Characterization of a Dialdehyde Chitosan Generated by Periodate Oxidation

This article reports the oxidation of Chitosan by using periodate and the characterization of the dialdehyde chitosan (DAC) generated by the reaction. Oxidised chitosan were further characterised by FTIR analysis, 1HNMR and TGA. The morphological analyses of oxidized chitosan by SEM confirmed the non change of elongated and fibrous network of chitosan. FTIR and TGA show no significant change on chemical structure and thermal properties successively. 1H NMR study confirmed the presence of imines generated by the reaction between dialdehyde chitosan and amino groups of chitosan (spontaneous assembling)

Hybrid materials based on polyethylene and MCM-41 microparticles functionalized with silanes: catalytic aspects of in situ polymerization, crystalline features and mechanical properties

New nanocomposites based on polyethylene have been prepared by in situ polymerization of ethylene in presence of mesoporous MCM-41. The polymerization reactions were performed using a zirconocene catalyst either under homogenous conditions or supported onto mesoporous MCM-41 particles, which are synthesized and decorated post-synthesis with two silanes before polymerization in order to promote an enhanced interfacial adhesion. The existence of polyethylene chains able to crystallize within the mesoporous channels in the resulting nanocomposites is figured out from the small endothermic process, located at around 80 C, on heating calorimetric experiments, in addition to the main melting endotherm. These results indicate that polyethylene macrochains can grow up during polymerization either outside or inside the MCM-41 channels, these keeping their regular hexagonal arrangements. Mechanical response is observed to be dependent on the content in mesoporous MCM-41 and on the crystalline features of polyethylene. Accordingly, stiffness increases and deformability decreases in the nanocomposites as much as MCM-41 content is enlarged and polyethylene amount within channels is raised. Ultimate mechanical performance improves with MCM-41 incorporation without varying the final processing temperature

Stimuli-responsive chitosan-starch injectable hydrogels combined with encapsulated adipose-derived stromal cells for articular cartilage regeneration

Tissue engineering strategies have been showing promising early results in articular cartilage lesions repair. Hydrogels based on natural origin polymers as chitosan glycerol-phosphate (CGP) thermosensitive formulation that can be implanted in a minimal invasive manner, represent a great promise as injectable scaffold choice for cartilage tissue engineering, but it lacks in mechanical properties. A different formulation, from which a firm texture gels results is, therefore, desirable. In this work we first aim to investigate the suitability of CGP to produce an injectable thermosensitive, pH-dependent solution, when combined with increasing concentrations of starch: 0.5% (I), 1% (II), and 1.5% (III). The data collected from the rheological measurements showed that the addition of starch to the CGP did not alter the transition temperature and confirmed the heating inducing gelation of all solutions, supporting the ability of these novel formulations to be applied as minimal invasive systems. The evaluation of the dynamic mechanical analysis of the hydrogels showed an increase in the storage modulus within increasing starch concentration, clearly demonstrating that best viscoelastic properties were obtained with the novel chitosan-starch based solution. The incorporation of starch also improved the degradation profile. All materials showed to be biocompatible through the cytotoxicity screening in vitro. These data suggested the potential of novel thermo-responsive chitosan-starch hydrogels to be used as injectable vehicles for cell delivery in cartilage tissue engineering applications. In a second phase, the potential of chitosan-b-glycerophosphate (CGP) and chitosan-bglycerophosphate- 1% starch (CST) hydrogels to induce chondrocytic differentiation and cartilage matrix accumulation were evaluated, as well as the influence of starch in the chondrogenesis of encapsulated adipose derived stromal (ADSC) cells. The ADSC were homogeneously encapsulated, remained viable, proliferated, and maintained the expression of typical chondrogenic markers genes, and deposited cartilage ECM molecules. Improved results were obtained within the novel CST constructs. The overall data suggest that chitosan-b-glycerophosphate-starch hydrogels could be considered for chondrogenic differentiation of adipose derived stromal cells for cartilage-engineered regeneration using minimal invasive techniques.The authors acknowledge the financial support to the Portuguese Foundation for Science and Technology (FCT) for the PhD fellowship to H. Sa-Lima (SFRH/BD/21779/2005) and for the Project PTDC/QUI/68804/2006; the European Union funded STREP Project HIPPOCRATES (NM3-CT-2003-505758); and the European NoE EXPERTISSUES (NMP3-CT-2004-500283)

