Shubham Jain

Nanoscale Topography on Black Titanium Imparts Multi-biofunctional Properties for Orthopedic Applications

We have developed a chlorine based reactive ion etching process to yield randomly oriented anisotropic nanostructures that render the titanium metal surface ‘black’ similar to that of black silicon. The surface appears black due to the nanostructures in contrast to the conventional shiny surface of titanium. The nanostructures were found to kill bacteria on contact by mechanically rupturing the cells as has been observed previously on wings of certain insects. The etching was optimized to yield nanostructures of ≈1 μm height for maximal bactericidal efficiency without compromising cytocompatibility. Within 4 hours of contact with the black titanium surface, 95% ± 5% of E. coli, 98% ± 2% of P. aeruginosa, 92% ± 5% of M. smegmatis and 22% ± 8% of S. aureus cells that had attached were killed. The killing efficiency for the S. aureus increased to 76% ± 4% when the cells were allowed to adhere up to 24 hours. The black titanium supported the attachment and proliferation of human mesenchymal stem cells and augmented osteogenic lineage commitment in vitro. Thus, the bioinspired nanostructures on black titanium impart multi-biofunctional properties toward engineering the next-generation biomaterials for orthopedic implants.

Synergistic interactions between silver decorated graphene and carbon nanotubes yield flexible composites to attenuate electromagnetic radiation

The need of todays highly integrated electronic devices, especially working in the GHz frequencies, is to protect them from unwanted interference from neighbouring devices. Hence, lightweight, flexible, easy to process microwave absorbers were designed here by dispersing conductive multiwall carbon nanotubes (MWNTs) and silver nanoparticles decorated onto two-dimensional graphene sheets (rGO@Ag) in poly(ε-caprolactone) (PCL). In this study, we have shown how dielectric losses can be tuned in the nanocomposites by rGO@Ag nano-hybrid; an essential criterion for energy dissipation within a material resulting in effective shielding of the incoming electromagnetic (EM) radiation. Herein, the conducting pathway for nomadic charge transfer in the PCL matrix was established by MWNTs and the attenuation was tuned by multiple scattering due to the large specific surface area of rGO@Ag. The latter was possible because of the fine dispersion state of the Ag nanoparticles which otherwise often agglomerate if mixed separately. The effect of individual nanoparticles on microwave attenuation was systematically assessed here. It was observed that this strategy resulted in strikingly enhanced microwave attenuation in PCL nanocomposites in contrast to addition of individual particles. For instance, PCL nanocomposites containing both MWNTs and rGO@Ag manifested in a SET of -37 dB and, interestingly, at arelatively smaller fraction. The SE shown by this particular composite makes it a potential candidate for many commercial applications as reflected by its exceptional absorption capability (91.3%).

Strontium eluting nanofibers augment stem cell osteogenesis for bone tissue regeneration.

Strontium is known to offer a therapeutic benefit to osteoporotic patients by promoting bone formation. Thus, toward engineering scaffolds for bone tissue regeneration we have prepared polymer nanocomposite scaffolds by electrospinning. Strontium carbonate nanoparticles (nSrCO3) were added to poly(ε-caprolactone) (PCL) at 10 and 20wt% to develop nanocomposite fibrous scaffolds (PCL/SrC10 and PCL/SrC20) with fiber diameter in the range of 300-500nm. Incorporation of nSrCO3 decreased crystallinity and the elastic modulus of PCL. The composite scaffolds released Sr(2+) ions with up to 65ppm in 4days from the PCL/SrC20 scaffolds. Cell studies confirmed that the composite scaffold with 20% nSrCO3 enhanced proliferation of human mesenchymal stem cells in vitro. There was marked increase in mineral deposition up to four folds in PCL/SrC20 suggesting enhanced osteogenesis. This was corroborated by increased mRNA and protein expression of various osteogenic markers such as BMP-2, Osterix and Runx2 in the PCL/SrC20 fibers. Thus, incorporation of nSrCO3 in polymer scaffolds is a promising strategy for bone tissue engineering as an alternative to the use of labile growth factors to impart bioactivity to polymer scaffolds.

