The possible use of natural silica nanoporous biomaterial from marine diatom for drug delivery applications was explored. Coscinodiscus concinnus have a homogeneous size distribution with radius of 220 ± 15 lm with surface featuring a mounded topography with about 2 lm wide porous domes organized on the surface in pentagonal packing. Streptomycin, used as a hydrophilic drug to demonstrate the in vitro oral drug delivery model based on diatom structure, mainly adsorbed on to the diatom silica surface (foramen), inside pores (cribrum) and into the internal hollow diatom structure (cribellum). The maximum drug loading capacity of streptomycin was 33.33 ± 2 %. The release was biphasic, involving initial burst release (first 6 h) mainly from the surface of diatom foramen, and sustained drug release (upto 7 days) from cribrum and cribellum. The study indicated that the live diatoms from marine environment, due to their unique features (easy cultivable, low-cost and biocompatibility), are a potential and alternative natural source of nanoporous siliceous material for in vitro oral drug delivery applications.

Titanium-6 aluminium-4 vanadium (Ti64) alloy was modified to a hydrophilic, cytocompatible, antibacterial and bioactive surface via a simple cost effective chemical treatment method. A fine porous network structure of sodium hydrogen titanate (SHT) was formed on the Ti64 alloy surface by using sodium hydroxide treatment. The incorporated Na + ions are replaced by Ag + ions by a subsequent silver nitrate treatment. Contact angle measurement indicated that the silver containing Ti64 alloy surface is hydrophilic at lower silver concentration. The antibacterial study of the thus prepared sample against Staphylococcus aureus confirmed the bacterial resistance of the Ti64 alloy. As evident from the AAS result, the sustained release of Ag into the culture medium results in antibacterial activity. Cytocompatibility studies on MG63 cell lines showed above 80% cell viability and also good cell attachment. This confirmed the nontoxic behavior of the present optimized silver concentration on the Ti64 surface for MG63 cells. In vitro bioactivity of the silver containing Ti64 sample in simulated body fluid showed bone-like apatite formation and the apatite-forming ability is not affected by Ag concentration or by heat treatment. Taken together, this surface modification study adds further information to our knowledge on the development of a bioactive Ti64 alloy with hydrophilicity, antibacterial activity and biocompatibility that may have considerable potential application as orthopedic and dental implants.

The 72-h IC(50), 7-d no observable effect concentration (NOEC), low observable effect concentration (LOEC), Chronic values were derived for copper on the growth of marine diatom, Odontella mobiliensis. The effect of copper was also studied on cell morphology, size, nitrate reductase and antioxidant enzymes (Catalase, Superoxide dismutase and peroxidase). The 72-h IC(50) of 298.4 ± 28.3, NOEC of 15.6, LOEC of 29.6 and chronic value of 21.5 μg Cu L(-1) were found in the present study. The chlorophyll a was significantly decreased with increasing concentrations of copper. The length of the cell (apical axis) was extended from 30.14 ± 5.98 μm at control to 71.4 ± 6.29 μm at 574 μg Cu L(-1), the spines were absent at 574 μg L(-1) and the cell structure was entirely damaged at 926 μg Cu L(-1). The antioxidant enzymes viz. Catalase, Peroxidase activities and Melondialdehyde were increased whereas the Nitrate reductase and activity was reduced at 21.5 μg Cu L(-1) during 7 days exposure.

Diatoms are unicellular algae that synthesize cell wall with silica that has highly ornate features on the nano to microscale. The porous silica nanoparticulate structure of three marine centric and one pennate diatoms namely, Coscinodiscus concinnus, Coscinodiscus sp., Odontella mobiliensis and Navicula directa were investigated by Field Emission Scanning Electron Microscopy (FESEM). Important morphological features like porous pattern, topography, pore size and shape were studied. The external layer (cribellum) of C. concinnus was found to be consisting of a characteristic pentagonal array of pores which were star in shape and irregular in size, with a diameter of 224.7 nm and a pore-to-pore distance of 160.6 nm. The second diatom species investigated, Coscinodiscus sp. showed frustule with radially-oriented pattern of alternating grid-like arrangements of pores with honeycomb topography with pore diameter of 132.1 and distance between arrays were 61.01 nm. The O. mobiliensis images showed well organisation of holes (foramen) showed hexagonal organisation and all the pores are circular with same size and pores of 328.6 nm diameter with pore to pore distance was 252.8 nm. The girdle view of N. directa was about 5 lm in diameter with values showing striae are parallel in whole and porous were observed in N. directa in the range of 278.3 nm, the gaps between regularly arranged pores were 145.6 nm was clearly observed. The internal and external structures of all the diatom frustules were different in pore arrangements. The present study showed that high-resolution FESEM results revealed the silica nanostructure with nanoporous material exhibited interesting application in antireflection, drug delivery and heavy metal adsorbing studies, which should be investigated further research will be a subject of future proposals by a flat form of present investigation.