Giulio D. Guerra

New composites of hydroxyapatite and bioresorbable macromolecular material.

Composite materials were prepared by mixing in different proportions of hydroxyapatite (HA) and poly(ε-caprolactone-oxyethylene-ε-caprolactone) block copolymer (PCL-POE-PCL) to produce a new resorbable material for biomedical applications. This material has proved to be very interesting for production of periodontal membranes. Mechanical properties are linearly proportional to the amount of HA introduced. Fourier transform infrared (FTIR) investigations have pointed out that HA is able to influence some close ε-caprolactone molecules to start its homopolymerization giving PCL with an end chain ionic bonding. HA grains are therefore surrounded by a film of PCL which grants close connection of HA grains within copolymeric matrix. This interface bond with PCL is, however, an interesting occurrence for preparations of HA/PCL composites. ©1999 Kluwer Academic Publishers

Hydroxyapatite/gelatin/gellan sponges as nanocomposite scaffolds for bone reconstruction

The aim of this work was the morphological, physicochemical, mechanical and biological characterization of a new composite system, based on gelatin, gellan and hydroxyapatite, and mimicking the composition of natural bone. Porous scaffolds were prepared by freeze–drying technique, under three different conditions of freezing. The morphological analysis showed a homogeneous porosity, with well interconnected pores, for the sample which underwent a more rapid freezing. The elastic modulus of the same sample was close to that of the natural bone. The presence of interactions among the components was demonstrated through the physicochemical investigation. In addition, the infrared chemical imaging analysis pointed out the similarity among the composite scaffold and the natural bone, in terms of chemical composition, homogeneity, molecular interactions and structural conformation. Preliminary biological characterization showed a good adhesion and proliferation of human mesenchymal stem cells.

Chitosan-Based Macromolecular Biomaterials for the Regeneration of Chondroskeletal and Nerve Tissue

The use of materials, containing the biocompatible and bioresorbable biopolymer poly()-2-amino-2-deoxy--D-glucan, containing some N-acetyl-glucosamine units (chitosan, CHI) and/or its derivatives, to fabricate devices for the regeneration of bone, cartilage and nerve tissue, was reviewed. The CHI-containing devices, to be used for bone and cartilage regeneration and healing, were tested mainly for in vitro cell adhesion and proliferation and for insertion into animals; only the use of CHI in dental surgery has reached the clinical application. Regarding the nerve tissue, only a surgical repair of a 35 mm-long nerve defect in the median nerve of the right arm at elbow level with an artificial nerve graft, comprising an outer microporous conduit of CHI and internal oriented filaments of poly(glycolic acid), was reported. As a consequence, although many positive results have been obtained, much work must still be made, especially for the passage from the experimentation of the CHI-based devices, in vitro and in animals, to their clinical application.

Novel biodegradable, biomimetic and functionalised polymer scaffolds to prevent expansion of post-infarct left ventricular remodelling

Over the past decade, a large number of strategies and technologies have been developed to reduce heart failure progression. Among these, cardiac tissue engineering is one of the most promising. Aim of this study is to develop a 3D scaffold to treat cardiac failure. A new three-block copolymer, obtained from δ-valerolactone and polyoxyethylene, was synthesised under high vacuum without catalyst. Copolymer/gelatine blends were microfabricated to obtain a ECM-like geometry. Structures were studied under morphological, mechanical, degradation and biological aspects. To prevent left ventricular remodelling, constructs were biofunctionalises with molecularly imprinted nanoparticles towards the matrix metalloproteinase MMP-9. Results showed that materials are able to reproduce the ECM structure with high resolution, mechanical properties were in the order of MPa similar to those of the native myocardium and cell viability was verified. Nanoparticles showed the capability to rebind MMP-9 (specific rebinding 18.67) and to be permanently immobilised on the scaffold surface.

Cationic polymerizations in the presence of an electric field with polarity periodically reversed

Abstract A study has been made of the polymerizations of anethole, isobutylvinylether and cyclohexylvinylether by iodine in ethylene dichloride solution, at 25° under high vacuum in the presence of a constant or periodically reversed polarity d.c. field. The influences of the reversal frequency, distance between the electrodes as well as mechanical stirring of the solution on the electric field effect (measured as R PE / R PO ) have been investigated. Experiments were carried out to evaluate separately, in both compartments of the cell, the amounts of titratable iodine and polymer formed as well as the polymerization rate after the electric field application. The field induced rate enhancement can be cancelled by suitable reversal frequencies and mechanical stirring, and depends on the distance between the electrodes. The results confirm that the field effect is mainly due to concentration gradients of active species as a consequence of field induced electrolytic phenomena.