Curcumin eluting nanofibers augment osteogenesis toward phytochemical based bone tissue engineering

Curcumin is a phenolic compound isolated from Curcuma longa that is known to exhibit wide ranging biological activity including potential benefits for bone growth. The aim of this work was to engineer curcumin eluting tissue scaffolds and investigate their potential use in bone tissue regeneration. We prepared curcumin loaded poly(ε-caprolactone) (PCL) nanofibers by electrospinning. Morphological characterization of the nanofibers revealed that the average diameter of neat fibers and that of fibers with 1 wt% and 5 wt% curcumin is 840  ±  130 nm, 827  ±  129 nm and 680  ±  110 nm, respectively. Fourier transformation infrared spectroscopy and 1H nuclear magnetic resonance confirmed the successful loading of the drug in fibers. In aqueous medium, the fibers released  ≈18% of the encapsulated drug in 3 d and  ≈60% in 9 d. The cell response to the curcumin loaded nanofibers was assessed using MC3T3-E1 pre-osteoblasts. Cell proliferation was moderated with increased loading of curcumin and was 50% lower on the fibers containing 5% curcumin at day 10 than the control fibers. Osteogenesis was confirmed by assaying the expression of alkaline phosphatase and staining of mineral deposits by Alizarin red stain, which were both markedly higher for 1% curcumin compared to neat polymer but lower for 5% curcumin. Mineral deposition was also confirmed chemically by Fourier transform infrared spectroscopy. These results were corroborated by increased gene and protein expression of known osteogenic markers in 1% curcumin. Thus, controlled release of curcumin from polymer scaffolds is a promising strategy for bone tissue regeneration.

Designer porous antibacterial membranes derived from thermally induced phase separation of PS/PVME blends decorated with an electrospun nanofiber scaffold

We report the development of porous membranes by thermally induced phase separation of a PS/PVME (polystyrene/polyvinyl[methyl ether]) blend, which is a typical LCST mixture. The morphology of the membrane after etching out the PVME phase was characterized by scanning electron microscopy. To give the membrane an antibacterial surface, polystyrene (PS) and poly[vinyl(methyl ether)]-alt-maleic anhydride (PVME-MAH) with silver nanoparticles (nAg) were electrospun on the membrane surface. Pure water flux was evaluated by using a cross-flow membrane setup. The microgrooved fibers changed the flux across the membrane depending on the surface properties. The antibacterial properties of the membrane were confirmed by the reduction in the colony count of E. coli. The SEM images show the disruption of the bacterial cell membrane and the antibacterial mechanism was discussed.

Improving antifouling ability by site-specific silver decoration on polyethylene ionomer membranes for water remediation: assessed using 3D micro computed tomography, water flux and antibacterial studies

Blending immiscible polymer blends often results in coarse microstructures due to interfacial driven coarsening. However, by introducing specific interactions between the constituents, the evolving microstructure can be tailor-made. Herein, water insoluble poly(ethylene-co-methacrylic acid) zinc salt (Surlyn) was blended with water soluble polyethylene oxide (PEO) in 50/50 (wt/wt) ratio to construct co-continuous structures that were not possible by blending PE and PEO at the same fraction. By selectively etching the water soluble phase (PEO), porous membranes can be designed with well-defined microstructure as assessed using X-ray micro-computed tomography and the pure water flux across the membranes was studied systematically. In order to impart an antibacterial surface, silver was directly reduced on the membrane surface utilizing the un-neutralized carboxylic acid moieties present in Surlyn as the reducing sites. This led to uniform decoration of silver on the surface which enhanced the antibacterial and antifouling properties. The presence of silver on the membrane was confirmed by X-ray photoelectron spectroscopy (XPS). The distribution of silver and the morphology of the porous Surlyn membrane was evaluated by field emission scanning electron microscopy (FESEM) coupled with EDAX analysis. The antibacterial activity was assessed using a standard plate count method wherein the bacterial cells were in direct contact with the silver decorated membranes. The content of silver present on the surface and the sustained release from the membrane surface was monitored using inductively coupled plasma optical emission spectrometry. The present study opens new avenues in designing efficient and scalable antibacterial membranes.

Multi-scale surface topography to minimize adherence and viability of nosocomial drug-resistant bacteria

Toward minimizing bacterial colonization of surfaces, we present a one-step etching technique that renders aluminum alloys with micro- and nano-scale roughness. Such a multi-scale surface topography exhibited enhanced antibacterial effect against a wide range of pathogens. Multi-scale topography of commercially grade pure aluminum killed 97% of Escherichia coli and 28% of Staphylococcus aureus cells in comparison to 7% and 3%, respectively, on the smooth surfaces. Multi-scale topography on Al 5052 surface was shown to kill 94% of adhered E. coli cells. The microscale features on the etched Al 1200 alloy were not found to be significantly bactericidal, but shown to decrease the adherence of S. aureus cells by one-third. The fabrication method is easily scalable for industrial applications. Analysis of roughness parameters determined by atomic force microscopy revealed a set of significant parameters that can yield a highly bactericidal surface; thereby providing the design to make any surface bactericidal irrespective of the method of fabrication. The multi-scale roughness of Al 5052 alloy was also highly bactericidal to nosocomial isolates of E. coli, K. pneumoniae and P. aeruginosa. We envisage the potential application of engineered surfaces with multi-scale topography to minimize the spread of nosocomial infections.