Paola Laurienzo

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.

Preparation and characterisation of compatibilised polycaprolactone/starch composites

Polycaprolactone/high amylose starch blends were prepared by the adding of a proper compatibiliser constituted by low molecular weight PCL modified on the terminal groups by using pyromellitic anhydride. Thermal, mechanical and morphological analyses were performed in order to show the better performances of these blends compared to mechanical ones obtained without the use of the compatibiliser. Finally, the biodegradability of the materials, by a compost simulation test, was also tested to assess the influence of the compatibiliser presence on the whole biodegradation process of PCL.

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.

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.

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.

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.

Alginate Hydrogels Coated with Chitosan for Wound Dressing

In this work, a coating of chitosan onto alginate hydrogels was realized using the water-soluble hydrochloride form of chitosan (CH-Cl), with the dual purpose of imparting antibacterial activity and delaying the release of hydrophilic molecules from the alginate matrix. Alginate hydrogels with different calcium contents were prepared by the internal setting method and coated by immersion in a CH-Cl solution. Structural analysis by cryo-scanning electron microscopy was carried out to highlight morphological alterations due to the coating layer. Tests in vitro with human mesenchymal stromal cells (MSC) were assessed to check the absence of toxicity of CH-Cl. Swelling, stability in physiological solution and release characteristics using rhodamine B as the hydrophilic model drug were compared to those of relative uncoated hydrogels. Finally, antibacterial activity against Escherichia coli was tested. Results show that alginate hydrogels coated with chitosan hydrochloride described here can be proposed as a novel medicated dressing by associating intrinsic antimicrobial activity with improved sustained release characteristics.

Crosslinker effects on functional properties of alginate/N-succinylchitosan based hydrogels

In this paper, physico-chemical, mechanical and antimicrobial properties of hydrogels based on alginate/N-succinylchitosan blends crosslinked by calcium or zinc ions containing cellulose microfibers were investigated and discussed. With respect to plain alginate hydrogels, the addition of N-succinylchitosan significantly improved properties such as swelling degree and stability in saline solution. The water vapour transmission rate confirmed that all the hydrogels were able to assure a moist wound environment. Morphological analysis showed a good embedding of fibres within the zinc crosslinked hydrogels. In addition, zinc-crosslinked hydrogels evidenced antimicrobial activity against two common skin pathogenic bacteria, Staphylococcus aureus and Escherichia coli. Cytotoxicity assays proved that the amount of zinc released is slightly over the toxic level. Overall, the characteristics of the zinc-crosslinked hydrogels showed their potential interest as materials for wound dressing.

Novel zinc alginate hydrogels prepared by internal setting method with intrinsic antibacterial activity

In this paper, a controlled gelation of alginate was performed for the first time using ZnCO3 and GDL. Uniform and transparent gels were obtained and investigated as potential wound dressings. Homogeneity, water content, swelling capability, water evaporation rate, stability in normal saline solution, mechanical properties and antibacterial activity were assessed as a function of zinc concentration. Gelation rate increased at increasing zinc content, while a decrease in water uptake and an improvement of stability were found. Release of zinc in physiological environments showed that concentration of zinc released in solution lies below the cytotoxicity level. Hydrogels showed antimicrobial activity against Escherichia coli. The hydrogel with highest zinc content was stabilized with calcium by immersion in a calcium chloride solution. The resulting hydrogel preserved homogeneity and antibacterial activity. Furthermore, it showed even an improvement of stability and mechanical properties, which makes it suitable as long-lasting wound dressing.

Rubber modification of polybutyleneterephthalate by reactive blending concurrently with polymerization reaction

Abstract Rubber modification of polybutyleneterephthalate (PBT) was accomplished by the addition of suitable functionalized ethylene-propylene copolymers (EPR) concurrently with the high temperature polycondensation of 1,4-butanediol and dimethylterephthalate. Ester and alcohol modified rubbers were tested in the polymerization process, and it was found that the type and amount of grafted groups can play a fundamental role because they determine mode and state of dispersion of the elastomeric phase inside the plastic matrix. An attempt was made to correlate the results obtained to the influence of the different kinds of grafted pendant groups on the polymerization equilibria of PBT.