Electrophoretic deposition (EPD) is attracting increasing attention as an effective technique for the processing of biomaterials, specifically bioactive coatings and biomedical nanostructures. The well-known advantages of EPD for the production of a wide range of microstructures and nanostructures as well as unique and complex material combinations are being exploited, starting from well-dispersed suspensions of biomaterials in particulate form (microsized and nanoscale particles, nanotubes, nanoplatelets). EPD of biological entities such as enzymes, bacteria and cells is also being investigated. The review presents a comprehensive summary and discussion of relevant recent work on EPD describing the specific application of the technique in the processing of several biomaterials, focusing on (i) conventional bioactive (inorganic) coatings, e.g. hydroxyapatite or bioactive glass coatings on orthopaedic implants, and (ii) biomedical nanostructures, including biopolymer–ceramic nanocomposites, carbon nanotube coatings, tissue engineering scaffolds, deposition of proteins and other biological entities for sensors and advanced functional coatings. It is the intention to inform the reader on how EPD has become an important tool in advanced biomaterials processing, as a convenient alternative to conventional methods, and to present the potential of the technique to manipulate and control the deposition of a range of nanomaterials of interest in the biomedical and biotechnology fields.

https://royalsocietypublishing.org/doi/pdf/10.1098/rsif.2010.0156.focus

Electrophoretic deposition of biomaterials

Recent progress in inorganic and composite coatings with bactericidal capability for orthopaedic applications.

Biofilms are a complex group of microbial cells that adhere to the exopolysaccharide matrix present on the surface of medical devices. Biofilm-associated infections in the medical devices pose a serious problem to the public health and adversely affect the function of the device. Medical implants used in oral and orthopedic surgery are fabricated using alloys such as stainless steel and titanium. The biological behavior, such as osseointegration and its antibacterial activity, essentially depends on both the chemical composition and the morphology of the surface of the device. Surface treatment of medical implants by various physical and chemical techniques are attempted in order to improve their surface properties so as to facilitate bio-integration and prevent bacterial adhesion. The potential source of infection of the surrounding tissue and antimicrobial strategies are from bacteria adherent to or in a biofilm on the implant which should prevent both biofilm formation and tissue colonization. This article provides an overview of bacterial biofilm formation and methods adopted for the inhibition of bacterial adhesion on medical implants.

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Bacterial adherence and biofilm formation on medical implants: A review

A method based on electrophoretic deposition (EPD) has been developed to produce uniform deposits of multi-walled carbon nanotubes on stainless-steel substrates. Aqueous suspensions were used under constant voltage conditions in the range of 5–50 V, with deposition times ranging from 0.5 to 10 min. The thickness of the coatings was controlled by variation of voltage and deposition time during EPD. Coatings of up to 10 μm thickness were achieved, with a homogeneous microstructure. The EPD technique is fast, effective, and can be applied to complex shapes. Possible applications are in heat extraction devices or porous coatings for tissue engineering scaffolds.

Multi-Walled Carbon Nanotube Coatings Using Electrophoretic Deposition (EPD)

The purpose of this paper is to present an up-to-date comprehensive overview of current research progress in the development of carbon nanotube (CNT)–ceramic nanocomposites by electrophoretic deposition (EPD). Micron-sized and nanoscale ceramic particles have been combined with CNTs, both multiwalled and single-walled, using EPD for a variety of functional, structural and biomedical applications. Systems reviewed include SiO2/CNT, TiO2/CNT, MnO2/CNT, Fe3O4/CNT, hydroxyapatite (HA)/CNT and bioactive glass/CNT. EPD has been shown to be a very convenient method to manipulate and arrange CNTs from well dispersed suspensions onto conductive substrates. CNT–ceramic composite layers of thickness in the range <1–50 μm have been produced. Sequential EPD of layered nanocomposites as well as electrophoretic co-deposition from diphasic suspensions have been investigated. A critical step for the success of EPD is the prior functionalization of CNTs, usually by their treatment in acid solutions, in order to create functional groups on CNT surfaces so that they can be dispersed uniformly in solvents, for example water or organic media. The preparation and characterisation of stable CNT and CNT/ceramic particle suspensions as well as relevant EPD mechanisms are discussed. Key processing stages, including functionalization of CNTs, tailoring zeta potential of CNTs and ceramic particles in suspension as well as specific EPD parameters, such as deposition voltage and time, are discussed in terms of their influence on the quality of the developed CNT/ceramic nanocomposites. The analysis of the literature confirms that EPD is the technique of choice for the development of complex CNT–ceramic nanocomposite layers and coatings of high structural homogeneity and reproducible properties. Potential and realised applications of the resulting CNT–ceramic composite coatings are highlighted, including fuel cell and supercapacitor electrodes, field emission devices, bioelectrodes, photocatalytic films, sensors as well as a wide range of functional, structural and bioactive coatings.

Electrophoretic deposition of carbon nanotube–ceramic nanocomposites

Electrophoretic deposition (EPD) has been used to obtain TiO2 coatings on three dimensional (3-D) SiC fibre (Nicalon ®-type) and carbon fibre substrates. Colloidal suspensions of commercially available TiO2 nanoparticles in acetylaceton with addition of iodine were used. The EPD parameters, i.e., deposition time and voltage, were optimised for each fibre type. Strongly adhered TiO2 deposits with high particle packing density were obtained. Scanning electron microscopy observations revealed high penetration of the titania nanoparticles into the fibre preforms. The TiO2 deposits were sintered at 800°C for 1 h in order to produce relatively dense and uniform TiO2 coatings covering completely the SiC or carbon fibres. For the carbon fibre/TiO2 system, an effort was made to produce a 3-D titania matrix composite by further infiltration of the porous fibrous preform with TiO2 by slurry dipping and subsequent pressureless sintering. The 3-D carbon fibre reinforced TiO2 matrix composites fabricated contained residual porosity, indicating further infiltration and densification steps are required to produce dense composites of adequate structural integrity. For SiC fibre fabrics, oxidation tests in air established the effectiveness of the TiO2 coating as oxidation protective barrier at 1000°C. After 120 h the increase of weight due to oxidation of coated fibres was more than twice lower than that of the uncoated fibres. TiO2 coated SiC fibre preforms are attractive materials for manufacturing hot gas filters and as reinforcing elements for ceramic matrix composites.

P. Karapappas

Papers

TiO2 coatings on silicon carbide and carbon fibre substrates by electrophoretic deposition