A Novel Method for the Preparation of Retinoic Acid-Loaded Nanoparticles

The goal of present work was to investigate the use of bioerodible polymeric nanoparticles as carriers of retinoic acid (RA), which is known to induce differentiation of several cell lines into neurons. A novel method, named “Colloidal-Coating”, has been developed for the preparation of nanoparticles based on a copolymer of maleic anhydride and butyl vinyl ether (VAM41) loaded with RA. Nanoparticles with an average diameter size of 70 nm and good morphology were prepared. The activity of the encapsulated RA was evaluated on SK-N-SH human neuroblastoma cells, which are known to undergo inhibition of proliferation and neuronal differentiation upon treatment with RA. The activity of RA was not affected by the encapsulation and purification processes

Novel hydroxyapatite/carboxymethylchitosan composite scaffolds prepared through an innovative ‘‘autocatalytic’’ electroless coprecipitation route

A developmental composite scaffold for bone tissue engineering applications composed of hydroxyapatite (HA) and carboxymethylchitosan (CMC) was obtained using a coprecipitation method, which is based on the ‘‘autocatalytic’’ electroless deposition route. The results revealed that the pores of the scaffold were regular, interconnected, and possess a size in the range of 20–500 lm. Furthermore, the Fourier transform infra-red spectrum of the composite scaffolds exhibited all the characteristic peaks of apatite, and the appearance of typical bands from CMC, thus showing that coprecipitation of both organic and inorganic phases was effective. The X-ray diffraction pattern of composite scaffolds demonstrated that calciumphosphates consisted of crystalline HA. From microcomputed tomography analysis, it was possible to determine that composite scaffolds possess a 58.9% 6 6% of porosity. The 2D morphometric analysis demonstrated that on average the scaffolds consisted of 24% HA and 76% CMC. The mechanical properties were assessed using compressive tests, both in dry and wet states. Additionally, in vitro tests were carried out to evaluate the wateruptake capability, weight loss, and bioactive behavior of the composite scaffolds. The novel hydroxyapatite/ carboxymethylchitosan composite scaffolds showed promise whenever degradability and bioactivity are simultaneously desired, as in the case of bone tissue-engineering scaffolding applications.Contract grant sponsor: European Union (STREP Project HIPPOCRATES); contract grant number: NMP3-CT-2003-50575

Marine Polysaccharides in Pharmaceutical Applications: An Overview

The enormous variety of polysaccharides that can be extracted from marine plants and animal organisms or produced by marine bacteria means that the field of marine polysaccharides is constantly evolving. Recent advances in biological techniques allow high levels of polysaccharides of interest to be produced in vitro. Biotechnology is a powerful tool to obtain polysaccharides from a variety of micro-organisms, by controlling the growth conditions in a bioreactor while tailoring the production of biologically active compounds. Following an overview of the current knowledge on marine polysaccharides, with special attention to potential pharmaceutical applications and to more recent progress on the discovering of new polysaccharides with biological appealing characteristics, this review will focus on possible strategies for chemical or physical modification aimed to tailor the final properties of interest

Peptide conjugate hydrogelators

Molecular gelators are currently receiving a great deal of attention. These are small molecules which, under the appropriate conditions, assemble in solution to, in the majority of cases, give long fibrillar structures which entangle to form a three-dimensional network. This immobilises the solvent, resulting in a gel. Such gelators have potential application in a number of important areas from drug delivery to tissue engineering. Recently, the use of peptide-conjugates has become prevalent with oligopeptides (from as short as two amino acids in length) conjugated to a polymer, alkyl chain or aromatic group such as naphthalene or fluorenylmethoxycarbonyl (Fmoc) being shown to be effective molecular gelators. The field of gelation is extremely large; here we focus our attention on the use of these peptide-conjugates as molecular hydrogelators