Mario Malinconico

Marine Derived Polysaccharides for Biomedical Applications: Chemical Modification Approaches

Polysaccharide-based biomaterials are an emerging class in several biomedical fields such as tissue regeneration, particularly for cartilage, drug delivery devices and gel-entrapment systems for the immobilization of cells. Important properties of the polysaccharides include controllable biological activity, biodegradability, and their ability to form hydrogels. Most of the polysaccharides used derive from natural sources; particularly, alginate and chitin, two polysaccharides which have an extensive history of use in medicine, pharmacy and basic sciences, and can be easily extracted from marine plants (algae kelp) and crab shells, respectively. The recent rediscovery of poly-saccharide-based materials is also attributable to new synthetic routes for their chemical modification, with the aim of promoting new biological activities and/or to modify the final properties of the biomaterials for specific purposes. These synthetic strategies also involve the combination of polysaccharides with other polymers. A review of the more recent research in the field of chemical modification of alginate, chitin and its derivative chitosan is presented. Moreover, we report as case studies the results of our recent work concerning various different approaches and applications of polysaccharide-based biomaterials, such as the realization of novel composites based on calcium sulphate blended with alginate and with a chemically modified chitosan, the synthesis of novel alginate-poly(ethylene glycol) copolymers and the development of a family of materials based on alginate and acrylic polymers of potential interest as drug delivery systems.

Poly (D,L-lactic acid)/poly (∈-caprolactone) blend membranes: preparation and morphological characterisation

With the aim of exploring possible application of the concept of blend compatibilisation into the field of biodegradable membranes, a study of the influence of random copolymer poly(D,L-lactide-co-∈-caprolactone) on the properties of corresponding homopolymer blends has been conducted. Blends of plain homopolymers and blends containing 5 and 10 wt% of a copolymer of suitable composition have been prepared in the melt and characterised for their molecular interactions using thermal, dynamic-mechanical, mechanical (tensile tests) and morphological analyses. The blends are characterised by a good dispersion of the poly-∈-caprolactone (PCL) minor phase into the poly(D,L-lactic acid) (PDLLA) matrix and better mechanical properties compared to plain PDLLA, and such characteristics further improve when adding the copolymer. Microporous blend membranes consisting of PDLLA and PCL were then prepared by a phase inversion method and characterised by scanning electron microscopy. The addition of compatibilising agent led to a highly homogeneous structure, while in absence of compatibiliser a clear phase separation occurred.

Ternary nylon-6/rubber/modified rubber blends: Effect of the mixing procedure on morphology, mechanical and impact properties

Abstract Ternary polyamide-based blends have been prepared by adding to nylon-6 (PA6) an ethylene-propylene random copolymer (EPM) and the same EPM functionalized by inserting onto its backbone maleic anhydride groups (EPM-g-SA). Two kinds of processing have been used: (a) one-step mixing in which the three components were simultaneously introduced in the mixer; (b) two-step mixing in which the two rubbers EPM and EPM-g-SA were separately premixed before the final mixing with PA6. Also binary PA 6 EPM -g- SA blends have been prepared to compare their properties with those of the ternary one. Mechanical tensile characterization at room temperature and impact Izod tests at different temperatures as well as a morphological analysis of smoothed samples have been performed on all the blends. It has been shown by a model reaction that both in binary and ternary blends an EPM-g-PA6 graft copolymer is formed, which acts as an interfacial agent between the rubbery dispersed phase and the polyamide matrix. The blends obtained by the one-step mixing showed a gross morphology and a very poor impact resistance, whereas the ones prepared by the two-step mixing exhibited very fine morphologies and excellent impact performances. In addition, as shown at least in the case of one ternary blend, there seems to be good morphological stability of these materials after a second processing. This has been attributed to the influence of the interfacial agent formed during the melt mixing of the two premixed rubbers with PA6.

Preparation and characterisation of composites based on biodegradable polymers for “in vivo” application

Abstract Poly( l -lactic) acid (PLLA), polycaprolactone (PCL), three different copolymers based on poly( l -lactic) acid and polyglycolic acid (PLLA-co-PGA), and their composites with hydroxyapatite obtained from bovine bone (ossein), were tested in order to have information on the thermal, morphological, mechanical and biochemical properties in view of their use as biocompatible/biodegradable materials. Ossein, which is essentially a biological hydroxyapatite, was found to improve the modulus and increase the hydrophilicity of the polymeric substrate. In addition, the size of the ossein particles was found to be critical for the improvement of mechanical properties. Finally, preliminary results on the in vitro biocompatibility of selected blends carried out by using primary cultures of human osteoblasts showed that the presence of hydroxyapatite stimulates a more positive cellular response.

Compatibilized Polymer Blends Based on PDLLA and PCL for Application in Bioartificial Liver

Porous scaffolds for tissue engineering applications based on poly(D,L-lactide)/poly(epsilon-caprolactone) compatibilized blends are described. The addition of a third polymer, namely poly( D, L-lactide-co-caprolactone) copolymer, has a profound effect on morphological properties of the blends scaffolds. In fact, the copolymer acts as compatibilizing agent and reduces the dimension of the dispersed phase of an order of magnitude. Such effect is function of the polymer composition. The efficiency of scaffolds obtained with poly( D, L-lactide) based blends containing 30% by weight of poly(epsilon-caprolactone) as dispersed phase toward hepatocytes has been tested by several biological assays and we found that they are able to promote a perfect adhesion, proliferation and growth of cells. Moreover, the addition of the copolymer significantly improves the biomedical performance of the scaffold.

