Deepak K. Pattanayak

Bioactive Ti metal analogous to human cancellous bone: Fabrication by selective laser melting and chemical treatments

Selective laser melting (SLM) is a useful technique for preparing three-dimensional porous bodies with complicated internal structures directly from titanium (Ti) powders without any intermediate processing steps, with the products being expected to be useful as a bone substitute. In this study the necessary SLM processing conditions to obtain a dense product, such as the laser power, scanning speed, and hatching pattern, were investigated using a Ti powder of less than 45 μm particle size. The results show that a fully dense plate thinner than 1.8 mm was obtained when the laser power to scanning speed ratio was greater than 0.5 and the hatch spacing was less than the laser diameter, with a 30 μm thick powder layer. Porous Ti metals with structures analogous to human cancellous bone were fabricated and the compressive strength measured. The compressive strength was in the range 35-120 MPa when the porosity was in the range 75-55%. Porous Ti metals fabricated by SLM were heat-treated at 1300 °C for 1h in an argon gas atmosphere to smooth the surface. Such prepared specimens were subjected to NaOH, HCl, and heat treatment to provide bioactivity. Field emission scanning electron micrographs showed that fine networks of titanium oxide were formed over the whole surface of the porous body. These treated porous bodies formed bone-like apatite on their surfaces in a simulated body fluid within 3 days. In vivo studies showed that new bone penetrated into the pores and directly bonded to the walls within 12 weeks after implantation into the femur of Japanese white rabbits. The percentage bone affinity indices of the chemical- and heat-treated porous bodies were significantly higher than that of untreated implants.

Osteoinduction of porous Ti implants with a channel structure fabricated by selective laser melting.

Many studies have shown that certain biomaterials with specific porous structures can induce bone formation in non-osseous sites without the need for osteoinductive biomolecules, however, the mechanisms responsible for this phenomenon (intrinsic osteoinduction of biomaterials) remain unclear. In particular, to our knowledge the type of pore structure suitable for osteoinduction has not been reported in detail. In the present study we investigated the effects of interconnective pore size on osteoinductivity and the bone formation processes during osteoinduction. Selective laser melting was employed to fabricate porous Ti implants (diameter 3.3mm, length 15 mm) with a channel structure comprising four longitudinal square channels, representing pores, of different diagonal widths, 500, 600, 900, and 1200 μm (termed p500, p600, p900, and p1200, respectively). These were then subjected to chemical and heat treatments to induce bioactivity. Significant osteoinduction was observed in p500 and p600, with the highest observed osteoinduction occurring at 5mm from the end of the implants. A distance of 5mm probably provides a favorable balance between blood circulation and fluid movement. Thus, the simple architecture of the implants allowed effective investigation of the influence of the interconnective pore size on osteoinduction, as well as the relationship between bone quantity and its location for different pore sizes.

Positively charged bioactive Ti metal prepared by simple chemical and heat treatments

A highly bioactive bone-bonding Ti metal was obtained when Ti metal was simply heat-treated after a common acid treatment. This bone-bonding property was ascribed to the formation of apatite on the Ti metal in a body environment. The formation of apatite on the Ti metal was induced neither by its surface roughness nor by the rutile phase precipitated on its surface, but by its positively charged surface. The surface of the Ti metal was positively charged because acid groups were adsorbed on titanium hydride formed on the Ti metal by the acid treatment, and remained even after the titanium hydride was transformed into titanium oxide by the subsequent heat treatment. These results provide a new principle based on a positively charged surface for obtaining bioactive materials.

Apatite-forming ability of titanium in terms of pH of the exposed solution

In order to elucidate the main factor governing the capacity for apatite formation of titanium (Ti), Ti was exposed to HCl or NaOH solutions with different pH values ranging from approximately 0 to 14 and then heat-treated at 600°C. Apatite formed on the metal surface in a simulated body fluid, when Ti was exposed to solutions with a pH less than 1.1 or higher than 13.6, while no apatite formed upon exposure to solutions with an intermediate pH value. The apatite formation on Ti exposed to strongly acidic or alkaline solutions is attributed to the magnitude of the positive or negative surface charge, respectively, while the absence of apatite formation at an intermediate pH is attributed to its neutral surface charge. The positive or negative surface charge was produced by the effect of either the acidic or alkaline ions on Ti, respectively. It is predicted from the present results that the bone bonding of Ti depends upon the pH of the solution to which it is exposed, i.e. Ti forms a bone-like apatite on its surface in the living body and bonds to living bone through the apatite layer upon heat treatment after exposure to a strongly acidic or alkaline solution.

