation of PVP-L number-average molecular weight on conversion. The CT value so obtained was 1.03 × 10-2, which is by about one order of magnitude higher than the CT value previously determined for a seemingly similar system, namely methyl isobutyrate/1-vinyl-2- pyrrolidinone (1.64 × 10-3). The resultant PVP-L oligomers were thoroughly characterised by means of 1H and 13C NMR, in order to ascertain the regular presence of the lactate functions at one of their chain terminals. NMR characterisations gave results in full agreement with the proposed structure. Moreover, the molecular weight values determined by NMR very closely agreed with those obtained by SEC. Preliminary biological evaluations of the PVP-L oligomers showed a complete lack of toxicity
Surface investigation of segregation effects in poly(e-caprolactone)-poly(ethylene glycol) based multiblock copolymers
No full textSynthesis, acid-base properties and preliminary cell compatibility evaluation of amphoteric poly(amido-hydrazine)s
No full textAmphoteric poly(amido-hydrazine)s (PAHYs) were obtained by
hydrogen-transfer polyaddition of hydrazine, 1,2-dimethylhydrazine and 1,1-
dimethylhydrazine to 2,2-bisacrylamidoacetic acid. These polymers were studied
for biomedical applications, such as degradability in water solution, acid–base
properties, and cell toxicity. They degraded rapidly in aqueous media under physiological
conditions, their molecular weight was reduced to about one-fourth, that
of the original polymer in less than two days. They exhibited a typical polyelectrolyte
behavior with isoelectric points between 4 and 5 and are prevailingly
anionic in the blood. In preliminary cell toxicity essays they proved to be remarkably
biocompatible, comparable in this respect to amphoteric poly(amido-amine)s
(PAAs), and much less toxic than poly-L-lysine and polyethylenimine
H-1 NMR studies of alginate interactions with amino acids
No full textThe interactions between alginate and the amino acids,histidine,
lysine,phenylalanine, and alanine,were studied by Proton Nuclear Magnetic
Resonance. The characterization of the amino acids interaction with alginate
was performed by 1D and 2D-NOESY experiments. Measurements of 1HNMR
nonselective and selective relaxation rates in the absence and presence of
alginate were used to calculate interaction constants between each amino acid
and alginate. The interaction constants were found to be related to the
hydrophobicity of the different amino acid side-chains. The interaction constant
between phenylalanine and Ca2þ crosslinked alginate was also determined.
There was no apparent differences observed in the crosslinked and the solution
amino acid–alginate interactions. On the basis of the experimental results
obtained,a mode
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Production of Bioglass® 45S5-Polycaprolactone composite scaffolds via salt leaching
No full textPolycaprolactone (PCL)-Bioglass 45S5 (45S5) composite scaffolds were produced by means of the salt- leaching technique. Various salts (NaCl, NaHCO3, and a mixture of them) were used with the aim of opti- mising the pores network; moreover several glass weight fractions and glass particle sizes were tested. The so-obtained composite scaffolds were characterized from a microstructural, mechanical and biolog- ical point of view; in particular, in view of the biomedical application of the materials, both in vitro and cytotoxicity tests were performed. The microstructure of the composite scaffolds possessed a well-devel- oped interconnected porosity, ideal for bone regeneration and vascularization. The mechanical properties of the PCL matrix were not altered by the introduction of the glass and the scaffolds ensured an easy han- dling. As regards the bioactivity, the prolonged contact of the 45S5 particles with the water used to remove the salt probably induced a reaction which promoted the development of calcite and altered the glass composition, suppressing the development of hydroxyapatite in vitro; however the response to the cytotoxicity test was promising, confirming the relevance of the PCL-45S5 composite scaffolds and justifying future efforts to improve the production technique, in order to limit the glass alteratio
Poli(amido-ammine) lineari o reticolate contenenti gruppi laterali guanidinici
No full textDisclosed are linear or branched poly(amidoamine)s contg. guanidine groups useful as transfection agents, as scaffolds for tissue engineering, and in general applications as biomaterials. The crosslinked poly(amidoamine) structures can swell in aq. media, thus giving rise to hydrogels. Thus, to a mixt. of 2,2-Bis(acrylamido)acetic acid and 4-aminobutylguanidine sulfate in water, LiOH is added and the mixt. is stirred until it becomes clear soln. After 72 h at room temp. the mixt. is acidified with HCl, filtered or dialyzed, and then lyophilized to give a white powder sol. in water
Poli(amido-ammine) lineari o reticolate contenenti gruppi laterali guanidinici
No full textDisclosed are linear or branched poly(amidoamine)s contg. guanidine groups useful as transfection agents, as scaffolds for tissue engineering, and in general applications as biomaterials. The crosslinked poly(amidoamine) structures can swell in aq. media, thus giving rise to hydrogels. Thus, to a mixt. of 2,2-Bis(acrylamido)acetic acid and 4-aminobutylguanidine sulfate in water, LiOH is added and the mixt. is stirred until it becomes clear soln. After 72 h at room temp. the mixt. is acidified with HCl, filtered or dialyzed, and then lyophilized to give a white powder sol. in water
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