Role of degree of grafting of functionalized ethylene-propylene rubber on the properties of rubber-modified polyamide-6

An amorphous random ethylene-propylene rubber (EPR) copolymer and EPR-g-succinic anhydride (EPR-g-SA) graft copolymer have been used as rubbery components to obtain binary polyamide (PA6)EPR or PA6EPR-g-SA and ternary PA6/EPR/EPR-g-SA blends by melt mixing. The influence of degree of grafting (DG) or EPR-g-SA on the morphology and tensile and impact properties of such blends has been investigated. Finer and more homogeneous dispersions of the rubbery domains and better impact properties are obtained with increasing degree of grafting in the blends. At equal DG values and for the compositions used, the binary PA6EPR-g-SA alloys show better behaviour than the ternary ones. These results are related to the presence of an (EPR-g-SA)-g-PA6 graft copolymer formed during melt mixing, which acts as an interfacial and emulsifying agent.

Unsaturated polyester resins from glycolysed waste polyethyleneterephthalate: synthesis and comparison of properties and performance with virgin resin

Recycling of polyethyleneterephthalate (PET) bottles for soft drinks is accomplished by depolymerization through glycolysis. Obtained intermediates are reacted with mixtures of saturated and unsaturated acids to obtain unsaturated polyesters (UP) suitable for use as a matrix for fibre-reinforced thermosetting composites. The influence of chemical structure of glycols on the chemo-rheological behaviour of resins, has been verified. By using di-ethylene glycol, the behaviour of the resulting UP closely resembles that of UP obtained from virgin monomers. Moreover, composite sheets containing UP developed in the present research, show enhanced toughness if compared with the analogous composite made of virgin UP resin.

Rubber modification of polyamide 6 during caprolactam polymerization: influence of composition and functionalization degree of rubber

Abstract Rubber-modified polyamides 6 (PA 6) were obtained directly during the hydrolytic polymerization of e-caprolactam (CL). An ethylene-propylene elastomer (EPR) and dibutyl succinate grafted EPRs (EPR-g-DBS) were used as rubbery components to yield binary PA 6/EPR-g-DBS and ternary PA 6/EPR-g-DBS blends having about 20% by weight of total rubber. Model reactions and selective extractions of the blends indicated that (EPR-g-DBS)-g-PA 6 copolymers are formed during the CL polymerization. The influence of the grafting degree of EPR-g-DBS and, for ternary blends, of the weight ratio EPR/EPR-g-DBS on the morphology and on the impact properties of the blends was also investigated. A finer and more homogeneous dispersion of rubbery domains has been found for binary blends, while ternary blends exhibit a quasi-bimodal distribution of rubbery domains. The impact properties of ternary blends are enhanced with the increase of the relative amount of functionalized rubber. The dependence of the morphological features and of the impact properties on the functionalization degree is more complex. Straightforward correlations between mode and state of dispersion of rubber domains and impact properties were not found.

Study of blends of nylon 6 with EVOH and carboxyl-modified EVOH and a preliminary approach to films for packaging applications

Blends of nylon 6 (Ny6) with ethylene-co-vinyl alcohol (EVOH) and EVOH modified with the introduction of carboxyl groups (EVOH–COOH) have been studied by Fourier transform infrared spectroscopy, scanning electron microscopy, differential scanning calorimetry, and dynamic-mechanical thermal analysis. The thermal and thermomechanical analyses of the blends show that the melting, crystallization, and relaxational behavior are affected by the blend composition and the presence of carboxyl groups on the EVOH chains. Nevertheless, microscopic and thermal investigations demonstrate the biphasic nature of the two-blend systems. Selective solvent extraction of the EVOH or EVOH–COOH phase in their blends and Fourier transform infrared analysis of the residual products indicates the occurrence of ionic linkages between the amino groups of the polyamide and the carboxyl groups of the modified EVOH, whereas specific interactions are evidenced for Ny6/EVOH blends. Tests performed on extruded Ny6/EVOH films show that the addition of EVOH effectively reduces the gas permeability of Nylon, whereas the addition of small amounts of EVOH–COOH helps to control and stabilize melt rheology.

Natural and Synthetic Hydroxyapatite Filled PCL: Mechanical Properties and Biocompatibility Analysis

Hydroxyapatite (Ca10(PO4)6(OH)2) is one of the most biocompatible ceramics because it is similar to the mineral constituents of human bone and teeth. Composites of hydroxyapatite (HA) and biodegradable polymers such as polycaprolactone (PCL) are interesting materials for medical applications, especially for bone replacement. With the aim to improve the properties of biodegradable polyester-based devices, we have prepared and characterized novel composites made of polycaprolactone and natural or synthetic hydroxyapatite. The composites were screened for cytocompatibility by a direct contact method, in view of the future application of these hydroxyapatite filled PCL polymers as scaffolds for bone engineering. Primary cultures of human bone marrow mesenchymal stem cells (MSC) were selected as the most appropriate models to study the in vitro performance of these materials.