Osteoconductive properties of methylpyrrolidinone chitosan in an animal model.

Bone defects were surgically produced in the tibiae of rabbits and medicated with freeze-dried methylpyrrolidinone chitosan. Histological observations 60 d after surgery showed a considerable presence of neoformed bone tissue, as opposed to controls, originating from the pre-existing bone as well as from the periosteum. The cationic nature and the chelating ability of the methylpyrrolidinone chitosan apparently favoured mineralization. Endosteal-periosteal and bone marrow osteoblast-like precursors, stimulated by growth factors entrapped in the coagulum-polysaccharide mixture, gave rise to intramembranous bone formation. The ultrastructural examination evidenced that bone osteoid was followed by mineralization of the tissue.

Stimulatory effect on bone formation exerted by a modified chitosan.

A novel modified chitosan carrying covalently linked imidazole groups (average molecular weight 700,000, degree of substitution 0.28, degree of acetylation 0.08) was used to stimulate bone formation in an animal model. Lesions (7 mm diameter) were surgically made in the femoral condyle of sheep and treated with the modified chitosan. Within 40 d after surgery, the neoformed tissue occluded the surgical hole and assumed a trabecular structure in the peripheral area of the lesion, while looking like a mineralization nodule in the central part in association with a fibrous component. In the control, no sign of osteoinduction or reparative process was observed and bone marrow was rich in adipocytes.

Solubility and structure of N-carboxymethylchitosan.

N-Carboxymethylchitosan from crab and shrimp chitosans was obtained in water-soluble form by proper selection of the reactant ratio, i.e. using equimolar quantities of glyoxylic acid and amino groups. HPLC determinations of glyoxylic and glycolic acids, in conjunction with NMR analysis, permitted identification of the structure of the product, which is partly N-mono-carboxymethylated (0.3), N,N-dicarboxymethylated (0.3) and N-acetylated depending on the level of deacetylation of the starting chitosan (0.08-0.15). The preparation can be made successfully even in the presence of large concentrations of glycolic acid. The use of enzymes exerting hydrolysing activity on the high-molecular-weight fractions helps to avoid gel formation during storage and precipitate formation on addition of anti-microbial agents.

Chitin-based poly(urea-urethane)s.

Chitins of various origins in DMA-LiCl solution have been reacted with excess 1,6-diisocyanatohexane (three or twelve equivalents per repeating unit) for 4-20 h. The resulting solutions were exposed to water vapor for 2 days and flexible and opaque materials were produced, which upon drying yielded powders whose main characteristics were insolubility in aqueous and organic solvents, remarkable crystallinity, typical infrared spectrum, high N/C ratio (0.287), and a high degree of substitution (0.29). Under the SEM structural features reminiscent of chitin were absent but no thermoplastic behavior was found by differential scanning calorimetry. Chitosan was similarly treated under heterogeneous conditions in anhydrous pyridine, and yielded reaction products with a lower degree of substitution (0.17). With partially hydrolysed chitosan, highly crystalline products were obtained.