Viscoelastic monitoring of starch-based biomaterials in simulated physiological conditions

Dynamic mechanical analysis (DMA) was used to investigate the solid-state rheological behaviour in a starch-based thermoplastic aimed to be used in different biomedical applications. The tested samples were processed by different injection moulding procedures. The dry samples were immersed in a simulated physiological solution and the relevant viscoelastic parameters were monitored against time. The decrease of stiffness due to swelling can be followed in real time, being less pronounced for the composite sample with hydroxyapatite (HA). The temperature control of the liquid bath was found to be very good. Frequency scans were also performed in wet conditions in samples previously immersed during different times, indicating that DMA is a suitable method to control in-vitro the changes on the viscoelastic properties of biomaterials during degradation

Three-dimensional layer-by-layer strategies for tissue engineering and nanomedicine

Layer-by-layer (LbL) is a self-assembly-driven surface modification strategy that allows the construction of nanostructured films onto substrates of any geometry, from simple bidimensional surfaces to more complex three-dimensional porous scaffolds. The principle behind LbL lies in the existence of multiple intermolecular interactions, such as electrostatic contacts, hydrophobic interactions, and hydrogen bonding, where the cooperative effects of multipoint attractions play the most important role. It is a technique that offers ease of preparation, versatility, fine control over the materials structure and robustness under physiological conditions. Although LbL has been mostly limited to the modification of planar surfaces, its potential lies in the capability to be extrapolated to 3D structures and coat increasingly complex geometries. Currently trending is the use of spherical templates – sacrificial or non-sacrificial – for applications in Nanomedicine, such as the construction of drug carriers or for the encapsulation of cells. The nanostructured nature of multilayered coatings makes it possible to build containers which permeability to molecules may be tuned simply by varying the number of involving layers or the class of materials involved. This way, in drug delivery it would be possible to construct structures in which the permeability of a drug to the exterior could be adjusted to a specific application or therapy, such as non-systemic approaches to cancer. In cell encapsulation, multilayer films could be employed to grant immune protection to the encapsulated biological materials, such as pancreatic islet cells, and enhanced control of both transport properties and surface physicochemical characteristics. Therefore, LbL presents an ambitious step in the development of effective encapsulating barriers for both active agents and cells

Synthesis and characterization of N-methylenephenyl phosphonic chitosan

Chitosan is a natural based polymer obtained by alkaline deacetylation of chitin, exhibiting excellent properties such as non‐toxicity, biocompatibility and biodegradability. N‐Methylenephenyl phosphonic chitosan (NMPPC) is synthesized from chitosan by reacting with phenyl phosphonic acid using formaldehyde. The NMPPC was characterized by FTIR, 31P‐NMR, X‐ray diffraction, scanning electron microscopy, thermogravimeteric analysis and solubility studies. A significant decrease of molecular weight was observed in the NMPPC. The TGA studies suggested that NMPPC has less thermal stability than chitosan. The X‐ray diffraction analysis showed that NMPPC was amorphous in nature. The solubility property of the polymer was improved after the incorporation of a phenyl phosphonic grou

Chemistry and applications of phosphorylated chitin and chitosan

Chitin and chitosan are natural based non-toxic, biodegradable and biocompatible polymers and have been used in biomedical areas in the form of sutures, wound healing materials and artificial skin, and for the sustained release of drugs as well as in various industrial applications. However, practical use of these polymers has been mainly confined to the unmodified forms. Recently, there has been a growing interest in chemical modification of chitin and chitosan to improve their solubility and widen their applications. Among them, phosphorylated chitin and chitosan have attracted considerable interest because of their various advantages: anti-inflammatory property, ability to form metal complexes, blood compatibility and formation of anionic polyelectrolyte hydrogels. The purpose of this review is to take a closer look of different synthetic methods of phosphorylated chitin and chitosan and their potential applications in environmental, food, fuel cell, and biomedical fields. Based on current research and existing products, some new and futuristic approaches in this context area are discussed.R. Jayakumar acknowledges the Portuguese Foundation for Science and Technology for providing him a Post-Doc scholarship (SFRH/BPD/14670/2003). This work was partially supported by FCT Foundation for Science and Technology, through funds from the POCTI and/or FEDER program. This work was partially supported by the European Union funded STREP Project HIPPOCRATES (NMP3-CT-2003-505758)

