Comparison of chitin structures isolated from seven Orthoptera species.

Differences in the physichochemical properties of the chitin structure of the exoskeleton of seven species from four genera were investigated in this study. The same method was used to isolate the chitin structure of the seven species. The physicochemical properties of the isolated chitins were revealed by ESEM, FTIR, TGA and XRD analyses. The FTIR, TGA and XRD results from the chitin samples were similar. The surface morphologies of the chitins were investigated by ESEM and interesting results were noted. While the surface morphologies of the chitins isolated from two species within the same genus were quite different, the surface morphologies of chitins isolated from species belonging to different genera showed similarity. It was determined that the dry weight chitin contents of the grasshopper species varied between 5.3% and 8.9%. The results of molecular analysis showed that the chitins from seven Orthoptera species (between 5.2 and 6.8 kDa) have low molecular weights. Considering that these invasive and harmful species are killed with insecticides and go to waste in large amounts, this study suggests that they should be collected and evaluated as an alternative chitin source.

Preferred crystallographic texture of alpha-chitin as a microscopic and macroscopic design principle of the exoskeleton of the lobster Homarus americanus.

The crystallographic texture of the crystalline alpha-chitin matrix in the biological composite material forming the exoskeleton of the lobster Homarus americanus has been determined using synchrotron X-ray pole figure measurements and the calculation of orientation distribution functions. The study has two objectives. The first one is to elucidate crystallographic building principles via the preferred synthesis of certain orientations in crystalline organic tissue. The second one is to study whether a general global design principle exists for the exoskeleton which uses preferred textures relative to the local coordinate system throughout the lobster cuticle. The first point, hence, pursues the question of the extent to which and why alpha-chitin reveals preferred textures in the lobster cuticle. The second point addresses the question of why and whether such preferred textures (and the resulting anisotropy) exist everywhere in the exoskeleton. Concerning the first aspect, a strong preference of a fiber texture of the orthorhombic alpha-chitin is observed which is characterized by a 020 crystal axis normal to the exoskeleton surface for the chitin matrix. The second question is tackled by studying samples from different parts of the carapace. While the first aspect takes a microscopic perspective at the basic structure of the biological composite, the second point aims at building a bridge between an understanding of the microstructure and the macroscopic nature of a larger biological construction. We observe that the texture is everywhere in the carapace optimized in such a way that the same crystallographic axis of the chitin matrix is parallel to the normal to the local tangent plane of the carapace. Notable differences in the texture are observed between hard mineralized parts on the one hand and soft membranous parts on the other. The study shows that the complex hierarchical microstructure of the arthropod cuticle can be well described by surprisingly simple crystallographic textures.

The exoskeleton of the lobster Homarus americanus as an example of a smart anisotropic biological material.

Many biological materials are composed of fibrils arranged according to well-ordered three-dimensional patterns. These materials often show a strong anisotropy in their properties. An essential characteristic of biological structures is their hierarchical organization from the nanometer to the millimeter scale. Lobster cuticle is a good example of this and a suitable model for studying these properties. In this study the structure of untreated as well as chemically and physically treated cuticle from the exoskeleton of the American lobster (Homarus americanus) was investigated using scanning electron microscopy. Fresh samples have been chemically decalcified and deproteinated and thermally treated to evaluate their resistance to degradation. Results showed that their structure is more complex than the commonly assumed model for arthropod cuticles. Stacked chitin-protein planes create the characteristic twisted plywood pattern found in arthropod cuticles. However, due to a well-developed pore canal system these planes are not simple arrays of parallel chitin-protein fibers. In lobster cuticle, interconnected fibers bend around the continuous lenticellate cavities of the pore canals to form a planar honeycomb-like structure. The chemically and thermally treated samples showed that the organic matrix retains its shape and structure despite the attack of chemical compounds or heat. It was also possible to study the distribution of the biominerals after the removal of the organic matrix. The observed residual structure gives a good impression of how the minerals (mainly calcite) are distributed inside the polymeric network.