Release of 5-fluorouracil by biodegradable poly(ester-ether-ester)s. Part I: release by fused thin sheets

The 5-fluorouracil release by biodegradable ɛ-caprolactone and L-lactide copoly(ester-ether-ester)s was tested. The drug-copolymer mixture was formed by fusion in thin sheets, which were dipped in Dulbeccos PBS for time intervals ranging from one hour to two months. Each experiment shows a fast initial release, which subsequently slows down and stops at a limiting value, depending on the copolymer composition. This behavior was attributed to an extraction of the drug present on the sheet surface, due only to its shape, and to hydrogen bonds between the drug and the copolymers. The results obtained lead to a possibility of using such copolymers as “time-delayed” drug-releasing systems, when formed in specimens with smaller surface-to-volume ratio, which could minimize the fast initial extraction.

Surface chemical immobilization of bioactive peptides on synthetic polymers for cardiac tissue engineering.

The aim of this work was the development of new synthetic polymeric systems, functionalized by surface chemical modification with bioactive peptides, for myocardial tissue engineering. Polycaprolactone and a poly(ester-ether-ester) block copolymer synthesized in our lab, polycaprolactone–poly(ethylene oxide)–polycaprolactone (PCL–PEO–PCL), were used as the substrates to be modified. Two pentapeptides, H-Gly-Arg-Gly-Asp-Ser-OH (GRGDS) from fibronectin and H-Tyr-Ile-Gly-Ser-Arg-OH (YIGSR) from laminin, were used for the functionalization. Polymeric membranes were obtained by casting from solutions and then functionalized by means of alkaline hydrolysis and subsequent coupling of the bioactive molecules through 1-(3-dimethylaminopropyl)-3-ethylcarbodimide hydrochloride/N-hydroxysuccinimide chemistry. The hydrolysis conditions, in terms of hydrolysis time, temperature, and sodium hydroxide concentration, were optimized for the two materials. The occurrence of the coupling reaction was demonstrated by infrared spectroscopy, as the presence on the functionalized materials of the absorption peaks typical of the two peptides. The peptide surface density was determined by chromatographic analysis and the distribution was studied by infrared chemical imaging. The results showed a nearly homogeneous peptide distribution, with a density above the minimum value necessary to promote cell adhesion. Preliminary in vitro cell culture studies demonstrated that the introduction of the bioactive molecules had a positive effect on improving C2C12 myoblasts growth on the synthetic materials.

Hydroxyapatite-collagen composites. Part I: can the decrease of the interactions between the two components be a physicochemical component of osteoporosis in aged bone?

The interactions of Type I acid soluble collagen (Col) with both carbonate-free hydroxyapatite (HA1100) and carbonate-rich one (CHA) were investigated. The aim was to ascertain whether the increase of bone CO32− with ageing could relate to the disease known as osteoporosis. HA1100-Col and CHA-Col composites with various ratios were prepared and examined. Scanning electron microscopy and differential scanning calorimetry showed a stronger adhesion of the Col matrix to the granules of HA1100 than to those of CHA. FT-IR spectroscopy showed that with HA1100 both multiple hydrogen bonds of Col peptide –NH groups with HA PO43−, and electrochemical interactions between Col peptide –C=O groups and HA Ca2+ were present. In the presence of CO32−, the interactions between –NH and phosphate were diminished, and Ca2+ interacted more strongly with CO32− than with peptide –C=O, so causing a separation between the two components of the bone extra-cellular matrix. The results obtained strengthen the hypothesis that the substitution of PO43− ions by CO32− ions in the HA lattice might be a significant component of osteoporosis, although further investigation is needed.

Fundamental studies on electroinitiated cationic polymerizations—II. Polymerization of isobutylvinylether in the presence of tetrabutylammonium tri-iodide

Abstract Studies were made of the kinetics and the initiation mechanism of the electrolytically initiated anodic polymerization of isobutylvinylether in the presence of tetrabutylammonium tri-iodide, carried out in divided cells in 1,2-dichloroethane. The dependence of the initial polymerization rate on the monomer and salt concentrations and on the current intensity for experiments carried out under continuous electrolysis as well as the internal order with respect to monomer were determined: a kinetic scheme based on a stationary state of the first type is proposed. The initiation mechanism was investigated by u.v.-visible spectrophotometric tests on polymerization solutions and by a kinetic study on polymerizations initiated by pulses of current. The results show that polymerization is initiated by anodically formed iodine.

Fundamental studies on electroinitiated cationic polymerizations—1: Some aspects of the electrolysis of tetrabutylammonium salts in chlorinated organic solvents

Abstract The electrolysis of tetrabutylammonium iodide and tri-iodide in 1,2-dichloroethane solution was studied in order to identify the anodically produced species which may be able to initiate cationic polymerizations of vinyl monomers. The electrolyses were carried out under constant current in divided cells; the anodic and cathodic solutions were subsequently recovered and analysed separately. The anodic process is electrolytic oxidation of the anion to iodine; the cathodic process is an electrolytic decomposition of the solvent to give hydrogen, ethylene, vinyl chloride and tetrabutylammonium chloride. The last compound was found also in electrolyses carried out in methylene chloride solution and was proved to be a powerful rate depressor for iodine initiated polymerizations. A mechanism for the electrodic processes is proposed.