Green synthesis of Si-incorporated hydroxyapatite using sodium metasilicate as silicon precursor and in vitro antibiotic release studies.

The aim of the current study is to synthesize nanosized silicon incorporated HAp (Si-HAP) using sodium metasilicate as the silicon source. The sol-gel derived samples were further subjected to microwave irradiation. Incorporation of Si into HAp did not alter the HAp phase, as confirmed by the X-ray diffraction analysis (XRD). Moreover, variation in the lattice parameters of the Si-incorporated HAp indicates that Si is substituted into the HAp lattice. The decrease in the intensity of the peaks attributed to hydroxyl groups, which appeared in the FTIR and Raman spectra of Si-HAp, further confirms the Si substitution in HAp lattices. The silicon incorporation enhanced the nanorods length by 70%, when compared to that of pure HAp. Microwave irradiation improved the crystallinity of Si-HAp when compared to as-synthesized Si-HAp samples. As-synthesized Si-incorporated HAp sample showed an intense blue emission under UV excitation. Microwave irradiation reduced the intensity of blue emission and exhibited red shift due to the reduction of defects in the Si-HAp crystal. The morphological change from rod to spherical and ribbon-like forms was observed with an increase in silicon content. Further, Si-HAp exhibited better bioactivity and low dissolution rate. Initially there was a burst release of amoxicillin from all the samples, subsequently it followed a sustained release. The microwave-irradiated HAp showed extended period of sustained release than that of as-synthesized HAp and Si-HAp. Similarly, the microwave-irradiated Si-incorporated samples exhibited prolonged drug release, as compared to that of the as-synthesized samples. Hence, Si-HAp is rapidly synthesized by a simple and cost effective method without inducing any additional phases, as compared to the conventional sintering process. This study provides a new insight into the rapid green synthesis of Si-HAp. Si-HAp could emerge as a promising material for the bone tissue replacement and as a drug delivery system.

Agarose encapsulated mesoporous carbonated hydroxyapatite nanocomposites powder for drug delivery.

The powder composites are predominantly used for filling of voids in bone and as drug delivery carrier to prevent the infection or inflammatory reaction in the damaged tissues. The objective of this work was to study the synthesis of agarose encapsulation on carbonated hydroxyapatite powder and their biological and drug delivery properties. Mesoporous, nanosized carbonated hydroxyapatite/agarose (CHAp/agarose) powder composites were prepared by solvothermal method and subsequently calcined to study the physico-chemical changes, if it subjected to thermal exposure. The phase of the as-synthesized powder was CHAp/agarose whereas the calcinated samples were non-stoichiometric HAp. The CHAp/agarose nanorods were of length 10-80nm and width 40-190nm for the samples synthesized at temperatures 120°C (ST120) and 150°C (ST150). The calcination process produced spheres (10-50nm) and rods with reduced size (40-120nm length and 20-30nm width). Composites were partially dissolved in SBF solution followed by exhibited better bioactivity than non-stoichiometric HAp confirmed by gravimetric method. Hemo and biocompatibility remained unaffected by presence of agarose or carbonate in the HAp. Specific surface area of the composites was high and exhibited an enhanced amoxicillin and 5-fluorouracil release than the calcined samples. The composites demonstrated a strong antimicrobial activity against E. coli, S. aureus and S. epidermidis. The ST120 showed prolonged drug (AMX and 5-Fcil) release and antimicrobial efficacy than ST150 and calcined samples. This technique would be simple and rapid for composites preparation, to produce high quality crystalline, resorbable, mesoporous and bioactive nanocomposite (CHAp/agarose) powders. This work provides new insight into the role of agarose coated on bioceramics by solvothermal technique and suggests that CHAp/agarose composites powders are promising materials for filling of void in bone and drug delivery applications.

Studies on the biofilm produced by Pseudomonas aeruginosa grown in different metal fatty acid salt media and its application in biodegradation of fatty acids and bioremediation of heavy metal ions.

Metal fatty acid salts (MFAS) in untreated industrial effluents cause environmental pollution. The use of biocompatible agents for remediation may help in reducing the harm caused to the ambient aquatic organism. Pseudomonas aeruginosa is a ubiquitous organism that thrives under harsh conditions and is resistant to toxic metal ions. The present study shows a proof-of-concept of using this organism in the biodegradation of MFAS. MFAS were prepared and we studied their effect on the growth of the planktonic form and the formation of biofilm by P. aeruginosa. We observed biofilm formation in the presence of all the MFAS when used as the sole carbon source, albeit the quantity of biofilm formed in the presence of cadmium and copper was less. There was no effect on the planktonic form of the organism but the formation of biofilm increased in the presence of magnesium palmitate. This study shows that metal ions play a pivotal role in the formation of biofilm. HPLC (high-performance liquid chromatography) analysis of the biofilm polysaccharide showed that hexose sugar was a major component when compared with pentose sugar. The structure of biofilm polysaccharide and the coordination of the metal ion with the biofilm polysaccharide were confirmed by FTIR (Fourier transform infrared spectroscopy) and Raman spectroscopy.