Formulation and in vivo evaluation of chlorhexidine buccal tablets prepared using drug-loaded chitosan microspheres.

This investigation deals with the development of buccal formulations (tablets) based on chitosan microspheres containing chlorhexidine diacetate. The microparticles were prepared by a spray-drying technique, their morphological characteristics were studied by scanning electron microscopy and the in vitro release behaviour was investigated in pH 7.0 USP buffer. Chlorhexidine in the chitosan microspheres dissolves more quickly in vitro than does chlorhexidine powder. The anti-microbial activity of the microparticles was investigated as minimum inhibitory concentration, minimum bacterial concentration and killing time. The loading of chlorhexidine into chitosan is able to maintain or improve the anti-microbial activity of the drug. The improvement is particularly high against Candida albicans. This is important for a formulation whose potential use is against buccal infections. Drug-empty microparticles have an anti-microbial activity due to the polymer itself. Buccal tablets were prepared by direct compression of the microparticles with mannitol alone or with sodium alginate. After their in vivo administration the determination of chlorhexidine in saliva showed the capacity of these formulations to give a prolonged release of the drug in the buccal cavity.

Design and evaluation of a mucoadhesive therapeutic agent delivery system for postoperative chemotherapy in superficial bladder cancer.

The most common treatment method is known as the transurethral resection (TUR) for the therapy of bladder cancer. Unfortunately, because of the recurrency of the tumoral tissues after TUR the chemotherapy or immunotherapy should be performed. In these kind of therapies the pharmacotherapeutics are infused intravesically into the bladder after TUR periodically (i.e. upto 6--36 weeks, each week). But these therapies are having very big problems (i.e. disturbancy to patients, adjustment of the suitable dosage, loss of active agents without using etc.). An alternative approach can be proposed as to design a pharmacotherapeutic agent delivery system, which will supply the suitable dosage of the agent for a certain time period to solve those problems. In this study; the pharmacotherapeutic agent (i.e. Mytomycin-C) delivery system was prepared by using a mucoadhesive polymer (i.e. chitosan) in the form of cylindirical geometry to facilitate the insertion of the carrier for in vivo studies. The chitosan carriers were prepared by cross-linking during the solvent evaporation technique. In the preparation of the chitosan carriers the chitosan polymers with different molecular weights, different amounts of cross-linker (i.e. glutaraldehyde) and different amounts of pharmacotherapeutic agent were used to obtain desired attachment onto the bladder wall and optimum release rate of the agent. On the other hand because of the gelous structure of the chitosan, the swelling behaviour of the polymer was evaluated by gravimetric determinations in aqueous media periodically.

Multiunit controlled-release diclofenac sodium capsules using complex of chitosan with sodium alginate or pectin.

This study explored the application of chitosan-alginate (CA) and chitosan-pectin (CP) complex films as drug release regulator for the preparation of multiunit controlled-release diclofenac sodium capsules. Pellets containing drug and microcrystalline cellulose, in a ratio of 3:5, were prepared in a fluidized rotary granulator. The pellets were coated with CA, CP, sodium alginate, pectin, and chitosan solutions. The pellets, equivalent to 75 mg drug, were filled into capsules. After 2 h of dissolution test in acidic medium, the amount of the drug released from any preparation was negligible. The pellets were further subject to pH 6.8 phosphate buffer More than 80% drug release at 12 h was observed with the uncoated pellets and those coated with sodium alginate, pectin or chitosan. Both 1% CA and 3% CP coated pellets exhibited drug release profiles similar to that of Voltaren SR75. It was found that approximately 60% and 85% of the drug were released at 12 and 24 h, respectively. Both Differential thermal analysis (DTA) and Fourier transform infrared spectroscopy (FTIR) analyses revealed complex formation between chitosan and these anionic polymers. It could be concluded that CA and CP complex film could be easily applied to diclofenac sodium pellets to control the release of the drug.