On the large capacitance of nitrogen doped graphene derived by a facile route

Recent research activities on graphene have identified doping of foreign atoms into the honeycomb lattice as a facile route to tailor its bandgap. Moreover, the presence of foreign atoms can act as defective centres in the basal plane, and these centres can enhance the electrochemical activities of the surface of graphene. Here, we report a facile synthetic approach towards the bulk synthesis of nitrogen doped graphene (N-Graphene) from graphene oxide using a hydrothermal process, with significant control over the extent of N-doping. The electrochemical activeness of N-Graphene (with 4.5 atomic% of nitrogen) is studied by conducting supercapacitor measurements. N-Graphene exhibits a remarkably high specific capacitance of 459 Fg−1 at a current density of 1 mA cm−2 in an electrolyte of 1 M H2SO4 with a high cycle stability compared to that of pristine graphene, which has a specific capacitance of 190 Fg−1. The structural destabilisation of graphene in higher pH/high amount alkaline treatment is demonstrated, and hence optimization of the amount of reagents is necessary in developing a graphene based high performance electronic or electrochemical devices.

Osteoinduction on acid and heat treated porous Ti metal samples in canine muscle.

Samples of porous Ti metal were subjected to different acid and heat treatments. Ectopic bone formation on specimens embedded in dog muscle was compared with the surface characteristics of the specimen. Treatment of the specimens by H2SO4/HCl and heating at 600°C produced micrometer-scale roughness with surface layers composed of rutile phase of titanium dioxide. The acid- and heat-treated specimens induced ectopic bone formation within 6 months of implantation. A specimen treated using NaOH followed by HCl acid and then heat treatment produced nanometer-scale surface roughness with a surface layer composed of both rutile and anatase phases of titanium dioxide. These specimens also induced bone formation after 6 months of implantation. Both these specimens featured positive surface charge and good apatite-forming abilities in a simulated body fluid. The amount of the bone induced in the porous structure increased with apatite-forming ability and higher positive surface charge. Untreated porous Ti metal samples showed no bone formation even after 12 months. Specimens that were only heat treated featured a smooth surface composed of rutile. A mixed acid treatment produced specimens with micrometer-scale rough surfaces composed of titanium hydride. Both of them also showed no bone formation after 12 months. The specimens that showed no bone formation also featured almost zero surface charge and no apatite-forming ability. These results indicate that osteoinduction of these porous Ti metal samples is directly related to positive surface charge that facilitates formation of apatite on the metal surfaces in vitro.

Silver incorporated antibacterial, cell compatible and bioactive titania layer on Ti metal for biomedical applications

Surface modification of titanium and titanium alloys is an attractive method to improve the biological affinity of orthopaedic and dental devices. Although osteointegration is enhanced by surface modifications, bacterial related infections sometimes lead to implant failure and secondary surgery. In the present study, attempts were made to incorporate the antimicrobial agent silver into titanium metal pre-treated with H2O2. Fine nano network structures of hydrated titania uniformly formed by the H2O2 treatment were decorated with silver particles of 5–10 nm by subsequent AgNO3, and, these silver particles remained stable over the titania network even after heat treatment. An antibacterial study of titanium metal subjected to H2O2–AgNO3 showed a zone of inhibition in Staphylococcus aureus compared to an H2O2 pre-treated and untreated control specimen. Steady release of silver from the thus treated titanium metals into simulated body fluid indicates that these silver particles are released as silver ions and are responsible for the antibacterial activity. About 99.7% bacterial killing efficiency was observed for a 6–8 ppm (1 mM AgNO3) silver containing Ti surface and is optimised as the highest tolerable silver limit. The cytotoxicity assay and cell adhesion study on MG63 osteosarcoma cell lines confirmed the present silver concentration does not show any toxicity. Further, bone like apatite formation of chemically and heat-treated titanium in simulated body fluid indicates this surface modification method could be suitable in various medical devices.

