Electrically conductive polymeric materials have recently attracted considerable interest from academic and industrial researchers to explore their potential in biomedical applications such as in biosensors, drug delivery systems, biomedical implants and tissue engineering. Conventional conductive homopolymers such as polypyrrole and PEDOT show promising conductivity for these applications, however their mechanical properties, biocompatibility and processability are often poor. This has led to more recent attention being directed towards conductive polymeric composites comprised of biostable/biocompatible polymers with dispersed conductive fillers such as graphene, carbon nanotubes and metallic nanoparticles. The major objective of this paper is to provide an up to date review of the recent investigations conducted in the development of conductive polymer composites focussing on the methods of their preparation, underlying concepts of their conductivity and the ways to tailor their properties. Furthermore, recent progress made in conventional conducting polymers and their composites/blends for biomedical applications is also discussed.

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Electrically conductive polymers and composites for biomedical applications

Electrically conducting polymers arenovel In thattheir surface pries induding charge density and wettability, canbereversibly changed with anapplied electrical potential. Suchproperties might render conducting polymers unique forbiological applications. However, themajority of research onconducting polymers hasbeencarried outunder nonbio lcondits. Wesyntheoptically transparent polypyrrole thinfinms andstudied theminenvironments suitable forprotein adsorption andmammalian cell culture. In viro studies demonstrated that extracellular matrix molecules, suchasfibronectin, adsorb efficiently ontopolypyrrole thin films andsupport cell attentunder serum-free conditions. Whenaortic endothelial cells werecultured onfibronectin- coated polypyrrole (oxidized) ineither chemicall defined medium orthepresence ofserum, cells spread normally and synthesized DNA.Incontrast, whenthepolymer wasswitched toits neutral state byapplying anelectrical potntil, bothcell extension andDNAsynthesis wereinhibited without affecting cell viability. Application ofasimilar electrical potential tocells cultured onindium tin oxide surfaces hadnoeffect oncell shape orfunction. Thesedatasuggest thatdectrially conducting polymers mayrepresent atype ofculture substrate which could provide anoninvasive meanstocontrol theshape andfunction ofadherent cells, independent ofanymediumalteration. Growth andfunction ofcultured cells iscommonly controlled byaddition ofmediumsupplements, including serum, de- fined growth factors, andsoluble hormones. However, in- teractions between cells andtheir culture substrate arealso critical forregulation oftheir growth andfunction. For example, mostmammalian cells areanchorage-dependent and, thus, mustattach andextend onasurface inorder to proliferate (1-5). Furthermore, thesamecells will remain quiescent anddifferentiate intheidentical growth factor- containing medium, ifcell spreading isprevented byaltering interactions between cells andsubstrate-adsorbed extracel-

Electrically conducting polymers cannoninvasively control the shapeandgrowth ofmammalian cells

Flexible electronic devices are necessary for applications involving unconventional interfaces, such as soft and curved biological systems, in which traditional silicon-based electronics would confront a mechanical mismatch. Biological polymers offer new opportunities for flexible electronic devices by virtue of their biocompatibility, environmental benignity, and sustainability, as well as low cost. As an intriguing and abundant biomaterial, silk offers exquisite mechanical, optical, and electrical properties that are advantageous toward the development of next-generation biocompatible electronic devices. The utilization of silk fibroin is emphasized as both passive and active components in flexible electronic devices. The employment of biocompatible and biosustainable silk materials revolutionizes state-of-the-art electronic devices and systems that currently rely on conventional semiconductor technologies. Advances in silk-based electronic devices would open new avenues for employing biomaterials in the design and integration of high-performance biointegrated electronics for future applications in consumer electronics, computing technologies, and biomedical diagnosis, as well as human-machine interfaces.

Silk Fibroin for Flexible Electronic Devices

Iron oxide nanoparticles have been widely used in many important fields due to their excellent nanoscale physical properties, such as magnetism/superparamagnetism. They are usually assumed to be biologically inert in biomedical applications. However, iron oxide nanoparticles were recently found to also possess intrinsic enzyme-like activities, and are now regarded as novel enzyme mimetics. A special term, "Nanozyme", has thus been coined to highlight the intrinsic enzymatic properties of such nanomaterials. Since then, iron oxide nanoparticles have been used as nanozymes to facilitate biomedical applications. In this review, we will introduce the enzymatic features of iron oxide nanozyme (IONzyme), and summarize its novel applications in biomedicine.

