Preparation, characterization and in-vitro studies of hydroxyapatite and biphasic of hydroxyapatite-tricalcium phosphate /co- polymeric biocomposites

Calcium phosphates with clinical applications constitute an interesting field of research and development in the production of useful biomaterials for implant fabrication and/or fixation. They exhibit very good biocompatibility and bone integration qualities. In this work hydroxyapatite [HAp] was prepared by precipitation method, while the biphasic hydroxyapatite/beta-tricalcium phosphate [H A/ beta-TCP] was prepared by heating the prepared HAp at 900°C for 5 hr in air. To improve bioactivity both HAp and HAp/ beta-TCP fillers were loaded onto grafted chitosan with two monomers, hydroxyethylmethacrylate [HEMA] and methylmethacrylate [MMA] during copolymcrization process. X-ray diffraction analysis revealed the HAp and biphasic HAp / beta-TCP phases for the prepared samples and proved integration and coating between these fillers and the copolymer. Thermogravimetric analyses of composites showed the attached layer of copolymer onto the surface of fillers particles were 59.818 and 37% for HAp and HAp/ beta-TCP composites, respectively. SEM and FTIR for fillers and composites confirmed the compatibility between the tillers and copolymer. In vitro studies were conducted by immersing the composites in simulated body fluid [SBF] at 37 °C for various time-points. Post-immersion results showed the formation of carbonated apatite layer on the surface of both fillers and their composites especially for HA tiller and it's composite. Also, deposition of Ca[2+] and PO[4][3-] ions onto the surface was achieved for HA filler and its composite more than biphasic filler and its composite as confirmed by FT-IR data. Therefore, these biocompoites can be used as bone substitutes or tissue engineering applications

Improvement of the cycling performance of LiMn[2]O[4] as cathode material for lithium batteries by Cr, Al, Co and Ni substitution

The main advantages of LiMn[2]O[4] spinel system are low cost, high cathode potential versus lithium and lack of toxic metals such as cobalt or nickel present in LiCoO[2] and LiNiO[2] cathode materials whereas the main drawback of the system is the fading capacity during cycling as compared to LiCoO[2] and LiNiO[2]. To improve the structural and electrochemical properties of LiMn[2]O[4], as cathode material for lithium secondary batteries, Co, Cr, AI and Ni ions were substituted for manganese ions. LiMn[2]O[4], and LiM[gamma]Mn[2-gamma]O[4] [M = Al, Co, Cr and Ni; gamma = 1/6] samples were prepared by solid state reactions. The X-ray powder diffraction patterns of the substituted samples are almost identical to the parent sample. A well defined highly pure spinel was characterized for all samples without observation of extra phases for substituted samples. The electrochemical performance of the prepared samples was evaluated through cyclic voltammetry and galvanostatic charge/discharge operations. The first discharge capacities of the substituted spinels are lower than that of LiMn[2]O[4], but better cycling performance and capacity retention was observed for the substituted spinels compared to the parent LiMn[2]O[4],. The improvement in the cycling performance of LiM[gamma]Mn[2-gamma]O[4][M = Co, Cr, Ni and Al; gamma = 1/6] compared to that of parent LiMn[2]O[4] is attributed to the stabilization of the spinel structure by the substituted metal cations