Effect of heat treatments on apatite-forming ability of NaOH- and HCl-treated titanium metal

Titanium (Ti) metal was soaked in HCl solution after NaOH treatment and then subjected to heat treatments at different temperatures. Their apatite-forming abilities in a simulated body fluid (SBF) were discussed in terms of their surface structures and properties. The nanometer scale roughness formed on Ti metal after NaOH treatment remained after the HCl treatment and a subsequent heat treatment below 700°C. Hydrogen titanate was formed on Ti metal from an HCl treatment after NaOH treatment, and this was converted into titanium oxide of anatase and rutile phases by a subsequent heat treatment above 500°C. The scratch resistance of the surface layer increased with the formation of the titanium oxide after a heat treatment up to 700°C, and then decreased with increasing temperature. The Ti metal with a titanium oxide layer formed on its surface showed a high apatite-forming ability in SBF when the heat treatment temperature was in the range 500–700°C. The high apatite-forming ability was attributed to the positive surface charge in an SBF. These positive surface charges were ascribed to the presence of chloride ions, which were adsorbed on the surfaces and dissociated in the SBF to give an acid environment.

Magnetic CoPt nanoparticle-decorated ultrathin Co(OH)2 nanosheets: an efficient bi-functional water splitting catalyst

Hydrogen generation via electrocatalytic water splitting is on the cutting edge of energy research. The kinetic burdens associated with the sluggish anodic oxygen evolution reaction (OER) and cathodic hydrogen evolution reaction (HER) cause a large amount of energy loss. Hence, these reactions must be catalyzed. Therefore, an array of magnetic CoPt nanoparticle (NP)-decorated ultrathin Co(OH)2 nanosheets was synthesized and applied for electrocatalytic water splitting in 1 M KOH. CoPt@Co(OH)2 required a minimum overpotential of 334 mV at 10 mA cm−2 in the OER and 226 mV at 50 mA cm−2 in the HER in addition to possessing exceptional stability upon cycling and chronoamperometry. The advantages of the magnetic property of CoPt@Co(OH)2 have been utilized for the first time to improve its stability. The aging study carried out at the CoPt@Co(OH)2-modified interface with and without magnetic support has shown that the magnetically co-stabilized interface was more stable even after 5 days of aging in 1 M KOH. This magnetism-assisted enhancement in the stability of a nanocatalyst-modified interface along with proper further developments will surely take the electrocatalysis of water splitting to a new level.

Snail Shell Derived Natural Hydroxyapatite: Effects on NIH-3T3 Cells for Orthopedic Applications

Hydroxyapatite [HAP] and tricalcium phosphate [ß-TCP] are a class of calcium phosphate related ceramic materials that are widely used in tissue regeneration and biomedical applications owing to their excellent bioactivity and biocompatibility. In this investigation, nanocrystalline pure HAP was prepared via sol–gel method by incorporating snail shell as calcium precursor with different phosphorus sources such as triethyl phosphate/phosphite (without using any additives like pH maintaining solutions or gelling agents). Nanocrystalline HAP and biphasic calcium phosphate (HAP + ß TCP) were prepared from triethyl phosphate and triethyl phosphite precursors, respectively. The prepared material was further characterized by powder XRD, IR, Raman spectroscopy, and thermo-gravimetrical analysis to confirm the phase purity, functional groups, and thermal stability. SEM coupled with EDAX was also used to examine the size, shape of particles, and elemental composition of Ca to P ratio in the material. Different phosphorus based HAP has shown rod and spherical shaped surface morphology which was further confirmed by TEM analysis. MTT assay was performed using NIH-3T3 fibroblast cell lines which indicated that the viability was not affected in various concentrations of pure nanocrystalline HAP (12.5–100 µg/ml). This study confirms the improved biocompatibility of biowaste converted HAP which would have implications in biomedical applications.