Nanostructured multilayers in the production of new devices for biomedical applications

Surface engineering is of the utmost significance in the conception of devices with an improved biological performance. By addressing physical and chemical features of interfaces, it has been possible to develop patterned and stimuli-responsive devices with tunable wettability and protein/cell adhesion properties with application in biomedicine and tissue engineering. While several surface engineering approaches exist, there is an increasing emphasis to non-harmful and versatile techniques to modify polymeric substrates: the sequential adsorption of proteins and polysaccharides, known as layer-by-layer (LbL) adsorption, is one of the most promising today. It is a simple and versatile technique where the cooperative effects of multipoint attractions allowing to produce robust coatings, even in substrates with complex geometries. Because it discards the need of organic and harmful solvents, it is an attractive technique for tissue engineering applications. Multilayer systems have already been proposed for different biomedical applications, including for biomimetic composite-like coatings, surfaces with smart properties, and to manipulate the adhesion and proliferation of cells

Study of the fosfosal controlled permeation through glutaraldehyde crosslinked chitosan membranes

Advanced material forum III : proceedings of the III International Materials Symposium, Aveiro, 2005Fosfosal, a phosphate derivative of salicylic acid, which presents both analgesic and antiinflammatory properties, was used as a model drug to study the potential of recently developed chitosan membranes (with different crosslinking degrees) to be used as drug release rate-controlling membranes. The fosfosal permeation across these membranes was studied using an in-house built developed diffusion cell with online automatic monitoring. Experiments were performed using phosphate buffer saline (PBS) solution at 37ºC. Different flow properties of the detection set up were determined in order to estimate the errors introduced by the automatic online monitoring system. For increasing crosslinking degrees the permeability initially decreased, and then increased, likely as a consequence of the crosslinking influence on a variety of properties like crystallinity and hydrophilicity that have opposite influence on permeability. In summary, it was possible to control the drug release profile by means of changing the degree of crosslinking of chitosan membranes and to follow the respective release kinetics by means of using the developed diffusion cell(undefined

Surface properties of extracts from cork black condensate

The insulation corkboard production generates black condensate (BC), a paste-like solid waste. It is hydrophobic and has the potential to be used as protective coating. To evaluate this potential, coatings were prepared from BC extracts and their surface behavior was evaluated by contact angle (CA) measurements. The CA dynamics were recorded as a function of time; advancing CAs were also registered; the approaches were applied according to Fowkes, Owens- Wendt-Rabel-Kaelble (OWRK), and Van Oss to determine the surface energy (SE) for each coating. Depending on the liquid probe, three phenomena were observed: water evaporation, diiodomethane diffusion into the coating, and rearrangement of the chemical groups on the coating surface, when glycerol was dropped onto the surface. Based on the results from the CA dynamics, the applicability of the coatings against hydrophobic environments was limited owing to its affinity to apolar compounds. The results show that the coating prepared by the toluene BC extract was the best coating. The key data were: water CA of 99.38, total SE (between 37.4 mN m-1 and 40.1 mN m-1), SE polar component (0.1 mN m-1), and the acidic and basic characters were negligible. It can be concluded that the BC extracts have potential for coatings.R.P. acknowledges a post-doc research grant BPD/39333/2007 from the Portuguese Foundation for Science and Technology (FCT). We gratefully acknowledge Amorim Isolamentos S.A. for the supply of black condensate

Smart thermoresponsive coatings and surfaces for tissue engineering : switching cell-material boundaries

The smart thermoresponsive coatings and surfaces that have been explicitly designed for cell culture are mostly based on poly(N-isopropylacrylamide) (PNIPAAm). This polymer is characterized by a sudden precipitation on heating, switching from a hydrophilic to a hydrophobic state. Mammalian cells cultured on such thermoresponsive substrates can be recovered as confluent cell sheets, while keeping the newly deposited extracellular matrix intact, simply by lowering the temperature and thereby avoiding the use of deleterious proteases. Thermoresponsive materials and surfaces are powerful tools for creating tissue-like constructs that imitate native tissue geometry and mimic its spatial cellular organization. Here we review and compare the most representative methods of producing thermoresponsive substrates for cell sheet engineering