Additive-Free Electrophoretic Deposition of Graphene Quantum Dots Thin Films.

The electrophoretic deposition (EPD) of graphene-based materials on transparent substrates is highly potential for many applications. Several factors can determine the yield of the EPD process, such as applied voltage, deposition time and particularly the presence of dispersion additives (stabilisers) in the suspension solution. This study presents an additive-free EPD of graphene quantum dot (GQD) thin films on an indium tin oxide (ITO) glass substrate and studies the deposition mechanism with the variation of the applied voltage (10-50 V) and deposition time (5-25 min). It is found that due to the small size (≈3.9 nm) and high content of deprotonated carboxylic groups, the GQDs form a stable dispersion (zeta-potential of about -35 mV) without using additives. The GQD thin films can be deposited onto ITO with optimal surface morphology at 30 V in 5 min (surface roughness of approximately (3.1±1.3) nm). In addition, as-fabricated GQD thin films also possess some interesting physico-optical properties, such as a double-peak photoluminescence at about λ=417 and 439 nm, with approximately 98 % visible transmittance. This low-cost and eco-friendly GQD thin film is a promising material for various applications, for example, transparent conductors, supercapacitors and heat conductive films in smart windows.

Overcoming the barrier of conventional electrochemical deposition of inorganic composites.

We present an electrochemical approach for depositing composites made of two insoluble inorganic materials, which cannot be obtained by the conventional electrochemical deposition from ionic speices. Applying a negative potential in an aqueous solution generates OH-, which simultaneously destabilizes dispersed nanomaterials, such as insoluble phosphates and sulfides and causes the deposition of a metal hydroxide from its dissolved ions.

Electrochemical Triggered Dissolution of Hydroxyapatite/Doxorubicin Nanocarriers.

The controlled release of drugs by an external stimulus is of pivotal interest and importance as a means of increasing administration efficacy. Accordingly, many responsive systems have been developed based on primarily pH, temperature, and light changes. Here, a novel electrochemical triggered release of a doxorubicin (Dox)-loaded hydroxyapatite (HAp) nanoparticle (NP) system is presented. Dox is loaded onto HAp NPs by producing a stable dispersion in DMSO. The Dox-HAp NPs are electrophoretically deposited on a stainless steel (S.S) surface. The adsorbed Dox-HAp NPs are released either by applying a moderate electrochemical potential pulse or upon scanning the potential. Two mechanisms were proposed. The first is that the positive potential induces the desorption of the Dox-HAp NPs. Alternatively, the positive potential could drive the oxidation of water and generation of protons, causing the dissolution of the Dox-HAp NPs. In situ characterization techniques, such as atomic force microscopy (AFM) and confocal microscopy, were used to gain insight on the release mechanism. All measurements allude to the electrochemically driven dissolution of the Dox-HAp NPs and release of the embedded drug. In vitro antitumor activity against both HT-29 and A2780 cancer cells revealed that the efficacy of the released Dox was not significantly affected by the electrochemical process. We believe that the electrochemically triggered release of NPs could be applied to many other responsive systems.

Synthesis, coating, and drug-release of hydroxyapatite nanoparticles loaded with antibiotics.

Post-surgery infections are considered the most challenging complication in the orthopedic and dental field. The local release of antibiotics is evidently highly efficient in delivering the drug to the vicinity of the infected area without the risk of systemic toxicity. Bioactive materials, such as hydroxyapatite (HAp) among other calcium phosphates, are reputed as superior antibiotic vehicles, and combine drug-delivery properties and enhanced osteoconductivity. Here, we report on the single-step electrophoretic deposition (EPD) of drug-loaded HAp nanoparticles (NPs) on titanium implants. This approach provides a purely bioactive coating with drug delivery properties in a simple, economic, and fast process. We synthesized pure HAp NPs with 12.5% and 12.8% loading weight percentages of gentamicin sulfate (Gs) and ciprofloxacin (Cip), and electrophoretically deposited them on a titanium substrate. Furthermore, we co-deposited Gs-HAp and Cip-HAp in one-step to yield a drug-loaded system consisting of two types of antibiotics. The drug-loaded NPs as well as the coatings were carefully characterized. The release profiles of the Gs-HAp and Cip-HAp NP coatings showed prolonged release of up to 10 and 25 days, respectively. The bioactivity test revealed superior bioactivity with enhanced precipitation of HAp crystals along with inorganic minerals, such as Mg2+, Na+, and Cl-. The antibacterial in vitro tests of the Cip and Gs-HAp coatings showed efficient inhibition of Pseudomonas aeruginosa bacteria.