In Situ Transformation of Chitosan Films into Microtubular Structures on the Surface of Nanoengineered Titanium Implants

There is considerable interest in combining bioactive polymers such as chitosan with titanium bone implants to promote bone healing and address therapeutic needs. However, the fate of these biodegradable polymers especially on titanium implants is not fully explored. Here we report in situ formation of chitosan microtube (CMT) structures from chitosan films on the implant surface with titania nanotubes (TNTs) layer, based on phosphate buffer-induced transformation and precipitation process. We have comprehensively analyzed this phenomenon and the factors that influence CMT formation, including substrate topography, immersion solution and its pH, effect of coating thickness, and time of immersion. Significance of reported in situ formation of chitosan microtubes on the TNTs surface is possibly to tailor properties of implants with favorable micro and nano morphology using a self-ordering process after the implant’s insertion

Graphene Oxide-Assisted Liquid Phase Exfoliation of Graphite into Graphene for Highly Conductive Film and Electromechanical Sensors

Here, we report a new method to prepare graphene from graphite by the liquid phase exfoliation process with sonication using graphene oxide (GO) as a dispersant. It was found that GO nanosheets act a as surfactant to the mediated exfoliation of graphite into a GO-adsorbed graphene complex in the aqueous solution, from which graphene was separated by an additional process. The preparation of isolated graphene from a single to a few layers is routinely achieved with an exfoliation yield of up to higher than 40% from the initial graphite material. The prepared graphene sheets showed a high quality (C/O ∼ 21.5), low defect (<i>I</i>_D/<i>I</i>_G ∼ 0.12), and high conductivity (6.2 × 10⁴ S/m). Moreover, the large lateral size ranging from 5 to 10 μm of graphene, which is believed to be due to the shielding effect of GO avoiding damage under ultrasonic jets and cavitation formed by the sonication process. The thin graphene film prepared by the spray-coating technique showed a sheet resistance of 668 Ω/sq with a transmittance of 80% at 550 nm after annealing at 350 °C for 3 h. The transparent electrode was even greater with the resistance only 66.02 Ω when graphene is deposited on an interdigitated electrode (1 mm gap). Finally, a flexible sensor based on a graphene spray-coating polydimethylsiloxane (PDMS) is demonstrated showing excellent performance working under human touch pressure (<10 kPa). The graphene prepared by this method has some distinct properties showing it as a promising material for applications in electronics including thin film coatings, transparent electrodes, wearable electronics, human monitoring sensors, and RFID tags