Iron Oxide Nanozyme: A Multifunctional Enzyme Mimetic for Biomedical Applications.

Zn1–xCoxO (x = 0, 0.05, 0.10, and 0.15) nanoparticles (NPs) were synthesized by a coprecipitation method. The crystalline sizes of synthesized samples were calculated from the powder XRD patterns, which were found to decrease with the increase of cobalt content. The FT-IR spectra confirmed the Zn–O stretching bands at 468, 456, 452, and 461 cm–1 for the respective ZnO NPs. SEM images demonstrated the distinct flowerlike morphology. The photoluminescence spectra of all the samples exhibited a broad emission in the visible range. XPS studies were carried out for Zn0.90Co0.10O NPs. The carriers (donors) bound on the Co sites were observed from the micro-Raman spectroscopic studies. The pure and Co-doped ZnO NPs showed significant changes in the M–H loop where the diamagnetic behavior of ZnO changes to ferromagnetic nature when doping with Co. Oxygen vacancies and zinc interstitials were found to be the main reasons for room-temperature ferromagnetism in the Co-doped ZnO NPs with the support of the results ob...

Effect of Cobalt Doping on Structural, Optical, and Magnetic Properties of ZnO Nanoparticles Synthesized by Coprecipitation Method

Polypyrrole (PPy), the earliest prepared conducting polymer, has good biocompatibility, easy synthesis and flexibility in processing. Compared with metal and inorganic materials, doped PPy has better mechanical match with live tissue, resulting in its many applications in biomedical field. This mini-review presents some information on specific PPy properties for tissue engineering applications, including its synthesis, doping, bio-modification. Although some challenges and unanswered problems still remain, PPy as novel biomaterial has promoted the development tissue engineering for its clinical application in the future.

Conducting polypyrrole in tissue engineering applications

Zn−ferrite film with hierachical structure and organic composite was prepared by the coprecipitation method, which has good ferromagnetism and photoluminescence (PL) properties. DMSA-modified Fe3O4 nanoparticles (NPs) with saturation magnetization of 55.6 emu/g were prepared by the one-step process, and bovine serum albumin (BSA) with different concentrations was bound on NPs by the carbodiimide method. After Fe3O4−BSA NPs had been adsorbed onto Zn−ferrite film by magnetic forces, the PL intensity of the films was seen to increase linearly with BSA concentration in the range of 0.25−1.5 mg/mL, suggesting that the films could be used for protein detection.

Preparation and Protein Detection of Zn−Ferrite Film with Magnetic and Photoluminescence Properties

Mn-doped ZnO rod arrays were successfully prepared on zinc substrate by a simple aqueous solution method. X-Ray diffraction and high resolution transmission electron microscopy results indicate the doped Mn2+ has successfully incorporated into the ZnO crystal lattice. The optical, magnetic and electrical properties of as-prepared ZnO rod arrays were all changed due to Mn2+ doping into ZnO rods. Photoluminescence spectra at room temperature suggest that the band gap increases with increasing the Mn concentrations in ZnO rods. The M–H curves of all Mn-doped ZnO rod arrays show obvious ferromagnetic characteristics at room temperature. The current–voltage characteristic curves of Mn-doped ZnO rod arrays indicate that the samples are typical semiconductors.

Jianwen Gu

Papers

Conducting polypyrrole in tissue engineering applications

Preparation and Protein Detection of Zn−Ferrite Film with Magnetic and Photoluminescence Properties

Preparation, structure and properties of Mn-doped ZnO rod arrays

Fabrication of conductive NGF-conjugated polypyrrole-poly(L-lactic acid) fibers and their effect on neurite outgrowth

Fabrication and neuron cytocompatibility of iron oxide nanoparticles coated with silk-fibroin peptides