Tripolyphosphate cross-linked macromolecular composites for the growth of shape- and size-controlled apatites.

Bioactive composites that enable the formation of calcium phosphates have received increased attention over the last decade, in the development of osteoconductive biomaterials for orthopaedic applications. In this work, tripolyphosphate (TPP)-cross-linked chitosan/gelatin composites (TPP-CG) were prepared for the growth of shape- and size-controlled calcium phosphates on/in the composites. The mineralization pattern of the composites, after soaking in the Ca(OH)(2) aqueous solution, clearly demonstrated oriented, needle-like nanocrystallites of calcium phosphates in the matrix with especially high Ca/P molar ratio (3.98) as detected by energy dispersive X-ray spectroscopy (EDX) analysis. Subsequent to mineralization in a simulated body fluid (SBF), the mineralized composites showed micro-scaled spherical aggregates deposited on the surface and granule-like nanocrystallites grew in the matrix. The Ca/P molar ratio (1.72) and X-ray diffraction pattern of the nanocrystallites grown in the composites were similar to those of hydroxyapatite (HAp). Osteoblastic differentiation of ROS cells cultured on the mineralized composites allowed an enhanced expression of the chosen osteogenic marker (alkaline phosphatase, ALPase). These results indicated that the composites mineralized with micro- and nano-scaled calcium phosphates with various structural features make them attractive for bone tissue engineering applications.

Hydrogel microspheres for stabilization of an antioxidant enzyme: effect of emulsion cross-linking of a dual polysaccharide system on the protection of enzyme activity.

Catalase is an antioxidant enzyme abundant in natural resources. However, the enzyme is usually inactivated by gastric acid and digestive enzymes after oral ingestion. In this study, carboxymethyl chitosan (CM-chitosan) and hyaluronic acid (HA) conjugate hydrogel microspheres have been prepared by an emulsion cross-linking technique to retain the activity of catalase in simulated gastrointestinal (GI) fluids. Cross-linking reduced the swelling capability and increased the resistance toward hyaluronidase digestion of prepared HA-CM-chitosan hydrogel microspheres. Catalase entrapped in the hydrogel microspheres exhibited superior stability over a wide pH range (pH 2.0 and 6.0-8.0) as compared to the native enzyme. The entrapped catalase was also protected against degradation by digestive enzymes. Following the treatments, the catalase-loaded microspheres, in contrast to native catalase, could effectively decrease the intracellular H2O2 level and protect HT-29 colonic epithelial cells against H2O2-induced oxidative damage to preserve cell viability. These results suggested that the HA-CM-chitosan hydrogel microspheres can be used for entrapment, protection and intestinal delivery of catalase for H2O2 scavenging.